JPH01314670A - Steering controller of front and rear wheel steering vehicle - Google Patents

Abstract

PURPOSE:To obtain good turning performance regardless of the coefficient of friction of the surface of a road, by correcting the goal steering force of a rear wheel determined from the deviation of a rear wheel goal steering angle decided according to wheel speed and a front wheel steering angle, and a real rear wheel steering angle, in proportion to the change of the front wheel steering angle by time. CONSTITUTION:Respective steering angle detection means A, B for detecting the steering angles of a front wheel and a rear wheel, and a vehicle speed detection means C are provided. And a rear wheel goal steering angle decision means D decides the goal steering angle of the rear wheel in proportion to the steering angle of the front wheel and vehicle speed detected, and also a rear wheel steering force decision means E decides the goal steering force of the rear wheel in proportion to the deviation of the rear wheel goal steering angle and a real rear wheel steering angle. And a front wheel steering speed detection means F for detecting the change of the front wheel steering angle by time is provided, the steering force correction means G corrects the rear wheel goal steering force in proportion to the change by time in such a way that the goal force is set smaller when the change by time is bigger. The goal steering force after correction controls a driving means H to steer the rear wheel to its goal steering angle.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a steering control device for a front and rear wheel steered vehicle that also steers the rear wheels. The present invention relates to a steering control device that improves turning characteristics by controlling according to changes in the vehicle.

(Prior Art) In front and rear wheel steered vehicles in which both the front wheels and the rear wheels are steered, steering performance is generally improved by controlling the steering angle ratio and phase of the front and rear wheels according to the vehicle speed.

Such front and rear wheel steering vehicles steer the rear wheels in the opposite direction (opposite phase) to the front wheels in a low vehicle speed range to reduce the turning radius (improve maneuverability), and also steer the rear wheels in the opposite direction (opposite phase) to the front wheels in a low vehicle speed range to reduce the turning radius (improve maneuverability). Stability is improved by steering the wheels in the same direction (same phase) as the front wheels.

Conventionally, a steering control device of this type for a front and rear wheel steered vehicle is known, such as the one described in Japanese Patent Application Laid-open No. 60-67272. The steering control device described in Japanese Patent Application Laid-Open No. 60-67272 outputs a pulse signal with a step angle corresponding to the steering speed to a pulse motor, steers the rear wheels by the pulse motor, and rotates the rear wheels at the steering speed. The aim is to improve the followability of the motor by making the motor respond according to characteristics.

(Problem to be solved by the present invention) However, in the above-mentioned steering control device of JP-A-60-67272, the output torque of the step motor is constant, and the rotation angle of the output shaft of the step motor is The steering angle of the rear wheels is determined at a predetermined ratio, and the steering angular velocity of the rear wheels is also uniquely determined according to the rotational speed of the output shaft of the step motor. For this reason, such steering control devices do not take into account the coefficient of friction of the road surface, and the rear wheels are always steered to the target angle, making it impossible to achieve turning angles depending on the road surface conditions. There was a problem.

On the other hand, in order to solve the above-mentioned problems, it is possible to control the turning angular velocity of the rear wheels according to the friction coefficient of the road surface, but it is essential to have a sensor that detects the friction coefficient of the road surface. There is a problem in that it increases manufacturing costs.

This invention was made in view of the above-mentioned problems, and an object of the present invention is to provide a steering control device that responds to the steering angular velocity of the rear wheels or the friction coefficient of the road surface without using sensors or the like. do.

(Means for Solving the Problem) As shown in the configuration diagram of FIG. 1, the steering control device for a front and rear wheel steered vehicle according to the present invention steers both the front wheels and the rear wheels in response to the steering of a steering wheel. In wheel steering vehicles,
Front wheel steering angle detection means for detecting the steering angle of the front wheels; rear wheel steering angle detection means for detecting the steering angle of the rear wheels; vehicle speed detection means for detecting vehicle speed; and the vehicle speed detected by the vehicle speed detection means. and rear wheel target steering angle determining means for determining a target steering angle of the rear wheels according to the steering angle of the front wheels detected by the front wheel steering angle detecting means; Rear wheel steering force determination means for determining a target steering force for the rear wheels according to a deviation between a target steering angle for the rear wheels and a steering angle for the rear wheels detected by the rear wheel steering angle detection means; front wheel steering speed detection means for detecting temporal changes in steering angle;
Steering force correction means for correcting the target steering force determined by the rear wheel steering force determination means in accordance with the temporal change detected by the steering speed detection means so that the target steering force determined by the rear wheel steering force determination means becomes smaller when the temporal change is large; The gist is to include a drive means for steering the rear wheels to a target steering angle using the target steering force corrected by the steering force correction means.

