U.S. patent application number 12/596151 was filed with the patent office on 2010-06-17 for device for use in exhaust aftertreatment system.
This patent application is currently assigned to VOLVO LASTVAGNAR AB. Invention is credited to Arne Andersson, Lennart Andersson.
Application Number | 20100146946 12/596151 |
Document ID | / |
Family ID | 39864153 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100146946 |
Kind Code |
A1 |
Andersson; Arne ; et
al. |
June 17, 2010 |
DEVICE FOR USE IN EXHAUST AFTERTREATMENT SYSTEM
Abstract
A device for use in an exhaust aftertreatment system for an
internal combustion engine is provided. The device comprises a
particulate filter system having a particulate filter (DPF) for the
collection of particles from the engine and a heating unit for the
intermittent burning of soot at a temperature suitable for soot
combustion. The particulate filter system is arranged to switch
between an operating mode for the collection of soot and an
operating mode for active regeneration. A bypass line extends
between the inlet and outlet of the particulate filter system. A
valve disposed in the bypass line allows opening or closing of an
exhaust gas flow through the bypass line, in dependence on the
operating mode of the particulate filter system, by a control
member.
Inventors: |
Andersson; Arne; (Molnlycke,
SE) ; Andersson; Lennart; (Varberg, SE) |
Correspondence
Address: |
WRB-IP LLP
1217 KING STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
VOLVO LASTVAGNAR AB
Goteborg
SE
|
Family ID: |
39864153 |
Appl. No.: |
12/596151 |
Filed: |
April 16, 2007 |
PCT Filed: |
April 16, 2007 |
PCT NO: |
PCT/SE07/00354 |
371 Date: |
January 10, 2010 |
Current U.S.
Class: |
60/287 ;
60/295 |
Current CPC
Class: |
F01N 2570/14 20130101;
F01N 9/002 20130101; F01N 2610/03 20130101; F01N 3/032 20130101;
Y02T 10/40 20130101; F01N 2900/1606 20130101; Y02T 10/47 20130101;
F01N 3/023 20130101; F01N 3/2882 20130101; F01N 2410/04 20130101;
F01N 2900/1406 20130101; F01N 3/20 20130101; F01N 3/025 20130101;
F01N 2240/36 20130101; F01N 13/02 20130101; F01N 2900/1404
20130101; F01N 3/021 20130101; F01N 3/106 20130101 |
Class at
Publication: |
60/287 ;
60/295 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/00 20060101 F01N003/00 |
Claims
1. A device for use in an exhaust aftertreatment system for an
internal combustion engine, comprising a particulate filter system
having a particulate filter (DPF) for the collection of particles
from the engine and a heating unit for the intermittent burning of
soot at a temperature suitable for soot combustion, the particulate
filter system being arranged to switch between an operating mode
for the collection of soot and an operating mode for active
regeneration, a bypass line extending between the inlet and outlet
of the particulate filter system, a valve disposed in the bypass
line, which allows opening or closing of an exhaust gas flow
through the bypass line, and a control member for operating the
valve in dependence on the operating mode of the particulate filter
system, so that the valve is open when the heating unit is
activated and closed when the particulate filter has cooled down
after such activation of the heating unit.
2. The device as claimed in claim 1, wherein the valve is a
so-called on/off valve, the bypass line being configured such that
the part-flow through this line is sufficient so that, in the
regeneration of the DPF system, the temperature in the exhaust line
downstream of this system is kept at a suitable level.
3. The device as claimed in claim 1, wherein the bypass line
contains a laminar flow resistor.
4. The device as claimed in claim 1, wherein the valve is
adjustable between different control positions.
5. The device as claimed in claim 4, wherein the valve is
adjustable in steps.
6. The device as claimed in claim 4, wherein the valve is
steplessly adjustable.
7. The device as claimed in claim 4, wherein a NOx-reducing
catalyst placed downstream of the particulate filter.
8. The device as claimed in claim 1, wherein the heating unit
comprises a fuel injector.
