GB2070730A

GB2070730A - Shock absorber piston valves

Info

Publication number: GB2070730A
Application number: GB8105915A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1980-02-27
Filing date: 1981-02-25
Publication date: 1981-09-09
Also published as: JPS56120841A; FR2476782A1; DE3107517A1

Abstract

A passage through a shock absorber piston is provided with a pressure responsive valve member which is movable to restrict flow through the passage. The valve member may act in both directions of flow. <IMAGE>

Description

SPECIFICATION Shock absorber The present invention relates generally to a hydraulic shock absorber which is applicable to an automotive vehicle suspension, for example. More specifically, the invention relates to a hydraulic shock absorber of which is variable the shock absorbing effect corresponding to piston stroke responsive to the shock applied thereto as well as application speed thereof.

Generally, the hydraulic shock absorber comprises a cylinder filled with a working fluid and a piston disposed within the cylinder so that it is moved along the cylinder in response to a shock applied to the shock absorber. The piston includes a shock absorbing means for absorbing the shock during motion of the piston by limiting flow of the working fluid therethrough. In the conventional hydraulic shock absorbers, the absorbing force produced in the working fluid by the shock absorbing means depends on the motion speed of the piston in the cylinder.

Namely, even if the piston stroke responsive to the shock is substantially small and therefore the piston stroke is substantially small, the absorbing force is grown larger than that of required, when the speed of the piston is substantially high. On the other hand, if the motion speed of the piston is rather low but the piston stroke responsive to the shock is substantially large, the absorbing force is too small to effectively absorb the shock.

An example given herebelow will help understanding the drawback or disadvantage of the conventional shock absorber, in which is explained the shock absorbing function of the conventional shock absorber of the automotive vehicle suspension. When the vehicle is driven on the substantially smooth plane and straight road, the piston stroke responsive to the road shock to be applied to the vehicle is ,substantially small to require substantially low shock absorbing effect. However, if the vehicle is driven at relatively high speed the application speed of the road shock is relatively high to produce unnecessarily high shock absorbing effect. This leads to low comfortability of vehicle driving.On the other hand, when the vehicle is driven through curved road or substantially uneven or rough road, it possibly happens that an insufficient shock absorbing effect is produced due torather low application speed of the shock.

Therefore, it is desirable for the shock absorbing effect to be responsive not only to the application speed of the shock but also to the piston stroke responsive to the shock. The improvement of the shock absorber illustrated hereafter achieves such requirements.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a shock absorber which varies an absorbing force against the shock applied thereto depending on not only the application speed of the shocl < but also the piston stroke responsive to the shock.

According to the present invention, there is provided a shock absorber comprising a movable piston disposed within a fluid chamber in movable position responsive to the shock applied to the shock absorber. The piston is formed with a plurality of fluid passages for communication between the upper and lower portions of the fluid chamber in relation to the piston. A valve member is disposed within each fluid passage so that it can limit a fluid flow through the fluid passage. The valve member limits the fluid flow in response to the piston stroke excessive to a predetermined value.

In the preferred embodiment, the shock absorber comprises a hydraulic shock absorber including, a hollow cylinder filled with a working fluid, a piston movably disposed within said cylinder and separating the interior of said cylinder into first and second fluid chambers, said piston being movable along said cylinder in response to a shock applied to the shock absorber, a fluid passage formed in said piston for communication between said first and second chambers, and a valve member disposed within said fluid passage for limiting fluid flow through said fluid passage, said valve member being operative in response to a piston stroke excessive to a predetermined value in order to produce an absorbing or resisting force against the piston motion.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description of the invention given hereinafter and from the accompanying drawings of a preferred embodiment of the invention which, however, should not be taken as limitative to the invention but for elucidation and explanation only.

