Summing Valve Arrangement

Abstract

There is disclosed control means that is operative to vary the horsepower output of a plurality of variable displacement pumps in response to the sum of the outputs of the pumps.

Description

BACKGROUND OF THE INVENTION

The present invention relates to horsepower controlling means and pertains more particularly to a summing valve arrangement that is operable to control the horsepower output from a plurality of hydraulic pumps.

Many hydraulic machines are designed to perform a plurality of functions either independently or simultaneously. These machines normally employ two or more variable displacement pumps, driven by a single internal combustion engine for supplying fluid to motors for performing the functions. Each pump is normally capable of delivering the entire horsepower output of the engine to the motor or motors which it is arranged to supply. Thus, when several functions are being performed simultaneously be motors that are supplied by separate pumps, the horsepower demand of the load may exceed the horsepower capability of the engine and cause it to stall.

Numerous prior art devices have been proposed for controlling the horsepower output of a variable delivery pump. These devices, however, have proven to be unsatisfactory because they tend to be expensive, unduly complicated and unreliable. Such devices normally employ complicated arrangements of cam and linkages.

One proposed system for controlling horsepower is disclosed in U.S. Pat. No. 2,932,948. This system, however, employs a complex arrangement of interconnected cams, levers, and pistons. This type of complex mechanism is subject to substantial frictional losses and tends to be insensitive to pressure changes.

A more simplified system is disclosed in British Pat. specification No. 1,128,657 filed Sept. 30, 1965. This more simplified system has the disadvantage of being responsive only to pump output pressure. This results in a lack of sensitivity to engine speed and consequently a lack of sensitivity to engine horsepower.

Other proposed solutions to the problem of horsepower control are disclosed in U.S. Pat. Nos. 2,080,810, 2,009,608 and 2,179,071. These systems also suffer from undue complexity and lack of sensitivity to actual engine horsepower.

SUMMARY OF THE INVENTION

It is, therefore, the primary object of the present invention to provide a simple and inexpensive control system for controlling the horsepower output of a plurality of pumps.

A further object of the present invention is to provide simple horsepower controlling means for a plurality of variable displacement pumps that eliminates the need for complicated arrangements of cams and linkages.

In accordance with the present invention, the output pressures from a plurality of variable displacements are summated and utilized to operate a valve to control fluid from a source for varying the displacement of said pumps.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration, partially in section of a pump control circuit embodying a preferred embodiment of the present invention;

FIG. 2 is a view taken generally along lines II--II of FIG. 1;

FIG. 3 is an elevational view in section of a modification of the summing valve of the present invention;

FIG. 4 is a schematic layout of an alternate embodiment of the present invention; and,

FIG. 5 is an end view, in section, of the summing valve of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, and in particular to FIG. 1, there is illustrated a horsepower controlling means comprising a pair of variable displacement pumps 10 and 12 driven by a common prime mover such as an internal combustion engine and each having a servo control motor and valve 14 and 16 interconnected by means of conduits 18 and 19. The servo motors 14 and 16 may be of conventional design.

The output from the pumps 10 and 12 is supplied by means of suitable conduits 20 and 22 for operation of the implements for a hydraulic machine such as an excavator or loader (not shown). It should be emphasized that this system is not limited to two pumps 10 and 12 but may include any number of variable displacement pumps. The pumps are arranged such that they are normally in the maximum flow position with the control means of the present invention operative to reduce the pump output in response to overload conditions in the operation control circuit.

A source of fluid pressure comprising in this embodiment a fixed displacement pump 24, preferably driven by the same prime mover or engine 25 which drives the variable displacement pumps, communicates by way of a conduit 26 and a summing valve 28 with the conduit 18 and 19 for supplying control fluid or pressure to the servo control systems 14 and 16 for varying the displacement of the pumps 10 and 12. The pump 24 is preferably driven by the same prime mover means as the variable displacement pumps 10 and 12, so that the source of control pressure will be related to the horsepower output of the prime mover.

The valve 28 comprises a housing 30 having a bore 32 communicating with inlet conduit 26 by means of an inlet passageway 33. The bore 32 is also in communication with conduits 18 and 19 by means of an annular passageway 68 and an outlet passageway 34. A spool 36 is slidably disposed in the bore 32 and biased by means of the spring 38 to a leftwardmost position to block communication between inlet passageway 33 and outlet passageway 34.

