JPH03273973A - Rear wheel steering device of vehicle - Google Patents

Abstract

PURPOSE:To effectively work both rear wheel steering and toe-in control in a vehicle having operable rear wheels and variable toe-in by providing such a constitution as to control the toe-in to reduce tow-in at a predetermined speed or more, a predetermined steering angle or more, or a predetermined horizontal G or more. CONSTITUTION:A 4WS.toe-in controller 10 moves a power rod 3 by a power cylinder 20 on the basis of the input information from a steering angle sensor, a vehicle speed sensor 13, and a G sensor 14, whereby rear wheels 1R are steered. In the power cylinder 20, the oil pressure from a pump 28 is supplied to and discharged from oil pressure chambers 24R, 24L through a rear wheel steering control valve 26 by passages 21R, 21L, and the pressure oil is supplied to and discharged from a central oil pressure chamber 23 through a toe-in control valve 27 by a passage 32. In this case, the toe-in control valve 27 is so controlled as to reduce the toe-in at the time of high speed when the rear wheel steering angle to the front wheel steering angle is small, while it prevents the interference of 4WS with the toe-in control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rear wheel steering device for a vehicle that can steer the rear wheels and has variable toe-in.

[Prior art and its problems] Recently, four-wheel steering (
There is a vehicle with G14Ws). (Tokuko Sho 57-4456
8) In such 4WS vehicles, the rear wheels are steered to the same side (same phase) as the front wheels at high speeds, which enables stable turns with little attitude change at high speeds. becomes. Note that the steering angle of the rear wheels relative to the steering angle of the front wheels (i.e., the steering ratio) is set to change depending on the vehicle speed. However, since such 4WS only steers the rear wheels by steering the front wheels, it does not contribute at all to improving stability when traveling straight.

On the other hand, as a way to improve straight-line stability, it is known that the toe-in of the rear wheels is made variable and the toe-in is controlled to be stronger at high speeds, and there is a system that combines this toe-in control with the aforementioned 4WS.

However, when toe-in control is combined with the above-mentioned 4WS, at high speeds, the steering angle of the rear wheels becomes extremely small relative to the steering angle of the front wheels, but the toe-in control strengthens the toe-in, so that The problem was that it was canceled out by the steering or toe-in, and as a result, the 4WS did not function effectively. In other words, the sideslip angle of the inner turning wheel is insufficient relative to the outer turning wheel, making it impossible to obtain sufficient corner link force.

[Object of the Invention] In view of the above-mentioned circumstances, the present invention has been made to provide a system that, even when 4WS and toe-in control are combined, the rear wheel steering and toe-in control are both effective without being canceled by the toe-in control. An object of the present invention is to provide a functional rear wheel steering device for a vehicle.

[Configuration of the Invention] Therefore, the rear wheel steering device for a vehicle according to the present invention includes at least a control device that controls the steering of the rear wheels in the same direction as the front wheels and variably controls the amount of toe-in, a vehicle speed detection device, and a steering angle detection device. The control device is configured to perform toe-in control to reduce toe-in at a predetermined speed or more, a predetermined steering angle or more, or a predetermined lateral G or more.

According to this, interference between 4WS and toe-in control can be prevented by reducing toe-in at high speeds when the steering angle of the rear wheels is small relative to the steering angle of the front wheels, and toe-in can be reduced when the steering angle exceeds a predetermined steering angle. By reducing toe-in above a certain lateral G, it is possible to provide a sufficient sideslip angle to the inner wheel during turns that require greater cornering force, allowing 4WS to function effectively and making stable turns possible. .

[Embodiments of the invention] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram of a steering mechanism of a vehicle equipped with a vehicle rear wheel steering device according to the present invention.

The illustrated vehicle is configured so that rear wheels IR... (IRR, IRL) can be steered, and the rear wheels IR...
Steering operation is performed by moving a power rod 3 that connects RR and IRL.

The power rod 3 is moved and operated by a power cylinder 20 inserted through the power rod 3, and the power cylinder 20 is controlled and driven by a 4WS/toe-in controller 10 as a control means. . That is, the 4WS/toe-in controller 10 controls the steering operation of the rear wheels IR.

The 4WS/toe-in controller 10 includes a ROMII as a storage means, and a steering angle sensor 12 as a steering angle detection means. Vehicle speed sensor 1 as vehicle speed detection means
The 4WS/toe-in controller 10 controls the movement of the power rod 3 based on these input information.

The power cylinder 20 is constructed as shown in a sectional view in FIG.

That is, the power rod 3 inserted through the goosink 21 is connected to the left and right rear wheels IRR within the goosink 21.

