U.S. patent application number 14/075481 was filed with the patent office on 2014-05-15 for method and device for calibrating an exhaust gas sensor.
This patent application is currently assigned to MAN Truck & Bus AG. The applicant listed for this patent is MAN Truck & Bus AG. Invention is credited to Andreas DOERING.
Application Number | 20140130569 14/075481 |
Document ID | / |
Family ID | 49326501 |
Filed Date | 2014-05-15 |
United States Patent
Application |
20140130569 |
Kind Code |
A1 |
DOERING; Andreas |
May 15, 2014 |
METHOD AND DEVICE FOR CALIBRATING AN EXHAUST GAS SENSOR
Abstract
A method for calibrating an exhaust gas sensor arranged in a
measurement chamber, includes providing a measurement chamber in or
adjacent to an exhaust channel of an internal combustion engine. At
the start of a calibration phase, exhaust gas present in the
measurement chamber is displaced by a filling of the measurement
chamber with calibration gas, and at the end of the calibration
phase, exhaust gas diffuses into and/or is introduced into the
measurement chamber.
Inventors: |
DOERING; Andreas; (MUENCHEN,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MAN Truck & Bus AG |
Muenchen |
|
DE |
|
|
Assignee: |
MAN Truck & Bus AG
Muenchen
DE
|
Family ID: |
49326501 |
Appl. No.: |
14/075481 |
Filed: |
November 8, 2013 |
Current U.S.
Class: |
73/1.06 |
Current CPC
Class: |
G01N 27/4175 20130101;
G01N 33/0006 20130101 |
Class at
Publication: |
73/1.06 |
International
Class: |
G01N 33/00 20060101
G01N033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2012 |
DE |
10 2012 021 928.8 |
Claims
1. A method for calibrating an exhaust gas sensor, wherein the
exhaust gas sensor is arranged in a measurement chamber in or
adjacent to an exhaust channel of an internal combustion engine,
the method comprising: displacing, at a start of a calibration
phase, exhaust gas present in the measurement chamber by filling
the measurement chamber with a calibration gas; and diffusing or
introducing exhaust gas into the measurement chamber at an end of
the calibration phase.
2. The method according to claim 1, wherein the step of filling
comprises introducing calibration gas into the measurement chamber
throughout the entire calibration phase so that a pressure in the
measurement chamber is maintained higher than a pressure
predominating in the exhaust channel.
3. The method according to claim 2, wherein during the calibration
phase, the measurement chamber is not completely screened from the
exhaust gas flow in the exhaust channel.
4. The method according to claim 1, further comprising, after the
end of the calibration phase, at least one of drawing and pressing
the exhaust gas into the measurement chamber.
5. The method according to claim 4, wherein, after the end of the
calibration phase, the exhaust gas is drawn into the measurement
chamber by a suction device.
6. The method according to claim 4, wherein after the end of the
calibration phase, the measurement chamber is connected fluidically
to a part of the exhaust system having a higher pressure than a
pressure in the measurement chamber, so that the exhaust gas is
pressed into the measurement chamber.
7. The method according to claim 1, wherein the internal combustion
engine is charged, and compressed fresh air from at least one
compressor is used as a calibration gas.
8. A device for calibrating an exhaust gas sensor, comprising: a
measurement chamber in which the exhaust gas sensor is arranged,
the measurement chamber being arranged one of in and adjacent to an
exhaust channel of an internal combustions engine; a screening
device selectively screening the measurement chamber from an
exhaust gas flow in the exhaust channel the screening device being
gas permeable at least part of the time; and a gas pipe connected
to the measurement chamber for exposing the measurement chamber to
a calibration gas.
9. The device according to claim 8, wherein the measurement chamber
is in the exhaust channel and consists of two perforated cylinders
arranged concentrically one inside the other, at least one of the
two perforated cylinders is movable about its longitudinal axis so
that the two cylinders form the screening device with a variable
screening effect.
10. The device according to claim 9, wherein the two perforated
cylinders each have at least two bores in cylinder walls of the two
perforated cylinders, wherein the two perforated cylinders are
movable from a non-aligned position into an aligned position to
open the measurement chamber to inflowing exhaust gas.
