U.S. patent application number 10/528147 was filed with the patent office on 2006-05-11 for internal combustion engine comprising a gas conveying system and operating method therefor.
This patent application is currently assigned to DaimlerChrysler AG. Invention is credited to Normann Freisinger, Thorsten Hergemoeller, Roland Kemmler, Hans-Georg Lehmann, Martin Matt.
Application Number | 20060096279 10/528147 |
Document ID | / |
Family ID | 31969202 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060096279 |
Kind Code |
A1 |
Freisinger; Normann ; et
al. |
May 11, 2006 |
Internal combustion engine comprising a gas conveying system and
operating method therefor
Abstract
1. Internal combustion engine comprising a gas conveying system
and operating method therefor. 2.1 The invention proposes an
internal combustion engine (1) having a gas conveying system with a
turbine (7) which can be driven by an airstream and a pump (8)
which can be driven by the turbine (7) and by means of which gas
can be fed to the exhaust system (3, 4, 5), as well as an operating
method therefor. 2.2. According to the invention, when the internal
combustion engine (1) is starting up, the quantity of fuel injected
into it is set as a function of the delivery capacity of the pump
(8). 2.3. Use in motor vehicles, in particular in passenger cars
having an internal combustion engine with fuel injection.
Inventors: |
Freisinger; Normann; (Lorch,
DE) ; Hergemoeller; Thorsten; (Fellbach, DE) ;
Kemmler; Roland; (Stuttgart, DE) ; Lehmann;
Hans-Georg; (Esslingen, DE) ; Matt; Martin;
(Untergrombach, DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
DaimlerChrysler AG
Epplestrasse 225
Stuttgart
DE
70567
|
Family ID: |
31969202 |
Appl. No.: |
10/528147 |
Filed: |
August 30, 2003 |
PCT Filed: |
August 30, 2003 |
PCT NO: |
PCT/EP03/09646 |
371 Date: |
October 21, 2005 |
Current U.S.
Class: |
60/289 |
Current CPC
Class: |
Y02T 10/26 20130101;
Y02T 10/12 20130101; F02D 41/062 20130101; F02D 41/0255 20130101;
F01N 3/22 20130101; F01N 3/32 20130101; Y02A 50/2322 20180101; F02D
2009/0279 20130101; Y02A 50/20 20180101; F02D 2009/0283
20130101 |
Class at
Publication: |
060/289 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2002 |
DE |
102 43 317.8 |
Claims
1. An internal combustion engine with fuel injection, having an
intake line (2), in which a throttle element (6) is arranged, an
exhaust system (3, 4, 5) and a gas conveying system having a
turbine (7), which can be driven by an air stream and to which a
turbine inlet line (9) and a turbine outlet line (10) are
connected, and a pump (8), which can be driven by the turbine (7)
and has a pump inlet line (11) and a pump outlet line (12), via
which gas delivered by the pump (8) can be fed to the exhaust
system (3, 4, 5), characterized in that when the internal
combustion engine (1) is starting up, the quantity of fuel injected
into it can be set as a function of the delivery capacity of the
pump (8).
2. The internal combustion engine as claimed in claim 1,
characterized in that the turbine (7) can be driven by a
part-stream of the combustion air taken in by the internal
combustion engine (1) via the intake line (2), the part-stream
being produced by a pressure gradient which is present across the
throttle element (6).
3. The internal combustion engine as claimed in claim 1,
characterized in that when the engine is starting up, the speed of
the internal combustion engine (1) can be set before the fuel
injection commences, by actuation of the internal combustion engine
(1) or by actuation of an auxiliary unit assigned to the internal
combustion engine (1).
4. The internal combustion engine as claimed in claim 1,
characterized in that when the engine is starting up, the throttle
element (6) can be set as a function of a pressure in the intake
line (2).
5. The internal combustion engine as claimed in claim 1,
characterized in that the turbine (7) can be driven by an airstream
which is generated by a gas conveying unit (15; 16) which is
arranged in the turbine inlet line (9) or in the turbine outlet
line (10) or is connected to the turbine inlet line (9) or to the
turbine outlet line (10).
6. The internal combustion engine as claimed in claim 5,
characterized in that the gas conveying unit is designed as an
electrically driven gas conveying unit (15).
7. The internal combustion engine as claimed in claim 5,
characterized in that the gas conveying unit is designed as an
evacuable gas vessel (16) arranged in the turbine outlet line
(10).
8. The internal combustion engine as claimed in claim 1,
characterized in that the gas stream delivered by the pump (8) can
be set as a function of an air/fuel ratio in the exhaust system (3,
4, 5).
