JPH01262261A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve the turning round property in the early stage of turning by steering the left and right rear wheels in opposite directions in the early stage of equiphase steering of the left and right rear wheels. CONSTITUTION:A rear wheel steering rod 13 is electrically controlled by an electronic unit 21 through a motor M. To this motor M are integrally installed an encoder E for converting the rotation of the motor M into an electric signal which is input to the electronic control device 21, a brake mechanism B operated by an electric signal from the electronic control unit 21, and a speed reducing mechanism 39. A pinion gear 41 is fixed to the output shaft 40 of the speed reducing mechanism 39. The electronic control unit 21 steers the rear wheels into toe-in state based on input signals from a car speed sensor 42, a steering angle sensor 43 and others, when the car speed is below a determined speed and the handle steering angle is below a small angle. When the car speed is not lower than the determined speed and the handle steering angle exceeds the small angle, the rear wheels are steered to the equiphase to the front wheels. Further, when the handle steering angle reaches the determined value, and the speed becomes less than the determined value, the rear wheels are steered to the antiphase against the front wheels.

Description

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

(Prior Art) Conventionally, four-wheel steered vehicles (dW
S car) is in practical use, but in this dWS car, as disclosed in Japanese Patent Laid-Open No. 61-9374, when the steering angle of the steering wheel is large, the left and right rear wheels are moved in opposite phase to the front wheels. In addition, when the steering angle of the steering wheel is small, the left and right rear wheels are steered in the same phase as the front wheels to improve running stability.

By the way, in the -C front two-wheel steering vehicle (ZWS vehicle), in order to generate cornering force by giving the rear wheels a sideslip angle when turning at medium and high speeds, the entire vehicle body must be
It is necessary to make it slide by that amount. That is, ZWS
A car turns with the car body facing inward with respect to the instantaneous direction of travel (tangential direction of the turning trajectory circle), and the car body slip angle is on the plus side. On the other hand, in dWS vehicles, the rear wheels are steered in the same phase as the front wheels to provide a slip angle independent of the vehicle body, which reduces the sideslip angle of the vehicle body and allows the instantaneous direction of travel and It becomes possible to turn in the same direction. In other words, in a dWS vehicle, by actively giving a steering angle (side slip angle) to the rear wheels, the vehicle body slip angle can be kept small. The cornering force generated by the vehicle acts in a direction that dampens yawing, which has the advantage of improving running stability.

In the rear wheel steering device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-9374, the steering angle of the steering wheel is set at a predetermined angle (
For example, when the angle is within about 240"", so-called "proportional control" is performed in which the rear wheels are steered in the same phase at the same time as the front wheels are steered, so at the moment when the vehicle body tries to change direction at the beginning of a turn, Cornering force also builds up on the rear wheels, acting in a direction that prevents yawing. For this reason,
The vehicle body will move in a parallel motion, and the vehicle body angle will be negative. In other words, the responsiveness to front wheel steering decreases, resulting in poor turning performance.In this case, the driver tries to correct it by turning the steering wheel more sharply, causing a sudden increase in the slip angle of the front wheels, which causes tire damage. There is a possibility that the grip force approaches the saturated region.

As a means to eliminate the yaw delay caused by this proportional control, for example, as disclosed in Japanese Patent Laid-Open No. 58-164477, after steering the front wheels, wait until sufficient yawing has occurred. "Delay control" that steers the rear wheels has been proposed, but this delay control improves turning performance compared to the proportional control described above, but the dWS
It lacks the maneuverability typical of a car, and has the drawbacks of poor driving stability and responsiveness.

Furthermore, as disclosed in, for example, Japanese Patent Laid-Open No. 61-175177, the rear wheels are momentarily steered to the opposite phase to the front wheels at the same time as the front wheels are steered, and then the rear wheels are steered to the same phase. ``Phase inversion control'' has been proposed. Although this phase reversal control significantly improves turning performance, it is inferior to the aforementioned proportional control and delay control in terms of running stability, and it does not cause a sense of discomfort due to large changes in vehicle behavior. In addition, it is necessary to suppress yawing overshoot and perform a turn that is balanced with lateral movement, so strict control is required in terms of responsiveness and accuracy.

(Object of the Invention) The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a rear wheel steering device that overcomes all the drawbacks of the above-mentioned proportional control, delay control, and phase reversal control.

