JPH069983B2 - Power steering device for front and rear wheel steered vehicles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a steering device for a front and rear wheel steered vehicle that steers front wheels and rear wheels in response to rotation of a steering handle, and particularly relates to a steering handle. The present invention relates to a power steering apparatus for a front and rear wheel steered vehicle in which a steering wheel and a rear wheel steering mechanism that steers the rear wheels are mechanically separated and their linkage is replaced by an electric control device.

[Prior art]

Conventionally, this type of technique has been disclosed in Japanese Patent Laid-Open Nos. 56-108351 and 57-15066, in which the steering amount of a steering lever is optically detected or the front wheel steering mechanism is turned. The steering angle speed is electrically detected to electrically control the steering angle of the rear wheel steering mechanism. With such a configuration, the connecting mechanism that mechanically connects the steering lever and the rear wheel steering mechanism or the front wheel steering mechanism and the rear wheel steering mechanism is eliminated, and the space necessary for disposing the connecting mechanism is effectively used. ing.

[Problems to be solved by the invention]

However, in the above conventional device, the electric control device unilaterally controls the steering angle of the rear wheel steering mechanism based on the steering amount of the steering lever or the steering amount of the front wheel steering mechanism. The reaction force received from the road surface will not be transmitted to the steering wheel. As a result, the steering reaction force, steering reaction force and steering wheel restoring force due to the rear wheel steering are not sent back to the steering wheel, and the driver cannot drive the vehicle with a steering feeling that matches the steering state of the vehicle. Steering stability of the vehicle deteriorates.

In order to solve the above problems, the present invention controls the rotation of the steering shaft based on the steering force applied to the steering wheel and the steering reaction force that the rear wheels receive from the road surface, and determines the rotation angle of the steering shaft. By controlling the steering angle of the rear wheels based on this, the rear wheels are steered according to the turning of the steering wheel, and the steering reaction force, the steering reaction force and the steering wheel restoration corresponding to the steering of the rear wheels are restored. An object of the present invention is to provide a power steering device for a front and rear wheel steered vehicle that generates force on a steering wheel.

[Means for solving problems]

In solving such problems, the structural features of the present invention are as follows.
As shown in FIG. 1, a steering wheel 1 (a steering wheel 20 of a basic configuration example, and a steering wheel 20 of a specific embodiment)
Corresponding to the rotation of the front wheel 2 (the front wheel 33 of the basic configuration example).
a, 33b, and the front wheels 33a, 33b of the specific embodiment,
And the wheels 80a and 80b of the modified example) and the rear wheel 3
(The rear wheels 43a and 43b of the basic configuration example, the rear wheels 43a and 43b of the specific example, and the wheels 80a and 80 of the modified example.
In the power steering apparatus for a front and rear wheel steered vehicle that steers the steering wheel 4 (corresponding to b), the steering shaft 4 coupled to the steering wheel 1 (corresponding to the steering shaft 21 of the basic configuration example and the steering shaft 21 of the specific example).
And a steering shaft actuator 5 for rotationally driving the steering shaft 4.
(Corresponding to the steering shaft motor 22 of the basic configuration example and the steering shaft motor 22 of the specific embodiment), and the front wheel steering control means 6 for steering the front wheels 2 according to the rotation of the steering shaft 4 (basic configuration. Example front wheel steering shaft motor 30, front wheel steering shaft 32, front wheel steering displacement amount sensor 37, front wheel steering shaft motor control circuit 51, front wheel target steering amount calculator 57, front wheel steering displacement amount calculator 58, etc. , And the front wheel steering shaft motor 30, the front wheel steering shaft 32, the front wheel steering displacement sensor 37, the microcomputer 71 for calculating the front wheel steering gear ratio αf in steps 106 to 108, and the coefficient in step 109. Calculation process of Kmpf (formula 20), steps 110 and 11
Calculation and output processing of the rotation control amount Msf (equation 25) of 1 and corresponding to the servo valve 81, the hydraulic cylinder 82, the steered shaft 83, the linear actuator 86, etc. of the modified example),
A rear wheel steering mechanism 7 that is mechanically coupled to the rear wheel 3 to steer the rear wheel 3 (a rear wheel steering shaft motor 40, a pinion 4 and a basic configuration example).
1, a rear wheel steering shaft 42, a rack shaft 44, etc., and a rear wheel steering shaft motor 40, a pinion 41, a rear wheel steering shaft 42, a rack shaft 44, etc. of a specific embodiment, and a servo valve 8 of a modified example.
1, a hydraulic cylinder 82, a steered shaft 83, a linear actuator 86, etc.), and a steering force sensor 8 for detecting a steering force applied from the steering wheel 1 to the steering shaft 4 (the steering force sensor 24 of the basic configuration example). , And a steering force sensor 24 of a specific embodiment), and a rear wheel steering reaction force sensor 9 (for a basic configuration example) that detects a rear wheel steering reaction force applied from the rear wheels 3 to the rear wheel steering mechanism 7. The rear wheel steering reaction force sensor 48, the rear wheel steering reaction force sensor 48 of the specific embodiment, and the steering reaction force sensor 85 of the modified example) and the rotation angle of the steering shaft 4 from the reference position are steered. The steering displacement amount sensor 10 (corresponding to the steering displacement amount sensor 23 of the basic configuration example and the steering displacement amount sensor 23 of the specific embodiment) that detects the displacement amount, and the detected steering force based on the output of the steering force sensor 8. Increases with the increase of and before First control amount determining means 11 for determining a first control amount for rotating the steering shaft 4 in the direction in which the steering force is applied (steps in the steering force calculator 53 of the basic configuration example and the microcomputer 71 of the specific example). 110
Corresponding to the calculation processing of the term Kmf · Fm in the rotation control amount Mm (equation 24)) and the output of the rear wheel steering reaction force sensor 9 and increase in accordance with the increase in the detected steering reaction force, and Second control amount determining means 12 for determining a second control amount for rotating the steering shaft 4 in the direction of returning to the reference position (a rear wheel steering reaction force calculator 56 of a basic configuration example, and a microcomputer of a specific embodiment). Steps 106 to 108 in 71
Corresponding to the calculation process of the rear wheel force reverse feed ratio βr, the calculation process of the coefficient Ksfr (equation 23) in step 109, and the calculation process of the term Ksfr · Fsr in the rotation control amount Mm (equation 24) in step 110). A steering shaft rotation control signal output unit 13 for controlling the rotation of the steering shaft 4 by outputting a steering shaft rotation control signal obtained by combining the first control amount and the second control amount to the steering shaft actuator 5 (of the basic configuration example). The term K in the rotation control amount Mm (equation 24) of step 110 in the steering shaft motor control circuit 50 and the microcomputer 71 of the specific example.
Subtraction processing of mf · Fm, Ksfr · Fsr, step 1
11 corresponding to the output processing of the rotation control amount Mm of the rear wheel 11) and the target steering amount of the rear wheel 3 based on the output of the steering displacement sensor 10 (rear wheel target turning amount determining means 14 (after the basic configuration example). Steps 106 to 108 in the wheel target turning amount calculator 59 and the microcomputer 71 of the specific embodiment.
Rear wheel steering gear ratio αr calculation process, step 1
09 coefficient Kmpr (formula 21) calculation process, step 1
The term Kmpr · Y in the rotation control amount Msr (equation 26) of 10
m) and a rear-wheel steering control signal according to the determined rear-wheel target steering amount to the rear-wheel steering mechanism 7 so that the rear-wheel steering amount is the determined rear-wheel target steering amount. The rear wheel steering control signal output means 15 for controlling the rear wheel steering mechanism 7 so as to obtain the desired amount (a rear wheel steering displacement amount sensor 47, a rear wheel steering axis motor control circuit 52, and a rear wheel steering displacement amount calculation). Bowl 6
0, the rear wheel steering displacement amount sensor 47 of the specific embodiment, the calculation process of the term Kspr · Ysr in the rotation control amount Msr (equation 26) of step 110 in the microcomputer 71, the rotation control amount Msr of the same step 110 ( Formula 26)
Subtraction processing of the inside terms Kmpr · Ym, Kspr · Ysr,
(Corresponding to output processing of the rotation control amount Msr in step 111).

[Action effect]

In the present invention configured as described above, the steering force sensor 8 detects the steering force applied to the steering shaft 4 by the rotation of the steering wheel 1, and the first control amount determining means 11 is based on the detected steering force. Determines a first control amount for rotating the steering shaft 4 in the direction in which the steering force is applied, and the steering shaft rotation control signal output means 13 outputs a steering shaft rotation control signal to the steering shaft actuator 5 by this first control amount. Then, the steering shaft actuator 5 rotates the steering shaft 4 in the direction in which the steering force is applied. The front wheel steering control means 6 steers the front wheels 2 according to the rotation of the steering shaft 4. The rotation angle of the steering shaft 4 from the reference position is detected by the steering displacement amount sensor 10 as the steering displacement amount, and the rear wheel target steering amount determination means 14 and the rear wheel steering control signal are based on the detected steering displacement amount. Since the output means 15 and the rear wheel steering mechanism 7 steer the rear wheels 3, the rear wheels 3 are steered according to the turning operation of the steering handle 1. At this time,
The rear wheels 3 receive a rear wheel steering reaction force in a direction opposite to the steering direction from the road surface, and this rear wheel steering reaction force is detected by the rear wheel steering reaction force sensor 9, and based on this detected steering reaction force. The second control amount determining means 12 determines a second control amount for rotating the steering shaft 4 in the direction of returning to the reference position, and the second control amount is determined by the steering shaft rotation control signal output means 13 as the first control amount. Is synthesized with. Then, based on the combined result, the steering shaft rotation control signal output means 13 outputs a steering shaft rotation control signal to the steering shaft actuator 5 to control the rotation of the steering shaft 4.

