U.S. patent application number 12/271307 was filed with the patent office on 2010-05-20 for cold-start engine loading for accelerated warming of exhaust aftertreatment system.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Adam Vosz.
Application Number | 20100122523 12/271307 |
Document ID | / |
Family ID | 42145843 |
Filed Date | 2010-05-20 |
United States Patent
Application |
20100122523 |
Kind Code |
A1 |
Vosz; Adam |
May 20, 2010 |
COLD-START ENGINE LOADING FOR ACCELERATED WARMING OF EXHAUST
AFTERTREATMENT SYSTEM
Abstract
The methods of the present invention are adapted to adjust
engine loading during catalyst warm up to accelerate heating of the
exhaust aftertreatment system and thereby decrease catalyst
light-off times. According to a preferred embodiment of the present
invention, the method includes: monitoring the current catalyst
temperature; determining if the current catalyst temperature is
less than a predetermined minimum catalyst temperature; and, if the
current catalyst temperature is less than the predetermined minimum
catalyst temperature, increasing the current engine load. The
current engine load is increased by activating a reducing agent
tank heating device and/or a reducing agent line heating
device.
Inventors: |
Vosz; Adam; (Shelby
Township, MI) |
Correspondence
Address: |
Quinn Law Group, PLLC
39555 Orchard Hill Place, Suite 520
Novi
MI
48375
US
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
42145843 |
Appl. No.: |
12/271307 |
Filed: |
November 14, 2008 |
Current U.S.
Class: |
60/285 ;
60/300 |
Current CPC
Class: |
Y02A 50/20 20180101;
Y02T 10/24 20130101; F01N 3/208 20130101; Y02T 10/12 20130101; F01N
2900/08 20130101; Y02A 50/2325 20180101; F01N 2610/10 20130101 |
Class at
Publication: |
60/285 ;
60/300 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Claims
1. A method for warming an exhaust aftertreatment system to improve
performance of a catalyst, comprising: monitoring a current
catalyst temperature; determining whether the current catalyst
temperature is less than a predetermined minimum catalyst
temperature; and increasing a current engine load if the current
catalyst temperature is less than the predetermined minimum
catalyst temperature; wherein increasing the current engine load
includes activating at least one of a reducing agent tank heating
device and a reducing agent line heating device.
2. The method of claim 1, wherein increasing the current engine
load includes calculating a minimum engine load required to
increase the current catalyst temperature to the predetermined
minimum catalyst temperature, and increasing the current engine
load to equal the minimum engine load.
3. The method of claim 2, wherein increasing the current engine
load further includes calculating a minimum alternator load
required to induce the minimum engine load, and commanding the at
least one reducing agent tank heating device and reducing agent
line heating device to generate the minimum alternator load.
4. The method of claim 3, wherein increasing the current engine
load further includes calculating a minimum electric draw of the at
least one reducing agent tank heating device and reducing agent
line heating device required to generate the minimum alternator
load.
5. The method of claim 2, wherein increasing the current engine
load further includes determining whether the current engine load
is less than the minimum engine load, and increasing the current
engine load if the current catalyst temperature is less than the
predetermined minimum catalyst temperature and the current engine
load is less than the minimum engine load.
6. The method of claim 2, wherein the minimum engine load is based
at least in part upon the current engine load and a current engine
speed.
7. The method of claim 1, wherein the predetermined minimum
catalyst temperature is based at least in part upon the current
engine load and a current engine speed.
8. The method of claim 1, wherein increasing the current engine
load further includes adjusting activation of the at least one
reducing agent tank heating device and reducing agent line heating
device in response to variations in vehicle operating
conditions.
9. The method of claim 1, further comprising: adjusting a fuel
command to compensate for the increase in engine load.
10. The method of claim 1, further comprising: monitoring a current
exhaust temperature; determining whether the current exhaust
temperature is less than a predetermined minimum exhaust
temperature; and increasing the current engine load if the current
catalyst temperature is less than the predetermined minimum
catalyst temperature and the current exhaust temperature is less
than the predetermined minimum exhaust temperature.
