Systems Engineering Approach in Development of Delphi Driver Protection Module (DDPM) by Virtual Engineering

In this paper, the design and development of the Delphi Driver Protection Module (DDPM) using a systems and virtual engineering approach is presented. LS-DYNA software tool was used in virtual prototype studies. The DDPM consists of driver side energy absorbing components. The components included in this module are 1) an adaptive Energy Absorbing (EA) steering column, 2) driver air bag, 3) steering wheel, 4) energy absorbing knee bolster, and 5) adjustable pedals. Each individual component was designed virtually and the virtual design was validated with limited test results. Further, a sub-system mini-sled model using a Blak Tuffy dynamic test was developed to study the functioning of the module due to upper torso loading during a crash. The results of this mini sled model were correlated with actual physical tests. For system level response study, a full finite element sled model was developed. The results of these studies using virtual engineering approach are presented. Introduction The modularization of automotive structures such as the door module, front end module, cockpit module, etc., are becoming common in automotive industry in order to minimize the production cost, reduce the development time and enhance performance of crashworthiness and occupant protection. These structures have to meet various government safety requirements as well as manufacturer’s internal requirements. Also, the safety star rating system for various crash conditions such as US NCAP, EURO NCAP, etc., is becoming a norm of the performance index and hence provides a commercial advantage to vehicle manufacturers. A virtual build of the vehicles based on mathematical analytical tool is replacing the more costly and time consuming hardware build and testing during development cycle. The virtual prototyping process optimizes the design using simulation software tools before the prototype build. Figure 1. DDPM In an event of a frontal collision or crash, the occupants of the vehicle are to be protected from serious injuries. Normally, the protective schemes include an advanced vehicle crumble zone, energy absorbing instrumental panel, knee bolster, steering columns and supplemental restraint Crash/Safety (2) 9 International LS-DYNA Users Conference 6-14 system such as airbags. The major driver side protective components are 1. An Energy Absorbing (EA) steering column and steering wheel, 2. A driver side air bag and 3. An energy absorbing knee bolster. The DDPM is an advanced safety system module that integrates the major components of the driver frontal system such as knee bolster, steering column, steering wheel and the driver air bag without the seat belts as shown in figure 1. . In addition to the energy absorbing components, the DDPM also includes brake pedal which will be moved forward during a crash event. The designs of the individual components are based on specific vehicle architecture and the performance requirements would vary widely. This paper will cover the process and methodology for understanding requirements, developing designs to meet those requirements, virtual testing for validating those designs using LS-DYNA and validation with limited physical tests. Systems Engineering Process The following Systems Engineering V-Diagram (Fig. 2) shows how all systems engineering steps are normally used in vehicle development program. Figure 2. Systems Engineering V-Diagram. The OEMs are required to meet many mandatory government safety regulations in full vehicle system level. These regulations are stipulated under Federal Motor Vehicle Safety Standards (FMVSS) by the government transportation agencies. These regulations cover all types of vehicle crashes; frontal impacts, side impact, pole impact, roll over etc. In addition to Government requirements, the OEMs have their own additional compliance requirements. 9 International LS-DYNA Users Conference Crash/Safety (2) 6-15 Frontal impact occupant protection regulation is covered by FMVSS208 [Ref. 1]. Typical vehicle level requirements are summarized in the following table. Injury Criter. HIC 15ms Neck Injury Nij Fz Crit. Tension (N) Fz Crit. Comp. (N) My Flex. N-m My Exten (N-m) Chest Accln. (g’s) Chest Defl. (mm) Femur Load (kN) HYB. III 50 %ile 700 1.0 4500 4500 310 125 60 63 10 HYB. III 5 %ile 700 1.0 3370 3370 155 62 60 52 5.8 Table 1. FMVSS 208 Vehicle level requirements. Sub-system level requirements are provided to verify the functioning of the components assembly. Typically a mini-sled model such as FMVSS 203 [2] is used to evaluate the steering column dynamic performance. The component performance requirement will widely vary depending upon the architecture of the full vehicle. In general, the individual component specifications may be following and may vary from OEM to OEM based on vehicle architecture. 1. KNEE BOLSTER (Femur Load) 1. For a 5 %ile occupant, the load is less than 6.8 kN per knee. 2. For a 50 %ile occupant, the load is less than 10kN per knee. 2. STEERING WHEEL 1. The wheel should not crack due to 60mm deflection at 6 and 12 O’clock positions. 2. The wheel frequency should be greater than 50 Hz. 3. STEERING COLUMN Column Stroke: 1. Column should stroke and not bind during frontal crash. 2. Column motion in a 30 mph zero degree frontal unbelted crash does not exceed 100mm in the horizontal direction Column Force The column force is with in the range 2kN – 8kN. Column NVH frequency The column frequency should be > 36Hz. There may be many more requirements in addition to above mentioned items. The driver side air bag will have many requirements and are not covered in this paper. Component Design and Validation The design of each of the above mentioned components are described briefly. The virtual prototyping and physical test validation are also given. Crash/Safety (2) 9 International LS-DYNA Users Conference 6-16 Knee Bolster A typical knee bolster is shown figure 3. It comprises of energy absorbing device for each knee. Figure 3. Knee Bolster Figure 4. EA Device The design and analysis of the EA device are documented in previous publication [3]. Various strap shapes were designed to meet the knee bolster requirements given in the table 1. Steering Wheel System The steering wheel deformation during crash is critical since its performance influences the injury number such as chest deflection. A typical steering wheel system is shown in figure 5. The static deflection analysis using LS-DYNA explicit option and the test result correlation are shown in figure 6 for 6 O’clock loading conditions. The performances of various 3D element types in LS-DYNA were also investigated. Figure 6. Steering Model and Analysis Load Vs. Deflection using solid elements with element fromulation 2 0 50