Spring devices – Vehicle – Torsion
Reexamination Certificate
1998-05-12
2001-03-06
Butler, Douglas C. (Department: 3613)
Spring devices
Vehicle
Torsion
C072S369000, C072S367100, C148S316000, C267S188000, C267S154000, C029S527100
Reexamination Certificate
active
06196530
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a stabilizer for motor vehicles which has a roughly round, preferably spherical, or annular, preferably toroidal, cross section, which has several stabilizer sections and which is made essentially U-shaped, having two legs connected by a U-back with arc-shaped transitional shoulder areas.
2. Description of Related Art
Stabilizers of the initially described type are essentially known, for example, from published German Patent Application OS 28 05 007. Such stabilizers are used on the front and/or rear axles of motor vehicles, and are used mainly to reduce the roll angle of motor vehicles when driving on curves. U-shaped stabilizers are attached with the free ends of the U-legs to the wheel guide parts, while in the shoulder area they are supported in rubber bearings located on the vehicle superstructure. For “weight reduction,” which in general is becoming more and more critical, stabilizers with a circular cross section have come into increasing use; therefore, stabilizers produced from pipes, i.e., so-called pipe stabilizers.
Since, at this point, the stress is greater in pipes than in comparable solid bars (D
a
solid bar<D
a
pipe), under high load they do not reach the required number of load cycles or they can be used for a given number of load cycles only for smaller loads.
Published German Patent Application OS 28 05 007 describes a stabilizer formed of a pipe bent in a U-shape. Here, the required number of load cycles at a given stress will be achieved by the stresses being the same in all stabilizer sections. They are therefore stabilizers with the same stress in all stabilizer sections.
In cases of very high stress, in the past, effective weight reduction in stabilizers was not possible or the stabilizers could not withstand the required number of load cycles.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a stabilizer, especially a pipe stabilizer, which withstand the required number of load cycles even under very high stress, or which enable even high weight reduction under normal stresses.
According to the first teaching of the invention, the aforementioned object is achieved by the individual stabilizer sections being dimensioned such that vibrational strength is optimized in the important stabilizer sections, in contrast to a stabilizer of uniform stress. Here, in the ideal case, the important stabilizer sections have quasi-uniform vibrational strength; but, due to restrictions (limits of diameter and stiffness), this object cannot always be achieved, for which optimization must always be done in the direction of the ideal case.
Optimization takes place by shifting the mechanical deformation work from the highly stressed shoulder arc or shoulder bearing area into the normally less stressed U-back and selectively also into the less stressed areas of the legs. This is done by reinforcing the shoulder arc or shoulder bearing area, therefore, by increasing the outside diameter D
a
, and if necessary, the wall thickness t, thus increasing the spring rate, and at the same time, by weakening the U-back and selectively additional areas of the legs, thereby reducing the outside diameter D
a
and possibly wall thickness t, causing the spring rate to drop there.
In the individual stabilizer segments, the base cross sections (before forming the stabilizers) are preferably constant with the corresponding transitions from one to the other stabilizer section, for reasons of production engineering and economy.
The change of cross sections in the individual stabilizer sections is selected such that the total spring rate corresponds to a comparable solid or pipe stabilizer with cross sections which are quasi-uniform over the entire stabilizer length.
By fixing individual areas with different, preferably constant cross sections, between the individual areas, and in the individual areas themselves, there are different stresses with peaks and valleys, so that there is no stabilizer with the same stress in all stabilizer sections.
It is important to mention that, in the U-back which accommodates more deformation work, the stress can be raised by up to 32% (reference=solid bar constant) or 17% (reference=pipe constant) in order to achieve, in the unloaded shoulder arc or shoulder bearing area, stress reductions of up to 12% (reference=solid bar constant) or 20% (reference=pipe constant).
In the prior art, attempts have been made to increase the service life or allowable stress of the stabilizer by reinforcing the most highly stressed stabilizer sections in different ways. In the stabilizer of the invention, however, the service life or allowable stress is significantly increased by the mechanical deformation work being displaced from the highly stressed shoulder arc or shoulder bearing area into the normally less stressed U-back by making the U-back “softer.”
The area in the U-back which accommodates more deformation work is preferably made with a smaller outside diameter than the transition areas. Thus, the U-back of the stabilizer of the invention is “softer” than the U-back of the known stabilizers; thus, it contributes much more to total deformation under operating load. The configuration of the stabilizer with an outside diameter reduced in the area of the U-back can be accomplished very easily in terms of production engineering, for example, by the corresponding tempering of the bar or pipe used for the stabilizer before or even after bending.
Alternatively the wall thickness of the stabilizer can be reduced in the area of the U-back. In addition, a combination of small outside diameter and reduced wall thickness of the stabilizer in the area of the U-back is possible to further reduce the weight.
According to a second teaching of the invention, the underlying object is achieved by increasing the strength by carburization of the outer and/or inner surface edge area of the stabilizer, especially in conjunction with an annealing process. In this case, carburization can take place both before the annealing process, then preferably also before tempering and forming the stabilizer, and also simultaneously with the annealing process.
Within the stabilizer production process, the carbon content of the material of the surface edge layer drops. Since the carbon content has an effect on the tensile strength of the material, reducing the carbon content in the especially stressed surface edge layer of the stabilizer reduces its vibrational strength. Therefore, carburization increases the tensile strength of the surface edge area of the stabilizer, and thus, the number of attainable load cycles is likewise increased. This effect is especially increased by annealing.
At high basic strength values, for example 1500-1800 MPa, increases of 10-50%, relative to basic strength, can be achieved in the carburized surface edge layer. In this way, the allowable stress or vibrational strength can be clearly increased.
Carburization increases the carbon content of the surface edge layer of the stabilizer, preferably, to such a degree that it is higher in the surface edge layer than within the stabilizer. In this way, the tensile strength is increased overall in the especially stressed surface edge layer of the stabilizer, as is the service life.
If the stabilizer in accordance with the invention is a pipe stabilizer, the allowable higher stress in the area of the U-back can be used to reduce the wall thickness in the area of the U-back. Here, the outside diameter over the entire length of the stabilizer can be constant or have a different value in the area of the U-back. By the possibility of changing both the inside diameter and outside diameter of the stabilizer in order to exploit the allowable higher stress in the area of the U-back, there are no problems in adhering to the outside dimensions of the stabilizer set by the motor vehicle manufacturer.
If the outside diameter of the stabilizer of the invention changes, this change can be made either sudden or co
Muhr Thomas
Schnaubelt Leo
Butler Douglas C.
Muhr und Bender
Nixon & Peabody LLP
Safran David S.
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