JPH0649465B2 - 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 that steers not only front wheels but also rear wheels. Regarding measures to improve stability.

(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. 55-77968, a front-wheel steering mechanism that steers front wheels and a rear-wheel steering mechanism. It is equipped with a rear-wheel steering mechanism that steers the vehicle, and changes the steering angle of the rear wheels in accordance with the steering angle of the front wheels and the vehicle speed.When the vehicle speed is low, the front and rear wheels are in opposite phases in opposite directions, and at high vehicle speeds. However, it is known that by making the wheels in the same direction and in the same phase, side slippage of the wheels can be prevented to improve running stability, and at the same time, small turning performance at low vehicle speed can be improved.

(Problems to be Solved by the Invention) However, when traveling on a downhill, the lateral grip force of the rear wheels with respect to the road surface is reduced as the center of gravity of the vehicle moves forward. When steered,
There is a problem in that the wheels tend to skid regardless of whether the vehicle is running at high speed or low speed, which impairs running stability.

The present invention has been made in view of such a point, and its purpose is to change the rear wheel steering characteristics as appropriate according to the inclination of the road surface, not to mention during normal traveling on a flat road, Even when traveling downhill, it is intended to prevent side slippage of the wheels as much as possible to ensure traveling stability.

(Means for Solving the Problem) In order to achieve the above object, the solution 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 characteristic. In a four-wheel steering system for a vehicle, comprising a rear-wheel steering mechanism for steering wheels, the rear-wheel steering mechanism includes a detection means for detecting a downhill condition of a road surface, and an output signal of the detection means. And a correction means for determining the downhill condition of the road surface and for correcting the rear wheel steering characteristics so that the rear wheels are steered with the characteristics corrected to the same phase side when the road surface is downhill as compared to when the road is flat. It was done.

(Operation) With the above configuration, in the present invention, the rear wheels are steered with the predetermined rear wheel steering characteristics during normal traveling on a flat road, and the traveling stability of the vehicle is ensured excellently.

Further, when traveling on a downhill, the rear wheel steering characteristic is corrected to the same phase side by the correction means, so that the lateral gripping force of the rear wheels with respect to the road surface is increased and traveling stability is ensured.

(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. The left and right tie rods 5 and 5 and the 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 and 8R are configured to be steered to the left or right on the basis of the rear wheel steering characteristics set in advance corresponding to the rotation direction and the rotation amount of 14.

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 operation rod 11, and the hydraulic chambers 18b, 18c are An oil supply passage 21 is connected to a control valve 20 for controlling the oil supply direction and the oil pressure to the power cylinder 18 via hydraulic passages 19a and 19b, respectively.
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. 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 and 16, the pinion shaft 17, the pinion 13 and the rack 12, pressure oil to the power cylinder 18 is applied. The supply assists the movement of the rear wheel operation rod 11.

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 receives a steering angle signal from a steering angle sensor 26 that detects a rear wheel steering angle from the steering amount of the steering wheel 3 in the front wheel steering mechanism 1 and a vehicle speed signal from a vehicle speed sensor 27 that detects a vehicle speed. , A downhill signal from a downhill sensor 28 as a detecting means for detecting a downhill depending on the inclination state of the road surface, and a battery power source 29 is connected.

Inside the controller 25, as shown in FIG. 2, a characteristic storage unit 30 for storing two types of steering ratio characteristics of front wheels and rear wheels with respect to the vehicle speed as shown in FIG. 3, and a steering angle sensor 2
The steering angle signal from the vehicle 6 and the vehicle speed signal from the vehicle speed sensor 27 are received, and the target steering angle of the rear wheels corresponding to the front wheel steering angle and the vehicle speed is determined from the steering ratio characteristics stored in the characteristic storage unit 30. A target turning angle calculation unit 31 for calculating, a pulse generator 32 for outputting a pulse signal corresponding to the target rear wheel turning angle calculated by the target turning angle calculation unit 31, and a pulse signal from the pulse generator 32 Receive pulse motor 14
And a driver 33 for converting into a drive pulse signal for driving the drive motor 24 of the hydraulic pump 23. 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 of the pulse motor 14 and the hydraulic pump 23. Steering ratio changing means 34 for controlling the drive motor 24 is configured.

