JP2003139046A - Axial piston pump for supplying fluid to counterbalance of rocker cam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for supplying the working pressure fluid to a rocker cam/rocker cradle joint part fluid pocket to dispense with supplying the fluid from a piston shoe to the rocker cam, as it is complicated to balance the piston shoe when the working pressure fluid of an axial piston pump is supplied to the fluid pocket through the piston shoe, a thrust face and the rocker cam, and the force corresponding to the pumping force added to the rocker cam/rocker cradle joint part is supplied. SOLUTION: In this rocker cam-type variable delivery axial piston pump 10, the working pressure fluid supplied to a pump housing 12 is passed through fluid passages 86, 88, 92, 96 formed in the rocker cam 38, and supplied to a pair of counter balancepockets 72, 74 formed on the rocker cam 38.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable displacement axial piston pump having a rocker cam pivotally mounted on a rocker cradle of a pump housing, thereby changing the capacity of the pump. Such a pump has a rotatably mounted pump barrel, which includes a plurality of longitudinal bores, each bore containing a pump piston. Each piston has a shoe pivotally attached to the head end projecting from the barrel and held against a thrust surface formed on a rocker cam. The prime mover rotates the barrel to reciprocate the piston,
This causes the pump fluid to slide on the thrust surface as a piston shoe. The pump capacity is determined by the angle of the rocker cam thrust surface. If the rocker cam is centered or off-stroke, the thrust surface is perpendicular to the piston axis and does not reciprocate. If the rocker cam is not centered or on-stroke, the thrust surface will be angled relative to the end of the shoe and the piston will reciprocate as the barrel rotates.

[0002]

2. Description of the Related Art As described in U.S. Pat. No. 3,967,541, a rocker cam can be rotated to change a pump displacement by a rotary servo control fluid motor.
Alternatively, as disclosed in the present application, the pump can be placed on-stroke by a spring that biases a rocker cam, such as is commonly used in pressure-compensated pumps, to a full on-stroke position. One type of pressure compensated pump is disclosed in U.S. Pat. No. 4,289,452.

During operation of the axial piston pump, the force generated by pumping the working pressure fluid is transmitted to the joint between the rocker cam and rocker cradle via the piston and thrust surface. As the working fluid pressure increases, the pumping force applied to the rocker cam / rocker cradle interface increases. To overcome pumping forces at the rocker cam / rocker cradle interface, fluid pockets are formed in either the rocker cradle or the rocker cam. Working pressure fluid is supplied to the fluid pocket through the piston shoe, thrust surface and rocker cam to provide a force that balances the pumping force applied to the rocker cam / rocker cradle interface. The balancing forces greatly reduce the forces with which pressure compensation control or rotary servo control must be able to make changes to the pump displacement.

Because balancing piston shoes is complex, it is necessary to provide a means for supplying working pressure fluid to the rocker cam / cradle interface fluid pocket so that there is no need to supply fluid from the piston shoe to the rocker cam. Is desirable.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide an axial piston pump for pumping a fluid at a set working pressure. A housing, a barrel rotatably attached to the housing, a plurality of bores in the barrel, a piston attached to each of the bores for reciprocal movement, and an end of each of the pistons. A shoe, a rocker cam support within the housing, and pivotally attached to a complementary arcuate bearing surface formed on the rocker cam support,
A pair of spaced rocker cams having arcuate bearing surfaces, a thrust surface of the rocker cam, and the shoe sliding on the thrust surface when the barrel is rotating, and the thrust surface of the rocker cam. A holddown for clamping the piston shoe to such thrust surface such that the piston reciprocates within each bore when is at an angle with the barrel axis; and each rocker cam bow. A counterbalanced fluid pocket formed in the surface of the bearing, a first fluid path formed in the housing and in communication with a source of working pressure fluid for directing working pressure fluid to one of the counterbalanced fluid pockets, Formed in a rocker cam to communicate one and the other of said counterbalance fluid pockets, Thus, the working pressure fluid supplied from the first fluid path to one of the counterbalance fluid pockets via the second fluid path is supplied to the other of the counterbalance fluid pockets via itself. A second fluid path is provided to provide an axial piston pump.

