GB2081419A

GB2081419A - Hydraulic shock absorber

Info

Publication number: GB2081419A
Application number: GB8122758A
Authority: GB
Original assignee: SHOWA Manufacturing; Showa Seisakusho Co Ltd
Current assignee: SHOWA Manufacturing; Showa Corp
Priority date: 1980-07-28
Filing date: 1981-07-23
Publication date: 1982-02-17
Also published as: DE3129208A1; JPS5728933U

Abstract

A hydraulic shock absorber for a vehicle body suspension comprises a piston 2 working in a main cylinder 1 filled with oil and enclosed within a co-axial auxilliary cylinder 3 and an outer tube 4. The main cylinder 1 has ports 16 and 17 respectively above and below the position taken up by the piston 2 when the vehicle is stationary, as shown in the drawing. When the stroke of oscillation of the piston is less than the distance between the ports 16 add 17 oil flows through these ports and only a slight shock absorbing effect is obtained. For larger strokes of the piston resulting from rough roads, flow through the ports 16 and 17 is interrupted and a stronger shock absorbing effect is obtained. <IMAGE>

Description

SPECIFICATION Hydraulic shock absorber This invention relates to hydraulic shock absorbers for the suspension of bodies of two orfourwheeled vehicles.

When running on a paved or sectional concrete road such vehicles receive minor shocks from the joints of the road. In these circumstances, the riding comfort of the vehicle can be improved by weakening the shock absorbing force of the hydraulic shock absorber in the suspension of the vehicle. On the other hand, when a vehicle runs on a bad road having large irregularities, the shock absorbing force has to be increased to prevent the vehicle body from bouncing, thereby ensuring running stability. In order to satisfy those two inconsistent requirements, a hydraulic shock absorber has been proposed in which the piston mechanism generating the shock absorbing force is devised to weaken the shock absorbing force against the minor vibrations.

However, the previous contruction failed to attain satisfactory results and had such a complex construction as to cause difficulty in operation.

According to the present invention, a hydraulic shock absorber for a vehicle body suspension comprises a piston having a piston rod and an oil communication passage for generating a shock absorbing force, a main cylinder slidably receiving the piston and filled with working oil, and an auxiliary cylinder disposed co-axially of and outside the main cylinder to define an annular clearance space with the main cylinder, the main cylinder being formed with two oil ports which are respectively spaced from the upper and lower sides of the piston when the vehicle is stationary and which connect the interior of the main cylinder with the annular clearance space.

An example of a hydraulic shock absorber in accordance with the invention will now be described, with reference to the accompanying drawings, in which: Figure lisa longitudinal section; and Figure 2 is a graph showing the characteristic curves in the extension stroke of the shock absorber of Figure 1.

In the hydraulic shock absorber shown in Figure 1, a piston 2 is slidably received in a main cylinder 1. A co-axial auxilliary cylinder 3 is disposed outside the main cylinder 1 and an outer tube 4 is disposed outside the auxilliary cylinder 3. The lower ends of the main cylinder and the outer tube are fixed to a bottom cover 5 and the upper ends of the main cylinder, the outer tube and the auxilliary cylinder are fixed to a rod guide 6 for example by press-fitting or welding. An oil seal 7 is mounted on the upper side of the guide 6 and a piston rod 8 passes through the rod guide and oil seal. The shock absorber thus defined is filled with an appropriate quantity of working oil 9. The piston 2 carries a piston ring 10 and is formed with an oil communication passage 11 for generating a shock absorbing force.On the upper side of the piston 2 there is arranged a disc valve 12 which is formed with an orifice 13 in alignment with the oil communication passage 11. In the lower end of the auxilliary cylinder 3 there is fitted an O-ring 14 which is forced into contact with the outer circu mference of the main cylinder 3 so as to prevent any leakage ofthe oil. The main cylinder 1 has its lower end formed with an oil passage 15 which provides communication between the inside thereof and the space between the auxilliary cylinder 3 and the outer tube 4. Finally, the main cylinder 1 is formed with two, respectively smaller and larger oil ports 16 and 17 which are spaced by respective distances e1 and e2 from the upper and lower sides of the piston 2 when the vehicle is stationary, as shown.

