GB2188985A

GB2188985A - Fluid pressure operated motor

Info

Publication number: GB2188985A
Application number: GB08609019A
Authority: GB
Inventors: Roland Arthur Warr
Original assignee: TRW Steering Systems Ltd
Current assignee: TRW Steering Systems Ltd
Priority date: 1986-04-14
Filing date: 1986-04-14
Publication date: 1987-10-14
Also published as: IT8720075A0; GB8609019D0; GB2188985B; IT1204517B

Abstract

Formed within the motor housing 4 is a helical recess 6 which forms with the surface of a cylindrical rod 1 a helical chamber. Carried by the rod 1 is a radial projection 9 which slidably engages in the recess 6. The housing 4 has ports 7, 8 through which a fluid pressure differential can be applied in the helical chamber across the projection 9 to displace that projection along the helical recess and thereby impart simultaneous axial and rotational displacement of the rod 1 relative to the housing 4. The helical recess 6 may be formed by a helical preform secured within a cylindrical bore of the housing 4 and the projection 9 may be a component secured to the rod 1. In an alternative arrangement the helical recess can be formed on the rod 1 by a helical preform secured thereto while the radial projection is carried to project from the bore of the housing and engage in the helical recess. <IMAGE>

Description

SPECIFICATION A fluid pressure operated motor TECHNICAL FIELD & BACKGROUND ART The present invention relates to a fluid pressure operated motor and is primarily concerned with such a motor from which can be derived simultaneous axial and rotational displacement.

In machining operations there may be a requirement for simultaneous axial and rotational displacement of a component such as a cutting tool. An example of such a requirement is to be found in our British Patent Specification No. 2,100,158, where a cutting tool for forming the teeth of a rack is subjected to axial displacement while being rotated about said axis to effect its cutting operation. By the proposal in our aforementioned prior Patent the axial displacement of the cutter is achieved by a double acting piston and cylinder device while the simultaneous rotation of the cutter is controlled by a gear system.The arrangement in the fom described in our prior Patent or a generally similar arrangement is widely employed but it is considered to be both cumbersome and expensive due to the requirement for a fluid pressure operated motor to provide the axial displacement and a gear system to provide the rotary displacement. It is an object of the present invention to provide a fluid pressure operated motor which provides simultaneous axial and rotational displacement and which alleviates the disadvantages of prior proposals in so far as it may be simply and inexpensively manufactured and be of a relatively compact construction.

STATEMENT OF INVENTION & ADVANTAGES According to the present invention there is provided a fluid pressure operated motor providing simultaneous axial and rotational displacement which comprises an axially extending tubular housing member; a core member mounted in the housing member and axially and rotationally displaceable relative thereto; a first of said members having a helical recess in a peripheral wall thereof which recess forms with an opposing peripheral wall of the second member a helically extending chamber; the second of said members having a radial projection on its said peripheral wall which engages in said helically extending chamber, and fluid ports communicating with said helically extending chamber on helically opposite sides of the projection and by which the projection can be subjected to a fluid pressure differential to cause relative displacement between said projection and said helical recess and thereby relative simultaneous axial and rotational displacement between the two members.

By the present invention it is envisaged that the projection and helical chamber in which the projection is located effectively act as a piston and helical cylinder device so that when the projection is subjected to a fluid pressure differential on opposite sides thereof within the helical chamber, relative displacement between the projection and the annular recess will drive one member with simultaneous axial and rotational displacement relative to the other member. Consequently fluid pressure and exhaust can be applied alternately to opposite sides of the projection in the helical chamber in a similar manner to a double acting piston and cylinder device to provide the required control to relative displacement between the two members.Usually the helical recess will be regular in so far as it will be of a constant pitch but, if required, the helix of the recess can have a varying pitch provided that the projection is unhindered during its displacement relative to the helical recess.

