JPH0829710B2 - 4-wheel steering system for vehicles - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a four-wheel steering device that steers the front and rear wheels of a vehicle, and particularly to an abnormality in a control system that controls the steering ratio of the front and rear wheels. Regarding measures against time.

(Prior Art) In recent years, a four-wheel steering system for a vehicle of this type has been drawing attention as a vehicle that can greatly change the traveling characteristics of the vehicle. As one example thereof, the present applicant has previously proposed, in Japanese Patent Laid-Open No. 60-193770, one in which the steering ratio of the front and rear wheels is variably controlled using the vehicle speed as a parameter.

That is, at low vehicle speeds, the steering ratios of the front and rear wheels are controlled in opposite phases, the steering characteristics are oversteered to improve the turning performance of the vehicle, while at high vehicle speeds the steering ratios are kept in phase and steering The characteristic is an understeer characteristic to ensure the running stability of the vehicle.

More specifically, a swing member that is connected to a rear wheel steering mechanism that steers the rear wheels of a vehicle and is movable in a predetermined movement axis direction and a swing center located on the movement axis line of the movement member. A swinging arm called a swash plate that moves, a connecting member that connects the swinging arm and the moving member, and a front wheel steering mechanism that steers the front wheels of the vehicle, and the connecting member moves the moving member. A rotation imparting arm that rotates around the axis is provided,
The steered ratio of the front and rear wheels is changed by changing the inclination angle of the swing center line of the swing arm with respect to the moving axis of the moving member by a stepping motor.

(Problems to be Solved by the Invention) In such a four-wheel steering system, if an abnormality such as a failure occurs in the control system for controlling the turning ratio, normal four-wheel steering control may not be performed. There is For example, if a stepping motor is used to change the turning ratio of the front and rear wheels as in the above proposed example, the stepping motor will be removed when an excessive load is applied by the stick of the gear mechanism that transmits the rotational force of the motor. Adjustment state (idling state)
Therefore, the target turning ratio cannot be accurately obtained. Therefore, in order to ensure the running safety of the vehicle, it is essential to establish a fail-safe system in the event of such an abnormality.

Therefore, the hydraulic cylinder that steers the rear wheels is provided with a centering mechanism that holds the steered angle of the rear wheels at zero, and the rear wheels are steered against the centering mechanism. A hydraulic valve system for supplying pressure oil to both hydraulic chambers is provided with a communication valve for connecting the hydraulic chambers of the hydraulic cylinder to each other to prohibit the operation of the hydraulic cylinders, and the control system of the turning ratio control means has failed. At times, it is conceivable to output the operation signal to the communication valve to prohibit the operation of the hydraulic cylinder and forcibly hold the steering ratio at zero by the centering mechanism.

However, in that case, if the communication valve is stuck by a stick or the like, the steering ratio may not be corrected to zero even though the operating signal is output to the communication valve. Therefore, further improvements are expected in order to secure even higher safety.

(Objects of the Invention) The present invention has been made in view of the above problems, and an object of the present invention is not only to activate the fail-safe system by the communication valve when the four-wheel steering control system is abnormal as described above, but also to By keeping the steering ratio fixed on the safe side, it is possible to suppress the unstable behavior of the vehicle even if it is impossible to correct the two-wheel steering state due to malfunction of the communication valve. Therefore, it is to further enhance the safety in the fail-safe mode.

(Means for Solving Problems) In order to achieve this object, the solving means taken by the present invention is to correct not only the operation of the communication valve but also the steering ratio to the same phase side when the control system is abnormal. The correction signal output is continuously output.

Specifically, as shown in FIG. 1, as a four-wheel steering system for a vehicle in which the front and rear wheels are simultaneously steered, the steering ratio of the front and rear wheels is controlled based on a preset steering ratio characteristic. And a hydraulic cylinder 17 for steering the rear wheels against the centering mechanism 17d, which has a built-in centering mechanism 17d for turning the steering angle of the rear wheels to zero. Is.

