JPH0138708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic power transmission system, and more particularly to a power steering system using a constant displacement pump driven by a prime mover operated at a variable speed. The present invention relates to hydraulic equipment such as the above.

[Conventional technology]

2. Description of the Related Art Hydraulic systems, which are used in automobile power steering systems and the like, and which use a constant discharge pump driven by a variable speed prime mover, are operated at a predetermined constant flow rate controlled by a flow control valve. The flow control valve also has a hydrodynamic function that bypasses a portion of the fluid to the pump inlet when the pump is operated at high speeds, replenishing the fluid sent to the load, the power steering booster. It also provides a mechanism.
However, when such hydraulic systems are operated at low speeds, the dimensions of the passageway for replenishing the flow rate with fluid returning from the booster are limited.
If the fluid has a high viscosity, especially when the controlled flow rate is high and at low temperatures, excessive vacuum may be created at the inlet and damage to the pump may occur due to cavitation. An example of such a typical system is
As shown in US Pat. No. 2,880,674 and US Pat. No. 3,207,077.

[Problem to be solved by the invention]

To further consider the problems of the prior art, hydraulic systems such as the one shown in the drawings have existed in the past that lack the passage 26 and conduit 27 according to the present invention. The problem here was how to increase the flow rate to the pump at low speeds. It would be easy to enlarge the dimensions of the passage 16 or provide a separate passage from the tank 14 to the inlet 17, but this is not possible due to the space and positional limitations of the existing pump specifications. It's impossible. That is, passage 1
6 would weaken the wall between the passageway and the high pressure chamber of the valve. Furthermore, due to the high-speed operating conditions of the flow control valve, there is a limit to the position of the opening of the passage 16 at the inlet 17 in relation to the land of the spool. That is, to assist in replenishing the pump with fluid during high speed operation, the opening of the passageway 16 is placed at a distance from the land of the spool so as to create an area of low pressure at the inlet 17 in the area where the passageway 16 opens. Ru. The low pressure area is created by the increased velocity of the high pressure fluid through the inlet 17 due to the restriction between the high pressure side of the land of the spool and the end of the inlet 17 (around the high velocity section). . It is clear that moving the opening of the passageway 16 in either direction will shift the opening from the low pressure region at the inlet 17. aisle 16
Even if another passage is provided around the area, the low pressure area for high speed operation will still be compromised. For this reason, it is unreasonable to try to cope with the low speed by enlarging the passage 16 or providing another passage.

SUMMARY OF THE INVENTION Therefore, the present invention provides a hydraulic system in which a flow control valve provides sufficient pressure fluid even at low speeds before performing bypass flow of fluid, thus increasing the range of controlled discharge volume and reducing noise caused by pump operation. To provide a device that can lower the level, reduce wear due to cavitation, reduce the tendency to create a vacuum and make effective use of the shaft seal, and increase the pressure at the inlet by regular replenishment with a flow control valve. The challenge is to do so.

[Means to solve the problem]

The present invention has been developed to provide a separate tank line and auxiliary passage in parallel to the low pressure chamber of the spool hole in order to obtain more fluid to the pump during low speed operation. I found a way. By locating the tank line parallel to the low-pressure side of the spool hole, the result is an increase in flow during high-speed operation, as will be clear from the description of the embodiments below. As will be explained later in connection with the drawings, the width of the spool land is less than the width of the opening from the spool hole to the inlet, and during high speed operation the inlet is located on both the high and low pressure sides of the spool hole. It communicates with Chiyamba.
In addition, high-pressure fluid flowing at a high velocity from the high-pressure side of the land to the inlet creates a secondary low-pressure region at the inlet adjacent to the low-pressure side of the land of the spool, and flows from the tank through the low-pressure side region. It assists the flow of fluid into the inlet, which supplements the normal flow from the tank to the inlet, thus increasing the capacity of the pump without increasing its size. Thus, in accordance with the present invention, an auxiliary passageway extending from the tank, upstream of the normal system fluid withdrawn from the tank, communicates with the inlet of the pump by an opening in the flow control valve. This passageway is isolated from the bypass flow by a flow control valve during normal low speed operation to provide supplemental flow to the inlet.

