Abstract:
A vehicle cab is pivoted to the chassis at the front and supported at the rear by a cab suspension unit that includes a laminate of interleaved elastomer and rigid plate layers. The laminate flexes in reaction to forces that act in the planes of the layers and is relatively resistant to forces that act normal to the layers such that it elastically absorbs shocks and vibrations from road irregularities and pitch and roll maneuvers and more stiffly resists acceleration and deceleration forces between the cab and the chassis.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This claims the benefit of U.S. Provisional Patent Application No. 60/679,426 filed May 10, 2005. 
     
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to a suspension for the cab of a vehicle of the type in which the cab is pivoted at the front of the cab to the chassis and has one or more vibration and shock dampening devices between the rear of the cab and the vehicle chassis, and in particular to an elastomeric device for such applications. 
       BACKGROUND OF THE INVENTION 
       [0004]    “Cab over” vehicles are well known, in which the truck cab is provided over the engine of the vehicle. In such vehicle constructions, the cab is typically pivoted to the chassis of the vehicle at the front of the cab, about a horizontal axis that runs laterally (perpendicular to the direction of normal straight line vehicle travel). The rear of the truck cab is typically supported with springs or air springs and shock absorbers between the rear of the truck cab and the vehicle chassis. As the cab pivots about the front axis, the rear of the cab bounces generally up and down. The springs and shock absorbers dampen the vibration and shocks which may otherwise be experienced by the driver as the cab pivots. 
         [0005]    Such springs, and air springs in particular, and shock absorbers for this application, have required maintenance and been prone to failure as the suspension loads, both in compression and in tension, can be significant. In particular, in many cab suspensions, the cab is hinged to the frame with two bushings in the front, one near each front corner. One or more of the air spring/shock units mount the rear of the cab to the chassis. These units have usually been provided either one in the middle or on a side, or one on each side of the rear of the cab. Such suspensions, particularly the three-point suspensions, can encounter a problem due to twist loading. This happens, for example, when the truck backs up to engage its fifth wheel trailer hitch with a semi-trailer. In such situations a large shock load can be applied that tends to twist the cab about a longitudinal axis. In the absence of anything firmly affixing one side of the cab, the cab rotates around its front axis and hits the suspension. This can place a significant load on the air springs and shocks, both in compression and in tension loading, when the suspension rebounds. 
         [0006]    In addition, the springs and shocks used previously required other structure around them to counter the acceleration and deceleration forces (fore and aft) that the vehicle cab is subjected to and to control lateral movement for pitch and roll movements of the cab when cornering. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention provides a vehicle cab suspension unit that supports the rear of a vehicle cab that is hinged at the front to a chassis of the vehicle to pivot relative to the chassis about an axis that is perpendicular to the direction of forward straight vehicle travel (the longitudinal axis of the vehicle). The suspension unit includes an elastomer and metal laminate in which metal layers are interleaved with elastomer layers, the elastomer layers being fixed to the metal layers at interfaces between the elastomer and metal layers such that sheer forces can be transmitted generally parallel to the layers from one layer to the next. The laminate is oriented between the chassis and the cab with the layers subjected to sheer forces when the cab pivots about the axis relative to the chassis. 
         [0008]    Although the layers need not be oriented in vertical planes, in the disclosed embodiment they are. Were it desired to change the stiffness of the suspension unit or its natural frequency, the unit could be oriented so that the layers were in planes at an angle to vertical. The load carrying capacity of the suspension unit would also be increased by so increasing the angle to vertical. 
         [0009]    Also, when the layers are oriented in vertical planes, the layers are subjected to compression from end to end (in the thickness direction of the layers) when the vehicle is stopped due to deceleration forces on the cab, and tension when the vehicle accelerates due to acceleration forces on the cab, which is desirable. The unit can also be arranged so that the layers are subjected to tension upon deceleration or compression upon acceleration, although since deceleration forces tend to be greater than acceleration forces, the former is preferable. The stiffness of the unit in compression and tension along the direction of the thickness of the layers is greater than the stiffness in sheer and therefore the unit is well adapted to counter the acceleration and deceleration forces of the vehicle. In addition, the characteristics of the unit in reaction to acceleration and deceleration forces can be adjusted by changing the angle of the layers to vertical, as described above, reducing its stiffness to acceleration and deceleration forces by increasing the angle between the planes of the layers and a vertical plane. 
