Abstract:
A suspension system with an axle lift system for use on vehicles is described, the axle lift system having control arms with an offset lift air bag configuration. The suspension system includes offset control arms and an off-axis lift air bag. The off-axis lift air bag is disposed away from and sometimes at an angle to the axis of the control arms.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Patent Application No. 62/002,038 filed May 22, 2014, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure relates to vehicles suspension systems and, in particular, to suspension systems for vehicles having lift axles. More specifically, this disclosure relates to systems for lifting axles incorporated into such vehicle suspension systems. 
     2. Discussion of Related Art 
     Vehicle suspension systems include a wide variety of configurations and structures. It is common in the vehicle industry to provide suspension configurations able to adjust the height of the suspension. In some suspensions, control arms are provided to hold an axle in place beneath a chassis. For some lift axle suspensions, a lift air bag is provided between the control arms to cause the axle to lift off the ground and toward the chassis upon inflation of the lift air bag. In such configurations the lift air bag is disposed substantially between the control arms. 
     SUMMARY OF THE INVENTION 
     In some embodiments, the axle lift system for a vehicle suspension comprises an upper air bag bracket attached to an upper control arm, a lower air bag bracket attached to an lower control arm, a lift air bag attached between the upper air bag bracket and the lower air bag bracket, wherein the lift air bag is disposed at an angle to the control arms. 
     In some embodiments, the control arms are disposed at an angle to the axle such that the first end of each control arm is offset from the second end with respect to the centerline of the chassis. In some of those embodiments, the control arms are disposed so that the control arms are attached to the axle so that the axle connection point is outboard relative to the point at which the control arm is attached to the chassis. In other embodiments, the control arms are disposed so that the control arms are attached to the axle so that the axle connection point is inboard relative to the point at which the control arm is attached to the chassis. 
     In some embodiments of the axle lift system the upper control arm comprises two portions which are disposed at an angle to each other along the longitudinal axis of the control arm; and the lower control arm comprises two portions which are disposed at an angle to each other. In some of those embodiments, the upper air bag bracket is attached to the second portion of the upper control arm and the lower air bag bracket is attached to the first portion of the lower control arm. 
     In some embodiments of the axle lift system, the upper air bag bracket is an air bag seat and at least one rib attaching the air bag seat to the upper control arm, and the lower air bag bracket is an air bag seat and at least one rib attaching the air bag seat to the lower control arm. 
     In some embodiments of the axle lift system, the lift air bag is disposed outboard of the control arms. In other embodiments of the axle lift system the lift air bag is disposed inboard of the control arms. 
     In some embodiments the suspension system utilizing the axle lift system comprises an axle; an upper control arm and a lower control arm pivotally attached to the axle, with the upper control arm substantially above the lower control arm; an upper air bag bracket attached to the upper control arm; a lower air bag bracket attached to the lower control arm; a lift air bag attached between the upper air bag bracket and the lower air bag bracket, wherein each of the control arms is disposed at a first angle to the axle such that the first end of each control arm is offset from the second end thereof with respect to the centerline of the chassis; wherein the lift air bag is disposed at a second angle to the control arms; and wherein the center axis of the lift air bag is substantially offset from the axis of the control arms. In some of these embodiments the center axis of the lift air bag is disposed outboard of the control arms to which it is attached. In other embodiments, the lift air bag is disposed inboard of the control arm to which it is attached. 
     A method for using the axle lift system is also described, comprising the steps of inflating the lift air bag until the upper and lower control arms pivot upwardly sufficiently to raise the axle a desired distance to a lifted position; operating the vehicle with the axle in the lifted position; deflating the lift air bag until the upper and lower control arms pivot downwardly sufficiently to lower the axle a desired distance to a lowered position; operating the vehicle with the axle in the lowered position. In some versions of the method the lifted position comprises a position wherein a tire mounted on the axle is not in contact with the ground, and the lower position comprises a position wherein a tire mounted on the axle is in contact with the ground. In some versions of the method the vehicle is provided with a suspension air bag for supporting the axle beneath the chassis, and comprises the steps of deflating the suspension air bag before or simultaneously with the step of inflating the lift air bag; and inflating the suspension air bag after or simultaneously with the step of deflating the lift air bag. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vehicle suspension system incorporating an embodiment of the axle lift system. 
         FIG. 2  is a detail perspective view of a vehicle suspension system incorporating an embodiment of the axle lift system. 
         FIG. 3  is a detail side view of a vehicle suspension system incorporating an embodiment of the axle lift system in a lowered position. 
         FIG. 4  is a cross-sectional side view of a vehicle suspension system incorporating an embodiment of the axle lift system. 
         FIG. 5  is a cross-sectional side view of a vehicle suspension system incorporating an embodiment of the axle lift system in a raised position. 
         FIG. 6  is a top view a vehicle suspension system incorporating an embodiment of the axle lift system. 
         FIG. 7  is a detail top view of a portion of a vehicle suspension system incorporating an embodiment of the axle lift system. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the figures, various views of a vehicle suspension incorporating an embodiment of the axle lift system is depicted. The suspension system comprises a variety of components that may vary in detail between various suspensions systems and embodiments of the axle lift system and are not limited to those shown in the figures. An axle  100  is provided with hubs  104  rotationally attached at each end thereof. The axle  100  may have steerable hubs  104  as shown in the figures, or the hubs may be non-streerable hubs with fixed orientations with respect to the axle  100 . Wheels with tires not shown in the figure are attached to the hubs for carrying the load applied to the axle  100  through the suspension system. The exact configuration of the axle  100  and wheels  104  are not limiting of the invention and can be modified as new axles  100  and wheels  104  are developed. The axle  100  is typically suspended beneath chassis  102  by various components such as hanger brackets  110 . The vehicle suspension system is designed to allow the axle  100  to be lifted up when desired, thus removing the load from the tires on hubs  104 . 
     At least two upper control arms  106  and at least two lower control arms  108  are provided for supporting the axle  100  beneath chassis  102 . Each first end  200  of the at least two upper control arms  106  and of the at least two lower control arms  108  are pivotally attached to the axle. Each of the at least two upper control arms are separated from the other upper control arms along the length of the axle  100 , and each of the at least two lower control arms are separated from the other lower control arms along the length of the axle  100 . Each of the at least two upper control arms  106  are attached substantially above, on the side of or adjacent to the axle  100 . Each of the lower control arms  108  are attached substantially below, on the side of or adjacent to the axle  100 . In some embodiments, the first end of each upper control arm is attached to the axle at a point that is approximately opposed to a point on which the first end of a lower control arm is attached forming a pair of opposed control arms. In the depicted embodiment, the axle  100  is pivotally attached to the control arms  106  and  108  by brackets  500 , and associated bolts and bushings; although in other embodiments a different method of attachment may be provided. 
     In the depicted embodiment, each of the control arms  106  and  108  are pivotally attached at a second end  202  thereof to hanger bracket  110 . Typically two hanger brackets  110  are provided, one for each end of the axle  100 , though in a different configuration there may be more hanger brackets  110  or the two brackets may be combined into a larger single bracket spanning the width of chassis  102 . The hanger brackets  110  are provided for attaching the axle  100  to the chassis  102  and providing support to the suspension system. A cross member  112  may be provided connecting the two hanger brackets  110 . In some embodiments, cross member  112  may support an air canister  114  for providing pressurized air to the various pneumatic systems of the suspension system. 
     A lift air bag  116  is connected to each upper and lower control arm pair. In the depicted embodiments lift air bag  116  is connected to the lower control arm  108  by lower lift bag bracket  204  and to upper control arm  106  by upper air bag bracket  206 . Inflating air bag  116  will cause control arms  106  and  108  to raise axle  100  and disengage the tires from the ground. In some embodiments, at least two brackets  118  are also attached to chassis  102  to connect suspension air bags  120  to chassis  102 . Suspension air bags  120  provide support to axle  100  to support it as it bears all or a part of the weight of chassis  102 . When lift air bags  116  are inflated and expand then air pressure is released from air bags  120  allowing them to compress and allowing axle  100  to rise up toward chassis  102 . When desired, the air pressure can be released from air bags  116  to lower axle  100  by control arms  106  and  108  while increasing the pressure in air bags  120  to take up a portion of the load on chassis  102 . 
     Referring now more specifically to  FIG. 3 , a side view of a vehicle suspension system incorporating the axle lift system is depicted. The upper control arms  106  have a first portion  300  and a second portion  302  disposed at an angle to the first portion  300 . Similarly, the depicted lower control arm  108  has a second portion  304  and a first portion  306  disposed at an angle to each other. In the depicted embodiment, bracket  204  is attached to second portion  306  of lower control arm  108  and bracket  206  is attached to second portion  302  of upper control arm  106 . In some embodiments the angles may be more or less than that shown in the figures, or the control arms may be substantially straight with no angle between the various parts of the control arms. In some embodiments the same angle is used on both upper and lower control arms while in other embodiments different angles may be used on the upper and lower control arms. In the depicted embodiments, brackets  110  and  500  are substantially vertical in orientation; however in other embodiments the brackets may be oriented non-vertically or may have angles or bends in their orientation. The upper and lower control arms, the hanger brackets  110  and the axle bracket  500  define a polygonal arrangement which changes as the axle is lifted. 
       FIG. 3  depicts the suspension system in the lowered position with the tire shown in dashed lines in contact with the ground.  FIGS. 4 and 5  are cross-sectional views of the suspension system along the axis labeled as  4 - 4  on  FIG. 1 .  FIG. 4  depicts the suspension system transitioning from a lowered position shown in solid lines, to a raised or lifted position shown in dashed lines.  FIG. 5  depicts the suspension system in the raised or lifted position with the tire shown in dashed lines no longer in contact with the ground. 