(Structure of the Invention) The present invention provides an AW vehicle equipped with a rear wheel steering device capable of steering the left and right rear wheels in at least the same phase with respect to the front wheels in accordance with the steering of the front wheels.
The S vehicle is characterized in that, at the beginning of the same-phase steering of the left and right rear wheels, the left and right rear wheels are steered in opposite directions, that is, into a toe-in state or a toe-out state.

Further, the present invention provides an AWS vehicle equipped with a rear wheel steering device capable of steering the left and right rear wheels in at least the same phase with respect to the front wheels in accordance with the steering of the front wheels. The present invention is characterized in that only one of the left and right rear wheels is steered in the same phase or in the opposite phase with respect to the front wheels.

(Effects of the Invention) According to the present invention, while improving turning performance at the initial stage of turning,
Driving stability can be ensured by preventing sudden changes in vehicle behavior.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a schematic perspective view of the entire four-wheel steering system equipped with a rear-wheel steering system according to a first embodiment of the present invention, in which a shaft 2 of a steering wheel 1 is installed in a rack-and-pinion gear box 3. A tie loft 4.4 is connected to both ends of a rack gear (not shown), and knuckle arms 6, 6 each supporting a front wheel 5.5 are connected to the tie rod 4.4, and the front wheel 5.5 is connected to a steering wheel. It is designed to be steered in the steering direction of the handle 1.

As shown in FIG. 6, which is a system diagram of the steering system, the rear wheel steering device main body 11 is mounted in a housing 11a so as to be driven by a motor M controlled by an electronic control device 21 to move left and right in the vehicle width direction. A supported rear wheel steering rod 13 is provided, and tie rods 14 are provided at both ends of the rear wheel steering rod 13.
14 is connected, and the rear wheel 15. is connected to the tie loft 14.14.
Knuckle arms 16 and 16 each carrying a 15 are connected to each other. With this configuration, the left and right rear wheels 15 are controlled in response to the steering of the front wheels 5.5 by the steering wheel 1.
．． 15 and front wheels 5.5 are in the same phase or in opposite phase so that they can be steered in the same direction.

Further, as shown in FIGS. 2 and 3, the rear wheel steering device main body 11 is supported on the vehicle body so as to be pivotable around an axis 17 extending in the vehicle width direction through the center of the cross pin of the universal joint 10. has been done.

A hydraulic cylinder 18 is a driving means for pivoting the rear wheel steering device main body 11 around the axis 17, and the upper end of the hydraulic cylinder 18 is connected to the axis 17 diagonally above the rear wheel steering rod 13. A piston rod 20 is attached to the vehicle body so as to be pivotable about an axis extending in parallel, and projects obliquely downward from the hydraulic cylinder 18.
The lower end of is fixed to the rear wheel steering device main body 11.

Figures 4 (a) to (C) and Figures 5 (al to (C1) show the steering conditions of the front wheels 5.5 and rear wheels 15.15, the operating conditions of the hydraulic cylinder '18, and the rear wheel steering system. This is an explanatory diagram showing the pivoting state of the main body 11, and the electronic control unit (ECU) 2.
1 controls the opening and closing of a relief valve 22 in the oil passage according to a vehicle speed signal and a steering angle signal, and the steering wheel is opened and closed when the vehicle speed is below a predetermined speed and even when the vehicle speed is above the predetermined speed. When the steering angle of 1 is zero or a predetermined small angle or more, the relief valve 22 is in an open state, so that the oil pumped up from the reservoir 24 by the oil pump 23 and pumped is returned to the reservoir 24 through the relief valve 22. Therefore, pressure oil is not supplied to the hydraulic cylinder 18, and the piston rod 20 is in the protruding position due to the spring force of the spring 25 (Fig. 4 (bl)).
1 is not pivoted (Fig. 4(C)), so the rear wheel 15.1
5 is not steered (Fig. 4 + al), on the other hand, the vehicle speed is higher than a predetermined speed, and the steering wheel 1 is not steered.
When the steering angle is a small steering angle below a predetermined angle, the electronic control device 21 closes the relief valve 22, and as a result, pressure oil flows from the oil pump 23 through the pipe 26 to the hydraulic cylinder 1.
8 and the piston rod 20 is retracted upward (Fig. 5 (bl)), and the rear wheel steering device main body 11 is pivoted upward (Fig. 5 (C)). 11 pivots upward, the left and right tie rods 14.
14 is drawn toward the center, the left and right rear ends 15.
15 is in a toe-in state, that is, the inner turning wheel is in opposite phase to the front wheel, and the outer turning wheel is in opposite phase to the front wheel (see Fig. 5 (a).
)) are steered in opposite directions.

