JP4747958B2 - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device capable of improving a steering feeling when returning a steering wheel from the vicinity of a locked position. <P>SOLUTION: This power steering device is provided with a basic assist torque computing part 31 finding a basic assist torque based on the steering torque of the steering wheel 16, a return torque computing part 32 computing a return torque acting in the direction of returning the steering wheel 16 in a neutral position based on steering angles of steering wheels WL and WR found from a detection value of a steering angle sensor 22, and an electric motor 17 applying a torque according to a target assist torque found by adding the basic assist torque to the return torque. The return torque computing part 32 increases the return torque in an area where an absolute value of the steering angle is a prescribed angle or more. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

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

Conventionally, a power steering device that assists a driver's steering operation has been widely used. As such a power steering device, Patent Literature 1 describes a device that improves the return characteristic of the steering wheel by increasing the friction compensation component between the tire and the road surface as the vehicle speed decreases.
Japanese Patent No. 3082483

  Generally, when the steering wheel is steered to near the lock (end) position and the turning angle of the steered wheel is near the maximum steered angle, the achievement rate of the Ackerman steering is lowered, and the steered angle of the steered wheel is reduced. SAT (Self Aligning Torque) generated in the direction is reduced. As a result, the return characteristic of the steering wheel is changed, and the steering feeling is deteriorated. In the power steering device described above, no consideration is given to the deterioration of the steering feeling when the steering wheel is returned from the vicinity of the lock position.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a power steering apparatus capable of improving the steering feeling when the steering wheel is returned from the vicinity of the lock position.

  A power steering device according to the present invention is attached to a vehicle and has a turning angle acquisition means for obtaining a turning angle of a turning wheel to be turned according to steering of the steering wheel, and a basic assist based on the steering state of the steering wheel. Based on the basic assist amount calculation means for calculating the amount and the turning angle of the steered wheel obtained by the turning angle acquisition means, the return correction amount for calculating the return correction amount acting in the direction to return the steering wheel to the neutral position Calculating means, and assist means for applying assist torque to the steering mechanism of the vehicle based on the basic assist amount and the return correction amount, wherein the return correction amount calculation means has an absolute value of the turning angle equal to or greater than a predetermined angle. Sometimes, the return correction amount is increased.

  According to the power steering device of the present invention, the assist torque applied to the steering mechanism of the vehicle is calculated based on the basic assist amount obtained from the steering state and the return correction amount obtained from the turning angle. Here, the return correction amount is increased when the absolute value of the turning angle is equal to or greater than a predetermined angle. Therefore, when the absolute value of the turning angle is equal to or larger than a predetermined angle, for example, when the steering wheel is in the vicinity of the lock position, it is possible to improve the return characteristic of the steering wheel.

  The return correction amount calculation means preferably increases the return correction amount during vehicle braking than during non-braking.

  Due to the characteristics of the suspension, the return characteristic of the steering wheel also changes depending on the braking state of the vehicle. In general, the steering wheel returns poorly during vehicle braking. According to the power steering device of the present invention, the return correction amount is increased during vehicle braking. Therefore, for example, even in a situation where the steering wheel is returned from the vicinity of the lock position while braking, the return characteristic of the steering wheel can be appropriately improved.

  Further, it is preferable that the return correction amount calculating means holds a state where the return correction amount is increased for a predetermined time after the braking of the vehicle is released.

  In this case, for example, even if the braking state and the non-braking state are alternately repeated, the increase state of the return correction amount is maintained for a predetermined time, thereby preventing the fluctuation of the return correction amount from occurring. The As a result, when the steering wheel is returned from the vicinity of the lock position, it is possible to prevent chattering of assist torque due to a change in the braking state.

  Further, the return correction amount calculation means increases the return correction amount when the vehicle deceleration is large compared to when the vehicle deceleration is small, and returns when the vehicle acceleration is large compared to when the vehicle acceleration is small. Is preferably reduced.

