US2009608A - Pump control - Google Patents

Description

J. K. DOUGLAS PUMP CONTROL Filed June 27, 1931 July 30, 1935.`

2 Sheets-Sheet 1 JAMES K. DDULAS.

July 30,1935. J. K. DOUGL AS 2,oo9,6o8

i .PUMP -CONTROL I Filed June 27, 1931 2 Sheets-Sheet? 1 iq. 2

16 7 "aa 27 1 28 s /9 ao'- na 'JAMES K. Dum; LASJ Patented July 30, 1935.

James K'. Douglas, Milwaukee, Wiz., aslgnor to The Oilgear Company, Milwaukee, Wii., a corp'oration o! Wisconsin Application June 27, 1931, Serial No. &7,268

11 Claims. (Cl. los-38) This invention reiates to controls for variable displacement pumps. v

The pump control to which the invention apy plies in particular enables a variabe displace- 5 ment pump to function as either a variabledelivery pump or a constant .delivery pump until thezpressure' created thereby reaches a predetermined maximum andto thenrfunction as a sub-` stantially'constant pressure" pump. 4 1 A pumpcontrol of this character ordinarily has a springior urging thestroke changing mechanisn of the pump toward full stroke position and as it is deflected, pressure in excess ofthe predetermined maximum was required to compress the spring sufflciently to reduce the pump stroke to substantiaily zero. i

30 As the maximum pump pressure is often high,

for instance 1500# per sq. in., and as the resistanceaincrease in a. spring *varis inversely according to its length, a small diametercontrol motor and a long fiexible spring were employed. but, in

35 practice, it was found that the' pump pressure sometimes rose as much as 400# above the dev sired maximum pressure before the stroke of the pump was reduced sufliciently 'to hold the pump pressure constant.

40 The invention is applicable to various types of pumps but, for the purpose of illustration, it will be described herein in connection with a radial pump such as that disclosed in Patent No. 1,578,233. v

45 That pump hasa circular actuator or driver which is driven from an external source of power and rotateson a stationary axis to rotate a cylinder barrel having a number of radial cylinders iormed therein. The cylinder'barrel is journaled 50 upon a shaft or pintle which is rigidly Secured in an arm or pendulum and normally'held out of axial alinement with the driver by a'spring, the spring being opposed by a hydra'ulic control motor which is open at all times to pump pressure 55 and tends to move the pintle into axial aline- However, as the resistance' of a spring increases u ment with the' driver. The cylinders have pistons fltted therein which' are reciprocated by the driver whenever the axis or the pintle is out of alinement with the axis of the driver, and the pintle has an intake port 'and passageway for the 5 delivery of liquid to the cylinders and a discharge port and passageway for the discharge or liquid from the cylinders.

Each cylinder communicates with the intake and discharge ports alternately during rotation of the cylinder barrel and, as the cylinders move from the one side of the-pintle to the other side thereof, thepressure existing in the high pressure I port acts .successively on the pstons, and intermittent forces called bridge reactions are created which tend to move-the pintle laterally. The pump isordinarily so constructed that the lateral comporents *of all these forces tend to move the pintle towardzero stroke position.

consequently; both these intermittent pintle forces and the force exerted by the stroke control motor must be resisted 'by the stroke control spring until the pump pressure reaches the predetermined maximum'. Further, the pintle forces vary as the pintle moves toward zero stroke position which makes it still more dicult to control the maximum pump pressure with any degree of accuracy.

An objectof the invention is to provide a pump control'which will cause a variable displacement pump to deliver fluid at predetermined volumes until a predetermined pressure had becn exceeded and thereafter adjust the pump displacement to hold that pressure constant.

Another object is to provide a. control of this character which is susceptible-of close adjustment.

Another object is to provide a pump c'ontr'ol which is unafiected by variation in the internal forces created within the, pump. 40

Another object is to provide a pump control which is unaffected by variations in spring reg sistance.

Another object isto operate the stroke 'control motor at pressures below pump pressure.