9. The internal combustion engine as claimed in claim 1,
characterized in that the gas stream delivered by the pump (8) can
be fed to an exhaust manifold (3) assigned to the exhaust system
(3, 4, 5) and/or direct to a catalytic converter (5) assigned to
the exhaust system (3, 4, 5).
10. The internal combustion engine as claimed in claim 1,
characterized in that exhaust gas can be fed to the pump (8) via
the pump inlet line (11), and the exhaust-gas stream delivered by
the pump (8) can be fed to the intake line (2).
11. The internal combustion engine as claimed in claim 1,
characterized in that a reduced-pressure vessel (17) connected via
the pump inlet line (11) can be evacuated by the pump (8).
12. A method for operating an internal combustion engine with fuel
injection and having an intake line (2), in which a throttle
element (6) is arranged, an exhaust system (3, 4, 5) and a gas
conveying system, which comprises a turbine (7) that can be driven
by an airstream and a pump (8) that can be driven by the turbine
(7), in which method, at least when the engine is starting up, gas
delivered by the pump (8) is fed to the exhaust system (3, 4, 5),
characterized in that when the internal combustion engine (1) is
starting up, the quantity of fuel injected is set as a function of
the delivery capacity of the pump (8).
13. The method as claimed in claim 12, characterized in that when
the engine is starting up, before the fuel injection begins the
throttle element (6) is held predominantly closed and is only
opened after the pump has reached a minimum delivery capacity.
14. The method as claimed in claim 12, characterized in that the
engine speed of the internal combustion engine (1) is increased as
it is starting up before the fuel injection begins.
15. The method as claimed in claim 12, characterized in that the
turbine (7), at least from time to time, is driven by an airstream
which is delivered by a gas conveying unit (15; 16) which is
arranged in the turbine inlet line (9) or the turbine outlet line
(10) or is connected to the turbine inlet line (9) or the turbine
outlet line (10).
16. The method as claimed in claim 12, characterized in that the
airstream delivered by the pump (8) is set as a function of an
air/fuel ratio in the exhaust system (3, 4, 5).
17. The method as claimed in claim 12, characterized in that one of
at least two addition points (13, 14) in the exhaust system (3, 4,
5) at which the airstream delivered by the pump (8) is added to the
exhaust gas is selected as a function of the operating state of the
internal combustion engine (1).
18. The method as claimed in claim 12, characterized in that the
airstream delivered by the pump (8) cools a definable part of the
exhaust system (3, 4, 5) if a predeterminable threshold value for a
temperature in the exhaust system (3, 4, 5) is exceeded.
19. The method as claimed in claim 12, characterized in that the
pump (8) at least from time to time removes exhaust gas from the
exhaust system (3, 4, 5) and feeds it to the intake line (2).
20. The method as claimed in claim 12, characterized in that a
reduced-pressure vessel (17) assigned to the internal combustion
engine (1) is evacuated by the pump (8) via the pump inlet line
(11) in order to operate a servo system operated by reduced
pressure.
Description
[0001] The invention relates to an internal combustion engine
comprising a gas conveying system and to an operating method
therefor.
[0002] U.S. Pat. No. 6,094,909 has disclosed an internal combustion
engine having a gas conveying system. The gas conveying system
comprises a turbine which can be driven by an airstream and a pump
which is driven by the turbine and can deliver gas into the exhaust
system. This gas conveying system is used when the internal
combustion engine is starting up, in order to feed secondary air to
the exhaust system so that unburnt fuel constituents can be
oxidized. The heat of combustion released is used to heat the
exhaust-gas purification system, which is therefore ready to
operate more quickly. The turbine is driven by an airstream that is
caused by a pressure gradient present across a throttle element in
the intake line. However, secondary air is only supplied to a
sufficient extent when the turbine or the pump which it drives has
reached a sufficient rotational speed, which takes a certain amount
of time, and consequently the gas conveying system cannot provide
secondary air immediately after the internal combustion engine has
been started up. The gas conveying system has no further functions
apart from the delivery of secondary air when the internal
combustion engine is starting up.
[0003] By contrast, it is an object of the invention to provide an
internal combustion engine comprising a gas conveying system and an
operating method therefor which allow the internal combustion
engine to operate with low emissions and allow good utilization of
the gas conveying system.
