Four-Node Planetary Drivetrain for Decoupled Motor Speed Control
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Solution Overview
Problem
Existing electric drivetrains are constrained by a fixed motor speed for a given road speed, limiting efficiency optimization, constant torque operation, and regenerative power capacity.
Innovation Solution
A drive train configuration with a four-node planetary gear set, where two motors are coupled to input nodes and an engine is coupled to a third input node positioned between them, allowing torque from all three sources to be summed at an output node, thereby decoupling motor speed from vehicle road speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional transmission with fixed gear ratios is used, then the structure is simple and reliable, but the motor speed is constrained to fixed values for given road speeds, limiting efficiency optimization and operating range
Solution Approach 1:
The patent employs a continuously variable transmission (CVT) mechanism that replaces fixed gear ratios with continuously adjustable speed ratios. The CVT allows the motor speed to be decoupled from vehicle road speed, enabling the motor to operate at optimal speeds across a wide range of operating conditions. This dynamic adjustment capability resolves the contradiction by providing infinite operating modes without requiring multiple discrete gearbox components.
Solution Approach 2:
The transmission system is designed to perform multiple functions: it enables all-electric mode, power split hybrid mode, and regenerative braking mode within a single unified structure. The CVT mechanism serves as a universal solution that accommodates different power sources (electric motor and internal combustion engine) and operating modes, eliminating the need for separate transmission systems for each mode.
2Power
If multiple electric motors with different torque and power capabilities are used, then the torque and power range is extended, but the system complexity and control difficulty increase
Solution Approach 1:
The patent combines multiple power sources (electric motor and internal combustion engine) through a power split transmission system where their outputs are mechanically integrated. The CVT mechanism merges the torque and power from both sources, allowing them to work together seamlessly across different operating modes. This merging approach extends the overall power capability while using a unified transmission structure rather than separate independent systems.
Solution Approach 2:
The CVT mechanism acts as an intermediary between the electric motor and the vehicle wheels, enabling independent control of motor speed and vehicle speed. This intermediary function allows the system to extend torque and power capabilities by operating the motor at optimal speeds regardless of vehicle speed, without requiring complex direct coupling mechanisms.
3Adaptability or versatility
If a CVT is used to provide continuously variable speed ratios, then infinite ratios are possible between operational speed ratio limits, but the motor speed is still constrained for a given road speed, limiting efficiency optimization
Solution Approach 1:
The patent implements a dynamic power split system where the CVT allows the electric motor speed to be independently controlled from vehicle road speed. This dynamic decoupling enables the motor to operate continuously at its most efficient speed point across all vehicle speeds, maximizing energy efficiency. The system actively adjusts the speed ratio to maintain optimal motor operating conditions rather than being constrained by fixed or limited ratio options.
Data Source
AI summary
Methods and systems are provided for an electric drive train of a hybrid electric vehicle (HEV). In one example, the electric drive train may include a four-node planetary gear set with a first motor coupled to a first input node, a second motor coupled to a second input node and an engine coupled to a third input node of the planetary gear set. The third node is positioned between the first and second input nodes. Torque delivered to each input node is summed at an output node of the four-node planetary gear set.