Measuring and testing – Volume or rate of flow – Proportional
Reexamination Certificate
1999-12-07
2001-12-25
Patel, Harshad (Department: 2355)
Measuring and testing
Volume or rate of flow
Proportional
C073S118040
Reexamination Certificate
active
06332356
ABSTRACT:
PRIOR ART
The invention is based on a measuring device for measuring the mass of a medium flowing in a line, also known as a flow rate meter. From German Patent DE 44 07209 C2, a measuring device is already known in which a flow conduit is integrated with a measuring module. The flow conduit receives the measuring element and tapers increasingly in the flow direction, beginning at an inlet opening. The tapered portion is adjoined by the S-shaped deflection conduit, which has a rectangular cross-sectional profile. The measuring module is embodied as a plug-in component. A substrate part of the measuring module can be inserted sealingly into the wall of the line to be measured and receives an electronic evaluation circuit.
As the measuring element, a micromechanical component, of the kind known for instance from German Patent Disclosure DE 43 38 891 A1, is especially suitable. In the measuring element known from DE 43 38 891 A1, two temperature-sensitive resistors are integrated; they can for instance comprise silicon oxide or silicon nitride, and they have low thermal conductivity and a low specific thermal capacity. The two temperature-sensitive resistors are thermally insulated from one another by a silicon frame. While one of the temperature-dependent resistors acts as the actual measuring sensor, the second temperature-dependent resistor serves as the sensor for the flowing medium.
From German Patent DE 36 27 465 C2, it is known to incline a measuring element for measuring the air quantity in an intake conduit by a predetermined angle relative to the flow direction, in order to reduce the adhesion of suspended particles to the measuring element. It is also known from this patent to provide the end faces of the measuring element both facing toward and away from the air stream with wedge-like protrusions, once again to lessen the adhesion of suspended particles in the air stream. From German Patent DE 39 41 330 C2, it is known to incline the surface of a temperature-sensitive measuring element by a predetermined angle relative to the flow direction of the medium to be measured. Since the angle dependency of the measuring characteristic is relatively great if the measuring element is inclined only slightly relative to the flow direction, or in an extreme case is oriented parallel to the flow direction, yet at greater angles of inclination between the measuring surface of the measuring element and the flow direction of the medium the angle dependency of the measuring characteristic is less, the teaching of this Patent yields a relatively reliable, replicable measurement result if the angle between the flow direction of the medium and the measuring surface of the measuring element is within a range of between 20° and 60°.
The known measuring devices have the disadvantage, however, that the measuring element can be destroyed by dirt particles, especially dust particles, and trained in the flowing medium, if the dirt particles collide with the measuring element. Especially when micromechanical components, of the kind described for instance in DE 43 38 891 A1, are used as the measuring elements, the dirt particles can strike the relatively thin diaphragm and do lasting harm. The result can be increased wear of the measuring element and premature failure. In addition, oily or greasy dirt particles can settle on the measuring element, and particularly on its diaphragm and act as adhesion promoters for solid particles, such as dust or grains of sand, and persistently soil the measuring element. This destroys the thermal coupling between the measuring element and the flowing medium, causing a shift in the measurement characteristic curve that necessarily leads to measurement errors. If the measuring device is used to detect the aspirated air in the intake conduit of an internal combustion engine, for instance, the result can be incorrect triggering of the fuel injection valves and thus a less than optimal setting of the fuel-air mixture, so that as the measuring element becomes increasingly soiled, the engine exhaust emissions become worse.
A further disadvantage of the known measuring device is that the measurement accuracy is still not optimal in the case of pulsating flows in the line to be measured.
ADVANTAGES OF THE INVENTION
The measuring device of the invention for measuring the mass of a medium flowing in the line, has the advantage over the prior art that dirt particles entrained in the flowing medium are largely prevented from impinging on the measuring element and at least are reduced. Particularly the diaphragm of a measuring element embodied as a micromechanical component is largely protected by the provision of the invention against the collision of dirt particles entrained in the flowing medium, so that the service life of the measuring element is prolonged substantially. By dividing the flow conduit into a measuring conduit, which receives the measuring element, and a bypass conduit that bypasses the measuring element, it is attained that the dirt particles are substantially carried away through the bypass conduit and bypass the measuring element, while relatively little contaminated medium flows past the measuring element through the measuring conduit. This reduces the risk of collision of the measuring element considerably, and especially a thin, vulnerable diaphragm of the measuring element, with the dirt particles considerably. Since the incidence of oily and greasy dirt particles on the measuring element is furthermore reduced, soiling from dust and other solid particles adhering to the measuring element is largely prevented. This counteracts any change in the characteristic curve and increases the reliability of the measurement result obtained. If the measuring device is used to detect the aspirated air mass in an internal combustion engine, the engine emissions are therefore not made permanently worse.
Advantageous refinements of and improvements to the measuring device defined herein are possible with the provisions recited in hereinafter.
It is especially advantageous if the flow conduit, between the inlet opening and the dividing point at which the flow conduit branches into the measuring conduit and the bypass conduit, has a curved portion, and the measuring conduit adjoins an inner region with a relatively small radius of curvature while the bypass conduit adjoins a peripheral region with a relatively large radius of curvature of the curved portion. As a result of the centrifugal forces acting on the dirt particles in the curved portion, the dirt particles are positively displaced outward into the peripheral region, so that the peripheral region of the curved portion is contaminated with relatively many dirt particles, while the inner region of the curved portion is contaminated with relatively few dirt particles. Most of the dirt particles therefore enter the bypass conduit bypassing the measuring element, and do not enter the measuring conduit, and the contamination of the medium bathing the measuring element is reduced markedly.
As an alternative to this, it is also possible to offset the measuring conduit radially from the inlet opening relative to a longitudinal axis of the line to be measured. As a result, the measuring conduit is located largely outside the flight path of the dirt particles, which extends substantially parallel to the longitudinal axis of the line and is thus predetermined by the projection of the inlet opening parallel to the longitudinal axis of the line.
Between the measuring conduit and the bypass conduit, a partition can be provided; the bypass conduit and the measuring conduit can either reunite downstream of the measuring element and emerge at a common outlet opening, or the measuring conduit and the bypass conduit can be extended onward in the measuring device in the form of separate conduits with separate conduits with separate outlet openings. Especially when the measuring conduit and the bypass conduit unite again downstream of the measuring element to form a common flow conduit, such as an S-shaped deflection conduit, it
Hecht Hans
Mueller Wolfgang
Greigg Ronald E.
Patel Harshad
Robert & Bosch GmbH
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