Main Relay Thermal Management via Charging Relay Conduction

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Solution Overview

Problem

Conventional main relay protection methods in motor-driven vehicles with externally-coupled chargers often lead to overheating, which can result in reduced vehicle acceleration, decreased fuel efficiency, and increased exhaust gas due to limitations in power supply or increased engine usage.

Innovation Solution

A main relay protection device that includes a controller to perform ON-control on charging relays when the main relay temperature exceeds a preset threshold, utilizing charging relays to efficiently transfer heat from the main relay to a bus bar, which is then radiated to a cooler charger-side portion, preventing overheating.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If conventional main relay protection methods are used without charging relay ON-control, then the system structure remains simple and operation is straightforward, but the main relay temperature rises excessively causing overheating

Engineering Contradiction:

Improvemain relay temperatureVSAvoidcontrol system complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The charging relay is used as an intermediary component to transfer heat from the main relay to the charger-side bus bar. By turning on the charging relay, a thermal conduction path is established that allows heat to flow from the high-temperature main relay through the bus bar to the cooler charger-side portion, effectively cooling the main relay without requiring dedicated cooling mechanisms.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The bus bar, which normally serves only as an electrical conductor, is utilized as a heat dissipation pathway. The inherent thermal conductivity of the bus bar material is leveraged to convert the electrical component into a thermal management component, transforming the potential harm of overheating into a beneficial cooling effect through passive heat conduction.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Productivity

If main relay temperature is not controlled, then device operation is simple, but vehicle acceleration is reduced and fuel efficiency decreases

Engineering Contradiction:

Improvevehicle acceleration performanceVSAvoidfuel consumption

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The control unit continuously monitors the main relay temperature and uses this feedback information to determine when to activate the charging relay for cooling. When the temperature exceeds a predetermined threshold, the control unit turns on the charging relay; when the temperature drops below the threshold, it turns off the charging relay. This closed-loop feedback control ensures optimal temperature management while minimizing unnecessary energy consumption.

Inventive Principle:

Principle #23Feedback

3Duration of action of stationary object

If main relay overheating occurs, then no additional cooling components are needed, but engine forced-operation control duration increases

Engineering Contradiction:

Improveengine forced-operation control durationVSAvoidoverheating effects

Core Design Contradiction:

Duration of action of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary cooling action by activating the charging relay before the main relay temperature reaches critical levels that would trigger engine forced-operation control. The control unit monitors temperature continuously and initiates cooling through the charging relay at predetermined thresholds, preventing the temperature from rising to levels that would require engine intervention and extend forced-operation duration.

Inventive Principle:

Principle #10Preliminary action

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 effectively reduces main relay temperatures, preventing overheating and associated issues like reduced acceleration and increased fuel consumption, while maintaining reliable vehicle operation and reducing the duration of engine forced-operation control.

Implementation Method 1

utilizing charging relays to efficiently transfer heat from the main relay to a bus bar, which is then radiated to a cooler charger-side portion

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

which is then radiated to a cooler charger-side portion

Methodology Applied

Scientific EffectThermal radiation: Thermal Radiation

Data Source

PatentUS10940768B2Main relay protection device

Publication Date: 2021.03.09 SUBARU CORP

AI summary

A main relay protection device includes a motor generator, a rechargeable driving battery, an externally-coupled charger, a main relay, a charging bus bar, a charging relay, a main relay temperature sensor, and a controller. The motor generator drives a vehicle. The battery supplies power to the motor generator. The charger charges the battery. The main bus bar is disposed between the battery and the motor generator. The main relay is disposed in the main bus bar. The charging bus bar is disposed between the main bus bar and the charger. The charging relay is disposed in the charging bus bar. The sensor is configured to detect a temperature of the main relay. The controller performs ON-control on the charging relay in a state where the main relay is turned on, if the detected temperature of the main relay is higher than or equal to a preset heat radiation starting threshold.