Patent Publication Number: US-2006001205-A1

Title: Jounce bumper

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. The bumper  100  has a general appearance as shown in  FIG. 1 . These could be mounted on a strut assembly, as shown in the U.S. Pat. No. 5,487,535, where the bumper surrounds the piston rod of the strut. A hole  110  through bumper  100  allows for passage of the piston rod. 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, as shown in U.S. Pat. No. 6,158,726, which discloses a bumper with the use of a rigid cup attached. An example of a rigid cup is shown in  FIG. 2 , and is identified as rigid cup  200 . The operation of a rigid cup assembly is shown in  FIGS. 3A-3C , illustrating a bumper assembly  350 . The rigid cup  310 , shown here with a lip  311 , acts to attach the bumper  100  to the vehicle or the strut (not shown) and limits the bumper distortion, thereby increasing its rate. A force, provided by a rod or other device  220 , acts upon the bumper assembly  350  in the direction F, as shown in  FIG. 3B . The force necessary to compress the bumper assembly  350  increases as the bumper is compressed and the bumper absorbs energy as it is compressing. As the bumper  100  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. Such state is illustrated in  FIG. 3C . 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.  
      To absorb this energy effectively, other designs have sought to modify the bumper cup whereby the jounce bumper is placed into an elastic cup. Such is disclosed in U.S. Pat. No. 6,485,008, which is incorporated by reference herein in its entirety. In such jounce bumper assembly, the bumper compresses into an elastic bumper cup, rather than the metal cup noted above. The bumper assembly is located between two objects, for example, a strut and suspension component. When a force compresses the bumper assembly, the bumper begins to compress into the bumper cup. As the force increases, the amount that bumper is compressed into bumper cup increases. In response to this increase, the bumper cup begins to expand outward at its rim portion. This combination of compression and expansion allows the bumper cup assembly to absorb more energy and the bumper assembly to be compressed into a smaller space than the rigid bumper cup designs. However, a problem with such bumper cup assemblies is that they do not provide a positive stop to the system.  
     SUMMARY OF INVENTION  
      One object of the invention is to provide a bumper assembly that overcomes the limiting effect a rigid cup has on a bumper assembly and overcomes the non-limiting effect of an elastic cup. 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 while at the same time providing a positive stop to the assembly.  
      These and other problems are overcome with a bumper assembly comprising a microcellular urethane (MCU) jounce bumper having a thermoplastic urethane (TPU) cylinder mounted therein. The MCU bumper in general has a hole along its longitudinal axis. The cylindrical TPU cylinder insert has an internal diameter the same size as the hole through the MCU bumper, an outer diameter smaller than the outer diameter of the MCU bumper, and an annular flange. The TPU insert is then mounted or molded inside the MCU bumper so that the central diameter and the hold of the MCU bumper are collinear and the insert abuts a bottom surface of the MCU bumper. As a force acts on the bumper assembly along its longitudinal axis, it begins to collapse and push slightly outward and inward. The insert will limit inward movement of the bumper, however, the flexibility of the thermoplastic urethane will allow the insert to move a little as a result of the movement inward and absorb a portion of the energy. As a result of the combination insert and bumper, the bumper assembly will be able to absorb more energy than a convention bumper while at the same time providing a positive stop to the bumper assembly.  
      In an alternative embodiment, the bumper with the insert is partially placed within a TPU cup attached to a surface of either a strut assembly or free standing in another assembly to increase the rate of the bumper. As a force acts upon the 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 bumper compresses within the TPU cup. Similarly to the previous embodiment, the insert will limit inward movement of the bumper, however, the flexibility of the thermoplastic urethane will allow the insert to move a little as a result of the movement inward and absorb a portion of the energy. Thus, the combination of the bumper, the insert 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 bumper assembly is capable of absorbing an increased amount of energy in a compact area while still allowing more travel of the strut assembly and providing a positive stop.  
      As a third embodiment of the invention, a rigid cup is used in place of the TPU cup. Such an assembly operates in a similar manner to the TPU cup, but does not expand radially on increase forces. The rigid cup also increases the rate of the bumper more than the TPU cup and provides a more definite stop. 
