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According to the feature that the torque of each wheel for the in-wheel motor drive electric vehicle is independently controllable, the left and right steering wheels’ driving force is changed to provide steering power, and the differential drive assisted steering is implemented. Considering the effect on vehicle stability by differential drive assisted steering system, the Carsim/Simulink was utilized to establish the model of the in-wheel motor drive electric vehicle, and a two-layer extension coordinated control system was designed for the stability of automotive differential drive assisted steering system. In the upper-layer controller, according to vehicle driving conditions, the extension coordination controller was established. The extension distance was computed in one-dimensional extension set instead of two-dimensional extension set, so as to solve the correlation function to determine the controllers’ output weights. In the lower-layer controller, the differential drive assisted steering controller was established based on steering wheel torque direct control strategy. Then the yaw moment controller was set up based on the switching of yaw rate control and sideslip angle control according to the different conditions of vehicle in the extension domain and non-domain. Next, the optimal drive torque of four wheels was distributed based on quadratic programming and three different constraint conditions were selected according to different domains. The Carsim and Matlab/Simulink were utilized to carry out the simulation under the double lane conditions with different road friction coefficient. The simulation results show that compared with differential drive assisted steering system working alone, when the road adhesion coefficient was 0.8, the control system can improve the road tracking ability that the lateral and longitudinal deviation respectively decrease by 50% and 30% , and the root mean square values of yawing angular velocity, the center of mass of side-slip angle and lateral acceleration were obviously decreased by 54.9%, 21.4% and 22.3% respectively; when the road adhesion coefficient was 0.4, the system can avoid vehicle’s instability and improve the driving safety.

Studying on online monitoring and fault diagnosis system for monitoring vibration, noise, temperature, torque, stress parameters of the driving axle's key parts has a very important practical significance. The system is composed of hardware and software, which are designed into several modules, including slow-speed data acquiring and saving module, fault diagnosis module, high-speed data acquiring module, database module, reliability prediction module, graphical output module. Combined with studies on fault mechanism of hypoid gears, the system can monitor the states of driving axle, and can also diagnoses different kind of faults of driving axle.

A vehicle nonlinear lateral and vertical dynamics model is built under crosswind disturbance. With the L2-gain method of disturbance suppression, the nonlinear H_∞output feedback controller is designed for electrical power steering (EPS) and active suspension system (ASS) with considerations of random road input and strong crosswind disturbance. Simula- tions for driver-vehicle-road closed-loop system are carried out by using Matlab soft'ware. The results show that the designed controller can suppress the disturbances effectively and improve handling stability, handiness and ride characteristics of a vehicle.