WO1995030833A1

WO1995030833A1 - Hydraulic axial piston unit

Info

Publication number: WO1995030833A1
Application number: PCT/US1995/004385
Authority: WO
Inventors: Charles E. Rose; Thomas A. Watts; John W. Grant
Original assignee: Caterpillar Inc.
Priority date: 1994-05-06
Filing date: 1995-04-10
Publication date: 1995-11-16

Abstract

An axial piston hydraulic unit (10) has a hardened port plate (31) positioned between a head (12) and a rotatable cylinder barrel (14). The port plate (31) has at least one aperture (49, 52) extending therethrough adjacent a leading edge (42, 43) of either an intake port (34) or a discharge port (37) of the port plate (31) with the aperture (49, 52) being in continuous communication with a pocket (48, 51) which is provided in the head (12) and opens into an associated one of an intake passage (36) or a discharge passage (41) in the head (12).

Description

Hydraulic Axial Piston Unit

Technical Field

This invention relates generally to hydraulic axial piston units and more particularly to one having a device for gradually increasing fluid communication between the piston bores in a rotatable barrel and intake and discharge passages in the housing.

Background Art

Axial piston hydraulic pumps and motors commonly have a hardened port plate stationarily positioned between a portion of the housing and a rotatable barrel. The port plate has a plurality of kidney shaped ports extending therethrough for fluid communication between the piston bores of the barrel and intake and discharge ports in the head. The port plates also typically have metering slots or grooves at the leading edge of the kidney ports for gradually increasing fluid communication between the piston bores and the respective intake and discharge passages in a manner which decreases hydraulic shock to alleviate noise and cavitation.

The port plate of one such pump is made relatively thin so that the slots can be stamped to expedite the manufacturing process of the port plates. A portion of the head forms the bottom of the slot.

One of the disadvantages found with such thin port plates is that the thickness of the port plate is one of the factors determining the size of the orifice area of the metering slot. This limits the flexibility of controlling the orifice area as the piston bores open into the intake or discharge ports. It has also been found that high stresses are induced in the port plate if the proper relationship of the plate thickness and slot size is not used. Thus, it would be desirable to utilize the advantages of the thin port plate design within a hydraulic axial piston unit while permitting a wider variety of metering slot geometries to be used for optimizing the operating characteristics of the axial piston unit.

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure of the Invention

In one aspect of the present invention, an axial piston hydraulic unit includes a head having intake and discharge passages therein, a rotatable barrel having a plurality of equally spaced, circumferentially arranged piston bores opening toward the head, and a port plate positioned between the barrel and the head and secured against rotation relative to the head. The port plate has an intake port and a discharge port extending therethrough to selectively serially communicate the piston bores with the intake and discharge passages as the barrel rotates. A means is provided adjacent a leading edge of at least one of the intake and discharge ports for providing initial communication between the piston bores and the associated one of the intake and discharge passages. The means includes a pocket in the head opening into the associated one of the intake and discharge passages and at least one aperture in the port plate continuously communicating with the pocket. Brief Description of the Drawings

Fig. 1 is a longitudinal sectional view of an axial piston pump incorporating an embodiment of the present invention. Fig. 2 is a sectional view taken along line

2-2 of Fig. 1.

Fig. 3 is a sectional view taken along line 3-3 of Fig. 1.

Fig. 4 is an enlarged plan view of a portion of Fig. 2 enclosed by line 4.

Fig. 5 is a sectional view taken along line 5-5 of Fig. 4.

Fig. 6 is an enlarged plan view of a portion of Fig. 2 enclosed by line 6. Fig. 7 is a sectional view taken along line

7-7 of Fig. 6.

Figs. 8-11 are plan views of alternate embodiments of the present invention.

Best Mode for Carrying Out the Invention

An axial piston hydraulic unit 10 includes a multi-piece housing 11 having a head 12 attached to a casing 13. The hydraulic unit 11 may be either a pump or a motor and has a rotatable barrel 14 disposed within the housing and secured to a shaft 16 suitably mounted for rotation about a longitudinal axis. The barrel is resiliently biased toward the head 12 by a spring 17 disposed between a ring 18 secured to the shaft and a ring 21 secured to the barrel. The barrel has a plurality of equally spaced, circumferentially arranged piston bores 22 each of which has an arcuate slot 23 opening toward the head. A plurality of pistons 24 are individually reciprocatably positioned within the piston bores 22. A slipper 26 is conventionally swivelably connected to an end of each piston. A swash plate 27 is positioned within the housing and has a planer cam surface 28 engaged by the slippers to reciprocate the pistons within the piston bores in a conventional manner. A port plate 31 is positioned between the barrel 14 and a planer surface 32 of the head 12 and is stationarily positioned and secured against rotation relative to the head by a pair of pins 33. The port plate 31 has an elongate arcuate intake port 34 continuously communicating with an intake passage 36 in the head and a plurality of arcuate discharge ports 37-39 continuously communicating with a discharge passage 41 in the head. Assuming that the barrel rotates clockwise relative to the port plate as viewed in Fig. 2, the intake port 34 has a leading edge 42. The discharge port 37 would be the leading discharge port and has a leading edge 43.

