JPS62238171A - Four wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To maintain high turning performance even when the brake is applied during a turning drive by providing correcting means for correcting the ratio of the rear wheel steering change angle to the front wheel steering change angle to an equal phase or neutral area. CONSTITUTION:A controller 25 receives a steering angle signal from a steering angle sensor 26 and an output signal from an ABS controller 28 adapted to control the brake fluid pressure in accordance with the rotating condition of a wheel and serving as grip condition detecting means for discriminating and detecting the grip condition of a tire. The controller 25 includes a characteristic selector 35 serving as correcting means adapted to receive the output signal from the ABS controller 28 to select a steering change ratio characteristic stored in a characteristic memory 30 in accordance with the grip condition of the tire and, when the grip condition of the tire is low, to correct the steering change ratio to an equal phase or neutral area so as to compute a desired steering change angle.

Description

[Detailed description of the invention] 3. 3FIIIJ description of the invention (industrial application field) The present invention relates to a four-wheel steering device for a vehicle that steers the rear wheels in response to the steering of the front wheels. It is.

(Prior Art) Conventionally, as a four-wheel steering system for this type of vehicle, a front wheel steering mechanism that steers the front wheels and a front wheel steering mechanism that steers the rear wheels have been used, for example, as disclosed in Japanese Patent Laid-Open No. 55-91457. Equipped with a rear wheel steering mechanism, the steering angle of the rear wheels is changed according to the steering angle of the front wheels and the vehicle speed, and the IF5 wheels and rear wheels are in opposite phases at low speeds and in the same phase at high speeds. It is known that this prevents the vehicle from slipping and improves running stability, as well as improves maneuverability at low speeds.

However, when the tire grip force is low, such as when driving on a low μ road such as a snowy road or an icy road, when the rear wheels are steered as in normal driving, the front and rear wheels will be in opposite phases. At low speeds, the vehicle is more likely to skid, which may impair driving stability. In particular, when the brakes are operated while the vehicle is running and turning, the grip force of the tires further decreases, making it more likely that the vehicle will skid.

For this reason, conventionally, in consideration of the fact that the vehicle speed decreases when the brakes are operated, if the vehicle decelerates due to J3 during wheel steering, the rear wheels are corrected to be in the same phase as the front wheels to improve driving stability. A four-wheel steering device designed to improve this is proposed in Japanese Patent Application Laid-Open No. 135370/1983.

(Problem to be Solved by the Invention) However, with the above device, when the vehicle decelerates, the rear wheels are always corrected to be in the same phase as the front wheels. Even if the situation is not directly related to the running stability of the vehicle, such as when you apply the brakes while descending while turning,
The invasion will be corrected to the same phase side, which may cause an inconvenience in that the turning radius increases and the intended turning characteristics cannot be achieved.

The present invention has been made in view of the above points, and is
Only when the vehicle is likely to become unstable due to low grip strength, the system uses predetermined controls to maintain driving stability.
It is an object of the present invention to provide a four-wheel steering system for a vehicle that can maintain high turning performance even during braking in other cases.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a front wheel steering mechanism that steers the front wheels in response to steering wheel steering, and a rear wheel steering mechanism that steers the front wheels in response to steering of the steering wheel. A four-wheel steering vAV for a vehicle equipped with a rear wheel steering mechanism that steers the vehicle. 1 is assumed. The rear wheel steering mechanism includes a steering ratio variable means for varying the ratio of the rear wheel steering angle to the front wheel steering angle (steering ratio) according to a steering ratio characteristic according to vehicle speed, and an anti-skid brake device. A detection means is connected to detect the operating state of the anti-skid brake device, and an output signal from the detection means can be inputted, and when a signal indicating the operation of the anti-skid brake device is inputted from the detection signal, the front wheel steering angle is changed. The present invention is configured to include a correction means for correcting the ratio of the opposing rear wheel turning angles to the same phase or a neutral range.

(Function) With the above configuration, in the present invention, when the tire grip force is low such as when driving on a low μ road, the anti-skid brake device is activated and its activation signal is input to the detection means, The steering ratio is corrected by the correcting means that receives the output from the correcting means, and by filling this corrected steering ratio, the rear wheels are in the same phase or in the neutral region, that is, the turning of the vehicle is alleviated, and driving stability is improved. This increases the grip of the wheels,
This will prevent the vehicle from skidding.

