Achieving An Affordable Low Emission Steel Vehicle; An Economic Assessment of the ULSAB-AVC Program Design

Vehicle weight reduction, reduced costs and improved safety performance are the main driving forces behind material selection for automotive applications. These goals are conflicting in nature and solutions will be realized by innovative design, advanced material processing and advanced materials. Advanced high strength steels are engineered materials that provide a remarkable combination of formability, strength, ductility, durability, strain-rate sensitivity and strain hardening characteristics essential to meeting the goals of automotive design. These characteristics act as enablers to costand masseffective solutions. The ULSAB-AVC program demonstrates a solution to these conflicting goals and the advantages that are possible with the utilization of the advance high strength steels and provides a prediction of the material content of future body structures. This paper provides an overview of the materials utilized in the ULSAB-AVC body structure and describes how these advanced materials, combined with effective design and advanced material processing, deliver a cost effective light-weight structure that satisfies the demanding crash performance requirements anticipated for 2004. The paper compares the ULSAB-AVC design to the previous ULSAB body structure program to provide a comparison of the influence increased crash performance requirements and materials have on the overall mass and cost of a vehicle body structure. This paper also describes the cost assessment of the ULSAB-AVC, which encompasses the entire vehicle manufacturing and assembly process. INTRODUCTION The ULSAB-Advanced Vehicle Concepts (AVC) Program focused on the development of steel applications for vehicles for the year 2004 and beyond. In its execution, concepts were developed for the popular European C-Class, or so-called Golf Class, and the North American Midsize Class (see Figure 1), which is the target for the PNGV program, hereafter referred to as PNGV-Class vehicle. Therefore, the vehicle body structures employ the unique advantages of advanced steel grades, which provide heightened strength with excellent part forming. ULSAB-AVC vehicle body structure uses 100 percent high-strength steel grades, of which over 80 percent are advanced high-strength steels. These steels are combined with the most advanced manufacturing and joining technologies to achieve the structurally efficient designs and safety features found in ULSAB-AVC concepts. Key to reaching the program objectives was meeting anticipated 2004 crash requirements with steel, achieving the delicate balance of mass efficiency without a compromise to safety. The resulting Midsize Class vehicle concept has a mass of less than a 1000 kg and has the capability of achieving a five-star safety rating. It also approaches the PNGV target mileage by achieving 68 miles per gallon in the combined U.S. Driving Cycle and 78 miles per gallon highway. With high-volume manufacturing of 225,000 units per year, the AVC concept would not cost more to manufacture than comparable family sedans. Benchmarking data indicate that the Midsize Class ULSAB-AVC concept vehicle selling price would be below the selling price of current vehicles in the same class. The ULSAB-AVC is the most recent addition to the global steel industry’s series of initiatives offering steel solutions to the challenges facing automakers around the world today. It succeeds ULSAB [1, 2], ULSAC [3] and ULSAS [4]. The ULSAB-AVC concepts revolutionize the kinds of steels normally applied to vehicle architectures, as well as demonstrating cutting edge steel vehicle design. In addition to extensive use of advanced steels, ULSAB-AVC features a full spectrum of the latest steel technologies, including tailor welded blanks, tailored tubes, advanced joining techniques and tube and sheet hydroforming. This project was envisioned by the collaborative efforts of 33 international steel producers forming the ULSABAVC Consortium. This concept, engineered by Porsche Engineering Services, Inc., Troy, Michigan, USA, brings the potential for safe, affordable, fuel efficient vehicles, which are environmentally responsible, to near-term reality. Detailed information on ULSAB-AVC can be found in reference [5, 6]. BODY STRUCTURE EVALUATION The influence of AHSS grades on an entire body structure is difficult to assess. It is not possible to make a direct comparison of the entire body structure designed to the same criteria. A comparison made between the ULSAB-AVC (PNGV class) and the ULSAB body structures is very similar to the challenge placed on current automotive designs. For the purposes of this comparison one can consider the ULSAB-AVC to be a redesign of the ULSAB. The ULSAB-AVC program was distinctly different from the preceding ULSAB program as described below: ULSAB-AVC: 1. Concept design of entire vehicle. 2. Utilized materials and processing technically feasible in 2004. 3. Designed to meet crash performance requirements anticipated in 2004. ULSAB: 1. Concept design of a body structure. 2. Utilized material and processing technology production capable in 1998. 3. Designed for crash performance requirements of 1996. This comparison is unique from the challenge typically place on the automotive designer in that both design programs are provided the luxury of starting from a clean sheet of paper and are not hampered with the constraints of modifying a previous design. This section of the paper provides a comparison between the body structure of the ULSAB-AVC (PNGV) and the ULSAB program. A comparison is made between the vehicle size, crash performance targets, materials utilized and the corresponding body structure mass and cost. Figure 1 provides a comparison of the overall body sizes and general internal packaging targets. The total length of the body structures are nearly identical. However, as is typically required of new designs to reduce air drag and improve fuel economy, the frontal area is reduced by reducing the width and height of the vehicle with a more streamlined shape to provide a predicted drag coefficient of .25. The reduction in external dimension is accompanied with an increase in internal passenger and cargo space. This complicates the design by reducing and restricting available package space for the body structure and reducing the available space for crush zones required to satisfy the crash performance targets. The difficulties placed upon the designer to satisfy the crash performance requirements with reduced packaging space are further exacerbated with the requirement to satisfy more severe crash events. The influence of Government mandates, the insurance industry and internal marketing strategies require the designer to satisfy increasingly severe crash environments with the expectation that the passenger survives these events with a reduced chance of injury. In addition, many automotive manufactures design their product to be marketed to several regions with different ULSAB ULSAB-AVC Dimension ULSAB