A piston and cylinder type damper is provided, with a cylinder (11) having a piston assembly (15) mounted for reciprocal movement therein. The piston assembly (15) divides the cylinder (11) into two separate chambers (12a, 12b), with a restricted flow path (30, 31) for passage therebetween of damping fluid contained within the cylinder. A piston rod (13) is mounted for reciprocal movement with respect to the cylinder (11) and acts via a first one of the chambers (12a) on the piston assembly (15) in a first direction. A seal assembly (17) is provided for sealing between the piston rod (13) and the cylinder (11) in order to retain damping fluid in the first chamber (12a). The seal assembly (17) is movable axially with respect to the cylinder (11), with the cylinder further including a centering device (24) for assisting alignment of the seal assembly (17).

This invention relates to dampers.

According to the invention there is provided a piston and cylinder type damper having a cylinder with a piston assembly mounted for reciprocal movement therein and dividing the cylinder into separate chambers with a restricted flow path for passage therebetween of damping fluid contained within the cylinder, and a piston rod mounted for reciprocal movement with respect to the cylinder and acting via a first one of said chambers on the piston assembly in at least a first direction, with a seal assembly being provided for sealing between the piston rod and the cylinder or a part attached thereto in order to retain damping fluid in said first chamber, with said seal assembly being movable axially with respect to the cylinder, and further comprising a centering device for assisting alignment of the seal assembly.

The invention also provides a piston and cylinder type damper having a cylinder with a piston assembly mounted for reciprocal movement therein and dividing the cylinder into separate chambers with a restricted flow path for passage therebetween of damping fluid contained within the cylinder, and a piston rod mounted for reciprocal movement with respect to the cylinder and acting via a first one of said chambers on the piston assembly in at least a first direction, with a seal assembly being provided for normally sealing between the piston rod and the cylinder or a part attached thereto in order to retain damping fluid in said first chamber, the damper further comprising means for allowing a bleed off of air from said first chamber.

The damper seen inFIG. 1is a linear piston and cylinder type damper having a piston assembly10that is reciprocably movable within an elongate cylinder11. The cylinder11contains a damping fluid, typically oil, with the piston assembly10effectively dividing the interior of the cylinder into separate chambers12a,12b(referred to herein for convenience as “upper” and “lower” chambers), with pathways through the piston assembly providing fluid communication between the two chambers, in known manner.

The piston assembly10includes a restricted passageway for flow of fluid into the upper chamber12aon the working (compression) stroke of the damper to provide a damping resistance to the inward movement of the piston rod13, in known manner. Here the restricted passageway is formed by two axially extending grooves30,31in a bore32of the body of the piston assembly10that receives the inner end of the piston rod13. The grooves30,31are arranged on diametrically opposite sides of the piston rod13, as seen inFIG. 2. Much larger passageways are exposed across the piston assembly10on the return stroke of the damper, in known manner, so that there is practically no resistance to the movement of the piston rod13out of the cylinder11.

The piston assembly10is acted on by the inner end of the piston rod13. The outer end of the piston rod13extends out of one end of the cylinder11via a cap14, which provides lateral guidance for the reciprocal axial movement of the piston rod. At its other end, the cylinder11is closed off by a plug50. The damper is arranged in use with the free end of the piston rod13in the path of movement of a component such as a drawer or door so as to damp its closing motion. In this case, the free end of the piston rod13is designed to be connected to another component, for which purpose it is formed with a groove41for the attachment of a circlip or the like.

The upper chamber12a, ie the chamber between the piston assembly10and the cap14, contains a mobile seal assembly15. The seal assembly15comprises a body16on which is mounted a sealing element17. The body16has a bore18therethrough to receive the piston rod13and is freely movable along it. A compression spring19is arranged between the cap14and the body16and acts to bias the body away from the cap.

The sealing element17has an inner annular lip20to engage the piston rod13in a fluid tight manner and an outer annular lip21to engage the inner bore of the cylinder11in a fluid tight manner. The sealing element17thus serves to prevent fluid from escaping from the upper chamber12a.

The seal assembly15is pressed by the biassing force of spring19onto the upper surface of the fluid in the upper chamber12a. The quantity of fluid in the upper chamber12awill vary as the piston assembly10moves in the cylinder11, due to variations in the volume taken up by the piston rod13within the chamber. The seal assembly15will thus move up and down with the variation in the fluid level. In this way, it is able to act to compensate for changes in the fluid volume in the upper chamber12ain operation. Floating seals of this nature are generally known in the art.