(Function) According to the steering control device for a front and rear wheel steering vehicle according to the present invention, the temporal change in the steering angle of the rear wheels occurs approximately in correspondence with the coefficient of friction of the road surface, and the determined target steering of the rear wheels is achieved. Since the force is corrected in accordance with the temporal change in the steering angle of the front wheels so that it becomes smaller when the temporal change is large, stability can be improved at normal steering speeds, and stability can be improved at high steering speeds. This can promote the occurrence of yawing, and in addition, the steering angular velocity of the rear wheels, that is, the transient steering angle, becomes jerky when the coefficient of friction of the road surface is small, and this improves stability on roads with a low coefficient of friction. This makes it possible to impart characteristics dependent on the friction coefficient of the running road surface to the steering angle of the rear wheels, and to obtain good turning characteristics regardless of the friction coefficient of the running road surface.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

2 to 6 show a steering control device for a front and rear wheel steering vehicle according to an embodiment of the present invention, and FIG. 2 is an overall schematic diagram;
FIG. 3 is a block diagram, and FIG. 4 is a flow chart.

In FIG. 2, reference numeral 11 denotes a steering handle, and the steering handle 11 is connected to a rack-and-pinion type steering gear mechanism 13 via a steering shaft 12. The steering shaft 12 is provided with a steering angle sensor (front wheel steering angle detection means) 14 for detecting the rotation angle of the steering shaft 12 and a steering speed sensor (front wheel steering speed detection means) 15 for detecting the rotational angular velocity of the steering shaft 12. It is being The steering angle sensor 14 is composed of an encoder and the like, and outputs a detection signal representing a steering angle (front wheel steering angle) to a controller 16, which will be described later.

Further, the steering speed sensor 15 is composed of a generator or the like connected to the controller 16, and outputs a detection signal representing the steering speed (temporal change in front wheel steering angle) to the controller 16. Needless to say, the steering speed sensor 15 can be replaced by a differential circuit or the like that performs a differential operation on the detection signal of the steering angle sensor 14.

As is well known, the steering gear mechanism 13 includes a pinion gear 13 that rotates integrally with the steering shaft 12.
Knuckle arms 1 of left and right front wheels 18FL and 18FR are provided at both ends of the rack 13b, respectively, and are provided with a rack 13b that meshes with a pinion gear 13a and a binion gear 13a and extends in the vehicle width direction.
9FL.

It is connected to 19FR via a steering linkage consisting of tie rods 17FL, 17FR, etc. These front wheels 18FL and 18FR each have a vehicle speed sensor 20F.
L, 20FR are provided, and these vehicle speed sensors 20FL,
It is connected to one side of the 20FR controller and outputs a signal representing the vehicle speed.

Furthermore, as will be described later, vehicle speed sensors 20RL and 20RR are also provided for the rear wheels 18RL and 18RR, respectively, and these vehicle speed sensors 20RL and 20RR are also connected to the controller 16 to output a signal representing the vehicle speed. Needless to say, the above-mentioned steering angle sensor 14 detects the moving distance of the rack 13b of the steering gear mechanism 13 or the front wheel +8FL.
.

It can be replaced with a sensor that detects the steering angle of the 18FR.

21 is connected to the controller 16 and the controller 1
The electric motor 21 is connected to a rack-and-pinion steering gear mechanism 23 via an output shaft or a bevel gear mechanism 22. Bevel gear mechanism 2
2 has a bevel gear 22b fixed to the output shaft of the electric motor 21 and a bevel gear 22a that rotates integrally with a binion gear 23a of the steering gear mechanism 23. The steering gear mechanism 23 is the aforementioned steering gear mechanism 23.
Similarly, it has a binion gear 23a and a rack 23b, and the binion gear 23a is connected to the electric motor 21 via a bevel gear mechanism 22, and both ends of the rack 23b are connected to the knuckle arms 19RL, 19 of the left and right rear wheels 18RL, +8RR, respectively.
It is connected to RR via a steering linkage consisting of tie rods 17RL, 17RR, etc. The rack 23b of the steering gear mechanism 23 is provided with a rear wheel steering angle sensor 24 that detects the moving distance of the rack 23b in the axial direction. The rear wheel steering angle sensor 24 is composed of a differential transformer or the like, is connected to the controller 16, and is connected to the rack 23.
The steering angle of the rear wheels 18RL and 18RR is detected with a moving distance of b0D8, and a signal representing the steering angle is output to the controller 16.