In the drawings: Figure 1 is a longitudinal section of a first embodiment of a shock absorber according to the present invention; Figure 2 is an enlarged section of the shock absorber of Fig. 1 taken along line 2-2 of Fig. 1; Figure 3 is a exploded partial perspective view of the piston of the shock absorber of Fig. 1; Figure 4 is an enlarged partial cross section of the shock absorber of Fig. 1, taken along line 4-4 of Fig. 2; Figure 5 is an enlarged perspective view of the valve member employed in the shock absorber of Fig. 1; Figure 6 is a graph showing varying of the opening area of a valve in the piston in relation to the relative position of a valve member; Figure 7 is a graph showing varying of shock absorbing force in relation to the stroke of the valve member and application speed of the shock;; Figure 8 is a similar view to Fig. 2 showing a modification of the first embodiment of the shock absorber; Figure 9 is a partial cross-section of a shock absorber taken along line 9-9 of Fig. 8; Figure 10 is a partial cross-section of the shock absorber taken along line 10-10 of Fig. 8; Figure 11 is a graph showing varying of shock absorbing force of the shock absorber of Fig. 8 in relation to the stroke of the valve member; Figure 12 is a perspective view of the piston employed in a second embodiment of the shock absorber according to the present invention, in which a part of piston is cut out for explanation; Figure 13 is a partial section of the piston of Fig. 12; Figure 14 is an enlarged perspective view of the valve member employed in the shock absorber of Fig. 12;; Figure 15 is an explanatory illustration showing motion of the valve member of the shock absorber of Fig. 12; Figure 16 is a graph showing varying of absorbing effect of the shock absorber of Fig.

1 2 in relation to the motion distance of the valve member; Figure 1 7 is a partial section of a modification of the shock absorber of Fig. 12; Figure 18 is a partial section of another modification of the shock absorber of Fig. 12; Figure 19 is a graph showing varying of shock absorbing force of the shock absorber of Fig. 18, in relation to the motion distance of the piston; Figure 20 is a partial section of a further modification of the shock absorber of Fig. 12; Figure 21 is a plan view of the valve member as a part of the shock absorbing means of the shock absorber of Fig. 1 2; Figure 22 is a partial section of a still further modification of the shock absorber of Fig. 12; Figure 23 is a graph showing varying of the shock absorbing effect of the shock absorber of Fig. 22;; Figure 24 is an exploded perspective view of a piston of a third embodiment of the shock absorber according to the present invention; Figure 25 is a cross section of the third embodiment of the shock absorber of Fig. 24; Figure 26 is a partial section of the shock absorber of Fig. 24 taken along line 26-26 of Fig. 25; Figure 27 is a graph showing varying of shock absorbing effect of the shock absorber of Fig. 24 in relation to motion distance of the piston; Figure 28 is a partial cross-section of a modification of the third embodiment of Fig.

24; and Figure 29 is a partial section showing another example of application of the invention, in which the valve is adapted for single action type piston.

DESCRIPTION OF THE EMBODIMENTS Referring now to the drawings, particularly to Figs. 1 to 5, there is illustrated a first embodiment of a shock absorber according'to the present invention. The shock absorber generally comprises a hollow cylinder 30 and a movable piston 32 disposed within the interior of the cylinder 30. A working fluid is filled in the cylinder 30 for building up absorbing force against a shock applied to the shock absorber. The top of the cylinder 30 is closed with a cover member 34 and a sealing member 36 which is located adjacent the cover member 34. Both of the cover member 34 and the sealing member 36 are formed with central openings 38 and 40 for receiving a connecting rod 42 therethrough. The connecting rod 42 has an annular connecting ring 44 at the top thereof and extends into the interior of the cylinder 30.The connecting rod 42 is formed with a thread portion 46 at the lower end thereof. The piston 32 is formed with a control opening 33 for receiving the thread portion 46 of the connecting rod 42 and is thus fixedly secured thereon by a fixing nut 48 engaged with the thread portion 46. Thus, the piston 32 is incorporated with the connecting rod 42 so that it may be moved with the connecting rod 42.