    
    
     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 bumper;  
       FIG. 2  is a perspective view of a bumper cup;  
       FIGS. 3A, 3B  and  3 C illustrate the operation of a prior art bumper using a rigid cup;  
       FIG. 4A  illustrates a thermoplastic insert according to a first embodiment of the invention;  
       FIG. 4B  illustrates a bumper according to the first embodiment of the invention;  
       FIG. 5  illustrates a bumper assembly according to the first embodiment of the invention;  
       FIG. 6  illustrates a blown up view of a second embodiment of the invention;  
       FIGS. 7A-7C  illustrate the operation of the first embodiment of the bumper assembly according to the invention;  
       FIGS. 8A-8C  illustrate the operation of the second embodiment of the bumper assembly according to the invention;  
       FIGS. 9A-9D  illustrate a mold and process for making a bumper assembly according to the invention; and  
       FIG. 10  illustrates a graphical comparison of the bumper assemblies according to the present invention with a prior art bumper 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. 3A, 3B  and  3 C. However, these assemblies do not allow for maximum energy absorption and maximum distance travel. On the other hand, dispensing with the rigid cup or using a flexible cup, while providing increased energy absorption and distance travel, does not provide the system with a definite stop. Accordingly, the preferred embodiments of this invention provide a bumper assembly with the energy absorption and distance travel of the flexible cup or no cup along with the definite stop of the rigid cup.  
      A parts view of the jounce bumper assembly according to a first embodiment of the invention is shown in  FIGS. 4A and 4B  and the assembled view is shown in  FIG. 5 . The same reference numerals will be used for the same parts in different views. The insert is shown in  FIG. 4A . As shown, the insert  400  generally comprises a cylindrical shape having a longitudinal hole  410  that has a diameter D along its length thereof. An annular flange portion  420  is provided around the outer surface  401  of the insert  400 . The flange  420  is shown near an upper side  440 , however, it may be at any position along the length of the insert  400 . Its use and operation will be described below. The insert  400  may also have a slit  430  along its length thereof to allow for expansion of the diameter of the hole  410 . The insert  400  may also have flat sides  450  along the inner surface of the hole  410 , which can be used in operation to prevent the insert from rotating about a shaft on which it may be mounted. However, these surfaces may be dispensed with if required.  
      The insert is made of a thermoplastic urethane (TPU), a material well known for its rigidity while simultaneously being flexible. Examples of formulations of TPU materials are available from U.S. Farathane Corporation, located in Sterling Heights, Michigan. The insert  400  can be made by any of a number of processes, such as extrusion molding, plastic injection molding or the like.  
      The bumper  500  is shown in detail in  FIG. 4B . It generally has a cylindrical shape along a length thereof and can comprise a hole  510  through the center thereof. If the bumper  500  is placed in a strut assembly, the piston rod of the strut would pass through hole  510  with the bumper operating to prevent the strut from bottoming out against a suspension component. The bumper  500  may be made of any compressible material that can absorb energy and return to its original shape after such absorption.  
      Preferably the bumper  500  is made of a microcellular urethane (MCU) and can be made from a process of molding, extrusion and the like. The microcellular urethane can be made by combining a prepolymer and a polyal in a manner known to those having skill in the art. An example of such a microcellular urethane combination is an AUTOTHANE  5000  prepolymer combined with an AUTOTHANE A5505 polyal, sold by Hyperlast Limited of Derbyshire, United Kingdom. Such components are combined in a manner known in the art to form the microcellular urethane.  
      Bumpers, such as bumper  500 , have a variety of shapes. In  FIGS. 4B and 5 , bumper  500  is a simple cylinder with a taper on one end, however, the bumpers  650  shown in  FIGS. 6 and 750  shown in  FIG. 7  have annular bumps. It should be noted that the specific design or shape for any bumper depends on the particular needs, compression requirements and design of the bumper assembly.  
