JPH04237678A - Front wheel steering device for rear wheel steered vehicle - Google Patents

Abstract

PURPOSE:To improve the difficulty in maintaining the straight advance performance of a vehicle due to the reduction of the neutral feeling of a steering wheel when rear wheels are steered to the same phase at least in a high speed region. CONSTITUTION:A power steering mechanism is installed on a front wheel steering mechanism, and in a small steering region in which the assisting force is made variable and front wheels are nearly at a neutral position, the assisting force is made large, while in the steering region in which front wheels are steered, the assisting force is made small. Accordingly, a driver recognizes the neutral state from the difference of the assisting force, i.e., the heaviness of the steering feeling for a steering wheel.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a front wheel steering system for a rear wheel steering vehicle that steers both the front wheels and the rear wheels.

0002

2. Description of the Related Art Rear wheel steered vehicles are known in which both the front wheels and the rear wheels are steered in order to improve the running performance of the vehicle. For example, Japanese Unexamined Patent Publication No. 63-300811 discloses so-called vehicle speed-sensitive rear wheel steering. Specifically, in a low speed region, the rear wheels are steered in opposite phases to improve the turning performance of the vehicle. A technique has been disclosed in which the rear wheels are steered in the same phase in a high-speed region to improve the steering stability of the vehicle.

0003

[Problems to be Solved by the Invention] By the way, in the process of developing the technology for steering the rear wheels in the same phase, the following problem was newly recognized. In other words, in order to stabilize lane changes at high speeds, when the steering characteristic of the rear wheels is set so that when the front wheels are slightly steered, the rear wheels are largely steered in the same phase, the steering wheel's neutral (Neutral) feeling was weakened, and it was recognized that there was a problem in which maintaining the straightness of the vehicle required attention.

When this problem is considered, the stronger the tendency to steer the rear wheels in the same phase, the weaker the yawing that accompanies the steering of the front wheels, and the weaker the turning feeling felt by the driver becomes. In addition, the cornering force also decreases, so the self-aligning torque decreases, and the response force from the tires becomes weaker, so the driver needs to be careful about maintaining the straightness of the vehicle. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a vehicle with rear wheel steering in which both the front wheels and the rear wheels are steered, and to easily maintain the straightness of the vehicle when the rear wheels are steered in the same phase. An object of the present invention is to provide a front wheel steering device for a rear wheel steering vehicle, which is configured to provide a front wheel steering device for a rear wheel steering vehicle.

[0005]

[Means for Solving the Problems] The present invention focuses on a power steering mechanism that is generally attached to a front wheel steering mechanism, and provides a neutral feeling to the steering wheel by making the assist force of this power steering mechanism variable. This is how it was done. in particular,

[0006] The rear wheels are steered along with the front wheels,
At least in high-speed regions, assuming that the vehicle is a rear wheel steered vehicle in which the rear wheels are steered in the same phase, a front wheel power steering mechanism attached to the front wheel steering mechanism and a front wheel power steering mechanism provided on the front wheel power steering mechanism, an assist force variable mechanism for changing an assist force for assisting the steering force of the vehicle; a vehicle speed detecting means for detecting vehicle speed; and a vehicle receiving a signal from the vehicle speed detecting means so that the front wheels are brought to a substantially neutral position at least when the front wheels are in a high speed region. The present invention is configured to include an assist characteristic control means for increasing the assist force in a certain minute steering range compared to the assist force in a steered range in which the front wheels are steered.

