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An ESC hydraulic modulator contains on/off valves and proportional valves. A complex model of one proportional valve is detailed and used as a basis for model reduction the activity index technique. One interesting aspect is that the technology of the proportional valves remains (i.e. ball valves under conical seat). As such, the parameters are physical parameters forming the ones to master (manufacturing tolerances) by the supplier to also master the dynamic behavior of the system. Once this has been done, a complete model of half an ESC braking circuit is built including the pump, the reservoir, the pipes and hoses as well as the calipers. The activity index technique is thus reused on the circuit to further reduce it to finally obtain a modeling level acceptable for real time purpose.

The description of the supply pressure hydraulic circuit and the couplings between its components are presented. A comparison between simulations and experiments is carried out. Using some linear facilities, it is possible to conclude that the low frequency modes mainly correspond to the wave effects of hydraulic lines which connect valves to each other. In order to maintain a pressure in the supply circuit, an electronic pressure control is necessary. The design of a control law needs to build different linear models for different levels of pressure since the system is very non linear. Three transfer functions are found for three pressure levels. These transfer functions are very similar to the ones used by the automatic control department and obtained by experiments. Using these transfer functions it is possible to design the control law.

Even if the brake judder is an often analyzed problem from the mechanical point of view, its influence on the hydraulic elements such as the braking and steering systems is not fully established. The aim of this paper is to present models of the hydraulic components connected to a model of the front suspension and thus having a view of the influence of these hydraulic elements on the amplification of the brake judder vibrations. Each models of the front suspension, the braking circuit and the hydraulically powered steering assistance are validated separately versus or measurements or other softwares. The introduction of the disc thickness variation (DTV) generates the braking judder of interest. Some first simulation results are shown to see couplings or influence of hydraulic components on vibration propagations.