Abstract:
A shock absorber comprising: a cylinder body has a piston rod movably received therein, a shock absorbing spring is mounted to the cylinder body and biased between the piston rod and the cylinder body, a buffering spring is mounted to an end of the piston rod in the cylinder body and biased between the inner edge of the cylinder body and the end of the piston rod.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a shock absorber, and more particularly to a shock absorber having a shock absorbing spring and a buffering spring, which is able to provide a perfect shock absorbing effect. 
     2. Description of the Prior Arts 
     Referring to FIG. 1, a conventional shock absorber for a bicycle (including scooter, motorcycle and the like) is shown to comprise a cylinder body  10 , a piston rod  11  extending into the cylinder body  10 , and a spring  13  associated operably with the cylinder body  10  and the piston rod  11 . The piston rod  11  includes a flange  111  and a cushion  112  defined at an end, the cylinder body  10  includes an adjustable stopping member  101  defined at a corresponding end, the piston rod  11  is movably positioned there by virtue of a limiter  12 . Furthermore, a spring  13  is biased between the flange  111  of the piston rod  11  and the stopping member  101  of the cylinder body  10 , such that the spring  13  is able to absorb the relative stress between the piston rod  11  and the cylinder body  10 , and a deformation effect of the spring  13  is eliminated by the relative displacement between the piston rod  11  and the cylinder body  10 . The conventional shock absorber described above has been commonly used, however, it has some disadvantages in operation as follows: 
     First, the spring  13  of the conventional shock absorber is normally in high elasticity coefficient in order to achieve an effective cushioning effect (the shock absorbing system is too stiff), however, the high elasticity coefficient spring is difficult to be deformed and compressed in case that the piston rod  11  and the cylinder body  10  relatively move under a pressure, moreover, it even won&#39;t be deformed in case of a minor pressure (no cushioning effect), resulting in a disadvantage of the shock absorbing effect. 
     Second, in order to keep the shock absorbing effect continuous operation, the manufacturers usually employ shock absorbing spring with high elasticity coefficient, however, the restoring force and recovering speed of the spring  13  are great, which will lead to self-percussion when the spring  13  reaches the elasticity ultimate (return to the initial position), also cause collisions between the spring  13  and the piston rod  11 , cylinder body  10  accompanied by noise. 
     Third, it should be pointed that the manufacturers usually don&#39;t have the shock absorber equipped with a buffering device in order to save cost, the collisions during the restoring course of the spring will not be buffered, thereby, it not only impairs the shock absorbing effect but also results in an uncomfortable riding. 
     Targeting at solving the above disadvantages, an effective hydraulic buffer was invented, however, the line piping, leak-proof element and liquid oil are very expensive, furthermore, the line piping should be thickened and no gas hole allowed (material cost is high), a plurality of sealing members should be employed, all these factors increased the production cost of the hydraulic buffer. 
     The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional shock absorber. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a shock absorber comprising: a piston rod movably received in a cylinder body, a shock absorbing spring is mounted to the cylinder body and biased therebetween, a buffering spring is mounted to an end of the piston rod in the cylinder body and biased between the inner edge of the cylinder body and the end of the piston rod. 
     The primary objective of the present invention is to provide a shock absorber having an ability of easing off the longitudinal expansion movement and compression movement of the shock absorbing spring so as to provide a smooth cushioning effect. 
     Another objective of the present invention is to provide a low cost shock absorber having a smooth cushioning effect by taking advantage of the relative motion of the two low cost springs. 
     A further objective of the present invention is to provide a shock absorber with comfortable cushioning effect, in which, the buffering spring eases off the longitudinal expansion movement and compression movement of the shock absorbing spring, preventing overly longitudinal expansion and self-percussion during the restoring course of the absorb shocking spring. 
     A further objective of the present invention is to provide a shock absorber, which is sensible to a slight shock by virtue of the restoring power of the buffering spring effectively reducing the compressing elasticity coefficient of the shock absorbing spring. 
    
    
     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which shows, for purpose of illustrations only, the preferred embodiment in accordance with the present invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a conventional shock absorber; 
     FIG. 2 is an exploded view of a shock absorber according to the resent invention; 
     FIG. 3 is a cross sectional view of showing in a state of equilibrium of a shock absorber according to the present invention; 
     FIG. 4 is another cross sectional view of showing a shock absorber according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 2-3, in which, a shock absorber of the present invention consists of a piston rod  20 , a cylinder body  30 , a shock-absorbing spring  40  and a buffering spring  50 . 
