JP2015186955A - Electric power steering device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of balancing a holding steering assistance function and a returning assistance function when a steering wheel is turned back, on a road with a cross slope.SOLUTION: The electric power steering device includes: an electric motor for giving assistance force to the steering by a steering wheel of a vehicle; a holding steering assistance current calculation unit, for, when the vehicle is made to go straight on a road with a cross slope, making the electric motor give holding steering assistance force for keeping a steering angle Sa of the steering wheel a holding steering angle Sah determined on the basis of the cross slope; and a restoration assistance current calculation unit for making the electric motor give returning assistance force for returning the steering wheel to a neutral position when the steering wheel is turned back. While the holding steering assistance current calculation unit makes the electric motor give the holding steering assistance force, the restoration assistance current calculation unit makes the electric motor give assistance force for returning the steering wheel to the holding steering angle Sah, instead of the returning assistance force.

Description

  The present invention relates to an electric power steering apparatus including an electric motor and a program.

In recent years, there has been proposed a power steering device that can reduce a steering burden when a vehicle travels straight on a road having a cross gradient (kant).
For example, the power steering device described in Patent Document 1 includes a motor that generates auxiliary steering torque, and a control amount setting unit that sets a control amount Ic for controlling the motor according to the steering torque of the driver; A cross slope detector for detecting a cross slope of a road on which the vehicle is traveling, a correction control amount setting section for setting a correction control amount Is for controlling the motor in accordance with the detected cross slope, a control amount Ic, It comprises an adder that adds the correction control amount Is ′ that has been gain-corrected, and a control unit that drives and controls the motor based on the added value.

In recent years, there has been proposed an apparatus for adding an assist force for returning to a neutral position (a position where the steering angle is zero degrees) when the steering wheel (steering wheel) is switched back.
For example, a power steering apparatus described in Patent Document 2 includes a steering angle detection unit, a calculation unit that calculates an actual steering angular velocity, a calculation unit that calculates a base correction steering angular velocity based on the steering angle, and a vehicle speed multiplication unit based on the vehicle speed. Calculation means for calculating a numerical value, calculation means for calculating the target steering angular speed by multiplying the base correction steering angular speed by the vehicle speed multiplication coefficient value, and calculating the base correction current value based on the difference between the target steering angular speed and the actual steering angular speed Computation means and computation means for adding the corrected current value to the assist base current value to obtain the assist target current.

JP 2006-44505 A JP 2006-123827 A

A steering assist function that provides an assisting force to maintain a steering angle according to the crossing slope in order to reduce the steering burden when the vehicle travels straight on a road with a crossing slope (kant) (kant road), It is desirable to provide a return assist function that provides an assist force for returning the steering wheel to the neutral position. However, the assist force for maintaining the steering angle corresponding to the crossing gradient and the assist force for returning to the neutral position when the steering wheel is returned are contradictory assist forces. Therefore, if both of these functions are provided, there is a risk that both straightness and steering wheel return to a road with a cross slope may deteriorate.
An object of the present invention is to realize both a steering assist function on a road having a cross slope and a return assist function when a steering wheel is turned back.

  For this purpose, the present invention relates to an electric motor that applies assisting force to steering of a steering wheel of a vehicle, and the steering angle of the steering wheel when the vehicle goes straight on a road with a cross slope. A steering assisting portion for imparting a steering assisting force to the electric motor to maintain a steering retaining angle determined based on a cross slope, and a return for returning the steering wheel to a neutral position when the steering wheel is switched back A return assist unit that applies an assist force to the electric motor, and the return assist unit is configured to replace the return assist force when the steering assist unit is applying the steering assist force. An electric power steering apparatus, wherein an assist force for returning to the steering angle is applied to the electric motor.

Here, the steering assist unit calculates an assist current required to apply the steering assist force to the electric motor, and the return assist unit applies the return assist force to the electric motor. The assist current required for the calculation may be calculated.
Further, the return assist unit may calculate an assist current necessary for applying the return assist force based on an assist current necessary for applying the steering assist force to the electric motor.

  From another point of view, according to the present invention, when the vehicle goes straight on a road with a cross slope, the computer holds the steering angle of the steering wheel of the vehicle at a steering angle determined based on the cross slope. A steering assist function for imparting a steering assist force for the electric motor to the electric motor, and a return assist function for imparting a return assist force to the electric motor for returning the steering wheel to the neutral position when the steering wheel is switched back, The return assist function includes an electric motor for providing an assist force for returning to the steered angle instead of the return assist force when the steer assist assist function is imparting the steer assist assist force. It is a program that realizes granting.

  ADVANTAGE OF THE INVENTION According to this invention, coexistence with the steering assistance function in the road with a cross slope and the return assistance function at the time of steering wheel switchback is realizable.

It is a figure showing the schematic structure of the electric power steering device concerning an embodiment. It is a schematic block diagram of a control apparatus. It is a schematic block diagram of a target current calculation part. It is the schematic of the control map which shows a response | compatibility with steering torque, vehicle speed, and base current. It is a schematic block diagram of a control part. It is a schematic block diagram of a steering auxiliary current calculation part. It is a schematic block diagram of an inclination angle detection part. It is the schematic of the control map which shows a response | compatibility with a total torque and a base inclination angle. It is the schematic of the control map which shows a response | compatibility with an inclination angle correction coefficient and a vehicle speed. It is the schematic of the control map which shows a response | compatibility with offset amount and a vehicle speed. It is the schematic of the control map which shows a response | compatibility with a steering assistance base current, and a deviation angle. It is the schematic of the control map which shows a response | compatibility with a vehicle speed and an electric current correction coefficient. It is a schematic block diagram of a restoration auxiliary current calculation unit. It is the schematic of the control map which shows a response | compatibility with a holding angle and a holding auxiliary current. It is the schematic of the control map which shows a response | compatibility with the correction | amendment base steering angular velocity and a steering angle. It is the schematic of the control map which shows a response | compatibility with a steering hold | maintained steering angular velocity and a steering hold angle. It is the schematic of the control map which shows a response | compatibility with a vehicle speed correction coefficient and a vehicle speed. The actual steering angular velocity with respect to the steering angle when the vehicle is traveling on a road with no cross slope at a vehicle speed of about 30 km / h, and the steering wheel is turned to the right after being turned from the neutral position, and the corrected target It is a figure which shows the change of a steering angular velocity and a target electric current. It is a figure which shows the change of the inclination angle and steering angle of a road surface at the time of moving to the road with a cross slope from the road without a cross slope while going straight. It is a schematic block diagram of the decompression | restoration auxiliary current calculation part which concerns on a modification. It is the schematic of the control map which shows a response | compatibility with a target steering angular velocity and a subtraction value.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an electric power steering apparatus 100 according to an embodiment.
Electric power steering device 100 (hereinafter, also simply referred to as “steering device 100”) is a steering device for arbitrarily changing the traveling direction of a vehicle, and in this embodiment, an automobile as an example of the vehicle. The structure applied to is illustrated.

