Shock absorber

Abstract: A shock absorber is provided a piston stroke dependent variable shock absorbing characteristics by means of a first and second flow restriction means associated with a piston (2). The first and second flow restriction means are arranged in a fluid path for communicating first (1a) and second (10) working chambers defined within a shock absorber cylindrical housing in series. The first flow restriction means associated with an orifice forming a part of the fluid path and has a predetermined relief pressure, for providing a predetermined first fixed flow restriction rate in response to a pressure difference between the first (1a) and second (1b) chambers smaller than or equal to the relief pressure and providing a second variable flow restriction rate in response to a pressure difference between the first and second chambers greater than the relief pressure. The second flow restriction means is associated with the orifice for providing a third variable flow restriction rate variable depending upon the pressure difference between the first and second chamber.

Description: The present invention relates generally to a hydraulic shock absorber, suitable for use in an automotive suspension system. More specifically, the invention relates to a valve construction in a hydraulic shock absorber. JP-U- 62-107131 discloses a typical construction of a conventional shock absorber. The disclosed shock absorber has a piston body separating the internal space of a shock absorber cylinder into upper and lower fluid chambers, and a base body which separates the lower fluid chamber from a reservoir chamber defined between inner and outer cylinders. The piston body and the base body are formed with orifices. An annular projection with plane tip end surface is formed at an orientation radially outward of the orifices. A constant orifice is formed through the annular projection. A valve plate is biased and seated onto the plane tip end surface. Accordingly, at relatively low piston speeds, the valve plate is maintained in contact with the contacting surface of the annular projection. Therefore, the working fluid only flows through the constant orifice to generate absorption with a characteristic proportional to the square of the piston speed. On the other hand, at intermediate and high piston speeds, the valve plate is deformed to generate absorption with a characteristic proportional to the power of two over three of the piston speed. With such construction, when the piston speed is lower than a relief speed at which the valve plate is deformed to open, all of the working fluid flows through constant orifice of constant path area. Therefore, the absorption characteristic becomes proportional to the square of the piston speed. Accordingly, leakage through gaps between the piston and cylinder and between the piston rod and guide will substantially influence the shock absorbing characteristics. In other words, the leakage has an effect equivalent to a variation of the path area in the constant orifice. Therefore, fluctuation of the shock absorbing characteristics, particularly at the low piston speed range, becomes significant. In addition, when the absorption is set at the piston speed of 0.1 m/s, absorption characteristics can be uniformly determined in a piston speed range lower than the set speed. Therefore, freedom of setting of the absorption characteristics is unacceptably narrow. An alternative construction of a shock absorber, having a multi-stage valve assembly, is disclosed in JP-U- Showa 61-47134, on which the preambles of claims 1 and 5 are based. In that previously proposed construction, an orifice through a piston body defines a path for fluid communication between upper and lower chambers of a shock absorber cylinder. First and second stage disc valves are disposed are above the other in series in the path of the fluid flow. The first stage valve is designed to respond to pressure to open for fluid communication therethrough. The second stage valve is designed to respond to a higher pressure than the first stage valve to open for fluid communication therethrough. The second stage valve also defines a constant orifice or orifices having a predetermined fixed fluid path area for permitting fluid flow therethrough at a limited flow rate even when the second stage valve is closed. Therefore, it is an object of the present invention to provide a shock absorber which can overcome the drawbacks of the prior art set forth above. Another object of the invention is to provide a shock absorber which can minimize fluctuation of absorption characteristics in the low piston stroke speed range. A further object of the invention is to provide a shock absorber which can provide greater freedom in setting shock absorbing characteristics, particularly in the low piston speed range. In order to accomplish the aforementioned and other objects, a shock absorber, according to the present invention, is provided having piston stroke dependent variable shock absorbing characteristics by means of a first and second flow restriction means associated with a piston. The first and second flow restriction means are arranged in series in a fluid path for communicating first and second working chambers within a shock absorber cylindrical housing. The first flow restriction means is associated with an orifice forming a part of the fluid path and has a predetermined relief pressure, for providing a predetermined first fixed flow impedance in response to a pressure difference between the first and second chambers smaller than or equal to the relief pressure and providing a second variable flow impedance in response to a pressure difference between the first and second chambers greater than the relief pressure. The second flow restriction means is associated with the orifice for providing a third variable flow impedance depending upon the pressure difference between the first and second chamber. According to one aspect of the invention, a valve construction for a hydraulic shock absorber disposed between relatively displaceable first and second members for absorbing energy of relative