GB2050561A

GB2050561A - Outer Tube of Telescopic Shock Absorber

Info

Publication number: GB2050561A
Application number: GB8015461A
Authority: GB
Original assignee: KAYABO KOGYO KK
Current assignee: KAYABO KOGYO KK
Priority date: 1979-05-10
Filing date: 1980-05-09
Publication date: 1981-01-07
Also published as: DE3017897A1; GB2050561B; JPS55161943U; FR2456262A1

Abstract

An outer tube (12) 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 12 is fixed to a knuckle spindle 13. The reduced rigidity in the upper portion allows the outer tube 12 to bend with the piston rod and reduces the frictional resistance between the piston rod and its guide. The rigidity of the upper end of the outer tube 12 is decreased by plastic stretching of the upper end of the tube (12) during manufacture, to reduce its wall thickness. <IMAGE>

Description

SPECIFICATION Telescopic Shock Absorber The present invention generally relates to a telescopic type shock absorber which is known in the art as a MacPherson type shock absorber and also specifically relates 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.

1145942.

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 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 1 47939 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.

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 n improved outer tube for a telescopic shock absorber which is relatively 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.

In accordance with a first aspect, the present invention provides a telescopic type shock absorber having an outer tube, the outer tube comprising a lower section and an upper section, the upper section having been plastically stretched such that the wall thickness of the upper section is smaller than the wall thickness of the lower section.

In accordance with a second aspect, the present invention provides a method of producing a telescopic type shock absorber having an outer tube comprising a lower and an upper section, said method comprising the step of plastically stretching the said upper section such that the wall thickness of the upper section is smaller than the wall thickness of the lower section.

A metal outer tube for a telescopic type shock absorber embodying the present invention comprises a lower section and an upper section which is plastically stretched in such a manner that a wall thickness of the upper section is smaller than a wall thickness of the lower section.

Preferably, the metal outer tube of the 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 being sufficient to withstand the maximum bending stresses which occur at the lower end where the tube is fixed to a knuckle spindle and the reduced rigidity in the upper portion allowing the outer tube to bend along with a piston rod and so reduce the frictional resistance between the piston rod and a bearing positioned in the outer tube through which the piston rod passes.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which Figure 1 is a vertical section of a telescopic shock absorber embodying the present invention; Figure 2 is a vertical section of the outer tube of the shock absorber shown in Figure 1; Figure 3 is a vertical section of a different outer tube of a shock absorber embodying the present invention; and Figure 4 is similar to Figures 2 and 3 but shows a further form of an outer tube of a shock absorber embodying the present invention.

While the outer tube for a telescopic shock absorber which embodies the present invention is susceptible of numerous physical variations, 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 numeral 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 1 6 are provided at the upper end of the outer tube 12.

An inner tube 1 7 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 1 8 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 1 7 below the piston 18 communicate with each other through holes (not shown) and these spaces are filled with hydraulic fluid or oil. The piston 1 8 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.

As illustrated in Figure 2, the outer tube 12 comprises a lower portion 1 2a and an upper portion 1 2b. The upper portion 1 2b is plastically stretched during manufacture by drawing or any other known process so that the wall thickness of the upper portion 1 2b is smaller than the wall thickness of the lower portion 1 2a. As illustrated, the inner diameters of the lower and upper portions 1 2a and 1 2b are substantially the same.

This arrangement provides sufficient strength and rigidity in the lower portion 1 2a to absorb the maximum bending stress which occurs at the junction of the tube 12 and knuckle spindle 13.

However, the thinner upper portion 1 2b is less rigid than the lower portion 1 2a and allows bending of the tube 1 2 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 plastic drawing process.

Figure 3 illustrates another form of outer tube of a shock absorber which embodies the present invention which is generally designated as 12' and comprises lower and upper portions 1 2a' and 1 2b' respectively. In this case, the upper portion 1 2b' has a smaller wall thickness than the lower portion 1 2a' but the inner diameter of the upper portion 1 2b' is larger than the inner diameter of the lower portion 1 2a'. The outer diameters of the portions 1 2a' and 1 2b' are substantially equal.

Figure 4 illustrates yet another form of outer tube 12" of a shock absorber embodying the present invention. The outer tube 12" comprises a lower portion 1 2a" and an upper portion 1 2b". In this case, the inner and outer diameters of the upper portion 1 2b" are smaller than the inner and outer diameters of the lower portion 1 2a" respectively. An advantage of this arrangement, as well as the outer tube 12 of Figures 1 and 2, is that a shoulder 1 2c is formed which supports the spring seat 22. Thus, the spring seat 22 and outer tubes 12 and 12" may be assembled together merely by placing the spring seat 22 over the tube 12 or 12" until it rests on the shoulder 1 2c.

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

1. A metal outer tube for a telescopic type shock absorber comprising a lower section and an upper section which is plastically stretched in such a manner that a wall thickness of the upper section is smaller than a wall thickness of the lower section.

2. A tube as in claim 1, in which an outer diameter of the upper section is smaller than an outer diameter of the lower section.

3. A tube as in claim 2, in which an inner diameter of the upper section is substantially equal to an inner diameter of the lower section.

4. A tube as in claim 1, in which an inner diameter of the upper section is larger than an inner diameter of the lower section.

5. A tube as in claim 4, in which an outer diameter of the upper section is substantially equal to an outer diameter of the lower section.

6. A tube as in claim 2, in which an inner diameter of the upper section is smaller than an inner diameter of the lower section.

7. A telescopic type shock absorber having an outer tube, the outer tube comprising a lower section and an upper section, the upper section having been plastically stretched such that the wall thickness of the upper section is smaller than the wall thickness of the lower section.

8. A method of producing a telescopic type shock absorber having an outer tube comprising a lower and an upper section, said method comprising the step of plastically stretching the said upper section such that the wall thickness of the upper section is smaller than the wall thickness of the lower section.

9. A telescopic type shock absorber substantially as hereinbefore described with reference to the accompanying drawings.