  The steering apparatus 100 includes a wheel-like steering wheel 101 that is operated by a driver to change the traveling direction of the automobile, and a steering shaft 102 that is provided integrally with the steering wheel 101. . The steering device 100 includes an upper connecting shaft 103 connected to the steering shaft 102 via a universal joint 103a, and a lower connecting shaft 108 connected to the upper connecting shaft 103 via a universal joint 103b. . The lower connecting shaft 108 rotates in conjunction with the rotation of the steering wheel 101.

  Steering device 100 includes tie rods 104 connected to left and right front wheels 150 as rolling wheels, and rack shaft 105 connected to tie rods 104. Further, the steering device 100 includes a pinion 106 a that constitutes a rack and pinion mechanism together with rack teeth 105 a formed on the rack shaft 105. The pinion 106 a is formed at the lower end portion of the pinion shaft 106. The rack shaft 105, the pinion shaft 106, and the like function as a transmission mechanism that transmits the rotational operation force of the steering wheel 101 as the rolling force of the front wheel 150. The pinion shaft 106 applies a driving force to roll the front wheel 150 by rotating with respect to the rack shaft 105 that rolls the front wheel 150.

  The steering device 100 also has a steering gear box 107 that houses the pinion shaft 106. The pinion shaft 106 is connected to the lower connection shaft 108 via the torsion bar 112 in the steering gear box 107. The steering gear box 107 has a steering torque T applied to the steering wheel 101 based on the relative rotation angle between the lower connecting shaft 108 and the pinion shaft 106, in other words, based on the twist amount of the torsion bar 112. Is provided.

  Further, the steering device 100 includes an electric motor 110 supported by the steering gear box 107 and a speed reduction mechanism 111 that reduces the driving force of the electric motor 110 and transmits it to the pinion shaft 106. The speed reduction mechanism 111 includes, for example, a worm wheel (not shown) fixed to the pinion shaft 106, a worm gear (not shown) fixed to the output shaft of the electric motor 110, and the like. The electric motor 110 applies a driving force for rolling the front wheel 150 to the rack shaft 105 by applying a rotational driving force to the pinion shaft 106. The electric motor 110 according to the present embodiment is a three-phase brushless motor having a resolver 120 that detects the rotation angle of the electric motor 110.

  In addition, the steering device 100 includes a control device 10 that controls the operation of the electric motor 110. An output signal from the torque sensor 109 described above is input to the control device 10. In addition, the control device 10 includes a vehicle speed sensor 170 that detects a vehicle speed Vc, which is a moving speed of the vehicle, via a network (CAN) that performs communication for sending signals for controlling various devices mounted on the vehicle. An output signal from the yaw rate sensor 180 or the like is input.

  The steering device 100 configured as described above drives the electric motor 110 based on the detected torque detected by the torque sensor 109 and transmits the generated torque of the electric motor 110 to the pinion shaft 106. Thereby, the torque generated by the electric motor 110 assists the driver's steering force applied to the steering wheel 101.

Next, the control device 10 will be described.
FIG. 2 is a schematic configuration diagram of the control device 10.
The control device 10 is an arithmetic logic operation circuit including a CPU, a ROM, a RAM, an EEPROM (Electrically Erasable & Programmable Read Only Memory), and the like.
The control device 10 includes a torque signal Td obtained by converting the steering torque T detected by the torque sensor 109 described above into an output signal, and a vehicle speed signal obtained by converting the vehicle speed Vc detected by the vehicle speed sensor 170 into an output signal. v, a yaw rate signal y obtained by converting the yaw rate detected by the yaw rate sensor 180 into an output signal, a rotation angle signal θs that is an output signal corresponding to the motor rotation angle θ of the electric motor 110 from the resolver 120, and the like. .

  Then, the control device 10 calculates (sets) a target current It necessary for the electric motor 110 to supply based on the torque signal Td, the vehicle speed signal v, and the like, and a target current calculation unit 20. And a control unit 30 that performs feedback control or the like based on the target current It calculated by. Further, the control device 10 calculates the motor rotation speed Nm based on the motor rotation angle calculation unit 71 that calculates the motor rotation angle θ of the electric motor 110 and the motor rotation angle θ calculated by the motor rotation angle calculation unit 71. A motor rotation speed calculation unit 72 to calculate and a steering angle calculation unit 73 to calculate a steering angle Sa that is a rotation angle of the steering wheel 101 are provided.

Next, the target current calculation unit 20 will be described in detail.
FIG. 3 is a schematic configuration diagram of the target current calculation unit 20.
The target current calculation unit 20 calculates a base current calculation unit 21 that calculates a base current Ib that serves as a reference for setting the target current It, and inertia compensation that calculates an inertia compensation current Is for canceling the inertia moment of the electric motor 110. A current calculation unit 22 and a damper compensation current calculation unit 23 that calculates a damper compensation current Id that limits the rotation of the motor are provided. Further, the target current calculation unit 20 determines a temporary target current Itf that is a temporary target current based on the values calculated by the base current calculation unit 21, the inertia compensation current calculation unit 22, and the damper compensation current calculation unit 23. A temporary target current determination unit 25 is provided as an example of a temporary target current determination unit. In addition, the target current calculation unit 20 includes a phase compensation unit 26 that compensates for the phase of the steering torque T detected by the torque sensor 109.

In addition, the target current calculation unit 20 includes a steering assist current calculation unit 27 that calculates a steering assist current Ih that is an electric current for the electric motor 110 to provide an assist force according to the steering condition of the steering wheel 101, and a steering. A restoration auxiliary current calculation unit 28 that calculates a restoration auxiliary current Ir that is a current for restoring the wheel 101 to a desired angle.
Further, the target current calculation unit 20 sets the temporary target current Itf determined by the temporary target current determination unit 25, the steering auxiliary current Ih calculated by the steering auxiliary current calculation unit 27, and the restoration auxiliary current calculation unit 28. And a final target current determination unit 29 as an example of target current determination means for finally determining the target current It based on the restoration auxiliary current Ir calculated in this manner.
The target current calculation unit 20 receives a torque signal Td, a vehicle speed signal v, a motor rotation speed signal Nms, a yaw rate signal y, and the like.

