JP2013147174A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly restrict steering assist when slip occurs by improving detection accuracy of wheel slip in assist control that is performed when failure in a torque sensor is detected.SOLUTION: An estimation steering calculation part 821 calculates an estimation steering angle θe based on wheel speed Vfl, Vfrm Vrl, Vrr. A cutoff frequency setting part 822 sets a high cutoff frequency in a circumference having high possibility that a difference between right and left wheel speed largely changes and sets a low cutoff frequency in a circumference having possibility except for the possibility based on a steering input state amount and a vehicle output state amount. A filtering part 823 performs filtering to the estimation steering angle θe by low pass filter having a set cutoff frequency characteristics.

Description

  The present invention relates to an electric power steering apparatus that generates a steering assist torque by driving a motor based on a steering operation of a driver.

  Conventionally, an electric power steering apparatus detects a steering torque applied to a steering wheel by a driver by a torque sensor, and calculates a target assist torque based on the detected steering torque. Then, the steering operation of the driver is assisted by controlling the current flowing through the motor so as to obtain the target assist torque. Such energization control of the motor is called assist control.

  If the torque sensor fails, the target assist torque cannot be calculated and assist control cannot be performed. On the other hand, Patent Documents 1 and 2 propose electric power steering devices that perform steering assist even when a torque sensor fails. The electric power steering apparatus proposed in Patent Document 1 estimates the self-aligning torque transmitted from the road surface to the steering mechanism when a failure of the torque sensor is detected, and based on the estimated self-aligning torque. Calculate the torque command value. Further, the friction coefficient μ between the road surface and the tire is estimated from the operating state of the ABS device (anti-skid control device). Based on the friction coefficient μ, the estimated value of the self-aligning torque increases as the friction coefficient μ increases. It is corrected so that

  In addition, the electric power steering apparatus proposed in Patent Document 2 is estimated using the first estimated steering angle estimated using the wheel speeds of the left and right wheels on the front wheel side and the wheel speeds of the left and right wheels on the rear wheel side. The average estimated rudder angle is obtained by averaging the two estimated rudder angles, and the target assist torque is calculated based on the average estimated rudder angle and the vehicle speed. In addition, based on the steering angle difference representing the difference between the first estimated steering angle and the second estimated steering angle, a slip gain that decreases as the steering angle difference increases is calculated, and this slip gain is used as the target assist torque. By multiplying, the steering assist is reduced when the wheel slips.

JP 2009-6985 A International Publication WO2011 / 048702

  However, the electric power steering device proposed in Patent Document 1 lacks practicality because the correction amount of the torque command value cannot be obtained unless the wheel is locked by a brake operation. The electric power steering apparatus proposed in Patent Document 2 does not have such a problem, but there is room for improvement in slip detection. In the electric power steering apparatus proposed in Patent Document 2, the first estimated steering angle and the second estimated steering angle are both calculated based on the wheel speeds detected by the wheel speed sensors of the left and right wheels. In general, the detected value of the wheel speed is likely to be affected by a disturbance due to road surface unevenness or the like or a vehicle state. For this reason, even if the wheel is slipping, the values of the first estimated rudder angle and the second estimated rudder angle may match, and in this case, slip may be detected. It is impossible to over-assist.

  As described above, in the electric power steering apparatus proposed in these patent documents, it is desired to improve the detection accuracy of the wheel slip during the assist control performed when the failure of the torque sensor is detected.

  The present invention has been made to cope with the above problem, and improves the wheel slip detection accuracy during assist control performed when a torque sensor failure is detected, so that steering assist is properly performed when slip occurs. The purpose is to restrict.

In order to achieve the above object, the present invention is characterized in that a steering torque sensor (21) for detecting a steering torque input from a steering handle to a steering shaft, and a motor for generating a steering assist torque provided in a steering mechanism ( 20), an abnormality detection means (72) for detecting an abnormality of the steering torque sensor, and when no abnormality of the steering torque sensor is detected, target steering is performed based on the steering torque detected by the steering torque sensor. A control amount setting means (70) for setting a target steering assist control amount using an alternative parameter different from the steering torque when an assist control amount is set and abnormality of the steering torque sensor is detected; A motor control that drives and controls the motor in accordance with the target steering assist control amount set by the control amount setting means. The electric power steering apparatus that includes a means (40, 60),
Estimated steering angle calculation that obtains the wheel speed of the left and right wheels on at least one of the front wheel side and the rear wheel side, and calculates the estimated steering angle that estimates the steering angle based on the acquired wheel speed through low-pass filter processing Means (821, 823), steering input state quantity obtaining means (22, S11, S12) for obtaining at least one of an actual steering angle or steering angular velocity as a steering input state quantity, and at least one of lateral acceleration or yaw rate of the vehicle Vehicle output state quantity acquisition means (30, 31, S11) for obtaining the vehicle output state quantity, and the magnitude of the steering input state quantity is greater than a reference input value or the magnitude of the vehicle output state quantity is a reference output value When the condition of greater than is satisfied, the cutoff frequency of the low-pass filter processing is set higher than when the condition is not satisfied. Cut-off frequency setting means (822, S 13 to S 16), and slip index calculation means (824) for obtaining an actual steering angle and calculating a deviation between the actual steering angle and the estimated steering angle as a wheel slip index. ), And when the target steering assist control amount is set using an alternative parameter different from the steering torque when an abnormality is detected in the steering torque sensor, the slip index set by the slip index calculation means increases. And assist limitation means (83, 825) for limiting the target steering assist control amount so that the target steering assist control amount is reduced.

  In the present invention, when an abnormality of the steering torque sensor is detected, the target steering assist control amount is set using an alternative parameter different from the steering torque. As an alternative parameter, for example, a steering angle can be used. When the steering angle is used, a target steering assist control amount that increases as the steering angle increases may be set. As another alternative parameter, for example, the lateral acceleration of the vehicle can be used. When the lateral acceleration is used, a target assist control amount that increases as the lateral acceleration increases may be set.

  When steering assist is applied using such alternative parameters, excessive steering assist works if the wheels are slipping. Therefore, in the present invention, the slip index calculating means calculates the wheel slip index, and the assist limiting means limits the target steering assist control amount so that the target steering assist control amount decreases as the slip index increases. In order to perform the calculation of the slip index, the present invention includes estimated steering angle calculation means, steering input state quantity acquisition means, vehicle output state quantity acquisition means, and cutoff frequency setting means.

