Metal working – Method of mechanical manufacture – Structural member making
Reexamination Certificate
2002-08-23
2004-11-02
Bryant, David P. (Department: 3726)
Metal working
Method of mechanical manufacture
Structural member making
C029S558000, C072S334000, C280S124134
Reexamination Certificate
active
06810586
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a control or link arm for use in the wheel suspensions of cars, and in particular a control arm made from aluminium, and a method for its manufacture.
PRIOR ART
Traditionally, control arms are made from steel. The arms are manufactured by stamping separate details of the arm out of steel sheets and pressing them into their desired shape. The separate elements are welded together into a hollow arm, which is then painted. These are techniques that have been in use for more than a century. The necessary equipment for making components for the suspension of cars according to this method is in wide use, and the method is standard in all industrialised countries. This means that components manufactured according to this method are cheap, and all the more so, since the raw materials are cheap as well.
However, these components and their method/means of manufacture also have their drawbacks. First, the steel components are relatively heavy. This is a drawback, since car manufacturers try to keep the weight of the movable components in vehicular wheel suspensions as light as possible to improve road handling. They also try to keep the overall weight of car down, to reduce fuel consumption. The manufacturers try to reduce the weight problem by stamping holes in the sheet material to lighten the component. Superfluous material is then removed, where this can be done without adversely affecting the strength of the component. However, the hollow component with its cut-outs are apt to collect snow and dirt in the harsh environment under the car. Humid dirt collects in pockets in the construction, which subsequently become growth sites for rust. The manufacturing process requires rather expensive tools. In addition, the component is made from several elements, and the separate steps in the production; stamping, welding and painting, have to be handled separately, that is, they cannot be handled in a single production line. If the manufacturer wants to change the form of the component, new dies must be made for the presses; this makes the change costly.
U.S. Pat. No. 5,800,024 describes back suspension constructions for vehicles, made from aluminium. Several of the embodiments shown are made from aluminium profiles, comprising a number of individual sub-components welded together into the finished product. The drawback of this technique is that the production becomes more complicated, demanding a very accurate shaping and welding of each individual sub-component. The sub-components have to be shaped very accurate if an automated production line is to be used. This relates also to the less important parts of the construction, i.e. sub-components that will experience little loading or not includes mounts, etc. Further, welding of aluminium is a difficult operation that has to be done in an inert atmosphere. Welding of loaded components is generally undesirable, as the structure of the material is impaired and the component becomes weakened and less corrosion resistant. In order to compensate for this weakening, the dimensions, i.e. the wall thickness, have to be increased. Thus, some of the weight reducing benefit of aluminium is lost.
U.S. Pat. No. 6,060,445 describes a control arm produced by hydro forming. In a hydro forming process, an elongated hollow tube, which can be of aluminium, is closed at both ends, placed in a hydro forming press with dies whereupon the tube is filled with a hydraulic fluid. The tube will expand under the pressure from the hydraulic fluid and attain the shape defined by the dies. The main benefit of this process is that the product will get a very accurate shape. However, there are also some drawbacks. Only profiles with walls of regular thickness can be used, else localized flow of the material will occur. Of the same reason mounting flanges on the profile must be avoided. Mounting details, like bushings, must be welded onto the profile. However, the biggest disadvantage is the high production costs.
One car manufacturer, BMW (Bayerische Motoren Werke, Germany) is currently using the production methods outlined above in some of its models. Suspension components are assembled from several individual pieces. To obtain the accuracy needed for automated welding, some of the pieces are produced by hydro forming. However, the cost of suspension components produced in this way precludes a more widespread use.
Aluminium control arms have also been made as cast/forged aluminium components. This is sometimes a good solution when components with a complex shape are involved. However, the drawback is more limited regulated weight reduction, when the shape has to be solid. Another drawback is that the properties of the materials used in cast/forged processes are generally inferior due to a “short” grain structure, which makes the material brittle.
BRIEF SUMMARY OF THE INVENTION
The present invention has as its objective to provide a control arm for use in wheel suspension units for cars, that is near optimum light in weight, is made from one piece, has no welds and has a aerodynamic shape which prevents the collection of dirt, and is corrosion resistant. A further objective of the present invention is to provide a method for manufacturing suspension components for cars that use cheaper tools than traditional methods, which tools might easily be adjusted to fit changes in the shape of the manufactured component, and which uses only one production line.
These and other objectives are met by a control arm according to the present invention.
In short, the present invention relates to a control arm made from a stock extruded aluminium profile designed in shape and variable wall thickness to make it simple to form and have good performance related to weight, which has a closed shape without any unnecessary openings, and might be produced in a single production line using standard machinery and a limited tool package for the stretch-bending and forming.
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patent: 6122948 (2000-09-01), Moses
“A Practical Guide to Low-Cost Production”, A Handbook of Product Design for Manufacturing; copyright 1986, McGraw-Hill.
Ruste Trygve
Waaler Rune
Bryant David P.
Jackson William E.
Raufoss Technology AS
Stites & Harbison PLLC
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