U.S. patent application number 10/479696 was filed with the patent office on 2004-09-16 for device and method for metering a reductant for eliminating nitrogen oxides from exhaust gases.
Invention is credited to Scharsack, Cord.
Application Number | 20040177606 10/479696 |
Document ID | / |
Family ID | 7687620 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040177606 |
Kind Code |
A1 |
Scharsack, Cord |
September 16, 2004 |
Device and method for metering a reductant for eliminating nitrogen
oxides from exhaust gases
Abstract
A method and a device are proposed for metering a reducing
agent, in which means are provided for supplying the reducing agent
into a catalytic converter system via a line, for the removal of
nitrogen oxides from the exhaust gases, particularly of a Diesel
engine, at the end of the line a metering means, especially a
metering valve, being situated, and means being provided for
regulating the pressure of the reducing agent in the line; the
means for regulating the pressure (11, 12, 13; 11, 52, 70; 11, 13,
100) and/or the metering means (7; 120) being able to interact with
a pressure recording element (12; 70; 100) which records pressure
changes on the output side of the metering means facing away from
the line, so that the pressure changes influence the pressure
regulation and the metering.
Inventors: |
Scharsack, Cord;
(Schoenaich, DE) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
7687620 |
Appl. No.: |
10/479696 |
Filed: |
April 29, 2004 |
PCT Filed: |
May 18, 2002 |
PCT NO: |
PCT/DE02/01800 |
Current U.S.
Class: |
60/286 ;
60/301 |
Current CPC
Class: |
F01N 2610/02 20130101;
F01N 2610/14 20130101; F01N 3/2066 20130101; F01N 2390/06 20130101;
Y02T 10/12 20130101; F01N 2610/1473 20130101; F01N 2390/04
20130101 |
Class at
Publication: |
060/286 ;
060/301 |
International
Class: |
F01N 003/00; F01N
003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2001 |
DE |
101 27 834.9 |
Claims
What is claimed is:
1. A device for metering a reducing agent, particularly urea or a
urea/water solution, having means for supplying the reducing agent
into a catalytic converter system via a line for removing nitrogen
oxides from the exhaust gases, especially of a Diesel engine, a
metering means, particularly a metering valve, being situated at
the end of the line, having means for regulating the pressure of
the reducing agent in the line, wherein the means for regulating
the pressure (11, 12, 13; 11, 52, 70; 11, 13, 100) and/or the
metering means (7; 120) are able to interact with a pressure
recording element (12; 70; 100) which records pressure changes at
the output side of the metering means facing away from the line, so
that the pressure changes have an influence on the pressure
regulation and the metering.
2. The device as recited in claim 1, wherein the difference or the
quotient of the value of the pressure in the line and the pressure
on the output side of the metering means facing away from the line
is kept constant.
3. The device as recited in one of the preceding claims, wherein
the means for regulating the pressure include a relief valve
(11).
4. The device as recited in claim 3, wherein the relief valve has a
pneumatic connection (13); the pressure recording element has an
additional line (12) connected to the relief valve; and the line is
connected to the pneumatic connection.
5. The device as recited in one of the preceding claims, wherein
the pressure recording element has a pressure sensor (70).
6. The device as recited in claim 5, wherein the pressure sensor is
connected to a regulator, especially to a regulator (52) integrated
into a control unit (40) which is able to control the means for
regulating the pressure and/or the metering means as a function of
the pressure changes.
7. The device as recited in one of the preceding claims, wherein
the metered reducing agent supply goes into a mixing chamber (8) to
form an aerosol, so that the aerosol is able to be introduced into
the catalytic converter system (30) via an aerosol line (25).
8. The device as recited in claim 7, wherein means (20, 21, 22, 23,
24, 63) are provided for metering an air supply into the mixing
chamber (8).
9. The device as recited in one of claims 1 through 6, wherein the
metering means are mounted on an exhaust gas pipe that leads to the
catalytic converter system, the output side of the metering means
facing away from the line penetrating into the exhaust gas
pipe.
