PISTON CYLINDER DEVICE

Abstract: The present invention relates to an arrangement by a piston-and-cylinder unit, comprising a cylinder member (1) and a piston member (2), movable therein, to which a piston rod (4) is connected. The cylinder member consists of a barrel pipe (7) and closure portions (6) at each end (5) of the cylinder member, the closure portion at one end exhibiting a bush (8). The bush is provided with a through bore (9) for the piston rod (4) and is enclosed by an end portion of the barrel pipe, said end portion being bent radially inwards, towards the piston rod and over a first circumferential surface (16) of the bush. The bush (8) is provided with a collar portion (14), exhibiting an external second circumferential surface of the bush, enclosing the circumferential of the piston rod and extending axially beyond the inwardly bent portion. The inwardly bent portion (18) of the barrel pipe terminates in a circumferential edge (19), located adjacent to a positive corner (22) of the bush, formed between the first circumferential surface (16) and the second circumferential surface.

Description: Piston cylinder device TECHNICAL FIELD The present invention relates to an arrangement by a piston-and-cylinder unit according to the preamble of the appended claim 1. BACKGROUND ART Piston-and-cylinder units are frequently located in an outdoor environment, exposed to varying temperature, air humidity, etc, providing a breeding ground for corrosive attacks. Examples of such piston-and-cylinder units might be so-called "gas springs" or "gas dampers" for force balancing and damping of various kinds of doors or lids. From EP-A1-0 364 851 , a piston-and-cylinder unit is previously known, disclosing an example of a method for reducing the corrosion problems. This known piston-and- cylinder unit exhibits a closure portion consisting of a bush, enclosed by an end por- tion of the barrel pipe of the piston-and-cylinder unit. Said end portion is bent inwards, towards the piston rod extending through the bush, so as to terminate the cylinder barrel with a circumferential edge that is generally directed perpendicularly to the longitudinal direction of the barrel pipe, i.e. the axial direction of the piston- and-cylinder unit. The barrel pipe is usually made of a resistant and relatively easily workable material, such as carbon steel, which is corrodible. Because of this, the barrel pipe is surface treated with corrosion-protective coatings, normally a pre- treatment and one or more coats of lacquer. It has, however, turned out that the circumferential edge receives a thinner coat of lacquer, resulting with time in corrosion attacks, which will limit the service life of the cylinder unit in many applications. On the piston-and-cylinder unit according to the referenced publication, a separate component has therefore been arranged in the form of a resilient protection ring of rubber, plastic or similar, covering the end portion of the barrel pipe and its inward- directed circumferential edge. Through this, a certain weather protection is obtained, as long as the protection ring is undamaged. However, rings of plastic, rubber, etc., have a limited service life and may also cause condensation that is not ventilated off but might as such create corrosion problems. Furthermore, such a protection ring entails an additional component, affecting adversely the cost of the known piston- and-cylinder unit. DISCLOSURE OF INVENTION The object of the present invention is to provide an arrangement, by which the corrosion problem described above is resolved without the need of dedicated sealing members. Said object is achieved by means of an arrangement, the characteristics of which are stated in the appended claim 1. By means of an arrangement according to the invention, the barrel pipe may be pro- vided with a highly covering corrosion protection, contributing positively to the service life of the piston-and-cylinder unit. Through utilising the surface tension effects created at an inner corner according to the invention, an improved lacquer coverage and a thicker coating layer is achieved, providing an improved corrosion protection. BRIEF DESCRIPTION OF DRAWINGS The invention will be explained in further detail below by means of an embodiment example, with reference to the enclosed drawings, in which: Fig. 1 illustrates, by a partially broken longitudinal section, a portion of a piston- and-cylinder unit, provided with the arrangement according to the invention in a first embodiment. Fig. 2 and Fig. 3 illustrate the arrangement according to the invention in a second and a third embodiment, respectively. PREFERRED EMBODIMENTS Fig. 1 shows, by means of the partially broken longitudinal section, one end of a piston-and-cylinder unit, for example consisting of a gas spring or gas damper for the balancing of forces and damping of opening and closing movements, respectively, of a door. The door may for example be the boot lid or the bonnet of an automotive vehicle. The piston-and-cylinder unit is comprised of a cylinder member 1 , enclosing a piston member 2, reciprocally movable in a linear motion inside the cylinder member. The piston member is connected to a piston rod 4, extending along the longitudinal axis 3 of the piston-and-cylinder unit and being displaceable together with said piston member 2, said piston rod extending from one end 5 of the cylinder member 1 through a closure portion 6, which, together with a barrel pipe 7 and an opposite closure portion, (not shown), located at the other end of the barrel pipe, defines the cylinder member. The illustrated closure portion 6, also defining the through passage for the piston rod 4, consists of a bush 8, preferably made of a non-corrodible material, e.g. plastic, bronze, or similar. The bush exhibits a cylindrical lead-through bore 9, sealingly enclosing the through piston rod 4. Further, the bush is designed as a generally cylindrical body 10, arranged in the barrel pipe at one end 5 thereof and exhibiting a generally cylindrical, radially outwards directed surface 11, in contact with the cylin- drical inner wall 12 of the barrel pipe. This connection may be gas or fluid tight, but usually, a separate sealing device is located in the barrel pipe below the bush. The bush 8 is further designed with a sleeve-like collar portion 13, defining an extension of the through bore 9 and exhibiting a substantially cylindrical, external surface 14, which, via a corner 20 transcends into a substantially flat, radially extending surface 16. The corner 20 thus defines a circumferential inner edge, whereas the radial surface 16 extends radially outwards, towards a circumferential external edge 17, where a transition takes place to the cylindrical envelope surface 11. The closure portion 6 also comprises, besides the bush 8, an end portion of the barrel tube, transcending substantially from the external edge 17 of the bush into an inwardly bent portion 18. More precisely, the bent portion in this first embodiment is continuously curved inwards, down towards the body 10 of the bush 8. This entails that the circumferential edge of the bent portion, which defines a radially inwards directed circumferential edge 19 of the barrel pipe, in this example receives a gen- eral direction towards the corner 20. Furthermore, the circumferential edge 19 of the bent portion 18 preferably exhibits as small a clearance 22 as possible in relation to the collar portion external surface 14. The circumferential edge 19 may further be sharp, through consisting of e.g. a cut edge, being cut at an angle relative to the inwardly bent portion 18. In order to protect the barrel pipe 7 from corrosion, it will be coated with a corrosion- protecting coating 23, for example applied by some form of paint coating method, e.g. wet enamelling. Advantageously, the coating method is of the electrostatic coating type, using a charging of the lacquer particles before application. Through shaping the bent portion 18 of the barrel pipe in the fashion discussed above, a positive corner 24 is further created at the circumferential edge 19, whereby surface tension effects create a thicker layer of lacquer at this corner. Hereby, an extra corrosion protection is provided at exactly that portion of the barrel 1 , which otherwise, with previously known designs, will have a weakened corrosion protection at the corresponding circumferential edge, as a thinner coating of lacquer will be formed at the cut edge, i.e. at the circumferential edge. The lacquer protection should, at the corner 20 of the bush, completely fill out the clearance 22 and form a well rounded transition to the collar section 13, in the shape of one single rounded portion 24. The second embodiment according to Fig. 2 differs from Fig. 1 by the inwardly bent portion 18a closely following the circumferential surface 16a, providing an advantageous filling of the inner corner 20a. In the third embodiment, according to Fig. 3, the circumferential surface 16b is conical, whereby the inwardly bent portion 18b takes the shape of a truncated cone. The corner 20b will be obtuse, creating a softly rounded portion 24b of the lacquer coating. Also in this case the circumferential edge 19b can be sharp. The invention is not limited to the embodiments described above and depicted in the drawings, but may be varied within the scope of the accompanying patent claims. For example, the bent portion 18 might be replaced by two bent portions, i.e. one bent portion around the edge 17 and a radial, inner, bent portion adjoining the circumferential edge 19, said portions being separated by a planar portion. The figures show only one side of the end portion of the barrel pipe; there is, however, a complete mirror-inverted symmetry in relation to the longitudinal axis 3.

Claims: CLAIMS 1. An arrangement by a piston-and-cylinder unit, comprising a cylinder member (1) and a piston member (2), movable therein, to which a piston rod (4) is connected, said cylinder member consisting of a barrel pipe (7) and closure portions (6) at each end (5) of the cylinder member, the closure portion at one end exhibiting a bush (8), provided with a through bore (9) for the piston rod (4) and enclosed by an end portion of the barrel pipe, said end portion being bent radially inwards, towards the piston rod and over a first circumferential surface (16) of the bush, characterised in that said bush (8) is provided with a collar portion (16), exhibiting an external second circumferential surface (14) of the bush, said collar portion enclosing the circumference of the piston rod and extending axially beyond the inwardly bent portion, and in that the inwardly bent portion (18, 18a, 18b) of the barrel pipe terminates in a circumferential edge (19, 19a, 19b), located adjacent to an inner corner (20/20/20b) of the bush, formed between the first circumferential surface (16) and the second circumferential surface. 2. The arrangement according to claim 1 , characterised in that said circumferential edge (19) is located so close to the collar portion (13), that a corrosion-protecting coating (23) of said end portion will fill out said corner (20) and create one single, rounded portion (24) extending from said inwardly bent portion to said second circumferential surface (14) of the bush. 3. The arrangement according to claim 2, characterised in that said inwardly bent portion (24) of the barrel pipe (7) exhibits a continuous inwards curve towards said corner (20). 4. The arrangement according to claim 2, characterised in that the first circumferential surface (16) extends generally perpendicularly to the longitudinal axis (3) of the piston rod (4), and that the inwardly bent portion (18a) generally closely follows the first circumferential surface. 5. The arrangement according to any one of claims 3 or 4, characterised in that said circumferential edge (19) is bevelled so as to define in shape the envelope surface of a truncated cone, having its base towards the first circumferential surface (16). 6. The arrangement according to claim 2, characterised in that the first circumferential surface (16b) defines in shape the envelope surface of a truncated cone, and that the circumferential edge (19b) is bevelled in relation to the inwardly bent portion (18b).

Inventors: ISAKSSON MALTE, KARLSSON TOMMY, ISAKSSON, MALTE, KARLSSON, TOMMY
Applicants: ISAKSSON MALTE, KARLSSON TOMMY, VOLVO PERSONVAGNAR AB, ISAKSSON, MALTE, KARLSSON, TOMMY
Application year: 1999
Main classification: F16F9
IPC codes: F16F9