JPS63315375A - Rear wheel steering unit for vehicle - Google Patents

Abstract

PURPOSE:To simplify the structure of a rear wheel steering unit by pushing a tie-rod on the operating rod moving side overcoming the holding force of a centering means so as to steer rear wheels. CONSTITUTION:Upon rightward steering of front wheels 2L, 2R, a drive means 25 for a rear wheel steering device 20 operates a step motor 29 under control of an electronic controller 30. Further, pressure oil from a hydraulic pump 38 is fed into a ]eft side hydraulic chamber 34b of a power cylinder 34 through a control valve 36 so that an operating rod 24 is moved to the right in the axial direction from its neutral position. Then the right end part of the operating rod 24 abuts against the bottom surface of a fitting section 26b of a coupling member 26 in a centering means on the rear right wheel side 3R so that the coupling member 26 or a tie rod 22 is pushed outward by a predetermined amount by the pushing force of the operating rod 24, overcoming the urging force of a coil spring 27. With this arrangement, the rear right wheel 3R which is on the outside in the turning direction is steered in the toe-in direction, that is, the rear right wheel 3R is steered in the same phase as that of the front wheels 2L, 2R.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rear wheel steering system for a vehicle, and in particular, for steering the front wheels, only the rear wheels on the outside in the turning direction of the vehicle are brought into the same phase as the front wheels. Concerning the improvement of things that steer.

(Prior Art) Conventionally, when the rear wheel steering of a vehicle is set to vA, the left rear wheel steers the left and right rear wheels independently, as disclosed in, for example, Japanese Patent Application Laid-Open No. 61-200064. The vehicle is equipped with a power cylinder for the rear right wheel, a power cylinder for the right rear wheel, and a control means for controlling the supply and discharge of pressure oil to the two power cylinders, and when the front wheels are steered to the left, the power cylinder for the right rear wheel is operated. It is known that the right rear wheel is steered to the left, and when the front wheels are steered to the right, a power cylinder for the left rear wheel is operated to steer the left rear wheel to the right.In this way, When steering the front wheels, steering only the outer rear wheels in the vehicle's turning direction in the same phase as the front wheels is because greater road resistance acts on the outer rear wheels than on the inner rear wheels. In order to ensure running stability when turning at high speed, it is sufficient to steer only the rear wheels of the car, and compared to steering both the left and right rear wheels in the same phase as the front wheels, it is necessary to steer the rear wheels of the car in the same phase as the front wheels. Piping is easy 1
11, and the pump capacity can also be reduced.

(Problems to be Solved by the Invention) However, in the conventional system described above, although only one of the left and right rear wheels is steered in accordance with the steering of the front wheel, there is a case where both the left and right rear wheels are steered. Similarly, since a pair of power cylinders are required as actuation means, the structure is complicated, and operation 1. There are various problems with II 611, layout, etc.

The present invention has been made in view of the above, and its purpose is to steer only the rear wheels on the inside and outside of the turning of the vehicle in the same phase as the front wheels when the front wheels are steered as described above. The purpose of the present invention is to simplify the structure of a rear wheel steering device by using only one actuating means.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention includes a pair of left and right centering means for holding the left and right rear wheels in substantially neutral positions via tie rods, and left and right tie rods. The present invention includes an actuating rod extending in the vehicle width direction between the two, and a drive means for moving the actuating rod in the axial direction, and as the actuating rod moves in the axial direction, the tie rod on the movable side of A is actuated. The rear wheel is steered by pushing the rear wheel against the holding force of the centering means.

(Function) With the above configuration, in the present invention, when the front wheels are steered to the left, the actuating rod moves to the right in the axial direction by the operation of the drive means, and the tie rod of the right rear wheel is moved by the actuating rod to the centering means. By being pushed against the holding force, the right rear wheel on the outside in the direction of turning 7 of the vehicle is steered to the left in the same phase as the front wheels. On the other hand, when the front wheels are steered to the right, the actuating rod moves to the left in the axial direction, and the tie rod of the left rear wheel is similarly pushed by the actuating rod, so that the left rear wheel is steered to the right. Ru.

