Abstract:
A suspension arm includes a shaft having a free end extending from an end of the suspension arm and a base end embedded within the said end of the suspension arm, and this shaft is configured to be press fitted into a tubular member of a compliance bush assembly. An opening is formed in the said end of the suspension arm that allows an anvil ( 41 ) to be inserted therein to engage the base end of the shaft so that the force of a press fitting process is prevented from affecting the remaining part of the suspension arm. Thus, the press fitting process can be facilitated because very little effort is required to place the suspension arm ready for a press fitting process, and the fixture for holding the suspension arm during a press fitting process can be simplified.

Description:
TECHNICAL FIELD 
   The present invention relates to a suspension arm having a shaft projecting therefrom and a method for press fitting the shaft into a bore of another member such as a tubular member of a compliance bush assembly. 
   BACKGROUND OF THE INVENTION 
   A vehicle wheel suspension system is interposed between a vehicle body and a corresponding wheel for the purpose of ensuring a favorable ride quality and a motion stability of the vehicle, and typically comprises a suspension arm pivotally attached to the vehicle body for a vertical swinging movement, a knuckle that rotatably supports a wheel and is pivotally connected to a free end of the suspension arm, a coil spring interposed between the knuckle and a suitable part of the vehicle body, and a shock absorber typically coaxially received in the coil spring and interposed between the knuckle and vehicle body. 
   The suspension arm is typically given with a highly complex shape, and comprises a shaft or pin projecting from an end of the suspension arm which is press fitted into a tubular member of a compliance bush mounted on a suitable part of the vehicle body. Refer to Japanese patent laid open publication No. 9-002035, for instance. 
   Conventionally, when press fitting the shaft or pin into a tubular member, the suspension arm is clamped to a support base, and the tubular member is forced onto the shaft or pin. As the suspension arm has a complex shape, there is some difficulty in holding the suspension arm in a stable manner. If the clamping force is excessively increased in an effort to firmly hold the suspension arm, the clamping force could deform the suspension arm. Also, the force of the press fitting may also cause the deformation of the suspension arm depending on the way the suspension arm is held in position. 
   Such problems could be overcome by suitably designing the clamping arrangement, but increasing the complexity of the clamping arrangement is undesirable because it means in an increase in the cost of the assembling fixture, and a reduction in the work efficiency of the assembling process. 
   BRIEF SUMMARY OF THE INVENTION 
   In view of such problems of the prior art, a primary object of the present invention is to provide a suspension arm of a wheel suspension system that can be favorably supported when press fitting a shaft or pin projecting therefrom into a bore of another member. 
   A second object of the present invention is to provide a suspension arm that does not require a complex support base when press fitting a shaft or pin projecting therefrom into a bore of another member. 
   According to the present invention, such objects can be accomplished by providing a suspension arm including a shaft having a free end extending from an end of the suspension arm and a base end embedded within the said end of the suspension arm, the shaft being configured to be press fitted into a bore of another member, wherein an opening is formed in the said end of the suspension arm that allows access to a part adjacent to the base end of the shaft. 
   Because the opening allows the base end of the shaft to be supported, either directly or indirectly, against the force of the press fitting process, the remaining part of the suspension arm is not subjected to the force of the press fitting process. As the suspension arm is not required to be firmly clamped against the force of the press fitting process, the suspension arm is prevented from being deformed by the clamping force remaining part is not required. Also, as the suspension arm can be placed ready for the press fitting process simply by inserting an anvil into the opening, the work efficiency of the press fitting process can be improved as opposed to the case where a complex clamping fixture is used for the press fitting process. 
   Preferably, the opening allows direct access for an anvil to engage a base end surface of the base end of the shaft. No part of the suspension arm itself is thereby subjected to the force of the press fitting process, and the suspension arm can be supported in a both simple and stable manner. 
   Typically, the suspension arm comprises an upper plate and a lower plate that are each stamp formed to a prescribed shape and welded to each other to at least partly define a closed cross section, and the shaft is welded to both the upper and lower plates. In such a case, the opening may be formed in at least one of the upper and lower plates. 
   According to a certain embodiment of the present invention, the opening is formed in each of the upper and lower plates in a mutually registered relationship such that an end surface of the shaft is recessed from corresponding edges of the openings, and the edges of the upper and lower plates may be supported by an anvil inserted into the opening. Because the reaction force of the anvil is applied to the base end of the shaft via a very short sections of the upper and lower plates, most part of the suspension arm is protected from the force of the press fitting process. 
   According to another embodiment of the present invention, the opening is defined by a recess formed in at least one of the upper and lower plates, and material of the at least one of the upper and lower plates is interposed between the recess and an end surface of the shaft. In this embodiment also, most part of the suspension arm is favorably protected from the force of the press fitting process. 
