| The primary element for developing hybrid electric urban buses applicable to domestic market is to provide a kind of hybrid powertrain system with which both the price and the complex degree of the powertrain system can be reduced without any vehicle performance degradation. The price of the hybrid electric urban buses developed abroad is still much expensive compared with domestic consumption level, even though its majority performance index are quite good. Little reference can be found for development of domestic hybrid electric urban buses from the schemes of the hybrid powertrain system abroad. Therefore, in this paper a novel biaxial coupling parallel hybrid electric powertrain system configuration is proposed as the study subject with which a one-way clutch is installed between the engine and torque coupler, a main clutch is installed between the transmission and the torque coupler. The proposed powertrain scheme can not only keep the merit of relative lower cost, moderate complex degree and quite good fuel economy but also can overcome the problems caused by the increased inertia of the motor and the torque coupler such as unreliable operating of the AMT and delay from gearshifting process as well; all the factors stated above makes the researched hybrid powertrain system to be with the most industrialization prospect for high power urban buses.Different hybrid powetrain system configuration makes the corresponding control strategy to be different. With the supporting research project of Parallel Hybrid Electric Urban Buses sponsored by Science and Technology Commission of Shanghai Municipality and Shanghai Automotive Engineering Academic,this dissertation makes a deepened study on the development of the control strategy and its implementation, the research emphasis are listed as follows:(1) At first, this dissertation makes an investigation on the development status of the hybrid electric vehicle at home and abroad, especially the powertrain system adopted by hybrid electric urban buses. After that, all the powertrain systems invested are compared from the scope of application, price and cost, structure complicated degree and performance index advantages and disadvantages. And then the useful experiences absorbed are provided as the basis for design of the specific hybrid powertrain system equipped with two clutches.(2) Under the environment of Matlab/Simulink, a computer simulation model for the researched hybrid electric urban buses is constructed by using the model building method combining theoretical analysis and bench test data. It provides the necessary simulation platform for the development of the control strategy.(3) Control strategy is the algorithm to realize vehicle energy management and powertrain control. Up to now, control strategy has been most researched and enriched with abundant literature among the research field of the hybrid electric vehicle. However, much of them addressed to the control algorithm emphasized on the energy management strategy, and the proposed control algorithms just only optimized the torque distribution for several steady operating mode. Parallel hybrid electric vehicle has many operating modes; it generally can be classified as steady operating mode and instantaneous operating mode. The status of the engine, the motor, clutches and the transmission system would change whenever necessary during the process of vehicle driving, and it makes the operating characteristic of hybrid powertrain is relative complex and the corresponding control technique is relative tough. Therefore, operating mode management strategy for the hybrid powertrain system is another aspect of the control strategy. In this paper, a hierarchical control strategy is designed for vehicle control, its energy management strategy determine the optimal torque distribution for the engine, the motor and the brake system; while the operating mode governor layer would determine the target operating mode of the hybrid system according to the optimal torque distribution and the current operating mode of the vehicle as well, and the target state of the engine, the motor, the clutches and the transmission would finally determined which can improve the performance of the vehicle in the end.(4) The energy management strategy of the proposed torque distribution control strategy is belong to base line control method; its main deficiency is that the engine is always working in low efficiency area, the optimization is limited and it is hard to maintain the balance of the battery soc. In order to overcome these drawbacks and make the hybrid system reach maximum overall efficiency as much as possible, an instantaneously optimization algorithm is introduced to rectify the torque distribution control strategy, the aim of it is to keep the balance of battery SOC and utilize more effectively the vehicular energy than it did before. Since the object of optimization is the engine operating points, once the system enters into the operating modes where the engine is tart part in driving, the instantaneous optimization algorithm is applying to calculate the optimal hybrid system operating points.(5) Thought of hierarchical control scheme is implemented for the investigated hybrid powertrain control system; the control system's CAN communication protocol incorporating with SAE J1939 standard are developed as well. Hardware design scheme which taken MC68376 as the control kernel is proposed In stead of using the traditional way to introduce the modular method for hardware system design, this paper puts great emphasis on the introduction of the hardware and software anti-interference design method for hybrid powertrain controller, which provided a stable and reliable implementation platform for control strategy.(6) According to the national standards, hybrid powertrain bench test and vehicle road field test are designed to test and validate the performance of the components and hybrid vehicle as well. Hybrid powertrain bench test includes key components performance test, outer characteristic test and the fundamental control function of the hybrid powertrain system. Road field test includes kinetic performances test and fuel economy test. Even though Kinetic performance test results of the hybrid bus is a slightly inferior compared with that of the prototype bus, it still satisfies the kinetic design requirement of the prototype bus. Fuel economy test results shows that the control strategy proposed in this paper is able to realize the expected operating modes and the smooth transitions between modes of the hybrid powertrain with acceptable drivability, and the battery SOC is controlled within rational operating range at the same time. The fuel economy improvement of the hybrid urban bus is up to 16.1% with SOC correction over the same conventional ICE buses, which demonstrates the effectiveness of the control strategy and reliability of the control system.
|
PDF Full Text Request