9. The device as claimed in claim 1, wherein the heating unit
comprises a burner.
10. The device as claimed in claim 9, wherein the heating unit
additionally comprises an oxidation catalyst.
11. The device as claimed in claim 2, wherein the bypass line
contains a laminar flow resistor.
12. The device as claimed in claim 2, wherein the valve is
adjustable between different control positions.
13. The device as claimed in claim 12, wherein the valve is
adjustable in steps.
14. The device as claimed in claim 12, wherein the valve is
steplessly adjustable.
15. The device as claimed in claim 12, wherein a NOx-reducing
catalyst placed downstream of the particulate filter.
16. The device as claimed in claim 2, wherein the heating unit
comprises a fuel injector.
17. The device as claimed in claim 2, wherein the heating unit
comprises a burner.
18. The device as claimed in claim 8, wherein the heating unit
additionally comprises an oxidation catalyst.
Description
BACKGROUND AND SUMMARY
[0001] The present invention relates to a device for use in an
exhaust aftertreatment system for an internal combustion engine,
comprising a particulate filter system having a particulate filter
(DPF) for the collection of particles from the engine and a heating
unit for the intermittent burning of soot at a temperature suitable
for soot combustion, the particulate filter system being arranged
to switch between an operating mode for the collection of soot and
an operating mode for active regeneration.
[0002] New emission requirements for diesel engines for heavy-duty
vehicles such as trucks and buses mean that particulate filters
which catch soot particles will begin to be used in the exhaust
system. These filters may need to be cleaned of soot by a raising
of the temperature so that the soot burns up. This generates
exhaust gases with high temperature, which can be harmful to the
environment in closed traffic environments, for example
terminals.
[0003] Given forthcoming emission requirements, Nox-reducing
catalysts will also be required in the exhaust system. If these are
placed after the particulate filter, they may become damaged by the
temperature produced by the soot combustion.
[0004] Various methods for avoiding harmfully high temperatures at
the outlet from a DPF system are known. For example, the DPF system
can be placed downstream of other exhaust aftertreatment systems. A
drawback with this method is that soot can disturb the functioning
in the NOx-reducing system. The problem of exhaust gases with high
temperature which can be harmful to the environment remains with
this method. Another method is to lead the exhaust gases past a
following exhaust aftertreatment system via a bypass line. Here
too, the problem of exhaust gases with high temperature which cap
be harmful to the environment remains.
[0005] WO2006/126922 describes a system with the intention of
keeping the temperature down after the DPF in soot regeneration. In
this, the intake air of the engine is mixed with the exhaust gas
from the DPF. A drawback with this solution is that it can affect
the engine characteristics as a result of some of the available
intake air being used for the aftertreatment system. A further
drawback with this known solution is, in installation terms, that
the air duct between the induction manifold and the exhaust pipe is
long.
[0006] U.S. Pat. No. 4,665,690 describes an exhaust aftertreatment
system with DPF, which comprises a valve with bypass line via the
DPF system. An injector upstream of the DPF unit is used to supply
a reaction agent to raise the temperature in the DPF unit. Here the
bypass line is used to regulate a suitably constant flow through
the DPF to prevent the DPF system from being damaged by the
temperature in this becoming too high, which means that the valve
should be continuously adjustable. This known device aims neither
to protect any following aftertreatment system from high
temperatures nor to protect the environment from exhaust gases with
extremely high temperatures.
[0007] It is desirable to provide a simple and effective device
which makes it possible to avoid the above-described problems.
[0008] A device according to an aspect of the invention is
characterized by a bypass line extending between the inlet and
outlet of the particulate filter system, a valve disposed in the
bypass line, which allows opening or closing of an exhaust gas flow
through the bypass line, and a control member for operating the
valve in dependence on the operating mode of the particulate filter
system. By virtue of this configuration of the device, a
part-quantity of the exhaust gases can be led past the particulate
filter and then remixed with the exhaust gas flow from the
particulate filter for the duration of the soot combustion.