[0006]

In order to achieve the above object, according to the present invention, there is provided a rocker cam which can be pivotally mounted to a cam support or a cradle as shown in FIGS. A pressure compensation type variable displacement axial piston pump 10 is provided. It will be appreciated that the pump 10 now includes a central housing 12 having a mounting pilot end 14 at one end and a port cap 16 at the other end. Bolts 17 connect the port cap 16 to the housing 12.

The housing 12 defines a cavity that houses a rotatable barrel 18 mounted on a drive shaft 20. The inner end of the drive shaft 20 is supported by a bearing 22 attached to the port cap 16. Drive shaft 20
Is a bearing 24 mounted in the housing 12.
However, it has a spline drive end 26 that is also supported and projects out of the housing 12.

The barrel 18 has a plurality of bores 28 that are equidistantly spaced from each other on the circumference of a circle around the axis of rotation. Each bore 2
8 includes a piston 30 having a spherical head 32. The shoe 34 is swed onto the head 32 of the piston 30 so that it can rotate about the piston end.
ge) has been done. Each shoe has a flat thrust or swash plate surface 36 formed on the surface of a pivotal rocker cam 38 utilizing a conventional shoe retainer assembly of the type described in detail in U.S. Pat. No. 3,904,318. It is urged against.

Referring to FIGS. 2-6, a rocker cam 38 includes a rocker cam support or cradle 44 formed on the mounting pilot end 14 within the housing 12.
It will be appreciated that it has a pair of arcuate bearing surfaces 40 that are received by complementary arcuate bearing surfaces 42 having. The rocker cam 38 rotates about a fixed shaft perpendicular to the rotation shaft of the barrel 18 to change the capacity of the pump 10. During operation, a prime mover (not shown) attached to the spline drive end 26 is mounted in the housing 12 within the drive shaft 2
Rotate 0 and barrel 18. When the thrust surface 36 of the rocker cam 38 is perpendicular to the rotation axis of the barrel 18,
The rotation of the barrel 18 causes the shoe to slide on the surface of the thrust surface 36, but since the piston 30 does not reciprocate within the bore 28, no pumping action will occur. In other words, the thrust surface 36
Is perpendicular to the axis of drive shaft 20, the pump is in the position of maximum fluid capacity. Since the rocker cam 38 and the thrust surface 36 are inclined from this position, the piston 30
Will reciprocate within the bore 28 as the shoe 34 slides over the thrust plate surface 36. When the piston 30 moves into the bore 28, that is, in the direction away from the valve plate 46, it moves from the suction port 48 to the cylinder bore 2.
Low pressure fluid is aspirated at 8. When the piston shoe 34 slides on the thrust surface 36 and moves toward the valve plate 46, the high pressure fluid is discharged from the discharge port 50. It should be noted that increasing the tilt angle of the thrust surface 36 increases the fluid capacity. The rocker cam 38 and thrust surface 36 in the position of maximum fluid capacity are shown in FIG. The rocker cam 38 can rotate clockwise to reduce the capacity of the pump 10. Although the pump 10 of the embodiment is a pressure-compensated pump that does not intersect the center, the present invention described below is a rocker cam type variable displacement shaft in which the rocker cam 38 can rotate clockwise across the center. The same applies to pistons, whereby the inlet and outlet are reversed and the device gives maximum fluid capacity in the opposite direction.
Such a pump is disclosed in US Pat. No. 5,076,145. The invention applies equally to rocker cam type variable displacement pumps having rotary servo or linear servo type control.

