JP5104028B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device for a vehicle.

  An electric power steering device for a vehicle detects a steering torque generated by a steering shaft with a torque sensor when a driver operates a steering wheel, and supplies the steering torque to a motor that generates a steering assist force based on the detected steering torque. The current command value, which is the control target value of the motor current to be calculated, is calculated. On the other hand, the motor current that actually flows through the motor is detected and fed back to the current command value. There is one configured to drive an electric motor with a motor current control value controlled so as to supply a steering assist force corresponding to a steering torque to a steering system.

  FIG. 4 is a diagram illustrating an example of the overall configuration of the electric power steering apparatus. A column shaft 102 of the steering wheel 101 is connected to a steering wheel tie rod 106 via a reduction gear 103, universal joints 104A and 104B, and a pinion rack mechanism 105. The column shaft 102 is provided with a torque sensor 110 that detects the steering torque of the steering wheel 101, and a motor 120 that supplies a steering assist force is connected to the column shaft 102 via a reduction gear 103.

  Electric power is supplied from the battery 104 via the ignition key 111 to the control device 130 that controls the electric power steering device. The control device 130 receives the ignition key ON signal, the detected steering torque T, and the vehicle speed V detected by the vehicle speed sensor 112. Based on the steering torque T and the vehicle speed V, a preset assist table is set. Alternatively, the current command value I is calculated from a predetermined arithmetic expression, and the motor 120 is driven by controlling the motor current based on the calculated current command value I.

  In the general electric power steering apparatus described above, the steering angle of the steered wheel (hereinafter referred to as the rudder angle) is limited due to structural limitations of the steering mechanism, and the steering mechanism that steers the steered wheel is used. Is provided with a rack end mechanism for preventing movement exceeding the rack movement limit (rack end).

  FIG. 5 is a cross-sectional view illustrating the rack end mechanism of the steering mechanism 140 that steers the steered wheels. A pinion shaft 141 connected to the steering wheel 101 is disposed in the gear housing 142 of the steering mechanism 140, and a rack 143 meshed with a pinion (not shown) disposed at the tip of the pinion shaft 141 is movable in the vehicle width direction. Has been placed. Tie rods 106 are connected to the left and right ends of the rack 143 through ball joints 144. A buffer member 145 is disposed at the end of the ball joint 144 on the rack 143 side, and the buffer member 145 contacts the inner surface of the gear housing 142 facing the buffer member 145 when the rack 143 reaches the movement limit. A stop member 146 is disposed, and the movement of the rack 143 in the vehicle width direction is stopped.

  In the following description, the rack movement limit and the stop member 146 provided at the rack movement limit may be simply referred to as a rack end. The state in which the rack of the steering mechanism is in contact with the rack end is generally called “end contact”.

  When the rack position that moves according to the steering angle of the steering wheel is in the vicinity of the rack end, if a larger steering torque is applied to the steering wheel, the motor is driven by a large current command value in response to the large steering torque. Since the steering assist force is applied to the steering device, the rack may collide violently with the rack end to generate a loud impact sound, or the rack end components may be damaged or deformed.

As a countermeasure, the control unit of the electric power steering apparatus determines whether or not the steering angle of the steering wheel exceeds a predetermined steering angle near the steering limit, and if the steering angle exceeds a predetermined steering angle near the steering limit, steering is performed. An output limiting unit that limits the output of the electric motor that applies the auxiliary torque (see Patent Document 1). In such a configuration, a predetermined steering angle near the steering limit is set to the load and steering speed of the steering wheel. Some have been proposed (see Patent Document 2), and others that mechanically reduce impact at the time of end application by a torque limiter (see Patent Document 3).
JP 2001-253356 A JP 2001-30933 A JP 2000-335431 A

  However, in the configuration disclosed in Patent Document 1 described above, it is necessary to provide a rudder angle estimation function in an expensive rudder angle sensor or control device in order to detect the rudder angle, which is disclosed in Patent Document 2. In the configuration, a steering speed sensor for detecting the steering speed is required, and in the configuration disclosed in Patent Document 3, it is necessary to incorporate a torque limiter, both of which require a new member, which increases the manufacturing cost. .