11. The device according to claim 8, wherein the measurement
chamber is directly adjacent to the exhaust channel and the
creening device comprises a gas-permeable membrane.
12. The device according to claim 8, further comprising a
controllable suction device connected to the measurement chamber,
and configured to draw the exhaust gas into the measurement chamber
after the end of the calibration phase.
13. The device according to claim 12, wherein the suction device
comprises a suction line and a controllable valve.
14. The device according to claim 8, wherein the measurement
chamber is connected fluidically to a part of the exhaust system
having a higher pressure than a pressure in the measurement
chamber, whereby the exhaust gas in the exhaust system is pressed
into the measurement chamber.
15. The device according to claim 14, wherein the exhaust gas is
extracted from the exhaust system one of upstream of an exhaust gas
turbine of an exhaust turbocharger, upstream of a choke device, and
upstream of a silencer.
16. The device according to claim 8, wherein the sensor is one of a
lambda sensor and an NO.sub.x sensor.
17. A vehicle with a device according to claim 8.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of DE 10 2012 021 928.8
filed Nov. 3, 2012, which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] The invention concerns a method for calibrating an exhaust
gas sensor and a device for calibrating an exhaust gas sensor.
[0003] To control the operation of internal combustion engines,
exhaust gas sensors are used which supply measurement signals to
the engine control system and/or to an exhaust gas aftertreatment
system. The exhaust gas sensors used are primarily lambda sensors
and. NO.sub.x sensors. To be able to perform an effective catalytic
reduction, for example by the controlled addition of urea, it is
necessary to determine the NO.sub.x emissions in the exhaust gas
flow from an internal combustion engine using NO.sub.x sensors. DE
101 00 420 A1 describes a method for controlling an exhaust gas
aftertreatment system in which a predefinable quantity of reducing
agent is supplied to the exhaust gas flow depending on the state of
the internal combustion engine and/or the exhaust gas
aftertreatment system.
[0004] To measure the oxygen content in the exhaust gas flow from
an internal combustion engine, lambda sensors are used which are
inserted as exhaust gas sensors in the exhaust system before and/or
after a catalytic converter.
[0005] The exhaust gas sensors used are subject to an ageing
process which means that during a lengthy operating period of an
exhaust gas sensor, the measurement curve changes as a function of
the operating period. To undertake calibration of a lambda sensor,
in vehicle engines it is known in principle to calibrate the lambda
sensor in overrun mode in which no exhaust gas is generated and the
lambda sensor is exposed to the aspirated ambient air. Provided
that the aspirated ambient air has an oxygen content of 20.942%, a
measurement value output by the lambda sensor can be corrected
accordingly if, because of a lengthy operating period, the lambda
sensor is supplying a measurement value deviating from the actual
value. Such a measurement value adaptation can be carried out for
example by applying a correction factor to the measurement value
output by the lambda sensor.
[0006] DE 10 2008 046 121 A1 discloses a method for calibrating an
exhaust gas sensor which is arranged in an exhaust pipe of an
internal combustion engine and protrudes laterally into an exhaust
channel. To calibrate the exhaust gas sensor, its measurement tip
is exposed to a passing flow of flushing air. This document also
mentions the possibility that a screening device can be guided at
the measurement tip in order to conduct the flushing air to the
measurement tip in a targeted fashion. In normal operating mode,
the screening device is removed from the exhaust pipe.
SUMMARY OF THE INVENTION
[0007] The invention is based on the object of specifying a method
for calibrating an exhaust gas sensor which allows calibration to
be performed as quickly and precisely as possible.
[0008] According to an embodiment of the invention, it is proposed
that at the start of the calibration phase, the exhaust gas present
in a measurement chamber in which the exhaust gas sensor is located
is displaced by a filling of the measurement chamber with
calibration gas, and that after the end of the calibration phase,
exhaust gas is diffused and/or introduced into the measurement
chamber. By a deliberate introduction of calibration gas with the
corresponding pressure, the exhaust gas present in the measurement
chamber before the calibration phase is quickly expelled therefrom.