FIG. 4 is a schematic diagram of a control map showing the correspondence between the steering torque T, the vehicle speed Vc, and the base current Ib.
The base current calculation unit 21 calculates a base current Ib based on the torque signal Ts obtained by phase compensation of the torque signal Td by the phase compensation unit 26 and the vehicle speed signal v from the vehicle speed sensor 170. In other words, the base current calculation unit 21 calculates the base current Ib according to the steering torque T phase-compensated by the phase compensation unit 26 and the vehicle speed Vc. The base current calculation unit 21 is, for example, a phase-compensated steering torque T (torque signal Ts), vehicle speed Vc (vehicle speed signal v), and base current that are created in advance based on empirical rules and stored in the ROM. The base current Ib is calculated by substituting the steering torque T and the vehicle speed Vc into the control map illustrated in FIG. 4 illustrating the correspondence with Ib.

  The inertia compensation current calculation unit 22 calculates the inertia compensation current Is based on the torque signal Ts and the vehicle speed signal v obtained by phase compensation of the torque signal Td by the phase compensation unit 26. In other words, the inertia compensation current calculation unit 22 calculates the inertia compensation current Is according to the steering torque T phase-compensated by the phase compensation unit 26 and the vehicle speed Vc. Note that the inertia compensation current calculation unit 22, for example, a phase-compensated steering torque T (torque signal Ts) and vehicle speed Vc (vehicle speed signal v) and inertia, which are created based on empirical rules and stored in the ROM in advance. The inertia compensation current Is is calculated by substituting the phase-compensated steering torque T and the vehicle speed Vc into the control map indicating the correspondence with the compensation current Is.

  The damper compensation current calculation unit 23 calculates the damper compensation current Id based on the torque signal Ts, the vehicle speed signal v, the motor rotation speed signal Nms, and the like, in which the torque signal Td is phase compensated by the phase compensation unit 26. In other words, the damper compensation current calculation unit 23 calculates the damper compensation current Id according to the steering torque T phase-compensated by the phase compensation unit 26, the vehicle speed Vc, and the motor rotation speed Nm. The damper compensation current calculation unit 23 is, for example, a phase-compensated steering torque T (torque signal Ts), vehicle speed Vc (vehicle speed signal v), and motor, which are previously created based on empirical rules and stored in the ROM. By substituting the phase-compensated steering torque T, vehicle speed Vc, and motor rotational speed Nm into the control map indicating the correspondence between the rotational speed Nm (motor rotational speed signal Nms) and the damper compensation current Id, the damper compensation current Id is obtained. calculate.

  The temporary target current determination unit 25 includes a base current Ib calculated by the base current calculation unit 21, an inertia compensation current Is calculated by the inertia compensation current calculation unit 22, and a damper calculated by the damper compensation current calculation unit 23. A temporary target current Itf is determined based on the compensation current Id. For example, the temporary target current determination unit 25 determines the current obtained by adding the inertia compensation current Is to the base current Ib and subtracting the damper compensation current Id as the temporary target current Itf.

The steering auxiliary current calculation unit 27 and the restoration auxiliary current calculation unit 28 will be described in detail later.
The final target current determination unit 29 includes a temporary target current Itf determined by the temporary target current determination unit 25, a steering auxiliary current Ih calculated by the steering auxiliary current calculation unit 27, and a restoration auxiliary current calculation unit 28. The current obtained by adding the restoration auxiliary current Ir calculated in step S3 is determined as the target current It.

Next, the control unit 30 will be described in detail.
FIG. 5 is a schematic configuration diagram of the control unit 30.
As shown in FIG. 5, the control unit 30 includes a motor drive control unit 31 that controls the operation of the electric motor 110, a motor drive unit 32 that drives the electric motor 110, and an actual current Im that actually flows through the electric motor 110. And a motor current detection unit 33 for detection. Further, the control unit 30 has a feedback current calculation unit 38 that calculates the feedback current If based on the actual current Im detected by the motor current detection unit 33 and the motor rotation angle θ calculated by the motor rotation angle calculation unit 71. doing.

  The motor drive control unit 31 performs feedback control based on a deviation between the target current It finally determined by the target current calculation unit 20 and the feedback current If calculated by the feedback current calculation unit 38 ( F / B) The control unit 40 and the PWM signal generation unit 60 that generates a PWM (pulse width modulation) signal for PWM driving the electric motor 110 are included.

  The feedback control unit 40 includes a deviation calculating unit 41 for obtaining a deviation between the target current It finally determined by the target current calculating unit 20 and the feedback current If calculated by the feedback current calculating unit 38, and the deviation is A feedback (F / B) processing unit 42 that performs feedback processing so as to be zero.

The feedback (F / B) processing unit 42 performs feedback control so that the target current It and the feedback current If match. For example, the feedback (F / B) processing unit 42 is proportional to the deviation calculated by the deviation calculating unit 41. Is proportionally processed, integrated by an integral element, and these values are added by an addition operation unit.
The PWM signal generation unit 60 generates a PWM signal for PWM (pulse width modulation) driving of the electric motor 110 based on the output value from the feedback control unit 40 and the motor rotation angle θ calculated by the motor rotation angle calculation unit 71. Generate and output the generated PWM signal.

  The motor drive unit 32 is a so-called inverter, and includes, for example, six independent transistors (FETs) as switching elements. Three of the six transistors are a positive line of a power source, an electric coil of each phase, The other three transistors are connected to the electric coil of each phase and the negative side (ground) line of the power source. Then, the driving of the electric motor 110 is controlled by driving the gates of two transistors selected from the six and switching the transistors.

The motor current detection unit 33 detects the value of the actual current Im flowing through the electric motor 110 from the voltage generated at both ends of the shunt resistor connected to the motor drive unit 32.
The feedback current calculation unit 38 is based on the arithmetic expression stored in advance in the ROM, the actual current Im detected by the motor current detection unit 33, and the motor rotation angle θ calculated by the motor rotation angle calculation unit 71. Is calculated.

