JPS6212472A - Four-wheel steering device for car - Google Patents

Abstract

PURPOSE:To improve traveling stability by detecting a car height state and correcting the ratio of the rear wheel steering angle against the front wheel steering angle in the same phase direction when the car height is high. CONSTITUTION:The controller 25 of a rear wheel steering mechanism 7 has an arithmetic unit calculating the steering angle of rear wheels in response to the front wheel steering angle and a car speed based on a pre-stored steering ratio characteristics and variably controls motor 14, 24 so that the rear wheel steering angle becomes a target angle. In this case, the ratio of the rear wheel steering angle against the front wheel steering angle in the steering ratio characteristics when the car height is high is displaced toward the same phase side as compared with that in the steering characteristics when the car height is low. As a result, grip forces of wheels against the road surface on a rough road can be increased, instability due to the high center of gravity of a car body is eliminated, and tumbling and a sideslip of a car can be prevented.

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.

(Problem to be Solved by the Invention) By the way, when a vehicle is driving on a rough road, a vehicle height adjustment device is usually used to avoid collision between the lower surface of the vehicle body and the road surface due to vertical vibration of the vehicle body. Although the height of the vehicle is increased, in this case, the center of gravity of the vehicle becomes higher, creating an unstable state and making the vehicle more likely to overturn. In addition, in the case of rough roads, the coefficient of friction μ of the road surface is generally low and tends to decrease, so there is a problem that the grip of the wheels on the road surface decreases, making it easier to cause skidding, which impairs driving stability. .

The present invention has been made in view of the above, and its purpose is to detect the vehicle height state and, when the vehicle height is high, to adjust the ratio of the rear wheel steering angle to the front wheel steering angle in the same phase direction. The purpose of this correction is to alleviate turning, increase the grip of the wheels, prevent the vehicle from overturning, skidding, etc., and improve running stability.

(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. In a four-wheel steering system for a vehicle, the rear wheel steering mechanism is configured to vary a ratio of a rear wheel steering angle to a front wheel steering angle in accordance with a predetermined steering ratio characteristic. a steering ratio variable means, a detection means for detecting a vehicle height condition, and a ratio of a rear wheel steering angle to a front wheel steering angle in the same phase direction when the vehicle height condition is high in response to an output signal from the detection means; The configuration includes a correction means for correction.

(Function) With the above configuration, in the present invention, when driving on a rough road with a high vehicle height, rear wheel steering is performed with respect to a front wheel steering angle that is varied by a steering ratio variable means according to a predetermined steering ratio characteristic. The angle ratio (steering ratio) is corrected in the same phase direction by the correction means, and the rear wheels are steered in the same phase direction, that is, in a direction that eases the turning of the vehicle, based on this corrected steering ratio. This increases the grip of the wheels and prevents the vehicle from tipping over or skidding.

(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, in which reference numeral 1 denotes a front wheel steering mechanism for steering left and right front wheels 21°2R; 1 includes a steering handle 3, a rack and pinion mechanism 4 that converts rotational motion of the steering handle 3 into linear motion;
left and right tie rods 5 for transmitting the operation of the rack and bin A mechanism 4 to the front wheels 2L, 2R and steering them left and right;
5 and a knuckle arm 6.6.

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 on 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 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 amount 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 has a left turning hydraulic chamber 18bJ5J and a right turning hydraulic chamber 18G partitioned in the vehicle width direction by a piston 18a fixed to the rear wheel operating rod 11, and the famous pressure chambers 18b, 18c. are hydraulic passages 19a, respectively.

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 SR 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.
On the other hand, when the rear wheel 81.8R is 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. Wheel operation rod 11
When the rear wheel operating rod 11 is moved in the axial direction (vehicle width direction), pressure oil is supplied to the power cylinder 18 to assist the movement of the rear wheel operating 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 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 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 the vehicle speed. and a vehicle height signal from a manually operated vehicle height adjustment switch 28 serving as a detection means for detecting the vehicle height state, and a battery power source 29 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. Steering in which the pulse motor 14 and the drive motor 24 of the hydraulic pump 23 are controlled by I so that the steering angle ratio (steering ratio) is varied according to a predetermined steering ratio characteristic so that the rear wheel steering angle becomes the target steering angle. Ratio variable means 3
4 are configured.