On the other hand, if the tires have high grip and the anti-skid brake system does not operate, the correction means will not operate and high turning performance will be maintained even if the brakes are operated while the vehicle is turning. It turns out.

(Embodiments) Hereinafter, embodiments of the present invention will be explained with reference to the drawings.
Jru.

FIG. 1 shows the overall configuration of a four-wheel steering system for a vehicle according to a first embodiment of the present invention, where 1 indicates left and right front wheels 2L.

Front wheel steering to steer 2R'g! The front wheel steering mechanism 1 includes a steering handle 3 and a rack &
and a nion mechanism 4, left and right tie rods 5, 5, and a knuckle arm 6.6 that transmit the operation of the rack and pinion mechanism 4 to the front wheels 2L, 2R to steer them left and right.

7 is a rear wheel steering mechanism that steers the left and right rear wheels 8L, 8R, and both ends of the rear wheel steering mechanism 7 steer the left and right rear wheels 8L, 8R.
Tie rod 9, 9 and knuckle arm 10.10 to R
Rear wheel operating rod 1 extending in the vehicle width direction and connected via
1. The rear wheel operating rod 11 is fitted with a hook 12.
is formed, and the pinion 13 meshing with the rack 12 is rotated by the pulse motor 14 via a pair of bevel gears 15, 16 and the pinion shaft 17, thereby corresponding to the rotation direction and rotation m of the pulse motor 14. rear wheel 8
The L and 8R are configured to be steered left and right.

Further, a power cylinder 18 is connected to the rear wheel operating rod 11, using the rod 11 as an operating rod.

The power cylinder 18 is connected to the rear wheel operating rod 11.
It has a left-turning hydraulic chamber 18b and a right-turning hydraulic chamber 18c partitioned in the vehicle width direction by a piston 18a, and the eight hydraulic chambers tab and 18c are connected to the power cylinder 18 through hydraulic passages 19a and 19b, respectively.
A hydraulic pump 23 is connected to the control valve 20 via an oil supply passage 21J3 and an oil return passage 22, and the hydraulic pump 23 is connected to a motor. 2
Rotationally driven by 4. Above control valve 2
0 detects the rotational direction of the binion shaft 17 and rotates the rear wheel 81.
When steering 8R to the left (counterclockwise in the figure), the oil supply passage 21 is communicated with the left-turn hydraulic chamber 18b, and the right-turn hydraulic chamber H1c is communicated with the oil return passage 22, while the rear wheel 8L is
, 8R is turned to the right (clockwise in the figure), the communication state is reversed to that described above, and at the same time, the hydraulic pressure from the hydraulic pump 23 is reduced to a pressure corresponding to the rotational force of the pinion shaft 17. Yes, bevel gear 15.16 due to pulse Tanabata 14
When the rear wheel operating rod 11 is moved in the axial direction (vehicle width direction) via the pinion shaft 17, the pinion 13J5 and the rack 12, the rear wheel operating rod 11 is moved by supplying pressure oil to the power cylinder 1a. I'm trying to help.

The operation of the pulse motor 148 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 section of the rear wheel steering mechanism 7. The controller 25 receives a steering angle signal from a steering angle sensor 2G that detects the front wheel steering angle from the steering wheel 1 of the steering wheel 3 in the front wheel steering mechanism 1, and controls the brake fluid pressure according to the rotational state of the wheels. An output signal from an ABS controller (anti-skid brake υ control device) 28, which has a function as a grip state detection means for determining and detecting the tire grip state, is inputted thereto, and a battery power supply 29 is connected. has been done.

As shown in FIG. 2, the controller 25 receives the steering angle signal from the steering angle sensor 2G and the vehicle speed sensor 21.
a target steering angle calculation section 31 that receives a vehicle speed signal from the vehicle and calculates a target steering angle of the rear wheels corresponding to the front wheel steering angle and the vehicle speed from the steering ratio characteristics stored in the characteristic storage section 30; A pulse generator 32 outputs a pulse signal corresponding to the target turning angle calculated by the turning angle calculation PIX 31, and a pulse motor 14 and a driving motor 24 of the hydraulic pump 23 in response to the pulse signal from the pulse generator 32. and a driver 33 for converting into a drive pulse signal to drive the vehicle. A steering ratio variable means 34 is configured to control the pulse motor 14 and the drive motor 24 of the hydraulic pump 23 so that the target steering angle is achieved.

Further, the controller 25 includes an ABS controller 2
In response to the output signal q from 8, the steering ratio characteristic stored in the characteristic storage section 30 is selected according to the grip condition of the tire, and a low μ is selected.
A characteristic selection section 35 is provided as a correction means for correcting the steering ratio to the same phase or neutral region when the grip force of the singing tie A7 is low during road running. 1 of the target steering angle in the target steering angle calculation unit 31 according to the steering ratio characteristics in the characteristic storage unit 30.
The best is now being held.

As shown in FIG. 3, the steering ratio characteristics stored in advance in the characteristic storage section 30 are changed to the steering ratio characteristics for normal driving in which the grip force of the tires is high. There are two types of steering ratio characteristics B in which the grip force is low. As the vehicle speed increases from low to high speed, the steering ratio k changes from a large value to zero in the opposite phase in the negative direction (the front and rear wheels are steered in opposite directions) to achieve the steering ratio characteristics for normal driving. In the medium speed range, the steering ratio k changes to the same phase in the positive direction (the front and rear wheels are steered in the same direction), and in the high speed range, the steering ratio k becomes large with the same phase. It is set to be. On the other hand, the steering ratio characteristic B when the tire grip force is low is:
Compared to the steering ratio characteristics, there is a tendency to deviate to the same phase side over the entire vehicle speed range from low to high speeds, and in the low speed range, the steering ratio k is zero, maintaining a neutral state, and in the middle In the speed range or high speed range, the steering ratio k is set to a value of the same phase in the positive direction. In addition to the steering ratio characteristics B shown in Figure 3, there are also steering ratio characteristics B that can maintain high running stability, as shown in Figure 4. Within the phase or neutral region, 8
It is possible to adopt various characteristics such as 1.8z and 83.

On the other hand, as shown in FIG. circuit 37, and a hydraulic pressure control section 38 in response to the output signal from the skid limit constant circuit 37.
and a driver 40 that generates a drive pulse to drive the solenoid valve 39 of the anti-skid play device 4, and controls the brake fluid pressure of the anti-skid play device 42 by driving the solenoid valve 39 according to the rotational state of the wheel. ing.

Here, the anti-skid brake device 42 includes a brake pedal 43, a 7-star cylinder 44 that operates in conjunction with the brake pedal 43, and a brake pad connected to the mask cylinder 44 via a hydraulic pipe 45. 4G
It consists of a disc brake 47 with a wide width and a hydraulic pressure control section 38 interposed in the hydraulic piping 45, and the hydraulic pressure control section 38 controls the brake hydraulic pressure generated in the mask cylinder 44 when the brake pedal 43 is depressed. It is designed to brake the wheels by

Next, to explain the operation and effect of the first embodiment, first, the grip state of the tire changes the operation of the solenoid valve 39 of the anti-skid brake g@42 to A
The mechanism detected by the BS controller 28 will be explained.

The above-mentioned anti-skid brake system "a42" is created as follows by the ABS controller 28.As shown in FIG.
3, the brake fluid pressure increases as shown in the figure. As the brake fluid pressure increases, the rotational speed of the wheels changes as shown in FIG. 8A, and the middle wheel acceleration/deceleration changes as shown in FIG. 8. Here, if the wheel acceleration/deceleration is within a range below a predetermined reference value, the grip of the tire is high, and if this reference value is exceeded, the rotational speed of the wheel rapidly decreases and skid occurs. As a result, it is determined that the gripping force of tie A7 has decreased.

