Abstract:
A multiple chamber piston includes a first fluid chamber and a second fluid chamber attached by a first channel and a third fluid chamber connected to a fourth fluid chamber by a second channel. Air chambers are provided between the first fluid chamber and the third fluid chamber as well as the second fluid chamber and the fourth fluid chamber. As a result, when vibration is to be attenuated, walls of the air chambers are able to bend and deform to increase compliance of the overall multiple chamber piston.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to multiple chamber pistons, and more particularly, the present invention relates to multiple chamber pistons having a high compliance to accommodate lower frequencies.  
         BACKGROUND OF THE INVENTION  
         [0002]    Presently, multiple chamber pistons are used for a plurality of damping applications on a vehicle, including engine mounting and suspension applications. Typically, this cylindrical device has an outer cylindrical surface attached to an unsprung mass, such as the vehicle axle, and the center portion attached to a sprung mass, such as the vehicle body. Additionally, the unsprung mass can be the vehicle engine with the vehicle body being the unsprung mass, thereby attenuating vibrations from the vehicle engine to the vehicle body. Multiple chamber pistons utilize at least two separate passages connecting two separate chambers within the device to attenuate and absorb undesirable vibrations. Each passage connecting respective chambers is tuned by adjusting the overall length and area of the passage. Typically, the lengths and cross sectional areas are chosen to attenuate frequencies of below 20 hertz. Accordingly, the longer and narrower the passage is, the lower the frequency the device attenuates. As a result, it is desirable to provide long and narrow passages within these devices to attenuate low frequencies.  
           [0003]    While the present state of the art serves to absorb unwanted vibrations in vehicles, some drawbacks exist. Specifically, during manufacturing, long and narrow passages are often difficult to manufacture. Manufacturing such passages requires the manufacturing processes to hold tight tolerances. And, because the surrounding walls are often an elastomeric material, the possibility of passage collapse increases as the passage is made more narrow. Moreover, longer passages require more distance through the device. As these devices are typically limited in size, it is not always possible to provide a long length passage. The present invention was developed in light of these and other draw backs.  
         SUMMARY  
         [0004]    In light of these and other drawbacks, the present invention provides a multiple chamber piston for attenuating vibrations in a vehicle that includes a bushing having a first fluid chamber connected to a second fluid chamber by a first channel. The bushing includes a third fluid chamber connected to a fourth fluid chamber by a second channel. The first fluid chamber and the third fluid chamber are separated by an air chamber. The second fluid chamber and the fourth fluid chamber are separated by a second air chamber.  
           [0005]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0007]    [0007]FIG. 1 is a perspective view of a multiple chamber piston bushing according to the present invention;  
         [0008]    [0008]FIG. 2 is a cross-sectional view along II-II of FIG. 1;  
         [0009]    [0009]FIG. 3 is a top plan view of a multiple chamber piston bushing without an outer metal casing according to the present invention;  
         [0010]    [0010]FIG. 4 is a cross-sectional view of a multiple chamber piston bushing according to a second embodiment of the present invention;  
         [0011]    [0011]FIG. 5 a  is a cross-sectional view of a multiple chamber piston bushing in operation according to the present invention;  
         [0012]    [0012]FIG. 5 b  is a cross-sectional view of a multiple chamber piston bushing in operation according to the present invention;  
         [0013]    [0013]FIG. 6 is a graphical view showing the kdynamic response and loss angle according to the present invention;  
         [0014]    [0014]FIG. 7 is a perspective view of a vehicle using a multiple chamber piston bushing according to the present invention; and  
         [0015]    [0015]FIG. 8 is a cross sectional view along IIX-IIX of FIG. 1.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    [0016]FIG. 1 shows a multiple chamber piston  10  having an outer metal casing  12  that surrounds and encapsulates a bushing  14 . The bushing is centered on hub  15 . The outer metal casing is generally cylindrical in shape that is designed to fit around bushing  14 . When in an unstressed state (when no external force is being applied to either hub  15  or outer metal casing  12 ), hub  15  and metal casing  12  share the same axis.  