[0004] According to the invention, this object is achieved by an
internal combustion engine has a throttle element (6), an intake
line (2), in which the throttle element (6) is arranged, an exhaust
system (3, 4, 5), and an air conveying system. The air conveying
system includes a turbine (7) and a pump (8). The turbine (7) has a
turbine inlet line (9) and a turbine outlet line (10), and is
driven by an air stream flowing through the turbine outlet line
(10). The pump (8) is driven by the turbine (7) and includes a pump
inlet line (11) and a pump outlet line (12) via which air delivered
by the pump (8) is fed to the exhaust system (3, 4, 5). During
engine start-up the air conveying system sets the quantity of
injected fuel as a function of the delivery capacity of the pump
(8). This object can also be achieved by a method that includes the
steps of, during engine start-up, feeding air delivered by the pump
(8) to the exhaust system (3, 4, 5) and setting the quantity of
fuel injected as a function of the delivery capacity of the pump
(8).
[0005] The internal combustion engine according to the invention is
distinguished by the fact that when the internal combustion engine
is being started up, the quantity of fuel injected into it can be
set as a function of the delivery capacity of the pump. It is
preferable for fuel to be injected only once a minimum delivery
capacity of the pump has been reached, so that the start of fuel
injection is dependent on the delivery capacity of the pump. The
result of this is that secondary air can be added to the exhaust
system at sufficient quantities with the aid of the pump when the
fuel injection begins, in order to allow after-oxidation of unburnt
fuel residues. After-oxidation converts incompletely burnt fuel by
oxidation. The heat of the reaction which is released quickly heats
the exhaust-gas purification system to its operating temperature,
in particular downstream of the point at which secondary air is
added. Consequently, effective exhaust-gas purification can be
achieved quickly. In particular, the level of harmful hydrocarbon
emissions (HC emissions) can be reduced during the starting phase.
By contrast, if the beginning of fuel injection is not matched to
the delivery capacity of the pump and, for example, fuel is
injected into the combustion chambers of the internal combustion
engine before the pump has reached a minimum delivery capacity, the
atmospheric oxygen required as a reaction partner for
after-oxidation of unburnt fuel in the exhaust system is not
present in sufficient quantities, and consequently relatively large
quantities of HC are emitted. On the other hand, if too little fuel
is injected in relation to the delivery capacity of the pump, the
air/fuel ratio (.lamda.) in the exhaust system required for
after-oxidation is too high, and after-oxidation likewise cannot
take place. This leads to late light-off of the exhaust-gas
catalytic converters, with the result that pollutants are emitted
for a relatively long period of time.
[0006] In one configuration of the invention, the turbine can be
driven by a part-stream of the combustion air taken in by the
internal combustion engine via the intake line, the part-stream
being produced by a pressure gradient which is present across the
throttle element. This measure makes it possible to dispense with
the need for additional units to drive the turbine of the gas
conveying system.
[0007] In a further configuration of the invention, when the engine
is starting up, the speed of the internal combustion engine can be
set before the fuel injection commences, by actuation of the
internal combustion engine or by actuation of an auxiliary unit
assigned to the internal combustion engine. It is preferable for
the speed of the internal combustion engine to be increased at the
beginning of the engine start-up operation. This makes it possible
to quickly empty the induction pipe region by the internal
combustion engine and to rapidly lower the induction pipe pressure.
Consequently, the mass of air sucked in per intake section is
rapidly reduced, so that an air/fuel ratio which is favorable for
operation of the internal combustion engine and for after-oxidation
can be set when the fuel injections begin. If the turbine of the
gas conveying system is driven by the pressure drop which is
present across the throttle element in the induction pipe,
moreover, the pump rapidly reaches a sufficient delivery capacity
as the result of the measure according to the invention.
Consequently, sufficient quantities of secondary air can be
delivered into the exhaust system even at a very early stage in the
starting phase, with the result that in turn effective exhaust-gas
purification can be provided quickly.
[0008] In a further configuration of the invention, the throttle
element in the intake line can be set as a function of a pressure
in the intake line. In particular if the turbine of the gas
conveying system is driven by the pressure drop that is present
across the throttle element in the induction pipe, it is possible
for the throttle element to be set in such a way according to the
quantity of air taken in by the internal combustion engine that the
turbine of the gas conveying system quickly reaches its rotational
speed. Consequently, the pump likewise quickly reaches a sufficient
delivery capacity.
[0009] In a further configuration of the invention, the turbine can
be driven by an airstream which is generated by a gas conveying
unit which is arranged in the turbine inlet line or in the turbine
outlet line or is connected to the turbine inlet line or to the
turbine outlet line. This measure allows the turbine to be run up
to speed and therefore the pump to reach a sufficient delivery
capacity independently of the differential pressure which is
present across the throttle element in the intake line.