[0009] According to one advantageous illustrative embodiment of the
invention, the valve is constituted by a so-called on/off valve,
the bypass line being configured such that the part-flow through
this line is sufficient to ensure, in the regeneration of the DPF
system, that the temperature in the exhaust line downstream of this
system is kept at a suitable level.
[0010] According to another advantageous illustrative embodiment of
the invention, the valve is adjustable in steps or steplessly
between different control positions.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The invention will be described in greater detail below with
reference to illustrative embodiments shown in the appended
drawings, wherein
[0012] FIG. 1 shows schematically a first illustrative embodiment
of the device according to the invention,
[0013] FIG. 2 shows, in corresponding manner to FIG. 1, a second
illustrative embodiment of the device according to the
invention,
[0014] FIG. 3 is a diagram illustrating the exhaust temperature in
soot combustion during a driving cycle, with non-adjustable valve,
and
[0015] FIG. 4 is a diagram illustrating the exhaust temperature in
soot combustion during a driving cycle, with adjustable valve.
DETAILED DESCRIPTION
[0016] FIG. 1 shows schematically an internal combustion engine 10,
expediently a diesel engine, which is connected by an exhaust line
11 to a particulate filter system 12 comprising an oxidation
catalyst (DOC) 13 and an actively regenerable particulate trap
(DPF) 14. An injector 15 for hydrocarbons (HC), for example diesel
fuel, is placed upstream of the DOC 13 and forms together with the
latter a heating unit for intermittently burning soot at a
temperature suitable for soot combustion. The particulate filter
system is here arranged to switch between an operating mode for the
collection of soot and an operating mode for active
regeneration.
[0017] When it is time to regenerate the DPF, HC are injected into
the exhaust gas stream by the injector 15 and are oxidized in the
DOC. The temperature in the exhaust gas stream is here raised
sufficiently to start a soot combustion in the DPF. Alternatively,
the temperature increase in the exhaust gas stream in the
regeneration can be achieved with the aid of a so-called
burner.
[0018] The exhaust aftertreatment system of the engine can also
comprise devices for Nox reduction, such as an EGR system for the
recirculation of exhaust gas to the inlet side of the engine.
[0019] According to the invention, a bypass line 16 is disposed
between the inlet and outlet of the particulate filter system 12,
i.e. past the DOC 13 and the DPF 14. A valve 17 in the bypass line
16 allows opening or closing of the exhaust gas flow through the
bypass line by a control member 18 for operating the valve 17 in
dependence on the present operating mode of the particulate
filter.
[0020] The control member 18 can be constituted, for example, by
the electronic control unit of the engine, which also controls the
switching between the two operating modes of the particulate filter
system and activation of the injector 15. In its simplest form, the
valve 17 can be of the on/off type.
[0021] With a valve 17 which only opens and closes, the valve is
opened when the heating unit 15 of the particulate filter system is
activated and is kept open until a time after the heating unit has
been switched off. The time for closing of the valve is calculated
such that the particulate filter has cooled. In this type of valve,
it is advantageous if the bypass line contains a laminar flow
resistor 19 in order to make approximately the same exhaust gas
flow component pass through the bypass line irrespective of the
operating point of the engine. The laminar flow resistor is
dimensioned such that an adequate part-quantity is made to flow
through the bypass line, somewhere within the range 20-70%
depending on the maximum exhaust temperature of the engine and the
desired maximum tailpipe temperature. If, for example, the exhaust
temperature from the engine is 300 degrees C. and the temperature
downstream of the particulate filter during regeneration is 700
degrees C., and if one half of the exhaust gases passes by the
particulate filter system, exhaust gases with a temperature of 500
degrees C. are obtained following mixing-in of the part-flow from
the bypass line 16.
[0022] FIG. 3 is a diagram which illustrates the exhaust
temperature in soot combustion during a driving cycle with
non-adjustable valve. Here, 40-50% of the exhaust gases pass
through the bypass line 16.
[0023] The valve 17 can alternatively be adjustable in steps or
continuously by the control member 18 according to FIG. 2, which
schematically shows an internal combustion engine according to FIG.