The piston 32 is formed with an annular groove 50 on the circumferential periphery thereof. An annular sealing member 52 is mounted on the circumferential groove 50 with abutment against the internal periphery of the cylinder 30. The interior of the cylinder 30 is thus divided into an upper and lower chambers 54 and 56. In the lower chamber 56, a free piston 58 is disposed in freely movable position. The free piston 58 has an annular sealing member 60 on the circumferential periphery thereof with abutment against the internal periphery of the cylinder 30. By the free piston 58, a chamber 62 is defined in the lower portion of the lower chamber 56. A gas is filled within the chamber 62 in order to absorb varying of the fluid pressure caused by varying of volume of the connecting rod 42 placed within the upper chamber 54 by the motion thereof.

As shown in Fig. 1, the cylinder 30 has a connecting ring 64 at the bottom thereof.

Though not appeared in the drawings, an elastic busing is preferably mounted on each connecting ring 44 and 64 for absorbing a vibration applied thereto. With both connect ing rings 44 and 64, the shock absorber is interpositioned between two members. In case of the shock absorber being applied to the vehicle suspension, the upper ring 44 is connected with the vehicle suspension upper link and the lower ring 64 is connected with the lower link.

As shown in Figs. 2 to 4, the piston 32 comprises an upper and a lower disc-shaped members 320 and 350. The upper discshaped member 320 is formed with a pair of openings 322 located in spaced apart and in parallel relationship. Each opening 322 comprises a small diameter cylindrical section 324, a large diameter cylindrical section 326 and an intermediate conical section 328. On the other hand, the lower disc-shaped member 350 is formed with a pair of openings 352 at corresponding location to the openings 322. Likewise to the opening 322, the opening 352 comprises a small diameter cylindrical section 354, a large diameter cylindrical section 356 and an intermediate conical section 358. Both of the disc-shaped members 320 and 350 are mated one another with axial alignment of the opposing openings 322 and 352.Thereby, as shown in Fig. 4, the piston 32 is provided fluid passages which are generally represented by reference numeral 66 with upper and lower ports 661 and 662, a upper and lower intermediate valve seat portions 663 and 664 and a valve chamber 665 defined by the large diameter cylindrical sections 328 and 358. Within the valve chamber 665, a valve member 68 with coneshaped heads 70 and 71 on both ends thereof is movably disposed. As shown in Fig.

5, the valve member 68 is formed with a plurality of grooves 72 on the vertical periphery of the intermediate portion 73 thereof.

The groove 72 acts for allowing the working fluid flow therethrough.

It should be noted that the valve member 68 can be made of any. suitable material, in practice. However, the valve member is preferably made of a synthetic resin or the like having a specific gravity substantially the same as that of the working fluid. Namely, in case that the valve member 68 is made of a metal having substantially larger specific gravity than that of the working fluid, the valve member neutral position cannot be set at the exactly vertical center of the fluid chamber except some suitable adjustment such as increasing friction between the internal periphery of the fluid passage 66 and the outer periphery of the valve member 68 or supporting the valve member 68 by a spring.Even if the metal valve member 68 has lower neutral position, this may not lead any serious problems to the shock absorber function, since the valve member 68 is usually moving up and down when shock absorber is working and there is no problem concerning the tendency of such valve member that produces a larger absorbing force against the expansion of the shock absorber than that against the contraction. An advantage of the resin valve member can be expected that it may minimize an inertia applied thereto.

As seen from Fig. 4, the valve member 68 is generally located at the neutral position when the shock is not applied to the shock absorber. The valve member 68 is movable in upward and downward direction in a stroke H.

Here, if the shock which causes a fluid pressure effecting to the valve member for moving the same between the fluid chambers 54 and 56, is applied to the shock absorber and thereby the shock absorber is contracted, the piston 32 is moved with reducing the volume of the lower chamber 56. A difference of the fluid pressure in the chambers 54 and 56 is thus built up by the motion of the piston 32.