11. A method for accelerated warming of an exhaust aftertreatment
system having a catalytic converter device with a catalyst for the
reduction and oxidation of emissions generated by an internal
combustion engine in a motorized vehicle, the method comprising:
establishing a target minimum catalyst temperature; monitoring a
current catalyst temperature; determining whether the current
catalyst temperature is less than the target minimum catalyst
temperature; calculating a minimum engine load required to increase
the current catalyst temperature to the target minimum catalyst
temperature; calculating a minimum alternator load required to
induce the minimum engine load; increasing a current engine load to
equal the minimum engine load if the current catalyst temperature
is less than the target minimum catalyst temperature; wherein
increasing the current engine load includes activating a reducing
agent tank heating device and a reducing agent line heating device,
and commanding the reducing agent tank heating device and reducing
agent line heating device to generate the minimum alternator
load.
12. The method of claim 11, further comprising: monitoring the
current engine load and a current engine speed; wherein
establishing the target minimum catalyst temperature is based at
least in part upon the current engine load and the current engine
speed.
13. The method of claim 11, wherein increasing the current engine
load further includes calculating a minimum electric draw of the
reducing agent tank heating device and reducing agent line heating
device required to generate the minimum alternator load.
13. The method of claim 11, wherein increasing the current engine
load further includes adjusting activation of the reducing agent
tank heating device and reducing agent line heating device in
response to variations in vehicle operating conditions.
14. The method of claim 11, further comprising: increasing a fuel
command to the engine to offset the increase in engine load
generated by activating the reducing agent tank and reducing agent
heating device.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to exhaust
aftertreatment systems. More particularly, the present invention is
drawn to methods for accelerated warming of motor vehicle exhaust
aftertreatment systems.
BACKGROUND OF THE INVENTION
[0002] Almost all conventional motorized vehicles, such as the
modern-day automobile, include an exhaust aftertreatment system for
mitigating the byproducts generated from operation of an internal
combustion engine. Most exhaust aftertreatment systems include a
catalytic converter for the reduction and oxidation of exhaust gas
emissions, and a muffler assembly or similar device for attenuating
noise generated by the exhaust emission process. The catalytic
converter is normally placed between the engine exhaust manifold
and the muffler of the automobile, but can also be integrated into
the muffler assembly.
[0003] Catalytic converters normally include a monolith substrate,
generally of the ceramic honeycomb or stainless steel foil
honeycomb type. The monolith substrate is coated with a catalyst
that contains a precious metal, such as platinum, palladium, or
rhodium. The precious metal functions to convert noxious or
otherwise environmentally unfriendly components of the exhaust gas,
such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen
oxides (NO.sub.x), into carbon dioxide (CO.sub.2), water (H.sub.2O)
and nitrogen (N). A "washcoat" is frequently employed to make
catalytic converters more efficient. The washcoat, most often a
mixture of silica and alumina, is added to the substrate, and forms
a rough, irregular surface which has a far greater surface area
than the flat core surfaces. The irregular surface gives the
monolith substrate a larger overall surface area, and therefore
more locations for active precious metal sites.
[0004] The NO.sub.x emissions from an internal combustion engine,
in particular a compression-ignited diesel engine, can also be
lowered with the aid of Selective Catalytic Reduction (SCR). SCR is
a means of converting NO.sub.x emissions into diatomic nitrogen
(N.sub.2) and water (H.sub.2O) using an aqueous reducing agent
introduced into the exhaust system, upstream of the hydrolysis
catalytic converter. The reducing agent that is used for SCR is
typically a gaseous ammonia (NH.sub.3), ammonia in aqueous
solution, or urea in aqueous solution. With regard to the latter,
urea serves as an ammonia carrier and is injected into the exhaust
system with the aid of a metering system. The urea is converted
into ammonia by means of hydrolysis, and the ammonia in turn
reduces the nitrogen oxides in the catalytic converter.
[0005] Some emission control devices, such as SCR systems,
catalytic converters, and associated exhaust gas oxygen (EGO) and
NO.sub.x sensors, require a minimum operating temperature to
function as desired. For example, one of the limitations to using
an aqueous urea solution in SCR is that it is subject to freezing.
