GB2225084A

GB2225084A - Variable-damping-characteristics shock absorber

Info

Publication number: GB2225084A
Application number: GB8921199A
Authority: GB
Inventors: Fumiyuki Yamaoka; Issei Kanari
Original assignee: Atsugi Unisia Corp
Current assignee: Hitachi Unisia Automotive Ltd
Priority date: 1988-09-19
Filing date: 1989-09-19
Publication date: 1990-05-23
Anticipated expiration: 2009-09-19
Also published as: DE3931240A1; AU614873B2; GB8921199D0; DE3931240C2; AU4155889A; GB2225084B

Description

1 2225084 VARIABLE-DAMPING-CHARACTERIS'IICS SHOCK ABSORBER i The present

invention relates to a generally to a variable damping characteristics shock absorber, suitable for use in an automotive suspension system.

Japanese Utility Model First (unexamined) Publication No.

61-164836 discloses a variable damping characteristics shock absorber of the type for which the present invention is directed.

In the disclosed construction, an orifice is formed through a piston for generating damping force in response to piston stroke according to relative displacement of a vehicular body and a suspension member which rotatable supports a road wheel. End of the flow restriction orifice is closed by a disc valve which opens and closes the end of the orifice. A fluid Dassage is formed through a piston rod in parallel relationship with the flow restriction orifice. A f low control means is associated with the fluid passage for adjusting fluid flow path in the fluid passage for adjusting damping characteristics.

In the shown construction, higher or harder suspension characteristics or greater damping force may be generated by greater magnitude of flow restriction provided by the flow control means. By greater magnitude flow restriction, smaller amount of working fluid flows through the fluid passage for generating greater fluid Dressure difference at both sides of the piston and thus generating greater damping force. On the other hand, lower or softer damping characteristics is obtained by smaller magnitude of flow restriction for allowing greater amount of working fluid to flow throucrh the fluid passacre. Bv areater amount of fluid flow 0 -5. C through the fluid passage may reduces fluid pressure difference at C> both sides of the piston for generating smaller magnitude of the 2 - damping force.

In such construction of shock absorbers, it has been observed that, at relatively low piston stroke speed range, the flow control means of the fluid passage is principally effective for generating damping force. On the other hand, at relatively high piston stroke range, the orifice is principally effective for generating damping force. Since the orifice and flow control means has different variation characteristics of magnitude of fluid flow restriction, smooth variation of damping characteristics through relatively wide piston stroke speed range.

Furthermore, neither of the orifice nor flow control means may provide linear characteristics in varying the damping characteristics, the prior proposed shock absorber is still not satisfactory in view of achievement of both of vehicular driving stability and riding comfort at any vehicular driving condition.

Therefore, it is an object of the present invention to provide a variable damping characteristics shock absorber which varies damping characteristics or damping force in essentially or close to linear characteristics.

In order to accomplish aforementioned and other objects, a shock absorber, according to the present invention, is provided a piston stroke speed dependent linear variation characteristics of damping force. The shock absorber includes a variable orifices in tandem fashion for achieving linear variation characteristics of ion of the piston stroke. One of damping force according to variat the variable orifices is provided a variation characteristics of flow restriction for greater variation rate of the damping force in low piston stroke speed range, and the other is provided a variation characteristics of flow restriction for greater variation rate of the daMDing force in the intermediate and high piston stroke speed ange. The variable orif;ce mav be provided in a piston assembly or in the alternative in a bottom 'Litting, in case of a double-action type shock absorber.

According to one aspect of the invention, a variable damping force shock absorber for damping relative displacement 0 1 between f irst and second movable members, variable of damping characteristics according to piston stroke speed comprises: a hollow cylinder defining therein first and second fluid chambers; a first damping force generating means responsive to piston stroke for generating first damping force variable according to a first variation characteristics in relation to variation of the piston stroke speed; a second damping force generating means responsive to the piston stroke for generating second damping force variation according to a second variation characteristics in relation to variation of the piston stroke speed; and damping force generating means the ffrst l=d see-ond being cooperative to each other in one direction of piston stroke for generating active damping force for damping relative movement of the fl,st and second movable members; and the f.rst and second variation characteristics being set for compensating to each other for providing substantially linear variation characteristics of the active damping force in accordance with variation of t)isLon stroke speed.