displacement between the first and second members, comprises a valve construction for a hydraulic shock absorber disposed between relatively displaceable first and second members for absorbing energy of relative displacement between said first and second members, comprising: a valve body arranged in use to be disposed within a hollow cylindrical housing and to separate an internal space of said housing into first and second chambers; an orifice formed through said valve body for communication between said first and second chambers for permitting fluid flow for balancing fluid pressure between said first and second chambers; members made of leaf spring material acting as first flow restriction means associated with said orifice and having a predetermined relief pressure, providing a first, fixed flow impedance at pressure differences between said first and second chambers smaller than or equal to said relief pressure and providing a second, variable flow impedance at pressure differences between said first and second chambers greater than said relief pressure; members made of leaf spring material acting as second flow restriction means, associated with said orifice and arranged in series with said first flow restriction means, providing a third flow impedance variable depending upon the pressure difference between said first and second chambers; characterised in that: a resilient member common to said first and second flow restriction means is provided for varying the flow impedance in said first flow restriction means and the flow impedance in said second flow restriction means; a first groove is provided on one axial end surface of said valve body in communication with said orifice and a second groove is provided on said one axial end surface radially outside said first groove; and said first flow restriction means acts in the path of fluid flow between said first and second grooves, and said second flow restriction means acts in the path of fluid flow from said second groove to one of said first and second chambers. According to another aspect of the invention, hydraulic shock absorber to be disposed between a first and second member relatively movable to each other for absorbing an energy causing relative movement between the first and second members, comprises: a hollow cylindrical housing filled with a working fluid, said cylindrical housing being mechanically associated with said first member for axial movement therewith; a piston disposed within the internal space of said cylindrical housing for separating the internal space of said cylindrical housing into first and second working chambers, said piston being mechanically associated with said second member for axial movement therewith; an orifice formed through said piston for communication between said first and second chambers for permitting fluid flow for balancing fluid pressure between said first and second chambers; members made of leaf spring material acting as first flow restriction means associated with said orifice and having a predetermined relief pressure, providing a predetermined first, fixed flow impedance in response to a pressure difference between said first and second chambers smaller than or equal to said relief pressure and providing a second, variable flow impedance in response to a pressure difference between said first and second chambers greater than said relief pressure; members made of leaf spring material acting as second flow restriction means, associated with said orifice and arranged in series with said first low restriction means, for providing a third, variable flow impedance variable depending upon the pressure difference between said first and second chamber; characterised in that: a resilient member common to said first and second flow restriction means is provided for varying said flow impedance in said first flow restriction means and said third flow impedance in said second flow restriction means; a first groove is provided on one axial end surface of said piston in communication with said orifice and, a second groove is provided on said one axial end surface, radially outside said first groove; and said first flow restriction means acts in the path of fluid flow between said first and second grooves, and said second flow restriction means acts in the path of fluid flow from said second groove to one of said first and second chambers. The piston may be movable according to movement of the second member relative to the first member at a speed corresponding to the speed of the second member, while the first flow restriction means varies the magnitude of the second flow impedance as a function of the relative speed of the piston and the cylindrical housing, and the second flow restriction means varies the magnitude of the third flow impedance as a function of the relative speed of the piston and the cylindrical housing. The first flow restriction means may produce an absorbing force for restricting relative motion between the first and second members, which varies at a rate proportional to the square of the motion speed of the piston when flow impedance is maintained at the first flow impedance and varying at a rate proportional to the power of two over three of the speed of the piston when flow impedance is the second flow impedance, and the second flow restriction varies the absorbing force for restricting relative movement between the first and second members, in proportion to the power of two over three the motion speed of the piston. The first and second flow restriction means may cooperate with each other to vary the absorbing force and to restrict relative movement between the first and second members in a substantially linear fashion. Furthermore, the shock absorber may comprise a resilient biasing means associated with the resilient member for exerting biasing force for the section of the resilient member oriented at a position corresponding to the orientation of the first groove so as to assure the first flow impedance of the first flow restriction means at a pressure difference between the first and second chambers smaller than or equal to the predetermined