[Technical Field]
[0001]
The present invention relates to a differential pressure flow meter, an exhaust gas analysis
device that uses this differential pressure flow meter, and a flow rate measurement method that uses this
5 differential pressure flow meter.
[Technical Background]
[0002]
Among the tests performed on vehicles is an on-road running test in which exhaust gas
10 emitted from the tail pipe of a vehicle is measured while this vehicle is running on a road.
[0003]
In this on-road running test, as is shown in Patent document 1, various types of exhaust gas
analyzers are installed in a vehicle. These exhaust gas analyzers sample the exhaust gas emitted from
the vehicle’s tail pipe and analyze each component contained in the exhaust gas. Moreover, for
15 example, a Pitot tube flow meter that is used to measure the flow rate of exhaust gas is mounted in the
tail pipe, and the emission mass of each component is calculated from the exhaust gas flow rate obtained
by the flow meter and from the concentrations of each component obtained by the exhaust gas analyzers.
[0004]
Here, the Pitot tube flow meter is provided integrally with an attachment pipe that is fitted onto
20 the tail pipe. The larger the pipe diameter of the attachment pipe, the greater the flow rate measurement
range of the Pitot tube flow meter. Furthermore, this Pitot tube flow meter is mounted so as to
correspond to the tail pipe diameter and the actual exhaust gas flow rate.
[0005]
However, because only one Pitot tube flow meter is provided in an attachment pipe, it is not
25 possible to alter the Pitot tube flow meter, for example, during an on-road running test.
[0006]
Moreover, in the case of a vehicle in which there is a large difference between the exhaust gas
flow rate when there is a low level of exhaust such as, for example, when the vehicle is idling, and the
exhaust gas flow rate when there is a high level of exhaust such as, for example, when the vehicle is
2
accelerating rapidly or is traveling at high speed, it is not possible to obtain both of these flow rates from
a single Pitot tube flow meter, and there are cases when the flow rate range does not cover at least one of
the exhaust gas flow rate when there is a low level of exhaust and the exhaust gas flow rate when there is
a high level of exhaust.
5 [0007]
Furthermore, some modern vehicles are equipped with a tail pipe having a larger diameter
than is required by the actual exhaust gas flow rate in order to improve the appearance of the vehicle.
In cases such as this, if an attachment pipe that matches the tail pipe diameter is attached, then the Pitot
tube flow meter that is used ends up having an excessively broad measurement range relative to the
10 exhaust gas flow rate.
[0008]
For these reasons, the accuracy of the exhaust gas flow rate measurement is adversely affected
and, as a result, there are also considerable measurement errors in the results of the emission mass
measurement of each component contained in the exhaust gas.
15
[Documents of the prior art]
[Patent documents]
[0009]
[Patent document 1] Japanese Unexamined Patent Application (JP-A) No. 2004-144574
20
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[0010]
The present invention was therefore conceived in order to solve the above-described problems,
25 and it is a principal object thereof to make it possible to measure a broad range of flow rates with a high
degree of accuracy.
[Means for Solving the Problem]
[0011]
3
Namely, the differential pressure flow meter according to the present invention is a differential
pressure flow meter that detects differential pressures in a fluid body flowing along a flow path, and
calculates a flow rate of the fluid body from those differential pressures, and has at least two differential
pressure detecting portions having mutually different measurement ranges. Note that the term
5 ‘mutually different measurement ranges’ refers not only to two measurement ranges that have no
mutually overlapping portions, but also to two measurement ranges that have partially overlapping
portions.
[0012]
If this type of structure is employed, then because at least two differential pressure detecting
10 portions having mutually different measurement ranges are provided, it is possible to measure a broad
range of flow rates with a high degree of accuracy.
[0013]
It is desirable that the at least two differential pressure detecting portions be provided with a
first differential pressure detecting portion and a second differential pressure detecting portion, and that
15 the first differential pressure detecting portion have a measurement range that is on the low flow rate side
of the second differential pressure detecting portion.
If this type of structure is employed, then by using the first differential pressure detecting
section to measure the low flow rate side, and using the second differential pressure detecting section to
measure the high flow rate side, it is possible to measure a broad range of flow rates highly accurately.
