U.S. patent application number 10/466505 was filed with the patent office on 2005-01-20 for device for metering a urea soulution.
Invention is credited to Berger, Joachim, Brinz, Thomas, Mahr, Bernd, Ripper, Wolfgang.
Application Number | 20050011183 10/466505 |
Document ID | / |
Family ID | 7671032 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050011183 |
Kind Code |
A1 |
Ripper, Wolfgang ; et
al. |
January 20, 2005 |
Device for metering a urea soulution
Abstract
A device for metering urea solutions permitting a reliable
reduction of nitrogen oxides in the exhaust gas of an internal
combustion engine is provided. This is achieved by the fact that
the device for metering the urea solution includes a sensor unit
for monitoring one or more physical state variables of an
enzyme-free Urea solution.
Inventors: |
Ripper, Wolfgang;
(Stuttgart, DE) ; Berger, Joachim; (Winterbach,
DE) ; Mahr, Bernd; (Plochingen, DE) ; Brinz,
Thomas; (Bissingen unter der Teck, DE) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
7671032 |
Appl. No.: |
10/466505 |
Filed: |
September 9, 2004 |
PCT Filed: |
January 18, 2002 |
PCT NO: |
PCT/DE02/00148 |
Current U.S.
Class: |
60/286 |
Current CPC
Class: |
F01N 2900/1814 20130101;
F01N 3/2066 20130101; G01N 33/0009 20130101; Y02T 10/40 20130101;
F01N 2900/1818 20130101; F01N 2900/1811 20130101; F01N 11/00
20130101; F01N 2610/02 20130101; B01D 53/90 20130101; B01D 53/9495
20130101; Y02T 10/12 20130101 |
Class at
Publication: |
060/286 |
International
Class: |
F01N 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 19, 2001 |
DE |
101 02 237.9 |
Claims
What is claimed is:
1. A device for metering a urea solution, in particular for
spraying the urea solution into the exhaust gas stream of an
internal combustion engine, wherein a sensor unit is provided for
monitoring one or more physical state variables of an enzyme-free
urea solution using a physical measuring sensor (3, 6, 9).
2. The device as recited in claim 1, wherein the measuring sensor
(3, 6) is designed for detecting an electric state variable.
3. The device as recited in one of the preceding claims, wherein
the measuring sensor (3, 6, 7) is designed for detecting the pH,
the dielectric constant, and/or the conductance of the enzyme-free
urea solution.
4. The device as recited in one of the preceding claims, wherein
the measuring sensor (3, 6, 7) includes at least two
electrodes.
5. The device as recited in one of the preceding claims, wherein at
least one electrode (3, 6, 7) has a structure for increasing the
surface area.
6. The device as recited in one of the preceding claims, wherein
two electrodes (3, 6) have an intermeshing comb-like structure.
7. The device as recited in one of the preceding claims, wherein at
least one third electrode (7) is provided for detecting at least
one second electric state variable.
8. The device as recited in one of the preceding claims, wherein
the measuring sensor (9) is designed for detecting a
physicomechanical state variable.
9. The device as recited in one of the preceding claims, wherein
the measuring sensor (9) is designed for measuring the viscosity
and/or density of the enzyme-free urea solution.
10. The device as recited in one of the preceding claims, wherein a
vibration generator (9) is provided.
11. The device as recited in one of the preceding claims, wherein
the vibration generator includes a quartz oscillator (9) and/or a
piezoelectric crystal.
12. The device as recited in one of the preceding claims, wherein a
sensor unit (1) having a measuring sensor (3, 6, 7) for an electric
state variable of the urea solution and having a measuring sensor
(9) for a physicomechanical state variable is provided, an analyzer
unit being provided for determining the urea concentration from the
two measured values.
13. The device as recited in one of the preceding claims, wherein a
temperature sensor is provided.
14. The device as recited in one of the preceding claims, wherein a
filling level sensor is provided for a storage container.
15. The device as recited in one of the preceding claims, wherein
the filling level sensor is a measuring sensor according to one of
the preceding claims.
16. The device as recited in one of the preceding claims, wherein a
plurality of filling level sensors is provided.
17. An internal combustion engine having catalytic exhaust gas
treatment, wherein a device for metering a urea solution according
to one of the preceding claims is provided.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a device for metering a
urea solution.
BACKGROUND INFORMATION
[0002] To reduce nitrogen oxides in the exhaust gas of motor
vehicles, urea solution has in the past been sprayed into the
exhaust gas during catalytic reduction. Urea is broken down into
carbon dioxide and ammonia by chemical reaction on a hydrolysis
catalyst. Ammonia then reacts selectively with nitrogen oxides to
form nitrogen and water, thus removing nitrogen oxides from the
exhaust gas.
