JPH0241469B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a flow rate drooping characteristic.
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, is easy to manufacture and operates reliably, especially on the hydraulic equipment side. This paper proposes a flow control valve in which pressure fluctuations have little effect on the supply flow rate.

Flow control valves with such drooping characteristics are generally used in vehicle power steering systems, as proposed in, for example, Japanese Patent Publications No. 7125-1982 and Japanese Patent Publication No. 40246-1971, 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 port) 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 PS 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 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 42.
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 47
The opening area of c 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, when PS is activated.

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 Qp
A part of the flow rate Q ₁ is fed to the PS, and the remaining flow rate Q _R is returned to the tank from the side channel opening 47c. Here, the most important factor determining the position of the valve is the opening degree of the side passage opening 47c, and the pressure _P1 on the upstream side of the primary flow orifice,
The valve is held at a position that ensures an opening that generates a flow rate Q _R while the tank side pressure P ₀ is approximately atmospheric pressure.

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 behind the primary flow orifice P ₂ increases to P′ ₂ ,
Naturally, the pressure P ₁ in front of the orifice also rises to P′ ₁ , so the pressure difference (P ₁ − P ₀ ) at the side channel opening is (P′ ₁
-P ₀ ), and if the opening area is the same, the flow rate Q _R to the bypass opening increases to Q′ _R. For this reason,
The flow rate to the PS, that is, the flow rate at the primary flow orifice, decreases, and the differential pressure at this orifice (P ₁ -
Since P ₂ ) decreases, the valve returns to the right due to the biasing force of the spring and becomes stable in the state shown in FIG. 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.

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. This means that when installed in a vehicle, the engine speed is the same,
In other words, even at the same vehicle speed, the more you turn the steering wheel, the more the flow increases and the steering force becomes lighter.Especially when you are trying to avoid an obstacle on the road, if you turn the steering wheel rapidly, As the weight suddenly became lighter, problems occurred where the steering wheel would get stuck at first and then suddenly come off, and sometimes there was even a danger of turning the steering wheel too much. 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 mentioned above (Japanese Patent Publication No. 40246/1983).

The present invention has been made in view of the above points, and
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 a variable orifice formed in the supply passage is installed in the circulation passage to open a valve in accordance with the pressure difference before and after it. A control valve is provided to recirculate a part of the fluid discharged from the pump, and this control valve is configured as a pressure control valve in which the pressure is regulated by a pilot valve during relief, and the oil flow is controlled by a main valve. In this flow control valve, a fixed orifice is provided in the pump discharge passage, and a variable orifice in the supply passage is used to constantly receive the differential pressure before and after the fixed orifice, regardless of load fluctuations on the hydraulic equipment side, to control the magnitude of this differential pressure. The variable orifice valve is constructed as a variable orifice valve that has an opening area as small as possible. At the same time, the spool valve is biased by a return spring in the downstream side oil chamber to restrict the opening area of the flow path leading to the annular groove by the land portion separated by the annular groove of the spool valve. This is a characteristic feature.

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, and as shown in the figure, the pressure is regulated by the pilot valve, and the pressure is controlled by the main valve to release the oil flow. It is configured as a control valve. Reference numeral 5 denotes a variable orifice valve provided in the supply passage 3, and the spool valve 4 is configured to receive a differential pressure before and after the variable orifice valve 5, that is, between the supply passages 3 and 3' through a passage 6. When the flow rate flowing through the supply channel 3 reaches a certain value, the differential pressure returns to the spring 4a.
When the force is overcome, 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 moves the spool 5b in the direction that increases this opening area. It is energizing. 5d, 5e
are 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 and 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 passage 3, that is, the pressure difference before and after the orifice 9, The spool 5b is moved to the left against the force 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 flow rates 3 and 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 across the variable orifice valve 5 increases, increasing the opening degree of the spool valve 4.
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 determining pin 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 flow rate is 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
Q ₁ 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 Q ₂ 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

As described above, the flow control valve according to the present invention has a variable orifice valve that is easy to manufacture and is configured to constantly receive a differential pressure across a fixed orifice regardless of load fluctuations on the hydraulic equipment side, and an orifice that controls the variable orifice valve. It is possible to obtain a desired flow rate drooping characteristic that does not change the flow rate even when the pressure fluctuates, and this fact that the flow rate does not change even when the pressure fluctuates can be said to be a unique effect of the present invention.

The variable orifice valve of the present invention guides the oil flow before and after the fixed orifice to the oil chambers on both sides of the spool valve fitted in the valve hole intersecting the supply flow path, and also directs the oil flow before and after the fixed orifice to the downstream side of the spool valve. This variable orifice valve restricts the opening area of the flow path leading to the annular groove by the land portion separated by the annular groove of the spool valve, which is biased by a return spring in the oil chamber. The amount of restriction of the flow path is determined by the position of the land portion with respect to the flow path, and since there is no flow-obstructing member such as a return spring in this flow path portion that flows through the annular groove, the flow rate is determined based on the differential pressure before and after the fixed orifice. You can expect accurate and stable valve throttling operation.

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, the control valve provided in the circulation path is constructed as a pressure control valve in which the pressure is regulated by the pilot valve during relief, and the oil flow is controlled by the main valve. The pressure override characteristic, which corresponds to the difference between the cracking pressure at which the valve begins to open and the relief set pressure, is significantly superior to so-called direct-acting type relief valves, and its operation is accurate and responsive, and there is almost no chattering phenomenon. Benefits that would otherwise not occur are obtained.

[Brief explanation of the drawing]

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. FIG. 6 is an explanatory diagram for explaining the operating mode of the conventional example shown in FIG. 6, and its characteristic diagram. 1... Pump discharge passage, 2... Circulation passage, 3...
Supply channel, 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 addition to providing a control valve for recirculating part of the fluid discharged from the pump, this control valve is configured as a pressure control valve in which the pressure is regulated by the pilot valve and the oil flow is controlled by the main valve during relief. In the flow control valve, a fixed orifice is provided in the pump discharge passage, and the variable orifice in the supply passage is constantly receiving the differential pressure before and after the fixed orifice, regardless of load fluctuations on the hydraulic equipment side. The variable orifice valve is constructed as a variable orifice valve whose opening area becomes smaller as the opening area increases.The variable orifice valve has oil flow before and after the fixed orifice in both side oil chambers of the spool valve fitted in the valve hole intersecting the supply flow path. At the same time, this spool valve is biased by a return spring in the downstream side oil chamber so that the land portion of the spool valve separated by the annular groove regulates the opening area of the flow path leading to the annular groove. A flow control valve characterized by: