1、1 Introduction The key task for the automobile industry and its suppliers in future lies in speedily developing and implementing ecologically sound and economically justifiable mobility systems. Light metals such as aluminum and magnesium along with glass and carbon fiber reinforced materials, ceram
2、ics and composites have opened up the potential for considerable weight reduction and for green vehicle concepts which can be realized economically. Aluminum in particular can provide the impetus for new designs for the next millennium. Decades ago, the use of aluminum in auto construction was seen
3、as an experiment； Today it is a vital factor in reducing weight and thus lowering fuel consumption. The average passenger car today contains 60 to 70 kg of aluminum, and current developments point to a doubling of this amount in the next few years. Motor vehicles both now and in future must meet req
4、uirements for: greater performance, greater safety, comfort, low pollution. Lightweight construction is not just about reducing weight； it is a question of -striking the right balance between reduced weight and structural efficiency. In vehicle construction this normally means making the best use of
5、 the generally very tight space available for individual components so as to allow weight to be minimized while still meeting all stiffness, strength, natural frequency or acoustical requirements. To achieve this, stresses must be distributed throughout the structure as evenly as possible. Modern nu
6、merical analysis methods such as FEA allow a very detailed analysis of system behavior, provide cost-efficient support for the complex process of optimization and thus make a huge contribution to advances in lightweight construction. Packaging, safety considerations, reproducibility and price place
7、restrictions on the degree of weight reduction achievable. The broad range of expertise available to Krupp Presta AG allows the company to analyze customer specifications for steering systems and provide appropriate solutions. 2 Requirements to be met by steering systems The steering is an important
8、 part of the feel of a car. The steering system should make driving an enjoyable experience with no unpleasant vibration from the road surface while guaranteeing the required hand- sing. It is also important that high safety requirements be met, both under normal conditions and in crash situations.
9、The key criteria for the steering system are thus as follows:rolling friction, torsional stiffness /strength, Damping, temperature, corrosion, durability / fatigue, weight. Crash kinematics and energy absorption steering column requirements:natural frequency / stiffness, mass, damping, space, streng
10、th (crash, misuse), ergonomics, handling, acoustics, crash kinematics and energy absorption. Other basic conditions:interfaces with adjacent components, installation, joining techniques, price. 3 Materials material light weighting can be achieved by using either stronger or lighter material. When st
11、iffness or natural frequency are Important sizing criteria, low density materials with a high modulus of elasticity by quired. Non-exotic materials must be selected which are readily recyclable, low in price and display good durability.Further requirements are set by the manufacturing and joining pr
12、ocesses. Steel, aluminum, magnesium and a variety of plastics are the materials of choice for steering systems. Low specific gravity, high corrosion resistance, low fabricating costs, high energy absorption and good recycle ability make aluminum a favored light weighting material. Owing to its high
13、energy content, up to 90% of the aluminum used in auto construction can be recycled (intelligent design / no mixing with other materials). The favorable energy balance of aluminum puts it at a great advantage over many other materials.In environmental terms aluminum scores highly. The large amounts
14、of primary energy required to make raw aluminum are offset over the lifetime of the vehicle. Composites could also become a very attractive proposition on account of their extreme stiffness, low weight and energy absorption capabilities. At present, howler, price is a problem, as are joining and qua
15、lity assurance. 4 Reducing component weight A focused strategy to reduce component weight requires a lightweight approach to design (force distribution, stresses), material (material selection), specifications (modified, realistic specifications) Key factors in lightweight design include 1: force fl
16、ows, material properties, ambient conditions safety requirements, reliability of joints, manufacture ability. Practical experience has shown that car makers specifications based on steel need to be revised for lightweighting. Requirements valid for a steel steering shaft, for example, can result in
17、severe oversizing of an aluminum shaft. Reducing component weight requires material compatible designs combined with material- compatible specifications. 5 Lightweight components As part of its development program Krupp Presta is replacing conventional steel steering components such as steering rods
18、 , shafts or forks with corresponding aluminum components produced by new processes. Weight savings of 20-30% are achievable depending on the basic conditions stipulated by the customer. Aluminum and magnesium die castings are already being used in steering columns , and further opportunities for we
19、ight reduction are being investigated. The lightweight steering column (Fig. 1) produced by Krupp Presta for the Audi A6 is a good example. By using magnesium die castings it has been possible to limit the weight of the steering column to just 5kg, a reduction of 15-20% over conventional (steel) des
20、igns. 6 Steering column design Experience has shown that it is possible to design steering columns for cars more or less on the basis of their natural frequency alone. Additional engineering work may be required to design critical parts which must not break in the case of a crash or misuse (e.g. the
21、ft). The main task when engineering a steering column is thus to achieve the highest possible natural frequencies while minimizing weight. Low-stiffness components are being analyzed and refined in an effort to achieve uniform loading of the structure. In solving this task, use is made of numerical
22、methods such as FEA. The structure is divided into finite elements which are characterized by specific deformation assumptions. Using FE analysis it is possible to examine complex structures, analyze sensitivities and links, discuss variations or ways of making improvements and optimize the structur
23、e numerically. Topological optimization is carried out for the analysis of low-stress areas and for the basic design of ribs and beads. CAD geometry data are processed in an FE pre-processor. Correct modeling of the following is essential, individual parts, stiffness, contact faces, kinematics mass.
24、 Modeling is followed by computation and evaluation of the data obtained. The deformation energy is a global measure for assessing stresses. Normalizing the element deformation energy by the element mass provides information on the stresses acting on the element relative to its mass. The kinetic ene
25、rgy is regarded as the influence of vibrating masses which have a negative effect on the natural frequency of the steering column. By evaluating stress and strain conditions, highly localized weak points or high-stress areas can be identified. 7 Conclusions Existing technologies must be continuously
26、 adapted and improved in line with the requirements of the auto industry. Systematic weight reduction is a major challenge and requires close cooperation between vehicle manufacturers and suppliers. Materials, fabricating and joining technologies must be further refined. One prerequisite for the continuing success of Krupp Presta is the flexibility to react to customer wishes and requirements. Reference 1 Klein, B.: Leichtbau-Konstruktion. Berech- nungsgrundlagen und Gestaltung. Braunschweig: Vieweg, 1997
