GB2047347A - A compressed air cylinder comprising a damping device - Google Patents

Abstract

The invention relates to a compressed air cylinder 10, 12 onto which is built a damping device 17 which is for completely jerk-free and safe braking of the piston 12 together with its piston rod 14 at the ends of its stroke. The damping device consists of a sleeve 24 slidingly arranged on the piston rod 14 and provided with a piston 25 which is sealingly slidingly guided in a damping chamber 26. The two sides of the damping chamber are connected to one another through a duct 43 and bores 37, 38 which can be varied as regards their through flow cross-section by throttle screws 39, 40. A gap 55 is formed between the sleeve 24 and the piston rod 14 whereby the sleeve 24 is pressure balanced. The sleeve is actuated by abutment discs 20, 22 directly in one direction but indirectly in the other direction by a second sleeve 61. <IMAGE>

Description

SPECIFICATION A compressed air cylinder comprising a damping device STATE OF THE ART The invention originates from a compressed air cylinder according to the type set forth in the main claim. With such a known compressed air cylinder it has been shown that under certain operating conditions the end position damping can occur too early since the sleeve is moved by adhesive friction especially at low stroke speeds of the piston rod.

ADVANTAGES OF THE INVENTION As opposed to this, the compressed air cylinder in accordance with the invention comprising the characterising features of the main claim has the advantage that the end position damping always takes place at the correct instant.

DRAWING An embodiment of the invention is illustrated in the drawing and is described in detail in the following specification. Figure 1 shows a longitudinal section through a working cylinder provided with a damping device, Figure 2 is a cross-section according to Il-Il in Figure 1.

DESCRIPTION OF THE EMBODIMENT A working piston 12 is sealingly slidingly guided in a cylindrical tube 10 which is closed at one end by a cover 11. The piston is fixed at one end of a piston rod 1 4 by means of a screw thread 13. A blind bore 15 is formed in the cover 11 and into which issues a transverse bore 1 6 which serves for the supply and discharge of compressed air. The other end of the cylindrical tube 10 is closed by a two-part housing 1 7 which accommodates a damping device. A longitudinal bore 1 8 into which issues a transverse bore 1 9 which likewise serves for the supply and discharge of compressed air, is formed in the housing portion 17' which directly engages the cylindrical tube 10. Thus, the working cylinder is made double acting.

The piston rod 1 4 extends through the entire housing 17 and an abutment disc 20 is fixed to its end with the aid of a screw thread 21. A similar abutment disc 22 is located at the opposite end of the piston rod, thus where the piston is located. It is forced against a shoulder 14' on the piston rod by the piston 12 and the screw thread 13.

An elongate sleeve 24 is sealingly and slidingly arranged on the piston rod 14 in the region of the housing 17. A piston which is sealingly slidingly arranged in a damping chamber 26 is fixed to the central portion of the sleeve 24; the sealing is provided by a sealing ring 27. The central portion of the sleeve 24, thus where the piston 25 is mounted, has a larger diameter; conical zones 24', 24" extend from this portion on both sides. A central longitudinal bore 51 formed in the housing portion 17" has the same diameter as the central portion of the sleeve 24. From the damping chamber 26, a plurality of stepped bores 29 lead on the one hand to an annular space 30, similar stepped bores 31 lead on the other hand to an annular space 32.Plate-like non-return valves 33, 34 which serve as suction valves and the stroke of which is limited by snap rings 35, 36, are arranged in all the stepped bores. A bore 37, 38 also leads from each annular space 30, 32 to the damping chamber 26. An adjustable throttle valve 39, 40 which consists of a screw with a pin 41 or 42 which projects into the bores 37 or 38, projects into each of the said bores. According to the depth to which they are screwed in, the passage from the damping chamber 26 through the bores 37, 38 to the annular spaces 30, 32 are throttled to a greater or lesser extent. The annular spaces 30, 31 are in communication with one another through a duct 43 shown in dotted lines. This is shown in dotted lines since it is displaced laterally with respect to the throttle screws 39, 40 (see Figure 2).A housing bore 45 which leads to the annular space 32 issues into the duct 43. An annular space 46 in which is arranged an accumulator 47, extends from the annular space 32.

