Measuring and testing – Volume or rate of flow – Proportional
Reexamination Certificate
1999-05-28
2001-10-09
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Proportional
C073S204220, C073S118040
Reexamination Certificate
active
06298720
ABSTRACT:
PRIOR ART
The invention is based on a measurement device for measuring the mass of a medium flowing in a line. A measurement device has already been disclosed by DE 44 07 209 C2 in which a measurement conduit and a deflection conduit are integrated into a measurement module. The measurement conduit contains the measuring element and narrows increasingly in the flow direction starting from an inlet opening. The measurement conduit is adjoined by the deflection conduit, which is embodied in an S-shape and has a rectangular cross sectional profile. The measurement module is embodied as a component that can be plug connected. A carrier part of the measurement module can be inserted in a sealed fashion into the wall of the line to be measured and contains an electronic evaluation circuit.
A micromechanical component is particularly suited as the measuring element, for example of the kind that is known from DE 43 38 891 A1. With the measuring element known from DE 43 38 891 A1, two temperature-sensitive resistors are integrated into separate membranes, which can be comprised, for example, of silicon oxide or silicon nitride and have a low heat conductivity and a low specific heat capacity. The two temperatures-sensitive resistors are thermally insulated from each other by means of a silicon frame. While one of the temperature-sensitive resistors functions as an actual measurement sensor, the second temperature-sensitive resistor is used as a sensor for the temperature of the flowing medium.
Inclining a measuring element, which is for measuring the air quantity in an intake conduit, in relation to the flow direction by a predetermined angle in order to reduce the adhesion of suspended particles on the measuring element is known per se from DE 36 27 465 C2. Furthermore, this reference discloses providing wedge-shaped projections on the end faces of the measuring element oriented toward and away from the air flow, likewise in order to prevent the adhesion of suspended particles of the air flow. The embodiment of the wedge-shaped projections is produced by means of anisotropic etching of a silicon substrate. DE 39 41 330 C2 has disclosed inclining the surface of a temperature-sensitive measuring element by a predetermined angle in relation to the flow direction of the medium to be measured. Since the angular dependency of the measurement characteristic curve is relatively great when the measuring element is only slightly inclined in relation to the flow direction or in the extreme instance, is aligned parallel to the flow direction, but the angular dependency of the measurement characteristic curve is less when there are greater inclination angles between the measurement surface of the measuring element and the flow direction of the medium, then according to the teaching of this reference, a relatively reliable and reproducible measurement result is produced when the angle between the flow direction of the medium and the measurement surface of the measuring element lies in a range between 20° and 60°.
The known measurement devices, however, have the disadvantage that the measuring element can be destroyed by dirt particles, in particular dust particles, transported along in the flowing medium, when the dirt particles collide with the measuring element. In particular when micromechanical components of the type that are described, for example, in DE 43 38 891 A1 are used as measuring elements, the dirt particles can strike the membrane, which is embodied as relatively thin, and can damage the membrane permanently. Therefore, an increased wear of the measuring element can occur as well as an early failure. Furthermore, dirt particles that contain oil or grease can collect on the measuring element, particularly on its membrane, which act as adhesives for solid-bodied particles, e.g. dust or grains of sand, and permanently contaminate the measuring element. The heat coupling between the measuring element and the flowing medium is impaired by the contamination so that a displacement of the measurement characteristic curve is produced, which inevitably causes measurement errors. When the measurement device is used to detect the intake air in the intake conduit of an internal combustion engine, for example an erroneous triggering of the fuel injection valves can occur and consequently, a non-optimal adjustment of the fuel/air mixture can occur, so that the exhaust values of the internal combustion engine worsen with increasing contamination of the measuring element.
A further disadvantage of the known measurement device is comprised in that the measurement precision is still not optimal when there are pulsating flows in the line to be measured.
ADVANTAGES OF THE INVENTION
The measurement device according to the invention for measuring the mass of a medium flowing in a line, has the advantage over the prior art that an impingement on the measuring element by dirt particles entrained in the flowing medium is prevented to the greatest extent possible, but is at least reduced. In particular, the membrane of a measuring element, which is embodied as a micromechanical component, is protected to the greatest extent possible against collision with dirt particles entrained in the flowing medium by means of the steps according to the invention so that the service life of the measuring element can be significantly extended. Inclining the measurement conduit longitudinal axis in relation to the line longitudinal axis produces a region in the measurement conduit that is screened in relation to the flight paths of particles entrained in the flowing medium, and the dirt particles do not get into this region or only do so in significantly reduced numbers. By disposing the measuring element in this region, the danger of the collision of the dirt particles with the measuring element, in particular the thin and sensitive membrane of the measuring element, is considerably reduced. Since the collision of dirt particles that contain oil or grease against the measuring element is furthermore reduced, a contamination through the adhesion of dust or other solid-bodied particles to the measuring element, in particular on the surface of the membrane of a measuring element that is embodied as a micromechanical component, is largely prevented. This counteracts a change in the characteristic curve and increases the reliability of the measurement result produced. When the measurement device according to the invention is used to detect the intake air mass of an internal combustion engine, the exhaust values of the engine can therefore be improved.
Advantageous improvements and updates of the measurement device disclosed are possible by means of the measures disclosed herein after.
In particular, it is advantageous if in addition, the exit plane of the measurement device that spans the outlet opening, is inclined in relation to the line longitudinal axis by a predetermined angle. This measure considerably improves the dynamics in a pulsating flow of the medium to be measured and produces an improved flow of the medium through the measurement conduit and the deflection conduit of the measurement device. The measuring element can advantageously be fastened to a plate that protrudes into the measurement conduit and the upstream end face of this plate is beveled by means of one or a number of oblique faces. This measure reduces the adhesion of dirt particles to the upstream end face of the plate. The measurement plate is preferably aligned in relation to the main flow direction in the measurement conduit so that the medium strikes the upstream end face with a lateral flow component which is disposed in the plane of the bezel-like oblique face. By means of this flow component, dirt particles adhering to the oblique. face are acted on with a force component along the oblique face and are consequently removed from the sensitive region of the measuring element. This self-cleaning effect can further improve the characteristic curve stability of the measuring element.
In a similar manner, the end faces of the defining walls of the meas
Konzelmann Uwe
Mueller Wolfgang
Fuller Benjamin R.
Greigg Edwin E.
Greigg Ronald E.
Patel Jagdish
Robert & Bosch GmbH
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