[0007]

According to the present invention, the driver knows the neutral position based on the magnitude of the assist force of the power steering mechanism, that is, the lightness and weight of the steering force required to operate the steering wheel. In other words, when the driver suddenly feels heavy on the steering wheel,
This will allow you to know the steering status of the front wheels. Therefore, the rear wheel control mode emphasizes the steering stability of the vehicle by setting the rear wheel steering characteristics in the small steering range where the front wheels have a small steering angle, by setting a characteristic in which the rear wheels are largely steered in the same phase. When this is adopted, the greater the tendency to steer the rear wheels in the same phase, the greater the width of the assist force (the difference between the assist force in the minute steering range and the assist force in the steered range). Just make it bigger.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings. In Fig. 1, 1R is the right front wheel, 1L is the left front wheel, 2R is the right rear wheel, 2L is the left front wheel, and the left and right front wheels 1R are
, 1L are linked by a front wheel steering mechanism A, and the left and right rear wheels 2R, 2L are linked by a rear wheel steering mechanism B. In the embodiment, the front wheel steering mechanism A includes a pair of left and right knuckle arms 3R, 3L and tie rods 4R, 4L, and a relay rod 5 that connects the pair of left and right tie rods 4R, 4L. A steering mechanism C is linked to the front wheel steering mechanism A, and in this embodiment, the steering mechanism C is of a rack and pinion type. That is, a rack 6 is formed on the relay rod 5, and a pinion 7 that meshes with the rack 6 is connected to a handle 9 via a shaft 8. As a result, when the handlebar 9 is turned to the right, the relay rod 5 is displaced to the left in FIG.
The vehicle is steered clockwise in the figure by an amount corresponding to the amount of operational displacement of the handle 9, that is, the steering angle. Similarly, when the steering wheel 9 is operated to turn to the left, the left and right front wheels 1R and 1L are steered to the left in accordance with the amount of displacement of this operation.

Similarly to the front wheel steering mechanism A, the rear wheel steering mechanism B also includes a pair of left and right knuckle arms 10R and 10L, respectively.
and tie rods 11R, 11L, and the tie rods 11
Relay rod 12 connecting R and 11L, and a power steering mechanism D in which the rear wheel steering mechanism B is a hydraulic type.
It is said to be configured with the following. This power steering mechanism D will be explained with reference to FIG. 2. A power cylinder 13 is attached to the relay rod 12, and the cylinder 13a is fixed to the vehicle body.
A piston 13d defines the inside into two chambers 13b and 13c,
It is integrated into the relay rod 12. This cylinder 1
The two chambers 13b and 13c in 3a are connected to piping 14 or 15.
It is connected to the control valve 16 via. Further, pipes 18 and 19 extending from a reservoir tank 17 are connected to the control valve 16, respectively, and an oil pump 20 driven by an engine (not shown) is connected to one pipe 18. Of course, piping 18
becomes a high-pressure passage, and piping 19 serves as a low-pressure passage.

The control valve 16 is of a so-called booster valve type, with a spool 16a and a sliding control rod 21, and an input portion 21a integrated with the spool 16a of the control rod 21. is also used as a moving member of the steering ratio changing device E (see the above publication), and the output portion 21b of the control rod 21 is integrated with the relay rod 12 of the rear wheel steering mechanism B.

In such a power steering mechanism D, as is known, when the control rod 21 is displaced leftward in FIG.
are displaced to the left in FIG.
Rotate clockwise in Figure 1 around L', rear wheel 2R,
2L is steered to the right. During this steering, the power cylinder 1 is
Hydraulic pressure is supplied into the chamber 13b of No. 3 to assist in driving the relay rod 12 (boosting effect). Similarly, when the control rod 21 is displaced rightward in FIG. 1, the rear wheel 2R
, 2L will be steered to the left.

Two chambers 13b, 1 of the power cylinder 13
Springs 13e and 13f for biasing the rear wheels toward the neutral position are disposed within the spring 3c. Of course, the biasing forces of the springs 13e and 13f are set so that the rear wheels can be held in a neutral position against the lateral force generated during turning, and the power cylinder 13 drives the relay rod 12 against this biasing force. It turns out.

The front wheel steering mechanism A also has a power steering mechanism F, similar to the rear wheel steering mechanism B. This power steering mechanism F includes a power cylinder 65 attached to the relay rod 5 of the front wheel steering mechanism A.
The cylinder 65a is fixed to the vehicle body, while the cylinder 65a is fixed to the vehicle body.
A piston 65d that defines two chambers 65b and 65c within the cylinder 65a is integrated into the relay rod 5. The two chambers 65b and 65c within this cylinder 65a are connected to the piping 6.
6 or 67, it is connected to a rotary control valve 68 (described in detail later) provided on the shaft 8 of the steering mechanism C. This control valve 6
8 is connected to a pipe 70 extending from a branch valve 69 connected to the discharge side of the oil pump 20, and a pipe 71 branching from a pipe 19 extending from the reservoir tank 17. Such a power steering mechanism F is
Boost the operating force of the handle 9 (chamber 6 of the power cylinder 65)
5b or 65c by supplying oil) and transmits it to the relay rod 5.

The control valve 68, a detailed circuit diagram of which is shown in FIG. 3, has a switching valve 80 and a reaction force mechanism 81, as is known. The switching valve 80 switches between the chambers 65b and 65 of the front wheel power cylinder 65 depending on the direction of rotation of the steering wheel 9.
This determines whether to supply oil to c.

The reaction force mechanism 8 has a reaction force chamber 81a connected to a pipe 82 branched from the pipe 70, and a piston 81b pressed by the pressure inside the reaction force chamber 81a. The greater the internal pressure, the greater the force required to rotate the steering wheel 9 (the restraining force on the torsion bars connected to the steering wheel 9 is increased to reduce the assist force). Further, a branch pipe 83 connected to the pipe 71 is branched from the pipe 82, and a reaction pressure variable (assist force Variable apertures 84 and 85 constituting variable means are connected.

The variable throttles 84 and 85 are set in conjunction with each other so that when the opening degree of one increases, the opening degree of the other decreases, and the opening degree of the throttle 84 on the pipe 82 side is set to "0". (the variable throttle 85 on the branch 83 side is made smaller from the maximum opening), the pressure in the reaction chamber 81a (reaction pressure)
becomes larger, and therefore the assist force becomes smaller (steering operation force becomes heavier).

The steering mechanism C and the rear wheel steering mechanism B are linked via a front wheel steering mechanism A and a steering ratio changing device E. From this steering ratio changing device E, an input rod 22 extends forward, and a pinion 23 is attached to the front end of the input rod 22.
is meshed with a rack 24 formed on the relay rod 5 of the front wheel steering mechanism A. Note that the output rod of the steering ratio changing device E is also used by the input portion 21a of the control rod 21 in the control valve 16, as described above. Note that since the steering ratio changing device E is already well known from the above-mentioned publications, detailed explanation thereof will be omitted.

The rear wheel steering is controlled by the control unit 51 to obtain a predetermined steering ratio characteristic by controlling the motor 44 for the steering ratio changing device E, and this control is performed according to the actual steering ratio characteristic. Feedback control is performed using the output from the sensor 45 that detects the steering ratio. The control of the rear wheel steering is here responsive to the vehicle speed, and an example of changing the steering ratio according to the vehicle speed is as shown in FIG. 4. When the control characteristics shown in FIG. 4 are applied, the rear wheel turning angle relative to the steering wheel steering angle changes in the same phase direction as the vehicle speed increases. This situation is shown in FIG.

The control unit 51 also controls the opening and closing of the variable throttles 84 and 85, that is, the variable control of the assist force exerted by the power cylinder 65. For this purpose, the control unit 51 includes sensors 87 and 88. A signal is input from The sensor 87 detects vehicle speed. The sensor 88 detects the steering angle of the steering wheel, that is, the steering angle of the front wheels (θH).

The variable apertures 84 and 85 are controlled based on the map shown in FIG. To explain the content of this control, as is clear from FIG. 6, basically, the pressure in the reaction force chamber 81a (reaction force pressure) is set to increase as the vehicle speed increases; The assist force is reduced (the steering wheel 9 becomes heavier) (basic vehicle speed sensitive control).