  As a countermeasure against this, the rate of change in the detected value of the motor current supplied to the electric motor that applies the steering assist torque is compared with a preset threshold value to determine whether the steering angle of the steering wheel has reached the steering limit. When it is determined that the steering limit has been reached, a configuration is conceivable in which the voltage command value or the duty ratio is limited to reduce the impact at the time of contact.

  FIG. 6 is a block diagram showing an example of the configuration of a control circuit in which the control function described above is incorporated in the control device 130 of the electric power steering device shown in FIG. Hereinafter, the configuration and operation of the control device 130 will be described.

  Steering torque T detected by torque sensor 110 and vehicle speed V detected by vehicle speed sensor 112 are input to current command value calculation unit 151. The current command value calculation unit 151 calculates a current command value I based on the input steering torque T and the vehicle speed V with reference to a preset assist table or based on a predetermined calculation formula.

  Motor angular velocity information output from the motor angular velocity detection unit 166 is input to the current command value compensation unit 153, and convergence compensation information for compensating the characteristics of the current command value I, inertia compensation information for the electric motor, self-aligning torque Output information etc.

  The adder 152 adds the convergence compensation information output from the current command value compensation unit 153, the inertia compensation information of the electric motor, the self-aligning torque information, and the like to the calculated current command value I to perform the required compensation. The compensated current command value Iref is output to the motor control unit 155.

  The motor control unit 155 controls a motor current supplied to the motor 120, and includes a plurality of functional elements. First, the subtracter 161 is fed back with a current command value Iref output from the adder 152 and a motor current detection value im detected by a motor current detection unit 165 (described later). A deviation (Iref-im) from the motor current detection value im is calculated.

  The calculated deviation (Iref−im) is subjected to PI (proportional and integral calculation) processing in the PI control unit 162, and the voltage control value EV with improved steering characteristics is output to the duty ratio calculation limiting unit 163.

  The duty ratio calculation limiting unit 163 determines the duty ratio D of the pulse width modulation signal (PWM signal) when driving the electric motor based on the input voltage control value EV, and the inverter 164 uses the determined duty ratio D. The semiconductor element is driven, and the electric motor 120 is driven. The motor current flowing through the electric motor 120 is detected by the motor current detection unit 165 and fed back to the subtractor 161 described above, and also input to a current change rate detection unit 160 described later.

  The determination of the duty ratio D in the duty ratio calculation restriction unit 163 is performed as follows.

  First, the configuration of the duty ratio calculation limiting unit 163 will be described. The duty ratio calculation limiting unit 163 calculates a duty ratio calculation unit 163a that calculates the duty ratio DVN based on the voltage control value EV, and sets the calculated duty ratio DVN to a predetermined value, for example, a limited duty ratio DVL that is limited to 3%. It comprises a limiter 163b for calculating, and a selection switch 163c for selecting the duty ratio DVN and duty ratio DVL.

  The selection switch 163c selects and outputs the duty ratio DVN to the inverter circuit 164 when the selection signal SL output from the current change rate detection unit 160 described later is SL0, and limits when the selection signal SL is SL1. The duty ratio DVL is selected and output to the inverter 164.

  The current change rate detection unit 160 determines whether or not the steering angle of the steering wheel exceeds a predetermined steering angle near the steering limit, that is, whether or not the “end contact” state is approached. The unit 160 includes a differentiating circuit 160a, a selection signal output unit 160b, and a threshold value memory 160c that stores a predetermined threshold value Δim set in advance.

  In the differentiation circuit 160a, a differential value of the input motor current detection value im is calculated. Then, in the selection signal output unit 160b, it is determined whether or not the differential value dim of the calculated motor current detection value im exceeds a predetermined threshold value Δim stored in the threshold value memory 160c, and the differential value dim is determined as the threshold value Δim. Is not exceeded (dim <Δim), the selection signal SL0 is output to the selection switch 163c, and when the differential value dim exceeds the threshold value Δim (dim> Δim), the selection signal SL1 is sent to the selection switch 163c. Is output.

  That is, the current change rate detection unit 160 determines that the change rate of the motor current detection value im suddenly increases from the differential value dim of the motor current detection value calculated by the differentiation circuit 160a and exceeds a predetermined threshold value Δim. When it is determined that the steering angle of the steering wheel has approached the steering limit, the selection signal SL0 output until then is switched to the selection signal SL1.

