JP4876716B2 - Electric power steering control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering control device capable of surely detecting overcurrent. <P>SOLUTION: When a battery voltage detection value VB becomes lower than a voltage lowering decision threshold value V<SB>DOWN</SB>, steering assist control processing is stopped (step S1 to S4). Subsequently, when the detection value becomes more than a voltage recovery decision threshold value V<SB>UP</SB>(step S5), overcurrent check processing is performed (step S7). When a lower stage side is made an open state and a duty control is performed for an upper stage in field effect transistors constituting a motor driving circuit 24, it is decided that the field effect transistor on the lower stage side is abnormal if power supply current flows in the motor driving circuit 24 in such a state. Conversely, when an upper stage side is made an open state and a duty control is performed for the lower stage side, it is decided that the field effect transistor on the upper stage side is abnormal when power supply current flows in this state. When it is not decided that the field effect transistors on both upper and lower stages are abnormal, it is decided that overcurrent is not generated. The steering assist control processing is resumed and steering assist is resumed (step S9). <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering control device that applies a steering assist force to an electric steering system by an electric motor.

  As this type of electric power steering control device, the motor current flowing in the electric motor is monitored, and when this motor current exceeds a preset threshold value for detecting an overcurrent, an abnormality may have occurred. When this state continues for a preset time or more, it is determined that the electric motor is locked or overcurrent has flowed, and a relay provided between the power supply and the drive circuit of the electric motor is provided. There has been proposed one that cuts off the current supply to the electric motor by switching to the open state (see, for example, Patent Document 1).

In addition, in order to avoid abnormal operation of the electric motor due to a decrease in the power supply voltage of the power supply that supplies power to the electric motor, the power supply voltage is monitored, and the power supply voltage falls below a preset threshold value. Sometimes, it is also proposed that the steering assist is stopped due to power supply voltage abnormality, the drive of the electric motor is stopped, and the steering assist is resumed when the power supply voltage recovers to a specified voltage.
Japanese Patent No. 11-059464

  However, as described above, the overcurrent to the electric motor is monitored, the steering assist is stopped when the overcurrent is detected, and the power supply voltage of the power supply for supplying power to the electric motor is monitored, and this power supply voltage is monitored. When the steering assist is stopped together when the value falls below the threshold value, it takes time until the overcurrent is actually detected even if the overcurrent has occurred. The driver could be uncomfortable.

  That is, for example, when the electric motor is driven and controlled by a motor drive circuit including a known three-phase bridge circuit in which two field effect transistors connected in series are connected in parallel, the field effect on the upper side of a certain phase. Of the transistors, for example, FET 1 and its lower field effect transistor FET 2, when a short circuit abnormality occurs in the upper field effect transistor FET 1, the upper field effect transistor FET 1 from the power source, its lower field effect transistor FET 2, There is a possibility that a through current may flow in a current path composed of ground.

Since this through current is basically an excessive current, the power supply voltage detected by the power supply voltage detection circuit decreases due to a voltage drop in the harness impedance of the battery line or the like.
For example, as shown in the timing chart showing the state of each part in FIG. 13, a short circuit abnormality occurs in the upper field effect transistor at time t1 (FIG. 13A), and accordingly, the power supply current flowing through the motor drive circuit changes. When the power supply current exceeds the overcurrent threshold at time t2, measurement of the duration time in which the power supply current exceeds the overcurrent threshold is started. Then, when this continuation time reaches a predetermined time set in advance, it is determined that there is an overcurrent abnormality.

  However, as shown in FIG. 13, the battery voltage decreases due to the occurrence of an overcurrent (FIG. 13 (c)), and the duration m during which the power supply current exceeds the overcurrent threshold is determined for the overcurrent determination. When the voltage drops to the voltage drop determination threshold at time t3 before reaching the specified time, the steering assist control processing is stopped at this time (FIG. 13D), and each field effect transistor constituting the motor drive circuit is opened. Switch to.

  For this reason, since the power supply current flowing through the motor drive circuit becomes substantially zero, when the battery voltage recovers and the battery voltage reaches the voltage return determination threshold at time t4, the normal steering assist control process is resumed, Duty control is performed on the upper and lower field effect transistors at a duty ratio of 50%, respectively (FIGS. 13E and 13F). At this time, the upper and lower field effect transistors are complementarily duty-controlled, and if the sum of the duty ratios for the upper and lower field effect transistors does not become 100%, the upper and lower field effect transistors are connected in series. Through current will not flow.

  Then, by restarting the steering assist control process, when a through current flows through the upper field-effect transistor in which the short circuit abnormality has occurred, the battery voltage decreases again. When the battery voltage drops to the voltage drop determination threshold at time t5 before the through current exceeds the overcurrent threshold continues for the specified time, the steering assist control process is stopped again, and the motor drive circuit is configured. Each field effect transistor is controlled to be open. After that, this operation will be repeated, and it may take time until this overcurrent is detected even though an overcurrent has actually occurred due to a short-circuit abnormality of the field effect transistor. There is sex.

As a method of avoiding this, it is conceivable to set the specified time for determining that the overcurrent is flowing to a shorter value. Even if a power supply current exceeding the threshold value flows, there is a possibility that it is erroneously determined that an overcurrent flows.
Therefore, the present invention has been made paying attention to the above-mentioned conventional unsolved problems, and an object thereof is to provide an electric power steering control device capable of more reliably detecting an overcurrent.

  In order to achieve the above object, an electric power steering control device according to claim 1 of the present invention includes an electric motor that applies a steering assist force to a steering system, steering torque detection means that detects steering torque, A bridge circuit that drives the electric motor including the switching element, and a steering assist control unit that drives and controls the electric motor via the bridge circuit based on the steering torque detected by the steering torque detection unit. A power supply voltage detection means for detecting a power supply voltage of a power supply that supplies power to the electric motor, and the steering assist when a power supply voltage detection value detected by the power supply voltage detection means falls below a preset voltage drop determination threshold value. Steering assist control stop means for stopping the steering assist control by the control means; and excess detection for detecting the occurrence of overcurrent in the bridge circuit. In the electric power steering control device comprising: a current detecting means; the overcurrent detecting means is configured to detect the overcurrent detecting switching element of the bridge circuit when the power supply voltage detection value falls below the voltage drop determination threshold value. A check operation control means for operating in the check mode, a power supply current detecting means for detecting a power supply current flowing in the bridge circuit when the switching element is operated in the check mode, and a power supply current detecting means Overcurrent determination means for determining the presence or absence of occurrence of overcurrent based on the detected power supply current value, and the steering assist control means, after the steering assist control is stopped by the steering assist control stop means, The overcurrent detection means detects that no overcurrent has occurred, and the power supply voltage detection value determines a preset voltage recovery. When a state exceeding the have value is characterized by resuming the steering assist control.

  According to the first aspect of the present invention, when the power supply voltage detection value detected by the power supply voltage detection means falls below the voltage drop determination threshold value and it is determined that the power supply voltage has dropped, the steering assist control is stopped, The steering assist according to the steering torque by the motor is stopped. Then, the switching elements constituting the bridge circuit for controlling the drive of the electric motor are controlled to operate in the overcurrent detection check mode. At this time, the presence or absence of occurrence of overcurrent is determined based on the power supply current flowing in the bridge circuit. Detected. Since it does not stop in the middle of detecting the presence or absence of overcurrent, such as when steering assist control is restarted before the presence or absence of overcurrent is determined, whether or not overcurrent has occurred Can be detected.

  Further, in the electric power steering control device according to claim 2 of the present invention, the check operation control means checks one of the upper side and the lower side of the switching elements constituting the bridge circuit. The switching device includes a duty control unit that controls all of the switching elements in an open state and duty-controls the switching element on the other side from a small duty ratio while increasing the duty ratio. As a result of determining that the switching element to be checked is abnormal when a value exceeds a predetermined threshold for determination, and performing the determination for each of the upper and lower switching elements as the check target, One of the features is that it is determined that an overcurrent has occurred when an abnormality is detected. .

  In the invention according to claim 2, among the switching elements on the upper stage side and the lower stage side constituting the bridge circuit, one of the switching elements is controlled to be in an open state, and the other side has the switching element. The duty is controlled while increasing from a state where the duty ratio is small. At this time, since the switching element on the check target side is in an open state, even if duty control is performed on the other side, the power supply current does not flow to the bridge circuit. Therefore, when the power supply current detection value at the power supply current detection means exceeds the judgment threshold value, the switching element is abnormal, that is, a short circuit abnormality has occurred, or an operation different from the control by the check operation control means is performed. In other words, it can be assumed that an overcurrent has occurred due to this. By performing the same processing while changing the check target, it is possible to detect the abnormality of the switching element to be checked on the other side.

