GB2060085A - Axial Piston Hydraulic Motor or Pump - Google Patents

Abstract

A hydraulic motor or pump has a plurality of axially movable pistons (8) in a rotatable cylinder block (2) coupled to a shaft (1). The pistons (8) ride against a cam surface (7) and the cylinders are vented to equally spaced control apertures (19) in one face of the block (2). A fixed control plate (4) adjacent that face has equally spaced alternating apertures (17, 18) radially aligned with those in the block (2), connected to annular conduits (15, 16) in the plate (4). The total number of apertures in the block (2) differs from that in the plate (4). Moments tending to tilt the plate (4) are balanced and the apparatus is optimum when the angular extents of the apertures are in accordance with disclosed relationships. <IMAGE>

Description

SPECIFICATION Axial Piston Hydraulic Motor This invention relates to an improved fluid power device, such as a motor or pump, having axially reciprocating pistons therein.

It is known to provide a fluid motor having two or more pistons in a rotatable cylinder block, the pistons being ported through control apertures similar apertures in a relatively fixed control plate.

A disadvantage of prior art devices of this type is that the power occurring during operation acts eccentrically, resulting in a movement which tends to tilt the rotatable cylinder block relative to the plate and to lift a portion of the block away from the plate. To prevent this undesirable tilting, it has been necessary to increase the axial force which holds the adjacent surfaces of the cylinder block and control plate together beyond the scalar force needed to oppose the axial piston force above. Wear is therefore increased.

An object of the present invention is to provide an improved axial piston motor or pump in which the tilting movement acting on the cylinder block is considerably reduced.

A further object is to provide a motor or pump of the type described wherein the control apertures are arranged and dimensioned to distribute piston forces symmetrically with respect of the axis of rotation of the piston plate.

Briefly described the invention includes a hydraulic apparatus of the type including a housing, a control plate fixedly mounted in said housing, means defining a plurality of circularly arranged apertures opening to a control side of said plate, a rotatable shaft extending into said housing mounted for rotation with said shaft, a plurality of axially movable pistons mounted in said block, said block having means defining a plurality of circularly arranged apertures in said block extending between said pistons and a surface of said block facing said control plate, the number of apertures in said block being different from the number of apertures in said plate, and a cam plate operatively associated with said pistons, the improvement wherein the angular extent of each of the apertures in said plate and the apertures in said cylindrical block are within 10% in either direction, of the values determined by the relationships a,+ a,=3 60 O/i a1=(36O0/z)-a1n wherein a, is the angular extent of each aperture in said control plate, a is the angular extent of each aperture in said cylinder block, i is the number of apertures in said control plate, z is the number of cylinders it said cylinder block, and a mn is the minimum angular spacing between apertures in said cylinder block.

In order that the manner in which the foregoing and other objects are attained in accordance with the invention can be understood in detail, a particularly advantageous embodiment thereof will be described with reference to the accompanying drawings, which form a part of this specification, and wherein: Fig. 1 is a longitudinal sectional view of an apparatus in accordance with the invention; Fig. 2 is a transverse sectional view along line Il-Il of Fig. 1 and in the direction of the arrows showing the upper half of the apparatus, the lower half thereof being a mirror image of the portion shown; Fig. 3 is a transverse sectional view along line Ill-Ill of Fig. 1 and in the direction of the arrows showing the upper half of the apparatus as in Fig.

2; and Fig. 4 is a schematic diagram illustrating the relative positions of, and angular relationships between, the control apertures in an apparatus according to the invention.

Turning now to the Figures in detail, as best seen in Fig. 1, the apparatus includes a rotatable shaft 1 with a generally cylindrical cylinder block 2 attached to the shaft by means of splines for rotation with the shaft. To the left of the cylinder block, as seen in Fig. 1, is a control plate 4 which has a central opening through which the shaft passes with clearance, the control plate having a control surface facing toward the cylinder block.

The cylinder face facing toward the cylinder block.

The cylinder block and a portion of the shaft is surrounded by and partially contained within a bell-shaped housing part 5, and to the left of the control plate is a plate-shaped housing part 6 which abuts the surface of control plate 4 opposite its control surface. The periphery of control plate 4 has a sufficiently great diameter to extend outwardly between the peripheries of housing parts 5 and 6 so that parts 4, 5 and 6 are held together firmly by a plurality of axial threaded fasteners or bolts 3 to form the complete housing.

The cylinder block contains eight pistons 8 which are axially movable, with respect to the central axis of shaft 1, within cylinder block 2, the pistons being evenly distributed about a circle in the block. A cam disc 7 is received within the interior right-hand portion of housing part 5 and is fixedly connected thereto by splines or the like between the interior of housing part 5 and the cylinder block. A ball 9 is associated with each piston and iies between the piston and the adjacent cam surface of disc 7. Cam disc 7 is a generally annular member having a cam surface which faces axially toward cylinder block 2. The cam surface being contacted by balls 9 has a sinusoidal shape and, in the present embodiment, has three peaks and three valleys, evenly distributed.

The shaft 1 is mounted in housing parts 5 and 6 by sets of roller bearings 10 and 11 to permit the shaft to be freely rotatable relative to the housing with the right-hand end of the shaft extending through housing part 5. The gap surrounding the shaft at the point where it penetrates housing 5 is closed by an annular sealing ring 12. A compression coil spring is inserted between the inner raceway of roller bearing assembly 10 and cylinder block 2, the spring surrounding shaft 1 and urging the cylinder block away from the raceway, i.e., urging the block to the left toward control plate 4.

