Abstract:
A coil spring mounting structure for a suspension strut includes a spring bracket secured to a shock-absorber. The spring bracket has a coupling hole, which is configured to receive a screw threaded end of a coil spring. Nuts are screw-coupled to the screw threads of the coil spring, thereby fixing the coil spring to the spring bracket.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a suspension strut for a car in which a coil spring is integrated and assembled with a shock-absorber. 
   2. Background of the Related Art 
     FIG. 1  is a perspective view showing a conventional car suspension strut (laid-opened Utility Model publication No. 2000-16340). 
   As shown in  FIG. 1 , a car suspension strut  100  consists of a shock-absorber  110  for generating a damping force by reciprocating a valve in the interior of the shock-absorber within which oil is filled, and a coil spring  140 ′ located in the outside of the shock-absorber  110  in order to restore a compressed shock-absorber to the former state. 
   The shock-absorber  110  consists of an external case  111  for receiving the valve (not shown) and a rod  120  connected to the valve (not shown). 
   To connect a knuckle and a strut, a knuckle bracket  112  is mounted on the external case  111 . A lower spring seat  150  is fixed to the external case  111  above the knuckle bracket  112 . According to the fixed location of the strut, instead of the knuckle bracket  112 , a cylindrical shaped bracket may be mounted on the lower portion of the external case  111 . 
   A lower spring pad  152  consisting of rubber material rests above the lower spring seat  150  and a coil spring  140 ′ is mounted above the lower spring pad  152 . 
   Also, an upper spring pad  162  is mounted above the coil spring  140  and then an upper spring seat  160  is inserted onto the rod  120  of the shock-absorber  110 . 
   An insulator  130  is mounted on the upper spring seat  160  in such a manner that the upper spring seat  160  and the insulator  130  are fixed to the rod  120  of the shock-absorber by a nut  125 . When the strut is installed in the front of a car, a bearing (not shown) may be installed in the inside of the insulator  130  so that the strut is rotated to a car body upon steering. 
   A bolt  132 , mounted on the insulator  130 , is a member fixing the strut  100  to the car body. 
   That is, the conventional suspension strut for the car has adopted a structure in which the lower spring seat  150  is fixed to the external case  111  of the shock-absorber through a welding and then the coil spring  140 ′ is installed in the lower spring seat  150 . Accordingly, a portion (hereinafter, referred to as a bottom part) at which the coil spring  140 ′ is contacted to the lower spring seat  150  is necessary. 
   The bottom part is commonly set to 0.75 turns on the basis of the number of winding turns of the coil spring  140 ′. In the case that a lower spring pad  152  is installed between the coil spring  140 ′ and the lower spring seat  150 , the bottom part is likewise included in the coil spring  140 ′. 
   Similarly, the coil spring  140  mounted on the conventional car suspension strut has a structure in which the coil spring includes a top part that contacts with the upper spring seat  160 . 
   In the above-described conventional art, there was a problem in that the setting of the bottom part having 0.75 turns of a coil spring is required and a material cost of the coil spring is high since the bottom part does not provide a spring function. 
   Further, to avoid the coil being located at the region neighboring the bottom part from being contacted with the spring seat to generate a stress concentration when the coil spring is subject to an overload, a lower spring pad or an upper spring pad may be adopted. However, another problem is that the spring pad that receives the bottom part of the coil spring is enlarged in size, thereby increasing the manufacturing cost. 
   SUMMARY OF THE INVENTION 
   An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
   Accordingly, one object of the present invention is to solve the foregoing problems by providing a coil spring mounting structure of a suspension strut that minimizes a bottom part of a coil spring, thereby reducing the material cost of the coil spring and simplifying a structure of a bushing mounted between the coil spring and the shock-absorber. 
   To achieve the above object, a coil spring mounting structure for a suspension strut of the present invention comprises a spring bracket fixed to a shock-absorber and having a coupling hole; a coil spring inserted to the coupling hole, having screw threads formed on an end thereof; and nuts screw-coupled with the screw threads for fixing the coil spring to the spring bracket. 
   Also, the coil spring mounting structure for the suspension strut of the present invention further comprises a second bracket fixed to the shock-absorber; a clamp located on the surface of the second bracket; bolts and nuts for fixing the second bracket and the clamp; and a bushing inserted between the clamp and the coil spring, the bushing having a through hole. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
       FIG. 1  is a perspective view showing a conventional strut; 
       FIG. 2  is a perspective view showing a mounting structure of a coil spring in accordance with the present invention; 
       FIG. 3  is a sectional view taken along line  3 — 3  of  FIG. 2 ; 
       FIG. 4  is a sectional view taken along line  4 — 4  of  FIG. 2 ; and 
       FIG. 5  is a perspective view of a bush. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Now, a preferred embodiment of the present invention will be described in reference to the accompanying  FIGS. 2  to  5 . Elements similar to those used in the conventional art are omitted in the figures. 
   Referring to  FIG. 2 , a spring bracket  220  and a second bracket  210  are fixed to an external case  111  of a shock-absorber  110  through a welding. 
   A coupling hole for receiving a screw thread  141  of a coil spring (will be described hereinafter)  140  is formed in the spring bracket  220 . 
   The screw thread portion  141  formed on the coil spring  140  is inserted into the coupling hole of the spring bracket  220  and then fixes the coil spring  140  and the spring bracket  220  through nuts  230 ,  230 ′. 
   A second bracket  210  neighboring the spring bracket  220  is fixed to the shock-absorber  110 . The second bracket  210  has a U-shaped section. Preferably, the second bracket  210  is mounted so that the longitudinal direction thereof is the same as the longitudinal direction of the shock-absorber. 
   A clamp  300  is located on the surface of the second bracket  210 , and the clamp  300  and the second bracket  210  are fixed by bolts  310  and nuts  330 . 
   A bushing  400  is inserted between the coil spring  140  and the clamp  300 . 
   As shown in  FIG. 5 , the bushing  400  has projection jaws  410  formed on both ends of a main body in which a through hole is formed. A slit  420  is formed between the through hole and a bottom of the bushing. 
   The second bracket  210  and the spring bracket  220  of the present invention may be provided in an external case of the shock-absorber and also may be provided in a rod located above the strut. That is, the brackets can be applied to a lower mounting structure as well as an upper mounting structure of the coil spring of the present invention. 
   Since the remaining structures of the car suspension strut of the present invention, except for the above-described parts referred to in  FIGS. 2  to  5  are the same as those of the conventional art shown in  FIG. 1 , the description of parts such as a knuckle bracket, an insulator  130 , etc., is omitted. 
   Now, an operation of the present invention will be described. 
   First, the nut  230  is screw-coupled with the screw portion  141  formed on the end of the coil spring  140 , and the remaining portion of the screw portion  141  is inserted into the coupling hole of the spring bracket  220 . Another nut  230 ′ is screw-coupled with the end of the coil spring  140 . The nut  230 ′ is tightened with a defined coupling torque to fix the coil spring  140  to the spring bracket  220 . 
   Because the coil spring  140  is fixed to the spring bracket  220  by nuts  230  and  230 ′, it is not required that the 0.75 turns of the bottom part are formed as in the conventional art. That is, most of the coils except for the screw portion  141  of the coil spring  140  provide an effective number of turns. 
   In the case of controlling a location at which the coil spring  140  is mounted on the spring bracket  220  by tightening nuts  230  and  230 ′, the effective number of turns of the coil spring  140 ′ is changed and accordingly a spring coefficient is also changed. That is, because the spring coefficient is changed when the locations of nuts  230  and  230 ′ screw-coupled on the coil spring  140 ′ are changed, it is possible that a characteristic of the device of the coil spring  140 ′ is finely tuned. 
   The coil spring  140  fixed to the shock-absorber may be mounted through the bushing  400 . That is, after widening the slit  420  in the bushing  400 , the coil spring  140  is inserted into the slit and then the clamp  300  is covered thereon. The clamp  300  and the second bracket  210  of the shock-absorber are fixed by bolts  310  and nuts  330 . The projection jaws  410  formed on the bushing  400  prevent the bushing  400  from being separated from the clamp  300 . 
   Because the bushing  400  is made of rubber material, when the load applied to the coil spring  140  is transferred to the shock-absorber, the bushing performs a vibration-proof function. 
   As the present invention adopts a structure in which a screw is formed on an end of a coil spring and the screw is fixed to a spring bracket by nuts, a material loss due to the bottom part as in the conventional art does not occur. That is, because the portion, which does not act as effective number of turns in the portion at which the coil spring and the spring bracket are coupled to each other, is minimized, the material cost and weight of the bottom part corresponding to the 0.75 number of turns of the coil spring is decreased. 
   Also, in accordance with the present invention, because the location of the portion at which the end of the coil spring and the spring bracket are coupled is controlled by nuts, it is possible that the spring coefficient of the coil spring is controlled finely. 
   Also, because the present invention adopts the structure in which the coil spring is fixed to the shock-absorber using the clamp and bushing, a large lower spring pad or a large upper spring pad as in the conventional art is not required, thereby reducing the material cost. 
   Further, in accordance with the present invention, the projection jaws and the slit are formed in the bushing, thereby facilitating an assembly of the bushing and preventing the bushing from being separated form the clamp. 
   While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.