  Therefore, when an abnormality has occurred as a result of determination on either the upper side or the lower side, it can be estimated that an overcurrent has occurred. Also, when performing duty control, the duty ratio is increased from a small state, that is, when the power supply current flows, the power supply current detection value increases as the duty ratio increases. Become. Therefore, it is possible to detect the occurrence of overcurrent only by flowing a relatively small power supply current until the power supply current detection value exceeds the determination threshold value.

  Further, in the electric power steering control device according to claim 3, the duty control means increases the duty ratio by setting a preset maximum duty ratio as an upper limit, and the maximum duty ratio is checked by the overcurrent determination means. The switching element is set based on a resistance value of an assumed current path of the power supply current and a determination threshold value used in the overcurrent determination unit when the switching element is determined to be abnormal. Yes.

  In the invention according to claim 3, when the overcurrent determination unit determines that the switching element to be checked is abnormal, the resistance value of the assumed current path of the power supply current and the overcurrent determination unit Since the maximum duty ratio is set based on the determination threshold value for the power supply current detection value, the determination threshold value for the power supply current detection value is exceeded in a state where the switching element is determined to be abnormal based on the maximum duty ratio. If the duty ratio through which the power supply current flows is calculated and this duty ratio is set as the maximum duty ratio, the switching element may be considered normal if the power supply current that exceeds the threshold for determination does not flow at this maximum duty ratio. It becomes possible. Therefore, by determining whether or not the switching element is abnormal when the maximum duty ratio is reached, it is possible to determine whether or not an overcurrent has occurred in a shorter time. For this reason, when the power supply voltage detection value exceeds the voltage return determination threshold value, the steering assist control is promptly resumed, and the time during which the steering assist control is stopped can be shortened. .

The electric power steering control device according to a fourth aspect is characterized in that the duty control means changes the duty ratio stepwise.
In the invention according to claim 4, since the duty control means changes the duty ratio stepwise when performing duty control, it is possible to change the power supply current flowing to the bridge circuit stepwise. When this occurs, the time required until the detected value of the power supply current flowing to the bridge circuit exceeds the determination threshold value can be shortened.

Further, in the electric power steering control device according to claim 5, the check operation control means sets one of the upper side and the lower side of the switching elements constituting the bridge circuit as a first check target. The first check target switching element is controlled to be in an open state and the other side is set as the second check target. The second check target switching element has a duty ratio in the vicinity of 100% set in advance. A first duty control means for controlling the duty while increasing the duty ratio until reaching a specified value, and a first preset current power detection value when the switching element is operated by the first duty control means . when it is less to be checked determining threshold value, after the control end by the first duty control means, Serial second checked switching element, the duty ratio duty control while reducing the duty ratio to reach 50% from the specified value, the first checked for the switching element, the duty ratio of 50% Second duty control means for performing duty control in a complementary manner with the first switching element while increasing the duty ratio until reaching the value, wherein the overcurrent determination means is the first duty control means. When the power supply current detection value when the switching element is operated exceeds the first check target determination threshold value, it is determined that an overcurrent has occurred in the first check target switching element; The power supply current detection value when the switching element is operated by the duty control means 2 is a preset second value. Overcurrent to said second checked switching element when exceeding a check target determining threshold value is characterized by determining that occurred.

  In the invention according to claim 5, any one of the upper side and the lower side is set as the first check target, and the other side is set as the second check target. In the first duty control means, All the switching elements to be checked are controlled to be in an open state, and the duty ratio of the second switching elements to be checked is controlled while increasing the duty ratio until the duty ratio reaches a specified value near 100%. Since the first check target, that is, the switching element on either the upper stage side or the lower stage side is controlled to be in an open state, even if the duty control is performed on the second check target switching element, the power source current inherently flows. There is no. Therefore, when it is determined that the power supply current detection value exceeds the determination threshold value and the power supply current is flowing, the first switching target switching element is abnormal, that is, a short abnormality has occurred or a check operation is performed. It can be considered that the operation is different from the control by the control means.

  On the other hand, in the second duty control means, the duty ratio is controlled to the specified value when the power supply current detection value when the switching element is operated by the first duty control means is equal to or less than the determination threshold value. The second check target switching element is duty-controlled while decreasing the duty ratio until the duty ratio reaches 50% from the specified value, and the first check target switching element has a duty ratio of 50. The duty ratio is increased until reaching%, and the duty control is complementarily performed with the switching element to be checked.

  At this time, it is determined that the power supply current detection value when the switching element is operated by the first duty control means is equal to or less than the determination threshold value, and the first check target switching element is normal. In addition, since the first check target switching element and the second check target switching element are complementarily duty-controlled, even if the first check target switching element is duty controlled, the power supply current is essentially Will not flow. Therefore, when it is determined that the power supply current detection value exceeds the determination threshold value and the power supply current is flowing, the second check target switching element can be regarded as abnormal. In addition, since the duty element of the first check target switching element is complementarily increased with that of the second check target switching element, the power supply before a relatively large power supply current flows through the bridge circuit. It is possible to detect the occurrence of overcurrent at a stage where the current value is lower.

The electric power steering control device according to claim 6 is characterized in that the first duty control means and the second duty control means change the duty ratio stepwise.
In the invention according to claim 6, since the first and second duty control means change the duty ratio stepwise when performing duty control, the power supply current flowing to the bridge circuit is changed stepwise. When an overcurrent has occurred, it is possible to shorten the time required until the detected value of the power supply current flowing to the bridge circuit exceeds the determination threshold value.

Further, in the electric power steering control device according to claim 7, the overcurrent detection means performs the overcurrent detection immediately after the power supply voltage detection value falls below the voltage drop determination threshold or in the vicinity thereof. It is characterized by that.
In the invention according to claim 7, since the overcurrent detection is performed immediately after the power supply voltage value detection value falls below the voltage drop determination threshold value or in the vicinity thereof, the overcurrent is not caused but temporarily. When the power supply voltage drops, the overcurrent detection is performed while waiting for the power supply voltage to recover, and the steering assist control can be resumed when the power supply voltage recovers. It is possible to shorten the time during which the steering assist control is stopped.

  Furthermore, in the electric power steering control device according to claim 8, the power supply voltage detection value before the power supply voltage detection value falls below the voltage drop determination threshold in the process until the power supply voltage detection value falls below the voltage drop determination threshold. Based on the power supply current value detected by the current detection means before the voltage drop detected by the current detection means before the voltage drop, the current detection means that detects the power supply current value that has flowed through the bridge circuit during the predetermined period of time, Voltage reduction factor estimation means for estimating whether or not the steering assist control means is due to steering assist control, and the overcurrent detection means is the voltage decrease factor estimation means that causes the power supply voltage decrease to be Overcurrent detection is performed only when it is assumed that the steering assist control is due to the steering assist control, and the steering assist control means determines that the factor of the power supply voltage drop is a factor other than the steering assist control. When the steering assist control is stopped by the steering assist control stop means, the steering assist control is performed when the power supply voltage detection value exceeds the voltage return determination threshold. It is characterized by resuming.

  In the invention according to claim 8, the current flows to the bridge circuit during a predetermined period in the process until the power supply voltage detection value falls below the voltage drop determination threshold before the power supply voltage detection value falls below the voltage drop determination threshold. Based on the power supply current value, it is inferred whether the cause of the power supply voltage drop is due to the steering assist control of the steering assist control means, and only when the steering assist control is inferred, the overcurrent detection means The overcurrent detection is performed, and the power supply current is not flowing in the bridge circuit, such as when the voltage drops due to cranking, and it is estimated that the steering assist control is not a factor, the overcurrent detection is not performed. Therefore, it is possible to prevent unnecessary overcurrent detection from being performed in a state where the power supply voltage decrease is not caused by the steering assist control, and accordingly, the time during which the steering assist control is stopped can be shortened. Is possible.

  According to the electric power steering control device of the first aspect of the present invention, when the power supply voltage detection value falls below the voltage drop determination threshold value, the steering assist control is stopped, and the switching element constituting the bridge circuit is overcurrent. The operation is performed in the check mode for detection, and the presence or absence of overcurrent is detected based on the power supply current flowing in the bridge circuit at this time, so steering assist control is resumed when the presence or absence of occurrence of overcurrent is reliably determined. Therefore, the overcurrent detection is not stopped before the occurrence of overcurrent is determined, and the overcurrent detection can be performed reliably.

  According to the electric power steering control device of the second aspect of the present invention, among the switching elements on the upper stage side and the lower stage side constituting the bridge circuit, one of the switching elements is set to be checked and all the switching elements are opened. The other side controls the duty of the switching element, and when the power supply current flows in the bridge circuit in this state, the switching element to be checked is determined to be abnormal, and this is determined for each of the upper stage side and the lower stage side. Therefore, the abnormality of the switching element can be accurately detected, and it can be easily and reliably detected whether or not an overcurrent is generated due to the abnormality of the switching element. Also, at this time, since the duty control is performed while increasing the duty ratio from a small state, when the power supply current flows through the bridge circuit, the power supply current is relatively small until it exceeds the determination threshold value. Whether or not an overcurrent has occurred can be detected simply by supplying a power supply current.

