Abstract
To increase the energy efficiency of road vehicles, an ideal transmission system should have a wide ratio coverage, a high torque capacity, and a high mechanical efficiency. Continuously variable units (CVUs) have been successfully implemented due to the smooth ratio variation, sufficient torque capacity, and ratio coverage. Hence, it will be beneficial to develop a hybrid powertrain comprising a CVU. In this paper, a design method called the “basic path diagram” (BPD) is proposed. It provides a simplified schematic of the system and represents the generic connections among the mechanical components. The system configurations synthesized by the BPD can be sorted according to three characteristics: Direction of power flows through the CVU, coupling pattern of the power inputs, and number of transmission paths parallel to the CVU. The first characteristic determines the number of times the CVU ratio coverage can be exploited, the second characteristic determines whether the torque of the power inputs can be independently controlled, and the third characteristic can help reduce the torque loading of the CVU. With the aid of a BPD, one of the possible system configurations is provided as an example. The result shows that the system can exploit twice the ratio coverage of the CVU and reduce the torque and power transmitted by the CVU in combination with planetary gearsets.
Highlights
One of the development goals for modern road vehicles is to enhance energy efficiency and reduce emissions
basic path diagram” (BPD), thethe system cancan be be sorted by the following three properties: Direction of power flows through the Continuously variable units (CVUs), sorted by the following three properties: Direction of power flows through the CVU, coupling pattern of the power inputs, and number of power transmission paths parallel to coupling pattern of the power inputs, and number of power transmission paths parallel the CVU
After simplifying the system elements and the transmission paths, there are only seven basic elements involved in the BPD, and the generic connection among different elements is shown
Summary
One of the development goals for modern road vehicles is to enhance energy efficiency and reduce emissions. The FPG is a graphical method developed by Chen [35] that represents the connection of clutches, brakes, and gearsets between power sources and outputs. For hybrid powertrains with multiple drive modes, the transmission path of power flow under different modes can be clearly described by the FPG. The FPG must show the complete connection of powertrain units with multiple types of gearsets, clutches, and brakes Some of these units and transmission paths may only be activated when the vehicle is reversing and are always idle when the vehicle is not in the reverse gear. The graph will become too complicated to assess all of the possible power paths of an existing system This complexity limits the ability of the designer to enhance the overall energy efficiency of the system by further developing additional drive modes. Maximum power outputsubsystems if there arethat multiple sources.with other transmission
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