GB1579677A

GB1579677A - Pistons

Info

Publication number: GB1579677A
Application number: GB2713177A
Authority: GB
Original assignee: Wickman Lang Ltd
Current assignee: Wickman Lang Ltd
Priority date: 1977-06-29
Filing date: 1977-06-29
Publication date: 1980-11-19

Description

(54) IMPROVEMENTS IN OR RELATING TO PISTONS (71) We, WICKMAN LANG LI MITED, a British Company, of Mary Street, Johnstone, Renfrewshire, Scotland do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to pistons.

In numerous applications where hydraulic pressure is supplied to a piston and cylinder device to actuate an operating member, considerable danger to an operator can exist if the supply of pressure to one or other side of the piston fails. Such loss of pressure can result in the operating member ceasing to function and if, for example, the operating member is the chuck of a lathe, the chuck will open and release the workpiece.

An object of the present invention is to provide a piston and cylinder arrangement which will obviate or mitigate the dangers occurring in such arrangements through loss of fluid pressure.

According to the present invention there is provided a piston for a piston and cylinder device comprising a pair of opposed convex or concave annular discs of substantially rigid, flexible material, means intermediate said pair of opposed discs for providing a fluid seal against a cylinder wall, said intermediate means permitting one of the discs which is concave in the direction of movement of the piston within its cylinder to be flexed clear of the cylinder wall when fluid pressure is applied to said disc and to be urged into locking engagement with the cylinder wall in the absence of such fluid pressure to prevent relative movement between the piston and the cylinder in which it may be located.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 illustrates a cross-sectional view of a piston in accordance with one embodiment of the invention, and Figure 2 illustrates a cross-sectional view of a piston in accordance with a second embodiment.

Referring to Figure 1 of the drawings, a piston and cylinder device for use in a hydraulic system, for example, for actuation for the chuck of a lathe, comprises a cylinder 1 within which is mounted a piston indicated generally by reference numeral 2.

The piston 2 consists of two thin-walled concave annular discs 3, 4 each provided with a boss or spacer 5, 6. The discs 3, 4 are mounted on a piston rod 7 on which they are locked by a nut 8. It will be noted that the discs 3, 4 are mounted on the piston rod so that the concave sides of each disc are facing each other. The space between the two discs 3, 4 is filled with a resilient material 9 which can be a rubber or synthetic plastics material which will permit flexing of the discs and at the same time will prevent ingress of pressure fluid from either side of the piston by forming a seal against the cylinder wall.

The outside diameter of the discs 3, 4 when flat is slightly larger than the bore of the cylinder 1 so that when fitting the piston into the cylinder it is necessary to flex the discs inwards and in the neutral position the discs bear against the cylinder in the convex form shown in the drawing and the resilient material 9 seals against the cylinder wall.

During normal operation of the piston, fluid pressure exists on both sides thereof and when it is necessary to move the piston in one direction or another, additional fluid pressure is applied to one side of the piston.

Assuming the piston is to be moved to the right, as shown in Figure 1 of the drawing, additional, fluid pressure is then applied to the outside surface of the disc 3. This additional pressure flexes the disc 3 so that its peripheral edge is flexed clear of the cylinder wall and the contracting peripheral edge of the disc 4 can easily be pulled along as a "trailing edge" as it will flex inwards. A reverse procedure takes place if the piston is to be moved in a leftwards direction.

If a situation develops wherein fluid pressure is lost on each side of the cylinder, the only force acting on the piston may be through the piston rod 7 which will attempt to push or pull the piston in one or other direction. In such an event, if for example the piston rod is pulled to the right, then the disc 4 will flex inwards as before but the disc 3 having pressure applied only over its central portion will tend to extend itself radially and will lock hard against the cylinder wall, thus preventing movement of the piston. The greater the application of force to the piston rod the greater the pressure will be applied by the disc 3 against the cylinder wall.

If the piston rod 7 is pulled leftwardly then a similar action takes place, but with the disc 4 applying the locking action against the cylinder wall.

If additional stiffncss to the piston is required then a rigid disc can be fitted between the two flexible discs 3, 4 so that it extends into the space fillcd with the resilient material 9. Also, if desired. the discs 3, 4 may be slotted to increase flexibility.