20 [0014]
As an example of the specific structure of the first differential pressure detecting portion and
the second differential pressure detecting portion, a structure in which the first differential pressure
detecting portion and the second differential pressure detecting portion detect a differential pressure
between a total pressure and a static pressure of the fluid body, and have a Pitot tube that is provided with
25 total pressure holes that are used to detect the total pressure, and static pressure holes that are used to
detect the static pressure may be considered. In this structure, in order to ensure that the measurement
range of the first differential pressure detecting portion is on the low flow rate side, it is desirable that the
total pressure holes and static pressure holes of the first differential pressure detecting portion be larger
than the total pressure holes and static pressure holes of the second differential pressure detecting portion.
4
[0015]
In order to enable the first differential pressure detecting portion to make highly accurate flow
rate measurements in a measurement range on the low flow rate side, and to enable highly accurate flow
rate measurements to be made by the second differential pressure detecting portion in a measurement
5 range on the high flow rate side, it is desirable that there be provided a flow rate calculating unit that,
when the flow rate of the fluid body which has been obtained using the first differential pressure
detecting portion or the second differential pressure detecting portion is less than a predetermined value,
outputs the flow rate of the fluid body obtained by the first differential pressure detecting portion as a
measurement value, and when the flow rate of the fluid body which has been obtained using the first
10 differential pressure detecting portion or the second differential pressure detecting portion is equal to or
greater than a predetermined value, outputs the flow rate of the fluid body obtained by the second
differential pressure detecting portion as a measurement value.
[0016]
The measurement range on the low flow rate side is easily affected by pressure variations that
15 are created by placing obstacles on the upstream side. Because of this, it is desirable that the first
differential pressure detecting portion be provided on an upstream side of the flow path, and that the
second differential pressure detecting portion be provided on a downstream side of the flow path.
If this type of structure is employed, then because this is not a structure in which a separate
differential pressure detecting portion is disposed on the upstream side of the first differential pressure
20 detecting portion, which has a measurement range on the low flow rate side, the measurements are not
affected by pressure variations caused by a separate differential pressure detecting portion, so that it is
possible for flow rates during low flow rate periods, such as when, for example, a vehicle is idling, to be
accurately measured.
[0017]
25 It is also desirable that the differential pressure flow meter be provided with an attachment pipe
that is attached to an aperture portion of an exhaust pipe, and forms a flow path along which exhaust gas
emitted from the exhaust pipe flows, and that the at least two differential pressure detecting portions be
provided in this attachment pipe.
If this type of structure is employed, it is possible to measure a flow rate using two or more
5
differential pressure detecting portions simply by attaching a single attachment pipe to an exhaust pipe.
[0018]
It is also possible for the differential pressure flow meter of the present invention to be
incorporated into an exhaust gas analysis device. In this case, it is desirable that the exhaust gas
5 analysis device be provided with the above-described differential pressure flow meter, and with an
exhaust gas analyzer that measures concentrations of predetermined components contained in the
exhaust gas, and that an exhaust gas sampling unit that samples the exhaust gas and guides it to the
exhaust gas analyzer be provided in the attachment pipe of the differential pressure flow meter.
[0019]
10 Furthermore, a flow rate measurement method according to the present invention is a flow rate
measurement method employing a differential pressure flow meter that detects differential pressures in a
fluid body flowing along a flow path, and calculates a flow rate of the fluid body from those differential
pressures, and that has a first differential pressure detecting portion and a second differential pressure
detecting portion that each have mutually different measurement ranges, and in which the measurement
15 range of the first differential pressure detecting portion is on the low flow rate side of the measurement
range of the second differential pressure detecting portion, wherein, when the flow rate of the fluid body
which has been obtained using the first differential pressure detecting portion or the second differential
pressure detecting portion is less than a predetermined value, the flow rate of the fluid body obtained by
the first differential pressure detecting portion is output as a measurement value, and when the flow rate
20 of the fluid body which has been obtained using the first differential pressure detecting portion or the
second differential pressure detecting portion is equal to or greater than a predetermined value, the flow
rate of the fluid body obtained by the second differential pressure detecting portion is output as a
measurement value.
