Seat Heater Capacitive Sensor Integration Using Common Mode Chokes
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Solution Overview
Problem
Existing capacitive occupant detection systems for vehicles face challenges in cost-efficiency and detection performance due to the use of high inductance components that support high DC currents, leading to expensive and complex designs.
Innovation Solution
A combined seat heater and capacitive occupancy sensor system that incorporates a heater network with common mode chokes and a capacitive sensing network with high-impedance amplifiers, allowing for the measurement of complex impedance and capacitance between the heating element and ground, using a common mode choke and a reference component to reduce measurement errors and improve sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high inductance components are used to support high DC currents in capacitive occupancy sensors, then the sensor can detect occupancy state, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent combines the heating element and capacitive sensor electrode into a single integrated component. The heating element serves dual purposes: providing thermal heating function and acting as the capacitive sensor electrode for occupancy detection. This eliminates the need for separate high inductance components, reducing device complexity while maintaining occupancy detection capability through measurement of complex impedance changes when an occupant is present
Solution Approach 2:
The heating element is designed to perform multiple functions simultaneously: it provides thermal heating to the seat and serves as the capacitive sensor electrode for occupancy detection. By making the heating element universal for both thermal and sensing functions, the patent eliminates the need for dedicated sensor components with high inductance, thereby reducing device complexity and manufacturing cost
2Reliability
If the capacitive sensor measures impedance of the heating element, then occupancy detection is achieved, but the heating function may be disturbed
Solution Approach 1:
The patent applies a periodic oscillating voltage signal to the heating element to enable capacitive sensing. This periodic signal allows the measurement circuit to determine complex impedance by measuring voltage and current at specific frequencies, enabling occupancy detection while the heating function operates continuously or intermittently based on thermal requirements, thus maintaining heating stability
Solution Approach 2:
The patent introduces a measurement circuit as an intermediary between the heating element and the control system. This measurement circuit measures the complex impedance of the heating element without directly interfering with the heating current flow. The measurement circuit can operate at high impedance during sensing while the heating function continues uninterrupted, or the system can alternate between measurement and heating modes
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 provides a cost-efficient and improved detection performance by accurately determining the occupancy state without disturbing the heating function, using a high-impedance amplifier to measure the oscillating voltage on the heating element and deriving the capacitance, which is sensitive to the presence of a conductive body.
Implementation Method 1
a heating element (10) connected between a first node (21) and a second node (22) to dissipate heat when a heating current is caused to flow between the first and second nodes
Implementation Method 2
a common mode choke (16) connecting the first and the second node to a third and a fourth node (23, 24), respectively
Implementation Method 3
the capacitive sensing network (28, 32, 40, 42) is connected to the heating element (10) to apply an oscillating current thereto and to derive a capacitive load of the heating element (10) from a voltage resulting on the heating element (10)
Data Source
AI summary
A combined seat heater and capacitive occupancy sensor comprises a heater network and a capacitive sensing network. The heater network includes a heating element (10) connected between a first node (21) and a second node (22) to dissipate heat. The capacitive sensing network is connected to the heating element to apply an oscillating current thereto and to derive a capacitive load of the heating element from the voltage resulting on the heating element. The heater network comprises a common mode choke (16) connecting the first and the second node to a third (23) and a fourth (24) node, respectively. The capacitive sensing network further comprises means to sustain the oscillating current in or to drive the oscillating current into the heating element as well as a high-impedance amplifier (32) having an input node operatively connected to the heating element to probe the resulting voltage, and an output node (44) to provide an output signal indicative of the voltage.