US2754806A - Hydraulically controlled variable stroke pump - Google Patents

Description

July 17, 1956 F. D. FUNSTON 2,754,806

HYDRAULICALLY CONTROLLED VARIABLE STROKE PUMP Filed Feb. 29, 1952 TO RESERVOIR 2g I 26 9 Z9 41 20 Z6 30 30 a 2/ \J 1' 4 m our 5/ I INVENTOR. F172: F. D. Funsfon AT TORNE Y United States Patent HYDRAULICALLY CONTROLLED VARIABLE STROKE PUMP Frederick D. Funston, Tujnnga, Calif., assignor to Bendix Aviation Corporation, North Hollywood, Calif., a corporation of Delaware Application February 29, 1952, Serial No. 274,138

2 Claims. (Cl. 121-41) This invention relates to a variable volume, constant pressure, piston type pumps in which the stroke of the piston is varied in response to the output pressure.

An object of the invention is to provide a practicable and relatively quiet pump of the type mentioned, capable of operating efficiently at relatively high pressures.

Another object is to provide smooth and positive variation of the stroke of a high pressure piston pump in response to variation in output pressure.

Other more specific objects and features of the invention will appear from the description to follow of a preferred embodiment of the invention.

Briefly, my pump is of the piston type having a piston reciprocated by a crankshaft through an articulated connecting rod linkage whereby the stroke can be varied. The linkage is adjusted by a hydraulic motor piston relatively powerful as compared to the stresses applied to the linkage by the reaction of the pump piston, and the position of the motor piston is determined by a relatively small spring-biased pressure responsive valve exposed to the output pressure of the pump.

A complete understanding of the invention may be had from the following detailed description with reference to the drawing, in which:

Fig. 1 is a side elevation of a 3-cylinder pump incorporating the invention.

Fig. 2 is a vertical cross-secti0n in the plane II-II of Fig. 1.

Fig. 3 is a detail cross-section in the horizontal plane Ill-III of Fig. 2 and Fig. 4 is a detail vertical cross-section corresponding to a portion of Fig. 2 but showing a different stroke adjustment.

Referring to Figs. 1 and 2, the pump therein disclosed comprises a base formed in two sections 11 and 12 for cenvenience in manufacture and repair. Standards 13 and 14 rising from opposite ends of the upper base section 11 rotatably support a drive shaft 15 which is shown as having a drive gear 16 on one end. The shaft 15 carries three cranks in the form of eccentrics 17, 17a, 17b associated with the three cylinders of the pump. Three connecting rods 18, 18a, 18b are mounted on the respective eccentrics 17, 17a, 17b.

Referring to Fig. 2, the connecting rod 18 associated with the rightmost cylinder (taken with reference to Fig. 1) is pivotally connected by a pin 19 to the upper end of a link 20 which is pivotally connected by a pin 21 at its lower end to the upper end of a pump piston 22 which is reciprocable in the pump cylinder 23. The connecting rod 18 is also pivotally connected by the pin 19 to one end of a link 24, the other end of which is pivotally connected by a pin 25 to one end of a bell crank lever 26 which is fulcrumed to a shaft 27 supported at its opposite ends in the standards 13 and 14 respectively. The outer end of the other arm of the bell crank lever 26 is connected by a pin 281 to one end of a link 28, the other end of which is pivotally connected to a cross member 29 which is seice cured to the upper end of a piston rod 30 which is secured at its lower end to a piston 31 which is reciprocable in a control cylinder 32 formed in the base 10. The opposite end of the cross member 29 is connected to one end of a link 28a, the other end of which is connected by a pin 271 to one arm of a second bell crank lever 26a, the other arm of which is connected to the link 24a associated with the middle connecting rod 18a. The bell crank lever 26a is formed integrally with a hub 301 rotatable on the shaft 27, and with an arm 26b, the outer end of which is pivotally connected to the link 24b associated with the left connecting rod 1812.

Each of the pump cylinders 23 is provided with an inlet valve 34 connecting it to an inlet manifold 35, and with an outlet valve 36 connecting it to an outlet or pressure manifold 37. Each reciprocation of a pump piston delivers to the outlet manifold a volume of fluid dependent upon the stroke of the piston, and the strokes of the pistons are automatically lengthened to increase the output when the pressure is low, and shortened to decrease the output when the output pressure is high. The strokes are determined by the positions of the bell crank levers 26, which positions are in turn determined by the position of the control piston 31.

Thus it will be observed from Fig. 2 that the link 24 must rotate about its pin 25, and that the path of movement of the pin 19 in response to rotation of the eccentric 17 is an are centered at the pin 25. This arcuate motion of the pin 19 is transmitted by the link 20 to the pump piston 22. When the bell crank lever 26 is in the position shown in Fig. 2 the arcuate movement of the pin 19 produces movement of the pump piston 22 through a substantial stroke. However, when the bell crank lever 26 is rocked counterclockwise into position to make the axis of the pin 25 coincident with the axis of the pin 21, as shown in Fig. 4, the arcuate movement of the pin 19 produces no movement of the pump piston 22.

It will be observed that the link 24 and pin 25 constitute a guide means guiding the pin 19 for arcuate motion about the pin 25, and they are defined as guide means in the claims.

The position of the control piston 31 is determined by pressure fluid admitted thereabove or therebelow from the pressure manifold 37 under the control of a valve 40 slidable in a cylinder 41 formed in the control piston rod 30. Movement of the valve 40 causes the piston 31 to move in the same direction, and the valve is urged downward by a spring 42 and upward by the fluid pressure in the fluid manifold 37.

Thus the piston 31 divides the cylinder 32 into an upper chamber 32a and a lower chamber 32b. The upper chamber 32a is connected to ports 43 in the valve cylinder 41, and the lower chamber 32b is connected to ports 44 in the valve cylinder. The valve 40 has three lands 49a, 40b, and 400, defining with the valve cylinder an exhaust chamber 40d and a pressure chamber 40:2. The exhaust chamber 40d is always in communication with a passage 45 in the piston rod 30 which connects to the upper open end portion of the valve cylinder 41. The pressure chamber 40e is communicated by a passage 46 in the valve with the lower end of the valve cylinder 41 which opens into a chamber 47 in the base 10 below the cylinder 32 and separated from the cylinder by a cylinder lower end wall member 48. Chamber 47 is connected to the pressure manifold 37 by a passage 37a so that it is filled with fluid at the outlet pressure. This pressure acts on the lower end of the valve 40 to urge it upwardly in opposition to the constant downward force produced by the spring 42 which is compressed between the cylinder lower wall member 48 and a disc 50 secured to an extension 40) on the lower end of the valve 40. A spider 40g on the extension 40) engages a stop ring 51 in the piston rod 30 3 to limit downward movement of the valve with respect to the piston rod.

The pump operates as follows. As shown in Fig. 2, the parts are in the position they occupy when the outlet pressure in the manifold 37 and the chamber 47 is at a low value. Under these conditions, the force of the spring 42 overcomes the pressure acting on the valve 40 to urge it upwardly, and the valve occupies its lowermost position with respect to the piston rod 30, in which the spider 40g rests on the retaining ring 51. The spider and retaining ring therefore transmit the force of the spring 42 to the piston rod 30 which moves into its lowermost position in which the control piston 31 is in the lower end of its stroke. At this time the chamber 32b below the control piston 31 is connected by the port 44, the valve chamber 40d, and the passage 45, to the open upper end of the valve cylinder 41. At the same time the upper chamber 32:: of the control cylinder is connected through the port 43, the valve chamber 40e, and the valve passage 46 to the chamber 47 so that Whatever pressure exists in the chamber 47 is acting against the upper face of the piston 31 to hold it down, in aiding relation to the force of the spring 42. The pressure in the chamber 4'7 acts always against the lower end of the piston rod 30 to urge 1t upwardly, but the effective area of this rod is less than the area of the upper surface of the piston 31, so that the pressure in chamber 32 overcomes the effect of the pressure in chamber 47 on the piston and piston rod assembly.

Under the conditions described, the bell crank lever 26 holds the linkage connecting the eccentric 13 to the pump piston 22 in position for maximum stroke, so that the pump delivers its maximum capacity into the outlet manifold 37. When the pressure in the outlet manifold 37 rises to a predetermined value, this same pressure in the chamber 47 becomes efiective to urge the control valve 40 upwardly and compress the spring 42. Upward movement of the valve carries the land 40b thereon across the port 43 to cut off the connection of pressure fluid to the upper chamber 32a and block this chamber so that the piston 31 is locked in position. At the same time, the land 40a on the valve blocks the port 44 to block flow of fluid into or out of the lower chamber 3%. A further increase in pressure raises the valve 40 until the land 4011 clears the port 43, and the land 40a clears the port 44. This permits fluid to discharge from the port 43 into the low pressure valve chamber 400., and admits fluid from the chamber 47 through the lower end of the valve cylinder 1 into the port 44. The pressure in the lower pump chamber 32b is sufficient to elevate the control piston 31, thereby shifting the linkage to reduce the stroke of the pump piston 22. As the pressure continues to increase, the stroke of the pump is reduced until it finally reaches Zero value, when the axis of the pin 25 is coincident with the axis of the pin 21.

it will be observed that the piston 31 has a follow-up action with respect to the valve 40. Thus as soon as the piston 31 rises in response to an upward movement of the valve 40 to carry the land 40b above the port 43, the piston then rises relative to the valve and cuts otl the port. The reverse action takes place when the pressure is falling and the valve 40 moves downward in response thereto.

An important feature of the invention is that whenever the follow-up movement of the piston 31 closes the ports 43 and 44, the fluid in the chambers 32a and 32b is blocked from escape, thereby locking the piston 31 positively in position, so that it cannot be shifted even to a slight extent by the reaction forces applied thereto from the pump linkage. This prevents the linkage from yielding with each cycle of the pump piston 22.

The pump, as disclosed, is intended to be located in a sump or reservoir so that fluid discharged through the open upper end of the valve cylinder 41 will return to the sump. However, if some other arrangement is desired, the upper end of the passage 41 can be connected to a return line by a flexible hose.

Although for the purpose of explaining the invention, a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

I claim:

1. Pressure-responsive stroke-adjusting means for a variable-stroke pump having a stroke-controlling element oscillatable through a fixed path and an outlet passage, said means comprising: a hydraulic motor having a motor cylinder and a piston reciprocable therein and adapted to be coupled to said stroke-controlling element of said pump for actuating it; valve means for said motor com prising a hollow piston rod extending from said piston member through both ends of said motor cylinder and defining a valve cylinder; a motor port in said valve cylinder extending through said piston rod to said motor cylinder on one side of said motor piston; a piston valve slidable in said valve cylinder and having lands defining with said valve cylinder a pressure chamber and an exhaust chamber; passage means communicating said exhaust chamber with one end of said hollow piston rod constituting an exhaust duct; passage means communicating said pressure chamber with the other end of said hollow piston rod; means defining a closed chamber beyond said motor cylinder and adapted to be connected to said output passage of said pump into which the other end of said hollow piston rod projects, whereby the pump output pressure is applicd to the other end of said valve cylinder and said valve piston to urge the latter toward said one end of said piston rod; spring means urging said valve piston toward said other end of said piston rod; said valve cylinder port and said valve piston chambers being so longitudinally disposed relative to each other that in a neutral position of the valve'piston with respect to the motor piston said port is intermediate said exhaust and pressure chambers defined by said pison valve, and movement out of said neutral position in either direction connects said port to that one of said chambers to produce following movement of the motor piston and restore it to neutral position with respect to said valve piston; and means for conveying fluid to and from said motor cylinder on the other side of said motor piston.

2. Apparatus according to claim 1 including inter-engaging stroke-limiting means on said valve piston and motor piston member, respectively, whereby said spring means is effective to move said piston member into position producing maximum stroke of said pump in the absence of opposing pressure forces.

References Cited in the file of this patent UNITED STATES PATENTS 1,292,457 Hall Jan. 28, 1919 1,418,952 Martin June 6, 1922 1,957,556 Schelling May 8, 1934 2,044,064 Dake June 16, 1936 2,070,935 Traut Feb. 16, 1937 2,303,597 Adelson Dec. 1, 1942 2,563,939 Kishline Aug. 14, 1951

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