Measuring and testing – Volume or rate of flow – Thermal type
Patent
1998-07-14
2000-11-07
Patel, Harshad
Measuring and testing
Volume or rate of flow
Thermal type
G01F 168
Patent
active
06142014&
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on a device for measuring the mass of a flowing medium, or flow rate meter, for air aspirated by an internal combustion engine. A device is already known (European Patent 0 458 998) that has a measurement element accommodated in a measurement stub, with a flow rectifier and a grid accommodated upstream of the measurement element. The flow rectifier is intended to generate as uniform a flow as possible over the entire inside cross section. The grid, durably secured in the flow rectifier, is intended to create superfine eddies in the flow, so that the flow conditions downstream of the grid can be made as constant as possible for the sake of stabilizing the measurement signal. To avoid a deviation from the characteristic curve of the measurement signal output by the measurement element, it is especially important that the grid be disposed in a precise alignment with the flow rectifier. This is done, in the known device, by embedding the grid in the heated state in a ring of the flow rectifier. The grid is a wire grid, which has individual wires woven together into a grid structure. The wires can still shift somewhat relative to one another. Embedding the wire grid in the plastic has the disadvantage that if there is a temperature change, and when the plastic of the flow rectifier ages, creepage can cause sagging of the wire grid. However, the sagging of the wire grid causes shifting among the individual wires of the grid, and as a consequence the characteristic curve the measurement element is disadvantageously altered. Because the grid is permanently secured to the flow rectifier, there is also the disadvantage that only relatively complicated and expensive flow rectifiers with grids of different mesh widths can be combined with one another. There is also the danger that plastic forced out when the grid is embedded in the heated state in the ring of the flow rectifier will remain behind in the flow rectifier, thus putting obstacles in the way of the flow which can lead to signal deviation, especially under mass-production conditions. Moreover, the intended embodiment of a ring, which protrudes from a surface of the flow rectifier that is disposed perpendicular to the flow, is relatively complicated to produce.
ADVANTAGES OF THE INVENTION
The device according to the invention for measuring the mass of a flowing medium, has the advantage over the prior art that flow rectifiers with a grid of differing mesh width or with different opening cross sections can be produced in an especially simple way. A particular advantage is that the production and assembly of the device are especially simple. It is especially advantageous that sagging of the grid can be averted, and consequently the accuracy and especially the stability of measurement in long-term operation of the device are increased.
By the provisions recited, advantageous refinements of and improvements to the device are attainable.
It is advantageous that grids of different mesh widths or different opening cross sections can be produced without entailing any special tooling expense. In addition, for an intended dismantling of the device, the flow rectifier and the grid are present individually, and thus can easily be separated for recycling. The mode of production of the grid by stamping is especially advantageous; it is thus possible to produce the opening cross sections of the grid with high accuracy, without increasing the production costs of the grid.
BRIEF DESCRIPTION OF THE DRAWINGS
An exemplary embodiment of the invention is shown in simplified form in the drawings and described in further detail below.
FIG. 1 is a fragmentary sectional view of the device of the invention;
FIG. 2 is a plan view on a grid of the device;
FIG. 3 is a side view of the grid of FIG. 2;
FIG. 4 is a detail, on a larger scale, of the grid of FIG. 2; and
FIG. 5 is a fragmentary sectional view of the grid taken along a line V--V in FIG. 4.
DESCRIPTION OF THE EXEMPLARY EMBODIMENT
In FIG. 1, a device 1 for measuring the mass of a flowing
REFERENCES:
patent: 3683692 (1972-08-01), Lafitte
patent: 4412449 (1983-11-01), Eiermann et al.
patent: 4986116 (1991-01-01), Usui et al.
patent: 5253517 (1993-10-01), Molin et al.
patent: 5918279 (1999-06-01), Hetch et al.
Greigg Edwin E.
Greigg Ronald E.
Patel Harshad
Robert & Bosch GmbH
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