       FIG. 5  illustrates the preferred embodiment of a bumper assembly  580 . The bumper assembly  580  has the bumper  500  with the insert  400  mounted or formed therein. The hole  410  of the insert  400  is aligned with the hole  510  of the bumper  500  so that each is collinear. Such alignment allows for the passage of a piston rod for a strut assembly if necessary. The insert  400  is generally placed at the lower side  560  of the bumper  500  to allow for maximum compression of the bumper from the opposite end of the bumper assembly  580 . The flange  420  operates when the bumper  500  has insert  400  mounted therein to prevent movement of the insert along the longitudinal direction of the hole  10 .  
      The operation of the bumper assembly  700  is shown in detail in  FIGS. 7A-7C . The bumper assembly  700  has a bumper  750  with an insert  400  mounted therein. The bumper assembly  700  is placed between a pair of objects  710  and  720  which in operation move with respect to each other. Such objects may be parts of a suspension that may collide with each other during shocks moving through the system. The bumper assembly  700  is placed between objects  710  and  720  to prevent collisions between them. When a force in a direction F does act on object  720 , as shown in  FIG. 7B , it begins to move towards object  710 , compressing bumper assembly  700  therebetween. Bumper  750  begins to compress, and to expand slightly outward from its longitudinal axis  760 . Bumper  750  also begins to expand inward towards its longitudinal axis  760 , creating pressure against insert  400 . Because of its flexibility, the insert  400  will compress slightly but will resist much of the pressure from the bumper  750 . As the force in the direction increases, as shown in  FIG. 7C , bumper  750  nearly fully compresses, reaching a maximum expansion away from the longitudinal axis  760  and maximum compression around the insert  400 .  
      A second embodiment of a bumper assembly  600  according to the invention is shown in  FIG. 6 , wherein the combination of a bumper  650  having an insert  400  mounted therein is partially inserted into a cup  610 . The cup may be either a metal or a plastic cup. For purposes of this embodiment a thermoplastic urethane (TPU) cup was used. Such material is well known as described above. The cup  610  generally has a cavity  611  along its central axis for receiving a portion of the bumper  650 , as shown.  
      The placement of bumper assembly  600  between objects  710  and  720 , as shown in  FIG. 8A , provides similar actions, but different results because of the cup  610 . As shown in  FIG. 8B , a force acts upon object  720  in the direction F towards object  710 . This begins to compress bumper  650  into the cavity  611  of the cup  610 . As the force continually compresses the bumper  650 , the bumper begins to expand slightly outward from its longitudinal axis  660  and inward toward the axis. As the bumper  650  compresses around the insert  400  embedded inside the bumper, the insert will compress slightly because of its flexibility, but will otherwise resist the inward expansion of the bumper. Conversely, as the bumper begins to expand outwardly, the pressure begins to expand the cup  610  radially at its rim  612  in the direction W. The rigidity of the TPU in conjunction with the flexibility, as noted above, reduces the outward expansion of the bumper  650 . Thus, the insert  400  and cup  610  absorb some of the energy that would otherwise be absorbed by the bumper  650  and thus the combination reduces the overall compression of the bumper assembly  600 , in comparison with the bumper assembly  700  with no cup.  
      As a third embodiment to that shown in FIGS.  6 ,  8 A-C, the cup could be made of metal or a non-flexible plastic or other material. This would have the effect of completely resisting the outward expansion of the bumper  650 , but would otherwise operate in a similar manner. The reduction in the outward expansion of the bumper  650  as a result of the rigid cup and the use of the insert  400  has the effect of reducing the overall compression of the bumper assembly in comparison with the bumper assembly  650  having a flexible cup  610 .  
      A comparison of various combinations of bumpers, inserts and cups is illustrated in  FIG. 10 . The graph shows a how much the bumper assembly will compress under a force of 10,000N. Four bumper assemblies were compared, a bumper with no insert, a bumper with an insert, a bumper mounted inside a rigid cup and a bumper with an insert mounted inside the cup. For each assembly, a similar bumper was used, as well as a similar insert and similar cup.  
