Electrically Variable Transmission with Three 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 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
An electrically variable transmission system with three planetary gear sets, two motor/generators, and up to six torque transfer devices, allowing for selective operation in power-split variable speed ratios and fixed speed ratios, optimizing energy efficiency and reducing emissions through regenerative braking and electric-only idling.
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 fuel consumption and emissions are improved, but weight and cost increase due to sufficient electric machinery
Solution Approach 1:
The transmission system divides power flow into two separate paths: a mechanical path through planetary gear sets and a electrical path through motor/generators. This segmentation allows the engine to operate independently while only the necessary portion of power is converted electrically, reducing the required size and weight of electric machinery compared to a full series hybrid system.
Solution Approach 2:
The system dynamically adjusts the proportion of power flowing through mechanical versus electrical paths based on operating conditions. The control system varies the torque split between the two paths, allowing the electric machinery to be sized for partial power conversion rather than full conversion, thereby reducing weight while maintaining fuel efficiency benefits.
2Use of energy by moving object
If electric machinery is used to transform all engine power from mechanical to electrical and back, then engine independence is achieved, but useful energy is lost in conversions
Solution Approach 1:
Power is segmented into two paths: a direct mechanical path that preserves energy by avoiding conversion losses, and an electrical path that enables engine independence. By routing power through the mechanical path when possible, the system minimizes energy loss from repeated mechanical-electrical conversions while still achieving engine independence during electrical path operation.
Solution Approach 2:
The system changes the operational parameters of power transmission by varying the torque split between mechanical and electrical paths. During conditions where engine independence is less critical, more power flows through the efficient mechanical path. During conditions requiring engine independence, the electrical path is engaged, optimizing the balance between energy efficiency and operational flexibility.
3Adaptability or versatility
If conventional mechanical transmissions are used with five or six different drive ratios, then some freedom in engine operation is allowed, but fuel consumption and emissions increase due to wide variations in engine demands
Solution Approach 1:
The system transitions from static, discrete gear ratios to a dynamic, continuously variable transmission system. The electrical path enables continuous adjustment of the effective gear ratio by varying the torque split between mechanical and electrical paths, allowing the engine to operate at optimal points across a wide range of vehicle speeds and loads, thereby reducing fuel consumption and emissions.
Solution Approach 2:
The transmission system performs multiple functions through its dual-path architecture: it provides continuous variable ratio transmission like a CVT, enables engine braking and regenerative braking through the generator, allows electric-only propulsion, and maintains mechanical direct drive capability. This multi-functionality replaces the need for multiple discrete gears while improving fuel efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system enhances vehicle acceleration, improves fuel economy, and reduces emissions by optimizing energy efficiency and package size, while providing a range of operating modes for improved performance and reduced fuel consumption.
Implementation Method 1
An electric generator can transform mechanical power from the engine into electrical power, and an electric motor can transform that electric power back into mechanical power at different torques and speeds
Implementation Method 2
A power-split transmission can use what is commonly understood to be 'differential gearing' to achieve a continuously variable torque and speed ratio between input and output. One form of differential gearing, as is well known to those skilled in this art, may constitute a planetary gear set.
Implementation Method 3
A series hybrid electric drive system also includes one or more electric energy storage devices. The typical device is a chemical electric storage battery, but capacitive or mechanical devices, such as an electrically driven flywheel, may also be included.
Data Source
AI summary
The electrically variable transmission family provides low-content, low-cost electrically variable transmission mechanisms including first, second and third 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 transfer devices are engaged to yield an EVT with a continuously variable range of speeds (including reverse) and 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.