JPS621675A - Four-wheel steering gear for vehicles - Google Patents

Abstract

PURPOSE:To moderate the degree of responsiveness in a car and make improvements in convergeability and driving stability, by steering rear wheels farther in the same phase direction than in time of the other steering wheel operations, when wheeling around for a lane alteration in case of a four-wheel drive vehicle. CONSTITUTION:At the time of steering wheel operation other than a lane lateration, a characteristic selecting part 36 selects a steeting ratio characteristic B from a characteristic memory part 30. And, a desired steering angle is calculated by a desired steering angle operational part 31 of a steering ratio variable device 34, whereby each steering angle of front and rear wheels is variably controlled, and rear wheels are steered in opposite phase to front wheels at the time of low speed but at the time of high speed, they are steered in the same phase. In case of the lane alteration, when a steering wheel is made to wheel around from steerage in a lane altering direction to the opposite direction, the characteristic selecting part 36 receives an output signal out of a wheel-around state detecting device 35, selecting a steering ratio characteristic A from the characteristic memory part 30, and is variably controlled by the steering ratio variable device 34. Since the steering ratio characteristic A is shifted to the same phase side as compared with the steering ratio characteristic B, rear wheels are steered in the same phase direction as front wheels.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel steering system for a vehicle that steers the rear wheels in response to the steering of the front wheels.

(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 that changes the steering angle of the front wheels according to the steering angle of the front wheels and the vehicle speed, with the front wheels and rear wheels being in opposite phases at low speeds and in the same phase at high speeds. Vehicles are known that are capable of preventing wheels from skidding and improving running stability, as well as improving maneuverability at low speeds.

(Problems to be Solved by the Invention) By the way, in both four-wheel steering and two-wheel steering vehicles, when changing the driving lane while driving, the steering wheel is first steered in the direction of changing lanes, and then The vehicle passes through the straight-ahead position and is turned back in the opposite direction, but when the steering wheel is turned back, the response of the vehicle to the steering wheel becomes more gradual than when other steering wheels are turned, in order to improve the vehicle's convergence or driving stability. It is desirable that 4
For wheel-steering vehicles, there is a strong demand for its realization.

The present invention has been made in response to such demands,
The purpose of this is to steer the rear wheels in the same phase direction as the front wheels when changing lanes, especially in vehicles with four-wheel steering, by steering the rear wheels in the same phase direction as the front wheels when changing lanes. The objective is to improve convergence or running stability by making the speed gentler.

(Means for Solving the Problems) In order to achieve the above objects, the solving means of the present invention includes a front wheel steering mechanism that steers the front wheels in response to steering wheel steering, and a front wheel steering mechanism that steers the front wheels in response to steering wheel steering. A four-wheel steering system for a vehicle comprising a rear wheel steering mechanism for steering rear wheels, wherein the rear wheel steering mechanism is configured to vary a ratio of a rear wheel steering angle to a front wheel steering angle according to a predetermined steering ratio characteristic. a steering ratio variable means, a detection means for detecting a state in which the steering wheel is steered in a predetermined direction, passes a straight ahead position and is turned back in the opposite direction; The present invention is configured to include a correction means for correcting the ratio of the rear wheel turning angle to the front wheel turning angle in the same phase direction when in the state.

(Function) With the above configuration, in the present invention, when the steering wheel is turned back in the case of changing lanes, the rear wheel steering angle is changed according to a predetermined steering ratio characteristic in the steering ratio variable means of the rear wheel steering mechanism. The angle ratio is corrected in the same phase direction by the correction means that receives the output signal from the detection means, and with this corrected steering ratio, the rear wheels turn more slowly than when other steering wheels are turned. It will be steered in the direction.

(Example) Embodiments of the present invention will be described below based on the drawings.

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.

