Device for measuring the amount of a flowing medium

A device for measuring the mass of a flowing medium, with a temperature-dependent measurement element that substantially reduces measurement errors due to a pulsating flow that is characterized by means of flow fluctuations. The device has a measurement conduit which extends from an inlet to an outlet that is adjoined by a first section piece of a deflection conduit. The medium flows from the outlet to the first section piece and is deflected by an edge face into a second section piece of the deflection conduit. The edge face of the first section piece of the deflection conduit is embodied as inclined in relation to the flow direction in the measurement conduit. The invention is provided for measuring the mass of a flowing medium, for the intake air mass of internal combustion engines.

PRIOR ART 
The invention is based on a device for measuring the mass of a flowing 
medium. DE-OS 44 07 209 has already disclosed a device that has a 
temperature-dependent measurement element that is accommodated in a 
measurement conduit. The measurement conduit extends in the device from an 
inlet to an outlet which is adjoined by an S-shaped deflection conduit. 
The deflection conduit is composed of a first section piece and a second 
section piece. The first section piece has a right-angled bend and 
transitions into the second section piece at an edge face. The flowing 
medium first flows from the outlet of the measurement conduit into the 
first section piece of the deflection conduit, which has a greater flow 
cross section than the measurement conduit, so that there is an abrupt 
flow transition in the form of a step in relation to the first section 
piece. Then the medium, having been deflected by the first section piece, 
travels from the corner along the edge face of the first section piece 
into the laterally adjoining second section piece of the deflection 
conduit and exits from this out of an outlet opening in order to mix once 
again with the medium flowing past the device. 
In an internal combustion engine, the opening and closing of the inlet 
valves of the individual cylinders produce considerable fluctuations or 
pulsations of the flow, whose intensity is a function of the intake 
frequency of the individual pistons or is a function of the speed of the 
engine. The pulsations of the flow propagate from the inlet valves via the 
intake line, to the measurement element in the measurement conduit, and 
beyond. The pulsations result in the fact that depending on the intensity 
of the pulsations, due to a thermal inertia and directional insensitivity 
of the measurement element, it produces a measurement result that can 
deviate considerably from the flow speed prevailing in the center of the 
measurement conduit and the intake air mass of the engine that can be 
calculated from it. The measurement conduit and the deflection conduit are 
matched to each other in their dimensions in such a way that with a 
pulsating flow in the intake line, the false indication of the measurement 
element that occurs due to the flow fluctuations is minimal. Nevertheless, 
at high pulsation frequencies and significant pulsation amplitudes, due to 
flow-acoustic processes in the deflection conduit, a false indication of 
the intake air mass can occur. In particular, this false indication is 
produced by virtue of the fact that with a pulsating flow downstream of 
the measurement element at the step between the outlet of the measurement 
conduit and the corner on the first section piece of the deflection 
conduit, a pressure wave can be produced which is reflected at the edge 
face of the deflection conduit at the bend so that the measurement signal 
of the measurement element experiences interference due to a feedback 
effect. 
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 a uniformly precise 
measurement result can be achieved virtually independent of a fluctuating 
or pulsating flow. This is advantageously possible without in the process 
having to change the distance between the edge face of the first section 
piece of the deflection conduit to the outlet of the measurement conduit 
so that the modulation of the overall conduit comprised of the measurement 
conduit and the deflection conduit is not impaired, by means of which a 
compact construction of the device can be maintained. 