relief pressure. The resilient biasing means preferably comprises a disc member having a diameter such that the outer circumferential edge corresponds to the outer edge of the first groove, and a bias spring acting on the disc member for exerting biasing force on the resilient member therethrough. The first and second grooves may be so constructed as to exert greater hydraulic force on the section of the resilient member at the position corresponding to the second groove than on the section of the resilient member at the position corresponding to the first groove. A first land may be defined between the first and second groove and have a first seating surface establishing sealing contact with the resilient member, and a second land may extend along the edge of the second groove and have a second seating surface establishing sealing contact with the resilient member, the first seating surface being axially offset with respect to the second seating surface. The first flow restriction means may include a constant path area orifice defined through the first land and means for forming a gap between the resilient means and the first seating surface in response to a pressure difference greater than the relief pressure. In the alternative, the first flow restriction means may include a constant path area orifice defined through the resilient means for permitting fluid flow from the first groove to the second groove over the first land, and means for forming a variable path area gap between the resilient means and the first seating surface in response to the pressure difference greater than the relief pressure. In addition, the shock absorber may further comprise a stopper means associated with the resilient member for limiting deformation of the resilient member. 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, should not be taken to limit the invention to the specific embodiment but are for explanation and understanding only. In the drawings: Fig. 1 is a section of the preferred embodiment of a shock absorber according to the present invention; Fig. 2 is an enlarged partial section of the preferred embodiment of the shock absorber of Fig. 1 ; Fig. 3 is a chart showing variation of absorption (kgf) in bounding and rebounding stroke in relation to piston speed; Fig. 4 is a graph showing absorbing characteristics of the preferred embodiment of the shock absorber of Fig. 1 in low piston speed mode; Fig. 5 is a graph showing absorbing characteristics of the present invention of the shock absorber in intermediate and high piston speed mode; Fig. 6 is a bottom view of a piston body employed in the preferred embodiment of the shock absorber of Fig. 1 ; Figs. 7 to 11 are bottom views of modifications of piston bodies which can be employed in the preferred embodiment of the shock absorber of Fig. 1 ; Fig. 12 is an enlarged partial section of another embodiment of the shock absorber according to the present invention; Fig. 13 is a partial section of a further embodiment of the shock absorber according to the present invention; Fig. 14 shows a bottom view of a valve plate employed in the shock absorber of Fig. 13 ; Fig. 15 shows a bottom view of the modified construction of the valve plate to be employed in the shock absorber of Fig. 13 ; Fig. 16 is a partial section of a still further embodiment of the shock absorber according to the present invention; Fig. 17 is an enlarged partial section of the major section of the shock absorber of Fig. 16 ; and Fig. 18 is a partial section of a yet further embodiment of the shock absorber according to the invention. Referring now to the drawings, particularly to Fig. 1 , the first embodiment of a shock absorber, according to the present invention, has a cylinder tube 1 defining an internal space filled with a working fluid. Though Fig. 1 shows only one cylinder, the shown embodiment is constructed as a double-action type shock absorber including coaxial inner and outer cylinders. The cylinder tube 1 illustrated in Fig. 1 is the inner cylinder. The outer cylinder is partially illustrated and represented by the reference numeral 5 . As seen from Fig. 1 , the outer cylinder 5 may comprise a bottomed cylinder tube. The coaxial inner and outer cylinder tubes 1 and 5 define therebetween a reservoir chamber 4 of annular section. The inner cylindrical tube 1 defines an internal space filled with a hydraulic working fluid. A piston assembly 2 is disposed within the internal space of the inner cylinder 1 to divide the space into upper and lower working chambers 1a and 1b . The lower working chamber 1b communicates with the fluid reservoir chamber 4 via a bottom valve assembly 3 . Though the drawing does not clearly show it, the reservoir chamber 4 comprises a lower section filled with the hydraulic working fluid, which lower section is in communication with the lower working chamber 1b , and an upper section filled with a gaseous or gas phase working fluid. The pressure of the gaseous working fluid in the upper section of the fluid reservoir chamber 4 is adjusted to a predetermined pressure so that the hydraulic working fluid pressure in the upper and lower working chambers 1a and 1b in the neutral and static condition of the shock absorber can be set at a predetermined neutral pressure. The piston assembly 2 is fixedly mounted on the lower end portion of a piston rod 6 which is connected to a vehicular body at the upper end. As shown in Figs. 1 and 2 , the piston rod 6 has a smaller diameter piston receptacle section 6b with a threaded lower end 6a . The piston assembly 2 comprises a retainer 2a , a washer 2b , an upper valve plate 2c , a piston body 2d , a lower valve plate 2e , a smaller diameter disc plate 2f , a washer 2g , a retainer 2h and a valve spring 2j . These components of the piston assembly 2 are assembled to the piston receptacle section 6b of the piston rod 6 with a rubber bushing 7 , as shown. A fastening nut 2k engages with the threaded end 6a of the piston rod so that the piston assembly 2 can be firmly fixed onto the lower end portion of the piston rod. The piston body 2d is formed with a center opening 203 , through