JPH0460868B2 - - Google Patents

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) In general, when steering a vehicle, it is preferable to change the steering ratio between the front wheels and the rear wheels in accordance with the steering angle of the steered wheels, which is approximately inversely proportional to the vehicle speed. is known. That is, in a low vehicle speed range, the steered wheels are steered with a large steering angle, but in this case, it is preferable to set the front wheels and rear wheels in opposite phases in order to improve the turning ability. On the other hand, in a high vehicle speed range, the steered wheels are steered even with a small steering angle, but in this case, the front and rear wheels must be in the same phase, or the non-steered wheels (usually the rear wheels)
It is preferable to reduce the steering angle to zero in order to improve running stability.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 55-91458, conventional four-wheel steering systems for vehicles employ a cam groove that moves according to the steering angle of the front wheels using a rod that cooperates with the steering of the front wheels. and a pin fixed to a rear wheel steering member for steering the rear wheels and slidably held in the cam groove, and the steering angle is large due to the sliding of the pin in the cam groove. It has been proposed that the front wheels and rear wheels are in opposite phases when the steering angle is small, and in the same phase when the steering angle is small.

However, in the above-mentioned conventional system, the steering ratio is made variable by the sliding of the pin in the cam groove, so the steering operation of the rear wheels tends to become unstable when the front wheels are steered. The steering was not carried out smoothly, resulting in poor operability.

(Objective of the Invention) As described above, an object of the present invention is to reduce the steering angle characteristics of the rear wheels required in steering a vehicle, particularly to reduce the steering angle of the rear wheels to zero when the steering angle of the front wheels is small. The characteristic of reverse phase when the steering angle is large is
Instead of the conventional sliding structure of pins and guide grooves, we improved the structure of the rod that transmits the steering force of the front wheels to the rear wheels, and used a power steering mechanism. The purpose of the present invention is to perform wheel steering operations smoothly to ensure that the above-mentioned steering angle characteristics can be exhibited with good operability.

(Structure of the Invention) In order to achieve the above object, the structure of the present invention provides the above four-wheel steering system for a vehicle, which includes a steering system that steers front wheels and a rear wheel steering system that steers rear wheels. The rear wheel steering device is configured to include the following means, members, etc.

Specifically, there is a power steering mechanism that steers the rear wheels by moving a steering rod connected to the rear wheel tie rod in its axial direction, and a power steering mechanism that transmits the steering force of the front wheels to the steering rod side of the power steering mechanism to steer the rear wheels. A transmission rod that is divided into two parts, front and rear, steers the wheels in a direction opposite to the steering direction of the front wheels in an opposite phase, and a transmission rod is provided at the division part of the transmission rod, and the steering force transmission amount of the front division rod is set to a predetermined value. a dead zone setting means for synchronizing the rear split rods and transmitting steering force from the front split rod to the rear split rod when the above occurs, and a dead band setting means provided on the rear split rod side of the transmission rod, The vehicle is configured to include a control valve for controlling the operation of the power steering mechanism, and neutral position biasing means for biasing and holding the control valve at a neutral position so that the rear wheels are not steered by the operation of the power steering mechanism.

With this configuration, when the steering angle of the front wheels is small, the dead band setting means prevents the front wheel steering force from being transmitted to the rear wheels via the transmission rod, and the neutral position biasing means moves the control valve to the neutral position. while maintaining the steering angle of the rear wheels at zero.
When the steering angle of the front wheels is large, the steering force of the front wheels is transmitted to the steering rod of the power steering mechanism via a transmission rod, and the power steering mechanism steers the rear wheels in the opposite phase. .

