US3777492A

US3777492A - Hydraulic apparatus including variable delivery pumps

Info

Publication number: US3777492A
Application number: US00116211A
Authority: US
Inventors: K Boydell; Flint J Eglington
Original assignee: Dowty Technical Developments Ltd
Current assignee: Dowty Technical Developments Ltd
Priority date: 1971-02-17
Filing date: 1971-02-17
Publication date: 1973-12-11
Anticipated expiration: 1990-12-11

Abstract

An hydraulic apparatus includes a variable-delivery pump, the delivery from which is controlled by a flow-sensing device. The flow through the device is determined by the position of a service-controlling selector valve. Upon adjustment of the selector valve from one position to another, the pump delivery is changed so as substantially to be in correspondence with the flow permitted by the new position of the selector valve.

Description

United States Patent 1 [1111 3,777,492 Boydell et al. 1 Dec. 11, 1973 HYDRAULIC APPARATUS INCLUDING 3,429,123 2/1969 Burroughs 60/52 vs VARIABLE DELIVERY PUMPS 3,219,259 11/1965 Horton 60/52 VS June 4, 1968 Inventors: Kenneth Raymond Boydell,

Breclons, Hardwick, near Tewkesbury; John Christopher Eglington Flint, Stroud, both of England Dowty Technical Developments Limited, Brockhampton, Cheltenham, England Filed: Feb. 17, 1971 Appl. No.: 116,211

Assignee:

Foreign Application Priority Data Qt at r a n -t-i -;:,2V ,.291

U.S. Cl 60/462, 60/445, 417/218 Int. CL. F15b 15/18, F04b 49/00 Field of Search 417/213, 218, 222;

References Cited UNITED STATES PATENTS Plate 60/52 VS Primary Examiner-Carlton R. Croyle Assistant ExaminerJohn J. Vrablik AttorneyYoung & Thompson [57] ABSTRACT 6 Claims, 3 Drawing Figures PATENTEU 1 3,777. 492

SHEET 3 BF 3 Fla. 3.

HYDRAULIC APPARATUS INCLUDING VARIABLE DELIVERY PUMPS FIELD OF THE INVENTION This invention relates to hydraulic apparatus including variable-delivery pumps.

SUMMARY OF THE INVENTION According to this invention an hydraulic apparatus includes a variable-delivery pump whose delivery is controlled by a flow-sensing device, the flow through which is determined by the position of a servicecontrolling selector valve in such manner that upon adjustment of the selector valve from one position to an other, the delivery from the pump is changed so as substantially to be in correspondence with the flow permitted by the new position of theselector valve.

Also, according to the invention an hydraulic apparatus includes a variable-delivery pump, a pump deliveryvarying means, a flow-sensing device operable upon said pump delivery-varying means, a selector valve connectible to a service for directing pump delivery thereto, an unloader valve by which some of the pump delivery can be diverted to flow through the flowsensing device when the selector valve is in positions other than fully open to said service, and means for operating the selector valve and the unloader valve simultaneously so that as the selector valve is being moved in one sense, (e.g. increasing the area of the service flow path), the unloader valve is being moved in the opposite sense, (e.g. decreasing the area of the flow path to the flow-sensing device), and the pump deliveryvarying means is being actuated by the flow-sensing device to adjust pump delivery, (e.g. in the increasing sense), so that it is substantially in correspondence with that permitted by the service flow path area at the selector valve.

In this way the pump delivery is automatically increased but only so far as is necessary, with the selector valve in said positions, to maintain a small flow through the unloader valve to tank andalso to supply only substantially the exact flow of liquid required for desired operation of said service. i

The flow-sensing device may include a servo motor of double-acting piston-and-cylinder type, and further include an orifice, with a passageway branched from a position upstream of the orifice connecting to one side of said servo motor, while a further passageway branched from a position downstream of the orifice connects to the other side of said servo motor.

The servo motor may include spring means for biassing it in the pump on-loading direction.

The selector valve and the unloader valve may be integral.

A plurality of said selector valves may be arranged in physically parallel manner, thereby forming a banked unit, each of the valves being connectible to control its respective service, but the variable-delivery pump and the flow-sensing device being common to the entire bank.

The said service controllable by the apparatus may be of single-acting type or alternatively may be of double-acting type.