(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. This four-wheel steering system includes front wheel steering [1110] that steers the left and right front wheels 2L and 2R by steering the steering wheel 1, and only the rear wheels 3L or 3R on the outside in the turning direction of the vehicle with respect to the steering of the front wheels 2L and 2R. and a rear wheel steering device 20 according to the first embodiment of the present invention.

The front wheel steering device 10 includes a steering rod 11 disposed in the vehicle width direction, and a steering rod 11 that is operated by steering the steering wheel 1.
A rack and pinion mechanism 12 that moves the steering wheel in the axial direction (vehicle width direction), and a power cylinder 13 that moves the steering rod 11 by assisting the steering of the steering wheel 1, is connected to the left and right front wheels 2L via tie rods 14.14 and knuckle arms 15.15.

2R are connected to each other.

On the other hand, the rear wheel steering device V120 has left and right rear wheels 3L, 3
R respectively knuckle arms 21, 21 and tie rod 22
．． a pair of left and right centering means 23a, 23b that maintain the centering member at a substantially neutral position (a state in which the amount of rolling is substantially zero) via 22;
An operating rod 24 is disposed extending in the vehicle width direction between the centering means 23a, 23b or the left and right tie rods 22.
1 width direction).

The centering means 23a and 23b have a connecting member 26 supported by a member (frame, etc.) on the vehicle body side so as to be displaceable in the vehicle width direction, as shown in detail in FIG. 2 for the centering means 23b on the right rear wheel side. The inner end of the tie rod 22 is connected to the outer end of the connecting member 26, and a stopper portion 26a that comes into contact with the vehicle body side member 4 to restrict the displacement position of the connecting member 26 inward of the body. is formed. Further, a cylindrical fitting part 26b that opens inward is formed at the inner end of the connecting member 26.
A boss portion 24a formed at the end of the actuating rod 24 is fitted into the inside b so as to be rotatable. A coil spring 27 is attached to the outer periphery of the inner end of the connecting member 26 and is attached to the fitting portion 26.
b It is disposed in a compressed state between the seven flange portions 26c on the inner end side and the vehicle body side member 4. Thus, the centering means 23a, 23b move the rear wheel 3L or 3R to approximately neutral position via the tie rod 22 by the biasing force of the coil spring 27 when the stopper portion 26a of the connecting member 26 is in contact with the vehicle body side member 4. Learn to hold it in place. The centering means 23a and 23b hold the rear wheel 3L or 3R at a substantially neutral position due to the movement of the operating rod 24 in the axial direction, so that the boss portion 24a of the operating rod 24 moves to the bottom of the fitting portion 26b of the connecting member 26. When the actuating rod 24 comes into contact with the connecting member 2G and receives a pressing force to move the connecting member 2G outward against the urging force of the coil spring 27, the actuating rod 24 or the connecting member 2 is released.
The rear wheels 3L or 3L are steered in the toe-in direction (forward direction) depending on the amount of movement of the wheel 6.

Further, the first stage drive 25 includes a step motor 29 which is connected to the operating O-rad 24 via a rack and nion mechanism 28 so as to be able to transmit torque, and an electronic controller 30 which controls the operation of the step motor 29. have. The electronic controller 30 includes a front wheel steering angle sensor 31 that detects the front wheel steering angle from the steering amount of the steering wheel 1, a vehicle speed sensor 32 that detects the vehicle speed, and a rear wheel steering angle that detects the rear wheel steering angle from the rotation of the step motor 29. A signal from the rear wheel steering angle sensor 33 is input, and the operation of the step motor 29 is feedback-controlled so that the rear wheels 3L and 3R are steered to a predetermined steering angle according to the front wheel steering angle and the vehicle speed. It is designed to be controlled.

The drive torque (rotational force) of the step motor 29 is not sufficient to move the operating rod 24 in the axial direction and steer the rear wheels 31.3R, and the drive means 25 operates the step motor 29. A power cylinder 3 that moves the actuating rod 24 by assisting the step motor 29 when
It has 4. The power cylinder 34 uses the operating rod 24 as an operating rod, and is partitioned into two left and right hydraulic chambers 3/Ib and 34C by a piston 34a fixed to the operating rod 24. The two hydraulic chambers 34b and 34C are communicated via hydraulic passages 35a and 35b, respectively, with a control pulp 36 that controls the oil supply direction and oil pressure to the power cylinder 34, and the control valve 36' has an oil supply passage 37 A hydraulic pump 38 is connected to the oil tank 4 via an oil return path 39.
0 is connected. The control pulp 36 is
Oil supply passage 37 depending on the rotation direction of step motor 29
to one hydraulic passage 35a or 35b, and the oil return passage 39 to the other hydraulic passage 35b or 35a, respectively, and at the same time reduce the hydraulic pressure from the hydraulic pump 38 to a pressure corresponding to the rotational force of the step motor 29. It is.

