GB2064662A

GB2064662A - Fluid Actuator

Info

Publication number: GB2064662A
Application number: GB8037885A
Authority: GB
Original assignee: PERLIT ENG DEV
Current assignee: PERLIT ENG DEV
Priority date: 1979-12-04
Filing date: 1980-11-26
Publication date: 1981-06-17
Also published as: GB2064662B

Abstract

A fluid actuator comprises a cylindrical body (11) defining an interior chamber (14) within which is located a piston assembly (15) which isolates fluid outlet means (5) at one end (12) of the chamber from fluid inlet means (1, 2, 3, 4) at the other end (13) of the chamber. Assembly (15) comprises a central cylindrical piston element (15D) concentrically surrounded by at least one annular piston element (15A, 15B, 15C) and is resiliently urged by spring (16) to seat against the end (13) of the body (11). Face seals (L, K, M and N) are provided at end (13) for respective piston elements (15A, 15B, 15C, 15D) and individual inlet ports (1, 2, 3, 4) penetrate the seals (L, K, M, N) to provide for fluid delivery against individual piston elements. Adjoining piston elements incorporate a one- way mechanical connection so that spring (16) enables all piston elements to be urged against end (13). <IMAGE>

Description

SPECIFICATION Fluid Actuator This invention relates to fluid actuators.

In the control of fluid-operated devices such as motors, rams, rotary/linear motion converters and the like, it is frequently required to effect a displacement of the movable component within the device which is only a fraction of the full displacement available. This has been achieved hitherto by the use of external mechanical constraints such as positional stops, clutches and brakes depending upon the nature of the fluidoperated device.

It is an object of the present invention to provide a fluid actuator for use with a fluid operated device which can be operated in a selective manner to effect selective fractional displacements of the movable component within the device.

According to the present invention there is provided a fluid actuator comprising a body defining a chamber within which there is located a piston assembly which isolates fluid outlet means at one end of the chamber from fluid inlet means at the other end of the chamber, said assembly being resiliently urged towards said fluid inlet means and comprising a central cylindrical piston element concentrically surrounded by at least one annular piston element, said fluid inlet means comprising a plurality of inlet ports respectively arranged to deliver fluid to act against said piston elements, the arrangement being such that by selective application of pressurised fluid to said inlet ports one or more of said piston elements is displaced towards the fluid outlet means.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, in which: Fig. 1 illustrates the piston assembly in abutment with the fluid inlet means, and Fig. 2 illustrates a different position of the piston assembly.

In the drawing the fluid actuator comprises a body 10 formed by a hollow cylindrical casing 11 with end walls 12, 13 thereby defining an interior chamber 14. The wall 12 contains a fluid outlet port 5 and the wall 13 contains fluid inlet ports 1, 2, 3, 4. Within the chamber 14 there is a piston assembly 15 which isolates port 5 from each of ports 1, 2, 3 and 4.The assembly 15 comprises a central cylindrical piston element 1 SD which is concentrically surrounded by annular piston elements 1 so, 1 SB and 1 so. The piston elements 1 5A, 1 SB, 1 so, 1 5D are slidable with respect to each other and sealing rings are located between adjoining elements and between element 1 SA and casing 11.

A helical spring 1 6 is seated in end wall 12 and bears against piston element 1 SA to urge that element towards wall 13. Piston element 1 SA has a one-way mechanical connection with element 1 SB by virtue of a radially projecting flange 1 5F which overlaps part of piston element 1 SB so that the resilient biassing force imposed by spring 1 6 on element 1 SA is transmitted to element 1 SB when flange 1 SF is in contact with piston element 1 SB. There are similar one-way connections between piston elements 1 SB and 1 SC and between 1 SC and 1 sod. Back pressure within the chamber 14 aids the operation of the spring 1 6 which can therefore be of minimal strength.

The inlet ports 1, 2, 3, 4 are respectively aligned with piston elements 1 so, 1 SB, 1 SC and 1 5D and at the respective interfaces between end wall 13 and the piston elements there are annular face seals L, K, M and N so that piston element 1 5A seats against face seal L, element 1 5B against face seal K, element 1 SC against face seal M, and element 1 SD against face seal N.

