JPH0129752B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a pressure oil relief device for power steering.

Conventionally, the constant pressure control of this type of pressure oil relief device for power steering is a mechanism that maintains the relief pressure near its maximum value, so when steering the left and right ends are locked and the steering is held, for example, when the steering wheel is turned all the way from a narrow road. When it takes a long time to get out onto a wide road with heavy traffic, the hydraulic pump is driven at a pressure of up to 70 kg/ ^cm2 , which causes the temperature of the hydraulic oil to rise and the relief operation to become unstable. This method has the drawbacks of causing hunting and wasting energy.

SUMMARY OF THE INVENTION An object of the present invention is to provide a power steering relief device that overcomes the drawbacks of the conventional devices as described above.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In FIG. 1, reference numeral 1 indicates a steering wheel, 2 a control valve controlled by the steering wheel, 3 a steering gear, and 6 an actuator.

In the illustrated case, this actuator is in the form of a conventional hydraulic cylinder, in which a double-acting piston (not shown) is accommodated. Wheels 8 are connected to both ends of this piston via ball joint studs 7. A control valve 2 is connected to the actuator 6 by piping, and this control valve is connected to piping 9, 9'.
A hydraulic pump 5 is connected by. This hydraulic pump is driven by a driver 4. This driving body is an engine, an electric motor, or the like. When the steering wheel is turned, pressure oil from the hydraulic pump is supplied to the actuator 6 via the pipes 9, 9' and the control valve 2, thereby providing power steering.

Relief means 10 are provided in the pipes 9, 9',
In the illustrated embodiment, this relief means comprises a relief valve. The detailed structure of this relief valve is shown in FIG. This relief valve is provided in a hydraulic passage between the hydraulic pump 5 and the actuator 6. This relief valve has a housing 19 which is provided with a line port 11 connected to the pipe 9 and a tank port 16 provided on the opposite side and connected to the pipe 9'. The housing also has a first relief section 20 formed adjacent to the line port 11 and a second relief section 21 formed contiguous with the first relief section. The second relief portion 21 has a larger diameter than the first relief portion 20. A first orifice 15 is formed in the first relief part 20 at the boundary with the line port 11, and a second orifice 13 is formed in the second relief part 21 at the boundary with the first relief part 20. It is formed. A valve body, for example a ball 14, is accommodated in the first relief part, and this ball is urged by a spring 18 via a guide 17 so as to be constantly in contact with the first orifice 15. In the state shown in FIG. 2, there is a slight gap between the guide 17 and the second orifice 13.

The operation of the above device will be explained with reference to FIGS. 3 and 4. First, a controlled constant amount of oil (9) is supplied from the hydraulic pump to the actuator as shown in FIG. Steering wheel 1 is fully turned and stationary,
Or, when the actuator is overloaded and becomes locked, the internal pressure of the pipe 9 increases due to the supply of pressure oil from the hydraulic pump 5 to the actuator, reaching point _P1 (70Kg/cm ² ) in Figure 4. . Then, the ball 14 of the relief valve moves down the first relief part against the spring 18 from the state shown in FIG. 3A to the state shown in FIG. the second orifice 13 is opened. Therefore, as shown in FIG. 4, the pressure inside the pipe 9 decreases from point P ₁ to point b ₁ until it reaches point P ₂ (30 kg/cm ² ) and is maintained in this state. In other words, the relief valve opens the first relief portion when the pressure in the hydraulic passage from the hydraulic pump 5 to the actuator 6 exceeds a first predetermined pressure, and the pressure decreases to a second predetermined pressure lower than that pressure. It is configured to hold the
This is based on the following operating principle.

That is, in the state before operation shown in FIG. 3a, the force acting on the ball 14 is determined by the discharge pressure of the hydraulic pump and the opening area of the line port 11. Since the opening area of the line port is set small, operation does not start until the pressure reaches point _P1 in Figure 4. When the pressure reaches point _P1 and the ball 14 begins to descend, the area of the pressure acting on the ball 14 becomes the opening area of the first relief portion 20 (see Figure 3b), and the ball 14 descends significantly. The pressure then decreases from P ₁ to P ₂ (see Figure 4). Thereafter, the downward force of the ball 14 determined by the pressure P ₂ and the opening area of the first relief part and the spring 1
The pressure P ₂ is kept constant so that the elastic force of 8 is balanced. The pressure of the pressure oil in this state is set to the limit allowed by the steering holding force of the steering wheel 1. In other words, the pressure decreases while the rudder is held. It should be noted that in the present invention, this pressure drop is achieved by the hysteresis characteristic of the relief means;
This allows the relief operation to be performed extremely stably. In FIG. 4, S is the relief holding area of the conventional device, and _c1 is the relief holding area of the device of the present invention. Also, a ₁ indicates a non-relief area.

According to the present invention, when the hydraulic pump that generates pressure fluid is used to operate the steering with excessive steering torque as described above, the relief operation is provided with a large hysteresis function to increase the pressure of the hydraulic pump to the limit allowed by the steering holding force. By lowering the pressure, there are practical benefits such as improving stability during relief and saving energy for the hydraulic pump power source, ie, the motor.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a steering system to which a relief device according to the present invention is applied, Fig. 2 is a sectional view of a relief valve of the present invention, Figs. The figure is a graph showing the relationship between the discharge amount of the hydraulic pump and the pressure of pressure oil from the hydraulic pump. DESCRIPTION OF SYMBOLS 1... Steering wheel, 5... Hydraulic pump, 6... Actuator, 10... Relief means.

Claims (1)

[Claims] 1 A hydraulic pump, a control valve connected to the hydraulic pump, an actuator connected to the control valve, and a relief valve provided in a hydraulic passage connecting the hydraulic pump and the actuator, the relief valve comprising: housing and
a line port formed at one end of the housing to communicate with a hydraulic passage from the hydraulic pump to the actuator; a first relief portion formed in the housing so as to communicate with the line port; and the first relief portion. a second relief part formed in the housing so as to communicate with the housing and having a larger diameter than the first relief part; a tank port formed in the housing so as to communicate with the second relief part; a valve body disposed in a relief portion; a first orifice is formed in the first relief portion at a boundary with the line port; and a first orifice is formed in the second relief portion. A second orifice is formed at the boundary of
A pressure oil relief device for power steering, characterized in that the valve body is configured to be movable between a first relief portion and a second relief portion depending on the magnitude of hydraulic pressure applied to a line port. .