Electrostatic Soot Sensor Guard Potential Switching
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Solution Overview
Problem
Existing electrostatic soot sensors face challenges in accurately measuring soot concentrations in exhaust gases due to issues with condensation of water, leading to unreliable measurements, especially when the sensor is cold, and require multiple current measuring elements, increasing production costs.
Innovation Solution
The electrostatic soot sensor employs a voltage supply that switches the guard potential from a first guard potential during the warm-up phase to a second guard potential during the measurement phase, allowing for the measurement of leakage and soot-induced currents with a single current measuring element, ensuring accurate measurements and reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cold soot sensor is used after starting a cold combustion engine, then the sensor cannot perform soot measurement, but water condensation deposits on the sensor causing instability and preventing reliable measurement
Solution Approach 1:
The patent applies a preliminary drying phase before measurement by maintaining a first guard potential that directs leakage current away from the measurement path. This preliminary action removes condensed water from the insulating body surface through controlled current flow, ensuring the sensor is ready for accurate measurement before soot detection begins.
Solution Approach 2:
The patent dynamically switches the guard electrode potential between two states: a first guard potential during the warm-up/drying phase to handle leakage currents, and a second guard potential during the measurement phase for accurate soot detection. This dynamic adaptation allows the sensor to operate reliably across different temperature conditions.
2Measurement precision
If multiple current measuring elements are used to measure leakage current and soot-induced current separately, then measurement accuracy improves, but production costs increase
Solution Approach 1:
The patent segments the measurement process into two distinct phases: a drying phase where leakage current is measured and handled separately, and a measurement phase where soot-induced current is measured. This temporal segmentation allows a single current measuring element to accurately perform both functions by switching its measurement context based on the operational phase.
Solution Approach 2:
The guard electrode acts as an intermediary that directs leakage current away from the measurement path during the drying phase. By using the guard electrode as a mediator, the system can measure and handle leakage currents without requiring a separate measuring element for soot detection, thus reducing component count while maintaining measurement accuracy.
3Device complexity
If the guard electrode is held at a constant potential, then the circuit is simple, but leakage currents during warm-up interfere with soot measurement
Solution Approach 1:
The patent makes the guard electrode potential dynamic by switching between a first guard potential during warm-up and a second guard potential during measurement. This dynamic adjustment allows the system to handle leakage currents during warm-up while ensuring accurate soot measurement during operation, resolving the conflict between circuit simplicity and measurement precision.
Solution Approach 2:
The patent changes the electrical parameter (guard potential) of the guard electrode based on operational phase. By adjusting the guard potential from a first value during warm-up to a second value during measurement, the system adapts to different operational conditions, preventing leakage current interference while maintaining measurement accuracy.
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 enables precise determination of the sensor's measuring readiness and reduces production costs by allowing accurate measurement of soot concentrations without interference from leakage currents, improving the reliability and cost-effectiveness of the sensor.
Implementation Method 1
an electric field is generated between a sheath electrode through which the gas flow passes and an inner electrode within this sheath electrode by applying a constant DC voltage
Implementation Method 2
the charging current for maintaining the constant DC voltage between the sheath electrode and the inner electrode is measured
Implementation Method 3
a guard electrode (16) arranged in the soot sensor (1) and which can be assigned a guard potential by the voltage supply (6)
Implementation Method 4
The first electrode (2) is electrically insulated from the second electrode (3) by means of the insulating body (5)
Implementation Method 5
condensation from the exhaust stream deposits on and inside the sensor, initially rendering it unstable for high-voltage operation
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to an electrostatic soot sensor having a voltage supply, wherein the electrostatic soot sensor has a first electrode, a second electrode, and a guard electrode, wherein the first electrode and the second electrode are electrically insulated from each other by an insulating body and the guard electrode is arranged between the first electrode and the second electrode, wherein the guard electrode is also electrically insulated from the first electrode and the second electrode by the insulating body, wherein a first electric potential is applied to the first electrode by means of the voltage supply and wherein a second electric potential is applied to the second electrode by means of the voltage supply such that a voltage arises between the first electrode and the second electrode. In order to specify an electrostatic soot sensor by means of which the measurement readiness of the electrostatic soot sensor can be determined reliably and accurately, a guard potential is applied to the guard electrode by means of the voltage supply (6), which guard potential corresponds to a first guard potential in the warm-up phase of the soot sensor and corresponds to a second guard potential in the measurement phase of the soot sensor.