Patent Publication Number: US-2006001311-A1

Title: Front steer axle air suspension system

Description:
BACKGROUND OF THE INVENTION  
      Heavy vehicles, such as tractor-trailers, have a tractor vehicle that includes front axle and a rear axle. The front axle is typically a front non-drive steer axle and the rear axle is typically a rear tandem drive axle. Air suspension systems are commonly used on the rear tandem drive axle. However, the front non-drive steer axle has traditionally used a mechanical or spring suspension. This is because front air suspensions have had limited success due to a sluggish feel generated by the air suspension on the front axle.  
      The front non-drive steer axle has an axle beam that extends between a pair of steering knuckles. The steering knuckles each include a spindle portion for supporting a wheel. A knuckle pin, also referred to as a kingpin, is used to attach each end of the axle beam to a respective steering knuckle. The kingpin defines a steering axis. A steering arm provides steering input to one of the steering knuckles. A tie rod assembly interconnects the steering knuckles to transfer steering input from one steering knuckle to the other steering knuckle. The kingpin provides articulation between the steering knuckles and axle beam so that a vehicle can execute turning maneuvers via the steering arm and tie rod assembly.  
      The front air suspension typically includes a pair of laterally spaced spring assemblies that are mounted to the axle beam at one end and mounted to a vehicle frame at an opposite end with a shackle. Air springs are positioned between the axle beam and the vehicle frame.  
      Another undesirable operational response for a front suspension on a front non-drive steer axle is referred to as a shimmy mode. The shimmy mode can exist with front suspensions having low lateral stiffness or insufficient damping. The shimmy mode is defined as front wheel rotation about the kingpin in phase, with a slight tramp mode. Tramp is related to wheel hop, which is a vertical oscillatory motion of a wheel between a road surface and a sprung mass. The tramp mode is a form of wheel hop in which a pair of wheels hop in opposite phase.  
      Many different solutions have been proposed to address the shimmy problem. One solution has been to change the caster angle. The caster angle is an angle, in side elevation, between the steering axis and the vertical. Another solution increased shackle bushing stiffness and/or shackle link thickness. Other solutions have included changing ride height, fixing the axle beam to the leaf spring assemblies, or providing kingpin damping. Each of these solutions has had limited success but has not eliminated the shimmy mode problem.  
      There is a need for an air suspension system that can be used on a front non-drive steer axle that improves ride and performance, as well as overcoming the other mentioned deficiencies in the prior art.  
     SUMMARY OF THE INVENTION  
      An air suspension system includes a lateral stiffener assembly that improves air suspension ride and performance. In one example, the air suspension system is used for a non-drive axle assembly having an axle beam defining a lateral axis extending between a pair of rotating wheels. The lateral stiffener assembly includes first and second arms that extend transverse to the lateral axis. The first arm has a first arm end supported by the axle beam at a first lateral side of a vehicle and the second arm has a first arm end supported by the axle beam at a second lateral side of the vehicle opposite the first lateral side. Each of the first and second arms has a second arm end that is mountable to a vehicle structure, such as a vehicle frame member, for example.  
      The air suspension system includes air springs that are supported by the axle beam. The air springs are mounted to the axle beam with a bracket. The lateral stiffener assembly is positioned on a first longitudinal side of the axle beam and the air springs are positioned on a second longitudinal side opposite from the first longitudinal side. The air springs are connectable to the vehicle frame member.  
      The vehicle frame member includes a pair of c-channels or support beams that extend in a longitudinal direction, which is transverse to the lateral axis. One support beam is positioned at the first lateral side and another support beam is positioned at the second lateral side. The air springs and the lateral stiffener assembly are connectable to the support beams.  
      In one disclosed embodiment, the second arm end for the first arm is mounted to the support beam at the second lateral side and the second arm end for the second arm is mounted to the support beam at the first lateral side. In this configuration, the first and second arms are non-parallel to each other and are positioned to form a X-shape relative to the pair of support beams.  