The above-described embodiment is configured such that the left and right rear @ 15.15 enters the toe-in state by pivoting the rear wheel steering device main body 11, but the relative relationship between the rear wheel steering device main body 11 and the tie rods 14.14 By changing the position, the left and right rear ends 15.15 become toe-out! It is also easy to configure the wheels to be steered in opposite directions.

FIG. 6 shows a system diagram of the steering system, in which the rear wheel steering rod 13 is configured to be electrically controlled by the electronic control device 21 via the motor M. The device main body 11 includes a rack and pinion type gear box 37, and tie rods 14.14 for steering the rear wheels 15.15 are connected to both ends of the rear wheel steering loft 13, which forms a part of the rack gear. ing. The motor M includes an encoder E that converts the rotation of the motor M into an electric signal and inputs it to the electronic control device 21, a brake mechanism B operated by the electric signal from the electronic control device 21, and a deceleration mechanism 39. It is installed integrally, and the deceleration mechanism 39
A pinion gear 41 that meshes with the rack gear of the rear wheel steering rod 13 is fixed to the output shaft 40 of the vehicle. Based on input signals from the vehicle speed sensor 42, steering wheel angle sensor 43, front wheel steering angle sensor 44, etc., the electronic control device 21 determines when the steering angle of the steering wheel 1 is within a minute angle 81 at a vehicle speed or higher than a predetermined speed. , motor M
is stopped and the brake mechanism B is activated,
The rear wheel 15.15 is prevented from being steered by the motor M, and instead the relief valve 22 of the hydraulic circuit is closed and the hydraulic cylinder 18 is actuated, whereby the rear wheel 15.15
to the toe-in state (see Fig. 5 (al~(c+)).Then, the steering angle of the steering wheel 1 is turned to a minute angle of 0.
When it becomes 1 or more, the rear wheel steering device main body 11 returns to its original position, and the left and right rear wheels 15.15 are steered in the same phase as the front wheels 5.5. Furthermore, if the steering angle of the steering wheel 1 reaches the angle θ2 and the vehicle speed is below a predetermined speed,
The electronic control device 21 controls the motor M so that the left and right rear wheels 15.15 are steered in opposite phase to the front wheels 5.5.

Fig. 7 fa) shows the actual steering angle of the rear wheels 15.15 relative to the steering angle of the steering wheel 1 when the vehicle speed is higher than a predetermined speed, and at the beginning of the same-phase steering of the left and right rear wheels 15.15 with respect to the front wheels, This shows that the left and right rear wheels 15.15 are once steered to the toe-in state.

However, in the case of FIG. 7 fa), since the toe-in state passes through the 2WS state and shifts to the same phase steering at the beginning of the same phase steering, a slight change in behavior is inevitable.

Therefore, as shown in Fig. 7 (bl), the outer turning wheels are shifted from the toe-in state to in-phase steering without returning to the neutral position, and the inner turning wheels are shifted from the opposite phase to the same phase at Lm!. It is preferable to control the steering so that the left and right rear wheels 15.15 are in a toe-in state with respect to each other for a predetermined time t at the beginning of a turn.

In this case, in the configurations shown in FIGS. 1 to 6, the hydraulic cylinder 1
Although it is necessary to operate the motor M in parallel with the operation of 8, by controlling the rear wheels 15 and 15 in this way, it is possible to quickly shift from toe-in control to in-phase control. That is, even if the inner turning ring is changed by load movement, the change in behavior is small, so that it is possible to achieve both controllability and stability.

This effect can also be obtained by controlling only the outer turning wheel to be in the toe-in state while the inner turning wheel is in the neutral position.

In addition, the toe-in control of the rear wheels at the initial stage of such in-phase steering may be of a vehicle speed sensitive type as shown in FIG. Therefore, in the FC+ shown in Fig. 7, the toe-in control time t is shortened as the vehicle speed increases.Furthermore, at high vehicle speeds of 90 km/h or higher, the vehicle speed does not require yaw; For reasons such as the inability of the occupants to follow changes in behavior, proportional control is used.