25 [Effects of the Invention]
[0020]
According to the present invention which has the above-described structure, because at least
two differential pressure detecting portions having mutually different measurement ranges are provided,
it is possible to measure a broad range of flow rates with a high degree of accuracy.
6
[Brief description of the drawings]
[0021]
[FIG. 1] FIG. 1 is a schematic view showing the structure of an exhaust gas analysis device
according to the present embodiment.
5 [FIG. 2] FIG. 2 is an enlarged cross-sectional view principally showing a tail pipe attachment
portion of the same embodiment.
[FIG. 3] FIG. 3 is a layout diagram as seen from an upstream side in a flow path direction
showing a positional relationship between differential pressure flow meters of the same embodiment.
[FIG. 4] FIG. 4 is a flowchart showing a flow rate measurement method of the same
10 embodiment.
[FIG. 5] FIG. 5 is a layout diagram as seen from an upstream side in a flow path direction
showing a positional relationship between differential pressure flow meters of a variant embodiment.
[FIG. 6] FIG. 6 is a cross-sectional view showing the structure of a differential pressure flow
meter of a variant embodiment.
15
[Best Embodiments for Implementing the Invention]
[0022]
Hereinafter, an embodiment of an exhaust gas analysis device that utilizes a differential
pressure flow meter according to the present invention will be described with reference made to the
20 drawings.
[0023] [Device structure]
An exhaust gas analysis device 100 of the present embodiment is a vehicle-mounted type of
exhaust gas analysis device that is mounted, for example, in a vehicle V, and analyzes in real time during
25 on-road travel the exhaust gas that is emitted from an internal combustion engine E of the vehicle V
while the vehicle V is traveling on a road. The exhaust gas analysis device 100 is a direct sampling
type of analysis device that does not dilute captured exhaust gas, but instead measures the unmodified
concentration thereof. Note that the exhaust gas analysis device 100 may also be a type of analysis
device that analyzes in real time during simulated traveling the exhaust gas that is emitted from an
7
internal combustion engine of a vehicle while this vehicle is performing simulated travel on a chassis
dynamometer.
[0024]
Specifically, as is shown in FIG. 1, this exhaust gas analysis device 100 is provided with a
5 differential pressure flow meter 2 that is attached to an aperture portion EH1 of an exhaust pipe EH that
is connected to the internal combustion engine E, and that measures a flow rate of exhaust gas emitted
from this exhaust pipe EH, and with a gas analyzer 3 that is used to measure the concentrations of
components needing to be measured that are contained in the exhaust gas emitted from the exhaust pipe
EH.
10 [0025]
The differential pressure flow meter 2 detects differential pressures in exhaust gas flowing
along a flow path, and calculates the flow rate of the exhaust gas from these differential pressures. The
differential pressure flow meter 2 is provided with an attachment pipe 21 that is attached to the exterior
of the aperture portion EH1 of the exhaust pipe EH, and with a first differential pressure detecting
15 portion 22 and a second differential pressure detecting portion 23 that are used to detect differential
pressures in the exhaust gas flowing through the attachment pipe 21.
[0026]
The attachment pipe 21 is formed as a straight pipe that is attached such that it covers an
external circumferential surface of the aperture portion EH1 of the exhaust pipe EH. In the present
20 embodiment, a round pipe having a circular cross-section is used for the attachment pipe 21. An
aperture portion at one end of the attachment pipe 21 is fitted over the aperture portion EH1 of the
exhaust pipe EH, while an aperture portion at another end thereof is left open. Exhaust gas is emitted
to the outside via this other end aperture portion.
[0027]
25 Moreover, in addition to the first differential pressure detecting portion 22 and the second
differential pressure detecting portion 23, an exhaust gas temperature gauge 4 that detects a temperature
Texh(t) of the exhaust gas, and an absolute pressure meter 5 that measures an exhaust gas pressure Pexh(t)
are also provided in the attachment pipe 21. Namely, the two differential pressure detecting portions 22
and 23 are served by the single exhaust gas temperature gauge 4 and the single absolute pressure meter 5.