  The return characteristic of the steering wheel also changes depending on the acceleration / deceleration of the vehicle. According to the power steering device of the present invention, when the vehicle deceleration is large, the return correction amount is increased compared to when the vehicle is small, and when the vehicle acceleration is large, the return correction amount is decreased compared to when the vehicle is small. . As a result, it is possible to appropriately improve the return characteristics of the steering wheel even in a situation where the steering wheel is returned from the vicinity of the lock position during vehicle deceleration or vehicle acceleration.

  The return correction amount calculation means preferably reduces the return correction amount when the vehicle speed is equal to or higher than a predetermined value.

  In this way, even if a functional defect occurs in the turning angle acquisition means, for example, when the vehicle is traveling at a relatively high speed equal to or higher than a predetermined value, the return correction is caused due to this functional failure. It is possible to suppress an adverse effect on the steering mechanism that may be given an amount.

  According to the power steering device of the present invention, it is possible to improve the steering feeling when the steering wheel is returned from the vicinity of the lock position.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.

  First, the configuration of the power steering apparatus 10 according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration of the power steering apparatus 10. In the present embodiment, as the power steering device 10, a rack coaxial type electric power steering device having a ball screw type conversion mechanism that converts the rotational torque of the electric motor into a force in the reciprocating direction of the rack shaft is used.

  In FIG. 1, WL and WR are a left front wheel and a right front wheel as steered wheels, and these left and right front wheels WL and WR are connected by a steering gear box 12 via a tie rod 11. The steering gear box 12 includes a rack shaft 13 and a pinion 14. The rack shaft 13 is slidable with respect to the steering gear box 12. A tie rod 11 is connected to both ends of the rack shaft 13, and a steering wheel 16 is attached to the pinion 14 via a steering shaft 15. When the steering wheel 16 is steered, the left and right front wheels WL and WR are steered through the steering shaft 15, the pinion 14, the rack shaft 13 and the tie rod 11.

  Although not shown, a ball screw groove is formed on a part of the outer peripheral surface of the rack shaft 13, and a ball screw corresponding to this ball screw groove is formed on the rotor of the electric motor 17 arranged coaxially with the rack shaft 13. A ball nut having a groove on the inner peripheral surface is fixed. A plurality of balls are accommodated between the pair of ball screw grooves, and the rotational movement of the electric motor 17 is converted into the reciprocating movement of the rack shaft 13 by the ball screw. That is, when the electric motor 17 is driven, the rack shaft 13 is driven in the axial direction, and steering is assisted.

  The electric motor 17 is connected to a motor driver 18, and applies an assist torque corresponding to the drive current supplied from the motor driver 18 to the rack shaft 13. The motor driver 18 supplies a drive current to the electric motor 17 in accordance with a command signal from an electronic control unit (hereinafter referred to as “EPS ECU”) 30. That is, the electric motor 17, the motor driver 18, and the EPS ECU 30 function as assist means described in the claims.

  The steering shaft 15 is provided with, for example, a torsion bar 20 that twists in accordance with the steering torque applied to the steering wheel 16, and the amount and direction of twisting of the torsion bar 20 are detected by the steering torque sensor 21. . The signal output from the steering torque sensor 21 is input to the EPS ECU 30.

  The steering shaft 15 is provided with a steering angle sensor 22 such as a rotary encoder. The steering angle sensor 22 outputs a signal corresponding to the direction and magnitude of the steering angle input by the driver. A signal output from the steering angle sensor 22 is input to the EPS ECU 30. In the EPS ECU 30, the steering angle of the steering wheel 16 input from the steering angle sensor 22 is compensated for the zero point, and the steered angles of the steered wheels WL and WR are acquired from the steering angle after the zero point compensation. Here, the EPS ECU 30 learns the output value of the steering angle sensor 22 as an offset of the steering angle sensor 22 when the output value from the yaw rate sensor or the lateral acceleration sensor is zero, that is, when the vehicle is in a straight traveling state. The zero value of the steering angle is compensated using the learning value (offset value). That is, the steering angle sensor 22 functions as a turning angle acquisition means described in the claims. In the following description, it is assumed that the steering angle and the turning angle take positive values during leftward steering and take negative values during rightward steering.

