Multi-mode Electrically Variable Transmission with Two Planetary Gear Sets
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Solution Overview
Problem
Conventional vehicle transmission systems, particularly those using internal combustion engines, face inefficiencies in fuel consumption and emissions due to varying demands and the need for multiple gear ratios, which can be addressed by developing an electrically variable transmission system that offers improved energy efficiency and reduced emissions.
Innovation Solution
The electrically variable transmission system incorporates two planetary gear sets, two motor/generators, a dog clutch, and four torque transfer devices, allowing for selective operation in both power-split variable speed ratio ranges and fixed speed ratios, enabling continuous variable speed ranges and up to four mechanically fixed forward speed ratios, reducing the size and cost of electric motor/generators required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a series hybrid electric drive system is used to allow continuous variation in torque and speed ratio, then the engine can operate independently for improved emissions and efficiency, but the weight and cost of electric machinery increases significantly
Solution Approach 1:
The transmission system is divided into two separate planetary gear sets (first and second planetary gear sets) that operate in parallel. Each gear set handles a portion of the power flow, allowing the system to achieve continuous variable ratio operation without requiring a single large electric machine to handle all power conversion, thereby reducing the weight and cost of electric machinery while maintaining emission benefits.
2Device complexity
If conventional mechanical transmissions with multiple gear ratios are used, then the structure remains simple, but fuel consumption and emissions increase due to varying engine demands
Solution Approach 1:
The transmission system dynamically switches between fixed ratio mechanical operation and continuously variable electrically-assisted operation. The control system adjusts the engagement of clutches and the operation of electric motor/generators based on driving conditions, allowing the engine to operate at optimal points for fuel efficiency and emissions while maintaining a relatively simple mechanical structure.
3Weight of moving object
If two planetary gear sets with multiple torque transfer devices are used to reduce electric machinery size, then the transmission structure becomes more complex
Solution Approach 1:
The first and second planetary gear sets are merged into a single integrated transmission structure with shared components. The first clutch connects the input shaft to both gear sets, and the clutches work together to coordinate power flow through the combined system. This merging approach allows the system to achieve the desired reduction in electric machinery size while managing structural complexity through integrated design.
Data Source
AI summary
The electrically variable transmission family of the present invention provides 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, four selectable torque-transfer devices, and a dog clutch. The selectable torque transfer devices are engaged singly or in combinations to yield an EVT with a continuously variable range of speeds (including reverse) and up to four mechanically fixed forward speed ratios. The torque transfer 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.