The motor rotation angle calculation unit 71 calculates the motor rotation angle θ based on the output signal of the resolver 120.
The motor rotation speed calculation unit 72 (see FIG. 2) calculates the motor rotation speed Nm of the electric motor 110 based on the motor rotation angle θ calculated by the motor rotation angle calculation unit 71, and the calculated motor rotation speed Nm is an output signal. The motor rotation speed signal Nms converted into is output.
The steering angle calculation unit 73 (see FIG. 2) is configured such that the rotation angle (steering angle) of the steering wheel 101 and the motor rotation angle θ of the electric motor 110 because the steering wheel 101, the speed reduction mechanism 111, and the like are mechanically coupled. The steering angle Sa is calculated based on the motor rotation angle θ calculated by the motor rotation angle calculation unit 71. For example, the steering angle calculation unit 73 performs steering based on the integrated value of the difference between the previous value and the current value of the motor rotation angle θ calculated periodically (for example, every 1 millisecond) by the motor rotation angle calculation unit 71. The angle Sa is calculated.

  Here, a state in which the torsion bar 112 has a zero twist amount is defined as a neutral state (neutral position), and the steering wheel 101 (lower connection shaft 108) and pinion shaft when the steering wheel 101 rotates clockwise from the neutral state (neutral position). The direction in which the relative rotation angle with respect to 106 changes (the direction in which the relative rotation angle occurs) is positive (the steering torque T is positive). On the other hand, the direction in which the relative rotation angle between the steering wheel 101 (lower connection shaft 108) and the pinion shaft 106 changes when the steering wheel 101 rotates counterclockwise from the neutral state (the direction in which the relative rotation angle occurs) is negative (steering). Torque T is negative). At this time, it is an output value from the torque sensor 109 when the relative rotation angle between the steering wheel 101 and the pinion shaft 106 is twisted in the clockwise direction from the neutral state (the torsion bar is twisted in the clockwise direction). The sign of the torque signal Td from the torque sensor 109 when the sign of the torque signal Td is positive and the relative rotation angle is twisted counterclockwise from the neutral state (the torsion bar is twisted counterclockwise) is negative. To do.

  When the sign of the torque signal Td from the torque sensor 109 is positive, the base current calculation unit 21 calculates the base current Ib so as to rotate the electric motor 110 in one rotation direction, and the base current Ib The direction of flow is positive. That is, as shown in FIG. 4, when the sign of the torque signal Td from the torque sensor 109 is positive and the steering torque T is positive, the base current calculation unit 21 calculates a positive base current Ib, Torque is generated in the direction of rotation in the direction of rotation. On the other hand, when the sign of the torque signal Td from the torque sensor 109 is negative, the base current calculation unit 21 calculates a negative base current Ib, and generates torque in a direction that rotates the electric motor 110 in the other rotation direction.

  Further, the sign of the steering angle Sa when the steering wheel 101 is rotated clockwise from zero degree is plus, and the sign of the steering angle Sa when the steering wheel 101 is rotated counterclockwise is minus. Further, the sign of the rotation direction of the electric motor 110 mechanically connected to the steering wheel 101 is added to the rotation direction of the electric motor 110 when the steering wheel 101 is rotated to the right (one rotation direction described above), The rotation direction of the electric motor 110 when the steering wheel 101 is rotated counterclockwise (the other rotation direction described above) is negative.

Next, the steering auxiliary current calculation unit 27 will be described.
FIG. 6 is a schematic configuration diagram of the steering assist current calculating unit 27.
The steering assist current calculation unit 27 is based on the inclination angle detection unit 271 that detects the inclination angle As of the cross gradient based on the steering torque T detected by the torque sensor 109 and the vehicle speed signal v from the vehicle speed sensor 170. And an offset amount setting unit 272 for setting an offset amount Aso for setting a dead zone region for the inclination angle As.

  Further, the steering auxiliary current calculation unit 27 subtracts the offset amount Aso set by the offset amount setting unit 272 from the tilt angle As calculated by the tilt angle detection unit 271, and the tilt angle As. A steering assist base current calculation unit 274 that calculates the steering assist base current Ihb based on a subtracted value from the offset amount Aso is provided.

  Further, the steering auxiliary current calculation unit 27 includes a correction coefficient setting unit 275 that sets a current correction coefficient Rc for correcting the steering auxiliary base current Ihb according to the vehicle speed Vc, and a steering auxiliary electric base current calculation unit 274. A multiplication unit 276 that calculates the steering holding auxiliary current Ih by multiplying the calculated steering holding base current Ihb and the current correction coefficient Rc set by the correction coefficient setting unit 275 is provided.

First, the tilt angle detector 271 will be described in detail.
FIG. 7 is a schematic configuration diagram of the tilt angle detection unit 271.
The tilt angle detection unit 271 sets a base tilt angle calculation unit 271a that calculates a base tilt angle Asb that is a base value of the tilt angle As, and a tilt that sets a tilt angle correction coefficient Ra based on a vehicle speed signal v from the vehicle speed sensor 170. An angle correction coefficient setting unit 271b and a base inclination angle correction unit 271c that multiplies the base inclination angle Asb and the inclination angle correction coefficient Ra are provided.
Further, the inclination angle detection unit 271 sets the inclination angle As based on the output from the crossing gradient traveling determination unit 271d that determines whether or not the vehicle is traveling on a road having a crossing gradient, and the output from the crossing gradient traveling determination unit 271d. An inclination angle setting unit 271e.

  The base inclination angle calculation unit 271a calculates the base inclination angle Asb based on the torque signal Td (steering torque T) from the torque sensor 109 and the target current It calculated by the target current calculation unit 20. For example, the base inclination angle calculation unit 271a calculates the base inclination angle Asb according to the total torque Ta obtained by adding the steering torque T detected by the torque sensor 109 and the assist torque generated by the electric motor 110 by the target current It. To do. The base inclination angle Asb is calculated on the basis of the total torque Ta because the straight traveling state of the vehicle is maintained by both the assist torque by the electric motor 110 and the driver's steering torque T on a road surface with a cross gradient. is there.

FIG. 8 is a schematic diagram of a control map showing the correspondence between the total torque Ta and the base inclination angle Asb. The control map shown in FIG. 8 is a schematic diagram of the control map when the vehicle speed Vc is a specific vehicle speed.
For example, the base inclination angle calculation unit 271a adds the target current to the control map illustrated in FIG. 8 that illustrates the correspondence between the total torque Ta and the base inclination angle Asb, which is previously created based on an empirical rule and stored in the ROM. The assist torque generated by the electric motor 110 is estimated based on the target current It calculated by the calculation unit 20, and the total torque Ta obtained by adding the estimated assist torque and the steering torque T detected by the torque sensor 109 is calculated. By substituting, the base inclination angle Asb is calculated.

