Brakes – Internal-resistance motion retarder – Resistance alters relative to direction of thrust member
Patent
1989-03-20
1991-03-26
Shoap, Allan N.
Brakes
Internal-resistance motion retarder
Resistance alters relative to direction of thrust member
16 49, 92172, 18832215, 277207R, F16F 936, F16J 912, F16J 924
Patent
active
050021656
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF THE INVENTION
This invention relates to sealing rings of the kind used to establish a peripheral seal between a piston and a cylinder in which the piston slides. More particularly, the invention is concerned with a sealing ring in or for an hydraulic damper, especially but not exclusively in or for use in a door closer.
Such sealing rings are commonly of circular shape in radial section (i.e. O-rings) but often other sectional shapes are employed. However, it is usual for the axial dimension of the sealing ring to be rather less than the corresponding dimension of the seating groove of the piston in which the ring is located. This enables swelling of the ring which tends to take place on prelonged exposure to hydraulic fluid to be accommodated without radial expansion.
In an hydraulic damper, the use of a sealing ring has a degree of axial clearance in this way can give rise to an undesirable deviation from the intended damping characteristic at the point where the direction of movement of the piston changes. For example, in the context of a door closer, a damper may include a piston which is movable relative to a cylinder in one direction with little resistance as the associated door is opened, whilst a significant resistance is established when the opposite movement occurs, as the door moves towards its closed position under the influence of spring or other actuating means. Movement of the sealing ring axially in its seating groove at the beginning of such closure movement, whilst only slight, nevertheless allows the door initially to move without any damping through a distance which at the free edge may amount to several centimeters. During such movement, the door gathers speed and when the damper becomes effective it can impose a sudden restriciton on the rate of movement, which causes the door to jolt or jerk, thereby setting up undesirable strain in the hinges, the closer, and the door itself.
It is one of the objects of the invention to provide a novel seal which can be fitted into its seating groove without axial play, so as to enable a damper to be substantially free from such initial undamped movement.
According to one aspect of the invention we provide a sealing ring which affords axially directed projections on one radial face at circumferentially spaced positions.
According to a further aspect of the invention we provide a piston and cylinder assembly including a sealing ring located in a seating groove wherein the sealing ring affords axially spaced radial faces which are spaced apart by a distance less than the axial width of the seating groove and a plurality of axially directed projections on one of said faces at circumferentially spaced positions so that the ring is held against axial movement within the groove.
The projections may be of circular shape in transverse section and preferably of generally conical form.
The radial faces of the sealing ring are preferably flat (apart from the projections) and the inner face is preferably of cylindrical form, with the inner face and each radial face meeting substantially at right angles, the groove being of rectangular shape in transverse section.
The outer face of the ring may include a chamfered portion adjacent to one or both radial faces, and a central cylindrical surface. Desirably, the outer diameter of the ring is controlled to a high degee of tolerance and may, for example, be machined to the required diameter.
The invention further resides in an hydraulic damper incorporating such a piston and cylinder assembly, and a door closer incorporating such a damper.
The invention will now be described by way of example with reference to the accompanying drawings wherein:
FIG. 1 shows one embodiment of sealing ring in accordance with the invention in end view;
FIG. 2 shows a corresponding diametral section of the sealing ring;
FIG. 3 shows a transverse section through one embodiment of door closer incorporating a hydraulic damper which utilises such a sealing ring.
In accordance with the invention a sealing ring 10 is formed with
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Samuel Heath & Sons PLC
Shoap Allan N.
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