JPH0117002B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to
Drooping), that is, a flow control valve that has the characteristic of reducing the flow rate supplied to hydraulic equipment below a certain amount when the pump discharge increases above a certain amount.

[Conventional technology]

Flow control valves with such drooping characteristics are generally used in vehicle power steering systems, as proposed in, for example, Japanese Patent Publication No. 45-7125, Japanese Patent Publication No. 50-40246, etc. Conventional devices that are useful for providing vehicle stability and appropriate steering feel during high-speed driving generally control the recirculation flow from the pump discharge passage to the circulation passage, and throttle the supply passage to the power steering device. Since the amount is controlled by a single spool valve, the amount of throttling in the supply flow path changes due to pressure fluctuations caused by the operation of the power steering device.
There has been a phenomenon in which the supply flow rate increases during steering, that is, when the pressure increases, depending on the degree of the increase. In addition to the above type, a valve device has also been proposed in which an adjustment rod is installed to change the amount of restriction in the supply flow path leading to the power steering device. processing,
It is difficult to maintain high precision in concentric machining of the adjusting rod and the orifice, and there are other problems, such as the flow rate changing due to pressure fluctuations, similar to the above-mentioned type.

Changes in flow rate due to pressure fluctuations will be explained with respect to the conventional device (Japanese Patent Publication No. 7125/1983) shown in FIGS. 6 to 10.

As shown in FIG. 6, in this flow control valve, an oil flow discharged from a pump (not shown) is introduced into a valve device 32c from an inlet opening 30c. A spool valve having large diameter portions 37c, 38c and a small diameter portion 39c is fitted into the valve device 32c and is urged rightward in the figure by a spring 34c. An adjustment rod 72 is integrally attached to the valve, and the downstream pressure of the primary flow orifice 42c is introduced to the left side of the valve via a pressure sensitive orifice 48c. Further, a side passage opening (overflow boat) 47c is provided in the valve hole 31c of the above-mentioned valve, so that a part of the oil flow from the pump can be returned to the tank as the valve moves to the left.

Therefore, the discharge flow from the pump is directed to the inlet opening 3.
0c, passes through the primary flow orifice 42c, and flows from the high pressure section 23 to the power steering system (hereinafter referred to as PS).
However, as the pump rotational speed increases and the amount of oil discharged increases, the flow rate passing through the primary flow orifice 42c also increases, and the pressure difference across the orifice increases. As mentioned above, the pressure upstream of the orifice is applied to the right side of the valve, that is, the working surface 40c, while the pressure downstream of the orifice is applied to the left side of the valve via the pressure sensitive orifice 48c, so that the primary flow orifice 42c
When the differential pressure between the front and rear reaches a predetermined value, the valve moves to the left against the bias of the spring 34c, and the large diameter portion 3 of the valve
8c opens the side passage opening 47c, a part of the pump discharge flow rate is returned to the tank, and the flow rate sent to the P.S. is kept constant. This state corresponds to the maximum flow rate shown in FIG. When the pump rotational speed further increases, the valve continues to move to the left, and at the same time, the adjustment rod 72 integrated with the valve also moves to the left, until the large diameter part of the adjustment rod 72 reaches the primary flow orifice 4.
This results in blocking a part of the opening area of the primary flow orifice 42c, increasing the differential pressure before and after the primary flow orifice 42c, and increasing the amount of leftward movement of the valve. Therefore, the side passage opening 4
The opening area of 7c increases, and as a result, the amount of supply to PS decreases. This state corresponds to the energy saving revolutions per minute range in FIG.

In conventional flow control valves that operate in this manner, the valve operates as shown in FIGS. 8, 9, and 10 when the pressure on the load side fluctuates, that is, during PS operation.

That is, FIG. 8 shows the state of the engine rotational speed N when the conventional control valve is not steered.

