Mass air flow metering device and method

Abstract

An airflow metering device, including a conventional airflow sensing device signally connected to a signal processor is shown, having an input flow signal correlatable to a magnitude of mass air flowing past the airflow sensing device. The signal processor is operable to determine a flow correction factor based upon a direction and magnitude of the mass air flowing past the airflow sensing device. The output of the airflow metering device is an accurate measure of airflow, and comprises the input flow signal of the airflow sensing device adjusted by the flow correction factor determined by the signal processor.

Description

TECHNICAL FIELD [0001] This invention pertains generally to internal combustion engine control systems, and more specifically to a method and apparatus to accurately meter flow of air into the internal combustion engine. BACKGROUND OF THE INVENTION [0002] A typical air meter for measuring air intake into an internal combustion engine operates on the principle of hot-film anemometry. A heated element is placed within the airflow stream, and maintained at a constant temperature differential above the air temperature. The amount of electrical power required to maintain the heated element at the proper temperature is a direct function of the mass flow rate of the air past the element. [0003] The measurement function of the typical mass air flow meter is performed using a bridge circuit, often referred to as a Wheatstone bridge, and shown as element 10 in FIG. 2. In this circuit, temperature-sensitive resistors are used as the ambient temperature sensor A1 and as the heated sensing eleme...

AI Technical Summary

Benefits of technology

The present invention provides an improvement over conventional air flow metering solutions by using a currently available air flow sensing element and circuitry to process and filter a raw signal output from the airflow meter, extract information regarding the magnitude and direction of airflow, provide compensation for the signal output, and deliver an accurate measure of airflow. The invention includes a digital filter that requires minimal execution time and capable of handling pulse frequencies observed during pulsing flow conditions, filtering out high frequency noise, while still able to detect onset of reverse flow. The airflow metering device includes an airflow sensing device signally connected to a signal processor, which is operable to determine a flow correction factor based upon the direction and magnitude of the mass air flowing past the airflow sensing device. The output of the airflow metering device comprises the input flow signal of the airflow sensing device adjusted by the flow correction factor determined by the signal processor. The invention also includes an algorithm operable to determine the flow mode based upon the characterized input flow signal and select the flow correction factor accordingly. The algorithm can detect the onset of reverse flow mode by detecting initial low levels of reverse airflow based upon a second derivative of the input flow signal. The invention provides a more accurate measure of airflow for use in internal combustion engines.

Problems solved by technology

The inability to determine direction of airflow may result in introduction of significant errors in measure of mass air flow into the engine during conditions wherein reverse flow conditions occur.

However the sensor output signal is extremely small (i.e. range of millivolts) and the corresponding signal-to-noise ratio is not large enough to allow reliable measurement.

Furthermore, it is difficult to manufacture and process the sensor, including placement of the sensors in the middle of the membrane.

Incorrect placement of sensors may result in a drift of the output signal over time.

Most importantly, such a membrane has proven to be fragile, thus reducing reliability of the device, causing customer dissatisfaction and high warranty costs.

This solution reduces error, but there still exists significant flow error.

A sophisticated filtering system, comprising elements including second-order digital filters and other elements consume substantial amounts of execution time, microprocessor time and computer memory, and is not feasible for implementation in a low-cost microcontroller used primarily in an airflow sensing device.

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