US3522998A - Constant pressure radial piston pump - Google Patents

Description

Aug. 4, 1970 B. 1.. JOHNSON CONSTANT PRESSURE RADIAL PISTON PUMP Filed Feb. 26, 1968 3 M B a 3% m.- /7 r o 2 4 3 7 l 2 l 2 3 2 I 2 2 w m FIG.3

INVENTOR. BRUCE L. JOHNSON AGENT United States Patent O 7" 3,522,998 CONSTANT PRESSURE RADIAL PISTON PUMP Bruce L. Johnson, Ames, Iowa, assignor to Deere & Company, Moline, III., a corporation of Delaware Filed Feb. 26, 1968, Ser. No. 708,414 Int. Cl. GOSg 1/10; F04b 1/10, 49/08 US. Cl. 417-221 9 Claims ABSTRACT OF THE DISCLOSURE toward a position of zero eccentricity with the result that i the stroke of the pump pistons is shortened.

BACKGROUND OF THE INVENTION The present invention relates generally to fluid translating apparatus and more particularly to a novel constant pressure, variable displacement pump wherein the output pressure of the pump can be maintained constant and the flow rate of the pump varied independently of the speed of rotation of the pump or the prime mover therefor.

Various variable displacement pumps have been constructed in the past, but they have all had undesirable characteristics which make them ill-suited for use in todays sophisticated bydraulic systems. In one form of a prior pump, the variable displacement feature was obtained by subjecting the entire drive mechanism chamber to the pump output pressure so that the fluid pressure would hold the reciprocating pistons off of a driven cam and thereby shorten the stroke of the pistons. The main drawbacks of this pump include insuflicient control of pressure and/or response to system requirements, and power losses while the pump was in a standby or idling condition.

In another form of prior pump, the reciprocating pistons were mounted in a driven rotor for rotation therewith and a piston actuating modulating ring surrounded the pistons. Provision was made to vary the eccentricity of the ring in response to the pump output pressure. The main drawback with this pump is the problems in the valving timing which arise as the speed of rotation of the pump varies.

SUMMARY OF THE INVENTION The main object of the present invention is to provide a constant pressure, variable displacement pump which is free from the drawbacks or deficiencies of prior pumps, and is of simple construction so as to be substantially free from breakdown and capable of economic manufacture.

In general, the apparatus of the persent invention comprises a pump which utilizes a movable wall such as a piston to effect the intake and exhaust of fluid so that the quantity of fluid translated per cycle is a function of the movement of the movable wall or, in the case of a piston, the length of the stroke of the piston.

Inasmuch as it is well known in the art that pumps of this type may utilize a diaphragm or bellows as the movable wall, whenever the term piston is used in the following 3,522,998 Patented Aug. 4, 1970 summary, description, and claims, it should be construed to include any type of movable wall.

In the apparatus according to the present invention, a plurality of radially arranged cylinders are provided in a pump body and have their inner ends opening into a central drive chamber. A plurality of pistons are reciprocally mounted within the cylinders and have their inner ends projecting into the drive chamber where they ride on the surface of a circular cam member which is mounted for rotation with a driven shaft. The length of the stroke of the pistons is varied by changing the eccentricity of the cam member with respect to the driven shaft. The ca-m member is normally spring biased to a position of maximum eccentricity to cause a maximum stroke length. The pump output pressure acts on a piston which urges the cam member toward a position of zero eccentricity to shorten the length of piston stroke as the output pressure of the pump increases. Provision is also made to vary the effective force of the spring either prior to or during operation of the pump.

The apparatus according to the present invention has improved control of pressure and/0r response to system requirements, has less power losses while in a standby or idling condition, has smooth torque requirements, is economical in manufacture and is free from valving timing problems.

Further objects and advantages will appear to those skilled in the art from a reading of the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawing:

FIG. 1 is a sectional side view of a fluid translating device constructed according to the present invention and with parts which are unimportant to an understanding of the present invention broken away;

FIG. 2 is a sectional end view taken along the line 22 of FIG. 1 and with a portion broken away to illustrate hidden pieces;

FIG. 3 is a sectional side view of the cam member taken along a diameter thereof; and

FIG. 4 is a schematic view illustrating valving for the fluid translating apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in more detail to the drawing, there is shown a fluid translating apparatus 2 including a pump housing 3 and housing cover 4. Only a portion of the fluid translating apparatus is illustrated and described because the undisclosed portion is well known to those skilled in the art and forms no part of the present invention. The housing 3 includes a central drive chamber 5 which is closed by the housing cover 4. A radially arranged cylinder 6 is provided in the housing 3 and has its inner end opening into the drive chamber 5. While only one cylinder is illustrated, it should be understood that a plurality of cylinders will be spaced about the chamber. As is well known by those skilled in the art, the outer ends of the cylinders are provided with intake and exhaust valves 44 and 45 respectively for admitting and exhausting fluid to and from said cylinder-s. Also, as is conventional, a high pressure delivery line 46 leads from the exhaust valves to direct the flow of fluid from the exhaust valves out of the housing.