  In addition to the steering torque sensor 21 and the steering angle sensor 22 described above, the EPS ECU 30 is also connected to a vehicle speed sensor 23, a longitudinal acceleration sensor 24, a stop switch 25, and the like.

  The vehicle speed sensor 23 is a wheel speed sensor attached to each wheel of the vehicle, and generates a pulse signal at a cycle corresponding to the speed of the vehicle. An output signal from the vehicle speed sensor 23 is input to the EPS ECU 30. The EPS ECU 30 calculates the vehicle speed based on the output signal of the vehicle speed sensor 23. The longitudinal acceleration sensor 24 is a sensor that detects acceleration / deceleration in the vehicle longitudinal direction (that is, vehicle acceleration and vehicle deceleration). The result detected by the longitudinal acceleration sensor 24 is also sent to the EPS ECU 30. The stop switch 25 is attached to the brake pedal and detects the operation state of the brake pedal. The stop switch 25 is turned on when the brake pedal is depressed, that is, in a braking state. Further, the brake pedal is turned off in a state where the depression of the brake pedal is released, that is, in a non-braking state. The result detected by the stop switch 25 is sent to the EPS ECU 30.

  The EPS ECU 30 includes a microprocessor that performs calculations, a ROM that stores a program for causing the microprocessor to execute each process, a RAM that stores various data such as calculation results, and a backup RAM in which the stored contents are held by a 12V battery. Etc.

  With the above configuration, the EPS ECU 30 includes a basic assist torque calculation unit 31 for obtaining a basic assist torque (basic assist amount) based on the steering torque, the turning angles of the steered wheels WL and WR, the vehicle speed, and the braking. A return torque calculator 32 for obtaining a return torque (return correction amount) acting in a direction to return the steering wheel 16 to the neutral position based on the state and acceleration / deceleration, and adding the basic assist torque and the return torque to obtain the target assist torque. A target assist torque calculation unit 33 for calculation is constructed. Here, the basic assist torque calculator 31 functions as a basic assist amount calculator, and the return torque calculator 32 functions as a return correction amount calculator.

  The EPS ECU 30 includes an electric motor control unit 34 that calculates a target current value based on the target assist torque obtained by the target assist torque calculation unit 33 and controls a current value supplied to the electric motor 17. Has been built.

  Next, the operation of the power steering apparatus 10 will be described with reference to FIGS.

  In the EPS ECU 30 constituting the power steering device 10, first, the basic assist torque is calculated by the basic assist torque calculator 31. The basic assist torque calculation unit 31 includes a two-dimensional map (basic assist torque map) that defines the relationship between the steering torque and the basic assist torque, and the basic assist torque is based on the steering torque read from the steering torque sensor 21. The basic assist torque is obtained by searching the map. The calculated basic assist torque is output to the target assist torque calculator 33. Here, the basic assist torque is a basic torque value for applying an assist force to the turning operation of the steering wheel 16.

  An example of the basic assist torque map is shown in FIG. As shown in FIG. 2, the basic assist torque map is set so that the basic assist torque increases as the steering torque increases.

  On the other hand, the return torque calculation unit 32 calculates the return torque that acts in the direction of returning the steering wheel 16 to the neutral position based on the turning angles of the steered wheels WL and WR, the vehicle speed, the braking state, and the acceleration / deceleration. The details of the return torque calculation method will be described later. The calculated return torque is output to the target assist torque calculator 33.

  In the target assist torque calculator 33, the basic assist torque obtained by the basic assist torque calculator 31 and the return torque obtained by the return torque calculator 32 are added to calculate the target assist torque. Then, the calculated target assist torque is output to the electric motor control unit 34.

  The electric motor control unit 34 determines a target current value for driving the electric motor 17 according to the target assist torque. The electric motor 17 is driven by supplying the output current controlled to coincide with the target current value to the electric motor 17. Specifically, the energization time of the switching element is determined based on the target current value, and a control signal is output to the motor driver 18 according to this. Thereby, a current corresponding to the target current value flows through the electric motor 17, and a torque corresponding to the current is applied to the rack shaft 13.

  Next, a return torque calculation method will be described with reference to FIG. FIG. 3 is a flowchart showing the processing procedure of the return torque calculation processing. This process is repeatedly executed at a predetermined timing in the EPS ECU 30 from when the power source of the EPS ECU 30 is turned on to when it is turned off.

  In step S100, it is determined whether or not the stop switch 25 is in an on state, that is, whether or not the vehicle is in a braking state. If the stop switch 25 is on, that is, if the vehicle is in a braking state, the process proceeds to step S102. On the other hand, when the stop switch 25 is in the off state, that is, when the vehicle is in the non-braking state, the process proceeds to step S108.

  In step S102, the control amount switching flag indicating the braking state / non-braking state of the vehicle is set to ON (represents the braking state). However, the control amount switching flag is kept on for 5 seconds after the stop switch 25 transitions from the on state to the off state, that is, after the brake pedal is released. The holding time is set in consideration of the time required for the steering wheel 16 to return from the vicinity of the lock (end) position to the neutral position, but the value of 5 seconds is an example, and the holding time is 5 seconds. It goes without saying that it is not limited to.

  Subsequently, in step S104, 0 (end) is set in a control amount switching start determination flag for controlling execution / end of the holding time count-up.

  In step S106, the control amount switching start determination counter that counts the holding time, that is, the elapsed time after the stop switch 25 changes from the on state to the off state, is reset to zero. Thereafter, the process proceeds to step S124.

  When step S100 is negative, that is, when the state of the stop switch 25 read this time is OFF, in step S108, it is determined whether or not the state of the stop switch 25 read last time is ON. Is called. Here, when the previous state is ON, that is, when it is determined that the brake pedal is immediately depressed, 1 (execution) is set in the control amount switching start determination flag described above in step S110. Is set. Thereafter, the process proceeds to step S112.

  On the other hand, when the previous state is also off, that is, when the brake pedal is released, the control amount switching start determination flag is not set to 1 (execution), and the process proceeds to step S112.

  In step S112, a determination is made as to whether or not the control amount switching start determination flag is 1 (execution). If the control amount switching start determination flag is 1, the process proceeds to step S114. On the other hand, when the control amount switching start determination flag is 0 (end), the process proceeds to step S124.

  In step S114, the value of the control amount switching start determination counter that counts the elapsed time after the stop switch 25 transitions from the on state to the off state is incremented by one.

  Subsequently, in step S116, whether or not the value of the control amount switching start determination counter has reached 5 seconds or more, that is, whether or not 5 seconds have elapsed since the stop switch 25 transitioned from the on state to the off state. Judgment is made. Here, when five seconds or more have elapsed since the stop switch transitioned from the on state to the off state, the process proceeds to step S118. On the other hand, when 5 seconds or more have not elapsed yet, the process proceeds to step S124.

  If more than 5 seconds have elapsed since the stop switch 25 transitioned to the off state, the control amount switching flag is set to off in step S118. In step S120, the control amount switching start determination flag is set to 0 (end), and in step S122, the control amount switching start determination counter is reset to zero. Thereafter, the process proceeds to step S124.

  In step S124, the turning angle of the steered wheels WL and WR obtained from the detection result of the steering angle sensor 22, the vehicle longitudinal acceleration / deceleration (vehicle acceleration or vehicle deceleration) detected by the longitudinal acceleration sensor 24, and the vehicle speed. The vehicle speed obtained from the detection result of the sensor 23 is read.

  In the subsequent step S126, a vehicle speed gain used for calculating the return torque is obtained based on the vehicle speed read in step S124. Specifically, the return torque calculation unit 32 is provided with a two-dimensional map (vehicle speed gain map) that defines the relationship between the vehicle speed and the vehicle speed gain, and the vehicle speed gain map is searched based on the vehicle speed. Vehicle speed gain is required.

  An example of the vehicle speed gain map is shown in FIG. As shown in FIG. 4, the vehicle speed gain map is set so that the vehicle speed gain is G1 in the region where the vehicle speed is 0 to v1 (km / h). In the range of v1 to v2 (km / h) (where v1 <v2), the vehicle speed gain is set to decrease from G1 to zero as the vehicle speed increases. Further, the vehicle speed gain is set to be zero in the region where the vehicle speed is v2 (km / h) or more.

  Subsequently, in step S128, a determination is made as to whether the control amount switching flag is on. When the control amount switching flag is on, that is, when the brake pedal is depressed or when 5 seconds have not elapsed since the depression was released (hereinafter, sometimes referred to as “during braking / holding”), step S130 The process moves on. On the other hand, when the control switching flag is not on, that is, when 5 seconds or more have elapsed after the release of the brake pedal is released (hereinafter sometimes referred to as “non-braking”), the process proceeds to step S134. To do.

  In step S130, the basic return torque during braking / holding is obtained based on the turning angle read in step S124. Specifically, the return torque calculation unit 32 is provided with a two-dimensional map (basic return torque map during braking) that defines the relationship between the turning angle and the basic return torque during braking / maintenance. Based on the steering angle, the basic return torque map during braking is searched to obtain the basic return torque during braking / holding.

  Here, an example of the braking basic return torque map is shown by a solid line in FIG. The basic return torque map during braking shows that the basic return torque is zero and the absolute value of the turning angle is equal to or greater than the predetermined angle (turning angle) when the absolute value of the turning angle is less than the predetermined angle (turning angle <| θ |). In the steering angle ≧ | θ |) region, the absolute value of the basic return torque is determined to increase as the absolute value of the turning angle increases.

  In FIG. 5, an example of a non-braking basic return torque map used during non-braking is shown by a broken line together with a braking basic return torque map selected during braking / holding. Here, in the non-braking return torque map, the basic return torque is zero in the region where the absolute value of the turning angle is less than the predetermined angle (the turning angle <| θ |), and the absolute value of the turning angle is the predetermined angle. In the above region (turning angle ≧ | θ |), the absolute value of the basic return torque is determined to increase as the absolute value of the turning angle increases.

  Further, as shown in FIG. 5, the braking basic return torque map has an absolute value of the turning angle that is equal to or larger than a predetermined angle (steering angle ≧ | θ |) as compared with the non-braking basic return torque map. In the region, the absolute value of the basic return torque for the same turning angle is determined to be larger. Hereinafter, the braking basic return torque map and the non-braking basic return map may be collectively referred to as a “basic return torque map”.

  Subsequently, in step S132, an acceleration / deceleration gain for correcting the basic return torque is obtained based on the vehicle deceleration read in step S124. Specifically, the return torque calculation unit 32 is provided with a two-dimensional map (deceleration gain map) that defines the relationship between the vehicle deceleration and the acceleration / deceleration gain, and the deceleration gain is determined based on the vehicle deceleration. The acceleration / deceleration gain is obtained by searching the map.

  Here, an example of the deceleration gain map is shown by a solid line in FIG. The deceleration gain map is determined so that the acceleration / deceleration gain is 1 when the vehicle deceleration is zero, and the acceleration / deceleration gain increases from 1 as the vehicle deceleration increases. In FIG. 6, an example of an acceleration gain map used during vehicle acceleration is shown by a broken line together with a deceleration gain map selected during vehicle deceleration. Details of the acceleration gain map will be described later. The deceleration gain map and the acceleration gain map may be collectively referred to as an “acceleration / deceleration gain map”. After the acceleration / deceleration gain is obtained based on the vehicle deceleration, the process proceeds to step S138.

  If it is determined in step S128 that the vehicle is not braked, in step S134, a basic return torque during non-braking is determined based on the turning angle. Specifically, the basic return torque at the time of non-braking is obtained by searching the above-mentioned non-braking basic return torque map based on the turning angle. Since the non-braking basic return torque map (see the broken line in FIG. 5) is as described above, the description thereof is omitted here.