which the smaller diameter piston receptacle section 6b of the piston rod 6 extends. The piston body 2d is also formed with a plurality of through holes 201 and a plurality of orifices 202 at radially and circumferential]y offset position to each other. As shown in Fig. 1 , the through holes 201 extend obliquely to the axis of the piston rod 6 and have upper ends opening into an outer annular groove 201a formed on the upper plane surface of the piston body 2d . The lower end of each of the through holes 201 directly opens to the lower working chamber 1b at the circumferentially extending tapered edge portion of the piston body. On the other hand, the orifices 202 extend in parallel to the axis of the piston rod 6 . Each of the orifices 202 has an upper end opening into an inner annular groove 202a . The inner annular groove 202a is formed coaxially with the outer annular groove 201a and separated by an annular land formed therebetween, which land has an upper plane surface 204 serving as a contact surface for establishing sealing contact with the lower surface of the upper valve plate 2c . Both of the annular grooves 201a and 202a communicate with the upper working chamber 1a via a communication path groove 205 extending through the land. The lower end of each orifice 202 opens into an inner annular groove 206 . The annular groove 206 is formed on the lower plane surface of the piston body 2d . An outer annular groove 207 is coaxially formed with the inner annular groove 206 on the lower plane surface of the piston body 2d . These annular grooves 206 and 207 are generally separated by an annular land formed therebetween. The land has a plane lower surface 208 on which the upper surface of the lower valve plate 2e is seated for establishing sealing contact. Another and outer annular land is also formed on the lower surface of the piston body, which outer annular land has a lower plane surface 209 to sealingly contact with the upper surface of the lower valve plate 2e . The annular grooves 206 and 207 are communicated to each other via a constant orifice 210 radially extending through the inner land. As shown in Fig. 2 , the lower valve plate 2e comprises three annular disc shaped members piled up or laminated to each other. These annular disc shaped members are formed by a resilient material such as leaf spring material, for resilient deformation in response to a working fluid pressure greater than a predetermined pressure. These annular discs are provided with an initial resilient force to resiliently and sealingly contact with the surfaces 208 and 209 of the lands. The lower valve plate 2e is associated with the smaller diameter disc 2f . The smaller diameter disc 2f has outer diameter substantially corresponding to the external diameter of the inner annular groove 206 . The smaller diameter disc 2f is associated with a valve spring 2j which is retained by means of a retainer 2h . The valve spring 2j normally biases the smaller diameter disc 2f upwardly and whereby bias the lower valve plate 2e onto the surfaces 208 and 209 . The operation of the first embodiment of the shock absorber as set forth above will be discussed hereinafter in terms of different modes of operations. Low Piston Speed Mode Assuming that the piston assembly strokes in rebounding direction at relatively low speed, the volume of the upper working chamber 1a decreases according to upward movement of the piston assembly 2 . According to decreasing of the volume, the fluid pressure in the upper fluid chamber 1a increases. Alternatively, according to the upward movement of the piston assembly 2 , the volume of the lower working chamber 1b increase to lower the fluid pressure. Therefore, pressure balance is destroyed. Therefore, the working fluid in the upper working chamber 1a flows into the orifice 202 through the communication path groove 205 . The pressurized fluid flows through the inner groove 206 , the constant orifices 210 and the outer groove 207 . By the pressure of the working fluid in the outer groove 207 , the circumferential portion of the valve plate 2e is deformed to permit the working fluid to flow into the lower working chamber 1b at a limited flow rate. During this action, flow restriction for the pressurized fluid by the constant orifice creates absorption. The magnitude of absorption at the constant orifice 210 is proportional to the square of the piston speed, as illustrated by broken line (2) in Fig. 4 . On the other hand, flow restriction through the gap formed between the circumferential portion of the valve plate 2e and the surface 209 creates another absorption, the magnitude of which is proportional to two thirds of the piston speed, as illustrated by the broken line (1) in Fig. 4 . By providing such flow restriction in tandem fashion, the total absorption characteristics obtained becomes as illustrated by solid lines in Figs. 3 and 4 . As can be seen from Fig. 3 , the absorption characteristics obtained by such arrangement is essentially linearly proportional to the piston stroke speed. This can be compared with the absorption characteristics obtained in the prior art. Therefore, according to the shown embodiment, fluctuation of the absorption in the low piston stroke range can be minimized. Intermediate and High Piston Speed Mode Assuming that the piston assembly 2 strokes in rebounding direction at intermediate and high speed, the pressure difference between the upper and lower fluid chambers 1a and 1b becomes greater than that in the low piston speed mode. In such case, greater hydraulic pressure is exerted on the lower valve plate 2e to cause greater magnitude deformation with downward shifting of the smaller diameter disc 2f as the hydraulic force overcomes the spring force of the valve spring 2j . Therefore, the portion of the valve plate 2e mating with the surface 208 of the land is shifted away from the mating surface 208 . Therefore, an annular flow restricting orifice is formed between the mating surfaces of the valve plate 2e and the land. In this way, the magnitude of absorption created by flow restriction in the gap formed between the valve plate 2e and