First and second means 46,47 are disposed adjacent the leading edges 42,43 of the intake port 34 and the discharge port 37, respectively for providing initial communication between the piston bores and the respective intake and discharge passages 36 and 41. The means 46 can be, for example, an arcuate pocket 48 in the head 12 and an arcuate elongate aperture 49 extending through the port plate in continuous communication with the pocket 48. The aperture 49 is circumferentially spaced from the leading edge 42 of the intake port 34. The pocket 48 is recessed from the surface 32 of the head and opens into the intake passage 36. Similarly, the means 47 can include a pocket 51 in the head and an elongate arcuate aperture 52 extending through the port plate in continuous communication with the pocket 51. The aperture 52 is circumferentially spaced from the leading edge 43 of the discharge port 37. Each of the apertures 49,52 are sized relative to the respective pocket^'s so as to define an orifice area less than the minimum flow area through the respective pockets. Thus the quantity of fluid passing through each aperture and associated pocket is always controlled by the effective size of the aperture and not the pocket. The effective size of the apertures is the cross-sectional area of the aperture in the plane of the port plate. The port plate in this embodiment is made from hardened steel and has a thickness of about 1.57 mm.

Figures 8-11 disclose alternate embodiments of the present invention. More specifically, in Fig. 8 the aperture 49 is basically an elongate arcuate aperture with an enlarged portion 53 adjacent the leading edge 42. In Fig. 9, the aperture 49 has a key hole shape. The embodiment of Fig. 11 includes three separate arcuate elongate apertures 49 while the embodiment of Fig. 10 includes a plurality of round apertures. The size, shape and number of apertures is selected to tailor the characteristics of the piston pressure as the piston passes from high pressure to low pressure or from low pressure to high pressure.

Industrial Applicability The operation of the present embodiment will be described as if the barrel 14 rotates clockwise relative to the port plate 31 as viewed in Fig. 2 so that the slots 23 and, thus, the piston bores 22 in the barrel sequentially communicate with the intake port 34 and the discharge ports 37-39. As the leading edge of each slot approaches the leading edge 42 for example, of the intake port, the initial communication between the intake passage 36 and the piston bores is through the aperture 49 and the pocket 48. It is readily apparent that the initial opening area between the respective slot and the aperture is very small and progressively increases until the aperture becomes fully communicative with the slot prior to the slot opens into the intake port . This allows the fluid pressure in the piston bore to substantially equalize prior to the slot opening into the intake port. The initial communication between the slots and the discharge passage 41 occurs in a similar manner through the aperture and the pocket 51. The geometry of the apertures determines the characteristic of the piston pressure as initial communication is established between the piston bores and the intake and discharge passages . The term geometry includes size, shape, number and location of the apertures relative to the intake and discharge ports. Thus, the combination of the aperture in the port plate and the pockets in the head provide increased flexibility in selecting the geometry of the apertures for tailoring the piston pressure characteristic for each hydraulic unit configuration.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

1. An axial piston hydraulic unit (10) comprising: a head (12) having an intake passage

(36) and a discharge passage (41) therein; a rotatable cylinder barrel (14) having a plurality of equally spaced circumferentially arranged piston bores (22) opening toward the head (12) ,* a port plate (31) positioned between the barrel (14) and the head (12) and secured against rotation relative to the head (12) , the port plate (31) having an intake port (34) and a discharge port

(37) extending therethrough to selectively serially communicate the piston bores (22) with the intake and discharge passages (36,41) as the barrel (14) rotates; and means (46,47) adjacent a leading edge (42,43) of at least one of the intake and discharge ports (34,37) for providing initial communication between the piston bore (22) and the associated one of the intake and discharge passages (36,41), the means (46,47) including a pocket (48,51) in the head opening into the associated one of the intake and discharge passages (36,41) , and at least one aperture (49,52) extending through the port plate (31) and continuously communicating with the pocket (48) .

2. The axial piston hydraulic unit (10) of claim 1 wherein the aperture (49,52) is an elongate slot.

3. The axial piston hydraulic unit (10) of claim 1 wherein the initial communicating means (46, 47) includes a plurality of apertures (49,52) in the port plate (31) .

4. The axial piston hydraulic unit (10) of claim 3 wherein the apertures (49,52) are circular.

5. The axial piston hydraulic unit (10) of claim 1 wherein the aperture (49,52) has a key hole shape.

6. The axial piston hydraulic unit (10) of claim 1 wherein the aperture (49,52) defines an orifice area less than the minimum flow area through the pocket (48,51) .