Multi-Speed Drive Unit for Electrically Variable Transmission
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Solution Overview
Problem
Multi-mode electrically variable transmissions face increased electric motor losses at higher vehicle speeds and limited reverse gear operation due to mechanical point chasing and compromised gearing ranges, which affect engine efficiency, torque requirements, and vehicle performance.
Innovation Solution
The design incorporates a planetary gear set with a sun gear, pinion gears, and a ring gear, coupled with first and second electric motors and driver gears, allowing for selective clutch activation to achieve variable output gear ratios, enabling efficient operation across city and highway speeds and providing engine-assisted reverse gear capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-mode EVT transmission is used, then the structure is simple, but electric motor losses increase at higher vehicle speeds due to mechanical point chasing
Solution Approach 1:
The transmission is divided into multiple operating modes with different gear ratios. A first mode provides a first gear ratio for city driving, while a second mode provides a second gear ratio for highway driving. This segmentation allows the system to optimize motor operating points for different speed ranges, reducing electric motor losses at higher vehicle speeds while maintaining structural feasibility through modular clutch mechanisms.
2Speed
If the gearing is optimized for highway driving, then highway performance is adequate, but city driving requires higher torque levels from electric motors
Solution Approach 1:
The transmission dynamically switches between two distinct gear ratios based on driving conditions. The first gear ratio is optimized for city driving with lower speeds and higher torque requirements, while the second gear ratio is optimized for highway driving with higher speeds and lower torque requirements. This dynamic adaptation allows smaller, less expensive electric motors to suffice for city driving while maintaining adequate highway performance.
3Device complexity
If electric motors provide all reverse propulsion, then the EVT structure is simple, but reverse operation is inadequate when battery power is limited
Solution Approach 1:
The transmission system is designed to perform multiple functions through its dual-mode capability. The same clutch mechanisms and gear ratios that optimize forward driving performance also enable reverse operation assistance. In reverse gear operation, the engine can provide propulsive force through the planetary gear set, supplementing or replacing electric motor power when battery power is limited, thereby improving reverse gear reliability without significantly increasing structural complexity.
Data Source
AI summary
A multi-speed drive unit is provided for an electrically variable transmission having a variable-range output gear ratio for a motor vehicle. The variable-range output electrically variable transmission has improved final drive gear ratios that allow the motor to be operated in its desired efficiency and/or performance range during both city and highway vehicle operation. Further, the variable-range output electrically variable transmission allows for increased vehicle speeds during electric vehicle operation and provides for the use of the vehicle engine during reverse gear operation.