JPH0481361A - Rear-wheel steering device - Google Patents

Abstract

PURPOSE:To safely return rear wheels to a neutral position by interposing an overlap type spool valve for direction selection in an oil passage between a direction selector valve and a power cylinder, and gradually draining the working oil in a power cylinder when the direction selector valve is broken. CONSTITUTION:In the hydraulic system for a rear wheel steering device, the discharge port of a tandem hydraulic pump 1 is connected to a bypass valve 2, hydraulic locking operation valve 3, left and right direction selector valves 11L and 11R of a hydraulic unit 10, direction selector spool valve 12, and a relief valve 4. The direction control spool valve 12 is operated by the direction selector valves 11L and 11R, and the spool valve 12 is made as the overlap type in which a land part 24 formed on the spool and the shoulder part 25 of a groove formed on a housing 20 are overlapped. When the direction selector valve 11L or 11R is broken during the steering with a large steering angle, and the spool valve 12 is returned to a neutral state, the working oil in a power cylinder 31 is gradually drained, and a steering rod is gradually returned to a neutral state.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a rear wheel steering system for a vehicle that can freely control the dynamic performance of the vehicle during steering, and in particular This is designed to reduce the impact when the rear wheel steering device returns to neutral when the switching valve fails.

(Prior Art) In a vehicle equipped with a rear wheel steering device, the rear wheels are steered together with the front wheels. By appropriately controlling the steering angle of the rear wheels in accordance with the steering angle of the front wheels, steering stability while the vehicle is turning can be dramatically improved.

As such a known example, Japanese Patent Application Laid-Open No. 63-19 shown in Fig. 3
Some of them are described in Japanese Patent No. 2660.

The rear wheel steering device of this example operates a directional control valve 91 integrated with a solenoid 94 in response to a signal from a controller, supplies hydraulic oil to a power cylinder 92 for rear wheel steering, and steers the rear wheels. It has become. In addition, this device has a return spring 93 disposed inside the power cylinder for rear wheel steering as a means for returning the rear wheels to neutral.
are using.

(Problem to be solved by the invention) However, in such a device, when the directional control valve malfunctions and returns to the neutral state, the rear wheels are returned to the neutral state at once by the action of the return spring. As a result, a shock occurs when returning to neutral, worsening steering stability.
There is also the problem that safety is compromised.

In addition, the directional switching valve of the above device is a direct-acting type in which the directional switching solenoid is integrated with the spool valve, so the entire valve is large and there is a problem that it is difficult to handle due to the arrangement of parts. There is. Furthermore, since it is a spool direct drive type, there are problems such as requiring a large current.

The present invention was made to solve these problems, and even if the directional control valve fails while steering the rear wheels, the rear wheels gradually return to the neutral position, thereby improving steering stability. It is an object of the present invention to provide a rear wheel steering device that can improve the performance of the vehicle. Furthermore, by making the solenoid for operating the valve separate from the spool valve body, the present invention attempts to provide a rear wheel steering device having a small, easy-to-handle directional switching spool valve.

[Structure of the Invention] (Means for Solving the Problem) The technical means taken to achieve the above-mentioned technical problem is that the rear wheel steering device includes a vehicle speed sensor that detects the speed of the vehicle and a steering angle of the front wheels. a steering angle sensor to detect the
an electronic control device that calculates an appropriate rear wheel steering angle according to the steering angle detected by the steering angle sensor; a hydraulic control unit that controls the rear wheel steering angle based on the calculation result of the electronic control device; and a rear wheel drive means for changing the steering angle of the rear wheels by hydraulic pressure controlled by a hydraulic control unit,
The hydraulic control unit is provided with a directional switching valve that switches directions in response to a signal from the electronic control device, and an overlap type directional switching spool valve that opens and closes an oil passage using hydraulic fluid supplied from the directional switching valve. It is.

