Automated Parking Brake (APB) are common systems on recent vehicles. They must fulfil NVH targets defined by car manufacturers. In this context, the dynamic behaviour of such a system should be well known to optimize its design and avoid noisy operation. For an APB system based on a geared transmission, the main source of excitation is generated by the meshing process. It is usually assumed that static transmission error (STE) and gear mesh stiffness fluctuations are responsible for noise radiated by the housing. They generate dynamic mesh forces which are transmitted to the housing through wheel bodies, shafts, and bearings. Housing vibratory state is directly related to the noise radiated from the gearbox (whining noise). Although the prediction of whining noise is rather well mastered for steel gears, the case of plastic gears brings some news challenges. The important flexibility of wheel bodies and the difficulty to control the micro-geometry makes harder the estimation of the resulting whining noise. This work presents an efficient method to compute the whining noise of a real industrial system with both plastic and metal gears. A complete measurements campaign has been carried out to attest the efficiency of the computation process in order to predict the dynamic behaviour of the system. First, the excitation is computed in a deterministic way. Then, a complete Finite Element Model (FEM) is built and tuned to represent the modal behaviour of the system. The dynamic response is then computed using an efficient computational scheme (Spectral Iterative Method, developed by the École Centrale de Lyon). The procedure is based on a modal approach developed in the frequency domain, particularly efficient to analyse systems having many degrees of freedom and subjected to parametrical excitation. The computation output result has shown a good agreement with accelerometer measurements. Finally, a vibro-acoustic model is used to simulate acoustic radiation emitted by the APB gearbox. The computed acoustic response has been compared to microphone measurements. Operational gear measurement and calculation model are analysed in frequency domain during idle phase. This allows us to correlate, and an algorithm is proposed to deal with the acoustic power and ERP. the relationship between those two calculations shows us a good behaviour and level from low and medium frequency ranges. Next step will be to introduce the DC motor in our model and will allow us to complete the modal behaviour from our system (mechanical and electrical).
Hitachi Astemo: Mr. Zaid Boussattine, Dipl.-Ing Thierry Chancerlier, Dr.-Ing Sylvain Thouviot, Dipl.-Ing. Remi Lemarie, Dipl.-Ing. Said Hamdi