Multi-mode Electrically Variable Transmission with Fixed Gear
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Solution Overview
Problem
Multi-mode electrically variable transmissions (EVTs) face issues such as higher transmission spin losses due to clutch drag and planetary gear set friction, limited kinematic variability, increased mechanical and electrical losses during highway operation, and inadequate reverse gear functionality, especially in extreme climates or when electric power is limited.
Innovation Solution
An improved input-split planetary gear set configuration for the multi-mode EVT, allowing for reduced clutch torques, enhanced kinematic variability, fixed gear operation for highway cruising, and reverse gear functionality by utilizing both electric motors for propulsion, ensuring efficient engine operation across city and highway driving conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a typical EVT uses a compromise gearing design between city and highway driving, then adequate vehicle speeds during highway driving are achieved, but city driving performance is degraded and top speed in battery electric vehicles is limited
Solution Approach 1:
The transmission system is segmented into multiple independent gear sets (first planetary gear set, second planetary gear set, and fixed gear set) that can operate independently or in combination. This segmentation allows the system to provide different gear ratios for different driving conditions (city vs. highway) without compromise, enabling both adequate highway speeds and improved city driving performance while extending top speed capability in battery electric vehicles.
2Adaptability or versatility
If a multi-mode EVT uses multiple planetary gear sets and clutch mechanisms for mode changing, then kinematic variability is improved, but transmission spin losses increase due to clutch drag and friction
Solution Approach 1:
The patent extracts the friction and drag losses by providing dedicated direct drive paths for each mode. The first direct drive path connects the first electric motor directly to the output when the first clutch engages, and the second direct drive path connects the second electric motor directly to the output when the second clutch engages. This extraction of direct drive capability eliminates the need for power to flow through multiple planetary gear stages during mode transitions, reducing transmission spin losses while maintaining kinematic variability.
3Speed
If a typical EVT operates during highway conditions, then vehicle speed is maintained, but mechanical and electrical losses increase
Solution Approach 1:
The transmission system dynamically switches between different operating modes based on driving conditions. During highway cruising, the system can engage the fixed gear set with the first electric motor to provide efficient direct drive operation, minimizing mechanical and electrical losses. The dynamic capability to switch between the first planetary gear set, second planetary gear set, and fixed gear set allows optimization of energy efficiency for sustained highway speeds.
4Device complexity
If a typical EVT relies solely on one electric motor for reverse gear operation, then the structure is simplified, but reverse propulsion capability is inadequate when electric power is limited
Solution Approach 1:
The transmission system provides universal reverse propulsion capability through multiple pathways. The first electric motor can provide reverse torque through the first planetary gear set, the second electric motor can provide reverse torque through the second planetary gear set, or the engine can provide reverse torque through the fixed gear set. This multi-functionality ensures that reverse propulsion is available even when electric power is limited, improving reliability while maintaining reasonable structural complexity.
Data Source
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AI summary
Multi-mode operation is provided for an electrically variable transmission for a motor vehicle. The multi-mode electrically variable transmission provides for multiple gear ratios and power flow configurations including fixed gear operation. The multi-mode electrically variable transmission incorporates a reverse gear for reverse operation.