Then, in the hydraulic piping system that supplies hydraulic pressure to both hydraulic chambers 17b and 17c of the hydraulic cylinder 17, both hydraulic chambers of the hydraulic cylinder 17 are
A communication valve (28) is provided which connects 17b, 17c to each other and prohibits the operation of the hydraulic cylinder (17).

Further, an abnormality detecting means 105 for detecting an abnormality in the control system of the turning ratio control means 104 is provided.

Further, when the output of the abnormality detecting means 105 is received and the control system of the turning ratio control means 104 is abnormal, the communication valve 28
The abnormal-time operating means 106 is provided for outputting the operation signal to the steering ratio control means 104 and outputting a correction signal for turning the steering ratio to the same phase side.

(Operation) With the above configuration, in the present invention, when the vehicle is traveling, the steering ratio of the front and rear wheels of the vehicle by the steering ratio control means 104 becomes the target steering ratio determined based on the steering ratio characteristics. Controlled as. Then, when an abnormality occurs in the control system of the turning ratio control means 104, the abnormal state is the abnormality detection means 10
5, the abnormal-time operating means 106 receiving the output signal of the abnormality detecting means 105 outputs an operating signal to the communication valve 28 to supply the hydraulic oil to both hydraulic chambers 17b, 17c of the hydraulic cylinder 17. The hydraulic cylinder 17 is stopped, the operation of the hydraulic cylinder 17 is prohibited, and the steering angle of the rear wheels is maintained at zero. At the same time, a correction signal for making the steering ratio on the same phase side is output from the abnormality operating means 106 to the steering ratio control means 104. Therefore,
Due to the parallel output of the operation signal to the communication valve 28 and the output of the correction signal to the turning ratio control means 104, by any chance,
Even if the communication valve 28 is in a malfunctioning state, as long as the actuator in the steering ratio control means 104 is normal, the steering ratio is fixedly held on the same phase side, which further improves the running safety of the vehicle. It can be further improved.

(Embodiment) An embodiment of the present invention will be described below with reference to the drawings starting from FIG.

In FIG. 2, 1 _{L to} 2 _R are the four wheels of the vehicle, the left and right front wheels 1 _L , 1 _R are the front wheel steering mechanism 3, and the left and right rear wheels 2 _L , 2 _R are the rear wheel steering. Mechanisms 12 are linked together.

The front wheel steering mechanism 3 includes a pair of left and right knuckle arms 4
_L and 4 _R and tie rods 5 _L and 5 _R, and the left and right tie rods 5
_The relay rod 6 connects _L and 5 _{R to} each other. Also,
A steering wheel 10 is linked to the front wheel steering mechanism 3 via a rack and pinion type steering mechanism 7. That is, a rack 8 is formed on the relay rod 6, and a pinion 9 meshing with the rack 8 is attached to the lower end of a steering shaft 11 having a steering wheel 10 connected to the upper end thereof. The left and right front wheels 1 _L and 1 _R are steered according to the operation.

On the other hand, the rear wheel steering mechanism 12 is similar to the front wheel steering mechanism 3 in that the left and right knuckle arms 13 _L and 13 _R and the tie rod 1 are used.
4 _L and 14 _R , a relay rod 15 that connects the tie rods 14 _L and 14 _{R to} each other, and a hydraulic power steering mechanism 16. The power steering mechanism 16 is
The power cylinder 17 is fixed to the vehicle body and serves as a hydraulic cylinder using the relay rod 15 as a piston rod. Inside the power cylinder 17, two hydraulic chambers 17b, 1 are provided by a piston 17a integrally attached to the relay rod 15.
7c, the hydraulic chambers 17b, 17c in this cylinder 17
Control valve 2 via hydraulic lines 18 and 19 respectively
Connected to 0. In addition, the control valve 20 includes an oil supply pipe 22 and an oil discharge pipe 23 that reach the reserve tank 21.
Are connected to each other, and the oil supply pipe 22 is provided with a hydraulic pump 24 driven by an in-vehicle engine (not shown). The control valve 20 is composed of a known spool valve type valve,
A tubular valve casing 20a integrally attached to 15 via a connecting member 25, and a spool valve (not shown) fitted in the valve casing 20a are provided. Then, according to the movement of the spool valve of the control valve 20, one hydraulic chamber 17b (17c) of the power cylinder 17
By supplying pressure oil from the hydraulic pump 24 to the power cylinder 17, the power cylinder 17 is operated to assist the driving force for the relay rod 15, and the rear wheels 2 _L , 2 _R are substantially steered. There is.