In the assembly seen inFIG. 3, the outer lip21of the sealing element17has an inner profile22that tapers in the axial direction. Also, the outer lip21is conveniently provided with a circumferentially extending rib23, ensuring essentially linear contact with the bore27of the cylinder11. The inner lip20of the sealing element17also preferably has a tapering profile28, as seen inFIG. 3.

Here, a collar24is mounted on the piston rod13between the piston assembly10and the cap14. The collar24fits snugly on the piston rod13but is freely movable along it. The collar24has a series of cutaways25around its periphery to allow for fluid to pass by it.

One of the functions of the collar24is to act as a deflector for fluid passing through the grooves30,31on the working stroke of the damper. The flow of fluid through these grooves30,31will be high if the damper experiences a large impact force, for example from a slammed drawer or door. If the jets of fluid that would result from such flows were allowed to act directly on the sealing element17, there may be a tendency for it to distort, with consequent loss of sealing integrity. The collar24serves to deflect such flows radially outwardly, thus eliminating or at least reducing this tendency to distortion. This function of the collar24is particularly useful when the piston rod13is in its fully extended position, as seen inFIG. 6, because that is when the grooves30,31through which the fluid will flow are nearest to the sealing element17.

A further feature of the collar24is that it has a conically-shaped end face26. In this case, the end face26is designed to enter into engagement with the tapering inner profile22of the outer lip21of the sealing element17. This is particularly advantageous in the manufacture of the damper. In the manufacturing process, a piston sub-assembly consisting of the piston assembly10, piston rod13, collar24and seal assembly15, is inserted into the cylinder11after it has been filled with a measured quantity of damping fluid, with the cap14then being applied to close off the cylinder. If there is any slight misalignment of the seal assembly15in this process, then withdrawing the piston rod13to its fully extended position will bring the collar24into engagement with the sealing element17and hence serve to centre it by action of the conically-shaped end face26on the tapering inner profile22of the outer lip21, as seen inFIG. 6. A similar effect might be achievable by providing a chamfered recess on the collar24to engage the tapering profile of the inner lip20, or of course the collar could include both such features.

Here the collar24is provided as an independently movable component. Instead, however, it could be formed as a part24′ to be mounted onto the piston assembly10, as seen inFIG. 7, or it could be formed as an integral part of the piston assembly.

A further feature of the damper seen inFIG. 1is a series of axially extending relief channels40that are provided in the bore27of the cylinder11towards its end with the cap14. The relief channels40come into operation in the assembly of the damper, and more specifically, during the step described above of inserting the piston sub-assembly into the fluid-filled cylinder.

When the cylinder11has been filled with a measured quantity of fluid, the piston sub-assembly is inserted into it to its fullest extent. At this point, if the fluid should contain any air bubbles, these will tend to percolate upwards and bleed out through the relief channels40. This will continue until the lip23of the mobile seal assembly15settles level with the opening into the relief channels40. This represents the uppermost limit of movement of the seal assembly15, which is achieved when the piston assembly is in its fully inserted position, as illustrated inFIG. 3. The lowermost limit of movement of the seal assembly15is the position seen inFIG. 6, which is in the fully extended position of the piston rod13.

FIG. 8shows a somewhat different form of damper to that seen inFIG. 1. In theFIG. 8damper, a compression spring60is located in the lower chamber, ie interposed between the piston assembly10and the plug50. The purpose of the spring60is to bias the piston assembly10and hence also the piston rod13into its extended position. The two dampers are otherwise the same in terms of their method of assembly and operation.

Another somewhat different form of damper is seen inFIG. 9. In this case, the cap14′ is designed to fit into the end of the cylinder11via a sleeve60that extends into a counter-bored section61of the cylinder bore27. The arrangement means that the sealing element17will engage with the inner surface of the sleeve60, rather than with the cylinder bore27as is the case with theFIG. 1damper. For convenience, the sleeve60may be designed to have the same internal diameter as the cylinder bore27.

The cap14′ is designed to fit into the end of the cylinder11with the sleeve60forming a fluid tight joint with the counter-bored section61. The seal assembly15still serves to seal off the upper chamber12a. In this case, however, it does so by means of both its sealing element17and the sleeve60.

The cylinder11still has relief channels40′ for bleeding off air in the manufacturing process, as in the case of theFIG. 1damper. Here, however, the relief channels40′ are formed on the inner surface of the sleeve60, rather than in the cylinder bore27.