The inclination angle correction coefficient setting unit 271b sets an inclination angle correction coefficient Ra for correcting the base inclination angle Asb calculated by the base inclination angle calculation unit 271a according to the vehicle speed Vc.
FIG. 9 is a schematic diagram of a control map showing the correspondence between the inclination angle correction coefficient Ra and the vehicle speed Vc.
The inclination angle correction coefficient setting unit 271b sets the inclination angle correction coefficient Ra based on the vehicle speed signal v from the vehicle speed sensor 170. For example, the inclination angle correction coefficient setting unit 271b adds the vehicle speed to the control map illustrated in FIG. 9 that shows the correspondence between the inclination angle correction coefficient Ra and the vehicle speed Vc, which is created based on an empirical rule and stored in the ROM in advance. The tilt angle correction coefficient Ra is calculated by substituting Vc.

The base inclination angle correction unit 271c multiplies the base inclination angle Asb calculated by the base inclination angle calculation unit 271a by the inclination angle correction coefficient Ra set by the inclination angle correction coefficient setting unit 271b, thereby correcting the corrected base. The inclination angle Asbc is calculated (Asbc = Asb × Ra).
In FIG. 9, considering that the self-aligning torque increases as the vehicle speed Vc increases, the inclination angle correction coefficient Ra is set to decrease as the vehicle speed Vc increases. Then, the base inclination angle correction unit 271c multiplies the base inclination angle Asb by the inclination angle correction coefficient Ra so that the inclination angle As increases as the vehicle speed Vc increases while maintaining the same inclination angle As. Correction is performed to set the inclination angle As that eliminates the self-aligning torque component. In FIG. 9, the inclination angle correction coefficient Ra is 1 when the vehicle speed is a specific vehicle speed that is the basis of the control map of FIG.

  The cross gradient running determination unit 271d determines whether or not the vehicle is traveling on a road having a cross gradient. For example, the cross slope traveling determination unit 271d generates a road having a cross slope when the vehicle travels straight ahead at a predetermined speed or higher and the travel continues for a predetermined time or longer with a steering torque T greater than or equal to a predetermined value. Determine that you are driving. That is, the cross gradient running determination unit 271d determines that the vehicle speed Vc detected by the vehicle speed sensor 170 is equal to or higher than a predetermined speed, the absolute value of the yaw rate detected by the yaw rate sensor 180 is equal to or lower than the predetermined yaw rate, and the torque sensor. When the traveling state in which the steering torque T detected at 109 is equal to or greater than the predetermined torque continues for a predetermined time or longer, it is determined that the vehicle is traveling on a road having a cross gradient.

  The inclination angle setting unit 271e determines the corrected base inclination angle Asbc calculated by the base inclination angle correction unit 271c as the inclination angle As when the crossing gradient traveling determination unit 271d determines that the vehicle is traveling on a road having a crossing gradient. When the crossing gradient traveling determination unit 271d does not determine that the vehicle is traveling on a road having a crossing gradient, zero is set as the inclination angle As.

Next, the offset amount setting unit 272 will be described in detail.
FIG. 10 is a schematic diagram of a control map showing the correspondence between the offset amount Aso and the vehicle speed Vc.
The offset amount setting unit 272 sets the offset amount Aso based on the vehicle speed signal v from the vehicle speed sensor 170. For example, the offset amount setting unit 272 substitutes the vehicle speed Vc into the control map illustrated in FIG. 10 that shows the correspondence between the offset amount Aso and the vehicle speed Vc, which is created in advance based on empirical rules and stored in the ROM. As a result, the offset amount Aso is calculated.
The offset amount Aso is a value for setting a dead zone region for the inclination angle As based on the vehicle speed signal v from the vehicle speed sensor 170.

The subtraction unit 273 calculates the deviation angle ΔAs by subtracting the offset amount Aso from the inclination angle As set by the inclination angle setting unit 271e.
When the deviation angle ΔAs calculated by the subtraction unit 273 is greater than zero, the steering auxiliary base current calculation unit 274 serves as a base for the steering auxiliary current Ih for applying the auxiliary steering torque according to the deviation angle ΔAs. The holding auxiliary base current Ihb is set.

FIG. 11 is a schematic diagram of a control map showing the correspondence between the steering assist base current Ihb and the deviation angle ΔAs.
The steering assist base current calculation unit 274 sets the steering assist base current Ihb corresponding to the deviation angle ΔAs calculated by the subtraction unit 273. The steering auxiliary base current calculation unit 274 is, for example, a control map illustrated in FIG. 11 that shows the correspondence between the steering auxiliary base current Ihb and the deviation angle ΔAs that is created based on an empirical rule and stored in the ROM in advance. Then, the steering assist base current Ihb is calculated by substituting the deviation angle ΔAs, and this is set as the steering assist base current Ihb.

On the other hand, when the deviation angle ΔAs calculated by the subtraction unit 273 is not larger than zero, the steering assist base current calculation unit 274 sets zero as the steering assist base current Ihb. That is, the steering auxiliary base current calculation unit 274 sets zero as the steering auxiliary base current Ihb when the inclination angle As set by the inclination angle setting unit 271e is smaller than the offset amount Aso.
Thus, the offset amount Aso defines a dead zone region in determining the steering assist current Ih. In the control map shown in FIG. 10, the greater the vehicle speed Vc, the smaller the offset amount Aso and the smaller the dead zone area.

FIG. 12 is a schematic diagram of a control map showing the correspondence between the vehicle speed Vc and the current correction coefficient Rc.
The correction coefficient setting unit 275 sets a current correction coefficient Rc corresponding to the vehicle speed Vc. For example, the correction coefficient setting unit 275 substitutes the vehicle speed Vc into the control map illustrated in FIG. 12 that shows the correspondence between the vehicle speed Vc and the current correction coefficient Rc, which is previously created based on an empirical rule and stored in the ROM. Thus, the current correction coefficient Rc is calculated and set as the current correction coefficient Rc.

  The multiplication unit 276 multiplies the steering auxiliary base current Ihb set by the steering auxiliary base current calculation unit 274 and the current correction coefficient Rc set by the correction coefficient setting unit 275 to calculate the steering auxiliary current Ih. And output.

