Abstract:
A lift assist for a bumper pivotally mounted to a vehicle frame for movement between a normally closed upright position and a forwardly projecting open position is disclosed. The bumper may be an animal protection bumper fitted to a heavy duty truck. The lift assist includes a torsion bar comprising a relatively short length of wire rope extending between first and second end fittings of the torsion bar, a first anchor assembly for securing the first end fitting to the bumper, and a second anchor assembly for securing the second end fitting to the vehicle frame. The second anchor assembly restrains rotational movement of the second end fitting when a torquing force is applied to the torsion bar, at the same time permitting contraction of the length of the wire rope when a torquing force is applied.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to torsion bars and to vehicle bumpers incorporating same. Implementation of the invention is especially suited for but not limited to pivotally mounted vehicle bumpers designed to remove large animals from the path of a moving vehicle. 
         [0002]    The risk of damage caused by collisions with animals such as moose, deer, elk, and other large animals is particularly serious for vehicles such as tractor-trailer and other heavy duty trucks which often move along roads at high speeds. They are unable to stop or navigate quickly within a short distance and collisions with animals are sometimes unavoidable. To address this risk, the result has been a number of front end bumper designs which are variously described as animal protection bumpers, grille guards, moose bumpers, bull bars, elk pushers, roo bars, etc. 
         [0003]    Because of the massive forces which can be generated in a collision with a large animal, a suitable animal protection bumper must be strong and is typically quite heavy. In the case of heavy duty tractor-trailer trucks where access to the vehicle engine is often gained by tilting the engine hood forwardly, the bumper is pivotally mounted to the vehicle frame. This enables the bumper to be lowered or pivoted from its normally closed upright position to an open position extending forwardly from the frame. When the bumper is in the open position, the hood can be tilted forwardly without interference from the bumper. The engine and other components carried under the hood can then be serviced by the truck driver or other worker. 
         [0004]    Both the lowering of a pivotally mounted bumper from its closed position to its open position and the subsequent raising of the bumper back to its closed position pose a risk of injury to the back. This can be so not only in normal conditions, but particularly so in conditions where the bumper is heavy and the worker&#39;s footing is poor as, for example, on icy, snowy or muddy surfaces. By way of example, the weight of the tilting portion of a pivotally mounted bumper for a heavy duty truck may approximate 220 pounds. While the weight distribution may be concentrated towards the pivot axis of the bumper, a worker nevertheless may be required to exert a significant lifting force (e.g. 85 pounds or more) to lower the bumper in a controlled manner to its open position or to raise it back to its closed position. 
         [0005]    Therefore, there exists a need for a lift assist that reduces the force which is required to be exerted by a worker when raising or lowering a pivotally mounted vehicle bumper, thereby reducing the risk that a back injury may occur. Preferably, the assist should be robust, should not involve undue mechanical complexity, and should be relatively compact. Compactness is desirable because the available space for installation may be limited. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In one aspect of the present invention, there is provided a lift assist for a bumper pivotally mounted to a vehicle frame for movement between a normally closed upright position and a forwardly projecting open position. The lift assist includes a torsion bar comprising a length of wire rope extending along the torsion bar axis between first and second end fittings, a first anchor assembly for securing the first end fitting to the bumper, and a second anchor assembly for securing the second end fitting to the vehicle frame. 
         [0007]    When the first and second anchor assemblies are secured to the bumper and vehicle frame, respectively, the first anchor assembly in cooperation with the second anchor assembly functions to transmit a torquing force from the bumper to the torsion bar in response to pivotal movement of the bumper between its closed and open positions. Cooperatively, the second anchor assembly functions to restrain rotational movement of the second end fitting when the torquing force is applied. Also, the second anchor assembly importantly permits contraction of the length of the wire rope when the torquing force is applied. 
         [0008]    Preferably, the end fittings of the wire rope torsion bar are swage fittings. These are mechanically simple, relatively low cost fittings. Suitable first and second anchor assemblies functioning in the manner described above can easily be connected with such fittings (e.g. by welding). 
         [0009]    The use of wire rope as part of a torsion bar is considered to be a significant feature. This feature recognizes that a length of wire rope per se is a relatively low cost item which can exhibit useful torsionally resilient characteristics. More particularly, it has been found that a relatively short length of wire rope can be axially twisted through an angle upwards of 90 degrees and provide a resilient return force. Normally, wire rope is used under tension in applications where it is desired to hoist or pull an object, or to arrest movement of an object. It is considered undesirable to subject the rope to torsional forces and desirable to alleviate such forces. Unless alleviated, such forces can lead to unwinding or knotting and ultimately to undesirable permanent deformation of the rope. The wire rope feature of the present invention takes advantage of the resilient torsional characteristics of the rope. 
