Multi-mode Electrically Variable Transmission with Planetary Gear Sets
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Solution Overview
Problem
Conventional vehicle transmission systems, particularly those in hybrid vehicles, face inefficiencies in fuel consumption and emissions due to the wide variation in engine demands, and the series hybrid electric drive system's weight and cost issues related to electric machinery for power conversion.
Innovation Solution
An electrically variable transmission system with two planetary gear sets, two motor/generators, a dog clutch, and four or five torque transfer devices, allowing for selective operation in power-split variable speed ratios and fixed speed ratios, reducing the need for continuous motor/generator connection and enabling regenerative braking and electric-only idling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a series hybrid electric drive system is used to allow engine independence from vehicle torque and speed requirements, then emissions and fuel consumption are improved, but the weight and cost of electric machinery increase significantly
Solution Approach 1:
The power flow is segmented into two separate paths: a mechanical path for direct power transmission and an electrical path for energy management. This allows the electric machinery to handle only the difference between engine output and vehicle demand, rather than the entire power flow, significantly reducing the size and weight of motors and generators while maintaining emission and fuel efficiency benefits.
2Adaptability or versatility
If continuous connection of motor/generators is used to achieve continuous power conversion, then flexibility in engine operation is improved, but device complexity and cost increase
Solution Approach 1:
The system dynamically switches between different operational modes (engine brake mode, generator mode, motor mode, direct mechanical connection) based on real-time vehicle conditions. This dynamic adaptability allows the motor/generators to be disconnected when not needed, reducing complexity while maintaining flexibility when required.
3Device complexity
If conventional mechanical transmission with fixed ratios is used, then device complexity is reduced, but fuel consumption and emissions increase due to wide variation in engine demands
Solution Approach 1:
The motor/generators serve multiple functions: they act as generators during braking to recover energy, as motors during acceleration to assist the engine, and can be disconnected to allow direct mechanical power transmission. This multi-functionality enables the system to maintain low complexity while achieving improved fuel economy and emissions across varying operating conditions.
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 improves vehicle acceleration, fuel economy, and emissions by optimizing energy efficiency, reducing the size and cost of electric motor/generators, and providing a range of operating modes including reverse, launch, and fixed ratios, while minimizing fuel consumption and emissions.
Implementation Method 1
A first planetary gear set has a sun gear, a ring gear, and a carrier. A second planetary gear set has a sun gear, a ring gear, and a carrier. Each planetary gear set provides differential gearing to achieve continuous variable torque and speed ratios.
Implementation Method 2
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 for the remainder of the vehicle drive system.
Implementation Method 3
The motor/generators are operably connected to an energy storage battery so that the battery can power the motor/generators during different operating modes.
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, and up to five selectable torque-transfer devices, and a dog clutch. The selectable torque transfer devices are engaged singly or in combinations of two 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.