JP2521934B2 - Control device for rear wheel steering in front and rear wheel steering vehicle - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front and rear wheel steering vehicle that steerably controls rear wheels in accordance with steering of front wheels, and more particularly to a front and rear wheel steering vehicle that copes with an abnormal occurrence of the steering control. The present invention relates to a control device for steering rear wheels in a vehicle.

(Prior Art) Conventionally, this type of device has an abnormality detecting means for detecting an abnormality relating to steering control of rear wheels and a rear wheel steering device as disclosed in, for example, Japanese Utility Model Laid-Open No. 60-161673. It is equipped with a neutral return mechanism that restores the rear wheels to the neutral state.
When the abnormality detecting means detects the abnormality, the neutral return mechanism is operated to return the rear wheels to the neutral state.

(Problems to be Solved by the Invention) However, in the above-described conventional device, even if the rear wheels are in any steering state, the rear wheels return to the neutral state immediately after the abnormality is detected. On the contrary, there is a problem that an unfavorable situation may occur in driving safety of the vehicle. For example, if the actual steering angle of the rear wheels is small, there is no problem in returning the rear wheels to the neutral position. And the controllability and stability of the vehicle are extremely deteriorated.
Also, if the actual steering angle of the rear wheels is decreasing, that is, if the rear wheels are returning to the neutral state, there is no problem in returning the rear wheels to the neutral state, but if the actual steering angle of the rear wheels is increasing. When the rear wheels are returned to the neutral position, the rear wheels are steered sharply contrary to the driver's intention, and the maneuverability and stability of the vehicle are extremely deteriorated.

The present invention has been devised in view of the above problems, and an object thereof is to provide front and rear wheel steering that copes with an abnormality in the rear wheel steering control so as to maintain the traveling safety of the vehicle against the abnormality. It is to provide a control device for steering rear wheels in a vehicle.

(Means for Solving Problems) In order to solve the above problems and achieve the object of the present invention,
The structural feature of the present invention is that, as shown in FIG.
A front wheel steering device 1 for steering a rear wheel RW, a rear wheel steering device 2 for steering a rear wheel RW, and a rear wheel steering device 2 for controlling the front wheel FW to steer the rear wheel RW for steering the front wheel FW. In a front and rear wheel steering vehicle including a steering control means 3 for controlling, a neutral return mechanism 2a incorporated in the rear wheel steering device 2 to return the rear wheel RW to a neutral state, and a rear wheel RW incorporated in the rear wheel steering device 2. Steering holding mechanism 2b for prohibiting the steering change of and holding the current steering state,
Steering state determining means 4 for determining whether the steering amount of the rear wheel RW is in a decreasing state or an increasing state, an abnormality detecting means 5 for detecting an abnormality relating to steering control of the rear wheel RW, and an abnormality detecting means 5
When the abnormality is not detected by the steering control means 3, the steering control means 3 permits the steering control of the rear wheels RW in accordance with the steering of the front wheels FW, and the abnormality detection means 5 detects the abnormality and the steering state determination means 4
When it is determined that the steering amount of the rear wheel RW is in a reduced state, the neutral return mechanism 2a is controlled to return the rear wheel RW to the neutral state, and the abnormality detection means 5 detects an abnormality and the steering state determination means. The selection control means 6 controls the steering holding mechanism 2b to hold the current steering state of the rear wheels RW when it is determined by 4 that the steering amount of the rear wheels RW is increasing.

(Operation of the Invention) In the present invention configured as described above, when there is no abnormality in the steering control of the rear wheels RW, the abnormality detection means 5 does not detect the abnormality, so the selection control means 6 controls the steering control. Since the steering control of the rear wheels RW by the means 3 is permitted, the rear wheels RW are steered by the rear wheel steering device 2 in accordance with the steering of the front wheels FW. On the other hand, if an abnormality occurs in the steering control of the rear wheels RW and the amount of the rear wheels RW is reduced at this time, the selection control means 6 controls the neutral return mechanism 2a to return the rear wheels RW to the neutral state. .
Also, when an abnormality occurs in the steering control of the rear wheel RW, the rear wheel RW
If the steering amount is increasing, the selection control means 6 controls the steering holding mechanism 2b to hold the current steering state of the rear wheels RW.

