GB2120418A

GB2120418A - Hydraulic pump control

Info

Publication number: GB2120418A
Application number: GB08210999A
Authority: GB
Inventors: Alastair John Young; Adrian John Chettle
Original assignee: Automotive Products PLC
Current assignee: Automotive Products PLC
Priority date: 1982-04-15
Filing date: 1982-04-15
Publication date: 1983-11-30
Also published as: EP0092315A2; JPS58193908A; EP0092315A3

Abstract

A fluid pressure supply system incorporates two pumping units P1 and P2 for supplying fluid under pressure to a load 13. Pump P1 supplies the load continuously. Pump P2 is also connected to the load 13 through a load valve 15 when pressure in the load is low but is connected to drain through the load valve when load pressure is high. A pressure relief valve 14 controls the load valve 15 by a connection from port 22 to port 28 which applies system pressure to the load valve at low pressure and drain pressure via port 23 at higher pressures in response to relief valve spool movement. The high control pressure moves load valve spool 25 to connect its inlet port 29 to load 13 through port 33. When system pressure is high and control pressure is low, inlet 29 is connected to drain port 31 so that pump P2 is off-load in that it is pumping direct to drain. In another embodiment, (Fig. 3, not shown) a combined valve 51 provides both functions of valves 15 and 14. <IMAGE>

Description

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GB 2 120 418 A 1

SPECIFICATION Hydraulic pump control

This invention relates to control of dual hydraulic pumps of for example power steering or 5 automatic transmission systems for motor vehicles.

Hitherto it has been common practice to provide a single pump. The rating of the pump is determined by the maximum flow rate and 10 pressure demand of the user. Such pumps typically operate at much less than maximum rating for the majority of operating time and much energy is wasted in pumping fluid up to relief valve pressure.

15 Dual output pumps or twin pumps have been proposed in which the first pump operates continuously and the second is brought on load as required by flow sensitive control means. Such control means include a flow restrictor upstream 20 of the user to sense the changeover point. A disadvantage with this arrangement is that the restrictor inevitably has a pressure drop across it, which results in the pump having to work that much above the maximum required user pressure. 25 According to the present invention there is provided control vaive means of a dual output pump for supplying fluid under pressure to a user and including relief valve means to limit the maximum supply pressure of fluid to said user, a 30 first pump outlet for direct connection to said user and a second pump outlet for connection to said user through ioad valve means, said relief valve means comprising a spool valve having an supply port for connection to the user supply, a drain port 35 and a valve spool movable against return spring means in response to increasing pressure at said supply port to connect the supply and drain ports above a predetermined supply pressure, said load valve means having an inlet port for connection to 40 the second pump outlet, an outlet port for connection to the user and a reservoir port, the load valve means being responsive to the position of the relief valve spool to connect said inlet and outlet ports below a predetermined supply 45 pressure and to connect said inlet and reservoir ports above that pressure.

Preferably said spool valve includes a signal port and a second drain port, the valve spool being movable to connect the supply port and signal 50 port below the predetermined supply pressure and to connect the signal and second drain ports above that pressure, the load valve means being responsive to fluid pressure at said signal port.

In one embodiment said relief valve means and 55 said load valve means comprise a spool valve having a common valve spool, said supply port and outlet port being common and the valve spool having an internal passage from the inlet to the outlet ports, a non-return valve in the passage 60 preventing fluid flow from the outlet to the inlet ports only.

Other features of the invention are included in the following description of three preferred embodiments shown, by way of example, only, in

65 the accompanying drawings in which:—

Fig. 1 is a schematic hydraulic circuit diagram showing the valve arrangement according to a first embodiment of the invention;

Fig. 2 is a diagram similar to Fig. 1 and showing 70 the valve arrangement of a second embodiment of the invention; and

Fig. 3 is a further diagram showing a simplified vaive according to a third embodiment of the invention.

75 With reference to Fig. 1 there is shown a fluid reservoir 11 from which a pump assembly 12 supplies fluid under pressure to a fluid user 13.

The pump assembly 12 comprises a main pump P1 and auxiliary pump P2 intended to be 80 brought on-load as required. The pump assembly may be of single dual output design or may comprise two independent pumps.

