JPH0285075A - Rear wheel steering device - Google Patents

Abstract

PURPOSE:To keep the ratio of the steering steering forces between the front and rear wheels to a proper value by restricting the max. steering angle at high speed in the steering with the reverse phase between the front and rear wheels, to a prescribed value smaller than that in case of low speed. CONSTITUTION:A pressure adjusting valve 41b which is selected by the first selector valve 40 which operates according to the car speed and lowers the max. pressure generated in the both conduits 38a and 38b to a prescribed value smaller than that in case of the lower speed is installed. Further, pressure control valves 31a and 31b which lower the working liquid pressure in each conduit 38a, 38b to zero at a neutral position in steering front wheels and increases the working liquid pressure in one of the above-described conduit 38a according to the steering angle, when the front wheels are steered in one direction, interlocked with the steering of the front wheels installed in the both conduits 38a and 38b, are installed. Further, the second selector valve 33 which carries out the switching of a pair of inlet ports 33a and 33b which communicate to the conduits 38a and 38b and a pair of outlet ports 33c and 33d communicating to the working chambers 36a and 36b of the working cylinder 35a and 35b, according to the car speed, is provided.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an input member that operates in response to the steering of the front wheels.
The present invention relates to a rear wheel steering device for a four-wheel steering vehicle that operates a rear wheel power steering device to steer the rear wheels.

[Conventional technology]

In this type of rear wheel steering device, there are two types of actuating device, an electric type and a mechanical type, for operating an input member of the rear wheel power steering device in conjunction with the steering angle of the front wheels. The electric type (for example, see Japanese Patent Application Laid-Open No. 59-227567) is equipped with a steering angle sensor that electrically detects the front wheel steering angle, a vehicle speed sensor, etc., and is controlled by a computer that operates based on input from these sensors. The input member is actuated by a servo motor. Also, mechanical ones (for example, JP-A-5
No. 5-91457), the front wheel steering angle is transmitted to the input member using a transmission shaft of considerable length provided along the longitudinal direction of the vehicle body.

[Problem to be solved by the invention]

The electric type described above can control the rear wheel steering angle as desired depending on the driving condition, but it requires a relatively expensive steering angle sensor, and if the computer goes out of control, the rear wheel steering angle will become unpredictable. It may result in an abnormal value. In addition, mechanical types can always reliably transmit the front wheel steering angle to the input member of the rear wheel power steering system, but it is necessary to install the transmission shaft of considerable length so that it does not interfere with other parts of the vehicle body. This makes it difficult to arrange each part, including the transmission shaft, on the vehicle body.

In order to resolve such difficulties, applicants should first file an application (
(Japanese Patent Application No. 63-77074), a pressure control valve that operates in response to the steering of the front wheels is installed in a conduit to which working fluid from a supply pump is supplied, so that the working fluid has a pressure proportional to the steering angle of the front wheels. We proposed a technology that applies this to the input member of the rear wheel power steering system via a switching valve that operates according to vehicle speed, thereby steering the rear wheels in the opposite phase to the front wheels at low speeds and in the same phase at high speeds.・However, with this technology, the pressure change characteristics for rear wheel steering are the same at low speeds (opposite phase) and at high speeds (same phase), so when the front wheel steering angle is increased at high speeds, the rear wheel The steering angle becomes too large and the ratio of cornering force between the front and rear wheels becomes inconsistent.

An object of the present invention is to prevent the rear wheel steering angle from becoming too large when the front wheel steering angle is increased at high speeds, so that the ratio of front and rear cornering forces becomes an appropriate value.