1 with following actively regenerable particulate filter system 12
and, in addition, a SCR catalyst 20 using a reducing agent, for
example urea, for Nox reduction. For this purpose, the reducing
agent is mixed into the exhaust gas stream upstream of the SCR
catalyst 20 from a tank by means of an injector 21.
[0024] Pressure sensors 22, 23 are placed upstream and downstream
of the particulate filter system 12 to detect the fall in pressure
over this system, which pressure fall can be used to determine when
regeneration shall occur. Temperature sensors 24, 25 are also
placed upstream and downstream of the particulate filter system 12
to detect the exhaust temperature firstly downstream of the engine
and secondly downstream of the particulate filter system 12.
[0025] In the illustrative embodiment according to FIG. 2, an
adjustable valve 17 is used, which, with the aid of preset values,
allows adjustment to a given target value in dependence on the
operating point and/or "closed loop" of the engine, with the aid of
one of the temperature sensors 24, 25 after the mix-in point. The
control unit 18 can also in this case be the same physical unit
which regulates other parts of the aftertreatment system and the
engine, otherwise there is, of course, a communication between
these.
[0026] FIG. 4 shows examples of temperatures in soot combustion
during a driving cycle with adjustable valve. In this case, 30-70%
of the exhaust gases pass through the bypass line 16.
[0027] The shunting of exhaust gases via the bypass line 16 means
that a certain quantity of exhaust gases will pass through the
exhaust system without cleaning steps for particles. In order that
this shall have a minimal effect upon the total emission picture,
the soot combustion should not occur too often, but only a small
percentage of the time. In order to minimize the quantity of soot,
the following measures can be taken, one or more in combination:
[0028] The laminar flow limiter can consist of a so-called open
filter (removes about 50% of the soot particles). [0029] When no
following aftertreatment unit is present downstream of the
particulate filter system 12, the adjustment of the valve 17 can be
dependent on the vehicle speed (rapid dilution of the exhaust gases
to low temperature at high vehicle speed). [0030] Via the injection
system for fuel to the cylinders, the engine can be reset to
produce less soot during the soot combustion. The engine will then,
however, produce a higher quantity of Nox, but with a Nox
aftertreatment unit which works at an optimal temperature for this
unit, the increased Nox quantity can then be taken care of. For
this purpose, the temperature which is used as the target value
after mixing-in should be the optimal temperature of the NOx
aftertreatment unit.
[0031] As a result of the device according to the invention, it
becomes possible to have the DPF unit before the NOx-reducing unit,
which keeps the NOx-reducing catalyst clean from soot and HC.
Moreover, it becomes possible to exploit the fact that some soot is
combusted with NO2, whereby the number of thermal soot combustions
can be minimized. The installation is space-saving in comparison
with an installation in which diluting air is taken from the
induction side.
[0032] Moreover, the gas exchange of the engine is not adversely
affected. In comparison with known solutions in which the
NOx-reducing unit is bypassed, the invention provides freedom to
choose which emission is wanted to be discharged (partially)
uncleaned during the soot combustion, with the possibility of
optimization via the control parameters of the engine. Moreover,
the fuel consumption can be reduced in relation to known solutions
in which NO2 combustion needs to be constant. The solution
according to the invention also provides freedom to choose catalyst
materials which may be better in respects other than regarding
thermal stability.
[0033] Furthermore, fuel can be saved with the invention if the
engine has such a combustion that no soot is formed (or less than
emission requirements) in part of the load range, the shunting via
the bypass line 16 reducing the fall in pressure of the exhaust
system. If the bypass line and the valve 17 are configured so that
the entire flow can pass through the bypass line, this can also be
used as a safety measure to prevent damage to the DOC and DPF, such
as overheating of the material and/or deactivation of any catalyst
coating on the filter in the regeneration.
[0034] The invention should not be deemed to be limited to the
above-described illustrative embodiments, but rather a number of
further variants and modifications are conceivable within the scope
of the following patent claims.
* * * * *