It is discontinuously divided into power rods 3R and 3L on the IRL side, and the shaft end of one power rod 3R is slidably fitted to the shaft end of the other power rod 3L, and each power rod 3R, A piston 31R is installed at each end of the shaft of 3L,
31L is formed, and this piston 31R and piston 31
Between the central hydraulic chamber 23 and each piston 31R, 3
Hydraulic chamber 2 is installed between 1L and site case sink 22 and 22, respectively.
It is composed of 4R and 24L.

The hydraulic pressure chambers 24R, 24L are supplied with pressure oil from a pump 28 through passages 21R, 21L formed through the casing 21 through a rear wheel steering control valve 26, and are discharged from the central hydraulic pressure chambers 24R, 24L. Pressure oil from a pump 28 is supplied to or discharged from the chamber 23 via a toe-in control valve 27 through a passage 32 formed in one power rod 3R.

The rear wheel steering control valve 26 is a 4-point, 3-position switching servo controller, and by switching the rear wheel steering control valve 26, pressure oil is supplied to one hydraulic chamber (24R or 24L), and pressure oil is supplied to the other hydraulic chamber (24R or 24L). Pressure oil is discharged from the hydraulic chamber (24L or 24R), or both side pressure chambers (24R or 24L) are discharged.
) and close the hydraulic circuit of the hydraulic chamber (24R or 24L).
It acts to keep the oil pressure constant.

The toe-in control valve 27 is a servo valve that switches between 2 points and 3 positions, and acts to supply, discharge, or retain pressure oil to the central hydraulic chamber 23 by switching the toe-in control valve 27. be.

According to the above configuration, power is controlled by switching the rear wheel steering control HARTZ 26, supplying pressure oil to one hydraulic chamber (for example, 24R), and discharging pressure oil from the other hydraulic chamber (24L). The power lot 3 is driven to move toward the discharge hydraulic chamber (24L), and by moving the power lot 3, rear wheel steering is performed. At this time, if the toe-in control HARTZ 27 is in the closed position, the oil pressure in the central hydraulic chamber 23 is maintained and the relative positions of the left and right power rods 3 do not change. In addition, each hydraulic chamber 24R124L is equipped with a center link spring 25.25, and when no hydraulic pressure is applied to both side pressure chambers 24R924L, the centering spring 25.25 automatically returns the rear wheels to the neutral position or steers the rear wheels. This is what you are meant to do.

At this point, when the toe-in control HARTZ 27 is switched and pressure oil is supplied to the central hydraulic chamber 23, the left and right power rods 3R
, 3L widens against the suppressing force of the centering springs 25, 25, and the total length of both power rods 3 becomes longer, thereby changing the toe-in of the rear wheels IR... In other words, the amount of toe-in of the rear wheels can be changed by controlling the pressure oil supply to the central hydraulic chamber 23.

The 4WS/toe-in controller 10 performs rear wheel steering control and toe-in control by controlling the operation of the rear wheel steering control valve 26 and toe-in control valve 27.

Next, the rear wheel steering control and toe-in control by this 4WS/toe-in controller 10 will be explained.

First, in the first embodiment, the toe-in amount with respect to the vehicle speed:V shown in FIG. 3 and the steering ratio with respect to the vehicle speed:V for determining the steering angle of the rear wheels as shown in FIG. The 4WS/toe-in controller lO receives information from the vehicle speed sensor 13 and steering angle sensor 12 according to the toe-in amount for vehicle speed=V and the steering ratio 2k for vehicle speed:V, as shown in the control flowchart in FIG. Vehicle speed, ■ and front wheel steering angle: After reading θf (Sl)
, the toe-in amount and the steering ratio: k are determined based on the vehicle speed: V (S2 and S3), and the front wheel steering angle: θ is determined based on the steering ratio 2.
The rear wheel steering angle: θf is calculated based on f (S4), the toe-in control valve 27 is operated and controlled to achieve the determined toe-in amount (S5), and the rear wheel steering control HARTS 26 is operated and controlled to adjust the rear wheel steering angle to the determined toe-in amount (S5). This is to perform steering (S6).

Here, the toe-in amount characteristic with respect to the vehicle speed shown in the third figure is that the vehicle speed rOJ is on the toe-out side by a predetermined amount, and then as the vehicle speed increases, the toe-in amount increases until the predetermined speed = VX. In addition, the amount of toe-in is set to gradually decrease at a predetermined speed of 78 or higher, so that even at high speeds where the steering rate of rear wheel steering is low, the increased toe-in cancels out the rear wheel steering. In order to prevent this, even when turning at high speed, it is possible to obtain sufficient cornering force by setting an appropriate sideslip angle on the inner wheel of the turn, and to perform stable turns.