In the control plate 4 are two annular channels 1 5 and 16 which are axially spaced apart and which have equal diameters. As seen in Figs. 1 and 3, the channels are coupled to the exterior of the apparatus by generally radially extending conduits 1 5a and 1 6a to which suitable exterior hoses or conduits can be connected. Toward the inside of the apparatus, each of the channels is connected to the control surface of the control plate by interior L-shaped channels opening at control apertures 1 7 and 18, channel 1 5 being connected to apertures 1 7 and channel 1 6 being connected to apertures 1 8. The control apertures are spaced apart by equal angles and are disposed on a single circle, this being illustrated in Figs. 3 and 4.As will be recognized, channels 15 and 1 6 are connected to points of various pressures, and the various pressures likewise prevail in the apertures 17, 18. As will be recognized in Figs. 3 and 4, the apertures from the two channels alternate, i.e., the apertures 17 alternate with apertures 18 as one proceeds about the circle.

On the control side of cylinder block 2 which faces toward the control plate and is adjacent thereto, the cylinder block is provided with control apertures 19, the number of which is equal to the number of cylinders, one aperture being aligned along a radius with each cylinder, the apertures again being spaced apart by equal distances and being of equal angular extent. All of apertures 17, 18 and 1 9 can be described as being "beanshaped", the term indicating that the openings are elongated in the circular direction and are slightly curved so that the inner and outer surfaces thereof lie on concentric circles.It will also be observed, as illustrated in Fig. 4, that the circles containing apertures 17, 18 and apertures 1 9 have equal diameters, and that the control apertures are all substantially the same width viewed in a radial direction. As best seen in Fig. 2, the apertures 1 9 are disposed radially inwardly with respect to the axes of pistons 8.

As seen in Fig. 4, the six control apertures 1 7 and 1 8 (three of each) in control plate 4 are shown in soiid lines and the control apertures, 19, totalling eight in number of the cylinder block 2 are shown in broken lines. The axial extent of each of control apertures 17, 18 of control plate 4 is illustrated as a control angle as and the control apertures 1 9 in cylinder block 2 have an angular extent identified as a,. The minimum distance between control apertures 1 9 is identified as amin.

Of particular significance to the present invention is the relationship between the angular extents of the control apertures. The operation of the apparatus disclosed is such that the counter moment acting on cylinder block 2 counteracts the tilting moment exerted by pistons 8 on the cylinder block 2 when the angular extents of the control apertures 1 7 and 19 satisfy the following relationships: a,+a,=360P/i az=(3600/z)-amin.

As indicated above, the terms used in these expressions have the meanings that aS is the angular extent of each of control apertures 1 7 and 18, a, is the angular extent of each of the control apertures 19 in cylinder block 2, i is the number of control apertures 17 and 18 in control plate 4, z is the number of pistons 8 in cylinder block 2, and a min is the minimum angular distance between two adjacent control apertures in the cylinder block. In the embodiment described aS is 250,a2 is 350, amin. is 100, i=6 and z=8.

The fulfillment of the preceding requisites results in an optimum decrease of the eccentric forces exerted by piston 8 on the cylinder block tending to separate the cylinder block from the control plate. A noticeable decrease is also achieved whenever the computed values a and a differ from these theoretical values by as much as +10%.

Whenever an axially reciprocating piston motor of the type described has the characteristics set forth above, then the control apertures circularly disposed in the control plate occupy a minimum angular region and the control apertures in the cylinder block are limited such that no bridging of two adjacent control apertures occurs in the control plate. Thus, in such a structure, a counter moment by an eccentric force acts during operation on the cylinder block which counters the tilting moment exerted by the piston on the cylinder block in such a way that the sum of the moments is considerably smaller than the tilting moment exerted by the pistons alone.

As will be recognized, the structure can be employed as an axial piston pump as well as an axial piston motor, the only difference being the direction in which the forces flow, i.e., whether the shaft acts as an input or output, and whether, correspondingly, conduits 1 5a and 1 6a act as outputs or inputs.

With the apparatus operating as a pump, shaft 1 is rotated by an external force, causing cylinder block 2 and pistons 8 to rotate relative to control plate 4 and also relative to cam disc 7. As the pistons rotate, the sinusoidal surface of the cam disc causes the pistons to move toward and away from plate 4, pumping fluid out of annular channel 16 and into annular channel 15, in which case 1 spa is an outlet and 1 6a is an inlet, coupled to a source of fluid. 1 5a is therefore the pressure side of the pump. As illustrated in Fig. 1, the piston 8 shown at the top of the figure is at or close to the end of its pumping stroke, while the piston at the bottom of the Figure is at or near the end of its inlet stroke.

When operating as a motor, fluid under pressure is supplied to 1 spa and channel 1 6 while 1 spa and 1 5 lead to a sump. The fluid drives the pistons, causing them to act on the cam surface to rotate shaft 1 through cylinder block 2.

While one advantageous embodiment has been chosen to illustrate the invention, it will be recognized that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended ciaims.

Claims (2)

Claims

1. An hydraulic apparatus of the type including a housing, a control plate fixedly mounted in said housing, means defining a plurality of circularly arranged apertures opening to a control side of said plate, a rotatable shaft extending into said housing, a cylinder block in said housing mounted for rotation with said shaft, a plurality of axially movable pistons mounted in said block, said block having means defining a plurality of circularly arranged apertures in said block extending between said pistons and a surface of said block facing said control plate, the number of apertures in said block being different from the number of apertures in said plate, and a cam plate operatively associated with said pistons, the improvement wherein the angular extent of each of the apertures in said plate and the apertures in said cylinder block are within 10%, in either direction, of the values determined by the relationships a,+a,=3600/i, az=(36O0/z)-amin.

wherein a9 is the angular extent of each aperture in said control plate, a, is the angular extent of each aperture in said cylinder block, i is the number of apertures in said control plate z is the number of cylinders in said cylinder block, and amin is the minimum angular spacing between apertures in said cylinder block.

2. An hydraulic apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.