US3793925A - Fluid pressure-operated piston/cylinder units - Google Patents

Abstract

The stroke of the piston of a pneumatic piston/cylinder unit is controlled by an auxiliary hydraulic piston/cylinder unit fitted to the base end of the main unit. Auxiliary piston is projected into main cylinder under static hydraulic pressure so that base position of main piston is determined by abutment with auxiliary piston. Adjustment of static pressure varies base position and hence stroke of main piston.

Description

D United States Patent 11 1 1111 3,793,925 Collin Feb. 26, 1974 [54] FLUID PRESSURE-OPERATED 2,430,597 11/1947 Acton 92/13.1 x PISTON/CYLINDER UNITS 2,55l,246 5/1951 92/63 X 2,650,572 9/l953 92/62 X [75] Inventor: Stanley Collin, Fleckney, England 2 33 4 4 95 92/62 X [73] Assignee: Livingston and Doughty Limited, i Le'cestershlre" England 3,514,950 6/1970 Davenport 1. 60/54.6 R x [22] Filed: June 15, 1972 Primary Examiner-Martin P. Schwadron [21] Appl' 262,968 Assistant ExaminerAbe Hershkovitz Attorney, Agent, or FirmRoberts B. Larson [30] Foreign Application Priority Data June 15, 1971 Great Britain 27906/71 [571 ABSTRACT The stroke of the piston of a pneumatic piston/cylin- [52] U.S. Cl 92/13.l, 92/63 r unit i ontrolled by an auxiliary hydraulic piston/- [51] Int. Cl. F01b 31/14, Fl5b 15/24 y n r unit fi e to he base en of the main unit. [58] Field of Search 92/l3.10, 13.4, 15, 62, 63 Auxiliary piston is projected into main cylinder under static hydraulic pressure so that base position of main [56] References Cit d piston is determined by abutment with auxiliary pis- UNITED STATES PATENTS ton. Adjustment of static pressure varies base position 2,244,562 6/1941 Loweke 92/63 x and hence Stroke of mam Plswn' 2,358,826 9/1944 Purat 92/l3.1 X 3 Claims, 1 Drawing Figure PAT ENIEn FEB26 m4 FLUID PRESSURE-OPERATED PISTON/CYLINDER UNITS This invention relates to fluid pressure-operated piston/cylinder units, and has for its object to provide a novel form of stop means for controlling the stroke of the piston of a unit of this kind.

According to the invention, the stroke of a main piston/cylinder unit is controlled by stop means comprising an auxiliary piston/cylinder unit to which a static fluid pressure is applied in use and which is arranged to provide a fluid pressure-biassed stop limiting movement of the piston of the main unit in one direction, whereby the magnitude of the static fluid pressure determines the stroke of piston of the main unit.

It will be appreciated that this fluid pressureoperated stop provides a readily-adjustable means of controlling the stroke of the piston of the main unit since the position at which the main piston is arrested can be varied simply by adjusting the static fluid pressure applied to the auxiliary unit.

Primarily, but not exclusively, the invention has been devised for controlling the stroke of a fast-moving pneumatic piston/cylinder unit, in which case the auxiliary unit is preferably hydraulically operated and provides for accurate control of the stroke of the main unit. It is, however, to be understood that there is no limitation in this respect.

The magnitude of the static pressure applied to the auxiliary piston/cylinder unit may be controlled by a valve in the supply line to the unit, or by varying the output of the pressure source, e.g., a conventional master cylinder.

Whatever means are used to control the fluid pressure, they are preferably calibrated to indicate to an operative the position in which the piston of the main unit will be arrested for each particular setting. The calibrations may be in terms of the length of stroke of the piston or in other appropriate units depending on the use to which the unit is put.

Preferably, the auxiliary piston/cylinder unit is mounted co-axially on the closed or base end of the main unit (i.e., the end remote from the piston) with its piston projecting into the cylinder of the main unit so that the stroke of the piston of the latter will be determined by abutment with the piston of the auxiliary unit. As the piston of the main unit is retracted towards the base end of the cylinder, it will move the auxiliary piston against the action of the static fluid pressure until the force moving the main piston equals the static pressure, when both pistons will be arrested.

In this construction, a bore will have to be provided in the base end of the main cylinder to receive the piston of the auxiliary cylinder. Preferably, the piston of the auxiliary unit projects through an axial bore in the base and of the cylinder of the main unit, a seal being provided around the auxiliary piston to prevent fluid leakage from the main cylinder.

To facilitate understanding of the invention and to enable it to be readily carried into practice, reference will now be made to the accompanying drawing which is alongitudinal sectional view through a fluid pressureoperated stop constructed in accordance with the invention, fitted to the base end of a main pneumatic piston/cylinder unit.

In the drawings, the main unit is generally designated 1 and has fitted to its base end 2 an auxiliary piston cylinder unit 3 which is hydraulically operated.

The main piston/cylinder unit 1 is basically of conventional form, comprising a cylinder 4 having a piston 5 slidably mounted therein. Cylinder 4 has the usual air line connections, the inlet/exhaust port at the base end of the cylinder being indicated at 6.

Numeral 7 denotes the base end fitment of the main unit 1. Normally, the fitment is solid at its centre. However, in this embodiment, it is provided with an axial bore 8 and with an externally screw-threaded boss 9 at its outer end.