         [0017]    Bushing  14 , in turn, has an outermost layer  18  that is rigid, made usually of steel or aluminum, and a second layer  50  positioned between outermost layer  18  and the core portion  52 . The core portion is preferably made of elastomeric material and is preferably glued or adhered to the inside surface of the second layer  50 , which is in turn adhered to the outermost layer  18 . Hub  15  is generally cylindrical in design with a smaller diameter than metal casing  12  to allow space therebetween for bushing  14 . Hub  15  has an aperture therethrough to allow a bolt, screw or other fastening means to pass therethrough for attachment to a vehicle a mass. As such, the outer metal casing  12  is to attach to one mass (either a sprung or unsprung mass), while the hub  15  is to attach to another mass. As a result, vibrations are absorbed by the multiple chamber piston  10  between hub  15  and metal casing  12  as will be described.  
         [0018]    Referring now to FIG. 2, the bushing  14  is shown and described in greater detail. In FIG. 2, bushing  14  is shown having first fluid chamber  16   a , second fluid chamber  16   b , third fluid chamber  16   c  and fourth fluid chamber  16   d . Additionally, bushing  14  also includes first air chamber  17   a  and second air chamber  17   b . Each of the above described chambers generally begin at the outer surface of bushing  14 , passing through second layer  50  and into core  52 , and extend inward in a substantially parallel fashion. As a result, when the multiple chamber piston is assembled, each of the above described chambers in bushing  14 , except  17   a  and  17   b , are sealed by outer metal casing  12 .  
         [0019]    Connecting first fluid chamber  16   a  and second fluid chamber  16   b  is first channel  18   a . Likewise, connecting third fluid chamber  16   c  and fourth fluid chamber  16   d  is second channel  18   b . first channel  18   a  and second channel  18   b  are formed by cutting portions out of outermost layer  18 . As a result, these channels are bounded by the cut areas of outermost layer  18  and second layer  50 . Preferably, each channel  18   a  and  18   b  extends radially around the bushing  14  proximate the surface thereof. These channels serve to connect each chamber to allow fluid flow therebetween. As can be understood, providing each channels  18   a  and  18   b  with different cross-sectional areas will serve to provide two different attenuation frequencies, as each allows a different volume of fluid to flow therethrough.  
         [0020]    Referring now to FIGS. 5 a  and  5   b , the operation of the present invention is shown and described. In FIG. 5 a , the above described chambers and channels are filled with a fluid. The fluid is preferably a glycol or fluid with an operating temperature as required by automotive manufacturers. In FIG. 5 a , a relative force F is applied to the outer metal casing with respect to hub  15 . In response to this force F, as shown in FIG. 5 b , first fluid chamber  16   a , third fluid chamber  16   c  and first air chamber  17   a  are deformed as shown. As a result, some fluid contained in first fluid chamber  16   a  and third fluid chamber  16   c  is sent via first channel  18   a  and second channel  18   b  respectively to second fluid chamber  16   b  and fourth fluid chamber  16   d . However, due to first air chamber  17   a , the chamber walls  20  are deformed inward toward first air chamber  17   a  and second air chamber  17   b . However, this can vary depending on the elastic shape. Due to the compliance of walls  20  because of first air chamber  17   a  and second air chamber  17   b , the multiple chamber piston according to the present invention is able to attenuate lower frequencies.  
         [0021]    In FIG. 6, the Kdynamic response for the multiple chamber piston is shown as A in the legend. As can be seen, two distinct loss angle peaks are achievable through varying the lengths and areas of channels  18   a  and  18   b  and the compliance of the walls.  
         [0022]    Referring now to FIG. 4, a second embodiment of the present invention is shown and described. In FIG. 4, orifices  22  passes through outer metal casing  12  to allow air to pass into and out of first air chamber  17   a  and second air chamber  17   b . This, in turn, provides lower resistance to flexing of walls  20 , thereby lowering the compliance of the multiple chamber piston  10  more so than that of the first embodiment described previously. However, it is noted that orifices  22  are not necessary, and that mere air pockets can be used that are completely sealed.  
         [0023]    As a result of the above, the walls  20  and the air gap provide additional compliance to the fluid chambers  16  without reducing the overall static spring rate of the bushing. This is not the case for prior art fluid bushings. Prior art fluid bushings can only increase compliance by altering rubber wall sections which typically determine the static rate of the busing.  
         [0024]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.