         [0010]    To better avoid permanent deformation, the length of the wire rope between the end fittings preferably does not substantially exceed 16 times the diameter of the rope. Preferably, the diameter of the rope is substantially within the range of ⅞ inches to 1⅜ inches. Beyond this, it may be found that deformation still can be avoided by enclosing the rope within a tubular constraint. However, the use of such a constraint will undesirably add to overall cost—and the resulting length may not be fittable within available space. 
         [0011]    In another aspect of the present invention, the torsion bar is adjustably preloadable to provide an angular return force in the direction of the bumper&#39;s closed position. Preferably, the preload mechanism is embodied in the second anchor assembly. 
         [0012]    In one embodiment, the second anchor assembly preferably includes an externally threaded stud axially aligned with the torsion bar axis and secured to the second end fitting; a torque locking block; an adjustment screw; and a support arm securable to the vehicle frame. The support arm includes a collar for holding the locking block in a manner permitting sliding movement of the block within the collar along while restraining rotational movement. 
         [0013]    The locking block comprises first and second internally threaded bores extending into opposed ends of the block, each bore being axially aligned with the torsion bar axis. The bores axially communicate with each other. The first bore is for threadably receiving the threaded stud. The second bore is for threadably receiving the adjustment screw. Preferably, the threading of the first bore is relatively coarse and the threading of the second bore is relatively fine. The adjustment screw has a length sufficient to extend through the second bore into the first bore to an adjustable point in the first bore limiting threading movement of the stud into the first bore. 
         [0014]    The foregoing and other features and advantages of the present invention will become further apparent from the following detailed description read in conjunction with the accompanying drawings. The detailed description and drawings are to be regarded as illustrative of the disclosure, rather than as limiting the scope of the invention as defined by the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of the front end of a heavy duty truck equipped with a bumper that is pivotal between closed and open positions, the bumper being shown in its upright or closed position. 
           [0016]      FIG. 2  is a perspective view showing the bumper in  FIG. 1  in a forwardly projecting open position to allow the engine hood of the truck shown in FIG. to be tilted forwardly 
           [0017]      FIG. 3  is an enlarged fragmentary view of a part of  FIG. 2  showing structural details of the lift assist and its installation. 
           [0018]      FIG. 4  is an exploded perspective view of the lift assist shown in  FIG. 3 , when not installed. 
           [0019]      FIG. 5  is an enlarged cross-sectional view of the torque locking block forming part of the lift assist shown in  FIGS. 3 and 4 . 
           [0020]      FIG. 6  is a front elevation view of the lift assist shown in  FIG. 5 , when assembled. 
           [0021]      FIG. 7  is a front elevation view of the lift assist, partially in cross-section showing the position of an adjustment screw prior to preloading of the torsion bar. 
           [0022]      FIG. 8  is a front elevation view similar to  FIG. 7 , but showing the position of the adjustment screw when the torsion bar is preloaded. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Referring now to  FIGS. 1 and 2 , there is shown an animal protection bumper generally designated  10  pivotally mounted to the front end of a heavy duty truck generally designated  20 . The truck includes an engine hood  21  and is of the type where the hood must be tilted forwardly to gain access to the engine (not shown) and other parts under the hood (e.g. radiator, etc.—also not shown). The truck also includes a grille  22 , headlights  24 , fenders  26 , and tires  28 , any or all of which parts together with hood  21  may suffer significant damage in the event the vehicle collides with a large animal when not protected by the bumper. The bumper serves to avoid or minimize such damage. As is typical, grille  22 , headlights  24  and fenders  26  tilt with hood  21 . 
         [0024]      FIG. 1  illustrates bumper  10  in its normally closed upright position.  FIG. 2  illustrates the bumper after having been pivoted to a forwardly extending open position. In the latter position, hood  21  may be tilted forwardly. 
         [0025]    Apart from the addition of lift assist  100  to be described below, bumper  10  is basically a conventional design, and it is mounted to truck  20  in a conventional manner. It includes a lower face plate  11 , a lower flange  12  extending rearwardly from the face plate, and an upper flange  17  also extending rearwardly from the face plate. A hole  18  (best seen in  FIGS. 2 and 3 ) extends through upper flange  17  for receiving a tow pin  42  (seen only in  FIG. 1  through opening  19  in face plate  11 ). Bumper  10  also includes vertically and horizontally extending interconnected cross-members extending above lower face plate  11  to shield hood  21 , grille  22 , headlights  24  and fenders  26  from unwanted impacts. 
