JPH0653500B2 - 4-wheel steering system for vehicles - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel steering system for a vehicle in which not only front wheels but also rear wheels are steered.

(Prior Art) Conventionally, as a four-wheel steering system for a vehicle of this type, as disclosed in, for example, Japanese Patent Laid-Open No. 55-91457, a front wheel steering mechanism that steers front wheels and a rear wheel steering mechanism. It has a rear wheel steering mechanism that steers the vehicle, and changes the steering angle of the rear wheels according to the steering angle of the front wheels and the vehicle speed.The front wheels and the rear wheels are in opposite phases at low speeds, and the same at high speeds. It is known that by making the phases in the same direction, it is possible to prevent the vehicle from slipping sideways to improve the running stability and to improve the small turning performance at low speed.

(Problems to be Solved by the Invention) However, in a state where the grip force of the tire is low, such as when traveling on a low μ road such as a snowy road or a frozen road, when the rear wheels are steered as in normal traveling, There is a problem in that the vehicle tends to skid regardless of whether it is running at high speed or low speed, which impairs running stability.

The present invention has been made in view of the above point, and its object is to make the rear wheel in the same phase direction as the front wheel in the state where the grip force of the tire is low compared to the case of the normal grip state. By turning it to
Regardless of the grip state of the tire, the vehicle always prevents side slippage to improve running stability.

(Means for Solving the Problem) In order to achieve the above object, the solving means of the present invention is based on a front wheel steering mechanism that steers the front wheels in accordance with steering of a steering wheel and a preset rear wheel steering angle characteristic. It is assumed that a four-wheel steering system for a vehicle includes a rear-wheel steering mechanism that steers rear wheels and an anti-skid brake system that prevents wheel slip. Further, the rear wheel steering mechanism is provided with a correction means for receiving the output signal from the anti-skid brake device and correcting the rear wheel steering angle characteristic in the same phase direction as the front wheels.

(Operation) With the above configuration, in the present invention, when the tire grip force is low such as when traveling on a low μ road, the rear wheel steering angle characteristic is
The output of the anti-skid brake device is corrected by the correction means, and the rear wheels are steered in the same direction as the front wheels, in the same phase direction, that is, in the direction to mitigate the turning of the vehicle, thereby increasing the grip force of the wheels. Therefore, it is possible to prevent the vehicle from skidding.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows the overall construction of a four-wheel steering system for a vehicle according to a first embodiment of the present invention. In the figure, 1 is the left and right front wheels 2
It is a front wheel steering mechanism that steers L and 2R. The front wheel steering mechanism 1 transmits a steering handle 3, a rack & pinion mechanism 4 for converting the rotational movement of the steering handle 3 to a linear movement, and an operation of the rack & pinion mechanism 4 to front wheels 2L, 2R. It consists of left and right tie rods 5 and 5 and knuckle arms 6 and 6 that steer them left and right.

Reference numeral 7 denotes a rear wheel steering mechanism that steers the left and right rear wheels 8L and 8R. The rear wheel steering mechanism 7 has left and right rear wheels 8L and 8R at both ends.
Rear wheel operating rod 11 extending in the vehicle width direction connected to the tie rods 9 and 9 and knuckle arms 10 and 10 to
Is equipped with. A rack 12 is formed on the rear wheel operating rod 11, and a pinion 13 meshing with the rack 12 is rotated by a pulse motor 14 via a pair of bevel gears 15 and 16 and a pinion shaft 17 to provide the pulse motor. The rear wheels 8L, 8R are configured to be steered to the left or right based on the rear wheel steering angle characteristics that are preset corresponding to the rotation direction and the rotation amount of the fourteen.

A power cylinder 18 having the rod 11 as an operating rod is connected to the rear wheel operating rod 11.
The power cylinder 18 has a left-turning hydraulic chamber 18b and a right-turning hydraulic chamber 18c partitioned in the vehicle width direction by a piston 18a fixed to the rear wheel operating rod 11, and the hydraulic chambers 18b, 18c are Hydraulic passage 1
An oil supply passage 21 is connected to the control valve 20 for controlling the oil supply direction and the oil pressure to the power cylinder 18 via 9a and 19b.
A hydraulic pump 23 is connected via the oil return passage 22 and the hydraulic pump 23 is rotationally driven by a motor 24. The control valve 20 detects the rotation direction of the pinion shaft 17 and communicates the oil supply passage 21 with the counterclockwise hydraulic chamber 18b when the rear wheels 8L and 8R are steered to the left (steering counterclockwise in the figure). In addition, while the right-turning hydraulic chamber 18c is communicated with the oil return path 22, when the rear wheels 8L, 8R are steered to the right (steering in the clockwise direction in the figure), the communication state opposite to the above is established, and at the same time, the hydraulic pump The hydraulic pressure from 23 is reduced to a pressure corresponding to the rotational force of the pinion shaft 17. Then, when the rear wheel operation rod 11 is moved in the axial direction (vehicle width direction) by the pulse motor 14 via the bevel gears 15, 16, the pinion shaft 17, the pinion 13, and the rack 12, pressure oil is supplied to the power cylinder 18. Thus, the movement of the rear wheel operation rod 11 is assisted.