  Subsequently, in step S136, an acceleration / deceleration gain for correcting the basic return torque is obtained based on the vehicle acceleration read in step S124. Specifically, the return torque calculation unit 32 is provided with a two-dimensional map (acceleration gain map) that defines the relationship between the vehicle acceleration and the acceleration / deceleration gain, and the acceleration gain map is searched based on the vehicle acceleration. Thus, the acceleration / deceleration gain is obtained.

  Here, an example of the acceleration gain map is shown by a broken line in FIG. The acceleration gain map is determined such that the acceleration / deceleration gain becomes 1 when the vehicle acceleration is zero, and the acceleration / deceleration gain decreases from 1 as the vehicle acceleration increases.

  After step S132 or step S136 is executed, in step S138, the basic return torque acquired in the above step is multiplied by the acceleration / deceleration gain and the vehicle speed gain to calculate the return torque. Thereafter, the process is temporarily exited.

  The return torque calculated by the above process is output to the target assist torque calculator 33 as described above. In the target assist torque calculation unit 33, the input return torque and the basic assist torque are added to calculate the target assist torque. Then, the current supplied to the electric motor 17 is controlled so that the target current value calculated based on the target assist torque matches the actual current value.

  According to this embodiment, in the region where the absolute value of the turning angle of the steered wheels WL and WR is equal to or greater than a predetermined angle (steering angle ≧ | θ |), the basic return torque is increased as the absolute value of the turning angle increases. The basic return torque map is determined so that the absolute value of is increased. Therefore, the return torque acting in the direction of returning the steering wheel 16 to the neutral position is increased in a region where the absolute value of the turning angle is equal to or larger than a predetermined angle. As a result, when the absolute value of the turning angle is equal to or larger than a predetermined angle, for example, when the steering wheel is in the vicinity of the lock position, the return characteristic of the steering wheel can be improved.

  In addition, the braking basic return torque map has the same turning angle in a region where the absolute value of the turning angle is equal to or larger than a predetermined angle (turning angle ≧ | θ |) compared with the non-braking basic return torque map. The absolute value of the basic return torque with respect to is determined to be larger. Therefore, the return torque is increased during vehicle braking than during non-braking. As a result, for example, even in a situation where the steering wheel 16 is returned from the vicinity of the lock position while braking, the return characteristic of the steering wheel 16 can be appropriately improved.

  According to this embodiment, the control amount switching flag indicating the braking state / non-braking state of the vehicle is held in the on state for 5 seconds after the stop switch 25 transitions from the on state to the off state. Therefore, for 5 seconds after the depression of the brake pedal is released, the basic return torque map at the time of braking is selected when the basic return torque is obtained, and the state where the return torque is increased as compared with that at the time of non-braking is maintained. As a result, even if the braking state and the non-braking state are repeated alternately, for example, the occurrence of vibration fluctuations in the return torque is prevented. As a result, when the steering wheel 16 is returned from the vicinity of the lock position, it is possible to prevent chattering of assist torque due to a change in the braking state.

  According to the present embodiment, the deceleration gain map is determined so that the acceleration / deceleration gain increases from 1 as the vehicle deceleration increases. The acceleration gain map is determined so that the acceleration / deceleration gain decreases from 1 as the vehicle acceleration increases. Therefore, the return torque increases as the vehicle deceleration increases, and the return torque decreases as the vehicle acceleration increases. As a result, in the situation where the steering wheel 16 is returned from the vicinity of the lock position when the vehicle is decelerated, the poor return of the steering wheel 16 can be improved and the steering wheel 16 is returned from the vicinity of the lock position when the vehicle is accelerated. Thus, it is possible to suppress the cutting of the steering wheel 16.