As is well known, in this rear wheel steering angle sensor 24, an AC pulse signal is input from the controller 16 to the primary coil, the core is displaced together with the rack 23b, and a differential signal is output from the secondary coil. In this embodiment, the electric motor 21 is provided exclusively for steering the rear wheels 18RL and 18RR, or the output of the electric motor 21 is provided for steering the rear wheels 18 as well as the front wheels 18FL and 18FR.
R.L.

It goes without saying that the present invention can also be achieved by adding a steering angle function generating mechanism to the transmission system of the steering force distributed to the rear wheels 18RR and rear wheels 18RL and 18RR.

The controller 16 includes a control circuit 25 as shown in FIG.
and a drive circuit 26, and a current sensor 28 of a drive circuit 26, which will be described later, is connected to the control circuit 25 together with the sensors 14, 15, 20.24 described above.
The two electric motors mentioned above are connected to this.

The control circuit 25 includes a constant voltage circuit 30, a microcomputer circuit 31, and human interface circuits 32, 33.
．． It is equipped with 34, 35° and 37 degrees. The constant voltage circuit 30 is connected to a battery via a fuse or the like, and supplies constant voltage power to each circuit. Human interface circuit 32
．． 33, 34° 35.37 are connected to the respective corresponding sensors 14, 15, 20, 24.28,
In addition, the microcomputer circuit 3
Connected to 1. A human power interface circuit 32 connected to the steering angle sensor 14 processes the output signal of the steering angle sensor 14 and sends the signal to the microcomputer circuit 31 to the front wheel 18F.
It outputs a signal representing the steering angle and direction of L and 18FR. A human power interface circuit 33 connected to the steering speed sensor 15 processes the detection signal of the steering speed sensor 15 and outputs a digital signal representing the steering speed to the microcomputer circuit 31. Further, an interface circuit 35 connected to the rear wheel steering angle sensor 24 includes an oscillation circuit, a rectifier circuit, a low-pass filter, etc.
An alternating current pulse signal is output to the primary coil, and the signal from the secondary coil is shaped and output to the microcomputer circuit 31. The interface circuit 34 connected to the vehicle speed sensor 20 is composed of a waveform shaping circuit, an arithmetic circuit, etc., and outputs a signal representing the vehicle speed to the microcomputer circuit 31 based on the output signal of each vehicle speed sensor 20. The interface circuit 37 connected to the current sensor 28 is
It includes an amplifier circuit, an A/D converter, etc., converts the output signal of the current sensor 28 into a digital signal, and outputs the digital signal to the microcomputer circuit 31.

The microcomputer circuit 31 includes a CPU, ROM, R
Each interface circuit 32, 33, 34 is equipped with an AM, a clock, etc., and operates according to a program stored in a ROM.
, 35. The duty factor of the +M current flowing to the electric motor 21 is determined by processing the manually input signals from each sensor through
PWM signals) g, h, i, and j are output to the drive circuit 26.

The drive circuit 26 includes a boost circuit 38, a gate 1 to live circuit 39, a current sensor 28, a relay circuit 41, a switch circuit 40, etc., and is connected to the gate l'live circuit 39 or the battery, and is connected to the switch circuit 40 or the relay. circuit 4
1 to the battery. switch circuit 40
are four field-effect transistors (FETs) Ql, Q
2. Q3゜Q4 are connected in a bridge shape, and these F
ETQl, Q2. Q3. The gate of Q4 is connected to a gate drive circuit 39. The drains of FETQl, Q2 are connected to the battery, and the sources are connected to FETQ3. Q4
The drain of FETQ3. Q4 is grounded through the source or current sensor 28 (one terminal of the battery)
and FETQI.

