U.S. patent application number 13/102247 was filed with the patent office on 2011-11-17 for method for controlling fresh air injection into the exhaust of an internal-combustion engine, notably of a motor vehicle.
Invention is credited to Jorg ANDERLOHR, Frederique Battin-Leclerc, Roda Bounaceur, Jacques Lavy, Antonio Pires Da Cruz, Franck Vangraefschepe.
Application Number | 20110277453 13/102247 |
Document ID | / |
Family ID | 43530695 |
Filed Date | 2011-11-17 |
United States Patent
Application |
20110277453 |
Kind Code |
A1 |
ANDERLOHR; Jorg ; et
al. |
November 17, 2011 |
METHOD FOR CONTROLLING FRESH AIR INJECTION INTO THE EXHAUST OF AN
INTERNAL-COMBUSTION ENGINE, NOTABLY OF A MOTOR VEHICLE
Abstract
The present invention relates to a method for controlling air
injection into the exhaust of an internal-combustion engine running
on a cycle during which the expansion phase (D) thereof has a
greater stroke than the compression phase (C) thereof and
comprising at least one cylinder (10) with a combustion chamber
(18), a piston (16), at least one intake means (24) with a valve
(28) associated with an intake pipe (26), at least one exhaust
means (30) with a valve (34) associated with an exhaust pipe (32),
fresh air injection means (48) at the exhaust and an exhaust line
(40) comprising at least one exhaust gas depollution means (46).
According to the invention, the method consists, during the cold
start phase of this engine and during the expansion phase (D)
thereof, in injecting fresh air into the exhaust and in opening
exhaust valve (34) when the pressure in the combustion chamber is
lower than the pressure prevailing at the exhaust so as to feed
into the exhaust gas present in the combustion chamber the fresh
air coming from this exhaust.
Inventors: |
ANDERLOHR; Jorg; (Rueil
Malmaison, FR) ; Pires Da Cruz; Antonio; (Rueil
Malmaison, FR) ; Vangraefschepe; Franck; (Nanterre,
FR) ; Lavy; Jacques; (Serpaize, FR) ;
Bounaceur; Roda; (Velaine en Haye, FR) ;
Battin-Leclerc; Frederique; (Haroue, FR) |
Family ID: |
43530695 |
Appl. No.: |
13/102247 |
Filed: |
May 6, 2011 |
Current U.S.
Class: |
60/287 |
Current CPC
Class: |
F02D 35/023 20130101;
Y02T 10/12 20130101; Y02T 10/18 20130101; Y02T 10/26 20130101; F01N
3/22 20130101; Y02A 50/2322 20180101; F02D 2041/001 20130101; F02D
41/1448 20130101; F01N 3/34 20130101; F02D 41/068 20130101; Y02A
50/20 20180101; F02D 41/0255 20130101; F02D 13/0273 20130101; F02D
41/064 20130101 |
Class at
Publication: |
60/287 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 2010 |
FR |
10/02036 |
Claims
1) A method for controlling air injection into the exhaust of an
internal-combustion engine, notably for a motor vehicle, running on
a cycle during which the expansion phase thereof has a greater
stroke than the compression phase thereof and comprising at least
one cylinder with a combustion chamber, a piston sliding in a
reciprocating motion between a top dead center and a bottom dead
center, at least one intake means with a valve associated with an
intake pipe, at least one exhaust means with a valve associated
with an exhaust pipe, fresh air injection means at the exhaust and
an exhaust line comprising at least one exhaust gas depollution
means, characterized in that it consists, during the cold start
phase of this engine and during the expansion phase thereof, in
injecting fresh air into the exhaust and in opening exhaust valve
when the pressure in the combustion chamber is lower than the
pressure prevailing at the exhaust so as to feed into the exhaust
gas present in the combustion chamber the fresh air coming from
this exhaust.
2) A control method as claimed in claim 1, characterized in that it
consists in opening the exhaust valve at a crank angle for which
the pressure in the combustion chamber is lower than the pressure
prevailing at the exhaust.
3) A control method as claimed in claim 1, characterized in that it
consists in injecting fresh air into exhaust pipe.
4) A control method as claimed in claim 1, characterized in that it
consists in injecting fresh air into exhaust manifold of exhaust
line.
5) A control method as claimed in claim 1, characterized in that it
consists in injecting fresh air into the exhaust before opening of
exhaust valve.
6) A control method as claimed in claim 1, characterized in that it
consists in injecting fresh air into the exhaust after opening of
exhaust valve.
7) A control method as claimed in claim 1, characterized in that it
consists in carrying out a succession of exhaust valve opening and
closing cycles in order to feed into combustion chamber the fresh
air coming from the exhaust.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for injecting
fresh air into the exhaust of an internal-combustion engine,
notably for a motor vehicle.