Due to such an action, when the driver is rotating the steering wheel 1 to rotate the vehicle, the force for rotating the steering shaft 4 by the rear wheel steering reaction force is applied to the steering shaft 4 by the steering wheel 1. Since it acts as a steering reaction force in the opposite direction to the rotation, the steering reaction force based on the rear wheel turning reaction force is sent back to the steering wheel 1. Further, when the driver holds the steering wheel 1 at the turning position and when the steering wheel 1 is returned to the neutral position, the force for rotating the steering shaft 4 by the rear wheel steering reaction force causes the steering shaft 4 to move to the reference position. The steering holding reaction force based on the rear wheel turning reaction force and the restoring force of the steering wheel 1 are applied to the steering wheel 1. As described above, the steering reaction force, the steering reaction force, and the restoring force based on the rear wheel turning reaction force corresponding to the turning operation are sent back to the steering handle 1, so that the steering stability of the vehicle is improved. .

〔Example〕

a. Basic Configuration The basic configuration of the present invention will be described with reference to the drawings. FIG. 2 shows a master unit A operated by a driver, a first slave unit B1 that steers front wheels, and a second slave unit B1 that steers rear wheels. Slave part B
2 shows an outline of a vehicle power steering system including an electric control device C that electrically controls the master unit A, the first slave unit B1, and the second slave unit B2.

The master unit A includes the steering shaft 2 fixed to the steering handle 20.
1 and a steering shaft motor 22 provided at the lower end of the coaxial shaft 21 to rotate and drive the steering shaft 21, and the steering shaft 21 detects the rotation angle of the coaxial shaft 21 from the reference position by the steering shaft motor 22 and detects the same rotation angle. The steering displacement amount sensor 23 that generates a signal indicating the steering displacement amount Ym proportional to the steering wheel 20 and the coaxial force 2 that is proportional to the steering force Fm applied from the steering wheel 20 to the steering shaft 21.
A steering force sensor 24, which is composed of a strain gauge for detecting the amount of twist generated in No. 1 and which generates a signal representing the steering force Fm, is attached. In this case, when the steering handle 20 and the steering shaft 21 rotate left (or right), the steering force Fm and the steering displacement amount Ym are positive (or negative), respectively.

The first slave unit B1 has a front wheel steering shaft motor 30 whose rotation is controlled by the electric control device C, and a front wheel steering shaft 3 having one end coupled by the motor 30 and a pinion 31 at the other end.
2 and the left and right front wheels 33a, 33b meshing with the pinion 31
The rack shaft 34 for steering control is provided. Rack shaft 3
4 is a left and right front wheel 33a, 33b via left and right tie rods 35a, 35b and left and right knuckle arms 36a, 36b.
The left and right front wheels 33a and 33b are steered by the reciprocating motion of the coaxial shaft 34 in the lateral direction of the vehicle body. The front wheel turning shaft 32 has a front wheel turning displacement which detects a rotation angle of the coaxial 32 from the reference position by the front wheel turning shaft motor 30 and generates a signal representing a front wheel turning displacement amount Ysf proportional to the rotation angle. The front wheel rolling sensor includes a quantity sensor 37 and a strain gauge that detects a twist amount generated in the front wheel steering shaft 32 in proportion to the front wheel steering reaction force Fsf applied to the front wheel steering shaft 32 from the left and right front wheels 33a and 33b. A front wheel turning reaction force sensor 38 for generating a signal representing the steering reaction force Fsf is attached.

In this case, the front wheel steering shaft 32 rotates right (or left), the rack shaft 34 is displaced left (or right), and the left and right front wheels 33a, 33b are steered left (or right). At this time, the front wheel turning reaction force Fsf and the front wheel turning displacement amount Ysf are both positive (or negative).

The second slave B2 is a rear wheel steering shaft motor 40 whose rotation is controlled by the electric control device C, and a rear wheel steering shaft 42 having one end coupled by the motor 40 and a pinion 41 at the other end.
And a rack shaft 44 that meshes with the pinion 41 and controls the steering of the left and right rear wheels 43a and 43b. Rack shaft 44
Are connected to the left and right rear wheels 43a and 43b via the left and right tie rods 45a and 45b and the left and right knuckle arms 46a and 46b, respectively, and the left and right rear wheels 43a and 43b are steered by the reciprocating motion of the coaxial shaft 44 in the lateral direction of the vehicle body. To do. The rear-wheel steering shaft 42 has a rear-wheel steering displacement that detects a rotation angle of the coaxial 42 from the reference position by the rear-wheel steering shaft motor 40 and generates a signal representing a rear-wheel steering displacement amount Ysr proportional to the rotation angle. The quantity sensor 47 and the left and right rear wheels 43a, 43b to the rear wheel steering shaft 4
A rear wheel steering reaction force that is a strain gauge that detects the amount of twist generated in the rear wheel steering shaft 42 in proportion to the rear wheel steering reaction force Fsr and that generates a signal representing the rear wheel steering reaction force Fsr. A sensor 48 is attached. In this case, the rear wheel steering shaft 42 rotates right (or left), and the rack shaft 4
4 is displaced in the left (or right) direction and left and right front wheels 43a, 4
When 3b is steered in the left (or right) direction, the rear wheel steering reaction force Fsr and the rear wheel steering displacement amount Ysr are positive (or negative).

The electric control device C outputs a control signal for controlling the rotation of the steering shaft 21 to the steering shaft motor 22 and a control signal for controlling the rotation of the front wheel steering shaft 32. A front wheel steering shaft motor control circuit 51 for outputting to 30 and a rear wheel steering shaft motor control circuit 52 for outputting a control signal for controlling the rotation of the rear wheel steering shaft 42 to the rear wheel steering shaft motor 40. The steering axis motor control circuit 50
A control amount Kmf · F calculated by the steering force calculator 53 connected to the steering force sensor 24 and proportional to the steering force Fm.
m, a control amount Ksff · Fsf + Ksfr · Fs calculated by the combined turning reaction force calculator 54 and corresponding to the combined turning reaction force of the front wheel turning reaction force Fsf and the rear wheel turning reaction force Fsr.
Input r and when the value is positive (or negative), the steering shaft 2
Rotation control amount for rotating 1 to the left (or right) Mm = Kmf.
A control signal representing Fm-Ksff.Fsr-Ksfr.Fsr is output. The combined turning reaction force calculator 54 includes a front wheel turning reaction force calculator 55 connected to the front wheel turning reaction force sensor 38.
To the control amount Ksff · F proportional to the front wheel turning reaction force Fsf
sf is supplied and a control amount Ksfr · Fsr proportional to the rear wheel steering reaction force Fsr is supplied from the rear wheel steering reaction force calculator 56 connected to the rear wheel steering reaction force sensor 48. The coefficient Kmf, the coefficient Ksff, and the coefficient Ksfr are the steering force Fm, the front wheel turning reaction force Fsf, and the rear wheel turning reaction force Fsr.
Indicates the degree of influence on the rotational torque of the steering shaft 21, and the coefficient Kmf and the coefficient Ksff are always positive. Further, the coefficient Ksfr is determined by the left and right rear wheels 43a and 43b.
Becomes positive when the wheels are steered in phase with the left and right front wheels 33a, 33b, and the left and right rear wheels 43a, 43b become
It becomes negative when steered in the opposite phase to 33b. The front wheel turning shaft motor control circuit 51 calculates a control amount Kmpf · Ym which is calculated by the front wheel target turning amount calculator 57 connected to the steering displacement amount sensor 23 and is proportional to the steering displacement amount Ym, and the front wheel turning displacement amount. When a front wheel steering amount is positive (or negative) by inputting a control amount Kspf · Ysf calculated by a front wheel steering displacement amount calculator 58 connected to the sensor 37 and proportional to the front wheel steering displacement amount Ysf. A rotation control amount Msf = Kmpf · Ym−Kspf · that rotates the shaft 32 to the right (or to the left).
A control signal representing Ysf is output. The coefficient Kmpf
And the coefficient Kspf indicate the degree of influence of the steering displacement amount Ym and the front wheel turning displacement amount Ysf on the rotation angle of the front wheel turning shaft 32, respectively. The coefficient Kmpf and the coefficient Kspf are shown.
Are both positive. The rear wheel steering shaft motor control circuit 52
A control amount Kmpr · Ym calculated by the rear wheel target turning amount calculator 59 connected to the steering displacement amount sensor 23 and proportional to the steering displacement amount Ym, and a rear wheel turning connected to the rear wheel turning displacement amount sensor 47. The control amount Kspr · which is calculated by the displacement amount calculator 60 and is proportional to the rear wheel steering displacement amount Ysr
A rotation control amount Msr = for inputting Ysr and rotating the rear wheel steering shaft 42 to the right (or left) when the value is positive (or negative)
A control signal representing Kmpr.Ym-Kspr.Ysr is output. The coefficient Kmpr and the coefficient Kspr are the steering displacement amount Ym and the rear wheel steering displacement amount Ysr, respectively.
2 shows the degree of influence on the rotation angle of 2, and the coefficient Kspr is always positive. Further, the coefficient Kmpr becomes positive when the left and right rear wheels 43a, 43b are steered in phase with the left and right front wheels 33a, 33b, and the left and right rear wheels 43a, 43b.
Is negative when the wheels are steered in opposite phase with respect to the left and right front wheels 33a, 33b.

