Study On Intelligent Gear Shift Strategy For Automatic Transmission Vehicles Based On Driver-Vehicle-Road System

Automatic transmissions are mechatronic products in fast development of electronic and automatic control technologies, by which driver fatigue and work intensity due to long distance driving can be reduced. Therefore, improvement of driving facilities further meets requirements of people on using vehicle. The gear shift schedule is one of the key technologies in the automatic transmission control system. With rapid development of car markets and industries, higher requirements to the automatic transmission are emerging. What the client's requirements are not only to realize the automation of shift operations, but also to satisfy the demands of different diving conditions and driver's intentions and to have the optimal vehicle performances such as good power capability, economical fuel consumption and fine ride comfort. Obviously, the intelligent shift technology will be the development trend of the automobile automatic transmission.In association with practical projects sponsored by“National Nature Science foundation”, the main purpose of this dissertation is the design of an intelligent gear shift strategy for automatic transmission under different road conditions and driver's intention. Focused on this aim, the studies of this paper are put forward as follows:Firstly, the vehicle powertrain model is established, which consists of engine, clutch, transmission, tire and vehicle submodels. By comparing the simulation results with the experimental data, the accuracy of simulation model is verified. The simulation model is applicable for analysis of dynamic and static performances of the vehicle with different design schemes, also for simplification of the development process of the transmission control strategies. In addition, the basic gear shift strategy, which includes optimal dynamic and economic shift schedules, is developed. The intelligent gear shift strategy is built up on this base.Then, for overcoming problems appearing when the automatic transmission vehicle by conventional gear shift strategy drives on slopes, according to principles of the vehicle longitudinal dynamics, a modified recursive least squares for online estimation of vehicle mass and road grade is proposed. In comparison of numerical results obtained by the recursive least squares with single forgetting factor, the modified algorithm is more efficient in estimation of parameters with different change rate. On these bases, the gearshift strategies on uphill and downhill slopes are then developed. By the vehicle road test results it is indicated that these strategies can improve the automatic transmission vehicle drive performance on slope and overcome the disadvantages of the conventional gear shift strategy.When the vehicle with traditional gear shift strategy drives on the road with low adhesion, the acceleration during launch process may cause serious traction skid of the driving wheel and thus result in the deterioration of the vehicle acceleration and stability performances. In the present research, a new gear shift strategy is proposed to focus on the traction control for the vehicle traveling on the low adhesion road. In the design of slip controller, firstly, the optimal slip ratio is estimated by analysis of the slope of the?-?curve. Then, by means of the theory of differential geometry, the slip ratio control system with non-linearity and uncertainty is transformed into a linear one, and the sliding mode control is applied for it. On the other hand, according to the dynamic programming, the throttle opening and gear position maps are developed in terms of the driving torque and the wheel angular speed. Then, the required throttle opening and gear position can be determined through looking up the maps. The simulation results indicate that the present gear shift strategy works efficiently in improving acceleration performance of the automatic transmission vehicles.Characteristics of different road conditions and driver's intentions, as well as problems encountered when the vehicle with the traditional gear shift strategy drivers in these conditions are analyzed. Accordingly, the recognition methods and the modified gear shift strategies for driver's intentions and road environments are developed and validated by road tests. Furthermore, based on the analysis of coupling condition of road conditions and driver's intentions, the integrative shift strategy is drawn up and the simulations are performed for validation of its effectiveness.At last, the hardware and software systems of automatic transmission controller are developed.In conclusion, the dissertation has systematically investigated the intelligent gear shift strategy for automatic transmission vehicles. Road test data and simulation results have improved that the new intelligent gear shift strategy, compared with the conventional strategy, shows a better drive performance.