The position of the valve member 36 for controlling the flow of fluid between inlet 33 and outlet 34 is controlled by pressure responsive means comprising a plurality of pistons 40, 42, 44 and 46 received in suitable bores in the housing 30 and operative to apply a force against the spool member 36 in response to pressure output from the pumps 10 and 12. Chambers 48, 50, 52 and 54 at the head of each of the pistons 40, 42, 44 and 46 are in communication by way of conduits 56 and 58 with the outputs of the variable displacement pumps 10 and 12. In particular, the chambers 48 and 52 are in communication by means of conduit 56 with the output of pump 10. Likewise chambers 50 and 54 are in communication by way of conduit 58 with the output of variable displacement pump 12. The valve spool 36 is also provided with further pressure responsive means which comprises a piston 60 disposed in a bore 62 formed in the spool 36 and having a pressure chamber 64 in communication by way of the passageway 66 with an annular passageway 68 in communication with bore 32 and outlet passageway 34. A metering slot 70 is formed on spool 36 to meter the flow of fluid from the inlet 33 to the entering of passageway 68. Thus, it is seen that with this arrangement pressure exerted in chamber 64 will be substantially the pressure acting in the passageway 34 and conduit 18 whether in communication with the inlet 33 or not.

When the spool 36 is moved to the right as a result of pressure from the pumps 10 and 12, a flow path is established between the inlet 33 from pump 24 and the outlet 34. The fluid is then directed from passage 34 by way of conduits 18 and 19 to the servo valves 14 and 16 of the variable displacement pumps 10 and 12.

The summing valve arrangement operates to control the horsepower output of the variable displacement fluid pumps 10 and 12. When both of the pumps 10 and 12 are operating, fluid is delivered along lines 20 and 22 of the various control valves controlling the implements. Since these pumps are variable in displacement, the flow rate delivered by the pumps can vary according to the demand from the working implements of the machine. So long as the flow rate and pressure of the system plus pump losses does not exceed the maximum horsepower of the prime mover or engine 25, the summing valve assembly will remain inactive. However, when the pressure in the output lines 20 and 22 exceeds a predetermined value, the flow delivery rate of the two variable pumps must then be decreased in order to prevent the pumps from stalling the engine 25 of the machine. Such stalling will occur when the pump demands more horsepower than the machine prime mover is capable of producing.

A portion of the output from pump 10 passes through a pressure reducing valve 55 along conduit 56 and into chambers 48 and 52. The portion of the fluid from pump 12 passes through pressure reducing valve 57 along conduit 58 and into the chambers 50 and 54. The purpose of the reducing valves 55 and 57 is to reduce the pressure output from the pumps by a factor of approximately 10 to 1. The pressure in the chambers 48, 50, 52 and 54 exert a force on pistons 40, 42, 44 and 46 and consequently on the valve 36. When the sum of these pressures exceeds a certain predetermined maximum pressure, the force of the pistons begin to move the spool 36 to the right against a force of spring 38. Communication is then established between annular inlet 33 and the outlet passage 34 by way of metering slot 70. This causes the output from pump 24 to be delivered along the conduits to servo valves 14 and 16 of the pumps 10 and 12. This pressurized fluid activates the servo valves and swivels the two pumps to a lower position of volumetric delivery.

The amount that the delivery rate of the two variable pumps is reduced is dependent on the distance that the spool 36 moves to the right which is dependent on the pressure in lines 56 and 58 working on the four pistons 40, 42, 44 and 46. Since the horsepower output of the pump is a function of the pressure and the volume, a reduction of the volume output permits the pressure to remain substantially the same or to even increase without an increase in horsepower requirement. When the pressure has dropped off sufficiently to permit the spool 36 to move back to the left and cut off communications between the inlet 33 and outlet 34, the pressure applied to the servo valves 14 and 16 will begin to relax due to a drain orifice 72 which permits the fluid from lines 18 and 19 to drain back to the sump. Thus, the stroke of the pumps begins to increase again until an equilibrium position is maintained.

Referring now to the embodiment of FIG. 3, the spool has been modified in a manner that it eliminates the drain orifice or restriction 72 and the spring 38 of the previous embodiment. In this embodiment, the spool 80 is nearly identical to the spool 36 of the previous embodiment. However, it has been provided with a slot 82 which provides communication between the passage 34 and the bore at the right hand end of the spool and consequently the drain passage 74 back to drain. In this manner, the orifice 72, a restriction of the previous embodiment is eliminated and replaced by a plug 84. In this manner, the lines 18 and 19 are drained only when required, that is, only when the spool 80 is in such a position as to cut off communication between inlet 33 and outlet 34. Another modification of spool 80 over the previous embodiment was to increase the diameter of bore 61 and piston 63 in order to provide the required force balance to position the spool 80 without the use of a spring such as 38 in FIG. 1.