In operation, pressurised fluid from a source (not shown) is selectively applied to one of the inlet ports 1, 2, 3 or 4 in order to displace one or more of the piston elements. For example, as shown in Fig. 2 with fluid applied to port 2 piston element 1 SB is displaced towards outlet port 5 and because of the one-way mechanical connection with piston element 1 SA this latter element is also displaced towards outlet port 5.

The total fluid displacement by the actuator 10 equals the longitudinal travel of piston elements 1 5A, 1 SB multiplied by the combined crosssectional area of the delivery side of the piston elements 1 so, 1 SB. When the pressure applied to inlet port 2 is released spring 1 6 returns piston elements 1 so, 1 SB to the Fig. 1 position. It will be noted that at the one-way connection between adjacent piston elements the leading face of one piston is chamfered, for example at 18. This permits pressurised fluid in chamber 14 to act on both sides of the overlapping flange, e.g. 1 5F thereby excluding the area of the flange from the expression defining the fluid displacement of the actuator.

In the event that it is desired to limit or vary the stroke of the assembly 1 5 an adjustable wall 1 9 can be fitted to the interior of the chamber 14 by a screw-threaded connection to socket 20 concentric with the outlet port 5 as illustrated in phantom in Fig. 1.

The actuator 10 may be used to provide an inching or incremental movement facility for a hydraulic motor, for example, by connecting port 5 to a tee piece in the hydraulic line between the hydraulic motor and the hydraulic power source and shut-off valve used for normal continuous operation of the motor. Then, to achieve rotational position-correction of the motor when at rest and with the shut-off valve closed the actuator 10 can be energised by application of fluid power (either hydraulic or pneumatic) to a selected inlet port 1, 2, 3 or 4 to deliver a selected hydraulic volume to the motor thereby causing incremental rotation thereof by a corresponding amount. With this arrangement the normal running of the motor is unimpeded since the piston assembly 1 5 of the actuator 10 isolates inlet ports 1, 2, 3, 4 from outlet port 5.

Various modifications may be made to the actuator described above, for example, the piston elements need not be four in number-any number could be used; a different form of spring biassing arrangement could be used and indeed such biassing could be applied individually to the piston elements thereby avoiding the need for the inter-piston one-way connection. The relative dimensions of the various illustrated components could be altered and, for example, the area of the piston element faces at the input side of the actuator could be greater than at the output side thereby providing a fluid-pressure amplification.

Claims

1. A fluid actuator comprising a body defining a chamber within which there is located a piston assembly which isolates fluid outlet means at one end of the chamber from fluid inlet means at the other end of the chamber, said assembly being resiliently urged towards said fluid inlet means and comprising a central cylindrical piston element concentrically surrounded by at least one annular piston element, said fluid inlet means comprising a plurality of inlet ports respectively arranged to deliver fluid to act against said piston elements, the arrangement being such that by selective application of pressurised fluid to said inlet ports one or more of said piston elements is displaced towards the fluid outlet means.

2. An actuator as claimed in claim 1 , wherein the face of each said piston element adjacent said fluid inlet means is engageable with an annular seal carried thereby and which is penetrated by the pertaining inlet port.

3. An actuator as claimed in claim 2, wherein said annular seals are mutually offset axially of the chamber and said piston elements have respective axial lengths whereby the face of said piston assembly adjacent said fluid outlet port is substantially planar when the piston elements are respectively seated against said annular seals.

4. An actuator as claimed in any preceding claim, wherein a biassing means resiliently urges one of said piston elements towards said fluid inlet means and adjoining piston elements include a one-way mechanical connection whereby all piston elements are urged towards said fluid inlet means.

5. An actuator as claimed in any preceding claim, wherein said chamber includes a positionadjustable end wall whereby the maximum stroke of said piston assembly can be adjusted.

6. A fluid actuator substantially as hereinbefore described with reference to the accompanying drawing.