Brakes – Internal-resistance motion retarder – Including seal or guide
Patent
1996-09-19
1998-06-16
Oberleitner, Robert J.
Brakes
Internal-resistance motion retarder
Including seal or guide
92165R, F16F 936
Patent
active
057656665
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to suspension struts, particularly, but not exclusively, suitable for automotive use.
BACKGROUND
A typical suspension strut comprises a pair of coaxially disposed tubes, the inner of which contains a piston operated by a piston rod extending from the assembly through an end closure for the strut, the end closure including both bearing and sealing means for the piston rod, to minimise friction and leakage. The other end of the strut is closed. The inner tube is usually full of fluid, typically oil, the outer tube only partly so. Displacement of the piston within the inner tube causes fluid to be transferred from the inner tube to the outer tube via a combination of one-way valves and ports, so that the rate of flow is not necessarily the same for each direction of piston movement. By this means, controlled damping of the piston movement can be achieved. Single tube struts are also known and operate in a generally similar way, by displacement of fluid from one end of the tube to the other in a controlled manner.
In automotive applications, the suspension strut is often used in combination with conventional coil springs and/or torsion bars to achieve acceptable road holding and shock absorption performance.
Because of the forces involved, a suspension strut is generally of all-metal construction, although a plastics coated metal bearing component is commonly used to support and guide the piston rod as part of the end closure where the rod leaves the strut tube assembly. It is usual to provide some form of elastomeric seal in this same area to prevent ingress of dirt and to minimise the risk of leakage of fluid. But for the most part, it is usual to manufacture the end closure through which the piston rod passes from metal, typically from sintered iron. This is because the closure not only serves to locate and guide the piston rod but also to locate the inner and outer tubes relative to one another, as well as providing internal passageways for controlled transfer of fluid from the inner tube to the space between the inner and outer tube. An additional function of the end closure for the tubes is the provision of some means for absorbing the impact caused by over-travel of the piston. Very often this is done by providing on the piston rod a coil spring which is compressed between the piston and the inner end of the closure when the piston overtravels towards the latter. The end closure of a suspension strut is thus exposed to significant stresses including twisting/bending forces, and up to now it has been thought essential to manufacture it from metal, including the attendant machining operations required to provide the close tolerances necessary for satisfactory assembly and operation.
Fitting and sizing the bearing bush is also an important requirement.
SUMMARY OF THE INVENTION
It is an object of the present invention to simplify the construction of the end closure for a suspension strut.
According to the present invention, a suspension strut comprises inner and outer tubes and incorporates an end closure constituted by a moulded plastics insert containing a sleeve bearing in the form of a metal bush, the insert being a press fit into the outer tube of the strut and the press fit region of the insert including a portion adapted to engage with and locate in a radial direction the inner tube of the strut, together with at least two circumferential ribs which extend radially from the insert to engage the inner surface of the outer tube, the material of said ribs being in compression, with said ribs being spaced apart axially of the strut to confer a degree of resilience onto the assembly and a fluid seal being provided at or adjacent the outer face of the end closure to minimize fluid losses from the strut along the relatively movable rod thereof.
The metal bush is preferably provided with a plastics working surface of, for example, a PTFE based bearing material. The plastics insert preferably contains integrally moulded passageways adapted to permit the transfer o
REFERENCES:
patent: 4057236 (1977-11-01), Hennells
patent: 4438834 (1984-03-01), Hanoke
patent: 5192057 (1993-03-01), Wydra
Ligier Jean-Louis
Provence Marc
Bartz C. T.
Glacier Vandervell SA
Oberleitner Robert J.
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