8
As a consequence, the structure of the attachment pipe 21 can be made simpler.
[0028]
The first differential pressure detecting portion 22 and the second differential pressure
detecting portion 23 detect a differential pressure AP between the total pressure and the static pressure of
5 the exhaust gas. The first differential pressure detecting portion 22 and the second differential pressure
detecting portion 23 have Pitot tubes 2P that are equipped with total pressure holes 2h1 that are used to
detect the total pressure, and static pressure holes 2h2 that are used to detect the static pressure, and a
differential pressure sensor 2S such as a differential pressure transmitter that detects the differential
pressure AP between the total pressure and the static pressure of the exhaust gas via the Pitot tubes 2P
10 [0029]
The Pitot tubes 2P have a total pressure intake pipe portion 2P1 in which the total pressure
holes 2h1 are formed and that introduces the total pressure into the differential pressure sensor 2S, and a
static pressure intake pipe portion 2P2 in which the static pressure holes 2h2 are formed and that
introduces the static pressure into the differential pressure sensor 2S. In this example, the openings of
15 the total pressure holes 2h1 face towards the upstream side of the flow path, while the openings of the
static pressure holes 2h2 face towards the downstream side of the flow path on the opposite side from
the total pressure holes 2h1. Note that in the present embodiment, a structure is employed in which the
single differential pressure sensor 2S is shared by both the first differential pressure detecting portion 22
and the second differential pressure detecting portion 23, however, it is also possible to form a structure
20 in which both the first differential pressure detecting portion 22 and the second differential pressure
detecting portion 23 have their own individual differential pressure sensor 2S.
[0030]
Here, the first differential pressure detecting portion 22 and the second differential pressure
detecting portion 23 of the present embodiment have mutually different flow rate measurement ranges.
25 Specifically, as is shown in FIG. 2, the first differential pressure detecting portion 22 has a measurement
range on the low flow rate side of the second differential pressure detecting portion 23. More
specifically, the total pressure holes 2h1 and the static pressure holes 2h2 of the first differential pressure
detecting portion 22 are larger than the total pressure holes 2h1 and the static pressure holes 2h2 of the
second differential pressure detecting portion 23. By making the total pressure holes 2h1 and the static
9
pressure holes 2h2 of the first differential pressure detecting portion 22 larger in this way, a structure is
created that makes it easier to receive pressure on the low pressure side in the first differential pressure
detecting portion 22, and makes it possible to accurately detect low differential pressures. Note that the
flow rate measurement range of the first differential pressure detecting portion 22 might be, for example,
5 from 0~3 m3/min, and the flow rate measurement range of the second differential pressure detecting
portion 23 might be, for example, from 0~10 m3/min. In the present embodiment, a case is shown in
which one flow rate measurement range is contained within the other flow rate measurement range.
[0031]
Moreover, in the present embodiment, the first differential pressure detecting portion 22 is
10 provided on the upstream side of the flow path, while the second differential pressure detecting portion
23 is provided on the downstream side of the flow path (see FIG. 2). Specifically, the position where
the Pitot tube 2P of the first differential pressure detecting portion 22 is inserted into the attachment pipe
21 is located on the upstream side of the position where the Pitot tube 2P of the second differential
pressure detecting portion 23 is inserted into the attachment pipe 21. At this time, it is desirable to
15 employ an arrangement in which the total pressure holes 2h1 and the static pressure holes 2h2 of the first
differential pressure detecting portion 22 are not superimposed on top of the total pressure holes 2h1 and
the static pressure holes 2h2 of the second differential pressure detecting portion 23 when viewed from
the flow path direction. For example, as is shown in FIG. 3, by employing an arrangement in which
the Pitot tube 2P of the first differential pressure detecting portion 22 extends orthogonally to the Pitot
20 tube 2P of the second differential pressure detecting portion 23, it is possible to prevent the total pressure
holes 2h1 and static pressure holes 2h2 of the respective Pitot tubes 2P from being mutually
superimposed on each other.
[0032]
Next, using the differential pressure AP obtained by the first differential pressure detecting
25 portion 22 and the second differential pressure detecting portion 23, a flow rate calculating unit 24 of the
differential pressure flow meter 2 calculates the flow rate of the exhaust gas.
[0033]
Specifically, the flow rate calculating unit 24 uses the following formula to calculate a
10
volumetric flow rate Qexh(t) [m3/min] of the exhaust gas in a standard state from the differential pressure
AP from the differential sensor S2 obtained from at least one of the first differential pressure detecting
portion 22 or the second differential pressure detecting portion 23, from the exhaust gas temperature
Texh(t) [K] obtained from the exhaust gas temperature gauge 4, and from the exhaust gas pressure Pexh(t)
5 [kPa] obtained from the absolute pressure meter 5.
[0034]
[Formula 1]
Qexh(t) = kx Pexh ( t) T0 AP
x 0 x
P 0 T ( t ) exh
10 Wherein k = Proportionality coefficient
P0 = Standard pressure (101.3 [kPa])
T0 = Standard temperature (293.15 [K])
ρ exh = exhaust gas concentration [g/m ] in a standard state.
Note that the proportionality coefficient K, the standard pressure P0, the standard temperature
15 T0, and the exhaust gas concentration ρ exh are input in advance.
[0035]
Here, as is shown in FIG. 4, the flow rate calculating unit 24 outputs the flow rate of the
exhaust gas using, for example, the following procedure.
The flow rate calculating unit 24 determines whether or not the exhaust gas flow rate Qexh(t)
20 obtained from the first differential pressure detecting portion 22 or the second differential pressure
detecting portion 23 is less than a predetermined value (step S1). If the exhaust gas flow rate Qexh(t) is
less than the predetermined value, then the flow rate calculating unit 24 outputs the exhaust gas flow rate
Qexh(t) obtained from the first differential pressure detecting portion 22 as a measurement value (step S2).
If, on the other hand, as a result of the determination made in step S1, the exhaust gas flow rate Qexh(t) is
25 found to be greater than the predetermined value, the flow rate calculating unit 24 outputs the exhaust
gas flow rate Qexh(t) obtained from the second differential pressure detecting portion 23 as the
measurement value (step S3). The flow rate calculating unit 24 performs this processing sequence
either continuously or at regular intervals until the flow rate measurement is ended (step S4).
11
Note that it is also possible to determine whether or not to switch the differential pressure
detecting portion that is to be used by comparing the exhaust gas flow rate Qexh(t) with a flow rate
measurement range. For example, the exhaust gas flow rate Qexh(t) may be compared with the flow
rate measurement range of the first differential pressure detecting portion 22, and if the exhaust gas flow
5 rate Qexh(t) is equal to or greater than an upper limit value of this flow rate measurement range or than a
predetermined value in the vicinity of this upper limit value, then the differential pressure detecting
portion to be used may be switched to the second differential pressure detecting portion 23.
Alternatively, the exhaust gas flow rate Qexh(t) may be compared with the flow rate measurement range
of the second differential pressure detecting portion 23, and if the exhaust gas flow rate Qexh(t) is equal to
10 or less than a lower limit value of this flow rate measurement range or a second predetermined value in
the vicinity of this lower limit value, then the differential pressure detecting portion to be used may be
switched to the first differential pressure detecting portion 22. The aforementioned predetermined
value in the vicinity of the upper limit value and predetermined value in the vicinity of the lower limit
value can be set arbitrarily by a user.
15 [0036]
Moreover, the gas analyzer 3 continuously measures the concentrations of components
needing to be measured (for example, CO, CO2, NOX, and THC and the like) that are contained in the
exhaust gas. Note that if the gas analyzer 3 is one that measures the concentrations of CO and CO2,
then an NDIR detector that employs a non-dispersive infrared absorption method (an NDIR method)
20 can be used, while if the gas analyzer 3 is one that measures the concentration of NOX, then a CLD
detector that employs a chemiluminescence detection method (CLD) can be used. If the gas analyzer 3
is one that measures the concentration of THC, then an FID detector that employs a flame ionization
detection method (FID) can be used. The gas analyzer 3 may be equipped with any one of these
detectors, or may be equipped with any combination of these detectors. Additionally, the gas analyzer
25 3 may be one that uses a variety of analysis methods in accordance with the components to be measured.
