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A hydraulic chamber is embedded in serial with the accumulator of a normal mono-tube magnetorheological fluid damper (MRFD). The damper stiffness can be adjusted by changing the accumulator volume with the hydraulic chamber. The hydraulic chamber is connected to an electric pump and controlled by the braking-by-wire (BBW) system. A modified bi-viscosity magnetorheological fluid (MRF) model that explicitly includes the parameter of control current is proposed. A dynamic model of this hydraulic MRFD is subsequently set up based on the MRF model. Experiments are conducted to validate the model and simulations are carried out to study the influences of accumulator volume on the external performances. Results show that the hydraulic chamber is able to provide rapid variations of the external force through accumulator volume changes.

The traditional vacuum booster is gradually replaced by Brake-by-Wire system (BBW) in modern passenger car, especially Electric Vehicle (EV). Some mechanical and hydraulic components are replaced by electronic components in Brake-by-Wire system. Using BBW system in modern passenger vehicles can not only improve the automotive safety performance, reliability and stability, but also promote vehicle maneuverability, comfort, fuel economy and environmental protection. Although vehicle's braking performance is greatly improved by using BBW, the system will inevitably consume some energy of the vehicle power supply, thus introducing unexpected drawback in comparison with the traditional vacuum assist braking system, since it doesn't need any electric power. Therefore, the analysis of energy consumption on typical main cylinder booster based BBW system under typical driving cycles will contribute to advanced design of current advanced braking system.