US3922956A

US3922956A - Hydraulic motors

Info

Publication number: US3922956A
Application number: US504117A
Authority: US
Inventors: Kenneth William Samuel Foster
Original assignee: Renold Ltd
Current assignee: Renold Ltd
Priority date: 1971-11-09
Filing date: 1974-09-09
Publication date: 1975-12-02
Anticipated expiration: 1992-12-02

Abstract

An hydraulic motor in which a rotatable assemblage of pistons and cylinders has pistons mounting roller followers which run in contact with an annular cam track. To limit the contact stresses at high torque output, the roller followers are disposed at least in part within the cylinders and have an axial length about equal to their diameter. To limit guide wear two stationary guide rings make sliding contact with the roller end faces. The guide rings locate and restrain the rollers axially and maintain their axes parallel. The rollers are tethered to the pistons to permit free wheeling with the rollers out of contact with the track. The rollers are cushioned on resilient, low friction, part cylindrical plastics surfaces which transmit the drive to the followers during the working stroke of the pistons.

Description

United States Patent Foster Dec. 2, 1975 [54] HYDRAULIC MOTORS 1,220,146 1/1971 United Kingdom 91/491 [75] Inventor: Kenneth William Samuel Foster,

prestbury, England Przrna ry ExamzrterW1ll1am L. Freeh Asststant Exammer-G. P. La Polnte Assigneei Renold Limited, Manchester, Attorney, Agent, or Firm-Flynn & Frishauf England [22] Filed: Sept. 9, 1974 ABSTRACT [21] APPL NO: 504,117 An hydraulic motor in which a rotatable assemblage of pistons and cylinders has pistons mounting roller Related APllllcatitm Data followers which run in contact with an annular ,cam [63] Continuation-impart of Set. No. 304,748, N 8, track. To limit the contact stresses at high torque out- 1972, abandoned. put, the roller followers are disposed at least in part within the cylinders and have an axial length about [30] Foreign Application Priority Data equal to their diameter. To limit guide wear two sta- Nov. 9, 1971 United Kingdom 52039/71 tiohaty guide tings make Sliding Contact With the roller end faces. The guide rings locate and restrain the rol- 52 us. 01. 91/491 lets axially and maintain their axes Parallel The 51 1m. (:1. F018 1/06 lers are tethered to the Pistons to permit free wheeling 58 Field of Search 91/491-498 with the rollers out of eentaet with the track- The lers are cushioned on resilient, low friction, part cylin- [56] References Cit d drical plastics surfaces which transmit the drive to the FOREIGN PATENTS OR APPLlCATlONS 6/1970 Germany 91/491 followers during the working stroke of the pistons.

2 Claims, 3 Drawing Figures US. Patent Dec. 2, 1975" 'shetiofz I 3,922,956.

HYDRAULIC MOTORS This application is a continuation-in-part application of my application Ser. No. 304,748, filed Nov. 8, 1972, now abandoned.

This invention relates to hydraulic motors and is concerned with hydraulic motors of the kind (hereinafter referred to as the kind described) comprising an annular cam track, a rotor comprising an assemblage of pistons and cylinders formed in a rotatable member and rotatable therewithin, the pistons mounting followers which, at least during operation of the motor, run in engagement with the track, and valve means for alternately supplying fluid under pressure into and for allowing it to exhaust from each cylinder of said assemblage as the assemblage rotates thereby to drive the followers on the outstroke of the pistons, so as to cause the assemblage to rotate, the pistons being driven on the instroke by the followers to exhaust the working fluid from the cylinders.

SUMMARY OF THE INVENTION An object of the present invention is to limit the contact stress between the followers and the track for high torque outputs.

A further object of the present invention is to limit the wear between the followers and their locating guides.

The invention provides an hydraulic motor of the kind described wherein the followers are formed by rollers disposed at least in part within the cylinders and the rollers make substantially line contact with the track.

The roller followers have an axial length which is about equal to their diameters and which is less than the diameter of the piston to which they are mounted.

