US3004492A

US3004492A - Piston pumps

Info

Publication number: US3004492A
Application number: US837661A
Authority: US
Inventors: Francis E Norlin
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1959-09-02
Filing date: 1959-09-02
Publication date: 1961-10-17
Anticipated expiration: 1978-10-17

Description

Oct. 17, 1961 F. E. NORLIN 3,004,492

PISTON PUMPS Filed Sept. 2, 1959 United States Patent F Filed Sept. 2, 1959, Ser. No. 837,661 3 Claims. (Cl. 103-37) This invention relates to pumps in which a plurality of pump cylinders are arranged in circular series parallel to each other and to the axis of the drive shaft, each of the cylinders having disposed therein a piston or plunger actuated by a cam or swash plate fixed on the drive shaft.

Pumps of the type forming the subject matter of this invention are provided with means to vary the displacement thereof, such means including means responsive to the discharge pressure of the fluid from the cylinders, as well as means for allowing the regulation of the pump discharge flow. Such means are desirable in pumps which are constantly running, as for example, those used in aircraft installations and where the displacement requirements vary over a range from a specified maximum to zero value. The structure forming the subject matter ofthe instant application includes a variance of the means for accomplishing the desired results described in copending United States applications, S.N. 573,543, filed March 23, 1956, entitled Variable Displacement Hydraulic Pump, now abandoned; S.N. 598,718, filed July 18, 1956, entitled Pump, now Patent No. 2,930,- 321; SN. 662,030, filed May 28, 1957, entitled Variable Displacement Hydraulic Pump, now Patent No. 2,943,- 574. In each of the aforementioned co-pending applications a spring operated valve means located within the piston is used in order to vary the displacement of the pump. This means, being spring actuated is quite feasible at comparatively low speed operation but contains an inherent drawback in high speed operation in that the spring may not be capable of functioning at the number of cycles necessary for optimum pump operation.

Therefore, itis the primary objective of this invention to provide an improved variable displacement pump of the type incorporating a plurality of circularly arranged cylinders having pistons therein actuated by means of a cam or swash plate, which will function satisfactorily at extended high speed operation.

A more particular object of this invention is to provide the above described pump with valve means which are .not dependent upon spring forces and satisfactory for high speed operation.

The pump, which forms the subject matter of the instant application, includes a plurality of pistons, each having an open end cavity therein, a flapper valve means located at the open end of each piston which is so constructed and arranged as to close the open end of the cavity during the discharge stroke of each piston. Pushrod means is located within the open ended cavity of each piston and operatively associated with each flapper type valve was to hold open the flapper valve during at least a portion of the piston discharge stroke in response to the pump discharge pressure, which pressure is effective toregulate the position of said pnshrod means. Fluid motor means, including a pilot valve responsive to pump discharge pressure, varies the position of a circular plate to regulate the travel of the pnshrod means within the piston cavity.

Otherv and more particular objects, advantages and uses of this invention will become apparent from a reading of the followingspecification taken in connection with the accompanying drawing which, forms a part thereof and wherein the single figure is a segmental and broken-away, axial sectional view of a portion of a fluid 3,004,492 Patented Oct. 17, 1961 2 v pump incorporating the preferred embodiment Of' this invention.

Referring now to the drawing, there is illustrated a pump, generally indicated at 10, having a housing comprising a body 11 and a cover 12. The cover has an inlet port 13 and an outlet port 14 which are in the form of tapped ports into which suction and discharge pipes or hoses (not shown), may be aflixed. The body 11 and cover 12 are connected by means such as bolts or the like (not shown).

A cylinder assembly is clamped between a shoulder 15 in the cover 12 and a shoulder 16 in the body 11, and the cylinder assembly is composed of a cylinder barrel block 17 and a guide block 18. The block 17 and 18 are annular in form and define with the cover 12 an inlet chamber 19 which communicates with the inlet port 13 by way of passage 20 formed in the cover 12. The cylinder barrel block 17 defines with the cover 12 a discharge chamber 21 which communicates with the outlet port 14 by Way of a passage 22 formed in the cover 12.

The cylinder barrel block 17 is bored through to form a plurality of radially arranged cylinders 23, and is formed to define with the block 18 inlet passages 24 communicating with the cylinders 23. The guide block 18 is bored through as at 25, the guide block bores being of the same diameter and in alignment with the cylinders. Each cylinder 23 has a discharge valve 26 associated therewith, seated by means of a coiled compression spring 27 against the outer face of the cylinder barrel block 17. The discharge valves are guided in pockets 28 formed in the cover 12, and they are disposed within the discharge chamber 21, as illustrated.