[0010] In a further configuration of the invention, the gas
delivery unit is designed as an electrically driven gas conveying
unit. The electrical driving of the gas conveying unit allows
accurate actuation of this unit and therefore of the gas conveying
system as a whole.
[0011] In a further configuration of the invention, the gas
conveying unit is designed as an evacuable gas vessel arranged in
the turbine outlet line. If the evacuated gas vessel is opened, air
is sucked into the vessel via the turbine and the turbine is
thereby driven. This requires virtually no auxiliary energy.
Therefore, the measure according to the invention allows the gas
conveying system to operate independently of the differential
pressure across the throttle element in a simple way.
[0012] In a further configuration of the invention, the gas stream
delivered by the pump can be set as a function of an air/fuel ratio
in the exhaust system. The gas stream delivered is preferably set
in such a way that conditions which are advantageous for the
after-oxidation are established downstream of the point at which
the secondary air is added. It is preferable for the setting to be
such that a .lamda. value of approximately 1.2 is established.
[0013] In a further configuration of the invention, the gas stream
delivered by the pump can be fed to an exhaust manifold of the
exhaust system and/or direct to a catalytic converter of the
exhaust system. This allows secondary air to be made available to
the exhaust-gas purification system at the location where
conditions are favorable for after-oxidation to occur. When the
internal combustion engine is starting up, it is preferable for the
secondary air to be fed to the exhaust manifold. If the internal
combustion engine is being operated under rich conditions after it
has been started up, secondary air may be added on the entry side
of a catalytic converter fitted in an underbody position in order
to oxidize the unburnt exhaust-gas constituents.
[0014] In a further configuration of the invention, exhaust gas can
be fed to the pump via the pump inlet line, and the exhaust-gas
stream delivered by the pump can be fed to the intake line. As a
result, the gas conveying system realizes exhaust-gas
recirculation. Accordingly, in addition to supplying secondary air,
which occurs predominantly in the starting phase, the gas conveying
system also performs a further function and is therefore better
utilized.
[0015] In a further configuration of the invention, a
reduced-pressure vessel connected via the pump inlet line can be
evacuated by the pump. The reduced pressure generated by the pump
in the reduced-pressure vessel can be used to drive servo units.
The gas conveying system therefore performs a further function and
is better utilized.
[0016] The method according to the invention is distinguished by
the fact that when the internal combustion engine is starting up,
the quantity of fuel injected is set as a function of the delivery
capacity of the pump. It is preferable for the injection of fuel to
begin when the pump has reached a minimum delivery capacity. This
ensures that no unburnt fuel constituents enter the exhaust system
without atmospheric oxygen being made available at the same time to
after-oxidize these unburnt fuel constituents. Matching the
quantity of fuel injected to the delivery capacity of the pump
ensures a .lamda. value which is optimum for after-oxidation in the
exhaust manifold.
[0017] In one configuration of the method, when the engine is
starting up and before the fuel injection begins, the throttle
element is held predominantly closed and is only opened after the
pump has reached a minimum delivery capacity. The result of this is
that conditions which allow effective after-oxidation of unburnt
fuel constituents are very quickly reached in the exhaust
system.
[0018] In a further configuration of the method, the engine speed
of the internal combustion engine is increased as it is starting up
before the fuel injection begins. Increasing the starting speed of
the engine allows the air which is present in the induction pipe to
be sucked out quickly, so that .lamda. values which are favorable
both for internal combustion engine operation and in the exhaust
system are very quickly established. The starting engine speed can
be increased by reducing the compression work performed by the
internal combustion engine. It is preferable for the throttling of
the internal combustion engine to be relieved, i.e. for the exhaust
valves to remain open for a certain period of time or completely
during the compression stroke. Furthermore, it is advantageous for
auxiliary units which are driven by the internal combustion engine
to be switched off or decoupled.
[0019] In a further configuration of the method, the turbine, at
least from time to time, is driven by an airstream which is
delivered by a gas conveying unit which is arranged in the turbine
inlet line or the turbine outlet line or is connected to the
turbine inlet line or the turbine outlet line. This allows the
turbine to be run up to speed quickly in the initial phase
irrespective of the differential pressure across the throttle
element in the intake line and therefore allows secondary air to be
delivered by the pump very quickly. The gas conveying unit is
preferably formed by an electrically operated pump or by a pressure
vessel or reduced-pressure vessel.
