Seat Occupant Sensing Electrode Layout for Empty Capacitance Reduction
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Solution Overview
Problem
Existing capacitance-based sensors in vehicle seats face accuracy issues in determining the occupant state due to variations in the empty seat capacitance, which affects the reliability of airbag deployment decisions, and are limited in covering various seating patterns.
Innovation Solution
A capacitance-based sensor system with an occupant sensing electrode, an empty seat capacitance reducing electrode, and an electric current sensing device, where the electrodes are arranged on opposite sides of a dielectric layer, and a drive device applies a voltage to reduce the empty seat capacitance, enhancing accuracy by isolating the capacitance generated by the occupant from the existing empty seat capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitance-based sensor is used to detect occupant presence, then the sensor can detect changes in dielectric constant between air, CRS, and human body, but the empty seat capacitance varies with seat size and material causing measurement inaccuracy
Solution Approach 1:
A ground electrode is introduced as an intermediary element between the detection electrode and the seat structure. This ground electrode serves as a reference point that stabilizes the measurement system, allowing the sensor to distinguish between empty seat capacitance variations and actual occupant presence by providing a consistent baseline for comparison.
Solution Approach 2:
The patent creates an equivalent electrical circuit model that replicates the capacitance relationships in the physical sensor system. By measuring capacitance between the detection electrode and ground electrode, and between the ground electrode and seat structure, the system creates a reference model that can distinguish empty seat conditions from occupied conditions without being affected by seat-specific variations.
2Measurement precision
If the capacitance measurement includes both occupant capacitance and empty seat capacitance, then the total capacitance can be measured, but the large ratio of empty seat capacitance deteriorates the accuracy of occupant determination
Solution Approach 1:
The capacitance measurement system is segmented into multiple measurement paths: one measuring capacitance between the detection electrode and ground electrode (C1), and another measuring capacitance between the ground electrode and seat structure (C2). This segmentation allows the system to separately evaluate the occupant-related capacitance change from the empty seat capacitance, preventing the latter from overwhelming the measurement.
Solution Approach 2:
The ground electrode acts as an intermediary that divides the measurement into manageable components. By introducing this intermediate reference point, the system can measure the change in capacitance relative to a stable baseline rather than measuring the total capacitance which is dominated by the empty seat capacitance.
3Measurement precision
If capacitance-based sensors are installed in vehicle seats, then occupant presence can be detected, but factory adjustment is required for each vehicle to compensate for variations in empty seat capacitance
Solution Approach 1:
The sensor system performs self-calibration by automatically establishing a baseline measurement when the seat is empty. The control unit stores this baseline capacitance value and uses it as a reference for subsequent occupancy detection, eliminating the need for manual factory adjustment for each vehicle while maintaining detection accuracy across different seat designs.
Solution Approach 2:
The system creates an electrical model of the specific seat installation by measuring and storing the empty seat capacitance characteristics during initial operation. This copied model serves as a unique reference for each vehicle-seat combination, allowing the sensor to adapt to the specific electrical characteristics of its installation environment without requiring manual adjustment.
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 improves the accuracy of occupant determination by reducing variations in measured capacitance, allowing for precise detection of occupants and reducing the need for additional adjustments in different vehicle types, while maintaining reliability in airbag deployment decisions.
Implementation Method 1
the capacitance between the two electrodes of the capacitance-based sensor varies depending on the type of the interposed object, which is interposed between the two electrodes
Implementation Method 2
a dielectric constant of the air is about 1. A dielectric constant of the CRS is about 2 to 5 although it may vary depending on a material of the CRS. Furthermore, a dielectric constant of the human body is about 50
Implementation Method 3
an electric current sensing device (an electric current sensing circuit) measures the capacitance as a sum of the capacitance Cb and the capacitance Co
Data Source
AI summary
An occupant sensing electrode is embedded in a seat. An empty seat capacitance reducing electrode is placed between the occupant sensing electrode and a seat frame of the seat in an opposed relationship to the occupant sensing electrode. A dielectric base film may be interposed between the occupant sensing electrode and the empty seat capacitance reducing electrode. The occupant sensing electrode may include a plurality of electrode portions. The electrode portions may include high potential electrode portions and low potential electrode portions.