The automatic gearshift algorithm and its dynamic control is an important research area in tracked vehicle design. In the paper the models of power train system such as engine, transfer gearbox, hydraulic torque converter, planetary gearbox, running gear propulsion system and virtual terrain are built. The program for gearshift algorithm design is developed. The model of designed gearshift algorithm is developed with MATLAB/simulink and finite state machine theory. The hydraulic control system is modeled with MATLAB/simulink and the oil pressures can be applied on the clutches and brakes of power train system. The planetary gearbox and other transmission parts are modeled through EASY5 power train library models and the gear contact stiffness, torsional stiffness of links between planetary gear sets and shafts are taken into consideration. The running gear system model are built with ADAMS, and the terrain loads from the interaction between terrain and tracks are applied on the sprocket extended to the power train, which considers the dynamic contacts among road wheel, track and terrain. Many terrain models including the slope, obstacle and road model with A, B, C, D etc. levels at different vehicle speeds can be built and integrated with the virtual prototyping models These different disciplinary models are integrated with MATLAB, ADAMS and EASY5 development environment and the virtual test can be done in various operation conditions. The integrated method is through the interfaces provided by these simulation software. It realizes the time synchronization between two different models of EASY5 and MATLAB/simulink with the digital electric circuit theory. The virtual test is been made in the integrated MATLAB/simulink development environment. The tracked vehicle's acceleration performance is simulated. The acceleration time from second gear to 32 km/h is about 14.5 seconds. Many other performances such as the virtual dynamic torque loads of rotating parts, the clutch torque capacity and the jerks of any parts in the power train can be obtained from simulation and can be verified with the physical tests later. There are some innovations in modeling method in this paper. Firstly, it builds many subsystem models with the virtual prototyping technology. Secondly, it builds the integration environment and interfaces. Many models of different areas are integrated to simulate transmission gearshift process. Thirdly, it provides a modeling method and environment for power train modeling and simulation. Fourthly, the acceleration performance of a tracked vehicle is simulated and the two results of virtual and physical tests are close.

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