At this moment, the working fluid in the chamber 56 is therefore forced to flow into the valve chamber 665 in the piston 32 through the ports 662. The fluid flowing through the ports 662 is discharged into the valve chamber 665 through the valve seat portions 664. The valve member 68 is thereby forced towards the ports 661 by the fluid pressure discharged within the valve chamber 665. Within the valve member stroke range h, where the top of the upper head 70 does not reach at the lower end of the ports 661, the open area S,(= 7r/4.d2) of the port 661 through which the working fluid flows into the upper chamber 54 is not varied. Thus, the absorbing force or resistance built up within the piston 32 by the valve member 68 is maintained unchanged in even minimum value.As shown in Fig. 6, if the valve member motion exceeds the range h1 and the valve member 68 further travels toward the intake portion 324, the open area of the port 661 is gradually reduced. The absorbing force is gradually increased corresponding to the reducing of the open area of the port 661. The valve member 68 is limited the motion toward the port 661 by abutting the upper edge of the intermediate portion 73 thereof against the lower end of the valve seat portion 663 at a travelling stroke H. At the uppermost position of the valve member 68, the open area of the port 661 is maintained in not completely closed condition for still providing communication between the chambers 56 and 54. If the shock absorber is expanded and thus the piston 32 travels toward the chamber 54 with reducing the volume of the chamber 54.At this time, the fluid pressure in the chambers 54 and 56 are differed. By the fluid pressure difference, the fluid in the chamber 54 flows toward the chamber 56 through the fluid passage 66. The fluid flows into the port 661 and is discharged to the valve chamber 665 from the port 661. The valve member 68 is thus moved downwardly.

Within the valve member stroke where the lower head 71 of the valve member 8 does not reach the upper end of the port 662, the open area of the intake portion is maintained unchanged at even. Therefore, the absorbing force or resistance against the piston is maintained at substantially constant value. If the valve motion stroke exceeds h, and the lower head 71 of the valve member 68 goes into the port 662, the open area of the port 662 is gradually reduced to increase absorbing force against the piston motion by limiting the fluid flow.

As shown in Fig. 7, the absorbing force or fluid flow resistance produced in the fluid passage 66 by the valve member motion also depends on the speed of piston motion as known to the conventional shock absorber. As seen from Fig. 7, depending on the piston stroke and the piston motion speed, increasing rate of the absorbing force against the piston motion is varied. Namely, the shock absorber according to the first embodiment of the present invention can improve comfort in riding the vehicle in case it applied on the vehicle, since the absorbing force produced thereby depends on both the piston stroke and the piston motion speed.

Figs. 8 to 10 show a modification of the first embodiment. In this modification, the piston 32 is formed with four fluid passages 741, 742, 743 and 744 in circumferentially constant intervals. Each fluid passage 741, 742, 743 and 744 is arranged to provide different maximum motion range H1, H2, H3 and H4 of the valve member 761, 762, 763 and 764 respectively disposed within the fluid passages. In each valve member 761, 762, 763 and 764 and the fluid passage 741, 742, 743 and 744, the dimensional relationship is varied so that each valve member motion stroke where each head 781, 782, 783 and 784 of each valve member 761, 762, 763 and 764 does not reach the inner end of intake portions is different from one another.In the shown modification, the valve member stroke ranges are arranged as to H, > H2 > H3 > H4 and h1 > h2 > hS > h4. As shown in Fig. 10, at the piston stroke where the valve member 764 exceeds the height h4, the head 784 of the valve member 764 gradually decrease the open area of the port 744. Thus, the absorbing force in the fluid passage 764 is increased. When the valve member moves by stroke H4, the absorbing effect is increased to A in Fig. 11. Likewise, if the valve member moves by the stroke H3, the absorbing force is increased. At this time, the absorbing force against the piston motion in the fluid passages 743 and 744 is substantially high and the absorbing force B of the shock absorber is sum of that in each fluid passage 743 and 744. By this, the shock absorber increases the absorbing force step by step.

