Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
1999-12-07
2001-08-14
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
C073S202500, C073S118040
Reexamination Certificate
active
06272920
ABSTRACT:
PRIOR ART
The invention is based on a device for measuring the mass of a flowing medium, also called a flow rate meter.
From European Patent Disclosure EP 0 087 621 B1, a device for measuring the mass of a medium flowing in a line, in particular the aspirated air mass of an internal combustion engine is known, in which a measuring element, for instance in the form of a hot wire, is placed in a bypass conduit embodied offset from the main aspiration conduit. The opening and closing of the inlet valves of the various cylinders of the engine cause considerable fluctuation or pulsation in the flow velocity in the bypass conduit, and the intensity of this fluctuation or pulsation depends on the aspiration frequency of the individual pistons, or on the engine rpm. These flow fluctuations adulterate the outcome of measurement, namely the average flow velocity prevailing in the bypass conduit and the aspirated air mass of the engine that can be calculated from the aspirated air, considerably. Depending on the intensity of the pulsation in the flow velocity, the mean flow velocity is demonstrably underindicated in the partial-load range of the engine, for instance, and overindicated when the throttle valve is fully open. To reduce these measurement errors that occur with pulsating flows, in the device known from EP 0 087 621 B1 certain longitudinal and cross-sectional relationships of the main aspiration conduit and the bypass conduit, which are ascertained by calculation and numerous measurements, are selected, and the location of the measuring element in the bypass conduit is prescribed. On the one hand, this limits the engineering and design possibilities and possibilities for installing device considerably, and on the other, the embodiment of the device requires a large installation space.
In German Patent Disclosure DE 4340 882 A1, to reduce the flow fluctuations, it is proposed that a flow tube in the form of an internal tube be disposed in the line to be measured, such as the aspiration conduit of an internal combustion engine. Once again, the measuring element is disposed in a bypass conduit, which is located approximately in the middle of the flow tube. The flow tube has friction faces on its inside that bring about a flow resistance that is dependent on the intensity of flow pulsation. At a high pulsation intensity, because of the effects of friction occurring in the peripheral region of the flow tube, the flow is therefore positively displaced into the inner region, that is, the region of the bypass conduit having the measuring element, so that an underindication occurring without the flow tube at a high pulsation intensity of the flow is effectively compensated for. The flow tube known from DE 43 40882 A1 has therefore fundamentally proved itself. A disadvantage, however, is that in practical operation a loud, irritating whistling noise occurs.
German Patent DE 44 07 209 C1 can also be referred to, in the sense that from this reference it is known to dispose the measuring element in a measurement conduit that tapers in the flow direction and which is adjoined by an S-shaped deflection conduit. With this arrangement, the independence of the outcome of measurement from the pulsation intensity of the flow can be further improved. In particular, the arrangement is largely invulnerable to a return flow, counter to the main flow direction, that occurs at high pulsation intensities.
ADVANTAGES OF THE INVENTION
The device according to the invention for measuring the mass of a medium flowing in a line, has the advantage that in operation no irritating whistling noises occur, or at least the whistling is noises are markedly reduced. The structural grooves according to the invention on the outlet end face surrounding the outlet opening prevent eddies in the region of the outlet opening of the flow tube from detaching, which would cause loud, irritating noises. It has been found that the structural grooves of the invention on the outlet end face surrounding the outlet opening do not lessen the above-described fluidic advantages of the flow tube that improve the accuracy of measurement.
Advantageous refinements of and improvements to the device defined herein are possible with the provisions recited hereinafter.
It has been demonstrated that by means of structural grooves of rectangular, triangular or trapezoidal cross-sectional profile, an especially effective reduction in irritating noises can be attained. Especially preferably, the structural grooves extend radially to the longitudinal axis of the flow tube and are disposed at equal angular intervals on the outlet end face. As a result, a uniform segmentation of the outlet end face is attained, which is advantageous for suppressing the irritating noises. The inlet end face surrounding the inlet opening of the float tube is preferably unstructured, in order not to increase the flow resistance in the region of the inlet opening.
REFERENCES:
patent: 2477436 (1949-07-01), Bannister
patent: 4418578 (1983-12-01), Blechinger
patent: 5133647 (1992-07-01), Herron et al.
patent: 5546794 (1996-08-01), Kuhn et al.
Konzelmann Uwe
Tank Dieter
Greigg Edwin E.
Greigg Ronald E.
Patel Harshad
Robert & Bosch GmbH
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