[0037]
An intake pipe 6 that is used to introduce sampled exhaust gas is connected to the gas analyzer
3. One end portion of this intake pipe 6 is connected to the gas analyzer 3, while an exhaust gas
sampling unit 7 that samples exhaust gas is provided at another end portion of the intake pipe 6. The
12
exhaust gas sampling unit 7 is provided in the above-described attachment pipe 21 of the differential
pressure flow meter. This exhaust gas sampling unit 7 is formed by a sampling pipe that captures a
portion of the exhaust gas flowing through the attachment pipe 21. Note that the exhaust gas sampling
unit 7 is provided on the downstream side of the first and second differential pressure detecting portions
5 22 and 23 inside the attachment pipe 21, and does not affect the pressure detection performed by the first
and second differential pressure detecting portions 22 and 23 such as by causing pressure variations or
the like.
[0038]
A concentration signal for each component acquired by the gas analyzer 3 is transmitted to a
10 higher-order computing device 8, and is then used, together with flow rate signals output from the flow
rate calculating unit 24 of the differential pressure flow meter 2, for the calculation of the emission mass
of each component.
[0039]
15 (Effects provided by the present embodiment)
According to the exhaust gas analysis device 100 according to the present embodiment that
has the above-described structure, because the two differential pressure detecting portions 22 and 23
having mutually different flow rate measurement ranges are provided, it is possible to measure a broad
range of flow rates with a high degree of accuracy. In particular, by using the first differential pressure
20 detecting portion 22 to make the measurements on the low flow rate side and using the second
differential pressure detecting portion 23 to make the measurements on the high flow rate side, it is
possible to measure a broad range of flow rates with a high degree of accuracy.
Moreover, because this is not a structure in which a separate differential pressure detecting
portion 23 is disposed on the upstream side of the first differential pressure detecting portion 22, which
25 has a measurement range on the low flow rate side, the measurements made by the first differential
pressure detecting portion 22 are not affected by pressure variations caused by a separate differential
pressure detecting portion 23, so that it is possible for flow rates during low flow rate periods, such as
when, for example, a vehicle is idling, to be accurately measured.
Furthermore, because the two differential pressure detecting portions 22 and 23 are provided in
13
the single attachment pipe 21, it is possible to perform a flow rate measurement using the two differential
pressure detecting portions 22 and 23 simply by attaching this attachment pipe 21 to the exhaust pipe
EH. Here, because the exhaust gas sampling unit 7 is provided in the attachment pipe 21, attaching the
exhaust gas sampling unit 7 can also be easily performed.
5
[0040]
(Additional embodiments)
Note that the present invention is not limited to the above-described embodiment.
[0041]
10 For example, in the above-described embodiment, the two differential pressure detecting
portions 22 and 23 are disposed such that they mutually intersect each other when viewed from the flow
path direction, however, as is shown in FIG. 5, it is also possible for the two to be disposed in such a way
that they do not mutually intersect each other such as, for example, by disposing them in parallel with
each other when viewed from the flow path direction. In this case, there are no particular restrictions
15 regarding the positions of the first differential pressure detecting portion 22 and the second differential
pressure detecting portion 23 in the flow path direction, and the two differential pressure detecting
portions 22 and 23 may either be placed side-by-side, or the first differential pressure detecting portion
22 may be positioned on the downstream side of the second differential pressure detecting portion 23.
[0042]
20 Moreover, in the above-described embodiment, a structure in which the two differential
pressure detecting portions 22 and 23 are provided is described, however, it is also possible for three or
more differential pressure detecting portions to be provided.
[0043]
Furthermore, in the above described embodiment, a structure is employed in which the two
25 differential pressure detecting portions 22 and 23 have mutually different Pitot tubes, however, as is
shown in FIG. 6, it is also possible to provide the total pressure intake pipe portion 2P1 and the static
pressure intake pipe portion 2P2 of the first differential pressure detecting portion 22, as well as the total
pressure intake pipe portion 2P1 and the static pressure intake pipe portion 2P2 of the second differential
pressure detecting portion 23 in the same single Pitot tube 2P. By doing this, the internal structure of
14
the attachment pipe 21 can be simplified, pressure variations can be suppressed, and the measurement
accuracy can be improved.