Thus, this modification makes the varying of absorbing force moderate so as not to give the passenger in the vehicle discomfort by rapidly increasing the absorbing effect when this is applied to the vehicle suspension.

Figs. 1 2 to 1 5 show a second embodiment of the shock absorber according to the present invention. A piston 100 comprises upper and lower disc-shaped members 110 and 1 30 with central openings 101. Through the central opening 101, the thread portion 102 of the connecting rod 103 is inserted to incorporably mount the piston 100 thereon. The piston 100 is fixedly secured on the connecting rod 103 by tighting the nut 104. Each of the disc-shaped members 110 and 1 30 is formed with stepped openings 111 and 1 31 respectively. The openings 111 asnd 1 31 have circular cross-section in every lateral sections.Each opening 111 and 131 comprises small diameter sections 11 2 and 1 32 and large diameter sections 11 3 and 1 33.

The large diameter sections 11 3 and 1 33 are mated in alignment upon the upper and lower members 110 and 1 30 being assembled into the piston so that they define a valve chamber 105 within the piston 32. The small dia,meter sections 11 2 and 1 32 serve as intake ports to establish communication between the fluid chambers 54, 56 and the valve chamber 105.

A valve member 106 is a plain thin plate having a elasticity to be deformed by the fluid flow in the valve chamber 105. In the preferred construction, the valve member 106 is made of a leaf spring of steel. The valve member 106 is welled on the internal vertical periphery 107 of the valve chamber 105, which vertical periphery 107 defines the central opening 101 of the piston 100. The valve member 106 is thus located at the vertically intermediate portion in the valve chamber 105 in it's neutral position.

Although the valve member 106 is mounted on the internal vertical periphery 107 in the shown embodiment, it is possible to alternate the position for the valve member to be welded anywhere of the vertical periphery defining the valve chamber 105.

As shown in Fig. 14, the valve member 106 is formed with a cut-out 108 on the free end thereof so as not to completely close the intake port 11 2 and 1 32 in the deformed position as in Fig. 1 5. The cut-out 108 in the shown embodiment may be replaced by one or more openings formed in the valve member 106 at the suitable location. For preventing the valve member 106 from completely closing the intake ports 11 2 and 132, various modifications can be embodied. For example, a pair of stoppers 109 can be provided adjacent the valve member 106 to limit the motion of the valve member, as shown in Fig.

17.

In operation, assuming the shock absorber is expanded and thereby the piston 100 is moved toward the upper fluid chamber, the fluid pressure in the upper fluid chamber becomes higher than that in the lower fluid chamber. By the pressure difference, the fluid in the upper fluid chamber is forced to the lower fluid chamber through the piston 1 00.

The fluid flows into the intake port 11 2 and is discharged into the valve chamber 1 05. The fluid in the valve chamber 105 forces the valve member 106 downwardly. Thus, the valve member 106 is deformed to vary the open area of the inner end of the port 1 32. In a range where the valve member 106 is deformed to the position represented by B in Fig. 15, the absorbing forces against the piston motion may not substantially vary since the open area of the intake portion may not substantially vary. From the valve member position B to C, the open area of the intake portion 1 32 is substantially varied and thus the absorbing force is rapidly increased. The varying of the absorbing force is illustrated in Fig. 16.

Fig. 1 8 shows a modification of the second embodiment of the present invention illus trated hereabove. In this modification, the upper and lower disc-shaped members 110 and 1 30 are varied in the thickness thereof.