[Means to solve the problem]

To this end, the rear wheel steering device according to the present invention includes a rear wheel power cylinder 26 that operates the operating rod 25, a return spring 28 that returns the operating rod 25 to the neutral position, and an input member 21, as illustrated in the accompanying drawings. The working fluid from the supply pump 37b is supplied to the rear power cylinder 2 according to the operating amount of the
In the rear wheel steering device, the rear wheel power steering device 20 is provided with a rear wheel power steering device 20 comprising a servo valve 23 that controls supply and discharge to the working chambers 6 and 6 and steers the rear wheels via the working rod 25.
8a, 38b and a supply pump 3 that supplies working fluid thereto.
7a, which is selected by a first switching valve 40 that operates depending on the vehicle speed when the vehicle speed is high, and the two pipes 38
a, 38b, and a pressure regulating valve 41b that lowers the maximum pressure generated in the pipes 38a and 38b to a predetermined value smaller than that at low speeds, and both the pipe lines 38a.

38b, and is operated in conjunction with front wheel steering, and in the front wheel steering neutral position, each of the pipes 38a.

When the working fluid pressure in 38b is set to 0, and the front wheels are steered in one direction, the working fluid pressure in one of the pipes 38a is increased according to the steering angle, and when the front wheels are steered in the other direction, the working fluid pressure in the other pipe 38a is increased. Pressure control valves 31a and 31b that increase the working fluid pressure in the passage 38b according to the steering angle, and a pair of working chambers 3 that actuate the input member 21 of the servo valve 23 in one direction and the other direction.
working cylinders 35a, 35b with 6a, 36b;
A return spring 29 that returns the input member 21 to the neutral position, a pair of inlet ports 33a, 33b communicating with the respective conduits 38a, 38b, and communicating with the respective working chambers 36a, 36b of the working cylinders 35a, 35b. A pair of exit ports
33c and 33d, and the inlet port 33
A, 33b and a second switching valve 33 for switching between outlet ports 33c and 33d.

[Effect]

When the front wheel steering angle is near the neutral position, the pressure control valve 31
a, 31b do not operate, no pressure is generated in the inlet ports 33a, 33b of the second switching valve 33, and therefore the input member 21 does not operate regardless of the operating state of the second switching valve 33, so the rear wheels are not steered. Not done. If the front wheel steering angle increases,
The pressure control valves 31a and 31b operate according to the steering direction, and the working fluid pressure in the corresponding pipe 38a or 313b increases, so that the pressure in the corresponding large port 33a or 33b changes according to the front wheel steering angle. Rise.

This pressure is controlled by a second switching valve 33 that is switched depending on the vehicle speed.
The input member 21 is applied to the working chamber 36a or 36b of either one of the working cylinders 35a, 35b through the input member 21, so that the input member 21 is operated in one direction. At low speeds, the rear wheels are steered in the opposite phase to the front wheels as the front wheel steering angle increases. In the case of high speed, the second switching valve 33 is switched and the first switching valve 40 is also switched at the same time to select the pressure regulating valve 41b, and the maximum pressure of both pipes 38a and 38b is set to a predetermined value smaller than that in the case of low speed. decrease to. Therefore, at high speeds, as the front wheel steering angle increases, the rear wheels are steered in the same phase as the front wheels.
The maximum steering angle of the rear wheels is limited to a predetermined value smaller than that at low speeds.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to steer the rear wheels according to the vehicle speed and the steering of the front wheels, and the maximum freezing steering angle at high speeds when the rear wheels are steered in the opposite phase to the front wheels is greater than that at low speeds. Since the steering force is limited to a small predetermined value, it is possible to set the ratio of the steering force between the front and rear wheels to a fair value, and it is possible to improve the steering characteristics when a large amount of steering is performed at high speed. In addition, the piping that transmits the pressure generated in response to front wheel steering to the actuating cylinder via the second switching valve is easy to bend, so there is no need to consider interference with surrounding parts, and the rear wheel steering system The arrangement becomes easy.

〔Example〕

The embodiments shown in the accompanying drawings will be described below.

