GB2057089A

GB2057089A - Hydraulic shock absorber with compensating chamber

Info

Publication number: GB2057089A
Application number: GB8024884A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1979-08-01
Filing date: 1980-07-30
Publication date: 1981-03-25
Also published as: DE3028905A1; JPS5624238A; FR2463329B1; FR2463329A1

Abstract

A shock absorber includes a piston rod 3 with a piston 2 axially reciprocally movable in a closed cylinder 1 where liquid is contained. The piston divides the inside of the cylinder into first and second chambers 20, 22. An elastomeric member 9 is provided to define a third liquid filled chamber 11 communicating with the second chamber 22 to allow the reciprocating movement of the piston rod and to add elasticity to the shock absorber. Optionally a second elastomeric member provides a fourth chamber communicating with the first chamber 20. A shield may be provided to limit expansion of the elastomeric walled chambers. <IMAGE>

Description

SPECIFICATION Shock absorber The present invention relates to a hydromatic telescopic shock absorber, particularly adapted for use in automotive vehicles, such as in the suspension system.

The De Carbon type shock absorber is well known, and is shown in Fig. 1 to include a cylinder 1 closed at both ends. The cylinder contains damping liquid 7 such as oil and a pressurized inert gas 8, such as nitrogen. A piston rod 3 passes axially through one end of the cylinder and carries a piston 2. The piston 2 fits axially in the cylinder and is provided with a plurality of axial orifices 6 which are associated with baffle plates and permit the liquid to flow through when the piston is moved in the cylinder. An auxiliary piston 5 is provided in the cylinder to separate the liquid and gas in the cylinder. The auxiliary piston 5 includes a flexible rubber sealing ring fitted into a groove in the cylindrical wall of the auxiliary piston.

The gas 8 is pressurized up to approximately 20kg/cm2 so as to pressurize the damping liquid.

A principal difficulty encountered with such a shock absorber is that the magnitude of the damping force provided by the shock absorber is dependent on the reciprocating speed of the piston and essentially is independent of the frequency and amplitude of vibration applied to the shock absorber.

Where such a shock absorber is used as a suspension shock absorber to dampen sprung and unsprung resonant vibrations, it produces an unnecessarily large damping force in the high frequency range, such as when the shock absorber receives a high frequency vibration when the automotive vehicle is running on a road having such a surface as to induce such high frequency vibration, for example, a road with an undulated surface, causing the reciprocating speed of the piston to increase to such high frequency range.

Since the magnitude of damping force provided by the De Carbon type shock absorber increases considerably in the high frequency range, the magnitude of force transmitted to the vehicle body from the shock absorber increases, thereby creating an uncomfortable ride and increasing the road noise transmitted to the passenger compartment.

The present invention is directed to overcoming the abovementioned difficulty and to providing a shock absorber which comprises a cylinder closed at both ends; a quantity of liquid contained within the cylinder; a piston axially movable in the cylinder to divide same into first and second chambers and immersed in the liquid; a piston rod coaxial with the cylinder and connected to the piston, the piston rod extending axially outwardly of the cylinder in a liquid tight manner through one of the ends of the cylinder, the piston having at least one orifice formed therein which permits the flow of liquid therethrough during axial reciprocation of the piston within the cylinder; and an elastomeric member defining a third chamber communicating with the second chamber, the liquid filling the third chamber.

Accordingly an object of the present invention is to provide a shock absorber having an expandable liquid chamber to accommodate a volume of damping liquid displaced from the cylinder to reduce the damping force in the high frequency range.

Another object of the present invention is to provide a shock absorber of greater simplicity in structure.

In the accompanying drawings, like reference numerals are used to designate like parts throughout all figures.

Fig. 1 is a view partly broken away to show an axial section of the above described De Carbon type shock absorber; Fig. 2 is a view similar to Fig. 1 illustrating a first embodiment of a shock absorber embodying the present invention; Fig. 3 is a graph showing damping constant vs.

frequency of applied vibration to the De Carbon type shock absorber illustrated in Fig. 1 and the shock absorber illustrated in Fig. 2; Fig. 4 is a view similar to Fig. 1 showing a second embodiment of a shock absorber according to the present invention; Fig. 5 is a graph showing spring constant vs.

piston position characteristics of the shock absorber illustrated in Fig. 2 and that of the shock absorber illustrated in Fig. 4; Fig. 6 is a graph showing damping constant vs.

piston position characteristics of the shock absorbers of Figs. 2 and 4; Fig. 7 is a view similar to Fig. 1 showing a third embodiment of a shock absorber according to the present invention; and Fig. 8 is a view similar to Fig. 1 showing a fourth embodiment of a shock absorber according to the present invention.

