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 six torque transmitting devices, allowing for selective operation in power-split variable speed ratios and fixed speed ratios, utilizing planetary gear sets or alternative gear arrangements to optimize energy efficiency and reduce the size and cost of electric motor/generators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
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 size
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 each path to handle only the necessary portion of power, reducing the size and weight of electric machinery while maintaining fuel efficiency benefits.
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 engagement of torque transmitting devices to optimize the mix of mechanical and electrical power transmission, allowing smaller electric machinery to suffice.
2Weight of moving object
If electric machinery size is reduced to decrease weight and cost, then weight and cost are improved, but the system cannot handle full engine power conversion
Solution Approach 1:
By segmenting power flow into mechanical and electrical paths, the system allows the mechanical path to handle the bulk of power transmission through planetary gear sets, while the electrical path handles only the variable portion through smaller motor/generators. This enables reduced electric machinery size while maintaining adequate power handling capacity.
Solution Approach 2:
The planetary gear sets serve multiple functions: they provide mechanical power transmission, enable variable speed ratios, and facilitate the splitting and recombining of power flows. This multi-functionality allows smaller electric machinery to achieve the same effective power handling as larger systems.
3Device complexity
If conventional mechanical transmissions with five or six fixed drive ratios are used, then device complexity is reduced, but fuel consumption increases due to wide engine operating range
Solution Approach 1:
The transmission system transitions from fixed mechanical ratios to dynamically adjustable variable speed ratios achieved through the combination of planetary gear sets and motor/generators. This dynamic capability allows continuous optimization of engine operating points, improving fuel consumption while maintaining relatively simple mechanical structures.
Solution Approach 2:
The motor/generators act as intermediaries between the engine and the drive system, enabling smooth transitions between different operating modes and ratios. This intermediary function allows for continuous variable ratio adjustment without requiring complex multi-gear mechanical transmissions.
4Adaptability or versatility
If power flows through both mechanical and electrical paths in parallel, then power transmission flexibility is improved, but device complexity increases with multiple torque transmitting devices
Solution Approach 1:
The system merges mechanical and electrical power transmission paths into a unified transmission architecture where the planetary gear sets and motor/generators work together. This integration allows flexible power distribution while sharing common structural elements, reducing overall complexity compared to separate systems.
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 achieves improved vehicle acceleration, fuel economy through regenerative braking and electric-only idling, and reduced emissions, while providing optimal performance, capacity, package size, and ratio coverage, enabling smaller and lighter transmissions with lower fuel consumption.
Implementation Method 1
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 2
An electric generator can transform mechanical power from the engine into electrical power
Implementation Method 3
an electric motor can transform that electric power back into mechanical power at different torques and speeds
Implementation Method 4
An electric storage battery used as a source of power for propulsion may be added to this arrangement
Data Source
AI summary
The electrically variable transmission family of the present invention 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, 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.