the surface 208 become proportional to the power two over three of the piston stroke speed, as illustrated by the broken line (2) in Fig. 5 . This absorption characteristic is combined with the absorption characteristic at the annular gap or orifice formed between the valve plate 2e and the surface 209 of the outer annular land, as illustrated by the broken line (1) of Fig. 5 . Therefore, by arranging the annular orifices in tandem fashion, substantially linear absorption characteristics can be obtained, as illustrated by solid line ((1) + (2)) in Fig. 5 . As will be appreciated herefrom, linear absorption characteristics can be obtained even at the intermediate or high piston speed range. The smaller diameter disk 2f and retainer 2h specifies the point of action of the spring force of the valve spring 2j at the position corresponding to the position of the valve plate 2e contacting with the surface 208 of the land. This stably defines the point of action of the spring force. On the other hand, the resilience of the valve plate 2e can be adjusted by adjusting the thickness of each resilient member used as a component or by varying the number of resilient members to be laminated. Since the absorption characteristic is variable depending upon the stiffness of the valve plate 2e , by adjusting the thickness of the resilient member and/or changing the number of the resilient plate, absorption characteristics can be adjusted for obtaining desired characteristics. In the preferred construction, the outer groove 207 may be provided with a wider width than the inner groove 206 for providing a greater path area. This ensures that a greater force is exerted on the section of the valve plate 2e corresponding to the groove 207 than is exerted on the section corresponding to the groove 206 . This ensures that the section of the valve plate 2e mating with the surface 208 of the inner annular land is maintained in sealing contact in the low piston stroke speed range. Therefore, in response to the low speed piston stroke, greater absorption can be generated in comparision with that to be created in response to the intermediate or high speed stroke. Here, in case of the application of the shock absorber for the automotive suspension system, lower piston speed and greater magnitude of vibration can be induced in a vehicle body to cause vehicular body attitude change. On the other hand, higher piston speed and smaller magnitude of vibration can be input through the road wheels as road shock. For the vehicle body induced vibration, it is desired to generate sufficient damping force to suppress vehicular body attitude change for better driving stability. On the other hand, for the road shock, softer suspension characteristics are desired so as not to transmit the vibration to the vehicle body for preventing rough ride feeling which otherwise caused by the vibration transmitted to the vehicle body. Therefore, the absorption characteristics provided by the aforementioned first embodiment of the shock absorber may afford both riding comfort and driving stability. In the shown embodiment of Figs. 1 and 2 , additional absorption can be generated by the bottom valve assembly 3 . The bottom valve assembly 3 comprises a valve spring 3b , a retainer 3c , a disc plate 3d , a lower valve plate 3e , a valve body 3f , an upper valve plate 3g , a washer 3h , a check spring 3j and a retainer 3k . These components are assembled on a bolt 3a in order, as shown. The components are secured to the bolt 3a by means of a fastening nut 3m . As seen, the valve body 3f is rigidly engaged with the lower end of the inner cylinder 1 to secure the bottom valve assembly 3 . The valve body 3f is formed with through holes 301 and orifices 302 . The upper end of the through holes 301 is closed by the valve plate 3g . On the other hand, the lower end of the through hole 301 is open to the reservoir 4 . With this construction, the fluid flow from the reservoir chamber 4 to the lower working chamber 1b is permitted and the fluid flow in the opposite direction is blocked. The lower ends of the orifices 302 open into an annular groove 206 which extends coaxially with an outer annular groove 207 . Inner and outer lands along the circumferential edges of the outer annular grooves 207 form seat surfaces 208 and 209 for the valve plate 3e . The upper ends of the orifices 302 open to an annular groove formed on the upper surface of the valve body, which annular groove is in communication withe the lower working chamber 1b via through openings 303 formed in the upper valve plate 3k . Therefore, the orifices permit fluid flow from the lower working chamber 1b to the reservoir chamber 4 and blocks fluid flow in the opposite direction. Similarly to the piston assembly described above, the bottom valve assembly 3 operates in two different mode depending upon the piston stroke. Each mode of operation will be discussed herebelow. Low Piston Stroke Speed Mode Assuming that the piston strokes in bounding direction with compressing the lower working chamber 1b at low speed, the pressurized fluid flows through the through openings 303 , the annular groove on the upper surface of the valve body 3f and the orifices 302 and then flows through the constant orifice 210 formed through the inner annular land formed between the inner and outer grooves 206 and 207 . The fluid pressure in the groove 207 acts on the valve plate 3e to cause deformation for establishing fluid communication between the lower fluid chamber 1b and the fluid reservoir chamber 4 so as to permit the fluid flow from the lower working chamber to the fluid reservoir chamber. During this mode of operation, the magnitude of absorption produced at the constant orifice is proportional to the square of the piston speed. On the other hand, the magnitude of absorption created at the gap formed between the valve plate 3e and the seating surface 209 of the outer annular land is proportional to two thirds of the piston speed. Therefore, similarly to that in the low piston speed mode of the piston assembly, linear characteristics of variation of absorption in relation to the piston speed