10. A method for metering a reducing agent, particularly urea or a
urea/water solution, the reducing agent being supplied in a metered
manner to a catalytic converter system, while the pressure of the
reducing agent is regulated, for the removal of nitrogen oxides
from the exhaust gases, especially of a Diesel engine, with the aid
of a metering means, particularly a metering valve, wherein the
pressure changes are recorded at the side of the metering means
facing the catalytic converter system and have an influence on the
pressure regulation and/or the control of the metering means.
Description
BACKGROUND INFORMATION
[0001] The present invention relates to a device and a method for
metering a reducing agent, particularly of urea or a urea-water
solution within the scope of a catalytic exhaust gas treatment,
according to the species defined in the independent claims.
[0002] In order to achieve a reduction in NO.sub.x components in
exhaust gases, reduction catalysts were developed, particularly for
Diesel engines, which are commonly subdivided into SCR catalysts
(selective catalytic reduction) and storage catalysts. The
so-called SCR catalysts reduce the nitrogen oxides by the use of a
reducing agent, such as urea and/or ammonia, which is added to the
exhaust gas, while the so-called storage catalysts are periodically
regenerated, preferably using hydrocarbons of the internal
combustion engine fuel that is carried along with it, in so-called
exhaust gas rich phases.
[0003] From German Patent Application DE 199 47 198 a device is
known which meters in urea as the reducing agent, to remove
nitrogen oxides in exhaust gases, such as from a Diesel engine. The
metering is performed via a valve which releases urea doses, which
are determined by the electrical control of the metering valve, its
throttling cross section and the pressure difference prevailing at
the throttle valve. The pressure prevailing before the valve is
measured and held constant within a tolerance range.
SUMMARY OF THE INVENTION
[0004] By contrast, the metering device according to the present
invention and the method according to the present invention, having
the characterizing features of the independent claims, have the
advantage of making possible a compensation of manufacturing
tolerances of the metering pipe and the metering line with respect
to metering accuracy, of maintaining metering accuracy in the case
of metering pipe outlet openings that are wearing and/or being
stopped up, and of eliminating the influence of the exhaust gas
counterpressure on the metering accuracy. Furthermore, no new
plotting of a valve characteristic curve is required in the control
unit, independently of the special design of the metering pipe and
the metering line, so that time advantages come about in the
application of the present invention.
[0005] Advantageous further refinements and improvements of the
method and the metering device described in the independent claims
are made possible by the measures described in the dependent
claims.
[0006] It is particularly advantageous to set a constant pressure
difference across the metering agent or rather, the metering valve,
so that the difference in the pressure before and after the
metering agent remains constant, independent of the metering
quantity and independent of changing environmental conditions.
Alternatively, in an advantageous manner, a constant pressure ratio
across the metering agent or the metering valve can be set, so that
the quotient of the reducing agent pressure upstream of the
metering agent and the pressure downstream of the metering agent
remains constant. This ensures a steady metering accuracy, so that
both an ammonia breakthrough as a result of overmetering and a loss
in nitrogen oxide conversion as a result of undermetering are
certainly able to be avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Exemplary embodiments of the present invention are shown in
the drawings and explained in greater detail in the following
description. The figures show:
[0008] FIG. 1 a metering system, connected together to a compressed
air tank, a urea tank and a catalytic converter system, and
[0009] FIG. 2 a corresponding system having an alternative metering
device.