It is preferred that the projection is relatively long within the helical chamber and is a close sliding fit within the helical recess to alleviate fluid leakage across the projection from one side of the projection to the other in the helical chamber. With such a relatively long projection, the latter conveniently has a part helical profile corresponding to the helix of the recess so that, as the projection and helical recess are displaced relative to each other, one can follow the helix of the other with a relatively smooth motion and with the opposing faces in closed proximity to each other (to alleviate fluid leakage over the length of the projection).

The helical recess can be formed in the internal peripheral wall of the tubular housing member or on the external peripheral wall of the core member while the projection is respectively located on the external peripheral wall of the core member or on the internal peripheral wall of the housing member as the case may be.

To facilitate manufacture, the helical recess conveniently comprises a helical member or preform which is securely attached to a cylindrical surface so that axially opposed and helically formed faces of the helical member form opposed side faces of the helical recess while the aforementioned cylindrical surface forms a root or bottom face of the helical recess.

Such a helical member may be received in and secured to a cylindrical bore to form the tubular housing or may be received on and secured to a cylindrical bar or similar part to form the core member (depending upon whether the projection is carried by the core member or by the tubular housing member).

Similarly the projection may be in the form of a separate component which is firmly secured to the member by which it is carried.

Preferably the helical recess and projection received therein are of constant and complementary rectangular section for ease of manufacture and to achieve uniformity (although it will be apparent that other cross sectional shapes can be employed).

The motor of the present invention will usually be intended for hydraulic fluid pressure operation but it will be appreciated that the invention can be used with advantage with gas pressure operation.

DRAWINGS One embodiment of a fluid pressure operated motor constructed in accordance with the present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings in which: Figure 1 diagrammatically illustrates an axial section through the motor; Figure 2 is a perspective view of a core which is to be displaced with simultaneous axial and rotary motion in the motor of Fig. 1; Figure 3 is an end view of the core shown in Fig. 2 and illustrates the manner in which a projection is attached thereto, and Figure 4 shows a helical preform which is incorporated in a housing of the motor in Fig.

1 to facilitate manufacture of a helical recess in that housing within which recess the projection referred to in Fig. 3 is received.

DETAILED DESCRIPTION OF DRA WINGS The motor shown in Fig. 1 has a cylindrical rod 1 which is intended to provide an output of the motor and, for example, carries a cutter 2 which is intended to be displaced along the axis 3 of the rod 1 and simultaneously rotated about said axis. The rod 1 is slidably mounted in a tubular housing 4 to extend, in sealed manner, through end plates or caps shown generally at 5 of the housing.

Formed within the housing 4 and located between the cylindrical surface of the rod 1 and the wall of the housing 4 which opposes that surface is a helical recess 6. The recess 6 follows a regular helix (in so far as it has a constant pitch) and is comprised in the wall of the tubular housing 4 to define, with the cylindrical surface of the rod 1, a helical chamber the cross-section of which is rectangular and constant throughout the helical extent of the recess 6. The cylindrical surface of the rod 1 is a close and smooth sliding fit within the opposing helical face 4a of the tubular housing.

Communicating with one end of the helical chamber formed by the recess 6 is a fluid port 7 in the tubular housing 4 while the other end of the helical chamber communicates with a fluid port 8 in the housing 4.

Mounted for displacement with the rod 1 and forming therewith a core member is a projection 9 which extends radially outwardly from the rod 1 to engage in the helical recess 6. The projection 9 is of part helical configuration complementary to the helix of the recess 6, is located on the rod 1 to mate in complementary manner with the helix of the recess 6, and is of rectangular section complementary to the section of the recess 6. As shown in Fig. 3, the projection 9 is conveniently secured by screws 10 to the cylindrical surface of the rod 1.