  According to the electric power steering control device of the third aspect, when the overcurrent determination unit determines that the switching element to be checked is abnormal, the resistance value of the current path assumed for the power supply current is Since duty control is performed while increasing the duty ratio with the maximum duty ratio set based on the threshold for determining the power supply current detection value in the overcurrent determination means as the upper limit, the duty ratio is increased unnecessarily Therefore, it is possible to detect whether or not an overcurrent has occurred at an appropriate timing, and to shorten the time for stopping the steering assist control accordingly.

  Further, according to the electric power steering control device of the fourth aspect, since the duty ratio is changed stepwise when performing duty control, the power supply current flowing to the bridge circuit can be changed stepwise. When a current is generated, the time required until the detected value of the power supply current flowing to the bridge circuit exceeds the determination threshold value can be shortened.

  According to the electric power steering control device of the fifth aspect, all of the first check target switching elements are controlled to be in the open state, and the second check target switching elements are defined to have a duty ratio of about 100%. Since the duty ratio is controlled while increasing the duty ratio until the value is reached, it is possible to easily detect the abnormality of the first check target switching element by detecting the power supply current that does not flow originally. Further, when there is no abnormality in the first check target switching element, the second check target switching element whose duty ratio is controlled to the specified value is changed until the duty ratio reaches 50% from the specified value. Since the duty control is performed while the duty ratio is increased while the duty ratio is increased until the duty ratio reaches 50%, the duty control is performed in a complementary manner with the first switching element. By detecting a power supply current that does not flow originally, an abnormality of the second switching element can be easily detected. Further, since the duty element of the first check target switching element is complementarily increased with that of the second check target switching element, the power supply current value before a large power supply current flows is lower. The abnormality can be detected.

  Further, according to the electric power steering control device of the sixth aspect, since the duty ratio is changed stepwise when performing duty control, the power supply current flowing to the bridge circuit can be changed stepwise. When a current is generated, the time required until the detected value of the power supply current flowing to the bridge circuit exceeds the determination threshold value can be shortened.

  Further, in the electric power steering control device according to claim 7, the overcurrent detection means performs the overcurrent detection immediately after or near the time when the power supply voltage detection value falls below the voltage drop determination threshold value. Overcurrent detection can be performed while waiting for the recovery of the power supply voltage. When the power supply voltage temporarily decreases, the steering assist control can be resumed promptly when the power supply voltage recovers. . Therefore, since the time during which the steering assist control is stopped can be shortened accordingly, the steering assist by the electric motor can be executed for a longer period, and the usability can be further improved.

  Furthermore, the electric power steering control device according to claim 8 detects the overcurrent by the overcurrent detection means only when the cause of the decrease in the power supply voltage is estimated to be the steering assistance control of the steering assistance control means. Therefore, it can be detected that unnecessary overcurrent detection is performed when the power supply voltage is not caused by steering assist control, such as when the voltage decreases due to cranking, and the steering assist control is stopped accordingly. Therefore, it is possible to improve usability.

Embodiments of the present invention will be described below.
First, a first embodiment will be described.
FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, in which 1 is a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2. . The steering shaft 2 has an input shaft 2a and an output shaft 2b. One end of the input shaft 2a is connected to the steering wheel 1, and the other end is connected to an output shaft 2b via a steering torque sensor 3 as steering torque detecting means. It is connected to one end.

The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6.
The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured as a rack and pinion mechanism having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

The output shaft 2b of the steering shaft 2 is connected to a reduction gear 10 that transmits a steering assist force to the output shaft 2b. The reduction gear 10 includes an electric motor 12 that generates a steering assist force for the steering system. The output shaft is connected.
The steering torque sensor 3 detects the steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, the steering torque sensor 3 is a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is converted into a torsional angular displacement, and the torsional angular displacement is detected by, for example, a potentiometer. The detected torque value T output from the steering torque sensor 3 is input to the controller 20.

  As shown in FIG. 2, the controller 20 detects a torque detection value T output from the steering torque sensor 3, a vehicle speed detection value V from the vehicle speed sensor 21, and a hall element that detects the rotational position of the rotor of the electric motor 12. Based on the rotor rotation angle θ detected by the rotor position detection circuit 13 constituted by a resolver, etc., and the motor drive current detected by the motor current detection circuit 22, a known steering assist control process is executed and inputted. A control arithmetic unit 23 that generates a steering assist force corresponding to the detected torque value T and the detected vehicle speed V by the electric motor 12 and calculates a motor current command value for performing a steering assist of the driver, and the electric motor 12 is driven. A motor drive circuit 24 for controlling the motor drive circuit 24 according to a motor current command value from the control arithmetic unit 23, A cutoff circuit 27 connected between the motor drive circuit 24 and the electric motor 12, a battery voltage detection circuit 28 for detecting the voltage of the battery 28a, and a power supply current detection circuit 29 for detecting a power supply current flowing in the motor drive circuit 24. And.

The motor current detection circuit 22 detects any two of the motor drive currents Iu, Iv, and Iw supplied to the respective phase coils of the electric motor 12, for example, Iu and Iw, and detects them for the motor drive current Iud. , Iwd is output to the control arithmetic unit 23.
Here, the current flowing between the motor drive circuit 24 and the electric motor 12 is detected and used as the motor drive current. However, the present invention is not limited to this, and the power supply current detected by the power supply current detection circuit 29 is used. May be used as a motor drive current.

As shown in FIG. 2, the motor drive circuit 24 includes two field effect transistors Qua and Qub connected in series, two field effect transistors Qva and Qvb connected in series, and connected in series. Field effect transistors Qwa and Qwb are formed of a bridge circuit connected in parallel. The connection point of field effect transistors Qua and Qub, the connection point of field effect transistors Qva and Qvb, and the connection point of field effect transistors Qwa and Qwb of this bridge circuit are connected to each phase coil of electric motor 12. A shunt resistor 29r for detecting the power source current in the power source current detecting circuit 29 is connected to the drain side of the upper field effect transistors Qua to Qwa, and the battery voltage V _{BAT of the} battery 28a is connected via the shunt resistor 29r. And applied to the drain side of the upper field effect transistors Qua to Qwa. The source side of the lower field effect transistors Qua to Qwa is grounded.

Here, the power source current detection shunt resistor 29r is connected between the upper field effect transistor and the battery 28a. However, the present invention is not limited to this, and the lower field effect transistors Qub, Qvb, Qwb and the ground are connected. You may connect between.
The FET gate drive circuit 26 controls each field effect transistor of the motor drive circuit 24 by PWM with duty ratios Du, Dv, and Dw determined based on the motor current command values Iut, Ivt, and Iwt output from the control arithmetic unit 23. (Pulse width modulation) is turned on / off by a signal, and thereby the magnitude of the current that actually flows through the electric motor 12 is controlled. When a control signal for controlling on / off of each field effect transistor is input from the control arithmetic unit 23, the designated field effect transistor is controlled to be turned on / off accordingly.

  The cutoff circuit 27 is a relay circuit that is individually inserted between each connection point of the field effect transistors Qua and Qub, Qva and Qvb, Qwa and Qwb, and the phase coils of the electric motor 12 of the motor drive circuit 24. The relay circuit RLY1, RLY2, and RLY3 are configured to switch the relay circuits RLY1, RLY2, and RLY3 to an open state when an abnormality occurs or when an overcurrent check process described later is performed, thereby cutting off the power supply to the electric motor 12.

Then, as described above, the control arithmetic unit 23 generates a motor current command value for driving and controlling the electric motor 12 and outputs the motor current command value to the FET gate drive circuit 26 and is detected by the battery voltage detection circuit 28. Based on the battery voltage detection value VB of the battery 28a and the power supply current detection value IB detected by the power supply current detection circuit 29, the battery voltage V _BAT of the battery 28a and the power supply current flowing in the motor drive circuit 24 are monitored, and the battery voltage V _BAT The steering assist control process is stopped when an abnormality in the lowering of the engine or the occurrence of overcurrent is detected, and the steering assist by the electric motor 12 is stopped.

FIG. 3 is a flowchart illustrating an example of a processing procedure of the monitoring process for monitoring the battery voltage and detecting the overcurrent, which is executed by the control arithmetic device 23. The control arithmetic unit 23 executes a steering assist control process in a known procedure to drive the electric motor 12 to generate a steering assist force according to the input steering torque and to perform the monitoring process at a preset cycle. Execute.
In this monitoring process, first, it is determined whether or not the voltage drop flag F is set to “1”. The voltage drop flag F is a flag indicating whether or not the battery voltage detection value VB has already fallen below the voltage drop determination threshold V _DOWN . The voltage drop flag F is set to “0” at the time of startup.