The operation of the power steering apparatus configured as described above is calculated by the coefficient Km.
The case where pr and the coefficient Ksfr are set to be positive will be described. When the steering handle 20 is rotated left (or right) by the rotation angle Xm while the vehicle is traveling straight, the steering handle 20 starts rotating. When the steering shaft motor 22
Does not rotate the steering shaft 21, that is, the steering shaft 21
Is in the reference position, the steering shaft 21 is attached to the steering wheel 2
A twist of 0 causes a twist. The twist of the steering shaft 21 is detected by a steering force sensor 24 composed of a strain gauge and supplied to the steering force calculator 53 as a phase steering force (or steering reaction force as a reaction) Fm. The steering force calculator 53 outputs a control amount Kmf · Fm obtained by multiplying the steering force Fm by a coefficient Kmf to the steering axis motor control circuit 50. The steering shaft motor control circuit 50 rotates the steering shaft 21 based on the control amount Kmf · Fm input from the steering force calculator 53 and the control amount Ksff · Fsf + Ksfr · Fsr input from the combined turning reaction force calculator 54. Control amount Mm = Kmf · Fm−Ksff
A control signal representing Fsf−Ksfr · Fsr is output, but when the steering wheel 20 starts rotating, the front wheel steering reaction force Fsf of the front wheel steering shaft 32 and the rear wheel steering reaction force Fsr of the rear wheel steering shaft 42 are output. Is zero, the control signal representing the rotation control amount Mm = Kmf · Fm of the steering shaft 21 is supplied to the steering shaft motor 22. In response to this control signal, the steering shaft motor 22 rotates the steering shaft 21 in the left (or right) direction, so that the steering shaft 21 starts rotating in the rotation direction of the steering handle 20.

By this rotation, the steering shaft 2 from the steering displacement amount sensor 23
The detected steering displacement amount Ym of 1 is input to the front wheel target turning amount calculator 57, and the front wheel target turning amount calculator 57 calculates the coefficient Kmpf.
Control amount Kmpf · Y obtained by multiplying the detected steering displacement amount Ym by
m is output to the front wheel steering shaft motor control circuit 51. At this time, since the turning displacement amount Ysf of the front wheel turning shaft 32 is zero, the front wheel turning shaft motor control circuit 51 sends a control signal representing the rotation control amount Msf = Kmpf · Ym of the front wheel turning shaft 32. Output to the rudder shaft motor 30, and the front wheel steered shaft motor 30 starts rotating the front wheel steered shaft 32 in the right (or left) direction.
By this rotation, the front wheel turning displacement amount Ysf accompanying the rotation of the front wheel turning shaft 32 becomes larger (or smaller) than zero, and the front wheel turning displacement amount calculator 58 multiplies the front wheel turning displacement amount Ysf by the coefficient Kspf. The control amount Kspf · Ysf is output to the front wheel steering shaft motor control circuit 51, and the control amount Kspf · Ysf is output.
Since sf gradually increases (or decreases) as the front wheel turning displacement amount Ysf increases (or decreases), the rotation control amount of the front wheel turning shaft 32 Msf = Kmpf · Ym−Kspf · Ysf.
The positive (or negative) level of the control signal indicating is gradually decreased, and the steering displacement amount Ysf of the front wheel steering shaft 32 becomes Ysf = K.
The rotation of the front wheel steering shaft 32 is stopped at the rotation position where the relationship of mpf · Ym / Kspf is established. The right (or left) rotation of the front wheel steering shaft 32 is performed by the rack shaft 34 via the pinion 31.
And the rack shaft 34 is displaced in the left (or right) direction. The left (or right) displacement of the rack shaft 34 is caused by the left and right tie rods 35a and 35b and the left and right knuckle arms 36.
It is transmitted to the left and right front wheels 33a and 33b via a and 36b to steer the left and right front wheels 33a and 33b in the left (or right) direction.

The detected steering displacement amount Ym of the steering shaft 21 from the steering displacement amount sensor 23 is also input to the rear wheel target turning amount calculator 59, and the rear wheel target turning amount calculator 59 uses the coefficient Kmpr to detect the steering wheel. The control amount Kmpr · Ym multiplied by the displacement amount Ym is output to the rear wheel steering shaft motor control circuit 52. At this time, since the turning displacement amount Ysr of the rear wheel turning shaft 42 is zero, the rear wheel turning shaft motor control circuit 52 sends a control signal indicating the rotation control amount Msr = Kmpr · Ym of the rear wheel turning shaft 42 to the rear wheel turning shaft. Output to the rudder shaft motor 40, and the rear wheel steered shaft motor 40 starts rotating the rear wheel steered shaft 42 in the right (or left) direction. By this rotation, the rear wheel steering displacement amount Y accompanying the rotation of the rear wheel steering shaft 42
Since sr becomes larger (or smaller) than zero, the rear wheel turning displacement amount calculator 60 calculates the coefficient Ksp to the rear wheel turning displacement amount Ysr.
The control amount Kspr · Ysr multiplied by r is output to the rear wheel steering shaft motor control circuit 52, and the control amount Kspr · Ysr gradually increases (or decreases) as the rear wheel steering displacement amount Ysr increases (or decreases). Therefore, the positive (or negative) level of the control signal representing the rotation control amount Msr = Kmpr.Ym-Kspr.Ysr of the rear wheel steering shaft 42 gradually decreases, and the steering displacement amount Ysr of the rear wheel steering shaft 42 becomes smaller. Ysr = Km
The rotation of the rear wheel steering shaft 42 is stopped at the rotational position where the relationship of pr · Ym / Kspr is satisfied. The right (or left) rotation of the rear wheel steered shaft 42 is transmitted to the rack shaft 44 via the pinion 41 to displace the rack shaft 44 in the left (or right) direction. The left (or right) displacement of the rack shaft 44 is caused by the left and right tie rods 45a and 45b and the left and right knuckle arms 46.
It is transmitted to the left and right rear wheels 43a and 43b via a and 46b to steer the left and right rear wheels 43a and 43b in the left (or right) direction.

On the other hand, the left and right front wheels 33a, 33b receive the front wheel steering reaction force Fsf in the right (or left) direction from the road surface by the steering in the left (or right) direction, and the front wheel steering reaction force Fsf is applied to the left and right knuckle arms. 36a, 36b, left and right tie rods 35a, 3
5b, the rack shaft 34, and the pinion 31 are transmitted to the front wheel steering shaft 32. Since this front wheel turning reaction force Fsf acts so as to rotate the front wheel turning shaft 32 in the left (or right) direction, it is in the opposite direction to the force by which the front wheel turning shaft motor 30 rotates the front wheel turning shaft 32. The front wheel steering shaft 32 is twisted. This twist is detected by a front wheel steering reaction force sensor 38 including a strain gauge, and is supplied to the front wheel steering reaction force calculator 55 as a front wheel steering reaction force (or a front wheel steering force as a reaction) Fsf proportional to the amount of twist. To be done. The front wheel turning reaction force calculator 55 calculates a coefficient Ksff for the front wheel turning reaction force (turning force) Fsf.
The control amount Ksff · Fsf multiplied by is output to the combined turning reaction force calculator 54.

Further, the left and right rear wheels 43a, 43b receive the rear wheel steering reaction force Fsr in the right (or left) direction from the road surface by the steering in the left (or right) direction, and the rear wheel steering reaction force Fsr is applied to the left and right knuckles. Arms 46a, 46b, left and right tie rods 45a, 4
Since the rear wheel steering shaft 42 is rotated in the left (or right) direction via the 5b, the rack shaft 44, and the pinion 41, the force by which the rear wheel steering shaft motor 40 rotates the rear wheel steering shaft 42 is In the opposite direction, the rear wheel steering shaft 42 is twisted. This twist is detected by a rear wheel steering reaction force sensor 48 including a strain gauge, and is supplied to the rear wheel steering reaction force calculator 56 as a rear wheel steering reaction force (or a rear wheel steering force as a reaction) Fsr that is proportional to the amount of twist. To be done. The rear wheel turning reaction force calculator 56 calculates a coefficient Ks for the rear wheel turning reaction force (rear wheel turning force) Fsr.
The control amount Ksfr · Fsr multiplied by fr is output to the combined turning reaction force calculator 54.

Then, the combined turning reaction force calculator 54 adds and combines the control amount Ksff · Fsf from the front wheel turning reaction force calculator 55 and the control amount Ksfr · Fsr from the rear wheel turning reaction force calculator 56 to combine them. Control amount Ksff · Fsf = Ksfr · Fs
The r is output to the steering axis motor control circuit 50. The steering shaft motor control circuit 50 controls the steering shaft 21 based on the control amount Kmf · Fm input from the steering force calculator 53 and the control amount Ksff · Fsf + Ksfr · Fsr input from the combined turning reaction force calculator 54. Rotation control amount Mm = Kmf · Fm-K
A control signal representing sff · Fsf−Ksfr · Fsr is output to the steering shaft motor 22, and the steering shaft motor 22 controls the rotation of the steering shaft 21 based on this control signal. In the rotation operation of the steering shaft 21 in the left (or right) direction, the control amount Kmf · Fm acts so as to rotate the steering shaft 21 in the left (or right) direction, and the steering shaft 21 moves in the left (or right) direction. When the steering shaft 21 rotates, the amount of twist of the steering shaft 21 decreases, so the steering force (steering reaction force) Fm proportional to this amount of twist decreases (or increases), and the control amount Kmf · Fm also decreases (or increases). On the other hand, the front wheel turning reaction force (steering force) Fsf applied to the left and right front wheels 33a, 33b and the left and right rear wheels 43a,
Rear wheel steering reaction force (rear wheel steering force) Fsr applied to 43b
Is the front wheel steering displacement amount Ysf and the rear wheel steering displacement amount Ysr, respectively.
Increases (or decreases) as increases (or decreases)
Therefore, the control amount Ksff · Fsf + Ksfr · F acting so as to rotate the steering shaft 21 in the right (or left) direction.
sr becomes large (or small). As a result, the steering shaft 2
Rotation control amount Mm = K for rotating 1 to the left (or right)
mf · Fm−Ksff · Fst−Ksfr · Fsr gradually decreases (or increases), and the rotation of the steering shaft 21 stops at the rotational position where the control amount Kmf · Fm and the control amount Ksff · Fsf + Ksfr · Fsr become equal. .