Preferably then, during the calibration phase, at least a small
quantity of calibration gas is still conducted into the measurement
chamber, in order to ensure that no exhaust gas can penetrate the
measurement chamber. After the end of the calibration phase,
exhaust gas is again introduced directly into the measurement
chamber, whereby the calibration gas therein escapes from the
measurement chamber and normal measurement operation can be resumed
very quickly. In principle here any suitable gas can be used as
calibration gas. An embodiment variant is particularly preferred in
which, in connection with charged internal combustion engines,
compressed fresh air from at least one compressor is used as
calibration gas.
[0009] During the calibration phase it can be sufficient if the
measurement chamber is not completely screened or isolated from the
exhaust gas flow, as would be the case for example if valves were
used, if a constant supply of calibration gas to the measurement
chamber ensures that no exhaust gas can penetrate the measurement
chamber. An incomplete screening of the exhaust gas flow can be
achieved for example if the measurement chamber is screened from
the exhaust gas flow via a gas-permeable membrane, or if the
calibration gas quantity supplied to the measurement chamber and/or
the pressure predominating in the measurement chamber are so great
that no exhaust gas can penetrate the measurement chamber.
[0010] A particularly advantageous embodiment provides that after
the end of the calibration phase, exhaust gas is drawn and/or
pressed into the measurement chamber in order to flush the
measurement chamber rapidly. For this, after the end of the
calibration phase, exhaust gas can be drawn into the measurement
chamber by means of a suction device. Alternatively or also
additionally, it can be provided that after the end of the
calibration phase, the measurement chamber is connected fluidically
to a part of the exhaust system in which a higher pressure
predominates than in the measurement chamber, so that the exhaust
gas is pressed into the measurement chamber.
[0011] The invention is also based on the object of creating a
device for calibrating an exhaust gas sensor which allows a
reliable calibration that can be performed as quickly as
possible.
[0012] According to an embodiment of the invention, the exhaust gas
sensor lies in a measurement chamber which is screened from the
exhaust gas flow present in the exhaust channel by means of a
screening device which is gas-permeable for at least part of the
time. Calibration gas can be introduced into the measurement
chamber via a gas pipe connected to the measurement chamber. By
arranging the exhaust gas sensor in a measurement chamber which can
be arranged in or directly adjacent to the exhaust channel, a
controlled gas exchange in the measurement chamber can be achieved
in order for example to be able to initiate the calibration phase
very quickly. Calibration gas can then be fed into the measurement
chamber via a gas pipe with corresponding pressure, causing a rapid
displacement of the exhaust gas previously present in the
measurement chamber. For the calibration gas to be able to be
introduced into the measurement chamber, it is necessary for the
screening device to be gas-permeable for at least part of the
time.
[0013] A screening device which is gas-permeable for part of the
time can consist of two perforated cylinders arranged
concentrically one inside the other, of which at least one is
movable about its longitudinal axis to change the screening effect.
By rotation about its longitudinal axis, the perforations of the
cylinder can be brought into an aligned position or into a
non-aligned position.
[0014] In an aligned position, the cylinder side walls are
permeable to the exhaust gas flow so that this can flow through the
measurement chamber, If however the cylinders are turned so that
the perforations are not aligned, there is an at least largely
sealed screening from the exhaust gas flow. The measurement chamber
can then be filled with calibration gas in order to perform
calibration of the exhaust gas sensor arranged in the measurement
chamber.
[0015] The perforations in the cylinder walls can be formed as
bores offset by 180.degree., This gives a measurement chamber which
is formed by concentrically arranged cylinders and which has a
relatively simple and reliable structure.
[0016] The measurement chamber can also be arranged directly
adjacent to the exhaust channel of an internal combustion engine,
wherein gas can be introduced into and extracted from the
measurement chamber via a gas-permeable membrane which forms a
screening device. Calibration gas can be introduced into the
measurement chamber via a gas pipe connected to the measurement
chamber, wherein exhaust gas present in the measurement chamber is
then displaced into the exhaust channel through the gas-permeable
membrane. During the calibration phase, a certain quantity of
calibration gas can be introduced continuously into the measurement
chamber to ensure that no exhaust gas penetrates the measurement
chamber through the gas-permeable membrane. At the end of the
calibration phase, the supply of calibration gas is stopped so that
exhaust gas can again penetrate the measurement chamber via the
gas-permeable membrane.