As shown in FIG. 1, the tandem type supply pump 37 driven by the automobile engine consists of a front wheel pump 37a and a rear wheel pump 37b, and a certain amount of working fluid discharged from the front wheel pump 37a is used to control the front wheel power steering. supplied to the servo valve 12 and the pressure control valve 313.31b of the device 10;
On the other hand, a certain amount of working fluid discharged from the rear wheel pump 37b is supplied to the servo valve 23 of the rear wheel power steering device 20. The front wheel power steering device 10 includes a front wheel servo valve 12 provided on the way to transmit the rotation of the steering handle 11 to a rack and pinion mechanism 13 that converts the rotation of the steering handle 11 into reciprocating motion of the front wheel operating rod 14.
The main component is a front wheel power cylinder 15 connected to the front wheel operating port 7 door 14. Front wheel servo valve 12
is operated in response to the steering wheel torque applied from the steering handle 11 via the input shaft 12a, and controls the supply and discharge of the working fluid supplied from the front wheel side pump 37a to both working chambers of the front wheel power cylinder 15, thereby increasing the amplification. The resulting steering force is output to the front wheel operating port v F 14 to steer the front wheels 18 via the steering link mechanism 16, and the used working fluid is discharged into the reservoir 39. A check valve 42 provided between the front wheel pump 37a and the servo valve 12 is configured so that the discharge pressure of the front wheel pump 37a is at a predetermined value (in this embodiment) so that the pressure control valves 31a and 31b described below function. This is to prevent the weight from falling below 6 kg/cnl).

As shown in FIG. 1, the operating member 17 fixed to the front wheel operating port 7 door 14 has a pair of cam members 30a.

30b, while a pair of pressure control valves 31 are provided on the vehicle body.
a and 31b are attached. Each pressure control valve] La
, 31b is a spool shaft 32 that can be pushed in elastically.
a, 32b, and its relief pressure is normally O, but increases to a predetermined pressure (6 kg in this example) as the amount of pushing of the spool shafts 32a, 32b increases.
/cj) and have the same characteristics. As shown in the figure, when the steering angle of the front wheels 18 is O, the rollers at the tips of each Subur shaft (32a, 32b) are in a position away from the cam members 30a, 30b, and the pushing amount is 0, but the front wheels 18 is steered to the right and the actuating member 17 moves to the left, one spool shaft 32a is pushed in by the cam 30a via the roller, and the relief pressure of the pressure control valve 31a increases as shown by the solid line in FIG. If the front wheel 18 is steered leftward, the relief pressure of the other pressure control valve 31b will rise as shown by the broken line.

First and second pressure regulating valves 41a, 41b are selectively connected to the discharge port of the front wheel pump 37a via a first switching valve 40. First and second pressure regulating valves 41a, 41
．． b are all pressure reducing valves, and the set pressure (4 kg/cd) of the second pressure regulating valve 41b is smaller than the set pressure (6 kg/c+J) of the first pressure regulating valve 41a, and the repressure regulating valve 41a
, 41b are in communication with each other. The first switching valve 4o is controlled by a control bag W50 that operates based on the vehicle speed detected by the vehicle speed sensor 51, and selects the first pressure regulating valve 41a when the vehicle speed is low or medium;
In the case of high speed, the second pressure regulating valve 41b is selected. Outlet bow 1- of repressure adjustment valve 41a, 41b
are in communication with the inlet port of each pressure control valve 313.31b via separate lines 38a, 38b, and each line 38
a, 38b have the same fixed apertures 34a, 34b, respectively.
is provided. An outlet port of each pressure control valve 31a, 31b communicates with a reservoir 39.

Both ends of a rod-shaped input member 21 that rotates an input shaft 23a of a rear wheel servo valve 23, which will be described later, via a rank pinion mechanism 22 are respectively fitted into cylinders in a fluid-tight manner to form a pair of operating cylinders 35a and 35b. Each operating cylinder 35a, 35b is provided with a pair of return springs 29 that bias the input member 21 to the illustrated neutral position. Each pressure control valve 31a, 31b and each operating cylinder 35a, 35b
The second switching valve 33 provided between the two is an open center type 4-bottom 3-position switching valve, and the second switching valve 33 is an open center type 4-point 3-position switching valve.
and 33b are communicated between the pressure control valves 31a and 31b of the conduits 38a and 38b and the fixed throttles 34a and 34b, respectively, and the output ports 33c and 33d are communicated with the working chambers 36a and 36b of the working cylinders 35a and 35b, respectively. There is. The second switching valve 33 is controlled by the control device so that when the vehicle speed is low, the element 33■ is selected, when the vehicle speed is medium, the element 3Lff is selected, and when the vehicle is high, the element 33I[I is selected. 40.