A piston or plunger 29 is slidably received in each of the cylinders 23 and extends through the co-extensive guide block bore 25 and the block member 18. Each piston 29 is provided .with an open ended cavity 30 which has an opening 31 at one end thereof adjacent the associated discharge valve 26; and an axially elongated inlet port 32 which is in at least partial communication with the pump inlet chamber 24 during the entire piston cycle.

"A conventional swash plate or cam is provided for reciprocating the piston or plunger 29 between their suction and discharge positions in the customary manner.

A flapper valve generally indicated at 33 is composed of a substantially circular disc member 34, which is adopted to seat on the flat surface 35 of each piston 29, and isheld in position by a retainer 36 affixed at the open end 31 of the cavity 30 in the piston 29 by some appropriate method such as turning. The retainer is constructed so as to have a plurality of extended members 37 which are bent radially inwardly in such a manner .as to limit the axial movement of the disc member 34.

Fluid is allowed to pass between the extended members 36 when the disc member 34 is forced to the limit of its axial travel as will be herein later described.

A hydraulically actuated pnshrod generally indicated at 38 has a central, substantially cylindrical portion 39,

a first axially extending portion 40 in contact with pump discharge pressure through fluid motor and through passage 43 in the piston body. A second axially extending portion 41 is directed towards the flapper valve 33 in such a way as to prevent the flapper valve from seating on the piston head during at least a portion of the piston discharge stroke when the pnshrod is sufliciently moved by the pump discharge pressure acting on the first axially extending member. A sleeve 44 is circumferentially mounted about piston 29 and is pinned to the pnshrod 38 by means of a pin 45 which passes from the sleeve through the elongated piston cavity inlet 32 and through the pnshrod 38.

Fluid motor means generally indicated by the letter M, including a pilot valve 47 being manually adjustable 3 byrneans of an adjustment screw 48 which varies the effectiveness of the pilot valve return spring 49, is included in the subject pump and is adequately described in any of the aforesatid co-pending applications. A. circular plate 50 of sutficient diameter to allow suitable contact ofa plate surface 51 with each sleeve '44 of" the piston on the sleeve surface 46, is slidably mounted on a cylindrical extension 52 of the fluid motor M and is urged against a shoulder 53 by a plate return spring 54. The related function of the above mentioned elements will be later herein described The following description sets forth the operation of the pump, described with reference to one of the plurality of pistons, it being understood that the operation of all the pistons is the same.

Assuming the cam or swash plate to be rotating, the piston 29 will be axially reciprocated'within the cylinders 23 between its suction and discharge positions. Fluid from a suitable source will flow through the inlet 13, into the passage 20 and into the chamber 19, through the passage 24 and into the piston cavity 30. During the suction stroke of the piston, fluid within the piston cavity 30 will exert a force on the flapper valve disc 34 causing it to unseat, allowing fluid to flow around the disc through the space between the extended members 37 and into the cylinder 23 in advance of the piston. As the piston returns on the discharge stroke the fluid within the cylinder '23 is compressed, forcing the flapper valve disc '34 to reseat' on the piston head, thus shutting off further fluid flow from the inlet side of the valve. As the piston continues on its discharge stroke, the fluid continues to be compresseduntil the pressure of the fluid is suflicient to overcome the force of spring 27 acting on valve 26, and valve 26 is forced open and the fluid is discharged to the chamber 21.

The discharge chamber is in communication, by appropriate passage means, with the end of the first axially extending portion 40, and as thepressure in the discharge chamber increases, the pressure is transmitted to the end of member 40forcing the pushrod 38 in the direction of the flapper valve 33. When the pushrod has been moved a suflicient distance, it contacts the disc member 34 by means of the second axially extending portion 41. The pushrod 38 remains in contact with the disc member 34 tending to hold it open, preventing its seating during at least a portion of the piston discharge stroke. The length of time that the pushrod acts on the fluid valve varies according to the position of the discharge pressure acting on the end of the first axially extending portion 40. In this manner the fluid in the cylinder in advance of the piston is allowed to return to the inlet side of the valve 33 for a portion of the discharge stroke, which accordingly decreases the volume of fluid in the cylinder and ultimately the discharge flow.

As the same time and in a similar manner, the fluid motor M, including the pilot valve 47 is placed in'communication with fluid discharge pressure. The effect of the fluid pressure actuating the fluid motor M -is to force the circular plate 50 to the left'in opposition to the circular plate return spring 54. Since, as previously stated, the circular plate is of suflicient diameter to contact the sleeve 44 pinned to the pushrod 38, in the normal position, the pushrod is restrained from any significant movement towards the valve 33 so that the pump op-- crates at near maximum discharge flow. As the fluid pressure increases,'however, the fluid motor M forces tor forces the circular plate 50 to its limit towards the left, the pump discharge flow of drops ultimately to zero.

