Ammonia Sensor PWM Heater Ground Potential Offset Correction

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Solution Overview

Problem

The existing ammonia sensors in urea SCR systems face accuracy issues due to instantaneous changes in ground potential when a heater controlled by pulse width modulation is switched on or off, affecting the electromotive force and thereby the detection accuracy of gas concentration.

Innovation Solution

A gas detection apparatus with a solid electrolyte body, electrodes, and a heater, where the power supply to the heater is controlled by pulse width modulation, includes a change amount calculation section to determine the electromotive force changes and a correction section to adjust the electromotive force, improving detection accuracy by accounting for changes in output voltage and oxygen concentration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a heater controlled by pulse width modulation is used to heat the solid electrolyte body, then the temperature control is improved, but the ground potential changes instantaneously causing electromotive force fluctuations that worsen detection accuracy

Engineering Contradiction:

Improvetemperature controlVSAvoiddetection accuracy

Core Design Contradiction:

TemperatureVSMeasurement precision

Solution Approach 1:

The ground potential change amount is calculated in advance based on the heater drive signal before the electromotive force measurement is performed. This preliminary calculation allows the system to compensate for the ground potential fluctuation by subtracting it from the measured electromotive force, thereby eliminating the detection accuracy degradation caused by PWM-controlled heater switching.

Inventive Principle:

Principle #10Preliminary action

2Use of energy by moving object

If the heater is switched between ON and OFF states for temperature control, then energy efficiency is improved, but the instantaneous ground level changes cause time constant delay in electromotive force response

Engineering Contradiction:

Improveenergy efficiencyVSAvoidresponse delay

Core Design Contradiction:

Use of energy by moving objectVSLoss of time

Solution Approach 1:

A ground potential change amount calculation section is introduced as an intermediary component that processes the heater drive signal and computes the corresponding ground potential fluctuation. This intermediary calculation enables the system to predict and compensate for the ground potential change, thereby eliminating the time constant delay in electromotive force response while maintaining the energy-efficient PWM switching operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If pulse width modulation is used for heater control, then temperature regulation precision is improved, but the ground potential instability increases causing electromotive force variations

Engineering Contradiction:

Improvetemperature regulation precisionVSAvoidground potential instability

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The system uses the heater drive signal as feedback to calculate the ground potential change amount. By continuously monitoring the heater control state and computing the corresponding ground potential fluctuation, the system can dynamically compensate for ground potential instability in real-time, thereby maintaining temperature regulation precision while eliminating the harmful effects of ground potential variations on electromotive force measurement.

Inventive Principle:

Principle #23Feedback

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 reduces the influence of electromotive force changes caused by power supply and impedance variations, enhancing the accuracy of gas concentration detection and reducing computational load by simple subtraction of calculated changes from the electromotive force.

Implementation Method 1

a heater for heating the solid electrolyte body, in which electric power supplied from a power supply to the heater is controlled by pulse width modulation so as to control the temperature of the solid electrolyte body

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

The gas detection apparatus detects the concentration of the target gas through use of an electromotive force generated between the pair of electrodes in accordance with the concentration of the target gas

Methodology Applied

Scientific EffectElectromotive force generation:

Data Source

PatentUS10473617B2Gas detection apparatus

Publication Date: 2019.11.12 NITERRA CO LTD

AI summary

A multi-gas detection apparatus is configured such that electric power supplied from a power supply to a heater is controlled by pulse width modulation so as to control the temperature of a first solid electrolyte body. The multi-gas detection apparatus detects the concentration of ammonia by using a first ammonia detection section in which an electromotive force is generated between a first reference electrode and a first detection electrode in accordance with the concentration of ammonia in the exhaust gas. The multi-gas detection apparatus calculates the amount of a change (i.e., offset voltage) in the ammonia electromotive force caused by change in the output voltage of the power supply. The multi-gas detection apparatus corrects the ammonia electromotive force generated in the first ammonia detection section through use of the calculated change amount.