As shown in FIG. 1, the rear wheel power steering device 20 has a rear wheel servo valve 23 and a rear wheel power cylinder 26 as main components. In the rear wheel power cylinder 26, a piston 26b is fluid-tightly fitted into a cylinder 26a fixed to the body of the automobile, and a rear wheel operating rod 25, which is fixed to the piston 26b and extends on both sides, is injected with fluid from both ends of the cylinder 26a. Return springs 28 are provided that project tightly and slidably between both sides of the piston 26b and the inner surfaces of both ends of the cylinder 26a to return the screw 1-26b to the neutral position shown. The rear wheel 19 is connected to both ends of the rear wheel operating rod 25 via a steering link mechanism 27 . The rear wheel servo valve 23 operates in accordance with the relative rotation of the input shaft 23a and the return shaft 23b, and distributes the working fluid supplied from the rear wheel side pump 37b to both the rear wheel power cylinders 26 through the distribution path. It is an oven center type 4-port throttle switching valve that supplies working fluid to one side of the chamber 26c and discharges working fluid from the other side to the reservoir 39. Input shaft 23a crawling/tsukubinion mechanism 2
The return shaft 23b is rotated by the human power member 21 via the
is connected to the rear wheel operating port Z through the rack and pinion mechanism 24! '2
It is designed to be rotated by 5.

Next, the operation of the above embodiment will be explained.

When the front wheel 18 is near the neutral steering position as shown in FIG. 1, the spool shafts 32a and 32b of the pressure control valves 31a and 31b are not pushed in, so the second switching valve 33 is not re-entered. No pressure is generated in 33a and 33b, so that regardless of the operating state of the second switching valve 33, the input member 21 is held in the neutral state by the return spring 29, and the rear wheel I9 is held in the neutral steering position by the return spring 28. Ru.

When the steering wheel 11 is rotated clockwise (or counterclockwise), the front wheel operating rod 14 moves to the left (or right) to steer the front wheels 18 to the right (or left), and at the same time, one The cam member 30a (or 30b) is connected to the spool shaft 3 of one pressure control valve 31a (or 31b).
2a (or 32b) to increase the relief pressure, one inlet port 33 of the second switching valve 33
The pressure at port a (or 33b) increases, while the pressure at the other inlet port 33b (or 33a) remains at zero. When the vehicle speed is low and the element 331 of the second switching valve 33 is selected, the pressure at one inlet port 33a (or 33b) is transferred from the outlet port 33c (or 33d) to one operating cylinder 35a (or 35b). Working chamber 36a
(or 36b) to move the input member 21 to the left (or right). This movement causes the rear wheel servo valve 230 to
The input shaft 23a rotates in a clockwise (or counterclockwise) direction when viewed from the rear, and transfers the working fluid from the rear wheel side pump 37b to the working chamber 26c on the right side (or left side) of the rear wheel power cylinder 26.
The left (or right) working chamber 26c is connected to the reservoir 39, and the rear wheel working loft 25 is moved to the left (or right).
to steer the rear wheels 19 leftward (or rightward). This movement of the rear wheel operating port/throat 25 rotates the return shaft 23b in the same direction as the input shaft 23a via the rank pinion mechanism 24 until the relative rotation angle of both shafts 23a and 23b becomes v□. The rear wheel operating rod 25 moves to the left (or right) against the return spring 28 and stops. That is, at low speeds, the rear wheels 19 are steered in a direction opposite to the steering angle of the front wheels 18. In this state, the first pressure regulating valve 41a is selected by the first switching valve 40, and both pipelines 38a, 33
Since b is set so that the maximum pressure is high < (6 kg/cd), the rear wheels 19 are proportionally steered until the front wheel steering angle reaches the maximum, as shown in characteristic A in Fig. 2. This allows for tight turning at low speeds.

