Ladder Frame Concept Development through Parametric Beam Modelling

Body-over-Frame is the primary type of construction used in SUVs, pick-ups, and other commercial vehicles in India. In this type of construction, the body, engine, suspensions etc. are mounted on the ladder frame. Since the frame acts as the skeleton of the vehicle, optimal design of frame at the concept stage of the vehicle program is critical for meeting all structural performance targets. Frontloading of these targets aids in architecture development and reduces future design modifications. The natural frequency response from the frame directly affects the NVH performance of the vehicle. This paper focuses on frontloading the natural frequency targets by performing concept-level simulations on the ladder frame even before creation of 3D concept data. A parametric beam model is created based on the reference vehicles. The beam model has been validated with correlation of more than 85% compared with CAE and physical testing outputs of existing vehicles. Modal analysis of frame using beam-modelling is extremely fast which enables statistical analysis by performing multiple iterations. A Design of Experiments (DOE) study is setup to understand the impact of the frame geometry, sections and weight parameters on the natural frequency and mode shapes. The output of this DOE study aids for further optimization of the beam model. The visualization of mode shapes of concept frame further benefits for defining mounting locations of various systems on the frame. The natural frequency response of the frame should be isolated from natural frequencies of all other major components mounted on the frame. The sensitivity analysis and critical parameter identification assists while modifying existing frame designs as well as developing novel frames. Design guidelines have been established to improve the structural performance of the frame with weight optimization of the frame. Concept-level modal analysis helps in frontloading structural performance targets in the architecture phase itself. This accelerates the overall product development process by reducing detailed engineering & CAE loops.