Combustion Pressure Sensor Ground Segmentation for Overheating
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Solution Overview
Problem
Combustion pressure sensors with built-in charge amplifiers face issues with overheating of signal lines and deterioration of detection accuracy due to potential differences between the in-vehicle computer's ground and the chassis ground, leading to undetected wire disconnections and noise interference.
Innovation Solution
Incorporating a ground separating capacitor between the ECU ground and the chassis ground, along with a reference voltage generating unit using a constant current circuit and resistor series connected to the power supply line, allows the voltage converting unit to accurately convert sensor outputs based on varying chassis ground potentials, while separating the ECU and chassis grounds to detect disconnections and suppress noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the charge amplifier is built in the housing of the combustion pressure sensor, then the cost is reduced by omitting the heat-resisting coaxial line, but the reliability deteriorates due to undetected wire disconnections and potential differences between grounds
Solution Approach 1:
The patent segments the ground system into two separate grounds: chassis ground (connected to the housing) and ECU ground (connected to the in-vehicle computer). This segmentation allows independent grounding paths, enabling disconnection detection while maintaining the built-in charge amplifier configuration that reduces cost.
Solution Approach 2:
The patent introduces a ground line as an intermediary element between the chassis ground and ECU ground. This ground line serves as a detectable connection path, allowing the system to monitor wire disconnections while maintaining the cost-effective built-in charge amplifier design.
2Device complexity
If the charge amplifier is built in the housing of the combustion pressure sensor, then the complexity is reduced by omitting the heat-resisting coaxial line, but harmful factors increase due to potential differences causing ground line overheating
Solution Approach 1:
The patent segments the grounding system into separate chassis ground and ECU ground paths, preventing potential difference-induced current flow through the signal ground line. This segmentation eliminates the overheating hazard while maintaining the simplified wiring structure of the built-in charge amplifier design.
Solution Approach 2:
The patent introduces a dedicated ground line as an intermediary that provides a controlled path for ground connections. This separate ground line isolates the signal path from potential difference effects, preventing overheating while maintaining wiring simplicity.
3Reliability
If a capacitor is arranged between the ECU ground and the chassis ground to prevent overheating, then the reliability improves by preventing ground line overheating, but the measurement precision deteriorates due to insufficient low frequency component reflection
Solution Approach 1:
The patent uses a ground line as an intermediary element that provides a direct conductive path between chassis ground and ECU ground. This approach prevents overheating through proper grounding while maintaining measurement precision by avoiding the frequency-filtering effects that capacitors would introduce.
4Measurement precision
If the capacity of the capacitor is enlarged to allow low frequency components to pass through, then the measurement precision improves by reflecting low frequency components, but harmful factors increase due to noise components being superimposed on the ECU ground
Solution Approach 1:
The patent employs a ground line as an intermediary that provides a stable, low-impedance ground reference without introducing noise. This approach maintains measurement precision for low frequency components while avoiding the noise superposition problem that would result from using large-capacity capacitors.
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 configuration effectively restricts overheating and noise interference, maintaining detection accuracy and enabling reliable detection of ground line disconnections by using the reference voltage generated based on the chassis ground, as shown in simulation results.
Implementation Method 1
a piezoelectric element 21 that detects a pressure inside of a combustion chamber of an engine
Implementation Method 2
a voltage generating circuit having a constant current circuit 311 and a resistor 312 connected in series with each other
Data Source
AI summary
In a combustion pressure sensor having built-in charge amplifier, signal line overheating and deterioration of detection accuracy is restricted. The combustion pressure sensor includes a sensor body that includes a piezoelectric element having one end connected to chassis ground through a housing and detects pressure in a combustion chamber of engine, and a charge amplifier that includes at least a voltage converting unit converting output of the sensor body into voltage signal and a reference voltage generating unit generating reference voltage supplied to the voltage converting unit and operates on power supplied from a signal processing unit disposed outside. The reference voltage generating unit includes a voltage generating circuit having a constant current circuit and a resistor connected in series. The voltage generating circuit has one end connected to power line extending from the signal processing unit, and the other end connected to the end of the piezoelectric element.