The damping force of Magnetorheological damper (MRD) can be controlled in a certain range by applying a steady magnetic field to reduce vehicle suspension vibration effectively. This paper presents the analysis of the damping characteristics of the twin-tube MRD, and the design of embedded control system for Twin-tube MRD used to semi-active vehicle suspension. The laws of varying damp force with current, displacement and frequency are investigated by testing for the damper, for instance the relationship curve of damping force vs. current. The control system is composed of controllable current driver and electrical control unit (ECU). ECU is developed based on MC9S12XDP512 chip. Signals that ECU acquired come from three types of sensor, i.e. digital temperature sensor, MEMS acceleration sensor and laser distance sensor embedded in MRD. The sampling frequency may exceed 400Hz. The programming is carried out in accordance with the state data acquisition and the improved On-Off control algorithm．Aiming at the high time response requirement of the MR damper, a Pulse-width modulation (PWM) current driver was designed. The hardware solutions drive circuit, interface circuit as wel1 as the software design of control system are discussed in detail. The proposed designed system has been put in actual MRD controlling application, whose test results prove its fast current response and high precision.

A semi-active suspension system is researched for a heavy tracked vehicle to improve its suspension performance. This is achieved through a vane magnetorheological damper (VMRD) with special magnetic circuit which may attenuate the leak of MRF from assembly gap. A innovative strategy named frequency domain control (FDC) is proposed based on a conclusion that, in the frequency domain,the influence of damping coefficient to transmissibility for different suspension performance indicators is in good consistency. FDC only requires accelerometers mounted on sprung mass, meaning low price and high reliability that the tracked vehicle requires. The experiment indicates the designed semi-active suspension system based on VMRFD has an excellent vibration suppressing ability.

As the most important transmission system of vehicles, the gearbox has a high fault rate, so it is meaningful to evaluate and diagnose its health condition and faults accurately. Autocorrelation -envelope analysis is a fault diagnosis method that can suppress the noise and reserve the periodic components of vibration signals. A conclusion has been deduced: amplitude modulated, frequency modulated, or amplitude& frequency modulated signals can be transformed into amplitude modulated signals with the same modulation frequency through autocorrelation processing. Therefore, the aucorrelation-envelope technique is suitable for extracting the fault features of gearbox from its vibration signal with the coexistence of amplitude modulation and frequency modulation. The simulation results verify the validity of the conclusion and the experiment of vehicle gearbox diagnosis indicates the effectiveness of this method.

Aimed to satisfy damping force change requirement of vehicle MRF suspension vibration control system, a controller of MRF suspension system based on On-Off control algorithm is designed, and a control system is carried out. The system takes single chip AT90CAN128 which obey the CAN bus protocols as micro-controller, and it accomplish AD conversion of sensor signal, design of On-Off algorithm and output of PWM voltage power control signal. The system also is used in vibration control experiment of tracklayer vehicle suspension system. The experiment shows that the controller can improve control accuracy, and the control effect is obviously.

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