Electric Heater Overheating Detection via Inductance Change
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Solution Overview
Problem
Modern electric vehicles with high electrical voltages face challenges in heating circuits due to missing or limited engine heat sources, leading to undesirable high current peaks in PTC resistance wires and reduced service life, necessitating a solution for overheating detection and prevention.
Innovation Solution
An electric heater with a temperature-dependent inductance heating element and an overheating detection device using a PWM circuit, which measures and compares the derivative of the current flowing through the heating element to detect overheating, allowing for quick shutdown and extending service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If PTC resistance wire is used as heating element, then heating function is achieved, but high current peaks occur at low temperatures
Solution Approach 1:
The patent uses a heating element whose resistance changes with temperature, specifically designed to have low resistance at low temperatures to avoid high current peaks, and high resistance at high temperatures to limit maximum current. This parameter change approach resolves the contradiction by making the resistance adaptive to temperature conditions.
Solution Approach 2:
The heating element's resistance is not static but dynamically changes with temperature. The patent employs a heating element with positive temperature coefficient characteristics that automatically adjusts its resistance based on operating temperature, thereby dynamically preventing harmful current peaks while maintaining heating effectiveness.
2Productivity
If maximum operating point of 600°C is allowed, then heating efficiency is improved, but service life of PTC resistance wire is excessively shortened
Solution Approach 1:
The patent incorporates an overheating detection device that continuously monitors the heating element's temperature via its inductance changes. When the temperature approaches dangerous levels, the system provides feedback to reduce or interrupt heating power, thereby preventing excessive temperatures that would shorten service life while still allowing efficient operation below the threshold.
Solution Approach 2:
The patent uses a heating element with inherent resistance characteristics that naturally limit current at high temperatures, providing a built-in protective effect before damage occurs. Additionally, the overheating detection system acts as a preventive measure, ready to intervene before critical temperatures are reached, thus cushioning against service life reduction.
3Reliability
If overheating detection device is added, then functional safety is improved, but device complexity increases
Solution Approach 1:
The patent utilizes the heating element's inductance property for dual purposes: both for generating heat and for temperature detection. The same heating element serves as both the heating component and the sensing element, eliminating the need for separate temperature sensors and reducing overall system complexity while maintaining high functional safety.
Solution Approach 2:
The patent combines the heating function and temperature detection function into a single integrated system. The heating element's electrical properties (inductance and resistance) are used both for heating and for monitoring temperature, merging multiple functions into one component to avoid increasing device complexity.
4Measurement precision
If inductance-based overheating detection is used, then measurement precision is improved, but difficulty of detecting and measuring increases
Solution Approach 1:
The patent replaces direct temperature measurement (which would require contact with hot surfaces and complex thermocouple arrangements) with electrical inductance measurement. The inductance of the heating element changes predictably with temperature, allowing indirect but precise temperature detection through simple electrical measurements, thereby reducing measurement difficulty while maintaining precision.
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 solution reduces undesirable starting behavior, extends the operating temperature range, and ensures functional safety by detecting overheating and preventing damage, with a heating element made from ferromagnetic materials like iron, nickel, and cobalt alloys that provide higher power density and longer service life.
Implementation Method 1
heating element (2) having an inductance (L_RHK) which changes as a function of temperature
Implementation Method 2
The heating element (2) has an inductance (L_RHK) which changes as a function of temperature. The heating element (2) consists of a material whose relative permeability increases up to a limit temperature
Data Source
Figure 1
Figure 2
Figure 3~3c
AI summary
The invention relates to an electric heater (1) for heating fluid streams with a heating element (2) and a control device (3) for controlling a heat output produced by the heating element (2), wherein the heating element (2) has an inductance (L_RHK) that changes on the basis of the temperature, and wherein an overheating detection device (4) is provided that is configured to sense a change in the current (Iheat) flowing through the heating element (2) caused by a change in the inductance (L_RHK) and to compare said sensed change with a previously defined limit value and to determine overheating in the electric heater (1) in the event of the limit value being exceeded. The invention further relates to a method for detecting overheating in such an electric heater (1).