   Typically, the other member comprises a tubular member of a compliance bush assembly, and the suspension arm comprises a lower arm of a strut wheel suspension system. 
   The present invention also provides a method for press fitting the shaft of the suspension arm according to claim  1  into a bore of another member, the method comprising: inserting an anvil projecting from a support base into the opening, and press fitting the shaft into the bore by pushing the other member onto the shaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Now the present invention is described in the following with reference to the appended drawings, in which: 
       FIG. 1  is a fragmentary perspective view showing a strut type vehicle wheel suspension system for a left front wheel using a suspension arm (lower arm) embodying the present invention; 
       FIG. 2  is an exploded perspective view of the lower arm and an associated compliance bush assembly; 
       FIG. 3  is a bottom view of the lower arm; 
       FIG. 4  is a sectional view taken along line IV-IV of  FIG. 2 ; 
       FIG. 5  is a sectional view taken along line V-V of  FIG. 3 ; 
       FIG. 6  is a perspective view showing how an anvil is inserted in the opening of the lower arm; 
       FIG. 7  is a view similar to  FIG. 5  showing a second embodiment of the present invention; and 
       FIG. 8  is a view similar to  FIG. 5  showing a third embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a strut type vehicle wheel suspension system for a left front wheel using a suspension arm embodying the present invention. This wheel suspension system comprises a lower (suspension) arm  2  having a base end pivotally connected to a vehicle body  100  for a vertical swinging movement, a knuckle  4  pivotally connected to a free end of the lower arm  2  via a ball joint  3 , a shock absorber  5  interposed between an upper part of the knuckle  4  and the vehicle body  100 , a suspension spring  6  coaxially disposed around the shock absorber  5  and likewise interposed between the knuckle  4  and vehicle body  100 , and a stabilizer  7  extending laterally across the vehicle body and having one end connected to the knuckle  4  for the front left wheel and another end connected to the knuckle for the front right wheel not shown in the drawing. 
   In this wheel suspension system  1 , when an impact from the road surface is applied to the wheel, the knuckle  4  pivotally supported by the lower arm  2  moves vertically, and is resiliently supported by the suspension spring  6 . The shock absorber  5  controls the undesired oscillatory movement of the vehicle body  100  which is otherwise caused by the suspension spring  6  and associated mass. 
     FIG. 2  is an exploded perspective view of the lower arm  2  and an associated compliance bush assembly  30 . The base end of the lower arm  2  is bifurcated into a front leg  8  and a rear leg  9 . The front leg  8  extends substantially linearly and along the lateral direction of the vehicle body  100  from the free end of the lower arm  2  whereas the rear leg  9  extends obliquely toward the inward and rearward of the vehicle body  100 . As shown in  FIGS. 3 to 5 , the lower arm  2  is essentially formed by welding an upper plate  10  and a lower plate  11  to each other, and the upper and lower plates  10  and  11  are each formed by a stamp formed steel sheet so that a closed cross section is defined in most part of the lower arm  2  except for end portions as will be described hereinafter. 
   The free end  12  of the lower arm  2  is formed solely by the upper plate  10 , and is formed with a through hole  13  extending in a vertical direction. The through hole  13  is typically formed by burring, and is configured to receive the ball joint  3 . 
   To the base end of the front leg  8  of the lower arm  2  is welded a collar  14  defining a bore extending in a fore-and-aft direction. The bore of the collar  14  receives a pin (not shown in the drawings) fixed to the vehicle body via a rubber bush. 
   To the base end of the rear leg  9  of the lower arm  2  is welded an end plate  17  extending perpendicularly to the fore-and-aft direction in such a manner that an opening defined by the upper plate  10  and lower plate  11  is closed by the end plate  17 . The end plate  17  is formed with a through hole  16  which is coaxial with the bore of the collar  14 . A shaft  18  having a circular cross section is closely passed into the through hole  16 , and the base end of the shaft  18  which is received within the space defined between the upper plate  10  and lower plate  11  is welded to the upper plate  10  and lower plate  11 . More specifically, the upper plate and lower plate are each provided with a track-shaped opening that exposes a surface of the shaft  18 , and the edge of the opening is welded to the shaft  18 . Thus, the shaft  18  includes a free end that protrudes from the end plate  17 , and a base end received within the lower arm  2 . 
