Exhaust Gas Sensor Voltage Modulation for PCV Flow Detection
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Solution Overview
Problem
Existing exhaust gas sensors face challenges in accurately measuring ambient humidity during engine non-fueling conditions due to the ingestion of positive crankcase ventilation (PCV) hydrocarbons, which can lead to overestimation of humidity and confound sensor outputs, especially in aging engines with increased PCV leakage.
Innovation Solution
The method involves modulating the reference voltage of the exhaust gas sensor with the intake throttle open and closed during deceleration fuel shut off (DFSO) events to differentiate between ambient humidity and PCV flow effects, allowing for a more accurate estimation of ambient humidity and PCV flow, and adjusting engine operating parameters accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the intake throttle is closed during deceleration fuel shut off (DFSO) to reduce airflow and improve fuel economy, then fuel consumption is reduced, but PCV hydrocarbons are drawn into the engine through piston rings and valves, causing the exhaust gas sensor to overestimate ambient humidity
Solution Approach 1:
The system performs periodic modulations of the reference voltage at the exhaust gas sensor during DFSO events, alternating between different reference voltage levels (e.g., 450mV and 1080mV). This periodic action allows the system to separate the PCV hydrocarbon effect from the ambient humidity signal by measuring sensor output at multiple voltage levels and comparing the differences, thereby maintaining measurement precision while allowing throttle closure for fuel economy.
Solution Approach 2:
The system changes the reference voltage parameter of the exhaust gas sensor dynamically during DFSO events. By modulating the reference voltage between different levels, the system creates different measurement conditions that allow it to distinguish between signals caused by ambient humidity and signals caused by PCV hydrocarbon ingestion, thus resolving the measurement accuracy problem while maintaining the fuel economy benefit of closed throttle.
2Measurement precision
If the intake throttle is open during DFSO to reduce PCV hydrocarbon ingestion and improve humidity measurement accuracy, then measurement precision is improved, but fuel economy deteriorates due to increased airflow
Solution Approach 1:
Instead of keeping the throttle continuously open, the system uses periodic voltage modulation at the sensor to achieve accurate measurements only when needed, while allowing the throttle to remain closed for fuel economy during most of the DFSO event. The periodic sensing action extracts accurate humidity data without requiring continuous open-throttle conditions.
Solution Approach 2:
The exhaust gas sensor, already present in the system for oxygen sensing, is made to serve dual purposes by modulating its reference voltage to also measure ambient humidity and detect PCV flow. This self-service approach eliminates the need for separate sensors or continuous throttle opening, achieving accurate measurements while maintaining fuel economy benefits.
3Measurement precision
If the reference voltage of the exhaust gas sensor is modulated to separate PCV flow effects from ambient humidity measurements, then measurement precision is improved, but device complexity increases due to additional control requirements
Solution Approach 1:
The exhaust gas sensor is made multi-functional by enabling it to perform both its traditional oxygen sensing function and new humidity sensing function through reference voltage modulation. The same sensor hardware is used for both purposes, eliminating the need for separate humidity sensors and reducing overall system complexity despite the additional control requirements for voltage modulation.
Solution Approach 2:
The system uses feedback from the sensor output at different reference voltages to calculate both ambient humidity and PCV flow. By comparing sensor readings taken at different voltage levels, the system automatically separates the two effects and provides accurate measurements, with the feedback mechanism handling the complexity of signal separation automatically.
4Reliability
If PCV flow is increased to identify engine degradation, then diagnostic capability is improved, but the interference with humidity measurement increases
Solution Approach 1:
The system performs periodic voltage modulation during DFSO events to create distinct measurement signatures. By measuring sensor output at multiple reference voltage levels and comparing the differences, the system can identify PCV flow patterns that indicate engine degradation while simultaneously extracting accurate ambient humidity data, as the periodic action separates the two measurement objectives in time and signal space.
Solution Approach 2:
The system changes the reference voltage parameter dynamically to create different measurement conditions. By comparing sensor responses at different voltage levels, the system can identify PCV flow effects (which will show consistent patterns across voltage changes) and separate them from ambient humidity effects, enabling both degradation detection and accurate humidity measurement even when PCV flow is present.
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 reduces the impact of PCV hydrocarbons on humidity measurements, enabling a more reliable estimation of ambient humidity and identifying engine component degradation, thereby improving the accuracy of engine control and performance.
Implementation Method 1
an exhaust gas sensor may be utilized to determine ambient humidity during the engine non-fueling conditions
Implementation Method 2
The PCV flow drawn in may be aggravated in an aging engine due to leakage of PCV gases past the piston rings and valves. The ingested hydrocarbons affect the output of the exhaust gas sensor
Data Source
AI summary
Methods and systems are provided for estimating a PCV flow to an engine based on the output of an exhaust gas oxygen sensor. During DFSO conditions, a reference voltage of the sensor is modulated initially with an intake throttle open and then with the intake throttle closed. PCV flow leaking past the piston valves in an aging engine, as well as an ambient humidity estimate, are inferred based on the outputs of the sensor during the modulating with the intake throttle open and closed.