Referring to Fig. 2, there is shown a first embodiment of a shock absorber according to the present invention which includes a cylinder 1 closed at the upper end by a circular end wall 4.

The cylinder 1 has an integrally formed lower end wall (no numeral). A piston rod 3 passes longitudinally slidably through the circular end wall 4. Suitable packing or sealing means is provided to insure a liquid-tight seal between the piston rod 3 and the end wall 4. The piston rod 3 is coaxial with the cylinder 1. At one end, the piston rod 3 carries a circular piston 2 to sealably slide along the inner wall surface of the cylinder 1.

The piston 2 is provided with a plurality of circularly spaced orifices, only one being shown at 6, which extend axially through the piston 2.

Disposed in the cylinder 1 is a predetermined quantity of a suitable liquid such as oil. The orifices 6 allow the oil to flow therethrough during reciprocation of the piston 2. The piston 2 divides the inside of the cylinder 1 into a first chamber 20 and a second chamber 22, both filled with oil.

A first elastomeric member 9 such as rubber defines a third chamber 11 communicating with the second chamber 22 via at least one orifice 12 formed in the cylinder side wall. The first elastomeric member 9 is in the shape of a tube surrounding the lower portion of the outer surface of the cylinder 1 and sealably attached to one end thereof by two steel bands 10. A second elastomeric member 9' identical to the first defines a fourth chamber 11' communicating with the first chamber 20 via at least one orifice 12' formed in the cylinder side wall. The second elastomeric member 9' surrounds the upper portion of the outer surface of the cylinder 1 and is sealably attached at the open ends thereof to the cylinder outer surface by two steel bands 10'.The size of each of the orifices 12 and 12' formed in the cylindrical side wall of the cylinder 1 is greater than that of each of the orifices 6 formed .in the piston 2. The total opening areas of the orifices 12 are greater than the total opening areas of the orifices 6. Likewise are the total opening areas of the orifices 12'.

In operation, as the piston 2 is moved downwardly from the position illustrated in Fig. 2, the oil pressure within the second chamber 22 below the piston 2 rises, thereby forcing such pressurized liquid through the orifice 12 to increase the volume of the chamber 11 to expand the intermediate portion of the elastomeric member 9.

The elasticity of the elastomeric members imparts a spring effect to the shock absorber according to the present invention.

Referring to Fig. 3, the line A shows a damping constant vs. frequency characteristic provided by the De Carbon type shock absorber illustrated in Fig. 1; the curve B shows that provided by the shock absorber of the present invention illustrated in Fig. 2. In the De Carbon type shock absorber, the damping constant increases substantially proportionately with vibration frequency. In the shock absorber according to the present invention, as the vibration frequency increases, although the resistance to flow through the piston orifices 6 increases to increase the damping oil pressure in the cylinder 1, such increased vibration is partially absorbed by the elasticity of the elastomeric members 9 and 9', so that the damping constant decreases, as shown by line B, after the frequency exceeds a peak frequency.This increase in damping constant only until this peak frequency is reached occurs because of the delay in response time of the fluid pressure increase in front of the moving piston 2 caused by the restricted flow through the orifices 6. This response delay is caused by the oil entering the third and fourth chambers 11 and 11' under vibration pressure pulses, and such pressure pulses being absorbed by the elastomeric members 9 and 9' and the elastic expansion of the third and fourth chambers.

As the vibration frequency of the piston approaches this response delay period, the sensitivity of the piston 2 to vibration decreases, causing the reverse effect in response to further frequency increase, to lower the damping constant at higher frequencies. It follows that this peak frequency can be regulated by altering the various factors affecting peak frequency-oil viscosity, size of the restrictive orifices 6, size of the cylinder and secondary chambers, elasticity of the members 9 and 9', etc.

When the shock absorber according to the present invention is to be used in an automotive vehicle suspension system, the peak frequency at which the damping constant is maximum is the unsprung resonant frequency which is determined by the vertical direction spring constant of the tire and the total weight of the tire and the associated road wheel. Since the damping force does not increase with frequency in the high frequency range, transmission of vibration from the road wheel to the vehicle body can be effectively dampened.