Further, in the power cylinder 17, a pair as a centering mechanism for urging the relay rod 15 to a neutral position (position where the turning angles θ _{R of the} rear wheels 2 _L and 2 _R become zero) via a piston 17a. The return springs 17d and 17d of the power cylinder 17 are compressed (when one of the hydraulic chambers 17
Return springs 17d, 17 when pressure oil is supplied to b (17c))
The rear wheels 2 _L and 2 _R are steered against the biasing force of d. Also, the hydraulic pipes 18 and 19 are respectively the hydraulic pipes 2
A normally closed solenoid valve that forms a communication valve via 6,27
28 (fail-safe solenoid valve), and when the solenoid opening / closing valve 28 is opened, both hydraulic chambers 17b, 17c of the power cylinder 17 are communicated with each other so that both hydraulic pressures are the same, and the power cylinder 17 as well as prohibiting the operation, two-wheel steering characteristics of the vehicle the return spring 17d, positioned piston 17a to the neutral position by the biasing force of the 17d, as always theta _R = 0 the turning angle theta _R of the rear wheels 2 _L, 2 _R It is configured to be in a steering state.

The relay rod 6 of the front wheel steering mechanism 3 has another rack other than the rack 8 constituting the steering mechanism 7.
29 is formed, a pinion 30 attached to the front end of a rotary shaft 31 extending in the vehicle front-rear direction is meshed with the rack 29,
The rear end of the rotary shaft 31 is linked to the rear wheel steering mechanism 12 via a steering ratio control mechanism 32.

The steering ratio control mechanism 32, as shown in detail in FIG.
A control rod 33 is held slidably on the moving axis l ₁ in the vehicle width direction with respect to the vehicle body, and one end of the control rod 33 is connected to the spool valve of the control valve 20. Further, the turning ratio control mechanism 32 includes a swing arm 36 whose base end is swingably supported by a U-shaped holder 34 via a support pin 35, and the holder 34 is a casing fixed to the vehicle body ( (Not shown) is rotatably supported via a support shaft 37 having a rotation axis l ₂ orthogonal to the movement axis l ₁ of the control rod 33. The support pin 35 of the swing arm 36 is located at the intersection of the axes l ₁ and l ₂ and extends in the direction orthogonal to the rotation axis l ₂ , and the holder 34
Is rotated about the support shaft 37 (rotation axis l ₂ ), the tilt angle formed between the support pin 35 at the tip and the movement axis l ₁ of the control rod 33, that is, swinging around the support pin 35. The tilting angle of the swing locus surface of the arm 36 with respect to a surface (hereinafter, referred to as a reference surface) orthogonal to the movement axis l ₁ is changed.

Further, one end of a connecting rod 39 is connected to the tip of the swing arm 36 via a ball joint 38, and the other end of the connecting rod 39 is connected to the other end of the control rod 33 via a ball joint 40. The control rod 33 is displaced in the left-right direction according to the displacement of the tip end of the swing arm 36 in the left-right direction in FIG.

The connecting rod 39 is slidably supported by a rotation imparting arm 41 via a ball joint 42 at a portion near the ball joint 38. The rotation imparting arm 41 is integrally provided with a large-diameter bevel gear 44 rotatably supported on the moving axis l ₁ via a support shaft 43. A bevel gear 45 attached to the end is meshed, and the rotation of the steering wheel 10 is transmitted to the rotation imparting arm 41.
Therefore, the rotation imparting arm 41 and the connecting rod 39 rotate about the movement axis l _{1 by} an amount corresponding to the rotation angle of the steering wheel 10, and the swing arm 36 accordingly.
When the axis of the pin 35 coincides with the moving axis l ₁ of the control rod 33, the ball joint 38 at the tip of the swing arm 36 swings on the reference plane. Just move the control rod 33
Is held stationary, but when the axis line of the pin 35 is inclined with respect to the movement axis line l _{1 and} the swing locus surface of the swing arm 36 is deviated from the reference plane, the swing arm 36 with the pin 35 as the center. 3, the ball joint 38 is displaced in the left-right direction in FIG. 3, and this displacement is transmitted to the control rod 33 via the connecting rod 39.
Moves along the moving axis l ₁ , and the control valve 2
It is configured to operate 0 spool valves. That is, even if the swing angle of the swing arm 36 about the axis of the support pin 35 is the same, the control rod 33
The displacement in the left-right direction changes with changes in the inclination angle of the pin 35, that is, the rotation angle of the holder 34.