In the practical construction, the first damping force generatmg means may comprise:

a primary path deffined in a valve body separating the first and second fluid chambers, for fluid communication between the first and second fluid chambers:

a first window opening defined on the valve body and communicated with the primary path, the first window opening being surrounded by a first land having a first. surface; and a first resilient valve means resiliently biased toward the surface for normalIv eslkablisIina sealing contact with the first surface and responsive to fluid flow in a first flow direction generated by the piston stroke in the one stroke direction for forming: a first flow restrictive path fo?- fluid communication from the f.-st window opening and one of the first and second fluid chambe7s for generating the firs' damping, Alse, the second da,-,nina force generating m.eans may C comprise:

a subsidiary path permitting fluid communication between the first and second fluid chambers; a second window opening formed on the valve body in fluid communication with the subsidiary path, the second window opening being defined by a second land with a second surface, and a second resilient valve means resiliently biased toward the second surface for normally establishing sealing contact with the second surface and responsive to fluid flow in a first flow direction generated by the piston stroke in the one stroke direction for forming a second flow restrictive path for fluid communication between the first and second window openings for generating the second damping force. The first and second damping force generating means may be oriented in tandem fashion with respect to the fluid flow so that the first and second damping force generating means are cooperative for generating the active damping force. Practically, the first damping force generating means is provided variation characteristics for providing greater damping force variation rate at low piston speed range, and the second damping force generating means is provided variation characteristics for providing greater damping force variation rate at intermediate and high piston stroke speed range.

In the preferred construction, the shock absorber may further comprise a third damping force generating means which is externally actuated for varying flow restriction magnitude for =1 - adjusting damping characteristics.

The first and second damping force generating means may be provided in a piston assembly.

Preferably, the shock absorber comprises a double action-type shock absorber having inner and outer cylinders, and the first and second damping force generating means are provided in a ing interposed between the first and second bottom fitting separat fluid chambers.

The first and second surfaces are oriented on the same plane and the first and second resilient valve means- may comprise a common valve member mating with both of the first and second surfaces. In such case, t.hlf,. shock absorber may further comprise an auxiliary resilient member exerting resilient force for the common valve member at the orientation corresponding to the second surface for resiliently restricting deformation magnitude, so that the first damping force generating means is provided variation characteristics for providing greater damping force variation rate at low piston speed range, and the second damping force generating means is provided variation characteristics for providing greater damping force variation rate at intermediate and high piston stroke speed range.

The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, sh(-,-,ild not be taken to limit the invention to the specific embodimen-. -:jt are for explanation and understanding only.

In the drawings:

Fig. 1 is a sectional view of the major part of the first )o embodiment of a variable damping characteristics shock absorber according to the present invention; Fig. 2 is a plan view of a piston employed in the first embodiment of the shock absorber of Fig. 1; Fig. 3 is a bottom view of the piston employed in the first embodiment of the shock absorber of Fig. L Fig. 4 is a sectional view showing construction of a bottom valve employed in the first embodiment of the shock absorber of Fig. L Fig. 5 is a graph showing relationship between a Pressure difference of inner and outer grooves and a piston stroke speed, during piston rebounding stroke:

Fig. 6 is a graph sho.,,;friL7 relations,D between a pressure diff-fe-rence off the outer groove and a lower fluid chamber and the ke speed:

01Ston stror, Fig. 7 is a graph sio,....tncr relationship between a damping force cre-e-at;ng in the reboundin:- strok-e and the piston cl; 1 i 1 - 3 5; 6 - stroke speed; Fig. 8 is a graph showing relationship between a damping force generating in the piston bounding stroke and the piston stroke speed; Fig. 9 is a sectional view of the major part of the second embodiment of a variable damping characteristics shock absorber according to the present invention; Fig. 10 is a plan view of a piston employed in the second embodiment of the shock absorber of Fig. 9; Fig. 11 is a bottom view of the piston employed in the second embodiment of the shock absorber of Fig. 9; and Fig. 12 i s a sectional view of the major part of the third embodiment of a variable damping characteristics shock absorber according to the present invention.