A pressure relief valve is preferably provided at the delivery side of thevariable-delivery pump.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a diagrammatic hydraulic circuit including 5 a variable-delivery pump, a selector valve and a service,

FIG. 2 is a more detailed, enlarged, partcrosssectional view of the selector valve shown in FIG. 1, and

FIG. 3 is a view similar to FIG. 2 but showing a banked selector valve arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to thedrawings, an hydraulic apparatus includes a variable-delivery pump 11 connected to draw hydraulic liquid from a tank 12 and to deliver this liquid under pressure into a passage 13. Although diagrammatically shown in FIG. 1, the pump in this embodiment is of the reciprocatory-piston swashplate type. The passage 13 incorporates a check valve 14 and connects to the casing of a selector valve 15. A tapping 16, taken from the passage 13 upstream of the check valve, incorporates a pressure relief valve 17 which discharges to the tank 12.

The selector valve is in the form of a spool valve as shown in FIG. 2 and is movable linearly to either side of a neutral position. As drawn both in FIG. 1 and FIG. 2, the valve is in its neutral position, and from the casing 18 of the valve connections are made to

pipes

19 and 20 which are respectively taken to the

chambers

21 and 22 on either side of the piston 23 of a service 24 in the form of a double-acting piston-and-cylinder type jack.

The valve spool 25 has four

lands

26, 27, 28 and 29, and has conventional spring-centering means 30 which bias the spool to its neutral position.

An annulus 31 formed between the

lands

26 and 27 is in communication through a port 32 with the pipe 19, while an annulus 33 formed between the

lands

28 and 29 is in communication through a port 34 with the pipe 20.

An annulus 35 is formed between the

lands

27 and 28 and the portions of these lands immediately adjacent the annulus are provided with inching grooves 36 of V- shape spaced circumferentially around the surface thereof as shown. An unloader valve, integral with the selector valve is thus formed.

When the valve spool 25 is displaced downwardly in the drawings to one side of the neutral position, the passage 13 is placed in communication with the pipe 20, while the pipe 19 is placed in. communication with tank 12 through a passage shown. in FIG. 1 by the line 37 and in FIG. 2 by the lower of the two ducts 37.

When the valve spool 25 is moved upwardly in the drawings to the other side of the neutral position, these connections are crossed over, the passage 13 being placed in communication with the pipe 19 and the pipe 20 being placed in communication with tank 12 through the upper duct 37.

The selector valve 15 is of the open-centre" type, meaning that when its spool 25 is in the neutral position, as drawn, the

lands

27 and 28 blank off communithe jack 24 is thus held substantially in a state of hycation of the

pipes

19 and 20 with the passage 13, and

passage 38 which is tapped from a point in the passage 13 just upstream of the check valve 14 and which communicates through an unloader port 39 in the casing 18, the annulus 35 and another unloader port 40 in the casing, and a continuation of the passage 38, with the tank 12. In this way, with the valve spool 25 in its neutral position, a direct through-route, by-passing the relief valve 17, is taken from the delivery side of the variable-delivery pump 11 to the tank 12.

That portion of the unloader passage 38 on the tank side of the selector valve incorporates an orifice 41, and as shown in FIG. 1, from a point upstream of this orifice a branch passageway 42 is taken to a chamber 43 formed to the left in FIG. 1 of the piston 44 of a double-acting servo motor 45 of telescopic type. From a point just downstream of the orifice 41 a further branch passageway 46 is taken to a chamber 47 to the right in the drawing of the piston 44 of the servo motor 45.

The piston rod 48 of the servo motor 45 is connected in convenient manner to a servo device 49. The piston rod 48 forms the input of the servo device. The servo device controls the operation of the delivery-varying mechanism of the variable-delivery pump 11. The delivery-varying mechanism is indicated diagrammatically by the arrow 50 in FIG. 1, and in this embodiment this mechanism takes the form of an adjustable swash-plate.

A coil spring 51 provided in the chamber 47 of the servo motor 45 biasses the piston 44 and the piston rod 48 in a direction ensuring that the pump is biassed in the on-loading direction.