[0044]
In the above-described embodiment a structure is employed in which at least two differential
5 pressure detecting portions are provided in a single attachment pipe, however, if a plurality of attachment
pipes are connected together in series then, in this structure, a single differential pressure detecting
portion may be provided in each attachment pipe. Namely, the differential pressure flow meter may
have two or more attachment pipes that are connected together in series, and a single differential
pressure detecting portion is provided in each one of these attachment pipes.
10 [0045]
In addition to this, in the above-described embodiment a case is described in which the
differential pressure flow meter is used in an exhaust gas analysis device, however, this differential
pressure flow meter may also be used in other types of analysis devices, or may be used by itself as an
independent differential pressure flow meter.
15 [0046]
Furthermore, it should be understood that the present invention is not limited to the abovedescribed
embodiments, and that various modifications and the like may be made thereto insofar as they
do not depart from the spirit or scope of the present invention.
20 [Description of the Reference Numerals]
[0047]
100 … Exhaust gas analysis device
2 … Differential pressure flow meter
21 … Attachment pipe
25 22 … First differential pressure detecting portion
23 … Second differential pressure detecting portion
2P … Pitot tube
2h1 … Total pressure holes
2h2 … Static pressure holes
15
24 … Flow rate calculating unit
3 … Exhaust gas analyzer
6 … Intake pipe
7 … Exhaust gas sampling unit
5 8 … Computing device
16
We Claim:
1. A differential pressure flow meter that detects differential pressures in a fluid body flowing
along a flow path, and calculates a flow rate of the fluid body from those differential pressures
5 comprising:
at least two differential pressure detecting portions having mutually different measurement
ranges.
2. The differential pressure flow meter as claimed in claim 1, wherein the at least two differential
10 pressure detecting portions are provided with a first differential pressure detecting portion and a second
differential pressure detecting portion, and
the first differential pressure detecting portion has a measurement range that is on the low flow
rate side of the second differential pressure detecting portion.
3. The differential pressure flow meter as claimed in claim 2, wherein the first differential
pressure detecting portion and the second differential pressure detecting portion detect a differential
pressure between a total pressure and a static pressure of the fluid body, and have a Pitot tube that is
provided with total pressure holes that are used to detect the total pressure, and static pressure holes that
are used to detect the static pressure, and
the total pressure holes and static pressure holes of the first differential pressure detecting
portion are larger than the total pressure holes and static pressure holes of the second differential pressure
detecting portion.
4. The differential pressure detecting portion as claimed in claim 2, wherein there is further
25 provided a flow rate calculating unit that, when the flow rate of the fluid body which has been obtained
using the first differential pressure detecting portion or the second differential pressure detecting portion
is less than a predetermined value, outputs the flow rate of the fluid body obtained by the first differential
pressure detecting portion as a measurement value, and when the flow rate of the fluid body which has
been obtained using the first differential pressure detecting portion or the second differential pressure
17
detecting portion is equal to or greater than a predetermined value, outputs the flow rate of the fluid body
obtained by the second differential pressure detecting portion as a measurement value.
5. The differential pressure flow meter as claimed in claim 2, wherein the first differential
5 pressure detecting portion is provided on an upstream side of the flow path, and the second differential
pressure detecting portion is provided on a downstream side of the flow path.
6. The differential pressure flow meter as claimed in claim 1, wherein there is provided an
attachment pipe that is attached to an aperture portion of an exhaust pipe, and forms a flow path along
10 which exhaust gas emitted from the exhaust pipe flows, and
the at least two differential pressure detecting portions are provided in the attachment pipe.
7. An exhaust gas analysis device comprising:
the differential pressure flow meter as claimed in claim 6; and
15 an exhaust gas analyzer that measures concentrations of predetermined components contained
in the exhaust gas, wherein
an exhaust gas sampling unit that samples the exhaust gas and guides it to the exhaust gas
analyzer is provided in the attachment pipe.
20 8. The exhaust gas analysis device as claimed in claim 7, wherein this exhaust gas analysis
device is capable of being mounted in a vehicle.