The output from main pump P1 is supplied directly to the user 13. A relief valve 14 limits 85 maximum system pressure and a load valve 15 diverts the output of auxiliary pump P2 to the user as will be described.

The relief valve 14 comprises a spool 16 returned to one end of its bore 17 by a spring 18. 90 An inlet port 19 is connected to the fluid circuit upstream of the user and a drain port 21 is provided to the reservoir 11. increasing fluid pressure in the relief valve will urge the spool 16 against the spring 18 to connect the inlet and 95 drain ports at the relief pressure.

A signal port 22 of the relief valve is connected to the inlet port 19 up to a predetermined pressure somewhat less than relief pressure, the spool thereafter connecting the signal port 22 to a 100 further drain port 23.

The load valve 15 also comprises a spool 25 urged to one end of its bore 26 by a return spring

27. A signal port 28 connected to the port 22 opens onto the end of the spool 25 remote from

105 spring 27.

In the rest position an inlet port 29 from auxiliary pump P2 is connected to a drain port 31. A passage through the spool 26 includes a nonreturn valve 32 and provides communication 110 between the inlet port 29 and an outlet port 33 connected to the user 13.

Operation of the load valve is as follows:—

Both pumps P1 and P2 are running. Pump P2 is , off-load being connected through inlet port 29 and 115 drain port 31. Communication between outlet port 33 and inlet port 29 is closed by the lands of the spool 26 and the non-return valve 32.

Fluid pressure rises from main pump P1 and the spool 16 of relief valve begins to move against its 120 return spring. Fluid pressure acts on the load valve spool 26 via inlet port 19 and signal ports 22 and

28.

At a predetermined fluid pressure the spool 25 will move against spring 27 to close the drain 125 port 31 and connect the inlet port 29 and outlet port 33 through the non-return valve 32. Further movement of the spool 25 connects the ports 29 and 33 directly bringing the pump P2 fully on-load to supplement the output of pump P1.

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GB 2 120 418 A 2

As fluid pressure progressively rises, further movement of the relief valve spool 16 closes communication between the inlet port 1 9 and signal port 22 and connects the port 22 to the 5 drain port 23.

The load valve spool 25 returns under the influence of springs 27 to connect the inlet port 29 and drain port 31, the pump P2 comes offload. Flow from port 33 to port 29 is prevented, as 10 before, by the non-return valve 32 and the lands of th spool 25.

Further pressure rise results in the relief valve spool connecting the inlet port 19 and drain port 21 to limit system pressure.

15 Should fluid demand from the user 13 increase beyond the capacity of main pump P1, system pressure will drop until the relief valve spool reconnects the inlet port 19 and signal port 22. The load valve spool 25 will move to bring the 20 auxiliary pump P2 on-load until user demand is satisfied.

In this way a considerable energy saving is effected, the pressure valves at which the auxiliary pump is brought on-load being determined by the 25 particular duty required.

Fig. 2 shows an alternative embodiment, the relief valve remains as in the previous example.

The load valve 35 has an inlet port 36, outlet port 37, signal port 38 and drain port 39 30 connected as previously described. A light spring 41 biases a spool 42 to one end of its bore 43 in which position the inlet port 36 and outlet port 39 are connected, the drain port 39 being closed by a land of the spool.

35 A non-return valve 44 is again provided in the spool to prevent flow of fluid from the outlet port 37 to the inlet port 36 when the valve is in operation.

Fluid pressure from the outlet port 37 acts 40 through a damping restriction 45 on one end of the spool 35 in opposition to the light spring 41, the signal port 38 opens to the other end of the spool.

Operation of the load valve is as follows:— 45 Initially the drain port 39 of the load valve is closed and both pumps P1 and P2 contribute to an increase of pressure to the user 13. Fluid pressure at the signal port 38 balances pressure at the outlet port 37, the light spring 41 holding the 50 spool 42 in the rest position. This arrangement gives a quick fill and fast initial pressure rise to the user 13.

Eventually the relief valve spool 16 connects the signal port 22 and drain port 23 as previously 55 described and a further increase of pressure shifts the load valve spool 42 against its return spring 41 to connect the inlet port 36 and drain port 39. Communication between the outlet port 37 and the inlet port 36 is prevented by the non-return 60 valve 44 and a land of the spool 42.