2R, the front wheel steering mechanism 1 includes a steering handle 3, a rack and pinion mechanism 4 that converts rotational motion of the steering handle 3 into linear motion, and the rack and pinion mechanism. 4 operation to the front wheel 2
It consists of left and right tie rods 5, 5 and a knuckle arm 6.6 which transmit information to L and 2R and 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. A rack 12 is attached to the rear wheel operating rod 11.
is formed, and the pinion 13 that meshes 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 of the pulse motor 14 and the rotation table. 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 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 eight hydraulic chambers 18b, 18c are Hydraulic passage 1 each
9a.

19b, communicates with a control valve 20 that controls the oil supply direction and oil pressure to the power cylinder 18,
A hydraulic pump 23 is connected to the control valve 20 via an oil supply passage 21 and an oil return passage 22.
The hydraulic pump 23 is rotationally driven by a motor 24. The control valve 20 detects the rotational direction of the pinion shaft 17 and communicates the oil supply passage 21 with the left rotation hydraulic chamber 18b when the rear wheels 8L and 8R are steered to the left (counterclockwise in the figure). In addition, the right diversion hydraulic chamber 18c is connected to the oil return path 2.
When the rear wheels 8L and 8R are steered to the right (clockwise in the figure), the communication state is opposite to the above.
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. Rear wheel operating rod 1
1 is moved in the axial direction (vehicle width direction), the rear wheel operating rod 11 is moved by supplying pressure oil to the power cylinder 18.
We are trying to help people move.

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 section of the rear wheel steering mechanism 7. The controller 25 receives a steering angle signal from a steering angle sensor 26 that detects the front wheel steering angle from the steering of the steering wheel 3 in the front wheel steering mechanism 1, and a vehicle speed signal from a vehicle speed sensor 7 that detects the vehicle speed. are respectively input, and the battery power source 28 is connected.

As shown in FIG. 2, the controller 25 receives the steering angle signal from the steering angle sensor 26 and the vehicle speed signal from the vehicle speed sensor 27, and determines the front wheel steering angle from the steering ratio characteristic stored in the characteristic storage section 30. and a target steering angle calculation unit 31 that calculates a target steering angle of the rear wheels corresponding to the vehicle speed, and a pulse generator that outputs a pulse signal corresponding to the target steering angle calculated by the target steering angle calculation unit 31. 32, and a driver 33 that receives a pulse signal from the pulse generator 32 and converts it into a drive pulse signal that drives the pulse motor 14 and the drive motor 24 of the hydraulic pump 23. A steering ratio that controls the pulse motor 14 and the drive motor 24 of the hydraulic pump 23 so that the rear wheel steering angle becomes a target steering angle by varying the steering angle ratio (steering ratio) according to a predetermined steering ratio characteristic. Variable means 34
is configured.

Further, the controller 25 receives a steering angle signal from the steering angle sensor 26, and determines whether the steering wheel 3 is steered in a predetermined direction when changing lanes, or when the steering wheel 3 is turned in the opposite direction after passing the straight-ahead position. The steering wheel 3 is provided with a turning state detecting means 35 for detecting the steering wheel, and receives an output signal from the detecting means 35.
a characteristic selection section as a correction means that selects the steering ratio characteristic stored in the characteristic storage section 30 according to the steering state of the steering wheel and corrects the steering ratio in the same phase direction when the steering wheel 3 is in the above-mentioned turning state; 36, and the target steering angle calculation section 31 calculates the target turning angle according to the steering ratio characteristic of the characteristic storage section 30 selected by the characteristic selection section 36.