[0020] In a further configuration of the method, the airstream
delivered by the pump is set as a function of an air/fuel ratio in
the exhaust system. The result of this is that conditions which are
favorable for the desired further reactions are established and
further reactions can therefore proceed in the desired way. It is
preferable for a .lamda. value of 1.2 to be set in the exhaust
manifold.
[0021] In a further configuration of the method, one of at least
two addition points at which the airstream delivered by the pump is
added to the exhaust gas is selected as a function of the operating
state of the internal combustion engine. On account of the fact
that secondary air can be fed to the exhaust system at at least two
locations, it is possible to react flexibly to the conditions in
the exhaust system, which depend primarily on the operating state
of the internal combustion engine.
[0022] In a further configuration of the method, the airstream
delivered by the pump cools a definable part of the exhaust system
if a predeterminable threshold value for a temperature in the
exhaust system is exceeded. With this configuration of the
invention, the gas conveying system additionally performs a cooling
function, with the result that it is better utilized, the exhaust
system can be operated more reliably and there is no need for other
forms of cooling measures.
[0023] In a further configuration of the method, the pump at least
from time to time removes exhaust gas from the exhaust system and
feeds it to the intake line. In this case, the exhaust-gas stream
fed to the intake line is preferably set as a function of the
operating state of the internal combustion engine. Consequently,
the gas conveying system performs an exhaust-gas recirculation
function, so that the exhaust-gas recirculation can be made
independent of the pressure conditions in the exhaust system and in
the intake system of the internal combustion engine. The
exhaust-gas recirculation quantity can be set as required on
account of being dependent on the operating state.
[0024] In a further configuration of the method, a reduced-pressure
vessel assigned to the internal combustion engine is evacuated by
the pump via the pump inlet line in order to operate a servo system
operated by reduced pressure. This further function of the gas
conveying system makes it possible to draw additional benefit from
this system and also constitutes a simplification with regard to
the components employed.
[0025] The text which follows provides a more detailed explanation
of the invention on the basis of drawings and associated
examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 shows a schematic block diagram of an embodiment of
the internal combustion engine according to the invention with gas
conveying system.
[0027] FIG. 2 shows a schematic block diagram of a further
embodiment of the internal combustion engine according to the
invention with gas conveying system.
[0028] FIG. 3 shows a schematic block diagram of a further
embodiment of the internal combustion engine according to the
invention with gas conveying system.
[0029] FIG. 4 shows a schematic block diagram of a further
embodiment of the internal combustion engine according to the
invention with gas conveying system.
[0030] FIG. 5 shows a schematic block diagram of a further
embodiment of the internal combustion engine according to the
invention with gas conveying system.
DETAILED DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 illustrates an internal combustion engine 1, which
is, by way of example, a four-cylinder reciprocating-piston engine
with spark ignition, referred to below just as engine for short,
with a gas conveying system, intake system and exhaust system. When
it is operating, the engine 1 takes in air via the intake line 2
with a throttle element 6 arranged therein and discharges exhaust
gas to the environment via the exhaust manifold 3 and the exhaust
pipe 4 connected to it. A catalytic converter 5 for purifying the
exhaust gas is arranged in the exhaust pipe 4. The catalytic
converter is in this case designed as a starting catalytic
converter arranged close to the engine. The engine 1 is assigned a
gas conveying system which comprises a turbine 7 and a pump 8. The
pump 8 can be driven via a drive shaft of the turbine 7. A turbine
inlet line 9 is connected to the turbine 7 on the inlet side, and a
turbine outlet line 10 is connected to the turbine 7 on the outlet
side. In each case the other end of the lines 9, 10 is connected to
the intake line 2, upstream or downstream, respectively, of the
throttle element 6, so that the turbine 7 is connected in parallel
with the throttle element. The airstream delivered by the turbine 7
can in this case be controlled by a controllable valve 20 in the
turbine outlet line 10. A pump inlet line 11, which is in
communication with the environment, is connected to the pump on the
entry side. A pump outlet line 12, which branches off to form the
addition points 13, 14 in the exhaust manifold 3 and in the exhaust
pipe 4, respectively, is connected to the pump on the outlet
side.
[0032] Furthermore, the engine 1 is assigned an injection system,
not indicated in more detail, for injecting fuel, either directly
into the combustion chambers of the engine 1 or into the inlet
region of the individual cylinders. Moreover, the engine 1 has an
engine control unit (not shown) for controlling or regulating
operation of the engine 1 and the systems assigned to the engine 1.