Thus through the action of the pushrod means 38 working in conjunction with the flapper valve 33 and the use of the fluid motor controlled by the valve, which is operable to position the circular plate 50, the pump may be continuously operated at varying discharge flows as required under spectific circumstances.

In high speed operation, the pistons of pumps of the general type herein described have a tendency to rotate within the cylinder. In the pumps of this type, preceding the one herein disclosed, the ability of'the piston to rotate freely has been prevented by the specific means used in operating the valve means Within the piston. In the present invention the only mechanical contact made between the piston and the outside means, that is the circular plate, is the contact of the plate surface 51 with the surface 46 of the sleeve 44 which circumvents the piston. Therefore, the piston 29 can freely rotate within its respective cylinder. I

While this invention has been described in connection with a certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation, and the scope of this invention is defined solely by the appended claims which should be construed as broadly as the'prior art will permit. I

What is claimed is:

1. In a positive displacement pump of the type having a casing, an inlet, an'outlet a plurality of circularly arranged parallel pistons in said casing, swash plate means for reciprocating said pistons so as to provide each piston with a suction stroke and a discharge stroke, an open ended cavity in the body of each piston, said cavity being in communication with said pump inlet; means defining a flapper valve consisting of a substantially circular disc retained at the open end of each piston in such a manner as to allow fluid from said cavity to bypass said valve means during the suction stroke of said piston, and to seat on said piston during the discharge stroke of said piston so as to prevent fluid from returning to the piston cavity; hydraulically actuated stroke varying means'comprising a central portion slidably and rotatably mounted within said cavity, a first axially extending member attached to said ,central portion in contact with said pump, and a second,

opposite, axially extending member being adapted to contact said flapper valve during at least a portion of said pump discharge stroke when the pressure at said outlet is sutflcient to position said stroke varying means against said flapper valve, holding itopen; a sleeve slidably and coaxially mounted about said piston and attached to said central portion of said stroke varying means; fluid motor means including an axially movable spring loaded, substantially circular plate, connected with a source of pump discharge pressure and responsive thereto; said motor means being operable to effect the position of said plate which is so constructed and arranged as to contact said sleeve and thereby regulate the effectiveness of said stroke varying'means in order that a constant discharge flow'is maintained as desired.

2. Ina piston displacement pump of the type having a casing, an inlet, an outlet, a plurality of circumferentially arranged parallel pistons disposed in said casing, swash plate means for reciprocating said piston whereby each piston makes an intake stroke and a discharge stroke,

means defining an open-ended cavity in the body of each pitson, said cavity being in communication with the pump inlet; means for varying the effectiveness of the discharge stroke of each piston for therebyvarying the output of said pump; said last named means comprising valve means on each said piston effective to be moved between a seat and unseat position to open and close the open end of said open-ended cavity the body of each said piston, a valve retaining means for holding said valve in position relative to the open end of said open-ended cavity, first means slidably retained in said piston cavity operatively associated with said valve means in communication with, and responsive to the pressure at said outlet whereby said first means is moved Within said piston cavity to unseat said valve means, and second means, also in communication with and responsive to the pressure at said outlet, said second means being further in communication with said first means whereby the position of said first means is determined by the position of said second means such that said first means unseats said valve means during a portion of the piston discharge stroke to regulate the effective discharge stroke of each said piston.

3. In a piston displacement pump of the type having a casing, an inlet, an outlet, a plurality of circumferentially arranged parallel pistons disposed in said casing, swash plate means for reciprocating said pistons whereby each piston makes an intake stroke and a discharge stroke, means defining an open-ended cavity in the body of each piston, said cavity being in communication with the pump inlet; means for varying the efiectiveness of the discharge stroke of each piston for thereby varying the output of said pump; said last named means comprising valve means on each said piston eifective to be moved between a seat and unseat position to open and close the open end of said open-ended cavity in the :body of each said piston, a valve retaining means for holding said valve in position relative to the open end of said open-ended cavity, first means consisting of a push rod having a central portion slidably retained in said cavity, a first axially extending member attached to said central portion in communication with, and responsive to the pressure at said outlet, and a second axially extending member attached to said central portion operatively associated with said valve means whereby axial movement of said push rod unseats said valve means, and second means, also in communication with and responsive to the pressure at said outlet, said second means being further in communication with said first means whereby the position of said first means is determined by the position of said second means such that said first means unseats said valve means during a portion of the piston discharge stroke to regulate the elfect-ive discharge stroke of each said piston.

References Cited in the file of this patent UNITED STATES PATENTS 1,682,736 Berry Sept. 4, 1928 2,005,008 Schaer June 18, 1935 2,385,784 Baker Oct. 2, 1945 FOREIGN PATENTS 1,125,458 France July 16, 1956