In the case of this embodiment, the hydraulic pump 38 is connected to the engine 41.
Although it is designed to be driven by an electric motor or the like, it may be configured to be driven by an electric motor or the like.

Further, 42 is a battery, and 43 is a fail-safe valve interposed in the oil supply passage 37 and the oil return passage 39, the switching of which is controlled by the electronic controller 30, and the switching of the fail-safe valve 43 is controlled by the step motor 29, etc. The pressure oil is returned to the oil tank 40 so that the pressure oil from the hydraulic pump 38 is not supplied to the power cylinder 34 in the event of a failure.

Next, to explain the operation of the rear wheel steering device ff20 in the above embodiment, when the vehicle is traveling straight, the driving means 25 of the rear wheel steering device 20 is in an inactive state, and the operating rod 24 is located at a neutral position. , its both ends (boss part 24a
) are in a state of being separated from the fitting portions 26b of the respective connecting members 26 assigned to the left and right centering means 23a, 23b with a predetermined gap (the state shown in FIG. 1). Both the centering means 23a and 23b are connected to the left and right rear wheels by the biasing force of the coil spring 27 via the tie rod 22 and the knockle arm 21 when the stopper portion 26a of the connecting member 26 is in contact with the middle rest side member 4. 3L and 3R are held at substantially neutral positions.

On the other hand, at the front wheel 2m, 2R left-turn turning port,), a3 is placed in the drive means 25 of the rear wheel steering giff 20, steps below υ1n of the electronic controller 30, and the power cylinder 34 is activated. Hydraulic chamber 34b on the left side of
Pressure oil from the hydraulic pump 38 is applied to the control pulp 36.
, the actuating rod 24 moves from the neutral position to the right in the axial direction. Then, the right end of the actuating rod 24 comes into contact with the bottom of the fitting part 26b of the connecting member 26 in the centering means 23b on the right rear wheel side, and the pressing force from the actuating rod 24 causes the connecting member 26 or the tie rod 22 to coil. It is pushed outward for a predetermined period against the biasing force of the spring 27, whereby the right rear wheel 3R on the outside in the turning direction is steered in the toe-in direction, that is, in the same phase as the front wheels 2L and 2R.

Furthermore, when the front wheels 2L and 2R are steered to the right, the actuating rod 24 moves from the neutral position to the left in the axial direction due to the operation of the step motor 29 and the supply of pressure oil to the right hydraulic chamber 34C of the power cylinder 34. The left end portion contacts the bottom of the fitting portion 26b of the connecting member 26 in the centering means 23a on the left rear wheel side, and the tie rod 22 is pushed outward against the biasing force of the coil spring 27 due to the pressing force from the operating rod 24. , the left rear wheel 3L is steered in the toe-in direction.

In this way, when the front wheels 2m and 2R are steered either to the left or to the right, the rear wheels 31- or 3R on the outside in the turning direction are steered in the same phase as the front wheels 2L and 2R, so that the turning movement of the vehicle is It is possible to ensure running stability at all times.

Moreover, the rear wheel steering device 20 only has one actuating rod 2.
4 in the axial direction by one drive means 24, it is possible to steer both the left and right rear wheels 3L and 3R, so the operation 11i11ti
It also has the advantage of being easy to install, increasing the fΔ reliability of operation, and increasing the degree of freedom in layout of component arrangement.