   A part of the lower plate  11  corresponding to the base or inner end of the shaft  18  is provided with a D-shaped opening  19  which exposes the inner or base end of the shaft  18 . In particular, the flat edge of the D-shaped opening  19  is substantially aligned with the inner end surface  18   b  of the shaft  18  or exposes a small length of the inner end of the shaft, and has a certain width and length that provides access to the internal part of the lower arm adjacent to the inner end of the shaft  18 . The end surface  18   b  of the shaft  18  defines a plane perpendicular to the axial direction of the shaft  18 . 
   The compliance bush assembly  30  comprises a centrally located metallic tubular member  30 , a rubber member  32  surrounding the tubular member  30  in a fixedly attached manner and a bracket  32  surrounding the rubber member  32  in a fixedly attached manner and configured to be fastened to the vehicle body  100 . 
   The shaft  18  protruding from the base end of the rear leg  9  of the lower arm  2  is press fitted into the metallic tubular member  31  of the compliance bush assembly  30 .  FIG. 6  illustrates how the shaft  18  is press fitted into the tubular member  31 . The lower arm  2  is turned on its side in preparation for the press fitting operation, as shown, and the arm is supported by a pair of support blocks  42 ,  42  and by a support base  40  that includes an anvil  41  that extends substantially in the shape of a bird beak, and is provided with a flat upper surface  41   a . The anvil  41  is narrow enough to be fitted into the opening  19 . When the anvil  41  is introduced into the opening  19 , the upper surface  41   a  of the anvil  41  can engage the end surface  18   b  of the shaft  18 . A remaining part of the support base  40  may lightly engage a suitable part of the lower arm  2  so that the base end surface  18   b  of the shaft  18  may sit on the upper surface  41   a  of the anvil  41  in a stable manner. 
   The tubular member  31  of the compliance bush assembly  30  is then pushed onto the shaft  18  by using a tool designed for such a purpose until the shaft  18  is forced into the tubular member  31  by a prescribed distance. The above components are configured and dimensioned such that the forcing of the tubular member  31  on to the shaft  18  will create an interference fit therebetween. The pressure applied to the tubular member  31  at the time of press fitting is transmitted to the shaft  18 , and this pressure is supported by the anvil  41 . Accordingly, due to the support provided by the anvil  41  at the time of press fitting, a major portion of the pressure applied to the tubular member  31  is absorbed and distributed by the support member  40 , and therefore, this absorbed pressure is not transferred to the remaining part of the lower arm situated below the anvil  41 . Therefore, the remaining part of the lower arm  2  is not subjected to any significant force. Therefore, the lower arm  2  is protected from any undue stress that could be otherwise caused by the force of the press fitting process or the clamping pressure for keeping the lower arm  2  stationary against the force of the press fitting process. Also, no sturdy support structure for firmly supporting the lower arm  2  having a highly complex structure is required. 
     FIG. 7  shows a second embodiment of the present invention. As this embodiment differs from the first embodiment only in the arrangement for supporting the lower arm  2  at the time of the press fitting process, the parts of the second embodiment corresponding to those of the first embodiment are denoted with like numerals without repeating the description of such parts. 
   In this embodiment the opening is defined by a recess  22  formed by stamp forming the lower plate  11  in such a manner that a part of the material  22   a  of the lower plate  11  is interposed between the recess  22  and the end surface  18   a  of the shaft  18 . In this embodiment also, the force required to support the lower arm  2  against the force of the press fitting process can be essentially directly supported at the base end of the shaft  18  so that the remaining part of the lower arm is free from any stress at the time of the press fitting process. 
     FIG. 8  shows a third embodiment of the present invention. As this embodiment differs from the first embodiment only in the arrangement for supporting the lower arm  2  at the time of the press fitting process, the parts of the third embodiment corresponding to those of the first embodiment are denoted with like numerals without repeating the description of such parts. 
   In this embodiment the opening  19 ,  20  is formed in each of the lower plate  10  and the upper plate  11  in a mutually registered relationship. The edge of each of these openings  19 ,  20  adjacent to the base end surface of the shaft  18  is defined by a linear or straight section perpendicular to the axial line of the shaft  18 . These linear sections of the openings are slightly offset from the end surface of the shaft  18  so that the anvil  41  is supported by these edges, instead of the end surface of the shaft  18 . Because the force required to support the lower arm against the force of the press fitting process is supported by the parts of the upper and lower plates defining the linear sections which are welded to the shaft in the immediate vicinity, the remaining part of the lower arm is free from any stress at the time of the press fitting process, and the advantages similar to those of the first and second embodiments can be obtained. 
   Although the present invention has been described in terms of preferred embodiments thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims. 
   The contents of the original Japanese patent application on which the Paris Convention priority claim is made for the present application and the contents of any related prior art mentioned in the disclosure are incorporated in this application by reference.