Referring now to the drawings, particularly to Figs. 1 through 3, the first embodiment of a shock absorber is formed as a double-action type shock absorber including an inner and an outer cylinders coaxially arranged to each other. In Fig. 1, only inner cylinder 1 is disclosed. The double-action type shock absorber per se is generally well known in the art and thus does not need to specifically disclose all construction thereof. Therefore, in the drawings, the outer cylinder is neglected for simplification of illustration on the drawings and associated disclosure.

A piston assembly 2 is slidingly or thrustingly disposed within the interior space of the inner cylinder 1 to define upper and lower fluid chambers A and B which are filled with a working fluid. The piston 2 is fixed to the lower end of a piston rod 3 with a retainer 4, a washer 5, an upper disc valve 6, a piston body 7, a f irst lower disk valve 8, a second lower disc valve 9, a washer 10, a spring seat member 11 and a spring 12. The components set forth above forms a piston assembly and retained at the lower end portion of the piston rod 3 by means of a fastening nut 13.

The piston body 7 is formed with an axially extending 3.5 fluid passages 7a and 7e. As can be seen from Fig. 1, the fluid a position closer to the outer periphery passage 7a is oriented all 4 1 1 of the piston body than that of the fluid passage 7e. Therefore, in the following discussion, the fluid passage 7a will be referred to as "outer axial passage" and the fluid passage 74 will be referred to as "inner axial passage". As seen from Figs. 2 and 3, in the shown embodiment, three outer axial passages 7a are formed with circumferential intervals. Each of the outer axial passages 7a is f ormed into an essentially are-shape, configuration having a predetermined circumferential width, ane has upper end opening to a groove 7al defined by continuous land 7b having a valve seat surface 7bl. The upper disc valve 6 has circumferential edge portions seating on the seat surface 7bl of the land 7b. As can be seen from Fig. 1, the upper disc valve 6 at a position completely closing the groove 7al seats on entire seat surface 7W. On the other hand, the lower end of the outer axial passage 7a is directly exposed to the lower fluid chamber B, so that the working fluid in the lower fluid chamber is free to flow therewithin.

On the other hand, the inner axial passages 7e respectively have circular cross sections. In the shown embodiment, six inner axial passages 7e are circumferentially arranged with equal intervals, as shown in Figs. 2 and 3. The upper end of each of inner axial passages 7e is directly exposed to the upper fluid chamber A via a clearance 7el defined between the upper face of the piston body 7 and the upper disc valve 6. The lower end of the inner axial passage 7e is open to an inner annular groove 7c which is defined between a central boss section 7g and an annular land 7f- The annular land 7f further defines an outer annular groove 7d with an annular land 7h as particularly shown in Figs. 1 and 3. The annular lands 7f and 7h respectively define valve seat surfaces 7P and 7W for seating thereon the first lower disc valve 8. Similarly to the upper disc valve 6, the first lower valve 8 normalIv seats on the seat surfaces 7P and 7W for sealing the inner and outer grooves 7c and 7d and is subject to the fluid pressure in the upper fluid chamber A introduced into the inner axial passages 7e via the clearance 7el.

The piston rod 3 is formed with an axially extending center 0Dening 3b. The center o ening 3b is communicated with 0 p the upper fluid chamber A via radially extending openings 3c. The radially extending openings 3c will be hereafter referred to as "upper ports". On the other hand, the center opening 3b is in fluid communication with the outer annular groove via radially extending opening 3d, an annular groove 3a and obliquely extending openings 7j which extends in oblique with respect to the axis of the piston rod 3. The radially extending openings will be hereafter referred to as "lower ports".

A rotary valve member 15 is rotatably disposed within the axially extending opening 3b for rotation thereabout. The rotary valve member 15 is supported or maintained by upper and lower thrust bushings 16 and 17. The rotary valve member 15 is fixed to the lower end of an actuator rod 18. The actuator rod 18 is connected to a rotary actuator (not shown) for rotatingly driving the actuator rod 18 and thus drives the rotary valve member 15.