      As shown in the graph, a bumper with no insert deflected the most under the 10KN compression, nearly 47 mm. Mounting an insert according to the present invention reduced the compression under the same force to about 43.5 mm. Placing the insertless bumper into a cup reduced the compression under the same force to about 38.5 mm and mounting the insert into the bumper in the cup reduced the compression to about 37 mm. Thus, an insert in either situation allows either bumper assembly, i.e., in a rigid cup or not, to absorb the same energy, but allows such absorption to occur in a smaller space. Thus, if a rigid stop is needed for a bumper assembly at a certain space, a selection of a particular insert mounted into the bumper would provide an assembly having a particular compression distance, in comparison to a bumper assembly without an insert. The use of a rigid or flexible cup would add to the tailoring of the bumper assembly to the particular application.  
      The invention further includes a method for making the bumper according to the invention, which will now be disclosed in conjunction with  FIGS. 9A-9D . The method includes using a mold  900 , which comprises generally two halves  901  and  902 . Half  901  comprises six guide holes  910 ,  911 ,  912 ,  913 ,  914  and  915  which align and accept guide pins  920 ,  921 ,  922 ,  923 ,  924  and  925 . When the guide pins are inserted into the guide holes, the mold halves  901  and  902  align, as shown in  FIG. 9B , and the mold is in the closed position.  
      The mold  900  has a pair of cavity halves  930  and  931 , one on each mold half for forming a bumper therein. A pair of runners  940  and  941  allow for guiding of material into the cavities  930  and  931  when the mold is put together. A pair of spare cavities  950  and  951  can be used at a later time.  
      A loader bar slot  960  and  961  in each mold half  901  and  902  allows for a loader bar  970  to be laid therein during the molding process. As shown in  FIG. 9C , the loader bar  970  is placed into the loader bar slot  960  in the half  901 . Note the loader bar  970  extends across the cavity  930  and fits into the loader bar slot  960  on both sides of the cavity.  
      In operation, the process beings by placing the TPU insert  400  onto the loader bar  970 , as shown in  FIG. 9D . The inner diameter of the insert  400  is the same as or slightly larger than the diameter of the loader bar  970 . The closeness of the diameters prevents material from being molded into the inner area of the insert  400 . The loader bar  970  is then placed into the loader bar slot  960  in the mold half  901 , with the insert  400  being slid along the loader bar so that the insert is located inside the cavity  930 . Preferably, but not required, the insert  400  is slid so that the end  460  of the insert abuts a bottom  935  of the cavity  930  (arrangement not shown).  
      Once the loader bar  970  with the insert is in place in mold half  901 , the second mold half  902  is placed onto mold half  901 . The loader bar  970  will stick out of the mold as shown in  FIG. 9B .  
      Away from the mold, the materials used to make the microcellular urethane bumper are mixed, such as the prepolymer and a polyal. Examples of such materials are the Autothane 5000 prepolymer and A5504 polyal, sold by Hyperlast Limited, noted above. These materials are mixed outside the mold and then injected into the runner of the assembled mold. The materials travel through the runner into the cavities  930  and  931  and surround the insert  400  and the loader bar  970 . Following the process for curing the combination of materials, the combination will become the microcellular urethane and form the bumper having the insert mounted therein.  
      Following curing, the mold is then pulled apart at the halves  901  and  902 . The loader bar  970  is removed and the bumper is slid off from the loader bar. Then a bumper  500 , as shown in  FIG. 5 , having an insert  400  mounted therein is created and can either be a free standing bumper assembly or be mounted in rigid or flexible cups as described above.  
      The foregoing describes embodiments of a bumper assembly that is placed between a couple of components to absorb the shock and energy therebetween. However, it should be noted that other embodiments of the present invention, and obvious modifications to those skilled in the art are possible without departing from the scope of the present invention. For example, the bumper assembly could be used in a strut assembly wherein the rod or shaft of the strut passes through the center of the bumper assembly, which prevents the strut assembly from “bottoming out” or when the cylinder of the strut impacts a component of the vehicle. The bumper assembly would provide a cushion to prevent this impact. The bumper assembly could also be used in other situations where it is desired for two objects to not meet at a hard impact.  
      From the foregoing description, it is evident that there are other changes, modifications or alterations that can come within the province of a person having ordinary skill in the art. It is evident that any such changes, modifications or alterations are specifically included in this description and this invention should only be limited by the claims following hereinafter.