(Function) According to the power cylinder described above, an overlap type directional switching spool valve is inserted into the oil path between the directional switching valve and the power cylinder as an actuator, so the directional switching valve may malfunction during large steering angle steering. Even when the directional switching valve returns to the neutral state and the directional switching spool valve returns to the neutral state, the hydraulic oil supplied to the power cylinder is gradually drained by the neutral return operation of the power cylinder. It is possible to reduce the impact when returning to neutral. In addition, since the directional switching valve is configured with the solenoid part and the directional switching spool part as separate parts,
The valve body can be made smaller, and the valve arrangement and other handling during design can be facilitated.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram depicting the system configuration of the apparatus of this embodiment. The front wheel steering mechanism 80 is a steering link wheel 8
Connected to 1. When the steering wheel 81 is turned, the directions of the front right wheel FR and the front left wheel FL change. The rotation angle of the steering wheel 81 is detected by the front wheel steering angle sensor ST1 and input to the electronic control unit ECU.

The hydraulic control unit 10 controls a power cylinder 31 as an actuator to change the directions of the left rear wheel RL and the right rear wheel RR. The power cylinder 31 can adjust the directions of the left rear wheel RL and the right rear wheel RR within an operating range of ±7 degrees. Further, the power cylinder 31 has a hydraulic locking means 50.
Built-in. When the hydraulic locking means 50 operates, the power cylinder 31 can adjust the directions of the left rear wheel RL and the right rear wheel RRO only within an operating range of ±1 degree. The directions of the left rear wheel RL and right rear wheel RR are detected by the rear wheel steering angle sensor ST2 and input to the electronic control unit ECLI. A vehicle speed sensor SPI is arranged near the right rear wheel RR. The vehicle speed sensor SPI detects the vehicle speed from the right rear wheel RR. The vehicle speed detected by the vehicle speed sensor SPI is input to the electronic control unit 1EcU.

Further, a vehicle speed sensor SP2 is disposed in the transmission 83 connected to the engine 82. Vehicle speed sensor SP2 detects the vehicle speed from output shaft 84 of transmission 83. The vehicle speed detected by vehicle speed sensor SP2 is controlled by electronic control bag WEC.
It is input to U.

The electronic control unit ECU controls the hydraulic control unit 10,
Adjust the orientation of the left rear wheel RL and right rear wheel RR.

Hereinafter, the overall configuration of the hydraulic system and the configurations of the hydraulic control unit 10, power cylinder 31, and hydraulic locking means 50 will be described in detail with reference to FIG.

FIG. 2 shows the hydraulic system of the present invention. In the same figure, the discharge ports of the tandem hydraulic pump 1 are a bypass valve 2, a hydraulic lock operation valve 3, and left and right directional switching valves IIL and l.
It is connected to the 1R1 direction switching spool valve 12 and the relief valve 4. The bypass valve 2 is for determining the line pressure, and the outlet of this valve is connected to the drain tank 5.The hydraulic lock operation valve 3 controls the movement of the rear wheel steering rod to adjust the tire turning angle. This is a valve for regulating the pressure to about ±1 degree in terms of conversion, and the outlet of this valve is connected to the hydraulic oil supply port of the chamber 55 of the hydraulic locking means 50 of the power cylinder.This hydraulic lock operation valve 3 is When an abnormality occurs in the system or the vehicle speed exceeds a predetermined value, hydraulic oil from the tandem hydraulic pump l is supplied to the chamber 54 of the hydraulic locking means 50.The left and right direction switching valves IIL and IIR operate the direction switching spool valve 12. This is the outlet port 14L of the directional control valve.

14R is the hydraulic oil chamber 22 of the direction switching spool valve 12
Connected to L and 22R. Further, the outlet ports 14 L and 14 R of the left and right directional switching valves IIL and IIR are normally connected to a drain tank via an oil passage 18. Hydraulic oil supply port 26 of directional switching spool valve I2
．． 27 is a tail connected to the tandem hydraulic pump 1. The outlet 28.29 of the directional spool valve I2 is connected to the oil chamber 47.48 of the power cylinder. In addition, the discharge port 30 of the direction switching spool valve is connected to the drain tank 5.
It is connected to the.