In a second embodinent of the invention as illustrated in Figure 2, the piston, instead of having facing discs which are concave towards each other as in the embodiment of Figure 1, has two facing discs 10, 11 the curvatures of which are oppositcly rclated, i.e. the concave sides of the discs face away from each other. The discs 10, 11 are mounted on a piston rod 12 by a nut 13 and are spaced from each other by bosses or spacers 14 and 15 respectively. Each of the mating spacers 14 and 15 has an annular peripheral groove which define a recess for locating an O-ring 16.

Each of the conve'-: discs 10, 11 is provided with a plurality of holes 17 through which fluid can pass from one side of each disc to the other.

Located between the two discs so as to be axially slideable on the spacers 14, 15 is a secondary piston member 18 of any suitable material. Tlle secondary piston member 18 extends to cylinder wall 19 and scals against it by means of an O-rin 20 carried in a peripheral recess in the member 18. The member 18 is also provided on each face with an integral peripheral rim 21 and 22 each of which in the neutral posilion of the piston is miintiined joist clear of the adjacent inner convex stir'act of the discs 10. 11 respectively.

In operation of this embodiment assuming fluid pressure exists on both sides of the piston, it will be apparent that such fluid pressure acts against each side of the secondary piston member 18 due to the passage of fluid through the holes 17. If it is desired to move the piston to the right as shown in Figure 2, additional fluid pressure is applied to the lefthand side of the piston and thus to the lefthand face of the secondary piston member 18 so that the latter slides to the right relatively to the piston rod 12 and the rim 22 engages the periphery of the disc 11 to flex it and reduce its outer diameter so that it is moved clear of the cylinder wall.

The piston can then be moved to the right with the periphery of the disc 10 "trailing".

If the piston is to be moved to the left as shown in Figure 2, the reverse situation applies, i.e. the secondary piston member 18 is moved to the left and the rim 21 engages the outer periphery of the disc 10 to flex it inwardly clear of the cylinder wall. If, however, fluid pressure is lost on each side of the piston and a force is applied to move the piston to the right or left solely through the piston rod 12, then the disc 10 or the disc 11, as the case may be, locks against the cylinder wall to prevent movement of the piston.

It will be readily apparent from the above described embodiments that an arrangement is provided incorporating either opposed pairs of convex or concave discs wherein that disc of the pair which has its concave surface facing the direction of movement of the piston can be flexed to allow the piston to move within the cylinder so long as effective fluid pressure exists on both sides of the piston. If that fluid pressure is removed, the concave disc is not flexed and locks against the cylinder wall.

By the term "substantially rigid flexible material" used hereinbefore and in the claims in relation to the discs is meant that the discs are sufficiently flexible to permit them to be flexed under the influence of fluid pressure and yet sufficiently rigid to effect the required locking engagement with the wall of a cylinder in which the piston is located and when such fluid pressure is absent.

WHAT WE CLAIM IS: 1. A piston for a piston and cylinder device comprising a pair of opposed convex or concave annular discs of substantially rigid, flexible material, means intermediate said pair of opposed discs for providing a fluid seal against a cylinder wall, said intermediate means permitting one of the discs which is concave in the direction of movement of the piston within its cylinder to be flexed clear of the cylinder wall when fluid pressure is applied to said disc and to be urged into locking engagement with the cylinder wall in the absence of such fluid pressure to prevent relative movement between the piston and the cylinder in which it

