For efficient fast control of suspension systems with magnetorheological dampers controlled by semi-active algorithms, the time response of the magnetorheological damper is one of the most important parameters which influences the performance of the suspension system. The time response of commercial magnetorheological dampers with common controllers is in the range of tens of milliseconds, which is too long for efficient real-time control of car suspension. This article describes the ways how to design magnetorheological damper with short response time. First part describes the elimination of long time response caused by high inductance of electrical circuit of magnetorheological damper using current controller. The second part describes elimination of long time response caused by eddy currents which are induced in the magnetic circuit of magnetorheological damper. The new piston of the magnetorheological damper is designed from material with high relative permeability but low electrical conductivity (ferrite). The time responses of magnetic induction and damper forces were measured and compared to original commercial Delphi damper. Results showed rapid improvement in time response when the current controller is used and when the piston is constructed from ferrite materials.

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Magnetorheological dampers seem to be suitable for the adaptive car suspension systems. For proper operation of the semi-active algorithms (skyhook, groundhook), the force response of the damper must be fast enough. In this paper, the response time of the Delphi vehicle MR damper is examined and the sources of the overall force time response on the control voltage are discussed. One of the main sources of the response time seems to be electro-magnetic circuit of the MR damper. A principle of an optimal controller for reducing response of the coil's current on the control voltage is designed. However, the measured overall force time response with fast current controller was not reduced as expected. Therefore, a FEM simulation of the magnetic circuit was made. It shows that after an optimization of the current controller, eddy currents in the coil's core cause long time response and therefore they are the limiting factor of the response time of the MR damper. These simulations were verified by the measurements and some recommendations about improving the pistons construction are given at the end.

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