(Effects of the Invention) As described above, according to the present invention, when the steering amount of the rear wheel RW is increased when the steering control of the rear wheel RW is abnormal, the rear wheel RW is steered. Since the vehicle is maintained in the state, it is possible to prevent the rear wheel RW whose actual steering angle tends to increase from suddenly reversing in the decreasing direction, and the running stability of the vehicle is kept good. Further, if the steering amount of the rear wheel RW is reduced when an abnormality occurs in the steering control of the rear wheel RW, the rear wheel RW is returned to the neutral state, so that the actual steering angle tends to decrease. The vehicle is steered in the same direction as when the abnormality occurred and is returned to the neutral state, and the running stability of the vehicle is kept good without unnaturalness with respect to the neutral return.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the entire front and rear wheel steering vehicle according to the present invention. This front and rear wheel steering vehicle is a front wheel steering device A that steers the left and right front wheels FW1 and FW2, a rear wheel steering device B that steers the left and right rear wheels RW1 and RW2, and an electric control device that electrically controls the rear wheel steering device B. It has C and.

The front wheel steering system A has a steering wheel 11. The steering handle 11 includes a steering shaft 12, a rack and pinion mechanism 13 including a pinion portion 13a and a rack portion 13b, a relay rod 14 integrally formed with a rack portion 13b, left and right tie rods 15a and 15b, and left and right knuckle arms 16a and 16b. The left and right front wheels are connected to the front left and right wheels FW1 and FW2.
FW1 and FW2 are steered. A control valve 17 is attached to the lower portion of the steering shaft 12, and the valve 17 powers the hydraulic oil discharged by the hydraulic pump 18 and supplied through the conduit P1 according to the steering torque acting on the steering shaft 12. The oil is supplied to one oil chamber of the cylinder 21, and the hydraulic oil from the other oil chamber of the cylinder 21 is discharged to the reservoir 22 via the conduit P2. The power cylinder 21 drives the relay rod 14 in accordance with the supply and discharge of the hydraulic oil, so that the left and right front wheels FW1,
It is designed to assist the steering of FW2.

The rear wheel steering system B has a step motor 23,
23 is controlled by the electric control device C to drive the steering shaft 24 in rotation. The steering shaft 24 includes a rack and pinion mechanism 25 including a pinion portion 25a and a rack portion 25b, a relay rod 26 integrally formed with the rack portion 25b, left and right tie rods 27a and 27b, and left and right knuckle arms 28a and 28b, and left and right rear wheels. It is connected to RW1 and RW2, and the left and right rear wheels RW1 and RW2 according to the rotation of the coaxial 24.
Is being steered. A control valve 31 is attached to an intermediate portion of the steering shaft 24, and the valve 31 controls the hydraulic oil discharged by the hydraulic pump 32 and supplied through the conduit P3 according to the steering torque acting on the steering shaft 24. The oil is supplied to one oil chamber of the power cylinder 33, and the working oil from the other oil chamber of the cylinder 33 is discharged to the reservoir 22 via the conduit P4. The power cylinder 33 drives the relay rod 26 in accordance with the supply and discharge of the hydraulic oil to assist the steering of the left and right rear wheels RW1 and RW2.

Further, the rear wheel steering device B has a neutral urging mechanism 34 for urging the left and right rear wheels RW1, RW2 to a neutral state, and a switching valve 35 interposed between the control valve 31 and the power cylinder 33.
The neutral urging mechanism 34 has disc-shaped left and right stopper members 34a, 34b which are fixed to the relay rod 26 so as to be separated from each other. Inside the left and right stopper members 34a, 34b and on the outer periphery of the relay rod 26, the left and right retainers 34c,
34d is assembled so as to be displaceable in the axial direction of the rod 26, and springs 34e that penetrate the rod 26 are assembled so as to urge the left and right retainers 34c, 34d outward at both ends thereof. . Further, the neutral urging mechanism 34 has a left and right overhanging portion 34g, which is extended on the inner periphery of the cylindrical housing 34f at a position such as the distance between the inner sides of the left and right stopper members 34a, 34b.
34h, and the two overhanging portions 34g, 34h prohibit the outward displacement of both retainers 34c, 34d. The switching valve 35 has first to third states, and each state is a spring.
It is controlled by 35a, 35b and electrode solenoids 35c, 35d. When both the electromagnetic solenoids 35c and 35d are in the non-excited state, the valve 35 is controlled to the first state (state shown in FIG. 2) and the control valve for the power cylinder 33 is controlled.
Allows 31 hydraulic fluid to be supplied and discharged. When the electromagnetic solenoid 35c is excited, the valve 35 is controlled to the second state (shifting state to the right in FIG. 2), prohibiting the communication between the control valve 31 and the power cylinder 33, and at the same time the oil chambers of both cylinders 33. It functions to permit the communication between them via the orifice 35d and to return the left and right rear wheels RW1 and RW2 to the neutral state in cooperation with the neutral biasing mechanism 34. When the electromagnetic solenoid 35d is excited, the valve 35 is controlled to the third state (the left shift state in FIG. 2) to prohibit the communication between the control valve 31 and the power cylinder 33, and to prevent the oil chambers of both cylinders 33 of the cylinder 33 from changing. It also prohibits communication between them, and functions to maintain the current steering state of the left and right rear wheels RW1, RW2.

