FLUID PRESSURE CYLINDER

Abstract: A fluid pressure cylinder comprising a cylinder tube (4, 31) and an end plate (2, 3, 30) being mounted into each side thereof, the end plates (2, 3, 30) being produced from a synthetic material are positioned inside the cylinder tube (4, 31) with their external surface (7b) in the same plane as the end surface (7a) of the cylinder tube, as well as permanently snap-in connected to cavities in the inner surface of the cylinder tube (4, 31) via means (8, 25, 24). A fluid pressure cylinder according to the invention provides a lightweight design which is simple to produce and assemble and which is free from pockets, projections and similar impurity accumulating areas on the fluid pressure cylinder.

Description: FLUID PRESSURE CYLINDER The present invention concerns a fluid pressure cylinder comprising a cylinder tube and, attached to each side thereof, an end plate. Fluid pressure cylinders of this kind are previously known. In this connection cylinders could be mentioned where the cylinder end plates are fixed to the cylinder tube by means screwing into the material of the tube or by means of tension rods between the end plates, said tension rods being arranged outside the cylinder tube or in specially arranged channels in the wall material of the cylinder tube. WO 88/1357 describes an example of a fastening arrangement for a cylinder. In this device the fastening between the end plate element and the cylinder tube is achieved by means of a flexible locking element being inserted from the outside into a partly conical space which is formed between the cylinder tube and the attached end plate element. Another solution to the problem of fastening an end plate element is to thread it to the cylinder tube. All of the above mentioned devices comprise well-functioning solutions to the problem of connecting end plates and cylin¬ der tubes in several applications, they however suffer from drawbacks that may be considerable in particular connections. Such drawbacks are: complicated and costly production of the end plate elements, time consuming and thus costly assembling of the piston cylinder aggregates, considerable weight as well as the existance of uneven surfaces as pockets, inward edges, ouward rods and so on on the outside of the cylinder aggregate, said irregularities bringing about considerable problems concerning the possibilities of keeping the aggre¬ gate clean from externally leaking oil and other impurities. It is therefore an aim of the present invention to provide a fluid pressure cylinder of the kind mentioned above, which solves these problems and thus is comprised of simply and cheaply producable elements, said elements allowing fast and precise assembling to a fluid pressure cylinder aggregate, comprises low weight as well as is free from impurity collec¬ ting pockets, protrusions and other irregularities. This aim is achieved according to the invention by the fluid pressure cylinder of the above mentioned kind being characterized by the features of the characterizing portion of claim 1. Beside the above mentioned aim a possibility is hereby also achieved of producing the parts in a very cost-worthy manner, as synthetic material is used in the end plates. By the features of claims 2 and 3, particular easy manu¬ facturing and assembling is achieved. The engaging positions of the hook elements are their rest positions, why the hook elements are forced radially inwards upon positioning of the end plate by means of a mounting cone or the like for the entering into the cylinder tube. By the feature according to claim 4, the engagement between the end plate and the cylinder tube is enhanced upon axial load directed towards the outside of the end plate. By the features according to claims 6 and 7, a particularly avantageous and simple fastening of the end plate is achieved. The features according to claims 8 to 10 entail further advantages in connection with an end plate being positioned on the piston rod side of the cylinder. By the features according to claim 11 a certain degree of impact cushioning control is achieved, whereby mass forces acting on the cylinder and the associated parts are reduced upon impact of the piston, particularly the forces acting on the end plates and their fastening portions. The invention is now described in greater detail with refe¬ rence to the annexed drawings relating to embodiments of the invention. In the drawing: Fig. la shows a section of a fluid pressure cylinder accor¬ ding to the invention with the associated piston and piston rod; Fig. lb shows a section of a portion of a piston side end plate; Fig. 2 shows a central section through an end plate according to the invention; Fig. 3 shows the end plate accoring to Fig. 2 in a plain view; Fig. 4 shows a section of a portion of an alternative faste- ner according to the invention; and Fig. 5 shows a snap-in ring for use in the embodiment of Fig. 4. Fig. la thus shows a piston cylinder aggregate 1 comprising a first end plate 2 and a second end plate 3, both being mounted to the respective end portion of a cylinder tube.4. The reference numerals 5 and 6 concern a piston being move- able withing the cylinder and a piston rod respectively. Each end plate 2, 3 is positioned within the cylinder tube 4 in such a way that its even outer surface 7b is flush with the end surface 7a of the cylinder tube, thereby obtaining an essentially totally planar end surface of the piston cylinder aggregate 1. Along its outer circumference each end plate 2, 3 is provided with outwardly facing hook elements 8, being evenly distri¬ buted around the periphery for engagement with undercut 10 locking grooves 9 in the cylinder tube 4. In the direction outwards from the respective cylinder end, the hook elements 8 are provided with undercuts 10b in correspondence with the undercuts 10 of the locking grooves 9 (Fig. 2) . Radially inside the hook elements 8, a free space 11 is provided for allowing resilient yielding movement inwards of the hook ele¬ ments 8, when the end plate is being positioned into the cylinder tube 4. Said free space 11 may also be used as a seat for a return spring 13, co-operating with a suitably designed surface of the piston 5. By applying a return spring in the relatively deep free space 11, the total length of the cylinder may be reduced. Axially most outwards, each end plate 2, 3 provides a