         [0026]    In  FIG. 2 , hood  21  and connected components (grille  22  etc.) have been tilted forward to a limited degree (i.e. about 40 degrees). With some trucks, the tilt may be up to 90 degrees. For the purpose of illustration, a 90 degree tilt is not shown in  FIG. 2  because this would mask various details of construction which appear in  FIG. 2 . Otherwise, it will be seen in that bumper  10  is carried by a steel sub-frame or framework  40  secured by couplings  41  (only two of which are shown) to main frame  30  of truck  20 . Framework  40  is basically an extension retrofitted to mainframe  10  and is considered to be part of the overall vehicle frame. 
         [0027]    In more detail, bumper  10  is connected to opposed sides of framework  40  by a pair of pivot pins  14  secured by brackets  15  to bumper face plate  11 . These pins permit pivotal movement of the bumper about pivot axis  16  shown in  FIG. 2 . When in its upright position, bumper  10  is also connectable with framework  40  by means of tow pin  42  noted above when the pin is inserted through hole  18  and thence through aligned holes  43  in the structure of framework  40 . 
         [0028]    In a representative manner,  FIGS. 1 and 2  indicate the relative size and positioning of a bumper lift assist  100  in accordance with the present invention. As will be appreciated from these figures, the lift assist is compact. The space which it occupies is relatively small and confined behind face plate  11  of bumper  10 . The scale of  FIGS. 1 and 2  is too small to show structural details of the lift assist. But, such details are shown in  FIGS. 3 to 8   
         [0029]    Referring now to  FIGS. 3 to 8 , lift assist  100  includes a torsion bar comprising a length of wire rope  101  extending between swage end fittings  103 ,  104 . The bar extends along torsion bar axis  102  shown in  FIG. 4 . When the lift assist is installed as shown in  FIG. 3 , axis  102  is preferably aligned with pivot axis  16  of bumper  10 . Excessive misalignment may impose undesirable stresses on the wire rope and other components of the lift assist. 
         [0030]    Wire rope  101  has a right hand lay. It is a standard piece of IWRC steel wire rope having a multiwired steel core and a plurality of multiwired steel wire strands (in the present case, six strands) helically wound about the core. Note that IWRC is an industry acronym for “independent wire rope core”. End fittings  103 ,  104  are also formed from steel. It will be understood by those skilled in the art that the wire rope could equally have a left hand as opposed to a right hand lay. Further, it will be understood that the core may be a fibrous or other core, or no core, as opposed to a core comprised of steel wires. 
         [0031]    Lift assist  100  further includes first and second anchor assemblies. The first anchor assembly comprises a support arm  105  and a flange  107  which are cast as a single part, then welded to end fitting  103 . Flange  107  includes bolt holes  108 ,  109 . When the lift assist is installed as shown in  FIG. 3 , flange  107  is bolted to bottom flange  12  of bumper  10  by means of a pair of bolts  140  (only part of one of which is shown) extending through bolt holes  108 ,  109  in flange  107 . 
         [0032]    The second anchor assembly comprises an externally threaded stud  121  which is axially aligned with torsion bar axis  102  and secured to end fitting  104  by means of a stud nut  122  welded to the fitting, a support arm  111 , an adjustment screw  123 , and a torque locking block  125 . 
         [0033]    Support arm  111  is cast as a single part. It includes a flange  113  at its proximal end and a collar  117  at its distal end. Flange  113  includes a pair of bolt holes  115 ,  116 . When the lift assist is installed as shown in  FIG. 3 , flange  113  is bolted to cross-member  44  of framework  40  by means of a pair of bolts  150 . 
         [0034]    Collar  117  has a hexagonal bore  119  extending through the collar in alignment with torsion bar axis  102 . Torque locking block  125  has an outer hexagonal shape and is slidingly held within the bore/collar for movement along axis  102 , pivotal or rotational movement within the bore/collar being restrained. 
         [0035]    Torque locking block  125  together with adjustment screw  123  are important components of the present embodiment. They facilitate preloading of the torsion bar, the primary operative component of which is wire rope  101 . As best seen in  FIG. 5 , torque locking block  125  comprises a first bore  126  with a relatively coarse thread and a second bore  127  with a relatively fine thread. The bores are axially aligned with torsion bar axis  102 . Stud  121  which has a left hand thread is threadably received by bore  126 . Adjustment screw  123  which has a right hand thread is threadably received by bore  127 . The bores communicate with each other and, as best seen in  FIGS. 7 and 8 , screw  123  has a length sufficient to extend through bore  127  into bore  126  to an adjustable point which limits threading movement of the stud into bore  126 . 