  The selection switch 163c of the duty ratio calculation limiting unit 163 selects the duty ratio DVN based on the selection signal SL0 and outputs it to the inverter 164 when the steering angle is not close to the steering limit. When the selection signal SL1 is input approaching the limit, a duty ratio DVL (for example, a duty ratio limited to 3%) is selected based on the selection signal SL1 and output to the inverter 164.

  That is, when it is determined that the differential value dim indicating the rate of change of the motor current detection value im suddenly increases and exceeds the predetermined threshold value Δim, it is determined that the steering limit has been reached and the duty ratio is limited. The impact at the time of the end contact can be reduced.

  And according to this structure, since a new member such as a steering angle sensor, a steering speed sensor, or a torque limiter is not required unlike the conventional control device, the manufacturing cost is not increased, and the conventional structure can be obtained. There is an advantage that can not be.

  However, since the motor current detection value im includes noise, when obtaining the rate of change of the motor current detection value, the influence of noise increases, making it difficult to compare with the threshold value Δim or to set the threshold value itself. It becomes. If a low-pass filter is used to avoid the influence of noise, the phase of the rate of change of the motor current detection value will be delayed, and the judgment on the steering limit will be delayed. It turns out that there is a disadvantage that the torque cannot be limited as expected. The object of the present invention is to solve the above-mentioned problems.

  The present invention solves the above problems, and the invention according to claim 1 is based on a steering torque detection unit that detects a steering torque input to a steering mechanism, and at least a steering torque detected by the steering torque detection unit. Drive control of the electric motor by a current command value calculation unit that calculates a current command value, an electric motor that supplies a steering assist torque to be applied to the steering mechanism, and a pulse width modulation signal that is calculated based on the current command value A motor control unit that performs a current command value change rate calculation unit that calculates a change rate of the current command value, and a predetermined threshold in which the calculated current command value change rate is set in advance. A steering limit determination unit that determines that the steering limit is exceeded, and when the steering limit is determined, the duty ratio of the pulse width modulation signal is limited. An electric power steering apparatus characterized by limiting the steering assist torque to be applied to the tearing mechanism.

  The current command value change rate calculation unit of the motor control unit includes a calculator that calculates a differential value of the current command value output from the current command value calculation unit, and the steering limit determination unit includes the current command value A steering limit determination device is provided for determining whether the differential value of the value exceeds a predetermined threshold value set in advance.

  Further, the motor control unit further includes a duty ratio calculation limiting unit that calculates and outputs the duty ratio of the pulse width modulation signal and outputs a limited duty ratio that limits the calculated duty ratio.

  The duty ratio calculation limiting unit calculates and outputs a duty ratio of the pulse width modulation signal based on the current command value, and when the steering limit determination unit determines that the steering limit is reached, the calculated duty ratio is calculated. Is limited and output as the duty ratio of the pulse width modulation signal for driving and controlling the electric motor, and the steering assist torque applied to the steering mechanism is limited.

  The steering limit determination unit of the motor control unit calculates a duty ratio that is determined to be not the steering limit when the current command value, the motor angular velocity, and the change rate of the motor angular velocity satisfy predetermined conditions. Do not limit.

  The invention according to claim 6 is a steering torque detector that detects a steering torque input to the steering mechanism, and a current command value calculator that calculates a current command value based on at least the steering torque detected by the steering torque detector. An electric motor that supplies a steering assist torque to be applied to the steering mechanism, and a motor control unit that drives and controls the electric motor based on the current command value using a pulse width modulation signal. A current command value phase advance value calculation unit for calculating a phase advance value of the current command value, and a steering for determining that the calculated current command value phase advance value exceeds a predetermined threshold value as a steering limit A limit determination unit, and when it is determined that the steering limit is reached, the steering assist is applied to the steering mechanism by limiting the duty ratio of the pulse width modulation signal. An electric power steering apparatus characterized by limiting the torque.

  The current command value phase advance value calculation unit of the motor control unit includes a filter circuit in which one or more phase advance / delay filters are connected in series, and the steering limit determination unit sets the output of the filter circuit in advance. A steering limit determiner for determining whether or not the predetermined threshold value is exceeded.

  Further, the motor control unit further includes a duty ratio calculation limiting unit that calculates and outputs the duty ratio of the pulse width modulation signal and outputs a limited duty ratio that limits the calculated duty ratio.