If the voltage drop flag is not F = 1, the process proceeds to step S2, and it is determined whether or not the battery voltage detection value VB is below the voltage drop determination threshold value V _DOWN . The lower threshold value V _{DOWN for} voltage drop determination is set to the lowest value of the battery voltage V _BAT that can accurately drive and control the electric motor 12.
While the battery 28a does not have a voltage drop and the battery voltage detection value VB detected by the battery voltage detection circuit 28 is equal to or higher than the voltage drop determination threshold V _DOWN , the battery voltage V _BAT is normal and electric. Assuming that the motor 12 can be accurately controlled, the process is terminated.

On the other hand, if the battery 28a has a voltage drop due to something, and the battery voltage detection value VB drops and falls below the voltage drop determination threshold V _DOWN , the process proceeds from step S2 to step S3, and the voltage drop flag is set to F = 1. Then, the process proceeds to step S4 to perform processing when the battery voltage is lowered. Specifically, the steering assist control process is stopped to stop the steering assist, and the field effect transistors Qua to Qwb of the motor drive circuit 24 are switched to the open state to prevent the electric motor 12 from malfunctioning.

In the next execution cycle of this monitoring process, since the voltage drop flag is set to F = 1, the process proceeds from step S1 to step S5, and the battery voltage detection value VB becomes the voltage return determination threshold value V _UP. It is determined whether or not the battery voltage is restored to the normal battery voltage range.
While the battery voltage detection value VB is equal to or lower than the voltage return determination threshold value V _UP , that is, while the battery voltage V _BAT has not returned to the normal voltage range, the processing is terminated as it is from step S5, and the battery voltage detection is performed. When the value VB exceeds the voltage return determination threshold value V _UP and returns to the normal voltage range, the process proceeds from step S5 to step S6, and the voltage drop flag is set to F = 0. Next, the process proceeds to step S7, and an overcurrent check process is performed to detect whether or not an excessive current is flowing in the motor drive circuit 24. Details thereof will be described later.

As a result of the overcurrent check process in step S7, if no overcurrent has occurred, the process proceeds to step S9, where the battery voltage V _BAT has recovered to the normal voltage range, and overcurrent has also occurred. Therefore, the steering assist control process is resumed by allowing the electric motor 12 to be normally driven and controlled.
On the other hand, if an overcurrent has occurred as a result of the overcurrent check process in step S7, the process proceeds from step S8 to step S10 to perform a process when an overcurrent occurs. Specifically, execution of the steering assist control process is prohibited, and each field effect transistor of the motor drive circuit 24 is controlled to be in an open state. Also, processing such as notifying the outside that an overcurrent has occurred is performed, and thereafter this monitoring processing is not performed.

The overcurrent check process in step S7 is performed according to the procedure shown in the flowchart of FIG.
First, in step S21, among the field effect transistors Qua to Qwb of the motor drive circuit 24, the lower stage field effect transistors Qub, Qvb, and Qwb are set as check targets, and a control signal for controlling these to an open state is output. Also, a control signal for switching the cutoff circuit 27 to the open state is output.
Next, the process proceeds to step S22, and duty control is performed on the upper field effect transistors Qua, Qva, and Qwa. At this time, duty control is performed while changing the duty ratio so that the duty ratio continuously increases from 0%.
Next, the process proceeds to step S23, and it is determined whether or not the power supply current detection value IB detected by the power supply current detection circuit 29 exceeds a preset current threshold value I1.

  Here, as described above, since the lower field effect transistors Qub, Qvb, and Qwb are controlled to be opened in the process of step S21, the upper field effect transistors Qua, Qva, and Qwa are set to duty in the process of step S22. Even if controlled, if the field effect transistors Qub, Qvb, and Qwb are operating normally, the through current that passes through the upper and lower field effect transistors does not flow, so that the power source current detection circuit 29 detects the current. The power supply current detection value IB is substantially zero.

  However, when a short circuit abnormality occurs in any of the lower field effect transistors Qub, Qvb, and Qwb, for example, when a short circuit abnormality occurs in the U-phase field effect transistor Qub, the battery 28a, A through current flows through a current path consisting of the upper-stage field-effect transistor Qua that is duty-controlled, the lower-stage field-effect transistor Qub that is short-circuited and conductive, and the ground. This will be detected.

Therefore, the current threshold I1 can be determined that a through current is flowing from the power supply current detection value IB at this time when the upper field effect transistor becomes conductive due to some abnormality. Set to a value.
When the power supply current detection value IB detected by the power supply current detection circuit 29 is larger than the current threshold value I1, the process proceeds from step S23 to step S25, and the lower field effect transistors Qub, Qvb, and Qwb malfunction due to conduction. Therefore, since it is estimated that the battery 28a is in a state where a voltage drop has occurred because an overcurrent has occurred due to this malfunction, it is determined that an overcurrent abnormality has occurred.

  On the other hand, when it is determined in step S23 that the power supply current detection value IB is equal to or less than the current threshold value I1 and no power supply current is flowing, the process proceeds from step S23 to step S24, and the upper stage in which duty control is performed. It is determined whether the duty ratio for the field effect transistors Qua, Qva, and Qwa has reached a preset duty ratio maximum value Dmax1. If the duty ratio has not reached the maximum value Dmax1, the process returns to step S22 to continue increasing the duty ratio and determine whether the power supply current detection value IB at this time is equal to or less than the current threshold value I1.

  Here, the maximum value Dmax1 of the duty ratio is equal to the short-circuit resistance value of the current path assumed for the power supply current when the lower field effect transistors Qub, Qvb, and Qwb are turned on due to malfunction, and the field effect. It is desirable to set based on the current threshold value I1 for determining that the transistor is abnormal in conduction. That is, if the assumed short resistance value and the current threshold value I1 for determining a conduction abnormality are determined, when this conduction abnormality occurs, the current path having a resistance corresponding to the short resistance value It is possible to calculate a duty ratio that allows the power source current IB flowing through the current to exceed the current threshold value I1.

  That is, when the power supply current detection value IB does not exceed the current threshold value I1 when the upper field effect transistor is duty controlled with the calculated duty ratio, the lower field effect transistors Qub, Qvb, Qwb It can be determined that no conduction abnormality has occurred. Therefore, by setting the duty ratio calculated in this way as the maximum value Dmax1, the power supply current detection value IB does not exceed the current threshold I1 when the duty ratio is increased to the maximum value Dmax1. In this case, it can be determined that the lower field effect transistors Qub, Qvb, and Qwb are normal, and whether or not the lower field effect transistors are operating normally without increasing the duty ratio to 100%. Can be confirmed. For this reason, it is possible to shorten the processing time required for determining whether or not the lower field effect transistor is operating normally, that is, whether or not an overcurrent has occurred.

On the other hand, when the duty ratio reaches the maximum value Dmax1, the check on the lower field effect transistors Qub, Qvb, and Qwb is finished, the process proceeds from step S24 to step S31, and then the upper field effect transistors Qua, Qva and Qwa are to be checked, and these are checked.
This check is performed in the same procedure as the check for the lower field effect transistors Qub, Qvb, and Qwb. First, the upper field effect transistors Qua, Qva, and Qwa are controlled to be in an open state.

Next, the process proceeds to step S32, and duty control is performed on the lower field effect transistors Qub, Qvb, and Qwb. At this time, duty control is performed while changing the duty ratio so that the duty ratio continuously increases from 0%.
Next, the process proceeds to step S33, and it is determined whether or not the power supply current detection value IB detected by the power supply current detection circuit 29 exceeds a preset current threshold value I2. The current threshold value I2 may be the same as the current threshold value I1 when the lower field effect transistor is to be checked, and is set in the same procedure as the current threshold value I1. May be.

  When the power supply current detection value IB of the power supply current detection circuit 29 is equal to or less than the current threshold value I2, the process proceeds to step S34, where it is determined whether the duty ratio has reached its maximum value Dmax2, and the duty ratio is the maximum value. If the value Dmax2 has not been reached, the process returns to step S32 to continue increasing the duty ratio and determine whether the power supply current detection value IB has exceeded the current threshold value I2. Note that the maximum value Dmax2 of the duty ratio is the same as the maximum value Dmax1, and the short-circuit resistance value assumed when the upper field effect transistors Qua, Qva, and Qwa are turned on due to malfunction and the electric field What is necessary is just to set based on the said current threshold value I2 for determining that an effect transistor is conduction abnormality.

When the power supply current detection value IB of the power supply current detection circuit 29 exceeds the current threshold value I2, the process proceeds from step S33 to step S35, and a short circuit abnormality occurs in any of the upper field effect transistors Qua, Qva, and Qwa. It is determined that a continuity abnormality has occurred due to a malfunction in the conduction state.
On the other hand, when the power supply current detection value IB does not exceed the current threshold value I2 until the duty ratio reaches the maximum value Dmax2, the process proceeds to step S36, and both the upper and lower field effect transistors are short-circuited. It is determined that no continuity abnormality or the like is in a normal state, that is, no overcurrent has occurred, and a control signal for switching the cutoff circuit 27 to the conductive state is output. If it is determined in the above procedure whether or not an overcurrent has occurred, the overcurrent check process is terminated, and the process returns to FIG. 3 and proceeds to step S8.

