Two-Speed Planetary Gearbox for EV Off-Road Torque Switching
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Solution Overview
Problem
Battery electric vehicles with single-speed gearboxes struggle to provide sustained high torque required for off-road driving while also meeting on-road performance and range requirements, as they lack the gearing necessary for efficient torque delivery in such conditions.
Innovation Solution
A two-speed coaxial gearbox assembly with three planetary gear sets and two selectively engageable clutches allows the electric vehicle to switch between on-road and off-road gears, providing high torque and low speed operation by engaging different clutch configurations, and only allows shifting when the vehicle is stationary to prevent accidental shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If higher ratio gearing is used to provide sustained high torque, then off-road torque capability is improved, but on-road performance and range are worsened
Solution Approach 1:
The gearbox employs two distinct gear ratios that can be dynamically selected based on driving conditions. A first gear ratio provides high torque multiplication for off-road sustained high torque requirements, while a second gear ratio offers lower multiplication for on-road efficiency. The system transitions from static single-ratio gearing to dynamic multi-ratio selection, allowing optimal performance across different operating environments.
Solution Approach 2:
The invention changes the gear ratio parameter based on driving conditions. By providing a first gear ratio with higher torque multiplication and a second gear ratio with lower torque multiplication, the system can adjust the torque-speed characteristics to match either off-road or on-road requirements, thereby optimizing both torque capability and energy efficiency across different scenarios.
2Force
If additional gearing is added to provide sustained high torque, then off-road performance is improved, but device complexity is worsened
Solution Approach 1:
The gearbox is segmented into two distinct gear ratio systems (first and second gear ratios) that can be independently selected. This segmentation allows the complex requirement of providing sustained high torque without oversimplifying, as each gear ratio is optimized for specific conditions. The segmentation also enables independent optimization of each gear set for its intended purpose.
Solution Approach 2:
The gearbox serves multiple functions through its two gear ratios: it provides high torque multiplication for off-road sustained high torque applications and lower torque multiplication for on-road efficiency. This multi-functionality allows a single gearbox unit to handle both off-road and on-road requirements, reducing the need for separate specialized systems.
3Use of energy by moving object
If single speed gearbox is used to meet on-road requirements, then energy efficiency is improved, but off-road sustained high torque capability is worsened
Solution Approach 1:
The system transitions from static single-speed gearing to dynamic two-speed selection. The first gear ratio is optimized for off-road sustained high torque with higher torque multiplication, while the second gear ratio is optimized for on-road energy efficiency with lower torque multiplication. The dynamic switching between these two configurations allows the system to adapt to different torque requirements.
Solution Approach 2:
The gear ratio parameter is changed based on driving conditions. When off-road sustained high torque is required, the system selects the first gear ratio with higher torque multiplication. When on-road energy efficiency is prioritized, the system switches to the second gear ratio with lower torque multiplication, thereby optimizing the torque-speed characteristics for each scenario.
Data Source
AI summary
A two-speed gearbox assembly includes a housing, a first planetary gear set configured to operably connect to an output of an electric motor, a second planetary gear set rotationally coupled to an output of the first planetary gear set, and a third gear set rotationally coupled to an output of the second planetary gearset. A first clutch is configured to selectively couple the first planetary gear set to the second planetary gear set, and a second clutch is configured to selectively ground a portion of the second planetary gear set to the housing. The gearbox assembly is selectively switchable between (i) an on-road first gear where the first clutch is engaged and the second clutch is disengaged, and (ii) an off-road second gear where the first clutch is disengaged and the second clutch is engaged to provide sustained high torque and low speed.