  The duty ratio calculation limiting unit calculates and outputs a duty ratio of the pulse width modulation signal based on the current command value, and when the steering limit determination unit determines that the steering limit is reached, the calculated duty ratio is calculated. Is limited and output as the duty ratio of the pulse width modulation signal for driving and controlling the electric motor, and the steering assist torque applied to the steering mechanism is limited.

  The steering limit determination unit of the motor control unit calculates a duty ratio that is determined to be not the steering limit when the current command value, the motor angular velocity, and the change rate of the motor angular velocity satisfy predetermined conditions. Do not limit.

  According to the first aspect of the present invention, the motor control unit includes a current command value change rate calculation unit that calculates a change rate of the current command value, and when the calculated current command value change rate exceeds a predetermined threshold value. A steering limit determination unit that determines that it is the steering limit is provided, and when it is determined that the steering limit is reached, the duty ratio of the pulse width modulation signal is limited to limit the steering assist torque applied to the steering mechanism.

  In the first aspect of the invention, since the steering limit is determined based on whether or not the rate of change of the current command value exceeds a predetermined threshold value set in advance, it is included in the current detection value as in the case of using the current detection value. It is possible to easily compare with the above-described threshold value and set the threshold value itself without being affected by noise.

  According to a sixth aspect of the present invention, the motor control unit includes a current command value phase lead value calculation unit that calculates a phase lead value of the current command value, and a predetermined threshold value in which the calculated current command value phase lead value is preset. A steering limit determination unit that determines that the steering limit is exceeded, and when determined to be the steering limit, the steering assist torque that is applied to the steering mechanism by limiting the duty ratio of the pulse width modulation signal. Limit.

  In the invention of claim 6, since the steering limit is determined based on whether or not the phase advance value of the current command value exceeds a predetermined threshold value set in advance, the current detection value is set to the current detection value as in the case of using the current detection value. Without being affected by the included noise, it is possible to easily compare with the threshold value and set the threshold value itself.

  Further, since the phase advance value obtained by advancing only the phase of the frequency component of the current command value at the time of contact is used, it is possible to determine the steering limit more quickly.

  Hereinafter, a control device for an electric power steering device according to an embodiment of the present invention will be described. The overall configuration of the electric power steering apparatus is not different from the configuration described above with reference to FIG. 4, and the rack end mechanism of the steering mechanism is not changed from the configuration described above with reference to FIG. In the description of the first and second embodiments, the overall configuration of the electric power steering apparatus will be omitted with reference to FIGS. 4 and 5 described above, and the configuration and function of the control apparatus will be described. . In the first embodiment described below, the control device 130 in FIG. 4 is read as the control device 10, and in the second embodiment, the control device 130 is read as the control device 50. 4 is replaced with the torque sensor 11, the vehicle speed sensor 112 is replaced with the vehicle speed sensor 12, and the electric motor 120 is replaced with the electric motor 30.

  The control device for the electric power steering apparatus according to the embodiment of the present invention avoids the influence of noise included in the motor current detection value in the detection of the steering limit based on the rate of change of the motor current detection value described in the subject of the invention. Therefore, the first embodiment that uses the motor current command value instead of the motor current detection value and the second embodiment that uses the phase advance value of the motor current command value instead of the motor current detection value. is there. Since the first embodiment and the second embodiment have common functional blocks, the common functional blocks will be described with the same reference numerals.

[First Embodiment]
FIG. 1 is a block diagram illustrating the configuration and functions of a control device 10 for an electric power steering device according to a first embodiment of the present invention.

  The steering current torque T detected by the torque sensor 11 and the vehicle speed V detected by the vehicle speed sensor 12 are input to the current command value calculation unit 15. The current command value calculation unit 15 refers to a preset assist table based on the input steering torque T and vehicle speed V or calculates a current command value I based on a predetermined calculation formula.

  Motor angular velocity information output from the motor angular velocity detection unit 28 is input to the current command value compensation unit 17, and convergence compensation information for compensating the characteristics of the current command value I, motor inertia compensation information, self-aligning torque information, and the like. Is output.

  The adder 16 adds the convergence compensation information, motor inertia compensation information, self-aligning torque information, and the like output from the current command value compensation unit 17 to the calculated current command value I to perform the required compensation. The compensated current command value Iref is output to the motor control unit 20.