  The estimated rudder angle calculation means obtains the wheel speeds of the left and right wheels on at least one of the front wheel side and the rear wheel side, and the estimated rudder angle obtained by estimating the steering angle based on the obtained wheel speed is subjected to low-pass filter processing. To calculate. The estimated steering angle can be expressed as a function of the difference between the wheel speeds of the left and right wheels, for example. The wheel speed (wheel speed detection value) includes noise (including errors) of various frequency components due to vibrations caused by road surface input, errors of the sensor itself, and the like. Therefore, in calculating the estimated rudder angle, a low-pass filter process is performed to reduce the influence of noise included in the wheel speed. For example, the estimated rudder angle calculated based on the wheel speed is low-pass filtered. Thereby, an estimated rudder angle with less noise can be obtained.

  The slip index calculating means calculates a deviation between the actual steering angle and the estimated steering angle as a wheel slip index. When wheel slip occurs, the actual steering angle (referred to as the actual steering angle) and the estimated steering angle take different values. In this case, it can be estimated that the greater the deviation, the greater the degree of slip. For this reason, the extent of slip can be determined from the magnitude of the deviation between the actual rudder angle and the estimated rudder angle. The actual rudder angle is acquired using, for example, a sensor that detects the rotation angle of the steering shaft, a sensor that detects the rotation angle of the motor, a sensor that detects the stroke of the rack bar, a sensor that detects the tire turning angle, and the like. be able to.

  As described above, the low-pass filter process is interposed in the calculation of the estimated steering angle. As the cut-off frequency of the low-pass filter processing is lowered, the ability to remove noise of various frequency components increases, but on the other hand, the phase delay of the estimated steering angle calculation value increases, and the calculated slip index value is appropriate. It will disappear.

  Therefore, in the present invention, in a situation where the phase delay of the calculated value of the estimated rudder angle tends to be large due to the low-pass filter processing, that is, in a situation where the difference between the wheel speeds of the left and right wheels changes quickly, the cutoff frequency of the low-pass filter processing. Is increased to suppress the phase delay of the calculated value of the estimated rudder angle. Such a situation can be estimated by the steering input state quantity acquisition means and the vehicle output state quantity acquisition means. The steering input state quantity acquisition means acquires at least one of an actual steering angle or steering angular velocity as a steering input state quantity. The vehicle output state quantity acquisition means acquires at least one of the lateral acceleration or the yaw rate of the vehicle as the vehicle output state quantity. The lateral acceleration and yaw rate may be detected and acquired by a lateral acceleration sensor or yaw rate sensor, or may be acquired by calculation. For example, the lateral acceleration and the yaw rate can be uniquely calculated from the left and right wheel speeds. Further, the yaw rate can be uniquely calculated from the vehicle speed and the steering angle.

  In a situation where the steering angle is large or the steering angular velocity is large, there is a high possibility that the difference between the wheel speeds of the left and right wheels changes rapidly. In addition, even in a situation where the lateral acceleration of the vehicle is high or a situation where the yaw rate of the vehicle is high, there is a high possibility that the difference in wheel speed between the left and right wheels will change rapidly. In such a situation, the phase delay of the calculated value of the estimated rudder angle tends to be large, and the calculated value of the slip index becomes inappropriate.

  Therefore, the cutoff frequency setting means satisfies the above condition when the condition that the magnitude of the steering input state quantity is larger than the reference input value or the magnitude of the vehicle output state quantity is larger than the reference output value is satisfied. The cut-off frequency for the low-pass filter processing is set higher than in the case where it is not. Therefore, in situations where the estimated steering angle phase lag tends to be large due to low-pass filter processing, the cutoff frequency of the low-pass filter processing is set high to keep the estimated steering angle calculated value phase delay small, In a situation where the phase delay of the estimated steering angle does not increase due to the filter processing, the noise can be reliably removed by setting the cut-off frequency of the low-pass filter processing low.

  As a result, according to the present invention, it is possible to satisfactorily balance the influence of the phase delay due to the filter processing of the estimated steering angle and the noise removal performance. Therefore, the detection accuracy of the wheel slip is improved, and the steering assist can be properly limited.

  In the above description, in order to help the understanding of the invention, the reference numerals used in the embodiments are attached in parentheses to the configurations of the invention corresponding to the embodiments. It is not limited to the embodiment defined by the reference numerals.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a functional block diagram of assist ECU. It is a graph showing a normal time assist map. It is a functional block diagram of an abnormal time assist torque calculation part. It is a graph showing a basic assistance map at the time of abnormality. It is explanatory drawing explaining calculation of an estimated steering angle. It is a flowchart showing a cut-off frequency setting routine. It is a graph showing a correction coefficient map. It is a flowchart showing an assist restriction routine. It is a graph showing transition of an actual rudder angle, an estimated rudder angle, and an estimated rudder angle after filter. It is a graph showing the cut-off frequency setting map as a modification. It is a graph showing the cutoff frequency setting map as another modification. It is a graph showing a friction compensation torque map. It is a graph showing a friction viscosity compensation torque map. It is a graph showing the upper limit map as a modification.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an electric power steering apparatus 1 for a vehicle according to the embodiment.

  The electric power steering apparatus 1 is configured according to a steering mechanism 10 that steers steered wheels by a steering operation of a steering handle 11, a motor 20 that is assembled to the steering mechanism 10 and generates steering assist torque, and an operating state of the steering handle 11. The electronic control unit 100 that controls the operation of the motor 20 is provided as a main part. Hereinafter, the electronic control unit 100 is referred to as an assist ECU 100.

  The steering mechanism 10 is a mechanism for turning the left and right front wheels Wfl and Wfr by rotating the steering handle 11, and includes a steering shaft 12 connected so that the steering handle 11 is integrally rotated at the upper end. A pinion gear 13 is connected to the lower end of the steering shaft 12 so as to rotate integrally. The pinion gear 13 meshes with a gear portion 14 a formed on the rack bar 14 and constitutes a rack and pinion mechanism together with the rack bar 14.

  The rack bar 14 has a gear portion 14 a housed in the rack housing 16, and both left and right ends thereof are exposed from the rack housing 16 and connected to the tie rod 17. A stopper 18 constituting a stroke end is formed at a portion where the rack bar 14 is connected to the tie rod 17, and the lateral movement stroke of the rack bar 14 is mechanically caused by contact between the stopper 18 and the end of the rack housing 16. Is regulated. The other ends of the left and right tie rods 17 are connected to knuckles 19 provided on the left and right front wheels Wfl and Wfr. With such a configuration, the left and right front wheels Wfl and Wfr are steered to the left and right according to the axial displacement of the rack bar 14 as the steering shaft 12 rotates about the axis.

  A motor 20 is assembled to the steering shaft 12 via a reduction gear 25. The motor 20 rotationally drives the steering shaft 12 about its axis through the reduction gear 25 by the rotation, and gives an assist force to the turning operation of the steering handle 11.

