Electric Powertrain Rimpull Torque Limiting for Gear Protection
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Solution Overview
Problem
The use of multi-speed transmissions with electric motors in machines poses challenges due to the high torque capabilities at low speeds, which can lead to excessive stress on the transmission components, increasing costs and potential damage, as existing solutions like U.S. Pat. No. 7,766,791 do not adequately address the issues associated with potentially damaging torques from electric motors.
Innovation Solution
An electric powertrain system with a multi-speed transmission and an electronic controller that monitors and adjusts the rimpull torque demand by shifting gears or reducing the electric motor torque command to prevent excessive torque from being applied to the transmission, thereby setting a rimpull torque limit for each gear to protect the transmission from damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an electric motor is used to provide torque to the traction devices, then fuel efficiency is improved and emissions are reduced, but the required motor size increases to meet torque and speed demands, increasing cost
Solution Approach 1:
The transmission system is segmented into multiple gear stages, allowing the electric motor to operate in different gear ratios. This enables the motor to be sized for optimal efficiency while the multi-speed transmission provides the necessary torque multiplication, resolving the contradiction between motor size and performance requirements
Solution Approach 2:
The system dynamically shifts between multiple gear ratios based on operating conditions. The electronic controller continuously monitors torque demand and adjusts the transmission gear selection, allowing the motor to operate in its efficient range while meeting varying torque requirements through dynamic gear changes
2Ease of manufacture
If a multi-speed transmission is used with an electric motor, then the required electric motor size is reduced, but the transmission components are exposed to high torques at low speeds, increasing the risk of damage and requiring a hardened (expensive) design
Solution Approach 1:
The electronic controller performs preliminary assessment of torque demand before torque is applied to the transmission. By evaluating the required torque and comparing it against current transmission state and gear limitations, the controller proactively prevents excessive torque application that could damage components
Solution Approach 2:
The system implements continuous feedback monitoring of transmission operating conditions and torque demand. The electronic controller receives feedback about current gear selection and torque requirements, and adjusts gear selection or torque commands in real-time to prevent damaging torque levels, allowing the use of less robust (cheaper) transmission components
3Reliability
If the transmission is designed to withstand high torques at all times, then reliability is improved, but manufacturing cost increases significantly
Solution Approach 1:
The system dynamically changes operating parameters (gear ratio, torque command) based on actual demand conditions. By adjusting these parameters in real-time, the transmission operates within safe limits under varying loads, maintaining reliability without requiring design for maximum possible torque at all times
Solution Approach 2:
The control system provides self-protection by automatically monitoring and limiting torque application based on current operating conditions. The electronic controller serves as a protective mechanism that prevents damage without requiring additional mechanical protection systems, reducing overall manufacturing cost while maintaining reliability
Data Source
AI summary
An electric powertrain includes an electric power source, an electric motor and a multi-speed transmission. The powertrain has an electronic controller. The controller determines a respective rimpull torque limit for the operating gear of the multi-speed transmission and determines whether the rimpull torque demand exceeds the rimpull torque limit. Upon determining that the rimpull torque demand exceeds the rimpull torque limit, the controller acts to either (i) shift the multi-speed transmission to a gear in which the respective rimpull torque limit is at or above the rimpull torque demand or (ii) reduce the electric motor torque command to a level for which the rimpull torque is below the respective rimpull torque limit for the operating gear of the multi-speed transmission.