An electric motor 21 is connected between the source train connection of Q3 and the source train connection of FETs Q2 and Q4. The booster circuit 38 converts the battery voltage to 1-voltage and outputs it to the gate drive circuit 39.
is a PWM signal pair input from the microcomputer circuit 31, and each FE of the switch circuit 40 is
TQ1. Q2. Q3. A drive signal is output to the gate of Q4. The current sensor 28 detects the current applied to the motor 21 and outputs a detection signal of this current to the above-mentioned interface circuit 37. Note that the switch circuit 40 is an FET
A duty factor drive signal corresponding to the PWM signal signal is input to the gate of QI, a PWM signal is input to the gate of FET Q2, a PWM signal i is input to the gate of FET Q3 (7), and a drive signal of the PWM signal J is input to the gate of FET Q4. The drive signals of the utility factors are manually operated.

Next, the operation of this embodiment will be explained with reference to FIG.

The steering control device for this front and rear wheel steering device controls the electric motor 21 by executing a series of processes shown in the flowchart of FIG. 4 in the microcomputer circuit 31.

When the ignition key is operated and the key switch is turned to the ON position, the microcomputer circuit 3
Power is supplied to the first class, and the microcomputer circuit 31
is activated. In step P1, the microcomputer circuit 31 is initialized, and data stored in internal registers and the like are erased and addresses are designated. Subsequently, in step P2, an initial failure diagnosis is performed according to a subroutine defined elsewhere, and the following processing is performed only when everything is functioning normally.

In step P3, the vehicle speed V is read from the output signal of each vehicle speed sensor 20, and in the subsequent step P4, the vehicle speed V is used as an address, and the data table 1 shown in FIG.
Search the steering angle ratio k from the map. This steering angle ratio includes the fifth
As is clear from the figure, it has a negative value (representing an opposite phase) in a low vehicle speed range smaller than the predetermined vehicle speed V1, and a positive value (representing the same phase) in a high vehicle speed range larger than the predetermined vehicle speed V1.

Next, in step P5, the output signal θ゛Ff! of the steering angle sensor 14 is received. - Read, and in step P6, calculate the steering angle θF (f9F-θ"F-0M) from the neutral position using the neutral correction coefficient θM of the steering angle sensor 14. This steering angle θF is determined by the rotation angle of the steering shaft 12 being
Front wheels 18FL, 18 to correspond to the steering angle of L, 18FR.
It does not represent the steering angle of the FR (hereinafter referred to as front wheel steering angle). continue,
Step P7 determines whether the front wheel steering angle θF is positive or negative, that is, the direction, and if the front wheel steering angle θF is positive, step P8 sets the flag F] to O, and if the front wheel steering angle θF is negative, the step After the front wheel steering angle θF is converted into a positive value (absolute value) in step P9, the flag F1 is set to 1 in step PIO. Then, in the next step pH, the front wheel steering angle θF is multiplied by the steering angle ratio k to calculate the target steering angle (rear wheel target steering angle) θRT of the rear wheels 18RL and 18RR.

Next, in step P12, the vehicle speed ■ or the predetermined vehicle speed ■
. It is determined whether the vehicle speed exceeds the specified vehicle speed ■ or the specified vehicle speed ■.

If it exceeds step P13゜PI3. Processes PI3 and also sets vehicle speed V or predetermined vehicle speed■. Below is step P16. P17° PI3 processing is performed. Step P
13, the value of flag F1 is determined, and if flag F1 is 1, flag F3 is set to 1 in step P14, and if flag F1 is 0, flag F3 is set to 1 in step PI5.
Set to O. Similarly, in step P16, the value of flag F1 is determined, and if flag F1 is 1, step P16 is determined.
17 sets flag F3 to 0, and also sets flag F 1 h
) is 0, the flag F3 is set to 1 in step P18.

In the subsequent step P19, the output signals θR1 and θR2 of the rear wheel steering angle sensor 24 are read, and in step P20, a failure diagnosis of the rear wheel steering angle sensor 24 is performed according to a subroutine defined elsewhere. In this step P20, the following process is executed only when it is diagnosed that the rear wheel steering angle sensor 24 is functioning normally. And step P21
, the output signal θR1°θR of the rear wheel steering angle sensor 24
2 is subtracted to calculate the rear wheel steering angle θR.