  Next, the operation of the first embodiment will be described with reference to the time charts of FIGS. 5 and 6, (a) is the battery voltage detection value VB, (b) is the duty ratio with respect to the upper field effect transistors Qua, Qva, and Qwa, and (c) is the lower field effect transistors Qub, Qvb, A duty ratio with respect to Qwb, (d) is a power supply current detection value IB.

  The control arithmetic unit 23 executes steering assist control processing according to a known procedure, and controls the drive current to the electric motor 12 by controlling the drive of each field effect transistor according to the input steering torque T and the detected vehicle speed V. To do. As a result, the electric motor 12 is driven and controlled, and a steering assist force corresponding to the steering torque T and the vehicle speed detection value V is applied to perform steering assist, thereby reducing the driver's steering load.

The monitoring process shown in FIG. 3 is executed together with the steering assist control process. The battery voltage detection value VB detected by the battery voltage detection circuit 28 is equal to or higher than the voltage drop determination threshold value V _DOWN , and the battery voltage V _BAT Is within the normal voltage range, the process is terminated as it is through step S1 to step S2 of FIG. 3, and the steering assist control process is subsequently executed.
From this state, when the battery voltage of the battery 28a drops for some reason, and the battery voltage detection value VB falls below the voltage drop determination threshold value V _DOUN at time t11 in FIG. 5, the monitoring process performs step S2 in FIG. From step S3, the voltage drop flag F is set to "1", the steering assist control process is stopped, and the field effect transistors Qua to Qwb of the motor drive circuit 24 are controlled to be opened.

As a result, the power supply to the electric motor 12 is stopped, so that the electric motor 12 does not perform an unintended operation.
Then, while the battery voltage V _BAT is low, the processing of step S1 and step S5 is repeated to stop the steering assist control process, and the power consumption of the battery 28a decreases as the steering assist control process stops. When the battery voltage recovers due to the above and the battery voltage detection value VB exceeds the voltage return determination threshold value V _UP at time t12, the process proceeds from step S1 in FIG. 3 to step S7 through steps S5 and S6. Then, after setting the voltage drop flag to F = 0, overcurrent check processing is performed.

  First, the lower field effect transistor is checked, the lower field effect transistor is controlled to be in an open state, the cutoff circuit 27 is controlled to be in an open state (step S21), and the upper field effect transistor is duty controlled (step S21). Step S22). At this time, the duty ratio for the upper field effect transistor is continuously increased from 0% as shown in FIG. That is, if a through current flows through the motor drive circuit 24, the duty ratio is controlled so that the through current gradually increases.

  Here, if the lower field effect transistor is operating normally without any short circuit abnormality, the lower field effect transistor is controlled to be open, so the upper field effect transistor is Even if the duty control is performed, the power supply current does not flow through the motor drive circuit 24, and the power supply current detection value IB does not exceed the threshold value I1. Therefore, when the duty ratio is gradually increased and the duty ratio reaches its maximum value Dmax1 at time t13, it is determined that the lower field effect transistor is operating normally, and the process proceeds from step S24 to step S31 in FIG. This time, the upper field effect transistor is checked.

  That is, the upper field effect transistor is switched to an open state (step S31), and the lower field effect transistor is duty controlled (step S32). At this time, as shown in FIG. 5C, the duty control is performed so that the duty ratio for the lower field effect transistor continuously increases from 0%. That is, if a through current flows, duty control is performed so that the through current gradually increases.

  Here, it is determined that the upper field effect transistor is operating normally without occurrence of a short circuit abnormality or the like. Therefore, since these upper field effect transistors are controlled to be in an open state and operate normally, even if the duty of the lower field effect transistor is controlled, the power supply current does not flow to the motor drive circuit 24. The current detection value IB does not exceed the current threshold value I2. Therefore, when the duty ratio is gradually increased and the duty ratio reaches its maximum value Dmax2 at time t14, the upper field effect transistor is assumed to be normal, and the process proceeds from step S34 to step S36. It is determined that no conduction abnormality such as a short circuit abnormality has occurred in the effect transistor, that is, no overcurrent has occurred, and the cutoff circuit 27 is switched to the conduction state.

Then, the process proceeds from step S8 in FIG. 3 to step S9. At this point, the steering assist control process is resumed, and the steering assist is resumed.
Therefore, when the battery voltage V _BAT of the battery 28a decreases due to some factor, the steering assist control process is stopped while the battery voltage V _BAT is decreasing, so that the electric motor 12 is not driven and controlled. When the electric motor 12 is driven and controlled in a state where the battery voltage V _BAT is low, the electric motor 12 performs an unintended operation, and an unintended steering assist force is applied, thereby giving the driver a sense of discomfort, It can be avoided that each part of the in-vehicle device becomes inoperable due to further decrease in battery voltage V _BAT .

  When a short abnormality occurs in one of the field effect transistors constituting the motor drive circuit 24, for example, the upper field effect transistor Qua of the U phase, from the state in which each part operates normally in this way. When each field effect transistor is controlled to be turned on / off by the steering assist control process, since the field effect transistor Qua is in a conductive state, a current path including the battery 28a, the field effect transistors Qua, Qub, and the ground is formed, and the through current May flow, that is, an overcurrent may flow.

For this reason, when the battery voltage V _BAT decreases due to a voltage drop of the harness impedance of the battery line or the like, and the battery voltage detection value VB falls below the voltage decrease determination threshold V _DOWN at time t21 in FIG. The process proceeds from step S2 to step S3, the voltage drop flag is set to F = 1, and then the process proceeds to step S4 to stop the steering assist control process and to open all the field effect transistors of the motor drive circuit 24. Control.

At this time, the field effect transistor Qua is in a conductive state due to a short circuit abnormality, but since all other field effect transistors are in an open state, no power source current flows through the motor drive circuit 24. Therefore, when the battery voltage V _BAT starts to recover and the battery voltage detection value VB exceeds the voltage recovery determination threshold value V _UP at time t22, the process proceeds from step S5 to step S6 to step S7, and the voltage drop flag is set. Set F = 0 and execute the overcurrent check process.

  First, the lower field effect transistor is checked, the lower field effect transistor is opened, and the upper field effect transistor is duty controlled while increasing the duty ratio. At this time, the upper field effect transistor Qua is in a conductive state because a short circuit abnormality has occurred, but the power supply current does not flow because the lower field effect transistor is in an open state. Therefore, when the duty ratio for the upper field effect transistor reaches its maximum value Dmax1 at time t23, the lower field effect transistor is determined to be normal (steps S21 to S24).

Next, the upper field effect transistor is checked, the upper field effect transistor is opened, and the lower field effect transistor is duty controlled while increasing the duty ratio.
In this case, since the upper field effect transistor is controlled in an open state, the power source current does not flow in this state, but the field effect transistor Qua is in a conductive state due to a short circuit abnormality. A through current flows through the current paths of Qua and Qub.

  At this time, since the duty ratio is gradually increased, the through current, that is, the power supply current gradually increases. When the power supply current detection value IB exceeds the current threshold value I2 at time t24, the process proceeds from step S33 to step S35. It is determined that a continuity abnormality has occurred in the upper field effect transistor, and an overcurrent has occurred due to this continuity abnormality, resulting in a decrease in battery voltage. Then, returning to FIG. 3, the process proceeds from step S7 to step S8 through step S8, and processing when an overcurrent occurs is performed. That is, the execution of the steering assist control process is prohibited, each field effect transistor of the motor drive circuit 24 is controlled to be in an open state, and the fact that an overcurrent abnormality has occurred is notified to the outside. Thereafter, this monitoring process is not executed.

Here, as described above, when it is determined whether or not an overcurrent is flowing based on the power supply current detection value IB detected by the power supply current detection circuit 29, the field effect transistor of the motor drive circuit 24 is short-circuited. Even if an abnormality or the like has occurred and an overcurrent has occurred, it may take some time to detect the overcurrent in some cases.
However, as shown in the first embodiment, after the battery voltage V _BAT is lowered, the battery voltage detection value VB exceeds the voltage return determination threshold value V _UP and the steering assist control process is resumed. Since the overcurrent check process is performed at the time before the overcurrent check is being performed, the overcurrent check process is canceled when overcurrent check is in progress and the occurrence of overcurrent has not been determined. Absent. Therefore, it is possible to reliably detect a conduction abnormality due to a short circuit abnormality or an operation abnormality of the field effect transistor, and it is possible to reliably detect the occurrence of an overcurrent associated therewith.

