Heating device
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Solution Overview
Problem
Existing heating devices in automobiles face challenges in meeting stringent electromagnetic compatibility requirements due to increased on-board supply voltages, especially when operated with pulse width modulated voltages, leading to significant electromagnetic emissions.
Innovation Solution
The heating device splits the heating load into two halves, each connected to opposite sides of a transistor switch, balancing parasitic capacitances and minimizing electromagnetic emissions by canceling out charging and discharging currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the heating device is operated with pulse width modulated voltage at high voltage, then heating efficiency is improved, but electromagnetic emissions increase
Solution Approach 1:
The heating resistor assembly is divided into two separate heating elements (first heating element and second heating element) connected in parallel, rather than using a single heating element. This segmentation allows the parasitic capacitances of each element to be balanced against each other, reducing common mode currents and electromagnetic emissions while maintaining PWM heating efficiency
Solution Approach 2:
The patent introduces asymmetry in the electrical configuration by connecting the first heating element to the high side of the PWM switch and the second heating element to the low side, creating intentionally unbalanced physical connections that result in balanced parasitic capacitance effects for emission reduction
2Power
If on-board supply voltage is increased to several hundred volts, then heating power is improved, but electromagnetic compatibility becomes more difficult to meet
Solution Approach 1:
By segmenting the heating load into two parallel heating elements with different PWM switch connections (high side and low side), the patent enables parasitic capacitance balancing that reduces common mode currents, thereby improving electromagnetic compatibility while maintaining high voltage heating power
Solution Approach 2:
The patent converts the harmful parasitic capacitances inherent in high voltage PWM circuits into a beneficial balancing effect. By intentionally designing the circuit so that parasitic capacitances of two heating elements are equal and oppositely polarized, the harmful electromagnetic emissions are reduced while the high voltage power benefit is retained
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 design significantly reduces radiated and conducted emissions, enhancing electromagnetic compatibility without increasing costs.
Implementation Method 1
Heating devices, like flow heaters, comprising a heating resistor assembly, e.g. a metallic heating plate with a resistive track
Implementation Method 2
heating resistors connected in series between the positive terminal and the negative terminal
Data Source
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AI summary
Disclosed is a heating device comprising a heating resistor assembly comprising a positive terminal (13), a negative terminal (14), and heating resistors (10, 10a, 10b) connected in series between the positive terminal (13) and the negative terminal (14), and a transistor switch (21) connected in series with the heating resistors (10). According the invention a first half (10a) of the heating resistors connects the positive terminal (13) to the transistor switch (21) and a second half (10b) of the heating resistors (10) connects the transistor switch (21) to the negative terminal (14).