Capacitive Occupant Sensor Fluid-Bladder Segmentation
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Solution Overview
Problem
Existing capacitive sensors with fluid-filled elastomeric bladders face challenges in maintaining the relationship between capacitance change and applied force as the area of occupant force increases, due to the limited expansion area of the bladder, which affects the accuracy of occupant classification.
Innovation Solution
A capacitive occupant sensor design featuring a primary region subjected to occupant-related forces and a secondary region isolated from these forces, with a fluid-filled elastomeric bladder and auxiliary conductor plates, where the secondary region is shielded from forces and measures fluid pressure to maintain the capacitance change and applied force relationship, using a spring clamp to manage fluid flow between regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the bladder expansion area is increased to accommodate larger occupant force areas, then the sensor can detect larger-area force distribution, but the relationship between capacitance change and applied force deteriorates due to reduced expansion area in the loaded region
Solution Approach 1:
The sensor is divided into a primary region for detecting occupant presence and a secondary region for detecting fluid pressure. The bladder is segmented into a primary region and a secondary region with an appendage. The secondary region is isolated from occupant forces but receives fluid pressure transmitted through the bladder, allowing independent measurement of overall applied force without being affected by local expansion limitations.
Solution Approach 2:
Fluid acts as an intermediary to transmit pressure from the primary region to the secondary region. The spring clamp acts as a mechanical intermediary to bias the appendage and control fluid flow between regions. This intermediary mechanism allows the secondary region to measure overall force through fluid pressure while remaining isolated from direct occupant contact forces.
2Measurement precision
If the dielectric material is made thin and locally compressible to improve capacitance sensitivity, then the capacitance change increases for small forces, but the sensor cannot maintain accurate measurement for large-area force distribution
Solution Approach 1:
The measurement function is segmented between two regions: the primary region uses thin compressible dielectric for high capacitance sensitivity to localized forces, while the secondary region measures fluid pressure for overall force magnitude. This segmentation allows each region to optimize for its specific measurement purpose without compromise.
Solution Approach 2:
Different regions of the sensor have different functional qualities: the primary region dielectric is thin and highly compressible for sensitivity to localized occupant contact, while the secondary region measures transmitted fluid pressure for overall force magnitude. Each region is optimized for its specific measurement role.
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 design enhances the accuracy and range of occupant classification by maintaining the relationship between capacitance change and applied force, even with large-area force distribution, and allows for precise detection and classification of occupants.
Implementation Method 1
When occupant-related seat force is applied to the sensor, fluid in the loaded region of the bladder is displaced to another region where the bladder can expand to accommodate the displaced fluid
Implementation Method 2
fluid in the loaded region of the bladder is displaced to another region where the bladder can expand to accommodate the displaced fluid
Implementation Method 3
A spring clamp normally biases fluid out of the appendage, but occupant-related force applied over a large area of the seat produces a flow of bladder fluid into the appendage against the bias force of the spring clamp
Implementation Method 4
An electronic controller detects changes in capacitance between the plates when the thickness of the intermediate dielectric material changes due to the forces applied to the seat by an occupant
Implementation Method 5
the dielectric is implemented with a fluid-filled elastomeric bladder
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
A capacitive occupant sensor (10) for a seat (12) has a dielectric in the form of a fluid-filled elastomeric bladder (22), and the sensor (10) includes a primary region (10a) that is subjected to occupant force and a secondary region (10b) that is shielded from occupant force. The secondary region (10b) includes an appendage (36) of the bladder (22) that is disposed beneath a back cushion (18) of the seat (12), either in a cavity (56) of the seat cushion (16) or below a frame element (14) that supports the seat cushion (16). A spring clamp (46) normally biases fluid out of the appendage (36), but occupant-related force applied over a broad area of the seat (16) produces a flow of bladder fluid into the appendage (36) against the bias force of the spring clamp (46). A pair of auxiliary conductor plates (52, 54) is oppositely disposed about the bladder appendage (36), and the capacitance between the auxiliary conductor plates (52, 54) is measured as an indication of fluid pressure in the bladder (22).