Two-Planetary Electrically Variable Transmission with Fixed Ratios
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Solution Overview
Problem
Conventional vehicle transmission systems, especially those using internal combustion engines, face inefficiencies in fuel consumption and emissions due to wide variations in engine demands, and series hybrid electric drive systems suffer from weight and cost issues related to electric machinery and energy losses in conversions.
Innovation Solution
The development of an electrically variable transmission system with two planetary gear sets, two motor/generators, and up to six torque transmitting devices, allowing for selective operation in power-split variable speed ratios and fixed speed ratios, which includes a dog clutch to reduce clutch spin losses and enable motor/generator operation at low speeds, and uses a compound-split and input-split architecture to minimize electrical component loads and energy usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a series hybrid electric drive system is used to allow engine independence from vehicle torque and speed requirements, then emissions and fuel efficiency are improved, but weight and cost increase due to sufficient electric machinery and energy losses in mechanical-to-electrical and electrical-to-mechanical conversions
Solution Approach 1:
The transmission system divides power flow into two separate paths: a mechanical path for direct torque transmission and an electrical path for energy management. This segmentation allows the engine to operate independently while reducing the size and weight of electric machinery needed, as only partial power conversion is required rather than complete conversion as in series hybrid systems.
2Device complexity
If conventional mechanical transmissions with five or six fixed drive ratios are used, then the system is simple and reliable, but fuel consumption and emissions increase due to wide variations in engine demands operating at average of approximately one-fifth of maximum power output
Solution Approach 1:
The transmission system dynamically switches between fixed ratio mechanical operation and variable ratio electrical operation based on driving conditions. This allows the engine to operate at optimal efficiency points across a wider range of vehicle speeds and loads, reducing fuel consumption while maintaining system simplicity through selective engagement of different operating modes.
3Adaptability or versatility
If electric motor/generators are used to transform mechanical power to electrical power and back, then continuous variation in torque and speed ratio is achieved, but energy losses occur in the conversion processes
Solution Approach 1:
The system uses electric motor/generators for only partial power transformation rather than complete conversion. The mechanical path handles direct torque transmission with minimal conversion losses, while the electrical path provides continuous variation capability when needed. This partial action approach reduces overall energy losses while maintaining adaptability.
Data Source
AI summary
An electrically variable transmission family is provided which has low-content, low-cost electrically variable transmission mechanisms including first and second differential gear sets, a battery, two electric machines serving interchangeably as motors or generators, up to six 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 at least four 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.