  As described above, the steering assist current calculation unit 27 holds the steering angle Sa of the steering wheel 101 at the steering angle Sah determined based on the crossing gradient when the vehicle goes straight on a road with a crossing gradient. A steering assist current Ih that causes the electric motor 110 to apply a steering assist force for performing the calculation is calculated. The steering assist current Ih is added to the target current It, thereby reducing the steering burden when the vehicle travels straight on a road with a crossing slope. In this manner, the steering assist current calculation unit 27 functions as an example of a steering assist unit that applies the steering assist force to the electric motor 110.

Next, the restoration auxiliary current calculation unit 28 will be described.
FIG. 13 is a schematic configuration diagram of the restoration auxiliary current calculation unit 28.
The restoration auxiliary current calculation unit 28 outputs from the steering angular velocity estimation unit 281 that estimates the actual steering angular velocity ωa that is the actual change rate of the steering angle Sa based on the output signal from the resolver 120 and the steering auxiliary current calculation unit 27. A steering angle calculating unit 282 that calculates a steering angle Sah that is a steering angle Sa to be steered by being assisted by the steering auxiliary current Ih that is provided.

In addition, the restoration auxiliary current calculation unit 28 calculates a correction base steering angular velocity ωcb that calculates a correction base steering angular velocity ωcb that is a base of the target steering angular velocity ωm that is a basis of the restoration auxiliary current Ir for correcting the temporary target current Itf. And a steered portion steering angular velocity calculating unit 284 that calculates a steered portion steering angular velocity ωch corresponding to the steered angle Sah calculated by the steered angle calculating unit 282.
Further, the restoration auxiliary current calculation unit 28 includes the correction base steering angular velocity ωcb calculated by the correction base steering angular velocity calculation unit 283 and the steering maintenance steering angular velocity ωch calculated by the steering maintenance steering angular velocity calculation unit 284. The target steering angular velocity ωm is calculated based on the target steering angular velocity ωm.

  The restoration assist current calculation unit 28 also includes a vehicle speed correction coefficient setting unit 286 that sets a vehicle speed correction coefficient Rv for correcting the target steering angular speed ωm according to the vehicle speed Vc, and a target steering calculated by the target steering angular speed calculation unit 285. A multiplication unit 287 that calculates a corrected target steering angular velocity ωmc by multiplying the angular velocity ωm by the vehicle speed correction coefficient Rv set by the vehicle speed correction coefficient setting unit 286.

Further, the restoration auxiliary current calculation unit 28 subtracts the actual steering angular velocity ωa estimated by the steering angular velocity estimation unit 281 from the corrected target steering angular velocity ωmc calculated by the multiplication unit 287, thereby obtaining a steering angular velocity for conversion into current. A subtraction unit 288 that calculates a certain steering angular velocity for conversion ωr (= ωmc−ωa) is provided.
The restoration auxiliary current calculation unit 28 includes a restoration auxiliary current setting unit 289 that sets (calculates) the restoration auxiliary current Ir based on the conversion steering angular velocity ωr calculated by the subtraction unit 288.

Next, each component provided in the restoration auxiliary current calculation unit 28 will be described in detail.
The steering angular velocity estimation unit 281 estimates the actual steering angular velocity ωa by differentiating the steering angle Sa calculated by the steering angle calculation unit 73 with respect to time.

The steering angle calculation unit 282 calculates the steering angle Sah based on the steering auxiliary current Ih output from the steering auxiliary current calculation unit 27.
FIG. 14 is a schematic diagram of a control map showing the correspondence between the steering angle Sah and the steering auxiliary current Ih.
The steered angle calculating unit 282 is, for example, a control map illustrated in FIG. 14 illustrating the correspondence between the steered angle Sah and the steered auxiliary current Ih, which is previously created based on an empirical rule and stored in the ROM. The steering angle Sah is calculated by substituting the steering auxiliary current Ih.
In the control map illustrated in FIG. 14, the steering angle Sah increases in the positive direction as the steering auxiliary current Ih increases in the positive direction, and the steering angle Sah increases as the steering auxiliary current Ih increases in the negative direction. It is set to increase in the negative direction.

The correction base steering angular velocity calculation unit 283 calculates the correction base steering angular velocity ωcb based on the steering angle Sa calculated by the steering angle calculation unit 73.
FIG. 15 is a schematic diagram of a control map showing the correspondence between the correction base steering angular velocity ωcb and the steering angle Sa.
The correction base steering angular velocity calculation unit 283 is, for example, a control map illustrated in FIG. 15 showing the correspondence between the correction base steering angular velocity ωcb and the steering angle Sa, which is created based on an empirical rule and stored in the ROM in advance. The correction base steering angular velocity ωcb is calculated by substituting the steering angle Sa calculated by the steering angle calculation unit 73.

  In the control map illustrated in FIG. 15, the correction base steering angular velocity ωcb increases in the minus direction as the steering angle Sa increases in the plus direction. When the steering angle Sa is smaller than zero, the correction base steering angular velocity ωcb suddenly increases in the negative direction. When the steering angle Sa increases, the correction base steering angular velocity ωcb increases in the negative direction gradually. Becomes smaller. On the other hand, as the steering angle Sa increases in the minus direction, the correction base steering angular velocity ωcb increases in the plus direction. When the steering angle Sa is smaller from zero to the minus direction, the correction base steering angular velocity ωcb suddenly increases in the positive direction. When the steering angle Sa increases in the negative direction, the correction base steering angular velocity ωcb increases in the positive direction. The rate of increasing gradually decreases.

The retained steering steering angular velocity calculation unit 284 calculates the retained steering steering angular velocity ωch based on the retained steering angle Sah calculated by the retained steering angle calculation unit 282.
FIG. 16 is a schematic diagram of a control map showing the correspondence between the steering holding steering angular velocity ωch and the steering holding angle Sah.
The steered steering steering angular velocity calculation unit 284, for example, the control illustrated in FIG. 16 showing the correspondence between the steered steering steering angular velocity ωch and the steered angle Sah that is created based on an empirical rule and stored in the ROM in advance. A steering angular velocity ωch is calculated by substituting the steering angle Sah calculated by the steering angle calculation unit 282 into the map.
The curve in the control map illustrated in FIG. 16 is the same as the curve in the control map illustrated in FIG. Therefore, when the steering angle Sa and the steering angle Sah are the same, the correction base steering angular velocity ωcb and the steering-amount steering angular velocity ωch are the same.