The valve member 106 is located at the vertical position where spaces between the valve member 106 and the lower end of the intake portion 11 2 and between the valve member 106 and the upper end of the intake portion 1 32 are respectively heights T1 and T2. In the shown embodiment, the T2 is larger than T1. In this construction, when the valve me'mber 106 is deformed upwardly, namely when the shock absorber is contracted, the valve member 106 will be deformed toward the intake portion 11 2 and the free end of the valve member 106 reaches the lower end of the intake portion 11 2 in response to relatively short piston stroke.On the other hand, when the valve member 106 is deformed downwardly, namely the shock absorber is expanded, the valve member 106 reaches the position B in Fig. 1 5 in relatively long piston stroke. Therefore, according to the present embodiment, the absorbing force is varied between the contracting and expanding of the shock absorber, as shown in Fig. 1 9. Such a shock absorber will be useful for the automotive vehicle suspension, since the difference of the shock absorbing force will serve the shock absorber more effective shock absorbing characteristic by varying the absorbing force in bounding side and rebounding side. The same effect will be expected by another modification illustrated in Fig. 20.In this modification, a pair of leaf springs 150 and 151 are fitted onto both surfaces of the valve member 106 so as to restrict the valve member motion in upward and downward directions. The spring plates 150 and 151 are varied in the elastic coefficients so that the deformation of the valve member 106 is varied in upward and downward directions in response to the fluid flow.

Here, returning to Fig. 14, there is shown one of principle construction of the valve member 1 06. As seen from Fig. 14 the valve member 106 comprises a circular central portion 1061 and movable tongue portions 1062 radially extending from the central portion 1061. The central portion 1061 is formed with a circular opening 1063 at the center thereof. Through the opening 1063, the valve member 106 is mounted around of the inner wall 107 of the piston 100 and is fixedly secured thereon by welding or other treatment. The valve member 106 is also modified as shown in Fig. 21. In Fig. 21, the chain line shows an example of modification having four movable tongue portions 1062 in radial directions.

Fig. 22 shows another modification of the second embodiment of the shock absorber. In this embodiment, the size of each valve chamber 1051 and 1052 is varied in relation to the other chamber. Like as the above described embodiment with reference to Fig.

13, the valve member 106 is secured on the internal periphery of the valve chamber 1051 and 1052 at the vertically intermediate position of the chamber. By varying the size of the chambers 1051 and 1052, the piston stroke where the valve member 106 is deformed to the position B of Fig. 15, is varied. Therefore, as shown in Fig. 23, the absorbing force is gradually increased depending on the piston stroke in response to the magnitude of the shock.

Figs. 24 to 26 show a third embodiment of the shock absorber according to the present invention. In the present embodiment, the piston 200 of the shock absorber is secured on the lower end of the connecting rod 210 by a nut 211 and is provided with a relief valves 230 and 232. As shown in JFigs. 24 and 25, the relief valve 230 and 232 are arranged in diametrically alignment and circumferentially aparting from the fluid passages 201. The relief valves 230 and 232 comprise through openings 233 and 234 formed in the piston 200 and disc-shaped leaf springs 235 and 236 fitted on upper and lower surfaces of the piston 200 through a fittings 240 and 241 facing thereto respectively. The springs 235 and 236 are respectively formed with pairs of openings 237 at the locations respectively corresponding to the ends of the fluid passages 201.The piston 200 is formed with cut-out 238 and 239 at the portions at the ends of the openings 233 and 234. The cut-out 238 is formed at the upper end of the opening 233 and the cut-out 239 is formed at the lower end of the opening 234.

The valve member 202 is provided with conical-shaped projections 203 and 204 on both surfaces at the free end thereof. Corresponding to the projections 203 and 204, the fluid passage 201 is formed with a conical portions 205 and 206 between the ports 207 and 208 and the valve chamber 209. Responsive to the fluid flow within the fluid passage 201, the valve member 202 is deformed and the projection 203 and 204 goes into the conical portion 205 and 206 to limit fluid flow therethrough and thus to increase absorbing force against the fluid flow. If the fluid pressure accumulated in one chamber exceeds a predetermined value, either one of the relief valves 230 or 232 becomes operative to relieve the pressurized fluid therethrough.

