Metal deforming – By application of fluent medium – or energy field – With actuated tool engaging work
Reexamination Certificate
2000-12-08
2002-07-16
Jones, David (Department: 3725)
Metal deforming
By application of fluent medium, or energy field
With actuated tool engaging work
C072S370220, C029S897200
Reexamination Certificate
active
06418770
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a method for improving the fatigue life of a stabilizer bar by employing autofrettage to the inner surface of the stabilizer bar.
Vehicles are commonly equipped with suspension systems for absorbing road shock and other vibrations, while providing for a smooth and comfortable ride. A suspension component, such as a stabilizer bar, is often used to increase roll rigidity and to improve the steering stability of the vehicle.
One common problem with tubular stabilizer bars is that fatigue fractures originate along the inner and outer surface of the tube. Shot peening is employed to relieve tensile stresses and to reduce fractures. In the shot peening process, a plurality of small beads are shot by a machine through an injection nozzle onto the surface of the smooth bar. The force of the small beads deforms the surface of the bar, creating a compressive stress which counteracts the tensile stress from every day use.
Shot peening the outer surface of the stabilizer bar assists in eliminating fractures on the outer surface of the bar. However, shot peening the inner surface of the formed tubular stabilizer bar is difficult due to bends formed in the stabilizer bar, and the nozzle of the machine is unable to access the entire inner surface of the tube. Therefore, in shot peening applications, most fractures will occur on the inner surface of the tube due to the difficulty in applying the shot peening process to the inner surface of the tube in the area of the bends.
Hence, there is a need in the art for a method for improving the fatigue life of a stabilizer bar by employing autofrettage to the inner surface of the stabilizer bar.
SUMMARY OF THE INVENTION
This invention relates to a method for improving the fatigue life of a stabilizer bar by employing autofrettage to the inner surface of the stabilizer bar.
In a preferred embodiment, an autofrettage process is applied to the interior surface of a formed vehicle stabilizer bar. During vehicle operation, the stabilizer bar is subject to tensile stresses caused from road shock and other vibrations. These tensile stresses decrease the fatigue life of the stabilizer bar and cause fractures. By employing an autofrettage process to the formed stabilizer bar, the amount of fractures along the inner surface of the stabilizer bar can be decreased.
In applying the autofrettage process, one end of the formed stabilizer bar is clamped. A pressurized fluid is introduced into the interior space of the stabilizer bar, filling the inner space and slightly increasing the inner diameter. As the inner surface is deformed, compressive stress forces are created.
The compressive stress forces counteract and oppose the tensile stress forces created from vehicle operation and everyday use. By counteracting the tensile stress forces, fractures on the inner surface of the bar can be minimized, increasing the fatigue life of the bar. Because a fluid is utilized, the autofrettage process can be applied to the entire inner surface of the stabilizer bar, including bend areas. Therefore, fewer areas on the interior surface of the stabilizer bar are missed by the autofrettage process, resulting in fewer fractures and a longer fatigue life.
A shot peening process is applied to the exterior surface of the stabilizer bar to minimize fractures on the exterior surface of the bar. A plurality of beads are shot by a machine to deform the exterior surface, creating a plurality of compressive stress forces to counteract the tensile forces.
In another embodiment, the autofrettage method is employed to a tubular torsion bar, increasing the fatigue life of the torsion bar.
Accordingly, the present invention provides a method for improving the fatigue life of a stabilizer bar by employing autofrettage to the inner surface of the stabilizer bar.
These and other features of the present invention will be best understood from the following specification and drawings.
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Carlson & Gaskey & Olds
Jones David
Meritor Suspension Systems Company
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