  The target steering angular velocity calculation unit 285 subtracts the steering maintaining steering angular velocity ωch calculated by the steering maintaining steering angular velocity calculating unit 284 from the correction base steering angular velocity ωcb calculated by the correction base steering angular velocity calculating unit 283. Thus, the target steering angular velocity ωm is calculated (ωm = ωcb−ωch).

The vehicle speed correction coefficient setting unit 286 sets the vehicle speed correction coefficient Rv based on the vehicle speed signal v.
FIG. 17 is a schematic diagram of a control map showing the correspondence between the vehicle speed correction coefficient Rv and the vehicle speed Vc.
The vehicle speed correction coefficient setting unit 286, for example, sets the vehicle speed Vc on the control map illustrated in FIG. 17 that shows the correspondence between the vehicle speed correction coefficient Rv and the vehicle speed Vc, which is previously created based on empirical rules and stored in the ROM. The vehicle speed correction coefficient Rv is calculated by substituting.

  In the control map illustrated in FIG. 17, the vehicle speed correction coefficient Rv increases as the vehicle speed Vc increases. The rate at which the vehicle speed correction coefficient Rv increases is greater when the vehicle speed Vc is smaller than when the vehicle speed Vc is large. In the present embodiment, the vehicle speed correction coefficient Rv is set to 1 when the vehicle speed Vc is 10 (km / h).

  The restoration auxiliary current setting unit 289 calculates the restoration auxiliary current Ir by multiplying the conversion steering angular velocity ωr calculated by the subtraction unit 288 by a predetermined conversion coefficient, and sets it as the restoration auxiliary current Ir.

  As described above, the restoration auxiliary current calculation unit 28 moves the steering wheel 101 to the neutral position when the steering wheel 101 is switched back when the vehicle does not travel on a road with a cross slope and the steering auxiliary current Ih is zero. A restoring assist current Ir for causing the electric motor 110 to apply a return assisting force for returning to 1 is calculated. Then, by adding the restoration auxiliary current Ir to the target current It, the steering wheel 101 is forcibly returned to the neutral position at the time of switching back. Thus, the restoration assist current calculation unit 28 functions as an example of a return assist unit that applies a return assist force to the electric motor 110.

Next, the operation of the steering device 100 configured as described above will be described.
As described above, the target current calculation unit 20 of the control device 10 restores the temporary target current Itf determined by the temporary target current determination unit 25 and the steering auxiliary current Ih calculated by the steering auxiliary current calculation unit 27. A value obtained by adding the restoration auxiliary current Ir calculated by the auxiliary current calculation unit 28 is set as a target current It.
Therefore, since the steering assist current Ih is zero when the vehicle is not traveling on a road with a cross slope, the target current calculation unit 20 uses a value obtained by adding the temporary target current Itf and the restoration assist current Ir as the target current. It is assumed to be It.

FIG. 18 shows a case where the vehicle is traveling on a road having no crossing gradient at a vehicle speed Vc of about 30 km / h, and the steering angle Sa corresponds to the steering angle Sa when the steering wheel 101 is turned to the right after being turned from the neutral position. It is a figure which shows the change of actual steering angular velocity (omega) a, corrected target steering angular velocity (omega) mc, and target electric current It.
Since the vehicle speed Vc is around 30 km / h, the vehicle speed correction coefficient Rv is a value larger than 1 (see FIG. 17). Moreover, since the steering assist current Ih is zero, the steering angular velocity ωch is zero. Therefore, the actual steering angular velocity ωa and the corrected target steering angular velocity ωmc with respect to the steering angle Sa are as shown in FIG. Then, since the restoration auxiliary current Ir is calculated by multiplying the conversion steering angular velocity ωr (= ωmc−ωa) by a predetermined conversion coefficient, the target current It with respect to the steering angle Sa is as shown in FIG.

  Even if the steering wheel 101 is turned off and then turned back in the released state, it returns to the neutral position by the target current It thus calculated. That is, the self-aligning torque acts to naturally reduce the steering angle Sa, but does not return to the neutral position due to the friction of the steering system, but the steering assist angle Ir is added to the target current It. Sa can be forcibly returned to the neutral position.

On the other hand, when the vehicle travels on a road with a cross slope and the steering assist current Ih is not zero, the target current calculation unit 20 sets a value in consideration of the steering assist current Ih as the target current It.
FIG. 19 is a diagram illustrating changes in the road surface inclination angle As and the steering angle Sa when moving straight from a road having no cross gradient to a road having a cross gradient.
In order to go straight, the steering angle Sa is increased as the inclination angle As increases, and when the vehicle moves to a road with a cross gradient (a road outside the dead zone), the steering angle Sa corresponding to the inclination angle As of the cross gradient and the vehicle speed Vc. Being steered to At this time, the steering assist current Ih is added to the target current It for assisting the vehicle to go straight on a road with a cross slope. Then, the corrected target steering angular velocity ωmc is obtained by multiplying the target steering angular velocity ωm (= ωcb−ωch) obtained by subtracting the steering-maintained steering angular velocity ωch from the correction base steering angular velocity ωcb by the vehicle speed correction coefficient Rv. Become. The steering steering steering angular velocity ωch is a value corresponding to the steering angle (steering angle Sah) that is maintained when the vehicle travels straight on a road having a cross gradient. Therefore, the restoration auxiliary current Ir for restoration to the steering angle Sah is added to the target current It. As a result, the steering angle Sa is maintained at the steering angle Sah for traveling straight on a road with a cross gradient.

Thus, according to the steering device 100 according to the present embodiment, when the vehicle travels straight on a road having a cross slope, the steering assist current Ih is supplied and the steered angle Sah that is steered is learned. The restoration auxiliary current Ir is supplied so that the steering angle Sa of the steering wheel 101 becomes the learned steering angle Sah.
Therefore, according to the steering device 100 according to the present embodiment, the electric motor 110 is provided with the steering assist force for maintaining the steering angle Sa of the steering wheel 101 at the steering angle Sah determined based on the cross gradient. Both the function and the function of returning the steering angle Sa of the steering wheel 101 to the neutral position at the time of switching back can be realized.

