Thermal Air Flowmeter Pulsating Response Correction
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Solution Overview
Problem
Conventional thermal air flowmeters experience errors during pulsating air flow due to response delays and differences between rising and falling flow responses, which are not accurately captured, leading to inaccuracies in detecting the actual air flow into an engine.
Innovation Solution
A thermal air flowmeter that calculates a flow correction value based on the temporal variation of the detected flow and uses a flow correction coefficient to correct the detected flow, employing a response compensations filter that adjusts the detected flow signal to achieve accurate and reliable air flow measurement without distorting the waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal air flowmeter uses a detection element with larger size and better thermal insulation to reduce response delay, then the response delay is reduced, but the device complexity and size increase
Solution Approach 1:
The patent changes the thermal parameters of the detection element by using a bridge circuit configuration with temperature-sensitive resistors arranged upstream and downstream of a heating resistor. This allows the system to detect temperature differences caused by air flow while maintaining a compact size, resolving the contradiction between response delay and device size.
Solution Approach 2:
The patent introduces a bridge circuit as an intermediary mechanism that translates the thermal effects into measurable voltage signals. The bridge circuit with resistors R1, R2, R3, and R4 acts as a mediator that amplifies and processes the small temperature differences, enabling accurate flow detection without requiring a large detection element.
2Measurement precision
If a thermal air flowmeter applies separate corrections to rising and falling characteristics, then the response difference between rising and falling is reduced, but the device complexity increases
Solution Approach 1:
The patent applies dynamic correction by detecting the direction of flow change (rising or falling) and selectively applying different correction values. The correction mechanism dynamically adjusts based on the current state of the detection element, using correction values stored in a correction value storing means. This allows precise compensation for response differences without requiring complex mechanical adjustments.
3Device complexity
If a thermal air flowmeter uses conventional detection methods during pulsating air flow, then the detection structure remains simple, but the detected average flow value deviates from the actual air flow due to response delay and air flow dependence
Solution Approach 1:
The patent implements feedback correction by continuously monitoring the detection element's response and comparing it with reference values stored in a correction value storing means. Based on this feedback, the system selectively applies appropriate correction values to compensate for response delay and air flow dependence, ensuring that the detected average flow value accurately reflects the actual air flow during pulsating conditions.
Solution Approach 2:
The patent performs preliminary correction by pre-storing correction values in a correction value storing means that account for expected response delays and air flow dependencies. These correction values are prepared in advance and selectively applied during detection, allowing the system to compensate for known errors before they affect the final measurement, thus maintaining simple detection structure while improving measurement precision.
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 solution enables accurate detection of air flow during large pulsating conditions, improving response reliability and reducing detection errors, ensuring the average detected flow value closely matches the actual air flow, even in non-steady states.
Implementation Method 1
a heat-generating resistor which heats fluid; a heating drive circuit which causes current to flow in the heat-generating resistor and thereby controls heating of the heat-generating resistor
Implementation Method 2
a temperature-sensitive resistor which detects a temperature of the fluid heated by the heat-generating resistor
Implementation Method 3
a basic structure which detects a flow of fluid based on the amount of heat of the fluid heated by the heat-generating resistor; Factor (3) has not been addressed. In this way, in thermal air flowmeters, due to a response difference between rising and falling of flow or to air flow dependence of the response
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An object of the invention is to provide a thermal air flowmeter which can reduce a detection error occurring during pulsating air flow due to a difference of response between rising and falling of detected flow or due to air flow dependence of response. A thermal air flowmeter (1) includes a heat-generating resistor (7) which heats fluid, a heating drive circuit (5) which causes current to flow in the heat-generating resistor (7) and thereby controls heating of the heat-generating resistor (7), and a temperature-sensitive resistor (9) which detects a temperature of the fluid heated by the heat-generating resistor (7). The thermal air flowmeter (1) detects a flow Q of the fluid based on the amount of heat of the fluid heated by the heat-generating resistor (7). Further included are: flow correction value calculating means (17) which calculates a flow correction value ca based on a variation dQ/dt of the detected flow Q and on a flow correction coefficient a set dependent on the detected flow Q; and flow correction means (18) which corrects the detected flow Q based on the flow correction value ca.