[0003] For reliable reduction of nitrogen oxides with a urea
solution, various parameters are important, in particular the urea
concentration in the aqueous solution.
[0004] Sensor applications known in the past for measuring the urea
concentration in the fields of medicine and biology have used
urease, which enzymatically and selectively breaks down urea to
form ammonia. Sensors then detect the influence of the ammonia on
the pH of the solution. Information regarding the urea
concentration is obtainable in this way.
[0005] One disadvantage of this method of measuring the
concentration of a urea solution is the instability of urease, in
particular in an environment where temperatures may vary greatly.
However, such temperature variations occur during use in motor
vehicles, so that previous sensors according to the related art are
not suitable for such an application.
[0006] Therefore, the object of the present invention is to propose
a device for metering urea solutions which may be used reliably for
reduction of nitrogen oxides, even under difficult conditions,
e.g., within broad temperature intervals.
SUMMARY OF THE INVENTION
[0007] Accordingly, a device according to the present invention for
metering urea is characterized in that a sensor unit is provided
for monitoring a physical state variable of an enzyme-free urea
solution. The sensor unit here preferably includes a measuring
sensor.
[0008] In this way, a measurement is possible directly on the basis
of the physical properties of urea in solution without intermediate
enzymatic breakdown. Accordingly, this measurement is not subject
to the instabilities to which an enzyme such as urease is
subject.
[0009] In an exemplary embodiment of the present invention, a
measuring sensor is provided for detecting one or more electric
state variables. Such a state variable may include, for example,
the pH, the dielectric constant and/or the conductance of the
solution. By measuring these or other electric state variables, it
is possible to obtain information regarding the properties of the
urea solution, e.g., its concentration. Measurement of these state
variables is comparatively unproblematical and in particular it is
possible to perform these measurements in situations of extreme
temperature variations.
[0010] Two electrodes may be provided to detect the electric state
variables, these electrodes protruding into the urea solution. By
applying an electric d.c. or a.c. voltage to the electrodes, it is
possible to determine directly the aforementioned electric state
variables, such as the pH, the dielectric constant, and/or the
conductance.
[0011] To improve the sensitivity of the measuring sensor the
electrodes may be provided with a structure which increases their
surface area. Such a surface area enlarging structure may be
achieved, e.g., by a comb-shaped design of the electrodes, which
additionally has the advantage that two electrodes designed in this
way may be arranged to intermesh, so that a small distance between
the two electrodes is adjustable simultaneously with a
comparatively large surface area. Due to the large surface area, in
particular in combination with the small distance, the test voltage
and/or test current may be reduced and therefore the control and
analyzing unit for a measuring sensor according to the present
invention may be designed with small dimensions. A separate
electrode may be provided for simultaneous determination of
multiple state variables, if necessary. For example, by using such
a third electrode, it is possible to determine the pH, while
another state variable, e.g., the dielectric constant, is
determined using the two aforementioned electrodes.
[0012] In an exemplary embodiment of the present invention, a
measuring sensor is provided for detecting one or more
physicomechanical state variables of the urea solution.
[0013] Such a physicomechanical state variable may be the viscosity
or density, for example.
[0014] Such physicomechanical state variables may be determined in
a traditional manner, e.g., by weighing the solution and/or a part
of the solution or by measuring the buoyancy of a displacement
body, etc. However, in an exemplary embodiment the
physicomechanical state variable is detected by a dynamic sensor.
Thus, a physicomechanical state variable may be measured with the
help of a vibration generator, for example. The behavior of the
urea solution when agitated with the help of mechanical vibration
depends to a significant extent on the physico-mechanical state
variables to be detected, e.g., the density or viscosity. In an
exemplary embodiment, this property may be detected directly on the
vibration generator itself by measurement technology, e.g., by
measuring the electric current, the frequency, etc.
[0015] A quartz oscillator may be used as the vibration generator.
However, any other known or future means for inducing mechanical
vibration is also conceivable. For example, a piezoelectric crystal
could also be used as well as a high-speed out-of-balance motor or
an electromagnetic coil in conjunction with a diaphragm based on
the loudspeaker principle.
[0016] In an exemplary embodiment, a sensor unit is provided with a
measuring sensor for an electric state variable and with a
measuring sensor for a physicomechanical state variable. The
measured values of the two measuring sensors are used in an
analyzer unit to determine the urea concentration in solution. By
analyzing two independent state variables, this yields the
possibility of a more accurate and more selective determination of
the urea concentration.
