Multi-mode Electrically Variable Transmission with Planetary Gear Sets
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Solution Overview
Problem
Conventional vehicle transmission systems, particularly those in hybrid electric vehicles, face challenges in achieving optimal energy efficiency, reducing fuel consumption, and minimizing emissions due to the wide variation in engine demands and the weight and cost of electric machinery required for continuous power conversion.
Innovation Solution
The development of an electrically variable transmission system with three planetary gear sets, two motor/generators, and five torque transmitting devices, allowing for selective operation in both power-split variable speed ratios and fixed speed ratios, enabling improved energy efficiency through regenerative braking and electric-only idling, and reducing the size and cost of electric motor/generators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a series hybrid electric drive system is used to allow continuous variation in torque and speed ratio, then energy efficiency and emissions are improved, but the weight and cost of electric machinery increases significantly
Solution Approach 1:
The transmission system is divided into multiple planetary gear sets (first, second, and third planetary gear sets) with distinct functions. The first planetary gear set handles power splitting, the second provides additional gear ratios, and the third enables direct mechanical connection. This segmentation allows the electric machinery to be smaller since it only needs to handle a fraction of the total power transmission, reducing weight while maintaining energy efficiency benefits.
Solution Approach 2:
Planetary gear sets serve as intermediary mechanical devices between the engine and the electric motor/generator. These gear sets enable torque multiplication and speed variation mechanically, reducing the burden on the electric machinery. The torque transmitting devices (clutches and brakes) act as intermediaries to selectively engage different power paths, allowing the system to achieve continuous variation in torque and speed ratio without requiring oversized electric components.
2Adaptability or versatility
If multiple torque transmitting devices are added to enable selective operation in power-split variable speed ratios and fixed speed ratios, then adaptability and versatility are improved, but device complexity increases
Solution Approach 1:
Each torque transmitting device (first clutch, second clutch, first brake, second brake, third brake) is designed to perform multiple functions. For example, the first clutch can engage for power-split operation, direct mechanical connection, or as part of fixed ratio transmission. The planetary gear sets serve multiple purposes: power splitting, torque multiplication, and enabling different speed ratios. This multi-functionality reduces the need for separate dedicated components for each operating mode, managing complexity while maintaining versatility.
Solution Approach 2:
The patent combines multiple power transmission paths (electrically variable path and direct mechanical path) into a single integrated transmission system. The planetary gear sets merge the functions of differential gearing and fixed ratio transmission. The torque transmitting devices are combined with the planetary gear sets to enable seamless transitions between operating modes. This merging creates a unified system that achieves adaptability without proportionally increasing complexity.
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
This solution enhances vehicle acceleration performance, improves fuel economy, and provides attractive marketing features by achieving better energy efficiency and emissions control while optimizing transmission performance, capacity, package size, and ratio coverage.
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. Planetary gearing is usually the preferred embodiment employed in differentially geared inventions
Implementation Method 3
five torque transmitting devices, including two brakes and three clutches
Data Source
AI summary
An electrically variable transmission family having low-content, low-cost electrically variable transmission mechanisms including three differential gear sets, a battery, two electric machines serving interchangeably as motors or generators and five selectable torque-transfer devices. The selectable torque transmitting devices are engaged to yield an EVT with a continuously variable range of speeds and five fixed speed ratios, including four mechanically fixed forward speed ratios and one reverse speed ratio. The torque transmitting devices and the first and second motor/generators are operable to provide six operating modes in the electrically variable transmission, including battery reverse mode, EVT reverse mode, series reverse mode, launch modes, continuously variable transmission range mode, and fixed ratio mode.