[Examples and effects]

According to the embodiment of the invention shown in the drawings, the device includes a constant displacement pump 10 driven by a prime mover, such as an automobile engine. The pump 10 is connected to a steering booster 1 via an orifice 11.
2. Supplying fluid to, for example, a linear or rotary hydraulic motor. In a typical arrangement, return fluid through line 13 flows to tank 14. Fluid from the tank typically flows via tank line 15 and passage 16 to pump inlet 17. Flow control valve 18 consists of a spool 19 with spaced apart lands 20, 21 and is disposed within bore 22 to permit bypass flow of fluid if the flow rate exceeds a predetermined value. A conduit 23 extends from the pump outlet and includes an orifice 24 to the spring end of the spool. When the flow rate exceeds a predetermined value, the land 21 moves to the position shown by the broken line, and a portion of the fluid is flowed through the return pipe 25 and flows out from between the land 21 and the end of the inlet 17. do. This creates a low pressure region around the exiting high pressure fluid stream, allowing the passageway 16 to draw in additional pressure fluid flow, thus replenishing the pump when it is running at high speed. Such an example, as mentioned above, is provided by U.S. Patent No.
No. 2880674 and No. 3207077.

According to the invention, an auxiliary passage 26 is provided and communicates with the tank 14 as schematically shown by a tank line 27. aisle 26
has the function of supplying auxiliary pressure fluid to the inlet 17 at low speed. Passage 26 is located upstream of passage 16 and is isolated from the bypass fluid when the flow control valve is in the closed position. By locating the tank line 27 in parallel with the tank line 15 on the low pressure side of the spool hole 22, the result is increased flow during high speed operation. That is, the width of the land 21 of the spool 19 is equal to the width of the hole 22.
The opening from the spool to the inlet 17 is smaller and, during high speed operation, the inlet 17 can communicate with both the high and low pressure side chambers of the spool bore 22. The high-pressure fluid flowing at a high speed from the high-pressure side of the land 21 to the inlet 17 forms a low-pressure region as described above, making it possible to suck fluid from the passage 16. A secondary low pressure region is created at the inlet 17 adjacent to the low pressure side of the tank 14 and the tank line 2
7. Facilitates fluid flow to inlet 17 via passageway 26 and this low pressure side region. This flow supplements the normal flow from tank 14 to inlet 17, thus making it possible to increase the capacity of the pump without increasing its size.

〔Effect of the invention〕

As described above, according to the present invention, even during low-speed operation before the flow control valve performs bypass flow, the passage 16
In addition, fluid is always supplied to the inlet 17 via the tank line 27 and the passage 26, thus improving the fluid replenishment at the inlet at low speeds, reducing the sound level and reducing the vacuum Wear and maintenance requirements due to cavitation damage and cavitation damage are also reduced. Also, during high-speed operation, fluid is also drawn from passage 26, so that the pressure at inlet 17 is increased and can replenish the supercharging amount provided by conventional flow control valves.

[Brief explanation of drawings]

The drawing is a schematic partial sectional view of the power transmission device of the present invention. 10...Pump, 12...Load (booster),
14...tank, 15...tank pipe, 16...
Passage, 17...Inflow port, 18...Flow rate control valve, 1
9... Spool, 20, 21... Land, 22...
...hole, 25...return conduit, 26...passage, 27...
...Tank line.

Claims (1)

[Scope of Claims] 1. A constant discharge pump 10 driven by a prime mover capable of operating at variable speed in a hydraulic system and having a predetermined flow rate for a load 12; a first tank line 15 having at least a first passage 16 to the inlet 17; a spool 19 having a first land 20 and a second land 21;
and a flow control valve including a hole 22 for returning part of the hydraulic fluid from the discharge port of the pump 10 to the conduit 2.
5 and return flow through the return line 25 is movable back to the inlet 17 of the pump region through the a flow rate control valve 18 configured to draw hydraulic fluid from the first passage 16 into the inlet port 17 by movement of the land 21; A second tank line 27 is provided, and the second tank line is connected to the two lands 2.
A power transmission device characterized in that it has an auxiliary second passage 26 extending through the flow control valve between 0 and 21 and in constant communication with said inlet 17. 2. According to claim 1, the flow control valve 18, the return line 25, the first passage 16 and the second passage 26 are arranged in the same housing as the pump 10. power transmission device. 3 On the upstream side of the first tank pipe line 15, only the return pipe line 25 and the second passage 26 intersect with the hole 22 in the same flow direction, and the second land 21 is connected to the return flow. The power transmission device according to claim 1 or 2, characterized in that the power transmission device is connected to the first passage at the inlet port 17 when the power transmission device is in a position to cause the flow to flow out.