Next, FIG. 8 shows a system diagram of a steering system in a second embodiment of the rear wheel steering device according to the present invention.The rear wheel steering device main body 11 in this embodiment has a motor M similar to that in FIG.
The left and right rear wheels 15.15 are steered in the same direction, but the rear wheel steering device main body 11 is not pivotable, and instead steers both the left and right rear wheels 15.15 in the same direction. Alternatively, link mechanisms 55L and 55R and hydraulic cylinders 45L and 45R are provided for steering either one of them to a toe-in state. Two-position switching valves 46L and 46R, an oil pump 47, and a reservoir 48 are provided for operating the hydraulic cylinders 45L and 45R, respectively, in response to an electric signal from the electronic control device 21. When the pistons 49 of the hydraulic cylinders 45L and 45R are locked to the vehicle body and hydraulic pressure is not supplied, the hydraulic cylinders 45L and 45R are connected to the left and right rear wheels by springs 50 and stoppers 51.
is held in the non-steering position, but the two-position switching valve 46L,
46R is actuated, hydraulic pressure is applied to the hydraulic cylinders 45L and 45R, so that the hydraulic cylinders 45L and 4
Since 5R moves against the spring force of the spring 50,
The rear wheels 15 are configured to be steered in the toe-in direction. With such a configuration, in this embodiment as well, when the vehicle speed is higher than a predetermined speed and the steering angle of the steering wheel 1 is within the small steering angle range of angle 01, electronic control is applied to both the two-position switching valves 46L and 46R. An electrical signal is input from the device 21 to operate the hydraulic cylinder 451.45R,
Although the left and right rear wheels 15.15 can be steered to a toe-in state, furthermore, according to this embodiment, the left and right rear wheels 15.15
It is also possible to steer only one of them to the toe-in state.

Furthermore, when the vehicle speed is below a predetermined speed and the steering angle of the steering handle 1 is greater than or equal to the predetermined angle 02, the left and right rear wheels 15.15 are steered in opposite phases by the operation of the motor M, thereby improving the ability to turn around easily. can be achieved.

Note that also in this embodiment, the hydraulic cylinders 45L, 45
By changing the configuration of R, the left and right rear wheels are 15.15
It is also possible to configure both or either one of them to be steered to a toe-out state.

The above explanation has clarified the configuration and operation of the embodiment of the rear wheel steering device according to the present invention, and FIG. This figure collectively shows the steering status of the rear wheels in the figure.

In Figure 9, ■ indicates toe-in steering of both left and right rear wheels, ■
indicates toe-in steering of only the outer wheel of the turn, ■ indicates toe-out steering of only the outer wheel of the turn, ■ indicates toe-out steering of only the inner wheel of the turn, ■
indicates toe-out steering of both left and right rear wheels. Also, ■ indicates a ZWS vehicle in which reverse rotation is not steered, ■ indicates in-phase steering, and ■ indicates anti-phase steering.

FIG. 10 shows the stability and retroactivity in each case of Φ to ■ in FIG. 9. As is clear from FIG. 10, according to the present invention, it is possible to improve retrospective performance at the initial stage of in-phase steering in an AWS vehicle, while preventing sudden changes in vehicle behavior and ensuring running stability. There is an advantage that it can be done.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of the entire four-wheel steering device equipped with a rear wheel steering device according to a first embodiment of the present invention, FIG. 2 is a plan view of the main parts of the rear wheel steering device, and FIG. Same side view, Fig. 4 fat~(C) and Fig. 5+al~ (C1 is an operation explanatory diagram, Fig. 6 is a system diagram of the steering system, Fig. 7 (81~(C)
1 is a control characteristic diagram, FIG. 8 is a system diagram of a steering system according to a second embodiment of the present invention, and FIG. 9 is an explanatory diagram showing a rear wheel steering state.
FIG. 10 is an explanatory diagram showing the turning performance and stability in each case of FIG. 9. 1-Steering wheel 4,--Tyroid 5-Front wheel 11--Rear wheel steering device main body 13-Rear wheel steering rod 15-Rear wheel 18--Hydraulic cylinder 20--Piston rod 21-Electronic control device 45
L, 45R - Hydraulic cylinder 46L, 46 R, - 2 position switching valve 55L, 55 R - Link mechanism M - Motor B - Brake mechanism E - Encoder

Claims (1)

[Claims] 1. In a vehicle equipped with a rear wheel steering device capable of steering the left and right rear wheels in at least the same phase with respect to the front wheels in accordance with the steering of the front wheels, the initial stage of the same phase steering of the left and right rear wheels. A rear wheel steering device for a vehicle, characterized in that the left and right rear wheels are steered in opposite directions. 2. In a vehicle equipped with a rear wheel steering device capable of steering the left and right rear wheels in at least the same phase with respect to the front wheels in accordance with the steering of the front wheels, at the beginning of the same phase steering of the left and right rear wheels, the left and right rear wheels A rear wheel steering device for a vehicle, characterized in that only one of the wheels is steered in the same phase or in the opposite phase with respect to the front wheels.