Film Thickness Measurement Device Electrostatic Capacitance
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Solution Overview
Problem
Existing film thickness measurement devices face challenges in accurately measuring oil film thickness in engine cylinders due to temperature-dependent electrostatic capacitance changes and the complexity and cost of resonant bridge circuit methods, which hinder real-time and precise measurements.
Innovation Solution
A film thickness measurement device that uses an electrostatic capacitance detection portion to charge the electrode with a constant current, detect changes in charging voltage, and calculate film thickness based on electrostatic capacitance differences, without requiring reference capacitors, and incorporates a press-fitted electrode with insulating and conductive layers, synchronized with crank rotation angle detection for accurate and cost-effective measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bridge circuit is used to measure electrostatic capacitance, then measurement capability is achieved, but temperature dependence causes measurement errors
Solution Approach 1:
The patent extracts and removes the temperature-dependent reference capacitors from the measurement system. Instead of using a bridge circuit with reference capacitors that are affected by temperature, the invention uses a constant current source to charge the measurement capacitor and measures the charging time or voltage, eliminating the reference capacitors that cause temperature-dependent measurement errors.
Solution Approach 2:
The patent replaces expensive and temperature-sensitive reference capacitors with a simple constant current source and timing circuit. The constant current source is a more robust and temperature-stable component that provides reliable measurements without the temperature dependence issues of reference capacitors.
2Measurement precision
If a resonant bridge circuit method is used, then temperature measurement errors are reduced, but high-speed real-time measurement becomes difficult
Solution Approach 1:
The patent employs periodic charging cycles of the measurement capacitor using a constant current source. By repeatedly charging and measuring the capacitor in periodic intervals, the system achieves real-time measurement capability while maintaining temperature stability. The periodic action allows for continuous monitoring without the complexity of resonant frequency sweeping.
Solution Approach 2:
The patent replaces the complex resonant bridge circuit mechanism with a simpler constant current charging mechanism. Instead of varying power supply frequency to find resonance, the system uses a fixed constant current source and measures charging characteristics, eliminating the need for frequency variation and enabling faster real-time measurements.
3Measurement precision
If a resonant bridge circuit method is used, then temperature effects are mitigated, but device complexity and cost increase
Solution Approach 1:
The patent extracts and removes the complex resonant bridge circuit components including multiple resistors, capacitors, and frequency variation mechanisms. The simplified constant current charging circuit retains only the essential measurement functionality while eliminating the sources of complexity and cost.
Solution Approach 2:
The patent replaces expensive resonant bridge circuit components with inexpensive constant current source components and simple timing circuits. The constant current source can be implemented with basic electronic components, significantly reducing device cost and complexity while maintaining measurement accuracy and temperature compensation.
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 solution enables accurate, real-time measurement of oil film thickness with reduced temperature effects and lower costs, eliminating the need for complex bridge circuit configurations, thus improving measurement precision and reducing operational expenses.
Implementation Method 1
measuring the electrostatic capacitance across the gap between the piston ring and the electrode
Implementation Method 2
charges the electrostatic capacitance by supplying a constant current to the electrode, detects the electrostatic capacitance based on changes in the charging voltage
Data Source
AI summary
A film thickness measurement device, which measures the film thickness of an oil film of lubricating oil, formed in a gap between a piston ring and an electrode provided flush with a piston ring sliding surface of a cylinder liner, by detecting the electrostatic capacitance across the gap, employs an electrostatic capacitance detection portion, which charges the electrostatic capacitance by supplying a constant current to the electrode, detects the electrostatic capacitance based on changes in the charging voltage accompanying the charging, and outputs a detection signal indicating the electrostatic capacitance, and a film thickness computation portion, which calculates the film thickness of the oil film based on the electrostatic capacitance indicated by the detection signal input from the electrostatic capacitance detection portion.