Vehicle Access Capacitive Sensor Circuit for Low-Emission Detection
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Solution Overview
Problem
Existing capacitive proximity sensors in vehicles face challenges in reducing radiated emissions while maintaining sensitivity, particularly for access points requiring significant detection electrodes like luggage compartments, leading to unreliable user detection due to electromagnetic disturbances.
Innovation Solution
A presence detection device with a first supply voltage, a detection capacitor, an intermediate capacitor, and a storage capacitor, where the detection capacitor is charged from the first supply voltage and the storage voltage, allowing the storage voltage to be reinjected to equalize the detection capacitor's voltage, reducing radiated emissions while maintaining sensitivity through an operational amplifier and intermediate resistor configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the supply voltage is reduced to lower radiated emissions, then electromagnetic disturbances are reduced, but the sensitivity of the detection capacitor decreases
Solution Approach 1:
The patent introduces an intermediate capacitor as a mediator between the detection capacitor and the storage capacitor. This intermediate capacitor receives charge from the detection capacitor and then transfers it to the storage capacitor, allowing the system to operate at lower voltages while maintaining detection sensitivity through the charge transfer mechanism.
Solution Approach 2:
The patent changes the voltage parameter by reducing the supply voltage from typical levels (e.g., 5V) to lower levels (e.g., 3.3V or 1.8V), which directly reduces radiated emissions. The sensitivity is maintained not by the voltage level itself but by the charge transfer mechanism through the intermediate capacitor, demonstrating a parameter change that resolves the contradiction.
2Difficulty of detecting and measuring
If a significant length detection electrode is used to detect presence for access points like luggage compartments, then detection range is improved, but radiated emissions increase causing electromagnetic disturbances
Solution Approach 1:
The patent changes the voltage parameter to lower levels, which reduces radiated emissions from the detection electrode while maintaining the electrode's physical dimensions and detection range. The lower voltage operation reduces the electromagnetic field strength without compromising the capacitive sensing capability.
Solution Approach 2:
The intermediate capacitor acts as a charge transfer mediator that allows the system to maintain sensitivity despite lower operating voltages. This enables the use of longer detection electrodes for extended range while keeping radiated emissions low through the intermediate charge transfer stage.
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 significantly reduces radiated emissions by lowering the supply voltage while maintaining sensitivity equal to or greater than prior art, enabling reliable user detection without causing electromagnetic disturbances in vehicle systems.
Implementation Method 1
a detection capacitor Cx adapted to be charged on account of the presence of a user
Data Source
AI summary
A device for detecting the presence of a user for the unlocking of an access point to a motor vehicle, includes a first generator of a first supply voltage, a detection capacitor adapted to be charged on account of the presence of a user, and a storage capacitor defining at the terminals thereof a storage voltage. The device also includes an intermediate capacitor, elements for charging the detection capacitor from the first supply voltage and the storage voltage, elements for discharging the detection capacitor into the intermediate capacitor, elements for charging the storage capacitor, the elements being configured so that the charge of the storage capacitor is equal to the charge of the intermediate capacitor, and elements for detecting the presence of a user for the unlocking of an access point to the motor vehicle on the basis of the charge of the storage capacitor.