Land vehicles – Wheeled – Running gear
Reexamination Certificate
2000-04-24
2001-12-11
Dickson, Paul N. (Department: 3618)
Land vehicles
Wheeled
Running gear
C280S124156, C280S124167
Reexamination Certificate
active
06328322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a drive axle suspension; and, more particularly, to a heavy-duty drive axle suspension capable of maintaining a substantially constant pinion gear angle while flexing to permit operationally sufficient independent movement of wheels coupled to the suspension.
2. Description of the Related Art
Heavy-duty truck drive axle suspensions typically comprise a pair of trailing arm suspension assemblies, each mounted parallel to and spaced from frame rails in the truck chassis. Each trailing arm suspension assembly comprises a trailing arm having one end pivotally mounted to a hanger bracket, which is rigidly mounted to one of the frame rails, and an air spring connecting the other end of the trailing arm to the frame rail. The suspension assemblies carry a drive axle differential comprising a housing from which extends a pinion gear and axle housings, containing the axle shafts. The axle housings connect the differential to the trailing arms through axle brackets. The pinion gear is connected to the engine through the drive shaft. The axle shafts mount the wheels and are driven by the engine through the connection between the drive shaft, pinion gear, and axle shaft.
A trailing arm suspension of this type translates road forces imparted to the wheels into a rotational movement of the trailing arms relative to the hanger brackets. The rotational movement of the trailing arm is cushioned by the air spring positioned between the end of the trailing arm and the frame rail.
A common design problem for drive axle suspensions is to keep the pinion gear parallel to the engine output shaft. The torque applied to the pinion gear from the engine through the drive shaft, results in torque applied to the drive tires which results in tractive effort being applied to the ground through the tire contact area. The reaction to the torque from the drive tires is a torque in the drive axle housing along its lateral axis, which is clockwise when viewed from the left side of the vehicle. This torque, when coupled to a single pivot suspension, tends to raise the forward end of the trailing arm and thus raises the frame a few inches with respect to the axle. This height rise changes the pinion angle dramatically.
The torque induced pinion angle change is exacerbated by newer high horsepower, high torque engines that produce substantially greater torque at lower rpms than previous engines. The new engines produce such high torque at such low rpms that each piston firing can result in a spike in the torque loading of the drive line components extending from the engine to the pinion gear of the differential. The magnitude of the torque load, in conjunction with a single pivot suspension, can alter the pinion angle dramatically, which sets up vibrations in the entire drive train. To prevent damage to drive line components and eliminate vibration, it is necessary to keep the pinion angle within predetermined limits.
One attempt to maintain the pinion angle at a substantially constant angle stiffened the suspension to prevent rotation around the suspension pivot in response to the torque reaction lifting force on the drive axle. One solution adds springs to the shock absorbers to prevent frame rise and subsequent pinion angle change.
The stiffening of the suspension to prevent the rotation of the axle housing can give rise to some additional undesirable operational characteristic. The suspension can be so stiff that it will reduce axle travel and, when the vehicle is lightly loaded and traversing slightly uneven ground, it may lose traction. Further, the spring in the shock absorber changes the ride characteristics and decreases the suspension's response over rough roads.
Therefore, it is desirable to have a drive axle suspension that maintains a substantially constant pinion angle while providing sufficient suspension flexibility to ensure the best possible performance and durability.
SUMMARY OF THE INVENTION
The invention relates to a drive axle trailing arm suspension adapted to support a drive axle. The drive axle comprises a differential housing having opposing drive axle housings, each containing a drive axle. The drive axles connect to a pinion gear through other gearing. The pinion gear forms an angle relative to the vehicle chassis and operably couples to a vehicle drive shaft for transferring engine torque to the drive axles through the differential.
The drive axle suspension preferably comprises a pair of trailing arm assemblies adapted to mount to opposite sides of a vehicle and support the drive axle housings. Each of the trailing arm assemblies comprises a trailing arm having a longitudinal axis. A first portion of the trailing arm is adapted to pivotally mount to a vehicle frame, preferably through a vehicle frame bracket, for pivotal movement in a generally vertical plane. An air spring is positioned between a second portion of the trailing arm and a vehicle frame for load support and pivotal movement of the trailing arm in the vertical plane. The drive axle trailing arm suspension further includes a torsion bar extending between the trailing arms. The trailing arms each have a blade-shaped beam capable of twisting about the trailing arm longitudinal axis substantially follow the motion of the attaching parts.
Preferably, the blade-shaped beam has a generally rectangular transverse cross section, which can vary over a wide range depending on the requirements of the suspension. The blade-shaped beam should be rigid in a vertical direction and flexible in a lateral direction. In general, the blade-shaped beam can have a height to thickness ratio in the range 6 to 20. The width of the transverse cross section is preferably ⅜ inch to ¾ inch, and the height is preferably 3 inches to 10 inches. The blade-shaped beam also has a yield strength of 60,000 psi to 180,000 psi. It is preferred that the blade-shaped beam be made from high-strength steel.
The torsion bar is preferably connected to the trailing arms by shrink fitting portions of the torsion bar within openings in each of the trailing arms. Each trailing arm assembly can further include an axle bracket that is adapted to mount an axle housing. The axle bracket is mounted to the trailing arm by a bushing assembly, where an outer sleeve of the bushing assembly is preferably shrunk-fit within an opening in the trailing arm. A second bushing assembly is preferably used to pivotally connect the trailing arm to a vehicle frame, generally through a hanger bracket. The second bushing assembly outer sleeve is preferably shrunk-fit within an opening in the trailing arm.
In one embodiment, a control arm has one end adapted to pivotally mount to a vehicle frame through the hanger bracket or other frame bracket and has a second end pivotally mounted to the axle bracket or the axle to form a parallelogram trailing arm assembly. There may be one control arm on one side or in the center, or two control arms, one on each side. Preferably, each axle bracket assembly is pivotally mounted to the trailing arm at a single point of rotation.
In another embodiment, the trailing arm assemblies can comprise a linkage connecting the torsion bar and a portion of a vehicle frame. The linkage preferably comprises an arm and a link connected by bushing assemblies. The arm comprises a first portion having an opening through which the torsion bar passes and a second portion having an opening in which the bushing assembly is received. The link has one portion connected to the bushing assembly and another portion adapted to connect to a vehicle frame. Preferably, the torsion bar is pressed within the arm first portion opening and a sleeve of the bushing assembly is shrunk-fit within the arms second portion opening. The linkage can include a second link spaced from and parallel to the first link.
In addition to the torsion bar extending between the trailing arms, a cross plate can span the trailing arms a spaced distance from the torsion bar. Preferably, the cross plate is mounted to a
Dickson Paul N.
Holland Neway International, Inc.
Rader, Fishman, Grauer & Mc Garry
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