Here, the steering ratio characteristics previously stored in the characteristic storage unit 30 are, as shown in FIG. 3, the steering ratio characteristics A for normal traveling on a flat road and the steering ratio characteristic for traveling on a downhill. There are two types of steering ratio characteristics B. 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 ratio k changes to the same phase in the positive direction (the front and rear wheels are steered in the same direction) in the medium speed range, and the steering ratio in the same phase in the high speed range. It is set so that k becomes large. Of the two steering ratio characteristics A and B, the steering ratio characteristic B for downhill traveling is compared with the steering ratio characteristic A for normal traveling over all vehicle speeds from low speed to high speed. In the low speed range where the steering ratio k tends to shift to the same phase side and the steering ratio k becomes a value 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 The steering ratio k is set to a larger value in the medium speed range or the high speed range in which the values of the same phase are in the positive direction.

Further, inside the controller 25, a characteristic selection unit 35 that further receives the downhill signal from the downhill sensor 28.
Is provided. When the downhill signal value of the downhill sensor 28 is less than the set value, the characteristic selecting section 35 selects the steering ratio characteristic A for normal traveling from the characteristic storing section 30, while the downhill signal is set. When the value is equal to or more than the value, the steered ratio characteristic B for downhill traveling is selected, and the target steered angle calculation unit 31 is selected according to the steered ratio characteristic of the characteristic storage unit 30 selected by the characteristic selection unit 35. The calculation of the target rear wheel turning angle is performed.

Therefore, the characteristic selection unit 35 causes the downhill sensor 28 to
It determines the downhill condition of the road surface based on the output signal of, and when the road is downhill, the steering ratio is for normal running so that the rear wheels are steered with the characteristics corrected to the same phase side as when flattened. The steering ratio characteristic A is changed to the steering ratio characteristic B for traveling on a downhill, and the correction means is provided.

Next, the operation and effect of the first embodiment will be described. During normal traveling on a flat road, in the controller 25 of the rear wheel steering mechanism 7, the characteristic selection unit 35 stores the characteristic in the characteristic storage unit 30. The steering ratio characteristic A for normal traveling is selected from the two selected steering ratio characteristics A and B, and based on the selected steering ratio characteristic A, the target steering ratio varying means 34 is operated. Since the target rear wheel turning angle is calculated by the rudder angle calculation unit 31, the turning ratio of the rear wheel turning angle to the front wheel turning angle is variably controlled according to the turning ratio characteristic A for traveling. As a result, the rear wheels 8L and 8R are steered in the opposite phase to the front wheels 2L and 2R at low vehicle speeds, and at the middle and high vehicle speeds.
The L and 2R are steered in the same direction and phase.

On the other hand, when traveling downhill, the characteristic selecting unit 35
Receives the downhill signal from the downhill sensor 28, selects the steering ratio characteristic B for downhill traveling from the characteristic storage unit 30 in place of the steering ratio characteristic A for normal traveling described above, The turning ratio is variably controlled by the turning ratio changing means 34 in accordance with the selected turning ratio characteristic B for traveling downhill.

In this case, since the steered ratio characteristic B for downhill traveling is deviated to the same phase side as compared with the steered ratio characteristic A for normal traveling, the rear wheels 8L and 8R are more than in normal traveling. Front wheels 2L, 2
The steering wheel is steered in the same direction as R to increase the lateral grip force of the rear wheels, and as a result, the wheels (the front wheels 2L, 2R and the rear wheels 8L, 8R) can slide sideways even when traveling on a downhill. It will be prevented as much as possible. Therefore, traveling stability can be improved.

Further, FIG. 4 shows the rear wheel steering mechanism 7 in the first embodiment.
7 shows a modified example of the controller 25 of FIG. The controller 25 is composed of a target turning angle calculation unit 31 ', a pulse generator 32' and a driver 33 ', and the turning ratio of the rear wheel turning angle to the front wheel turning angle is stored in the characteristic storage unit 30'. In addition to the turning ratio varying means 34 ', which is variably controlled according to a predetermined turning ratio characteristic (corresponding to the turning ratio characteristic A for normal traveling stored in the characteristic storage unit 30 in the first embodiment). Upon receiving a downhill signal from the downhill sensor 28, with respect to the target rear wheel turning angle calculated by the target turning angle calculating section 31 'of the turning ratio varying means 34' according to the increase of the inclination angle of the road surface. The correction unit 36 is provided as a correction unit that gradually corrects the steering ratio in the in-phase direction by adding the corrected steering angle in the positive direction.

Therefore, in the case of the modified example, the steering ratio characteristic for normal traveling is gradually corrected in the same phase direction in accordance with the increase in the inclination angle of the downhill. The control accuracy of the steering ratio becomes finer than when the steering ratio characteristic is switched from that for normal driving to that for downhill driving when the tilt angle of the vehicle becomes equal to or greater than the set value, and driving stability is improved. Can be further improved.