Restraining means in the form of two stationary restraining rings is provided on the motor casing the rotor rotating between said rings and the rings making sliding contact with the roller followers for locating and restraining the roller followers axially with their axes of rotation parallel with the axis of rotation of the assemblage of pistons and cylinders.

The restraining rings are retained axially in the motor casing and slidably engage opposite circular end faces of the roller followers respectively, the rotatable member having cut-away portions on opposite sides thereof to provide a clearance between said rotor and said rings.

BRIEF DESCRIPTION OF THE DRAWINGS A specific embodiment of the present invention will now be described by way of example with reference t the accompanying drawings wherein:

FIG. 1 is a cross section of line XX in FIG. 2 showing an hydraulic motor according to this invention,

FIG. 2 is a section on lines AA and BB in FIG. 1 on the two sides of the line CC in FIG. 2 respectively, and

FIG. 3 is an enlarged view of a portion of FIG. 2.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS Referring to the accompanying drawings, the motor comprises a stationary

casing comprising parts

1, 3, 4, 6, 22, 25 and 36 as described in detail in my US. Pat. No. 3,844,198, issued Oct. 29, 1974.

The casing fixedly mounts an annular cam disc 27 presenting an annular cam track and, rotatable therewithin, a rotor comprising an assemblage of pistons 60 and cylinders 51, formed in a cylinder block 52, as described in my hereinbefore mentioned US. Pat. No. 3,844,198, in which in certain instances, different reference numerals are used. The pistons 60 mount roller followers 63 in engagement with the track of the disc 27.

Valve means is provided for alternately supplying fluid under pressure into, and allowing it to exhaust from, the cylinders 51 as the assemblage of pistons and cylinders rotates. The valve means is as described in detail in my US. Pat. No. 3,875,851, issued Apr. 8, 1975.

On the outstroke of the pistons the roller followers 63 are driven against the cam track and the pistons are in turn driven on the instroke by the followers 63 running in engagement with the cam track.

The cam disc 27 has four lobes as shown in FIG. 1. These control the movement of the pistons 60 in the cylinders 51. Because of the shape of the profile of the cam lobes and the angular disposition of the lobes in relation to the sets of inlet and outlet ports supplying pressure fluid to, and allowing it to exhaust from the cylinders 51, a component of force at to the centre of each cylinder and acting in a plane normal to the axis of rotation of the assemblage of cylinders and pistons is generated on each outstroke of each piston. This force drives the assemblage of pistons and cylinders in rotation to provide the output drive from the motor since the outlet ports are uncovered in appropriate sequence and the back-pressure in the exhaust passages is only sufficient to maintain the roller followers 63 in contact with the cam track and does not therefore significantly resist rotation of the assemblage of pistons and cylinders.

There are three cylinders 51 provided to any two lobes on the cam disc and the lobes are so shaped and arranged that the sum of the torques applied by pistons on the outstroke remains substantially constant.

Each piston 60 has a cross boring 61 at its crown, the axis of the cross boring lying parallel with the axis of rotation of the

assemblage

51, 60 and normal to the piston and cylinder axis. The cross boring presents a part cylindrical bearing surface for the roller follower 63 mounted on the piston which extends through an angle greater than whereby the roller is anchored to the piston so as to be retained thereon irrespective of the movement of the piston in its cylinder and irrespective of the engagement of the roller with the cam track. The roller follower has an axial length equal to the length of the cross boring which is symmetrically disposed in relation to the axis of the piston, and the roller follower is disposed at least in part within the cylinder during rotation of the piston and cylinder assemblage, having an axial length which is less than the cylinder diameter. Thus, the piston is cut away on opposite sides as at 68 and 69, as more clearly seen in FIG. 3, and the cylinder block 52 is cut away on opposite sides as at 70 and 71 to accommodate

identical steel rings

201 and 202.

The

rings

201 and 202 slidably engage the circular end faces of the roller followers 63 and act to locate the roller followers axially and also to maintain the roller axes parallel with the rotational axis of the assemblage of pistons and

cylinders

51,60. Thus, the

rings

201 and 202 maintain the roller followers in correct rolling relationship with the cam track.