         [0036]    Advantageously, the torsion bar and particularly wire rope  101  thereof is preloadable. Without preloading, the torsion bar will provide a limited return force between the open and closed positions of bumper  10 . But, a significantly greater return force will be enabled if the torsion bar and particularly wire rope  101  is preloaded with a bias towards the bumper&#39;s closed position. 
         [0037]    Preloading the torsion bar is a potentially dangerous task and should be carefully approached. With lift assist  100  installed as shown in  FIG. 3  and bumper  10  in its closed position as shown in  FIG. 1 , the job can be done by a worker positioned under truck  50  where there is access to the lift assist from below and behind. At first instance, adjustment screw  123  is threaded into torque block  125  until it just touches stud  121  as shown in  FIG. 7 . Then, a wrench is applied to stud nut  122 , and the nut is turned in the direction that bumper  10  closes. This increases the twist in wire rope  101 . 
         [0038]    Due to space constraints, the travel of the wrench may be limited. When the end of available wrench movement is reached, that position should be held, and adjustment screw  123  should be threaded inwardly into torque lock block  125 , then tightened with a second wrench. It can be helpful to have a co-worker present to tighten the adjustment screw. Once the screw has been tightened, the hold on the wrench can be relaxed and a new purchase can be made on stud nut  122  to continue the preload operation. 
         [0039]    The foregoing steps are repeated until stud nut  122  has been adjusted (tightened) approximately 60° from its initial position prior to preloading. 
         [0040]    At this point the worker(s) should clear the underside of the truck, and the bumper should be opened. Then, the preload of lift assist  100  is checked by allowing bumper  10  to lower towards its fully open position. If the bumper reaches that position, but is relatively heavy to lift from that position, then the lift assist should be further preloaded. If the bumper reaches the fully open position and balances or closes with a light force, then the preload operation is complete. 
         [0041]    If the bumper does not fully open under its own weight, no attempt should be made to force it down. Rather adjustment screw  123  should be loosened slightly, and the balance rechecked. It is not necessary to apply a force to stud nut  122  when loosening the screw, but the torque to loosen will be quite high. An extension on the wrench may be used to loosen the screw  123  more easily. 
         [0042]      FIG. 8  indicates the position of adjustment screw  123  after preloading has been completed. Its position has advanced into torque locking block  125  from the position shown in  FIG. 7 . Concurrently, torque locking block  125  has been slidingly drawn a distance D 2  through collar  117  (compare with distance D 1 ≈0 in  FIG. 7 ) 
         [0043]    Unloading lift assist  100  is done by fully loosening the adjusting screw  123 . As noted above, it is not necessary to use a wrench on stud nut  122  during unloading. 
         [0044]    In an experimental case where a lift assist similar to that described above was constructed and installed on a truck  20 , the bumper  10  was about 8 feet in width, 5 feet in height, and weighed about 220 pounds. The preload applied to the torsion bar was about 280 foot pounds, the diameter of wire rope  101  being about 1.25 inches and its length between fittings  103 ,  104  being about 16 inches. It was found that the force required to lift the bumper upwardly from its fully open position was only 15 pounds. In the fully open position, the degree of rotation was about 90° and not merely to the partially open position shown in  FIG. 2 . It may also be noted that stud  121  had a diameter of 1 inch and a length of 1.375 inches protruding from stud nut  122  with 8 threads per inch; adjustment screw  123  had a diameter of 0.750 inches and a length of 2 inches with 16 threads per inch. 
         [0045]    The use of a coarse thread for stud  121  and cooperatively within bore  126 , and the use of a fine thread for adjustment screw  123  and cooperatively within bore  127 , is a significant feature. Because the stud has a coarse thread, the ratio of its advance to the degree of its rotation is high. When torque is applied, stud  121  tends to screw into torque locking block  125  (bore  126 ). Screw  123  provides a stop which holds back the stud&#39;s advance. But, having a fine thread, its ratio of retreat to the degree of its rotation is low. For the screw to retreat and allow the stud to advance, it must make more revolutions than the stud. For example, in the experimental case noted above, the stud with 8 threads per inch must make one revolution in order to advance 0.125 inches. But, for the screw to retreat and allow such an advance, the screw with 16 threads per inch must make two revolutions. As the end face of the stud bears against the end face of the screw there is friction between the faces. The stud tries to advance twice as far as the screw will allow for the same amount of rotation. In other words, the stud bears harder and harder against the screw until the force is equalized by compression and friction forces of the stud and the screw against each other, and the screw threads in the torque locking block  125 . 
         [0046]    It should be understood that workable results can be achieved without the employment of coarse and fine threads. Both stud  121  and screw  123  may have coarse threads. 
         [0047]    The scope of the claims should not be limited by the foregoing example, but should be given the broadest interpretation consistent with the description as a whole.