press- fit, alternatively a close fit to the cylinder tube 4, and to further enhance the sealing in this area, the cylinder tube 4 is provided with a ring-shaped groove for a sealing element 12. Further, each end plate is comprised with impact cushioning protrutions 14 for the co-operation with the piston 5, said protrutions being comprised of an uninterrupted ring-shaped formation, sector-shaped formations or bosslike projections. The reference signs 15 and 16 refers to inlet/oulet for the pressure fluid, said inlet/outlet being connected to the cylinder rooms via bores, leading to the respective locking groove 9. The second end plate 3, being positioned on the piston rod side, is provided with a seat for a piston rod sealring element 17 and further, which is clear from Fig. lb, a guiding surface 18 for the co-operation with and guiding of the piston rod, cavities for lubricate, which are comprised of slots 19, being evenly distributed around the circumfe¬ rence, and a wiper lip 20, for wiping impurities off the piston rod, said lip being separated from the guiding surface 18 by means of an annular groove 21. The shown cylinder is intended mainly as a clamping element where the transverse forces are relatively limited, as the second end plate 3 cannot be expected to withstand any consi¬ derable transverse forces. Fig. 2 shows the first end plate 2, the central wall of which being essentially thinner than the total axial dimension of the plate, whereby a free space 23 is formed radially inside the impact cushioning protrution 14. To avoid curling of the central portion of the plate, and for supporting the impact cushioning protrution, supporting flanges 22 are provided between the impact cushioning protrution and the central portion of the end plate 2, said flanges having a triangular shape seen in an axial section. Fig. 2 also clearly shows the undercuts 10b of the hook elements 8, which contribute to the hook elements 8 being subject to a radially outward directed force, when they are subject to a fluid pressure and/or an impact pressure in the direction outwards from the cylinder. This way loading enhances the fastening between the endplate and the cylinder tube. Fig. 3 thus shows the end plate 2 according to Fig. 2 in a plain view, where the dimensions of the hook elements 8 in a circumferencial direction is evident. According to this embodiment, the end plate 2 is provided with 20 evenly distributed hook elements 8, the mutual distances of which being dimensioned to allow the inward resilient yielding movement that is presupposed upon positioning the end plate 2 into the cylinder tube 4. In the embodiment shown, a very large load carrying engaging surface is thus provided between the hook elements 8 of the end plate 2 and the undercut groove 9 of the cylinder tube 4. Contrary to the above described embodiments where conical mounting sleeves per se previously known are used when positioning the end plates into the cylinder tubes, there is no need for an external mounting tool in the embodiment according to Fig. 4. In this embodiment each of the end plate 30 and the cylinder tube 31 is provided with a groove 25 and 26 respectively, said grooves in a mounted position limiting a space within which a snap-in ring 24 is positioned, for locking interaction between the two grooves. The end plate 30 is inwardly provided with a conical surface 27, which upon mounting of the plate 30 forces a snap-in ring 24 to resiliantly yield outwards to allow insertion of the end plate 30, said snap-in ring being arranged in a groove 26 in the cylinder tube 31. When the groove 25 is positioned in the same plane as the groove 26 the snap-in ring 24 will snap radially inwards to obtain the desired locking interaction. Fig. 5 shows the snap-in ring 24, on the perifery of which three spring tounges 29 are evenly distributed to obtain coaxial alignment of the snap-in ring 24 with the cylinder tube 31 prior to mounting of the end plate 30. The snap-in ring 24 is also provided with an interruption 28 for allowing the inward/outward resiliant yielding of the ring. Even if the invention is useful in many different cylinder applications it is particularly applicable as a compact pneumatic cylinder, where it is essential that the external dimensions of the aggregat are limited from installation points of view, particularly in applications where a large number of cylinders are used in a limited area and where it is thus a problem to obtain space for conventional cylinders. The low weigt contributes to making the aggregate easy to handle. The end plates are produces from a synthetic material as a thermoplastic or a thermoelastic, in particular acetal resin has been found suitable, as this material provides the necessary resiliant and resistant properties. The cylinder tube is suitably manufactured from a light weight metal as an Al-alloy and the snap-in ring from a metal, as spring steel or a suitable synthetic material as nylon. The snap-in ring may be provided with a number of tongues that differs from three, e.g. two, four or five. The snap-in ring may also be produced without spring tongues. The cylinder is thus provided with even surfaces which do not accumulate impurities and which are easy to keep clean, why it is very suitable in industry with high hygienic demands. Preferrably the external sides of end plates are totally planar without ejections marks or the like, and the line separating the surfaces 7a and 7b is hardly perceptible due to the fit between the parts. To somewhat enhance the radial load carrying properties of the end plate 3, it may possibly be modified with a per se previously known outwardly directed guiding bead for the piston rod. When mounted, the end plates are permanently engaged to the cylinder tube, and if a cylinder breaks down it is replaced in its entirity. A broken end plate may of course be cut off from the cylinder tube and be replaced with a new one. It is desired that the engaging surface of the hook elements is as large as possible, why the above described distribution of the hook elements is preferred, but if allowed by the load, a different number of hook elements with reduced dimen¬ sions in the circumferencial direction may be used. It is finally mentioned that the inward resilient yielding movement when mounting the hook elements is enhanced if the hook elements have small dimensions in the circumferencial direction.

Claims: CLAIMS 1. Fluid pressure cylinder comprising a cylinder tube (4, 31) and an end plate (2, 3, 30) fastened at each end thereof, c h a r a c t e r i z e d in - the end plates (2, 3, 30) being produced from a synthetic material; - that each end plate (2, 3, 30) is mounted within the cylin¬ der tube (4, 31) with its outer surface in the same plane as the end plane of the cylinder tube; and - that means (8, 9, 10; 24, 25, 26) are provided for perma¬ nent snap-in connection between the end plate (2, 3, 30) and cavities (9; 26) in the inner surface of the cylinder tube (4; 31). 2. Cylinder according to claim 1, c h a r a c t e ¬ r i z e d in that said means include resilient hook elements (8) being integral with the end plate (2, 3), said elements further being evenly distributed around the circumference of the end plate, and the engaging positions of which essen¬ tially being their rest positions. 3. Cylinder according to claim 2, c h a r a c t e ¬ r i z e d in said hook elements (8) co-operating with said cavities (9) in the cylinder tube. 4. Cylinder according to claim 2 or 3, c h a r a c t e ¬ r i z e d in that said cavity is comprised of an undercut (10) groove (9) and that the hook elements (8) are provided with corresponding undercuts (10) on its engaging side in a direction towards the outside of the end plate. 5. Cylinder according to any of the claims 2-4, c h a r a c t e r i z e d in that an annular free space (11) is provided inside the hook elements (8) , said free space being dimensioned to allow the radial inward resilient yielding movement of the hook elements (8) when mounting the end plate, as well as possibly receiving a return spring, which co-operates with the piston (5) and which is arranged axially with respect thereto. 6. Cylinder according to claim 1, c h a r a c t e ¬ r i z e d in that said means includes a snap-in ring (24) , said ring in the mounted position engaging into an essentially annular groove (25) in the circumferencial surface of the end plate as well as in an essentially annular groove (26) in the inner surface of the cylinder tube. 7. Cylinder according to claim 6, c h a r a c t e ¬ r i z e d in that said snap-in ring (24) is provided with spring tongues (29) , being distributed around the circumfe¬ rence, for the coaxial allignment of the snap-in ring with the cylinder tube (31) . 8. Cylinder according to any of the previous claims, c h a r a c t e r i z e d in that the piston rod side end plate (3) of the cylinder (1) axially most outward is being provided with an integral wiper lip (20) for the co-operation with the piston rod (6) . 9. Cylinder according to any of the previous claims, c h a r a c t e r i z e d in that the piston rod side end plate (3) of the cylinder (1) is provided with an integral guiding surface (18) , co-operating with the piston rod, as well as axial cavitites (19) comprising spaces for lubricant on an axial portion thereof. 10. Cylinder according to claim 8 or 9, c h a r a c t e ¬ r i z e d in that the end plate (3) is provided with a seat for a piston rod sealing element (17) . 11. Cylinder according to any of the previous claims, c h a r a c t e r i z e d in that the end plate (2, 3) is provided with one or more integral impact cushioning pro¬ trutions (14) , of e.g. ring, sector or boss like configu¬ ration directed axially inwards.

Inventors: DISBO BO, GRANBERG RUNE, DISBO, BO, GRANBERG, RUNE
Applicants: DISBO BO, GRANBERG RUNE, MECMAN AB REXROTH, AB REXROTH MECMAN
Application year: 1993
Main classification: F16J10
IPC codes: F15B15, F16J10