If the urea solution freezes, it will not function in its desired
manner as a reducing agent, nor will it freely flow to the
reduction site. As such, line heaters are utilized to warm the
aqueous urea. In addition, the catalyst coating inside of the
catalytic converter requires a minimum "activation" temperature for
efficient operation. As such, a considerable amount of overall
tailpipe hydrocarbon emissions is generated during engine
cold-start. During such time, the emissions-reducing catalysts are
largely ineffective because they have not reached the temperature
at which significant catalytic activity can be maintained, also
known as catalytic "light-off".
SUMMARY OF THE INVENTION
[0006] The methods of the present invention are adapted to adjust
engine loading during catalyst warm up to accelerate heating of the
exhaust aftertreatment system and thereby decrease catalyst
light-off times. In so doing, overall tailpipe nitrogen oxide
emissions generated during engine cold-start are significantly
reduced.
[0007] According to one embodiment of the present invention, the
method includes: monitoring the current temperature of the
catalyst; determining if the current catalyst temperature is less
than a predetermined minimum catalyst temperature; and, if the
current catalyst temperature is less than the predetermined minimum
catalyst temperature, increasing the current engine load. The
current engine load is increased in accordance with the present
invention by activating a reducing agent tank heating device, a
reducing agent line heating device, or both. Adjusting the engine
load during cold-start using, for example, the urea tank and line
heaters will allow for precise calibration of the catalytic
converter warm up cycle.
[0008] According to one aspect of this particular embodiment, the
method also includes calculating the minimum engine load required
to increase the current catalyst temperature to the predetermined
minimum catalyst temperature. The current engine load is thus
increased to equal the minimum engine load if the current catalyst
temperature is less than the predetermined minimum catalyst
temperature.
[0009] According to another aspect, the method also includes
calculating the minimum alternator load necessary to induce the
minimum engine load required to increase the current catalyst
temperature to the predetermined minimum catalyst temperature. In
this instance, the reducing agent tank heating device, reducing
agent line heating device, or both, are commanded to generate the
minimum alternator load. Ideally, the method will then also include
calculating the requisite minimum electric draw of the reducing
agent tank heating device and reducing agent line heating device to
generate the minimum alternator load.
[0010] As part of another aspect of this embodiment, the method
also includes determining whether the current engine load is less
than the minimum engine load. To this regard, the current engine
load is increased if both the current catalyst temperature is less
than the predetermined minimum catalyst temperature and the current
engine load is less than the minimum engine load.
[0011] In accordance with another aspect, the minimum engine load
and predetermined minimum catalyst temperature parameters are each
based, at least in part, upon the current engine load and
speed.
[0012] According to yet another aspect, the method adjusts
activation of the reducing agent tank heating device and/or
reducing agent line heating device in response to variations in
vehicle operating conditions (e.g., changes in vehicle speed,
tractive demands, electric system demands, etc.). Adjusting
activation of the reducing agent tank heating device and/or
reducing agent line heating device in this manner allows the system
to shift engine loading into an optimal zone for catalyst warm-up
and light-off.
[0013] According to even yet another aspect, the method also
includes adjusting engine fuel command to compensate for the
increase in engine load generated via activation of the reducing
agent tank heating device/reducing agent line heating device.
[0014] In accordance with yet another facet of this embodiment, the
method also includes: monitoring the current temperature of the
exhaust gas; determining whether the current exhaust temperature is
less than a predetermined minimum exhaust temperature; and
increasing the current engine load if both the current catalyst
temperature is less than the predetermined minimum catalyst
temperature and the current exhaust temperature is less than the
predetermined minimum exhaust temperature.
[0015] The above features and advantages, and other features and
advantages of the present invention will be readily apparent from
the following detailed description of the preferred embodiments and
best modes for carrying out the present invention when taken in
connection with the accompanying drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a block diagram or flow chart illustrating a
method according to a preferred embodiment of the present
invention;
[0017] FIG. 2 is a graphical illustration of conversion efficiency
as a function of catalyst temperature at various exhaust mass flow
rates; and
[0018] FIG. 3 is a graphical illustration of catalyst temperature
as a function of engine load at various engine speeds.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Referring to the drawings, FIG. 1 illustrates a control
algorithm for regulating the temperature of an exhaust gas
aftertreatment system in a motorized vehicle (not shown).