In addition, the overcurrent check process performs drive control to detect each overcurrent of each field effect transistor of the motor drive circuit 24 in a state where the battery voltage V _BAT is recovered and the steering assist control process is stopped. Since the presence or absence of the occurrence of overcurrent is detected, it can be accurately detected without being affected by other control processing.
Further, as described above, when the overcurrent check process is performed, the duty ratio at the time of performing the duty control of the field effect transistor is gradually increased, and whether or not there is an abnormality when the preset maximum value Dmax1 or Dmax2 is reached. Has been confirmed. Since the maximum values Dmax1 and Dmax2 set the minimum value of the duty ratio that can accurately detect the presence or absence of conduction abnormality, this determination is required while accurately detecting the presence or absence of conduction abnormality. The required time can be shortened.

Therefore, it is possible to shorten the time required until the steering assist control process is restarted, to quickly restart the steering assist, and to further reduce the driver's steering load.
In addition, when the overcurrent check is performed, the duty ratio is gradually increased. Therefore, when the through current flows due to the conduction abnormality, the abnormality is detected when the through current exceeds the current threshold value I1 or I2. The presence / absence can be determined, that is, the presence / absence of an abnormality, that is, the presence / absence of an overcurrent can be determined at a stage where the through current is a smaller current value. Therefore, it is possible to determine whether or not an overcurrent has occurred by supplying a power supply current having a relatively low current value without supplying an excessive current. Therefore, the power consumption of the battery 28a can be reduced by that amount, and an overcurrent check can be performed efficiently. Also, when an overcurrent occurs, the motor drive circuit 24 before the large current for overcurrent detection flows. Overcurrent can be detected at the time.

  In the first embodiment, the case where the presence / absence of overcurrent is determined when the duty ratio is increased to the maximum value Dmax1 or Dmax2 has been described. However, the duty ratio is set to the maximum value Dmax1 or Dmax2. Needless to say, it is possible to determine the occurrence of overcurrent by increasing the value to a larger value, for example, about 100%.

Next, a second embodiment of the present invention will be described.
Since the second embodiment is the same as the first embodiment except that the procedure of the overcurrent check process is different, detailed description of the same part is omitted.
FIG. 7 is a flowchart illustrating an example of a processing procedure of overcurrent check processing according to the second embodiment.
In the overcurrent check process in the second embodiment, first, the lower field effect transistor is checked in the same manner as the overcurrent check process in the first embodiment. This process is the same as in the first embodiment, and controls the cutoff circuit 27 to an open state, controls the lower field effect transistor to an open state, and gradually increases the duty ratio while increasing the duty ratio. The duty of the effect transistor is controlled, and it is determined whether or not the power supply current detection value IB detected by the power supply current detection circuit 29 at this time exceeds the current threshold value I1 (steps S21 to S23).

When the power supply current detection value IB exceeds the current threshold value I1, the process proceeds from step S23 to step S25, and it is determined that a conduction abnormality has occurred in the lower field effect transistor.
On the other hand, when the power supply current detection value IB is less than or equal to the current threshold value I1, the process proceeds from step S23 to step S24a to determine whether the duty ratio reaches 100% or an upper limit set in the vicinity thereof, When the duty ratio has not reached the upper limit value, the process returns to step S22 and duty control is performed while the duty ratio is continuously increased.

When the power supply current detection value IB is equal to or lower than the current threshold value I1 and the duty ratio reaches 100%, it is determined that the lower field effect transistor is normal, and the process proceeds to step S41. Check the upper field effect transistor.
When the upper field effect transistor is checked, duty control is performed so that the duty ratio of the upper field effect transistor gradually decreases from a specified value set to 100% or a value in the vicinity thereof. For the field effect transistors, the duty control is performed so that the duty ratio gradually increases from 0%. At this time, the duty ratio for the upper and lower field effect transistors is changed in a complementary manner, and duty control is performed so that the upper and lower field effect transistors do not become conductive at the same time.

  Next, the process proceeds to step S42, where it is determined whether or not the power supply current detection value IB exceeds the current threshold value I3. When the power supply current detection value IB exceeds the current threshold value I3, the process proceeds to step S45. The upper field effect transistor is determined to be abnormal in conduction. On the other hand, when the power supply current detection value IB is less than or equal to the current threshold value I3, the process proceeds to step S43, where it is determined whether the duty ratio for the upper and lower field effect transistors has reached 50%, and has reached 50%. If not, the process returns to step S41 to continuously change the duty ratio to perform duty control. When the duty ratio reaches 50%, the upper field effect transistor is assumed to be normal, and the process proceeds from step S43 to step S44. It is determined that all of the lower field effect transistors are normal and no overcurrent has occurred, and the cutoff circuit 27 is switched to a conductive state.

The current threshold I3 is detected when the upper and lower field effect transistors are duty-controlled as described above when the upper field effect transistors become conductive due to some abnormality. From the value IB, it is set to a value at which it can be determined that a through current is flowing.
Therefore, as shown in the time chart of FIG. 8, when the battery voltage V _BAT drops for some reason and the power supply voltage detection value VB falls below the voltage drop determination threshold V _DOWN at time t31, the steering assist control is performed at this time. The processing is stopped, and all the field effect transistors of the motor drive circuit 24 are controlled to be open.

In FIG. 8, (a) is the battery voltage detection value VB, (b) is the duty ratio for the upper field effect transistor, and (c) is the duty ratio for the lower field effect transistor.
When the battery voltage V _BAT recovers from this state and the battery voltage detection value VB exceeds the voltage recovery determination threshold value V _UP at time t32, the overcurrent check process of FIG. 7 is executed.

  First, the lower field effect transistor is checked, the lower field effect transistor is in an open state, the upper field effect transistor is duty controlled while gradually increasing the duty ratio, and a conduction abnormality occurs in the lower field effect transistor. Otherwise, the power source current does not flow through the motor drive circuit 24, and therefore the lower field effect transistor is determined to be normal. On the contrary, if a conduction abnormality has occurred in the lower field effect transistor, the through current flows by controlling the duty of the upper field effect transistor, so that when the power supply current detection value IB exceeds the current threshold value I1. A continuity error is detected.

  Then, when the duty ratio reaches the specified value near 100% at time t33 without detecting the conduction abnormality, the upper field effect transistor is checked next, and the upper field effect transistor sets the duty ratio to near 100%. The lower field effect transistor gradually increases its duty ratio from 0% and complementarily duty-controls these.

  Here, since the duty control is performed so that both the upper and lower field effect transistors are not conductive, if the upper field effect transistor has no conduction abnormality, the lower field effect transistor is duty controlled. However, the power supply current does not flow. Therefore, when the duty ratio reaches 50%, it is determined that the upper field-effect transistor is normal. At this point, it is determined that no overcurrent has occurred, the overcurrent check process is terminated, and the steering assist is performed. To resume.

  Therefore, when checking the upper field effect transistor, the duty ratio is not increased to 100%, but the presence or absence of conduction abnormality is determined when it reaches 50%. The time required for processing can be shortened. Therefore, the steering assist control process can be resumed promptly when there is a continuity abnormality, that is, no overcurrent has occurred, so that steering assist can be performed more accurately.

  Further, if a conduction abnormality occurs in the upper field effect transistor, it is determined that the conduction abnormality occurs when the power supply current detection value IB exceeds the current threshold value I3. A conduction abnormality can be detected at a small stage. That is, since an abnormal conduction, that is, an overcurrent can be detected at an earlier stage, it is possible to quickly cope with the overcurrent.

  Further, when checking the upper field effect transistor, duty control is performed while increasing the duty ratio of the lower field effect transistor from 0%, and at this time, the duty ratio of the upper field effect transistor is 100%. The upper and lower field effect transistors are complementarily duty controlled so that no overcurrent flows when a certain amount of duty is open, that is, when a certain amount of current is flowing. Since it can be determined, the time until the start of control can be shortened.

Further, it is possible to determine whether or not the field effect transistor has a conduction abnormality at a stage where the duty ratio is relatively small, that is, it is possible to suppress the amount of current flowing to the motor drive circuit 24 for abnormality detection, and power consumption accordingly. In addition, it is possible to prevent a large current from flowing through the motor drive circuit 24 in a state where an overcurrent can occur.
In the second embodiment, the field effect transistor on the lower stage side is checked, and then the field effect transistor on the upper stage side is checked. At this time, the field effect transistors on the upper stage side and the lower stage side are In this case, the duty ratio is changed in a complementary manner until the duty ratio reaches 50%, but the upper field effect transistor may be checked first. In this case, the lower field effect When the transistors are checked, the upper-stage and lower-stage field effect transistors may be changed together until the duty ratio reaches 50%, and the duty control may be performed in a complementary manner.

In the first and second embodiments, as shown in FIGS. 5B and 5C or FIGS. 8B and 8C, when the field effect transistor is checked, the upper stage Although the duty ratios of the side and lower stage field effect transistors are continuously changed linearly, for example, the duty ratio may be changed stepwise as shown in FIG.
Thus, by changing in steps and appropriately setting the rate of the change, the time required until the duty ratio reaches its maximum value Dmax or near 100% can be shortened. The change ratio of the duty ratio is set to a value that is twice the previous value, for example, 1, 2, 4, 8, 16,. Set (for example, more than electrical time constant). By setting in this way, a current approximately twice that of the previous time flows, so that the detection time can be shortened without excessive current flowing rapidly.