As shown in FIG. 3, the turning state detection means 35 includes a right steering determination section 37 that determines whether the steering wheel 3 is steered to the right based on the steering angle signal from the steering angle sensor 26; A left steering determining section 38 that determines whether the steering wheel 3 is steered to the left based on the steering angle signal from the angle sensor 26, and the right steering determining section 37.
A first timer 39 receives an output signal from the left steering discriminator 38 and outputs an output signal for a predetermined period of time after the output signal is no longer input. When receiving an output signal from the second timer 40 which issues an output signal for a predetermined period of time from when no input is received, the output signal from the first timer 39, and the output signal from the left steering determination section 38, that is, when the driving lane is changed to the right side of the vehicle. A first AND circuit 41 that issues an output signal when changing lanes, and an output signal from the second timer 40.
゛A second AND circuit 42 that issues an output signal when receiving the output signal from the right steering determination section 37, that is, when changing the driving lane to the lane on the left side of the vehicle;
The OR circuit 43 receives the output signals from the AND circuits 41 and 42, and the OR circuit 43 issues an output signal to the characteristic selection section 36 even if the lane change is made to either the left or right side of the vehicle. It is configured as follows.

On the other hand, as shown in FIG. 4, the steering ratio characteristics stored in advance in the characteristic storage section 30 include a steering ratio characteristic A for changing lanes, and a steering ratio characteristic A for steering other than changing lanes. There are two types of ratio characteristic B. These steering ratio characteristics A and B basically have opposite phases in which the steering ratio becomes softer in the negative direction as the vehicle speed increases from low speed to high speed (a state in which the front and rear wheels are steered in opposite directions).
The steering ratio k changes from a large value to close to zero in the medium speed range, and 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 changes to the same phase in the positive direction. The steering ratio k is set to be large. Of both steering ratio characteristics A and B, the steering ratio characteristic A for changing lanes is on the same phase side over the entire vehicle speed range from low speed to high speed compared to the other steering ratio characteristics B. In the low speed range where the steering ratio k is in the opposite phase in the negative direction, the steering ratio k approaches zero or changes to the same phase in the positive direction, and the steering ratio k is in the positive direction. The steering ratio K is set to a larger value in the medium speed range or high speed range where the values are in the same phase.

Next, to explain the operation and effect of the first embodiment, in the case of steering other than changing lanes, the controller 25 of the rear wheel steering mechanism 7 uses the characteristic selection section 36.
Two types of steering ratio characteristics A stored in the characteristic storage unit 30 in
Steering ratio characteristic B is selected from B, and the target turning angle is calculated by the target turning angle calculation unit 31 of the steering ratio variable means 34 based on the selected steering ratio characteristic B. , the steering ratio of the rear wheel steering angle to the front wheel steering angle is the steering ratio characteristic B.
The rear wheels 8L and 8R are steered in the opposite phase to the front wheels 2L and 2R at low speeds, and the rear wheels 8L and 8R are steered in the opposite phase to the front wheels 2L and 2R at high speeds.
It is steered in the same phase as L and 2R.

As a result, as in the case of a conventional four-wheel steering system, it is possible to improve turning performance and running stability during cornering, and it is also possible to improve maneuverability when parking the vehicle in a garage.

On the other hand, in the case of changing lanes, when the steering wheel 3 is steered in the lane changing direction, when the driver passes the straight ahead position and turns back in the opposite direction, the characteristic selection section 36
In response to the output signal from the turning state detection means 35, the characteristic storage unit 30 stores the steering ratio characteristic A for changing lanes instead of the above-mentioned steering ratio characteristic A for steering other than changing lanes.
The steering ratio is variably controlled by the steering ratio variable means 34 according to the selected steering ratio characteristic A.
゛In this case, the steering ratio characteristic A for changing lanes is shifted to the same phase side compared to the steering ratio characteristic B for steering other than changing lanes, so the rear wheels 8L.

8R is steered in the same phase direction as the front wheels 2L and 2R, which are the side wheels that suppress turning, compared to when the steering wheel is operated other than when changing lanes as described in -L. Therefore, the responsiveness of the vehicle to steering wheel steering is relaxed, and the convergence or running stability of the vehicle can be improved.

Here, in the case of changing lanes, the state in which the steering wheel 3 is steered toward the lane change side, the state in which the steering wheel 3 is turned to the opposite direction after passing through the straight-ahead position is the state in which the state in which the steering wheel 3 is steered is turned back to the opposite direction.
The mechanism detected by 5 will be explained using FIG. 5, taking as an example the case where the driving lane is changed to the lane on the right side of the vehicle.

In the case of this lane change, first, the steering wheel 3 is steered from the straight-ahead position to the right direction, which is the lane change side. At this time, an output signal is output from the right steering determination section 37 of the turning state detection means 35 to the first timer 39.

Next, the steering handle 3 is turned from the rightward direction to the leftward direction after passing through the straight-ahead position. When the steering wheel 3 passes through the straight-ahead position (point P in FIG. 5), the output signal from the right steering discriminator 37 is no longer input to the first timer 39.
An output signal from the first timer 39 is output to the first AND circuit 41 for a predetermined time T. Further, when the steering wheel 3 passes the straight-ahead position and is steered to the left, an output signal is output from the left steering determination section 38 to the first AND circuit 41.

As described above, when the output signal from the first timer 39 and the output signal from the left steering determination unit 38 are input to the first AND circuit 41, which almost coincides with the time P, the first AND circuit 41 outputs an output signal to the A circuit 43, and the OR circuit 43 outputs an output signal to the characteristic selection section 36 as a detection signal of the switching state.

In addition, even in the case of changing lanes, when the steering wheel 3 is steered in the direction of changing lanes (the stage before time P in Fig. 5), the steering ratio is changed in the same way as when steering the steering wheel for purposes other than changing lanes. The steering ratio is controlled according to characteristic B, and good turning performance can be maintained.

FIG. 6 shows a modification of the controller 25 of the rear wheel steering mechanism 7 in the first embodiment. The controller 25 includes a target steering angle calculation section 31', a pulse generator 32', and a driver 33', and stores the steering ratio of the rear wheel steering angle to the front wheel steering angle in a characteristic storage section 30.
A variable steering ratio that is variably controlled according to a predetermined steering ratio characteristic stored in ' (corresponding to the steering ratio characteristic B for steering other than lane changes stored in the characteristic storage section 30 in the first embodiment) The target steering angle calculation section 31' of the steering ratio variable means 34' receives the output signal from the turning state detection means 35 and calculates the result when the steering wheel 3 is in the turning state. The system is equipped with a correction section 44 as a correction means for adding a corrected turning angle to the target turning angle, thereby correcting the steering ratio in the same phase direction.

Further, FIG. 7 shows the steering ratio characteristics in the case where the steering ratio is controlled by controlling the rear wheel steering angle θR according to the magnitude of the front wheel steering angle θF as another modification of the first embodiment. This is what is shown. This steering ratio control based on the steering angle is based on the fact that the front wheel steering angle θF is small at high speeds and becomes large at low speeds, and the steering ratio of the rear wheel steering angle θR with respect to the front wheel steering angle θF is adjusted. Basically, the steering ratio characteristics are similar to steering ratio control based on vehicle speed, such that the front and rear wheels are in opposite phases at low speeds and in the same phase at high speeds. It is set.

Also, in the case of steering ratio control using the above-mentioned rudder angle,
The steering ratio characteristic is the steering ratio characteristic C for changing lanes.
and steering ratio characteristics for steering other than lane changes.
There are different types. Compared to other steering ratio characteristics, the steering ratio characteristic C for changing lanes tends to deviate toward the same phase side in the positive direction of the rear wheel steering angle θR over the entire range of the front wheel steering angle θF. When the steering wheel is turned back when changing lanes, the rear wheels are steered in the same phase direction as the front wheels according to this steering ratio characteristic C, as in the case of the first embodiment, compared to when the steering wheel is turned other than when changing lanes. Ru. Note that in the case of steering ratio control using the steering angle, the vehicle speed sensor 27 for detecting vehicle speed as in the first embodiment is not required.

Furthermore, FIG. 8 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 mechanism 7' in this four-wheel steering system is similar to that of the four-wheel steering system of the first embodiment. Instead of electrically steering the rear wheels 8L and 8R by the operation of the pulse motor 14 as in the rear wheel steering mechanism 7 shown in FIG. It was designed to turn the steering wheel.

That is, the rear wheel steering mechanism 7' includes a steering ratio changing device 50 made of gears, etc., and the rear end of a transmission rod 51 extending in the direction of the vehicle body i11 is connected to the steering ratio changing device 50. A pinion 53 is provided at the front end of the rod 51 and meshes with a shaft 52 formed on the rack shaft 4a of the rack and pinion mechanism 4 of the front wheel steering mechanism 1. Further, a sliding member 54 extends from the steering ratio changing device 50, and a rack 12 and a pinion 13 are connected to the rear wheel operating rod 11 with respect to a rack 55 formed on the surrounding member 54.
A pinion 56 provided at the front end of the pinion shaft 17 connected via the pinion 56 meshes with the pinion 56 . However, the front wheel steering mechanism 1
The steering force is transmitted from the rack shaft 4a of the rack and pinion mechanism 4 via the transmission rod 51 to the steering ratio changing device 50, and the steering ratio is changed in accordance with the control of the controller 25 in the steering ratio changing device @50. After the steering force is applied to the sliding member 5
4 and the pinion shaft 17 to the rear wheel operating rod 11, so that the rear wheels 8L and 8R are steered left and right. The other configuration of the four-wheel steering device is the same as that of the four-wheel steering device of the first embodiment, and the same members are given the same reference numerals and their explanations will be omitted.

And the above-mentioned steering ratio changing device Ii! The controller 25 itself that controls the controller 50 is the same as in the first embodiment,
Moreover, it goes without saying that the same effects and effects can be achieved thereby.

(Effects of the Invention) As described above, according to the four-wheel steering system for a vehicle according to the present invention, when turning the steering wheel in the case of changing lanes, the steering ratio variable means in the control section of the rear wheel steering mechanism adjusts the predetermined steering direction. The ratio of the rear wheel steering angle to the front wheel steering angle, which is varied according to the ratio characteristic, is corrected in the same phase direction by the correction means, and with this corrected steering ratio, the rear wheels turn more slowly than when other steering wheels are turned. Since the vehicle is steered in the same phase direction as the steering wheel, it is possible to improve convergence or running stability when changing lanes while maintaining good turning performance during other steering operations.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and are shown in FIGS. 1 to 4.
The figures show a first embodiment, in which 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,
FIG. 3 is a block diagram of the switching state detection means, and FIG.
The figure is a diagram showing steering ratio characteristics in the case of steering ratio control using the vehicle speed of the controller. FIG. 5 is an explanatory diagram for explaining a mechanism for detecting the reversed state of the handle in the reversed state detection means. 6 and 7 each show a modification of the first embodiment, FIG. 6 is a diagram corresponding to FIG. 2, and FIG. 7 shows the steering ratio characteristics in the case of steering ratio control using the steering angle of the controller. FIG. FIG. 8 is a diagram corresponding to FIG. 1 showing the second embodiment. 1... Front wheel steering mechanism, 7.7'... Rear wheel steering mechanism,
25... Controller, 26... Rudder angle sensor, 34
゜34'... Steering ratio variable means, 35... Turning state detection means, 36... Characteristic selection section, 44... Correction section.

Claims (1)

[Claims] (1) A four-wheel steering system for a vehicle comprising 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 rear wheels in response to steering of the front wheels. The rear wheel steering mechanism includes a steering ratio variable means that varies the ratio of the rear wheel steering angle to the front wheel steering angle according to a predetermined steering ratio characteristic, and a steering ratio variable means that changes the straight-ahead position from a state where the steering wheel is steered in a predetermined direction. a detection means for detecting a state in which the steering wheel has passed and has been turned back in the opposite direction; and a detection means for receiving an output signal from the detection means, and a ratio of a rear wheel turning angle to a front wheel turning angle when the steering wheel is in a turning state so as to be in the same phase direction. A four-wheel steering device for a vehicle, comprising a correction means for correcting the vehicle.