A flow connection provided in the deflection conduit is for external flow 
and is disposed in the intake line in the form of an opening, by means of 
which a residual interference of the pressure wave in the deflection 
conduit, which could still exist, can be completely eliminated, thus 
producing a further improvement of the measurement result. Furthermore, 
the device has markedly reduced measurement signal noise, which can be 
generated by turbulences that occur in the measurement conduit.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
FIG. 1 shows a partial sectional side view of a device indicated with 1, 
which is used for measuring the mass of a flowing medium, in particular 
the intake mass of internal combustion engines. The device 1 preferably 
has a slim, block-shaped form that extends radially elongated in the 
direction of a longitudinal axis 10 and is inserted, for example so that 
it can slide into an opening 6 of an intake line 7, which opening is 
recessed into a wall 5. The device 1 is sealed by means of a sealing ring 
3 in the wall 5 and is connected to the wall, for example, by means of a 
screw connection not shown in detail. The crosshatched wall 5 is part of 
the for example cylindrically embodied intake line 7 through which the 
engine can take in air from the environment via an air filter not shown in 
detail. The wall 5 of the intake line 7 adjoins a flow cross section which 
in the case of the cylindrical intake line 7, has an approximately 
circular cross section, at whose center, a center axis 11 extends in the 
axial direction parallel to the wall 5 and is oriented perpendicular to 
the longitudinal axis 10. The device 1 protrudes with a part referred to 
below as the measurement part 17 into the flow medium, wherein the 
measurement part 17 extends, for example, to above the center of the 
intake line 7 and is symmetrically divided by a plane through the center 
axis 11, which is disposed in the plane of the drawing, so that a 
temperature-dependent measurement element 20 that is accommodated in the 
measurement part 17 can be flowed against to as great an extent as 
possible without interfering edge influences of the wall 5. In the 
exemplary embodiments according to FIGS. 1 to 3, the medium flows from 
right to left, wherein corresponding arrows 29 indicate the flow 
direction. 
The device 1 is composed of one piece including the measurement part 17, a 
supporting part 18, and a securing part 19, and is produced, for example, 
out of plastic using injection molded plastic technology. The measurement 
element 20 is embodied, for example, as plate-shaped and, as can be 
inferred, for example, from DE-OS 36 38 138, has one or more 
temperature-dependent resistors 28 which, in the form of resistive films 
so-called hot-film resistors, are mounted on a plate-shaped ceramic 
substrate that is used as a supporting body 22. However, as shown in FIGS. 
1 and 3 and as can be inferred from the prior art, for example from DE-OS 
43 38 891, it is also possible to embody the measurement element 20 in the 
form of a so-called micromechanical component. The measurement element 20 
has a supporting body 22 with a membrane-shaped sensor region produced by 
means of etching, with an extremely low thickness and a number of 
resistive films likewise produced by etching, which constitute at least 
one temperature-dependent measurement resistor 28 and for example one 
heating resistor. The measurement element 20 is therefore comprised of at 
least one plate-shaped carrying body 22, e.g. comprised of ceramic, and at 
least one temperature-dependent resistor 28. The carrying body 22 is 
accommodated flush in a recess 34 in a container 23, e.g. comprised of 
metal and is secured there, for example, by means of glue. Oriented toward 
the flow 29, the container 23 has a leading edge that is preferably 
embodied as beveled. By means of connection lines 24 that extend on the 
inside of the device 1, the individual resistive layers 28 of the 
measurement element 20 are electrically connected to an electronic 
evaluation circuit 25, which is represented with dashed lines in FIG. 1 
and contains, for example, a bridge-like resistive measurement circuit. 
The evaluation circuit 25 is accommodated, for example, in the supporting 
part 18 or in the securing part 19 of the device 1. If the evaluation 
circuit 25 is accommodated, for example, in the supporting part 18, then 
it is possible to cool the circuit, for example, by means of a cooling 
body and the medium flowing in the intake line 7. With a plug connection 
26 provided on the securing part 19, the electrical signals generated by 
the evaluation circuit 25 can, for example, also be supplied to a further 
electronic control device for evaluation. A detailed description of the 
function and construction of temperature-dependent measurement elements is 
not necessary since this can be inferred by one skilled in the prior art. 
