Heater Supply Circuit With Fail-Safe Thermal Current Interruption
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Solution Overview
Problem
Existing vehicle safety devices in electric and hybrid electric vehicles may resume current supply to loads after initial interruption due to abnormalities in the control means, compromising the reliability of current interruption during temperature-related issues.
Innovation Solution
A vehicle safety device with first and second interrupting means that set the supply line to an interrupted condition when the load reaches specific temperatures, ensuring it cannot be returned to an energized state, utilizing bimetal switches and IGBTs to manage current flow and prevent resumption, even in abnormal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control means open the switch based on temperature signal to interrupt current, then current interruption is achieved, but reliability of current interruption deteriorates due to possible control means abnormalities after interruption
Solution Approach 1:
The patent divides the interrupting system into two independent segments: first interrupting means (controlled switch) and second interrupting means (temperature-responsive switch). Each segment operates independently with different triggering mechanisms, so that failure in one segment does not affect the other. This segmentation ensures that even if control means become abnormal, the second interrupting means remains functional to maintain current interruption.
Solution Approach 2:
The patent introduces a temperature-responsive intermediary element (such as a bimetallic strip or PTC thermistor) that directly responds to temperature changes without requiring control means. This intermediary acts as a backup mechanism that bypasses the control system, ensuring current interruption reliability even when control means become abnormal.
2Reliability
If single interrupting mechanism is used to stop current at abnormal temperature, then simple control is achieved, but safety is worsened due to possible resumption of current after control means failure
Solution Approach 1:
The patent applies different local qualities to different interrupting mechanisms: the first interrupting means uses controlled switching for normal operation, while the second interrupting means uses inherent temperature-responsive properties of materials (such as bimetallic strip deformation or PTC resistance increase). This combination of different local qualities ensures that at least one mechanism remains effective under various abnormal conditions.
Solution Approach 2:
The patent implements beforehand cushioning by preparing a backup interrupting mechanism (second interrupting means) that is ready to activate if the primary mechanism fails. This cushioning approach ensures that even if control means become abnormal after current interruption, the system maintains safety through the pre-positioned backup mechanism.
3Ease of operation
If control means are used to interrupt current supply, then operational control is achieved, but risk of accidental reactivation increases when control means become abnormal
Solution Approach 1:
The patent inverts the control logic of the second interrupting means: instead of requiring a control signal to interrupt current (like the first means), the second interrupting means automatically interrupts current when temperature reaches a predetermined level, and requires active intervention to resume. This inverted approach prevents accidental reactivation by making the system inherently safe without requiring control means.
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
Enhances the reliability of current interruption by ensuring the supply line remains in an interrupted state, preventing accidental reactivation and improving safety during temperature-related abnormalities, thereby protecting the vehicle's systems from overheating or short circuits.
Implementation Method 1
first interrupting means for setting the supply line in an interrupted condition when a temperature of the load reaches a first set temperature
Implementation Method 2
control current applied to an insulated gate bipolar transistor (IGBT)
Data Source
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AI summary
A vehicle safety device (100) installed in a hybrid electric vehicle or an electric vehicle is provided to be capable of interrupting a current supplied from a direct current power supply (11) to an electric heater (5d) via a supply line (12). The vehicle safety device (100) includes first interrupting means (20, 22) adapted to set the supply line (12) in an interrupted condition when a temperature of the electric heater (5d) reaches a first set temperature and second interrupting means (30, 31, 32) adapted to set the supply line (12) in the interrupted condition such that the supply line (12) cannot be returned to an energized condition when the temperature of the electric heater (5d) reaches a second set temperature that is higher than the first set temperature.