Abstract:
A suspension for a trailer vehicle that allows the trailer itself to be used as a ramp. The suspension has an axle having an axis and wheels at each end of the axle. The axle is pivotally connected to the vehicle at a pivotal connection and the axis of the axle is offset from the pivotal connection to the vehicle. An actuation device having a first and second end is pivotally connected to the axle at its first end. The actuation device is movable between a retracted length and extended length. Shifting the actuation device between its retracted and extended lengths causes the axle to pivot about the pivotal connection on the trailer, thereby changing the height of the vehicle relative to the ground surface. The trailer can be used as a ramp, thus, eliminating the need for separate ramps.

Description:
BACKGROUND OF THE INVENTION 
     Trailers for hauling equipment are frequently equipped with ramps, but even so, these trailers remain inadequate. The ramps are sometimes hinged to the trailer itself, thus wasting space on the trailer when the ramps are folded up. Other ramps are separate pieces that are moved into placed when being used to load the trailer, then must be stowed on the trailer. In either case, the ramps waste space on the trailer. Typically the weight and unwieldy nature of the ramps makes them difficult to use. 
     Another difficulty of the ramps is their steep angle relative to the ground. In an effort to save space on the trailer when the ramps are stowed and save weight in the ramps, the ramps are made to a relative short length when compared to the length of the trailer. Short ramps have a fairly steep angle that makes loading and unloading a trailer difficult. Ideally, a gradually sloped ramp would be used, but longer ramps weigh more and take more space on the trailer when not being used. 
     SUMMARY OF THE INVENTION 
     The present invention is a suspension for a trailer or other vehicle that allows the trailer itself to be used as a ramp. The suspension has an axle having an axis and wheels for contacting a ground surface at each end of the axle. The axle is pivotally connected to the vehicle at a pivotal connection and the axis of the axle is offset from the pivotal connection to the vehicle. A rigid actuation device having a first and second end is pivotally connected to the axle at its first end. The actuation device is movable between a retracted length and extended length. Shifting the actuation device between its retracted and extended lengths causes the axle to pivot about the pivotal connection on the trailer, thereby changing the height of the vehicle relative to the ground surface. 
     The central axes of the wheels may be offset from the axis of the axle and below the pivotal connection on the vehicle. 
     The wheels may be connected to the axle through a resilient torsional connection. 
     In another aspect of the invention, the actuator is a hydraulic cylinder. 
     In another aspect of the invention, a lock may be included to prevent rotation of the axle. 
     In another aspect of the invention, a second axle may be included behind the first axle and the axles are connected with a connecting member so that movement of the first axle, causes movement of the second axle. In this configuration the pivotal connection of the actuator to the first axle may be closer radially to the pivot point than where the connecting member is pivotally connected to the first axle. In this case, the second axle will be caused to rotate more than the first axle when the actuator is moved from its retracted to its extended length. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the top of a double axle embodiment of the invention; 
         FIG. 2  is a side view of the trailer shown in  FIG. 1  in its lowered position; 
         FIG. 3  is a side view of the trailer shown in  FIGS. 1-2  in its raised position; 
         FIG. 4  is a perspective view of the trailer shown in  FIGS. 1-3  showing the underbody and suspension components; 
         FIG. 4A  is a perspective view showing the locking mechanism on the trailer of shown in  FIG. 4  in its locked position; 
         FIG. 4B  is a perspective view showing the locking mechanism on the trailer shown in  FIG. 4  in its unlocked position; 
         FIG. 5  is a side sectional view taken about the line  5 - 5  in  FIG. 1 , showing the suspension components in their positions corresponding to the raised position of the trailer; 
         FIG. 6  is a side sectional view taken about the line  5 - 5  in  FIG. 1 , showing the suspension components in their positions corresponding to the lowered position of the trailer; 
         FIG. 7  is a side view of a single axle embodiment of the invention; 
         FIG. 8  is a side view of the trailer shown in  FIG. 7  in its lowered position; 
         FIG. 9  is a perspective view of the trailer shown in  FIGS. 7 and 8  showing the underbody and suspension components; 
         FIG. 10  is a sectional view of the trailer in its raised position taken about the line  10 - 10  in  FIG. 9 ; and 
         FIG. 11  is a sectional view of the trailer in its lowered position taken about the line  10 - 10  in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The present invention is related to a trailer  10  that may have its rearmost portion lowered so that the trailer  10  is inclined, thus eliminating the need for a separate ramp. The suspension  12  of the trailer allows the rear edge  14  of the trailer to be lowered to the ground  16 . The lowered position of the trailer  10  is shown in  FIG. 2 . The trailer  10  may be made in a two axle version, or a single axle version  10 ′. Although it is not shown in the figures, it is contemplated that an enclosed box style trailer may be constructed according to the present invention. 
