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.
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.
A front non-drive steer axle is shown generally at 20 in
An air suspension system 32, shown in
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 AR. 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
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
As shown in
The c-channels 38, 40 each include a shackle 60 for mounting the opposite ends of the first and second arms 5256 to the vehicle frame 36. The shackle 60 includes a bracket 60a and a pair of drop links 60b and 60c, as known.
In the example of
The example of
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 78a , 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 78a 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 78b that are inserted through the bracket 78a and into the tube 76. The fasteners 78b do not extend through the first and second leaf springs 70, 72. Instead, one fastener 78b 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 78a 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.
A beam member 86 extends in a generally lateral direction, parallel to the lateral axis of rotation AR, 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
The beam member 86 is preferably a resilient member that can have a c-shape 86a as shown in
The first and second arms 82, 84 each include a first end mounted to the second piece 44b of bracket 44 and a second end mounted to the shackle 60. The first end is preferably mounted to the second piece 44b 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
The beam member 106 is preferably a resilient member that can have a c-shape as shown in
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.