[0017] In addition, a device according to the present invention may
be combined with a temperature sensor. Since the state variables to
be determined may under some circumstances be dependent upon
temperature, correction of errors due to temperature variations is
possible through simultaneous measurement and consideration of
temperature in analysis of the state variable detected, e.g., for
determination of the urea concentration in solution.
[0018] In combination with a metering device for urea solution a
filling level sensor may be provided for measuring the degree of
filling of a storage container for the urea solution. In an
exemplary embodiment, such a filling level sensor is combined
directly with a measuring sensor according to the present invention
for detecting one or more physical state variables.
[0019] The measuring sensor according to an exemplary embodiment of
the present invention shows definite differences in the measurement
in solution in comparison with the measurement in the gas phase, so
a filling level may also be readily measured in this way. To do so,
various embodiments of the measuring sensor according to the
present invention are again conceivable. For example, a measuring
sensor according to the present invention may be mounted at a
certain filling level and used as a threshold value sensor as the
filling level passes the threshold value. For a more precise
filling level measurement at different filling levels, a plurality
of sensors may also be mounted at different levels. Such a sensor
system may be mounted, e.g., in a sensor housing which extends over
the corresponding height or on a rod-shaped sensor mount, for
example.
[0020] A continuous filling level measurement may be achieved by
designing the measuring sensor according to an exemplary embodiment
of the present invention to extend over a corresponding height. The
sensor signal here is a function of the ratio of sensor areas
situated in the gas phase or in the liquid solution. These sensor
areas in turn vary with the filling level, so that information
about the filling level is obtainable from the sensor signal in
this way.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 shows a schematic diagram of an exemplary embodiment
of a measuring sensor according to the present invention.
DETAILED DESCRIPTION
[0022] Sensor unit 1 is mounted on a sensor plate 2. A comb-shaped
electrode 3 is divided into two areas 4, 5. Individual teeth of the
comb structure are spaced farther apart in upper area 5 than in
lower area 4. In upper area 5, another electrode 6 engages with a
corresponding comb structure. The two electrodes 5 and 6 extend
over a large area of sensor plate 2 and constitute a filling level
sensor. A third electrode 7 is situated opposite lower area 4 of
electrode 3. The comb structure of electrode 7 corresponds to the
finer comb structure of lower area 4 of electrode 3, i.e., the
teeth are not as far apart.
[0023] Together with lower area 4 of electrode 3, electrode 7 forms
a measuring sensor according to an exemplary embodiment of the
present invention for measuring an electric state variable, e.g.,
the conductivity, the dielectric constant, etc.
[0024] Electric terminals 8 for electrodes 3, 6, 7 are provided in
the lower area of sensor plate 2. These electric terminals 8 may be
connected via a plug connector in a manner not shown in greater
detail here.
[0025] Beneath lower area 4 of electrode 3, i.e., beneath electrode
7, a quartz oscillator 9 is shown as an oscillation generator for
detecting a physicomechanical state variable, e.g., viscosity or
density. Quartz oscillator 9 is also contacted via terminals 8.
[0026] In an exemplary embodiment, sensor plate 2 may be designed
at least partially as a PC board on which the electrodes are
implemented in the form of flat printed conductors. In exemplary
embodiment, however, sensor plate 2 may function as a mounting
plate for mountable electrodes.
[0027] With the help of sensor unit 1 according to FIG. 1, one or
more electric state variables such as the dielectric constant, the
conductivity, the pH or the like, as well as one or more
physicomechanical state variables such as density or viscosity may
be detected. At the same time, sensor unit 1 also functions as a
filling level sensor because of the extent of upper area 5 of
electrode 3 and opposing electrode 6. Sensor unit 1 is therefore
mounted in the interior of a container for a urea solution, so that
electrodes 3 and 6 are at least partially immersed in the urea
solution.
[0028] With the help of sensor unit 1 according to the exemplary
embodiment of the present invention, it is possible to reliably
monitor the state of a urea solution even under adverse conditions,
e.g., over a wide temperature interval. Such a sensor unit 1 is
therefore suitable for use even in the area of exhaust gas
processing of motor vehicles.
[0029] List of Reference Numbers:
[0030] 1 sensor unit
[0031] 2 sensor plate
[0032] 3 electrode
[0033] 4 area
[0034] 5 area
[0035] 6 electrode
[0036] 7 electrode
[0037] 8 terminals
[0038] 9 quartz oscillator
* * * * *