The rotary actuator has been disclosed in U. S. Patent No.

4,776,437, issued on October 11, 1988 and assigned to the common assignee to the present invention, for example. The disclosure of

U. S. Patent 4,776,437 is herein incorporated by reference for the sake of disclosure. The rotary valve member 15 defines a lower end opened bore communicated with the center opening 3b of the piston rod 3. The rotary value members have a plurality of radially extending openings at an axial position corresponding to the position of the upper ports 3c. The radially extending openings of the rotary valve member 15 having different diameters to adjacent ones so as to provide different fluid flow path areas at different angular positions. In the shown embodiment, the rotary valve member 15 is formed with smaller diameter openings 15b and a greater diameter openings 15c with 90 0 of angular intervals. Therefore, according to angular position of the rotary valve member 15, one of the openings 15b and 15c are selectively aligned with the Upper ports 3c for providing different path area for fluid communication between the interior space of the rotary valve member 15 and the upper fluid chamber A. As can be seen from Fig. 1, the interior Space of the rotarv valve member 15 is in fluid communication with the center opening 3b of the piston rod 3 for defining a chamber C extending in axial direction. Therefore, the chamber defined by the interior space of the rotary valve member 15 and the center opening 3b will be hereafter referred to as "axial chamber". The rotary valve member 15 is also formed with a plurality of radially extending openings at an axial position corresponding to the lower ports 3d.

Similarly to the foregoing openings 15b and 15c, the shown embodiment is formed with openings 15d and 15e having different diameters. As can be seen from Fig. 1, the opening 15d is adapted to be aligned with the lower ports 3d at the angular position of the rotary valve member 15 where the openings 15b are aligned with the upper ports 3c, and have smaller diameter than that of the opening 15e.

The nut 13 is engaged with the threaded lower end of the piston rod, The nut def ines a lower end opened bore 13a through which the interior space of the central opening 3b of the piston rod 3 communicates with the lower fluid chamber B. A check valve assembly 14 including an annular valve seat 14a fixed to the lower end of the nut 13, a valve disc 14b and a bias spring 14c, is disposed within the bore 13a. The valve disc 14b is normally biased toward the valve seat- 14a by means of the bias spring 14c in order to permit fluid flow directed from the lower fluid chamber B to the upper fluid chamber A via the center opening 3b and to block fluid flow in the opposite direction. The spring seat 11 is associated with the nut 13 for movement therealong. The spring seat 11 has a cylindrical section 11a and an outwardly and essentially horizontal flange-like section 11b on which one end of the spring 12 is seated. The other end of the spring 12 is seated on the stepped section of the nut. Therefore, the spring seat 11 is normally biased upwardly.

The second lower disc valve 9 has the external diameter substantially corresponding to the outer diameter of the annular form seat surface 7P. The flange-like section 11b of the spring seat 11. Therefore, the spring seat 11 is associated with the second lower disc valve 9 for exerting biasing force of the spring 12 to the latter and thus exerting the spring load onto the first disc valve 8.

t As shown in Fig. 4, a bottom valve assembly 20 is fitted to the lower end of the inner cylinder 1 for controlling fluid communication between the lower fluid chamber B and an annular reservoir chamber D defined between the inner cylinder 1 and an outer cylinder 19. The bottom valve assembly 20 includes a bottom fitting 201 rigidly fitted to the lower end of the inner cylinder 1.

The bottom fitting 20' defines axial openings 20a and 201b for fluid communication between the lower fluid chamber B and a chamber E defined between the bottom fitting 201 and a bottom closure 25.

The upper end of the axial opening 20a opens to an outer annular groove 21a defined between lands 21b and 21c, which outer annular groove is closed by an upper disc valve 21. Adjacent the upper disc valve 21 is provided a stopper washer 24 which restricts magnitude of deformation of the disc valve for defining maximum path area to be formed between the land 21e and the outer circumferential edge portion of the upper disc valve 21. The lower end of the axial opening 20a is exposed to the chamber E. On the other hand, the upper end of the axial opening 20b opens to an inner annular groove 21d which is in direct fluid communication with the lower fluid chamber B via a through opening 21e formed through the disc valve 21. The lower end of the axial opening 20b opens to an annular groove 22a defined between land 20c and a center bore 20f. A first lower disc valve 22 seats on the land 20e for normally closing the annular groove 22a. A second lower disc valve 23 seating on an annular land 20d is placed in spaced apart relationship with the first lower disc valve 22 via a spacer washer 23b. The land 20d is formed with radially extending groove 20e serving as flow restricting orifice.

