GB2045389A

GB2045389A - Piston-cylinder assemblies

Info

Publication number: GB2045389A
Application number: GB8010717A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-04-11
Filing date: 1980-03-31
Publication date: 1980-10-29
Also published as: SE446217B; FR2454028B3; SE8002713L; GB2045389B; IT8021423V0; DE2914624A1; FR2454028A3; DE2914624C2

Abstract

A moulded plastics piston (13) is retained on the piston rod (14) and is rigidly connected thereto by means of a snap connection (16, 17). The piston (13) carries a peripheral seal (22) likewise retained thereon by means of a snap connection (23, 24). The piston (13) may include at least one integral bush projecting axially therefrom and which is tightly mounted on the piston rod (14) and forms an integrated damping piston. The piston may also have a buffer ring bonded to one end thereof. <IMAGE>

Description

SPECIFICATION A pressure medium-actuated working cylinder, especially a pneumatic cylinder The invention orginates from a pressure medium-actuated working cylinder especially a pneumatic cylinder according to the type set forth in the main claim. With one known pneumatic cylinder, the piston consists for example of a steel disc which is covered on both sides and peripherally by a peripheral seal for example of rubber or synthetic rubber. The piston is mounted astride on the piston rod passing through it. The mounting of the piston on the piston rod and the rigid connection with the latter takes place by means of a screw connection by means of which the piston is rigidly clamped axially against a flange on the piston rod or especially against a sleeve mounted on the piston rod which functions as a damping piston and in its turn abuts against a flange on the piston rod.The expenditure involved in fixing the piston is extremely high. Sometimes, the piston rod must be flanged many times and furthermore it must be provided with screw threads. This requires considerably high production costs. Sometimes, flanges provided on the piston rod weaken it and also weaken its mechanical strength for example due to the notch effect. Hollow shafts are frequently not possible, above all with the piston rods of small diameter. A further disadvantage is the really large number of individual parts which such a working cylinder has.

Moreover, there are considerable masses to be moved with a corresponding reduction in efficiency. Also, having regard to operating safety, such a known working cylinder leaves much to be desired. The fact must be taken into consideration that, after a certain period of time, the screw fixing of the piston on the piston rod slackens and becomes loose. Apart from leakage in the sealing of the clyinder chambers on both sides of the piston, this can lead to damage until the cylinder becomes unusable.

ADVANTAGES OF THE INVENTION As opposed to this, the pressure mediumactuated working cylinder in accordance with the invention, especially a pneumatic cylinder, comprising the characterising features of the main claim, has the following advantage. The outlay for fixing is extraordinary low due to the snap connection. The piston rod can be substantially simplified as regards its design. Multiple flanges and screw threads are made superfluous. The costs of production for the piston rod may be considerably reduced. Furthermore, a considerably greater mechanical strength for the piston rod is produced. Also, with small diameter piston rods, hollow shafts are then possible without any problems. Due to the snap connection between the piston and the piston rod, the number of individual parts provided for each working cylinder is substantially reduced.Furthermore, the design of the piston as a plastics moulding makes provision for further individual elements even during the shaping of the piston, for example bushes or sleeves integral with the piston, which form an integrated damping piston. Also, the means for providing the peripheral seal on the piston can be substantially simplified since it can also be provided as a plastics moulding during manufacture of the piston. Thus, the way is also open for fixing a peripheral seal to the piston, for example likewise by means of a snap connection.

Furthermore, it is an advantage that the masses to be moved are reduced whereby an increase in efficiency is made possible. Furthermore, the working cylinder is made lighter thereby. The operating safety is likewise increased. A highstrength and permanent rigid connection between the piston and the piston rod is produced so that even after a long period of time there is no fear that the piston will slacken and be released from the piston rod. For producing the connection, the snap connection between the piston and the piston rod requires a certain elasticity. This is also to the benefit of a reliable seal so that the danger of leakage in the cylinder chamber sealing on both sides of the piston is substantially reduced even over long periods of use.In all, an extraordinarily operationaily safe and stable arrangement is produced with substantially fewer parts and which is very economical.

Advantageous further developments and improvements of the pressure medium-actuated working cylinder, especially a pneumatic cylinder, set forth in the main claim are made possible by the measures set forth in the sub-ciaims.

DRAWING The invention is described in detail in the following with the aid of the embodiments illustrated in the drawings. There is shown in: Figure 1 a diagrammatic axial longitudinal section of a part of a pneumatic cylinder in accordance with a first embodiment, Figure 2 a diagrammatic axial longitudinal section of a part of a pneumatic cylinder in accordance with a second embodiment, Figure 3 a diagrammatic axial longitudinal section of a part of a pneumatic cylinder in accordance with a third embodiment, Figure 4 an axial longitudinal section of a piston in accordance with a fourth embodiment.

DESCRIPTION OF THE EMBODIMENTS The pressure medium-actuated working cylinder, illustrated in Figure 1 only by way of example, in the form of the pneumatic cylinder 10 has a cylinder tube 11 with an end cover 12 and a piston 1 3 which is rigidly connected to a piston rod 14. The piston 1 3 is mounted astride the piston rod 14 which passes through it in the region of a central opening 1 5.

The piston 13 is formed as a plastics moulding and indeed as an injection moulding. It is connected to the piston rod 14 and rigidly retained thereon by means Of an especially snap connection. A component of the said snap connection is, on the one hand, at least one retaining rib 1 6 on one part, in this instance on the piston 13, and on the other hand at least one groove-like recessed annular channel 1 7 on the other part, in the illustrated embodiment on the piston rod 14.

The retaining rib 1 6 on the piston 1 3 extends annularly and projects within a radial plane towards the piston rod 14 at least slightly but sufficiently for the snap connection. It can be appreciated that this retaining rib 1 6 is located within the central opening 1 5 in the piston 1 3.

The retaining rib 1 6 is also formed as a plastics moulding during the moulding of the piston 13 and thus requires no special additional manufacturing outlay.

On forcing the piston 13 onto the piston rod 14 and when an axial overlap of the retaining rib 1 6 is achieved, the annular channel 1 7 associated with the retaining rib 1 6 takes up a substantially accurate and positive fit so that a reliable seal is produced thereat. The snap connection consisting of the retaining rib 16 and the annular channel 17 is provided substantially in the region of the centre of the axial longitudinal extent of the piston 13.

The piston 13 has a cylindrical shape with a substantially axial extension, thus a shape deviating considerably from the disc shape. The axial shoulder sections 1 8 and 1 9 on both sides of the piston 1 3 extend all around the outer peripheral surface 20 of the piston rod 14 and above all tightly whilst sealing off possible intermediate gaps between the piston 13 and the peripheral surface 20 of the piston rod 14. Thus, a reliable seal exists between the two parts.

The piston 1 3 is forced onto the piston rod 14 and indeed on its left-hand end in Figure 1, which can take place, for example, by machine. in so doing, the piston 1 3 is pushed on axially until its inner retaining rib 1 6 snaps automatically into the annular channel 1 7 in the piston rod 14 due to resilient restoration after some resilient deformation. A high-strength snap connection is then produced which also has a certain amount of elasticity. The shape of the piston 1 3 illustrated in Figure 1 is uncomplicated and easy to produce.

This shape is extraordinarily suited to injection moulding techniques. In that manner, an extraordinarily economic piston 13 is produced.

Moreover, the other parts of the pneumatic cylinder 10 are characterised by stability, a high degree of operating safety, smaller masses to be moved and an economical configuration wherein the number of the individual parts of the entire pneumatic cylinder 10 is substantially reduced in comparison to previous cylinders.

On its outer peripheral surface 21 the piston 13 carries a peripheral seal 22 of a particular kind.

The latter is retained on the piston 13 by means of a snap connection. The components of this snap connection are, on the one hand, radially projecting shoulder portions for example in the form of an annular shoulder 23 on the piston 1 3 and on the other hand a groove-like recessed annular channel 24 which accommodates the annular shoulder 23 when snapped in. The annular channel 24 is included within the peripheral seal 22. The peripheral seal 22 is mounted around the outer peripheral surface 21 of the piston 13 and is supported on the latter all round and on all sides.

The peripheral seal 22 is especially fitted and shaped in cross-section. It has two outer sealing lips 25 and 26 spaced from one another which project axially in opposite directions that is to say, the left-hand sealing lip 25 in Figure 1 projects towards the left and the right-hand sealing rib 26 towards the right. These two outer sealing lips 25 and 26 serve for sealing with respect to the inner surface of the cylinder tube 11. Futhermore, at the level of each outer sealing lip 25, 26, the peripheral seal 22 has an inner sealing lip 27 or '28 each of which serves for sealing with respect to the outer peripheral surface 21 of the piston 1 3.

The annular channel 24 in which the annular shoulder 23 engages, is arranged axially between the left-hand sealing lips 25, 27 on the one hand and the right-hand sealing lips 26, 28 on the other hand. This form of peripheral seal 22 is particularly simple and cheap. It leads to extraordinary effective sealing characteristics and also facilitates a rapid and easy snapping of the peripheral seal 22 onto the piston 1 3. In addition, a secure retention on the piston 13 of the snapped on peripheral seal 22 is guaranteed.It is also to be understood that the shape of the peripheral seal 22 can be fashioned in some other way The second embodiment according to Figure 2 differs from the first embodiment in that the piston 113 has an axially projecting abutment rib 1 30 acting as an axial damper on one axial side, in the representation in Figure 2 on its left-hand axial side. The abutment rib 1 30 is, for example, stuck on. In a modified example, the abutment rib 130 can also be an integral part of the moulding of the piston 113.

On its other axial side, in Figure 2 in the region of the right-hand shoulder section 11 9, the piston 11 3 has a bush 1 31 made integral therewith. The bush is tubular and its diameter is considerably smaller than that of the piston 113. The bush 131 extends over a considerable axial length which, for example, can amount to many times the axial length of the piston 113. The bush 131 forms a damping piston integral with the piston 11 3 and thus integrated therewith. Thus, the.latter is also formed as a plastics moulding during the production of the piston 113. The bush 131 surrounds the piston rod 114 rigidly around its outer peripheral surface 120 and at least substantially free of intermediate gaps and indeed over the entire axial length of the bush 131.

At its free end, to the right in Figure 2, the bush 131 carries a sealing lip 132 tightly surrounding the peripheral surface 1 20 of the piston rod 11 4.

This lip likewise forms an intregrally moulded component of the bush 131. The sealing lip 132 is formed by a bush end section reducing in crosssection up to a bevelled end edge. Also this piston 11 3 formed entirely integrally is formed as a plastics moulding and indeed as an injection moulding and is forced onto the piston rod 114, for example, by machine. The snap connection corresponds to that of the first embodiment as does the peripheral seal of the piston 11 3.

In the third embodiment shown in Figure 3, references are used for the parts which correspond to the first and second embodiments increased by 200 so that reference can be made to the descriptioh of the previous embodiments so as to avoid repetition.

The third embodiment according to Figure 3 differs from the other two embodiments in that the piston 213 carries bushes 231 and 235 integral therewith and projecting axially on both sides each of which acts as an integrated damping piston. The peripheral .seal of the piston 213 otherwise corresponds in like manner to that of the first embodiment. A further distinction over the first and second embodiments consists in the fact that, in the third embodiment according to Figure 3, the piston rod 214 passes axially through the piston and carries the annular channel 21 7 as a part of the snap connection at its central region instead of at the end of the rod. Thus, an extraordinarily stable piston rod 214 is produced with this arrangement passing completely through.The necessity for dividing the piston rod 214 as opposed to the previously known solutions does not arise.

In the fourth embodiment illustrated in Figure 4, references are used for the parts as previously described for the same purpose which correspond to those of the previous embodiments increased by 300. The piston 313 according to Figure 4 corresponds substantially to the piston 21 3 according to Figure 3 however with the advantageous modification that, with the piston 313, the peripheral seal 322 is also an integrally moulded component of the piston 313. Thus, the peripheral seal 322 is then an integral component of the piston 31 3 instead of being snapped on.

Moreover, the material of the peripheral seal 322 can be softer and more resilient than that of the remainder of the piston 31 3 insofar as that can be accomplished with injection moulding techniques.

Claims

1. A pressure medium actuated working cylinder, especially a pneumatic cylinder, the piston of which has the piston rod passing through it and is rigidly connected thereto, characterised in that, the piston is formed as a plastics moulding and is retained on the piston rod and connected to the latter by means of a snap connection.

2. A working cylinder according to claim 1 characterised in that, on the one hand, the snap connection has at least one annular retaining rib on one part, especially on the piston, projecting into the radial plane and within the central opening of the piston and has, on the other hand, at least one groove-like recessed annular channel on the other part, especially on the piston rod, associated with the retaining rib and accommodating the latter on snapping in.

3. A working cylinder according to claim 1 or 2 characterised in that the snap connection is provided substantially in the region of the centre of the longitudinal dimension of the piston.

4. A working cylinder according to one of claims 1 to 3 characterised in that the piston has a cylindrical shape with a substantially axial dimension and that at least the axial shoulder sections at both ends of the piston tightly fit all around the outer peripheral surface of the piston rod whilst sealing off intermediate gaps between the piston and the peripheral surface of the piston rod.

5. A working cylinder according to one of claims 1 to 4 characterised in that, on at least one axial side, the piston has a bush integral therewith and of smaller diameter which extends over a substantial axial length and forms an integrated damping piston.

6. A working cylinder according to claim 5 characterised in that the piston carries bushes integral therewith and projecting on both axial sides.

7. A working cylinder according to claim 5 or 6 characterised in that the bush surrounds the outer peripheral surface of the piston rod over the entire axial length of the bush rigidly and free from intermediate gaps.

8. A working cylinder according to one of claims 5 to 7 characterised in that, at its free end, the bush carries a sealing lip tightly surrounding the peripheral surface of the piston rod.

9. A working cylinder according to claim 8 characterised in that the sealing lip is an integral component of the bush, and is preferably formed by a bush end section reducing in cross-section up to a bevelled end edge.

1 0. A working cylinder according to one of claims 1 to 9 characterised in that the piston has an axially projecting abutment rib acting as an axial damper on one axial side.

11. A working cylinder according to claim 10 characterised in that the abutment rib is an integrally moulded component of the piston.

12. A working cylinder according to one of claims 1 to 11 characterised in that the piston is forced onto the piston rod.

1 3. A working cylinder, especially according to one of claims 1 to 12, wherein a peripheral seal is retained on the piston, characterised in that, the peripheral seal is provided on the outer peripheral surface of the piston and is supported on the latter on surfaces all around.

14. A working cylinder according to claim 13 characterised in that the peripheral seal has two sealing lips spaced from one another and projecting axially away from one another for sealing off with respect to the cylinder tube and inner sealing lips for sealing off with respect to the piston.

1 5. A working cylinder according to claim 13 or 14 characterised in that the peripheral seal is a part integrally moulded with the piston (Figure 4).

1 6. A working cylinder according to claim 13 or 14 characterised in that the peripheral seal is retained on the piston by means of a snap connection.

17. A working cylinder according to claim 16 characterised in that, on the one hand, the snap connection has radially projectirg shoulder portions, preferably an annular shoulder, on one part, especially on the piston and has, on the other hand, recesses, preferably a groove-like recessed annular channel on the other part, especially within the peripheral seal, associated with the shoulder parts and accommodating the latter by snapping on.

18. A working cylinder according to claim 1 7 characterised in that the recess, especially the annular channel, is arranged axially between the outer and inner sealing lips of the peripheral seal on both sides.

1 9. A pressure medium-actuated working cylinder substantially as herein described with reference to Figure 1, Figure 3 or Figure 4 of the accompanying drawings.