US3889578A - Axial piston rotary barrel type hydraulic pumps or motors - Google Patents

Abstract

The invention obviates distortion in the cylinder liners of axial piston pump/motors by flooding a space around the liners with working fluid derived from the pump/motor ports, so that the liners are subject to equal internal and external pressures.

Description

United States Patent 1 Clerk 1 AXIAL PISTON ROTARY BARREL TYPE HYDRAULIC PUMPS OR MOTORS June 17, 1975 2,518,787 8/1950 Huhtala 92/164 2,678,247 5/1954 Geyer 92/169 2.815.718 12/1957 Avery 91/498 3,169.488 2/1965 Galliger i. 91/507 3,656.407 4/1972 Hause 91/494 Primary ExaminerWilliam L. Freeh Attorney, Agent, or Firm-Imirie, Smiley & Linn [57] ABSTRACT The invention obviates distortion in the cylinder liners of axial piston pump/motors by flooding a space around the liners with working fluid derived from the pump/motor ports, so that the liners are subject to equal internal and external pressures.

4 Claims, 2 Drawing Figures [76] Inventor: Robert Cecil Clerk, Edison House,

Fullerton Rd., Glenrothes, Fife, Scotland [22] Filed: June 15, 1973 [21] App]. No.: 370,345

[52] US. Cl. 91/499 [51] Int. Cl. F0lb 13/04 [58] Field of Search 91/499, 507, 498; 92/169, 92/164 [56] References Cited UNlTED STATES PATENTS 2,487,920 11/1949 Celenza 92/169 fi f PATENTEDJUK 17 I975 SHEET FIG.|

AXIAL PISTON ROTARY BARREL TYPE HYDRAULIC PUMPS OR MOTORS BACKGROUND OF THE INVENTION This invention relates to axial piston rotary barrel type hydraulic pumps or motors with means for reducing strain in the cylinder walls.

In high pressure hydraulic pumps and motors. and in particular axial piston configurations, the assembled running clearance of the pistons in the cylinders is partly determined by the anticipated strain distortion of the cylinders under pressure as it affects the circularity and linear alignment of the cylinder bores. However. this same strain at the same time increases the diametral running clearance of the cylinder over the piston, and as the leakage slip past the piston is a cube function of the clearance and a linear function of the pressure, the tendency to high leakage at high pressure is usually met by increasing the length of the leakage path, i.e.. the length of the piston, in spite of this causing greater susceptibility to the effects of cylinder distortion not to mention increasing the mass and inertia of the piston and its frictional surface area.

It is well known to form the cylinder bores by inserting pre-honed sleeves into the barrel. but care is usually exerted in ensuring that the sleeves fit snugly in the bores of the barrel so as to transfer the pressure stress to and share the strain with the barrel material, the pressure fluid being excluded from this area to obviate creep leakage between sleeve and barrel. In other engineering applications wet-liners" are quite common. but the fluid in the space within a cylinder block bore external of the sleeve is not the pressure working fluid but usually a coolant.

SUMMARY OF THE INVENTION The object of the present invention is to provide a form of cylinder within a barrel which is not susceptible in any marked degree to the pressure of the working fluid and the concomitant strain effects in the main operating area of the piston within the cylinder, so that the working clearance of the piston within the cylinder can be a constant regardless of pressure, and the length of the piston can be minimised to permit a precisely de' fined leakage varying only with working pressure by the linear function.

A further object is to enable lower production and assembly costs to be achieved and to allow a wider choice in the material specification of the barrel. as the strain modulus will be less critical.

According to the invention I provide an axial piston rotary barrel type hydraulic pump or motor having a cylinder barrrel including a plurality of substantially axially aligned cylinder bores each of which is fitted with a cylinder liner sealed at its ends to that bore to provide an annular space between the inner wall of the bore and the outer wall ofthe liner, and channels connecting the annular spaces to the cylinder ports so that the spaces are flooded with an subject to the pressure of the working fluid.

Preferably the radial widths of the annular spaces towards the port ends of the bores are made greater than at the remote ends. and this can be achieved either by reducing the thickness of the liners or by enlarging the bore diameters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a central vertical section through a cylindri cal barrel showing one cylinder and liner in detail, and

FIG. 2 is a central vertical section through an alternative form of cylinder and liner.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1, the cylinder barrel 1 is provided with a plurality of oversize, substantially axial bores which receive liners 2.

The liners are inserted from the bottom of the barrel and are sealed to the bores by O- rings 3 and 4 and are kept in place by a star plate 5.

A narrowing of free the section of the liners towards their upper ends provides an enlargement of the volume of annular chambers 6 formed between them and the cylinder barrel 1.

Channels 7 connect the chambers 6 to the cylinder ports 8 which communicate with working fluid transfer ports 12 in a fixed valve block 13 so that those chambers are flooded with and pressurised by the working fluid.

In the alternative form of cylinder shown in FIG. 2 like references are employed as for FIG. I.

The liner 2 in this case is inserted from the top of the cylinder barrel 1 and is sealed to the oversize bore therein by O- rings 3 and 4.

The ring 4 is located between a chamfered keep ring 9 and a shoulder 10 formed on the liner 2. while the ring 3 is trapped in a groove formed in a barrel cover plate II, which in fact is extended upwardly in its central part to constitute a bearing sleeve (not shown).

As before the annular space 6 is flooded with and pressurised by working fluid admitted by channels 7 from the port 8.

For certain pump or motor applications the liners are only loosely entrapped by the star plate and are thus able to rotate randomly to equalise the cylinder bore wear due to either high speed centrifuging of the piston masses or the driving or driven torque transmitted by the pistons.

I claim:

I. An axial piston rotary barrel type hydraulic pump- /motor having a cylinder barrel including a plurality of substantially axially aligned cylinder bores each of which includes a cylinder port in one end communicating with a Working fluid transfer port in a stationary valve block, each of said bores being fitted with a cylinder liner sealed at both of its ends to said bore, the outer diameter ofsaid liner being substantially less than the inner diameter of said bore, to provide a free annular space between the inner wall of the bore and outer wall of the liner. and channels connecting said annular spaces to said cylinder ports whereby said annular space is entirely closed except for communication with said cylinder port through said channels, so that said spaces are flooded with and subject to the pressure of said working fluid.

2. A pump/motor according to claim I, in which the radial widths of the annular spaces towards the port ends of the bores are greater than at the remote ends.

3. A pump/motor according to claim 1 in which *O rings are employed to seal the liners to the cylinder bores.

4. A pump/motor according to claim 1 in which the length of said liners is less than the length of said cylinder bores, so that said liners are free to rotate in said cylinder bores.

Claims (4)

1. An axial piston rotary barrel type hydraulic pump/motor having a cylinder barrel including a plurality of substantially axially aligned cylinder bores each of which includes a cylinder port in one end communicating with a working fluid transfer port in a stationary valve block, each of said bores being fitted with a cylinder liner sealed at both of its ends to said bore, the outer diameter of said liner being substantially less than the inner diameter of said bore, to provide a free annular space between the inner wall of the bore and outer wall of the liner, and channels connecting said annular spaces to said cylinder ports whereby said annular space is entirely closed except for communication with said cylinder port through said channels, so that said spaces are flooded with and subject to the pressure of said working fluid.

2. A pump/motor according to claim 1, in which the radial widths of the annular spaces towards the port ends of the bores are greater than at the remote ends.

3. A pump/motor according to claim 1 in which ''''O'''' rings are employed to seal the liners to the cylinder bores.

4. A pump/motor according to claim 1 in which the length of said liners is less than the length of said cylinder bores, so that said liners are free to rotate in said cylinder bores.

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