[0017] To achieve an accelerated penetration of exhaust gas into
the measurement chamber, exhaust gas can also be drawn from the
exhaust channel through the gas-permeable membrane via a suction
line connected to the measurement chamber. The suction process can
be carried out by means of a controllable suction device which for
example can consist of a suction line--already present in any
case--from an engine aspiration system, and a controllable valve in
a suction line leading to the measurement chamber. Alternatively or
in some cases also additionally, it can be provided that the
measurement chamber is connected fluidically to a part of the
exhaust system in which a higher pressure predominates than in the
measurement chamber, so that the exhaust gas is pressed into the
measurement chamber. Preferably here the exhaust gas is extracted
upstream of an exhaust gas turbine of an exhaust turbocharger
and/or upstream of a choke device and/or upstream of a
silencer.
[0018] The invention is explained in more detail below with
reference to exemplary embodiments shown in the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In the drawings
[0020] FIG. 1 is a schematic depiction of an internal combustion
engine with an exhaust gas aftertreatment system, in which an
exhaust gas sensor is connected to the exhaust channel,
[0021] FIG. 2 is a schematic depiction of an arrangement of an
exhaust gas sensor in a measurement chamber adjacent to an exhaust
channel,
[0022] FIG. 3 is a schematic depiction of a measurement chamber
which is formed in an exhaust channel and has an exhaust gas
sensor,
[0023] FIG. 4 is a section view along section line A-A in the
region of the measurement chamber in FIG. 3 which is formed by two
cylinders arranged one inside the other,
[0024] FIG. 5 is a section view along section line A-A as in FIG.
4, but with an inner cylinder rotated through 90.degree., and
[0025] FIG. 6 is a schematic depiction of an alternative variant of
the embodiment shown in FIG. 1 with which, after the end of the
calibration phase, exhaust gas can be pressed into the measurement
chamber.
[0026] FIG. 1 shows an internal combustion engine 1 with an exhaust
turbocharger 2, to which an exhaust channel 4 is connected which
leads to a catalytic converter 3. Downstream of the catalytic
converter 3 is an exhaust channel 5, adjacent to which is a
measurement chamber 6 with an exhaust gas sensor 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The measurement chamber 6, as shown in FIG. 2, is connected.
fluidically to the exhaust channel 5 via a gas-permeable membrane 8
(FIG. 2). To be able to introduce calibration gas into the
measurement chamber 6, a gas pipe 9 is connected to the measurement
chamber 6, via which for example air as a calibration was can be
fed according to the direction of arrow 10 via a controllable valve
11. On the output. side the air is extracted from a compressor 12
belonging to the turbocharger 2, and enters the measurement chamber
6 when valve 11 is open. The compressor 12 here serves as the
pressure generator and is part of the exhaust turbocharger 2 which
is driven by exhaust gas from the internal combustion engine 1 via
the turbine 13 of the turbocharger 2.
[0028] The calibration gas, for example air, supplied. by the
compressor to the measurement chamber 6 can be used to calibrate a
lambda sensor where fitted, whereas in the case of other sensors
such as for example NOx, NH3 or soot sensors, it can be used to
determine the zero point.
[0029] In the embodiment example of FIG. 1, a further calibration
gas with a predefined composition can be fed into the measurement
chamber 6 via the gas pipe 9 via a second controllable valve 14. In
this case the valve 11 is closed. The calibration gas for example
has a predefined NO.sub.x concentration, whereby for example a
correction factor can be determined for an exhaust gas sensor
formed as an NO.sub.x sensor if the measurement value determined by
the exhaust gas sensor deviates from the actual value of the
NO.sub.x concentration supplied.