[0010] FIG. 3 shows a control circuit diagram and
[0011] FIG. 4 shows another alternative metering device.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0012] In FIG. 1, 1 denotes a urea tank, from which a urea/water
solution is conveyed, via a urea line 1a having a check valve 2 and
a filter 3 designed as a filtering strainer, sucked in by a
metering pump 4 that is controlled by the engine speed, and via a
check valve 6 to a metering valve 7 of a mixing chamber 8. A
quantity that is conveyed in excess is returned via a relief valve
11 and a return line 1b provided with a check valve 2a to the
intake side of the pump. A relief valve is known, for example, from
DE 198 05 070 C2. In FIG. 1 of DE 198 05 070 C2, such a valve is
furnished with reference numeral 5 and is designated there as a
diaphragm valve, since a diaphragm separates a first chamber
conveying the fluid, whose pressure is to be controlled, from a
second chamber having a spring. This spring presses on the
diaphragm against an outlet opening that carries off excess
quantities of fluid, which is situated in the first chamber. The
second chamber (reference numeral 20 in DE 198 05 070 C2) is also
able to have pressure applied to it via lines, so that the pressure
that is to be set via the relief valve may be varied. This can be
performed hydraulically, as described in DE 198 05 070 C2, or
pneumatically. The connection of such a line to the relief valve is
denoted in the present Application as pneumatic connection 13. To
pneumatic connection 13 is connected a line 12, such as in the form
of a hose, whose other end is connected to mixing chamber 8, so
that relief valve 11 is able to control the pressure of the
urea/water solution in line 1a as a function of the pressure in the
mixing chamber. Between relief valve 11 and metering pump 4, a
pressure damper or pulsation damper 5 is connected to line 1a. From
an air pressure container 20, air pressure is able to be introduced
into the mixing chamber via an air pressure line 24 having a
pressure limiter 21, a two-way valve 22 and a check valve 23. An
aerosol line 25 goes from mixing chamber 8 to catalytic converter
30, which has an exhaust gas supply 29 on one side and an exhaust
gas outlet 31 on the other side. Urea tank 1 is provided with a
fluid level sensor 62 and a temperature sensor 61. Temperature
sensors 64 and 65 measure the temperature of the exhaust gas at the
inlet and the outlet of catalytic converter 30. Furthermore, a
pressure sensor 63 is provided between two-way valve 22 and check
valve 23. A controller 40 is connected electrically both to sensors
61 to 65 and to metering valve 7. Via a CAN data line 41 (CAN is
short for "controlled area network"), controller 40 is connected to
the voltage supply and to additional electronic components in the
motor vehicle, especially to the engine control unit.
[0013] Metering valve 7 meters the required urea/water solution
into mixing chamber 8. In the mixing chamber, an aerosol and a wall
film are generated by the compressed air being applied to the
urea/water solution which are introduced into catalytic converter
30 via aerosol line 25. In this context, controller 40 records
signals which are received by a superordinated engine control unit
via CAN data line 39 as well as the signals from pressure,
temperature and fluid level sensors 61 to 65, which are known per
se, and are not explained in greater detail here. Valve 22
regulates the pressure in the compressed air line. From the sensor
data, controller 40 computes a urea metering quantity that is to be
added to an exhaust gas flowing through catalytic converter 30. To
do this, the controller uses data on the engine operating state
supplied from the engine control unit via data line 41, as well as
sensor data originating from the metering device and the catalytic
converter. Depending on its construction, the pressure in mixing
chamber 8 may vary as a function of the selected dimensions of line
25 and of the metering pipe reaching in to the exhaust gas tract,
and of the geometry and the number of outlet openings on the
metering pipe. In addition, the exhaust gas counterpressure also
influences the pressure in the mixing chamber, for example, as a
result of a particulate filter situated downstream from catalytic
converter 30. Such influences on the mixing chamber pressure may be
dependent upon conditions of manufacturing, the application
involved, the wear occurring or the process. Now, hose line 12
ensures that, independently of these influences, the metering
quantity provided by the controller is actually injected into the
exhaust gas tract: for if an increased mixing chamber pressure is
present at the relief valve via the hose line, this regulates the
pressure in line 1a to a higher value and to the extent that the
difference of the pressures before and after the metering valve
remain constant or that the ratio of the pressures before and after
metering valve 7 remains constant.
