Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
1998-06-15
2001-01-09
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06170327
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an air mass meter for the intake port of an internal combustion engine, with a temperature sensor which records the temperature of the air in the intake port, and with a heating element which has a strip-shaped substrate and a heating resistor applied to one side of the substrate.
An earlier, commonly owned international application (WO 95/21370) describes an air mass meter which has a temperature sensor resistor and a sensor heating resistor. The sensor heating resistor is heated to a predetermined excess temperature, as compared with the temperature measured at the temperature sensor resistor. The electric current, which flows through the sensor heating resistor, and the voltage, which drops across a temperature-independent series resistor, are, when squared, directly proportional to the heating capacity which is delivered in the sensor heating resistor. The air mass flow can thus be determined from these variables.
Deposits of dirt on the onflow surface of the sensor heating resistor which face into the flow may lead to variations in heat transfer on the sensor heating resistor. The increasing deposits of dirt result in an increasingly greater measuring error.
A prior art air mass meter described in German published, non-prosecuted patent application DE 38 38 466 A1 has a temperature sensor and a heating element with a striplike substrate and a heating resistor applied to the substrate. A body member is arranged on one end face of the substrate, facing into the flow of the air. That body member is disposed and configured such that, when the air mass meter is new, a flow profile is already established around the substrate which resembles the flow profile that is established, without the body, as a result of deposits of dirt after a certain amount of operating time. Deposits of dirt on the body member may, however, lead to a variation in heat transfer on the heating resistor. Increasing deposits of dirt thereby result in an increasingly greater measuring error.
For the purpose of eliminating deposits of dirt, a prior art air mass meter described in German patent DE 42 28 524 C1 has a U-shaped yoke which is mounted movably in a frame. A first free end region brushes against the onflow surface of the sensor heating resistor. A second free end region of the yoke is driven by the air flow in the intake port. The position of the first free end region consequently varies with the velocity of the air flow. The first end region of the yoke thus eliminates deposits of dirt on the onflow surface mechanically. The disadvantage of this air mass meter, however, is that is requires complicated mechanical parts in order to eliminate the deposits of dirt.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an air mass meter, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type and which reduces measuring errors as a result of deposits of dirt on an end-face onflow surface of a heating element.
With the foregoing and other objects in view there is provided, in accordance with the invention, an air mass meter for an intake port of an internal combustion engine, comprising:
a temperature sensor disposed in an intake port of an internal combustion engine for measuring a temperature of air flowing in the intake port;
a heating element disposed in the intake port, the heating element being formed of a strip-like substrate and a heating resistor applied to one side of the substrate;
a disturbance body disposed in the intake port downstream of the heating element relative to a flow of air in the intake port;
the heating element and the disturbance body being configured and placed at a relative distance from one another, such that a heat transfer from the heating element to the air flowing in its vicinity is influenced only negligibly by deposits of dirt on an onflow surface of the heating element, in that a relative error due to the deposits of dirt does not increase sharply above a predetermined critical air throughput after a predetermined operating time of the air mass meter.
In accordance with an added feature of the invention, the heating element has a cuboid shape, with a length of the heating element parallel to the air flow between 0.5 and 0.9 mm, and a ratio of the length to a height of the onflow surface in a range from 3 to 6.
In accordance with an additional feature of the invention, the length is 0.6 mm, the height of the onflow surface is 0.15 mm and a width of the heating element is 9 mm.
In accordance with another feature of the invention, the substrate of the heating element is a glass substrate and the disturbance body consists of metal.
In accordance with a further feature of the invention, the disturbance body is aligned with the heating element in a direction of flow of the air.
In accordance with again another feature of the invention, the heating resistor is a platinum resistor disposed in a meandering resistance path on the substrate.
In accordance with a concomitant feature of the invention, there is provided a reheating element disposed between the heating element and the disturbance body.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an air mass meter, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 4803875 (1989-02-01), Kuhn et al.
patent: 4944182 (1990-07-01), Gneiss et al.
patent: 5319971 (1994-06-01), Osswald et al.
patent: 2171800A (1986-09-01), None
patent: 2179161A (1987-02-01), None
Published International Application No. 95/21370 (Wildgen et al.), dated Aug. 10, 1995.
Greenberg Laurence A.
Lerner Herbert L.
Patel Harshad
Siemens Aktiengesellschaft
Stemer Werner H.
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