OBU - Masters Dissertation

Oxford Brookes University

Front Suspension Design & Analysis

Abstract:

The focus of this project is on the front suspension system for an amateur electric race car as proposed by Dallara Automobili. The first (current) year of the project was limited to overall vehicle design. This report outlines the research and methodology taken to design the front suspension for the Dallara vehicle. The suspension system was designed specifically for an amateur racing series with specific performance goals. These include:

• Controllable and predictable handling

• Linear roll response

• Large range of tune-ability (to accommodate driver preference)

A road-map and analysis of suspension parameters and their respective justifications are discussed. These parameters include:

• Justification to suspension design configuration

• Main spring rates and IR

• ARB spring rates and IR

• All suspension hard-point locations

Suspension parameters including spring rates, ARB rates, and IRs were optimized through use of a spreadsheet created in Microsoft Excel. All parameters were optimized with the following targets:

• Total Lateral Load Transfer Distribution (TLLTD): 45 - 50% Front

• Roll Gradient: 0.7-0.8 deg/g

• WnR > WnF by 10%

• Lowest front & rear spring rates used for maximum tractive effort

A full front suspension model was created in the multi-body dynamic software MSC Adams (a detailed model break down is presented). This model was used for two main purposes: to model all suspension kinematic properties and to provide a two-post rig simulation for damper optimization.

Four-way adjustable digressive dampers were simulated in the Adams model. Low speed damper values were optimized by minimizing vehicle roll response time given a lateral acceleration. The low speed damping Adams response was successfully validated by comparing results to a one-DOF Simulink model. High speed damper values were optimized by minimizing contact patch force variation, given a swept sine wave input (representing generic track road inputs). An Adams design study was used, and the vehicle response was successfully validated by comparing results to a two-DOF Simulink model. An OEM spring / damper setup was suggested for manufacturing given the optimized damper curves.

This project proved successful, and a detailed front suspension configuration was presented to Dallara. This work, along with input from the other Dallara suspension team members, has provided a strong foundation for future development.

Optimized damper response from example step steer input.

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