In detail, assuming the shock absorber is contracted and the fluid pressure in the chamber located below the position 200 is increased beyond the predetermined value, the pressurized fluid acts through the cut-out portion 239 on the spring 235 to open the end of opening 234. Thus, the pressurized fluid flowing into the opening 234 opens the spring 235 and flows into the chamber located over the piston 200.

It will be appreciated that the construction of the relief valve is not specified to that given hereabove. The valve construction may be modified in various forms. For examples, Fig.

28 shows modification of the relief valve constructions.

In Fig. 28, the relief valve 250 comprises an opening 251 formed in the piston 200.

The opening 251 is communicated with the fluid chambers on upper and lower sides of the piston 200 through upper and lower ports 252 and 253. Further, kthe opening 251 is communicated with the chambers through outlet passages 254 and 255 opening at the intermediate portion of the opening 251. A valve member 256 is movably provided within the opening 251. The valve member 256 is urged from both sides thereof by coil springs 257 and 258 having an urging force substantially equal to each other. Thus, the valve member 256 is normally located at the neutral position where the valve member 256 blocks communications between the opening 251 and the both chambers through the outlet passages 254 and 255.If the fluid pressure accumulated in one of the fluid chamber in excess of the spring force, the valve member 256 is moved by the fluid pressure to establish one of the communications between the opening 251 and the outlet passages 254 and 255. Thus, if the fluid pressure is accumulated in excess of a set force of the spring 257 and 258, the relief valve becomes operative to relieve the pressurized fluid.

In this embodiment, the absorbing effect produced in the shock absorber is varied according to a characteristics corresponding to piston motion speed as illustrated in Fig. 27.

It should be further appreciated that, kthough the specific embodiments illustrated hereabove show the examples in which the shock absorbing means according to the present invention are applied to the single cylinder, double action type shock absorbers, the present invention can be applied to the double cylinder, single action type ones. For example, Fig. 29 shows one example of the valve construction to be formed in the piston or bottom valve of the double cylinder, single action type shock absorber. In Fig. 29, the valve member 270 comprises a conicalshaped head 271, a larger diameter section 272 and a smaller diameter section 273. T4ie valve member 270 is received within the valve chamber 274 having a conical valve seat portion 275. The valve chamber 274 communicates with the upper and lower fluid chambers through the ports 276 and 277.

The larger diameter section 272 of the valve member 270 is formed with a plurality of vertical grooves 278 for permitting fluid flow therethrough. Thus constructed valve produces the absorbing force variable similarly to the above-mentioned examples only when the piston is moved downwardly and thus the valve member is moved upwardly.

Further, it is to be noted that while hereinabove shows the specific embodiments of the present invention for illustration in detail of the invention, the specific constructions of the embodiments should be understood as merely examples embodying the present invention.

Namely, the present invention includes all jof the possible embodiments and modifications within the principles of the invention. Unnecessary to say, the piston construction according to the present invention is applicable for any shock absorber available from the market.

Claims

1. A hydraulic shock absorber comprising: a hollow cylinder filled with a working fluid; a piston movably disposed within said cylinder and separating the interior of said cylinder into first and second fluid chambers, said piston being movable along the internal periphery of said cylinder in response to a shock applied to the shock absorber; a fluid passage formed in said piston for communication between said first and second chambers; and a valve member disposed within said fluid passage for limiting fluid flow through said fluid passage, said valve member being operative in response to a piston stroke in order to change an absorbing force against the piston motion.

2. A shock absorber as set forth in claim 1, wherein said fluid passage comprises a valve chamber receiving said valve member and ports respectively connecting said valve chamber with said first and second fluid chambers, said valve membver is movable with respect to respective opposing ends of said ports to limit open area of said ports in response to the piston stroke.