can be obtained. Intermediate and High Piston Speed In the piston bounding stroke at intermediate or high speed, the greater fluid pressure in the grooves 206 and 207 acts on the valve plate 3e to cause greater magnitude of deformation in the valve plate. Therefore, the valve plate 3e is displaced away from the seating surface 208 as well as from the seating surface 209 . Therefore, the characteristics of variation of absorption becomes proportional to the power of two over three of the piston speed. Similarly to the piston assembly, the smaller diameter disc 3d and the valve spring 3b specify the point of action of the spring force to assure steady variation of the absorption in relationship to the piston stroke speed. Furthermore, the valve plate 3e comprises a plurality of resilient members laminated to each other. Similarly to the valve plate 2e of the piston assembly 2 , the variation characteristics of absorption can be adjusted by adjusting the thickness of each resilient member and/or by adjusting the number of resilient members to be laminated. Fig. 7 shows a modification of the foregoing first embodiment of the shock absorber according to the invention. In Fig. 7 , the piston assembly has a valve body formed with through holes 7a , orifices 7b , an inner groove 7c , an outer groove 7e , inner and outer lands having valve seating surfaces 7d and 7f . Constant orifices 7g are formed through the inner annular land for establishing fluid communication between the inner and outer grooves 7c and 7e . As seen, the outer circumferential edge of the inner groove 7c and the inner circumferential edge of the outer groove 7e are parallel to each other and formed into a non-circular configuration. Namely, the width of the inner groove 7c is widened at the position of the orifices 7b . Fig. 8 shows another modification of the foregoing first embodiment of the shock absorber according to the invention. In Fig. 8 , the piston assembly has a valve body formed with through holes 8a , orifices 8b , an inner groove 8c , an outer groove 8e , inner and outer lands having valve seating surfaces 8d and 8f . Constant orifices 8g are formed through the inner annular land for establishing fluid communication between the inner and outer grooves 8c and 8e . As seen, the inner groove 8c is separated into a plurality of arc shaped segments at the positoins where the orifices 8b are provided. Fig. 9 shows another modification of the foregoing first embodiment of the shock absorber according to the invention. In Fig. 9 , the piston assembly has a valve body formed with through holes 9a , orifices 9b , an inner groove 9c , an outer groove 9e , inner and outer lands having valve seating surfaces 9d and 9f . Constant orifices 9g are formed through the inner annular land for establishing fluid communication between the inner and outer grooves 9c and 9e . As seen, the inner groove 9c is circular. On the other hand, the outer groove has alternately arranged narrower and wider sections. The wider width sections are arranged at places where the constant orifices 9g are formed. Fig. 10 shows another modification of the foregoing first embodiment of the shock absorber according to the invention. In Fig. 10 , the piston assembly has a valve body formed with through holes 10a , orifices 10b , an inner groove 10c , an outer groove 10e , inner and outer lands having valve seating surfaces 10d and 10f . Constant orifices 10g are formed through the inner annular land for establishing fluid communication between the inner and outer grooves 10c and 10e . As seen, the inner groove 10c is circular. On the other hand, the outer groove 10e is separated into a plurality of arc shaped segments at the positions where the constant orifices 10g are provided. Fig. 11 shows another modification of the foregoing first embodiment of the shock absorber according to the invention. In Fig. 11 , the piston assembly has a valve body formed with through holes 11a , orifices 11b , an inner groove 11c , an outer groove 11e , inner and outer lands having valve seating surfaces 11d and 11f . Constant orifices 11g are formed through the inner annular land for establishing fluid communication between the inner and outer grooves 11c and 11e . As seen, the inner groove 11c is separated into a plurality of arc shaped segments. On the other hand, the outer groove 11e is also separated into a plurality of arc shaped segments at the positions where the constant orifices 11g are provided. Fig. 12 shows the second embodiment of a shock absorber according to the present invention. The second embodiment has essentially the same construction to the aforementioned first embodiment except for the following particular points. Therefore, in order to avoid redundant discussion which may cause confusion, the common part is omitted from the drawings and discussion given herebelow. As shown in Fig. 12, the lower surface 221 of the piston body 2d oriented at the inside of the inner annular groove 206 is lower than the valve seating surface 209 of the outer annular land so that the valve seating surface 209 projects downwardly beyond the plane of the surface 221 . On the other hand, the valve seating surface 208 is above the level of the surface 221 . Namely, the downward distance from a reference plane a to the surfaces 221 , 208 and 209 are respectively A , B and C , and these three distances are so related that C > A > B. With the construction set forth above, the valve plate 2e is deformed at the section between the surfaces 221 and 208 and at the section between the surfaces 208 and 209 . Therefore, the valve plate 2e can be prestressed to increase the contact force in contacting with the associated seating surfaces to assure a liquid tight seal. This enables the variation rate of the absorption relative to variation of the piston speed to be increased. Furthermore, a pressure relieving point at the valve seating surface 208 can be raised to a higher level. This extends the possible variation range of the absorption. Fig. 13 shows the third embodiment of the shock absorber according to the present invention. The third embodiment of the