       FIG. 4  shows a perspective view of the suspension  12  as viewed from underneath the trailer  10 . The suspension  12  has a first, front axle  20  and a second, rear axle  22  that is located rearward of the first axle. Each axle  20 ,  22  has a connecting plate  24  that is pivotally connected to the trailer  10  about a pivot pin  26 . The front connecting plate  24 ′ has a notch  28  in a forward facing direction. The connecting plates  24 , are welded to the axles  20 ,  22 . The axles  20 ,  22  each include a torsion assembly  30  that provides a resilient torsional connection to an arm  32  to which wheels  34  are mounted so that the axes of the wheels  34  are offset from the axis of the corresponding axle  20 ,  22  to which the wheels  34  are attached. Since the arms  32  are all the same length, the axes of the wheels on opposite sides of each axle are aligned. The torsional assembly  30  is well known in the suspension art for absorbing shock from traveling over an uneven surface and is commonly used in trailer suspensions. 
     A hydraulic cylinder  38  that acts as a rigid actuator has a first end  40  and a second end  42 . The hydraulic cylinder  38  is capable of shifting between an extended position shown in  FIG. 6  and a retracted position shown in  FIG. 5 . The first end  40  of the hydraulic cylinder  38  is pivotally connected to the first axle  20  at a pin  44  held between the connecting plate  24 ′ and an inner connecting plate  46 . The axis of the pin  44  is a first radial distance D 1  away from the axis of pivot pin  26 . Each side of the trailer  10  is configured in the same manner, each having a hydraulic cylinder  38 .  FIG. 4  shows this. The second end  42  of the hydraulic cylinders  38  are pivotally connected to the trailer  10 . An end of a tie rod  48  is pivotally held by pin  49  between connecting plates  24 ′ and  46  at a radial distance D 2  that is greater than D 1 . 
     When the trailer  10  is being driven down a road, the hydraulic cylinder  38  is in its retracted position as shown in  FIG. 5 . The retracted position of the hydraulic cylinder  38  corresponds to the raised position of the trailer  10 . In this position, the force exerted on the wheels  34  tends to rotate the axles  20 ,  22  in a counterclockwise direction as viewed in  FIG. 5 . This is because the wheels  34  are located behind the pivot pin  26 . Thus, in the absence of the hydraulic cylinder  38 , the connecting plates  24 ,  24 ′ tend to rotate counterclockwise as viewed in  FIGS. 5 and 6 . In case of failure of the hydraulic cylinder  38 , a safety lock  50  is attached to the trailer  10 . The safety lock has a bolt  52  that is slidable between a locked position shown in  FIG. 4A  and an unlocked position shown in  FIG. 4B . When the bolt  52  is in its locked position, it rests against a stop  54 . As such, movement of the connecting plate  24 ′ is prevented. The connecting plate  24  on the rear axle  22  is also prevented from rotating through the connection of the tie rod  48 . 