Further, FIG. 5 shows a steering ratio characteristic when the steering ratio is controlled by calculating the rear-wheel steering angle θ _R according to the magnitude of the front-wheel steering angle θ _F as a modification of the first embodiment. It is shown. Steering angle ratio control by this steering angle, the front wheel turning angle theta _F is smaller than at high vehicle speed, steering of the rear wheel steering angle theta _F for the front wheel turning angle theta _F based on the actual situation that becomes large at the time of low vehicle speed The steering ratio characteristic is basically the same as in the case of steering ratio control by vehicle speed, in which the front wheel and the rear wheel are in opposite phases at low vehicle speeds and at the same phase at high vehicle speeds. Is set to.

Then, even in the case of the steering ratio control by the steering angle,
As the steering ratio characteristic, the steering ratio characteristic C for normal traveling is used.
And a steering ratio characteristic D for traveling on a downhill. Compared with the steering ratio characteristic C for normal traveling, the steering ratio characteristic D for downhill traveling has a rear wheel steering angle θ _{R in} the same phase in the positive direction over the entire range of the front wheel steering angle θ _F. When the inclination angle of the downhill is equal to or more than the set value, the rear wheels are in the same phase direction as the front wheels as compared with the normal running in the same manner as in the first embodiment in the state where the inclination angle of the downhill is equal to or more than the set value. Be steered to. In the case of the steering ratio control based on the snake angle, the vehicle speed sensor 27 for detecting the vehicle speed as in the first embodiment is necessary.

Furthermore, 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 device is an alternative to electrically steering the rear wheels 8L, 8R by the operation of the pulse motor 14 as in the rear-wheel steering mechanism 7 in the four-wheel steering device of the first embodiment. In addition, the rear wheels 8L and 8R are mechanically steered by utilizing the steering force of the front wheel steering mechanism 1.

That is, the rear wheel steering mechanism 7'includes a steering ratio changing device 37 including gears and the like. A rear end of a transmission rod 38 extending in the vehicle front-rear direction is connected to the steering ratio changing device 37, and a front end portion of the transmission rod 38 is connected to a rack shaft 4a of the rack and pinion mechanism 4 of the front wheel steering mechanism 1. A pinion 40 that meshes with the formed rack 39 is provided. Further, a sliding member 41 is extended from the turning ratio changing device 37. With respect to a rack 42 formed on the sliding member 41, the rack 12 and the pinion 1 are attached to the rear wheel operation rod 11.
The pinion 43 provided at the front end of the pinion shaft 17 connected through 3 meshes with the pinion shaft 17. 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 37 via the transmission rod 38, and the controller 25 controls the steering ratio changing device 37. After the steering ratio is changed in accordance with the above, the steering force is applied to the rear wheel operation rod 11 via the sliding member 41 and the pinion shaft 17.
The rear wheels 8L and 8R are steered to the left and right by being transmitted to. The other configurations of the four-wheel steering system are the same as those of the four-wheel steering system of the first embodiment.
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 37 is the same as in the case of the first embodiment, and it is needless to say that the same operation / effect can be achieved thereby.

(Effects of the Invention) As described above, according to the four-wheel steering system for a vehicle of the present invention, during traveling on a downhill, the preset rear wheel steering characteristic is corrected in the same phase direction by the correction means, and the rear wheel steering characteristic is corrected. Since the lateral grip force on the road surface is increased, the wheels can be prevented from slipping and the running stability can be improved.

[Brief description of drawings]

The drawings show an embodiment of the present invention and are shown in FIGS.
1 shows 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,
FIG. 3 is a diagram showing a turning ratio characteristic in the case of turning ratio control according to the vehicle speed of the controller. 4 and 5 each show a modified example of the first embodiment. FIG. 4 shows the equivalent diagram of FIG. 2, and FIG. 5 shows the steering ratio characteristics in the case of the steering ratio control by the steering angle of the controller. FIG. 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 ・ ・ ・ Downhill sensor, 30 ・ ・ ・ Characteristic storage unit, 34, 34 '…… Turning ratio varying means, 35 ……
Characteristic selection unit, 36 ... Correction unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Miyoshi 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) Reference JP-A-49-118126 (JP, A)

Claims (1)

[Claims] 1. A vehicle comprising: 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 preset rear wheel steering characteristics. In the wheel steering device, the rear wheel steering mechanism determines a downhill state of the road surface based on an output signal of the detecting means and a detecting means for detecting the downhill state of the road surface. A four-wheel steering system for a vehicle, comprising: a correction unit that corrects the rear wheel steering characteristic so that the rear wheels are steered with a characteristic that is corrected to the same phase side as when the vehicle is flat.