  The motor control unit 20 controls a motor current supplied to the electric motor 30 and includes a plurality of functional elements. First, the subtracter 21 is fed back with a motor current detection value im detected by a motor current detector 27 described later to the current command value Iref output from the adder 16, and the current command value Iref and A deviation (Iref-im) from the motor current detection value im is calculated.

  The PI control unit 22 improves the steering characteristic of the calculated deviation (Iref-im), and performs PI (proportional and integral calculation) processing on the input deviation (Iref-im) to improve the steering characteristic. The voltage control value EV is output to the duty ratio calculation limiting unit 23.

  The duty ratio calculation limiting unit 23 calculates the duty ratio D of the pulse width modulation signal (PWM signal) for driving the motor based on the input voltage control value EV, and the calculated reference duty ratio DVN or limited The limited duty ratio DVL is output. The duty ratio calculation limiting unit 23 will be described in detail later.

  The inverter 24 is constituted by a plurality of semiconductor elements, and the semiconductor elements are driven by the duty ratio D (DVN or DVL) of the pulse width modulation signal (PWM signal) described above to drive the electric motor 30. The motor current im flowing through the electric motor 30 is detected by the motor current detector 27 and fed back to the subtractor 21 described above.

  The duty ratio calculation limiting unit 23 is configured to calculate a reference duty ratio DVN based on the input voltage control value EV, and the calculated reference duty ratio DVN is limited to a predetermined value, for example, 3%. The limiter 23b for calculating the limit duty ratio DVL and a selection switch 23c for selecting and outputting either the duty ratio DVN or the duty ratio DVL.

  The selection switch 23c selects the reference duty ratio DVN when the selection signal SL output from the steering limit determination unit 26 described later is SL0, and selects the limited duty ratio DVL when the selection signal SL is SL1. And output to the inverter 24.

  The current command value change rate calculation unit 25 calculates the current command value change rate in order to determine whether or not the steering angle of the steering wheel has exceeded the steering limit, that is, whether or not it is in the “end contact” state. . That is, when the steering wheel is in the “end contact” state, the steering torque increases rapidly, so the current command value also increases rapidly. For this reason, by detecting the rate of change of the current command value, it is possible to detect whether or not it is in the “end contact” state.

  The current command value change rate calculation unit 25 includes a differentiating circuit and calculates a differential value dIref of the input current command value Iref. The calculated differential value dIref is output to the steering limit determination unit 26 at the subsequent stage.

  The steering limit determination unit 26 determines whether or not the steering angle of the steering wheel has exceeded the steering limit, that is, whether or not it is in the “end contact” state. The steering limit determination unit 26a and a predetermined threshold value set in advance. And a threshold memory 26b storing ΔIm.

  In order to prevent erroneous determination of whether or not the steering angle of the steering wheel exceeds the steering limit (whether or not it is in the “end contact” state), the steering limit determination unit 26 determines the differential value of the current command value Iref, the motor angular velocity, Use the rate of change of motor angular speed. Therefore, a motor angular velocity change rate calculator 29 is provided to calculate the motor angular velocity change rate detected by the motor angular velocity detector 28 and input it to the steering limit determiner 26a.

  In the steering limit determination unit 26a, the differential value dIref of the current command value output from the current command value change rate detection unit 25 is compared with the threshold value ΔIm stored in the threshold value memory 26b, and the differential value dIref becomes the threshold value ΔIm. It is determined whether it has been exceeded. When the differential value dIref does not exceed the threshold value ΔIm (dIref <ΔIm), the selection signal SL0 is output to the selection switch 23c, and when the differential value dIref exceeds the threshold value ΔIm (dIref> ΔIm), the selection signal SL1. Is output to the selection switch 23c.

  In addition, (1) The absolute value of the current command value | Iref | is equal to or greater than a predetermined value (the current command value increases when the end contact state is reached), and (2) The absolute value of the motor angular velocity | ω | (3) The rate of change of the absolute value of the motor angular speed | ω | (the motor angular speed is slowed when in the “end contact” state) If (1) and (2) above are satisfied and (3) is zero, it is determined that it is not in the “end contact” state, and even if the differential value dIref of the current command value exceeds the threshold value ΔIm, It is assumed that the duty ratio DVL limited by the selection switch 23c of the duty ratio calculation limiting unit 23 to be described is not selected.

