OUTER TUBE FOR TELESCOPIC SHOCK ABSORBER

Abstract: A metal outer tube (12) of a telescopic type shock absorber (11) is formed in such a manner as to have its rigidity decrease from a lower end to an upper end thereof. The rigidity in the lower end portion is sufficient to withstand the maximum bending stresses which occur at the lower end where the tube (12) is fixed to a knuckle spindle (13). The reduced rigidity in the upper portion allows the outer tube (12) to bend along with a piston rod (21) and reduces the frictional resistance between the piston rod (21) and a bearing (14).

Description: Background of the Invention The present invention generally relates to a telescopic type shock absorber which is known in the art as a MacPherson type shock absorber and more specifically to an improved outer tube for such a shock absorber. The overall configuration of a telescopic shock absorber to which the present invention relates is known in the art per se and disclosed in numerous publications typified by U.S. patent nos. 2,624,592 and 3,490,785 and British patent no. 1,145,942. The telescopic shock absorber comprises an inner tube, a piston carried at the lower end of a piston rod and which is sealingly slidable in the inner tube and an outer tube which coaxially surrounds the inner tube and piston rod; The piston rod slides through a bearing fixed to the upper ends of the inner and outer tubes and is fixed at its upper end to a vehicle suspension. The lower end of the outer tube is fixed to a knuckle spindle for a wheel. The vehicle is supported by means of the wheel, knuckle spindle, shock absorber and suspension. The inner and outer tubes are filled with hydraulic fluid to dampen relative telescopic movement between the piston rod and the inner and outer tubes and thereby dampen road shocks resulting from the operation of the vehicle. The maximum bending stress occurs at the lower end of the outer tube where it is fixed to the knuckle spindle and progressively decreases in the upward direction. Prior art telescopic shock absorbers comprise outer tubes which have uniform inner and outer diameters and wall thicknesses. The wall thickness and inner and outer diameters are selected to be sufficient to absorb the maximum bending stress in-the lower portion of the outer tube. Thus, the upper portion of the outer tube is overdesigned and excessively rigid. Excess rigidity of the outer tube prevents the outer tube from bending along with the piston rod during operation of the vehicle. This increases the frictional resistance between the piston rod and the bearing at the upper end of the tubes, preventing smooth operation of the shock absorber and increasing wear to an unnecessarily high extent. One prior art attempt to overcome this problem is to increase the clearance between the piston rod and the bearing. Although this somewhat improves the frictional resistance situation, it makes it very difficult to perform accurate wheel alignment of the vehicle. Another prior.art expedient is disclosed in Japanese utility model application no. 50-147939 and involves reducing the thickness of the outer tube from the lower portion to the upper portion thereof. However, this requires a machining operation to cut the taper which greatly increases the cost and production time of the outer tube. Summary of the Invention A metal outer tube for a telescopic type shock absorber embodying the present invention has a substantially uniform wall thickness and is plastically stretched in such a manner that the tube tapers inwardly from a lower portion to an upper portion thereof. In accordance with the present invention, a metal outer tube of a telescopic type shock absorber is formed in such a manner as to have its rigidity decrease from a lower end to an upper end thereof. The rigidity in the lower end portion is sufficient to withstand the maximum bending stresses which occur at the lower end where the tube is fixed to a knuckle spindle. The reduced rigidity in the upper portion allows the outer tube to bend along with a piston rod and reduces the frictional resistance between the piston rod and a bearing. It is an object of the present invention to provide an improved outer tube for a telescopic shock absorber which features reduced internal friction and wear. It is another object of the present invention to provide an improved outer tube for a telescopic shock absorber which is easy and economical to manufacture on a commercial production basis. It is another object of the present invention to provide a generally improved outer tube for a telescopic shock absorber. Other objects, together with the foregoing, are attained in the embodiments described in the following description and illustrated in the accompanying drawing. Brief Description of the Drawing Figure 1 is a vertical sectional view of a telescopic shock absorber embodying the present invention; Figure 2 is a vertical sectional view of an outer tube of the present shock absorber; and Figure 3 is a vertical section of another outer tube embodying the present invention. Description of the Preferred Embodiments While the outer tube for a telescopic shock absorber of the present invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodiments have been made, tested and used, and all have performed in an eminently satisfactory manner. Referring now to Figure 1 of the drawing, a telescopic type shock absorber embodying the present invention is generally designated by the reference number 11 and comprises a metal outer tube 12. The lower end of the outer tube 12 is fixedly connected to a knuckle spindle 13 which, although not illustrated, rotatably supports a wheel of a vehicle. A bearing 14 and oil seal 16 are provided at the upper end of the outer tube 12. An inner tube 17 is fixed in place inside the outer tube 12 in a coaxial manner and a piston 18 is slidable in the inner tube 17. An annular seal 19 is provided to the piston 18 for sealing engagement with the inner wall of the inner tube 17. The space between the tubes 12 and 17 and the interior of the tube 17 below the piston 18 communicate with each other through holes (not shown) and these spaces are filled with hydraulic fluid or oil. The piston 18 is further provided with a valve (not shown) to dampen movement of the piston 18 in the tube 17. The shock absorber 11 further comprises a piston rod 21 which extends upwardly from the piston 18 through the bearing 14 and seal 16 and is connected to a suspension of the vehicle through a resilient rubber bushing (not shown). Further illustrated are a spring seat 22 and a coil suspension spring 23 which is operatively mounted between the spring seat 22 and the suspension. A stop 24 is fixed to the piston rod 21 to prevent overextension of the shock absorber 11 through abutment with the lower end of the bearing 14. The outer shell 12 is illustrated in Figure 2 and has a uniform wall thickness. However, the diameter of the tube 12 progressively decreases from the lower end portion to the upper end portion thereof. This configuration is produced by plastic stretching of the tube 12 using any known method such as drawing during manufacture. This arrangement provides sufficient strength and rigidity in the lower portion to absorb the maximum bending stress which occurs at the junction of the tube 12 and knuckle spindle 13. However, the thinner upper portion is less rigid than the lower portion and allows bending of the tube 12 to follow the configuration of the piston rod 21. As a result, the clearance between the piston rod 21 and bearing 14 may be made very small and wheel alignment very accurate. An expensive machining operation to taper the tube 12 is eliminated since the desired result is accomplished by a simple, fast and inexpensive drawing process. Figure 3 illustrates another outer tube 12' embodying the present invention in which the wall thickness is uniform but the diameter of the tube 12' decreases from the lower portion to the upper portion thereof in a stepwise manner. As illustrated, the diameter is reduced in four steps as indicated at 12a, 12b, 12c and 12d. In summary, it will be seen that the present invention overcomes the drawbacks of the prior art and provides a telescopic shock absorber of greatly improved construction and operation. Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

Claims: WHAT IS CLAIMED IS: 1. A metal outer tube for a telescopic type shock absorber having a substantially uniform wall thickness and being plastically stretched in such a manner that the tube tapers inwardly from a lower portion to an upper portion thereof. 2. A tube as in claim 1, in which the tube tapers inwardly in a continuous manner. 3. A tube as in claim 1, in which the tube tapers inwardly in a stepwise manner.

Inventors: HORIYAMA, OSAMU, NAKADA, ETSURO, OGAWA, MOTOAKI
Applicants: KAYABA KOGYO KABUSHIKI KAISHA
Application year: 1980
Main classification: B60G15
IPC codes: B60G13, F16F9