(Effects of the Invention) Therefore, according to the four-wheel steering system for a vehicle of the present invention, by effectively utilizing the split structure of the transmission rod and the power steering mechanism, desired rear wheel rotation can be achieved without requiring a large steering force. It is possible to reliably obtain the steering angle characteristics (the characteristic that the rear wheel steering angle is zero when the front wheel steering angle is small, and the opposite phase when the front wheel steering angle is large), resulting in high-speed stability. It is possible to easily improve performance and maneuverability while maintaining good operability. Furthermore, when the transmission rod is in the dead zone, the control valve of the power steering mechanism is biased and held in the neutral position by the biasing means, and the steering angle of the rear wheels is reliably maintained at zero, resulting in the above-mentioned high-speed stability. Furthermore, the holding means itself can be made smaller. Furthermore, the steering force transmission system does not have any locations where a large bending moment acts, and this combined with the small steering force provides the effect of reliably preventing failures due to member damage.

(Example) Hereinafter, an example as a specific example of the technical means of the present invention will be described based on the drawings.

FIG. 1 shows the overall configuration of a four-wheel steering system for a vehicle according to the present invention, in which reference numeral 1 denotes a steering system for steering left and right front wheels 2L, 2R, and the steering system 1 includes a steering wheel 3 to be steered, , a pinion 4a and a rack 4b that convert the steering force (steering input) of the steering wheel 3 into a stroke (reciprocating motion) in the vehicle width direction and transmit the same, and left and right front wheels whose base ends are connected to each end of the rack 4b. Knuckle arms 6, 6 have one end connected to the tip of each tie rod 5, 5, and the other end connected to the left and right front wheels 2L, 2R, respectively. 5,5
Stroke in the vehicle width direction to move the left and right front wheels 2L,
It is configured to steer 2R left and right.

Reference numeral 7 denotes a rear wheel steering device for steering the left and right rear wheels 8L, 8R, and the rear wheel steering device 7 includes left and right knuckle arms 9, 9 whose one ends are connected to the left and right rear wheels 8L, 8R. and left and right rear wheel tie rods 10, 10 whose tips are connected to the other ends of the respective knuckle arms 9, 9.

Further, the rear wheel steering device 7 includes a power steering mechanism 11 that strokes rear wheel tie rods 10, 10 in the vehicle width direction. The power steering mechanism 11 includes a hydraulic chamber 13 formed in a housing 12, and an operating rod 14 extending in the vehicle width direction through the hydraulic chamber 13.
and an input shaft 15 extending perpendicularly to the operating rod 14 and toward the front of the vehicle body. The input shaft 15 and the operating rod 14 are configured such that a pinion portion 15a formed at the rear end of the input shaft 15 and a rack portion 14a formed at one end of the operating rod 14 mesh with each other. The rotational motion of the operating rod 14 is converted into a stroke in the axial direction, that is, in the vehicle width direction, and is transmitted.
Both ends are connected to the base ends of left and right tie rods 10, 10, respectively. On the other hand, the hydraulic chamber 13 is partitioned left and right into a left chamber 13L and a right chamber 13R by a piston 16 fixed to the operating rod 14, and each of the chambers 13L and 13R is connected through hydraulic passages 17a and 17b, respectively. It communicates with a control valve 18 that controls the oil supply direction and oil pressure to the hydraulic chamber 13, and a hydraulic pump 20 is connected to the control valve 18 via an oil supply passage 19.

The control valve 18 detects the rotation direction of the input shaft 15, and when the rear wheels 8L and 8R are steered to the left (counterclockwise in the figure), the hydraulic pump 2
0 to the right chamber 13R of the hydraulic chamber 13, and when the rear wheels 8L and 8R are steered to the right (clockwise in the figure), the hydraulic pump 20 is connected to the left chamber 13R of the hydraulic chamber 13.
3L, and simultaneously reduces the hydraulic pressure from the hydraulic pump 20 to a pressure corresponding to the rotational force of the input shaft 15. Therefore, when the operating rod 14 is stroked by the input shaft 15, the stroke of the operating rod 14 is assisted by supplying pressure oil to the hydraulic chamber 13, so that the left and right tie rods 10, 10 are stroked in the vehicle width direction. There is.