At this time, the pump driven by the engine has a flow rate of
An oil flow of Qp is discharged, a part of the flow rate Q1 is fed to the PS, and the remaining flow rate QR is returned to the tank from the side channel opening 47c. Here, the most important factor that determines the position of the valve is the opening degree of the side passage opening 47c, and the pressure on the upstream side of the primary flow orifice.
Between P1 and tank side pressure P0, which is approximately atmospheric pressure,
The valve is held at a position that ensures an opening that generates the flow rate QR.

Next, when the vehicle is steered at the above-mentioned rotational speed, that is, when the pressure increases, the valve is in the state shown in FIG. 9. When the pressure on the PS side, that is, the pressure P2 behind the primary flow orifice increases to P′2,
Naturally, the pressure P1 in front of the orifice also rises to P′1, so the pressure difference (P1 − P0) at the side passage opening increases to (P′1 − P0), and if the opening area is the same, the pressure difference at the side passage opening The flow rate QR increases to QR′. For this reason, the flow rate to PS, that is, the flow rate at the primary flow orifice, decreases, and the differential pressure (P1 - P2) at this orifice decreases, so the valve returns to the right due to the biasing force of the spring, resulting in the state shown in Figure 9. becomes stable.
In this state, the adjustment rod integrated with the valve moves to the right together with the valve, resulting in an increase in the flow path area of the first flow orifice and an increase in the flow rate supplied to the PS.

[Problem to be solved by the invention]

As described above, in the conventional flow control valve, a phenomenon has been observed in which the flow rate fed to the PS increases as the load increases in the high rotation range. When installed in a vehicle, this results in a characteristic that the more you turn the steering wheel, the more the flow increases and the steering force becomes lighter, even at the same engine speed and, in other words, the same vehicle speed. In some cases, if you turn the steering wheel too quickly, it will start out heavy and suddenly become lighter, causing problems such as the steering wheel getting stuck at first and then suddenly coming off, and sometimes even causing the danger of turning the steering wheel too much. It was hot. Thus, conventional flow control valves have the disadvantage of losing their drooping characteristics when the valve pressure increases. This also applies to the other conventional example (Japanese Patent Publication No. 50-40246) mentioned above. Therefore, an object of the present invention is to obtain a flow control valve in which pressure fluctuations on the hydraulic equipment side hardly affect the supply flow rate.

[Means to solve the problem]

In the present invention, the pump discharge passage is branched into a supply passage that communicates with the hydraulic equipment and a circulation passage that directly communicates with the oil tank, and the circulation passage has a variable orifice that is formed in the supply passage. In the flow control valve, the flow control valve is provided with a control valve that opens in accordance with the flow of the fluid discharged from the pump to recirculate a part of the fluid discharged from the pump. The variable orifice valve is configured as a variable orifice valve that receives a pressure difference between the front and rear and reduces its opening area as the pressure difference increases, and the variable orifice bubble is provided with a stopper means for regulating the minimum value of the opening area. This is characterized in that a drooping characteristic of the flow rate that does not change due to changes in load can be obtained.

[Effect]

According to the present invention, the PS
is activated and the pressure in the supply flow path increases, the flow rate in the fixed orifice part of the pump discharge passage does not change, so the control position of the variable orifice valve that receives the differential pressure before and after the fixed orifice Without any fluctuation, the variable orifice valve is regulated to a minimum control flow rate by its stopper means.

〔Example〕

The present invention will be described below with reference to the illustrated embodiments.
In Fig. 1, 1 is a pump discharge passage, 2 and 3 are a circulation passage and a supply passage branched from this passage 1, respectively.The circulation passage 2 is directly connected to an oil tank (not shown), and the supply passage 3 is connected through a PS. It communicates with the oil tank. 4 is a control valve that changes the communication area between the pump discharge passage 1 and the circulation passage 2, that is, a spool valve; 5 is a variable orifice valve provided in the supply passage 3; It is configured to receive a differential pressure before and after the variable orifice valve 5, that is, between the supply passages 3 and 3', and when the flow rate flowing through the supply passage 3 reaches a constant value, the pressure difference causes the force of the return spring 4a. When the spool valve 4 overcomes this, the spool valve 4 moves to the right in the figure, and its land 4b unblocks the discharge passage 1 and the circulation passage 2 and begins to communicate the circulation passages.