The electric control unit C has a front wheel steering angle sensor 36, a rear wheel steering angle sensor 37 and a vehicle speed sensor 38. Front wheel steering angle sensor 36
Is attached to the steering shaft 12, detects the steering angle δf of the left and right front wheels FW1 and FW2 by measuring the rotation angle of the coaxial shaft 12, and outputs an analog type front wheel steering angle signal representing the steering angle δf. The rear wheel steering angle sensor 37 is attached to the steering shaft 24 and is coaxial.
The steering angle δr of the left and right rear wheels RW1 and RW2 is detected by measuring the rotation angle of 24, and an analog type rear wheel steering angle signal representing the steering angle δr is output. Note that these steering angles δf,
δr becomes “0” when the left and right front wheels FW1, FW2 and the left and right rear wheels RW1, RW2 are in the neutral state, and becomes positive as the left and right front wheels FW1, FW2 and the left and right rear wheels RW1, RW2 are steered in the right (or left) direction. (Or negative) value, and its absolute value becomes large. Further, in the present embodiment, the front and rear wheel steering angle sensors 36, 37
Is configured to detect the steering angles δf and δr by measuring the rotation angles of the steering shafts 12 and 24.
The steering angles δf and δr may be detected by measuring the amount of axial displacement of 4,26. The vehicle speed sensor 38 is provided in the vicinity of the right rear wheel RW2, and picks up the rotation of the rear wheel RW2 to output a vehicle speed signal having a frequency proportional to the rotation speed of the rear wheel RW2, that is, the vehicle speed V. In the present embodiment, the vehicle speed sensor 38 outputs the vehicle speed signal having a frequency proportional to the vehicle speed V by picking up the rotation of the right rear wheel RW2. However, the left rear wheel RW1 or the left and right front wheels FW1 and FW2 are output. The vehicle speed signal may be output by picking up rotation. Alternatively, the rotation of a transmission (not shown) may be picked up and a vehicle speed signal may be output.

A microcomputer 41 is connected to the front wheel steering angle sensor 36, the rear wheel steering angle sensor 37 and the vehicle speed sensor 38. The microcomputer 41 has a read-only memory (hereinafter referred to as ROM) 4 connected in common by a bus 41a.
1b, a central processing unit (hereinafter referred to as CPU) 41c, a writable memory (hereinafter referred to as RAM) 41d, a timer circuit 41f, an input interface circuit 41g, and an output interface circuit 41h. The ROM 41b stores a program corresponding to the flowchart of FIG. 3 and a target steering angle ratio K (FIG. 4) having a characteristic that gradually changes from negative to positive as the vehicle speed V increases in the form of a table. Note that the target steering angle ratio K is negative (or positive) means that the left and right rear wheels RW1, RW2 are steered in the opposite direction (or the same direction) to the left and right front wheels FW1, FW2, that is, in the opposite phase (or the same phase). This means that the steering angle ratio K is "0", which means that the left and right rear wheels RW1, RW2 are not steered regardless of the steering of the left and right front wheels FW1, FW2. The CPU 41c executes the program in response to the closing of the ignition switch, and the RAM 41d temporarily stores the data necessary for executing the program. The timer circuit 41f measures time according to a command from the CPU 41c. The input interface circuit 41g is connected to the front wheel steering angle sensor 36, the rear wheel steering angle sensor 37 and the vehicle speed sensor 38, and converts each analog type steering angle signal from the front wheel steering angle sensor 36 and the rear wheel steering angle sensor 37 into an analog digital signal. In addition to incorporating the analog-to-digital converter, a waveform shaper for shaping the vehicle speed signal from the vehicle speed sensor 38 into a rectangular wave signal is included. Output interface circuit 41
h is a memory circuit that is connected to the step motor 23 and the electromagnetic solenoids 35c and 35d, and stores the digital type control data set by the execution of the program, and outputs a drive pulse signal to the step motor 23 according to the control data. It incorporates a drive pulse generating circuit, an exciting circuit for controlling the electromagnetic solenoids 35c, 35d to be excited or de-excited according to the control data, and the like.

The operation of the embodiment configured as described above will be described with reference to the flowchart of FIG.

When the ignition switch is closed, the CPU 41c starts executing the program in step 50, initializes the RAM 41d, the input interface circuit 41g and the output interface circuit 41h in step 51, and advances the program to step 52. At step 52, the CPU 41c sets the RAM 41d
The old vehicle speed detection data V _OLD , which represents the previous detection value of the vehicle speed V, the old front wheel steering angle detection data δ f _OLD , which represents the previous detection value of the front wheel steering angle δf, and the previous detection of the rear wheel steering angle δr. The old rear wheel steering angle detection data δr _OLD representing the value and the old rear wheel steering angle instruction data δr * _OLD representing the previous instruction value of the rear wheel steering angle δr are stored in the RAM 41d and are detected this time as the vehicle speed V. New vehicle speed detection data V _NEW , front wheel steering angle δf
New front wheel steering angle detection data δf _NEW , which represents the current detected value of
It is updated by new rear wheel steering angle detection data δr _NEW representing the current detected value of the rear wheel steering angle δr and new rear wheel steering angle instruction data δr * _NEW representing the current instruction value of the rear wheel steering angle δr. After the processing of step 52, the CPU 41c, in step 53,
The vehicle speed V is calculated based on the vehicle speed signal supplied from the vehicle speed sensor 38 to the input interface circuit 41g and waveform-shaped by the circuit 41g, and the calculated value is stored in the RAM 41d as new vehicle speed detection data V _NEW , and the front wheel steering is performed. Input interface circuit 41 from the angle sensor 36 and the rear wheel steering angle sensor 37
The front wheel steering angle signal and the rear wheel steering angle signal supplied to the g and converted into digital signals by the same circuit 41g are stored in the RAM 41d as new front wheel steering angle detection data δf _NEW and new rear wheel steering angle detection data δr _NEW . . After step 53, CPU41c
Is the stored new vehicle speed detection data V in step 54.
Target rudder angle ratio table in ROM41b based on _NEW (Fig. 4)
The target steering angle ratio K (V _NEW ) corresponding to the vehicle speed V is determined with reference to the determined target steering angle ratio K (V _NEW ) and the new front wheel steering angle data δf _NEW stored in the RAM 41d. Multiply, and the multiplied value K (V _NEW ) · δf _NEW is added to the new rear wheel steering angle instruction data δ.
It is stored in RAM41d as r * _NEW . These steps 5
By the processes 2 to 54, old and new vehicle speed detection data V _NEW , V _OLD , old and new front wheel steering angle detection data δf _NEW , δf _OLD , old and new rear wheel steering angle detection data δr _NEW , δr _OLD, and old and new rear wheel steering angle instruction data δr * _NEW and δr * _OLD are updated respectively.

Next, in step 55, the CPU 41c determines, for example, (1) below.
By detecting the presence / absence of a failure in the steering control system for the left and right rear wheels RW1, RW2 as described in (3), the rear wheels RW1, RW2 can be detected.
It is determined whether or not the steering wheel is normally steered.

(1) When the old and new vehicle speed detection data V _NEW , V _OLD , the old and new front wheel steering angle detection data δf _NEW , δf _OLD, and the old and new rear wheel steering angle detection data δr _NEW , δr _OLD each show an abnormally large value, the steering control is performed. It is determined that there is an abnormality in one of the lines.