  A steering torque sensor 21 and a steering angle sensor 22 are assembled to the steering shaft 12 at an intermediate position between the steering handle 11 and the reduction gear 25. The steering torque sensor 21 detects, for example, a twist angle of a torsion bar (not shown) interposed in an intermediate portion of the steering shaft 12 by a resolver or the like, and inputs from the steering handle 11 to the steering shaft 12 based on the twist angle. The detected steering torque Tr is detected. As for the steering torque Tr, the operation direction of the steering wheel 11 is identified by positive and negative values. For example, the steering torque Tr when the steering handle 11 is steered in the right direction is indicated by a positive value, and the steering torque Tr when the steering handle 11 is steered in the left direction is indicated by a negative value. In this embodiment, the torsion angle of the torsion bar is detected by a resolver, but it can also be detected by another rotational angle sensor such as an MR sensor.

  The steering angle sensor 22 detects the steering angle θs. As will be described later, since the steering angle detected by the steering angle sensor 22 and the estimated steering angle estimated by calculation based on the wheel speed are used as the steering angle, the steering angle detected by the steering angle sensor 22 is used. θs is called an actual steering angle θs. For the steering angle, the steering direction is identified by a positive or negative value. For example, the steering angle in the right direction with respect to the neutral position is indicated by a positive value, and the steering angle in the left direction is indicated by a negative value. In the present embodiment, the steering angle sensor 22 detects the rotation angle of the steering shaft 12, but detects the rotation angle of the motor 20 and the turning angles of the left and right front wheels Wfl and Wfr, which are physical quantities corresponding to the actual steering angle. You may comprise as follows. Moreover, you may comprise so that the displacement stroke of the axial direction of the rack bar 14 may be detected.

  Next, the assist ECU 100 will be described. As shown in FIG. 2, the assist ECU 100 calculates a target control amount of the motor 20 and outputs a switch drive signal corresponding to the calculated target control amount, and is output from the electronic control circuit 50. And a motor drive circuit 40 that energizes the motor 20 in accordance with the switch drive signal.

  Various motors 20 can be employed. For example, when a DC brushless motor is used, a three-phase inverter may be used as the motor drive circuit 40. When a brushed motor is used, an H bridge circuit may be used as the motor drive circuit 40. . In the present embodiment, description will be made assuming that a DC brushless motor is used.

  The electronic control circuit 50 includes a microcomputer including a CPU, ROM, RAM, and the like, various input / output interfaces, a switch drive circuit that supplies a switch drive signal to the motor drive circuit 40, and the like.

  Focusing on the function, the electronic control circuit 50 calculates the motor assist amount so that a current corresponding to the target assist torque Ta * flows to the motor 20 and the target assist torque calculator 70 for calculating the target assist torque Ta *. And a motor control unit 60 that outputs a switch drive signal corresponding to the motor energization amount to the motor drive circuit 40. The processing in each functional unit is repeatedly executed at a predetermined short period by the microcomputer.

  The target assist torque calculation unit 70 includes a normal assist torque calculation unit 71, an abnormal assist torque calculation unit 80, an abnormality detection unit 72, and a control switching unit 73. The normal assist torque calculation unit 71 receives the abnormality determination flag Ffail output from the abnormality detection unit 72. When the abnormality determination flag Ffail is “0”, the target assist torque Ta1 is calculated and the abnormality determination flag Ffail is calculated. Is “1”, the calculation block stops the calculation process. The abnormality assist torque calculation unit 80 receives the abnormality determination flag Ffail output from the abnormality detection unit 72, calculates the target assist torque Ta2 when the abnormality determination flag Ffail is “1”, and calculates the abnormality determination flag Ffail. Is “0”, the calculation block stops the calculation process.

  The abnormality detection unit 72 determines whether or not the steering torque sensor 21 is abnormal. When it is determined that there is no abnormality, the abnormality determination flag Ffail is set to “0”, and when it is determined that there is an abnormality. Sets the abnormality determination flag Ffail to “1”, and outputs the set abnormality determination flag Ffail to the normal assist torque calculation unit 71, the abnormal assist torque calculation unit 80, and the control switching unit 73.

  The control switching unit 73 inputs the target assist torque Ta1 calculated by the normal assist torque calculating unit 71 and the target assist torque Ta2 calculated by the abnormal assist torque calculating unit 80, and the abnormality determination flag Ffail is “0”. ", The target assist torque Ta1 is selected, and when the abnormality determination flag Ffail is" 1 ", the target assist torque Ta2 is selected. Then, the selected target assist torque Ta1 (or Ta2) is set to the target assist torque Ta *, and the target assist torque Ta * is output to the motor control unit 60.

  Details of each functional unit of the target assist torque calculation unit 70 will be described later.

  The motor control unit 60 includes a current feedback control unit 61 and a PWM signal generation unit 62. The current feedback control unit 61 receives the target assist torque Ta * output from the control switching unit 73, and generates the target assist torque Ta * by dividing the target assist torque Ta * by the torque constant of the motor 20. The target current I * required for the calculation is calculated. Then, a motor current Im (referred to as an actual current Im) detected by a current sensor 41 provided in the motor drive circuit 40 is read, and a deviation between the target current I * and the actual current Im is calculated, and this deviation is used. The target voltage V * is calculated so that the actual current Im follows the target current I * by proportional-integral control. Then, a PWM control signal (switch drive signal) corresponding to the target voltage V * is output to the switching element of the motor drive circuit (inverter) 40. As a result, the motor 20 is driven and an assist torque that follows the target assist torque Ta * is applied to the steering mechanism 10.

  In this embodiment, since a DC brushless motor is used, the current feedback control unit 61 inputs the motor rotation angle θm detected by the motor rotation angle sensor 23 provided in the motor 20 and rotates the motor. The angle θm is converted into an electrical angle, and the phase of the target current is controlled based on the electrical angle.

  Next, each functional unit of the target assist torque calculation unit 70 will be described in detail. The normal assist torque calculation unit 71 inputs the vehicle speed Vx detected by the vehicle speed sensor 24 and the steering torque Tr detected by the steering torque sensor 21, and refers to the normal assist map shown in FIG. The assist torque Ta1 is calculated. The normal assist map is stored in the normal assist torque calculation unit 71, and is association data in which the relationship between the steering torque Tr and the target assist torque Ta1 is set for each of a plurality of representative vehicle speeds Vx. The target assist torque Ta1 is set such that it increases as the magnitude (absolute value) of the torque Tr increases and decreases as the vehicle speed Vx increases. The target assist torque Ta1 is calculated so as to work in the direction of the steering torque Tr.