A piston 7 is reciprocally mounted within the cylinder -6 and has its inner end projecting into the drive chamber 5. The piston 7 is urged out of the cylinder 6 and into the chamber 5 by a compression spring 8 which acts between the outer end of the cylinder 6 and the inner end of the piston.

A drive shaft 9 is rotatably journaled in the housing 3 by a bearing member 10. The inner end of the drive shaft 9 terminates in an annular flange 11 located within the housing 3. A stub shaft 12 forms an integral part of the annular flange 111 and is positioned eccentrically with respect to the drive shaft 9. The stub shaft 12 projects forwardly from the annular flange 11 into an opening 13 provided in a mechanism housing 14. The mechanism housing 14 includes a mounting shaft 15 which is rotatably journaled in the pump housing cover 4 by a bearing member 16 so that the mechanism housing rotates with the drive shaft 9.

A piston actuating circular cam member 17 is eccentrically mounted on the stub shaft 12 between the flange 11 and mechanism housing 14. The cam member 17 includes a bore 18 which rotatably receives the stub shaft 12. The bore 18 is positioned eccentrically to the center axis of the circular cam member so that by rotating the cam member about the stub shaft 12, it is moved between a position which is concentric with respect to the drive shaft and positions which are eccentric with respect to the drive shaft. A second stub shaft 19 projects forwardly from the cam member on the central axis thereof and projects into the mechanism housing. The cam member 17 is also provided with bearings 20 and an outer race 21 which engages the inner end of the piston 7 to reduce sliding wear on the inner end of the piston.

The mechanism housing 14 is provided with a bore 22 which extends from a periphery thereof, through the central axis, to a point adjacent the opposite periphery. A piston 23 is slidably received within the closed end of the bore 22 for reciprocal movement and has a cam positioning member 24 secured to the inner end thereof. In the embodiment illustrated, the cam positioning member is of rectangular construction and has an enlarged annular end portion 25 opposite from the piston for slidably engaging the wall of the bore to guide the cam positioning member upon reciprocation. The piston 23 is biased toward the closed end of the bore 22 by a compression spring .26 located within the bore 22 and acting between the annular end portion 25 of the cam position ing member and a closure plug 27 for the open end of the bore 22.

A passageway or conduit 47 connects the delivery line and a passageway 28. The passageway 28 extends through the pump housing cover 4 to a small chamber formed by mating openings in the pump housing cover and the mounting shaft 15 of the mechanism housing. The chamber 30 is located along the axis of rotation of the mechanism housing 14. A seal 29 prevents leakage from the chamber 30 between the pump housing cover 4 and the end of the mounting shaft 15. A passageway 31 located in the mechanism housing 14 connects the chamber 30 and the closed end of the bore 22 so that fluid pressure from the pump exhaust port acts on the piston 23 to move the cam positioning member against the force of the spring 26.

The cam positioning member is provided with an opening 32 which is inclined with respect to the axis of rotation of the mechanism housing 14 and slidably receives a casing 33 whose outer surface is similarly in clined. The casing 33 has a central bore 34 which is parallel to the axis of rotation of the mechanism housing 14 and receives the stub shaft 19 which is mounted on the cam member and which projects through an opening 35 in the wall of bore 22. With the stub shaft 18 position within the casing 33, movement of the cam positioning member 24 will rotate the cam 17 about the stub shaft 12 between positions eccentric and concentric to the drive shaft. By reciprocating the casing 33 into and out of the opening 32, the efiective force of the spring 26 is varied since the spring can be compressed or released without changing the position of cam member.

Referring now to the mechanism for moving the easing 33, a setscrew 36 threadedly engages and extends through the pump housing cover 4 along an axis concentric with the axis of rotation of the mechanism housing, through the chamber 30 and into a small bore 37 which extends from the chamber 30 to the bore 22. A shaft 38 is slidably mounted in the bore 37 in abutment with the setscrew 36 and has an enlarged plate-like end 39 which bears against the end of the casing 33 to limit the movement of the casing 33 in one direction. The shaft 38 is provided with the enlarged plate-like end so the engagement with casing is not lost as the cam positioning member reciprocates within the bore 22. The casing is urged out of opening 32 and against the end of the shaft 28 by a plunger 40. The plunger 40 extends through the stub shaft 19 along the axis thereof and is biased against the casing 33 by a spring 41 which is positioned within a bore 42 in the cam member 17 and acts between the plunger and a spring retaining cap 43. If the setscrew 36 is turned out of the cover 4, the spring 41 and plunger 40 cause the casing 33 and shaft 38 to foliow the setscrew, and if the setscrew is turned into the cover 4, the spring 41 will be compressed as the casing forces the plunger into the stub shaft. Since the setscrew is positioned along the axis of rotation of the mechanism housing, the casing can be moved either during or prior to operation of the pump.

