WRAF Sensor AFR Modeling Using Dynamic Time Constant Adjustment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Wide Range Air Fuel sensors (WRAF) in internal combustion engines face accuracy issues due to aging, which affects the accuracy of air/fuel ratio measurements, leading to deviations in sensor response behavior and erratic fuel correction multipliers, especially under transient conditions.
Innovation Solution
A method is provided to update the time constant and filter coefficients of a transfer function used to model the air/fuel ratio at the sensor location, by comparing the computed modelled air/fuel ratio with actual sensor readings, and applying correction factors based on the gradient ratio and flow rate, using a look-up table to store and amend correction factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If WRAF sensor is used to measure air/fuel ratio, then fuel control accuracy is improved, but sensor aging causes measurement precision to deteriorate over time
Solution Approach 1:
The patent dynamically adjusts the time constant parameter of the transfer function based on exhaust flow rate and sensor aging characteristics. By changing the time constant parameter in response to aging, the model maintains accuracy despite sensor degradation. The system monitors sensor output deviations and adapts the time constant to compensate for aging effects, thereby maintaining measurement precision over the sensor's operational life.
Solution Approach 2:
The system continuously compares the modeled AFR (using transfer function with time constant) against actual sensor readings and uses this feedback to detect sensor aging. When deviations exceed thresholds, the system triggers recalibration or adjustment of the time constant parameter. This closed-loop feedback mechanism enables the system to compensate for sensor degradation and maintain reliable measurements throughout the sensor's service life.
2Ease of manufacture
If transfer function with fixed time constant is used to model AFR at sensor location, then modeling simplicity is maintained, but accuracy deteriorates under varying flow conditions and sensor aging
Solution Approach 1:
The patent transforms the static time constant into a dynamic parameter that varies with exhaust flow rate and sensor aging state. The time constant is no longer fixed but adapts in real-time based on operating conditions and detected sensor degradation. This dynamic approach maintains modeling simplicity (still using transfer function structure) while significantly improving accuracy across varying flow conditions and throughout sensor life.
Solution Approach 2:
The system changes the time constant parameter based on exhaust flow rate ranges and sensor aging detection. Different flow conditions require different time constant values to accurately model the AFR dynamics. By implementing parameter changes rather than using a fixed value, the model maintains simplicity in structure while achieving high accuracy across diverse operating conditions.
3Measurement precision
If sensor signal is adjusted to compensate for pressure variation, then measurement accuracy under varying pressure is improved, but device complexity increases
Solution Approach 1:
The patent introduces a transfer function with time constant as an intermediary model between the sensor reading and the controlled fuel injection. Rather than directly adjusting the sensor signal for pressure compensation, the system uses the dynamic model to predict the relationship between injected fuel and sensor output. This intermediary modeling approach handles pressure variations implicitly through the dynamic response characteristics, avoiding complex direct signal adjustment mechanisms.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
In an engine, a method of providing a model which provides the parameter of the air/fuel (A/F) ratio (AFR3) at a point in the exhaust system of said engine at a point where an air/fuel sensor is located, comprising a) providing a first model which provides the air/fuel ratio which is outlet from the exhaust manifold of said engine (AFR1);b) measuring or estimating the volumetric flow through the exhaust; c) applying a transfer function to said A/F ratio (AFR1) determined by said first model to provide a model of the A/F ratio at the location of said sensor (AFR3), said transfer function including a first order (lag) filter, said transfer function being dependent on said volumetric flow determined from b), said transfer function having a time constant τ, equivalent to a filter coefficient of K where Κ=1/τ; said time constant τ or filter coefficient being determined dependent on flow rate, characterised in amending the value of the determined time constant τ or filter coefficient K, by applying a a correction factor; said correction factor being determined or updated based on the following further steps:d) measuring the A/F ratio (AFR4) at said point by said A/F sensor;e) over a time period, comparing the computed value of the modelled A/F ratio (AFR34) at the sensor location from step c) with the value from the actual A/F sensor(AFR4);f) determining or amending one or more correction factors (cf/CR1) to filter coefficients (K) or time constants (τ) of said applied transfer function based on said comparison.