The controller 25 also includes a vehicle height adjustment switch 28.
The characteristics storage unit 3 receives the vehicle height signal from the
Select the steering ratio characteristic stored in 0 and select the high vehicle height l-
It is equipped with a characteristic selection unit 35 as a correction means for correcting the steering ratio in the same phase direction when the vehicle height signal is 1rGl (
The target steering angle calculation section 31 calculates the target turning angle according to the steering ratio characteristic in the characteristic storage section 30 selected by the characteristic selection section 35.

Here, as shown in FIG. 3, the steering ratio characteristics stored in advance in the characteristic storage section 30 are different from the steering ratio characteristics when the vehicle height is low to the steering ratio characteristics when the vehicle height is high. There are two types of characteristic B. This dual steering ratio characteristic A.

Basically, B is such that as the vehicle speed increases from low to high speed, the steering ratio k changes from a large value to close to zero in the opposite phase in the negative direction (the front and rear wheels are steered in opposite directions). death,
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 is set to increase with the same phase. . And both steering ratios mentioned above.

Among characteristics A and B, steering ratio characteristic B when the vehicle height is high is:
Compared to other steering ratio characteristics A, it tends to deviate to the same phase side over the entire vehicle speed range from low speed to high speed, and in the low speed range where the steering ratio k has a value of opposite phase in the negative direction, the steering ratio In the medium speed range or high speed range where the steering ratio k approaches zero or changes to the same phase in the positive direction, and the steering ratio k becomes the same phase value in the positive direction, the steering ratio k is set to a larger value. ing.

The vehicle height adjustment device that adjusts the middle height by switching the vehicle height adjustment switch 28 is composed of a suspension unit 36 that suspends the vehicle body, as shown in FIGS. 4 to 6, and each suspension unit 36
Both have a height-adjustable shock absorber 37,
It includes a coil spring 38 arranged around the coil spring 38 and an air chamber 39. The air chamber 39 is connected to an air pump 43 operated by an electromagnetic motor 42 via an air vibrator 41.
Alternatively, a three-way switching valve 44 that selectively switches communication with the atmosphere, and a control valve 45 that controls air supply to the air chamber 39 are provided. The electromagnetic motor 42° three-way switching valve 44 and control valve 4
5 are operated and controlled by a vehicle height adjustment controller 46, which receives a vehicle height signal from the vehicle height adjustment switch 28 and switches the three-way switching valve 44 and the control valve 45. A vehicle height adjustment device is configured that controls the air supply to three air chambers to raise or lower the vehicle height by controlling opening and closing.

That is, when the vehicle height adjustment device increases the vehicle height, the air chamber 3
9 and the air pump 43 communicate with each other.
At the same time, the electromagnetic motor 42 and the control valve 45 are turned on for a predetermined period of time and then turned off after a predetermined period of time, thereby supplying air into the three air chambers and raising the vehicle height. On the other hand, when lowering the vehicle height, the vehicle height adjustment controller 46 receives the OFF signal from the vehicle height adjustment switch 28 and switches the three-way switching valve 44 so that the air chamber 39 communicates with the atmosphere. At the same time, by turning on the control valve 45 for a predetermined period of time and then turning it off after a predetermined period of time, air is released from the air chamber 39 to the atmosphere, thereby lowering the vehicle height.

Here, the specific structure of the shock absorber 37 will be explained in detail with reference to FIGS. 5 and 6. The shock absorber 37 includes an upper case 47 that is attached to the vehicle body via an elastic body 47a, and The lower case 48 is provided to be movable up and down relative to the lower case 48 and is attached to the wheel via a bracket 49.