The roller followers are supported on the bearing surfaces presented by the cross borings 61 on a lining 82 of friction reducing material reinforced with metal strip. The friction reducing material may be a plastics material which is coated onto the metal strip and the metal strip may be curled to fit the cross borings.

The roller followers may be parallel, or crowned (i.e. slightly tapered towards their ends) in known fashion, to reduce edge stresses in the rollers.

The

rings

201 and 202 are retained axially in the easing between the cam disc 27 and the bottom of

recesses

203 and 204 formed in the

casing halves

22 and 25 respectively. The

recesses

203 and 204 have a width equal to or slightly greater than the thickness of the

rings

201 and 202.

The

rings

201 and 202 may be formed integrally with the

casing halves

22 and 25 if desired.

The

recesses

203 and 204 are not circumferentially continuous with respect to the casing halves but are calised in internal bosses round the bolts 26 and dowels 28 as clearly shown for the recesses 204 in FIG. 1.

The

rings

201 and 202 are fixed with respect to the motor casing and act to restrain the roller followers 63 axially and with their axes of rotation parallel with the axes of rotation of the piston-and-

cylinder assemblage

51,60.

The confronting surfaces of the

retaining rings

201, 202 and the roller follower end faces are relatively movable. Because of this relative movement, a hydrodynamic lubricating film of the working fluid supplied to the motor is formed between the confronting faces of the

retaining rings

201, 202 and the roller end faces, thereby reducing or preventing wear of these surfaces and faces during operation of the motor.

Thus, the working life of the motor is considerably, improved, more particularly since the retaining rings are required to maintain the axes of the roller followers 63 parallel to the axes of rotation of the piston and cylinder assemblage so that purely rolling contact of the roller followers with the cam track is maintained, and wear of the roller end faces allows the rollers to take up a scewed position which interferes with the maintenance of such purely rolling contact, such that still further wear ensues.

The roller followers 63 have substantially line contact with the cam track. This allows for a high torque output for a given contact stress.

Because the roller followers 63 are positioned at least in part within the cylinders, the overall radius of the motor is reduced, thereby reducing its physical size for a given motor rating and still further limiting the contact stress between the roller followers and the cam track for high torque ourput by virtue of the lesser radius at which the roller followers are required to operate.

The use of the low-friction material presenting plastics surfaces to transmit the drive to the roller followers on the outstroke of the pistons considerably reduces friction losses at the cylindrical roller surfaces. It also accommodates any roller crowning without any special machining.

Since the roller followers are tethered to the pistons the roller followers may be retracted with the pistons out of contact with the cam track to put the motor into a free wheeling mode. This may be achieved by supplying fluid under pressure into the motor casing around the outside of the assemblage of pistons and

cylinders

51, 60 and venting the fluid pressure inlet to 4 the fluid pressure supply ports of the valving means to tank. This has the effect of driving the pistons to the bottoms of their bores.

The roller followers 63 may be hollow if desired. This not only reduces their weight, with advantage, but also increases the deformation of the rollers when transmitting drive, giving rise to an increased radius of curvature at the line of contact, whereby the contact stresses may be still further reduced.

A motor according to the present invention and constructed generally as hereinbefore described may be provided with an assemblage of two or more rows of pistons and

cylinders

51, 60 as described in my hereinbefore mentioned U.S. Pat. Nos. 3,844,198 and 3,875,851. The pistons mount roller followers as described herein with reference to FIGS. 1 and 2. The individual rows of pistons and cylinders may each rotate within its own cam disc identical with that described herein, adjacent cam discs being separated by a plain spacer ring. Altematively,-in the case of roller followers mounted as described herein with reference to FIGS. 1 and 2 the individual cam discs and spacers ring or rings could be replaced by a single, wide cam disc. However, the use of a plurality of discs is preferred, particularly if adjacent cylinders or adjacent rows are staggered as described in my hereinbefore mentioned U.S. Pat. Nos. 3,844,198 and 3,875,851 instead of being placed side by side.

Each lining 82 is preferably composed of a sintered, loosely packed layer of metal particles of graded size, supported on the metal backing strip, a and a plastics film supported by and keyed to the sintered layer, the plastics film forming the bearing surface.