A sector gear 46 as a worm wheel is attached to the support shaft 37 of the holder 34 in order to change the inclination angle of the support pin 35 with respect to the moving axis l _1, that is, the inclination angle of the holder 34 with respect to the reference plane.
A worm gear 48 on a rotating shaft 47 is meshed with the. A bevel gear 49 is attached to the rotating shaft 47, and a bevel gear 49 has a stepping motor as an actuator.
The bevel gear 50 mounted on the output shaft 51a of the gear 51 is meshed, and by operating the stepping motor 51 to rotate the sector gear 46, the inclination angle of the holder 34 with respect to the reference plane is changed to change the rear wheel _2L. , 2 _R Steering angle θ _R, that is, front and rear wheels 1 _L , 2
The steering ratio of _L (1 _R , 2 _R ) (rear wheel steering angle θ _R / front wheel steering angle θ _F ) is controlled, and, for example, the sector gear 46 has its center line as the center line of the rotary shaft 47 of the worm gear 48. Neutral position at right angle (at this time, the ball joint 38 at the tip of the swing arm 36 rotates on the reference plane, and the steered angle θ _R of the rear wheels 2 _L , 2 _R becomes θ _R = 0) When the vehicle is rotated in one direction from, the steering ratios of the front and rear wheels 1 _L , 2 _L are controlled in the opposite phase in which the rear wheels 2 _L , 2 _R face in the opposite direction to the front wheels 1 _L , 1 _R , while When rotated in the other direction, the steering ratio is controlled so that the rear wheels 2 _L , 2 _R face the same direction as the front wheels 1 _L , 1 _{R in the} same phase.

Further, on the support shaft 37 of the holder 34, there is provided a turning device composed of a potentiometer as a turning ratio detecting means for detecting the actual turning ratio R controlled by the stepping motor 51 based on the turning angle of the sector gear 46. A steering ratio sensor 101 is provided. The casing that supports the holder 34 includes a sector gear 46 on the left and right sides of the sector gear 46.
The stopper members 52 and 53 on the opposite phase side and the same phase side, which are pins for restricting the rotation range of the sector gear 4 are attached.
The control position of the stepping motor 51 when 6 contacts the stopper member 52 on the opposite phase side is set to its initial position. Further, in FIG. 3, 54 is a rear wheel steering mechanism.
This is a rod stopper that regulates the maximum movement range of the relay rod 15 in 12.

The stepping motor 51 and the solenoid on-off valve 28 are the control unit 10 including a microcomputer.
Configured to be actuated by the output from 0,
This control unit 100 has a vehicle traveling speed V
Vehicle speed sensor 102 for detecting (vehicle speed), the hydraulic pipe 26,
The respective detection signals of the hydraulic pressure sensor 103 for detecting the hydraulic pressure in 27 and the turning ratio sensor 101 are input. Then, in the control unit 100, the signal of the vehicle speed V detected by the vehicle speed sensor 102 is input, the detected vehicle speed V is collated with the preset turning ratio characteristic, and it is determined in accordance with the vehicle speed V. A stepping motor is set so that the target turning ratios of the front and rear wheels 1 _L , 2 _L (1 _R , 2 _R ) are set and the turning ratios of the front and rear wheels 1 _L , 2 _L become the target turning ratio set above. 51 by driving the rotates the sector gear 46, by changing the inclination angle with respect to the reference surface of the holder 34, by changing the turning angle theta _R of the rear wheels 2 _L, 2 _R, front and rear wheels 1 _L, 2 _The turning ratio control means 104 is configured to variably control the _L turning ratio to a target value.

In addition, as shown in FIG. 4 and FIG. 5, the steering ratio characteristic is such that the steering ratios of the front and rear wheels 1 _L and 2 _L change depending on the vehicle speed V.
When the vehicle speed V is low, the rear wheels 2 _L , 2 _R are steered in the opposite direction to the front wheels 1 _L , 1 _R in order to improve the turning performance of the vehicle. When the vehicle speed V reaches a predetermined value while the ratio becomes negative, the steering ratio becomes zero and the front wheels 1 _L , 1 _R
The steering angle θ _{R of the} rear wheels 2 _L , 2 _R is maintained at θ _R = 0 regardless of the turning of the vehicle, and the vehicle enters the normal two-wheel steering state. When driving at a higher speed, the rear wheels 2 _L , 2 _R are in the same direction as the front wheels 1 _L , 1 _{R in} order to improve the grip of the rear wheels 2 _L , 2 _R during cornering and improve running stability. That is, the steering ratio is set to be positive by steering in the same phase. Fig. 4 shows the steering wheel steering angle (steering wheel) when the vehicle speed changes.
FIG. 5 shows the characteristics of the rear wheel steering angle with respect to the turning angle of 10), and FIG. 5 shows the steering ratio characteristics with respect to the vehicle speed at the predetermined steering wheel steering angle.

The output signal of the steering ratio sensor 101 is input as a feedback signal, and the feedback signal controls the stepping motor 51 so that the actual steering ratio matches the target steering ratio. There is. Further, when the actual turning ratio controlled by the stepping motor 51 does not match the target turning ratio, it is considered that the stepping motor 51 is in an abnormal state of so-called step-out (idling), and the fail-safe mode is set. Is configured to transition to.

Here, in the microcomputer of the control unit 100, the stepping motor 51 as described above is used.
FIG. 6 shows a signal processing procedure performed for controlling the operation of the stepping motor 51 and the electromagnetic opening / closing valve 28 when the fail-safe mode is entered due to an abnormality in the control system of the steering ratio control means 104 such as step out of FIG. A brief description will be given based on.

First, in the first step S ₁ , it is determined whether or not an abnormal state such as a failure has occurred. If the determination is NO, that is, there is no abnormality, the process proceeds to step S ₂ and normal control is performed.

On the other hand, when the determination by the abnormality such as failure becomes to YES, by communicating the both hydraulic chambers 17b, 17c between the electromagnetic on-off valve 28 (fail-safe solenoid valve) and by ON-operation power cylinder 17 in step S _3, The operation of the power cylinder 17 is prohibited. As the power cylinder 17 stops operating, the turning angles θ _R of the rear wheels 2 _L , 2 _R are kept at θ _R = 0 by the biasing forces of the return springs 17d, 17d as the centering mechanism, and the steering characteristics of the vehicle are maintained. Is forcibly maintained in the two-wheel steering characteristic. After that, the routine proceeds to step S ₄ , where it is judged whether the hydraulic pressure in the hydraulic pipes 26, 27 detected by the hydraulic sensor 103 is higher than a predetermined value A or not. here,
When it is determined to be NO due to the decrease in the hydraulic pressure to the predetermined value A or less, the electromagnetic opening / closing valve 28 operates normally and the power cylinder 17
It is considered that the pressure in both hydraulic chambers 17b, 17c has dropped, and the control is ended.

However, when the detected hydraulic pressure is higher than the predetermined value A, it is considered that the power cylinder 17 has malfunctioned such as a stick, and the process proceeds to steps S ₅ and S ₆ where the steering ratio is the same as the stepping motor 51. The signal on the phase side is continuously output for a fixed time, and the control is ended after the elapse of the fixed time.

Therefore, in this embodiment, the step S ₁ in the control routine described above, the abnormality detecting means 105 an abnormality in the control system is to detect that it has occurred in the steering ratio control unit 104 is configured.

Pursuant to the step S ₃ to S _6, the abnormality detecting means
When the control system of the turning ratio control means 104 receives an output of 105 and outputs an operation signal to the electromagnetic on-off valve 28 (communication valve), both hydraulic pressures of the power cylinder 17 are output after the operation signal is output. When the hydraulic pressure in the chambers 17b, 17c has not dropped below a predetermined value A, a correction signal for making the steering ratio on the same phase side is output to the stepping motor 51 of the steering ratio control means 104 for a certain period of time. The abnormal-time operating means 106 is configured.

 Next, the operation of the above embodiment will be described.

First, when the ignition key switch is turned on in order to drive the vehicle which is in the stopped state, the control initial position of the stepping motor 51 is positioned accordingly. After that, when the vehicle shifts to the traveling state, the vehicle speed V at that time is detected by the vehicle speed sensor 1 along with the operation of the steering ratio control means 104.
The detection signal is output from the vehicle speed sensor 102 to the control unit 100, and the target steering ratio according to the vehicle speed V is calculated by comparison and comparison with the steering ratio characteristic in the control unit 100. A pulse signal corresponding to the steering ratio is output to the stepping motor 51 to drive the motor 51. By driving the motor 51, the sector gear 46 rotates and the swing locus surface of the swing arm 36 connected to the sector gear 46 is changed in inclination with respect to the reference plane. By this change, the operation of the steering wheel 10, that is, the front wheel 1 is performed. The movement direction and the movement distance of the control rod 33 with respect to the movement of the connecting rod 39 that rotates around the movement axis l ₁ in association with the steering of _L and 1 _R changes, and the rear wheel moves in accordance with the movement of the control rod 33. 2 _L , 2 _R is front wheel 1
The power cylinder 17 of the power steering mechanism 16 steers so that the calculated target steered ratio is obtained with respect to _L and 1 _R. Thus, 4-wheel 1 _L to 2 _R of the vehicle in the opposite phase steering ratio at the time of low vehicle speed, at the time of high vehicle speed is controlled so turning ratio is respectively in phase.

Further, during the control for the stepping motor 51, the actual turning ratio is detected by the turning ratio sensor 101,
The step-out of the stepping motor 51 is detected based on the comparison between the detected turning ratio and the target turning ratio. Then, such a stepping of the stepping motor 51 and the steering ratio sensor 101
When there is no failure of the above and there is no abnormality in the control system of the turning ratio control means 104, the above control is continued as it is and the steering characteristic of the vehicle is controlled to the four-wheel steering characteristic.

On the other hand, when an abnormality occurs in the control system of the turning ratio control means 104 due to step-out of the stepping motor 51 or the like, the fail safe mode is entered in order to ensure the traveling safety of the vehicle. That is, first, when the electromagnetic opening / closing valve 28 is turned ON, the hydraulic pressures in both hydraulic chambers 17b, 17c of the power cylinder 17 become the same and the operation of the power cylinder 17 is stopped, and the hydraulic pressure in both hydraulic chambers 17b, 17c is stopped. Return spring 17d, 17d
The steering angle θ _R of the rear wheels 2 _L , 2 _R is maintained at θ _R = 0 by the urging force of the vehicle, and the steering characteristics of the vehicle are forcibly maintained in the two-wheel steering control. Can be improved.

After the operation signal is output to the solenoid opening / closing valve 28, the hydraulic pressure sensor 103 detects the hydraulic pressure in the hydraulic pipes 26, 27, that is, the hydraulic chambers 17b, 17c of the power cylinder 17, and the detected hydraulic pressure is equal to or less than a predetermined value A. When it has decreased to 0, it can be determined that the operation of the power cylinder 17 has been stopped due to the normal operation of the electromagnetic opening / closing valve 28, and therefore the control thereafter is not performed.

However, if the solenoid on-off valve 28 is in a malfunctioning state due to a stick or the like, communication between the hydraulic chambers 17b and 17c of the power cylinder 17 is hindered, so the detected hydraulic pressure becomes higher than the predetermined value A. . At this time, the steering ratio control means 104 of the control unit 100 continues to output a correction signal to the stepping motor 51 for a certain period of time so that the steering ratio is on the same phase side. For this reason, as long as the stepping motor 51 is normal, the steering ratio is kept in the same phase side, the behavior of the vehicle body is suppressed, and thus the running safety of the vehicle in the fail-safe mode can be further improved. .

In the above embodiment, the case where the present invention is applied to the four-wheel steering system in which the steering ratios of the front and rear wheels 1 _L and 2 _L of the vehicle are variably controlled according to the vehicle speed V is shown. Can also be applied to a four-wheel steering system in which a stepping motor is directly driven according to the turning angle of the front wheels.

Further, in the above embodiment, the stepping motor 51 is used as an actuator for controlling the turning ratio of the front and rear wheels 1 _L , 2 _L , but the present invention controls the turning ratio by another actuator such as a DC motor. It can also be applied to the four-wheel steering system described above.

(Effects of the Invention) As described above, according to the present invention, the front and rear wheels are steered based on a predetermined steering ratio characteristic set in advance, and a control system for controlling the steering ratio of the front and rear wheels is also provided. In the event of an abnormality, in a four-wheel steering system for a vehicle in which both hydraulic chambers of a hydraulic cylinder that steers the rear wheels are connected by a communication valve to maintain a two-wheel steering state, in the event of an abnormality in the control system,
In addition to the above-mentioned operation of the communication valve, by outputting a signal that corrects the steering ratio to the same phase side, even if the communication valve malfunctions when the control system is abnormal, the steering ratio control As long as the actuator is normal, the unstable behavior of the vehicle body can be suppressed by keeping the steering ratio on the same phase side, and thus the safety in the fail-safe mode can be further improved.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of the present invention. 2 to 6 show an embodiment of the present invention, FIG. 2 is a plan view schematically showing the overall construction of a four-wheel steering system, and FIG. 3 shows a rear wheel steering mechanism and a steering ratio control mechanism. Skeleton diagram shown in perspective
FIG. 4 is a characteristic diagram illustrating the characteristic of the rear wheel steering angle with respect to the steering wheel steering angle when the vehicle speed changes, FIG. 5 is a characteristic diagram showing the steering ratio characteristic with respect to the vehicle speed at a predetermined steering wheel steering angle, and FIG. 6 is the control. It is a flowchart figure which shows the control procedure with respect to the stepping motor and electromagnetic opening / closing valve which are processed in the fail-safe mode in a unit. 1 _L , 1 _R ...... Front wheel, 2 _L , 2 _R ...... Rear wheel, 3 ...... Front wheel steering mechanism, 12 ...... Rear wheel steering mechanism, 17 ...... Power cylinder, 17b,
17c …… hydraulic chamber, 17d …… return spring, 18,19…
… Hydraulic piping, 22 …… Oil supply pipe, 23 …… Oil discharge pipe, 24 ……
Hydraulic pump, 28 ... Electromagnetic on-off valve, 32 ... Steering ratio control mechanism, 51 ... Stepping motor, 100 ... Control unit, 103 ... Hydraulic sensor, 104 ... Steering ratio control means, 105 ... Abnormal Detecting means 106 ... means for operating in an abnormal state

Claims (1)

[Claims] 1. A four-wheel steering system for a vehicle in which not only front wheels but also rear wheels are steered, wherein a steering ratio for controlling front and rear wheels based on a preset steering ratio characteristic. Control means and a centering mechanism for turning the steering angle of the rear wheels to zero are built-in, and pressure oil is supplied to both hydraulic chambers for steering the rear wheels against the centering mechanism and both hydraulic chambers of the hydraulic cylinders. Anomaly detection that detects that an abnormality has occurred in the communication valve, which is arranged in the hydraulic piping system and connects both hydraulic chambers of the hydraulic cylinder to each other to prohibit the operation of the hydraulic cylinder, and the control system of the above-mentioned turning ratio control means Means and the output of the abnormality detection means, when the control system of the steering ratio control means is abnormal, the operating signal is output to the communication valve, and the steering ratio is set to the steering ratio control means in the same phase side. And an abnormal-time operating means for outputting a correction signal Of the vehicle and wherein the Rukoto 4
Wheel steering device.