SHOCK ABSORBER WITH SEAL HEAD FIXED IN ROTATION

Technical Field The present invention relates to the field of shock absorbers of the type that is positioned concentrically inside a helical spring, and in particular to so-called TTX shock absorbers for off-road use. These shock absorbers are provided with a seal head, through which the piston rod of the shock absorber extends.

Background Art

TTX shock absorbers are often constructed from an outer tube and an inner tube, inside which a piston with a piston rod is arranged in such a way as to be capable of displacement. The piston rod projects from the shock absorber through a seal head, which, on the one hand, centres the inner tube in the outer tube and, on the other hand, provides a seal against the outer tube and against the piston rod. The seal head is threaded internally into the outer tube from one end of the shock absorber. The shock absorber is usually provided with a piston support arranged around the piston rod and resting against the piston and constituting a spacer between the piston and one side of the seal head. In addition, the shock absorber is provided with a stop rubber situated outside the damper around the piston rod. The stop rubber is so arranged as to restrict the maximum compression of the damper in a gentle manner by coming into contact with the other side of the seal head.

When these types of shock absorber operate, the piston support abuts against the seal head when the shock absorber is in its fully extended position, while the stop rubber abuts against the seal head in the event of a strong compression of the shock absorber. These repeated impacts against the seal head, both from the top side and from the bottom side, produce vibrations

in the seal head, which vibrations exhibit a tendency to cause the seal head to work loose and unscrew from the outer tube, with the result that the shock absorber is deprived of its function in full or in part.

US Patent 4,438,834 depicts a number of embodiments of a shock absorber having a protective cover, which is connected via a threaded coupling to the outer tube of the shock absorber and locks the seal head securely in this way. A number of the embodiments are internally threaded, and a number of the embodiments are externally threaded onto the outer tube. The patent also depicts embodiments, in which the protective cover is pressed securely to the outer tube by the deformation of the same.

US Patent 4,240,531 depicts a shock absorber, the protective cover of which is locked to the shock absorber with a ring nut via a threaded coupling.

US Patent 5,667,041 also depicts a shock absorber provided with a seal head, although this is locked to the shock absorber in the sense that a sealing cover is welded to the outer tube, which means that dismantling of the seal head is not possible.

Object of the Invention

The object of the present invention is to eliminate tendencies for the seal head to be unscrewed in the case of shock absorbers of the kind in which dismantling of the seal head is possible.

A further object of the invention is to make available a guard which eliminates impacts directly against the seal head of the shock absorber.

Summary of the Invention

The above-mentioned object is achieved by the present invention in the form in which it can be appreciated

from the independent Patent Claim. Appropriate embodiments of the invention are set forth in the dependent Patent Claims.

The invention relates to a shock absorber comprising an inner tube, arranged in which is a damping piston capable of axial displacement in the inner tube, which damping piston demarcates a compression chamber from a return chamber. The damping piston is connected to a piston rod which extends through a seal head and out from the shock absorber. The seal head is connected to one end of the inner tube and is connected in a sealing manner to the inner cylindrical surface of an outer tube, in conjunction with which a media passage is arranged between the return chamber and the compression chamber via a connecting gap formed between the outer tube and the inner tube. In conjunction with this, a damping medium is so arranged as to be forced between the return chamber and the compression chamber, and vice versa, when the shock absorber is operating. The end of the outer tube is closed by a protective cover provided with a piston rod opening, which protective cover is connected with a press fit to the outer tube for the enclosure of the aforementioned seal head.

The protective cover in one embodiment is also connected to the aforementioned seal head with a press fit.

The seal head of the shock absorber in a further embodiment is connected internally to the outer tube by means of a threaded coupling so arranged as to permit the seal head to be screwed into the outer tube.

In a further embodiment, the seal head is provided with a lower stop surface, and the protective cover is provided with an upper stop surface, in conjunction with which the aforementioned stop surfaces are

situated opposite one another when the shock absorber is assembled.

The seal head in yet another embodiment is provided with an assembly ring having an outer cylindrical surface, which assembly ring is oriented concentrically in relation to the piston rod when the shock absorber is assembled in order to form an annular gap around the piston rod. In a variant of this embodiment, the protective cover is provided with a pressure ring positioned concentrically in relation to the piston rod opening of the protective cover, which pressure ring extends into the annular gap between the outer tube and the assembly ring with a press fit against both the outer tube and the assembly ring. Alternative configurations of this embodiment within the scope of the invention are that the protective cover can be provided with a pressure ring, which engages with a press fit with the seal head alone, that is to say not in combination with the outer tube, and with a press fit in this case, too.

The seal head and the protective cover in a further embodiment are also assembled inside the outer tube so that the aforementioned lower stop surface and the aforementioned upper stop surface are situated at a distance from one another.

In a further embodiment, the aforementioned stop surfaces are positioned adjacent to the inner surface of the outer tube. Other positions of these stop surfaces radially are also possible.

In a further embodiment, the aforementioned stop surfaces are oriented in a plane, of which the normal runs parallel to the axial direction of the piston rod.

The seal head in further embodiments is provided with a collar, on which the whole of the end surface of the

inner tube rests along the whole of its axially outermost internal periphery and is provided with a radial supporting surface for which stabilizes the inner tube concentrically in relation to the outer tube. The seal head is provided in conjunction with these embodiments with at least one radial media passage from the return chamber to the connecting gap. The media passage can also be positioned through the inner tube, or even through both the inner tube and the seal head. The media passage can consist of two or more holes, preferably being of a sufficiently large number or of a sufficiently large size to ensure that the flow that is able to pass through the holes is at least the same as the flow through the connecting gap.