shock absorber has essentially the identical construction to that of the first embodiment except for the construction of the constant orifices. As shown in Fig. 13, the constant orifices formed through the land between the grooves 206 and 207 in the former embodiments are replaced by a hole or groove 330 formed in the uppermost resilient member 331 of the valve plate 2e . The second layer resilient member 332 forms the bottom of the hole 330 to define paths bypassing the land so as to form constant orifice between the valve seating surface 208 and the upper surface of the second layer resilient member 332 . As shown in Fig. 14 , the holes 330 are arranged at regular intervals. Alternatively, the holes 330 in Fig. 14 can be replaced with the cut-out 333a illustrated in Fig. 15 . Figs. 16 and 17 shows the fourth embodiment of the shock absorber according to the present invention. In this embodiment, the retainer 400 for the valve spring 21 is formed with a radially extending flange 401 having a diameter slightly greater than the diameter of the valve plate 2e . The flange 401 is opposed to the valve plate 2e with a predetermined clearance D therebetween. The flange 401 serves as stopper flange for restricting the deformation of the valve plate 2e . The presence of the flange 401 makes it possible to form the valve member with resilient members having a lower coefficient of resilience. Therefore, the initial response of the valve member in causing deformation can be set higher. On the other hand, the flange 401 prevents the valve plate 2e from causing excessive deformation. By limiting the deformation range, left of the valve plate can be expanded. As shown in Fig. 18 , the flange 401 of the retainer 400 in the embodiment of Fig. 17 , can be replaced with a stopper plate 500 formed separately from the retainer 2h . The stopper plate 500 may produce substantially the same effect as that achieved by the embodiment of Fig. 17 . 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. For example, though the shown embodiments are illustrated in terms of the shock absorber with constant resilient force of valve spring, the valve spring may comprise a progressive spring to vary the spring force depending upon the piston stroke. In addition, the second and subsequent embodiments may be applicable not only for the piston assembly but also for the bottom valve assembly.

Claims: A valve construction for a hydraulic shock absorber disposed between relatively displaceable first and second members for absorbing energy of relative displacement between said first and second members, comprising: a valve body arranged in use to be disposed within a hollow cylindrical housing and to separate an internal space of said housing into first and second chambers; an orifice formed through said valve body for communication between said first and second chambers for permitting fluid flow for balancing fluid pressure between said first and second chambers; members made of leaf spring material acting as first flow restriction means associated with said orifice and having a predetermined relief pressure, providing a first, fixed flow impedance at pressure differences between said first and second chambers smaller than or equal to said relief pressure and providing a second, variable flow impedance at pressure differences between said first and second chambers greater than said relief pressure; members made of leaf spring material acting as second flow restriction means, associated with said orifice and arranged in series with said first flow restriction means, providing a third flow impedance variable depending upon the pressure difference between said first and second chambers; characterised in that: a resilient member common to said first and second flow restriction means is provided for varying the flow impedance in said first flow restriction means and the flow impedance in said second flow restriction means; a first groove is provided on one axial end surface of said valve body in communication with said orifice and a second groove is provided on said one axial end surface radially outside said first groove; and said first flow restriction means acts in the path of fluid flow between said first and second grooves, and said second flow restriction means acts in the path of fluid flow from said second groove to one of said first and second chambers. A valve construction as set forth in claim 1, wherein said valve body is movable according to movement of said first member relative to said second member at a speed corresponding to the speed of said first member, said first flow restriction means varies said second flow impedance as a function of the speed of said valve body, and said second flow restriction means varies said third flow impedance as a function of the speed of said valve body. A valve construction as set forth in claim 2, wherein said first flow restriction means produces an absorbing force for restricting relative motion between said first and second members, which varies at a rate proportional to the square of the speed of said valve body when flow impedance is maintained at said first flow impedance and varying at a rate proportional to the power of two over three of the speed of said valve body when flow impedance is said second flow impedance, and said second flow restriction varies the absorbing force for restricting relative movement between said first and second members, in proportion to the power of two over three of said speed of said valve body. A valve body as set forth in claim 2, wherein said first and second flow restriction means cooperate with each other for varying absorbing force to restrict relative movement between said first and second members in substantially linear fashion. A hydraulic shock absorber to be disposed between first and second members relatively movable to each other for absorbing an energy causing relative movement between said first and second members, comprising: a hollow cylindrical housing filled with a working fluid, said cylindrical housing being mechanically associated with said first member for axial movement therewith; a piston disposed