Abstract:
The invention relates to a shock absorber loaded therearound with a compression coil spring so improved that a side force generated by the compression coil spring can be effectively alleviated by making both or any one of an upper sheet  13  mounted to an absorber rod  3  and a lower sheet  16  mounted on an absorber tube  2  so as to be loaded therebetween with the compression coil spring  17  free to rock relatively to each other in a predetermined direction or in any direction.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a suspension system for vehicle in the form of a shock absorber loaded therearound with a compression coil spring and more particularly to such suspension system for a vehicle adapted to alleviate a force generated by the compression coil spring and directed perpendicularly to a coil axis (referred to hereinafter as “side forces”). 
     2. Description of the Prior Art 
     Recently, high strength spring steel has been put to practical use and various improved working techniques such as special shot peening in order to obtain a light weight and compact product. Such efforts have increased design stress as well as pitch angle of a suspension coil spring. However, such improvement has often been accompanied with an apprehension that, even when the spring seat is displaced only in the coil axis (so-called parallel compression), a side force might be generated. Particularly when the shock absorber is loaded with such compression coil spring, such side force may often cause an absorber rod and an absorber tube to be jammed together and eventually may result not only in uncomfortable drive conditions, but also premature deterioration of the shock absorber. 
     To avoid such problems, various efforts have been made to alleviate the side force, for example, upper and/or lower sheets have been inclined or offcentered on the basis of a value obtained from various experiments or analytical research according to the finite element method. 
     SUMMARY OF THE INVENTION 
     This invention aims to solve the problem as both said experiments and said analytical research used to determine slants or eccentricities of the upper and lower sheets take to much time and do not necessarily give accurate values. 
     The invention is achieved by a suspension system for a vehicle which comprises a compression coil spring and a shock absorber, characterized by upper and lower sheet mounted on an absorber rod and on an absorber tube so as to be loaded with said compression coil spring disposed therebetween and being adapted for relatively rocking in a predetermined direction. With such arrangement, in response to a side force generated in the compression coil spring, both or any one of the upper and lower sheets tilt(s) in a predetermined direction or in any direction and consequently the compression coil spring can be smoothly curved and thereby avoid the absorber rod and the absorber tube being jammed together. If this manner, an adverse affection of the side force can be alleviated without demand for experiment as well as analysis to determine slant angles or eccentricities of the upper and lower sheets. The invention is further designed and arranged so that any one of said upper sheet and said lower sheet are or is adapted for relatively rocking around one axis of two axes which are substantially orthogonal to each other in order that the invention can be realiably realized. The invention is further arranged in that said one axis of two axes is or are defined by rollers, balls or substantially V-sectioned recesses and substantially V-sectioned projections. The invention is further arranged such that an angle by which said upper sheet and said lower sheet can rock relatively to each other is limited to a value less than a predetermined value. Appropriate experiments and analytical research according to the finite element method indicate that such arrangement is effective to avoid a side force which might abruptly increase when an excessively large load is applied to the compression coil spring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axially sectional view showing a first embodiment of the invention; 
     FIG. 2 is an exploded perspective view showing important parts thereof; 
     FIG. 3 is a view similar to FIG. 1, showing a second embodiment of the invention; 
     FIG. 4 is a view similar to FIG. 2, showing important parts of the second embodiment; 
     FIG. 5 is a view similar to FIG.  1 ,, showing at third embodiment of the invention; and 
     FIG. 6 is a graphic diagram plotting characteristics exhibited by the first embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Details of the invention will be more fully understood from the following description given hereunder in reference with the accompanying drawings. 
     FIGS. 1 and 2 show a first embodiment of the invention, in which a shock absorber is designated generally by reference numeral  1 . The shock absorber  1  comprises an absorber tube  2  mounted on a lower arm (not shown), an absorber rod  3  extending upward from said absorber tube  2 , a cushion rubber  5 , and a fixture  4  to which said absorber rod  3  is fixed with interposition of said cushion rubber  5 . Said fixture  4  is secured to a car body b by bolts a. 