Brief Description of the Drawings

The invention will now be described in more detail with the help of illustrative embodiments and with reference to the accompanying drawings, in which Figure 1 depicts a section through an assembled shock absorber in its maximum extended position according to the present invention; Figure 2 depicts a first detail from Figure 1; Figure 3 depicts a second detail from Figure 1.

Description of the Invention

Figure 1 depicts a shock absorber 1 comprising an inner tube 2, arranged in which is a solid damping piston 3 capable of axial displacement, which damping piston demarcates a compression chamber 4 from a return chamber 5. The damping piston 3 is connected to a piston rod 6 which extends through a seal head 7 and out from the shock absorber. The seal head 7 is connected on the one hand to one end 8 of the inner tube 2 and is connected in a sealing manner to the inner cylindrical surface 10 of an outer tube 9 provided with an end 12. The purpose of the seal head is to seal the two damping chambers from the surroundings in combination with retaining both the

inner tube and the outer tube in place, so that a connecting gap 11 is produced between these tubes. A media passage is arranged in this case between the return chamber 5 and the compression chamber 4 via the connecting gap 11 formed between the outer tube 9 and the inner tube 2. A damping medium in the form of a hydraulic fluid is so arranged in this case as to be forced between the return chamber 5 and the compression chamber 4, and vice versa, when the shock absorber is operating.

The connecting gap in this case is connected via adjustable valves (not illustrated here) to a pressure reservoir (also not illustrated) and is pressurized with a positive pressure so that a certain minimum pressure is always present inside the chambers. The characteristic of the shock absorber can be adjusted with these valves.

In addition, the end 12 of the outer tube is closed with a protective cover 13 provided with a piston rod opening 14. The seal head 7 is installed in the outer tube 9 by means of a threaded coupling 15. The protective cover 13 is connected by a press fit to the outer tube 9 for the enclosure of the seal head 7, on the one hand in order to protect it against impacts, and on the other hand to prevent the seal head from working loose by unscrewing. The protective cover is also connected by a press fit to the seal head, which can be configured in a plurality of different ways, of which one way is depicted in Figure 1 and Figure 2.

The damping piston is also connected to a piston support 21, which constitutes a spacer between the damper piston and a support surface 22 provided with an extension guard 23 mounted on the seal head 7. The extension guard eliminates metal-to-metal contact between the damper piston and the seal head with the shock absorber in its extreme position. The piston

support 21 helps the return chamber 5 to maintain a certain minimum volume in order to ensure that the damping medium is able to flow unobstructed between the return chamber and the compression chamber. Extending between the return chamber 5 and the connecting gap 11 is a radial media passage 24, which, in the embodiment depicted in Figure 1, is positioned in the seal head 7. The piston support is also provided with a radial piston support passage 25.

In order to support and seal the passage of the piston rod through the seal head, the seal head is provided with a bush 26 and an X-ring 27. A scraper ring 28 is also installed in the seal head in order to prevent the ingress of dirt into the shock absorber.

The piston rod 6 extends through a spring support 29 and terminates in an end eye 30, which is fitted to a wheel axle or a wheel suspension. Fitted concentrically around the piston rod 6 and bearing against the spring support 29 is an annular stop rubber 31, which restricts the length of stroke 32 to a free stroke 33.

Figure 2 shows how the seal head 7 is provided with a bottom stop surface 41, which faces towards and is positioned directly opposite an upper stop surface 42 on a compression ring 43 in the protective cover 13 when this is installed in the shock absorber. The compression ring 43 is positioned concentrically in relation to the piston rod and the piston rod opening and extends inwards in the direction of the seal head. The seal head is also provided with an assembly ring 44 integrated concentrically in relation to the piston rod 6 and provided with an outer cylindrical surface 45, so that an annular gap 46 is formed between the cylindrical surface 45 of the assembly ring and the internal cylindrical surface 10 of the outer tube 9 when the seal head is installed. The compression ring 43 extends into this annular gap with a press fit

against both the cylindrical surface 10 of the outer tube 9 and the cylindrical surface 45 of the assembly ring 44. It can also be appreciated from Figure 2 that the bottom stop surface 41 and the top stop surface 42 are positioned in the gap 46, and that they are situated at a distance from one another. The stop surfaces 41, 42 are also positioned adjacent to the internal periphery of the outer tube, so that the two contact surfaces make direct contact with one another at an angle, which is preferably 90°. The aforementioned contact surfaces are thus oriented in a plane, of which the normal is parallel to the axial direction of the piston rod.

Figure 3 depicts an upper part of the seal head 7, which is provided with an annular collar 51 that is removably connected to the end 8 of the inner tube 2 and, in particular, to an axial part of the peripheral inner end surface 52 of the end towards an annular surface 53 on the collar 51. The contact between the surfaces 52, 53 preferably extends along the whole of the axially outermost inner periphery of the end 8. The collar 51 is also provided with a radial supporting surface 54, which bears against the end surface 55 of the inner tube 2. The design of the collar 51, with the annular surface 53 and the radial supporting surface 54, helps to stabilize the inner tube 2 concentrically in relation to the outer tube 9.

The embodiments according to the above description help to secure the seal head against rotation in the event that it is exposed to impacts, either from the under side or from the upper side.