The chamber E defined in the bottom fitting 20' is communicated with the reservoir chamber D via an radial path 20g defined through the circumferentially extending cylindrical portion of the bottom fitting.

The operation of the aforementioned first embodiment of the shock absorber will be discussed herebelow with respect to bounding and rebounding mode operations.

During piston rebounding stroke to cause compression of 1 the volume of the upper fluid chamber A, the pressure of the working fluid in the upper fluid chamber is naturally increased to be higher than that in the lower fluid chamber B. As a result, the working fluid flow from the upper fluid chamber A to the lower fluid chamber B is generated. Part of the working fluid is then flows into the inner axial passage 7e via the clearance 7el. Then, the working fluid having pressure higher than that in the lower fluid chamber B becomes active on the portion of the first lower disc valve 8 opposing to the inner annular groove 7c to cause deformation of the first and second disc valves 8 and 9 to flow into the outer annular chamber 7d and subsequently into the lower fluid chamber B through an annular clearance defined between the circumferential edge portion of the first disc valve 8 and the seat surface 7W of the lland 7h.

On the other hand, the other part of the working fluid flows into the axial chamber C via the upper ports 3c and the openings 15c or 15d which are aligned with the upper ports. At this time, since the fluid pressure in the axial chamber C is held higher than that in the lower fluid chamber B, the valve disc 14b is tightly seated on the valve seat 14a for blocking fluid flow therethrough. Therefore, the fluid flows into the outer annular groove 7d via the opening 15d or 15e, the lower ports 3d, the annular groove 3a and the oblique passage 7j and subsequently flows into the lower fluid chamber B defined between the circumferential portion of the first disc valve 8 and the seat surface 7W of the land 7h.

At this time, since magnitude of deformation of the first lower disc valve 8 with respect to the seat surface 7V is restricted bv the resilient force of the second lower disc valve 9 as loaded the spring force of the spring 12, the deformation magnitude of the first lower disc valve 8 at the portion corresponding to the seat surface 7V is limited to provide greater flow restriction. Such flow restriction may be substantial while the pressure difference between the upper and lower fluid chambers A and B is relativelv small- Since the pressure difference between the upper and lower fluid chambers is essentially proportional to the piston stroke, the flow restriction may be substantial at low piston stroke range. On the other hand by increasing of the piston stroke speed, the pressure difference becomes greater to overcome the spring force of the spring 12 to cause shifting of the spring seat 11 away from the second lower disc valve 9. As a result, only resilient forces of the first and second lower disc valves 8 and 9 become active for restricting the path area for allowing greater deformation to provide wider path area. If the pressure difference becomes substantial, orifice effect of the tandem orifices become smaller in generating damping force.

Therefore, in the shown construction, the orifices are defined between the first disc valve 8 and the seat surface 7V of the land 7f and between the first disc valve 8 and the seat surface 7h' of the land 7h in tandem fashion. At relatively low piston speed range, these orifices are principally effective for generating damping force for relatively low pressure difference between the upper and lower fluid chambers A and B and thus for small magnitude of deformation of the first disc valve 8. On the other hand, at intermediate and higher piston speed range, greater pressure difference between the upper and lower fluid chambers A and B is generated for causing greater deformation magnitude of the first disc valve 8, therefore throttling effect of the orifices becomes smaller. Therefore, at this speed range, the orifice effect of the openings 15b or 15c and 15d or 15e is principally active for generating damping force.

