US 3911791 A
The invention provides an axial piston pump/motor whose stroke is controlled by a tiltable swash-plate carried on a non-rotary tilt member by a thrust bearing wherein torque reaction to piston thrust and swash plate drive is transmitted directly to the pump/motor mainshaft by spherically jointed links.
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Description (OCR text may contain errors)
United States atent [191 Clerk Oct. 14, 1975 SWASH-PLATE DRIVE FOR AXIAL PISTON PUMPS/MOTORS  Inventor: Robert Cecil Clerk, Edison House,
Fullerton Road, Glenrothes, Fife, Scotland  Filed: June 15, 1973  App]. No.: 370,346
 US. Cl 91/499; 74/60  Int. Cl. F01B 13/04  Field of Search 74/60; 91/499, 485; 417/218  References Cited UNITED STATES PATENTS 1,840,866 1/1932 Rayburn 91/506 2,151,415 3/1939 Bennetch 74/60 2,157,852 5/1939 Grosser 74/60 2,227,998 1/1941 Borer et al.... 74/60 2,256,952 9/1941 Sappington... 74/60 3,426,686 2/1969 Anderson 417/218 3,495,542 2/1970 Kratzen 91/485 Primary Examiner-William L. Freeh Attorney, Agent, or FirmLerner, David, Littenberg & Samuel  ABSTRACT The invention provides an axial piston pump/motor whose stroke is controlled by a tiltable swash-plate carried on a non-rotary tilt member by a thrust bearing wherein torque reaction to piston thrust and swash plate drive is transmitted directly to the pump/motor mainshaft by spherically jointed links.
2 Claims, 2 Drawing Figures FIGI Sheet 2 of 2 U.S.. Patent Oct. 14, 1975 PEG. 2
SWASH-PLATE DRIVE FOR AXIAL PISTON PUMPS/MOTORS This invention relates to a swash-plate drive for pumps and motors having axially moving pistons.
In axial piston hydraulic pumps where the length of stroke and movement of the pistons is effected and controlled by a swash-plate of variable tilt angle, it is normal practice for a driving shaft torque to be transmitted to the reactive swash-plate through the medium of a multi-cylinder barrel (splined or keyed to the driving shaft) and the pistons, the remote or cantilevered ends of which are fitted with articulated shoes conforming to the swash-plate relative angularity during each revolution of the barrel.
This system has several disadvantages, the more prominent of which are (a) the difficulty and cost of ensuring true alignment of the barrel on the shaft and in relation to a matting port-face of the pump casing which controls the distribution of the pumped pressure fluid, (b) the very high friction and poor wear resulting from the natural cantilever action of the drive torque loading transmitted by the pistons and acting on the lip of the cylinder mouths, (c) the low mechanical efficiency of a necessary articulated shoe accommodation to the swash-plate.
It is known to utilise articulated connecting rods between the pistons and a rotating swash-plate member to improve disadvantage but with a variable tilt angle swash-plate it has still been found necessary to transmit the driving torque via the remote end of each piston by mechanical contact with a precisely located swelling on each connecting rod intermediate of its length between the *spherical" articulate ends. Unfortunately, this does not provide any appreciable alleviation of the loading transmitted to the cylinder mouth as in disadvantage (b).
The object of the present invention is to provide a method of transmitting the driving torque directly between the mainshaft and a rotating swash-plate, bypassing the rotating barrel, the cylinders, pistons and articulated connecting rods, which are thus able the better to handle the axial pumping loads with only minor parasitic drag torques. This applies not only to pumps but to hydraulic motors of similar configuration, the difference being that in a motor the torque generated at the swash-plate serves to drive the mainshaft.
To this end what we propose is an axial piston pump (or motor) having variable tilt angle swash-plate stroke control and rotary port-face hydraulic distribution control, characterised by a rotary swash-plate member in which the piston-thrust torque reaction or developed torque on the rotary swash-plate member is transmitted directly to the mainshaft by spherically jointed links inter-connecting that member to the shaft, the cylinder barrel being only indirectly located rotationally on the mainshaft by a sleeve loosely keyed thereto, and the rotary swash-plate member being supported by a thrust bearing on a non-rotary tilt member.
However, a preferred arrangement utilises a universal spider in which the radial outward arms on the mainshaft and the radial inward arms of the rotating swash-plate are inter-connected as pairs by spherically jointed links. By designing the links as a flattened C, the orthogonal stub ends can be adapted to use commercially available spherical end units with positive lubrication from a mainshaft gallery.
A preferred construction form of the invention is illustrated in the accompanying drawings in which:
FIG. 1 is a central vertical cross-section showing a swash-plate at 25 stroke angle;
' FIG. 2 is a plan view of the swash-plate at zero stroke angle.
The mainshaft l of an axial piston pump/motor is forged or cast integrally with three radial arms 2.
Each of the arms 2 is fitted with a part-spherical cup bearing 3 to receive the stub end of a flattened C shaped link 4, one of which is shown in the drawings. These stub ends are extended with centrifugal balance weights 5.
The opposite stub-ends of the links 4 are received in part-spherical cup bearings 6 in inwardly directed arms 7 of the rotary swash-plate 8.
The swash-plate 8 is carried in an annular thrust bearings 9 in the non-rotational tilt member 18, which is tilted about trunnions 10 by control levers (not shown) connected to lugs 11.
The part-spherical ends of piston rods 12 are received in cup bearings 13 in the rotary swash-plate 8.
The pump/motor cylinder barrel l4, bolted to a sleeve 15 loosely keyed to the shaft 1 is shown supported from the pump/motor stator casing 16 by a flanged keep nut 17.
Piston torque reaction (in the case of a pump) or developed thrust (in the case of a motor) is transmitted to the shaft 1 through the medium of the rotary swashplate 8, links 4 and arms 2 (constituting a universal joint) and end thrust is taken by the bearing 9 in the stationary tilt member 18. Rotary port-face hydraulic distribution control is utilised.
1. An axial piston pump/motor having variable tilt angles swash-plate stroke control and rotary port-face hydraulic distribution control, characterized by a rotary swash-plate member in which piston-thrust torque reaction and developed torque on the rotary swashplate member is transmitted directly to a rotary main driving shaft by spherically jointed links interconnecting said rotary swash-plate member to said shaft, a cylinder barrel being located on a sleeve loosely keyed to said driving shaft so that piston-thrust torque reaction and developed torque is not transmitted directly from said cylinder barrel to said driving shaft, and the rotary swash-plate member being supported by a thrust bearing on a non-rotating tilt member.
2. An axial piston pump/motor according to claim 1,
in which the links are of flattened C formation.