(2) Differences between old and new vehicle speed detection data V _NEW , V _OLD , old and new front wheel steering angle detection data δf _NEW , δf _OLD, and old and new rear wheel steering angle detection data δr _NEW , δr _OLD When the value is too large to be obtained, it is determined that there is an abnormality in any of the steering control systems.

(3) When the difference between the new rear wheel steering angle detection data δr _NEW and the old rear wheel steering angle instruction data δr * _OLD is larger than the predetermined value, the left and right rear wheels RW1 and RW2 are normally steered by the step motor 23. If not, it is determined that the steering control system is abnormal.

In this step 55, the various sensors 36 to 38, the step motor 23, etc. are all normal and there is no abnormality in the steering control system of the left and right rear wheels RW1, RW2, that is, the rear wheels RW1, RW2 are normally steered. If it is determined that the program is present, the CPU 41c determines “YES” in step 55 and executes the program in step 5
Proceed to 6.

In step 56, the CPU 41c causes the new rear wheel steering angle instruction data δr * stored in the RAM 41d by the processing in step 54 above.
The difference between the _NEW and the new rear-wheel steering angle detection data [delta] r _NEW stored in RAM41d by the processing in step 53 data [delta] r * _NEW -
δr _NEW is calculated and error data δr * _NEW −δr _NEW is output to the output interface circuit 41h. The circuit 41h stores the difference data δr * _NEW −δr _NEW , and at the same time stores the difference data δr * _NEW −δr _NEW in correspondence with the step motor 23.
A drive pulse signal for rotationally driving the motor is output to the motor 23. The step motor 23 is driven by this drive pulse signal to move the steering shaft 24 to the difference data δr * _NEW −δr.
Rotate only by the angle corresponding to _NEW . At this time, the electromagnetic solenoids 35c and 35d are in the non-excited state, and the switching valve 35 is set to the first state by the springs 35a and 35b to allow the communication between the control valve 31 and the power cylinder 33. The cylinder 33 cooperates with the control valve 31 to assist the steering of the left and right rear wheels RW1 and RW2 by the step motor 23, and the rear wheels RW1 and RW2 have the difference data δr * _NEW −δ.
r Only steered by _NEW . As a result, the steering angles δr of the left and right rear wheels RW1 and RW2 correspond to the new rear wheel steering angle instruction data δr *. At this time, the right stopper member 34b (or the left stopper member 34a) causes the right retainer 34d (or the left retainer 34c) to move in the left direction (or the right direction) along with the displacement of the relay rod 26 in the left direction (or the right direction). Since the left retainer 34c (or the right retainer 34d) is prevented from being displaced in the left direction (or the right direction) by the left overhanging portion 34g (or the right overhanging portion 34h), the spring 34e is compressed.

After the processing of step 56, the CPU 41c resets the timer circuit 41f and activates the circuit 41f in step 57, and then stops the progress of the program until the circuit 41f finishes measuring the minute time Δt. That is, after the reset,
CPU41c has a minute time measured by the timer circuit 41f.
Continuing to determine whether or not t has been reached, the measured value is
When t is reached, the program is returned to step 52, and the circulation process consisting of steps 52 to 57 is continuously executed thereafter. As a result, as long as there is no abnormality in the steering control system of the left and right rear wheels RW1 and RW2 and proper steering of the rear wheels RW1 and RW2 is ensured, the same rear wheels RW1 and RW2 have steering angles δf of the left and right front wheels FW1 and FW2. Depending on the vehicle speed V, the front wheels FW1 and FW2 are steered in opposite phase or in phase.

The left and right rear wheels RW1, RW formed by the processing of steps 52 to 57
If an abnormality occurs in the steering control system of the left and right rear wheels RW1, RW2 during the steering control of 2, the CPU 41c determines "NO" in step 55 and advances the program to the abnormality processing routine including steps 60 to 67. . In this abnormality processing routine,
Since the control method differs depending on the steering state of the left and right rear wheels RW1 and RW2 at the time of abnormality, the operation of the present embodiment will be described below for each type of the steering state.