Fig. 5 shows pressure difference between the inner and outer grooves 7c and 7d in relation to piston stroke magnitude. It should be appreciated. in the characteristics shown in Figs. 5 through 8, the line a shows characteristics obtained at the angular position of the rotary valve member 15 where the openings 15c and 15e are aligned with the upper and lower ports 3c and 3d, the line b shows characteristics obtained at the angular position of the rotary valve member 15 where the openings 15b and 15d are aligned with the wDr)er and lower ports, and the line c shows characteristics obtained at the angular position of the rotary valve member where the upper and the lower ports are fully blocked. As 1 13 will be appreciated, this pressure dif f erence exhibits orif ice effect at the orifice defined between- the first lower disc valve 8 and the seat surface 7P of the land 7f. Therefore, because of substantial restriction of deformation by the spring force exerted through the second lower disc valve, variation rate of the pressure difference is held small in the low piston stroke range. On the other hand, variation rate of pressure difference becomes greater according to increasing of the piston stroke speed. In addition, as can be observed from Fig. 5, the variation characteristics of the pressure difference obtained at the orifice between the inner and outer grooves 7c and 7d is close to linear characteristics. This tendencv is increased as increasing the piston stroke speed.

Fig. 6 shows variatie--)n of pressure difference between the outer groove 7d and the lower fluid chamber B. As can be seen from Fig. 6, at any of the angular position of the rotary valve member 15, greater variation rate of the pressure difference is cause at low piston stroke speed range. The variation rate of the pressure difference is reduced according to increasing of the piston stroke speed. Furthermore, the characteristics of variation of the variation rate of the pressure difference at the intermediate and high piston stroke speed range is substantially linear.

Since orifices defined between the first lower disc valve 8 and the seat surface 7P and between the first lower disc valve 8 and the seat surface 7W are arranged in tandem fashion, the damping characteristics to be generated becomes combination of the characteristics of Figs. 5 and 6. Therefore, substantialIv linear damping characteristics in relation to the piston stroke speed can be obtained at any piston stroke speed range.

In the piston bounding stroke, the volume of the lower fluid chamber B is compressed to cause higher fluid pressure.

Therefore, fluid flow from the lower fluid chamber B to the upper fluid chamber A is generated.

Part of the working fluid flows into the outer axial passage 7a. for exerting fluid pressure to the corresponding portion of the upper disc valve 6 to cause deformation of the latter. By ar orifice is formed between the upper disc deformation, an annu.

1 valve 6 and the seat surface 7b' of the land 7b for permitting fluid flow therethrough. The other part of the working fluid flows into the axial chamber C by shifting the valve disc 14b away from the valve seat 14a. Then, the working fluid in the axial chamber C is flows through the openings 15b or 15c and the upper port 3c into the upper fluid chamber A.

At the same time, the increased fluid pressure in the lower fluid chamber B acts on the first lower disc valve 22 for causing deformation to open an annular orifice between the mating surface of the disc valve and the seat surface 20c. Therefore, the working fluid pressure acts on the second lower disc valve 23.

While the piston stroke speed is relatively low, the pressure differencebetween both sides of the second lower disc valve 23 is held small so as not to cause deformation of the disc valve. As a result, the second lower disc valve stays on the seat surface of the land 20d. Therefore, fluid flow is then permitted only through the radially extending groove 20e. Since radially extending groove provides flow restriction, damping force is generated. On the other hand, at the intermediate and high piston stroke speed range, the pressure difference between both sides of the second lower disc valve 23 becomes substantial to cause deformation of the disc valve for forming an annular orifice to permit fluid flow into the chamber E.

Combination of orifice effect in the annular orifice formed between the upper disc valve 7bI of the land 7b, the orifice effect in the radially extending groove 22e and the orifice effect in the annular orifice formed between the second lower disc valve 23 and the seat surface of the land 20d, linear characteristics in iCS variation of the daMDing characteriSt in the piston bounding in relation to the piston stroke speed can be obtained as shown in Fig. 8.

Fig. 9 shows the second embodiment of a variable damping force shock absorber according to the present invention.

The shown embodiment is differentiated from the foregoing first embodiment in the construction for establishing fluid communication between the axial chamber C and the annular groove 7d. Also, in k 1 the shown embodiment, the upper port and the associated radially extending opening are omitted. Therefore, the components and constructions common to the foregoing first embodiment will be represented by the same reference numerals to the former embodiment and will not be discussed in detail in order to avoid redundant discussion for clarity of the disclosure.