In the embodiment where the pump 10 is shown as a pressure compensator, the piston 52 is slidably mounted in a bore 54 formed in a cylinder 56 that is rigidly mounted in the port cap 16.
A spring 58 provided around the cylinder 56 is provided on a button 60 attached to one side of the rocker cam 38 and a piston 52.
And rocker cam is rotated to the position of maximum fluid capacity. The stroke piston 62 is the biasing piston 52.
Is slidably mounted in a bore 64 of a cylinder 66 which is fixedly secured to the port cap 16 at a position within the pump housing 12 opposite the diameter of the position. The stroke piston 62 engages a button 68 mounted on the rocker cam 38 at a position that is diametrically opposite the position of the button 60.

In the pressure compensating pump, it is necessary to reduce the capacity of the pump when the pressure of the discharge fluid becomes excessive. If this happens, the stroke piston 6
By supplying pressure fluid to the end of 2 and moving it out of bore 64, rocker cam 38 is rotated clockwise (as shown in FIG. 3) toward the reduced fluid volume position. The stroke piston 62 continues to rotate the rocker cam 38 until the discharge pressure of the working fluid falls below the maximum setting. When the pressure is below the maximum setting, the pressure fluid is not supplied to the stroke piston 62, and the urging spring 58 moves the stroke piston 52 to the outside to rotate the rocker cam 38 in the counterclockwise direction, thereby causing the displacement of the pump. To increase. Since the present invention is for any type of rocker cam type pump that is independent of its volume control, the pressure compensation mechanism of pump 10 need not be further described.

As described above, when the rocker cam 38 rotates counterclockwise so that the working fluid is discharged at a relatively high pressure from the pump 10, a large pumping force is exerted through the piston 30 on the rocker. It extends to the cam 38. The pumping force is transmitted to the rocker cam support 44 via the complementary arcuate bearing surfaces 40 and 42. The large pumping force causes a large frictional force at the joint between the rocker cam bearing surface 40 and the rocker support bearing surface 42 to cause rocker support 44.
It makes the movement of the rocker cam 38 inside very difficult. To reduce the frictional force between rocker cam 38 and rocker support 44, a planar bushing 70 is inserted between rocker cam arcuate bearing surface 40 and rocker support arcuate bearing surface 42, as shown in FIG. . The flat bushing 70 reduces the frictional force to some extent, but is not itself suitable for reducing the frictional force to a satisfactory level.

As a result, working pressure fluid is supplied to the counterbalance pockets 72 and 74 formed in the rear surface 76 of the rocker cam 38 as shown in FIGS. 2, 5 and 6. The areas of the counterbalance pockets 72 and 74 are designed to reduce the force required to pivot the rocker cam 38 within the cam support 44 to within the desired level when receiving working pressure fluid. Traditionally, working pressure fluid has been supplied to the counterbalance pocket of the rocker cam. Here, the source of working pressure fluid is a pumping piston and the fluid is supplied to the piston shoe and then to the bore of the thrust plate, such as is connected to the counterbalance pocket.

Applicants have discovered a unique method for supplying working pressure fluid to counterbalance pockets 72 and 74 formed in the rear surface 76 of rocker cam 38 such that the fluid source is within housing 12. did.

With reference to FIGS. 2 and 4-7, it will be seen that a fluid passage 78 is formed in the housing 12 which is connected to a source of working pressure fluid (not shown).
The fluid passage 78 is open to a fluid passage 80 formed in the housing 12, and one end of the fluid passage 78 is closed by a plug 82. The plug may be replaced by a sensor or other device that utilizes the pressure fluid used for control purposes.

