Planetary EV CVT for Motor Efficiency Across Torque-Speed Range
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Solution Overview
Problem
Electric vehicles face limitations in range due to the lower energy density of electric batteries compared to fossil fuels, necessitating minimized driveline losses to maximize range, and existing transmissions often compromise between efficiency and dynamic performance.
Innovation Solution
A continuously variable transmission (CVT) design is proposed, featuring a planetary gear train with two sun gears, planet gears, ring gears, and carriers, along with brakes and a transmission motor, which allows for optimal gear ratio adjustment based on operating conditions to maintain the electric motor within its most efficient torque-speed region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single ratio transmission is used in electric vehicles, then the structure is simple and reliable, but the dynamic performance and efficiency are compromised due to inability to operate motor at optimal torque-speed regions
Solution Approach 1:
The patent applies a continuously variable transmission (CVT) mechanism that dynamically adjusts gear ratios based on motor operating conditions. The CVT uses a planetary gear train with variable ratio capability, allowing the system to continuously optimize the gear ratio to keep the motor operating at its optimal efficiency point across different vehicle speeds and load conditions, thereby resolving the contradiction between simple structure and energy efficiency.
2Use of energy by moving object
If a continuously variable transmission (CVT) is added to extend gear ratio range, then the energy efficiency improves, but the device complexity increases
Solution Approach 1:
The patent merges the CVT mechanism with the existing single-speed transmission by integrating a planetary gear train that can operate in multiple modes. The system combines a fixed-ratio planetary gear set with a variable ratio mechanism, allowing it to function as both a simple single-speed transmission and a continuous variable transmission depending on operating conditions, thus reducing the overall complexity increase while maintaining energy efficiency benefits.
Solution Approach 2:
The transmission system is designed with multi-functionality, where the planetary gear train can operate in different configurations to provide both fixed-ratio and variable-ratio transmission modes. This universal design allows the same hardware to serve multiple purposes: simple direct drive at certain operating points and optimized variable ratio at others, reducing the need for separate transmission systems and minimizing complexity.
3Device complexity
If a dual-brake transmission without motor is used, then the structure is simpler, but the range of achievable gear ratios is limited
Solution Approach 1:
The patent introduces a transmission motor as an intermediary element that works in conjunction with the dual-brake transmission system. This transmission motor provides the additional torque needed to enable the planetary gear train to achieve a wider range of gear ratios, including overdrive and reverse modes, without requiring a completely different transmission architecture. The transmission motor acts as a mediator that extends the capability of the simpler dual-brake structure.
Data Source
AI summary
A continuously-variable transmission (CVT) has: a gearbox having a first planetary gear train, a second planetary gear train, a first rotating spool defined by one of two sun gears, two ring gears, and two carriers of the first and second planetary gear train, a second rotating spool defined by another one of the two sun gears, the two ring gears, and the two carriers, an input defined by a remaining one of the first sun gear, the first carrier, and the first ring gear, and an output defined by a remaining one of the second sun gear, the second carrier, and the second ring gear; a first brake operatively connected to the first rotating spool; a second brake operatively connected to the second rotating spool; and a transmission motor drivingly engaged to the first rotating spool or to the second rotating spool.