The auxiliary pump P2 is consequently brought off-load and idles, further pressure increase from main pump being eventually limited by the relief valve 14.

65 Should fluid demand from the user 13 increase beyond the capacity of the main pump, fluid pressure will drop until the relief valve spool reconnects the signal port 22 with the inlet port 19. Fluid pressure at the outlet port 37 will be balanced by that at the signal port 38 and the spool 42 will move under the influence of light spring 14 to reconnect the inlet port 36 and outlet port 37. Initial connection is via the non-return valve 44 until the outlet port 37 is uncovered by the closing land of spool 42 to establish direct communication.

The auxiliary pump is thus brought on-load until the user demand is satisfied as described for the previous embodiment.

Fig. 3 shows a somewhat simplified valve 47 in which the functions of the relief valve and load valve are combined. The valve 47 is similar to the load valve of the Fig. 2 embodiment with the exceptions that the signal port is open to atmosphere, the light return spring is replaced by a relief valve spring 48. An additional drain port 49, for connection to the outlet port 37 is normally closed by a land 51 of the spool 52.

Operation of the combined valve is as follows:—

Initially the spool 51 is returned by the spring 48 and both pumps P1 and P2 contribute to the increase of pressure to the user 13 via edge B. As pressure at the outlet port 37 rises the spool begins to move against its return spring until the inlet port 36 is cut off from the outlet port 37 by edge B of the spool, and is connected to the drain port 39. Excess pressure in pump P2 passes through the non-return valve 44 until edge C opens to connect P2 to drain. The pump P2 is now off-load and idling.

Further increase of pressure moves the spool 51 progressively against the effect of the spring 48 until the drain port 49 is connected via edge A. This port serves as the relief valve port to limit pressure rise of the main pump P1 ■

An increase in user demand will cause the spool 51 to be returned until the drain port 49 is closed and if the capacity of pump P1 is not sufficient the spool will retreat further to reconnect the inlet port 36 and outlet port 37 as previously described.

It will be apparent from the foregoing descriptions that the load valve may control two independent pumps and any reference in this specification to a dual output pump should also be taken as a reference to two independent pumps connected in parallel.

Claims

1. Control valve means of a dual output pump for supplying fluid under pressure to a user and including relief valve means to limit the maximum supply pressure of fluid to said user, a first pump outlet for direct connection to said user and a second pump outlet for connection to said user through load valve means, said relief valve means comprising a spool valve having an supply port for connection to the user supply, a drain port and a valve spool movable against return spring means

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GB 2 120 418 A 3

in response to increasing pressure at said supply port to connect the supply and drain ports above a predetermined supply pressure, said load valve means having an inlet port for connection to the 5 second pump outlet, an outlet port for connection to the user and a reservoir port, the load valve means being responsive to the position of the relief valve spool to connect said inlet and outlet ports below a predetermined supply pressure and 10 to connect said inlet and reservoir ports above that pressure.

2. Control valves means according to Claim 1, wherein said spool valve includes a signal port and a second drain port, the valve spool being movable 15 to connect the supply port and signal port below the predetermined supply pressure and to connect the signal and second drain ports above that pressure, the load valve means being responsive to fluid pressure at said signal port. 20 3. Control valve means according to Claim 2, wherein the load valve means comprise a spool valve having an end port for connection to the signal port and a valve spool movable in response to fluid pressure at the end port from a first

25 position in which the inlet and outlet ports are connected to a second position in which the inlet and drain ports are connected.

4. Control valve means according to Claim 3, wherein the valve spool of the load valve means

30 includes an internal passage from the inlet to the outlet ports, a non-return valve in the passage preventing fluid flow from the outlet to the inlet ports only.

5. Control valve means according to Claim 4, 35 wherein supply pressure acts on one end of the valve spool of the load valve means in opposition to a light spring and fluid pressure at said end port.

6. Control valve means according to Claim 1, wherein said relief valve means and said load

40 valve means comprise a spool valve having a common valve spool, said supply port and outlet port being common and the valve spool having an internal passage from the inlet to the outlet ports, a non-return valve in the passage preventing fluid 45 flow from the outlet to the inlet ports only.

7. Control valve means substantially as described herein with reference to Fig. 1 or to Fig. 2 or to Fig. 3 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office. 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.