In addition, in a region where the rear wheels 2 are steered in the same phase (a region where the vehicle speed is 50 km/h or more), the reaction pressure is reduced (the assist force is increased) near the neutral position. It is set. That is, when the steering wheel 9 is at an almost neutral position (in a small steering angle region), the steering wheel 9
is relatively light, and is set to become relatively heavy when the handle 9 is rotated. This results in
To improve the steering feeling of a steering wheel 9 by reducing the turning feeling due to a reduction in yawing caused by steering the rear wheels 2 in the same phase, or by reducing the neutral return force due to a reduction in self-aligning torque. becomes possible.

Furthermore, the small steering angle range that makes the steering feel of the steering wheel 9 lighter varies from the medium speed range (approximately 50 km/h) to the high speed range (approximately 50 km/h).
100 km/h or more), L1 to
As shown in L3, the width of the area is set small,
This is intended to ensure both straightness in the high speed range and clearance of the handlebar 9 in the medium speed range. Furthermore, as shown by H1, H2, and H3 in the same figure, the difference H between the reaction force pressure in the minute area and the reaction force pressure in the steering area is adjusted as the vehicle speed increases, in accordance with the basic vehicle speed sensitive control. I tried to make it smaller.

Although one embodiment of the present invention has been described above, the difference H in the reaction force pressure, that is, the difference between the assist force in the small steering angle region and the assist force in the steering region, is determined based on the characteristics of rear wheel steering. It may be made larger or smaller depending on the settings. That is, as shown by the broken line in FIG. 4, when the rear wheels 2 are given a characteristic of largely steering in the same phase, the reaction pressure difference H may be increased accordingly.

[0024]

As is clear from the above description, according to the present invention, the neutral position of the steering wheel can be physically determined from the weight of the steering wheel, which makes it possible to maintain the straightness of the vehicle at least when driving at high speeds. This makes it easy to secure.

[Brief explanation of the drawing]

FIG. 1 is an overall system diagram showing one embodiment of the present invention.

FIG. 2 is a cross-sectional system diagram showing details of a power steering device for rear wheels.

FIG. 3 is a diagram of a hydraulic circuit attached to a power steering device for front wheels to vary assist force.

FIG. 4 is a diagram showing an example of rear wheel steering characteristics.

FIG. 5 is a diagram showing an example of rear wheel steering characteristics.

FIG. 6 is a characteristic diagram showing an example of assist force (reaction pressure) control in a power steering device for front wheels.

[Explanation of symbols]

1 Front wheel 2 Rear wheel 51 Control unit 65 Power cylinder 68 Control valve 81 Reaction force mechanism 84, 85 Variable assist force mechanism 87 Vehicle speed sensor 88 Steering wheel steering angle sensor A Front wheel steering mechanism B Rear wheel steering mechanism

Claims (2)

[Claims] [Claim 1] In a rear wheel steered vehicle in which the rear wheels are steered together with the front wheels, and the rear wheels are steered in the same phase at least in a high speed range, a front wheel steering mechanism attached to the front wheel steering mechanism is provided. a power steering mechanism; a variable assist force mechanism provided in the front wheel power steering mechanism for changing an assist force that assists the steering force of the front wheels; a vehicle speed detecting means for detecting vehicle speed; and a signal from the vehicle speed detecting means. assist characteristic control means for increasing the assist force in a small steering range in which the front wheels are at a substantially neutral position, compared to the assist force in a steered range in which the front wheels are steered, at least when the front wheels are in a high speed range; A front wheel steering device for a rear wheel steering vehicle, comprising: 2. In claim 1, the steering characteristic of the rear wheels in a small steering area where the front wheels have a small steering angle includes:
When a characteristic that causes large steering in the same phase direction is set, compared to when a characteristic that causes small steering is set,
The difference between the assist force in the minute steering area and the assist force in the steering area is increased.