3. A shock absorber as set forth in claim 2, wherein said valve member is a movement flowing in said valve chamber, said valve member has conical heads on upper and lower ends thereof, which heads act for grad ually reducing the open area of said fluid passage, said valve member is located apart from said inner ends of the ports.

4. A shock absorber as set forth in claim 2, wherein said valve member is an elastic plane member opposing to said inner ends of the ports so that it may gradually reduce the open area of the ports responsive to the piston stroke.

5. A shock absorber as set forth in any one of claims 1 to 4 inclusive, wherein said piston is formed with a plurality of fluid passages respectively receiving the valve members therein, said valve members are varied in the relationship with the fluid pas sages for varying the changing point of the absorbing force where the valve member be gins to limit the fluid flow therethrough.

6. A shock absorber as set forth in claim 1, 2, 3 or 4, wherein said piston is further provided with a relief means for relieving the pressurized fluid when the fluid pressure ex ceeds a predetermined value.

7. A shock absorber as set forth in claim 6, wherein said relief means comprising an opening connecting the first and second fluid chamber and an elastic closure member elasti cally urged to close the end of said opening and is releasable from said end of opening in res'ponse to a fluid pressure exceeding the predetermined value.

8. A shock absorber as set forth in claim 6, kwherein said relief means comprises through opening connected with said first and second fluid chambers through ports and a movable valve member slidably disposed within said opening, said valve member clos ing an outlet passage connecting said opening with said first and second fluid chambers in neutral position, and said valve member being moved in response to a fluid pressure exceeding a set pressure.

9. A hydraulic shock absorber comprising: a hollow cylinder filled with a working fluid therein; a piston movably disposed within said cylin der and separating the interior of the cylinder into first and second fluid chambers, said piston being connected with an upper mem ber movable relative to said cylinder, and said piston being movable up and down in response to a shock applied to said shock absorber; a fluid passage formed in the piston for communication between said first and second fluid chambers, said fluid passage including a first and second port communicating a valve chamber formed at the intermediate portion of said fluid passage with said first and second fluid chambers respectively; and a valve member disposed within said valve chamber of said fluid passage and movable with respect to both inner ends of said first and second ports, said valve member limiting open area of said inner end of either one of said first and second ports for limiting fluid flow therethrough.

1 0. A shock absorber for a suspension of an automotive vehicle comprising: a hollow cylinder filled with a working fluid and connected with a vehicle suspension lower member; a piston movably disposed within the interior of said cylinder and separating said interior of the cylinder into a first and a second fluid chambers, said piston being connected with a vehicle suspension upper member so that the piston is moved corresponding to relative displacement of said vehicle suspension upper and lower members; at least one fluid passage formed in said piston for communication between said first and second fluid chambers, said fluid passage including a valve chamber and first and second port respectively connecting said valve chamber to said first and second fluid chambers; and a valve member disposed within said valve chamber and being displaced the relative position with respect to the inner ends of said first and second ports corresponding to the piston stroke, said valve member reducing an open area of the inner end of one of said first and second ports for limiting fluid flow therethrough in order to change absorbing force against the shock applied to the shock absorber.

11. A shock absorber as set forth in claim 9 or 10, wherein valve member is normally placed at a neutral position where said valve member is spaced apart from both inner ends of said first and second port by a predetermined distance so that there is a lost motion of said valve member during which the effective area of said fluid passage remains unchanged.

1 2. A shock absorber as set forth in claim 9 or 10, wherein said valve member is a movement made of a synthetic resin having a substantially the same specific gravity as that of the working fluid, said valve member has conical heads on upper and lower ends thereof so that it can gradually reduce the open area of said inner ends of the first and second ports responsive to the piston stroke.

1 3. A shock absorber as set forth in claim 9 or 10, wherein said valve member is a leaf spring deformably disposed within said valve chamber and reduces the open area of the inner ends of the first and second ports, gradually.