The auxiliary piston/cylinder unit 3 which forms the stop means referred to above comprises a cylinder 10 having a stepped bore 11 which is initially open at both ends. At the end adjacent the main cylinder, the bore has an internal screw-threaded portion 12 which screws onto an externally threaded boss 9 on the bottom end fitment 7 of the main cylinder. The opposite end of bore 11 has internal threading 13 to receive a hydraulic coupling 14 for connection to a source of hydraulic pressure (see later).

A piston 15 is slidably mounted in bore 11, being formed with a shoulder 16 which, when the piston is retracted (as illustrated), abuts against the step in bore 11. A return spring 17 biasses piston 5 to its retracted position, in which the end of piston 15 inside the main cylinder 4 is flush with the inside face of the fitment 7 and hence clear of piston 5; in this position the piston can perform its full stroke. Arranged inside a recess formed in fitment 7 is a rubber seal 18 which surrounds piston 15 to prevent air leakage from the main cylinder 4.

Inside the cylinder 10, a sealing cup 19 is urged by a spring 20 against the end of piston 15 remote from the main cylinder, the fluid pressure delivered through coupling 14 acting on the piston through this cup.

The hydraulic pressure applied to the auxiliary piston/cylinder unit 3 may be derived from any convenient source. The drawing includes a block diagram of a preferred arrangement; thus, a conventional master cylinder M is connected to the unit through a manuallyadjustable valve V by which the magnitude of the static fluid pressure can be controlled.

In use, a selected static hydraulic pressure is applied to the sealing cup 19 through coupling 14 to project the opposite end of the piston 15 into the main cylinder. When the piston 5 in the main cylinder is retracted, it abuts against and moves piston 15 leftwards in the drawing until a position is reached at which both pistons come to rest. This position is determined by the magnitude of the static fluid pressure and by the pressure exerted by the piston of the main unit and defines the stroke of piston 5. By adjusting the static pressure valve, the retracted position of the main piston and hence its stroke can be adjusted as required.

We claim:

1. In combination, a main fluid pressure-operated piston/cylinder unit, and adjustable stop means comprising an auxiliary piston/cylinder unit which is associated with the main unit and to which a static fluid pressure is applied in use, said auxiliary unit being adapted to provide a fluid pressure-biassed stop limiting movement of the piston of the main unit in one direction, whereby the magnitude of said static fluid pressure determines the stroke of the piston of the main unit, the auxiliary piston/cylinder unit being mounted coaxially on the base end of the main unit with its piston projecting into the cylinder of the main unit so that the stroke of the piston of the latter will be determined by abutment with the piston of the auxiliary unit, the piston of the auxiliary unit projecting through an axial bore in the base end of the cylinder of the main unit, a seal being provided around the auxiliary piston to prevent fluid leakage from the main cylinder, the base end of the main cylinder being formed with an externally screw-threaded boss on which the auxiliary unit is mounted through internal screw threading at the relevant end of the auxiliary cylinder, the piston of the auxiliary unit being provided with a return spring which, in the absence of said static fluid pressure, biasses the piston to a retracted position clear of the main piston so that the latter can perform its normal full stroke, the end of the auxiliary piston remote from the main unit being provided with a sealing cup which is spring-biassed against the piston, the arrangement being such that the said static fluid pressure is applied to the end of the auxiliary unit remote from the main unit and acts on the auxiliary piston through the intermediary of said sealing cup.

2. Stop means according to claim 1, wherein the retracted position of the piston of the auxiliary unit is defined by a shoulder on the piston which abuts against a step formed in the auxiliary cylinder.

3. Stop means according to claim 1, wherein the static fluid pressure is applied to the auxiliary unit by a master cylinder which is connected thereto through adjustable pressure control means calibrated in terms of the length of stroke of the main piston produced for each pressure setting.

Claims (3)

1. In combination, a main fluid pressure-operated piston/cylinder unit, and adjustable stop means comprising an auxiliary piston/cylinder unit which is associated with the main unit and to which a static fluid pressure is applied in use, said auxiliary unit being adapted to provide a fluid pressure-biassed stop limiting movement of the piston of the main unit in one direction, whereby the magnitude of said static fluid pressure determines the stroke of the piston of the main unit, the auxiliary piston/cylinder unit being mounted coaxially on the base end of the main unit with its piston projecting into the cylinder of the main Unit so that the stroke of the piston of the latter will be determined by abutment with the piston of the auxiliary unit, the piston of the auxiliary unit projecting through an axial bore in the base end of the cylinder of the main unit, a seal being provided around the auxiliary piston to prevent fluid leakage from the main cylinder, the base end of the main cylinder being formed with an externally screw-threaded boss on which the auxiliary unit is mounted through internal screw threading at the relevant end of the auxiliary cylinder, the piston of the auxiliary unit being provided with a return spring which, in the absence of said static fluid pressure, biasses the piston to a retracted position clear of the main piston so that the latter can perform its normal full stroke, the end of the auxiliary piston remote from the main unit being provided with a sealing cup which is spring-biassed against the piston, the arrangement being such that the said static fluid pressure is applied to the end of the auxiliary unit remote from the main unit and acts on the auxiliary piston through the intermediary of said sealing cup.

2. Stop means according to claim 1, wherein the retracted position of the piston of the auxiliary unit is defined by a shoulder on the piston which abuts against a step formed in the auxiliary cylinder.

3. Stop means according to claim 1, wherein the static fluid pressure is applied to the auxiliary unit by a master cylinder which is connected thereto through adjustable pressure control means calibrated in terms of the length of stroke of the main piston produced for each pressure setting.

Images