(1) When the steering amount of the left and right rear wheels RW1, RW2 is small In this case, the absolute value of the new rear wheel steering angle detection data δr _NEW |
Since δr _NEW | is less than a predetermined small steering angle value ε (for example, about 0.5 degree), the CPU 41c makes a “YES” determination at step 60 based on the condition | δr _NEW | ≦ ε, and proceeds to step 63. The left and right rear wheels RW1 and RW2 are returned to the neutral state. That is, CPU41c
Outputs the control data for controlling the electromagnetic solenoid 35c to the output interface circuit 41h in step 63. The circuit 41h stores this control data and at the same time,
The electromagnetic solenoid 35c is excitation-controlled based on the same data.
Due to the dust excitation control, the switching valve 35 shifts to the right in FIG. 2 and is set to the second state, prohibiting the communication between the control valve 31 and the power cylinder 33 and communicating between the left and right oil chambers of the cylinder 33. Through the orifice 35d.
At this time, the relay rod 26 is displaced to the left (or to the right) as the left and right rear wheels RW1 and RW2 are steered to the right (or to the left), and the right stopper member 34b and the right retainer 34d (or the left stopper member) are displaced. 34a and the left retainer 34c) are displaced leftward (or rightward), the spring 34e causes the right retainer 34d (or left retainer 34c) to press in the rightward direction (or leftward direction) and thus the right stopper member 34b. (Or the left stopper member 34c) and the relay rod 26 are pressed rightward (or leftward). By this pressing, the hydraulic oil in the right oil chamber (or left oil chamber) of the power cylinder 33 gradually flows into the left oil chamber (or right oil chamber) via the orifice 35d, and the relay rod 26 moves to the right direction (or left direction). ) Is gradually displaced to the left and right rear wheels
RW1 and RW2 are steered leftward (or rightward), that is, in the neutral direction. When the relay rod 26 returns to the neutral position, the right retainer 34d (or the left retainer 34c) contacts the right overhanging portion 34h (or the left overhanging portion 34g), and the displacement of the rod 26 stops. As a result, the left and right rear wheels R1W, RW2 return to the neutral state. After the processing of step 63, the CPU 41c causes step 64
The program execution is completed at, and after that, the left and right rear wheels RW1, RW
2 is maintained in a neutral state, and the vehicle can run as a conventional two-wheel steering vehicle. In addition to the above embodiment,
By providing a lock device that mechanically prohibits the rotation of the steering shaft 24 or the displacement of the relay rod 26, after the neutral return, the lock device is operated to more firmly perform the neutral return of the left and right rear wheels RW1, RW2. Good to do.

(2) When the steering amounts of the left and right rear wheels RW1, RW2 are large but the steering amounts are in a decreasing state In this case, the absolute value of the new rear wheel steering angle detection data δr _NEW |
δr _NEW | is larger than the above steering angle value ε and the absolute value of new rear wheel steering angle instruction data δr * _NEW | δr * _NEW | is the absolute value of old rear wheel steering angle instruction data δr * _OLD | δr * _OLD | Since it is small, the CPU 41c determines “NO” based on the condition of | δr _NEW | ≦ ε in step 60, and | δr * in step 61.
_{Based on} the condition _NEW | ≧ | δr * _OLD |, “NO” is determined, and in step 65, the left and right rear wheels RW1, RW2 are gradually returned to the neutral state. That is, the CPU 61c executes the same processing as in the above step 63 in step 65 to restore the left and right rear wheels RW1, RW2 to the neutral state. After the processing of step 65, the CPU 41c advances the program to step 57, delays the progress of the program by a minute time Δt in step 57, and then returns the program to step 52. After that, as long as this state continues, CPU4
In step 1c, the circulation process of steps 52 to 55, 60, 61, 65, 57 is executed to gradually return the left and right rear wheels RW1, RW2 to neutral. When the absolute value | δr | of the steering angles δr of the left and right rear wheels RW1 and RW2 becomes less than or equal to the absolute value ε, the CPU 41c determines “YES” in step 60 as in the above case, and continues in step 63. And control the left and right rear wheels RW1, RW2 to return to the neutral position,
In step 64, the execution of the program ends. As described above, when the steering amounts of the left and right rear wheels RW1 and RW2 are large but the steering amounts are also in the decreasing direction, steps 52 to 55, 60, 61, 65, 57
The left and right rear wheels RW1 and RW2 are gradually controlled to return to the neutral state by the circulation processing and the processing of steps 52 to 55, 60 and 64. Since the neutral return in this case matches the steering tendency of the left and right rear wheels RW1, RW2 before the abnormality occurred, even if the steering amount of the rear wheels RW1, RW2 is large, the steering of the rear wheels RW1, RW2 is not It matches the driver's will, and it is "0" from the state where the steering amount is large.
Even if it changes to, it does not deteriorate the maneuverability of the vehicle.