  The selection switch 23c of the duty ratio calculation limiting unit 23 selects the duty ratio DVN based on the selection signal SL0 and outputs it to the inverter 24 when the steering angle of the steering wheel is not at the steering limit. Is at the steering limit, a duty ratio DVL (for example, a duty ratio limited to 3%) is selected based on the selection signal SL1, and is output to the inverter 24.

  That is, when it is determined that the rate of change of the current command value Iref increases rapidly and the differential value dIref of the current command value exceeds the predetermined threshold value ΔIm, it is determined that the steering limit has been reached and the pulse width modulation signal ( Since the duty ratio D of the PWM signal is limited to the limited duty ratio DVL, it is possible to reduce the impact at the time of contact.

  And according to this structure, since a new member, such as a steering angle sensor, a steering speed sensor, or a torque limiter, is not required unlike the conventional control device, the manufacturing cost is not increased and the conventional structure can be obtained. There is an advantage that can not be.

  Further, since the current command value Iref and its differential value dIref do not contain noise, the differential value dIref of the current command value and the threshold value ΔIm can be compared and the threshold value itself can be set without being affected by noise. Can do.

  In addition, in the prior art described above, when a low-pass filter is used to avoid the influence of noise, a delay occurs in the phase of the change rate of the motor current detection value, and the judgment on the steering limit is delayed. Although there was a disadvantage that the steering assist torque for reducing the impact at the time could not be limited as expected, the present invention does not use the low-pass filter, so the above-mentioned disadvantage does not occur.

[Second Embodiment]
FIG. 2 is a block diagram illustrating the configuration and functions of the control device 50 of the electric power steering device according to the second embodiment of the present invention.

  The steering current torque T detected by the torque sensor 11 and the vehicle speed V detected by the vehicle speed sensor 12 are input to the current command value calculation unit 15. The current command value calculation unit 15 refers to a preset assist table based on the input steering torque T and vehicle speed V or calculates a current command value I based on a predetermined calculation formula.

  Motor angular velocity information output from the motor angular velocity detection unit 28 is input to the current command value compensation unit 17, and convergence compensation information for compensating the characteristics of the current command value I, motor inertia compensation information, self-aligning torque information, and the like. Is output.

  The adder 16 adds the convergence compensation information, motor inertia compensation information, self-aligning torque information, and the like output from the current command value compensation unit 17 to the calculated current command value I to perform the required compensation. The compensated current command value Iref is output to the motor control unit 20.

  The motor control unit 20 controls a motor current supplied to the electric motor 30 and includes a plurality of functional elements. First, the subtracter 21 is fed back with a motor current detection value im detected by a motor current detector 27 described later to the current command value Iref output from the adder 16, and the current command value Iref and A deviation (Iref-im) from the motor current detection value im is calculated.

  The PI control unit 22 improves the steering characteristic of the calculated deviation (Iref-im), and performs PI (proportional and integral calculation) processing on the input deviation (Iref-im) to improve the steering characteristic. The current control value EV is output to the duty ratio calculation limiting unit 23.

  The duty ratio calculation limiting unit 23 calculates the duty ratio D of the pulse width modulation signal (PWM signal) for driving the motor based on the input voltage control value EV, and the calculated reference duty ratio DVN or limited The limited duty ratio DVL is output. The duty ratio calculation limiting unit 23 will be described in detail later.

  The inverter 24 is constituted by a plurality of semiconductor elements, and the semiconductor elements are driven by the duty ratio D (DVN or DVL) of the pulse width modulation signal (PWM signal) described above to drive the electric motor 30. The motor current im flowing through the electric motor 30 is detected by the motor current detector 27 and fed back to the subtractor 21 described above.

  The duty ratio calculation limiting unit 23 is configured to calculate a reference duty ratio DVN based on the input voltage control value EV, and the calculated reference duty ratio DVN is limited to a predetermined value, for example, 3%. The limiter 23b for calculating the limit duty ratio DVL and a selection switch 23c for selecting and outputting either the duty ratio DVN or the duty ratio DVL.

  The selection switch 23c selects the reference duty ratio DVN when the selection signal SL output from the steering limit determination unit 26 described later is SL0, and selects the limited duty ratio DVL when the selection signal SL is SL1. And output to the inverter 24.