Note that the change ratio of the duty ratio does not have to be uniform. For example, it may be changed at a relatively small change rate in the vicinity of the duty ratio at which the power supply current equivalent to the through current can flow, and may be changed at a relatively large change rate until the vicinity of the duty ratio is reached. can do.
In each of the above embodiments, the case where the duty ratio is increased from 0% has been described. When an abnormality occurs in the field effect transistor, the abnormality of the field effect transistor is detected from the power supply current value IB at this time. When the duty ratio that can be used is known, the duty ratio may be increased from a value in the vicinity of the known duty ratio.

Next, a third embodiment of the present invention will be described.
Since the third embodiment is the same as the first embodiment except that the procedure of the monitoring process is different, detailed description of the same part is omitted.
In the third embodiment, the monitoring process is performed according to the procedure shown in FIG.
In FIG. 10, the processing from step S51 to step S54 is the same as the processing from step S1 to step S4 of the first embodiment, and first, it is determined whether or not the voltage drop flag is set to F = 1. If the voltage drop flag is not F = 1, the process proceeds to step S52 to determine whether or not the battery voltage detection value VB is below the voltage drop threshold V _DOWN . When the battery voltage detection value VB is equal to or higher than the voltage drop threshold V _DOWN , it is determined that the battery voltage V _BAT is in the normal voltage range, and the process is terminated as it is.

On the other hand, when the battery voltage detection value VB is lower than the voltage drop threshold V _DOWN , the process proceeds to step S53, the voltage drop flag is set to F = 1, and then the process proceeds to step S54. To stop the steering assist control process, and control each field effect transistor of the motor drive circuit 24 to be in an open state to cut off the power supply to the electric motor 12.
Next, the process proceeds to step S55, and an overcurrent check process is performed. This overcurrent check process can be applied to any of the overcurrent check processes described in the first embodiment or the second embodiment.

  As a result of the overcurrent check process, if no overcurrent has occurred, the process is terminated as it is, and the steering assist control process is continued. However, when it is determined that an overcurrent has occurred, steps S56 to S57 are performed. The process at the time of occurrence of overcurrent is performed, the execution of the steering assist control process is prohibited, and each field effect transistor of the motor drive circuit 24 is switched to the open state to indicate that an overcurrent abnormality has occurred. Notify

On the other hand, when the voltage drop flag is set to F = 1 in the process of step S51, the process proceeds from step S51 to step S58 to determine whether or not the battery voltage detection value VB exceeds the voltage return determination threshold value V _UP. When the battery voltage detection value VB is equal to or lower than the voltage recovery determination threshold value V _UP , the process is terminated as it is because the battery voltage is not recovered, and the battery voltage detection value VB is the voltage recovery determination threshold value V. When the voltage exceeds _UP , it is determined that the battery voltage V _BAT has recovered to the normal voltage range, the process proceeds to step S59, the voltage drop flag is set to F = 0, the process proceeds to step S60, and the steering assist control is performed. The processing is resumed and the steering assist is resumed.

Thus, in this third embodiment, is performed overcurrent checking processing when the battery voltage detected value VB falls below the voltage drop determination threshold V _DOWN.
In other words, since the overcurrent check process is performed during the waiting time waiting for the battery voltage to recover, the overcurrent check process has already been completed when the battery voltage recovers to the normal voltage range. Since the process is advancing, if it is determined that the battery is normal as a result of the overcurrent check process, the steering assist control process can be resumed immediately when the battery voltage is restored to the normal voltage range.
Therefore, the time during which the steering assist control process is stopped can be further shortened, and in other words, the time during which the steering assist is stopped can be shortened, so that the usability can be further improved. it can.

Next, a fourth embodiment of the present invention will be described.
Since the fourth embodiment is the same as the first embodiment except that the processing procedure of the monitoring process is different, detailed description of the same part is omitted.
In the fourth embodiment, the monitoring process is performed according to the procedure shown in FIG.
First, in step S1, it is determined whether or not the voltage drop flag is set to F = 1. If the voltage drop flag is not set to F = 1, the process proceeds to step S1a and is detected by the power supply current detection circuit 29. The power supply current detection value IB is stored.

  In this storage process, a process of storing the power supply current detection value IB in the current sampling period and the power supply current detection value IB between the previous sampling period and the previous sampling period in a predetermined storage area is performed. That is, each time the power supply current detection value IB is read, the power supply current detection values stored in the storage area are sequentially updated and stored, and the latest power supply current detection values IB for a predetermined period are stored in the storage area.

Next, the process proceeds to step S2, and the processing from step S2 to step S4 is the same as that in the first embodiment, and the processing is ended as it is when the battery voltage detection value VB is equal to or higher than the voltage drop determination threshold value V _DOWN. However, when the battery voltage detection value VB is below the voltage drop threshold V _DOWN , the voltage drop flag is set to F = 1, the process at the time of battery voltage drop is performed, and the steering assist control process is stopped. At the same time, all the field effect transistors constituting the motor drive circuit 24 are switched to the open state.

Next, the process proceeds to step S4a, where, for example, an average value is calculated based on each power supply current detection value IB in a predetermined number of sampling periods from the previous period stored in a predetermined storage area in the process of step S1a. the battery voltage detection value VB calculates a representative value of the previous power supply current from the time it is detected that falls below the voltage drop determination threshold V _DOWN, is set as the voltage drop before current value. Then, the process ends.

In the next sampling cycle, since the voltage drop flag is set to F = 1, the process proceeds from step S1 to step S5, and it is determined whether or not the battery voltage detection value VB exceeds the voltage return determination threshold value V _UP. If not, the process is terminated. When the battery voltage detection value VB exceeds the voltage return determination threshold value V _UP , the battery voltage V _BAT returns to the normal voltage range and the process proceeds to step S6, and the voltage drop flag is set to F = 0. (Step S6).

Next, the process proceeds to step S6a, and it is determined whether or not the current value before voltage drop set in step S4a exceeds a preset threshold value. This threshold value is such that the power source current flows through the motor drive circuit 24 in a predetermined period immediately before the battery voltage detection value VB reaches a state below the voltage drop determination threshold value V _DOWN. It is determined whether the battery voltage V _BAT has decreased due to the drive control, or whether the battery voltage V _BAT has decreased due to a factor other than power supply to the motor drive circuit 24 such as cranking. For example, it is set to a value that is equal to or greater than the value of the current that flows during normal control.

When the current value before the voltage drop is equal to or lower than the threshold value, the drop in the battery voltage V _BAT is caused by a factor other than the power supply to the motor drive circuit 24 such as cranking, It is determined that there is no need to check for the occurrence of overcurrent, and the process proceeds to step S9 to restart the steering assist control process.
On the other hand, when the current value before the voltage drop exceeds the threshold value, the power supply current flows through the motor drive circuit 24 immediately before the battery voltage V _BAT falls below the voltage drop judgment threshold value V _DOWN , and the battery voltage When it is predicted that the decrease in power is caused by supplying power to the motor drive circuit 24, the process proceeds to step S7 to perform overcurrent check processing. This overcurrent check process may be performed according to any procedure of the first embodiment and the second embodiment.

If the result of the overcurrent check process is normal, the process proceeds to step S9 to restart the steering assist control process. If the result is abnormal, the process proceeds to step S10, and the process when an overcurrent occurs is performed. The execution of the steering assist control process is prohibited, the field effect transistors constituting the motor drive circuit 24 are switched to the open state, and the occurrence of overcurrent is notified to the outside.
As described above, in the fourth embodiment, the overcurrent check process is executed only when it is predicted that the cause of the decrease in the battery voltage V _BAT is due to the power supply to the motor drive circuit 24. When the cause of the decrease in the battery voltage V _BAT is predicted to be due to other factors such as cranking, the overcurrent check process is not performed.

Therefore, when the cause of the decrease in the battery voltage V _BAT is caused by factors other than the motor drive circuit 24 such as cranking, the steering assist control is promptly performed when the battery voltage detection value VB returns to the voltage return determination threshold value V _UP. Processing can be resumed. Therefore, the time during which the steering assist control process is stopped can be further shortened, that is, the usability can be further improved.

In the processing of step S1a of FIG. 11 calculates the representative value from the last time the battery voltage detection value VB falls below the voltage recovery determination threshold V _UP based on the power source current value in a predetermined period However, the present invention is not limited to this, and the representative value is calculated based on the power supply current value in a predetermined period before immediately before the battery voltage detection value VB falls below the voltage recovery determination threshold value V _UP. In short, the power supply current value in any period can be determined as long as it can be determined whether or not the decrease in the battery voltage V _BAT is caused by the supply of the power supply current to the motor drive circuit 24. May be used.