As shown in FIG. 2, which is a sectional representation along a line II--II 
in FIG. 1, the measurement part 17 of the device 1 has a block-shaped form 
and has a measurement conduit 30 that extends along a measurement conduit 
axis 12 that runs through the center of the measurement conduit 30, from 
an inlet 35, which for example has a rectangular cross section, to an 
outlet 36, which for example likewise has a rectangular cross section. The 
device 1 is installed in the intake line 7, preferably with the 
measurement conduit axis 12 parallel to the center axis 11. However as 
shown in FIG. 2 by means of the measurement conduit axis 12' indicated 
with dashed lines, it is also possible to install the device 1 with a 
rotated installation position so that the measurement conduit axis 12' can 
enclose an angle of a few degrees with the center axis 11. As shown in 
FIG. 1, the measurement conduit 30 transitions into an S-shaped deflection 
conduit 31. The measurement conduit 30 is defined by a top face 37 farther 
from the center axis 11 and a bottom face 38 closer to the center axis 11, 
as well as two side faces 39, 40 shown in FIG. 2. In the exemplary 
embodiment according to FIG. 1, the measurement conduit 30 is disposed 
with its measurement conduit axis 12 for example eccentric to the center 
axis 11. However as shown in FIG. 3, a second exemplary embodiment of the 
device 1 according to the invention, it is also possible to dispose the 
measurement conduit 30 with its measurement conduit axis 12 central to or 
in the region of the center axis 11 of the intake line 7. The container 
for the plate-shaped measurement element 20 is secured on one side in the 
supporting part 18 against the top face 37 so that with the measurement 
element 20 on its two side faces 21 that extend approximately parallel to 
the measurement conduit axis 12, the container 23 is circulated around by 
a medium. 
As shown in FIG. 2, the side faces 39, 40 of the measurement conduit 30 
extend diagonal to a plane 14 that contains the measurement conduit axis 
12 and the longitudinal axis 10 and with this plane, enclose an acute 
angle so that viewed in the flow direction 29, the measurement conduit 30 
tapers axially in order to feed with its smallest cross section at the 
outlet 36 into a first section piece 32 of the deflection conduit 31. The 
measurement element 20 is disposed in the container 23, upstream of the 
narrowest point of the measurement conduit 30 or upstream of the outlet 36 
in the measurement conduit 30. The tapering of the measurement conduit 30 
provided in the flow direction 29 brings about the fact that in the region 
of the measurement element 20, a uniform parallel flow can prevail that is 
as free from interference as possible. In order to prevent burbling in the 
region of the inlet 35 of the measurement conduit 30, the inlet region of 
the measurement conduit 30 has a rounded edge surface 42, which is shown 
in FIG. 1. 
According to the invention, an edge face 45 of the first section piece 32 
of the deflection conduit 31, which edge face is disposed in the 
projection of the outlet 36 in the flow direction 29 on the opposing wall 
of the deflection conduit 31, is not embodied as perpendicular to the flow 
29, but is inclined in relation to it so that an inclination angle .alpha. 
enclosed by the measurement conduit axis 12 and the edge face 45 is 
preferably approximately 45 degrees. However, it is also possible to 
embody the edge face 45 with an inclination angle .alpha. that is in the 
range of approximately 30 to 60 degrees. As shown in FIG. 1, downstream of 
the edge face 45, a second section piece 33 of the deflection conduit 31 
adjoins the first section piece 32 lateral to it or lateral to the 
direction of the longitudinal axis 10. The inclined edge face 45 is 
provided in order to divert the medium flowing from the outlet 36 of the 
measurement conduit 30 into the first section piece 32 along the edge face 
45 into the second section piece 33. The edge face 45 extends 
approximately to the cutting line II--II or to the center axis 11 in FIG. 
1. In the direction of the longitudinal axis 10, the edge face 45 has a 
width br that is slightly smaller than the width b of the measurement 
conduit 30 in the direction of the longitudinal axis 10. However, it is 
also possible to embody the edge face 45 with a width br that corresponds 
to the width b of the measurement conduit 30. The width br of the edge 
face 45, though, should be at least 2/3 the width b of the measurement 
conduit 30. As shown in FIG. 2, perpendicular to the width br, the edge 
face 45 has a depth tr that preferably corresponds approximately to the 
depth t of the measurement conduit 30 perpendicular to its width b at the 
inlet 35. However, it is also possible to embody the edge face 45 with a 
depth tr that is slightly less than the depth t of the inlet 35 of the 
measurement conduit 30. Adjacent to the edge face 45, the wall of the 
first section piece 32 extends approximately in the direction of the 
longitudinal axis 10. 