In the shown embodiment, the oblique passage 7j in the former embodiment is replaced with radially extending grooves 7m and 7n. The radially extending grooves 7m and 7n are constructed and arranged for establishing fluid communication with the port 3c and 3d formed through the piston rod 3. On the other hand, the radially extending orifice 7m is in fluid communication with the inner annular groove 7c, and the radially extending orifice 7n is in fluid communication with the outer annular groove 7d.

With the shown construction, the high pressure fluid in the upper fluid chamber A flows into the inner axial passage 7e via the clearance 7e' and subsequently into the inner annular groove 7c during piston rebounding stroke. The working fluid in the annular groove 7c flows into the axial chamber C via the radially extending groove 7m and the port 3c. At this time, the fluid pressure in the axial chamber C is higher than that in the lower fluid chamber B. Therefore, the valve disc 14b is held at the position tightly seated on the valve seat 14a. Therefore, the working fluid in the axial chamber C flows into the radially extending groove 7n via the radially extending opening 15c or 15d and the port 3d. Theref ore, the fluid pressure is introduced into the outer annular chamber 7d.

With the action set forth above, the fluid pressure is acted on both in the inner and outer grooves 7c and 7d for establishing linear variation of the damping characteristics as that achieved by the former embodiment.

On the other hand, in the piston bounding stroke, the part of the working fluid flows through the outer axial passage 7a and the orifice defined between the upper disc valve 6 and the seat surface 7b' of the land 7b. Another part of the working fluid flows into the axial chamber C by shifting the disc valve 14b away from the valve seat 14a, The fluid in the axial chamber C flows into the radially extending groove 7m via the radially extending opening 15c or 15d and the port 3c and subsequently into the inner axial passage 7e via the inner annular groove 7c. Therefore, linear variation of the damping characteristics can be obtained by the operation of the upper disc valve 6 and the bottom valve assembly which is identical construction to that in the former embodiment.

Fig. 12 shows the third and perhaps the best mode embodiment of a variable damping force shock absorber according to the present invention. The shown embodiment has common components and constructions to the foregoing first embodiment.

The common components will be represented by the same reference numerals to the first embodiment and will not be discussed in detail The shown embodiment is differentiated from the first and second embodiments in the construction for establishing fluid communication between the axial, chamber C and the outer annular groove 7d. In the shown embodiment, the radially extending groove 7p is formed on the lower surface of the piston body 7. The radially extending groove 7p establishes fluid communication between the outer annular groove 7d and an axially extending groove 7r which is in fluid communication with an upper end opened annular groove 7s. The annular groove 7s is in fluid -;on with the axial chamber C.

communicall On the other hand, the piston rod 3 is formed of upper and lower radially extending ports 3b at axially offset positions to each other. Both of upper and lower ports 3b are in fluid communication with the upper fluid chamber A. The ports 3b are, in turn, in fluid communication with the axial chamber via radially extending openings 15a. 15b and 15c, 15d, in which the opening 15a has different diameter to the opening 15b and the opening 15c has different diameter to the opening 15d. In this respect, though Fig.

12, all of the openings 15a, 15b and 15c, 15d are aligned with the ports 3b. these openings may be aligned with or shifted away from the port 3b for varying flow restriction provided therefore.

In the shown construction, the working fluid flows into the outer annular groove 17d from the upper fluid chamber via the k 1 ports 3b and the radial openings 15a or 15b and 15c or 15d during piston rebounding stroke. This fluid-pressure thus introduced into the outer annular groove 7d cooperates with the fluid pressure introduced into the inner annular groove 7c via the inner axial passage 7e for providing linear variation characteristics of the damping characteristics as that provided in the first embodiment.

Since the fluid action during the piston bounding stroke is identical to that in the foregoing first embodiment, essentially the same linear variation characteristics can be obtained.

In addition, in the shown embodiment, since the fluid communication between the axial chamber and the upper fluid chamber is established with axially offset two radial openings, each opening can be smaller than that in the former embodiments.

