Cylinder Pressure Sensor Offset Compensation via Level Shifting
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Solution Overview
Problem
Existing cylinder inner pressure sensors in internal combustion engines face detection accuracy issues due to offset voltage drift caused by temperature and pressure changes, leading to a narrow dynamic range for A/D converter circuits and reduced gain settings.
Innovation Solution
A cylinder inner pressure detector system that includes a reference voltage output circuit, a level shift circuit, and a controller to adjust the sensor signal levels, ensuring the offset voltage is compensated, allowing for a wider dynamic range and higher gain settings in A/D converters, thereby improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gain of the cylinder inner pressure sensor and/or input circuit is set low to accommodate offset voltage changes, then the sensor signal remains within the A/D converter input range, but the dynamic range of the A/D converter circuit becomes narrow
Solution Approach 1:
The patent applies preliminary action by measuring the offset voltage during a suction stroke before the actual pressure measurement, and using this measured offset to adjust the A/D converter's reference voltage or input range settings. This allows the system to prepare the appropriate gain and range settings in advance, ensuring the signal fits within the input range while maximizing the dynamic range for actual pressure detection.
Solution Approach 2:
The patent changes the parameter of the A/D converter circuit by dynamically adjusting the reference voltage level or gain based on the measured offset voltage. Instead of using a fixed low gain setting, the system modifies the A/D converter parameters adaptively, allowing higher gain settings when the offset is compensated, thereby expanding the dynamic range while maintaining signal integrity.
2Reliability
If the gain of the cylinder inner pressure sensor and/or input circuit is set low to accommodate offset voltage changes, then the sensor signal remains within the A/D converter input range, but the detection accuracy of the cylinder inner pressure is reduced
Solution Approach 1:
The system performs preliminary measurement of the offset voltage during the suction stroke and uses this information to configure the A/D converter settings before actual pressure measurement. This preliminary configuration enables the use of higher gain settings that improve detection accuracy while ensuring the signal remains within the acceptable input range through offset compensation.
Solution Approach 2:
The patent implements feedback by continuously monitoring the offset voltage and using this feedback to adjust the A/D converter's reference voltage or gain settings. This closed-loop approach ensures that the system maintains optimal detection accuracy by adapting to offset changes while keeping the signal within the input range, thereby resolving the contradiction between reliability and measurement precision.
3Reliability
If offset drift compensation is performed using data processing methods, then the offset drift is not reduced, but the gain must be set low to keep the sensor signal within the input range
Solution Approach 1:
The patent measures the offset voltage during the suction stroke in advance and uses this measured value to adjust the A/D converter settings before actual pressure measurement. This preliminary adjustment allows the system to use higher gain settings that expand the dynamic range, while the offset compensation ensures the signal remains within the input range, thereby resolving the contradiction between reliability and adaptability.
Solution Approach 2:
The system dynamically changes the A/D converter parameters (reference voltage or gain) based on the measured offset voltage. Instead of using a fixed low gain setting, the patent adjusts the converter parameters adaptively, allowing the system to maximize the dynamic range while ensuring the compensated signal fits within the input range.
4Reliability
If the sensor and/or amplifier are reset to cancel offset drift, then the offset voltage is reduced just after reset, but the offset drift occurs before reset and requires low gain settings
Solution Approach 1:
The patent performs preliminary measurement of the offset voltage during the suction stroke and uses this measured offset to configure the A/D converter settings before actual pressure measurement. This approach eliminates the need for resetting the sensor or amplifier, as the offset is measured and compensated electronically. The system can then use higher gain settings that improve detection accuracy while maintaining signal integrity through software-based offset compensation.
Solution Approach 2:
The system implements feedback by continuously monitoring the offset voltage and using this feedback to adjust the A/D converter settings. This eliminates the need for periodic resets and allows the system to maintain optimal detection accuracy throughout operation, resolving the contradiction between reliability (offset reduction) and measurement precision (detection 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
The system secures a wider effective dynamic range for A/D converters, enabling higher gain settings and improved resolution for accurate inner pressure detection, even under conditions of offset drift.
Implementation Method 1
The pressure in the combustion chamber is applied to a Piezo electric device via a diaphragm of the sensor. An output voltage of the Piezo electric device is output through an amplifier circuit in the sensor.
Data Source
AI summary
An cylinder inner pressure detector of an internal combustion engine includes: a reference voltage output circuit for outputting a reference voltage having a level, which is selected among multiple levels according to a switching signal; a level shift circuit for shifting a level of a sensor signal of an inner pressure sensor by a selected level of the reference voltage toward a signal potential side corresponding to a low pressure side of cylinder inner pressure; a first A/D converter circuit for converting the shifted sensor signal from an analog signal to a digital signal; and a controller for outputting the switching signal, which provides the reference voltage such that the reference voltage has the level on the signal potential side corresponding to the low pressure side from an offset voltage, and for detecting the cylinder inner pressure based on the digital signal output from the first A/D converter.