  In calculating the target assist torque Ta1, various compensation torques may be added to the target assist torque Ta1. For example, the normal assist torque calculation unit 71 inputs the actual steering angle θs detected by the steering angle sensor 22 and adds a compensation torque corresponding to the steering angular velocity ω obtained by differentiating the actual steering angle θs with respect to time. Also good. In this case, referring to the friction compensation torque map shown in FIG. 13, a friction compensation torque for compensating the frictional force component in the steering mechanism 10 may be added, or referring to the friction viscosity compensation torque map shown in FIG. In addition to the friction component, a friction viscosity compensation torque for compensating the viscosity component may be added. Further, these compensation torques may be switched according to the vehicle speed Vx.

  When the abnormality determination flag Ffail output from the abnormality detection unit 72 is “0”, the normal-time assist torque calculation unit 71 repeatedly executes such calculation processing at a predetermined short cycle, and the target assist torque that is the calculation result Ta1 is output to the control switching unit 73.

  The abnormality detection unit 72 determines whether the steering torque sensor 21 is abnormal. The steering torque sensor 21 can calculate the steering torque by detecting the torsion angle of the torsion bar provided in the middle of the steering shaft 12, and the rotation angle at one end and the rotation angle at the other end of the torsion bar are calculated. The torsion angle is detected from the angle difference. The steering torque sensor 21 includes a rotation angle sensor such as a resolver or an MR sensor in order to detect the rotation angle. In addition to the calculated value of the torsion angle corresponding to the steering torque Tr, the detection signal of the rotation angle sensor is also sent to the assist ECU 100. Output. Note that only the detection signal of the rotation angle sensor may be output to the assist ECU 100 and the assist ECU 100 may calculate the steering torque.

  The rotation angle sensor provided in the steering torque sensor 21 outputs a voltage signal corresponding to the rotation angle. Therefore, when the voltage value of the output signal is out of the proper range, it is considered that a disconnection or a short circuit has occurred in the rotation angle sensor. Also, for example, when using a rotation angle sensor whose output voltage periodically changes in a sine wave shape, such as a resolver, even when the output voltage is fixed to a constant value, disconnection or short-circuiting may occur. It is thought that it occurred.

  The abnormality detection unit 72 detects an abnormality of the steering torque sensor 21 as described above based on the output voltage of the rotation angle sensor (determines whether there is an abnormality). Then, according to the abnormality determination result of the steering torque sensor 21, the abnormality determination flag Ffail is set to “1” (abnormal) or “0” (abnormal).

  Next, the abnormality assist torque calculation unit 80 will be described. The normal assist torque calculation unit 71 described above calculates the target assist torque Ta1 based on the steering torque Tr, but cannot calculate the target assist torque Ta1 when the steering torque sensor 21 fails. Therefore, the abnormal assist torque calculator 80 calculates the target assist torque Ta2 instead of the normal assist torque calculator 71 when an abnormality of the steering torque sensor 21 is detected.

  As shown in FIG. 4, the abnormal assist torque calculation unit 80 includes a basic assist torque calculation unit 81, an assist limit calculation unit 82, and an assist limit unit 83. The basic assist torque calculation unit 81 inputs the vehicle speed Vx detected by the vehicle speed sensor 24 and the actual steering angle θs detected by the steering angle sensor 22, and refers to the abnormal basic assist map shown in FIG. The basic assist torque Tbase is calculated. The abnormal basic assist map is stored in the basic assist torque calculation unit 81, and is association data in which the relationship between the actual steering angle θs and the basic assist torque Tbase is set for each of a plurality of representative vehicle speeds Vx. It has a characteristic of setting a basic assist torque Tbase that increases as the magnitude (absolute value) of the actual steering angle θs increases and increases as the vehicle speed Vx increases. The basic assist torque Tbase is set to the same sign as the actual steering angle θs. Accordingly, if the actual steering angle θs is rightward, the basic assist torque Tbase that works in the right steering direction is set, and if the actual steering angle θs is leftward, the basic assist torque Tbase that works in the left steering direction is set. . The basic assist torque calculation unit 81 outputs the calculated basic assist torque Tbase to the assist restriction unit 83.

  It should be noted that the basic assist torque calculation unit 81 may add a compensation torque corresponding to the steering angular velocity ω obtained by differentiating the actual steering angle θs with respect to the basic assist torque Tbase in the calculation of the basic assist torque Tbase. Good. For example, the compensation torque map shown in FIG. 13 or FIG. 14 may be stored, and the friction compensation torque or the friction viscosity compensation torque may be added with reference to the compensation torque map.

  The assist restriction calculation unit 82 includes an estimated steering angle calculation unit 821, a cutoff frequency setting unit 822, a filtering unit 823, a slip index calculation unit 824, and a correction coefficient setting unit 825. The estimated rudder angle calculation unit 821 uses the left front wheel speed Vfl detected by the left front wheel speed sensor 26, the right front wheel speed Vfr detected by the right front wheel speed sensor 27, and the left rear wheel speed sensor 28. The detected left rear wheel speed Vrl and the right rear wheel speed Vrr detected by the right rear wheel speed sensor 29 are inputted, and two estimated steering angles are calculated. One of the two estimated rudder angles is an estimated rudder angle θf calculated from the left front wheel speed Vfl and the right front wheel speed Vfr, and the other is the left rear wheel speed Vrl and the right rear wheel speed. This is the estimated steering angle θr calculated from the wheel speed Vrr. Hereinafter, the estimated steering angle θf is referred to as a front wheel side estimated steering angle θf, and the estimated steering angle θr is referred to as a rear wheel side estimated steering angle θr.

Ｇは予め設定されている舵角換算用のギヤ比（オーバーオールギヤ比）を表し、ａは左右後輪Ｗrl，Ｗrrのトレッド、ｂは車両のホイールベースを表す。 From the geometric relationship between the wheel speed and the turning center at the time of turning of the vehicle shown in FIG. 6, the front wheel side estimated steering angle θf can be calculated by the following equation (1), and the rear wheel side estimated steering angle θr is And can be calculated by the following equation (2). Here, the front wheel side estimated steering angle θf and the rear wheel side estimated steering angle θr are the steering angles converted around the steering shaft.

G represents a gear ratio (overall gear ratio) for steering angle conversion set in advance, a represents the tread of the left and right rear wheels Wrl and Wrr, and b represents the wheel base of the vehicle.

The estimated rudder angle calculation unit 821 calculates the estimated rudder angle θe by the following equation (3) using the front wheel side estimated rudder angle θf and the rear wheel side estimated rudder angle θr.
θe = k · θf + (1-k) θr (3)
Here, k is a weighting coefficient for setting a weighting between the front wheel side estimated steering angle θf and the rear wheel side estimated steering angle θr, and is set according to a vehicle driving method or the like. For example, the estimated steering angle θe may be an average value of the front wheel side estimated steering angle θf and the rear wheel side estimated steering angle θr (k = 1/2).