For this purpose, various sensors and measurement pick-ups (not
shown), such as for example pressure sensors, an air mass flowmeter
in the intake line 2 and exhaust-gas and temperature sensors in the
exhaust pipe 4, are arranged in the intake system and in the
exhaust system. The signals from the sensors are recorded and
evaluated by the engine control unit. Moreover, the engine 1 is
assigned a starter (not shown), operation of which initiates the
starting operation and maintains the starter until the engine is
operating independently.
[0033] The mode of operation of the installation illustrated in
FIG. 1 is explained below.
[0034] In a first field of use, the gas conveying system is used to
achieve low-emission starting or warming-up of the engine 1. For
this purpose, it is crucial that the catalytic converter 5 arranged
in the exhaust pipe 4 be able to operate with sufficient
efficiency, i.e. at what is known as its light-off temperature,
sufficiently quickly. For this purpose, after a certain instant in
the starting operation, the engine is operated with a rich air/fuel
ratio, and the reducing constituents in the rich exhaust gas
obtained are burnt by after-oxidation upstream of the catalytic
converter 5. In the text which follows, the air/fuel ratio of the
mix fed to the engine 1 is referred to as engine .lamda. or
.lamda..sub.E. The heat of combustion which is released during the
after-oxidation heats the catalytic converter 5, so that the
catalytic converter 5 can quickly perform its purification
function. As a result of secondary air being supplied, the exhaust
gas reaches the oxygen content required for the after-oxidation to
proceed. The supply of secondary air is effected by the pump 8
driven by the turbine 7. Actuation of a switching unit (not shown)
in the pump outlet line 12 opens up the addition point 13 in the
exhaust manifold 3 for the addition of secondary air and blocks the
addition point 14. The pressure drop which is present across the
throttle element 6 and is caused by the flow of the air taken in by
the engine 1 is used to drive the turbine. This pressure drop acts
across the turbine inlet line 9 and the turbine outlet line 10 and
therefore causes air to flow across the turbine 7, thereby driving
the turbine 7 and the pump 8 coupled to it.
[0035] A precondition for the after-oxidation to take place is that
a combustible mixture be present. Therefore, for low-emission
starting of the engine, it is important to match the fuel injection
quantity and secondary air delivery. The aim is for the
after-oxidation to commence as early as possible when starting up
the engine 1.
[0036] According to the invention, during the starting operation
the quantity of fuel injected is set as a function of the delivery
capacity of the pump 8. It is preferable for no fuel to be injected
initially when the starting operation begins, since at this instant
the pump 8 is not yet delivering any secondary air. The reason for
this is that the pressure drop across the throttle element 6 is not
initially present or is too low. Since the speed of the engine 1,
at typically approximately 200 rpm, is relatively low during the
starting operation, a pressure drop across the throttle element is
built up relatively slowly. To accelerate the build-up of pressure,
the throttle element is set as a function of the reduced pressure
which is present in the intake line 2 downstream of the throttle
element 6. It is preferable for the throttle element to be
completely closed in the absence of reduced pressure during the
starting operation. This is the case right at the beginning of the
starting operation. The result of this is that the air in the line
volume between throttle element 6 and air inlet of the engine
cylinders is rapidly sucked out by the engine. Consequently, a
differential pressure across the throttle element 6 is quickly
built up, and accordingly the turbine 7 quickly reaches its
rotational speed and the pump 8 delivers secondary air
correspondingly quickly.
[0037] The injection of fuel preferably only begins when the pump 8
has reached a minimum delivery capacity, which can be determined,
for example, with the aid of a rotational speed sensor at the pump
8. The period of time from the beginning of starter actuation to
the beginning of fuel injection can advantageously also be set in a
time-controlled fashion. In this case, it is possible, for example,
to make use of a table stored in the engine control unit, in which
the periods until the fuel injection begins are stored. In this
case, it is additionally possible to take account of the coolant
temperature of the engine 1 or the ambient temperature.
[0038] The quantity of fuel injected per unit time is preferably
set in such a way that an engine .lamda. of approximately
.lamda..sub.E=0.8 results. Therefore, an ignitable mixture is
present in the combustion chambers of the engine 1, and the engine
1 can continue to operate without starter assistance. When this
independent engine running begins, the engine speed, the intake air
quantity and the pressure drop across the throttle element 6 rise.
In accordance with the setting as a function of reduced pressure,
the throttle element 6 is opened when a predeterminable
reduced-pressure value is reached. The quantity of secondary air
delivered into the exhaust manifold 3 by the pump 8 is limited with
the aid of the setting valve 20 in the turbine exhaust line 10 in
such a way that conditions which are favorable for after-oxidation
result in the exhaust manifold 3. The secondary air quantity is
preferably set in such a way that an air/fuel ratio, also referred
to below as exhaust-gas .lamda. or .lamda..sub.EG, of approximately
.lamda..sub.EG=1.2 is set for the exhaust gas.