Input shaft 15 of the power steering mechanism 11
A pinion portion 15b is formed at the front end of the input shaft 15b in the same manner as the rear end thereof, and a rack 21 that meshes with the pinion portion 15b is disposed perpendicular to the input shaft 15, and on the outer periphery of the rack 21, When the power steering mechanism 11 is not activated, its malfunction causes damage to the rear wheels 8.
Set springs 22, 22 are provided as neutral position biasing means for biasing and holding the input shaft 15 or control valve 18 of the power steering mechanism 11 in the neutral position via the rack 21 so that the wheels L and 8R are not steered. ing.

Further, 23 is a transmission rod as a steering input shaft of the rear wheel steering device 7 extending in the longitudinal direction of the vehicle body,
The transmission rod 23 has a pinion portion 23a at its front end that meshes with the rack 4b of the steering device 1, and its rear end is connected to the front end of the input shaft 15 of the power steering mechanism 11, and has a vehicle width of the rack 4b. Direction stroke i.e. front wheel 2
The steering forces of L and 2R are converted into rotational motion and transmitted to the input shaft 15 of the power steering mechanism 11, and the power steering mechanism 11 is operated to drive the rear wheels 8.
The wheels L and 8R are steered in opposite phases to the front wheels 2L and 2R.

Further, the transmission rod 23 is divided into two parts, front and rear, at approximately the center thereof, and a front divided rod 23b is formed.
and a rear split rod 23c, and these split rods 23b, 23c are connected by a connecting member 24. The connecting member 24 has a cylindrical hollow member 25 fixed to the rear end of the front split rod 23b and a front end of the rear split rod 23c, and is rotatably fitted into the hollow member 25. For example, two protrusions 26a, 26a are formed on the outer periphery of the shaft member 26, and the hollow member 25 has two protrusions 26a, 26a that protrude in the radial direction. Engagement grooves 25a, 25a are formed correspondingly. The width of each engagement groove 25a in the circumferential direction is equal to the width of the protrusion 26a.
The thickness of the engaging groove portion 2 is set larger than that of the engaging groove portion 2.
A dead zone region 27 is formed between 5a and the protrusion 26a. That is, when the steering force of the front wheels 2L, 2R is large, the engagement groove 25a and the protrusion 26a engage with each other as shown in FIG.
4, the hollow member 25 and the shaft member 26 rotate together, and the rotational movement of the front split rod 23b of the transmission rod 23 is transferred to the rear split rod 23 via the connecting member 24.
When the steering force of the front wheels 2L and 2R is small, the engagement groove 25 rotates in synchronization with the rear split rod 23c as shown in FIG. 2a.
a and the protrusion 26a do not engage with each other, and the rotational motion transmission described above is not performed (hereinafter, the time when such rotational motion transmission is not performed is referred to as a dead zone period), and the connection member 24 is , has a function as a dead band area setting means for setting a dead band area 27 for the steering force transmission of the transmission rod 23.
Reference numeral 28 is a return spring provided in the housing 12 of the power steering mechanism 11, which urges the operating rod 14 to the neutral position when the power steering mechanism 11 is not in operation.

Therefore, in the above embodiment, when the steering wheel 3 is steered, the front wheels 2L and 2R are
Depending on the steering force (steering angle), the front wheels are steered to the left or right by tie rods 5, 5.

On the other hand, the rear wheels 8L and 8R may or may not be steered depending on the magnitude of the steering force. That is, when the steering force is small and the amount of steering force transmitted by the front split rod 23b of the transmission rod 23 is less than a predetermined value, the connecting member 23 connecting the front split rod 23b and the rear split rod 23c of the transmission rod 23 is activated. Since it is in the dead zone region, the steering force is not transmitted as a rotational motion to the input shaft 15 of the power steering mechanism 11 via the transmission rod 23, and the power steering mechanism 11 is maintained in a non-operating state. When the connecting member 24 is in the dead zone region (when the power steering mechanism 11 is inactive), the input shaft 15 and control valve 18 of the power steering mechanism 11 are set by the set spring 22, and the operating rod 14 is set by the return spring. 28, the rear wheel dirods 10, 10 are reliably held in the neutral position, and the rear wheels 8L, 8R are stably maintained at zero steering angle.