  The estimated rudder angle calculation unit 821 outputs the calculated estimated rudder angle θe to the filtering unit 823. The wheel speeds Vfl, Vfr, Vrl, and Vrr detected by the wheel speed sensors 26 to 29 include noises (including errors) of various frequency components due to vibrations caused by road surface input and the pitch error of the sensor itself. Yes. Therefore, the filtering unit 823 receives the estimated steering angle θe output from the estimated steering angle calculation unit 821, and performs a low-pass filter process on the estimated steering angle θe. Thereby, an estimated rudder angle with less noise can be obtained. In this case, the lower the cut-off frequency of the low-pass filter processing, the higher the noise removal capability of various frequency components. On the other hand, the phase delay of the calculated value of the estimated steering angle increases.

  The estimated rudder angle is used for wheel slip determination as described later. When the wheel slips, the self-aligning torque transmitted from the road surface to the steering mechanism 10 is in a reduced state. Therefore, if the steering assist is performed with the same force as when the wheel is not slipping, the steering wheel 11 is overassisted. It becomes easy to cut too much and promotes slip. Therefore, in this embodiment, as will be described later, when a deviation between the estimated rudder angle and the actual rudder angle (steering angle deviation) is set as a slip index, and wheel slip is detected based on the rudder angle deviation, It operates to limit the steering assist and eliminate slip.

  However, if the phase delay of the calculated value of the estimated steering angle becomes large due to the low-pass filter process, the estimated steering angle becomes a value delayed from the actual steering angle, and the slip index that is the deviation between the two is not appropriate. In particular, in a situation where the difference between the wheel speeds of the left and right wheels ((Vfl−Vfr), (Vrl−Vrr)) changes rapidly, the calculation result of the slip index is greatly affected.

  Therefore, in the situation where there is a high possibility that the difference between the wheel speeds of the left and right wheels is likely to change quickly, the assist limit calculation unit 82 sets the cut-off frequency of the low-pass filter process high, and the difference between the wheel speeds of the left and right wheels changes quickly. In a situation where there is little risk of such occurrence, a cutoff frequency setting unit 822 that switches to set the cutoff frequency of the low-pass filter process to be low is provided.

  The cut-off frequency setting unit 822 inputs a signal representing the vehicle lateral acceleration Gy detected by the lateral acceleration sensor 30 and a signal representing the vehicle yaw rate γ detected by the yaw rate sensor 31. The directions of the lateral acceleration Gy and the yaw rate γ are identified by signs (positive and negative) as in the steering angle.

  The lateral acceleration of the vehicle is uniquely determined from the wheel speeds Vfl and Vfr of the left and right wheels or the wheel speeds Vrl and Vrr. Therefore, the cut-off frequency setting unit 822 inputs the wheel speeds Vfl, Vfr, Vrl, Vrr detected by the wheel speed sensors 26 to 29 instead of the detection signal of the lateral acceleration sensor 30, and sets the lateral acceleration Gy to the wheel. You may make it acquire by calculation using the function (Gy = f (Vfl, Vfr) or Gy = f (Vrl, Vrr)) of speed Vfl, Vfr or wheel speed Vrl, Vrr.

  Also, the yaw rate of the vehicle is uniquely determined from the wheel speeds Vfl and Vfr of the left and right wheels or the wheel speeds Vrl and Vrr. Therefore, the cut-off frequency setting unit 822 inputs the wheel speeds Vfl, Vfr, Vrl, Vrr detected by the wheel speed sensors 26 to 29 instead of the detection signal of the yaw rate sensor 31, and the wheel speeds Vfl, Vfr or The yaw rate γ may be obtained by calculation using a function of the wheel speeds Vrl and Vrr (γ = f (Vfl, Vfr) or γ = f (Vrl, Vrr)). Further, the yaw rate is uniquely determined from the steering angle and the vehicle speed. Therefore, the cut-off frequency setting unit 822 receives the vehicle speed Vx detected by the vehicle speed sensor 24 and the steering angle θs detected by the steering angle sensor 22 in place of the detection signal of the yaw rate sensor 31, and outputs the vehicle speed Vx. The yaw rate γ may be obtained by calculation using a function of the steering angle θs (γ = f (Vx, θs)).

  FIG. 7 shows a cutoff frequency setting routine executed by the cutoff frequency setting unit 822. The cut-off frequency setting routine is repeatedly executed at a predetermined short cycle. In step S11, the cutoff frequency setting unit 822 calculates the actual steering angle θs detected by the steering angle sensor 22, the lateral acceleration Gy detected by the lateral acceleration sensor 30, and the yaw rate γ detected by the yaw rate sensor 31. Read. Subsequently, in step S12, the steering angular velocity ω is calculated from the actual steering angle θs. The steering angular velocity ω can be obtained, for example, by differentiating the actual steering angle θs with respect to time.

  Subsequently, in step S13, the cutoff frequency setting unit 822 determines that the magnitude | ω | of the steering angular velocity ω is larger than the reference value ωref, or the magnitude | θs | of the actual steering angle θs is larger than the reference value θref. Determine whether or not. The steering angular velocity | ω | and the actual steering angle | θs | represent the steering input state quantity input to the steering handle 11 by the driver. The reference value ωref and the reference value θref are determination reference values that determine whether or not the difference between the left and right wheel speeds is likely to change quickly.

  When the steering input state quantity (| θs | or | ω |) is larger than the reference value (ωref or θref), the difference between the left and right wheel speeds is likely to change quickly. Since the estimated rudder angle θe is calculated as a function of the difference between the left and right wheel speeds, in a situation where the difference between the left and right wheel speeds changes rapidly, the phase delay of the estimated rudder angle due to the low-pass filter processing is reduced. There is a need to. Therefore, when the steering input state quantity (| θs | or | ω |) is larger than the reference value (ωref or θref) (S13: Yes), the cutoff frequency setting unit 822 determines the cutoff frequency fc in step S14. Is set to a preset high-side cutoff frequency fhigh.

  On the other hand, when the steering input state quantity (| θs | or | ω |) is equal to or less than the reference value (ωref or θref) (S13: No), the cutoff frequency setting unit 822 determines the lateral acceleration Gy in step S15. It is determined whether or not the magnitude | Gy | is greater than the reference value Gyref or the magnitude | γ | of the yaw rate γ is greater than the reference value γref. Lateral acceleration | Gy | and yaw rate | γ | represent vehicle output state quantities (vehicle behavior state quantities). The reference value Gyref and the reference value γref are determination reference values for determining whether or not the difference between the left and right wheel speeds is likely to change quickly.