Another object is to provide a pump control which may be adjusted during operation of the pump tooregulate the pressure created by the Another object is to provide a control which will cause the pump to respond instantly to adjustment of the control.

Another object is to provide a pump control which may be accurately adjuste'd 'by turning a single screw.

Another object is to provide a pump (control which is compact and, emcient.

Another object is to provide a control of this character with a free return resistance valve for controlling the delivery oi' fluid to the stroke changing mechanism oi' the pump.

According to the invention in its principal aspect, the stroke control motor is free from pump pressure until pump pressure reaches a predetermined maximum and then fluid is delivered under pressure to the motor to operate it.

According to another aspect of the invention, fluid is delivered to' the control motor at a pressure below pump pressure.

The invention further provides a free return resistance valve which is-interposed between the control motor and the outlet of the pump and prevents pressure fluid from reaching this motor until pump pressure has reached a predetermined maximum.

The invention is illustrated in the accompanying drawings in which the views are as follows:

Fig. 1 is a schematic drawing showing a variable displacement pump connected into a hydraulic circuit and provided with a' control in which the invention is embodied.

Fig. 2 is a central longitudinal section through the free return resistance valve shown in Fig. 1.

Fig. 3 is a central longitudinal section through a modified form of free return resistance valve.

The invention is shown applied to a variable displacement pump I which is not illustrated nor described in detail herein as it is substantially the same as the pump shown in Patent No. 1,578,233 except for the stroke changing mechanism employed.

The stroke or displacement of the pump l is varied by moving the upper end of its pendulum 2, the lower end of which is journaled upon a stationary shaft 3. The upper end of the pendulum 2 is pivoted to a control rod 4 which has one of its ends arranged in a guide 5 carried by the casing 6 of the pump I and its other end provided with a piston 'I which is fitted in a cylinder 8 also carried by the pump casing 6. The piston 'I and the cylinder 8 constitute a fluid motor for reducing the stroke of the pump upon the pump pressure exceeding a predetermined maximum.

The rod 4 has a helical compression spring 9 arranged thereon between a wall of the casing 6 and a nut u which is threaded upon the rod 4 and adjustable to vary the initial tension of the spring 9. A pendulum 2 is urged toward full stroke position by the spring 9 which holds it against a stroke adjusting mechanism ll until the pressure created by the pump reaches a pre determined maximum and then liquid acting upon the piston 1 moves the pendulum 2 toward zero stroke position against the action of the spring 9 until the pump is delivering just sufllcient liquid to maintain the predetermined maximum pressure constant.

The stroke adjusting mechanism H has been shown as simply a stop screw threaded through a stationary rib and adjustable to vary the stroke of the pump, but stroke adjusting mechanism may be employed which is operable either manually or automatically to vary the stroke of the pump and thus adjust its delivery as desired for all conditions except when the pump pressure exceeds a predetermined'maximum, such as the stroke adjusting mechanism shown in Patent No. 1,753,562 issued April 8, 1930 to John P. Ferris.

The pump l is supplied with liquid at a low "pressure by a gearpump !2 and discharges its output into a supply pipe !3 froni which liquid is supplied to the cylinder 8 through a free return resistance valve |4 whenever the pressure in the supply pipe !3 reaches a predetermined maximum.

The flow of liquid through the valve |4 is controlled by its plunger' |5 which Controls communication between an inlet chamber IS and a port l'l and between the port ll and an exhaust chamber s.

Liquid is supplied to the valve |4 through a pipe I 9 which connects the inlet chamber ll to the supply pipe |3. When the valve l4 is open, liquid is supplied to the cylinder 8 through a pipe 20, which connects the cylinder 8 to the port l'l, and liquid delivered through the pipe 20 in excess of the requirements of the cylinder 8 is exhausted through a low pressure relief valve 2! connected between the pipe 20 and a drain pipe 22 which connects the exhaust chamber |8 with the sump of the pump l.

