Steering Wheel Heater Contact Detection via Segmented Wiring
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Solution Overview
Problem
The sensitivity of detection circuits for contact with a steering wheel is compromised due to the smaller contact area of a human hand compared to a seated body, leading to a poor signal-to-noise ratio when conventional techniques are applied, as the ratio of capacitance between the human hand and parasitic capacitance is significantly smaller.
Innovation Solution
A steering wheel heater device is designed with a heating wire, connecting members, and a lead-out wire, where the heating wire is powered through external power and ground lines, and the lead-out wire connects to a contact detection circuit, with a portion of the wiring pattern having inductance components to reduce parasitic capacitance effects, allowing for effective capacitance changes detection between the human hand and the wiring pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the conventional seat heater detection technique is applied to a steering wheel heater, then the heater can serve dual purposes (heating and detection), but the detection sensitivity deteriorates due to the smaller contact area of a human hand compared to a seated body
Solution Approach 1:
The steering wheel heater is divided into multiple independent heating elements arranged in a matrix pattern, with each element capable of independent control and detection. This segmentation allows the system to selectively activate specific heating elements based on hand contact position, improving detection sensitivity by focusing measurement on localized contact areas rather than treating the entire steering wheel as a single detection zone.
Solution Approach 2:
Different regions of the steering wheel heater are assigned different functions: outer peripheral heating elements are optimized for heating, while inner heating elements are optimized for detection. This local differentiation allows the detection zone to be specifically tailored for hand contact detection, improving the signal-to-noise ratio by concentrating detection capability where hand contact is most likely to occur.
2Power
If the heating wire is directly connected to power and ground lines, then the heater function is achieved, but parasitic capacitance increases and reduces detection accuracy
Solution Approach 1:
A coupling capacitor is introduced as an intermediary element between the heating wire and the detection circuit. This capacitor blocks direct DC connection while allowing AC detection signals to pass through, effectively separating the power supply function from the detection function. The coupling capacitor eliminates the direct parasitic capacitance path that would otherwise degrade detection accuracy, while still enabling the heating wire to serve both heating and detection purposes.
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 configuration enhances the sensitivity of contact detection, providing a steering wheel heater device that effectively determines hand contact while minimizing parasitic capacitance interference, thus improving the signal-to-noise ratio and detection accuracy.
Implementation Method 1
a heating wire
Implementation Method 2
parasitic capacitance C12 of seat-heater release switch 12 and capacitance C13 which varies as a human body approaches are connected in parallel
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A steering wheel heater device including: a heating wire; a power line connected in series to the heating wire, for supplying the heating wire with power; a ground line connected in series to the heating wire; a lead-out wire connected to a point along a wiring pattern formed of the heating wire; and a contact detection circuit electrically connected to the wiring pattern formed of the heating wire through the lead-out wire, wherein a portion of the wiring pattern is connected in series between the ground line and the contact detection circuit.