  When the vehicle output state quantity (| Gy | or | γ |) is larger than the reference value (Gyref or γref), the difference between the left and right wheel speeds is likely to change rapidly. Therefore, when the vehicle output state quantity (| Gy | or | γ |) is larger than the reference value (Gyref or γref) (S15: Yes), the cutoff frequency setting unit 822 advances the process to step S14. The cut-off frequency fc is set to a preset high-side cut-off frequency fhigh.

  On the other hand, when the vehicle output state quantity (| Gy | or | γ |) is equal to or less than the reference value (Gyref or γref) (S15: No), the difference between the left and right wheel speeds is less likely to change quickly. is there. In this case, the cut-off frequency setting unit 822 sets the cut-off frequency fc to the preset low-side cut-off frequency low (<fhigh) in step S16.

  When the cut-off frequency setting unit 822 sets the cut-off frequency fc in step S14 or step S16, the cut-off frequency setting unit 822 outputs the set cut-off frequency fc to the filtering unit 823 and temporarily ends the cut-off frequency setting routine. Then, the above-described processing is repeated at a predetermined calculation cycle.

ここで、ｓはラプラス演算子を表す。 The filtering unit 823 receives the estimated rudder angle θe output from the estimated rudder angle calculation unit 821 and the cut-off frequency fc output from the cut-off frequency setting unit 822. Based on the cut-off frequency fc, the following equation is obtained. A first-order low-pass filter represented by the transfer function H (s) shown in (4) and (5) is set.

Here, s represents a Laplace operator.

The filtering unit 823 filters the estimated steering angle θe using a low-pass filter H (s). A value after filtering the estimated steering angle θe is referred to as an estimated steering angle θe_fil. The estimated rudder angle θe_fil after the filter can be calculated by the following equation (6), for example.
θe_fil (n) = b ₁ θe (n) + b ₂ θe (n−1) + b ₃ θe (n−2)
-A ₁ θe_fil (n-1) -a ₂ θe_fil (n-2) (6)
Here, a ₁ , a ₂ , b ₁ , b ₂ , b ₃ are discretization coefficients of the low-pass filter H (s). The last (n) is the current value, (n-1) is the previous value (one calculation cycle before), and (n-2) is the previous value (two calculation cycles). Represents.

The filtering unit 823 outputs the calculated estimated steering angle θe_fil to the slip index calculating unit 824. The slip index calculation unit 824 receives the actual steering angle θs detected by the steering angle sensor 22 and the estimated steering angle θe_fil output from the filtering unit 823, and calculates the deviation between the actual steering angle θs and the estimated steering angle θe_fil. A certain steering angle deviation | Δθ | is calculated by the following equation (7).
| Δθ | = | θe_fil−θs | (7)

  If slip occurs in any of the front, rear, left and right wheels, the steering angle deviation | Δθ | increases. Further, the greater the steering angle deviation | Δθ |, the greater the degree of slip. Accordingly, the slip index calculation unit 824 sets the steering angle deviation | Δθ | as a slip index indicating the degree of slip of the wheel. The slip index calculation unit 824 outputs the steering angle deviation | Δθ | to the correction coefficient setting unit 825.

  The correction coefficient setting unit 825 calculates a correction coefficient Ca corresponding to the steering angle deviation | Δθ | with reference to a correction coefficient map indicated by a solid line in FIG. The correction coefficient map is stored in the correction coefficient setting unit 825. In a range where the steering angle deviation | Δθ | is equal to or less than the reference value Δθ1, the correction coefficient Ca is set to 1 (Ca = 1.0), and the rudder angle deviation | Δθ | In the range where the angle deviation | Δθ | exceeds the reference value Δθ1, the correction coefficient Ca is set to be smaller as the steering angle deviation | Δθ | is larger. The correction coefficient setting unit 825 outputs the calculated correction coefficient Ca to the assist restriction unit 83.

  The assist limiting unit 83 receives the basic assist torque Tbase output from the basic assist torque calculating unit 81 and the correction coefficient Ca output from the correction coefficient setting unit 825, and executes the assist limiting routine shown in FIG. In step S21, the assist limiting unit 83 obtains the target assist torque Ta2 by multiplying the basic assist torque Tbase by the correction coefficient Ca (Ta2 = Ca × Tbase). Subsequently, in step S22, it is determined whether or not the target assist torque Ta2 is larger than an upper limit value Ta2max.

  When the target assist torque Ta2 is larger than the upper limit value Ta2max (S22: Yes), the assist restriction unit 83 changes the target assist torque Ta2 to the upper limit value Ta2max (Ta2 ← Ta2max) in step S23. That is, the target assist torque Ta2 is reduced to the upper limit value Ta2max. On the other hand, when the target assist torque Ta2 is equal to or lower than the upper limit value Ta2max, the process of step S23 is skipped. The upper limit Ta2max is a value set in advance in consideration of fail-safe. The assist limiting unit 83 repeatedly executes an assist limiting routine at a predetermined cycle, and outputs the calculated target assist torque Ta2 to the control switching unit 73. Thereby, in the motor control part 60, steering assist control is performed according to the target assist torque Ta * (= Ta2) limited according to the slip state of the wheels.

  According to the electric power steering apparatus 1 described above, even when the steering torque sensor 21 is out of order, the abnormal assist torque calculator 80 calculates the target assist torque Ta * instead of the normal assist torque calculator 71. Therefore, the steering assist can be continued. In this case, the abnormal assist torque calculation unit 80 sets the basic assist torque Tbase based on the vehicle speed Vx and the actual steering angle θs, and further, the steering angle that is a deviation between the actual steering angle θs and the estimated steering angle θe_fil. The deviation | Δθ | is calculated as a slip index, and the target assist torque Ta * is calculated such that the steering assist becomes smaller as the steering angle deviation | Δθ | As a result, when a wheel slip occurs, the steering assist is limited to prevent the steering handle 11 from being overcut by excessive assist, and appropriate steering assist can be performed.

  In calculating the estimated steering angle θe_fil, the steering input state (| θs | or | ω |) is larger than the reference value (ωref or θref), or the vehicle output state quantity (| Gy | or | γ |) Is larger than the reference value (Gyref or γref), the cut-off frequency fc of the low-pass filter processing is set to the high-side cut-off frequency fhigh, the steering input state is less than the reference value, and the vehicle output state quantity is When the reference value is lower than the reference value, the cut-off frequency fc of the low-pass filter process is set to the low-side cut-off frequency flow. That is, in a situation where the phase delay of the estimated steering angle θe_fil is likely to increase due to the low-pass filter processing, the cutoff frequency fc of the low-pass filter processing is set high to minimize the phase delay of the estimated steering angle θe_fil. In a situation where the processing does not increase the phase delay of the estimated steering angle θe_fil, the cut-off frequency fc of the low-pass filter processing is set low to reliably remove noise.