In operation of the hydraulic apparatus abovedescribed, with the selector valve spool 25 in its neutral position as drawn, and with the variable-delivery pump 11 being driven, a small quantity of hydraulic liquid is delivered through the passage 13, the unloader passage 38, the

unloader portion

39, 40, and the orifice 41, to the tank 12. In this embodiment this small flow is of the order of 0.5 gallons per minute, which is sufficient to give rise to a high pressure drop across the orifice 41 which sets the servo motor 45 in an equilibrium position, just on stroke, so as to maintain the small delivery flow from the pump 11.

Under these conditions, the service 24 is of course stationary, being substantially hydraulically locked by virtue of the

lands

27 and 28 of the spool 25 closing over their adjacent porting in the casing 18 of the valve.

When it is'required to contract the service 24, the spool 25 is moved downwardly in the drawing. Initially this movement throttles the

unloader portion

39 and 40, causing a reduction in flow through the orifice 41. Consequently, the pump output pressure rises correspondingly because the by-pass passage flow is reducing whilst the pump delivery-flow momentarily remains at the same value. As the service 23 starts to move, the supply from the pump, in this embodiment at 1500 p.s.i., is now being directed both to one side of the service and, at a reduced flow, through the orifice.

The reduction in flow through the orifice reduces the pressure differential acting across the piston 44 of the servo motor 45 so that the coil spring 51 moves the piston to the left and effects movement of the deliveryvarying mechanism 50 of the pump 11 in a direction towards the pump full delivery condition. The orifice and servo motor thus form a flow-sensing device.

During such transition between the neutral position of the valve spool and the full closure of the unloader passage 38 there will be a range of flows, reducing in magnitude across the orifice 41, which corresponds to a range of pressure drops across the piston 44 of the servo motor. The rate of the coil spring 51 must therefore be chosen so that for the range of positions of the valve spool in this transitional state there is a corresponding range of positions in which the spring is in equilibrium with the control pressure drop across the orifice 41. Hence, each length condition of the spring 51 corresponds to a unique delivery flow condition of the pump.

The unloader flow is of course always the excess of delivery over demand during the transition.

When the selector spool 25 reaches a position in which the unloader passage is completely closed, the

lands

26 and 29 are so positioned that the

pipes

19 and 20 are subject to full flow conditions. Since no flow now occurs across the orifice 41 no pressure drop is generated across it and thus the piston 44 is subjected only to the pressure of the spring 51 which biasses the pump 11 onto full stroke.

It will be understood that during the transition between the neutral position of the valve spool 25 and the full flow operation of the service, the inching slots 36 afford very precise control of the pump and of the service.

When the selector valve spool 25 is moved back towards its neutral position, initially the inching slotcontrolled unloader porting 39 and 40 will be cracked open, whereupon flow through the passage 38 and orifree 41 will be re-established, while delivery flow to the service 23 will be reduced by the amount of this reestablished flow, the pump 11 momentarily remaining at the same stroke. Such flow through the orifice 41 will however de-stroke the pump until equilibrium pressure drop is reached and thus delivery flow to the service will be reduced a second time.

When the selector valve spool 25 fully reaches the neutral position, the service 24 becomes substantially hydraulically locked again and the flow through the unloader passage 38 and through the orifice 41 is such as to cause the pump 11 to return to its low delivery condition in which the flow rate to tank 12 through the orifice 41 is of the order of 0.5 gallons per minute.

When it is required to extend the service 23, the selector valve spool 25 is moved upwardly in the drawings, but the system operates in a manner similar to that for service contraction, except that the passage 13 is now placed in communication with the pipe 19, while the pipe 20 is placed in communication with the tank 12 through the upper duct 37.

By the invention, therefore, an apparatus is provided where a variable-delivery pump gives substantially exactly the flow necessary for the required rate of operation of the associated service, but, except when the selector valve spool is at or close to its fully selected position the apparatus maintains a mean datum flow of 0.5 gallons per minute through the unloader passage, this flow providing the motive fluid for at least assisting in pump displacement servo control.

The apparatus is advantageous over conventional open-centre valve arrangements used in conjunction with fixed-displacement pumps where power is wasted when the pressure is high and the service flow is small.

