Ignition Device Thermal Cutout Circuit Voltage-Dependent Protection
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Solution Overview
Problem
Existing ignition devices for internal combustion engines fail to adequately protect the primary winding of the ignition coil from high temperatures, particularly when power supply voltage decreases, leading to potential overheating and component failure.
Innovation Solution
The ignition device incorporates a thermal cutout circuit that lowers the forcible turn-off temperature of the switching element when the power supply voltage decreases, ensuring the primary current is stopped before the primary winding overheats, by adjusting the reference voltage used in the comparator circuit to change the turn-off temperature based on power supply voltage levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the primary current is limited to a constant value, then the switching element is protected from excessive current, but the primary winding may overheat when power supply voltage decreases
Solution Approach 1:
The thermal cutout circuit dynamically adjusts the forcible turn-off temperature threshold based on power supply voltage levels. When voltage decreases, the threshold is lowered to ensure the switching element turns off before the primary winding overheats, even though the switching element itself is running cooler due to reduced power dissipation at lower voltages
Solution Approach 2:
The system changes the temperature parameter (forcible turn-off threshold) based on operating conditions (power supply voltage). At low voltage, the threshold is reduced to account for the shifted heat balance, ensuring protection of the primary winding while maintaining normal operation at higher voltages
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 protects the primary winding from high temperatures by ensuring the switching element is turned off at a lower temperature when power supply voltage is low, preventing overheating and extending the lifespan of the ignition components.
Implementation Method 1
a temperature sensor for measuring the temperature of the switching element
Implementation Method 2
both the switching element and the primary winding generate heat due to the primary current
Implementation Method 3
the loss in the switching element is reduced, resulting in a reduced amount of heat generated
Data Source
AI summary
An ignition device capable of more reliably protecting a primary winding of an ignition coil from high temperature is provided. The ignition device includes an ignition coil, a switching element, a temperature sensor, and a thermal cutout circuit. A primary winding of the ignition coil is connected to a DC power supply and the switching element. The temperature sensor is provided to measure the temperature of the switching element. The thermal cutout circuit forcibly turns off the switching element when the temperature of the switching element becomes higher than a predetermined forcible turn-off temperature Toff. The thermal cutout circuit is configured to lower the forcible turn-off temperature Toff when the power supply voltage Vb of the DC power supply decreases.