Two-Speed Seamless Transmission for Electric Vehicles
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Solution Overview
Problem
Current transmission systems for electric vehicles face challenges in achieving a balance between efficiency and dynamic performance due to their design origins from internal combustion engine vehicles, leading to inefficiencies and discomfort in passenger experience.
Innovation Solution
A two-speed seamless transmission system utilizing dual-stage planetary gear sets with interconnected sun and ring gears, controlled by friction brakes to manage gear shifts without torque interruption, allowing for continuous power transmission and optimized gear ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single ratio transmission is used in electric vehicles, then the structure is simple and cost is reduced, but the dynamic performance and efficiency are compromised
Solution Approach 1:
The transmission system is divided into two distinct planetary gear sets (first and second planetary gear sets), each providing different gear ratios. This segmentation allows the system to achieve multiple gear ratios without using a complex multi-stage transmission, thereby improving efficiency and dynamic performance while maintaining relatively simple structure.
Solution Approach 2:
The patent combines two planetary gear sets into a single integrated transmission system where the sun gear, ring gear, and planet gears of both sets share common components. This merging approach enables the system to provide multiple gear ratios (first gear ratio and second gear ratio) without significantly increasing structural complexity or component count.
2Productivity
If multi-speed transmissions from ICE vehicles are used in EVs, then gear ratio optimization is achieved, but clutches and torque convertors are required causing complexity and energy loss
Solution Approach 1:
The patent extracts and eliminates the need for clutches and torque convertors from the transmission system by leveraging the inherent bidirectional torque capability of electric motors. This extraction simplifies the transmission structure while maintaining the ability to provide optimized gear ratios for different driving conditions.
Solution Approach 2:
The patent replaces the mechanical clutch and torque converter systems with an electrically-controlled brake mechanism that applies braking force to the ring gear or sun gear to achieve gear ratio changes. This substitution eliminates complex mechanical coupling components while maintaining gear optimization capabilities.
3Ease of operation
If clutches are used for gear changing, then start-ups and idle running are enabled, but torque interruption occurs causing discomfort and reduced reliability
Solution Approach 1:
The patent replaces the mechanical clutch system with an electrically-controlled brake mechanism that maintains continuous torque transmission during gear changes. The brake applies controlled friction to the ring gear or sun gear, enabling gear ratio changes without disengaging the torque path, thereby eliminating torque interruption and improving reliability and passenger comfort.
4Productivity
If traditional gear changing methods are used, then gear ratio transitions are achieved, but shifting time and energy dissipation increase
Solution Approach 1:
The patent replaces traditional mechanical gear changing mechanisms with an electrically-controlled brake system that can rapidly adjust gear ratios by applying brake force to different components. This substitution enables faster gear transitions with reduced shifting time and minimized energy dissipation, as the electric brake can be precisely controlled and engaged/disengaged quickly without mechanical wear or torque interruption.
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 enhances the efficiency and dynamic performance of electric vehicles by minimizing energy dissipation and shifting time, maintaining constant output torque and speed, and improving passenger comfort through seamless gear changes.
Implementation Method 1
a sun gear brake allowing the first and second sun gears to be prevented from rotating; and a ring gear brake allowing the first and second ring gears to be prevented from rotating
Data Source
AI summary
Multi-speed transmission for electric vehicles (EVs) can reduce the size of the electric motor and provide an appropriate balance between efficiency and dynamic performance. Currently used multi-speed transmissions for EVs were initially designed for internal combustion engine (ICE) vehicles. Since ICEs cannot operate below certain speeds and their speed control during gear changes is not an easy task, the presence of clutches or torque convertors is inevitable for start-ups, idle running and gear changing. This, however, is not the case for EVs as electric motors are speed controllable in a wide range of operating speeds. Accordingly, transmissions without clutches or torque converters are established for EVs.