JPS628866A - Four wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve the running stability by providing the characteristics of a steering angle ratio between a front and a rear wheel with a blind area where no steering of the rear wheel is effected in the range where the steering angle of the front wheel is small. CONSTITUTION:The actuation of both a pulse motor 14 and a drive motor 24 for a hydraulic pump 25 is controlled by signals outputted from a controller 25 that is a control section of a rear wheel steering mechanism 7. Both a signal from a steered angle from a steering angle sensor 26 which detects the steered angle of a front wheel based on the amount of a steering handle 3 actually steered in a front wheel steering mechanism 1, and a signal for a vehicle speed from a vehicle speed sensor 27 are inputted into the controller 25. A ratio of the steered angle of the rear wheel to that of the front wheel is controlled in accordance with the specified characteristics of the steering angle ratio by means of controlling both the pulse motor 14 and the drive motor 24. And a blind area where no steering of the front wheel is effected, is provided for the range where the steering angle of the front wheel is small, and the range of the blind area is set differently depending on the vehicle speed.

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. 59-77971. 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, the front and rear wheels are in opposite phases at low speeds and in the same phase at high speeds. There is a known vehicle that prevents wheels from skidding and improves running stability, as well as improves maneuverability at low speeds.

In that case, at low speeds when the rear wheels are steered in the opposite phase and the vehicle's maneuverability becomes agile, in a region where the front wheel steering angle is small, there is a dead zone in which the rear wheels are not steered even if the front wheels are steered. By providing this, the rear wheels are steered with some play in relation to the front wheels, and even if the driver does not intend to steer, the rear wheels are also steered as the steering wheel swings slightly to the left or right. The system prevents the vehicle from being overly steered and matches the steering feel to that of conventional driving, improving steering stability.

(Problem to be Solved by the Invention) However, in the above-mentioned vehicle, although the rear wheel steering characteristics related to the dynamic performance of the vehicle change with the vehicle speed, the width of the dead band does not change as the vehicle speed increases. Since it is always constant even when the vehicle speed changes, there is a problem in that the human driving sense is not sufficiently adapted to the steering feeling caused by changes in vehicle speed, and therefore stable maneuverability cannot be obtained.

The present invention has been made in view of the above points, and its purpose is to provide a dead zone in which the rear wheels are not steered in a region where the front wheel steering angle is small, and to adjust the dead zone according to the vehicle speed. By having different widths, the purpose is to ensure that the steering feeling always matches the human driving sense even when the vehicle speed changes, and to ensure stable maneuverability and improve driving stability. .

(Means for Solving the Problems) In order to achieve the above object, 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 vehicle speed control mechanism that steers the front wheels in accordance with the steering of the steering wheel. This four-wheel steering device is equipped with a rear wheel steering mechanism that steers the rear wheels with front and rear wheel steering ratio characteristics that are different from each other, that is, when the vehicle speed is low, the front and rear wheels are in opposite phase, and when the vehicle speed is high, the front and rear wheels are in the same phase. Therefore, in the front and rear wheel steering ratio characteristics, a dead zone is provided in which the rear wheels are not steered in a region where the front wheel steering angle is small, and the dead zone is set to a different width depending on the vehicle speed. The width increases when the vehicle speed is low.

The configuration is such that it changes to become smaller at high speeds.

(Function) With the above configuration, the four-wheel steering system for a vehicle according to the present invention has a dead zone in which the rear wheels are not steered even when the front wheels are steered, with a width that varies depending on the vehicle speed, that is, an increase in the vehicle speed. Accordingly, by setting the width of the dead zone to be small, the width of the dead zone is large during low speed driving, and the rear wheels are not steered unless the front wheel turning angle becomes larger than the width of the predetermined dead zone. As the vehicle speed increases, the width of the dead zone gradually decreases, so the rear wheels begin to turn when the front wheel steering angle is small. This will match the steering feel and provide stable maneuverability.

(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 2 m of left and right front wheels.

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. The operation of mechanism 4 is controlled by the front wheel 2.
It consists of left and right tie rods 5.5 and knuckle arms 6.6 that 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 on 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 direction and amount of rotation 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 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 2o 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 180 is connected to the oil return path 2.
On the other hand, when the rear wheels 8L and 8R are steered to the right (clockwise in the figure), the communication state is reversed 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, and the rear wheel is operated by the pulse motor 14 via the bevel gears 15, 16, pinion shaft 17, pinion 13, and rack 12. When the 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 pulse motor 14 and the drive motor 24 of the hydraulic pump 23 are operated by control signals output from a controller 25 which 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 the like.
A vehicle speed signal from a vehicle speed sensor 27 that detects the vehicle speed is input to each of them, and a battery power source 29 is also 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 vehicle speed signal from the vehicle speed sensor 27, and according to the magnitude of the vehicle speed, the characteristic storage section 30
The steering ratio characteristic selected by the characteristic selection section 35 is provided as a correction means for correcting the steering ratio in the same phase direction (in the direction of the arrow in FIG. 4). The target steering angle calculation section 31 calculates the target steering angle according to the steering ratio characteristics stored in the storage section 30.

Here, as shown in FIG. 3, the steering ratio characteristics stored in advance in the characteristic storage section 30 basically indicate that as the vehicle speed increases from low speed to high speed, the steering ratio k changes in the negative direction. In the opposite phase (the front and rear wheels are steered in opposite directions), the steering ratio shifts from a large value to close to zero, and in the middle 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). In the high speed range, the steering ratio k is set to be large with the same phase.

As shown in FIGS. 4 and 5, the above-mentioned steering ratio characteristic changes depending on the vehicle speed, and the front wheel steering angle θ
A dead zone in which the rear wheels are not steered is provided in a region where F is small, and the widths of the dead zone h+, hz...
It is set so that as the vehicle speed increases, the phase gradually decreases continuously from the opposite phase to the same phase.

Next, to explain the operation and effect of the first embodiment, the controller 25 of the rear wheel steering mechanism 7 has a steering angle sensor 2.
A target steering angle θR of the rear wheels is calculated based on the steering angle signal from the vehicle speed sensor 6 and the vehicle speed signal from the vehicle speed sensor 27. That is,
As shown in FIG. 2, the characteristic selection section 35 corrects the steering ratio characteristic from the characteristic storage section 30 based on the vehicle speed signal from the vehicle speed sensor 27, and also changes the steering ratio based on the steering ratio characteristic. By calculating the target steering angle in the target steering angle calculating section 31 of the means 34, the steering ratio of the rear wheel steering angle to the front wheel steering angle is variably controlled in accordance with the above steering ratio characteristic, and the rear wheels 8L, 8R is steered in the opposite phase to the front wheels 2m and 2R at low speeds, and is steered in the same phase as the front wheels 2L and 2R at high speeds.

In that case, a dead zone in which the rear wheels are not steered is provided in a region where the front wheel steered angle θF is small, so if the front wheel steered angle θF calculated by the controller 25 is smaller than the width of the dead zone. In this case, the rear wheel steering angle θR is kept at zero phase, the rear wheels are not steered, and when the front wheel steering angle θF exceeds the width of the dead band, the vehicle speed changes as shown in Figure 4. Based on the corresponding steering ratio characteristics, a rear wheel steering angle θR corresponding to the front wheel steering angle θF is obtained, and the rear wheels are steered. In addition, the width of the dead zone is set to gradually decrease as the vehicle speed increases, so the front wheel turning angle θF at which the rear wheels begin to turn becomes smaller as the vehicle speed increases. ,
The rear wheels, which are steered in response to steering wheel steering, gradually become more sensitive. As a result, even when the vehicle speed changes, the steering feeling always matches the human driving sensation, providing stable maneuverability and improving driving stability.

Furthermore, FIG. 6 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 37 made of a gear or the like, and a rear end of a transmission rod 38 extending in the longitudinal direction of the vehicle body is connected to the steering ratio changing device 37.
A pinion 40 is provided at the front end of the transmission rod 38 and meshes with a hook 39 formed on the rack shaft 4a of the rack and pinion mechanism 4 of the front wheel steering mechanism 1. Also,
A sliding member 41 extends from the steering ratio changing device 37, and a rack 42 formed on the sliding member 41 has the following functions:
A pinion 43 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 it. 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 device 37 via the transmission rod 38,
After the steering ratio is changed in accordance with the control of the controller 25 in the steering ratio change/receiver W137, the steering force is applied to the sliding member 4.
1 and the pinion shaft 17 to the wheel contact operating rod 11, the rear wheel 81.8R is configured to be 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.

The controller 25 itself that controls the steering ratio changing device 37 is the same as in the first embodiment, and
Of course, similar actions 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, in the front and rear wheel steering characteristics where the front and rear wheels are in opposite phases at low speeds and in the same phase at high speeds, a dead zone is created in the region where the front wheel steering angle is small. The width of the dead band is set so that it is large when the vehicle speed is low and small when the vehicle speed is high.
A good steering feeling that corresponds to changes in vehicle speed can be obtained, so
Stable maneuverability is obtained and driving stability is improved.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and are shown in FIGS. 1 to 5.
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 diagram showing the steering ratio characteristic in the case of steering ratio control using the vehicle speed of the controller, FIG. 4 is a diagram showing the relationship between the front wheel steering angle and the rear wheel steering angle in the steering ratio characteristic, and FIG. The figure is a diagram showing the relationship between vehicle speed and dead zone amount in steering ratio characteristics. FIG. 6 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, 27
...Vehicle speed sensor, 34...Steering ratio variable means, 35.
...Characteristic selection section. Patent applicant Mazda Motor Corporation 77'-:
``'iFigure 1Figure 3Figure 4Figure 5People

Claims (2)

[Claims] (1) 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 with front and rear wheel steering ratio characteristics that differ with respect to vehicle speed in response to steering of the front wheels. The front and rear wheel steering ratio characteristics include a dead zone in which the rear wheels are not steered in a region where the front wheel steering angle is small, and the dead zone varies depending on the vehicle speed. A four-wheel steering device for a vehicle, characterized in that widths are set to differ depending on the vehicle. (2) The front and rear wheel steering ratio characteristics are opposite in phase when the vehicle speed is low and in phase when it is high, and the width of the dead band gradually changes to become smaller as the vehicle speed increases. Claim No. (1) set forth in
A four-wheel steering device for the vehicle described in Section 3.