Then, in this state, when the driver further applies a force in the left (or right) rotation direction to the steering wheel 20 in order to rotate the steering wheel 20 further left (or right), the control amount K
mf · Fm is a controlled variable Ksff · Fsf + Ksfr · Fs
It becomes larger (or smaller) than r, and the steering shaft 21 further rotates in the left (or right) direction. When the driver weakens the force applied to the steering wheel 20, the control amount Ksff · F
When sf + Ksfr · Fsr becomes larger (or smaller) than the control amount Kmf · Fm, the steering shaft 21 starts rotating in the right (or left) direction.

Further, a case where the coefficient Kmpr and the coefficient Ksfr are set to be negative will be described. When the steering handle 20 is rotated in the left (or right) direction, the left and right front wheels 33a, 33b are steered in the left (or right) direction as in the case described above.
Since the coefficient Kmpr is negative, the left and right rear wheels 43a, 43b are steered in the opposite direction to the right (or left) direction, that is, the left and right front wheels 33a, 33b, contrary to the above case. By this steering, the rear wheel steering reaction force Fsr acting on the left and right rear wheels 43a, 43b.
Will act in the opposite direction to the above case, and the positive and negative signs of the rear wheel steering reaction force Fsr will be opposite to those in the above case, but since the coefficient Ksfr is set to a negative value, the control amount Ksfr.
The positive and negative signs of Fsr are the same as in the above case, and the control amount Ksfr · Fsr acts so as to rotate the steering shaft 21 in the right (or left) direction as in the case of the above case.

As described above, when the driver is turning the steering wheel 20, holding the steering wheel 20 in the turning position, and returning the steering wheel 20 to the neutral position, the front wheel steering reaction force Fsf. Also, the control amount Ksff · Fsf + Ksfr · Fsr based on the rear wheel steering reaction force Fsr acts to return the steering wheel 20 to the neutral position.
The steering reaction force, the steering holding reaction force, and the restoring force of the steering wheel 20 corresponding to the above are applied.

If the control based on the front wheel turning displacement speed and the rear wheel turning displacement speed is added to the above basic configuration, the front wheel turning shaft 32 by the front wheel turning shaft motor 30 and the rear wheel turning by the rear wheel turning shaft motor 40. The rotation of the shaft 42 can be controlled more stably. In this case, the front wheel steering displacement amount Ysf and the rear wheel steering displacement amount Ysr are each differentiated, each differentiation result is multiplied by a predetermined coefficient, and the multiplication result is each rotation control amount Ms of the front wheel steering shaft 32.
f and the rotation control amount Msr of the rear wheel steered shaft 42 are added.

b. Determining Variables and Their Meanings Before describing specific examples of the present invention shown in the above basic configuration, the coefficients Kmf, Ksff, and
The calculation method and properties of Ksfr, Kmpf, Kmpr, Kspf, Kspr and various variables calculated in the concrete examples will be described with reference to the drawings.
It is a control block diagram which represented the basic composition of the present invention of the figure by the equivalent circuit.

Subtractors 50a, 51a, 52a respectively show the subtracting action of the steering shaft motor control circuit 50, the front wheel steering shaft motor control circuit 51, and the rear wheel steering shaft motor control circuit 52, and a multiplier 53a, 55a, 56a, 57a, 58
a, 59a and 60a are steering force calculator 53, front wheel turning reaction force calculator 55, rear wheel turning reaction force calculator 56, front wheel target turning amount calculator 57, front wheel turning displacement amount calculator 58, respectively. The rear wheel target turning amount calculator 59 and the rear wheel turning displacement amount calculator 60 correspond to their multiplication effects, and the adder 54a corresponds to the combined turning reaction force calculator 54 to add them. Is shown. The blocks 22a, 30a, 40a correspond to the steering shaft motor 22, the front wheel steering shaft motor 30, and the rear wheel steering shaft motor 40, respectively, and have functions Km / S, K.
sf / S and Ksf / S represent respective rotation control characteristics of the steering shaft motor 22, the front wheel steering shaft motor 30, and the rear wheel steering shaft motor 40.

The subtractor 61 controls the steering shaft 21 according to the difference between the rotational displacement amount Xm of the steering shaft 21 rotated by the steering force applied to the steering wheel 20 and the steering displacement amount Ym of the steering shaft 21 rotated by the steering shaft motor 22. The amount of twist Xm-Ym
Is the equivalent circuit, and the multiplier 62 has a twist amount Xm-Ym.
It is an equivalent circuit for calculating the steering reaction force applied to the steering shaft 21 from the steering shaft motor 22 as a reaction of the steering force and the steering force proportional to, and the constant 1 / Cm is the elastic coefficient of the steering shaft 21. The subtracter 63 is a front wheel turning displacement amount Ysf of the front wheel turning shaft 32 that is rotated by the turning force of the front wheel turning shaft motor 30.
Is an equivalent circuit representing the twist amount Ysf-Xsf generated in the front wheel steering shaft 32 in accordance with the difference between the rotational displacement amount Xsf of the front wheel steering shaft 32 corresponding to the front wheel steering amount of the left and right front wheels 33a and 33b. The multiplier 64 uses the left and right front wheels 33 as a reaction of the front wheel turning force and the front wheel turning force that are proportional to the twist amount Ysf-Xsf.
It is an equivalent circuit for calculating the front wheel turning reaction force applied to the front wheel turning shaft 32 from a and 33b, and the constant 1 / Csf is the elastic coefficient of the front wheel turning shaft 32.

The subtractor 65 is a rear wheel steering shaft 42 according to the rear wheel steering displacement amount Ysr of the rear wheel steering shaft 42 that rotates by the rear wheel steering force of the rear wheel steering shaft motor 40 and the rear wheel steering amounts of the left and right rear wheels 43a and 43b. The multiplier 66 is an equivalent circuit representing the twist amount Ysr-Xsr generated in the rear wheel steering shaft 42 according to the difference from the rear wheel rotational displacement amount Xsr, and the multiplier 66 is a rear wheel steering force proportional to the twist amount Ysr-Xsr. And the left and right rear wheels 43 as a reaction of the rear wheel steering force.
This is an equivalent circuit for calculating the rear wheel steering reaction force applied to the rear wheel steering shaft 42 from a and 43b, and the constant 1 / Csr is the elastic coefficient of the rear wheel steering shaft 42.

In the control block configured as described above, the following equation holds when considering the system balance (steady state).

Kmf · Fm = Ksff · Fsf + Ksfr r · Fsr (Equation 1) Kmpf · Ym = Kspf · Ysf (Equation 2) Kmpr · Ym = Kspr · Ysr (Equation 3) Further, the steering shaft 21 , Steering force (steering reaction force) Fm, front wheel steering force (front wheel steering reaction force) Fsf, rear wheel steering force (rear wheel steering reaction force) applied to the front wheel steering shaft 32 and the rear wheel steering shaft 42, respectively.
The relationship between Fsr and the twist amounts Xm-Ym, Ysf-Xsf, Ysr-Xsr generated on the shafts 21, 32, 42 is expressed by using elastic coefficients 1 / Cm, 1 / Csf, 1 / Csr. And becomes like this.

Fm = (1 / Cm). (Xm-Ym) .. (Equation 4) Fsf = (1 / Csf). (Ysf-Xsf) ... (Equation 5) Fsr = (1 / Csr). (Ysr -Xs r) (Equation 6) Here, the left and right front wheels 33a, 33b and the left and right rear wheels 43a,
43b is not in contact with the road surface, that is, a state in which the front wheel turning reaction force and the rear wheel turning reaction force from the road surface are not received (Fsf =
0, Fsr = 0), the ratio of the rotation angles transmitted from the master unit A to the first slave unit B1 and the second slave unit B2, that is, the rotational displacement amount Xm of the steering shaft 21 according to the rotation amount of the steering handle 20. Left and right front wheels 33a, 33
b and the respective rotational displacement amounts Xsf of the front wheel steering shaft 32 and the rear wheel steering shaft 42 according to the respective steering amounts of the left and right rear wheels 43a, 43b,
If the ratio of Xsr is defined as the front wheel steering gear ratio αf and the rear wheel steering gear ratio αr, these gear ratios αf and αr are expressed by the following equations from (Equation 1) to (Equation 6).

αf = Xsf / Xm = Kmpf / Kspf (Equation 7) αr = Xsr / Xm = Kmpr / Kspr (Equation 8) As shown in (Equation 8), the rear wheel steering gear ratio αr is , When the coefficient Kmpr is positive (or negative),
It becomes positive (or negative). Then, these gear ratios αf, α
Changing the value of r means that the left and right front wheels 33a and 33b and the left and right rear wheels 4 are set for the same turning amount of the steering wheel 20.
This means changing the turning amounts of 3a and 43b, and in the embodiments described later, these gear ratios αf and αr are treated as selectable parameters that indicate steering characteristics and that change according to the vehicle speed.

