F2010A025
Comparative Analysis of Transmission Efficiency for One Mode and Two Mode Power Split Transmission
Growing attention to saving petroleum energy and preventing global warming has been pressing the automotive industry to produce automobiles with less exhaust emission and better fuel economy. Under these circumstances, various types of hybrid electric vehicle (HEV) such as series HEV, parallel HEV and power split HEV have been proposed. Among them, the power split HEV has been spotlighted in automobile market starting from Toyota Prius. The first power split HEV, Prius, contains a one mode power split transmission which only has input split configuration composed of one planetary gear set splitting the power from engine and two motor-generators. Due to its simple configuration and continuously variable transmission (CVT) effect of two motor-generators, it shows higher system efficiency than the other types of HEV. A two mode power split transmission consists of two power split configurations which are input split and compound split. It can reduce the power which passes through the two motor-generators and is expected to improve transmission efficiency and reduce motor-generator power capacity, which are directly related to economics. However, to operate the two mode power split transmission, two or more planetary gears, clutches and brakes should be employed. It also has to work with a hydraulic pump whose maximum capacity is larger than that of the one mode power split transmission to operate the additional clutches and brakes. These factors can reduce the overall transmission efficiency of the two mode power split transmission and eliminate the expectation that the two mode power split transmission's efficiency is higher than that of the one mode power split transmission. In this paper, detailed transmission models of the one mode and two mode power split transmission are developed including torque losses from planetary gears, clutches, brakes, and hydraulic pump. The power split transmission is a multi-input system and it can be difficult to analyze the transmission efficiency. Thus, a calculation methodology of transmission efficiency is suggested. From simulation results of the one mode and two mode power split hybrid electric vehicles, whose fuel economy and transmission efficiency are compared.
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Session: Consumption and Emission Reduction