     In the configuration shown in  FIG. 3 , air bags  120  are inflated and supporting the load on the suspension system. Air bags  116  are deflated or maintained at a lower pressure so that the control arms  106  and  108  hold the axle in contact with the ground. Referring now to  FIG. 4 , the air bags  120  are deflated or reduced air pressure is maintained in them to allow them to compress vertically and air bags  116  are inflated or held with increased pressure causing them to expand along their length. The expansion of the air bags  116  forces control arms  106  and  108  to pivot on bracket  110  and change orientation in the direction of the arrow thus lifting axle  100  and the attached hubs, thus raising the tire to the upper position shown in dashed lines no longer in contact with the ground. Referring now to  FIG. 5 , the inflated air bags  116  have reoriented and reshaped the polygon created by the control arms  106  and  108  and the brackets  110  and  500  to lift axle  100  and the tire shown in dashed lines off the ground. 
     Referring now to  FIG. 5 , the depicted embodiment of bracket  206  comprises air bag seat  502  which is attached to upper control arm  106  by at least one rib  504 . Similarly, bracket  204  comprises air bag seat  506  attached to lower control arm  108  by at least one rib  508 . In some embodiments, the air bag seats and the ribs are formed from a single piece of bent or cast metal and in some embodiments they may be welded to one another. The brackets are welded or otherwise attached to the control arms in the desired configuration. 
     Referring now more specifically to  FIGS. 6 and 7 , bottom views of an embodiment of the lift suspension system are depicted. As can be seen clearly in this view, control arms  106  and  108  extend from axle  100  and chassis  102  at a non-perpendicular angle. Specifically, in the depicted embodiment, the control arms  106  and  108  extend outwardly from the chassis  102  as the arms  106  and  108  extend from brackets  110  to axle  100 . In some embodiments, the offset control arms  106  and  108  provide more lateral stability as compared to control arms that extend perpendicularly to axle  100 . The longitudinal axis  310  of the control arms  106  and  108  are disposed at an angle  312  ranging from 45 to 85 degrees as measured from axis of the inboard portion of the axle  100 . 
     The control arms  106  and  108  are provided with lower and upper air bag brackets  204  and  206 , respectively to support the lift air bags  116 . Brackets  204  and  206  are offset from the center lines of the control arms  106  and  108  to dispose the lift air bags  116  to the outboard or inboard side of the control arms. “Outboard” in this context refers to the relative disposition of items in relation to the centerline of the chassis  102 , wherein an item to the “outboard” is farther from the centerline. “Inboard” in this context refers to the relative disposition of items in relation to the centerline of the chassis  102 , wherein an item to the “inboard” is closer to the centerline. The outboard or inboard location of the lift air bags  116  allows the control arms  106  and  108  to pivot closer together than other lift air bag configurations, thus providing more travel between the lowered and lift positions of the suspension. 
     Referring now to  FIG. 7 , a detailed bottom view of an embodiment of the lift suspension system is depicted. Lift air bag  116  is disposed between bracket  204  attached to lower control arm  108 , and bracket  206  attached to upper control arm  106 . Bracket  700  and bolt  704  are provided to pivotally attach first end  200  of lower control arm  108  to axle  100 . Bracket  702  and bolt  706  are provided to pivotally attach second end  202  of lower control arm  108  to bracket  110 . Similar brackets and bolts are provided to pivotally attach the upper control arm  106  to axle  100  and bracket  110 . 
     The center or longitudinal axis  708  of lift air bags  116  is offset from the lengthwise or longitudinal axis of control arms  106  and  108 . The axis  708  is also at an angle to the longitudinal, or lengthwise, axis of control arms  106  and  108 . In the depicted embodiment, axis  708  is substantially perpendicular to axle  100 , though it need not be in other embodiments. Brackets  204  and  206  extend in an outboard direction from control arms  106  and  108 , and are angled to hold the air bag  116  on axis  708 . In some embodiments, the bracket  700  is offset from bracket  702  by 2.75 inches though this offset may vary in different embodiments. The axis  708  is disposed outboard of the control beams  106  and  108 , and is not disposed between the two control arms, although a portion of lift air bag  116  is disposed between the control arms  106  and  108 . In some embodiments, the angle  714  between the axis  708  and the longitudinal axis of control arms  106  and  108 , and angle  712  are complementary angles. 
     In an additional embodiment of the lift suspension system, the brackets  204  and  206  are offset from the center lines of the control arms  106  and  108  in the onboard direction disposing the lift air bags  116  to the inboard side of the control arms. In such an embodiment the configuration of the brackets may be reversed so that the brackets  204  are attached to lower control arm  108  and brackets  206  are attached to upper control arm  106 . 
     Many different arrangements of the various components depicted, as well as components not shown, are possible without departing from the spirit and scope of the present invention. Embodiments of the present invention have been described with the intent to be illustrative rather than restrictive. Alternative embodiments will become apparent to those skilled in the art that do not depart from its scope. A skilled artisan may develop alternative means of implementing the aforementioned improvements without departing from the scope of the present invention. 
     It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations and are contemplated within the scope of the claims. Not all steps listed in the various figures need be carried out in the specific order described.