Steering system development using test rig and driving simulators

Abstract: Conventional model-based development approaches such as Model-in-Loop (MiL) and Software-in-Loop (SiL) have been used in electric power assisted steering (EPAS) development in recent years, but when it involves a physical motor and the vehicle communication network, the development mostly comes down to real vehicle testing and tuning. The objective and outcome of this master thesis is to develop a Hardware-in-Loop (HiL) environment that involves the real EPAS powerpack and human Driver-in-Loop (DiL) using a static driving simulator. The focus is on the study of the performance of the HiL rig in terms of its ability to reproduce steering related Objective Metrics (OMs).In this thesis work, the initial part deals with the study of EPAS systems, HiL test-rigs, objective metrics and real-time simulation environment. The second part deals with the modeling and verification methods of an EPAS system along with HiL testrigs using high and low fidelity vehicle models and steering systems in the MiL and SiL environment.As this thesis work deals with the HiL test rig, some practical problems were faced. These involve implementation and HiL architecture, data transmission between the test rig and the real time simulation environment with rest-bus simulation. Several HiL test-rig issues and limitations are addressed: 1. EPAS torque measurement noise; 2. System bandwidth limitation from control and hardware perspectives; 3. Simulation model; 4. System delays and cogging. Due to these drawbacks the testing scenarios are currently limited between low to mid-frequency vehicle manoeuvres. OM values from HiL simulations accurately compare with real-test data, but the subjective steering feel can still be quite different which is not rep-resented by OMs. Furthermore, the system can be improved by smoothing the reference and control signals by an implementation of low-pass filters or observers, and potentially by different servo control strategies and compensators. Once fully functional, the HiL simulation will be useful during early stage steering system development, being sensitive to changes in a similar way to a real vehicle during testing.