[0002] It more particularly relates to such a method applied to an
engine running on a cycle during which the expansion phase is
longer than the compression phase, as for a Miller cycle.
BACKGROUND OF THE INVENTION
[0003] As it is generally known, the pollutants emitted during cold
start of internal-combustion engines, notably spark-ignition
engines, are a problem for car manufacturers.
[0004] In fact, during this cold start, the exhaust gas depollution
means these engines are usually equipped with, such as a catalyst,
do not have a sufficiently high operating temperature, referred to
as light-off temperature, to be able to treat these pollutants
efficiently.
[0005] A large part of the pollutants contained in this exhaust
gas, such as unburnt hydrocarbons (HC) and/or carbon oxides (CO),
is therefore discharged to the atmosphere without being treated
beforehand, which represents a quite significant nuisance.
[0006] For this catalyst to be able to rapidly reach its operating
temperature, it is well known to provide fast light-off thereof by
injecting fresh air into the exhaust line and upstream from this
catalyst.
[0007] More particularly, it is notably known to inject this fresh
air downstream from the exhaust valves so as to provide the exhaust
gas circulating in the exhaust pipe with oxygen in order to achieve
combustion with the unburnt HC contained therein.
[0008] Such a post-combustion allows, on the one hand, to directly
reduce partly the HC and the CO, and on the other hand to increase
the temperature of the exhaust gas that will thereafter flow
through the catalyst while increasing the temperature thereof.
[0009] It has been observed that, to achieve this post-combustion,
it is necessary to feed the fresh air as close as possible to the
exhaust valves, a place where the exhaust gas temperature is the
highest. However, since the air supplied is cold in relation to the
burnt gas that is very hot, the mixing rate is a determining factor
for this post-combustion. In fact, if a large amount of cold air is
present, the chemical reactions are stopped. On the other hand, if
this amount of air is insufficient, the heat release due to the
reaction of the mixture is not sufficient to start the combustion
of this mixture.
[0010] This therefore requires very precise adjustment of the
amounts of fresh air and of exhaust gas present at the exhaust in
order to obtain the appropriate mixture, failing which it is not
possible to achieve post-combustion of the fresh air/exhaust gas
mixture.
[0011] The present invention aims to overcome the aforementioned
drawbacks by means of a method for injecting fresh air into the
exhaust which allows to achieve post-combustion of the fresh
air/exhaust gas mixture whatever the quality of this mixture.
SUMMARY OF THE INVENTION
[0012] The invention therefore relates to a method for controlling
air injection into the exhaust of an internal-combustion engine,
notably for a motor vehicle, running on a cycle during which the
expansion phase thereof has a greater stroke than the compression
phase thereof and comprising at least one cylinder with a
combustion chamber, a piston sliding in a reciprocating motion
between a top dead center and a bottom dead center, at least one
intake means with a valve associated with an intake pipe, at least
one exhaust means with a valve associated with an exhaust pipe,
fresh air injection means at the exhaust and an exhaust line
comprising at least one exhaust gas depollution means,
characterized in that it consists, during the cold start phase of
this engine and during the expansion phase thereof, in injecting
fresh air into the exhaust and in opening the exhaust valve when
the pressure in the combustion chamber is lower than the pressure
prevailing at the exhaust so as to feed into the exhaust gas
present in the combustion chamber the fresh air coming from this
exhaust,
[0013] The method can consist in opening the exhaust valve at a
crank angle for which the pressure in the combustion chamber is
lower than the pressure prevailing at the exhaust.
[0014] The method can consist in injecting fresh air into the
exhaust pipe.
[0015] The method can consist in injecting fresh air into the
exhaust manifold of the exhaust line.
[0016] The method can consist in injecting fresh air into the
exhaust before opening of the exhaust valve.
[0017] The method can consist in injecting fresh air into the
exhaust after opening of the exhaust valve.
[0018] The method can consist in carrying out a succession of
exhaust valve opening and closing cycles in order to feed into the
combustion chamber the fresh air coming from the exhaust.
BRIEF DESCRIPTION OF THE FIGURES
[0019] Other features and advantages of the invention will be clear
from reading the description hereafter, given by way of
non-limitative example, with reference to the accompanying figures
wherein:
[0020] FIGS. 1 to 4 are diagrams showing an internal-combustion
engine in different running configurations and using the method
according to the invention, and
[0021] FIG. 5 shows the various engine valve lift laws according to
FIGS. 1 to 4, between an open position (O) and a closed position
(F) as a function of crank angle (V).
DETAILED DESCRIPTION
[0022] In FIGS. 1 to 4, the engine shown is an indirect-injection
internal-combustion engine, notably a gasoline and preferably a
spark-ignition engine. This example is not limitative and the
invention described hereafter can also apply to a direct-injection
internal-combustion engine, preferably an auto-ignition engine, in
particular of diesel type.
[0023] The engine described has the specific feature of running on
a specific cycle, such as the Miller cycle, during which its
expansion phase has a longer stroke than its compression phase, as
described in the rest of the description.
[0024] This engine comprises at least one cylinder 10 with a
cylinder body 12 closed by a cylinder head 14. A piston 16 slides
within cylinder body 12 in a rectilinear reciprocating motion under
the effect of a rod controlled by a crankshaft (not shown), thus
forming a combustion chamber 18. This chamber is thus delimited by
the cylinder head, lateral wall 20 of the cylinder body and upper
part 22 of the piston.
[0025] This piston moves between a top dead center position (PMH in
the figure) where upper part 22 of piston 16 is the closest to
cylinder head 14 and a bottom dead center position (PMB) where this
upper part is the furthest from this cylinder head.
[0026] The cylinder head carries at least one intake means 24 with
an intake pipe 26 from which access to combustion chamber 18 is
controlled by an intake valve 18. The cylinder head also carries at
least one exhaust means 30 with a exhaust pipe 32 associated with
an exhaust valve 34 for communication with this chamber.
[0027] Opening/closing of the intake and exhaust valves is
controlled by specific means. The latter must allow the lift laws
of these valves to be varied, as regards their opening/closing time
as well as their opening height, independently of one another or in
combination with one another. By way of example, these means are of
camshaft type, more commonly known as VVT (Variable Valve Timing),
VVL (Variable Valve Lift) or VVA (Variable Valve Actuation).
[0028] In the example described in connection with FIGS. 1 to 4,
intake valve 28 and exhaust valve 34 are provided with VVA type
means, 36 and 38 respectively, allowing the lift laws thereof to be
varied.
[0029] The engine described is an indirect-injection engine with
fuel injection means (not shown) carried by the cylinder head that
spray fuel into intake pipe 26 so as to obtain a fuel mixture with
the intake air circulating therein. This fuel mixture is then fed
into combustion chamber 18 through the intake valve.
[0030] This type of fuel injection can be advantageously associated
with means for igniting the fuel mixture present in chamber 18,
such as spark plug ignition (not shown).
[0031] Exhaust means 30 are connected to an exhaust line 40 that
essentially comprises an exhaust manifold 42 connected to the
outlet of exhaust pipe 32, an exhaust tube 44 and depollution means
for the gas circulating in this line, such as a catalyst 46,
advantageously a three-way catalyst.
[0032] This engine also comprises air injection means 48 at the
exhaust. These means include an air injector (symbolized in the
figures by dotted line 50) that is connected by any known means to
an air pump 52. This injector is arranged on exhaust pipe 32 in
such a way that the air jet coming from this injector reaches the
inside of this pipe advantageously as close as possible to exhaust
valve 34 and downstream thereof, considering the direction of
circulation of the exhaust gas from the combustion chamber to
exhaust manifold 42.
[0033] Means 36, 38 controlling valves 28, 34, the fuel injection
means and air injection means 48 are controlled by a computing unit
(not shown), more commonly referred to as engine calculator, an
engine is usually provided with.
[0034] The purpose of this calculator is notably to control
opening/closing of the valves, the fuel injection parameters, such
as the injection time in the engine cycle and/or the fuel injection
duration, and the injection parameters of the air injected into the
exhaust pipe.
[0035] The description of the method hereafter is given in
connection with a spark-ignition indirect-injection engine of FIGS.
1 to 4 associated with FIG. 5 that illustrates the lift laws of its
intake and exhaust valves.
[0036] In the example of FIG. 1, the engine is in the intake phase
A configuration, with a stroke Ca of piston 16 from top dead center
PMH to bottom dead center PMB.
[0037] In the vicinity of top dead center PMH, control means 36
therefore control the opening of intake valve 28 until the piston
reaches its bottom dead center PMB in order to feed into combustion
chamber 18 the fuel mixture present in the intake pipe. Control
means 38 control the maintenance in closed position of exhaust
valve 34 throughout this intake phase.
[0038] From this bottom dead center PMB, the piston has a reverse
stroke when achieving a phase referred to as compression phase C
where it moves from its bottom dead center PMB to its top dead
center PMH. This piston displacement is divided in two parts, a
discharge stroke Cr and a compression stroke Cp, as described in
detail hereafter.
[0039] As shown in FIGS. 2 to 5, during discharge stroke Cr, intake
valve 28 is open and piston 16 performs stroke Cr between the
bottom dead center PMB and a crank angle Va where intake valve 28
is moved toward the closed position thereof. During this stroke,
part of the fuel mixture present in chamber 18 leaves this chamber
through pipe 26.
[0040] Of course, it is within the capacity of the person skilled
in the art to determine the crank angle Va allowing to meet the
engine power request.
[0041] Furthermore, this person skilled in the art will make sure
to close the intake valve so that the fuel mixture present in the
intake pipe is not discharged out of the engine and remains
confined in this intake pipe (or, at worst, in the intake manifold
this engine usually comprises).
[0042] From crank angle Va, the intake and exhaust valves are
closed and piston 16 continues to move until it reaches top dead
center PMH so as to achieve compression stroke Cp of the fuel
mixture between angle Va and this PMH referred to as compression
top dead center.
[0043] From this compression top dead center PMH, the fuel mixture
present in the combustion chamber is ignited by generating burnt
gas (or exhaust gas). After this combustion, the engine achieves an
expansion phase D between this PMH and PMB, with an expansion
stroke Cd and an air injection stroke Ci, as illustrated in FIG.
3.
[0044] During this expansion phase and in cases where the engine is
in a cold start state, notably when catalyst 46 has not reached its
light-off temperature and the temperature of the exhaust gas is not
high enough to provide fast catalyst heating, fresh air is injected
into the exhaust so as to increase the exhaust gas temperature.
[0045] More precisely, fresh air is predominantly injected inside
the combustion chamber because the hottest areas, locally rich
(fuel desorbed in cracks, etc.) and at high pressure are within
this chamber.
[0046] Therefore, as illustrated in FIGS. 3 and 5, during expansion
phase D, the piston follows an expansion stroke Cd during which
this piston moves from top dead center PMH to a crank angle Ve
before bottom dead center PMB.
[0047] Control means 38 control then opening of exhaust valve 34 at
this angle. This angle Ve is preferably determined when the
pressure in the combustion chamber is lower than the pressure
prevailing at the engine exhaust, generally considered at the level
of exhaust manifold 42 or of the exhaust pipe.
[0048] These various pressures can be evaluated from charts
contained in the calculator and established in connection with the
different operating points of the engine. These pressures can also
be measured, for example by pressure detectors arranged in the
combustion chamber and in the exhaust manifold/exhaust pipe.
[0049] Simultaneously or quasi-simultaneously with this exhaust
valve opening, air pump 52 is actuated and fresh air is fed through
injector 50 into exhaust pipe 32 and in the vicinity of this valve.
Of course, exhaust gas is already present in this pipe and this
thus provides a mixture of fresh air and of exhaust gas.
[0050] As already mentioned, it is in the combustion chamber that
the conditions are the most favourable for combustion, as a result
of the high temperatures prevailing therein and of the presence of
unburnt hydrocarbons in the cracks of this chamber.
[0051] Thus, upon opening of exhaust valve 34 and during stroke Ci
from crank angle Ve to the vicinity of PMB, fresh air is sucked
into the chamber through the open exhaust valve. This allows a
reactive mixture to be obtained more readily in the combustion
chamber with the residual burnt gas and the fresh air fed into this
chamber.
[0052] Post-combustion of the residual burnt gas is thus initiated
in the chamber with heat release until the engine has completed its
expansion phase at the top dead center referred to as expansion
PMB, with closing of the intake valve.
[0053] Alternatively, it is possible to inject fresh air into the
exhaust manifold which can only simplify the air injection
means.
[0054] In this context, injecting air into the exhaust has been
mentioned above, which comprises feeding this air into the exhaust
pipe or into the exhaust manifold.
[0055] As it is well known, the operating mode of the engine
continues with an exhaust phase E and a stroke Ce of the piston
between the expansion PMB and its PMH, as illustrated in FIGS. 4
and 5.
[0056] During this phase, the high-temperature gas contained in
combustion chamber 18 is expelled from this chamber towards exhaust
pipe 32 through exhaust valve 34 which is in open position, and
under the impulse of the displacement of piston 16 towards top dead
center PMH.
[0057] This gas is then sent to exhaust line 40 where it flows
through catalyst 46 while speeding up its temperature rise through
thermal exchange.
[0058] In the vicinity of the piston PMH, the exhaust valve is
closed, the operating cycle of the engine is resumed from FIG. 1
and continued until catalyst 46 has reached its operating
temperature.
[0059] The time required to obtain depollution of the exhaust gas
circulating in line 40 is thus greatly shortened.
[0060] The present invention is not limited to the embodiment
examples described above and it encompasses any variant and
equivalent.
[0061] Notably, it is possible for air pump 52 to be in operation
before the exhaust valve of FIG. 3 opens. This affords the
advantage of allowing suction of fresh air that has already been
placed in the vicinity of the exhaust valve, when the latter is
open.
[0062] It is also possible to perform, from angle Ve, a succession
of exhaust valve opening/closing cycles associated with air
injection until the piston has reached the PMB position. This has
the effect of promoting air and burnt gas mixing in the combustion
chamber.
* * * * *