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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.

In a monotube magnetorheological fluid damper (MRFD), there usually exists a compensation chamber with designated initial gas pressure. This enclosed compensation chamber works as an air spring to some degree to provide force to the working piston. In this work, in order to extend the external damping force range and improve the controlling efficiency, a structure of MRFD with three additional accumulators is proposed. These additional accumulators are connected to the atmosphere through an air pump and the compensation chamber with a barometric valve. The external damping force range thus can be rapidly adjusted through mode shifting with this configuration. A mathematical model of this damper with coupled effects between the air and the magnetorheological fluid (MRF) is developed. Comparing the bench tests results with some simulation outcomes, the simulation model of this MRFD is validated.