      In another disclosed embodiment, the second arm end for the first arm is mounted to the support beam at the first lateral side and the second arm end for the second arm is mounted to the support beam at the second lateral side. In this configuration, the first and second arms extend generally parallel to the support beams and are generally perpendicular relative to the lateral axis. A stiffener member is used to interconnect the first and second arms. The stiffener member comprises a beam or tube that is generally parallel to the lateral axis and includes a first end mounted to the first arm and a second end mounted to the second arm.  
      The air suspension system utilizes a lateral stiffener assembly to improve air suspension ride and performance by reducing shimmy. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a perspective view of a front non-drive steer axle assembly.  
       FIG. 2  is a partial perspective view of one example of an air suspension for a front non-dive steer axle incorporating the subject invention.  
       FIG. 3  is a partial perspective view of another example of an air suspension incorporating the subject invention.  
       FIG. 4  is a partial perspective view of another example of an air suspension incorporating the subject invention.  
       FIG. 5  is a partial perspective view of another example of an air suspension incorporating the subject invention.  
       FIG. 6  is a perspective view of a lateral stiffener shown in  FIG. 5 .  
       FIG. 7  is a perspective view of another lateral stiffener.  
       FIG. 8  is a partial perspective view of another example of an air suspension incorporating the subject invention.  
       FIG. 9  is a perspective view of a bracket used in the example of  FIG. 8 .  
       FIG. 10  is a partial perspective view of another example of an air suspension incorporating the subject invention.  
       FIG. 11  is a perspective top view of a lateral stiffener shown in  FIG. 10 .  
       FIG. 12  is a perspective bottom view of the lateral stiffener of  FIG. 11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A front non-drive steer axle is shown generally at  20  in  FIG. 1 . The front non-drive steer axle  20  includes a generally rigid axle beam  22  extending between first and second wheel ends  24 ,  26 . The first and second wheel ends  24 ,  26  are laterally spaced apart from each other and define a lateral axis of rotation A R . The front non-drive steer axle  20  also includes a steering arm  28  and tie rod assembly  30  that cooperate to turn the first and second wheel ends  24 ,  26  during steering maneuvers, as known in the art.  
      An air suspension system  32 , shown in  FIG. 2 , includes a pair of air springs  34  positioned between the axle beam  22  and a vehicle frame  36 . The vehicle frame  36  includes a first c-channel  38  positioned on one lateral side of a vehicle and a second c-channel  40  positioned on an opposite side of the vehicle. The first and second c-channels  38 ,  40  extend in a generally longitudinal direction along a length of the vehicle. The longitudinal direction is generally perpendicular to a lateral direction defined by the lateral axis of rotation A R .  
      Each air spring  34  is supported on an air spring support arm  42  that is positioned on one longitudinal side of the lateral axis of rotation A R . A mounting bracket  44  attaches each air spring support arm  42  to the axle beam  22 . The mounting bracket  44  also attaches one end of a shock absorber  46  to the axle beam  22 . An opposite end of the shock absorber  46  is mounted to the vehicle frame  36 .  
      The bracket  44  can be a single piece bracket or a multiple piece bracket. In the configuration shown in  FIG. 2 , the bracket  44  includes a first piece  44   a  and a second piece  44   b.  The first piece  44   a  is used to mount the air spring support arm  42  and shock absorber  46  to the axle beam  22 . The second piece  44   b  attaches a lateral stiffener assembly  50  to the axle beam  22 .  
      The lateral stiffener assembly  50  is solely incorporated into the air suspension system  32  to increase lateral stiffness. The lateral stiffener assembly  50  is not intended to add roll stiffness. In the example of  FIG. 2 , the lateral stiffener assembly  50  includes a first arm  52  having one end mounted to the second piece  44   b  of bracket  44  at a first lateral side  54  of the vehicle and a second arm  56  having one end mounted to the second piece  44   b  of bracket  44  at a second lateral side  58  of the vehicle. The first arm  52  has an opposite end mounted to the vehicle frame  36  at the second lateral side  58  and the second arm  56  has an opposite end mounted to the vehicle frame  36  at the first lateral side  54 . In one example, the first and second arms  52 ,  56  are formed from a resilient spring material to allow flexing during vehicle operation. Any type of spring material known in the art could be used to form the first and second arms  52 ,  56 .  
