Occupant Classification System Wet Seat Interference
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Solution Overview
Problem
Conventional occupant classification systems in vehicles face challenges in accurately distinguishing between adult and child seats, especially in wet seat situations, due to unreliable grounding systems and interference from seat heaters, which affect capacitive sensing measurements.
Innovation Solution
The system employs a sensing element with a measurement circuit that measures in-phase and quadrature components of the current sent to the sensing electrode, ensures the seat pan and seat back frame are grounded, and uses a controller to classify occupants, with the heating element and sensing element positioned a predetermined distance apart to minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the seat heater element is positioned close to the sensing element to save space and reduce installation complexity, then device complexity is reduced, but the heater interferes with capacitive sensing measurements reducing measurement precision
Solution Approach 1:
The system implements time-division multiplexing where the heater and sensor operate at different time intervals. The heater is activated during heating periods while the sensor takes measurements during non-heating periods, eliminating interference between the two functions while maintaining close physical proximity for space efficiency
Solution Approach 2:
The system dynamically switches between heating and sensing modes, with the heater control electronics enabling/disabling the heater based on operational requirements. This dynamic control allows the same physical space to serve both heating and sensing functions without mutual interference
2Measurement precision
If the heater element is made to float (high impedance to ground) to reduce interference with capacitive sensing, then measurement precision improves, but the system reliability deteriorates due to inconsistent floating and sensitivity to mechanical orientation changes
Solution Approach 1:
The heater is electrically decoupled from ground during sensing operations by switching it to high-impedance state, effectively extracting it from the ground reference during measurement periods. This eliminates the interference path while maintaining a reliable grounded connection during heating periods, achieving both precision and reliability through temporal separation
Solution Approach 2:
The heater control electronics act as an intermediary that manages the electrical connection state of the heater. By controlling the switching between grounded and floating states, the intermediary enables the system to achieve both reliable grounding when needed and interference-free sensing when required
3Measurement precision
If separate mats are used for heater and sensor element to minimize interference, then measurement precision improves, but device complexity increases due to additional installation processes and extra layers
Solution Approach 1:
The heater and sensor elements are integrated into a single combined mat structure rather than using separate mats. This merging reduces installation complexity by eliminating the need for multiple separate components and their associated installation procedures while maintaining measurement precision through temporal separation of heating and sensing operations
4Device complexity
If only current amplitude measurement is used to simplify the measurement circuit, then device complexity is reduced, but measurement precision deteriorates due to overlapping readings between child seat and adult cases in wet seat situations
Solution Approach 1:
The measurement system transitions from one-dimensional amplitude-only measurement to two-dimensional measurement by adding quadrature component detection. This additional dimension provides extra information that enables differentiation between overlapping cases (child seat vs adult in wet conditions) without significantly increasing circuit complexity
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 effectively separates adult and child seat classifications during wet conditions, providing consistent and reliable occupant classification by ensuring a stable grounding path and minimizing the impact of seat heater interference on capacitive sensing.
Implementation Method 1
When a vehicle seat is wet, a loading current out of the sensing electrode increases. When a rear facing infant seat (RFIS) contains an infant during a wet seat situation (RFIS/wet), the current out to the electrode may be higher than an adult occupant situation.
Implementation Method 2
a measurement circuit that is configured to measure in-phase and quadrature components of a current sent out to the sensing electrode
Implementation Method 3
Some conventional systems, a seat pan and seat back frame may be grounded because of a connection through seat tracks and a seat back angle adjuster to the floor pan.
Data Source
AI summary
An occupant classification system classifies occupants on a vehicle seat and is capable of separating child seats from adults during wet seat cases. In the system, the seat structure is grounded. The classification system includes a measurement circuit, an identifying circuit, and a controller. The measurement circuit is configured to measure in-phase and quadrature components of a current sent out to the sensing element. The identifying circuit is configured to identify if a seat pan and a seat back frame of the vehicle seat are grounded to a circuit ground. The controller is configured to use measurements of the measurement circuit to classify the occupant. The sensing element can be located in a sensing mat that further includes a heating element.