JPH0335539B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to controlling the flow rate of pressurized fluid discharged from a pump to a power steering device via an orifice, and surplus flow being returned to the suction side through a bypass passage. The present invention relates to a control device, and particularly to a flow rate control device for a power steering device that reduces the flow rate sent to the power steering device as the pump rotation speed increases.

<Prior art> Conventionally, as a flow control device having the above functions,
A pressure difference is generated before and after the control throttle based on the increase in the discharge flow rate due to an increase in the number of pumps, and this pressure difference displaces the control spool to variably control the opening area of the orifice, as shown in Fig. 1A. As shown, there is a system in which the discharge flow rate Q is lowered when the pump rotation speed N reaches a constant rotation speed.

However, according to such a conventional device, the pressure difference across the control throttle increases due to the increase in the viscosity of the pressure fluid at low temperatures, and as a result, the control spool displaces and closes the orifice.
As shown in Figure 2, there was a problem in that the required flow characteristics could not be obtained.

<Purpose of the Invention> The present invention has been made to solve the above-mentioned conventional problems, and its purpose is to prevent the flow rate characteristics of the pressure fluid from changing regardless of changes in the viscosity of the pressure fluid at low temperatures. It is to do so.

<Structure of the Invention> The present invention has been made to achieve the above object, and includes an orifice provided in the middle of a supply passage for sending pressure fluid from a pump to a power steering device, and a portion of the pressure fluid. A flow rate control spool valve that adjusts the opening degree of the bypass passage in order to return surplus flow to the suction side of the pump, and a union provided in the inner periphery of the storage hole housing the flow rate control spool valve and the supply passage. a control spool formed between the inner end and the outer periphery; and a control spool that is displaced in response to a pressure difference before and after the control throttle and controls the opening degree of the orifice in a direction that closes when the stress difference becomes large; The inner end outer circumferential side of the union of the control orifice is made of a shape memory alloy that stores a shape in which the aperture of the control aperture is large when the temperature is low and the aperture is small at room temperature. The present invention relates to a flow control device for a power steering device.

<Examples> Examples of the present invention will be described below based on the drawings. In Fig. 2, 10 is a pump housing;
This pump housing 10 is provided with a storage hole 11 passing through it, a union 21 is screwed into one end of the storage hole 11 in a fluid-tight manner, and a stopper 25 is attached to the other end of the storage hole 11. are fitted in a liquid-tight manner.

The spool valve 22 is connected to the union 2 in the storage hole 11.
The first valve chamber 32 and the second valve chamber 33 are slidably inserted between the first valve chamber 32 and the second valve chamber 33 in the storage hole 11.
is formed. Further, the spool valve 22 is biased by a spring 26 interposed in the second valve chamber 33 and elastically abuts on a control spool 23 (described later), so that the spool valve 22 is connected to the supply passage 12 and the bypass passage 13 provided in the pump housing 10. communication is cut off. Note that the bypass passage 13 communicates with the suction chamber of the fluid pump.

The control spool 23 is slidably inserted into the inner hole of the union 21, and the control spool 23 is slidably inserted into the inner hole of the union 21. energized,
It resiliently abuts against the inner end step 21b of the inner hole of the union 21. This control spool 23 has a communication hole 23a that communicates the second valve chamber 32 with the control spool 23 and the empty space 34 between the control spools 23.
are formed, and this communication hole 23a is connected to each orifice 24a,
The first valve chamber 32 and the outlet 21a of the union 21 are communicated through 24b. Further, a union 21 is provided on the end surface of the stepped portion 23b of the control spool 23.
A pressure introduction hole 21c provided in is open. This pressure introduction hole 21c communicates with the supply passage 12, and causes the control spool 23 to slide against the spring 27 when the supply pressure exceeds a predetermined pressure.

The orifice forming member 24 is provided with a control nozzle 24c as well as orifices 24a and 24b, which will be described later. ，
The second valve chamber 33 is communicated through the valve 14. As a result, a part of the fluid on the downstream side of each orifice 24a, 24b is guided into the second valve chamber 33, pressures before and after each orifice 24a, 24b act on both ends of the spool valve 22, and each orifice 24a, 24b
The spool valve 22 moves in the axial direction according to the differential pressure before and after the pressure difference, and adjusts the opening degree of the bypass passage 13 in order to keep the differential pressure constant.

Thus, the orifice forming member 24 has a first orifice 24a formed approximately at its center, and a second orifice 24b consisting of a plurality of small hole groups formed at the outer periphery of the first orifice 24a. ing. These first and second orifices 24
a, 24b are usually the first valve chamber 32 and the outlet port 2.
1a, and the movement of the control spool 23 closes the first orifice 24a and controls its opening degree.

The union 21 has a substantially cylindrical shape, and its inner end is loosely fitted into the storage hole 11, and a restriction sleeve 35 is fixed to the outer periphery of the inner end. The control sleeve 35 forms a control throttle 31 between the inner periphery of the storage hole 11, and communicates the supply passage 12 with the first valve chamber 32 via the control throttle 31. When the discharge flow rate of the working fluid supplied to the supply passage 12 increases, this control throttle 31 is formed between the upstream side and the downstream side, that is, the space 34 communicating with the supply passage 12 and the first valve chamber 32 due to the flow passage resistance. A pressure difference is generated, and the control spool 23 is axially displaced in response to this pressure difference. Further, the control sleeve 35 constituting the control aperture 31 is made of a shape memory alloy. This shape memory alloy memorizes each shape according to the temperature of the pressure fluid passing through the control aperture 31. For example, when the temperature of the pressure fluid is room temperature, as shown in the virtual image in FIG. The opening degree of the control diaphragm 31 is decreased when approaching the inner periphery, and when the temperature is low, the opening degree of the control diaphragm 31 is increased when it is spaced apart from the inner periphery of the storage hole 11, as shown by the solid line in FIG. It's becoming like that.

The outlet 21a of the union 21 is connected to a normally open servo valve device of the power steering device, and the supply passage 12 is communicated with a discharge chamber of the fluid pump.

In the flow control device configured in this way,
When the fluid pump is driven by the vehicle engine,
The working fluid is supplied from the discharge chamber of the fluid pump to the supply passage 12
supplied to The supplied working fluid is supplied to the first valve chamber 32 through the control throttle 31, and from the first valve chamber 32 to the communication hole 23a and each orifice 24.
It is fed from the outlet 21a of the union 21 to the power steering device via the channels a and 24b.

When the rotational speed of the fluid pump is low, the discharge flow rate of the working fluid is small, so the spool valve 22 closes the bypass passage 13 and directs the entire amount of working fluid to the power steering device through the orifices 24a and 24b. However, when the discharge flow rate of the working fluid increases as the rotational speed of the fluid pump increases, the spool valve 22 slides to keep the differential pressure across the orifices 24a, 24b constant and opens the bypass passage 13. , the excess flow of working fluid is returned through the bypass passage 13 to the suction chamber of the fluid pump. As a result,
The working fluid supplied to the power steering system is maintained at a predetermined amount Q1 shown in FIG. 1 determined by each orifice 24a, 24b.

Furthermore, when the rotational speed of the fluid pump further increases as the vehicle starts to run at high speed, and the discharge flow rate of the working fluid supplied to the supply passage 12 increases, fluid resistance in the control throttle 31 causes the flow rate in the supply passage 12 to increase. The fluid pressure increases and the supply passage 12 and the first valve chamber 3
A differential pressure is generated between the two, and the pressure in the supply passage 12 is transferred to the control spool 23 through the pressure introduction hole 21c.
acts as a pressing force that causes the spring 27 to slide against the spring 27. Therefore, the pressure in the supply passage 12 is increased by the spring 27 in response to an increase in the discharge flow rate of the working fluid.
When the force increases until it overcomes the biasing force of , the control spool 2
3 gradually slides against the spring 27, and finally the first orifice 24a is completely closed.
The supply flow rate of the working fluid supplied to the power steering device is the flow rate Q2 determined by the second orifice 24b.
will be maintained.

By operating the control spool 23 in this manner,
When the vehicle is running at low speeds, the flow rate supplied to the power steering system is increased to ease steering operation, and as the vehicle moves to high speeds, the flow rate supplied to the power steering system is gradually reduced. , it is possible to gradually make steering operation heavier and provide high-speed stability without causing any discomfort to the driver.

By the way, when the pressure fluid is at room temperature, normal flow characteristics can be obtained as described above, but when the temperature of the pressure fluid is low, such as at the start of operation, the viscosity of the fluid is high, so the control throttle 31 is restricted. As the resistance increases, a pressure difference is generated before and after the control throttle 31, and as a result, the control spool 23 slides and the orifice 24
a is closed, making it impossible to secure the necessary flow rate as shown in FIG. 1B.

However, in the present invention, since the control sleeve 35 constituting the control throttle 31 is formed of a shape memory alloy, the control sleeve 35, which has the shape shown in the imaginary line when the pressure fluid is at room temperature, as shown in FIG. 35 changes to the shape shown by the solid line, and as a result, the opening degree of the control orifice 31 becomes larger, so that the increase in the throttling resistance of the control orifice 31 is suppressed regardless of the increase in the viscous resistance of the pressure fluid. This eliminates the movement of the control spool 23 and the resulting drop in flow rate, making it possible to accurately control the required flow rate.

<Effects of the Invention> As described above, the flow rate control device for a power steering device of the present invention has an orifice provided in the middle of a supply passage for sending pressure fluid from a pump to a power steering device, and a flow rate control device for a power steering device of the present invention. A flow rate control spool valve that adjusts the opening degree of the bypass passage so that a portion of the flow is returned to the suction side of the pump as a surplus flow, and a flow rate control spool valve that is provided on the inner periphery of the storage hole housing the flow rate control spool valve and in the supply passage. a control spool that is displaced in response to a pressure difference before and after the control spool and controls the opening of the orifice in a direction that closes when the stress difference becomes large; The inner end outer circumferential side of the union of the control orifice is made of a shape memory alloy that stores a shape in which the aperture opening of the control aperture is large at low temperatures and small at room temperature. Therefore, the advantage is that changes in flow characteristics due to changes in the viscosity of the pressurized fluid at low temperatures can be effectively prevented with a simple structure in which the outer periphery of the inner end of the union is made of shape memory alloy. has.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIG. 1 is a graph showing flow rate characteristics with respect to pump rotation speed, FIG. 2 is a sectional view showing the flow rate control device of the present invention, and FIG.
The figure is a partially enlarged sectional view showing the main parts of the flow control device. 12... Supply passage, 13... Bypass passage, 2
2... Spool valve, 23... Control spool, 24
a, 24b...orifice, 31...control aperture.

Claims (1)

[Claims] 1. An orifice provided in the middle of a supply passage that sends pressurized fluid from the pump to the power steering device;
A flow rate control spool valve that adjusts the opening degree of the bypass passage in order to return a portion of the pressure fluid to the suction side of the pump as a surplus flow, an inner periphery of the storage hole housing the flow rate control spool valve, and the supply passage. A control orifice formed between the inner end outer periphery of a union provided therein and a control orifice that is displaced according to the pressure difference before and after the control orifice, and when the stress difference becomes large, controls the opening of the orifice in the direction of closing. and a control spool for controlling the inner end outer peripheral side of the union of the control orifice using a shape memory alloy that memorizes a shape in which the aperture opening of the control aperture is large at low temperatures and small at room temperature. A flow control device for a power steering device, characterized in that: