US3496873A

US3496873A - Axial-piston pump with control rods

Info

Publication number: US3496873A
Application number: US693844A
Authority: US
Inventors: Klaus Winter
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1967-01-05
Filing date: 1967-12-27
Publication date: 1970-02-24
Anticipated expiration: 1987-02-24
Also published as: DE1653630B1; FR1551385A; GB1172137A

Description

Feb. 24, 1970 K. WINTER AXIAL-PISTON PUMP WITH CONTROL RODS 5 Sheets-Sheet 1 Filed Dec. 27. 1967 2 3 0W 8 w d Q 3 t w a wq 5 m\\\\\\\\\\\\\ K. WINTER 3,

AXIAL-PISTON PUMP WITH CONTROL RODS Filed Dec. 72.7A 1967 3 Sheets-Sheet 2 Klaus Wi'n'rer INVENTOR.

. ATTORNEY 24, 31976 K. WINTER 3,496,873

AXIAL-PISTON PUMP WITH CONTROL Robs Filed Dec. 2?, 1967 s Sheets-Sheet s Klaus Winf'er mvem'on.

BY M

A'I'I'ORNEY Unite States Patent 3,496,873 Patented Feb. 24, 1970 U.S. Cl. 103-37 Claims ABSTRACT OF THE DISCLOSURE An axial-piston pump with swash-plate hydraulic apparatus and a nonrotating cylinder block in which a set of pistons reciprocate and cause the circulation of a working fluid through intake and discharge valves. The length of the piston stroke and, with it, the capacity of the pump can be controlled manually or, alternatively,

automatically by utilizing a variable pressure differential via rods extending into the pistons.

The invention relates to a hydraulic machine and, more particularly, to an axial-piston pump comprisin a reservoir for the fluid medium in which the fluid is delivered to an array of pistons concentrically disposed about a drive shaft and driven in and out of their respective cylinders in a direction parallel to the drive shaft by rotation of a swash-plate hydraulic apparatus mounted on the drive shaft at a fixed (or possibly variable) angle of tilt relative to the shaft axis.

In prior axial-piston pumps with swash-plate mechanisms the adjustment of controllable components was often fOund to be uneconomical and liable to introduce complications which offset any advantages to be gained from the apparatus. Regulation of the volume and direction of the fluid flow through changes in the angle between the swash plate and the pistons, which was designed to control the variable displacement of such pumps, was apt to introduce friction effects in the drive coupling and to aggravate, through accompanyin temperature fluctuations, damage through wear and tear, inadequate lubrication and insufficient filtra ion. Similar d sadvantages were encountered when the rotating cylinder barrel had to be axially shifted.

It is an object of my present invention to overcome the disadvantages of known axial piston pumps with swash-plate apparatus, and to provide a simple and inexpensive mechanism which is easy to control and to maintain, and which gives trouble-free service.

A more specific object of my invention is to p ovide an improved axial piston pump in which a swash plate tilted with respect to the axis of its supporting drive shaft rotates with respect to non-rotatable pistons concentrically disposed about a cylinder block and lon itud nally displaces the pistons in their cylinders, the direction of rotation being reversible.

Still ano her obiect of th s invention is to rovide an improved system for controllin the length of the efl ective piston stroke in order to vary the volume of the displaced hydraulic fluid and through it, the output to be deliver d by the axial-piston pump.

These objects and others, which will become apparent hereinafter, are attained, in accordance with the present invention. through control rods slidably received in respective bores inside the pistons and passing through the intake valves which separate the intake chamber from the annular pumping chambers which serve as working spaces for the pistons. The rods, attached at one end to a support plate mounted in the cover of the pump housing and terminating in leading edges at their other ends, proximate to the swash plate, alternately block and unblock the thrust exerted upon the compression side of the intake valves by covering 0r uncovering, accordin to the desired length of the stroke, orifices which lead from the piston bore to the pumping chamber. With respect to manual operation, the support plate for the rods can be longitudinally displaced through interaction of a threaded spindle driven by gear means. According to another feature of the present invention, the longitudinal variation of the piston stroke through the control rods is effected by differential hydraulic action upon two piston surfaces of dissimilar area.

The above and other objects, features and advantages of my invention will become more readily apparent from the following description, reference being made to the accompanying drawin in which:

FIG. 1 is a longitudinal cross-sectional view of a pump according to my invention;

FIG. 2 is an axial cross-sectional view taken on the line II-II of FIG. 1; and

FIG. 3 is a longitudinal cross-sectional view showing alternate adjusting means for the assembly of FIG. 1.

In the drawing there is shown a housing 1.9 which forms a cylinder block 19a and is closed at its lefthand and by a cover 20, with a seal 28 provided at the junction of these adjoining parts. The hydraulic fluid, e.g. oil, which also serves to lubricate the moving parts of the pump is supplied to the intake compartment 6 via a port 37, from the reservoir (not shown). The compartment 6 is thus formed between the cover 20 and the cylinder block 19a. The load is supplied with fluid under pressure from the outlet fitting 38 which forms part of an outlet means described in greater detail below. The housing itself is attached by lugs 33 to a support. Power from a prime or secondary mover is delivered to a drive shaft 1 which is journaled in sealed bearing 26 in a hearing plate 42 held in place by a split ring 27. The inner end of drive shaft 1 includes a boss 29 which fits accurately for pivotal movement of a swash plate 2. Swash plate 2, tilted at an acute angle relative to the axis of drive shaft 1, is rotated about the shaft axis on the shaft. Swash plate 2 is rotatably supported by ball bearings 30 having an inner thrust race 31 (against which the swash-plate disk 2 applies the axial reaction force of the pumping action) and outer race 32 resting against plate 42. The ball bearings are centered on the axis of drive shaft 1. A recess 35a in the cylinder block 19a beyond the swash plate 2 receives roller (needle) bearings 35 to take up unequal radial forces developed during rotation of the swash plate in pumping action.

In the cylinder block 19a there are located several tubular pistons 5 angularly spaced around the cylinder periphery at uniform intervals, so that their longitudinal axes are parallel to the axis of drive shaft 1. Each piston, fitted into a cylinder bore 7a, defines therewith a working space or pumping chamber 7 and is urged by springs 3 resiliently against a slidable piston shoe 4, swiveling on the head of the piston; thus each piston is driven back and forth in its cylinder as the orbiting swash plate alternately compresses and relieves the springs 3. Fluid from the intake compartment is channeled through a double springloaded intake check valve 8 which has the form of a ringplate valve, to the pumping chambers 7, thence via the outlet check valve 9 and from there to a discharge duct 14 of the outlet means and via chamber 10 to the load.

A bleeder screw 34, threaded into the pump housing, permits venting of air for priming the pump. Each piston 5 contains in a longitudinal bore 5a through its center a compression rod 11 which at one end is firmly attached by a head 46 to a support plate 15 axially movable on the pump cover 20 and located in the intake compartment 6.

3 At its other end, proximate to the swash plate, each control rod 11 has a leading edge 16 with which it alternately covers and uncovers, with each piston stroke, an orifice 17 which leads radially out of the piston bore and into a longitudinal channel 25 cut in the form of a groove in the outer piston surface and from there to the annular space 7.

The support plate 15 which holds the array of control rods 11 is threaded onto a spindle sleeve 14 forming the fluid passage or outlet duct inside the cover 20. A drive gear 13 is attached to the axially fixed rotatable sleeve 14 and meshes with a driving gear 41. When a handwheel 12 is manually rotated, these gears advance the support plate 15 which is screwed onto the sleeve 14 and whereby longitudinally displace the control rods 11 attached to the support plate extend into the pistons 5.

During the suction stroke, while the piston is moving from left to right as shown in FIG. 1, fluid is drawn through the intake valve 8 and, after orifice 17 has been unblocked, also through that opening into the interior of the piston along groove 25, During the compression stroke, while the piston is moving from the right to the left as viewed in FIG. 1, fluid from the annular chamber 7 of progressively decreasing volume, is forced through the orifice 17 and through the piston bore a, 5a, 5a" into the swash-plate compartment 45 until the leading edge 16 of the control rod 11 blocks the orifice. At that point the effective portion compression stroke starts and moves fluid from the annular chamber through the compression valve 9 to the compression chamber compartment 45 is connected via a passage 45a, 45b with intake compartment 6. The compression stroke ends when piston 5 has reached its leftmost position.

Manual adjustment of the control rods in a longitudinal direction, by way of the support plate 15, the handwheel 12 and the gear transmission 13 and 41, controls the length of the compression stroke and thereby the output of the axial piston pump. An alternate arrangement for the adjustment of the control rods is illustrated in FIG. 3. In contrast to the preceding system a sleeve 18 forming the fluid passage of the outlet duct is longitudinally slidable inside the housing 19. Inside cover 20 with its cylindrical extension 46 there is a spindle 21 coaxially aligned with the longitudinal axis of the sleeve 18. Part of spindle 21 extends into a chamber 48- that is connected with the outlet chamber 10' and is provided with external threads onto which is screwed a hexagonal head 24. This hexagonal head cooperates with hexagonal recess 48 preventing rotation of the head and supports the spring 22. The knee-shaped support plate 23, which carrier control rods 11 on its periphery as in FIG. 1, is attached at its hub to sleeve 18 by two circlips 47 that hold it in a perpendicular position relative to the longitudinal axis of the sleeve. A stepped shoulder 49 of the sleeve 18 in the intake chamber 6 decreases one differential-piston area 50 of the sleeve 18 relative to an oppositely effective area 51, both of which are under pressure from the fluid in chamber 10. When springs 22 are relaxed, as viewed in the drawing, sleeve 18 is moved to the left because its right frontal area offers a greater surface to the pump pressure than does the left frontal area. As soon as the pressure, defined as force per unit area, is equalized between the two frontal areas, tightening of springs 22 holds the sleeve in a certain position from which it is shifted only when another pressure difference builds up between the two areas. The greatest displacement to the left which the sleeve 18 can be given corresponds to the distance 52 between the control rods 11 and the pump cover 20.

Through support plate 23 which is attached to the sleeve 18, and the control rods 11 affixed to the support plate, the sleeve motion constitutes the essential part of a servomechanism in which variations in the pressure of the pump are automatically compensated for by variations in the stroke length of the pistons.

I claim:

1. An axial-piston pump comprising:

housing means having an axis and formed with a plurality of axially extending cylinders angularly spaced about said axis;

a plurality of pistons respectively received in said cylinders and axially reciprocable therein while defining with said housing means pumping chambers of variable volume;

an input shaft rotatably mounted in said housing means and having a head rotatable about said axis and cooperating with said pistons at one end thereof for reciprocating same upon rotation of the shaft, the other ends of said pistons terminating within said cylinders;

intake-valve means communicating with said chambers proximal to said other ends of said pistons for delivering fluid to said chambers during an intake stroke of the respective piston enlarging the corresponding chamber;

outlet means in said housing means including a respective check valve communicating with each of said chambers proximal to said other ends of said pistons for discharging fluid from said chambers unidirectionally during a compression stroke of the respective piston decreasing the volumes of the corresponding chamber, said pistons being each formed with an axially extending bore opening at said other ends, an aperture at a location intermediate said ends and communicating between said bore and said chamber, and a vent passage opening into said bore proximal to said one end; and

control means for establishing effective portions of the compression strokes of said pistons, said control means comprising:

respective axially extending, angularly spaced, mutually parallel control rods each slidably received in a respective one of said bores and extending into the latter through said other end of the respective piston for selectively blocking and unblocking the respective apertures, said rods having corresponding extremities projecting from said pistons at said other ends,

a control body centered on said axis and extending outwardly therefrom while engaging said extremities of said rods, and

mechanism for axially shifting said body toward and away from said shaft to regulate the point in each stroke of each piston at which the rod obstructs the respective aperture to define the effective piston stroke, thereby confining the fluid within the respective chamber for the respective effective portion of the compression stroke.

2. An axial piston pump as defined in claim 1 wherein said apertures are generally radial orifices formed in each piston and communicating between the corresponding piston bore and pump chamber, said control rods each having a control edge alternately blocking and unblocking the respective orifice during each piston reciprocation, said pistons and said cylinders each define an axially extending channel along the outer wall of the respective piston communicating between the respective pumping channel and the respective radial orifice.

3. An axial piston pump as defined in claim 2 wherein said mechanism includes an axially fixed spindle rotatably mounted on said housing means remote from said head, and means external of said housing means for rotating said spindle, said body threadedly engaging said spindle and being nonrotatable for axial advance upon rotation of said spindle, said means for rotating said spindle comprising a driven gear connected to said spindle, a driving gear rotatably mounted in said housing means and meshing with said driven gear and a handwheel operable externally of said housing and connected with said driving gear for manually rotating same, said spindle being tubular and centered on said axis while forming said outlet means.

4. An axial-piston pump as defined in claim 2 wherein said adjusting means includes a differential piston axially shiftable in said housing means and subjected to the fluid pressure at said outlet means for axially displacing said body, said differential piston forming a tube centered on said axis and forming an outlet conduit, said differential piston having a net effective surface area exposed to the pressure at said outlet means tending to advance said control rods into said pistons upon an increase in fluid pressure at said outlet means.

5. An axial-piston pump as defined in claim 2 wherein said control means includes a tubular member coaxial with said shaft and opposite the latter, means enabling displacement of said body axially along said tubular member, means connecting said tubular member with said chambers through said check valves for forming an outlet duct in said tubular member, and an outlet port formed in said housing means and communicating with the interior of said tubular member,

References Cited UNITED STATES PATENTS 1,940,524 12/1933 Bellem e181. 105 37 1,943,034 1/1934 Myers l03158 5 2,439,879 4/1948 Allen 103-37 2,524,235 10/1950 Schenk 103 -37 2,821,926 4/1958 Miller et al 103- 37 2,839,002 6/1958 Williams 103158 10 2,981,198 4/1961 Nettel 103 158 FOREIGN PATENTS 844,436 4/1939 France. 646,371 11/1950 Great Britain.

WILLIAM L. FREEH, Primary Examiner Us. 01. X.R. 103-173