Abstract:
An automotive suspension assembly providing a jounce stop arrangement. The elastic bumper is placed into a flexible cup. The flexible cup connects to the surface of the cylinder of a strut assembly or other assembly. Upon application of a force upon the elastic bumper, the elastic bumper collapses into the flexible cup. The flexible cup also expands in reaction to the force upon the elastic bumper. The assembly provides dual system of absorbing the energy from an impact in the combination of collapsing and expanding of the elastic bumper and flexible cup.

Description:
This invention relates to a jounce bumper for motor vehicle suspensions systems either in the strut assemblies or other locations. 
     BACKGROUND OF INVENTION 
     Microcellular urethane bumpers are used in vehicle suspensions to absorb energy during jounce and to act as a supplemental spring. These could be mounted on a strut assembly, as own in the U.S. Pat. No. 5,487,535, where the bumper surrounds the piston rod of the strut. This bumper prevents the cylinder of the strut assembly from impacting heavily the mounting assembly. The bumpers could also be mounted in other locations, as shown in U.S. Pat. No. 5,725,203, where the bumper is free standing to prevent a control arm of the suspension from impacting with the vehicle frame. 
     Bumpers can be mounted in a free state or within a rigid cup. U.S. Pat. No. 6,158,726 discloses a bumper with the use of a rigid cup attached. The rigid cup acts to attach the bumper to the vehicle or the strut and limits the bumper distortion, thereby increasing its rate. The force necessary to compress the bumper increases as the bumper is compressed and the bumper absorbs energy as it is compressing. As the bumper is compressed, the resistance to compression increases to the point where the bumper acts as a solid, and transfers the remaining energy from the impact to the vehicle. The use of a rigid cup or another constraint limits the bulging of the bumper, thereby reducing the amount of travel needed to reach the point where the bumper becomes a solid. 
     In general, when more energy must be removed, a larger bumper is used. Recent styling trends are dictating the use of low profile tires, which in effect removes an important energy management element. To counteract the loss of the cushioning given by higher profile tires, the jounce bumpers must absorb much greater amounts of energy. In most cases, there is not enough space to package a bumper large enough to absorb the amount of energy experience during an impact. 
     SUMMARY OF INVENTION 
     One object of the invention is to provide a bumper assembly which overcomes the limiting effect a rigid cup has on a bumper assembly. Another object of the invention is to provide a compact bumper assembly capable of absorbing a larger amount of energy than a similar sized bumper assembly, and provide more travel of the strut assembly. 
     These and other problems are overcome by a bumper assembly comprising a microcellular urethane (MCU) jounce bumper placed into a thermoplastic urethane (TPU) cup. The MCU bumper is partially placed within the TPU cup, which is attached to a surface of either a strut assembly or is free standing in another assembly. As a force acts upon the MCU bumper, it begins to press into the TPU cup. Upon an increasing force being applied, the TPU cup begins to expand outwardly at its opening at the same time the MCU bumper compresses within the TPU cup. Thus, the combination of the bumper and the cup act in unison to receive the force, and allow more travel of the strut assembly as the cup expands. As a result, the combination bumper assembly is capable of absorbing an increased amount of energy in a compact area while still allowing more travel of the strut assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a MCU bumper; 
     FIGS. 2,  2 A and  2 B are perspective views of the combination TPU cup and MCU bumper of the present invention within a strut assembly illustrating the sequential compression of the bumper and cup upon the application of a force; 
     FIGS. 3,  3 A and  3 B are front views of a prior art bumper using a rigid cup and its reaction on application of a force; 
     FIG. 4 is a graph illustrating a comparison of the increase in energy absorbance of and the increase of travel allowed by the present invention; 
     FIG. 5A is a perspective view of a preferred embodiment of the present invention located between a pair of opposing objects; and 
     FIG. 5B is a perspective view of a preferred embodiment of the present invention located within a strut assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     When the vehicle travels over a bump, a strut assembly collapses to absorb the shock. Upon incurring a force greater than the force the strut can handle, the strut will bottom out, or completely collapse. Bumper assemblies provide a cushion between the cylinder of the strut and the surface to which the strut is attached. In some strut assemblies, a rigid cup is used to mount the bumper, as shown in FIGS. 3,  3 A and  3 B. The bumper assembly  350  consists of a rod portion  220 , a compressible bumper  100  and a rigid cup  310 . In typical circumstances, rod portion  220  is the cylindrical tube of the strut assembly, bumper  100  is made of some compressible material to absorb the shock of the bump and rigid cup  310  holds bumper  100  and is connected to the cylinder of a strut (not shown) or is connected to a surface (not shown) to prevent rod portion  220  from impacting the surface or cylinder. 