     The lowered position of the trailer  10  is shown in  FIGS. 2 and 6 . In the lowered position, the bolt  52  is moved ahead of the front stop  54 . The hydraulic cylinder  38  is extended into its extended position shown in  FIG. 5 , which rotates the connecting plates  24 ,  24 ′. This action pivots the axles  20 ,  22  relative to the trailer so that the wheels  34  are rotated upward relative to the trailer  10 , thus lowering the trailer. As can be seen in  FIG. 2 , the angle of the trailer forms a ramp with the ground  16  and is a gentle slope from the hitch  56  to the rear edge  14  of the trailer  10 . As a consequence of geometry, the rear wheels  34  of the trailer must be raised more than the front wheels  34  of the trailer  10 . This is because the bottom of the trailer is progressively nearer the ground  16  near the rear edge  14 . Thus, the wheels  34  must be pivotally retracted at different rates. This is accomplished by the relative locations where the pivot pin  44  attaches to the connecting plate  24 ′ with respect to the pivot pin  26  and where the pivot pin  49  attaches to the connecting plate  24 ′ with respect to the pivot pin  26 . Because the distance D 1  between where the hydraulic cylinder  38  attaches to the connecting plate  24 ′ is shorter than distance D 2  where the tie rod  48  connects to the connecting plate  24 ′, movement of the hydraulic cylinder  38  will cause greater movement in the tie rod  48 . As the tie rod  48  moves more than the hydraulic cylinder, the rear axle  22  will be rotated more than the front axle  20 . The greater rotation in the rear axle  22  raises the rear wheels  34  more than the front wheels  34 . Thus, all of the wheels  34  contact the ground  16  when the trailer  10  is in its raised and lowered positions. 
     Although gravity will tend to rotate the axles  20 ,  22  into the position shown in  FIG. 6 , having rigid actuating mechanisms is important. The fact that the hydraulic cylinder  38  and tie rod  48  are rigid means that the suspension  12  does not need to rely on gravity to shift from the raised position to the lowered position. In prior art designs, gravity was relied upon to rotate axles. In the present invention, the hydraulic cylinder  38  rotates the axles. Because the hydraulic cylinder  38  is a dual acting cylinder, it can exert force as it retracts and extends. When the hydraulic cylinder pushes toward its extended position, the trailer  10  is moved to its lowered position shown in  FIG. 6 . When the hydraulic cylinder pulls, or retracts, the trailer is raised into the position shown in  FIG. 5 . A benefit of not relying on gravity to rotate the axles  20 ,  22  of the present invention is that the center of the wheels  34  can be located forward of the pivot pin  26  and the trailer will still function. In the prior art, wheels had to be placed substantially behind the pivotal location on the trailer to generate the moment needed to turn the axles. 
     A single axle version of the suspension  12 ′ is shown in  FIGS. 7-11 . This version of the suspension  12 ′ functions in much the same way as the two axle version, the main difference being the lack of a second axle. In the single axle version, the connecting plates  60  are welded in a central location on the axle  62  to receive the end  42  of a single hydraulic cylinder  38 . The axle  62  pivots about pivot pins  64  on the trailer  10 ′. The pins extend through outer plates  66  near the ends of the axle  62 . When the hydraulic cylinder  38  is extended, the trailer  10 ′ will be in its lowered position shown in  FIGS. 8 and 11 . When the hydraulic cylinder is in its retracted position, the trailer  10 ′ will be in its raised position shown in  FIGS. 7 and 10 . The single axle version also has a safety lock  50  that functions in the same manner as the double axle version of the suspension  12 . 
     When the user of the trailer  10 ,  10 ′ wishes to lower the trailer, he will first unlock the lock  50 . Then he will use controls operatively connected to the hydraulic cylinder(s)  38  to extend the cylinder(s)  38 . This will lower the trailer  10 ,  10 ′ in a gradual angle that gently slopes from the hitch  56  to the rear edge  14 . Using the length of the entire trailer  10 ,  10 ′ to act as the ramp saves the space taken by separate ramps as well as providing a more gradual angle than separate ramps that are shorter than the trailer  10 ,  10 ′ could provide. When the user wishes to raise the trailer, he will retract the hydraulic cylinder(s)  38 . This will put the trailer  10 ,  10 ′ in the raised position for traveling. Once the trailer  10 ,  10 ′ is in the raised position, the lock  50  will be put in to the locked position shown in  FIG. 4A . 
     The invention is not limited to the details given above, but may be modified within the scope of the following claims.