The end of the sleeve 24 remote from the piston 22 penetrates into a space 49. Between the sleeve 24 and the piston rod 14 a gap 55 is formed over the entire length which, for example, is so designed that longitudinal grooves 56, 57 are formed at the inner diameter of the sleeve at both ends by a longitudinal spline. Transverse grooves 59, 60 are located at both ends. The longitudinal bore 1 8 is in communication with the space 49 through these transverse grooves and the gap 55.

In this manner the sleeve 24 is pressure balanced.

Extending from the sleeve an additional sleeve 61 is sealingly slidingly arranged on the piston rod and which is moved in bores 62, 63 of a housing 64 which is fixed to the housing portion 17". It is sealed in the bores by seals 65, 66. The sleeve 61 projects beyond the housing 17" and is sealed with respect to the piston rod by a seal 67. A snap ring 69 is arranged at the inner portion of the sleeve 61 and which outwardly limits the movement of the sleeve when the snap ring 69 engages the shoulder 64' on the housing 64.

The compressed air cylinder is actuated in known manner either by supplying compressed air to the bore 1 6 or to the bore 19 and which is forced out from the other respective bore. The pressure medium supplied to the bore 1 9 arrives in the cylindrical tube through the gap 50 formed between the sleeve 24 and the bore 1 8.

It will be assumed that the working piston is located in the left-hand illustrated end position and that compressed air is supplied to the bore 1 9. The working piston is then moved towards the cover 11. When it arrives at the end of its stroke the abutment disc 20 engages the sleeve 61 whereupon the latter is set in motion and after a short distance strikes against the sleeve 24. Then the piston 25 must express the fluid pressure medium contained in the damping chamber 26.

This arrives through the gap formed by the sleeve 24 and the bore 51 and the bore 37 restricted by the throttle 39 in the space 30 and from there through the duct 43 in the annular chamber 32.

The gap is increasingly reduced by the conical zone 24' so that during this operation, the working piston is smoothly braked over a relatively short path by the gap reduction and the action of the throttle 41. Thus, the pressure medium present in the chamber 26 is expressed over the described path to the annular space 32 and from the latter arrives through the stepped bore 31 and the open non-return valve 34 to the other side of the damping chamber 26. In so doing, the nonreturn valves 33 engage the shoulders on the stepped bores 29 so that, from the latter, no pressure medium can arrive in the annular space 30.

If compressed air is then supplied to the bore 16, the piston 12 is moved towards the left and towards the end of the stroke the abutment disc 22 engages the sleeve 24 whereupon the piston 25 is likewise pushed towards the left and forces pressure medium into the bore 38. This is restricted by the throttle 40 and the gap in the bore 51 also narrows increasingly so that the pressure medium can then only flow to the annular space 32 in a throttled manner and from there arrive in the annular space 30 through the duct 43. In so doing, the non-return valve 34 engages the shoulders in the stepped bore 31.

From the annular space 30, the pressure medium flows through the stepped bores 29 and the open non-return valves 33 once again to the other side of the damping chamber 26. The damping device is filled with fluid pressure medium through the bore 45.

Claims (6)

1. A compressed air cylinder comprising a device for damping the movement of the working piston at the ends of its stroke, wherein pressure fluid is conveyed from a damping space through a throttle and the device consists of a unit built separately onto the working cylinder and which has a piston slidingly guided in a damping chamber the piston being part of a sleeve slidingly arranged on the piston rod and being movable longitudinally of the piston rod together with the sleeve at the ends of its stroke, wherein the two sides of the damping chamber subdivided by the piston are connected to one another by throttlable connection characterised in that a gap through which two spaces arranged respectively at the ends of the sleeve is formed between the sleeve and the piston rod.

2. A compressed air cylinder according to claim 1 characterised in that radially extending grooves are formed at the ends of the sleeve.

3. A compressed air cylinder according to claim 1 and/or 2 characterised in that longitudinal splines by which the sleeve is mounted on the piston rod are formed at the ends of the sleeve.

4. A compressed air cylinder according to one of claims 1 to 3 characterised in that the sleeve cooperates with a second sleeve which projects beyond the housing for the damping device and is actuable by an abutment disc.

5. A compressed air cylinder according to one of claims 1 to 4 characterised in that the second sleeve is made step-like and is sealed with respect to the housing by means of two sealing rings.

6. A compressed air cylinder comprising a damping device, substantially as herein described with reference to the accompanying drawings.