  The current command value phase advance value calculation unit 51 determines whether or not the steering angle of the steering wheel has exceeded the steering limit, that is, whether or not it is in the “end contact” state. The phase advance value is calculated.

  In the first embodiment described above, the differential value dIref of the current command value Iref is used as a numerical value indicating the current command value change rate. However, in the second embodiment, whether or not the “end contact” state is set. Therefore, the current command value IrefP in which only the phase of the frequency component of the current command value Iref is advanced is used.

  The current command value phase lead value calculation unit 51 includes a filter circuit in which one or more phase lead / lag filters are connected in series, and only the phase of the frequency component of the current command value Iref input by the filter circuit. Is output to the steering limit determination unit 26 at the subsequent stage.

  FIG. 3 is a diagram for explaining the characteristics of a filter circuit in which one or more phase advance / lag filters are connected in series. The horizontal axis represents frequency, and the vertical axis represents phase advance angle and amplitude. . As shown in FIG. 3, the current command value Iref is designed to have a large phase advance angle and amplitude in the “end contact” state. In addition, by connecting a plurality of filters (two in this case) in series, the phase advance angle and the difference in amplitude can be increased, and the end contact state can be reliably determined.

  That is, as shown in FIG. 3, when one filter is used, the difference in amplitude of the frequency component at the time of end contact and other than the end contact is (b), but two filters are used in series. In this case, the difference between the amplitudes of the frequency components at the time of the end contact and other than the end contact is (a), and an amplitude difference (a) larger than the difference (b) in amplitude when one is used. Thus, it is possible to reliably determine the contact state.

  The steering limit determination unit 26 determines whether or not the steering angle of the steering wheel has exceeded the steering limit, that is, whether or not it is in the “end contact” state. The steering limit determination unit 26a and a predetermined threshold value set in advance. And a threshold memory 26b storing ΔIm.

  In order to prevent erroneous determination of whether or not the steering angle of the steering wheel exceeds the steering limit (whether or not it is in the “end contact” state), the steering limit determination unit 26 determines the differential value of the current command value Iref, the motor angular velocity, Use the rate of change of motor angular speed. Therefore, a motor angular velocity change rate calculator 52 is provided to calculate the motor angular velocity change rate detected by the motor angular velocity detector 28 and input it to the steering limit determiner 26a.

  In the steering limit determination unit 26a, the current command value IrefP obtained by advancing only the phase output from the current command value phase advance calculation unit 51 is compared with the threshold value ΔIm stored in the threshold memory 26b, and the phase advanced current. It is determined whether or not the command value IrefP exceeds the threshold value ΔIm, and when the current command value IrefP that has advanced only the phase does not exceed the threshold value ΔIm (IrefP <ΔIm), the selection signal SL0 is output to the selection switch 23c. When the current command value IrefP whose phase has been advanced exceeds the threshold value ΔIm (IrefP> ΔIm), the selection signal SL1 is output to the selection switch 23c.

  In addition, (1) The absolute value of the current command value | Iref | is equal to or greater than a predetermined value (the current command value increases when the end contact state is reached), and (2) The absolute value of the motor angular velocity | ω | (3) The rate of change of the absolute value of the motor angular speed | ω | (the motor angular speed is slowed when in the “end contact” state) If (1) and (2) above are satisfied and (3) is zero, it is determined that the state is not in the “end contact” state, and the current command value IrefP obtained by advancing only the phase of the current command value is the threshold value. Even if ΔIm is exceeded, it is assumed that the limited duty ratio DVL by the selection switch 23c of the duty ratio calculation limiting unit 23 described below is not selected.

  The selection switch 23c of the duty ratio calculation limiting unit 23 selects the duty ratio DVN based on the selection signal SL0 and outputs it to the inverter 24 when the steering angle of the steering wheel is not at the steering limit. Is at the steering limit, a duty ratio DVL (for example, a duty ratio limited to 3%) is selected based on the selection signal SL1, and is output to the inverter 24.

  That is, when it is determined that the current command value IrefP, which is advanced only in phase, rapidly increases and exceeds the predetermined threshold value ΔIm, it is determined that the steering limit has been reached and the duty cycle of the pulse width modulation signal (PWM signal) is determined. Since the ratio D is limited to the limited duty ratio DVL, it is possible to reduce the impact at the time of contact.

