Abstract: Multi-Mode e-Transmission, a New and Fuel-efficient Drivetrain Configuration for HEV/PHEV

The multi mode e-transmission developed by GKN has been in production at Shanghai GKN Huayu driveline system Co. Ltd. This e-transmission has an unique architecture which can support different driving modes such as pure EV, serial hybrid and parallel hybrid. By supporting different driving modes it can help a HEV or PHEV car to fulfill best fuel-efficiency while ensure its dynamic performance characteristics.

The multi mode e-transmission adopts a multi-plate clutch system which is driven by a hydraulic pump. The clutch switches on and off the power flow from ICE to output differential, thus control the driving mode shifting between parallel hybrid and serial hybrid. By adopting an unique actuation strategy, the impact during clutch engagement is eliminated and a seamless mode shift is guaranteed. The hydraulic pump is driving by a geared shaft which is engaged to the ring gear on output differential, thus the clutch can be engaged only when the vehicle speed is over a certain threshold speed. In the low speed range the ICE can’t drive the vehicle directly, this enables a very simple but robust design of a fixed gear ratio between ICE and wheel, also the unintended clutch engagement is completely eliminated when vehicle is steady and is charging the battery by ICE-driven generator.

By carefully selecting gear ratio between ICE and generator and setting vehicle speed threshold for parallel hybrid mode, the fuel efficiency of the vehicle is highly enhanced. On a mid-size 2100 kg PHEV SUV with a 1.4 liter 4 cylinder ICE, a fuel consumption of 1.9L/100km is achieved under NEDC.
The multi mode e-transmission follows a modular design concept and can be easily modified or configured to meet various vehicle performance requirements, such as modification of gear ratio between ICE and generator, including the park-by-wire system etc.. It also can be easily tailored to become a range extender e-transmission by taking out hydraulic pump and clutch system. This can support customer’s vehicle configuration variety which reducing cross vehicle complexity, the development lead time and development cost will also be significantly reduced.

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