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. cylinder wall and the contracting peripheral edge of the disc 4 can easily be pulled along as a "trailing edge" as it will flex inwards. A reverse procedure takes place if the piston is to be moved in a leftwards direction. If a situation develops wherein fluid pressure is lost on each side of the cylinder, the only force acting on the piston may be through the piston rod 7 which will attempt to push or pull the piston in one or other direction. In such an event, if for example the piston rod is pulled to the right, then the disc 4 will flex inwards as before but the disc 3 having pressure applied only over its central portion will tend to extend itself radially and will lock hard against the cylinder wall, thus preventing movement of the piston. The greater the application of force to the piston rod the greater the pressure will be applied by the disc 3 against the cylinder wall. If the piston rod 7 is pulled leftwardly then a similar action takes place, but with the disc 4 applying the locking action against the cylinder wall. If additional stiffncss to the piston is required then a rigid disc can be fitted between the two flexible discs 3, 4 so that it extends into the space fillcd with the resilient material 9. Also, if desired. the discs 3, 4 may be slotted to increase flexibility. In a second embodinent of the invention as illustrated in Figure 2, the piston, instead of having facing discs which are concave towards each other as in the embodiment of Figure 1, has two facing discs 10, 11 the curvatures of which are oppositcly rclated, i.e. the concave sides of the discs face away from each other. The discs 10, 11 are mounted on a piston rod 12 by a nut 13 and are spaced from each other by bosses or spacers 14 and 15 respectively. Each of the mating spacers 14 and 15 has an annular peripheral groove which define a recess for locating an O-ring 16. Each of the conve'-: discs 10, 11 is provided with a plurality of holes 17 through which fluid can pass from one side of each disc to the other. Located between the two discs so as to be axially slideable on the spacers 14, 15 is a secondary piston member 18 of any suitable material. Tlle secondary piston member 18 extends to cylinder wall 19 and scals against it by means of an O-rin 20 carried in a peripheral recess in the member 18. The member 18 is also provided on each face with an integral peripheral rim 21 and 22 each of which in the neutral posilion of the piston is miintiined joist clear of the adjacent inner convex stir'act of the discs 10. 11 respectively. In operation of this embodiment assuming fluid pressure exists on both sides of the piston, it will be apparent that such fluid pressure acts against each side of the secondary piston member 18 due to the passage of fluid through the holes 17. If it is desired to move the piston to the right as shown in Figure 2, additional fluid pressure is applied to the lefthand side of the piston and thus to the lefthand face of the secondary piston member 18 so that the latter slides to the right relatively to the piston rod 12 and the rim 22 engages the periphery of the disc 11 to flex it and reduce its outer diameter so that it is moved clear of the cylinder wall. The piston can then be moved to the right with the periphery of the disc 10 "trailing". If the piston is to be moved to the left as shown in Figure 2, the reverse situation applies, i.e. the secondary piston member 18 is moved to the left and the rim 21 engages the outer periphery of the disc 10 to flex it inwardly clear of the cylinder wall. If, however, fluid pressure is lost on each side of the piston and a force is applied to move the piston to the right or left solely through the piston rod 12, then the disc 10 or the disc 11, as the case may be, locks against the cylinder wall to prevent movement of the piston. It will be readily apparent from the above described embodiments that an arrangement is provided incorporating either opposed pairs of convex or concave discs wherein that disc of the pair which has its concave surface facing the direction of movement of the piston can be flexed to allow the piston to move within the cylinder so long as effective fluid pressure exists on both sides of the piston. If that fluid pressure is removed, the concave disc is not flexed and locks against the cylinder wall. By the term "substantially rigid flexible material" used hereinbefore and in the claims in relation to the discs is meant that the discs are sufficiently flexible to permit them to be flexed under the influence of fluid pressure and yet sufficiently rigid to effect the required locking engagement with the wall of a cylinder in which the piston is located and when such fluid pressure is absent. WHAT WE CLAIM IS:

1. A piston for a piston and cylinder device comprising a pair of opposed convex or concave annular discs of substantially rigid, flexible material, means intermediate said pair of opposed discs for providing a fluid seal against a cylinder wall, said intermediate means permitting one of the discs which is concave in the direction of movement of the piston within its cylinder to be flexed clear of the cylinder wall when fluid pressure is applied to said disc and to be urged into locking engagement with the cylinder wall in the absence of such fluid pressure to prevent relative movement between the piston and the cylinder in which it

may be located.

2. A piston as claimed in Claim 1, in which the discs are disposed so as to be concave towards each other, and said intermediate means comprises resilient material located in the space between said discs and extending to the periphery thereof to permit sealing against the wall of a cylinder when fitted therein.

3. A piston as claimed in any preceding Claim, in which the resilient material is selected from rubber and synthetic plastics material.

4. A piston as claimed in Claim 1, in which the discs are disposed so as to be convex towards each other, and have a plurality of holes defined therein to permit passage of fluid into the space between the discs, and said intermediate means comprises es a secondary piston located in the space between the discs and adapted to seal against the cylinder wall when fitted therein and abutment means on each side of said secondary piston adjacent the periphery thereof for engaging each disc adjacent its periphery to effect flexing thereof.

5. A piston according to Claim 4, in which the abutment means comprises an integral peripheral rim extending outwardly from the piston in a direction parallel to the axis of the piston.

6. A piston as claimed in any preceding Claim, in which each piston is radially slotted.

7. A piston and cylinder device comprising a cylinder, a piston rod operatively disposed within the cylinder, and carried on said piston rod a piston as claimed in any preceding claim.

8. A piston for a piston and cylinder device substantially as hereinbefore described with reference to Figure 1, or Figure 2 of the accompanying drawings.