[0039] The time required to deliver a sufficient quantity of
secondary air can be shortened still further if the starting speed
of the engine 1 is increased during the starter operation.
According to the invention, this is achieved by reducing the
compression work performed by the engine 1. With a variable
compression ratio, this is reduced in the starter phase of the
starting operation. Furthermore, it is advantageous to relieve the
throttling of the engine 1 by opening the outlet valves in the
compression stroke. It is also advantageous to temporarily decouple
auxiliary units which are driven by the engine 1. By way of
example, it is possible to decouple a generator or a coolant pump.
This reduces the mechanical power loss from the engine 1 and
increases the engine speed during starter operation.
[0040] After stable and independent engine running and the
light-off temperature of the starting catalyst 5 have been reached,
the starting operation can be considered to have ended and the
addition of secondary air to the exhaust manifold 3 is concluded.
The ending of the addition of secondary air can be effected by
closing the setting valve 20 or closing a switching device (not
shown) in the pump outlet line 12.
[0041] In a further field of use, the gas conveying system is
employed to reduce emissions during rich operation of the engine 1
outside the starting operation, for example during acceleration or
under full load. Under these conditions, a pressure drop which is
sufficient to operate the turbine 7 is present across the throttle
element. In this application of the gas conveying system, the pump
8 passes secondary air into the exhaust gas at the addition point
14 on the entry side of a catalytic converter 5 which is in this
case preferably arranged remote from the engine. In the process, an
exhaust-gas .lamda. of approximately .lamda..sub.EG=1.0 is set.
Under these conditions, reducing exhaust-gas constituents are
oxidized by the catalytic converter 5 and the level of pollutants
is reduced even during acceleration or full-load operation.
[0042] In a further application area, the gas conveying system is
used to cool part of the exhaust system. By way of example, the
pump 8 can be used to blow relatively cool ambient air into the air
gap of a catalytic converter housing or exhaust manifold with air
gap insulation. This function of the gas conveying system is
preferably activated when a determining temperature in the exhaust
system is exceeded. This prevents the exhaust system from being
overheated or damaged and maintains the function of components
which have a purifying action.
[0043] FIG. 2 diagrammatically depicts the arrangement of the
engine 1 and the gas conveying system in a further preferred
embodiment. The designation of functionally equivalent components
corresponds to that employed in FIG. 1. In addition to the
embodiment illustrated in FIG. 1, the gas conveying system is in
this case assigned a further gas conveying unit, which is designed
as an electrically driven air pump 15 which is connected to a
branch of the turbine inlet line 9. Moreover, a shut-off valve 21,
which can be used to shut off the connection to the intake line 2
upstream of the throttle element 6, is provided in the turbine
inlet line 9. The turbine 7 can be run up to speed more quickly
with the aid of the air pump 15 when the engine 1 is starting up.
For this purpose, at the beginning of starter operation, the
shut-off valve 21 is closed, the valve 20 is opened and the air
pump is switched on. Therefore, air is delivered via the turbine 7
virtually as soon as the starting operation begins. Consequently, a
quantity of secondary air which is sufficient for after-oxidation
can be fed to the exhaust manifold 3 after just a short time
irrespective of the build-up of differential pressure across the
throttle element 6, and the fuel injection is performed in the same
way as in the embodiment shown in FIG. 1. When a sufficient
differential pressure has been built up across the throttle element
6, the air pump is switched off and the shut-off valve 21 is
opened. The turbine 7 is then driven by the airstream flowing
through the lines 9, 10, which is caused by the differential
pressure across the throttle element 6. All the further functions
of the gas conveying system are present in the same way as in the
embodiment shown in FIG. 1.
[0044] FIG. 3 diagrammatically depicts the arrangement of the
engine 1 and the gas conveying system in a further preferred
embodiment. Functionally equivalent components are designated by
the same references as in FIG. 1. In addition to the embodiment
illustrated in FIG. 1, the gas conveying system is in this case
assigned a further gas conveying unit, which is designed as an
evacuable gas vessel 16 which is arranged in a secondary branch of
the turbine outlet line 10. The gas vessel can be shut off on the
inlet side and the outlet side by a shut-off valve 22 and 23,
respectively. The turbine 7 can be run up to speed more quickly
with the aid of the evacuated gas vessel 16 during starting of the
engine 1. For this purpose, when the starter operation begins, the
shut-off valve 22 is opened on the inlet side of the evacuated gas
vessel 16. The valves 20 and 23 remain closed. Therefore, air is
conveyed into the evacuated gas vessel 16 via the turbine 7
virtually as soon as the starting operation begins. Consequently, a
quantity of secondary air which is sufficient for after-oxidation
can be fed to the exhaust manifold 3 after a short time
irrespective of the build-up of differential pressure across the
throttle element 6, and the fuel injection is performed in the same
way as in the embodiment shown in FIG. 1. When a sufficient
differential pressure has been built up across the throttle element
6, the valve 20 is opened and the valve 22 is closed. The turbine 7
is then driven by the airstream through the turbine inlet line 9
and the branch of the turbine outlet line 10 provided with the
valve 20. The airstream is in this case produced by the
differential pressure across the throttle element 6. To enable the
turbine to be run up to speed quickly independently of the build-up
of differential pressure across the throttle element 6, the gas
vessel 16 must of course be of sufficient size. All the further
functions of the gas delivery system are similar to the embodiment
shown in FIG. 1. For renewed evacuation of the gas vessel 16,
during normal engine operation the valve 23 is open and the valve
22 is closed. In particular at an engine operating point with a
high subatmospheric pressure downstream of the throttle element 6,
such as for example during overrun operation at a high engine
speed, the gas vessel 16 can be evacuated sufficiently for a
further starting operation.
[0045] FIG. 4 diagrammatically depicts the arrangement of the
engine 1 and the gas conveying system in a further preferred
embodiment. Functionally equivalent components are designated by
the same references as those used in FIG. 1. With the embodiment
illustrated in FIG. 4, it is possible to provide exhaust-gas
recirculation in addition to the functions of the embodiment
illustrated in FIG. 1. For this purpose, the gas delivery system
has a branch, provided with a valve 24, of the pump inlet line 11,
which branch is in communication with the exhaust pipe 4. That part
of the pump inlet line 11 which is in communication with the
environment can likewise be shut off by the valve 25 arranged
therein. Furthermore, a branch of the pump outlet line 12 which
leads into the intake line 2 downstream of the throttle element 6
is provided. This branch can likewise be shut off by the settable
valve 26. if the gas delivery system is not required to deliver
secondary air, during normal engine operation the pump 8 can
deliver exhaust gas into the intake line 2 at the addition point
18. For this purpose, the valve 24 is opened and the valve 25 is
closed. The valve 26 is opened according to the exhaust-gas
recirculation rate that is to be provided. The pump 8 is driven as
described above by the airstream across the turbine 7 caused by the
differential pressure across the throttle element 6. The embodiment
shown in FIG. 4 can provide a higher exhaust-gas recirculation rate
compared to standard exhaust-gas recirculation systems with passive
exhaust-gas recirculation, in which the recirculated quantity of
exhaust gas is determined by the differential pressure that is
present between exhaust pipe and intake pipe. The reason for this
is the active exhaust-gas delivery provided by the pump 8. All the
further functions of the gas delivery system are present in the
same way as in the embodiment shown in FIG. 1.
[0046] FIG. 5 diagrammatically depicts the arrangement of the
engine 1 and the gas conveying system in a further preferred
embodiment. Functionally equivalent components are designated by
the same designations as in FIG. 1. Unlike in the embodiment
illustrated in FIG. 1, the pump inlet line 11 is in this case
connected to an evacuable gas vessel 17. A connection to the
environment which can be shut off by a valve 27 is still present.
If the gas conveying system is not required to deliver secondary
air, the gas vessel can be evacuated by the pump 8 during normal
engine operation. For this purpose, the valve 27 is closed. The air
which is extracted from the gas vessel 17 can be fed to the exhaust
gas via the pump outlet line 12 or can be released to the
environment via a branch which is not shown. Servo systems which
are operated by reduced pressure, are connected to the gas vessel
17 and are not indicated in more detail here can be operated by the
reduced pressure generated in the gas vessel 17. All the further
functions of the gas conveying system are still present in the same
way as in the embodiment shown in FIG. 1.
[0047] With the embodiments of internal combustion engine and gas
conveying system in accordance with the invention, it is possible,
as illustrated, to provide low-emission operation of the internal
combustion engine. The functions of the gas conveying system which
are present in addition to the delivery of secondary air means that
the gas conveying system is utilized better and that some
components can be eliminated. In this context, it will be
understood that modifications to the embodiments illustrated are
possible within the scope of the invention by the use of additional
lines or valves in the gas converying system.
* * * * *