Furthermore, in the case of high speed, the pressure of the element 33I [1 is selected and one large port)-33a (or 33b) of the second switching valve 33 is transmitted to the outlet port 33d (or 33C), so that the rear wheel 19 It is steered in the same phase direction as the steering angle of the front wheels 18. In this state, the second pressure control valve 41b is selected by the first switching valve 40, and the maximum pressure in both pipes 38a and 38b is lower than in the case of low speed (4 kg/cnl).
Therefore, as shown in characteristic B in Fig. 2, the rear wheels 19 are steered proportionally until the front wheel steering angle reaches a medium level, but if the front wheel steering angle increases further, the rear wheels 19 are steered proportionally. Also, the steering angle of the rear wheels 19 remains constant, and even if the front wheel steering angle becomes large, the rear wheel steering angle does not become too large. In this case, the maximum steering angle of the rear wheels is the second pressure regulating valve 41b.
This can be adjusted by changing the set pressure, and this allows the front and rear wheels to generate appropriate cornering force even when the steering wheel is turned sharply at high speeds, allowing for responsive turns.

Further, in the case of medium speed, since the element 33I11 of the second switching valve 33 is selected, the pressures of the lower ports 33c and 33d are the same, and the rear wheel 19 is held in a neutral state by the return spring 28.

Further, a pressure control valve 31a that operates in response to steering of the front wheels,
31b to the operating cylinders 35a, 35b via the first switching valve 33 is easily bent, so there is no need to consider interference with surrounding parts, and each part of the rear wheel steering system Parts can be easily arranged.

[Brief explanation of drawings]

The accompanying drawings show an embodiment of the rear wheel steering device according to the present invention, in which FIG. 1 is an overall configuration diagram, FIG. 2 is a characteristic diagram of the rear wheel steering angle with respect to the front wheel steering angle, and FIG. 3 is a diagram showing the characteristics of the rear wheel steering angle with respect to the front wheel steering angle. FIG. 3 is a characteristic diagram of relief pressure versus front wheel steering angle. Description of key points 20...Rear wheel power steering device, 21...Input member,
23... Servo valve (rear wheel servo valve), 25... Operating rod (rear wheel operating port, DO), 26... Rear wheel power cylinder, 28... Return spring, 29... Return spring , 31
a, 31b...pressure control valve, 33---second switching valve,
33a, 33b...large port, 33c, 33d...
・Outlet port, 35a, 35b...Operating cylinder, 3
6a, 36b... Working chamber, 37a... Supply pump (
front wheel side pump), 37b... supply pump (rear wheel side pump), 38a, 38b... pipeline, 40... first switching valve, 41b... pressure regulating valve (second pressure regulating valve) .

Claims (1)

[Claims] A rear wheel power cylinder that operates a working rod, a return spring that returns the working rod to a neutral position, and a supply/discharge control of working fluid from a supply pump to the working chamber of the rear wheel power cylinder according to the operating amount of the input member. In a rear wheel steering device comprising a rear wheel power steering device comprising a servo valve that steers the rear wheels via the operating rod, the rear wheel steering device is provided between a pair of conduits and a supply pump that supplies working fluid thereto. a pressure regulating valve that is selected by a first switching valve that operates according to the vehicle speed to reduce the maximum pressure generated in the two pipes to a predetermined value smaller than that when the vehicle speed is low; and It is operated in conjunction with the steering of the front wheels, and when the front wheels are in the neutral position, the working fluid pressure in each of the pipes is 0, and when the front wheels are steered in one direction, the working fluid pressure in one of the pipes is a pressure control valve that increases the pressure in accordance with the steering angle and increases the working fluid pressure in the other pipe in accordance with the steering angle when the front wheels are steered in the other direction; a working cylinder having a pair of working chambers for actuation in the other direction; a return spring for returning the input member to a neutral position; a pair of inlet ports communicating with each of the conduits and communicating with each working chamber of the working cylinder; 1. A rear wheel steering device comprising: a second switching valve having a pair of outlet ports and switching between the inlet port and the outlet port according to vehicle speed.