The deflection conduit 31 composed of the first section piece 32 and the 
second section piece 33 preferably has a rectangular cross section, which 
approximately corresponds to the cross sectional area of the inlet 35 of 
the measurement conduit 30 so that, the flow cross section abruptly 
increases at a step 43 at the outlet 36 between the measurement conduit 30 
and the deflection conduit 31. Downstream of the outlet 36, the medium 
flowing in the measurement conduit 30 first travels into the first section 
piece 32, is deflected against the edge face 45, and flows from this on 
into the second section piece 33. As shown by an arrow 46 drawn in FIGS. 1 
and 3, the medium then leaves the second section piece 33 via an outlet 
opening 47 and arrives in the intake line 7 essentially lateral to the 
flow direction 29. Like the deflection conduit 31, the outlet opening 47 
has, for example, a rectangular cross section and is provided on a lower 
external face 50 of the measurement part 17 oriented parallel to the 
measurement conduit axis 12. As shown in FIGS. 1 and 3, the edge surface 
42 of the measurement part 17 that opposes the flow 29 adjoins to the 
right of the rectangular outlet opening 47, lateral to the lower external 
face 50 and upstream of the inlet 35 of the measurement conduit 30, this 
edge surface leads in a rounded form from the lower external face 50 to 
the bottom face 38 of the measurement conduit 30 until reaching the inlet 
35. 
The inclined embodiment of the edge face 45 in the deflection conduit 31 
brings about the fact that interferences in the flow arising from the 
outlet 36 of the measurement conduit 30, which can occur, for example, in 
the form of whirls or in the form of pressure waves, are reflected against 
the edge face 45. Depending on the point of origin of the whirls or the 
pressure waves over the width of the step 43 or the outlet 36 extending in 
the direction of the longitudinal axis 10, a different distance is 
produced in relation to the edge face 45 so that the individual whirls or 
pressure waves produced along the width are reflected against the edge 
face 45 in a time-delayed fashion with the result that they are 
additionally deflected in their direction and are on the whole weakened in 
their interfering action on the measurement element 20. As a result of 
this time and location-dependent reflection of interferences against the 
edge face 45, an influence on the electrical signal emitted by the 
measurement element 20 can be prevented. This results in the fact that a 
false indication of the measurement element 20 that would otherwise occur 
in the event of a pulsating flow can be sharply reduced or even prevented. 
In FIG. 3, a second exemplary embodiment according to the invention, in 
which all the same parts or those with equivalent functions are indicated 
with the same reference numerals from FIGS. 1 and 2, an opening 55 in the 
deflection conduit 31 is shown downstream of the edge face 45, which 
opening, for example in the form of a bore, produces a connection of the 
flow in the deflection conduit 31 to the external flow in the intake line 
7. The opening 55 is embodied, for example, as a circular bore that 
extends from one of the side walls 27 of the measurement part 17 over the 
intersecting region from the first section piece 32 into the second 
section piece 33 of the deflection conduit 31. However as shown with 
dashed lines in FIG. 3, it is also possible to provide the opening 55 
extending starting from the lower external face 50 of the measurement part 
17 to the second section piece 33. The opening 55 has a relatively small 
cross section and has an opening diameter of a few millimeters, for 
example 2 mm. Naturally, there can also be a number of openings 55. By 
means of the at least one opening 55, the resonance chamber that is formed 
by the deflection conduit 31 and is for the pressure waves exiting 
downstream of the outlet 36 of the measurement conduit 30 can be 
influenced in such a way that due to a pressure compensation brings about 
a weakening in the pressure waves reflected against the edge face 45. 
Through the size of the cross section of the at least one opening 55, the 
natural frequency of the resonance chamber can be tuned to the frequency 
of the outgoing pressure waves in such a way that it produces a further 
improvement of the measurement result delivered by the measurement element 
20. 
Furthermore, the at least one opening 55 allows for the possibility that 
due to the pressure compensation of the flow in the deflection conduit 31 
in relation to the flow in the intake line 7, pressure waves in the 
deflection conduit 31, which are possibly weakened further, can escape 
into the intake line 7 without disadvantageously influencing the 
measurement result delivered by the measurement element 20 in the process. 
The foregoing relates to preferred exemplary embodiments of the invention, 
it being understood that other variants and embodiments thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.