When the above-described apparatus is in operation, and if inertial forces and friction are neglected, there will be three distinct torques which will tend to rotate the cam member 17 about the stub shaft 12. The first of these torques is a spring torque supplied by the spring 26 acting on the stub shaft 19, and tends to increase the eccentricity of the cam member 17. The spring torque is inversely proportional to the amount of eccentricity of the cam member 17, and if the maximum eccentricity of the cam member 17 is limited to a relatively small amount, the spring torque will be substantially linearly related to the amount of eccentricity of the cam member.

The second torque which will tend to rotate the cam member 17 about the stub shaft 12 is a pressure torque supplied by the pump output pressure acting on the stub shaft 19 through the piston 23. The pressure torque tends to decrease the eccentricity of the cam member 17, and if the maximum eccentricity of the cam member 17 is limited to a relatively small amount, the pressure torque will be substantially directly proportional to the pump output pressure.

The third torque is a load torque and is supplied by the pump output pressure resisting the outward movement of the piston 7. The load torque is directly proportional to the product of the pump output pressure and the amount of eccentricity of the cam member 17. If the pump is rotated in a counterclockwise direction as viewed in FIG. 2, the load torque will tend to increase the eccentricity of the cam member 17.

The net torque tending to rotate the cam member 17 about the stub shaft 12 is the algebraic sum of the spring torque, the pressure torque, and the load torque. If the spring rate is chosen so that, as the amount of eccentricity of the cam member varies, the spring torque will increase or decrease in a direct relationship to and in the same amount as the decrease or increase, respectively, of the load torque at rated pressure, and the initial spring torque is made equal to the pressure torque at rated pressure, the net torque which tends to rotate the cam member 17 about the shaft 12 will be zero when the pump is operating at rated pressure. If the pump is operating at less than rated pressure, the net torque will tend to increase the eccentricity of the cam member 17. When the pump is operating above the rated pressure, the net torque will tend to decrease the eccentricity of the cam member 117.

Assuming now, for the sake of simplicity of description, that the spring torque and the load torque are a single torque which tends to move the cam member 17 to an eccentric position, and referring to this single torque as the force provided by the spring 26 on the stub shaft 19, the above-described pump will operate as follows:

Prior to operating the pump, the force of spring 26 will have moved the cam positioning member to the posi tion illustrated which in turn moved the cam member to the eccentric position as illustrated. In operation, power is delivered to the drive shaft 9 by a prime mover. Rotation of the shaft causes simultaneous rotation of the mechanism housing 14 and cam member 17 so that the cam member causes radially outward movement of the piston 7. As the cam member rotates past the piston 7, the force of spring 8 moves the piston radially inwardly. The intake stroke of the piston serves to draw fluid through the intake valve 44 and into the cylinder. As the cam member continues to rotate with the drive shaft, it will again cause radially outward movement of the piston 7. The fluid which is now in the cylinder 6 will be forced out the exhaust valve 45 to the high pressure delivery line 46. As the pump continues to operate, fluid pressure will build up in the delivery line 46. As the pressure in the line 46 builds up, the fluid will flow through the conduit or passageway 47 which connects the delivery line 46 and passageway 28, through passageway 28, chamber 30, and passageway 31, and into the closed end of bore 22 where it exerts a force on the piston 23. The fluid pressure acting on the piston 23 will move the piston and cam positioning member against the force of the spring 26 to compress the spring and rotate the cam member about the stub shaft 12 toward the concentric position. As the cam member 17 is moved toward the concentric position, the length of the piston stroke is shortened since the cam member cannot move the piston radially outward as far as it previously did and also will not allow the piston to move as far inward as it previously did. The shortened piston stroke results in less fluid flow to the exhaust port.

When the pressure of the fluid in the delivery line 46 has reached a predetermined maximum value, the pump rated pressure, the fluid pressure will have moved the cam positioning member a sufficient distance to rotate the cam member about the stub shaft 12 to the concentric position. With the cam member in the concentric position, the piston 7 will have no movement and hence no additional fluid will be supplied to the exhaust port even though the cam member continues to rotate. The pump will remain in this standby or idling condition until the pressure in the delivery line 46 drops.