In addition, the above embodiment has a control configuration in which the amount of toe-in is determined based on the vehicle speed and the amount of toe-in is decreased when the vehicle speed exceeds a predetermined speed, or as shown in FIG.
The amount of toe-in is determined by
A control configuration may be adopted in which the amount of toe-in is reduced when the toe-in amount is greater than or equal to Hx. According to this, an appropriate sideslip angle can be given to the inner wheel during a turn when a large corner link force is required.

Next, a second embodiment of rear wheel steering control and toe-in control by the 4WS/toe-in controller 10 will be described.

In this embodiment, it is determined whether the vehicle is traveling straight or turning based on the front wheel steering angle information=of inputted from the steering angle sensor 12, and toe-in control is performed using dedicated characteristics for each. That is,
ROMII has two characteristics: one in which the amount of toe-in increases according to the vehicle speed as shown in Figure 7, and the other in which the amount of toe-in decreases in accordance with the lateral G detected and input by the G sensor 14 as shown in Figure 8. Two characteristics are memorized, and of these two characteristics, the characteristic that increases the amount of toe-in according to the vehicle speed when driving straight, and the characteristic that decreases the amount of toe-in according to the lateral G when turning is selected and used. It is something.

FIG. 9 shows a control flowchart for the vehicle speed sensor 1.
3. From the steering angle sensor 12 and G sensor 14, vehicle speed: v,
After reading front wheel steering angle=of and lateral G:G (S12)
, the front wheel steering angle: θf is compared with the predetermined straight-ahead/turning determination steering angle: θL (513), and when it is determined that the vehicle is going straight, toe-in is performed according to the vehicle speed: V based on the vehicle speed response characteristics shown in Figure 7. In addition to determining the amount (S14), when it is determined that it is a turn, the lateral G:G is determined based on the lateral G corresponding characteristics shown in FIG.
The amount of toe-in is determined according to (S14). Thereafter, as in the first embodiment described above, the steering ratio is 2 k based on the vehicle speed: V.
(S15), and also sets the steering ratio to 2 and the front wheel steering angle,
The rear wheel steering angle: θ is calculated based on θf, and the toe-in control valve 27 is operated to achieve the determined toe-in amount (S5), and the rear wheel steering control valve 26 is
The rear wheel steering is performed by controlling the operation (S6).

According to this, straight-line stability can be improved by increasing toe-in according to the vehicle speed when driving straight, and when turning with a predetermined lateral G or more that requires large cornering force, an appropriate sideslip angle is applied to the inner wheel of the turn. By applying this force, it is possible to perform stable turns.

[Effects of the Invention] As described above, according to the rear wheel steering device for a vehicle according to the present invention, even when 4WS and toe-in control are combined, the rear wheel steering is not canceled by the toe-in control, and S
Both wheel steering and toe-in control function effectively, making it possible to achieve both improved straight-line stability and stable turning.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a vehicle equipped with a vehicle rear wheel steering device according to the present invention, FIG. 2 is a sectional view of a power cylinder that is a rear wheel steering and toe-in variable mechanism, and FIG. 3 is a first embodiment. 4 is a diagram showing the characteristics of the steering ratio as a function of the vehicle speed. FIG. 5 is a control flowchart of the first embodiment. FIG. 6 is a diagram showing the toe-in characteristics as a function of the steering angle. 8 is a diagram showing toe-in characteristics based on vehicle speed of the second embodiment, FIG. 8 is a diagram showing toe-in characteristics based on lateral G of the second embodiment, and FIG. 9 is a control flowchart of the second embodiment. IFL, IFR...Front wheel IRL, IRR...Rear wheel 10...4WS/toe-in controller 12...Steering angle sensor (steering angle detection means) 13...Vehicle speed sensor (
Vehicle speed detection means) 14...G sensor (lateral G detection means) Fig. 2 Fig. 0 Fig. 4 Fig. Fig. Fig. 8 Fig. Fig. 8

Claims (3)

[Claims] (1) A vehicle in which rear wheels can be steered and toe-in is variable, comprising at least a control device for controlling the steering of the rear wheels in the same direction as the front wheels and variable control of the amount of toe-in, and a vehicle speed detection means. A rear wheel steering device for a vehicle, wherein the control device performs toe-in control to reduce toe-in at a predetermined speed or higher. (2) In a vehicle in which rear wheels can be steered and toe-in is variable, at least a control device for controlling the steering of the rear wheels in the same direction as the front wheels and variable control of the amount of toe-in, and a steering angle detection means are provided. A rear wheel steering device for a vehicle, wherein the control device performs toe-in control to reduce toe-in at a predetermined steering angle or more. (3) In a vehicle in which rear wheels can be steered and toe-in is variable, at least a control device for controlling the steering of the rear wheels in the same direction as the front wheels and variable control of the amount of toe-in, and a lateral G detection means are provided. A rear wheel steering device for a vehicle, wherein the control device performs toe-in control to reduce toe-in at a predetermined lateral G or more.