The metal backing strip may be of low carbon steel and the sinter material a bronze type. Suitable plastics materials for the bearing surface may be based on Acetal, Polyvinylidene fluoride, Polysulfone, Polyamide, Polyimide, and others with the necessary chemical properties for compatibility with the lubricating fluid, physical properties to support the load without unwanted permanent distortions, thermal properties to retain the physical strength and dissipate unwanted heat, and desirable low coefficient of friction when in contact with the follower in the presence of the lubricating fluid.

Alternatively, the plastics films may be attached to the backing strip by a suitable adhesive or may be attached by a direct coating process applicable to the particular plastics material being used.

The roller followers 63 are preferably of an axial length about equal to their diameter. Preferably also the diameter of the roller followers is between 0.65 and 0.75 the diameter of the piston 60.

Instead of being hollow, the roller followers may be only partially hollow, and the roller follower ends are not necessarily closed. Thus, the roller followers could be cylindrical tubes.

The cross borings 61 may present part cylindrical bearing surfaces of or less, the cross borings themselves however, still subtending an angle of more than 180, so as to loosely tether the roller followers to the pistons. This reduces the frictional drag of the roller followers on 'the bearing surfaces.

Parts shown in the accompanying drawings which have not been described herein or which have not been described herein in detail, are fully and clearly described in one ot other of my hereinbefore mentioned U.S. Pat. Nos. 3,844,198 and 3,875,851, and the disclosures of these are to be regarded as incorporated by reference in the present specification.

I claim: 1. An hydraulic motor comprising: an annular cam track, an assemblage of pistons and cylinders rotatable therewithin, said pistons being mounted on a rotatable member to form a rotor;

roller followers mounted to respective pistons so that 1 the roller followers are disposed at least in part within the cylinders, the roller followers, at least during operation of the motor, running in engagement with and making substantially line contact with the cam track, and the roller followers having an axial length which is about equal to their diameters and'which is less than the diameter of the piston to which they are mounted;

restraining means on the motor casing and making sliding contact with the roller followers for locating and restraining the roller followers axially with their axes of rotation parallel with the axis of rotation of the assemblage of pistons and cylinders, said restraining means comprising two stationary retaining rings between which said rotor rotates, said rings being retained axially in the motor casing and slidably engaging opposite circular end faces of the roller followers respectively,

said rotatable member having cut away portions on opposite sides thereof to provide a clearance between said rotor and said rings, and

valve means for alternately supplying fluid under pressure'into and for allowing it to exhaust from each cylinder of the assemblage of pistons and cylinders as the assemblage rotates, to thereby drive the followers on the outstroke of the pistons so as to cause the assemblage to rotate, the pistons being driven on the instroke by the followers to exhaust the working fluid from the cylinders.

2. An hydraulic motor according to claim 1 wherein said retaining rings are removably mounted on the motor casing.

Claims

1. An hydraulic motor comprising: an annular cam track, an assemblage of pistons and cylinders rotatable therewithin, said pistons being mounted on a rotatable member to form a rotor; roller followers mounted to respective pistons so that the roller followers are disposed at least in part within the cylinders, the roller followers, at least during operation of the motor, running in engagement with and making substantially line contact with the cam track, and the roller followers having an axial length which is about equal to their diameters and which is less than the diameter of the piston to which they are mounted; restraining means on the motor casing and making sliding contact with the roller followers for locating and restraining the roller followers axially with their axes of rotation parallel with the axis of rotation of the assemblage of pistons and cylinders, said restraining means comprising two stationary retaining rings between which said rotor rotates, said rings Being retained axially in the motor casing and slidably engaging opposite circular end faces of the roller followers respectively, said rotatable member having cut away portions on opposite sides thereof to provide a clearance between said rotor and said rings, and valve means for alternately supplying fluid under pressure into and for allowing it to exhaust from each cylinder of the assemblage of pistons and cylinders as the assemblage rotates, to thereby drive the followers on the outstroke of the pistons so as to cause the assemblage to rotate, the pistons being driven on the instroke by the followers to exhaust the working fluid from the cylinders.