Heating Wire Circuit for Capacitive Touch and Heating
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Solution Overview
Problem
Existing electric heating systems in vehicles, which use heating wires for both heating and capacitive touch detection, face inefficiencies due to parasitic capacitances from field effect transistors and additional impedances like diodes, leading to suboptimal thermal power conversion and interference in capacitive measurements.
Innovation Solution
A circuit structure employing MOS-FETs as switching elements, allowing the heating wire to be connected in series during heating mode and switching to a blocking state for capacitive measurement, using alternating voltages and shielding to improve capacitive decoupling and reduce parasitic capacitances, enabling efficient heating and reliable capacitive detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If field effect transistors are used to separate the heating wire from heating poles during measuring mode, then capacitive measurement interference is reduced, but parasitic capacitances from the transistors cause disturbances in determining the actual measuring capacitance
Solution Approach 1:
The patent extracts and removes the switching elements (field effect transistors) and additional impedances (diodes) from the circuit path between the heating wire and heating poles during measuring mode. By completely disconnecting these components through opening switches, the parasitic capacitances they generate are eliminated from the measurement circuit, thereby improving capacitive measurement accuracy without any residual interference.
Solution Approach 2:
The patent introduces opening switches as intermediary elements that completely disconnect the heating wire from the heating poles during measuring mode. These switches act as mediators that isolate the measurement circuit from the heating circuit, ensuring that no parasitic capacitances from transistors or diodes can affect the capacitive measurement, while still allowing the heating function to operate when the switches are closed.
2Measurement precision
If additional impedances like diodes are used to support the insulating effect during measuring mode, then capacitive measurement interference is reduced, but ohmic losses increase and heating efficiency decreases
Solution Approach 1:
The patent extracts and removes additional impedances (diodes) from the circuit, replacing them with opening switches that provide isolation without introducing ohmic losses. The switches completely open the circuit path during measuring mode, achieving the insulating effect needed for accurate capacitive measurement while maintaining full heating efficiency when the switches are closed, as there are no diodes to cause voltage drops or power losses.
3Reliability
If diodes are used to shield the connecting line during measuring mode, then capacitive measurement reliability is improved, but heating current efficiency is reduced due to ohmic losses
Solution Approach 1:
The patent introduces opening switches as intermediary elements that completely disconnect the heating wire from the heating poles during measuring mode. These switches provide reliable isolation for capacitive measurement without the ohmic losses associated with diodes, ensuring both measurement reliability and heating current efficiency are optimized.
Solution Approach 2:
The patent extracts diodes from the circuit and replaces them with opening switches, eliminating the source of ohmic losses while maintaining the isolation function needed for reliable capacitive measurement. This extraction improves heating current efficiency by removing the energy-dissipating diodes while preserving measurement reliability through complete circuit disconnection.
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 approach enhances the efficiency of heating power conversion while maintaining or improving the reliability of capacitive approach measurements, reducing ohmic losses and interference, thus optimizing both heating and detection functions.
Implementation Method 1
the heating wire is flooded with an electric heating current supplied by two poles at two different heating potentials, wherein a heating voltage drops on the heating wire
Implementation Method 2
the capacitance of the heating wire relative to a reference potential is determined by applying to the heating wire an alternating voltage from an AC voltage source
Data Source
AI summary
A circuit structure and a method for carrying out an alternating heating and capacitive measuring mode by a common heating wire is presented. The method includes carrying out a heating mode, during which from a switching by a control circuit switching elements are in a conducting state, the switching elements are connected in series, so that the heating wire is supplied with a heating current from two different heating potentials; triggering a change into a detecting mode by the control circuit, so that the switching elements switch from the heating mode into a measuring mode, during which the switching elements are in a blocking state, so that the two different heating potentials are each interrupted several times; carrying out the measuring mode, in which the capacitance of the heating wire relative to a reference potential is determined by a detecting circuit by applying to the heating wire an alternating voltage.