Research On Ratio Shift Control Strategy Of Metal Belt CVT In Non-stable State

The Metal Belt CVT is a type of ideal transmission for passenger cars.Compare with the widely used Automatic Transmission (AT) currently, it has many advantages, such as the function is good, the structure is simple and the price is low, etc. Along with the technological advance, The Metal Belt CVT is acquiring bigger and bigger development with its excellent no class characteristic. The control strategy of CVT affects the quality of transmission, the fuel economy, the dynamic performance and the emission. To exert the excellences of CVT fully, it has become a kind of inevitable choice to control the engine and the transmission synthetically. Ratio control is the core of the control system of CVT, and it is very important to the vehicle's performances. Through establish the ratio shift control strategy, can make the vehicle according to driver's intention automately realize dynamic optimum matching between vehicle's running resistance and engine's output power. In this way, it can exert vehicle's fuel economy and dynamic performance to limiting condition, meeting its requirement on fuel economy and dynamic performance. So the car have the best driving performance.To the vihecle,it works in Unsteady-Stage conditions most of the time.So it is important to establish the ratio shift control strategy of Metal Belt CVT in Unsteady-Stage conditions.Among CVT's control system, speed ratio control is one of the key technologies. In order to study the ratio shift control strategy of Metal Belt CVT in Unsteady-Stage conditions, The paper based on Fiat engines and Metal Belt Continuously Variable Transmission(CVT). The specific work is as follow: 1. The no class transmission is an old concept, it has been a target for the people from the automobile appeared. The ratio of the Metal Belt CVT can change continuously within the scope of design, enable the engine work in the best appearance, prolong its service life, improve the fuel economy and dynamic performance, reduce exhaust, and carry out integrated control of the engine and CVT.2. Base on lots of literatures, in order to make a general outline on CVT, this paper introduces CVT's development condition, internal actuality and development trend. Then analyses CVT's merit and key technologies, and indicate that in order to guarantee favorable entire car performance, speed ratio control is the key. Finally, confirms this paper's research sense and research content.3. Load bearing characteristic and speed characteristic is different toward different engines. So the object speed ratio was also different. Matching engine was studied in this paper. Firstly, according to different throttle angle, carry out the universal character experiment of this matching engine through speed characteristic test. And then analyses the extraneous factors which impacted the engine performance, and did modification process about test data. Secondly, use the experiment data to build the torque numerical model, gasoline consumption numerical model and universal characteristic of the engine using formula fitting process. And then speed adjustment characteristic of the engine can be founded, which was the foundation of achieving the best economy and the best power ability for CVT system and the warranty of realizing and simulating of control in CVT system.4. According to the characteristics of the engine and the test data, establishs the mathematical model of the engine, and establishs the engine output torque model in steady-state.Then approximates the engine output torque model in non-steady-state. Using MATLAB/Simulink to establish engine simulation model, CVT—power train simulation model and ratio control with PID method model, and combines them together to get the MATLAB/Simulink model of CVT entire car with PID control method. The entire car model can judge the state of cars.5. According to the driver's require of the vehicle's performance and the state of the vehicle's state,establish the corresponding speed ratio control strategy,to make sure that the cars achieve performance requirements under the driver's subjective intention.According to the entire car model, and simulation analyses in non-steady-state.To establish the corresponding Ratio Control Strategy model in non-steady-state conditions.