  And according to this structure, since a new member, such as a steering angle sensor, a steering speed sensor, or a torque limiter, is not required unlike the conventional control device, the manufacturing cost is not increased and the conventional structure can be obtained. There is an advantage that can not be.

  In addition, since the current command value IrefP in which only the phase is advanced does not include noise, it can be compared with the threshold value ΔIm without being influenced by noise, and the threshold value itself can be set. Further, by using the current command value IrefP in which only the phase is advanced, it can be determined that the steering limit has been reached more quickly.

  In addition, in the prior art described above, when a low-pass filter is used to avoid the influence of noise, a delay occurs in the phase of the change rate of the motor current detection value, and the judgment on the steering limit is delayed. Although there has been a disadvantage that the steering assist torque for reducing the impact at the time cannot be limited as expected, the present invention does not use the low-pass filter, so the above-mentioned disadvantage does not occur.

  Whether the rack of the vehicle steering mechanism is near the rack end is determined based on the current command value. When the rack is near the rack end, a pulse width modulation signal (PWM signal) for driving the electric motor is determined. It is a control device for an electric power steering apparatus configured to limit the duty ratio, limit the output of the electric motor, and avoid damage to the steering mechanism.

The block diagram explaining the structure and function of the control apparatus of the electric power steering apparatus of 1st Embodiment. The block diagram explaining the structure and function of the control apparatus of the electric power steering apparatus of 2nd Embodiment. 6A and 6B illustrate characteristics of a filter circuit according to a second embodiment. The figure explaining the whole structure of an electric power steering device. Sectional drawing explaining the rack end mechanism of a steering device. The block diagram explaining the structure and function of the control apparatus of the conventional electric power steering apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 50 Control apparatus 11 Torque sensor 12 Vehicle speed sensor 15 Current command value calculation part 16 Adder 17 Current command value compensation part 20 Motor control part 21 Subtractor 22 PI control part 23 Duty ratio calculation restriction part 23a Duty ratio calculation part 23b Limiter 23c selection switch 24 inverter 25 current command value change rate calculation unit 26 steering limit determination unit 26a steering limit determination unit 26b threshold memory 27 motor current detection unit 28 motor angular velocity detection unit 29 motor angular velocity change rate calculation unit 30 electric motor 51 current command value Phase advance value calculation unit 52 Motor angular velocity change rate calculation unit

Claims (5)

A steering torque detector for detecting a steering torque input to the steering mechanism;
A current command value calculation unit that calculates a current command value based on at least the steering torque detected by the steering torque detection unit;
An electric motor for supplying a steering assist torque to be applied to the steering mechanism;
A motor control unit that drives and controls the electric motor by a pulse width modulation signal calculated based on the current command value;
The motor control unit includes a current command value change rate calculation unit that calculates a change rate of the current command value, and a steering limit when the calculated current command value change rate exceeds a predetermined threshold value. An electric power comprising a steering limit determination unit for determining, and when determined to be a steering limit, limiting a duty assist ratio applied to the steering mechanism by limiting a duty ratio of the pulse width modulation signal. Steering device.   The current command value change rate calculation unit of the motor control unit includes a calculator that calculates a differential value of the current command value output from the current command value calculation unit, and the steering limit determination unit The electric power steering apparatus according to claim 1, further comprising a steering limit determination unit that determines whether or not the differential value exceeds a predetermined threshold value set in advance.   The motor control unit further includes a duty ratio calculation limiting unit that calculates and outputs the duty ratio of the pulse width modulation signal and outputs a limited duty ratio that limits the calculated duty ratio. 2. The electric power steering apparatus according to 2.   The duty ratio calculation limiting unit calculates and outputs the duty ratio of the pulse width modulation signal based on the current command value, and when the steering limit determination unit determines that the steering limit is reached, the calculated duty ratio is predetermined. 4. The electric motor according to claim 3, wherein the duty ratio limited by the ratio is selectively output as a duty ratio of a pulse width modulation signal for driving and controlling the electric motor, and the steering assist torque applied to the steering mechanism is limited. Power steering device. The steering limit determination unit of the motor control unit limits the duty ratio calculated by determining that it is not the steering limit when the current command value, the motor angular velocity, and the rate of change of the motor angular velocity satisfy predetermined conditions. The electric power steering apparatus according to claim 4, wherein the electric power steering apparatus is not.

Images