The operation of the pulse motor 14 and the drive motor 24 of the hydraulic pump 23 is controlled by a control signal output from a controller 25 that is a control unit of the rear wheel steering mechanism 7. The controller 25 includes a steering angle signal from a steering angle sensor 26 for detecting a front wheel steering angle from the steering amount of the steering wheel 3 in the front wheel steering mechanism 1 and a blurring hydraulic pressure depending on a rotation state of the wheels. And an output signal from an ABS controller (anti-skid brake device) 28 that has a function of controlling the vehicle and determining and detecting the grip state of the tire are input, and a battery power source 29 is connected.

Then, the controller 25, as shown in FIG. 2, receives the steering angle signal from the steering angle sensor 26 and the vehicle speed sensor 2
A target steered angle calculation unit 31 for receiving a vehicle speed signal from the steering wheel ratio characteristic stored in the characteristic storage unit 30 and calculating a front wheel steered angle and a rear wheel target steered angle corresponding to the vehicle speed; A pulse generator 32 that outputs a pulse signal corresponding to the target rear wheel turning angle calculated by the target turning angle calculation unit 31, and a pulse motor 14 and a hydraulic pump 23 for receiving a pulse signal from the pulse generator 32 Motor 24
And a driver 33 that converts the driving pulse signal into a driving pulse signal. With these, the ratio of the rear wheel turning angle to the front wheel turning angle (turning ratio) is made variable according to a predetermined turning ratio characteristic so that the rear wheel turning angle becomes the target turning angle.
4 and a turning ratio varying means 34 for controlling the drive motor 24 of the hydraulic pump 23.

The controller 25 is the ABS controller 2
In response to the output signal from the steering wheel 8, the steering ratio characteristic stored in the characteristic storage unit 30 is selected according to the grip state of the tire, and the low μ is selected.
A characteristic selection unit 35 is provided as a correction unit that corrects the steering ratio in the in-phase direction when the tire grip force is low, such as when traveling on a road. The characteristic storage unit selected by the characteristic selection unit 35 is provided. The target turning angle is calculated in the target turning angle calculation unit 31 according to the turning ratio characteristic of 30.

As shown in FIG. 3, the steering ratio characteristics stored in advance in the characteristic storage unit 30 are the steering ratio characteristics A for normal running when the tire grip is high and the low μ road etc. There are two types, namely, the steering ratio characteristic B when the grip force of the tire is low. The both steering ratio characteristics A and B are basically large as the vehicle speed increases from a low speed to a high speed when the steering ratio k is in the negative direction and in the opposite phase (the front and rear wheels are steered in the opposite direction). The value shifts from the value to zero, and the steering k changes to the same phase in the positive direction (a state in which the front and rear wheels are steered in the same direction) in the medium speed range.
In the high speed range, the steering ratio k is set to be large in the same phase. Of the two steering ratio characteristics A and B, the steering ratio characteristic B in the state where the tire grip force is low is the whole vehicle speed range from low speed to high speed as compared with the steering ratio characteristic A for normal traveling. In the low speed range in which the steering ratio k becomes the value of the opposite phase in the negative direction, the steering ratio k approaches zero or changes to the same phase in the positive direction. The steered ratio k is set to a larger value in the medium speed region or high speed region where the steering ratio k has the same phase value in the positive direction.

On the other hand, as shown in FIG. 4, the ABS controller 28 includes the wheel rotation detection sensor 4 for detecting the rotation speed of the wheels.
1, a skid determination circuit 37 for determining the skid state of the wheel, and a drive pulse for driving the solenoid valve 39 of the hydraulic pressure control unit 38 in response to the output signal from the skid determination circuit 37 are generated. Driver 4
0, the solenoid valve 39 is driven according to the rotation state of the wheel to control the brake fluid pressure of the brake system 42 to prevent the wheel from slipping. Here, the brake system 42 includes a brake pedal 43, a master cylinder 44 that operates in conjunction with the brake pedal 43, and a brake pad 46 that is connected to the master cylinder 44 via a hydraulic pipe 45. It comprises a brake 47 and a hydraulic pressure control section 38 provided in the hydraulic pipe 45. The brake hydraulic pressure generated in the master cylinder 44 by the depression operation of the brake pedal 43 is controlled by the hydraulic pressure control section 38 to control the wheel. It is designed to brake.