Further, the left and right front wheels 33a and 33b are fixed (Xsf =
0) and the left and right rear wheels 43a, 43b are not in contact with the road surface (Fsr = 0), the ratio of the force transmitted from the first slave unit B1 to the master unit A, that is, the steering reaction force with respect to the front wheel steering reaction force Fsf. If the ratio of the force Fm is defined as the front wheel force reverse feed ratio βf, this force reverse feed ratio βf is expressed by the following equation from (Equation 1).

βf = Fm / Fsf = Ksff / Kmf (Equation 9) Then, changing the force reverse transmission ratio βf means changing the steering reaction force Fm for the same front wheel turning reaction force Fsf. In the embodiment described later, the force reverse transmission ratio βf is treated as a selectable parameter that indicates the steering characteristic and that changes according to the vehicle speed.

In addition, when the left and right front wheels 33a and 33b are not in contact with the road surface (Fsf = 0) and the left and right rear wheels 43a and 43b are fixed (Xsr = 0), the second slave B2 transmits to the master unit A. Force ratio, that is, rear wheel steering reaction force F
If the ratio of the steering reaction force Fm to sr is defined as the rear wheel force reverse feed ratio βr, this force reverse feed ratio βr is expressed by the following equation from (Equation 1).

βr = Fm / Fsr = Ksfr / Kmf ... (Equation 10) As shown in (Equation 10), this force reverse transmission ratio βr is positive (or negative) when the coefficient Ksfr is positive (or negative). Or negative). Then, changing the force reverse transmission ratio βr means changing the steering reaction force Fm with respect to the same rear wheel turning reaction force Fsr, and in the embodiment described later, this force reverse transmission ratio βr.
r is treated as a selectable parameter that indicates steering characteristics and that changes according to the vehicle speed.

Further, the ratio between the steering reaction force Fm and the rotational displacement amount Xm is set as the steering elastic coefficient Qm, and the ratio between the front wheel turning reaction force (front wheel turning force) Fsf and the rotational displacement amount Xsf is set as the front wheel steering elastic coefficient Qsf. Moreover, if the ratio of the rear wheel steering reaction force (rear wheel steering force) Fsr and the rotational displacement amount Xsr is the rear wheel steering elastic coefficient Qsr, the following equation holds: Qm = Fm / Xm (equation 11) Qsf = Fsf / Xsf ... (Equation 12) Qsr = Fsr / Xsr ... (Equation 13) It should be noted that the front-wheel steering elastic coefficient Qsf is the left and right front wheels 33a, 33
b is a constant determined by the friction between the tire and the road surface, and the rear wheel steering elastic coefficient Qsr is the left and right rear wheels 43a, 43.
It is a constant determined by the friction between the tire b and the road surface.

On the other hand, the rotational displacement amount Xm is based on (Equation 1), (Equation 2), (Equation 4), (Equation 5), (Equation 7), (Equation 9), (Equation 10): Xm = Xsf / αf + (Cm · βf + Csf / αf) · Fsf + Cm · βf · Fsr · · (Equation 14), and the rotational displacement Xm is expressed by (Equation 1),
(Equation 3), (Equation 4), (Equation 6), (Equation 8), (Equation 9),
Based on (Equation 10), Xm = Xsr / αr + (Cm · βr + Csr / αr) · Fsr + Cm · βf · Fsf ··· (Equation 15) If the left and right front wheels 33a and 33b are fixed (Xsf = 0) and the left and right rear wheels 43a and 43b are not in contact with the road surface (Fsf = 0), the front wheel steering elastic coefficient Qsf is set to the value Qsf∞. Value Qsf∞
From (Equation 1), (Equation 9), (Equation 14), Qsf∞ = αf · βf / (αf · βf · Cm + Csf + αf · βf · Cm · Fsr / Fsf) (Equation 16) expressed. Further, the left and right front wheels 33a, 33b are not in contact with the road surface (Fsf = 0) and the left and right rear wheels 43
If the rear-wheel steering elastic coefficient Qsr in the state in which a and 43b are fixed (Xsr = 0) is the value Qsr∞, the value Qsr
∞ is expressed by (Equation 1), (Equation 10) and (Equation 15) as follows: Qsr∞ = αr · βr / (αr · βr · Cm + Csr + αr · βf · Cm · Fsf / Fsr) (Equation 17) Represented by. Then, when the steering elastic coefficient Qm is expressed by using the front wheel turning elastic coefficient Qsf and the rear wheel turning elastic coefficient Qsr, the steering elastic coefficient Qm is calculated by the following equations (1), (9),
Based on (Equation 10) and (Equation 12) to (Equation 17), It is expressed as. Here, the value Qsf∞ is the left and right front wheels 33.
Considering that a and 33b are front wheel steering elastic coefficients in a fixed state, the value Qsf∞ is extremely larger than the front wheel steering elastic coefficient Qsf in the normal state (Qsf∞ >> Q
sf), and the value Qsf∞ is equal to the left and right rear wheels 43a, 43.
Considering that b is a rear-wheel steering elastic coefficient in a fixed state, the value Qsr∞ is extremely larger than the rear-wheel steering elastic coefficient Qsr at the normal time (Qsr∞ >> Qsr). 18) is transformed into the following equation.

Qm = αf ・ βf ・ Qsf + αr ・ βr ・ Qsr ・ ・
(Equation 19) Then, changing the product αf · βf and the product αr · βr, respectively, means that the steering elastic coefficient Qm, that is, the steering shaft 2
Steering force F required for the same amount of rotational displacement Xm of 1
means a change of m, and in the embodiment described later, the product αf of these
.Beta.f and products .alpha.r.beta.r are treated as selectable parameters that indicate steering characteristics and that change according to the vehicle speed.

Inversely, the coefficients Kmpf, K are obtained by the above (Equation 7) to (Equation 10).
When mpr, Ksff, and Ksfr are calculated, the coefficient Kmp
f, Kmpr, Ksff, and Ksfr are given by the following equations.

Kmpf = αf · Kspf (Equation 20) Kmpr = αr · Kspr (Equation 21) Ksff = βf · Kmf ... (Equation 22) Ksfr = βr · Kmf ... (Equation 23) where , Kspf, Kspr, Kmf, Kmf are relative values to the coefficients Kmpf, Kmpr, Ksff, Ksfr, respectively, and thus are defined as constants in the embodiments described later, and the coefficients Kmpf, Kmpr, Ksff, Ks are defined.
fr is a front wheel steering gear ratio αf, a rear wheel steering gear ratio αr, a front wheel force reverse feed ratio βf, and a rear wheel force reverse feed ratio β.
Treated as a value that changes with r.

C. Specific Examples As described above, the coefficients Kmpf, Kmpr, and Ksf are based on the front wheel steering gear ratio αf, the rear wheel steering gear ratio αr, the front wheel force reverse feed ratio βf, and the rear wheel force reverse feed ratio βr.
f and Ksfr are calculated by a microcomputer, and left and right front wheels 33a and 33b and left and right rear wheels 43a and 43
A specific embodiment of the present invention for controlling the steering of each b will be described with reference to the drawings. FIG. 4 shows a master unit A operated by a driver.
A first slave unit B1 that steers the left and right front wheels 33a and 33b, a second slave unit B2 that steers the left and right rear wheels 43b and 43b, a master unit A, a first slave unit B1 and a second slave unit B2.
The power steering apparatus for vehicles provided with the electric control apparatus C which electrically controls the slave part B2 is shown. Master part A,
The first slave unit B1 and the second slave unit B2 have substantially the same configuration as that of the basic configuration shown in FIG.

The master unit A includes a steering wheel 20, a steering shaft 21, a steering shaft motor 22, a steering displacement amount sensor 23, and a steering force sensor 24.
Is equipped with. The steering displacement amount sensor 23 includes a slider 23b that slides on a grounded resistor 23a according to the rotation of the steering shaft 21, and a voltage source 23c connected to both ends of the resistor 23a. The left (or right) rotation of the slider 23b outputs a positive (or negative) voltage signal representing the steering displacement amount Ym proportional to the rotation angle of the steering shaft 21 with respect to the reference position. The steering force sensor 24 is a strain gauge 24 attached to the steering shaft 21 and having a resistance value that changes according to the amount of twist of the coaxial shaft 21.
a and a fixed resistor 24 with this strain gauge 24a as one side
a bridge circuit formed by b, 24c and 24d, a connection point of the strain gauge 24a and a resistor 24b, and resistors 24c and 2
It consists of a voltage source 24e connected between the connection points of 4d. The steering force sensor 24 is a positive (or negative) force representing a steering force Fm proportional to the amount of twist generated in the steering shaft 21 in accordance with the left (or right) rotation of the steering handle 20 from the connection point of the strain gauge 24a and the resistor 24d. Outputs voltage signal. The connection point between the resistors 24b and 24c is grounded.