The projection 9 effectively forms, within the helical chamber comprising the recess 6 a piston which, when subjected to a fluid pressure differential (provided through ports 7 and 8) across its helically opposed end faces, will be displaced along the helical recess 6 and thereby drive the rod 1 both axially and rotationally relative to the tubular housing 4. It will be apparent that by appropriate application of fluid under pressure and exhaust alternately to the respective ports 7 and 8, the projection 9 and helical chamber comprising the recess 6 can serve as a double acting piston and cylinder device to reciprocate the simultaneous axial and rotary motion which is applied to the cutter 2.

The helical recess 6 can be machined as an integral part of the tubular housing 4. However, it is preferred for convenience of manufacture that the recess 6 is partly defined by a helical preform which is fitted within and secured to a plane cylindrical bore in the housing 4. Such a preform is shown in Fig. 4 which comprises a helical insert 11 of rectangular section and having a pitch corresponding to that of the helical recess 6. The outer peripheral helical face 4b of the preform 11 lies on a notional cylinder corresponding in diameter to that of a plane bore within which the preform is to be received in the tubular housing 4 while the inner peripheral helical face 4a of the preform lies on a notional cylinder which is co-axial with the first mentioned cylinder and corresponds in diameter to that of the cylindrical rod 1 which is to be slidably received within the insert 11.When positioned within the bore of the housing 4, the axially opposed side faces 12 and 13 of the insert define with the cylindrical surface of the bore in the housing the helical recess 6 within which the projection 9 is helically displaceable.

The insert 11 is secured to the tubular housing 4, conveniently by screws 20 which pass through the wall of the housing into the body of the insert 11 although it will be appreciated that other means of retention can be provided such as an adhesive.

It will be seen from Fig. 2 that the part helical form of the projection 9 is relatively long in the direction of the helix so that, with the projection engaging as a close sliding fit within the helical chamber formed by the recess 6 and fluid leakage which occurs from one side of the projection to the other (between the walls of the projection and those of the recess 6) is likeiy to be negligible.

Claims

1. A fluid pressure operated motor providing simultaneous axial and rotational displace ment which comprises an axially extending tubular housing member; a core member mounted in the housing member and axially and rotationally displaceable relative thereto; a first of said members having a helical recess in a peripheral wall thereof which recess forms with an opposing peripheral wall of the second member a helically extending chamber; the second of said members having a radial projection on its said peripheral wall which engages in said helically extending chamber, and fluid ports communicating with said helically extending chamber on helically opposite sides of the projection and by which the projection can be subjected to a fluid pressure differential to cause relative displacement between said projection and said helical recess and thereby relative simultaneous axial and rotational displacement between the two members.

2. A motor as claimed in claim 1 in which the helix of the recess is substantially regular.

3. A motor as claimed in either claim 1 or claim 2 in which the projection has a part helical profile substantially corresponding to the helix of the recess.

4. A motor as claimed in any one of the preceding claims in which the projection is substantially complementary to and received as a close sliding fit within the helical recess to alleviate fluid leakage across the projection from one side thereof to the other in the helical chamber.

5. A motor as claimed in any one of the preceding claims in which the helical recess is of constant rectangular section.

6. A motor as claimed in any one of the preceding claims in which the helical recess comprises a helical member or preform which is securely attached as part of the first member so that axially opposed and helically formed faces of the helical member form opposed side faces of the helical recess for that member.

7. A motor as claimed in claim 6 in which the helical member or preform is securely attached to a cylindrical surface of the first member and said cylindrical surface forms a root or bottom face of the helical recess.

8. A motor as claimed in either claim 6 or claim 7 in which the helical member or preform is securely attached by screws or adhesive.

9. A motor as claimed in any one of claims 6 to 8 in which the helical member or preform is received in and secured to a bore to comprise said tubular housing member and the projection is carried by the core member.

10. A motor as claimed in any one of claims 6 to 8 in which the helical member or preform is received on and secured to a bar part to comprise said core member and the projection is carried by the tubular housing member.

11. A motor as claimed in any one of the preceding claims in which the radial projection comprises a component which is secured as part of the second member.

12. A fluid pressure operated motor substantially as herein described with reference to the accompanying illustrative drawings.