CVT Ratio Control Algorithm by Considering Powertrain Response Lag 2004-01-1636

A CVT ratio control algorithm is proposed to improve the engine performance by considering the powertrain response lag. In the CVT powertrain, there exists a response lag, which results from the throttle response, engine torque dynamics, CVT filling time, CVT shift dynamics, and the drive shaft dynamics including the tire. This response lag causes the deviation of the engine operation from the optimal operation line for the minimum fuel consumption. In the CVT ratio control algorithm suggested in this paper, the desired CVT speed ratio is modified from the vehicle velocity, which is estimated after the time delay due to the powertrain response lag. In addition, the acceleration map is constructed to estimate the vehicle acceleration from the throttle pedal position and the CVT ratio. Using the CVT ratio control algorithm and the acceleration map, vehicle performance simulations and experiments are performed to evaluate the engine performance and fuel economy. From the simulation results, it is found that the fuel economy can be improved about 3.6% for FUDS by the ratio control algorithm for the target vehicle. It is found from the experimental results that the engine operation trajectory by the algorithm is shifted to the more efficient brake specific fuel consumption region compared with that of the conventional CVT vehicle, which contributes to the improvement of the fuel economy.