         [0010]    In addition, in another feature of the invention, the stiffness of the unit can be varied by varying the thicknesses of the layers. Thicker elastomer layers combined with thinner metal layers, within the same size envelope of the unit, result in a more flexible unit, whereas thinner elastomer layers combined with thicker metal plates results in a stiffer unit. Also, the hardness of the elastomer can be varied to also vary the stiffness. 
         [0011]    The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a portion of a vehicle incorporating a suspension unit of the invention; 
           [0013]      FIG. 2  is a rear perspective view of the vehicle of  FIG. 1  in which the unit is visible; 
           [0014]      FIG. 3  is a left side plan view of the vehicle of  FIGS. 1 and 2 ; 
           [0015]      FIG. 4  is a top perspective view illustrating the area of the vehicle in which the suspension unit is mounted; 
           [0016]      FIG. 5  is a perspective view of the unit mounted to the vehicle; and 
           [0017]      FIG. 6  is a perspective view of the elastomer and metal plate laminate which is included in the suspension unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]      FIGS. 1-5  illustrate a vehicle  8  including a cab  12  (only the lower portion of which is shown), a chassis  10  and a suspension unit  14  of the invention. The cab  12  is pivotally mounted to the chassis  10  so as to rotate about axis  16  or an axis parallel to axis  16  by any suitable means, which may be conventional. Near the front of the cab  12 , the axis  16  runs laterally, being generally horizontal and perpendicular to the direction  18  of normal forward straightline travel of the vehicle  8 . The vehicle  8  has ground engaging front wheels  20  (the rear wheels not being shown) that support a beam  22  from which the primary suspension of the vehicle is mounted, the primary suspension including leaf springs  24  and shock absorbers  26  that extend between the beam  22  and the chassis  10 . The suspension unit  14  provides a secondary suspension for the cab between the cab  12  and the chassis  10 . 
         [0019]    Referring primarily to  FIGS. 3-5 , the suspension unit  14  includes two brackets  30  and  32  and an elastomer laminate  34 . The bracket  30  is bolted or otherwise affixed to the driver side rail  33  of the chassis  10  so that it is fixed relative to the chassis. The chassis end of the laminate  34  is fastened by fasteners  36  to a plate  38  of the bracket  30  that has the surface against which the laminate  34  is bolted extending in a plane that is lateral to the direction of motion of the vehicle  18 . The opposite end of the laminate  34  is bolted by bolts  40  to a plate  42  of the bracket  32  that has the surface against which the laminate  34  is bolted also extending in a plane which is perpendicular to the direction of forward motion  18 , and spaced rearwardly from the plate  38 . As illustrated, the two plates  38  and  42  are parallel to one another and both perpendicular to the direction  18  of forward straight motion. The bracket  32  is a right angle bracket with a gusset  44  between the vertical plate  42  and the horizontal plate  46 . The bracket  32  is supported by the laminate  34  from the bracket  30  and therefore from the chassis  10 . 
         [0020]    Mounted to the flange  46  is a locking unit  50 , which may be conventional, (fasteners not shown but would be bolted to flange  46 ) that locks pin  52  that is fixed to bracket  55  ( FIG. 4 ), and bracket  55  is bolted to the cab  12 . The locking unit  50  is releasable to release pin  52  so that the cab  12  can be pivoted up about axis  16  from the position shown in  FIG. 1 . 
         [0021]    The laminate  34  is made of metal, typically steel, plates  54  which are vulcanized or otherwise bonded or securely affixed to elastomer layers  56  of the unit  34 . The interfaces between the elastomer layers  56  and the plates  54  may be flat or may have surface features that provide a mechanical connection. There is a plate  54  at each end of the laminate  34  into which the holes for the respective fasteners  36  and  40  are drilled and tapped, and so the end plates serve as the method by which to secure the laminate  34  to the chassis bracket  30  and to the floating bracket  32 , the floating bracket securing the cab  12 . 
