Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
1997-10-17
2001-07-31
McCall, Eric S. (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
C073S861630
Reexamination Certificate
active
06267006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The instant invention relates to an air induction assembly disposed in an intake passage through which air flows to an internal combustion engine. More specifically, the instant invention relates to the use of a plurality of flow conditioning elements to produce a uniform airflow with low turbulent fluctuations to the mass air flow sensor under all vehicle and engine speeds.
2. Description of the Related Art
It is known to those skilled in the art to use a mass air flow sensor, including those of the hot wire or hot film anemometry type, to measure the air flow rate entering an engine. The mass air flow sensor (MAFS) outputs an analog voltage signal that corresponds to the mass of air flowing through the air induction system. The output from the MAFS is used to maintain the desired air-fuel ratio so that performance, fuel economy and emission targets are met.
To provide an accurate indication of airflow, the MAFS must receive airflow of uniform velocity having a low magnitude of turbulent fluctuations over all engine and vehicle speeds. Airflow will exhibit some measure of turbulence and that turbulence can be described as the average fluctuation of the fluid from its average velocity.
When airflow having a high magnitude of turbulent fluctuations is presented to the MAFS, noise is created in the MAFS output signal as a direct indication of the airflow turbulence variation entering the MAFS. Much of this turbulence variation is caused from the ever present pulsation from the engine valve train and pistons. The pulsation creates signal noise which is particularly influential at low engine rpm.
Further, as with any fluid flow through a conduit, there is a considerable difference in the velocity between the airflow near the inner surface of the air induction duct and the airflow near the center of the air induction duct. This variation in velocity may be described as a parabola-like profile defining the relative velocity of the airflow within the air induction duct. The apex points downstream and the amplitude depends on the input velocity of the airflow. These airflow variations combine to increase fluctuations in the area adjacent to the MAFS, preventing consistent accurate measurements.
It is known to reduce the magnitude of the airflow turbulence variation by providing the air induction system with an air flow uniforming device upstream of the mass air sensor. Mollet, U.S. Pat. No. 4,397,192, teaches a mesh structure disposed within the air induction conduit perpendicular to the direction of the fluid flow and upstream from a sensor to provide a reduction in the oscillating air flow turbulence and provide a uniform flow of air across the sensor. However, as the mesh structure is disposed over the entire air induction conduit there is a corresponding restriction in the airflow which may pass through the mesh structure and to the engine. This decrease in airflow translates into a decrease in engine horsepower. Further, in addition to increased cost, the mesh structure may collect debris, corrode, or freeze, all of which again further restrict airflow and therefor engine horsepower.
It is further known to dispose within an air intake duct a swirl generating means with an air flow sensor mounted thereon. Takashima, U.S. Pat. No. 5,476,012, teaches a cone axially supported in the center of an air intake duct by guide vanes attached to the inner surface of the duct. Fixed to the downstream portion of the cone is the air flow sensor. The guide vanes are operative to swirl the air in cooperation with the cone.
The assembly taught by Takashima has the disadvantages of being difficult to fabricate and restricting the airflow provided to the engine. Further, as the airflow is swirling, the axial velocity of the airflow is reduced. The restricted and reduced velocity airflow therefor cause a corresponding decrease in engine horsepower. The instant invention provides uniform airflow with minimum restriction to the MAFS over all engine and vehicle speeds and does not generate a swirl therein. Further, the instant invention provides a structure which only partially extends into the airflow duct. This allows the manufacture of a simple and cost effective one piece design without the need for costly tooling.
Other variations of an airflow sensor supported in the air duct are taught by Woddbury, U.S. Pat. No. 5,481,925, and Kurrle, U.S. Pat. No. 4,602,515. Both of these references add the complexity of using the airflow sensor support members as airflow collecting pipes. The airflow sensor is not directly in the airflow path but is provided with airflow samples from the independent collecting pipes. The airflow is sampled over the cross section of the duct, and then travels radially inwardly to the centrally mounted airflow sensor pod. The airflow is therefor not conditioned prior to being provided to the air flow sensor located within the airflow path, but simply collected and fed to the air flow sensor.
It is desirable to create an airflow that has a uniform velocity and a low magnitude of turbulent fluctuations. It is further desirable to produce an air induction assembly that does not restrict the central portion of the air intake duct preventing a decrease in engine horsepower.
SUMMARY OF THE INVENTION
Responsive to the disadvantages of the prior art, the instant invention provides an air induction assembly with flow conditioning elements which reduce the magnitude of airflow turbulence variation entering the MAFS while providing a negligible restriction of airflow to the engine.
The air induction assembly provides a conduit member which has an upstream portion, a downstream portion and a intermediate portion therebetween. The conduit defines an air flow path between the upstream conduit portion to the downstream conduit portion. The conduit member may be further shaped as a venturi to provide for the air flow path. A MAFS is located in the intermediate conduit portion and is placed in fluid communication with the air flow path. The MAFS being operative to generate an output signal corresponding to the volumetric air flow rate within the intermediate conduit portion. A plurality of flow conditioning elements in the air flow path upstream of the mass air flow sensor direct airflow of uniform velocity and low magnitude of turbulent fluctuations to the mass air flow sensor. The uniform airflow is provided under all vehicle and engine speeds without excessively restricting the air flowing to the engine.
Each flow conditioning element partially extends inwardly from the conduit members inner surface towards the conduit member axial centerline. The plurality of flow conditioning elements may be circumferentially arrayed on a plate attached to the conduit member or integrally formed on the conduit members inner surface. The flow conditioning elements need only be in fluid communication with the air flow path and positioned upstream of the mass air flow sensor.
According to one embodiment of the instant invention, the conduit member consists of a plurality of sections. One section being a filter support plate providing integrally molded flow conditioning elements in fluid communication with the air flow path. In another embodiment of the instant invention, the air induction assembly is located downstream of a filter element and contained within a protective housing.
Another embodiment of the invention provides for the flow conditioning elements to be integrally formed on the inner surface of the conduit member thus providing a light weight, low cost, simple to produce member.
Accordingly, an object of the instant invention is to provide an air induction system which provides a repeatable turbulent and uniform air flow to the MAFS under all vehicle and engine speeds. Another object of the instant invention is to eliminate any structure from the central portion of the air intake duct, and thus preventing a corresponding decrease in engine horsepower.
An advantage of the instant invention is the use of flow conditioning elements which reduce the
Bugli Neville Jimmy
Cranmer Laura Lou
Iyer Jayanthi
Khami Roger
Owings Dale Edward
Ford Motor Company
MacMillan Sobanski & Todd LLC
McCall Eric S.
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