     With interposition of a thrust bearing  6 , a base plate  7  underlies a lower surface of the fixture  4 , and there are arranged an intermediate plate  10  and an upper sheet  13  in this order below said base plate  7 . A compression coil spring  17  is provided between a lower sheet  16  fixed on the absorber tube  2  and said upper sheet  13  with interposition of lower and upper insulators  18 ,  19 , respectively. 
     Referring to FIG. 2, the base plate  7  is formed at its diametrically opposite peripheral zones, i.e., at its opposite peripheral zones on an axis X—X passing a center of this plate  7  with inverted V-shaped recesses  8 ,  8  each opened downward at an obtuse angle. The base plate  7  is provided an its lower surface in the vicinity of its periphery with a pair of rubber stoppers  9 ,  9  which are also diametrically opposite but on an axis being orthogonal to said axis X—X. The base plate  7  has its central boss  7   a  fitted into the thrust bearing  6  so that said base plate  7  is rotatable only around the absorber rod  3 . 
     The intermediate plate  10  is formed at its diametrically opposite peripheral zones, i.e., on an axis X—X passing a center of this plate  10  with inverted V-shaped projections  11 ,  11  each pointed upward at an acute angle. These projections  11  are adapted to be received by said recesses  8 ,  8 , respectively, so that the intermediate plate  10  is able to rock around the axis X—X by an angle limited by said stoppers  9 ,  9 . The intermediate plate  10  is further provided at its diametrically opposite peripheral zones, i.e., at its opposite peripheral zones on an axis Y—Y being orthogonal to said axis X—X with inverted V-shaped projections  12 ,  12  each pointed downward at an acute angle. 
     The upper sheet  13  is formed at its diametrically opposite peripheral zones, i.e., at its opposite peripheral zones on an axis Y—Y passing a center of this sheet  13  with V-shaped recesses  14 ,  14  each opened upward at an obtuse angle. These recesses  14 ,  14  are adapted to receive said projections  12 ,  12 , respectively, so that the upper sheet  13  can rock around said axis Y—Y relatively to the intermediate plate  10 . An angle by which the upper sheet  13  can rock relatively to the intermediate plate  10  is limited by rubber stoppers  15  formed integrally with insulators  19  on upper surface of the upper sheet  13  at its peripheral zones which are diametrically opposite on an axis being orthogonal to said axis Y—Y. Specifically, these rubber stoppers  15  are adapted to come in contact with the intermediate plate  10  and thereby to limit the angle by which the upper sheet  13  can rock around the axis Y—Y relatively to the intermediate plate  10 . 
     According to the embodiment as has been described above, the intermediate plate  10  is able to rock around the axis X—X relatively to the base plate  7  and the upper sheet  13  is able to rock around the axis Y—Y relatively to the intermediate plate  10 . Thus, the upper sheet  13  is able to rock relatively to the absorber rod  3  in any direction. 
     Advantageous effect offered by such construction will be discussed. Relative approach of the car body and the wheels causes the absorber rod  3  to retract into the absorber tube  2  and the compression coil spring  17  is correspondingly compressed so as to generate a side force. The upper sheet  13  tilts in the direction of said side force and absorbs this side force. It thereby effectively avoids or prevents the absorber rod  3  and the absorber tube  2  being jammed together. In this way, the shock absorber  1  can smoothly expand and contract. 
     With respect to a case in which the upper sheet is fixed as it has usually been in the prior art and a case in which the upper sheet is made free to rock in any direction as it is adopted by the above-described embodiment, the compression coil spring of the following specifications as indicated below has been analyzed by the inventor according to the finite element method. The analytical research has been conducted in the presence of the stopper and in the absence of the stopper. Result of the analysis indicated, as seen in FIG. 6, a fact that the side force is minimized when the upper sheet is free to rock and, even under a large load, the presence of the stopper is effective to prevent the side force from abruptly increasing. 
     SPECIFICATIONS: 
     Diameter of coil wire: 12.9 mm 
     Diameter of coil: 134 mm 
     Total number of turns: 5.38 
     Free height: 410.5 mm 
     Installation height: 205.0 mm 
     Maximum angle of rocking: 2.86° 
     According to the second embodiment of the invention as shown in FIGS. 3 and 4, an upper sheet  20  and a lower sheet  21  are initially positioned at angles corresponding to lead angles of upper and lower spring seats of a compression coil spring  17 . The upper sheet  20  is rotatably mounted on the absorber rod  3  with interposition of the thrust bearing  6 . 
     A base plate  22  is fixed to the absorber tube  2  and is formed with a pair of upwardly opened recesses  23 ,  23  diametrically opposed to each other on an axis X—X passing a center of this base plate  22 . An intermediate plate  24  overlying said base plate  22  is formed with a pair of downwardly opened recesses  25 ,  25  cooperating with said upwardly opened recesses  23 ,  23  formed by an intermediate plate  24 , respectively, so an to hold rollers  28 ,  28  therebetween. By this arrangement, the intermediate plate  24  is able to rock around the axis X—X. The intermediate plate  24  is additionally formed on its upper surface with a pair of upwardly opened recesses  26 ,  26  diametrically opposed to each other on an axis Y—Y which is orthogonal to said axis X—X. A lower sheet  21  overlying said intermediate plate  24  is formed on its lower surface see with a pair of downwardly opened recesses  27 ,  27  diametrically opposed to each other on an axis Y—Y cooperating with said upwardly opened recesses  26 ,  26  formed by the intermediate plate  24 , respectively, so as to hold rollers  29 ,  29  therebetween. By this arrangement, the lower sheet  21  is able to rock around the axis Y—Y relatively to the intermediate plate  24  and, therefore, able to rock in any direction relatively to the base plate  22  fixed to the absorber tube  2 . 
     Similarly to the first embodiment, even when a side force is generated as a compressive load which is applied to the compression coil spring  17 , such side force is absorbed by the lower sheet  21  rocking in the direction of such side force and there occurs no apprehension that the absorber tube  2  and the absorber rod  3  might be jammed together. 
     It should be understood that the base plate  22  and the lower sheet  21  are provided with respective pairs of rubber stoppers  30 , wherein the stoppers provided on the bass plate  22  are diametrically opposed to each other on the axis which is orthogonal to the axis on which the stoppers provided on the lower sheet  21  are diametrically opposed to each other. 
     According to the third embodiment of the invention as shown in FIG. 5, rollers  34 ,  34  spaced from each other on an axis X—X are held between a base plate  31  rotatably supported around the absorber rod  3  with interposition of the thrust bearing  6  and a support plate  32  which is integral with an upper sheet  33  in the same manner as in the previously described second embodiment. Similarly, rollers  37 ,  37  spaced from each other on an axis Y—Y are held between a base plate  35  fixed to the absorber tube  2  and a lower sheet  36 . With a consequence, rocking of the upper sheet  33  around the axis X—X is combined with rocking of the lower sheet  36  around the axis Y—Y, allowing these upper and lower sheets  33  and  36  to rock in any direction so that a side force generated by the compression coil spring  17  may be effectively absorbed by the shock absorber. 
     The third embodiment is similar to the second embodiment in that the angles by which the upper sheet  33  and the lower sheet  36  can rock are limited by stoppers  38  provided on the support plate  32  and the lower sheet  36 . 
     In the second and third embodiments, the rollers  28 ,  29 ,  34 ,  37  may be replaced by balls. 
     According to all the embodiments as have been described above, the upper and lower sheets are made free to rock relatively to each other in any direction by the arrangement such that these sheets are free to rock relatively to each other around the respective axes which are orthogonal to each other. However, it is also possible to determine the direction of the side force applied to the compression coil spring by an appropriate experiment or analytical research according to the finite element method so that the upper and lower sheets may be free to rock relatively to each other only in the direction thus determined. Such alternative arrangement will advantageously simplify the structure according to the previous embodiments without deterioration of the desired effect because said relative rocking of those sheets can be achieved around a single axis.