While the vehicle whose body is suspended by the hydraulic shock absorber just described is running on a flat road, the piston 2 is held at substantially the same position as that when the vehicle is stationary, as shown. If the vehicle receives shocks from the joints or bumps on the road, the piston 2 vibrates vertically with strokes smaller than the abovespecified distances el and t2. As a result, when the piston 2 descends, the valve 12 is opened so that the oil below the piston 2 flows to the space above it, partly through the oil communication passage 11 and partly through the space between the main cylinder 1 and the auxilliary cylinder 3 and through the smaller oil port 16 from the larger oil port 17.

When the piston ascends, the valve 12 is closed so that the oil above the piston flows to the space below partly through the orifice 13 and partly through the space between the main cylinder and the auxilliary cylinder and through the larger oil port 17 from the smaller oil port 16. As a result, the shock absorbing force becomes far weaker than it would be if the oil flowed only through the oil communication passage 11 of the piston, so that riding comfort can be attained.

When the vehicle runs on a rough road, however, it receives much stronger shocks from the road surface so that the piston vibrates with strokes longer than the distance between the oil ports 16 and 17. In these circumstances, therefore, when either the upper or lower side of the piston 2 passes over either the oil port 16 or 17, the oil communication therethrough is interrupted so that the oil is allowed to flow only through the oil communication passage 11 of the piston whereby a strong shock absorbing force is generated by the oil communication passage 11 or the orifice 13. As a result, the vibrations of the vehicle body are restricted so that shocks due to the body hitting the road surface can be prevented while maintaining running stability.

Curves indicating the aforementioned characteristics are illustrated in Figure 2, in which the abscissa indicates a stroke L taken with reference to the position of the piston when the vehicle is stationary and in which the ordinate indicates a shock absorbing force F in the extension stroke of the shock absorber when the velocities V1, V2 and so on of the piston are used as parameters. In Figure 2, ea denotes the position of the oil port 16 and e2 denotes the position of the oil port 17.

In a shock absorber constructed according to the present invention, when the stroke exceeds a predetermined range, the shock absorbing force is au gmented to block large vibrations of the vehicle body. As a result, good riding comfort can be attained when the vehicle runs on a flat road. At the same time, even when the vehicle runs on a rough road, generation of abnormally large vibrations is avoided, which might adversely affect the running stability. Moreover, the shock absorber of the present invention can operate reliably and stably although it has a simple construction.

Claims

1. A hydraulic shock absorber for a vehicle body suspension and comprising a piston having a piston rod and an oil communication passage for generating a shock absorbing force, a main cylinder slidably receiving the piston and filled with working oil and an auxilliary cylinder disposed co-axially of and outside the main cylinder to define an annular clearance space with the main cylinder, the main cylinder being formed with two oil ports which are respectively spaced from the upper and lower side of the piston when the vehicle is stationary, and which connect the interior of the main cylinder with the annular clearance space.

2. A shock absorber according to claim 1 further comprising an outer tube disposed outside the auxilliary cylinder and co-axially with both the main cylinder and the auxilliary cylinder and defining with the auxilliary cylinder an annular space communicating with the inside of the main cylinder via an oil passage.

3. A shock absorber according to claim 1 or claim 2, wherein the effective area of the oil port of the main cylinder which is on the same side of the piston as the piston rod is smaller than that of the other oil port.

4. A shock absorber according to any one of the preceding claims further comprising a disc valve mounted on the side of the piston adjacent the piston rod and having an orifice in alignment with the oil communication passage of the piston.

5. A shock absorber according to any one of the preceding claims, further comprising an O-ring mounted in the end of the auxilliary cylinder remote from the piston rod and contacting the outer circumference of the main cylinder.

6. A hydraulic shock absorber for a vehicle body suspension substantially as described and as illustrated with reference to Figure 1 of the accompanying drawings.