The first slave unit B1 includes a front wheel steering shaft motor 30, a pinion 31, a front wheel steering shaft 32, left and right front wheels 33a and 33b, a rack shaft 34, left and right tie rods 35a and 35b, left and right knuckle arms 36a and 36b, and front wheel steering displacement amounts. A sensor 37 and a front wheel turning reaction force sensor 38 are provided. The front wheel turning displacement amount sensor 37 includes a slider 37b that slides on a resistor 37a that is grounded at a midpoint according to the rotation of the front wheel turning shaft 32.
The front wheel steering shaft 3 is provided with a voltage source 37c connected to both ends of the resistor 37a, and by rotating the slider 37b to the right (or left), that is, turning the left and right front wheels 33a and 33b to the left (or right).
A positive (or negative) voltage signal representing the front wheel turning displacement amount Ysf proportional to the rotation angle of 2 is output. The front wheel turning reaction force sensor 38 is attached to the front wheel turning shaft 32 and has a strain gauge 38a whose resistance value changes according to the amount of twist of the coaxial shaft 32, and fixed resistances 38b, 38c, 3 with the strain gauge 38a as one side.
A bridge circuit formed by 8d and a strain gauge 38a,
The voltage source 38e is connected between the connection point of the resistor 38b and the connection point of the resistors 38c and 38d. The front wheel turning reaction force sensor 38 is a front wheel turning reaction proportional to the amount of twist generated on the front wheel turning shaft 32 in response to left (or right) turning of the left and right front wheels 33a and 33b from the connection point of the strain gauge 38a and the resistance 38d. Force Fs
It outputs a positive (or negative) voltage signal representing f. The connection point of the resistors 38b and 38c is grounded.

The second slave unit B2 includes a rear wheel steering shaft motor 40, a pinion 41, a rear wheel steering shaft 42, left and right rear wheels 43a and 43b, a rack shaft 44, left and right tie rods 45a and 45b, left and right knuckle arms 46a and 46b, and rear wheel steering displacement. An amount sensor 47 and a rear wheel steering reaction force sensor 48 are provided. The rear wheel turning displacement amount sensor 47 is configured in the same manner as the front wheel turning displacement amount sensor 37 by the resistor 47a, the slider 47b and the voltage source 47c, and the left (or right) turning of the left and right rear wheels 43a, 43b is performed. Therefore, the steering displacement amount Y proportional to the rotation angle of the rear wheel steering shaft 42
It outputs a positive (or negative) voltage signal representing sr. The rear wheel steering reaction force sensor 48 includes a strain gauge 48a and a fixed resistance 48.
b, 48c, 48d and the voltage source 48e are configured in the same manner as the front wheel steering reaction force sensor 38, and the left and right rear wheels 43a,
A positive (or negative) voltage signal representing the rear wheel steering reaction force Fsr proportional to the amount of twist generated in the rear wheel steering shaft 42 in response to the left (or right) steering of 43b is output.

The electric control device C controls the steering displacement amount Ym from the steering displacement amount sensor 23, the steering force (or steering shaft reaction force) Fm from the steering force sensor 24, the front wheel steering displacement amount Ysf from the front wheel steering displacement amount sensor 37, Front wheel steering reaction force (or front wheel steering force) Fsf from front wheel steering reaction force sensor 38, rear wheel steering displacement amount sensor 4
Rear wheel steering displacement amount Ysr from 7, rear wheel steering reaction force sensor 4
The rear wheel steering reaction force (or rear wheel steering force) Fsr from 8 and the rotation of the output shaft of the transmission are picked up, and the vehicle speed V from the vehicle speed sensor 70 that generates a pickup signal corresponding to the vehicle speed is input, The rotation control amount Mm of the steering shaft motor 22,
A microcomputer 71 for calculating the rotation control amount Msf of the front wheel steering shaft motor 30 and the rotation control amount Msr of the rear wheel steering shaft motor 40 is provided.

The microcomputer 71 uses the sensors 23 and 2 described above.
4, 37, 38, 47, 48, 70, and an input port 71a for inputting detected values, and a read-only memory (for storing a program corresponding to the flowchart shown in FIG. 5 and constants necessary for executing the program ( A central processing unit (hereinafter simply referred to as CPU) 71c that executes a program, a writable memory (hereinafter simply referred to as RAM) 71d that temporarily stores variables necessary for executing the program, and a program The output port 71 for outputting the rotation control amount Mm of the steering shaft motor 22, the rotation control amount Msf of the front wheel steering shaft motor 30, and the rotation control amount Msr of the rear wheel steering shaft motor 40 calculated by executing
e, these input ports 71a, ROM 71b, CP
The bus 71f is provided for commonly connecting the U 71c, the RAM 71d, and the output port 71e. Input port 71
In a, each sensor 23, 24, 37, 38, 47, 4
An analog-digital converter (hereinafter, simply referred to as an A / D converter) 73 for converting an analog signal supplied from 8, 70 through a multiplexer 72 into a digital signal is connected, and the multiplexer 72 is connected to each of the sensors 23, 24, 3
The analog signals from 7, 38, 47, 48, 70 are
In response to a control signal supplied from the PU 71c via the input port 71a, it selectively outputs to the A / D converter 73 in a time division manner, and the A / D converter 73 synchronizes this output signal with this output signal. Converted to digital signal and input port 71
is being supplied to a. Multiplexer 72, steering displacement amount sensor 23, steering force sensor 24, front wheel turning displacement amount sensor 3
7, front wheel steering reaction force sensor 38, rear wheel steering displacement amount sensor 4
7 and the rear wheel steering reaction force sensor 48 are provided between the buffer amplifiers 74a, 74b, 74c, 74d, 74e and 74, respectively.
f is connected. Further, between the multiplexer 72 and the vehicle speed sensor 70, a waveform shaping circuit 70 for shaping the pickup signal from the vehicle speed sensor 70 into a rectangular wave signal.
a, a frequency / voltage converter (hereinafter simply referred to as f / V converter) 70b for inputting this rectangular wave signal and converting it into a voltage signal showing a voltage value proportional to the frequency of the signal, and an f / V converter 70b. A buffer amplifier 70c for supplying the output of the above to the multiplexer 72 is connected. Further, the input port 71a is connected with a select switch 75 for selecting one of three types of steering characteristics (light mode, normal mode, sports mode) that the driver changes according to the vehicle speed. The steering shaft motor 2 is connected to the output port 71e.
A digital-to-analog converter (hereinafter simply referred to as a D / A converter) that performs digital-to-analog conversion of the rotation control amount Mm of 2
76a is connected, and the D / A converter 76a converts the rotation control amount Mm into an analog signal and controls the steering shaft motor 22 via the power amplifier 77a.

Further, D / A converters 76b and 76c for respectively converting the rotation control amount Msf of the front wheel steering shaft motor 30 and the rotation control amount Msr of the rear wheel steering shaft motor 40 into digital-analog are connected to the output port 71e, D / A converter 76b,
Reference numeral 76c converts the rotation control amount Msf and the rotation control amount Msr into analog signals, respectively, and transmits the front wheel steering shaft motor 30 and the rear wheel steering shaft motor 40 via the power amplifiers 77b and 77c.
Are controlled respectively. Further, the output port 71e has a display 7 for displaying the selected steering characteristic of the select switch 75.
5a is connected.

The operation of the vehicle power steering apparatus configured as described above will be described with reference to the flowchart shown in FIG. 5. When the ignition switch is turned on, the CPU 71c starts executing the program from step 100, and the program is executed. Go to step 101.

In step 101, the CPU 71c inputs the selection state of the select switch 75, sets the mode selection flag S to "0" when the select switch 75 selects the write mode, and selects the normal mode. The mode selection flag S is set to "1", and when the sports mode is selected, the mode selection flag S is set to "2", and the mode selection flag S is temporarily stored in the RAM 71d. After entering the mode selection information in step 101,
The CPU 71c outputs this mode selection information to the display 75a via the output port 71e in step 102 to light up and display the steering characteristic mode selected in the display 75a, and advances the program to steps 103 and 104. C
The PU 71c determines the steering displacement sensor 23 in step 103.
To steering displacement amount Ym, steering force sensor 24 to steering force (or steering reaction force) Fm, front wheel steering displacement amount sensor 37 to front wheel steering displacement amount Ysf, front wheel steering reaction force sensor 38 to front wheel steering reaction force ( Front wheel steering force) Fsf, rear wheel steering displacement amount sensor 4
The rear wheel steering displacement amount Ysr from 7 and the rear wheel steering reaction force (or rear wheel steering force) Fsr from the rear wheel steering reaction force sensor 48 are input and stored in the RAM 71d respectively, and in step 104, the vehicle speed sensor 70 outputs the vehicle speed. V is input and stored in the RAM 71d, and the program proceeds to step 105. In step 105, the CPU 71c reads out the mode selection flag S and determines the mode by the value of the mode selection flag S,
When the mode selection flag S is "0", it is determined that the light mode is selected as the steering characteristic, and step 10 is performed.
When the mode selection flag S is "1", it is determined that the normal mode is selected as the steering characteristic, and the process proceeds to step 107, and when the mode selection flag S is "2", the steering is performed. It is determined that the sports mode is selected as the characteristic, and the process proceeds to step 108.

