Patent Application
20110101630
Shape of anti-roll bars for automobile suspension systems are usually designed from a standpoint of avoiding physical interference with other components mounted on the bottom of a vehicle. Also the diameter of the bar is usually pre-selected and fixed to achieve a desired anti-roll stiffness. By setting a limit or limits to the shape (to avoid interference with other components) and fixing the diameters of the anti-roll bars there is little design flexibility to allow engineers/designers to adjust the resultant stress a given anti-roll bar will experience in use.
One well known method for reducing stress in anti-roll bars involves increasing the radius of bent portions of the anti-roll bars. However, this approach is not always possible when interference of other components becomes an issue or when clamping position of the anti-roll bars is difficult to change.
In order to improve the durability of anti-roll bars, there have been a couple of conventional approaches as follows: 1) Material approach: use of high strength material(s) and materials having high hardness; and 2) Manufacturing approach: use of efficient shot peening process that will create a compressive residual stress layer that will resist surface cracking.
The present invention provides a new design approach to fabricating anti-roll bars which involves slightly modifying the bend shape of the anti-roll bars.
According to one embodiment the present invention provides an anti-roll bar for a vehicle suspension system which comprises at least one bend having a non-constant radius which reduces peak stresses applied to the at least one bend.
The present invention further provides a suspension system for a vehicle which comprises an anti-roll bar having at least one bend having a non-constant radius which reduces peak stresses applied to the at least one bend.
The present invention also provides a method of reducing peak stress in bends of anti-roll bars which method comprises configuring bends in anti-roll bars so that the bends do not have constant radii of curvature.
The present invention will be described with reference to the attached drawings which are non-limiting examples only, in which:
The present invention is directed to a method of configuring and fabricating anti-roll bars so that stresses experienced under load are distributed and maximum stresses are reduced or smoothed out. This distribution and reduction of stresses allows the resulting anti-roll bars have extended useful product lives as compared to prior art anti-roll bars.
Anti-roll bars are coupled to vehicle suspension systems near opposite ends of the anti-roll bars by clamps. By convention, the first bends that are formed in anti-roll bars outside of the clamps are referred to as “shoulder bends.” Accordingly reference herein to shoulder bend identifies the first bends that are formed in anti-roll bars outside of the clamps. Some anti-roll bars include substantially straight central portions between their shoulder bends. Other anti-roll bars can have multiple bends between and/or outside of their shoulder bends. Although peak stresses can develop along shoulder bends, other in some configurations peak stresses can develop in bend portions other than shoulder bends. Accordingly, while reference and discussion is made herein to shoulder bends, the manner of designing bends in anti-roll bars is not limited only to shoulder bends, but is rather applicable to any bend(s) that experience stresses that can be reduced or distributed according to the present invention.
According to the present invention bent areas that are formed in the anti-roll bars do not have a constant radius of curvature. This approach departs from traditional anti-roll bars in which of the bent areas have constant radii. During the course of the present invention it was discovered that the peak stress values which usually develop at the bends of conventional anti-roll bars (having constant radius bends) when the anti-roll bars are deformed can be distributed so as to reduce the peak stress values.
In order to evaluate and study the relationship of stress distribution to bend shapes of anti-roll bars various bend shapes of anti-roll bars were tested and bend shapes were changed to determine how shape changes effected stress distribution of anti-roll bars.
The procedure followed during the course of the present invention to determine optimal bend shapes for stress reduction involved expressing bend shapes experimentally as Bezier curves with five control points. For a given initial curve, three control points are independently readjusted within a certain position range while two control points are fixed so as to maintain a continuity of the bar shape (e.g., limited by manufacturability), so that thousands of bend shapes can be created and subjected to loads. Following this approach the best shape which minimizes the peak stress can be determined via finite element analysis (FEA). This procedure proved that the maximum stresses on the bend of an anti-roll bar can be reduced if the bend shape is not in the shape of a partial circle, i.e. does not have a constant radius of curvature. This discovery runs against the conventional use of constant radius dies about which anti-roll bars are conventionally bent.
Whereas the present invention provides bent shapes for portions of anti-roll bars that distribute and reduced areas of high stress, the actual manner of fabricating and bending the bars involves substantially conventional technologies such as bending dies. Howbeit the use of appropriately shaped dies, such as dies that do not have a constant radius are used according to the present invention. Likewise, other machinery or apparatus that are used to bend bars can be similarly modified to form bends that do not have constant radii or continuous bends.
According to another embodiment of the present invention it was discovered that bent shapes in which adjacent portions have different radii of curvature also can be used to distribute and reduced areas of high stress
The constant radius bend of the conventional bend shown in
It is noted that overall shape of the bend formed by a combination of curved and straight portions in
The bent portions of the anti-roll bars discussed herein are the shoulder bends. In a simple shaped anti-roll bar as shown in
Other embodiments that are encompassed by the reference to non-constant radii include bends that have middle portions with radii of curvature that are larger or smaller than one or more side or adjacent portions. Further a non-constant bend can comprise two or more portions that have different radii of curvature and are not limited to the non-limited example shown in
Although the present invention has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications can be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as described above.