Specifically, an improved method for accelerated warming of motor
vehicle exhaust aftertreatment systems is shown in FIG. 1 in
accordance with a preferred embodiment of the present invention,
designated generally as 100. The method 100 preferably includes at
least those steps shown in FIG. 1--i.e., steps 101-115. However, it
is within the scope and spirit of the present invention to omit
steps, include additional steps, and/or modify the order presented
in FIG. 1. It should be further noted that the method 100
represents a single operation. As such, it is contemplated that the
method 100 be applied in a systematic and repetitive manner, run in
real-time to continuously adjust engine loading and optimize
operation of the exhaust aftertreatment system.
[0020] The control algorithm 100 preferably resides in an engine
control module (ECM, not shown). In other words, the series of
blocks shown in FIG. 1 may represent individual steps performed by
the ECM. The ECM is a constituent part of the vehicle's powertrain
system, which includes an internal combustion engine (ICE)--e.g., a
4-stroke compression-ignited diesel engine or a 4-stroke
spark-ignited gasoline engine (neither of which are explicitly
depicted herein). The vehicle will also include many other standard
components and systems, such as suspension, drive train, brake
system, steering and body components, that are also well known in
the art. Thus, these structures will not be individually
illustrated or explicitly discussed in detail herein.
[0021] The vehicle will also include an exhaust aftertreatment
system utilized to mitigate the byproducts generated from operation
of the ICE, and route the exhaust gasses away from the engine for
subsequent expulsion into the ambient atmosphere. The exhaust
system includes a number of exhaust pipes or conduits that fluidly
couple a catalytic converter device of conventional architecture to
an exhaust manifold of the ICE. Other exhaust aftertreatment
devices may also be included. For example, a muffler or silencer
that is fluidly communicated with a resonator may be placed
downstream from the catalytic converter device via a second
intermediate exhaust pipe.
[0022] The exhaust system also includes a Selective Catalytic
Reduction (SCR) assembly. The reducing agent used in this exemplary
embodiment is an aqueous urea solution, which is stored in a
reducing agent storage vessel (also referred to herein as "urea
tank"). A metering control apparatus, which is assigned to the urea
tank, has an electrically actuated pump for delivering the reducing
agent to a delivery site (which may be upstream from or directly at
the catalytic converter device) via a feed line. The metering
control apparatus controls an electromagnetic metering valve which
regulates the distribution of urea solution. An electrical heater
device operates to selectively heat the urea tank, for example,
during cold-start operation. An electrical line heater may also be
employed to heat the reducing agent as it exits the tank. While the
methods of the present invention may be used in any vehicle having
a reducing agent reservoir and corresponding heating device, the
present invention is particularly well suited for use with a
vehicle having a compression-ignited diesel-fueled internal
combustion engine (ICE) assembly.
[0023] With reference again to FIG. 1, the method starts at step
101 with monitoring the current temperature of the catalyst inside
of the catalytic converter, which can be accomplished, for example,
using a precious metal resistor-precise thermo couple. In step 103,
the method then determines whether the current catalyst temperature
is below a target minimum catalyst temperature. The target minimum
catalyst temperature may be predefined as a single optimal
temperature for all operating conditions, or determined
contemporaneously with step 103 using a map of temperatures as a
function of the current engine speed and load. For example, FIG. 2
illustrates the relationship between catalyst temperature, in
degrees Celsius (.degree. C.), and the conversion efficiency of the
catalyst (i.e., ratio of NO.sub.x entering catalytic converter
versus NO.sub.x leaving the catalytic converter) at several exhaust
mass flow rates, provided in kilograms per hour (kg/hr). As can be
seen in FIG. 2, a 250.degree. C. catalyst temperature produces
approximately an 85% efficiency or better, regardless of mass flow
rate. As such, the target minimum catalyst temperature may be
predefined at 250.degree. C. for this particular catalytic
converter configuration. Alternatively, if a 90% or better
efficiency is required, the target minimum catalyst temperature may
be varied depending upon the exhaust mass flow rate, engine speed,
and/or engine load to achieve a 90% efficiency.