     The bump incurred in effect imposes a force upon the bumper assembly  350  in the direction F shown in FIG.  3 A. The force in direction F causes bumper  100  to increasingly compress as the amount of force increases. Any bumper has a certain amount of force over which it will not compress further. If that force is achieved with bumper  100 , it will not compress further into cup  310 , providing a maximum amount of energy bumper assembly  350  will absorb. Further, the bumper assembly will provide a maximum amount of travel of the strut assembly. FIG. 3B shows bumper assembly  350  at a maximum collapsed state. The bumper  100  has completely compressed within the rigid cup  310 . The rod  220  cannot move any further toward rigid cup  310 . Any force in direction F applied to the bumper assembly that is greater than the amount need to completely compress the bumper  100  is transferred directly to the vehicle. 
     FIGS. 1,  2 ,  2 A and  2 B illustrate bumper assembly  250  embodying the present invention. It consists of rod portion  220 , a bumper  100  and flexible cup  210 . Bumper  100  can be made of microcellular urethane (MCU) or an equivalent shock absorbing material. It has a configuration designed to cause it to collapse into the flexible cup  210 . Bumper  100  also has an aperture  110  for allowing the shaft of a strut to pass through it which allows the bumper to maintain perfect alignment with the strut, consisting of strut shaft  551  and strut cylinder  550 , and frame member  552  (only a portion of which is shown), as shown in FIG.  5 B. An arrangement similar to this arrangement is shown in reference to U.S. Pat. No. 5,487,535, described above. If bumper assembly  250  is free standing without being mounted onto a strut, as discussed above with reference to U.S. Pat. No. 7,725,203 where the bumper assembly is located between a control arm of the suspension and the vehicle frame, bumper  100  may not have aperture  110 . As shown in FIG. 5A, a second member  501  is displaceable relative to a first member  500  with the combination of bumper  100  and flexible cup  210  preventing contact between the first and second member  500  and  501 . 
     Flexible cup  210  is used to hold bumper  100  and to attach bumper assembly  250  to either a strut assembly or any surface to which the bumper assembly  250  is to be attached. Flexible cup  210  is preferably made of thermoplastic urethane (TPU), but can be made of other materials with similar features. The advantage of using such a flexible cup design is its ability to expand upon application of sufficient force. 
     The sequence of operation is of bumper assembly  250  is shown in FIGS. 2,  2 A and  2 B. Rod portion  220  is in alignment with flexible cup  210  with bumper  100  there between. When rod  220  applies a force upon bumper assembly  250  in the direction F, bumper  100  begins to compress and thus collapse into flexible cup  210 . As the amount of force increases, bumper  100  further compresses and flexible cup  210  begins to expand outwardly at its mouth  212  in the direction W. Thus, both bumper  100  and flexible cup  210  react to the force applied on bumper assembly  250 . Upon application of a force greater than the force required to completely compress bumper  100 , bumper assembly  250  allows for the rod portion to travel further in the direction F, as is shown in FIG. 2B (compare to FIG.  3 B). Bumper assembly  250  is also capable of absorbing greater energy as both bumper  100  and flexible cup  210  absorb energy from the rod portion  220 . 
     FIG. 4 shows a graph demonstrating the utility of the present invention. A bumper assembly using a rigid cup and a bumper assembly using a flexible cup were each compressed under similar conditions and the results were recorded. The graphs reflect the results of the same bumper  100  being compressed into rigid cup  310  and flexible cup  210 . The graphs show both the energy deflection and the load deflection using a 25 kN force and reversing the force. 
     After a test run using the rigid cup  310 , rod member  220  was able to travel about 30 mm following initial contact with bumper  100  under a constant force of 25 kN as illustrated by line RF. Under the same operating conditions but using flexible cup  210 , rod member  220  traveled 33 mm, as illustrated by line PF. The use of flexible cup  210  allows about 10% more travel of rod member  220 . 
     During the same test procedure, the amount of energy the bumper assemblies absorbed was also recorded. Rigid cup  310  was capable of absorbing 90 J during the trial, as illustrated by line RE. Again under the same operating conditions but using, flexible cup  210 , the bumper assembly  250  is capable of absorbing about 125 J, as illustrated by line PE. The use of the flexible cup provides the ability to absorb about 38% more energy. 
     Thus, the use of the bumper assembly  250  including bumper  100  and flexible cup  210  provides substantially more travel for cushioning and can absorb substantially more energy than bumper assembly  350  using a rigid cup  310  even though both assemblies have essentially the same configuration. When using rigid cup  310  in bumper assembly  350 , bumper  100  is completely collapsed under the force of 25 kN, which is shown in the graphs by the difference between the amounts of energy absorbed. As bumper  100  was completely collapsed, the excess energy (35 kN) is transferred to the vehicle. However, bumper assembly  250  with flexible cup  210 , still capable of absorbing the 35 kN, is in effect able to withstand about a 38% greater impact than bumper assembly  350 . 
     The foregoing describes an embodiment of a bumper assembly for use in a strut assembly. The invention may be used in other assemblies or forms, such as a free standing bumper, or used in a differing manner within the strut assembly. Further, other embodiments of the present invention, and obvious modifications to those skilled in the art can be made without departing from the scope of the present invention.