The following is a directional control valve 11L that constitutes the system.

The configurations of the 11R1 direction switching spool valve 12, the power cylinder 31, and the hydraulic locking means 50 will be described in detail.

Since the left-right direction switching valves 11L and IIR have the same shape, the configuration of the left-hand direction switching valve 11L in the figure will be described here.

The directional control valve 11L has a supply port 13 formed in the housing.
L, a delivery port 14L, and a valve member 15 disposed opposite to the supply port. The valve member 15 is normally connected to the spring 16.
is pressed to the right in the figure, closing the supply port 13L and communicating the delivery port 14L with the oil passage 18. In addition, the valve member 1
5 is provided with a solenoid 17. solenoid 1
When 7 is energized, the valve member 15 is attracted to the left, and the supply port 13L and the delivery port 14L are communicated with each other.

The directional switching spool valve 12 has a valve housing 20
A spool 21 disposed within the housing, oil chambers 22L, 22R formed at both ends of the spool 21, and spool return springs 23L, 23R disposed in the oil chambers.
Equipped with. This spool valve is of an overlap type in which a land portion 24 formed on the spool and a shoulder portion 25 of a groove formed on the housing 20 overlap. Incidentally, although the land portion 24 and shoulder portion 25 of this spool valve 12 overlap, the outlet port 2
A slight oil passage is formed in the overramp portion between 8.29 and the discharge port 30. Therefore, the directional valve 12
Even if the power cylinder 31 is in a neutral state, the oil chamber 47 of the power cylinder 31
．． When high-pressure hydraulic oil comes from 48, the high-pressure hydraulic oil is drained through a small oil passage. Oil chambers 22L and 22R formed at both ends of the spool are connected to outlet ports 14L and 14R of left and right directional control valves ILL and IIR.

The direction switching spool valve 12 also has two supply ports 26.2 through which hydraulic oil is supplied from the tandem hydraulic pump 1.
7, two outlets 28, 29 for sending hydraulic oil to the power cylinder, and a discharge port 30 for returning hydraulic oil to the drain tank.
is formed. Now, when hydraulic oil is supplied to the left oil chamber formed at the end of the spool valve, the spool 21 moves to the right. This connects the supply port 26 and the outlet 28, and also connects the outlet 29 and the outlet 30.

As a result, hydraulic oil is supplied to the oil chamber 47 of the power cylinder, and the hydraulic oil in the oil chamber 48 is drained and the sliding piston 39 is drained.
moves to the right in the figure.

The power cylinder 31 includes a substantially cylindrical body 32, sealing members 33, 34 that seal both ends of the body, and a steering rod 35 slidably supported on the sealing members. A partition wall 36 is firmly fixed between the sealing members 33, 34. The partition wall 36 is connected to a stepped portion 37 formed on the body.
It is held between rings 38. Further, a sliding piston 39 is firmly fixed to the steering rod. Furthermore, a stop ring 40 is fixed to the steering rod 35,
When the steering rod is moved, this stop ring 40 closes the sealing member 3.
A cylindrical member 41 is fixed to the sealing member 33 so as not to interfere with the sealing member 33. A pair of retainers 42, 43 are inserted into the steering rod 35. A pair of retainers 42
．． A return spring 44 is disposed between the springs 43 and 43. A sleeve 4 is provided between the retainer 42 and the sliding piston 39.
5 has been inserted. The sleeve 45 is slidably inserted around the outer periphery of the steering rod 35. The retainer 43 is in contact with a stop ring 40 fixed to the steering rod.

Therefore, when the sliding piston 39 moves toward the sealing member 33, the sleeve 45 and the retainer 42 slide together with the sliding piston 39. At this time, retainer 4
3 is in contact with the cylindrical member 41 of the sealing member and cannot be moved, so the return spring 44 is compressed. Furthermore, when the sliding piston 39 moves toward the sealing member 34, the retainer 43 slides together with the stop ring 40 and the steering piston 39. At this time, retainer 4
2 is in contact with a stepped portion 46 formed on the body and cannot be moved, so the return spring 44 is compressed. Note that the position of the stepped portion 46 is determined so that the rear wheel is in the straight-ahead position at the position where the retainer 42 and the stepped portion 46 abut. Further, the position of the cylindrical member 41 is the same as that of the retainer 43.
The rear wheels are set in a straight-ahead position at the position where the cylindrical member 41 and the cylindrical member 41 come into contact with each other.

The hydraulic locking means 50 comprises a pair of sliding pistons 51, 52 and three chambers 53, 54, 55 delimited by the sliding pistons 51, 52. sliding piston 51
．． 52 is slidably inserted into the outer periphery of the steering rod 35. The sliding piston 51.52 can slide between snap rings 56.57 fixed to the steering rod. Furthermore, the sliding piston 51 , 52 has a larger cross-sectional area than the sliding piston 39 . The chambers 53 , 55 are connected to the drain tank 5 , and the chamber 54 is connected to the outlet of the hydraulic lock-activated valve 3 .

When an abnormality occurs in the system or the vehicle speed increases above a predetermined value, the hydraulic lock activation valve 3 is activated. Then, the hydraulic lock operation valve 3 opens, hydraulic oil flows into the chamber 54, and the chamber 54 expands. As a result, the sliding pistons 51, 52 move to a position where they come into contact with snap rings 56, 57 fixed to the steering rod. When the steering rod moves to the left in the figure in this state, the sliding piston 51 moves to the left in the figure together with the steering rod while being in contact with the snap ring 56. However, the sliding piston 5
1 has a larger cross-sectional area than the sliding piston 39, so when the sliding piston 51 comes into contact with the sealing member 34, the steering rod 3
5 stops moving. As a result, the range of movement of the steering rod is limited until the sliding piston 51 comes into contact with the sealing member 34. When the steering rod moves to the right in the figure, the movement of the steering rod is similarly limited. At this time, the hydraulic oil in the chambers 53 and 55 is drained through the discharge ports 58 and 59.

Next, the action will be explained.

When the steering wheel 81 is turned, the directions of the front right wheel FR and the front left wheel FL change. steering wheel 8
The rotation angle of 1 is detected by the front wheel steering angle sensor STI and input to the electronic control unit ECU. For example, when the solenoid 17 of the directional control valve 11L is activated by a signal from the electronic control unit ECU, the valve member 15 is sucked to the left, and the supply port 13L and the outlet port 14 of the directional control valve are
It communicates with L. As a result, the left oil chamber 2 of the spool valve
Hydraulic oil is supplied to 2L, and the spool 21 moves to the right. The supply port 26 and the delivery port 28 of the spool valve communicate with each other, hydraulic oil flows into the oil chamber 47 of the power cylinder, the steering rod moves to the right, and the rear wheels are steered. This movement of the steering rod is detected by the rear wheel steering angle sensor, and the electronic control unit EC detects the movement of the steering rod.
It is input to U. Note that in this state, the hydraulic lock operation valve 3 is in an inactive state, so no hydraulic oil is supplied to the chamber 55. Therefore, the hydraulic lock mechanism 50 does not operate, and the steering rod 35 can steer the rear wheels at a large steering angle. In addition, the directional control valve 11R
When the solenoid is activated, the steering wheel head moves to the left in the same manner as above, and the rear wheels are steered.

Further, if an abnormality occurs in the system during steering at a large steering angle, or if the vehicle speed exceeds a predetermined value, the hydraulic long lock operation valve 3 is activated and hydraulic oil is supplied to the chamber 55 of the hydraulic lock mechanism. As a result, the sliding pistons 51, 52 move toward the steering rod 35.
The chamber expands by moving until it comes into contact with the snap rings 56, 57.

Since the cross-sectional area of the sliding pistons 51, 52 is larger than the cross-sectional area of the sliding piston 39, the steering rod is forced back to an approximately neutral state. In this state, the steering rod 35 can only move within the range regulated by the sliding piston 51, the sealing member 34, and the sliding piston 52 and the partition wall 36. Therefore, when an abnormality occurs in the system, the steering rod returns to a substantially neutral position, and furthermore, the steering angle of the rear wheels is regulated, thereby improving driving stability.

Furthermore, if the solenoid of the direction switching valve fails during steering at a large steering angle, the hydraulic oil in the oil chamber of the direction switching spool valve 12 is drained, and the spool valve returns to the neutral state. Along with this, the steering rod 35 attempts to return to neutral due to the action of the return spring 44. However, since the direction switching spool valve 12 is of an overlap type, the hydraulic oil of the power cylinder is drained through a small oil passage between the land portion and the shoulder portion of the valve 12. For this reason,
The hydraulic oil in the power cylinder is not drained all at once, and the steering rod gradually returns to the neutral state. Therefore, even if the directional control valve fails during steering at a large steering angle, the steering stability will not be impaired.

〔Effect of the invention〕

According to the present invention, even if the directional control valve fails during steering at a large steering angle and the directional control spool valve returns to the neutral position, the hydraulic fluid in the power cylinder is transferred to the overlapping direction control spool valve. Since the water is gradually drained from the tank, the rear wheels return to the neutral position slowly, and steering stability is not compromised in the event of a failure. Moreover, since rapid pressure fluctuations in the oil passage can be reduced, safety is also improved.

Furthermore, since the directional switching valve and the directional switching spool valve are configured separately, the operating current can be reduced compared to conventional solenoid direct-acting spool valves. Furthermore, since the spool valve for direction switching can be made smaller, the arrangement of parts becomes easier.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a rear wheel steering system according to an embodiment of the present invention, FIG. 2 is a diagram showing the overall configuration of a hydraulic system, and FIG. 3 is a schematic diagram of a conventional rear wheel steering system. Description of main parts of the diagram 1 - Tandem hydraulic pump 2 - Bypass valve 3 - Hydraulic lock operation valve 10 - Hydraulic control unit 11L, IIR - Direction switching valve 12 - One-way switching spool valve 13L, 13R - Supply ports 14L, 14R - Outlet port 15 - Valve member 16 - Spring 17 - Solenoid 18 - Oil passage 20 - Valve housing 21 - Spools 22L, 22R - Oil chambers 23L, 23R - Spool return springs 24 - Land Part 25 - Shoulder part 26, 27 - Supply port 28. 29 - Delivery port 30 - Discharge port
31-Power cylinder 32-・Body
33.34 - Sealing member 35 - Steering rod 36
- Partition wall 37 - Stepped part 38 - 0 ring 40 - Stop ring 56, 57 - Snap ring 39.5L52 - Sliding piston 41 - Cylindrical member 42, 43 - Retainer 44 - Return spring 45 - Three 7 46-Stepped part 50-Hydraulic lock mechanism 53.54.55--Chamber 80-Front wheel steering mechanism 81-Steering wheel 82-Engine 83-Transmission 84-Output shaft SPI, 5P2-Vehicle speed sensor S T 1 -m-Front wheel steering angle sensor S T 2-Rear wheel steering angle sensor patent

Claims (1)

[Claims] The rear wheel steering system includes a vehicle speed sensor that detects the speed of the vehicle, a steering angle sensor that detects the steering angle of the front wheels, and calculates an appropriate rear wheel steering angle according to the steering angle detected by the steering angle sensor. a hydraulic control unit that controls the steering angle of the rear wheels based on the calculation results of the electronic control device; and a rear wheel drive that changes the steering angle of the rear wheels using the hydraulic pressure controlled by the hydraulic control unit. The hydraulic control unit has a directional switching valve that switches directions in response to a signal from the electronic control device, and an overlap type directional switching valve that opens and closes an oil passage using hydraulic oil supplied from the directional switching valve. A rear wheel steering device characterized by comprising a spool valve.