  According to this embodiment, the vehicle speed gain map is set so that the vehicle speed gain decreases from G1 to zero as the vehicle speed increases. Further, in a region where the vehicle speed is v2 (km / h) or higher, the vehicle speed gain is set to be zero. Therefore, when the vehicle is traveling at a relatively high speed of v2 or more per hour, even if a functional defect occurs in the steering angle sensor 22 or the like, for example, there is a possibility that a return torque is applied due to this malfunction. It is possible to suppress adverse effects.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in this embodiment, a power steering device having a configuration in which the electric motor 17 disposed on the axis of the rack shaft 13 applies assist torque to the rack shaft 13 via a ball screw (rack axis assist type) is used. An electric motor and a speed reducer may be mounted on the shaft 15 so that they provide assist torque to the steering shaft 15 (column shaft assist type). Moreover, it is good also as a structure (pinion shaft assist type) which mounts an electric motor and a reduction gear on the pinion 14, and gives them the assist torque to them.

  In the present embodiment, the turning angle of the steered wheels WL and WR is acquired using a value obtained by compensating the detected value of the steering angle sensor 22 with the zero point, but the steered angle that outputs a signal corresponding to the steered angle. It is good also as a structure which acquires a steering angle directly using a sensor.

  In the acceleration / deceleration gain map of the present embodiment, the acceleration / deceleration gain is linearly increased as the vehicle deceleration increases, and the acceleration / deceleration gain is linearly decreased as the vehicle acceleration increases. However, the acceleration / deceleration gain is increased stepwise as the vehicle deceleration increases, and the acceleration / deceleration gain is decreased stepwise as the vehicle acceleration increases. It may be.

It is a figure showing the composition of the power steering device concerning an embodiment. It is a figure which shows an example of a basic assist torque map. It is a flowchart which shows the process sequence of a return torque calculation process. It is a figure which shows an example of a vehicle speed gain map. It is a figure which shows an example of a basic return torque map. It is a figure which shows an example of an acceleration / deceleration gain map.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Power steering apparatus, 11 ... Tie rod, 12 ... Steering gear box, 13 ... Rack shaft, 14 ... Pinion, 15 ... Steering shaft, 16 ... Steering wheel, 17 ... Electric motor, 18 ... Motor driver, 20 ... Torsion bar, DESCRIPTION OF SYMBOLS 21 ... Steering torque sensor, 22 ... Steering angle sensor, 23 ... Vehicle speed sensor, 24 ... Longitudinal acceleration sensor, 25 ... Stop switch, 30 ... EPS ECU, 31 ... Basic assist torque calculating part, 32 ... Return torque calculating part, 33 ... Target assist torque calculator 34: Electric motor controller WL: Front left wheel WR: Front right wheel

Claims (5)

A turning angle obtaining means for obtaining a turning angle of a turning wheel attached to the vehicle and steered according to steering of the steering wheel;
Basic assist amount calculating means for calculating a basic assist amount based on the steering state of the steering wheel;
A return correction amount calculating means for calculating a return correction amount that acts in a direction to return the steering wheel to a neutral position based on the turning angle of the steered wheel obtained by the turning angle obtaining means;
Assisting means for applying assist torque to the steering mechanism of the vehicle based on the basic assist amount and the return correction amount;
The power correction apparatus according to claim 1, wherein the return correction amount calculation means increases the return correction amount when the turning angle is near a maximum turning angle .   2. The power steering apparatus according to claim 1, wherein the return correction amount calculation unit increases the return correction amount when braking the vehicle as compared with when not braking.   3. The power steering apparatus according to claim 2, wherein the return correction amount calculation unit holds the state in which the return correction amount is increased for a predetermined time after the braking of the vehicle is released.   The return correction amount calculation means increases the return correction amount when the vehicle deceleration is large compared to when the vehicle deceleration is small, and when the vehicle acceleration is large, the return correction amount compared to when the vehicle acceleration is small. The power steering device according to claim 1, wherein the power steering device is reduced.   The power steering device according to any one of claims 1 to 4, wherein the return correction amount calculation means decreases the return correction amount when the speed of the vehicle is equal to or higher than a predetermined value.

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