In the fourth embodiment, the case where the present invention is applied to the first embodiment has been described. However, the present invention is not limited to this, and the present invention can also be applied to the third embodiment.
In each of the above embodiments, when performing the overcurrent check process, the upper and lower field effect transistors are individually driven. In order to realize this, the PWM signals for the upper-stage and lower-stage field effect transistors may be configured to be individually settable. Further, when the upper and lower field effect transistors are configured to be driven in a complementary manner, that is, the lower duty ratio D _L is D _L = 100−D _U with respect to the upper duty ratio D _U. In the case of being configured to be set automatically, the upper stage field effect transistor and the lower stage field effect transistor may be configured in hardware so that they can be individually controlled to the open state. For example, in the configuration of the controller 20 shown in FIG. 2, as shown in FIG. 12, the control calculation for each field effect transistor constituting the motor drive circuit 24 is provided between the control calculation device 23 and the FET gate drive circuit 26. An upper stage FETON / OFF permission circuit 32 and a lower stage FETON / OFF permission circuit 33 for cutting off the supply of the PWM control signal from the device 23 are provided, and these upper stage FETON / OFF permission circuit 32 and lower stage FETON / OFF permission circuit 33 are provided. What is necessary is just to perform on-off control complementarily by the control arithmetic unit 23. The upper FET ON / OFF permission circuit 32 includes, for example, a diode and an NPN transistor connected to each of the PWM control signal supply lines corresponding to the upper field effect transistor from the control arithmetic unit 23 to the FET gate drive circuit 26. The collector side of the NPN transistor is connected to the cathode side of the diode, and the emitter side of the NPN transistor is grounded. The lower stage FET ON / OFF permission circuit 33 is similarly configured.

Here, in the above embodiment, the control arithmetic device 23 and the FET gate drive circuit 26 correspond to the steering assist control means, and the battery voltage detection circuit 28 corresponds to the power supply voltage detection means.
In FIG. 3, the process of step S4 corresponds to the steering assist control stop means, and the process of step S7 corresponds to the overcurrent detection means. In FIG. 10, the process of step S54 corresponds to the steering assist control stop unit, and the process of step S55 corresponds to the overcurrent detection unit.

  Further, the processes of steps S21 and S22, step S24, steps S31 and S32, and step S34 in FIG. 4 correspond to the check operation control means and the duty control means, and the processes of steps S23 and S33 correspond to the power supply current detection means. Steps S25, S35, and S36 correspond to overcurrent determination means. The maximum duty ratio values Dmax1 and Dmax2 in steps S24 and S34 correspond to the maximum duty ratio.

In addition, the processes in steps S21 and S22 and step S24a in FIG. 7 correspond to the first duty control means, and the processes in steps S41 and S43 correspond to the second duty control means.
Further, in FIG. 11, the processing of step S1a and step S4a corresponds to the current detection means before voltage drop, and the processing of step S6a corresponds to the voltage drop factor estimation means.

It is a schematic structure figure showing one embodiment of the present invention. FIG. 2 is a block diagram illustrating a specific configuration of the controller in FIG. 1. It is a flowchart which shows an example of the process sequence of the monitoring process performed with the controller of FIG. It is a flowchart which shows an example of the process sequence of the overcurrent check process of FIG. It is a time chart with which it uses for description of operation | movement of this invention. It is a time chart with which it uses for operation | movement description of this invention. It is a flowchart which shows an example of the process sequence of the overcurrent check process in 2nd Embodiment. It is a time chart used for operation | movement description of 2nd Embodiment. It is explanatory drawing for demonstrating the other change method of a duty ratio. It is a flowchart which shows an example of the process sequence of the monitoring process in 3rd Embodiment. It is a flowchart which shows an example of the process sequence of the monitoring process in 4th Embodiment. It is a block diagram which shows the other structure of a controller. It is a time chart with which conventional operation | movement description is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Steering shaft 3 Steering torque sensor 12 Electric motor 20 Controller 21 Vehicle speed sensor 22 Motor current detection circuit 23 Control arithmetic device 24 Motor drive circuit 26 FET gate drive circuit 28 Battery voltage detection circuit 28a Battery 29 Power supply current detection circuit

Claims (8)

An electric motor for applying a steering assist force to the steering system;
Steering torque detection means for detecting steering torque;
A bridge circuit for driving the electric motor including a plurality of switching elements;
Steering assist control means for drivingly controlling the electric motor via the bridge circuit based on the steering torque detected by the steering torque detection means;
Power supply voltage detection means for detecting a power supply voltage of a power supply for supplying power to the electric motor;
Steering assist control stop means for stopping steering assist control by the steering assist control means when a power supply voltage detection value detected by the power supply voltage detection means falls below a preset voltage drop determination threshold;
In the electric power steering control device comprising: overcurrent detection means for detecting the presence or absence of occurrence of overcurrent in the bridge circuit,
The overcurrent detection means, a check operation control means for operating the switching element of the bridge circuit in a check mode for overcurrent detection when the power supply voltage detection value falls below the voltage drop determination threshold;
A power supply current detecting means for detecting a power supply current flowing in the bridge circuit when the switching element is operated in the check mode;
Overcurrent determination means for determining presence or absence of occurrence of overcurrent based on a power supply current detection value detected by the power supply current detection means,
After the steering assist control is stopped by the steering assist control stop means, the steering assist control means detects that no overcurrent has occurred in the overcurrent detection means, and the power supply voltage detection value is preset. The electric power steering control device, wherein the steering assist control is resumed when the voltage recovery determination threshold value is exceeded. The check operation control means sets one of the upper side and the lower side among the switching elements constituting the bridge circuit as a check target, opens all the switching elements, and sets the switching elements on the other side. , Having a duty control means for controlling the duty while increasing the duty ratio from a small state,
The overcurrent determination unit determines that the switching element to be checked is abnormal when the power supply current detection value exceeds a predetermined threshold for determination, and sets each of the upper-stage side and lower-stage side switching elements. 2. The electric power steering control device according to claim 1, wherein as a result of performing the determination as the check target, it is determined that an overcurrent has occurred when an abnormality is detected on either side. The duty control means increases the duty ratio with a preset maximum duty ratio as an upper limit,
The maximum duty ratio is the resistance value of the current path assumed for the power supply current and the overcurrent determination unit when the overcurrent determination unit determines that the switching element to be checked is abnormal. 3. The electric power steering control device according to claim 2, wherein the electric power steering control device is set based on a determination threshold value.   4. The electric power steering control device according to claim 2, wherein the duty control means changes the duty ratio stepwise. The check operation control means sets one of the upper stage side and the lower stage side among the switching elements constituting the bridge circuit as a first check target, and opens all the switching elements subject to the first check. And the other side is set as the second check target, and the switching element of the second check target is duty-controlled while increasing the duty ratio until the duty ratio reaches a predetermined value near 100% set in advance. First duty control means;
By the first duty control means when the power supply current detection value when the switching element is operated by the first duty control means is less than or equal to a preset first check target determination threshold value After the control is completed, the second check target switching element is duty-controlled while decreasing the duty ratio until the duty ratio reaches 50% from the specified value, and the first check target switching element is duty-controlled. A second duty control means for performing duty control complementarily with the first switching element while increasing the duty ratio until the ratio reaches 50%,
The overcurrent determination means includes
When the power supply current detection value when the switching element is operated by the first duty control means exceeds the first check target determination threshold, an overcurrent is generated in the first check target switching element. Determine that it has occurred,
When the power supply current detection value when the switching element is operated by the second duty control means exceeds a preset second check target determination threshold value, the second check target switching element is excessive. 2. The electric power steering control apparatus according to claim 1, wherein it is determined that an electric current is generated.   6. The electric power steering control device according to claim 5, wherein the first duty control means and the second duty control means change the duty ratio stepwise.   7. The overcurrent detection unit according to claim 1, wherein the overcurrent detection unit performs overcurrent detection immediately after the power supply voltage detection value falls below the voltage drop determination threshold or in the vicinity thereof. The electric power steering control device according to Item 1. In the process until the power supply voltage detection value falls below the voltage drop determination threshold, the power supply current value that has flowed through the bridge circuit during a predetermined period before the power supply voltage detection value falls below the voltage drop determination threshold. Current detecting means for detecting a voltage drop before voltage drop;
Based on the power supply current value detected by the current pre-voltage drop current detection means, a voltage reduction factor estimation means for estimating whether the cause of the power supply voltage decrease is due to steering assist control in the steering assist control means; With
The overcurrent detection means performs overcurrent detection only when the voltage drop factor estimation means estimates that the cause of the power supply voltage drop is due to the steering assist control,
When it is estimated that the factor of the power supply voltage drop is caused by a factor other than the steering assist control, the steering assist control unit stops the steering assist control by the steering assist control stop unit, and then The electric power steering control device according to any one of claims 1 to 7, wherein the steering assist control is resumed when a voltage detection value exceeds a voltage return determination threshold value. .

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