9. A flow rate measurement method employing a differential pressure flow meter that detects
differential pressures in a fluid body flowing along a flow path, and calculates a flow rate of the fluid
25 body from those differential pressures, and that has a first differential pressure detecting portion and a
second differential pressure detecting portion that each have mutually different measurement ranges, and
in which the measurement range of the first differential pressure detecting portion is on the low flow rate
side of the measurement range of the second differential pressure detecting portion, wherein,
when the flow rate of the fluid body which has been obtained using the first differential
18
pressure detecting portion or the second differential pressure detecting portion is less than a
predetermined value, the flow rate of the fluid body obtained by the first differential pressure detecting
portion is output as a measurement value, and when the flow rate of the fluid body which has been
obtained using the first differential pressure detecting portion or the second differential pressure detecting
5 portion is equal to or greater than a predetermined value, the flow rate of the fluid body obtained by the
second differential pressure detecting portion is output as a measurement value.

claims.
1.A differential pressure flow meter that detects differential pressures in a fluid body flowing
along a flow path, and calculates a flow rate of the fluid body from those differential pressures
5 comprising:
at least two differential pressure detecting portions having mutually different measurement
ranges.
2. The differential pressure flow meter as claimed in claim 1, wherein the at least two differential
10 pressure detecting portions are provided with a first differential pressure detecting portion and a second
differential pressure detecting portion, and
the first differential pressure detecting portion has a measurement range that is on the low flow
rate side of the second differential pressure detecting portion.
3. The differential pressure flow meter as claimed in claim 2, wherein the first differential
pressure detecting portion and the second differential pressure detecting portion detect a differential
pressure between a total pressure and a static pressure of the fluid body, and have a Pitot tube that is
provided with total pressure holes that are used to detect the total pressure, and static pressure holes that
are used to detect the static pressure, and
the total pressure holes and static pressure holes of the first differential pressure detecting
portion are larger than the total pressure holes and static pressure holes of the second differential pressure
detecting portion.
4. The differential pressure detecting portion as claimed in claim 2, wherein there is further
25 provided a flow rate calculating unit that, when the flow rate of the fluid body which has been obtained
using the first differential pressure detecting portion or the second differential pressure detecting portion
is less than a predetermined value, outputs the flow rate of the fluid body obtained by the first differential
pressure detecting portion as a measurement value, and when the flow rate of the fluid body which has
been obtained using the first differential pressure detecting portion or the second differential pressure
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detecting portion is equal to or greater than a predetermined value, outputs the flow rate of the fluid body
obtained by the second differential pressure detecting portion as a measurement value.
5. The differential pressure flow meter as claimed in claim 2, wherein the first differential
5 pressure detecting portion is provided on an upstream side of the flow path, and the second differential
pressure detecting portion is provided on a downstream side of the flow path.
6. The differential pressure flow meter as claimed in claim 1, wherein there is provided an
attachment pipe that is attached to an aperture portion of an exhaust pipe, and forms a flow path along
10 which exhaust gas emitted from the exhaust pipe flows, and
the at least two differential pressure detecting portions are provided in the attachment pipe.
7. An exhaust gas analysis device comprising:
the differential pressure flow meter as claimed in claim 6; and
15 an exhaust gas analyzer that measures concentrations of predetermined components contained
in the exhaust gas, wherein
an exhaust gas sampling unit that samples the exhaust gas and guides it to the exhaust gas
analyzer is provided in the attachment pipe.
20 8. The exhaust gas analysis device as claimed in claim 7, wherein this exhaust gas analysis
device is capable of being mounted in a vehicle.
9. A flow rate measurement method employing a differential pressure flow meter that detects
differential pressures in a fluid body flowing along a flow path, and calculates a flow rate of the fluid
25 body from those differential pressures, and that has a first differential pressure detecting portion and a
second differential pressure detecting portion that each have mutually different measurement ranges, and
in which the measurement range of the first differential pressure detecting portion is on the low flow rate
side of the measurement range of the second differential pressure detecting portion, wherein,
when the flow rate of the fluid body which has been obtained using the first differential
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