Electrically Variable Transmission with Three Planetary Gear Sets
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Solution Overview
Problem
Conventional vehicle transmission systems face inefficiencies in fuel consumption and emissions due to the wide variation in engine demands, and series hybrid electric drive systems are heavy and costly due to the need for extensive electric machinery for power conversion.
Innovation Solution
The development of an electrically variable transmission system with three or four planetary gear sets, two motor/generators, and seven or eight torque transmitting devices, allowing for selective operation in power-split variable speed ratios and fixed speed ratios, which reduces the need for continuous electric power conversion and enhances regenerative braking and idling capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a series hybrid electric drive system is used to improve fuel consumption and emissions, then the engine can operate with improved efficiency and emissions, but the system becomes heavy and costly due to the need for extensive electric machinery for power conversion
Solution Approach 1:
The transmission system is divided into multiple planetary gear sets (first, second, and third planetary gear sets) that handle different portions of power transmission. Each gear set processes a fraction of the total power, allowing the electric motor/generator to be smaller since it only needs to handle its designated portion rather than the entire engine power output.
Solution Approach 2:
Instead of converting 100% of engine power through electric machinery as in a series hybrid system, the invention uses partial action by having only a portion of the power flow through the electric motor/generator while the remainder flows through mechanical pathways, thereby reducing the size and weight of electric components.
2Adaptability or versatility
If continuous electric power conversion is used to achieve continuous variation in torque and speed ratio, then the torque and speed ratio can be continuously adjusted, but the size and cost of electric motor/generators increases
Solution Approach 1:
The power transmission is segmented into multiple pathways with different gear sets, each handling specific torque and speed ratio requirements. This allows the electric motor/generator to be sized for only a portion of the total power conversion needs while mechanical gear sets handle the remainder, achieving continuous variation without requiring oversized electric machinery.
Solution Approach 2:
Planetary gear sets serve as intermediary mechanisms between the engine and the electric motor/generator, and between the electric motor/generator and the final drive. These mechanical intermediaries enable continuous torque and speed ratio variation by combining mechanical gearing with partial electric power conversion, reducing the burden on the electric motor/generator size.
Data Source
AI summary
The electrically variable transmission family of the present invention provides low-content, low-cost electrically variable transmission mechanisms including three or four differential gear sets, a battery, two electric machines serving interchangeably as motors or generators, seven or eight selectable torque-transfer devices and possibly a dog clutch. The selectable torque transmitting devices are engaged to yield an EVT with a continuously variable range of speeds (including reverse) and up to six mechanically fixed forward speed ratios. The torque transmitting devices and the first and second motor/generators are operable to provide five operating modes in the electrically variable transmission, including battery reverse mode, EVT reverse mode, reverse and forward launch modes, continuously variable transmission range mode, and fixed ratio mode.