However, as shown in Figure B, when the wheel deceleration increases and reaches the first reference value -bO (point b1 in the figure), the rotational speed of the 11th wheel rapidly decreases from around the 81st point. In order to move toward a skid state, the output signal from the ABS controller 28 energizes the solenoid valve 39 with a laminar flow of iH, as shown in FIG. In this state, as shown in 1ii1 [fiA, the rotation speed of the wheel further decreases to 82 points, which is parallel to the slope line 9,1 obtained from the relationship with other wheels from the above 81 point, and 9JR. When reaching the intersection point of the inclined line 2 and the above curve separated by a predetermined interval ΔL, the solenoid valve 39 is activated by the output signal from the ABS controller 28.
A high Wi current of i^ (i^>1ε) is applied to reduce the brake fluid pressure. As a result, when the wheel deceleration decreases and returns to the first reference value -bo (point b2 in the figure), the current applied to the solenoid valve 39 by the output signal from the ABS controller 28 is changed to iε again. The brake fluid pressure is maintained at a predetermined pressure P2. With this brake fluid pressure maintained at a predetermined pressure P2, the deceleration of the vehicle body gradually decreases from point b2 in the figure, and the acceleration/deceleration reaches zero b
When the O point is exceeded and the acceleration begins to increase and reaches the second reference value + b, o (3 points b in the same figure), A[3S
By reducing the current to the solenoid valve 39 to zero in response to the output signal from the controller 28, the brake fluid pressure increases again. As a result, when the acceleration of the wheel becomes smaller and returns to the second reference point 1ifi+bzo (point b4 in the same figure), the solenoid valve 39 is energized again by the output signal from the ABS controller 28 and the current is increased to i[. The brake fluid pressure is maintained at a predetermined pressure P, and the wheels are prevented from becoming prone to snipping.

On the other hand, -F Note A [3S controller 28 sends an output signal to the solenoid valve 39 and also sends an output signal to the controller 25, indicating that when the wheel is heading toward a skid state, the grip force of the tire has decreased. It is determined that the condition exists. Thus, the operation signal to the solenoid valve 39 is output to the controller 25 as a detection signal of a decrease in tire grip force. That is, the controller 25 functions as a detection means for detecting the operating state of the anti-skid brake IAji 42.

As a result, based on the output signal from the ABS controller 28, the controller 2 of the rear wheel steering mechanism 7
5, during normal driving (when no output signal as a detection signal from the ABS controller 28 is input), one of the two types of steering ratio characteristics A and B stored in the characteristic selection section 30 is selected. The steering ratio characteristic for normal driving is selected, and the 11-mark steering angle is calculated based on the selected steering ratio characteristic A using the target steering angle 31 of the steering ratio variable means 34. As a result, the steering ratio of the rear wheel steering angle to the front wheel steering angle is controlled by variable fl, II according to the above steering ratio characteristics, and the rear wheels 8L, 8R are steered in the opposite phase to the front wheels 2L, 2R at low speeds. At high speeds, the front wheels 2L and 2R are steered in the same phase.

On the other hand, if the tire's grip strength is reduced,
The characteristic selection section 35 includes the anti-skid brake device 4
In response to the output signal from the ABS controller 28 indicating the operation of step 2, the steering ratio characteristic B in which the tire grip force is low is selected from the characteristic storage section 30 instead of the steering ratio characteristic during normal driving described above. Then, the steering ratio is variably controlled by the steering ratio variable means 34 according to the selected steering ratio characteristic B.

In this case, the steering ratio characteristic B when the tire grip h is low is that the steering ratio is in the same phase or in the neutral region, so the rear wheels 8L and 8R1fi are steered to the same phase or neutral position as the front wheels 2L and 2R. This means that the turning of the vehicle is suppressed. As a result, the wheels (front wheels 2
It is possible to prevent sideways skidding of the rear wheels (L, 2R and rear wheels 8L, 8R), and it is possible to improve running stability.

In the first embodiment, the tire grip condition was determined using the activation signal from the ABS controller 28 to the solenoid valve 39 of the anti-skid brake system @42. It may be used as a detection signal of the tire grip state by detecting the grip state of the tire, and it may be used as a detection signal of the grip state of the tire, and it may be used as a detection signal of the grip state of the tire. Therefore, it is possible to determine that the grip force of the tire is lower as the tire grips.

FIG. 7 shows the overall configuration of a four-wheel steering system for a vehicle according to a second embodiment of the present invention, and the rear wheel steering vlA lateral 7' in this four-wheel steering system is different from that in the four-wheel steering system of the first embodiment. Instead of electrically steering the rear wheels 81.8R by operating the pulse motor 14 like the rear wheel steering mechanism 7, the rear wheels 8L and 8R are mechanically steered using the steering force of the front wheel steering mechanism 1. It was designed to be steered.

In fact, the rear wheel steering mechanism 7' is equipped with a steering ratio changing device 50 consisting of gears and the like, and the steering ratio changing device! The rear end of a transmission rod 51 extending in the rear direction of the vehicle body tts is connected to 50, and the front wheel steering mechanism 1 is connected to the front end of the transmission rod 51.
A binion 53 is provided which meshes with a recess 52 formed on the rack shaft 48 of the rack and binion mechanism 4.

Further, a motion member 54 is extended from the steering ratio changing device 50, and a rack 12 and a pinion 1 are connected to the rear wheel operating rod 11 in response to a depression 55 formed on the motion member 54.
A pinion 56 provided at the front end of the pinion shaft 11 connected through the pinion 3 is engaged with the pinion 56. Thus, 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 IA device 50 via the transmission rod 51, and in the steering ratio changing device 150, the control 0- 52
5, the steering force is transmitted to the rear wheel operating rod 11 via the latent member 54 and the pinion shaft 27, so that the rear wheels 8L and 8R are steered left and right. It is configured to In addition, four-wheel steering Kf
The rest of the configuration of fl is the same as the four-wheel steering system of the first embodiment, and the same members are given the same reference numerals and their explanations will be omitted.

The controller 25 itself that controls the steering ratio changing device 50 is the same as in the first embodiment, and it goes without saying that it can provide the same functions and effects.

(Effects of the Invention) As described above, according to the four-wheel steering system for a vehicle according to the present invention, the operating state of the anti-skid brake device is detected by the detection means, and the operating signal of the anti-skid brake device is input to the nuclear detection means. Then, the correction means that receives the output signal from the detection means corrects the steering ratio of the steering angle of the front wheel to the front wheel steering angle, which is variably controlled by the steering ratio variable means, to be in the same phase or in the neutral range, According to this corrected steering ratio characteristic, the model wheels are steered in a direction that reduces the turning of the vehicle, increasing the grip of the wheels and preventing the vehicle from rolling over, thereby improving driving stability. can be achieved. On the other hand, when the activation signal of the anti-skid brake device is not input to the detection means, the steering ratio is not corrected. Due to the steering ratio correction effect, it is possible to eliminate the inconvenience that the intended turning characteristics cannot be obtained, and it is possible to maintain high turning performance.

[Brief explanation of drawings]

1 to 6 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 FIGS. 3 and 4 are a heavy speed controller diagram. Fig. 5 is a block diagram of the ABS controller and brake system, and Fig. 6 shows wheel rotational speed, acceleration/deceleration, and N energized to the solenoid valve. FIG. 3 is a diagram showing changes in flow and brake fluid pressure. Further, FIG. 7 is a diagram corresponding to FIG. 1 showing the second embodiment. 1...Front wheel steering mechanism 7.7'...Encroaching wheel steering mechanism 25...Controller 28...Δ8S
Control D-Ra 34...Steering ratio variable means 35...Characteristic selection section 42...Anti-skid brake! ! Figure 2 Figure 5 Figure 3 Figure 4

Claims (1)

[Claims] a front wheel steering mechanism that steers the front wheels according to steering wheel steering;
A four-wheel steering device for a vehicle comprising a rear wheel steering mechanism that steers the rear wheels in accordance with the steering of the front wheels, wherein the rear wheel steering mechanism is configured to change the rear wheel steering angle with respect to the front wheel steering angle. a steering ratio variable means that varies the ratio according to a steering ratio characteristic depending on the vehicle speed; a detection means that is connected to the anti-skid brake device and detects the operating state of the anti-skid brake device;
It is possible to input an output signal from the detection means, and when a signal indicating the operation of the anti-skid brake device is input from the detection means, the ratio of the rear wheel steering angle to the front wheel steering angle is set to the same phase or to a neutral range. A four-wheel steering device for a vehicle, comprising a correction means for correcting the vehicle.