The plunger IS is urged at all times toward open position by liquid acting upon a piston 23 which is arranged upon the end of the plunger and fitted in the leit end of the valve casing.

Liquid from the pipe !3 is supplied to the left end of the valve !4 through a branch of the pipe |9 which has a choke coil 24 connected therein to reduce the rate of flow of liquid therethrough.

The port ll is normally closed to the pipe !9 by a piston 25 which is formed upon the plunger I 5 and spaced from the piston 23 so that the pistons 23 and 25 are arranged at opposite ends of the inlet chamber !6 and prevent liquid from escaping therefrom when the plunger IS is in closed position.

The port l'l is normally open to an annular groove 26 which is formed in the periphery of the piston 25 and connected to the exhaust chamber |8 by a duet 21 which extends through the right end of the plunger !5.

The valve l4 is so arranged that the cylinder 8 and the pipe 20 are'kept flooded with liquid at all times but, as the cylinder 8 is normally open to the drain pipe 22, no pressure can be created therein until the plunger' !5 is forced to the right to close the port l'l' to the groove 28 and open it to the inlet chamber IS. consequently, the full force of the spring s is available for holding the pendulum 2 rmly against the adjusting mechanism ll and the pump is thereby preventad from vibrating under the influence of the pintle forces.

The liquid supplied to the left end of the valve |4 urges the plunger !5 to the right against a stop plate 28 which is suitably apertured to provide communication between the duet 21 and the exhaust chamber |8 and normally rests against a shoulder 29 formed in the valve caslng.

The stop plate 28 may be providedwith a convex face to engage a complementary concave face on the plunger 15 and it is urged against the shoulder 29 by a. helical compression spring 30 which is arranged within the exhaust chamber l8 between thestop plate 28 and an adjusting screw 3| threaded through the end of the valve casing and held in adjusted position by a lock nut 32. r

The liquid in the left end of the valve |4 is always at pump pressure, and the force exerted by this liquid upon the piston 23 is resisted by the spring 30 which is adjusted by the screw :I to hold the stop plate 28 against its seat until the pump essure reaches a predetermined maximum.

For the purpose of illustration, the pump I is shown as having its supply pipe l3 connected to a port-33 in a control valve 34 which has two other ports 35 and 33 arranged upon opposite sides of the port 33 and connected. respectively,

by pipes 31 and 33 to opposite ends of a hydraulic motor 33 for delivering liquid thereto to recipro-` cate its pisten 40.

Both ends oi the control valve 34 are connected to a return pipe 4l which is connected to the drain pipe 22 and may have a low pressure relief valve 42 connected therein for preventing air from entering the valve 34 and the motor 33 and for providing back pressure upon the plston 40. v

The flow of liquid through the valve 34 is controlled by its plunger 43 which is provided with a handle 44 for Operating it. When the plunger 43 is in the position shown, liquid delivered by the pump l will flow from the pipe l3 through the valve 34 and the pipe 33 to the rear end of the motor 33 and advance its pisten 40 which will expel liquid from the i'ront end oi' the motor 4 through the pipe 31 and 'the valve 34 into the return pipe 4l.

If the handle 44 is moved to the position shown in dotted lines at 45, the plunger 43 will block the ports 35 and 33 and the piston 40 will remain stationary.

If the handle 44 is moved to the position shown in dotted lines at 43, liquid will flow from the pipe' |3 through the valve 34 and the pipe 31 to the front end o'i' the motor 39 and retract its pisten 40 which will expel liquid from the rear end of the motor 39 through the pipe 38 and the valve 34 into the return pipe 4l.

The pressure createdvbythe pump l will vary in accordance with the load carried by the motor 39 and, if the motor should be subjected to a load greater than a predetermined maximum o: -ii the control valve 34 should be operated to close communication between the pipe |3 'and the motor 39, the pump pressure would rise above the predetermined maximum determined by the adjustment of the spring 30 and the liquid ,entering the left end of the valve 14 would move the 'plunger I5 against the resistance oi' the spring 30 into the position shown in Fig. 2.

