Research On Shift Quality Of Automatic Transmission For City Bus

At present, the city development has been limited by traffic jam in our country. Because the land resources of city are sparse, it is necessary to develop the public traffic to accelerate the city development. City bus is an important part of public traffic. Advanced technology of city bus has important significance for preferential development of public traffic.With the development of people living level, travelling comfort of bus has to be improved to fit the higher and higher demand. In order to improve the competitiveness of city bus, ride comfort must be improved radically. The performance of drive system is the key factor that impact the ride comfort, and the automatic transmission (AT) is the important part of bus drive system, so the shift quality of vehicle must be improved in order to improve ride comfort according to running characteristic of start and shift frequently of city bus. It is the most effective method to improve the shift quality that automatic transmission is used, and this method can not only improve the ride comfort, but also can reduce the labor intensity of driver.Shift Schedule and Quality of City BusIt is discussed that dynamic shift schedule is much more suitable for the city bus which run nonsteady in most time because of the running characteristics of start, shift, acceleration, deceleration and stop of city bus. The shift quality of city bus is the important factor for consideration to design drive system of vehicle, and the factors that impact shift quality are summarized: (1) movement timing of shift actuator; (2) inertia energy; (3) friction torque of shift actuator. The impact degree of factors is estimated by the three evaluation index of vehicle shock degree, dynamic load of drive system and vehicle sensitivity, and the third one is applied less. There are two modes to control shift quality, the first one is open-loop control and the second one is closed-loop control. The closed-loop control has the high requirement of data collection system, and the design of control system is complex, so it is the develop direction of shift quality control of city bus.Simulation Analysis Model of Shift ProcessThe mathematical models of torque converter whose stator can reverse and the fixed axis transmission are established based on the motor performance and the structure parameters of drive system of GYB-100 hydraulic mechanic AT of the city bus.The shift quality of city bus is analysised with the models, the various and relationships of physical quantities during shift, and the simulation models are established using the mathematical models.The Control Methods to Improve Shift QualityEngine is the power source of drive system, and the performance of drive system is impacted by its performance. The rotate speed control of engine is suitable for shift quality control of ATM city bus, and the torque control of engine is suitable for shift quality control of AT city bus, during shift, the output torque of engine is decreased by reducing fuel injection quantities, or delay ignition and so on. The reduced torque control of engine and simulation analysis are realized by reducing throttle opening of engine in this paper, the shift quality is improved and the wave of output torque is decreased by reducing torque control.Serious shock may be lead by unreasonable lap timing of binding components, and the components abrasion is strengthened, so simulation analyses are introduced about three different instances: reasonable lap of binding components, drive intermit and overlap excess. And the conclusions are summarized: during deive intermit, binding components abrasion is graveness with abrasion time and shock degree increasing; during overlap excess, although balance state can be achieved in short time, impact is particularly serious.The law of oil pressure change during binding components is the key factor that can impact shift quality, and two different shift qualities about two laws of oil pressure change are analysed in this paper, and the impact of shift shock because of the oil pressure and changes during shift with the simulation results.Simulation and Analysis of Electric-Hydraulic Control SystemShift quality of AT is improved by the method of improving performance of elctrohydraulic control system now, and the performance of elctrohydraulic control system play an very important role in shift quality. The performance of electro-hydraulic proportional valve impacts the performance of hydraulic system. Under the working theroy of hydraulic valve , the model of hydraulic valve is established and simulated with hydraulic simulation software, dynamic response characteristics are obtained, that can accomplish actions and realize balance state in a short time, and the requirements of AT can be satified. The simulation model are established about the law of oil pressure changes during exactly control aparting and binding with electrohydraulic proportional valve, and the shock impacts during shift about the performance of electrohydraulic proportional valve and the law of two different oil pressure are discussed in this paper.