Device for measuring the mass of a flowing medium of air aspirated by an internal combustion engine

#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.

#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.

#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;

#In FIG. 1, a device 1 for measuring the mass of a flowing medium, or flow rate meter, especially for measuring the flow rate of the air aspirated by internal combustion engines, is shown. The engine may be a mixture-compressing engine with externally supplied ignition, or an air-compressing engine with self-ignition. The device 1 has a measurement part 2, which is introduced, for instance in plug-in fashion, into a measurement stub 5 of the device 1. The measurement part 2 is by way of example slender, rodlike, and parallelepiped in shape, extending in elongated fashion in the direction of a plug-in shaft 10, and is introduced, for instance in plug-in fashion, into an opening made in a wall 8 of the measurement stub 5. The wall 8 defines a flow cross section, for example of circular cross section, in the middle of which a center axis 11 extends, this axis being oriented in the direction 18 of the flowing medium, parallel to the wall 8, and perpendicular to the plug-in shaft 10. The direction of the flowing medium is indicated by arrows 18 in FIG. 1, in which it extends from left to right.

#A measurement element 14 is introduced with the measurement part 2 into the flowing medium. A measurement conduit 15 is formed in the measurement part 2 of the device 1, and the measurement element 14 for measuring the medium flowing in the measurement stub 5 is accommodated in this conduit. The construction of such a measurement part 2 with a measurement element 14 is well known to one skilled in the art, for instance from German Published, Non-Examined Patent Application DE-OS 44 07 209, whose disclosure is hereby expressly incorporated by reference.

#Upstream of the measurement element 14, a flow rectifier 20 and a grid 21 are provided. The flow rectifier 20 comprises plastic and is produced by injection molding, for example. The grid 21 provided downstream of the flow rectifier 20 comprises a slow-reacting metal, such as special steel.