When the hydraulic system supplied by the pump requires additional fluid, the pressure in the delivery line 46 drops to a value below the pump rated pressure. As the pressure in the delivery line drops, so does the fluid pressure acting on the piston 23. A decrease in pressure acting on the piston 23 allows the force of the spring 26 to move the cam positioning member so as to rotate the cam member about the stub shaft 12 to an eccentric position. The movement of the cam positioning member and the eccentricity of the position which the cam member assumes are dependent on the magnitude of the pressure drop in the delivery line 46. With the cam member again in an eccentric position, it will move the piston radially outward to supply more fluid to the delivery line to bring the fluid pressure in the delivery line back to the predetermined maximum value.

It should be kept in mind that the above description of operation holds true only when the cam member is rotated in a counterclockwise direction as viewed in FIG. 2. If the pump is rotated in a clockwise direction as viewed in FIG. 2, the position of the cam member 17 will not be under the control of the torques as explained above since the load torque would not tend to increase the eccentricity of the cam member 17.

Should it be desired to vary the pump rated pressure or the predetermined maximum value of the fluid pres sure in the delivery line, it is only necessary to adjust the setscrew. Adjustment of the setscrew has the effect of changing the effective force of the spring 26 which in turn changes the value of the pressure which is required to act on the piston 23 to move the cam member to the concentric position.

I claim:

1. In a fluid translating apparatus including a housing having a plurality of radially arranged cylinders having their inner ends opening into a central drive chamber, a plurality of pistons reciprocally mounted in said cylinders and having inner ends projecting into said central chamber, valve means for admitting and exhausting fluid to and from the outer ends of said cylinders, and outlet means communicating with said exhaust valve means, the improvement comprising: a drive shaft projecting into said chamber, an eccentric stub shaft mounted on the inner end of said drive shaft, a circular cam member eccentrically mounted on said stub shaft for rotation with said drive shaft and rotation about said stub shaft between positions eccentric and concentric to the drive shaft, said circular cam member engaging the inner ends of said pistons, a mechanism housing mounted in said firstmentioned housing concentrically to said drive shaft for rotation therewith, a position controlling member mounted for reciprocal movement in said mechanism housing along a line radial to the axis of rotation of said mechanism housing, and a second stub shaft mounted on the axis of said circular cam member extending into an opening pro vided in said position controlling member whereby reciprocal movement of said position controlling member rotates said cam member about said first-mentioned stub shaft between concentric and eccentric positions.

2. A fluid translating apparatus as set forth in claim 1 in which said first mentioned stub shaft projects into an opening provided in said mechanism housing to thereby transmit the rotary motion of said drive shaft to said mechanism housing.

3. A fluid translating apparatus as set forth in claim 1 in which said position controlling member is normally biased in a direction to rotate said cam member to an eccentric position by a first force producing means and is urged in an opposite direction by a second force producing means whereby the position of said position controlling member and said cam member is dependent on the forces of said first and second force producing means.

4. A fluid translating apparatus as set forth in claim 3 in which said second force producing means is responsive to fluid pressure in said outlet means whereby the position of said cam member is dependent on the fluid pressure in said outlet means,

5. A fluid translating apparatus as set forth in claim 3 in which said second force producing means includes a fluid pressure responsive means slidably mounted in a chamber and acting on said position controlling member, and passage means connecting said chamber and said outlet means whereby the position of said position controlling member and said cam means is dependent on the fluid pressure in the outlet means.

6. A fluid translating apparatus as set forth in claim 3 wherein said first force producing means includes a spring means acting on said position controlling member.

7. A fluid translating apparatus as set forth in claim 6 wherein the opening provided in said position controlling member is inclined with respect to the axis of rotation of said mechanism housing, a casing having an outer surface which is inclined with respect to the axis of rotation of said mechanism housing is slidably and reciprocally received within sad inclined opening, the stub shaft on said cam member is slidably received within a bore provided in said casing, and including means to vary the position of said casing within said inclined opening 7 While said mechanism is rotating whereby the effective force of said spring means may be varied while said apparatus is running.

8. A fluid translating apparatus as set forth in claim 7 wherein said second force producing means is responsive to fluid pressure in said outlet means whereby the position of said cam member is dependent to the fluid pressure in said outlet means.

9. A fluid translating apparatus as set forth in claim 8 wherein said means to vary the position of said casing includes a spring loaded plunger mounted within the stub shaft on said cam member and having an and projecting therefrom and biasing said casing in one direction, and an adjusting screw means extending along the axis of rotation of said mechanism housing and bearing against said casing to normally prevent said casing from moving under the force of said plunger.

References Cited UNITED STATES PATENTS Dunn 103162 Peterson 10338 Kraus 103-38 Thompson l03l61 Holden et a1. l033 8 Cutler 74--5 7 1 Entwistle 103161 Balaban 74-571 Allen 10338 McFarland 74571 US. Cl. X.R.

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