In the calculation of steps 106, 107 and 108, C
The PU 71c reads out the vehicle speed V from the RAM 71d, and based on the vehicle speed V and the type of operation characteristic mode, the front wheel steering gear ratio αf and the rear wheel steering gear shown in the characteristic diagrams of FIGS. 6A to 6D. Ratio αr, the above ratio α
The product of f and the front wheel force reverse feed ratio βf αf · βf and the ratio αr
And the rear wheel force reverse feed ratio βr are read out from the parameter table provided in the ROM 71b to obtain the respective ratios αf and αr, and the respective products αf and βf and αr are calculated with the respective ratios αf and αr. -Calculate each ratio βf and βr by dividing βr. The characteristic diagram of FIG. 6A shows changes in the value of the front wheel steering gear ratio αf in each mode with respect to the vehicle speed V.
Each of these ratios αf has a substantially constant value even if the vehicle speed V changes in all modes, but is a larger value in the light mode L and the sports mode S than in the normal mode N. This is because even if the steering amount in the light mode L and the sports mode S and the steering amount in the normal mode N are the same, the front wheel steering amount in the light mode L and the sports mode S is higher than that in the normal mode N. It means to grow. The characteristic diagram of FIG. 6B shows changes in the value of the rear wheel steering gear αr in each mode with respect to the vehicle speed V. In all modes, these ratios αr become negative as the vehicle speed V increases from zero. It changes positively and continuously, and the maximum absolute value of each ratio αr is about 1/3 of the value of each ratio αf. Further, the vehicle speed values at which the ratios αr become zero in the order of the normal mode N, the light mode L, and the sports mode S increase in the ratios αr. As a result, the left and right rear wheels 43a, 43b are steered in reverse phase to the left and right front wheels 33a, 33b in the low vehicle speed range, and the left and right rear wheels 43a, 43b in the high vehicle speed range.
Is steered in the opposite phase with respect to the left and right front wheels 33a and 33b, and is in the normal mode N, the light mode L, and the sports mode S.
The left and right rear wheels 43a, 43b are steered in reverse phase with respect to the left and right front wheels 33a, 33b until the vehicle speed increases in the order of. The steering amounts of the left and right rear wheels 43a and 43b are the same as the left and right front wheels 33.
It is about 1/3 of the steering amount of a and 33b. The characteristic diagrams of FIGS. 6C and 6D are the product αf · βf of the front wheel steering ratio αf and the front wheel power transmission ratio βf and the product αr of the rear wheel steering ratio αr and the front wheel power transmission ratio βr in each mode with respect to the vehicle speed V.
The change in each value of βr is shown. The product αf · βf
In all the modes, the product αr · βr has a constant value when the vehicle speed V is low, and increases with the increasing vehicle speed V in the order of the light mode L, the normal mode N, and the sports mode S. This means that the steering force required to rotate the steering wheel 20 gradually increases as the vehicle speed V increases, and the steering force is increased in the order of the light mode L, the normal mode N, and the sports mode S. It means to grow.

In the above step 106 (or 107, 108), the front and rear wheel steering gear ratios αf, αr and the front and rear wheel force reverse transmission ratio β
After calculating f and βr, the program proceeds to step 109, and the CPU 71c determines the coefficient Kmpf,
Kmpr, Ksff, Ksfr are calculated by using the front and rear wheel steering gear ratios αf and αr and the front and rear wheel force reverse feed ratios βf and βr.
And the coefficients Kspf and Ksp stored in the ROM 71b.
It is calculated by executing the calculations shown in (Equation 20) to (Equation 23) based on r and Kmf. Next, at step 110, the CPU 71c calculates the rotation control amount Mm of the steering shaft motor 22 and the rotation control amounts Msf and Msr of the front and rear wheel steering shaft motors 30 and 40 by the calculation coefficients Kmpf and Kmp.
mpr, Ksff, Ksfr, the above coefficients Kspf, Ks
pr, Kmf, and steering displacement amount Ym, steering force (or steering reaction force) Fm, front and rear wheel steering displacement amounts Ysf, Ysr, front and rear wheel steering reaction force (or steering force) Fsf, Fsr. ) To (Equation 26).

Mm = Kmf * Fm-Ksff * Fsf-Ksfr * Fsr ... (Formula 24) Msf = Kmpf * Ym-Kspf * Ysf. ． (Formula 25) Msr = Kmpr * Ym-Kspr * Ysr. ． (Equation 26) After the calculation in step 110, the program executes step 111
Then, the CPU 71c controls the rotation control amount Mm of the steering shaft 21 and the rotation control amounts Msf and Ms of the front and rear wheel turning shafts 32 and 42.
A control signal indicating r is output to D / via the output port 71e.
It outputs to the A converters 76a, 76b, 76c. The D / A converters 76a, 76b and 76c are power amplifiers 77, respectively.
The rotations of the steering shaft motor 22 and the front and rear wheel steering shaft motors 30 and 40 are controlled via a, 77b and 77c. Steering axis 2
1 rotation controlled operation, and front and rear wheel steering shafts 32, 4
The operation of controlling the rotation of the two wheels to steer the left and right front wheels 33a, 33b and the left and right rear wheels 43a, 43b is the same as the operation shown in the basic configuration.

After the calculation in step 111, the program is step 1
12, the CPU 71c reads the steering displacement amount Ym from the RAM 71d in step 112, and outputs the steering displacement amount Ym.
Absolute value | Ym | is less than or equal to a predetermined small value W, that is, it is determined whether or not the vehicle is in a substantially straight traveling state. In this determination, when the CPU 71c determines “YES”, that is, the absolute value | Ym | of the steering displacement amount Ym is equal to or less than the above value W, the process returns to the execution of the calculation in step 101 and steps 101 to 105, 106 (or 107, 108),
When the circulation calculation of 109 to 112 is executed and it is determined that “NO”, that is, the absolute value | Ym | of the steering displacement amount Ym is larger than the value W, the process returns to the execution of the calculation of step 103 and steps 103 to 105 and 106 (or 107, 108),
The rotation calculation of 109 to 112 is executed to control the rotation of the steering shaft 21, the front wheel steering shaft 32, and the rear wheel steering shaft 42. As described above, when the vehicle is in a substantially straight traveling state, the program passes step 101 to enable the mode change,
When the vehicle is in a turning state, the program proceeds to step 1
By making the mode change impossible by not passing 01, the front and rear wheel steering gear ratios αf, αr
The discontinuous changes in the steered angles of the left and right front wheels 33a, 33b and the left and right rear wheels 43a, 43b, and the respective products αf of the ratios αf, αr and the front and rear wheel force reverse feed ratios βf, βr.
It is possible to eliminate a discontinuous change in the steering force (or steering reaction force) determined by βf, αr and βr.

As will be understood from the above description of the operation, in the above-described embodiment, the left and right front wheels 33 are operated according to the turning operation of the steering wheel 20 by the calculation of steps 103 and 109 to 111.
a, 33b and the left and right rear wheels 43a, 43b are steered, and the front wheel steering reaction force and the rear wheel steering reaction force generated by the steering of the left and right front wheels 33a, 33b and the left and right rear wheels 43a, 43b are used as steering reaction forces. Since the steering wheel 20 is fed back to the steering wheel 20, the driver can operate the left and right front wheels 33a and 33b and the left and right rear wheels 43.
The vehicle can be driven while feeling the steering reaction force, the steering holding reaction force, and the restoring force of the steering wheel according to the turning of a and 43b. In addition, this steering reaction force is applied to steps 104 and 106 (or 10
7, 108) increases as the vehicle speed V increases, and thus steering stability becomes good. Further, front and rear wheel steering gear ratios αf, αr and respective products of these ratios αf, αr and front and rear wheel force reverse transmission ratios βf, βr αf · βf, αr ·
Since the characteristic of βr can be selected by the calculation of steps 101 and 105, the left and right front wheels 33a and 33b and the left and right rear wheels 33a and 33b associated with the turning transfer steering of the steering wheel 20 according to the personality of the driver or the driving situation of the vehicle. The turning amount and steering force (steering reaction force) of 43a and 43b can be changed.

d. Modification Example Next, the first slave unit B1 or the second slave unit of the above-described specific embodiment
A modified example of the slave portion B2 will be described with reference to the drawings. FIG. 7 shows the left and right front wheels 33a, 33b or the left and right rear wheels 4 of FIG.
The 3rd slave part B3 which steers the right and left wheels 80a and 80b corresponding to 3a and 43b is shown.

The third slave portion B3 is a hydraulic cylinder 82 to which oil discharged from a hydraulic pump (not shown) is applied via a servo valve 81.
And the left and right wheels 80a, 8 driven by the hydraulic cylinder 82.
A steering displacement amount sensor 84 for detecting a displacement amount of the steering shaft 83 coaxial with the steering shaft 83 for steering 0b as a steering displacement amount Ysa, and a steering reaction force Fsa applied from the right wheel 80b to the steering shaft 83.
The steering reaction force sensor 85 for detecting The servo valve 81 is connected at its neutral position by spools 81b, 81c, 81d fixed to the servo shaft 81a to a conduit P1 connected to a reservoir (not shown), a conduit P2 connected to a hydraulic pump, and a reservoir. By closing each of the conduits P3 and displacing the servo shaft 81a to the left in the figure when switched to the first position, the pressure oil supplied from the conduit P2 is supplied to the right chamber 8 of the hydraulic cylinder 82 via the conduit P4.
2a and the oil from the conduit P5 connected to the left chamber 81b of the hydraulic cylinder 82 is guided to the reservoir via the conduit P1. Further, when the servo valve 81 is switched to its second position, the servo shaft 81a is displaced rightward in the drawing to supply the pressure oil supplied from the conduit P2 to the left chamber 82b via the conduit P5, and Right chamber 8 of hydraulic cylinder 82
Oil from conduit P4 connected to 2a is led to the reservoir via conduit P3. The displacement of the servo shaft 81a in the left (or right) direction is provided at one end of the servo shaft 81a, and is supplied from the microcomputer 71 and the D / A converter 76b or 76c in FIG. 4 via the power amplifier 77b or 77c. The rotation control amount Msf or Msr of the above specific embodiment
Linear actuator 86 which is driven and controlled by a control signal Msa corresponding to
Controlled by.