Next, in step 22, it is determined whether the rear wheel steering angle θR is positive or negative, and if the rear wheel steering angle θR is positive, the flag F2 is set to O in step P23, and if the rear wheel steering angle θR is negative, the flag F2 is set to O. In step P24, the rear wheel steering angle θR is converted into a positive value (absolute value).
After that, the flag F2 is set to 1 in step P25. In the next step P26, the flag F2 and the flag F3 are
and determines the value of flag F2. If the values of F3 are different, the process of step P27 is performed, and if the flags F2 and F3 are the same value, the processes of steps P28 to P33 are performed. In step P27, the deviation ΔθR is calculated by adding the rear wheel target steering angle θRT and the rear wheel steering angle θR. Further, in step P28, the rear wheel steering angle θR is subtracted from the rear wheel target steering angle θRT to calculate the deviation ΔθR, and after this, in step P
29 to determine whether the deviation ΔθR is positive or negative. This step P2
9, when it is determined that the deviation ΔθR is negative, the deviation ΔθR is made into a positive value in step P30, and then step I)3
1. P32. P33 and replaces the value of flag F3. That is, the value of flag F3 is determined in step P31, and if flag F3 is 0, flag F3 is replaced with 1 in step P32, and if flag F3 is 1, step P33 is performed.
The flag F3 is replaced with O.

In the following step P34, the steering speed δFft is read from the detection signal of the steering speed sensor ]5, and in step P35
Then, a map search is performed for the correction coefficient α from the data table 2 shown in FIG. 6 using the steering speed θF as an address. Then, in step P36, the deviation ΔθR is corrected by multiplying the deviation ΔθR by the correction coefficient α. As is clear from FIG. 6 above, the correction coefficient α is approximately 1 in the region where the steering speed θF is low, and gradually decreases to zero in the region where the steering speed δF is high. Therefore, the deviation ΔθR corrected by the correction coefficient α
becomes small in a region where the steering speed δF is high.

Next, in step P37, a map search is performed for the rear wheel steering force from the data table 3 shown in FIG. 7 using the height difference ΔeR as an address. This rear wheel steering force is generated by the electric motor 21
It represents the duty factor, that is, the current value, of the current applied to the current, and has a dead zone of O in a low deviation area close to 0, increases as the deviation increases, and takes a constant value in a high deviation area.

In this step P37, the deviation ΔθR is corrected based on the steering speed δF as described above, and becomes smaller than the deviation calculated in steps P27 and P28 in the region where the steering speed eF is large, so that the steering force and the steering speed are It is smaller in regions where δF is large than in regions where δF is small.

Subsequently, in step P3B, it is determined whether the rear wheel steering force is O or not, and if the rear wheel steering force is 0, the process proceeds to step P3.
9, set the PWM signals g, h, i, and j to O, 0, 1, respectively.
I is set, and if the rear wheel drive force is not 0, the value of the flag F3 is determined in step P40. This step P
40, when it is determined that the flag F3 is 0, 1.0 is set to each of the PWM signals g, h, t, and j in step P41.
,0. D is set, and if it is determined that the flag F3 is 1, the PWM signal g is set in step P42.

0, 1 for h, i, j, respectively. Set D and O. Then, in step P43, PWM signals g1h, i, and j are output. Therefore, the electric m21 has rear wheels 18RL, 18
A current of duty factor D is applied in accordance with the steering direction of RR, and a steering force corresponding to the current is applied to the rear wheels 18RL and 18R.
R is steered to the target steering angle, and when the power is not energized, the winding is short-circuited to perform electric braking to maintain the rear wheel steering angle at the target steering angle.
Do it. Thereafter, in step P44, failure diagnosis of the drive system such as the electric motor 21 and the switch circuit 40 is performed according to a subroutine defined elsewhere, and the series of processes from step P2 is repeated again.

As mentioned above, regarding the steering control device of this embodiment,
A current corresponding to the deviation ΔθR between the actual steering angle θR of the rear wheels 18RL and 18RH and a target steering angle θRT determined according to vehicle speed etc. is applied to the electric motor 21, and the deviation is reduced by the electric motor 21 between the rear wheels 18RL and 18RR. Turn the wheel as much as possible. The deviation ΔθR between the detected rear wheel steering angle θR and the target steering angle θRT is corrected to decrease when the steering speed δF is large, that is, when the friction coefficient of the road surface is small, and the rear wheel steering force becomes smaller. The steering angular velocity of the rear wheels, that is, the transient steering angle, can be given characteristics dependent on the friction coefficient of the road surface, and excellent turning performance can be obtained regardless of the friction coefficient of the road surface.