[0024] If, at step 103, the current catalyst temperature is greater
than (i.e., hotter) or equal to the target minimum catalyst
temperature, the control algorithm 100 returns to step 101. If, at
step 103, the current catalyst temperature is less than (i.e.,
cooler) the target minimum catalyst temperature, the method 100
proceeds to step 105. In step 105, the control algorithm 100
detects the current engine speed, preferably in revolutions per
minute (rpm), and engine load, preferably in Newton-meters (Nm).
According to preferred practice, the engine speed and engine load
are monitored continuously throughout execution of method 100.
[0025] Contemporaneous with step 105, the minimum engine load
required to increase the current catalyst temperature to the
predetermined minimum catalyst temperature is calculated in step
107. The minimum engine load parameter is based, at least in part,
upon the current engine load and speed. FIG. 3 of the drawings
illustrates the relationship between catalyst temperature, in
degrees Celsius (.degree. C.), and engine load, preferably in
Newton-meters (Nm), at various engine speeds, provided in
revolutions per minute (rpm). By way of example, if the target
minimum catalyst temperature is 250.degree. C. and the engine is
idling during vehicle startup at 800 rpm, the engine load will have
to be increased to approximately 152 Nm to achieve the desired
catalyst temperature. If, however, the engine is running at 1000
rpm, the minimum engine load parameter would be set to
approximately 112 Nm to achieve the desired 250.degree. C. catalyst
temperature.
[0026] Prior to, contemporaneous with, or immediately after steps
105 and 107, the current engine load is adjusted to equal or exceed
the minimum engine load established above. The current engine load
is increased in accordance with the present invention by activating
the urea tank heater and line heater, either individually or in
concert, at step 111. Exhaust temperature generally rises as engine
load increases, whereas exhaust temperature generally falls as
engine load decreases. To ensure that the urea tank heater and/or
line heater generate sufficient additional load on the engine
during activation, the method also includes, in step 109,
calculating the minimum alternator load necessary to induce the
minimum engine load. This may also require calculating the minimum
electric draw of the urea tank heater and/or line heaters necessary
to generate the minimum alternator load. In this instance, the
method 100 commands the reducing agent tank heater, reducing agent
line heating device, or both, to generate the minimum alternator
load.
[0027] Adjusting the engine load, for example, during cold-start
using the urea tank heater and line heaters will accelerate heating
of the exhaust aftertreatment system and thereby decrease catalyst
light-off times. The present invention also allows for precise
calibration of the catalytic converter warm up cycle. In addition,
regulating engine load in accordance with the present invention is
effectively seamless to the vehicle operator, as turning on the
urea tank and corresponding heating elements is an entirely
invisible process to an end user.
[0028] Prior to step 111, it is desirable that the method 100
determine whether the engine is already operating at or above the
minimum engine load. If the current engine load is already equal to
or greater than the minimum engine load required to achieve the
target minimum catalyst temperature, the method 100 returns to step
101. If not, the method 100 will proceed, as described above, to
step 111.
[0029] With continuing reference to FIG. 1, step 113 of method 100
provides for adjusting the urea tank and line heater activity in
response to variations in vehicle operating conditions. Such
operating conditions may include, but certainly are not limited to,
changes in vehicle speed, tractive demands, electric system
demands, etc. Adjusting activation of the reducing agent tank
and/or reducing agent heating device in this manner allows the
system to shift engine loading into an optimal zone for catalyst
warm up and light-off. Due to the additional loading on the engine,
the fuel command may need to be adjusted to offset the additional
demand. Accordingly, in step 115, the method 100 also includes
adjusting engine fuel command to compensate for the increase in
engine load generated via activation of the reducing agent tank
and/or reducing agent heating device.
[0030] Prior to completing the control algorithm, it may be
desirable to monitor the current temperature of the exhaust gas,
which may be accomplished, for example, using an electrical exhaust
gas temperature (EGT) gauge. Thereafter, the method 100 will
determine whether the current exhaust temperature is less than a
predetermined minimum exhaust temperature. In this instance, the
current engine load is increased if both the current catalyst
temperature is less than the predetermined minimum catalyst
temperature and the current exhaust temperature is less than the
predetermined minimum exhaust temperature.
[0031] While the best modes for carrying out the present invention
have been described in detail herein, those familiar with the art
to which this invention pertains will recognize various alternative
designs and embodiments for practicing the invention within the
scope of the appended claims.
* * * * *