Using DIRAC’s Virtual Point Transformation, OEMs can now predict in-vehicle Electric Power Steering sound & vibration performance based on supplier data and vehicle noise transfer functions.
For a German automotive OEM, VIBES engaged in a project analyzing the Electric Power Steering (EPS) system as a noise source. The motor and transmission parts generate vibrations, that propagate into the vehicle’s interior through several structural paths, causing modest levels of noise.
This project was executed following steps 1 to 6 of the Source Characterization Workflow. An important and key aspect of the measurements is the design of the supporting structure of the EPS in the testing environment. The test-rig supports had to be carefully engineered to ensure it was strong enough to bear the load (axial) of the actuators when exerting a realistic tie-rod force on the EPS. Secondly, the dynamic behavior of the EPS on the bench had to show a good signal-to-noise ratio. Therefore, the supports were modeled in a Finite Element package to check whether the design filled the requirements.
DIRAC was used to prepare, measure and analyze the FRF measurements. While performing the actual measurement, every single measurement point was evaluated on the fly using virtual point technology and quality indicators. This ensured that the resulting FRF-matrix was suitable for the characterization of the EPS with blocked forces. The vehicle’s noise transfer functions – from the EPS coupling points to the microphones at driver’s ears position – were measured with DIRAC too. Using the virtual point transformation, the transferability of the blocked forces was ensured, as the EPS points collocate.
The key results in the project:
- Overall resources are reduced (the measurement effort is reduced by >50%) and the NVH evaluations of all EPS-vehicle combinations are performed efficiently without actually mounting each EPS in the vehicles.
- Improved quality of the NVH prediction in a large frequency range (multiple kHz), as the EPS is tested in a controlled environment, thereby avoiding external (noise) disturbances.
- New EPS variants can be quickly evaluated in all vehicle models using already existing vehicle NTFs, greatly benefiting early-phase development.