On the other hand, the steering force is large and the transmission rod 23
When the amount of steering force transmitted to the front split rod 23b exceeds a predetermined value, the steering force is transferred to the front split rod 23b.
3 to the input shaft 15 of the power steering mechanism 11 and the power steering mechanism 11 is operated, the rear wheel tie rods 10, 10 are stroked in the left and right direction.
The rear wheels 8L, 8R are steered in opposite phase to the front wheels 2L, 2R.

In this way, when the steering angle of the front wheels 2L, 2R is small, the steering angle of the rear wheels 8L, 8R remains zero, and when the steering angle of the front wheels 2L, 2R is large, the steering angle of the rear wheels 8L, 8R is changed. Since a rear wheel turning angle characteristic in which the steering angles are in opposite phases can be obtained, it is possible to improve running stability in a high vehicle speed range and to improve turning ability in a low vehicle speed range.

Further, the rear wheel turning angle characteristics as described above are obtained by transmitting rotational motion through the connecting member 24 having the dead zone region 27 in the transmission rod 23, which is divided into the front divided rod 23b and the rear divided rod 23c. When the rotational motion is transmitted, the rear wheels 8L and 8R are reliably and smoothly steered by the operation of the power steering mechanism 11, so the steering force can be small. , and the steering feeling can be made extremely smooth, thereby ensuring good operational stability and operability.

Moreover, when the power steering mechanism 11 is not operating, that is, when the transmission rod 23 is in the dead zone region, the set spring 22 allows the input shaft 15 of the power steering mechanism 11 and the control valve 18 to be connected to each other.
However, due to the return spring 28, the operating rod 1
4 are biased and held at their neutral positions, the steering angles of the rear wheels 8L and 8R can be reliably maintained at zero, further improving the running stability, and the setting spring 22 itself can be maintained at zero. It is also possible to achieve miniaturization.

Furthermore, when transmitting the steering force, there is no place where a large bending moment acts, such as in the connecting member 24, which only transmits rotational force in the axial direction, and the provision of the power steering mechanism 11 reduces the steering force. In addition to this, damage to members due to steering force transmission can be reliably prevented, and durability can also be improved.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is an overall configuration diagram, and FIGS. 2a and 2b are operation explanatory diagrams showing the operating state of the connecting member. 1... Steering device, 2L, 2R... Front wheels, 7... Rear wheel steering device, 8L, 8R... Rear wheels,
10... Tie rod, 11... Power steering mechanism, 15... Input shaft, 18... Control valve, 22... Set spring (neutral position biasing means), 23... Transmission rod, 23b... Front split rod, 23c... Rear split rod, 24...
...Connecting member (dead zone setting means), 27... Dead zone area.

Claims (1)

[Scope of Claims] 1. A four-wheel steering device for a vehicle comprising a steering device that steers the front wheels and a rear wheel steering device that steers the rear wheels, wherein the rear wheel steering device is configured to steer the rear wheels. A power steering mechanism that steers the rear wheels by moving a steering rod connected to a tie rod in its axial direction; A transmission rod that is divided into two parts, front and rear, which steers the steering wheel in a direction opposite to the steering direction and in an opposite phase, and a transmission rod that is provided at a divided part of the transmission rod, when the amount of steering force transmitted from the front division rod exceeds a predetermined value. a dead zone setting means for synchronizing the rear split rods to transmit steering force from the front split rods to the rear split rods; and a dead zone setting means provided on the rear split rod side of the transmission rod for controlling the operation of the power steering mechanism. A four-wheel steering system for a vehicle, comprising: a control valve; and neutral position biasing means for biasing and holding the control valve in a neutral position so that the rear wheels are not steered by the operation of the power steering mechanism. .