      As shown in  FIG. 2 , the first and second arms  52 ,  56  are non-parallel to each other and extend transversely to the axle beam  22  and lateral axis of rotation A R . In this configuration, the first and second arms  52 ,  56  are orientated to form an “X” relative to the first and second c-channels  38 ,  40 .  
      The c-channels  38 ,  40  each include a shackle  60  for mounting the opposite ends of the first and second arms  52   56  to the vehicle frame  36 . The shackle  60  includes a bracket  60   a  and a pair of drop links  60   b  and  60   c,  as known.  
      In the example of  FIG. 2 , both ends of the first and second arms  52 ,  56  are supported in bushing mounts  65 . The bushing mounts  65  preferably have a high lateral rate, which means that the bushings are very stiff in a side-to-side direction.  
       FIG. 3  shows another example of a lateral stiffener assembly  62 . This lateral stiffener assembly is similar to that shown in  FIG. 2  and includes first and second arms  64 ,  66  formed from a resilient spring material. In this example, however, the first and second arms  64 ,  66  each include curved end portions  68 .  
      The example of  FIG. 4  includes first and second leaf springs  70 ,  72  that extend in a generally longitudinal direction parallel to the first and second c-channels  38 ,  40 . The first and second leaf springs  70 ,  72  are resilient, flexible members. The first and second leaf springs  70 ,  72  each have one end attached to the axle beam  22  with the bracket  44  and an opposite end attached to the shackle  60  in a manner similar to that described above.  
      A lateral stiffener assembly  74  interconnects the first and second leaf springs  70 ,  72 . The lateral stiffener assembly  74  includes a tube  76  that is clamped to the first and second leaf springs  70 ,  72  with a clamp assembly  78 . One clamp assembly  78  is used for each of the first and second leaf springs  70 ,  72 .  
      The clamp assembly  78  includes a bracket  78   a  , which is positioned at one of an upper or lower surface of the first and second leaf springs  70 ,  72 . The tube  76  is positioned opposite the bracket  78   a  at the other of the upper or lower surface of the first and second leaf springs  70 ,  72 . The clamp assembly  78  also includes a plurality of fasteners  78   b  that are inserted through the bracket  78   a  and into the tube  76 . The fasteners  78   b  do not extend through the first and second leaf springs  70 ,  72 . Instead, one fastener  78   b  is positioned at each lateral side of the respective first or second leaf spring  70 ,  72 . In this configuration, the first and second leaf springs  70 ,  72  are clamped between the bracket  78   a  and tube  76 .  
      The tube  76  can have any type of cross-sectional shape. A square tube is shown, however, an oval, circular, rectangular, or other shape could also be used. Further, a solid bar could also be used, however, a tube configuration is preferred for weight reduction.  
       FIGS. 5, 6 , and  7  show an example of another lateral stiffener assembly  80 . In this example, the lateral stiffener assembly  80  includes first and second arms  82 ,  84  that extend in a generally longitudinal direction parallel to the c-channels  38 ,  40 . The first and second arms  82 ,  84  are preferably formed in a c-channel shape, however, other shapes could also be used. The first and second arms  82 ,  84  are generally parallel to each other and are positioned on the first and second lateral sides  54 ,  58 , respectively. The first and second arms  82 ,  84  each include a first arm end that is mounted to the axle beam  22  via bracket  44  and a second arm end that is mounted to the vehicle frame  36  via the shackle  60 , as described above.  
      A beam member  86  extends in a generally lateral direction, parallel to the lateral axis of rotation A R , and is spaced longitudinally from the axle beam  22 . The beam member  86  is bolted, welded, or otherwise attached to the first and second arms  82 ,  84 . Further, the beam member  86  can be positioned at any longitudinal position along the first and second arms  82 ,  84  relative to the axle beam  22 . In the configuration shown in  FIG. 5 , the beam member  86  is positioned longitudinally closer to bracket  44  than shackle  60 . Longitudinal position could vary to accommodate additional components in a limited packaging space.  