(3) When the steering amounts of the left and right rear wheels RW1 and RW2 are large and the steering amounts do not tend to decrease In this case, the absolute value of the new rear wheel steering angle detection data δr _NEW |
δr _NEW | is larger than the above steering angle value ε, and the absolute value of new rear wheel steering angle instruction data δr * _NEW | δr * _NEW | is the absolute value of old rear wheel steering angle instruction data δr * _OLD | δr * _OLD | Therefore, the CPU 41c determines “NO” based on the condition of | δr _NEW | ≦ ε in step 60, and | δr * _NEW | in step 61.
If YES is determined based on the condition of ≧ | δr * _OLD |, the absolute value of new rear wheel steering angle instruction data δr * _NEW | δr * _NEW | is changed to new rear wheel steering angle instruction data δr in step 62. the absolute value of the _NEW | _{δr NEW} | was subtracted subtraction value _{| δr * NEW | - | δr} NEW |
Is greater than or equal to a predetermined small steering angle value α (for example, about 0.5 degrees).

In this determination, the subtracted value | δr * _NEW | − | δr _NEW |
Is a steering value α or more, that is, when the new rear wheel steering angle instruction data δr * _NEW indicates a value for steering the left and right rear wheels RW1, RW2 by a steering value α or more larger than in the current steering state,
The CPU 41c makes a “YES” determination at step 62, and at step 66 controls the left and right rear wheels RW1, RW2 to maintain the current steering state. That is, the CPU 41c outputs the control data for controlling the excitation of the electromagnetic solenoid 35d to the output interface circuit 41h in step 66. The circuit 41h stores this control data and, at the same time, controls the excitation of the electromagnetic solenoid 35d based on the data. Due to this excitation control, the switching valve 35 shifts to the left in FIG. 2 and is set to the third state, prohibiting the communication between the control valve 31 and the power cylinder 33 and communicating between the left and right oil chambers of the power cylinder 33. Is also prohibited. As a result, the hydraulic oil in the left and right oil chambers of the cylinder 33 is confined in each oil chamber, and the displacement of the relay rod 26 is prohibited, so that the current steering state of the left and right rear wheels RW1, RW2 is maintained. After the processing of step 66, the CPU 41c advances the program to step 57, delays the progress of the program by a minute time Δt at step 57, and then returns the program to step 52. After that, as long as this state continues, the CPU 41c executes the circulation process of steps 52 to 55, 60 to 62, 66, 57 and keeps the current steering state of the left and right rear wheels RW1, RW2.