A hollow roll pin 84 is mounted in the central bore of the planar bushing 70, the cam support arcuate bearing surface 42 and the corresponding bore in the housing 12. The roll pin 84 serves two purposes. Roll pins 84 secure the planar bushing 70 to the rocker cam support or cradle 44 and also provide a fluid path 80.
By intersecting the fluid path 80 with the fluid path 86 formed in the rocker cam 38 and arcuate cam surface 40. The fluid path 86 intersects the angled fluid path 88, which is formed in the rocker cam 38 and is closed by the plug 90. The fluid path 88 intersects an oppositely angled path 92, which is closed at one end by a plug 94. A fluid path 96, similar to fluid path 86, has a fluid path 92 at one end.
And the other end of the rear surface 7 of the rocker cam 38.
6 is open to the fluid pocket 74 formed. Looking at FIG. 2, it will be seen that the planar bushing 70 is secured to the cam support surface 44 by roll pins 98.

[0017]

As described above, according to the present invention, the working pressure fluid source is taken in the cam housing and is formed on the rear surface 76 of the rocker cam 38 (communicating through the path formed in the rocker cam 38). It will be appreciated that it provides a method for supplying fluid to the counterbalance pockets 72 and 74. This greatly simplifies the supply of pressure fluid to the counterbalance pockets 72 and 74.

[Brief description of drawings]

FIG. 1 is a perspective view of a rocker cam type pump incorporating the present invention as seen from a suction port side and a discharge port side.

2 is a partial side view of the pump of FIG. 1. FIG.

3 is an axial cross-sectional view of the pump taken along line 3-3 of FIG.

FIG. 4 is a partial cross-sectional view of a pump housing having a rocker cradle formed therein.

FIG. 5 is a perspective view of the pump with the housing removed to show the rocker cam and other internal components.

FIG. 6 is a perspective view of a rocker cam.

FIG. 7 is a partial rear view of the rocker cam shown in FIG.

[Explanation of symbols]

10 Axial piston pump 12 housing 18 barrels 20 drive shaft 28, 64 bore 30, 52, 62 pistons 34 shoe 36 Thrust surface 38 Rocker cam 48 Suction port 50 outlets 72,74 Counterbalance pocket 86, 88, 92, 96 Fluid path

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ficredam A. Damchu             43017 Dubley, Ohio, United States             Derkin Circle 3310 (72) Inventor Anthony El Rayleigh             43061 Ost, Ohio, United States             Lander Marysville Road 9562 (72) Inventor Robert E. Stakeley             43015 Delau, Ohio, United States             Bear Moore Road 7175 (72) Inventor Robert Sea Hodges             48098 Toro, Michigan, United States             Lee Herb Moore 6360 F term (reference) 3H070 AA00 BB04 BB06 CC27 DD47                 3H071 AA01 BB01 CC27                 3H075 AA01 BB03 BB13 CC15 CC19                       DB24

Claims (2)

[Claims] 1. An axial piston pump for pumping fluid at a set working pressure, comprising: a housing, a barrel rotatably attached to the housing, a plurality of bores in the barrel, and Pistons mounted for reciprocating motion in the bores, shoes mounted on the ends of each piston, rocker cam supports within the housing, and complementary arcuate bearing surfaces formed on the rocker cam supports. A pair of spaced rocker cams pivotally mounted on the rocker cam having a bowed bearing surface; a thrust surface of the rocker cam; and the shoe on the thrust surface when the barrel is rotating. When sliding, the thrust surface of the rocker cam makes an angle with the axis of the barrel. A holddown for clamping the piston shoe against such thrust surface for reciprocating motion within each bore; a counterbalance fluid pocket formed on each rocker cam bow bearing surface; A first fluid path formed therein for receiving a source of working pressure fluid; and a first fluid path formed in the housing for directing working pressure fluid to one of the counterbalance fluid pockets.
A second fluid path in communication with the fluid path and one of the counterbalance fluid pockets formed in the rocker cam for communicating with the other, whereby the first fluid path through the second fluid path. An axial piston pump, comprising: a third fluid passage through which working pressure fluid supplied to one of the counterbalance fluid pockets is supplied to the other of the counterbalance fluid pockets through itself. 2. The axial piston pump according to claim 1, further comprising a pressure compensation control unit.