Electric Vehicle CVT Powertrain for Motor Downsizing and Launch Torque
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Solution Overview
Problem
The existing electric passenger car powertrains with fixed gearing are limited by maximum vehicle speed and torque levels, which restricts downsizing of electric machines (EM) without compromising launch performance and efficiency.
Innovation Solution
Incorporating a variator unit with an asymmetric speed ratio range into the gearing, allowing for continuous speed ratio variation between the EM and driven wheels, enabling EM downsizing by reducing peak torque and rotational speed requirements while maintaining peak power and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed ratio gearing is used to connect the EM to the driven wheels, then the powertrain structure is simple, but the maximum vehicle speed is limited by the maximum rotational speed of the EM and the launch performance is limited by the maximum torque level
Solution Approach 1:
The patent applies a continuously variable transmission (CVT) with a variator unit that provides dynamic speed ratio adjustment between the EM and driven wheels. The variator unit includes movable elements that allow continuous variation of the speed ratio, enabling the system to adapt to different operating conditions and overcome the speed limitation of fixed ratio gearing without requiring multiple discrete gear stages.
2Device complexity
If a fixed ratio gearing is used to connect the EM to the driven wheels, then the powertrain structure is simple, but the launch performance is limited by the maximum torque level
Solution Approach 1:
The CVT with variator unit enables dynamic adjustment of torque multiplication ratio. During launch conditions, the variator unit provides high speed ratio reduction to amplify the EM torque to the driven wheels, and during high-speed operation, it provides lower ratio to maintain efficiency, thus improving launch performance without compromising maximum speed.
3Weight of moving object
If the EM is downsized to reduce peak torque level, then the EM size and cost are reduced, but the peak power and continuous power are compromised
Solution Approach 1:
The patent changes the operating parameters of the EM by introducing the CVT system. The variator unit allows the EM to operate at optimized speed and torque points across different vehicle operating conditions. This enables downsizing of the EM while maintaining peak power output because the CVT ensures the EM operates in its most efficient range, extracting maximum power from a smaller motor through optimal speed ratio management.
Data Source
Figure 1~3
AI summary
The invention relates to a powertrain for a fully electric vehicle comprising an electric machine (1), a driven wheel (2) and a gearing (3) that is arranged between the electric machine (1) and the driven wheel (2) and that provides a driving connection there between, which gearing (3) includes at least a first speed reduction stage (31) providing a fixed first speed ratio, a variator unit (40) providing a variable speed ratio and a second speed reduction stage (32) providing a fixed second speed ratio between an input gear wheel (35) and an output gear wheel (36) thereof, whereof the input gear wheel (35) rotates as one with the output shaft of variator unit (40). According to the invention, a maximum overall speed ratio provided by the gearing (3) between the electric machine (1) and the driven wheel (2) amounts to at least 20:1.