Digital Controller for Wideband Oxygen Sensor
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Solution Overview
Problem
Existing wideband oxygen sensor systems with analog control circuits struggle to accurately measure oxygen concentrations in exhaust gases during transitioning states due to temperature-dependent internal resistances, leading to instability and inability to resolve dynamic oxygen changes in internal combustion engines.
Innovation Solution
A digital controller for wideband oxygen sensors that uses a computer to regulate the oxygen sensor's temperature and pressure, employing a pump control circuit, reference voltage circuit, and Nernst read circuit to maintain a steady output voltage and accurately determine oxygen concentrations by comparing digital signals with stored reference information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an AC signal is directed through a resistor to measure internal resistance of the Nernst cell, then reasonably accurate measurements are obtained, but the AC signal creates oscillations within the analog control circuit causing instability
Solution Approach 1:
The patent replaces the analog control circuit with a digital control system. The microcontroller measures the Nernst cell resistance by directing an AC signal through a known resistor and calculating the resistance ratio digitally, eliminating the oscillation problem inherent in analog circuits while maintaining measurement accuracy.
2Stability of the object's composition
If a low-pass filtering circuit is used to remove the AC signal, then the analog feedback loop can operate properly, but the system speed is severely slowed down preventing resolution of transitioning oxygen concentrations
Solution Approach 1:
The patent replaces the analog feedback loop with a digital control system that samples the Nernst cell output voltage and processes it digitally. This eliminates the need for low-pass filtering while maintaining stability, allowing the system to respond rapidly to changing oxygen concentrations during engine transitions.
3Reliability
If the temperature of the oxygen sensor is maintained to keep internal resistances constant, then specified resistance values are achieved, but temperature-dependent variations still affect measurement accuracy during dynamic conditions
Solution Approach 1:
The patent implements a feedback mechanism where the microcontroller continuously measures the Nernst cell resistance and uses this information to compensate for temperature-dependent variations. By monitoring the actual resistance values and adjusting the control algorithm accordingly, the system maintains measurement accuracy despite temperature changes during dynamic engine operation.
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 digital controller enables accurate detection of oxygen concentrations during both steady and transitioning states, improving the system's responsiveness and accuracy without the need for low-pass filtering, thus enhancing the sensor's performance in dynamic engine conditions.
Implementation Method 1
A Nernst cell produces an output voltage that is dependent upon a difference in concentration of free oxygen in a test medium
Implementation Method 2
The pump cell is an electrochemical device which selectively pumps free oxygen within the test medium into and out of the shared volume in direct proportion to an electric current directed to the pump
Data Source
AI summary
An apparatus and method are provided for digitally controlling an oxygen sensor. The apparatus comprises a computer and digital circuitry coupled to the oxygen sensor to convey information between the oxygen sensor and the computer. The oxygen sensor includes a pump cell and at least one Nernst cell configured to indicate the difference in oxygen content in a test medium relative to a reference medium. A pump control circuit operates the pump cell according to signals received from the computer based on output signals from the Nernst cell. A reference voltage circuit enables the computer to determine impedances of the oxygen sensor as a function of sensor temperature and pressure. A Nernst read circuit transmits output signals from the oxygen sensor digitally to the computer. Digital signals received by the computer are compared with stored reference information so as to determine the oxygen content of the test medium.