2018-01-1016 Published 0 3 Apr 2018 © 2018 SAE International. All Rights Reserved.A New Strategy to Optimize the Economy Performance of the New Power-Split Hybrid Transmission Platform CHS-HT2800 Ji Gao, Tong Zhang, Haisheng Yu, Chen Wang, Huijun Cheng, and Fuxiang Ge Corun Chs Technology Co., Ltd. Citation: Gao, J., Zhang, T., Yu, H., Wang, C. et al., “A New Strategy to Optimize the Economy Performance of the New Power-Split Hybrid Transmission Platform CHS-HT2800,” SAE Technical Paper 2018-01-1016, 2018, doi:10.4271/2018-01-1016. Abstract CORUN CHS has recently developed a new power-split hybrid transmission platform CHS-HT2800, which has added 2 clutches compared to CHS-HT1800. With involvement of 2 E-motors CHS-HT2800 has 9 forward gears, including 3 electric forward gears and 6 hybrid forward gears. Among the 6 hybrid gears 4 gears are fixed-ratio gears and the remaining 2 gears are eCVT gears. This paper describes a strategy, designed for CHS-HT2800, how to select the optimal mode, the optimal gear and the optimal work point of the engine to achieve the best economy performance in the real traffic. Because it is universally accepted, that the WLTC cycle can represent real world vehicle operation on urban and extra-urban roads, motorways, and freeways. The introduced strategy will be validated with the help of the WLTC cycle. Introduction The CHS-HT1800 is the first generation electromechan - ical power-split full-hybrid transmission developed by CHS [ 1, 2, 3]. Geely EC7-PHEV, which is equipped with the CHS-HT1800, has already successfully come into the market. In order to further improve the acceleration perfor - mance and economy of CHS-hybrid system, CHS is devel - oping the second generation power-split hybrid transmission CHS-HT2800, which is derived from CHS-HT1800. The most important improvement in the structure is the addition of two clutches C0 and C1, which produce more gears depending on the states of the clutches and brakes. Compared to CHS-HT1800 the number of EV gears is increased from 1 to 3, and the number of hybrid gears from 2 to 6. Among the 6 hybrid gears 2 gears are eCVT gears and 4 gears are fixed-ratio gears. The ratios of the 4 fixed-ratio gears are set close to the ratios of 1 st, 3rd, 4th and 5th gear of a conventional 5-speed automatic transmission. One fixed-ratio gear is designed to improve the low-speed acceleration performance, and the other 3 fixed-ratio gears are designed to improve fuel economy of middle- and high-speed driving. In the fixed-ratio gears, the engine can drive the vehicle directly and the two motors can stay in the standby mode. CHS-HT2800 can be seen as a combination of eCVT and 5AT-based P2, rather than a classic eCVT. More gears bring not only the flexibility of the system to improve the fuel economy but also the difficulty of control. This paper will introduce a strategy about how to choose an appropriate driving mode, gear and engine operating point in view of fuel economy in the complex urban conditions. This strategy is developed based on the structural characteristics of CHS-HT2800 and the practical engineering experience during the development of CHS-HT1800. Structure of CHS-HT2800 CHS-HT2800 is derived from CHS-HT1800 and therefore has a similar structure and working mechanism. Both hybrid transmissions have two planetary gear sets, two motors (E1 and E2) and two brakes (B1 and B2). The main improvements are as follows: •A doption of CR-CR structure ( Figure 2 ) instead of Ravingneaux planetary ( Figure 1 ); •A ddition of C0 wet clutch. The engine can be decoupled from the carrier of the planetary set in the first row. The carrier can rotate without dragging the engine. Therefore 2 EV gears, namely 2G and 3G ( Table 1 ) have been added, which can improve the maximum speed and system efficiency in EV mode; •A ddition of C1 wet clutch. The engine can be coupled with the large motor E2 by closing C1. According to the different combinations of B1, B2