FIG. 8 shows a steering control device for a front and rear wheel steered vehicle according to another embodiment of the present invention. In addition, in the same figure, step P
1 to step P33, step P34, step P3
5. Steps P38 to P44 are respectively the same as steps P1 to P33, step P37, step P34, and steps P38 to P44 in FIG. 4 described above, and their explanations will be omitted.

In this embodiment, in step P36, a map search is performed for the corrected steering force Ds using the steering speed bF as an address from the data table 4 shown in FIG. Correct the force DS. As is clear from FIG. 9, the corrected steering force Ds is
Since it has a characteristic that it gradually increases from 0 to a predetermined value in the region where the steering speed δF is high, the steering force after subtracting this corrected steering force Ds becomes smaller in the region where the steering speed δF is high. Therefore, in this embodiment as well, characteristics depending on the coefficient of friction of the road surface can be imparted to the steering speed of the rear wheels, and good turning characteristics can be obtained regardless of the coefficient of friction of the road surface.

In each of the embodiments described above, the electric motor 21 drives the rear wheel 1.
It goes without saying that the present invention can also be achieved by steering 8RL and 18RR, or by using a hydraulic actuator.

(Effects of the Invention) As explained above, the steering control device for a front and rear wheel steered vehicle according to the present invention adjusts the steering force of the rear wheels according to the temporal change in the steering angle of the front wheels. The steering angle of the rear wheels can be given characteristics that depend on the coefficient of friction of the road surface, eliminating the influence of the coefficient of friction of the road surface on the steering angle of the rear wheels, allowing for good turning regardless of the coefficient of friction of the road surface. Performance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a steering control device according to the present invention. Second
7 to 7 show a steering control device according to an embodiment of the present invention, FIG. 2 is an overall schematic diagram, FIG. 3 is a block diagram,
FIG. 4 is a flowchart, and FIGS. 5, 6, and 7 are data tables used for control processing. 8 and 9 show a steering control device according to another embodiment of the present invention, with FIG. 8 being a flowchart and FIG. 9 being a data table of control processing. 11... Steering handle 14... Rudder angle sensor (front wheel steering angle detection means) 15...
Steering speed sensor (front wheel steering speed detection means) 16...Controller 18FL, 18FR...Front wheel +8RL, 18RR...Rear wheel 20...Vehicle speed sensor (vehicle speed detection means) 21...Electric 81! (Drive means) 24... Rear wheel steering angle sensor 25... Control circuit 26... Drive circuit 31... Microcomputer circuit (rear wheel target steering angle determining means, rear wheel steering force determining means, steering force Amendment Means) Patent Applicant Agent: Honda Motor Co., Ltd.
Patent Attorney Part 2 1) Part 1 Patent Attorney
Kuni Ohashi Patent Attorney
Koyama Yu 4th figure table layout] 0
P take table sill 2 01 Distance 6゜0 Stirring speed 6゜Fig. 8F26F3 F26 F2;F3 r2-t”3 QRTMo○RF27 P28△eR≦○
F29 ΔOR2○ to ΔθR−ΔθR4ゝ○

Claims (1)

[Scope of Claims] In a front and rear wheel steered vehicle that steers both the front wheels and the rear wheels in accordance with the steering of a steering wheel, there is provided a front wheel steering angle detection means for detecting the steering angle of the front wheels; and a front wheel steering angle detection means for detecting the steering angle of the rear wheels. a rear wheel steering angle detection means for detecting a vehicle speed; a vehicle speed detection means for detecting a vehicle speed; Rear wheel target steering angle determining means for determining a steering angle, and a rear wheel target steering angle determined by the rear wheel target steering angle determining means and a rear wheel turning angle detected by the rear wheel steering angle detecting means. Rear wheel steering force determining means for determining a target steering force for the rear wheels according to the deviation from the steering angle; front wheel steering speed detecting means for detecting temporal changes in the steering angle of the front wheels; Steering force correction means for correcting the target steering force determined by the rear wheel steering force determination means in accordance with the detected temporal change so that it becomes smaller when the temporal change is large; and the steering force correction means. A steering control device for a front and rear wheel steered vehicle, comprising: a drive means for steering rear wheels to a target steering angle using a corrected target steering force.