In addition, in the determination of step 62, the subtraction value | δr
* _NEW |-| δr _NEW | is less than the steering angle value α, that is, the new rear wheel steering angle instruction data δr * _NEW is the left and right rear wheels RW1, RW2.
If the value indicates that the steering wheel is steered in the neutral direction from the current steering state, or if it is the value that steers in the range smaller than the steering angle value α even when the steering wheel is in the opposite direction to the neutral direction, the CPU 41c determines `` N
"O" is determined, and in step 67, the left and right rear wheels RW1 and RW2 are steered to the steering angle represented by the new rear wheel steering angle instruction data δr * _{NEW, and} then controlled to maintain the steering angle. . That is, the CPU 41c executes the above step in step 67.
The left and right rear wheels RW1 and RW2 are steering-controlled in the same manner as the process of 56, and the steering angle δr of the left and right rear wheels RW1 and RW2 by the steering control is detected by the rear-wheel steering angle sensor 37, and the detected rear wheels are detected. The steering control is executed until the steering angle δr matches the value represented by the new rear wheel steering angle instruction data δr * _NEW ,
When they match, the steering states of the left and right rear wheels RW1, RW2 are held and controlled in the same manner as the processing of step 66. as a result,
The left and right rear wheels RW1 and RW2 are steered to the steering angle represented by the new rear wheel steering angle instruction data δr * _NEW , and the steering state is maintained. After the processing of step 67, the CPU 41c returns the program to step 52 through the processing of step 57, and if the steering amounts of the left and right rear wheels RW1 and RW2 are still large and the steering amounts do not tend to decrease, steps 52 to 55, 60 to 62,66 (67), 57
The left and right rear wheels RW1 and RW2 are controlled to be steered or retained by performing the circulation processing of. In addition, during the circulation process,
If the steering amount of the left and right rear wheels RW1, RW2 becomes smaller or the steering amount tends to decrease, as described above, steps 52 to 55, 6 are performed.
The left and right rear wheels RW1, RW2 are returned to the neutral state by the processing of 0, 63 or the processing of steps 52 to 55, 60, 61, 65, 57. As described above, when the steering amounts of the left and right rear wheels RW1, RW2 are large and the steering amounts do not tend to decrease, the steering amounts of the left and right rear wheels RW1, RW2 are controlled by the processing of steps 62 and 66 so as not to increase. At the same time, since the steering amounts of the rear wheels RW1 and RW2 are gradually reduced by the processing of steps 62 and 67 so as not to suddenly change to “0”, the steering amounts of the left and right rear wheels RW1 and RW2 are suddenly changed. Deterioration of controllability and stability of the vehicle is prevented.

As can be understood from the above operation description, according to the above-described embodiment, when an abnormality occurs in the steering control system of the left and right rear wheels RW1, RW2, the processing of steps 60 to 62 causes the left and right rear wheels RW1, RW2 to be processed.
The steering state of the vehicle is detected, and steps 63, 6 are detected according to the detection result.
Step motor 23 and switching valve 3 by the processing of 5 to 67
Since the left and right rear wheels RW1, RW2 are selectively returned to neutral or the current steering state of the rear wheels RW1, RW2 is maintained and controlled by controlling the left and right rear wheels RW1, RW2, Is steered in reverse, and the rear wheels RW1 and RW2 do not change suddenly, and the running stability of the vehicle is better maintained.

[Brief description of drawings]

1 is a diagram corresponding to the configuration of the invention described in the claims, FIG. 2 is an overall schematic diagram of a vehicle according to an embodiment of the present invention, and FIG. 3 is executed by the microcomputer of FIG. 4 and FIG. 4 are diagrams showing the characteristics of the steering angle ratio with respect to the vehicle speed. Explanation of symbols A ... front wheel steering device, B ... rear wheel steering device, C ... electric control device, FW1, FW2 ... front wheels, RW1, RW2 ... rear wheels, 23 ...
Step motor, 31 ... Control valve, 33 ... Power cylinder, 34 ... Neutral biasing mechanism, 35 ... Switching valve, 36 ...
… Front wheel steering angle sensor, 37 …… Rear wheel steering angle sensor, 38 ……
Vehicle speed sensor, 41 ... Microcomputer.

Claims (1)

(57) [Claims] 1. A front-wheel steering device for steering front wheels, a rear-wheel steering device for steering rear wheels, and a rear-wheel steering device for controlling front wheels, for steering rear wheels in response to front-wheel steering. In a front and rear wheel steering vehicle including steering control means for controlling, a neutral return mechanism incorporated in the rear wheel steering device for returning the rear wheels to a neutral state, and a steering change of the rear wheels incorporated in the rear wheel steering device. A steering holding mechanism that prohibits and holds the current steering state, steering state determination means that determines whether the steering amount of the rear wheels is in a decreasing state or an increasing state, and an abnormality that detects an abnormality related to steering control of the rear wheels. Detection means, and when the abnormality is not detected by the abnormality detection means, the steering control means allows the steering control of the rear wheels in response to the steering of the front wheels, and the abnormality detection means detects the abnormality and the steering state determination means. By the rear wheel When it is determined that the steering amount is in a reduced state, the neutral return mechanism is controlled to return the rear wheels to the neutral state, and an abnormality is detected by the abnormality detection means and steering of the rear wheels by the steering state determination means. For rear wheel steering in a front and rear wheel steering vehicle, characterized in that selection control means for controlling the steering holding mechanism to hold the current steering state of the rear wheels when it is determined that the amount is in an increasing state is provided. Control device.