The invention is not limited to an hydraulic apparatus having one selector valve, as in other embodiments two or more selector valves may be arranged in physically parallel manner to form a banked unit, each selector valve of the bank being connected to control a respective service. However, in such embodiments a single unloader passage, such as the unloader passage abovedescribed with reference to the drawings, a single orifice and a single servo motor for control of the deliveryvarying mechanism of a single variable-delivery pump, are common to the entire bank. FIG. 3 shows a banked selector valve

arrangement including spools

50 and 51 which are similar to the spool 25 of FIG. 2. Each

spool

50, 51 is associated with a

respective service

53, 54. Although shown in two separate parts the casing 55 of the selector valve is of monobloc form.

The pressure supply conduits to each valve and the service conduits from each valve to the respective service are similar to that shown in FIG. 2 and bear similar reference numerals, with a conduit 56 connecting the two supply conduits 13.

However, the open-center passage 38 is common to the valve block, as is the orifice 41,

passageways

42 and 46 and a double-acting servo motor associated with those passageways and which is similar to that servo motor shown at 45 in FIG. 1.

This servo motor controls the delivery-varying mechanism of the variable-delivery pump which supplies liquid under pressure, to the valve block and which is similar to the pump shown atll in FIG. 1.

In operation the system controls the delivery setting of the pump in dependence upon the required rate of operation of one or other, or both of the services, as the case may be.

Again, the invention is not limited to the selector valve or valves being of the spool type, as in other embodiments it or they may be of other type, for example of the type in which the slider is of rectangular crosssection, either slidable linearly or arcuately. Further, the variable-delivery pump need not be of the reciprocatory-piston and swash-plate type, as in other embodients other forms of variable-delivery pump, for example of the spill-type or radial-piston type, may with advantage be employed.

. Although in the embodiment described with reference to the drawings the service is a double-acting service, in other embodiments single-acting services may instead be employed and again the invention is not limited to services of telescopic type, as services of other form may also be employed.

Having described our invention, we claim:

1. An hydraulic apparatus including a variabledelivery pump, a pump delivery-varying means, a flowsensing device operable upon said pump deliveryvarying means, a selector valve connected through first conduit means to receive delivery flow from said pump, second conduit means connected to a service, said selector valve when moved away from its neutral position to an operative position connecting said first conduit means to said second conduit means whereby said delivery flow is directed to said service, third conduit means for liquid exhausting from said service, said third conduit means, with said valve in said operative position, directing said exhausting liquid to tank, an unloader passage branched from a point in said first conduit means on the upstream side of said selector valve and connected to tank, a check valve positioned in said first conduit means between said point and said selector valve to permit flow only in a direction towards said selector valve, an unloader valve in said unloader passage, an orifice, forming part of said flow-sensing device, positioned in said unloader passage, means for operating the selector valve and the unloader valve simultaneously whereby when the selector valve is in its neutral position, so that the service is inoperative, the unloader valve is fully open, and when the selector valve is moved to such an operative position that said first conduit means is fully open to said second conduit means, the unloader valve is fully closed, the flowsensing device including a servomotor in circuit with said orifice whereby when the selector valve is in its neutral position said servomotor is operable to cause the pump delivery-varying means to hold the variabledelivery pump just on stroke.

2. An hydraulic apparatus as claimed in claim 1, said pump delivering a small circulating flow of liquid through said first conduit means into the unloader passage and thence to tank, and upon movement of the selector valve away from the neutral position the unloader valve so moving toward its closed position that the flow through the unloader passage is throttled thus to produce such change in pressure differential in said servomotor as to effect change in pump delivery to meet the demands of the new setting of the selector valve.

3. An hydraulic apparatus including a variabledelivery pump, a pump delivery-varying means, a flowsensing device operable upon said pump deliveryvarying means, a selector valve connected through first conduit means to receive delivery flow from said pump, second conduit means connected to a service, said selector valve when moved away from its neutral position to an operative position connecting said first conduit means to said second conduit means whereby said delivery flow is directed to said service, third conduit means for liquid exhausting from said service, said third conduit means with said valve in said operative position directing said exhausting liquid to tank, an unloader passage branched from a point in said first conduit means on the upstream side of said selector valve and connected to tank, a check valve positioned in said first conduit means between said point and said selector valve to'permit flow only in a direction towards said selector valve, an unloader valve in said unloader passage, an orifice, forming part of said flow-sensing device, positioned in said unloader passage, means for operating the selector valve and the unloader valve simultaneously whereby when the selector valve is in its neutral position the unloader valve is fully open, and when the selector valve is moved to such an operative position that said first conduit means is fully open to said second conduit means, the unloader valve is fully closed, the flow-sensing device including a servomotor of double-acting piston-and-cylinlder type, with a passageway branched from a position upstream of said orifice to connect to one side of said servomotor, and a passage branched from a position downstream of said orifice to connect to the other side of said servomotor, it being arranged that when the selector valve is in its neutral position, so that the service is inoperative, a small flow of liquid predetermined by the size of said orifice passes through said open unloader valve and said unloader passage to tank, the pressure drop then occurring across said orifice causing said servomotor to hold the pump delivery-varying means in a condition so as to maintain the variable-delivery pump just on stroke.