Consequently, the rotary valve member can be constructed smaller for reducing required force for rotatingly driving and positioning the same at desired angular pos ition. Also, since the radially extending groove 7p of the shown embodiment is axially elongated groove, fluid communication can be assured even when the piston body and the piston rod tolerate.

While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding of the invention, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention set out in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A variable damping force shock absorber for damping relative displacement between first and second movable members, variable of damping characteristics according to piston stroke speed comprising:

chambers; z a hollow cylinder defining therein first and second fluid a first damping force generating means responsive to piston stroke for generating first damping force variable according to a first variation characteristics in relation to variation of the piston stroke speed; a second damping force generating means responsive to the piston stroke for generating second damping force variation according to a second variation characteristics in relation to variation of the piston stroke speed; and said first and second damping force generating means being cooperative to each other in one direction of piston Stroke for generating active damping force for damping relative movement of said first and second movable members; and said first and second variation characteristics being set for compensating to each other for providing substantially linear variation characteristics of said active damping force in accordance with variation of piston stroke speed.

2. A shock absorber as set forth in claim 1, wherein said first damping force generating means comprises a primary path defined in a valve body separating said first and second fluid chambers, for fluid communication between said first and second fluid chambers; a first window opening defined on said valve body and communicated with said primary path, said first window opening being surrounded by a first land having a first surface; and a first resilient valve means resiliently biased toward said surface for normally establishing sealing contact with said first 3 5 surface and responsive to fluid flow in a first flow direction generated by the pistor stroke in said one stroke direction for f 1 forming a first flow restrictive path for fluid communication from said first window opening and one of said first and second fluid chambers for generating said first damping force.

3.

A shock absorber as set forth in claim 2, wherein said second damping force generating means comprises:

a subsidiary path permitting fluid communication between said first and second fluid chambers; a second window opening formed on said valve body in fluid communication with said subsidiary path, said second window opening being defined by a second land with a second surface, and a second resilient valve means resiliently biased toward said second surface for normally establishing sealing contact with said second surface and responsive to fluid flow in a first flow direction generated by the piston stroke in said one stroke direction for forming a second flow restrictive path for fluid communication between said first and second window openings for generating said second damping force.

4.

A shock absorber as set forth in claim 1, wherein said first and second damping force generating means are oriented in tandem fashion with respect to said fluid flow so that said first and second damping force generating means are cooperative for generating said active damping force.

5. A shock absorber as set forth in claim 4, wherein said f irst damping f orce generating means is provided variation characteristics for providing greater damping force variation rate at low piston speed range, and said second damping force generating means is provided variation characteristics for providing greater damping force variation rate at intermediate and high piston stroke sDeed ranoe.

6.

A shock absorber as set forth in claim 1, which further comprises a third damping f orce generating means which is externally actuated ffor varying f low restriction magnitude for adjusting damping characteristics.

7. A shock absorber as set forth in claim 1, wherein said first and second damping force generating means are provided in a piston assembly.

8. A shock absorber as set forth in claim 1, which comprises a double action-type shock absorber having inner and outer cylinders, and said first and second damping force generating means are provided in a bottom fitting separating interposed between said first and second fluid chambers.

9. A shock absorber as set forth in claim 3, wherein said first and second surfaces are oriented on the same plane and said first and second resilient valve means comprises a common valve member mating with both of said first and second surfaces.

10. A shock absorber as set forth in claim 9, which further comprises an auxiliary resilient member exerting resilient force for 20 said common valve member at the orientation corresponding to said second surface for resiliently restricting deformation magnitude, so that said first damping force generating means is provided variation characteristics for providing greater damping force variation rate at low piston speed range, and said second damping force generating 25 means is provided variation characteristics for providing greater damping force variation rate at intermediate and high piston stroke speed range.

11, A shock absorber as claimed in any two or more of claims 1 to 10.

12. A variable-damping-force shock-absorber sub stantiallY as hereinbefore described with reference to, and as shown in, Figs. 1 to 8 of the accompanying drawings.

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13. A shock-absorber as claimed in claim 12, modified substantially as hereinbefore described with reference to, and as shown in, Figs. 9 to 11 or Fig. 12 of the accompanying drawings.