The plunger |5 would first move the groove 23 out of communication with the port |1, thereby closing communication between the cylinder 3 and 'the drain pipe 22, and would then open the port |1 slightly to the chamber !6 toallow liquid. to flow through the pipe 20 into the cylinder 3 and force the pisten 1 'to the right against the resistanceof the' spring 9 andthereby move the pendulum 2 toward zero stroke position.

The pendulum 2 moves toward zero stroke position until the pump is delivering just suflicient liquid to maintain the pressure in the pipe !3 at the predetermined maximum determined by the adjustment of the spring 33.

When the pressure in the pipe l3 drops below the predetermined maximum, the spring 30 returns the plunger 15 to its initial position, thereby opening the cylinder 3 to the drain pipe 22 and allowing the spring 3 to swing the pendulum 2 against the stroke adjusting mechanism II and causing the pump to again deliver liquid at the predetermined maximum. A

As the liquid in the cylinder 3 'remains atatmospheric pressure until the valve |4 is opened and as the high pressure liquid is throttled through a restricted opening formed by the ad- Jacenkedges ot the port |1 and the pisten 23, the ;ligid enters the cylinder 3 at low pressure and acts upon the piston1 which has sumcient area to enable liquid at low pressure to compress the spring 3 and move the pendulum 2 toward zero stroke position.

.As the liquidenters the cylinder 3 at low pressure and increases in pressure only enough to overcome the resistance ot the spring 3, the pressure in the pipe |3 does notrise an appreclable amount above the predetermined maximum before the displacement of the pump has been reduced sufli'ciently to maintain the predetrmined maximum pressure constant.

The choke 24 restricts the flow ot liquid to and from the left end of the valve |4sufllciently to prevent violent movements otthe plunger I! but it is large enough to allow the passage of suflicient liquid to move the plunger il promptly and smoothly,

When the pump is Operating against a positive resistance, as by closing the control valve 34, and ,the screw 3| is turned, the pressure created by the pump will vary practically simultaneously with the movement ot the screw 3l.

The valve shown in Fig. 3 is similar in many respects to the valve shown in Figs. 1 and 2, and

like parts of the two valves and the pipes connected thereto have' been indicated by like reterence numerals. u

The flow of liquid through this valve is controlled by its plunger 41 which is held against the stop plate 23 by liquid supplied to the lert end ot the valve through the pressure pipe !3.

The plunger 41 controls two ports 43 and 49 both oi' which are connected to the cylinder 3 of the stroke changing mechanism by the pipe 20.

The port 43 is normally closed and the port 49 is normally open to the drain pipe 22 so that the cylinder 3 is i'ree !rom pressure until the plunger 41 is operated. When the pump pressure reaches a predetermined maximum, the'torce exerted by the liquid upon the left end ot the plunger 41 moves it to the right to close the port 49 and open the port 48. High pressure liquid then flows through the restricted opening formed by the edges of the piston 25 'and the port 43'and reaches the cylinder 8 at low' pressure andoperates the stroke changing mechanism as' previously. described.

The invention herein set forth is susceptible of various' modiflcations' and adaptations without departingvfrom' the scope thereoi as hereatter claimed. i

The invention is hereby claimed as follows:

1. A control-tor a variable displacement pump having mechanism for changing its stroke and a fluid motor !or operating said mechanism, comprising a resistance valve pr lided with a casing having an'axial bore communicating with a drain channel and connected to said motor and to the outlet of said pump. a spring arranged within said casing, and a valve plunger fltted in said bore for controlling the flow of fluid therethrough and normallyheld by said spring 4 i 2,oo9,eoa

cient to maintain said maximum pressure within a narrow pressure range. a pipe for directing fluid from said pump to the end of said bore to act upon the end oi' said plunger, and a choke connected into said pipe for modulating' the eflect of said fluid upon said plunger.