      The beam member  86  is preferably a resilient member that can have a c-shape  86   a  as shown in  FIG. 6  or can have a u-shape with transversely extending flanges  86   b  as shown in  FIG. 7 . Other cross-sectional shapes could also be used.  
      The first and second arms  82 ,  84  each include a first end mounted to the second piece  44   b  of bracket  44  and a second end mounted to the shackle  60 . The first end is preferably mounted to the second piece  44   b  with a bushing mount  85 . The second end is preferably mounted to the shackle  60  with a bushing mount  87 . The bushing mounts  85 ,  87  have a high lateral rate, as described above. The bushing mounts allow movement of the first and second arms  82 ,  84  relative to the axle beam  22  and vehicle frame  36 .  
      As discussed above, the bracket  44  can be formed from multiple pieces or can be integrally formed as a single piece bracket  88 , as shown in  FIGS. 8 and 9 . One single piece bracket  88  is positioned at each of the first and second lateral sides  54 ,  58  of the vehicle. The single piece bracket  88  includes a first portion  90  for mounting the air spring support arm  42  and the bracket  88  to the axle beam  22 , a second portion  92  for mounting the shock absorber  46  to the axle beam  22 , and a third portion  94  for attaching the first and second arms  82 ,  84  to the axle beam  22 .  
       FIGS. 10, 11 , and  12  show another example of a lateral stiffener assembly  100 . In this example, the lateral stiffener assembly  100  includes first and second arms  102 ,  104  that extend in a generally longitudinal direction parallel to the c-channels  38 ,  40 . The first and second arms  102 ,  104  are generally parallel to each other and are positioned on the first and second lateral sides  54 ,  58 , respectively. A beam member  106  extends in a generally lateral direction, parallel to the lateral axis of rotation A R , and is spaced longitudinally from the axle beam  22 . The beam member  106  is bolted, welded, or otherwise attached to the first and second arms  102 ,  104 .  
      The beam member  106  is preferably a resilient member that can have a c-shape as shown in  FIGS. 11 and 12 . Other cross-sectional shapes could also be used. Further, the beam member  106  and the first and second arms  102 ,  104  can be formed from separate pieces or integrally formed as a single piece member as shown in  FIGS. 11 and 12 .  
      The first and second arms  102 ,  104  each include a first end mounted to the bracket  44  and a second end mounted to the shackle  60 . In this example, the first end is a ball stud attachment  110  that allows movement of the first and second arms  102 ,  104  relative to the axle beam  22  and the second end is a bushing attachment  112  that allows movement of the first and second arms relative to the vehicle frame  36 .  
      Lateral stiffness is very important to successful responsiveness for a front non-drive steer axle  20  having an air suspension system  32 . Use of a lateral stiffener assembly in combination with a torsionally stiff axle beam  22 , as described above, can provide high lateral stiffness in the air suspension system  32 . The lateral stiffener assembly improves and maintains a desired level of lateral stiffness without influencing roll or vertical suspension characteristics.  
      The lateral stiffener assembly is connected to the axle beam  22  with a joint connection such as a bushing, bearing, ball joint, or other similar connection to provide high lateral and radial rates but low rotation rates. The lateral stiffener assembly is also connected to the shackle  60  with a bushing connection having similar rates as the joint connection to the axle beam  22 .  
      An important feature to this design is the interaction with an axle member, i.e. the axle beam  22 , that provides a high torsional response that is reacted through front suspension members. Front suspension member connection to the vehicle frame  36  should also have high lateral and radial stiffness rates but a low rotational rate. The air spring  34  is designed to respond to 100% of the required vertical loading requirements, which focuses front and rear attachment points to support lateral, fore-aft, and braking loads. Roll loads are reacted through the front suspension member connection.  
      Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.