[0014] Alternatively, the metering device may also be used without
the support of compressed air, i.e. without using components 20 to
24 and 63.
[0015] FIG. 2 shows an additional, alternative specific embodiment,
in which the same components as in FIG. 1 are given the same
reference numerals. In comparison to FIG. 1, relief valve 11 has no
pneumatic connection connected to the mixing chamber via a line.
Instead, controller 40 has a regulator 52 that is electrically
connected to relief valve 11 via a line 51, and it is integrated
into the controller as software. Furthermore, a pressure sensor 70
detects the pressure in mixing chamber 8 and conducts its pressure
signals on to regulator 52.
[0016] An adjustment of the reducing agent pressure in line 1a
takes place here by electrical control of the relief valve, at
increased pressure in the mixing chamber the relief valve first
returning an excess quantity of reducing agent into tank 1 via line
1b at a corresponding increased pressure in line 1a, so that the
pressure difference and the ratio of the pressures before and after
metering valve 7 remain constant.
[0017] An adjustment of the metering quantity of urea/water
solution can be made alternatively or in combination with
electrical control of the relief valve by correction
characteristics maps, stored in regulator 52, for the variation of
the metering valve control. Metering valve 7 is controlled by the
control unit as soon as there is a requirement for reducing agent
in the exhaust gas tract. In this connection, the metering takes
place in pulsed form, so that an on/off ratio can be defined, which
is derived from the ratio of the time durations of closed valve
states to open valve states during the time of the control.
Regulator 52 is able to vary this on/off ratio as a function of the
measured pressure prevailing in the mixing chamber. If the pressure
in the mixing chamber increases for any reason mentioned before,
the proportion of the time of open valve states is increased, so
that in spite of the increased counterpressure, the metering valve
is able to inject the required metering quantity into the mixing
chamber. FIG. 3 shows an exemplary control algorithm for this.
According to FIG. 3, regulator 52 processes an on/off ratio value
80 proportional to the T, by a conversion unit 85 determining the
setpoint pressure value in the mixing chamber that results from a
currently present on/off ratio value (such as via a stored linear
function). As is symbolically represented in summation node 87,
from this setpoint pressure value, mixing chamber actual value 86
is subtracted, which is reported to regulator 52 by pressure sensor
70. The difference value is supplied to a correction value
computing unit 88, which, as a function of the difference value,
determines a correction value for the on/off ratio. The stored
correction characteristics curve required for this, in a diagram in
which the correction values are plotted along the ordinate and the
difference values along the abscissa, has, for instance, the shape
of a straight line going through the origin and having a negative
slope, for difference values that are large in absolute value, the
straight line going over into curve sections having a low slope in
absolute value or a slope of zero. As symbolized by branching node
81 and line 82, the correction value is added in summation node 83
to currently set on/off ratio value 80, so that regulator 52 is
able to set, via line 51, a correcting on/off ratio 84 at relief
valve 11.
[0018] FIG. 4 illustrates a metering device which, in modification
of a system as shown in FIG. 1, has neither means for metering air
nor a mixing chamber. The metering valve, here given reference
numeral 120, is mounted directly on exhaust gas pipe 110 that leads
to catalytic converter 30, so that its opening penetrates directly
into the exhaust gas tract. Pneumatic connection 13 of relief valve
11 is connected via a hose line 100 to exhaust gas pipe 110.
[0019] Analogous to the system shown in FIG. 1, relief valve 11
sets the pressure in line 1a as a function of the pressure
prevailing after metering valve 120, the pressure in exhaust gas
pipe 110.
[0020] Alternatively to hose connection 100, the solution may also
be applied that uses a regulator 52 connected to a pressure sensor
corresponding to FIG. 2, the pressure sensor measuring the pressure
in exhaust gas pipe 110. The guiding magnitude in controller 52 is
then not the mixing chamber pressure, but rather the exhaust gas
counterpressure prevailing in the exhaust gas pipe.
* * * * *