<Modification>
The restoration auxiliary current calculation unit 28 according to the above-described embodiment may be configured as follows.
FIG. 20 is a schematic configuration diagram of the restoration auxiliary current calculation unit 48 according to the modification. Constituent elements having the same functions as constituent elements in the restoration auxiliary current calculating unit 28 according to the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

The restoration auxiliary current calculation unit 48 according to the modification includes the above-described steering angle calculation unit 282, the steering angle Sah calculated by the steering angle calculation unit 282, and the steering angle Sa calculated by the steering angle calculation unit 73. Based on this, a deviation steering angular velocity estimation unit 481 that estimates an actual deviation steering angular velocity ωd that is an actual change speed of the steering angle Sa with respect to the steering holding angle Sah is provided.
Further, the restoration auxiliary current calculation unit 48 calculates a target steering angular velocity ωm that calculates a target steering angular velocity ωm based on the steering angle Sah calculated by the steering angle calculation unit 282 and the steering angle Sa calculated by the steering angle calculation unit 73. Part 485 is provided.

Further, the restoration assist current calculation unit 48 multiplies the vehicle speed correction coefficient setting unit 286 described above, the target steering angular speed ωm calculated by the target steering angular speed calculation unit 485 and the vehicle speed correction coefficient Rv set by the vehicle speed correction coefficient setting unit 286. And a multiplier 287 for calculating the corrected target steering angular velocity ωmc.
Further, the restoration auxiliary current calculation unit 48 subtracts the actual deviation steering angular velocity ωd estimated by the deviation steering angular velocity estimation unit 481 from the corrected target steering angular velocity ωmc calculated by the multiplication unit 287, thereby steering for conversion into current. A subtraction unit 288 that calculates a conversion steering angular velocity ωr (= ωmc−ωd) that is an angular velocity, and a recovery auxiliary current setting that sets (calculates) the recovery auxiliary current Ir based on the conversion steering angular velocity ωr calculated by the subtraction unit 288. Part 289.

  The deviation steering angular velocity estimation unit 481 time-differentiates a subtraction value (Sa−Sah) obtained by subtracting the steering angle Sah calculated by the steering angle calculation unit 282 from the steering angle Sa calculated by the steering angle calculation unit 73. Thus, the actual deviation steering angular velocity ωd is estimated.

The target steering angular velocity calculation unit 485 is based on a subtraction value (Sa−Sah) obtained by subtracting the steering angle Sah calculated by the steering angle calculation unit 282 from the steering angle Sa calculated by the steering angle calculation unit 73. A target steering angular velocity ωm is calculated.
FIG. 21 is a schematic diagram of a control map showing the correspondence between the target steering angular velocity ωm and the subtraction value (Sa-Sah).
The target steering angular velocity calculation unit 485 is, for example, a control map illustrated in FIG. 21 that shows the correspondence between the target steering angular velocity ωm and the subtraction value (Sa-Sah) that is created based on an empirical rule and stored in the ROM in advance. The target steering angular velocity ωm is calculated by substituting the subtraction value (Sa−Sah) into
In the control map illustrated in FIG. 21, the target steering angular velocity ωm increases in the negative direction as the subtraction value (Sa-Sah) increases in the positive direction, as in the control map illustrated in FIG.

  When the steering assist current Ih is zero when the steering assist current Ih is zero when the vehicle is not traveling on a road with a cross gradient, the restoration assist current calculation unit 48 according to the modified example of the above configuration places the steering wheel 101 in the neutral position. A restoring assist current Ir for causing the electric motor 110 to apply a return assisting force for returning to 1 is calculated.

  On the other hand, when the vehicle travels on a road with a cross slope and the steering assist current Ih for assisting the vehicle to travel straight on the road with a cross slope is added to the target current It, the target steering angular velocity ωm is calculated from the steering angle Sa. It is calculated using the subtraction value (Sa-Sah) obtained by subtracting the steering angle Sah and the control map illustrated in FIG. That is, the target steering angular velocity ωm corresponding to the deviation of the steering angle Sa from the steering angle Sah is set. Then, a converted steering angular velocity ωr (= ωmc−ωd), which is a deviation between the corrected target steering angular velocity ωmc obtained by correcting the target steering angular velocity ωm and the actual deviation steering angular velocity ωd estimated by the deviation steering angular velocity estimation unit 481. Based on this, the restoration auxiliary current Ir is set (calculated). This restoration auxiliary current Ir is a current for setting the steering angle Sah to the neutral position (steering angle Sah) of the steering angle Sa and assisting the restoration to the neutral position, and the steering angle Sa is set to the steering angle Sah. This is the current for matching. When the steering angle Sa coincides with the steering angle Sah (Sa-Sah = 0), the target steering angular velocity ωm is zero and the actual deviation steering angular velocity ωd is also zero, so that the restoration assist current Ir is zero. Retained.

  Therefore, the steering assisting force for maintaining the steering angle Sa of the steering wheel 101 at the steering angle Sah determined based on the cross gradient is also obtained by the steering device 100 having the restoration assisting current calculation unit 48 according to this modification. Both a function to be imparted to the electric motor 110 and a function to return the steering angle Sa of the steering wheel 101 to the neutral position at the time of switching back can be realized.

DESCRIPTION OF SYMBOLS 10 ... Control apparatus, 20 ... Target electric current calculation part, 27 ... Steering auxiliary current calculation part, 28, 48 ... Restoration auxiliary current calculation part, 30 ... Control part, 100 ... Electric power steering apparatus, 110 ... Electric motor

Claims (4)

An electric motor that applies assisting force to the steering wheel of the vehicle;
When the vehicle travels straight on a road having a cross slope, the steering motor is provided with a steering assist force for maintaining a steering angle of the steering wheel at a steering angle determined based on the cross slope. An assist section;
A return assist unit that applies a return assist force to the electric motor for returning the steering wheel to a neutral position when the steering wheel is switched back;
With
The return assist unit gives the electric motor an assist force for returning to the steered angle instead of the return assist force when the steered assist unit is giving the steered assist force. An electric power steering device. The steering assist unit calculates an assist current required to give the steering assist force to the electric motor,
The electric power steering apparatus according to claim 1, wherein the return assist unit calculates an assist current necessary for applying the return assist force to the electric motor. The return assist unit calculates an assist current required for applying the return assist force based on an assist current required for applying the steering assist force to the electric motor. 3. The electric power steering apparatus according to 1 or 2. On the computer,
When the vehicle travels straight on a road with a cross slope, the wheel holding assist force is applied to the electric motor to hold the steering angle of the steering wheel of the vehicle at a steering angle determined based on the cross slope. Assist function,
A return assist function for giving the electric motor a return assist force for returning the steering wheel to a neutral position when the steering wheel is switched back;
With
The return assist function gives the electric motor an assist force for returning to the steered angle instead of the return assist force when the steered assist function is giving the steered assist force. A program that makes things happen.

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