Next, the operation and effect of the first embodiment will be described. First, the mechanism by which the grip state of the tire is detected by the ABS controller 28 that controls the operation of the solenoid valve 39 of the anti-skid brake device will be described.

The ABS controller 28 operates the antiskid brake device as follows. That is, as shown in FIG. 5, when the vehicle is braked, the brake fluid pressure increases as the brake pedal 43 is depressed, as shown in FIG. As the brake fluid pressure increases, the wheel rotation speed changes as shown in FIG. 7A and the wheel acceleration speed as shown in FIG. Here, when the acceleration / deceleration of the wheel is within the range of a predetermined reference value or less, the grip force of the tire is high, and when the reference value is exceeded, the rotation speed of the wheel is rapidly reduced and the skid It is determined that the tire grip force has decreased due to the situation.

That is, as shown in FIG. 9B, when the wheel deceleration increases and reaches the first reference value −bo (point b in FIG. ₁ ), the rotation speed of the wheel sharply decreases from around point a _1. In order to go to the skid state, the current i _E is applied to the solenoid valve 39 by the output signal from the ABS controller 28 to keep the brake fluid pressure at the predetermined pressure P ₁ .
As shown in Figure B in this state, is parallel to the inclined line l ₁ obtained from the relationship between the other wheel from a _2-point (above a ₁ point decreases the rotational speed of the wheel is further and lines l
_When reaching the intersection point of the slope line l ₂ separated by ₁ and a predetermined interval Δl and the above-mentioned A curve), the ABS controller 28
The output signal from the sonoid valve 39 causes i _A (i _A >
i _E ), a high current is applied to reduce the brake fluid pressure.
As a result, the deceleration of the wheel is reduced and the first
When it returns to the reference value -bo ( ₂ points in the figure b), ABS again
Solenoid valve 3 according to output signal from controller 28
The current supplied to 9 is reduced to i _E , and the brake fluid pressure is maintained at the predetermined pressure P ₂ . With the brake fluid pressure maintained at the predetermined pressure P ₂ , the deceleration of the vehicle body gradually decreases from the point b _{2 in} the figure and exceeds the point bo at which the acceleration / deceleration is zero, and conversely the acceleration increases. the second reference value each _{+ b} 2 o (figure _{b 3}
When the point is reached, the brake fluid pressure rises again by making the current to the solenoid valve 39 zero by the output signal from the ABS controller 28. By this,
The acceleration of the wheels becomes smaller and the second reference value + b ₂ o
When returning to ( ₄ points in the same figure), the current supplied to the solenoid valve 39 is raised to i _E again by the output signal from the ABS controller 28, the brake fluid pressure is maintained at the predetermined pressure P ₃ , and the wheels are skided. Preventing the situation.

On the other hand, the ABS controller 28 uses the solenoid valve 3
In addition to sending the output signal to 9, the output signal is also sent to the controller 25, and when the wheels are in the skid state,
It is determined that the grip force of the tire is reduced.
Thus, the operation signal to the solenoid valve 39 is output to the controller 25 as a detection signal of the tire grip force reduction.

As a result, based on the output signal from the ABS controller 28, the controller 25 of the rear wheel steering mechanism 7 operates in the normal traveling mode (the ABS controller 28).
In the case where the output signal as the detection signal from is not input), the steering ratio characteristic A for normal traveling is selected from the two types of steering ratio characteristics A and B stored in the characteristic selection unit 30. The target turning angle calculation unit 31 of the turning ratio varying means 34 calculates the target turning angle based on the selected turning ratio characteristic A, so that the turning angle of the rear wheel with respect to the turning angle of the front wheel is changed. The steering ratio is variably controlled according to the steering ratio characteristic A, and the rear wheels 8
L and 8R are steered in the opposite phase to the front wheels 2L and 2R at low speed, and steered to the same phase as the front wheels 2L and 2R at high speed.

On the other hand, if the tire grip is low,
The characteristic selection unit 35 receives the output signal from the ABS controller 28, and replaces the steering ratio characteristic A for normal traveling described above with the steering ratio characteristic B in the state where the tire grip force is low, as a characteristic storage unit. The steering ratio is selected from 30 and the steering ratio is variably controlled by the steering ratio varying means 34 according to the selected steering ratio characteristic B.