2. A control for'a variable displacement pump having mechanism for changing its stroke and a fluid motor for Operating said mechanism, comprising a resistance valve provided with a casing having an axial bore communicating with a drain channel and connected to said motor and to the outlet of said pump. a spring arranged within said casing, and a valve plunger fltted in said bore for controlling the flow of fluid therethrough and normally held by said spring in position to close communication between said pump and said motor and to maintain communication between said motor and said drain and subjected to pump pressure whereby it is caused to move against the resistance of said spring in response to a predetermined pump pressure to close said.

motor to saiddrain and then open it to said pump to permit fluid to flow from said pump to said motor to operate it and thereby cause said stroke changing mechanism to reduce the output of said pump until it is just suflicient to maintain said maximum pressure within a narrow pressure range, and a`relief valve connected between said resistance valve and said motor to limit the pressureof the liquid delivered to said motor. v

3. A control as deflned in claim 1, including a relief valve connected between said resistance valve and said motor to limit the pressure of the liquid delivered to said motor.

4. A control, for a pump having mechanism for varying its displacement and a fluid motor for Operating said mechanism, comprising a valve casing communicating with a drain channel and connected to said fluid motor and to the outlet of said pump, a valve arranged in said casing for controlling the flow of fluid to and 'from said fluid motor, means exerting a continuous force upon said valve for holding it in position to close communication between said fluid motor and said pump and to establish communication between said fluid motor and said drain, and a servomotor mechanically connected to said valve and hydraulically connected to said pump for ,moving said valve against said force into position to close communication between said fluid motor and said drain and to establish communication between said fluid motor and said pump upon pump pressure reaching a predetermined maximum to thereby enable said fluid motor to operate said displacement varying mechanism to reduce pump output until it is just sufiicient to maintain said predetermined pressure within a narrow pressure range.

5. A control as deflned in claim 4, including a relief'valve connected between said valve casing and said fluid motor to limit the pressure of the liquid delivered to said motor.

6. A control as deflned in claim 4, including a. choke connected between said servo-motor and said pump to limit the rate at which pump displacement may be varied.

7. A control as deflned in claim 4, including a 'elief valve connected between said valve casing and said fluid motor to limit the pressure ot the liquid delivered to said motor, and a choke connected between said servo-motor and said pump to limit the rate at which pump displacement A may be varied. x

8. A control, for a pump having mechanism for varying its displacement and a fluid motor for Operating said mechanism, comprising a valve casing communicating with a drain channel and connected to said fluid motor and to the outlet oi' said pump. a valve arranged in said casing for controlling the flow of fluid to and !rom said fluid motor, means exerting a continuous force upon said valve for holding it in position to close communication between said fluid motor and said pump and to establish communication between said fluid motor and said drain, means operable from outside said casing for adjusting said means to vary the initial force exerted thereby upon said valve, and a servo-motor'mechanically connected to said valve and hydraulically connected to said pump for moving said valve against said force into position to close communication between said fluid motor and said drain and to establish communication between said fluid motor i said pump to limit'the rate at which pump displacement may be varied.

10. A control, for a pump having mechanism for varying its displacement and a fluid' motor for Operating said mechanism, comprising a valve casing communicating with a drain channel and connected to said fluid motor and to the outlet of said pump, a valve arranged in said casing for controlling the flow of fluid to and from said fluid motor, a spring arranged within said casing and normally holding said valve in position to close communication between said fluid motor and said pump and to establish communication between said fluid motor and said drain, and a servo-motor mechanically connected to said valve and hydraulically connected to said pump for moving said valve against said spring into position to close communication between said fluid motor and said drain and to establish communication between said fluid motor and said pump upon pump pressure reaching a predetermined maximum to thereby enable said fluid motor to operate said displacement varying mechanism to reduce pump output until it is just suflicient to maintain said predetermined pressure within a narrow pressure range.

11. A control as deflned in claim 10, including an adjust-ing screw operable from outside said casing for adjusting the tension of said spring, and a positive stop for limiting the action of said spring upon said valve.

JAMES K. DOUGLAS.

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