As is clear from FIG. 2, the variable orifice valve 5 has a spool 5b having a land 5a slidably fitted into a valve hole 7 formed to intersect with the supply channels 3 and 3'. The amount of throttling of the flow path, that is, the opening area of the variable orifice is determined by the position of the land 5a with respect to the flow path 3, and the return spring 5c attaches the spool 5b in the direction that increases this opening area. It is strong. Reference numerals 5d and 5e indicate first and second flow rate determining pins protruding from both ends of the spool 5b, which regulate the sliding ends of the spool 5b in both directions to determine the maximum and minimum opening areas. The valve hole 7 into which this spool 5b is fitted
The chamber 8 communicates with the upstream side of an orifice 9 formed in the pump discharge passage 1 via a passage 10, and the pressure difference between this chamber 8 and the supply flow passage 3, that is, the pressure difference before and after the orifice 9, The spool 5b is moved to the left against the force of the spring 5c to reduce the opening area of the supply channel 3' by the land 5a.

According to the present flow rate control valve having the above configuration, the flow rate (control flow rate) flowing through the supply channels 3, 3' can have characteristics as shown in FIG. 3, for example. That is, in the low speed rotation range (low flow range) of the pump driven by the vehicle engine, the spool valve 4 comes into contact with the stopper 11 by the force of the return spring 4a, and the land 4b connects the discharge passage 1 and the circulation passage 2. On the other hand, the return spring 5c of the variable orifice valve 5 brings the first flow rate determining pin 5d into contact with the end wall of the valve hole 7 to maintain the maximum opening area (throttling area). Therefore, all of the pump discharge flow rate flows into the supply channels 3, 3', and the pump discharge flow rate and the control flow rate are proportional as shown in region a of FIG.

Next, when this controlled flow rate reaches a certain value, the spool valve 4 begins to move to the right in FIG. , the surplus flow is sent to the circulation path 2. Therefore, the controlled flow rate as shown in region b in FIG. 3 becomes a substantially constant value. Note that at this time, the spool 5b of the variable orifice valve 5 does not move.

When the pump discharge flow rate increases further, the differential pressure before and after the orifice 9 overcomes the force of the return spring 5c pressing the spool 5b of the variable orifice valve 5, causing the spool 5b to move to the left in FIG. The flow path 3' begins to be further narrowed down. For this reason, the controlled flow rate flowing through the supply channel 3 decreases, and the differential pressure before and after the variable orifice valve 5 increases, and the opening degree of the spool valve 4 increases.
The amount of reflux becomes large. The differential pressure before and after the orifice 9 increases as the pump discharge flow rate increases.
As shown in region c of FIG. 3, as the pump discharge flow rate increases, the spool 5b further narrows the flow path and reduces the control flow rate.

When the spool 5b is moved by the above operation and the second flow rate determination piston amount 5e comes into contact with the bolt plug 12, the opening area of the variable orifice valve 5 is maintained at the minimum constant value, and therefore the control The flow rate becomes approximately constant (region d in Figure 3). In addition, the third
The graph indicated by a broken line in the figure is the actual pump discharge flow rate, and the flow rate corresponding to the difference between this and the control flow rate is recycled from the spool valve 4 to the circulation path 2 in each of the above regions.

With the above flow control valve, P is controlled by steering operation.
Even if S is activated and the pressure in the supply passages 3, 3' increases, the flow rate at the orifice 9 portion of the discharge passage 1 does not change, so the variable orifice valve 5
The spool 5b never changes its position. The flow rate flowing through the orifice 9 does not change depending on the load of the PS and is controlled only by the pump rotation speed. Therefore, in theory, there is no possibility that the controlled flow rate will change due to pressure fluctuations in the supply channel 3. , you can get stable output of PS.