  Here, the effect of this embodiment is demonstrated using a comparative example. In order to prevent erroneous correction due to noise included in the wheel speed, as shown by a broken line in FIG. 8, if a correction coefficient map provided with a large dead zone is used, the actual steering angle can be reduced without performing low-pass filter processing. The assist can be limited by using the deviation | Δθ | between θs and the estimated steering angle θe as a slip index (comparative example). However, in the comparative example configured as described above, the correction coefficient Ca is not reduced while the steering angle deviation | Δθ | does not exceed the reference value Δθ2, so that the limitation of the steering assist is delayed or the limitation of the steering assist is not performed. It may be enough. Therefore, in the comparative example, in order to prevent over-assist, it is necessary to set the upper limit value Ta2max of the target assist torque Ta2 to a small value from the beginning. In this case, since a sufficient steering assist cannot be obtained in a situation where a large steering assist torque is required, for example, while traveling on a dry road surface, the driver's steering force burden increases.

  On the other hand, when noise is removed by the low-pass filter process, a phase delay occurs in the estimated steering angle θe_fil after the filter process. In particular, if the cut-off frequency fc of the low-pass filter is set low in order to ensure noise removal, the phase delay becomes large, and the original estimated steering angle and filter processing due to the influence of the phase delay as shown in FIG. A large error occurs between the estimated steering angle and the later estimated steering angle. Therefore, when the turning speed of the vehicle is high, the estimated steering angle cannot be calculated correctly. As a result, an appropriate slip index cannot be obtained, and the steering assist limitation cannot be properly executed.

  On the other hand, according to the present embodiment, as described above, the cut-off frequency fc of the low-pass filter process is varied according to the steering input state quantity and the vehicle output state quantity. The error of | is reduced. Thereby, the basic assist torque Tbase can be corrected appropriately. Further, since the error of the steering angle deviation | Δθ | is reduced, the dead zone in the correction coefficient map can be set small (see FIG. 8). Accordingly, the steering assist can be appropriately limited when the wheel slips, so that the upper limit value Ta2max of the target assist torque Ta2 can be set to a large value. Therefore, sufficient steering assist can be obtained in situations where a large steering assist torque is required, such as when driving on a dry road surface, and the driver's steering force burden is reduced.

  As described above, according to the electric power steering apparatus 1 of the present embodiment, it is possible to satisfactorily balance the effect of the phase delay due to the filter processing of the estimated rudder angle and the noise removal performance, and to prevent the wheel slip. The detection accuracy is improved, and the steering assist can be properly limited.

  The electric power steering apparatus 1 according to the present embodiment has been described above, but the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, in the present embodiment, the cut-off frequency fc in the low-pass filter process is switched between two levels of high and low. For example, as shown in FIG. You may make it switch in steps. Further, as shown in FIG. 12, it may be varied linearly according to the steering input state quantity and the vehicle output state quantity. In any case, the cut-off frequency fc may be set to increase as the steering input state quantity and the vehicle output state quantity increase. In addition, when a plurality of cutoff frequencies fc corresponding to the state quantity are calculated at the same time, any one of them (for example, the maximum value) may be selected, or combined calculation (for example, average) (Calculation).

  In the present embodiment, as a method of limiting the steering assist when the slip is detected, the basic assist torque Tbase is multiplied by the correction coefficient Ca. However, regarding the limitation of the steering assist, the upper limit value of the target assist torque Ta * is set. It can also be implemented by reducing Ta2max. For example, an upper limit value setting unit 825 is provided instead of the correction coefficient setting unit 825. The upper limit setting unit 825 stores an upper limit map as shown in FIG. 15, and refers to the upper limit map to calculate the upper limit Ta2max corresponding to the steering angle deviation | Δθ |. This upper limit map sets the upper limit Ta2max to the basic upper limit Ta2max0 (upper limit when no slip is detected) in a range where the steering angle deviation | Δθ | is equal to or less than the reference value Δθ1. In the range where | Δθ | exceeds the reference value Δθ1, the upper limit value Ta2max is set to be smaller as the steering angle deviation | Δθ | is larger. The upper limit setting unit 825 outputs the calculated upper limit Ta2max to the assist limiting unit 83. The assist limiting unit 83 compares the basic assist torque Tbase with the upper limit value Ta2max. If the basic assist torque Tbase does not exceed the upper limit value Ta2max, the assist limiting unit 83 sets the basic assist torque Tbase to the target assist torque Ta2 (Ta2 ← Tbase When the basic assist torque Tbase exceeds the upper limit value Ta2max, the upper limit value Ta2max is set to the target assist torque Ta2 (Ta2 ← Ta2max). Therefore, the steering assist can be appropriately limited according to the steering angle deviation | Δθ |.

  In the present embodiment, the steering angle θs and the steering angular velocity ω are acquired as the steering input state quantities, and when at least one of them exceeds the reference value, the cutoff frequency fc of the low-pass filter process is increased. Although set, the configuration may be such that either the actual steering angle θs or the steering angular velocity ω is acquired as the steering input state quantity.

  Further, in the present embodiment, the lateral acceleration Gy and the yaw rate γ are acquired as the vehicle output state quantities, and when at least one of them exceeds the reference value, the cutoff frequency fc of the low-pass filter process is set high. However, it may be configured to acquire either the lateral acceleration Gy or the yaw rate γ as the vehicle output state quantity. Further, when obtaining the yaw rate by calculation, any of the first calculated yaw rate calculated from the wheel speed Vfl, Vfr or the wheel speed Vrl, Vrr and the second calculated yaw rate calculated from the vehicle speed Vx and the steering angle θs is acquired. You may do it. In addition, when both the first calculation yaw rate and the second calculation yaw rate are acquired and at least one of the calculation yaw rates exceeds a reference value, the cutoff frequency fc of the low-pass filter process is set high. Also good.

  In this embodiment, the front wheel side estimated rudder angle θf and the rear wheel side estimated rudder angle θr are calculated, and the estimated rudder angle θe is calculated based on the two estimated rudder angles θf and θr. Estimate one of the estimated steering angles, that is, the estimated front wheel side steering angle θf calculated from the front wheel speeds Vfl and Vfr, or the rear wheel side estimated steering angle θr calculated from the rear wheel speeds Vrl and Vrr. The configuration may be such that the steering angle θe is set. In this case, it is not necessary to acquire the wheel speeds of the four wheels, and the wheel speeds on the front wheel side or the rear wheel side may be acquired. Further, the front wheel side estimated rudder angle θf and the rear wheel side estimated rudder angle θr may be calculated, and either one may be selected. For example, calculate the rudder angle deviation between the front wheel side estimated rudder angle θf and the actual rudder angle θs and the rear wheel side estimated rudder angle θr and the rudder angle deviation between the actual rudder angle θs and slip the larger rudder angle deviation It may be set as an index.

  In this embodiment, when calculating the estimated rudder angle θe_fil, the low-pass filter process is performed on the estimated rudder angle θe output from the estimated rudder angle calculation unit 821. You may make it carry out with respect to the wheel speed Vfl, Vfr, Vrl, Vrr detected by the sensors 26-29. In this case, a filtering unit 823 is provided on the input side of the estimated rudder angle calculation unit 821. The filtering unit 823 performs low-pass filter processing on the wheel speeds Vfl, Vfr, Vrl, Vrr using the low-pass filter H (s) corresponding to the cutoff frequency fc set by the cutoff frequency setting unit 822, The wheel speeds Vfl_fil, Vfr_fil, Vrl_fil, and Vrr_fil after the low-pass filter processing are output to the estimated steering angle calculation unit 821. The estimated rudder angle calculation unit 821 calculates an estimated rudder angle θe_fil based on the wheel speeds Vfl_fil, Vfr_fil, Vrl_fil, and Vrr_fil.

  In the present embodiment, the basic assist torque Tbase is calculated using the actual steering angle θs as an alternative parameter of the steering torque. However, the estimated steering angle can be used instead of the actual steering angle θs. Further, lateral acceleration acting on the vehicle can be used as an alternative parameter of the steering torque without using the steering angle. In this case, a target steering assist amount (for example, basic assist torque Tbase) that increases as the lateral acceleration increases may be set. The lateral acceleration may be detected by a sensor or may be obtained by calculation.

  In the present embodiment, the correction coefficient Ca is linearly decreased as the steering angle deviation | Δθ | increases within the range where the steering angle deviation | Δθ | exceeds the reference value Δθ1. Instead, the correction coefficient Ca may be reduced stepwise. For example, the correction coefficient Ca may be changed in two steps as the steering angle deviation | Δθ | increases.

  In this embodiment, the vehicle speed sensor 24, the steering angle sensor 22, the wheel speed sensors 26 to 29, the lateral acceleration sensor 30, and the yaw rate sensor 31 are provided, and the vehicle speed, the actual steering angle, the wheel speed, the lateral acceleration, and the yaw rate are set. Although detected, these sensors are not provided, and represent the vehicle speed, actual steering angle, wheel speed, lateral acceleration, and yaw rate detected by another vehicle ECU (for example, vehicle attitude control ECU) provided in the vehicle. Information may be acquired via a communication line. Further, the lateral acceleration and the yaw rate may be obtained by calculation as described above.

  In the present embodiment, the column assist type electric power steering device that applies the torque generated by the motor 20 to the steering shaft 12 has been described. However, the rack assist type that applies the torque generated by the motor to the rack bar 14 is described. An electric power steering device may be used.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 20 ... Motor, 21 ... Steering torque sensor, 22 ... Steering angle sensor, 24 ... Vehicle speed sensor, 26-29 ... Wheel speed sensor , 30 ... Lateral acceleration sensor, 31 ... Yaw rate sensor, 40 ... Motor drive circuit, 50 ... Electronic control circuit, 60 ... Motor controller, 70 ... Target assist torque calculator, 71 ... Normal assist torque calculator, 72 ... Abnormal Detecting unit 73 ... Control switching unit 80 ... Abnormal assist torque calculating unit 81 ... Basic assist torque calculating unit 82 ... Assist limit calculating unit 83 ... Assist limiting unit 821 ... Estimated steering angle calculating unit 822 ... Cut Off-frequency setting unit, 823 ... filtering unit, 824 ... slip index calculation unit, 825 ... correction coefficient setting unit, 1 0: electronic control unit (assist ECU), Ffail: abnormality determination flag, Ta *: target assist torque, Ta1: target assist torque, Ta2: target assist torque, Tr: steering torque, θs: steering angle (actual steering angle), Vx: vehicle speed, Vfl: left front wheel speed, Vfr: right front wheel speed, Vrl: left rear wheel speed, Vrr: right rear wheel speed, Gy: lateral acceleration, γ: yaw rate, ω: steering angular speed, θf ... Estimated front wheel side steering angle, θr: Estimated rear wheel side steering angle, θe: Estimated steering angle (before filter processing), θe_fil: Estimated steering angle (after filter processing), | Δθ | ... Steering angle deviation (slip index), Ca ... correction coefficient, Tbase ... basic assist torque, fc ... cut-off frequency.

Claims (1)

A steering torque sensor for detecting a steering torque input from the steering handle to the steering shaft;
A motor provided in the steering mechanism for generating steering assist torque;
An abnormality detecting means for detecting an abnormality of the steering torque sensor;
When an abnormality of the steering torque sensor is not detected, a target steering assist control amount is set based on the steering torque detected by the steering torque sensor, and when an abnormality of the steering torque sensor is detected, A control amount setting means for setting a target steering assist control amount using an alternative parameter different from the steering torque;
An electric power steering apparatus comprising: motor control means for driving and controlling the motor according to the target steering assist control amount set by the control amount setting means;
Estimated steering angle calculation that obtains the wheel speed of the left and right wheels on at least one of the front wheel side and the rear wheel side, and calculates the estimated steering angle that estimates the steering angle based on the acquired wheel speed through low-pass filter processing Means,
Steering input state quantity acquisition means for acquiring at least one of an actual steering angle or steering angular velocity as a steering input state quantity;
Vehicle output state quantity acquisition means for acquiring at least one of a lateral acceleration or a yaw rate of the vehicle as a vehicle output state quantity;
When the condition that the magnitude of the steering input state quantity is larger than the reference input value or the magnitude of the vehicle output state quantity is larger than the reference output value is satisfied, compared to the case where the condition is not satisfied, Cut-off frequency setting means for setting a high cut-off frequency for the low-pass filter processing;
Slip index calculation means for obtaining an actual steering angle and calculating a deviation between the actual steering angle and the estimated steering angle as a slip index of a wheel;
When an abnormality of the steering torque sensor is detected and a target steering assist control amount is set using an alternative parameter different from the steering torque, the target is increased as the slip index set by the slip index calculation means increases. An electric power steering apparatus comprising: an assist limiting unit that limits the target steering assist control amount so that the steering assist control amount becomes small.

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