Here, when the vehicle is turning, the load acting on the rear wheel 3L or 3R on the outside in the turning direction gradually increases as the vehicle turns, and the grip force of the rear wheel 3L or 3F on the road surface also depends on this vJ weight. Therefore, when the rear wheel steering device 20 steers the rear wheels 3L or 3R on the outside in the turning direction in response to the steering of the front wheels 2L and 2R, the rear wheel steering relative to the amount of front wheel steering changes. It is preferable that the steering ratio characteristic of the amount is as shown in FIG. 3, FIG. 4, and FIG. 5, respectively. The steering ratio characteristic shown in FIG. 3 is such that the rear wheel steering angle θR increases below a predetermined value θH1 of the front wheel steering angle θR, and gradually decreases above a predetermined value θH1. The steering ratio characteristic shown in the figure is the front wheel steering angle θ
When H is less than a predetermined value θH2, the rear wheel turning angle θR increases, and the increase M is a first-order ordinary differential function of the front wheel turning angle θH 〈dθH
/dt), and changes from a solid line to a broken line in accordance with the magnitude of the front wheel steering angle θH, and when the front wheel steering angle θH exceeds a predetermined value θH2, the rear wheel steering angle θR remains approximately constant. be. Furthermore, the steering ratio characteristics shown in FIG. 5 are such that when the front wheel steering angle θ+1 is zero (that is, when the vehicle is traveling straight), the rear wheel steering angle θR is previously steered by a predetermined amount in the toe-in direction. It is something. Note that in both steering ratio characteristics, the rear wheel steering amount θR is set to increase as the vehicle speed increases.

FIG. 6 shows a rear wheel steering system 1ff according to a second embodiment of the present invention.
20' shows the overall configuration of a four-wheel steering system for a vehicle. The rear wheel steering device 20' of the second embodiment uses an electric actuator 50 in place of the power cylinder 13 in the first embodiment in the drive means 25 for moving the actuating rod 24 in the axial direction. . As shown in detail in FIG. 7, the electric actuator 5o has a rotating member 51 that is screwed into a threaded portion 24a formed on the outer peripheral surface of the actuating rod 24, and is operated by rotating the rotating member 51 and feeding the screw. It is configured to move the rod 24. The operation of the electric actuator 5° is controlled by an electronic controller 52 that is separate from the electronic controller 30 that controls the operation of the step motor 29. A signal from the torque sensor 53 is input. Note that 54 is a fail-proof switch interposed between the electronic controller 52 and the battery 42. Further, the other configurations of the rear wheel steering device 20' and the configuration of the front wheel steering device [10] are the same as in the first embodiment, and the same members are given the same reference numerals and their explanations will be omitted.

Also in the second embodiment, the front wheel 2I-12R
When steering, the actuating rod 24 is moved in the axial direction by the operation of the step motor 29 and the electric actuator 50, and the outer rear wheel 3L or 3R in the turning direction is steered in the same phase as the front wheels 2L, 2R. As in the case of the first embodiment, it is possible to improve running stability when the vehicle is turning, and the structure of the rear wheel steering f+i position 20' is simplified, so that operational reliability can be improved. The effect of this can be obtained.

<Effects of the Invention> As described above, according to the rear wheel steering device of the present invention, the rear wheel on the outside in the turning direction can be moved in the same phase as the front wheel with respect to steering of the front wheel using one drive means and one actuating rod. By simplifying the configuration, it is possible to simplify the operation control and improve the degree of freedom in terms of layout.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and FIG. 1 is an overall configuration diagram of a four-wheel steering system for a vehicle equipped with a rear wheel steering device according to the first embodiment, and FIG. 2 shows the centering means of FIG. 1. It is an enlarged view of the vicinity, and FIG. 3, FIG. 4, and FIG. 5 are diagrams showing steering ratio characteristics, respectively. FIG. 6 is a diagram corresponding to FIG. 1 according to the second embodiment, and FIG. 7 is a schematic diagram of the operating section of the electric actuator. 3m, 3R... Rear wheel, 20.20'... Rear wheel steering device, 22... Tie rod, 23a, 23b... Centering means, 24... Operating rod, 25... Drive means. Patent applicant: Mazda Motor Corporation Patent applicant: NSK Ltd., 1st agent 1) Hiroshi
;・−−・.

Claims (1)

[Claims] 1) A pair of left and right centering means for holding the left and right rear wheels in substantially neutral positions through tie rods, an actuation rod extending in the vehicle width direction between the left and right tie rods, and and a drive means for moving the rear wheels, and as the actuating rod moves in the axial direction, the movable tie rod is pushed by the actuating rod against the holding force of the centering means to steer the rear wheels. A rear wheel steering device for a vehicle, characterized in that: