EV Transmission Thermal Circuit Using Waste Heat for Efficiency
Solution Overview
Problem
In electrical vehicles, the drivetrain efficiency is compromised due to temperature-dependent losses in transmission, which are exacerbated at lower temperatures, leading to higher oil viscosity and reduced efficiency.
Innovation Solution
A thermal management system that utilizes heat losses from on-board units such as power electronics and electrical machines to heat up the transmission, maintaining a higher average temperature and efficiency, while protecting these units from excessive temperatures through a 3-way control valve and multiple operation modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transmission is cooled to protect power electronics and electrical machine from excessive temperatures, then the reliability of these units is improved, but the transmission efficiency deteriorates due to lower temperature
Solution Approach 1:
The cooling system is segmented into multiple independent circuits: a first cooling circuit for the power electronics, a second cooling circuit for the electrical machine, and a third cooling circuit for the transmission. This segmentation allows each component to be cooled to its optimal temperature independently, resolving the contradiction between protecting temperature-sensitive components and maintaining transmission efficiency.
Solution Approach 2:
A heat exchanger is introduced as an intermediary device between the transmission cooling circuit and the other cooling circuits. The heat exchanger enables thermal energy transfer from the transmission to the coolant loops of the power electronics and electrical machine, allowing the transmission to operate at higher temperatures for efficiency while the intermediary transfers excess heat to protect the temperature-sensitive components.
2Loss of energy
If the transmission operates at higher temperature to improve efficiency, then the energy loss is reduced, but the risk of overheating power electronics and electrical machine increases
Solution Approach 1:
The cooling system is segmented into multiple independent circuits: a first cooling circuit for the power electronics, a second cooling circuit for the electrical machine, and a third cooling circuit for the transmission. This segmentation allows each component to be cooled to its optimal temperature independently, resolving the contradiction between protecting temperature-sensitive components and maintaining transmission efficiency.
Solution Approach 2:
Temperature sensors are placed throughout the system to monitor the thermal state of the transmission, power electronics, and electrical machine. The control unit receives this feedback and dynamically adjusts the cooling system operation, including activating the heat exchanger when transmission temperature is high and adjusting coolant flow rates, to prevent harmful thermal effects on temperature-sensitive components while maintaining transmission efficiency.
3Device complexity
If a single cooling circuit is used for all components, then the device complexity is reduced, but the ability to optimize temperature for each component deteriorates
Solution Approach 1:
The cooling system is segmented into multiple independent circuits: a first cooling circuit for the power electronics, a second cooling circuit for the electrical machine, and a third cooling circuit for the transmission. This segmentation allows each component to be cooled to its optimal temperature independently, resolving the contradiction between protecting temperature-sensitive components and maintaining transmission efficiency.
Solution Approach 2:
The heat exchanger serves multiple functions: it acts as a heat source for the power electronics cooling circuit, a heat source for the electrical machine cooling circuit, and a heat sink for the transmission cooling circuit. This multi-functionality allows a single device to manage thermal requirements across multiple components, achieving temperature optimization without proportionally increasing system complexity.
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
The system achieves higher average transmission efficiency by maintaining a higher temperature, while ensuring the on-board units operate within safe temperature limits, thereby optimizing energy use and reducing battery size requirements.
Implementation Method 1
coolant of the cooling system is made to pass the on-board units
Implementation Method 2
The circuit is designed with a 3-way control valve to avoid that the coolant is circulated to the transmission when it is close to its operating temperature
Implementation Method 3
coolant can be circulated in the unit for heating up or to the front cooler for cooling
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The present invention concerns a method of thermal management of a transmission of an axle (4) of an electrical vehicle and a circuit used for the method. The circuit comprises a coolant pump (1), one or more on-board units, a three way valve (5) and the axle (4), which axle (4) comprises a transmission. Coolant of a cooling system of the vehicle is made to pass the on-board units to pick up heat losses. The on- board units may be power electronics (2), an electrical machine (3), a battery and/or an on-board charger.