     A coupling portion  21  and a flange  22  are formed in turn at a first end of a rod portion  23  of the piston rod  20  respectively. A second end of the rod portion  23  is formed with a threaded portion  24 . The piston rod  20  includes a cushion  25  mounted to the rod portion  23 . A nut  26  and a washer  27  are engaged with the threaded portion  24  of the rod portion  23 , the washer  27  has a flange portion  28  formed thereof. 
     The cylinder body  30  is a hollow pipe formed with threads  35  on the outer surface, including a cover  31  threadedly engaged with a first end thereof, the cover  31  is interiorly set with a limiting member  32 , the limiting member  32  has a passage  33  interiorly formed therethrough which is corresponding to the rod portion  23  of the piston rod  20 , the passage  33  employed to ensure the rod portion  23  of the piston rod  20  sliding steadily in the cylinder body  30 , moreover, limiting the washer  27  of the piston rod  20  to slide in the cylinder body  30  without sliding out. A flange  34  is formed on the limiting member  32  where corresponding to the bottom edge of the inner cylinder body  30 , the flange  34  is formed about the periphery of the passage  33 . The cylinder body  30  has a coupling portion  37  formed at an end corresponding to the cover  31 . Furthermore, a stopping member  36  is screwed with threads  35  of the cylinder body  30  corresponding to the coupling portion  37 . 
     The shock absorbing spring  40 , having a predetermined elasticity coefficient, is movably mounted to the cylinder body  30  with a first end abutting against the flange  22  of the piston rod  20  and a second end abutting against the stopping member  36  of the cylinder body  30 . 
     The buffering spring  50 , having a predetermined elasticity coefficient relatively minor than that of the shock absorbing spring  40 , is movably mounted to the rod portion  23  of the piston rod  20  with a first end abutting against the limiting member  32  of the cylinder body  30  and a second end abutting against the flange portion  28  of the washer  27  of the piston rod  20 , the inner edge of the first end of the buffering spring  50  is mounted to the flange  34  by annularly abutting against the periphery thereof while the inner edge of the second end of the same abuts against the periphery of the rod portion  23  and positioned there. 
     Referring now to FIGS. 3-4, wherein, in an unloaded condition or in case of no pressure (as shown in FIG.  3 ), the shock absorbing spring  40  will outwardly push the flange  22  of the piston rod  20  and the stopping member  36  of the cylinder body  30  so that the piston rod  20  and the cylinder body  30  are forced to extend outward, the expanding force of the shock absorbing spring  40  enables the buffering spring  50  to be compressed longitudinally and store a restoring force, thereby, at this moment, the buffering spring  50  has a greatest restoring force while the shock-absorbing spring  40  in a status of most easy to be compressed (in an ever relaxed status). 
     Referring to FIG. 4, wherein, in case of a shock or under pressure, the shock absorbing spring  40  is compressed to force the piston rod  20  and the cylinder body  30  to draw back, although the shock is not great enough to cause a complete compression of the shock absorbing spring  40 , due to the restoring force of the buffering spring  50  is simultaneously released, the buffering spring  50  will cooperate with shocking power to compress the shock absorbing spring  40 , as a result, the shock absorber of the present invention will have a smooth reaction at the beginning of a shock (kind of comfortable). In an initial course of a shock, the buffering spring  50  will help to compress the shock absorbing spring  40  with its greatest restoring force, after the compression of the shock absorbing spring  40 , the restoring force of it is relatively strengthened while that of the buffering spring  50  is reduced, thereby the shock-absorber of the present invention is able to provide a comfortable shock absorbing effect and which is up to an ergonomical requirements. 
     When the shock absorber of the present invention starts to recover, due to the restoring force of the shock absorbing spring  40  is ever greatest while that of the buffering spring  50  is relatively weak, the shock absorbing spring  40  will expand rapidly and lead to a simultaneous extending movement of the piston rod  20  and cylinder body  30 . With the extending movement of the shock absorbing spring  40 , which causes a longitudinal compression of the buffering spring  50  to store energy. The extending movement of the shock absorbing spring  40 , shortly before it corning to end, will lead to an inward compression movement of the buffering spring  50 . At this moment, the buffering spring  50  start to gain and gradually store a restoring force which is adverse to that of the shock absorbing spring  40 , thereby, the buffering spring  50  will absorb an overly expanding force of the shock absorbing  40  (the compressing restoring force of the buffering spring  50  is adverse to that of the shock absorbing spring  40 ), such that prevent an over-rapid longitudinal expansion movement of the shock absorbing spring  40  and collisions on other parts (reaching the end), furthermore, buffering the strikes generated from an over-rapid longitudinal expansion movement at the end of a longitudinal compression movement. 
     While we have shown and described various embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.