         [0022]      FIG. 6  illustrates the portion of the laminate  34  not including the end plates  54 .  FIG. 6  illustrates the interface surface  60  of the elastomer layer  56  on the bracket  30  end of the laminate  34  to be flat, and the facing interface surface of the end plate  54  would be similarly flat, the plates  54  and interleaved elastomer layers  56  being fixed together in a mold in which the elastomer layers  56  are cast and molded or vulcanized to the interleaved plates  54 . The elastomer laminate  34  disclosed is commercially available from Cooper Standard of Novi, Mich. as part of the E-Z Cruise System. 
         [0023]    In the application of the elastomer laminate  34  to a vehicle cab suspension, the laminate may be oriented with its layers vertical, as illustrated in  FIGS. 2-5 , or the layers may be oriented at an angle, for example, so as to lie in a plane that is angled forwardly from vertical. Such an angled plane would still, preferably, be perpendicular to the direction  18  in the horizontal direction, in other words when viewed in a top view. This would make the effective stiffness of the laminate  34  greater since a vertical load applied between the two brackets  30  and  32  would result in a force component normal to the plane of the layers of the laminate  34 , tending to compress or extend the layers in their thickness direction. In this direction, the elastomer layers are quite stiff, as are the metal layers, of course. However, in directions that lie in the planes of the layers, i.e., in the sheer directions—the plane of the height and width, the elastomer layers are relatively flexible, not only vertically, but also laterally (side to side). While angling the laminate  34  makes it stiffer to vertical movements between the cab and chassis, such angling makes the laminate  34  more flexible to acceleration and deceleration forces which are exerted between the chassis  10  and the cab  12 . These are generally forces in the direction of line  18  and either tend to compress the layers of the laminate  34  or pull them apart, i.e., subject them to tension in the thickness direction. Angling the layers as described above would break these acceleration and deceleration forces into components, relative to the laminate, with one component acting to compress the layers and the other component acting in sheer on the layers, resulting in less resistance of the laminate  34  to counteract forces so directed. 
         [0024]    Another way that the laminate  34  may be loaded is during cornering maneuvers of the vehicle when the cab tends to pitch and roll relative to the chassis. These forces are mainly in the planes of the laminate layers when the laminate is oriented vertically as illustrated in  FIGS. 2-6 , and therefore, the laminate is relatively flexible and able to conform to these forces while suspending the cab and absorbing and dampening harshness which may otherwise be present in these forces. 
         [0025]    Only one suspension unit  14  is illustrated because in the vehicle illustrated, the cab is provided only on one side of the vehicle, this being in a yard truck-type application. For other types of vehicles where the cab extends across the full width of the vehicle, such as in over-the-road trucks, two or more of these suspension units  14  may be provided, for example, one on each side, or one on each side and one in the middle, or only one in the middle. 
         [0026]    The stiffness of the laminate  34  can also be varied by varying the relative thicknesses of the elastomer layers  56  and the plate layers  54 . This can be done within the dimensional envelope of the laminate  34 , i.e., maintaining the same spacing from one end of the laminate  34  to the other. By making the elastomer layers thinner and the plate layers thicker, the stiffness is increased, and by making the elastomer layers  56  thicker and the plate layers  54  thinner, the stiffness is decreased. In addition, the stiffness can be varied by varying the hardness of the elastomer layers  56 . 
         [0027]    It is also noted that from one end to the other, i.e., from the forward end to the rearward end, the laminate  34  extends upwardly. This is desirable to give clearance at the top of the laminate  34  for downward movements of the rear end of the laminate  34  without the underside of the cab hitting on the top ends of the plates  54 . In a different configuration, this may not be necessary, and the layers of the laminate  34  could be made aligned along a straight horizontal line with one another rather than angling up. 
         [0028]    A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiments described, but should be defined by the claims that follow.