Two-Speed Electric Drive Unit with Planetary Gear Sets
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Solution Overview
Problem
Modern motor vehicles with multiple drive-axles face challenges in efficiently managing speed ratios and torque distribution between driven wheels during turns, as conventional differentials require opposite wheels to rotate at different speeds, leading to uneven torque application.
Innovation Solution
A two-speed electric drive-unit with planetary gear-sets and torque-transmitting devices that allow selective speed ratios and torque distribution, including an electronic limited slip differential (eLSD) to maintain equal rotational speeds and balanced torque between output members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional differential is used to allow wheels to rotate at different speeds during turns, then the vehicle can negotiate turns smoothly, but the torque distribution becomes uneven and power transmission efficiency decreases
Solution Approach 1:
The system dynamically switches between two operational modes: a first speed ratio configuration for normal operation and a second speed ratio configuration during turns. This dynamic adaptation allows the system to optimize power transmission efficiency during straight-line driving while providing enhanced turn negotiation capability when needed, resolving the contradiction between continuous different speed operation and efficient power transmission.
Solution Approach 2:
The patent changes the speed ratio parameter between two distinct configurations. The first speed ratio is optimized for power transmission efficiency during straight-line driving, while the second speed ratio provides enhanced torque distribution for turn negotiation. By switching between these parameter configurations based on operating conditions, the system resolves the contradiction between maintaining efficient power transmission and enabling smooth turn negotiation.
2Ease of operation
If opposite driven wheels rotate at different speeds during turns, then the vehicle can turn smoothly, but the torque application becomes uneven affecting vehicle stability
Solution Approach 1:
The system dynamically adjusts the speed ratio configuration based on whether the vehicle is turning or traveling straight. During turns, the second speed ratio configuration is engaged to provide appropriate differential speed while maintaining stability. During straight-line travel, the first speed ratio configuration is used to maximize power transmission efficiency. This dynamic switching resolves the contradiction between allowing speed differential for turning and maintaining vehicle stability.
3Device complexity
If a single speed ratio is used in the drive-unit, then the structure is simpler, but the vehicle cannot optimize performance for different driving conditions
Solution Approach 1:
The system implements a dynamic two-speed mechanism that switches between first and second speed ratios based on driving conditions. The first speed ratio is optimized for power transmission during straight-line driving, while the second speed ratio is optimized for turn negotiation. This dynamic dual-speed approach provides performance optimization for different conditions while maintaining relatively simple planetary gear-set architecture.
Solution Approach 2:
The planetary gear-sets are designed to provide multiple functions through two distinct speed ratio configurations. The same physical gear-sets serve both straight-line driving optimization and turn negotiation optimization by switching between configurations. This multi-functionality resolves the contradiction between structural simplicity and adaptability for different driving conditions.
Data Source
AI summary
An electric drive-unit encased in a housing includes an electric motor, a first output member, and a second output member. The drive-unit also includes first, second, and third planetary gear-sets, each having first, second, and third nodes. The first gear-set has one node connected to the electric motor. The second gear-set has one node connected to the first planetary gear-set, another node connected to the first output member, and the remaining node fixed to the housing. The third gear-set has one node connected to the first gear-set and another node connected to the second output member. The drive-unit additionally includes a first torque-transmitting device configured to selectively connect one third gear-set node to the housing to thereby affect a first speed-ratio. Furthermore, the drive-unit includes a second torque-transmitting device configured to selectively connect one first gear-set node to one of the third gear-set nodes to thereby affect a second speed-ratio.