wherein a plurality of said selector valves are arranged in physically parallel manner, thereby forming a banked unit, each of the valves being connectible to control its respective service, but the variable-delivery pump and the flow-sensing device being common to the entire bank.

Claims

1. An hydraulic apparatus including a variable-delivery pump, a pump delivery-varying means, a flow-sensing device operable upon said pump delivery-varying means, a selector valve connected through first conduit means to receive delivery flow from said pump, second conduit means connected to a service, said selector valve when moved away from its neutral position to an operative position connecting said first conduit means to said second conduit means whereby said delivery flow is directed to said service, third conduit means for liquid exhausting from said service, said third conduit means, with said valve in said operative position, directing said exhausting liquid to tank, an unloader passage branched from a point in said first conduit means on the upstream side of said selector valve and connected to tank, a check valve positioned in said first conduit means between said point and said selector valve to permit flow only in a direction towards said selector valve, an unloader valve in said unloader passage, an orifice, forming part of said flowsensing device, positioned in said unloader passage, means for operating the selector valve and the unloader valve simultaneously whereby when the selector valve is in its neutral position, so that the service is inoperative, the unloader valve is fully open, and when the selector valve is moved to such an operative position that said first conduit means is fully open to said second conduit means, the unloader valve is fully closed, the flow-sensing device including a servomotor in circuit with said orifice whereby when the selector valve is in its neutral position said servomotor is operable to cause the pump deliveryvarying means to hold the variable-delivery pump just on stroke.

3. An hydraulic apparatus including a variable-delivery pump, a pump delivery-varying means, a flow-sensing device operable upon said pump delivery-varying means, a selector valve connected through first conduit means to receive delivery flow from said pump, second conduit means connected to a service, said selector valve when moved away from its neutral position to an operative position connecting said first conduit means to said second conduit means whereby said delivery flow is directed to said service, third conduit means for liquid exhausting from said service, said third conduit means with said valve in said operative position directing said exhausting liquid to tank, an unloader passage branched from a point in said first conduit means on the upstream side of said selector valve and connected to tank, a check valve positioned in said first conduit means between said point and said selector valve to permit flow only in a direction towards said selector valve, an unloader valve in said unloader passage, an orifice, forming part of said flow-sensing device, positioned in said unloader passage, means for operating the selectoR valve and the unloader valve simultaneously whereby when the selector valve is in its neutral position the unloader valve is fully open, and when the selector valve is moved to such an operative position that said first conduit means is fully open to said second conduit means, the unloader valve is fully closed, the flow-sensing device including a servomotor of double-acting piston-and-cylinder type, with a passageway branched from a position upstream of said orifice to connect to one side of said servomotor, and a passage branched from a position downstream of said orifice to connect to the other side of said servomotor, it being arranged that when the selector valve is in its neutral position, so that the service is inoperative, a small flow of liquid predetermined by the size of said orifice passes through said open unloader valve and said unloader passage to tank, the pressure drop then occurring across said orifice causing said servomotor to hold the pump delivery-varying means in a condition so as to maintain the variable-delivery pump just on stroke.

4. An hydraulic apparatus as claimed in claim 3, wherein said servomotor includes spring means for biassing it in the pump on-loading direction.

5. An hydraulic apparatus as claimed in claim 3, wherein the selector valve and the unloader valve are integral.

6. An hydraulic apparatus as claimed in claim 3, wherein a plurality of said selector valves are arranged in physically parallel manner, thereby forming a banked unit, each of the valves being connectible to control its respective service, but the variable-delivery pump and the flow-sensing device being common to the entire bank.