The lower end of the upper case 47 and the lower case 48
The upper end of the upper case 47 is connected to the upper end of the upper case 47 via a rolling diaphragm 50, and the insides of both cases 47 and 48 are partitioned by a seal member 51, thereby forming a sealed air chamber 39 within the upper case 47. Note that this air chamber 39 is connected to the air pump 43 via the air vibrator 41 as described above, and the air chamber 39 is
The vehicle height is adjusted by adjusting the air pressure inside the coil spring 38. Spring retainers 52 and 53 are fixed to the upper case 47 and the lower case 48, respectively.
is installed.

The lower case 48 is composed of an outer cylinder 54 and an inner cylinder 55. A piston rod 56 hanging from the upper case 47hS is inserted into the inner cylinder 55 so as to be able to move vertically. The interior of the inner cylinder 55 is partitioned into an upper oil chamber 58 and a lower oil chamber 59 by a main valve 57 provided at the lower end. Further, a bottom valve 60 is provided at the lower end of the inner cylinder 55, and a space between the inner cylinder 55 and the outer cylinder 54 is configured as a reservoir chamber 61.

Further, as shown in enlarged detail in FIG. 6, the main valve 57 is an extension provided so as to allow the working fluid to pass only in the direction from the upper oil chamber 58 to the lower oil chamber 59 side by means of a check valve 62. It has a side orifice 63 and a contraction side orifice 65 which is provided to allow the working fluid to pass only in the direction from the lower oil chamber 59 to the upper oil chamber 58 by means of a check valve 64 . Further, the main valve 57 includes a sleeve 66 whose inside passes through a through hole 66a to the upper oil chamber 58 and which directly communicates with the lower oil chamber 59, and a sleeve 66 that is rotatably fitted into the sleeve 66. The valve body 67 of the orifice valve 68 has a control rod 69 inserted into the piston rod 56. via step motor 6
9a and a sleeve 66 as shown.
When the through hole 66a in the valve body 67 and the through hole 67a in the valve body 67 match, the upper oil chamber 58 and the lower oil chamber 59 are communicated with each other.

Next, to explain the operation and effect of the first embodiment, when the vehicle height is low, in the controller 25 of the wheel contact steering mechanism 7, the characteristic selecting section 35 selects the The steering ratio characteristic △ when the vehicle is low is selected from the types of steering ratio characteristics A and B, and the target steering angle of the steering ratio variable means 34 is adjusted based on the selected steering ratio characteristic A. By calculating the target steering angle in the calculation unit 31, the steering ratio of the rear wheel steering angle to the front wheel steering angle is variably controlled according to the steering ratio characteristic A, and the rear wheels 8m and 8R are controlled at low speeds. In this case, the front wheels 2L and 2R are steered in opposite phase, and at high speed, the front wheels 2L and 2R are steered.
It is steered in the same phase as 2R.

On the other hand, when the vehicle height is high, the characteristic selection section 35 receives the output signal from the vehicle height adjustment switch 28 and selects a high vehicle height instead of the steering ratio characteristic A when the vehicle height is low. The current steering ratio characteristic B is selected from the characteristic storage section 30, and the steering ratio is variably controlled by the steering ratio variable means 34 in accordance with the selected steering ratio characteristic B.

In this case, the steering ratio characteristic B when the vehicle height is high is shifted to the same phase side compared to the steering ratio characteristic when the vehicle height is low, so the rear wheels 8L and 8R have a low vehicle height. Front wheel 2 than when
It is steered in the same phase direction as L and 2R, and the turning of the vehicle is suppressed. This is because increasing the vehicle height is often selected when driving on rough roads, so it can increase the grip of the wheels on the road surface on rough roads, and as a result, the vehicle height can be increased. This eliminates the instability caused by a higher center of gravity of the vehicle body, preventing the vehicle from overturning, and also prevents the vehicle from skidding, improving driving stability.

In the first embodiment, the manually operated vehicle height operation switch 28 is used as the vehicle height state detection means, and the HIGI- (signal or LOW signal) of the vehicle height adjustment switch 28 can be detected as the vehicle height signal. However, it is also possible to automatically detect the vehicle height state using a vehicle height sensor.In this case, not only can the same operation and effect as in the first embodiment described above be achieved, but also the above-mentioned 1 detected by the vehicle height sensor
! If the vehicle height condition is low due to a high signal, it can be determined that the road surface condition is good, and if the vehicle height condition is low, it can be determined that the road surface condition is poor.Therefore, the vehicle height signal can be used to determine the road surface condition. You will be able to do so.

Furthermore, 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 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 8m 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' is equipped with a steering ratio changing device 7o made of a gear or the like, and the rear end of a transmission rod 71 extending in the longitudinal direction of the vehicle body is connected to the steering ratio changing device 70.
A binion 73 is provided at the front end of the transmission rod 71 and meshes with a hook 72 formed on the rack shaft 4a of the rack and binion mechanism 4 of the front wheel steering mechanism 1. Also,
The calendar movement member 14 extends from the steering ratio changing device 70, and a rack 75 formed on the sliding member 74 has the following functions:
A pinion 76 provided at the front end of a pinion shaft 17 connected to the rear wheel operating rod 11 via a rack 12 and a pinion 13 meshes with the pinion 76 . However, front wheel steering v1 configuration 1
The steering force is transmitted from the rack shaft 4a of the rack & pinion mechanism 4 via the transmission rod 71 to the steering ratio change Vt[70, and the steering ratio is changed in the steering ratio change device 70 according to the control of the controller 25. After that, the steering force is applied to the rear wheel operating rod 11 via the sliding member 74 and the pinion shaft 17.
The configuration is such that the rear wheels 8L and 8R are steered to the left and right by being transmitted to the rear wheels 8L and 8R. Note that the other configurations of the four-wheel steering device are the same as the four-wheel steering device of the first embodiment,
Identical members are given the same reference numerals and their explanations will be omitted.

The controller 25 itself that controls the steering ratio changing device 7o 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, when the vehicle height is high, the steering angle of the rear wheels relative to the steering angle of the front wheels is variably controlled by the steering ratio variable means. The steering ratio is corrected in the same phase direction by the correcting means, and the rear wheels are steered in the same phase direction with this corrected steering ratio, that is, in a direction that eases the turning of the vehicle, thereby increasing the grip force of the wheels.
It is possible to prevent the vehicle from overturning by eliminating instability caused by an increase in the vehicle height and the center of gravity, and it is also possible to prevent the vehicle from skidding, thereby improving running stability.

[Brief explanation of the drawing]

1 to 6 show the 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. Figures showing steering ratio characteristics in the case of steering ratio control, Figures 4 to 6 show the vehicle height adjustment device, Figure 4 is a schematic diagram of the overall configuration, and Figure 5 is an enlarged cross-section of the main parts of each suspension unit. 6 are enlarged cross-sectional views of essential parts of the shock absorber. Further, FIG. 7 does not show the second embodiment, but is a diagram equivalent to FIG. 1. 1... Front wheel steering mechanism, 7.7'... Rear wheel steering mechanism,
25...Controller, 2nd...Car adjustment switch, 34...Steering ratio variable means, 35...Characteristic selection section. Patent applicant: Mazda Motor Corporation
Before Rinto 1) Hiroshi
:, l-, 'r・□, ko1 ゛Figure 1Figure 3Figure 4KFigure 6q

Claims (1)

[Claims] (1) A four-wheel steering device for a vehicle, comprising a front wheel steering mechanism that steers the front wheels in response to steering of the steering wheel, and a rear wheel steering mechanism that steers the rear wheels in response to the steering of the front wheels. , the rear wheel steering mechanism includes: a steering ratio variable means for varying the ratio of a rear wheel steering angle to a front wheel steering angle according to a predetermined steering ratio characteristic; a detection means for detecting a vehicle height state; 4-wheel steering of a vehicle, characterized in that it is provided with a correction means for correcting the ratio of the rear wheel turning angle to the front wheel turning angle to the same phase direction when the vehicle height state is high in response to an output signal from the detection means. Device.