within the internal space of said cylindrical housing for separating the internal space of said cylindrical housing into first and second working chambers, said piston being mechanically associated with said second member for axial movement therewith; an orifice formed through said piston for communication between said first and second chambers for permitting fluid flow for balancing fluid pressure between said first and second chambers; members made of leaf spring material acting as first flow restriction means associated with said orifice and having a predetermined relief pressure, providing a predetermined first, fixed flow impedance in response to a pressure difference between said first and second chambers smaller than or equal to said relief pressure and providing a second, variable flow impedance in response to a pressure difference between said first and second chambers greater than said relief pressure; members made of leaf spring material acting as second flow restriction means, associated with said orifice and arranged in series with said first flow restriction means, for providing a third, variable flow impedance variable depending upon the pressure difference between said first and second chamber; characterised in that: a resilient member common to said first and second flow restriction means is provided for varying said flow impedance in said first flow restriction means and said third flow impedance in said second flow restriction means; a first groove is provided on one axial end surface of said piston in communication with said orifice and, a second groove is provided on said one axial end surface, radially outside said first groove; and said first flow restriction means acts in the path of fluid flow between said first and second grooves, and said second flow restriction means acts in the path of fluid flow from said second groove to one of said first and second chambers. A shock absorber as set forth in claim 5, wherein said piston is movable according to movement of said second member relative to said first member at a speed corresponding to the speed of said second member, said first flow restriction means varies said second flow impedance as a function of the relative speed of said piston and said cylindrical housing, and said second flow restriction means varies said third flow impedance as a function of the relative speed of said piston and said cylindrical housing. A shock absorber as set forth in claim 6, wherein said first flow restriction means produces an absorbing force for restricting relative motion between said first and second members, which varies at a rate proportional to the square of the speed of said piston when flow impedance is maintained at said first flow impedance and varying at a rate proportional to the power of two over three of the speed of said piston when flow impedance is said second flow impedance, and said second flow restriction varies the absorbing force for restricting relative movement between said first and second members, in proportion to the power of two over three of said speed of said piston. A shock absorber as set forth in claim 6, wherein said first and second flow restriction means cooperate with each other for varying absorbing force to restrict relative movement between said first and second members in substantially linear fashion. A shock absorber as set forth in claim 5, which further comprises a resilient biasing means associated with said resilient member for exerting biasing force for the section of said resilient member at a position corresponding to the position of said first groove so as to assure said first flow impedance of said first flow restriction means at a pressure difference between said first and second chambers smaller than or equal to said predetermined relief pressure. A shock absorber as set forth in claim 9, wherein said resilient biasing means comprises a disc member having a diameter so that the outer circumferential edge corresponds substantially to the outer edge of said first groove, and a bias spring acting on said disc member for exerting biasing force to said resilient member therethrough. A shock absorber as set forth in claim 5, wherein said first and second grooves are constructed so that greater hydraulic force is exerted on the section of said resilient member at the position corresponding to said second groove than that on the section of said resilient member at the position corresponding to said first groove. A shock absorber as set forth in claim 5, wherein a first land defined between said first and second groove and having a first seating surface establishing sealing contact with said resilient member, and a second land extending along the edge of said second groove and having a second seating surface establishing sealing contact with said resilient member, said first seating surface being oriented at axially offset position with respect to said second seating surface. A shock absorber as set forth in claim 12, wherein said first flow restriction means includes a constant path area orifice defined through said first land and means for forming a gap between said resilient means and said first seating surface in response to the pressure difference greater than said relief pressure. A shock absorber as set forth in claim 12, wherein said first flow restriction means includes a constant path area orifice defined through said resilient means for permitting fluid flow from said first groove to said second groove over said first land, and means for forming a variable path area gap between said resilient means and said first seating surface in response to the pressure difference greater than said relief pressure. A shock absorber as set forth in claim 5, which further comprises a stopper means associated with said resilient member for limiting the deformation of said resilient member.

Inventors: SASAKI MITSUO C O ATSUGI MOTOR, YAMAOKA FUMIYUKI C O ATSUGI MO, SASAKI, MITSUO C/O ATSUGI MOTOR PARTS, YAMAOKA, FUMIYUKI C/O ATSUGI MOTOR PARTS
Applicants: ATSUGI UNISIA CORP, ATSUGI UNISIA CORPORATION
Application year: 1989
Main classification: F16F9
IPC codes: F16F9