Note that the flow rate characteristics shown in FIG. 3 are merely representative flow rate characteristics that are schematically illustrated, and various changes are possible. For example, the first flow rate in the same figure
Q1 can be changed by changing the initial throttle amount by changing the length of the first flow rate determining pin 5d of the variable orifice valve 5, and similarly, the second flow rate Q2 can be changed by changing the length of the second flow rate determining pin 5e. This can be changed by changing the final minimum aperture amount. Furthermore, by changing the spring constant of the return spring 5c of the variable orifice valve 5, the slope of the drooping characteristic can be changed as shown in FIG. Figure 5 s, t, u
It is obvious that the position of the inflection point can be changed as in

〔Effect of the invention〕

As described above, the flow rate control valve according to the present invention can obtain desired flow rate drooping characteristics that do not change in flow rate even when the load fluctuates by using a variable orifice valve that is easy to manufacture and an orifice that controls the valve. The fact that the flow rate does not change even with pressure fluctuations can be said to be a unique effect of the present invention.

In addition, in the present invention, since the fixed orifice is provided in the pump discharge passage, for example, when this is provided on the circulation passage side, the fixed orifice must be installed after the spool valve that controls the opening degree of the circulation passage has opened. No differential pressure can be applied to the variable orifice valve, and a region where the controlled flow rate is approximately constant, such as the region b in FIG. 3, is necessarily required, and there is no risk of losing the degree of freedom in characteristics. That is, in the present invention, the fixed orifice in the pump discharge passage allows a differential pressure to be generated across the orifice even immediately after the pump discharges, so that the pressure can be increased immediately from the point where the pump rotation speed is low without going through the area b in Fig. 3. It is possible to freely select a flow rate characteristic that allows the control flow rate to be reduced, and therefore the control flow rate can be increased only at extremely low speeds to lighten the steering, and it is possible to secure sufficient steering force while driving, which is an energy-saving feature. This has the effect of improving steering safety and steering feel, and providing steering characteristics with high steering reliability.

Furthermore, in the present invention, since the variable orifice valve is provided with a stopper means for regulating the minimum value of its opening area, there is no fear that the opening degree of the variable orifice valve will approach zero as much as possible. It has the advantage of being adjustable to select the appropriate minimum control flow rate at high speeds.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part showing an embodiment of a flow control valve according to the present invention, FIG. 2 is an enlarged view of a portion of FIG. 1, and FIGS. 3, 4, and 5 are respectively Graphs schematically showing flow characteristics obtained by the invention, FIGS. 6 and 7 are cross-sectional views showing conventional flow control valves and their characteristic diagrams, FIGS. 8, 9, and 10. 6 is an explanatory diagram and its characteristic diagram for explaining the operating mode of the conventional example shown in FIG. 6. FIG. 1... Pump discharge passage, 2... Circulation passage, 3... Supply passage, 4... Spool valve, 5... Variable orifice valve, 9... Orifice.

Claims (1)

[Claims] 1 The pump discharge passage is branched into a supply passage that communicates with the hydraulic equipment and a circulation passage that communicates directly with the oil tank, and the circulation passage is provided with a variable orifice formed in the supply passage that is opened according to the pressure difference before and after it. In the flow control valve equipped with a control valve that recirculates a part of the fluid discharged from the pump, a fixed orifice is provided in the pump discharge passage, and a variable orifice in the supply passage is controlled to control the differential pressure before and after the fixed orifice. In response to this, the valve is configured as a variable orifice valve that reduces the opening area as the differential pressure increases.
A flow control valve characterized in that the variable orifice valve is provided with a stopper means for regulating the minimum value of the opening area.