Turning now to FIG. 4, there is illustrated a modified arrangement of the control system. Identical components, as in the previous embodiment, are identified by the same numerals. In this embodiment, all the major pumps in the system, whether fixed or variable displacement, contribute in supplying fluid for actuation of the summing valve 28. Thus, a portion of the fluid for controlling the summing valve is from a pump whose output is in proportion to engine speed. In this embodiment, the output is supplied to pressure sensitive cylinder arrangements 81, 82, 85, 87 and 89 similar to those in the previous embodiment. The size and/or number of the pressure response chambers 81, 83, 85, 87 and 89 may vary in accordance with the ratio of the load from each pump to that of the total pump load. In other words, the actuating force contributed from each pump is in proportion to the total system. For example, a pump supplying only half the horsepower of a second pump in the system would also be arranged to have, for example, one sensing element as compared to two for the second pump, if the diameters of the sensing elements are the same.

The source of fluid for activating the servo control valves 14 and 16, in this embodiment, comes from the pumps being controlled rather than from a totally independent source, as in the previous embodiment. For example, the supply line 56 is tapped by a branch conduit 86 and supplies through a check valve 88 to the inlet conduit 90 of the control valve 28. The supply line 91 from pump 24 is tapped by branch conduit 92 having a check valve 94 and supplies to the inlet conduit 90. A branch conduit 96 taps the supply from conduit 58 and supplies it by way of the check valve 98 to the inlet 90. With this arrangement, the supply into or across the control valve 28 from inlet 90 will be from the pump having the greatest outlet pressure. Again, it should be emphasized that the present control system is not to be limited to a specific number of variable displacement pumps but may be used in conjunction with any number of variable pumps either alone or in combination with a number of fixed displacement pumps.

While the present invention has been described with respect to particular embodiments, it is to be understood that many changes may be made in arrangement in parts without departing from the spirit and scope of the appended claims.

Claims

What is claimed is:

1. A horsepower controlling system, said system comprising in combination:

a plurality of variable displacement pumps driven by a common prime mover and including pressure responsive means for varying the displacement of said pump,

a source of actuating pressure comprising a fixed displacement pump driven by said common prime mover for actuating said pressure responsive means;

a valve having a bore in communication with said source of actuating pressure and with said pressure responsive means;

a spool disposed in said bore and operative to control said communication;

means comprising a plurality of individual pistons communicating with and responsive to the sum of the outputs of said variable displacement pumps to actuate said valve to thereby communicate said actuating pressure with said actuating means to alter the displacement of said pumps; and,

a piston selectively communicating with said source of actuating pressure and operatively connected to said valve to oppose said plurality of individual pistons.

2. The invention of claim 1 wherein said source of actuating pressure is a fixed displacement pump driven by said common prime mover.

3. The combination of claim 1 comprising a pressure reducing valve operatively connected between said valve actuating means and the output of said variable displacement pump.

4. The horsepower controlling system of claim 1 wherein said source is the one of said variable displacement pumps having the highest pressure output.

5. A horsepower controlling system for controlling the horsepower output of a plurality of variable displacement pumps driven by a single prime mover, said system comprising:

a source of control pressure comprising a fixed displacement pump driven by said prime mover for controlling the displacement of said pumps;

a valve having a pre-determined bias to a cut-off position for controlling the communication of said control pressure with said pump displacement means;

means responsive to the sum of the output pressure of said pumps for moving said valve to control said control pressure;

pressure responsive means responsive to the output of said variable displacement pumps to bias said valve in a direction to provide open communication between said source of control pressure and said pump displacement controlling means, said pressure responsive means comprising a plurality of pistons disposed in cylinders,

said cylinders being in communication with the output of said pumps at one end of said piston; and,

the other end of said piston in operative engagement with said valve means.

6. The system of claim 5 comprising:

a piston disposed at the opposite end of said valve from said plurality of pistons; and,

said piston being responsive to communicate one end of said piston with said source of control pressure when said valve is positioned for open communication, whereby said piston urges said valve toward a non-communicating position.

7. The system of claim 6 wherein said spool includes means to provide communication between said pump displacement controlling means and a sump.