In this case, since the steering ratio characteristic B in the state where the tire grip force is low is deviated to the same phase side as compared with the steering ratio characteristic A for normal traveling, the rear wheels 8L, 8R are in normal traveling. Therefore, the vehicle is steered in the same phase direction as the front wheels 2L, 2R, and the turning of the vehicle is suppressed. As a result, the sideslip of the wheels (the front wheels 2L, 2R and the rear wheels 8L, 8R) due to the reduction of the grip force on the road surface on a snowy road or an icy road can be prevented, and the running stability can be improved. it can.

FIG. 6 shows the overall construction of a four-wheel steering system for a vehicle according to a second embodiment of the present invention. The rear wheel steering mechanism 7'in this four-wheel steering system is the rear wheel steering system in the four-wheel steering system of the second embodiment. The rear wheel 8 is driven by the operation of the pulse motor 14 like the wheel steering mechanism 7.
Instead of electrically steering L and 8R, front wheel steering mechanism 1
The rear wheels 8L and 8R are mechanically steered by utilizing the steering force of.

That is, the rear wheel steering mechanism 7'includes a steering ratio changing device 50 including gears and the like, and a rear end of a transmission rod 51 extending in the vehicle body front-rear direction is connected to the steering ratio changing device 50.
A pinion 53 that meshes with a rack 52 formed on the rack shaft 4 a of the rack and pinion mechanism 4 of the front wheel steering mechanism 1 is provided at the front end of the transmission rod 51. Also,
A sliding member 54 is extended to the turning ratio changing device 50,
A pinion 56 provided at the front end of a pinion shaft 17 connected to the rear wheel operation rod 11 via the rack 12 and the pinion 13 meshes with the rack 55 formed on the sliding member 54. Then, the steering force of the front wheel steering mechanism 1 is transmitted from the rack shaft 4a of the rack and pinion mechanism 4 to the steering ratio changing device 50 via the transmission rod 51, and the controller 25 controls the steering ratio changing device 50. The steering force is transmitted to the rear wheel operation rod 11 via the sliding member 54 and the pinion shaft 27 after the steering ratio is changed in accordance with the above, so that the rear wheels 8L and 8R are steered to the left and right. Has been done. The other configurations of the four-wheel steering system are the same as those of the four-wheel steering system of the first embodiment, and the same members are designated by the same reference numerals and the description thereof will be omitted.

The controller 25 itself for controlling the turning ratio changing device 50 is the same as that of the first embodiment, and
As a result, it is of course possible to achieve the same action and effect.

(Effects of the Invention) As described above, according to the four-wheel steering system for a vehicle of the present invention, the grip state of the tire is detected from the operating state of the anti-skid brake device, and the rear wheel steering is performed when the grip force of the tire is low. The angular characteristic is corrected in the same phase direction as the front wheels by the correction means that receives the output signal from the anti-skid brake device, and the rear wheel is in the same phase direction, that is, the vehicle turns with the corrected steering angle characteristic. Since the vehicle is steered in a direction that alleviates the vehicle, the gripping force of the wheels is increased, and side slip of the vehicle can be prevented, so that traveling stability can be improved.

[Brief description of drawings]

1 to 5 show a first embodiment, FIG. 1 is an overall configuration diagram of a four-wheel steering system for a vehicle, FIG. 2 is a block configuration diagram of a controller, and FIG. 3 is steering according to a vehicle speed of the controller. Fig. 4 is a diagram showing a turning ratio characteristic in the case of ratio control, Fig. 4 is a block configuration diagram of an ABS controller and a brake system, and Fig. 5 is a wheel rotation speed, acceleration / deceleration, a current supplied to a solenoid valve and a brake fluid pressure. It is a figure which shows the change of. FIG. 6 is a view corresponding to FIG. 1 showing the second embodiment. 1 ... Front wheel steering mechanism, 7, 7 '... Rear wheel steering mechanism, 25
...... Controller, 28 …… ABS controller, 34
...... Turning ratio varying means, 35 ...... Characteristic selection section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Reihiro Watanabe 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) Reference JP-A-57-60974 (JP, A) JP-A-61 -200065 (JP, A) JP-A 61-113562 (JP, A) Actually developed Shou 57-19172 (JP, U)

Claims (1)

[Claims] 1. A front wheel steering mechanism that steers the front wheels in response to steering of a steering wheel, and a rear wheel steering mechanism that steers the rear wheels based on a preset rear wheel steering angle characteristic. In a four-wheel steering system for a vehicle equipped with an anti-skid brake device for preventing slip, the rear-wheel steering mechanism receives the output signal from the anti-skid brake device and sets the rear-wheel steering angle characteristics in the same direction as the front wheels. 4 of a vehicle characterized by including a correcting means for correcting in the same phase direction
Wheel steering device.