Search Results

In this paper, gear ratios of a two-speed transmission system are optimized for an electric passenger car. Quasi static system models, including the vehicle model, the motor, the battery, the transmission system, and drive cycles are established in MATLAB/Simulink at first. Specifically, since the regenerative braking capability of the motor is affected by the SoC of battery and motors torque limitation in real time, the dynamical variation of the regenerative brake efficiency is considered in this study. To obtain the optimal gear ratios, iterations are carried out through Nelder-Mead algorithm under constraints in MATLAB/Simulink. During the optimization process, the motor efficiency is observed along with the drive cycle, and the gear shift strategy is determined based on the vehicle velocity and acceleration demand. Simulation results show that the electric motor works in a relative high efficiency range during the whole drive cycle.

Historically slip in a CVT was regarded as destructive. The reason for this was that slip was not controllable and since it is unstable always resulted in damage to the variator. Recent publications suggest that limited amounts of slip in a pushbelt type variator can be allowed [6]. This opens the door to other strategies for lowering the powerconsumption of CVT's. Not only can slip be used for optimizing variator efficiency [1], actuation efficiency can also be greatly improved. If the safety margin is eliminated, the clamping force can be reduced by more than 25%. This can be directly translated into a 25% decrease in actuation power. Shifting behaviour is also influenced by slip [3]. This effect can be used to greatly reduce the power needed for fast shifting during emergency stopping, tip-shifting and kickdown actions. Using this strategy the force needed for shifting is reduced, and with it the power needed from the actuation system is reduced.