The hydraulic cylinder 82 includes a piston 82c that slides in the hydraulic cylinder 82 by the pressure oil supplied from the servo valve 81, and the rudder shaft 83 fixed to the piston 82c is displaced in the axial direction by the sliding of the piston 82c. Let Further, the steered shaft 83 is provided with left and right wheels 80a, 87b via left and right tie rods 87a, 87b and left and right knuckle arms 88a, 88b.
The left and right wheels 80a and 80b are steered by the displacement of the steering shaft 83. Steering displacement amount sensor 84
Is a resistor 8 which is grounded at a midpoint according to the displacement of the steered shaft 83.
4a, and a voltage source 84c connected to both ends of the resistor 84a. A left (or right) displacement of the slider 83b causes a steering displacement amount Ysa of the steering shaft 83. A positive (or negative) voltage signal representing the above is output to the buffer amplifier 74c or 74e in FIG. Steering reaction force sensor 85
Is a strain gauge 85a that is attached to the steered shaft 83 and has a resistance value that changes according to tension and compression of the coaxial shaft 83, and fixed resistors 85b, 85c, and 85d having the strain gauge 85a as one side.
And a voltage source 85e connected between the connection point of the strain gauge 85a and the resistance 85b and the connection point of the resistances 85c and 85d, and the connection point of the resistances 85b and 85c is grounded. This steering reaction force sensor 85 is connected to the right wheel 80b from the connection point of the strain gauge 85a and the resistance 85d.
Strain gauge 8 of the steering shaft 83 according to the left (or right) steering of the
A positive (or negative) voltage signal representing a steering reaction force (steering force) Fsa proportional to the amount of tensile (or compression) strain generated in the portion where 5a is attached is supplied to the buffer amplifier 74d or 74f of FIG. Is output to.

The operation of the third slave unit B3 configured as described above will be described. The linear actuator 86 is replaced with the linear actuator 86 from the microcomputer 71 of FIG. 4 in place of the rotation control amounts Msf and Msr in the above-described specific embodiment. A control signal corresponding to the control amount Msa for driving and controlling is supplied. The control amount Msa is determined according to the characteristic of the linear actuator 86, and is substantially equivalent to the rotation control amounts Msf and Msr. When the level of the control signal supplied to the linear actuator 86 is positive (or negative), the servo shaft 81a is displaced in the left (or right) direction, and the hydraulic pressure from the hydraulic pump is transferred to the hydraulic cylinder 82.
To the right chamber 82a (or the left chamber 82b). By this pressure oil supply, the piston 82c and the steered shaft 83 are displaced in the left (or right) direction, and the left and right wheels 8a, 87b and the left and right wheels 8a, 88b are passed through them.
0a and 80b are steered in the left (or right) direction. The turning displacement amount Ysa of the turning shaft 83 is detected by the turning shaft displacement amount sensor 84 and sent to the microcomputer 71. At this time, the right wheel 80b receives a steering reaction force acting from the road surface in the right (or left) direction shown in the figure, which blocks the steering, and the steering reaction force rolls through the right knuckle arm 88b and the right tie rod 87b. It is transmitted to the rudder axle 83. This steering shaft 8
The steering reaction force transmitted to the steering wheel 3 acts in the opposite direction to the force generated by the hydraulic cylinder 82, so that the steering shaft 83 is distorted in tension (or compression) according to the steering reaction force (steering force). . Steering reaction force (steering force) Fs proportional to the amount of distortion of the steered shaft 83
a is detected by the steering reaction force sensor 85 and is sent to the microcomputer 71. Accordingly, the first slave B1 or the second slave unit B2 according to the above-described specific example.
Even if is replaced with the third slave B3, which is a modified example thereof, the same effect as that of the above specific embodiment can be achieved.

e. Other Modifications In the above-described specific embodiments, the front wheel steering gear ratio αf for each mode is set to a substantially constant value even if the vehicle speed V changes. However, in the characteristics shown in FIG. When V is small, front wheel steering gear ratio αf in each mode
May be slightly increased, or when the vehicle speed V is high, the ratio αf may be slightly decreased. This allows
Even when the steering amount of the steering wheel 20 is small when the vehicle is traveling at low speed, the steering amounts of the left and right front wheels 33a and 33b are large to reduce the burden on the driver for turning the vehicle, and when the vehicle is traveling at high speeds. The influence of the steering amount of 20 on the turning amounts of the left and right front wheels 33a and 33b is reduced, and the traveling stability of the high-speed vehicle is improved.

Further, the front wheel steering gear ratio αf and the rear wheel steering gear ratio αr may be determined in consideration of the change in the steering displacement amount Ym. In this case, CPU7
1c is the absolute value | Ym of the steering displacement amount Ym input in step 103 to each ratio αf, αr calculated in step 106 (or 107, 108) in the calculation of step 106 (or 107, 108). Multiply the parameter by increasing with |. This gives the same absolute value |
Since the absolute values | αf | and | αr | of the respective ratios αf and αr increase as Ym | increases, the steering wheel 2
As the steering amount of 0 increases, the left and right front wheels 33a, 33
The amount of change in the steered amounts of b and the left and right rear wheels 43a and 43b becomes large. As a result, in order to turn the vehicle, the steering wheel 2
The burden on the driver who performs 0 operation is reduced.

Further, in the above-described specific embodiment, the front and rear wheel steering shafts 3
The rotational positions of 2, 42 are the front and rear wheel steering displacement amount sensors 37,
The front and rear wheel steering shaft motors 30, 40 are controlled by feeding back the front and rear wheel steering displacement amounts Ysf, Ysr to the front and rear wheel steering shaft motors 30, 40. The microcomputer 71 calculates the target rotation step number of the motor 30 according to the steering displacement amount Ym from the steering displacement amount sensor 23, and rotates the motors 30 and 40 based on the calculation result. If the amount of displacement is controlled, the above feedback control becomes unnecessary.

Further, in the above specific embodiment, the left and right front wheels 33a,
Although 33b is controlled by the single front wheel steering shaft motor 30, the left front wheel 33a and the right front wheel 33b may be independently controlled by two motors. further,
In the present invention, the left and right front wheels 33a, 33b may be steered by a front wheel steering mechanism that mechanically connects the front wheels 33a, 33b and the steering handle 20.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the configuration of the invention described in the claims, FIG. 2 is a diagram showing a basic configuration of a vehicle power steering apparatus according to the present invention, and FIG. 3 is shown in FIG. 5 is a control block diagram showing a control state in the basic configuration, FIG. 4 is a schematic diagram of a vehicle power steering system showing a specific embodiment of the invention, and FIG.
FIG. 6 is a flow chart of a program executed by the microcomputer of FIG. 4, FIGS. 6A to 6D are diagrams showing steering characteristics in a specific embodiment of the present invention, and FIG. 7 is a first slave unit of FIG. It is a diagram showing a modification of the second slave unit. Explanation of code 20 ... Steering handle, 21 ... Steering shaft, 22 ... Steering shaft motor, 23 ... Steering displacement sensor, 24 ... Steering force sensor, 30, 40 ... Steering shaft motor, 32 , 42, 8
3 ... Steering shaft, 33a, 33b, 43a, 43b, 80
a, 80b ... Wheels, 37, 47, 84 ... Steering displacement amount sensor, 38, 48, 85 ... Steering reaction force sensor, 50 ...
... Steering axis motor control circuit, 51, 52 ... Steering axis motor control circuit, 53 ... Steering force calculator, 54 ... Combined steering reaction force calculator, 55, 56 ... Steering reaction force calculator, 57, 59
...... Target turning amount calculator, 58, 60 …… Turning displacement amount calculator, 70 …… Vehicle speed sensor, 71 …… Microcomputer, 75 …… Select switch, 81 …… Servo valve, 8
2 ... Hydraulic cylinder, 86 ... Linear actuator.

Claims (1)

[Claims] 1. A power steering apparatus for a front and rear wheel steered vehicle that steers front wheels and rear wheels according to rotation of a steering wheel, wherein a steering shaft coupled to the steering wheel and a steering shaft for rotationally driving the steering shaft. An actuator, a front wheel steering control unit that steers the front wheels in response to the rotation of the steering shaft, a rear wheel steering mechanism that is mechanically coupled to the rear wheels to steer the rear wheels, and a steering handle to the steering shaft. A steering force sensor for detecting a steering force applied to the rear wheel, a rear wheel steering reaction force sensor for detecting a rear wheel steering reaction force applied to the rear wheel steering mechanism from a rear wheel, and a steering shaft from a reference position of the steering shaft. A steering displacement amount sensor that detects a rotation angle as a steering displacement amount, and a steering displacement sensor that increases in accordance with an increase in the detected steering force based on the steering force sensor output and that rotates the steering shaft in a direction in which the steering force is applied. 1st to determine 1 controlled variable
A control amount determining means, and a second amount that increases in accordance with an increase in the detected turning reaction force based on the output of the rear wheel turning reaction force sensor and that rotates the steering shaft in a direction to return to the reference position
Second control amount determining means for determining a control amount, and a steering shaft for controlling the rotation of the steering shaft by outputting a steering shaft rotation control signal obtained by combining the first control amount and the second control amount to the steering shaft actuator. Rotation control signal output means, rear wheel target steering amount determining means for determining a target steering amount of rear wheels based on the output of the steering displacement amount sensor, and rear wheel steering according to the determined rear wheel target steering amount. A rear wheel steering control signal output means for outputting a control signal to the rear wheel steering mechanism to control the rear wheel steering mechanism such that the steering amount of the rear wheels becomes the determined rear wheel target steering amount. A power steering device for a front and rear wheel steering vehicle, which is characterized in that