[0030] FIG. 2 shows in enlarged view the region where the
measurement chamber 6 borders the exhaust channel 5. An exhaust gas
sensor 7, connected electrically to a measurement system not shown
in more detail, protrudes into the measurement chamber 6. Also the
gas pipe 9 shown in FIG. 1 and a further suction line 15 are
connected to the measurement chamber 6. The measurement chamber 6
is partly screened from the exhaust gas, which flows through the
exhaust channel 5 in the arrow direction 16, by a gas-permeable
membrane 8 forming a screening device.
[0031] If air or another calibration gas is fed into the
measurement chamber 6 via gas pipe 9 according to the arrow
direction 17, wherein the suction line 15 is blocked by a closed
valve 18, this has the consequence that exhaust gas present is
displaced from the measurement chamber 6 into the exhaust channel 5
through the membrane 8. Then only air or calibration gas is still
present in the measurement chamber 6, so that a calibration
measurement can be performed.
[0032] To end the calibration phase in the exemplary embodiment
shown. according to FIG. 2, exhaust gas is drawn into the
measurement chamber 6 through the membrane 8 via suction line 15
when the valve 18 is open. The gas pipe 9 is now blocked. By
drawing exhaust gas into the measurement chamber 6, the exhaust gas
sensor 7 is quickly fully exposed to exhaust gas and the exhaust
gas sensor can again be used for exhaust gas measurement in normal
measurement operation.
[0033] The embodiment according to FIG. 6 shows an alternative, or
in some cases also an additional, possibility to the embodiment in
FIG. 1 for filling the measurement chamber with exhaust gas,
wherein after the end of the calibration phase the exhaust gas is
pressed into the measurement chamber. For this it is advantageous
to extract exhaust gas at a point at which a higher exhaust gas
back pressure predominates, so that the exhaust gas is pressed into
the measurement chamber because of the pressure difference. In the
case of internal combustion engines 1 with exhaust gas charging, it
is therefore suitable to extract the exhaust gas upstream of the
exhaust turbine 13, since here a significantly higher pressure
predominates than downstream of the exhaust turbine 13. The
extraction is preferably controlled or regulated by means of a
controllable valve 14'. However extraction upstream of choke points
or fittings which raise the back pressure, such as silencers,
catalytic converters or choke flaps, is in principle possible and
conceivable. The duration and frequency of the calibration phases
can be set or modified depending on the operating state of the
internal combustion engine and/or the exhaust gas aftertreatment
system.
[0034] FIG. 3 shows a preferred embodiment of a measurement chamber
19 which is arranged in an exhaust channel 5 and formed by two
perforated cylinders 20, 21 arranged concentrically one inside the
other. The exhaust gas sensor 7 protrudes into the measurement
chamber 19. A gas pipe 9 is connected to the measurement chamber
19, via which air or flushing gas or calibration gas can be
conducted into the measurement chamber 19. The gas pipe 9 can be
closed by means of a controllable valve 11.
[0035] In the exemplary embodiment shown, the outer cylinder 20 and
the inner cylinder 21 each have bores 22, 23 arranged offset by
180.degree. (FIG. 4). In FIG. 3 these bores 22, 23 as in the
section view in FIG. 4--are arranged non-aligned so that the
measurement chamber 19 is blocked to the exhaust gas flow. The
inner cylinder 21 can however be rotated by 90.degree., according
to the double arrow shown, into a position shown in FIG. 5. In this
position the bores 22, 23 align so that a part of the exhaust gas
can flow into and through the measurement chamber 19. In the
position shown in FIG. 5, the measurement chamber 19 is open to the
exhaust gas flow so that the exhaust gas sensor 7 can perform an
exhaust gas measurement for the oxygen proportion or NO.sub.x
concentration. If however the inner cylinder 21 is in the position
shown in FIG. 4, the system is in a calibration phase in which
calibration gas can be introduced into the measurement. chamber 19
via the gas pipe 9.
[0036] A further suction line (not shown here) can be connected to
the measurement chamber 19 in order to be able to introduce gas via
the gas pipe 9 unhindered when the measurement chamber 19 is
closed. The cylinders 20, 21 can however also have gas-permeable
regions to allow the accelerated introduction of gas.
* * * * *