Furthermore, the shock absorber according to the present invention is provided with the spring effect, so that it can be used in an engine suspension system. In this case, the peak frequency at which the damping constant is maximum should be the critical frequency (about 1OHz) above which the engine begins to vibrate.

Referring to Fig. 4, a second embodiment is shown which is substantially similar to the first embodiment illustrated in Fig. 2, but is provided with an outer rigid steel collar 13. The collar 13 is attached at one end to the lower end of the outer surface of the cylinder 1 and surrounds the outer surfaces of the elastomeric members 9 and 9' with a clearance S therebetween. The collar 1 3 limits the expansion of the elastomeric members to thereby alter the elasticity characteristics thereof and the expansion characteristics of the third and fourth chambers 11 and 1 1'. Thus, a desired damping constant and spring constant can be obtained.

Fig. 5 is a graph showing spring constant vs.

piston position (in the contractable direction) characteristics, and Fig. 6 is a graph showing damping constant vs. piston position (in the contractable direction) characteristics with the frequency and amplitude being fixed. In each graph, the characteristic line of the Fig. 2 shock absorber is shown as the dotted line C, and the solid lines D and E designate the Fig. 4 shock absorber characteristics after the elastomeric member 9 contacts the collar 13. The solid line D illustrates the case when the clearance S is relatively small and the solid line E illustrates the case where the clearance S is larger. Thus, it is obvious from Figs. 5 and 6 that as the clearance S decreases, the damping constant and spring constant increase in response to piston position, thereby increasing the degree of dependency upon piston position.

In a third embodiment shown in Fig. 7, a variation in volume corresponding to the stroke of the piston rod 3 is absorbed by the expansion of the lower elastomeric member 9, so that the damping characteristic in the piston downstroke direction is substantially the same as that of the shock absorber shown in Fig. 2, and the damping characteristic in the piston upstroke direction is as in a conventional shock absorber.

Fig. 8 shows a fourth embodiment including a collar 13 attached to the shock absorber shown in Fig. 3 to accomplish the spring constant dependency on the clearance S.

Claims

1. A shock absorber comprising: a) a cylinder closed at both ends; b) a quantity of liquid contained within said cylinder; c) a piston axially movable in said cylinder to divide same into first and second chambers and immersed in said liquid; d) a piston rod coaxial with said cylinder and connected to said piston, said piston rod extending axially outwardly of said cylinder in a liquid tight manner through one of said ends of said cylinder; said piston having at least one orifice formed therein which permits the flow of liquid therethrough during axial reciprocation of said piston within said cylinder; and e) an elastomeric member defining a third chamber communicating with said second chamber, said liquid filling said third chamber.

2. A shock absorber as claimed in claim 1, further comprising a second elastomeric member defining a fourth chamber communicating with said first chamber, said liquid filling said fourth chamber.

3. A shock absorber as claimed in claim 1, further comprising an outer collar for limiting the expansion movement of said first elastomeric member.

4. A shock absorber as claimed in claim 2, further comprising an outer collar for limiting the expansion movement of said first and second elastomeric members.

5. A shock absorber as claimed in claim 1, 2, 3 or 4, wherein said elastomeric member is a tube seal ably attached at the open ends thereof to the outer surface of said cylinder.

6. A shock absorber as claimed in claim 5, including a plurality of steel bands wrapping said respective open ends of each said elastomeric member to sealably attach same to the outer surface of said cylinder.

7. A shock absorber as claimed in claim 1 or 3, including a fluid flow orifice providing the communication between said second and third chambers.

8. A shock absorber as claimed in claim 2 or 4, including fluid flow orifices providing the communication between said second and third chambers and said first and fourth chambers, respectively.

9. A shock absorber as claimed in claim 1 or 3, wherein the outer surface of said cylinder and said elastomeric member cooperates to define said third chamber.

10. A shock absorber as claimed in claim 2 or 4, wherein the outer surface of said cylinder and said elastomeric members cooperate to define said third and fourth chambers, respectively.

11. A shock absorber constructed and arranged as substantially described and illustrated in connection with Fig. 2 or Fig. 4 or Fig. 7 or Fig. 8 of the accompanying drawings.