SE541371C2

SE541371C2 - Method and system for controlling exhaust gases resulting from combustion

Info

Publication number: SE541371C2
Application number: SE1550976A
Authority: SE
Inventors: John Gaynor; Torbjörn Eliassen
Original assignee: Scania Cv Ab
Priority date: 2015-07-06
Filing date: 2015-07-06
Publication date: 2019-09-03
Also published as: DE102016007208A1; DE102016007208B4; SE1550976A1

Abstract

The present invention relates to a method for controlling exhaust gases resulting from combustion in an internal combustion engine (101), said internal combustion engine (101) having at least one combustion chamber (i1-i6) and an intake side (402) for receiving air for use in combustion, said internal combustion engine (101) further being arranged to discharge exhaust gases resulting from said combustion. The method includes:- when said internal combustion engine (101) is delivering at least a first work, providing a flow of air from said intake side (402) for mixing with exhaust gases resulting from said combustion, the flow of air bypassing said at least one combustion chamber (i1-i6), and- when said internal combustion engine (101) is delivering a second, lower than said first, work, recirculating at least part of exhaust gases resulting from said combustion to said intake side (402).

Description

METHOD AND SYSTEM FOR CONTROLLING EXHAUST GASES RESULTING FROM COMBUSTION Field of the invention The present invention relates to combustion processes, and in particular to a method and system for controlling an exhaust gas stream. The present invention also relates to a vehicle, as well as a computer program and a computer program product that implement the method according to the invention.

Background of the invention With regard to vehicles in general, and at least to some extent heavy/commercial vehicles such as trucks, buses and the like, there is constantly ongoing research and development with regard to increasing fuel efficiency and reducing exhaust emissions.

This is often at least partly due to growing governmental concern in pollution and air quality, e.g. in urban areas, which has also led to the adoption of various emission standards and rules in many jurisdictions.

These emission standards often consist of requirements that define acceptable limits for exhaust emissions of vehicles being provided with internal combustion engines. For example, the exhaust levels of e.g. nitric oxides (NOx), hydrocarbons (HC), carbon monoxide (CO) and particles are regulated for most kinds of vehicles in these standards.

The undesired emission of substances can be reduced by reducing fuel consumption and/or through the use of aftertreatment (purifying) of the exhaust gases that results from the combustion process.

Exhaust gases from the internal combustion engine can, for example, be treated through the use of a catalytic process.

There exist various kinds of catalytic converters, where different types can be used for different kinds of fuel and/or for treatment of different kinds of substances occurring in the exhaust gas stream.

For example, a common kind of catalytic converters that are used in particular for reduction of nitric oxides, N0X, is Selective Catalytic Reduction (SCR) catalytic converters.

There also exist other kinds of catalytic converters that are commonly used in particular in the reduction of exhaust emissions resulting from combustion in commercial/heavy vehicles. Such catalytic converters include e.g. oxidation catalytic converters. Catalytic converters being used for aftertreatment of an exhaust gas stream in general have in common that at least a minimum temperature must be maintained in the catalytic converter in order to ensure that the desired reactions occur. Furthermore, the catalytic converters may also be temperature sensitive in the regard that too high temperatures may be damaging.

Summary of the invention It is an object of the present invention to provide a method and system that controls exhaust gases resulting from combustion in a combustion chamber. The exhaust gases can, for example, be controlled on the basis of a temperature condition of the exhaust gases. In this way a temperature condition of one or more aftertreatment components being subjected to the exhaust gas stream can also be controlled. This object is achieved by a method according to claim 1.

According to the present invention, it is provided a method for controlling exhaust gases resulting from combustion in an internal combustion engine, said internal combustion engine having at least one combustion chamber and an intake side for receiving air for use in combustion, said internal combustion engine further being arranged to discharge exhaust gases resulting from said combustion. The method includes: - when said internal combustion engine is delivering at least a first work, providing a flow of air from said intake side for mixing with exhaust gases resulting from said combustion, the flow of air bypassing said at least one combustion chamber, and - when said internal combustion engine is delivering a second, lower than said first, work, recirculating at least part of exhaust gases resulting from said combustion to said intake side.

With regard to exhaust gases resulting from combustion there are various ways of treating these exhaust gases in order to reduce harmful emissions into the surroundings of the vehicle. For example, it is common, at least with regard to heavy/commercial vehicles, that nitric oxides NOxare reduced. Nitric oxides NOxare formed during a combustion process for different reasons. However, the main reason for the generation of NOx, at least with regard to combustion according to e.g. the diesel or Otto principle, consists of thermal generation of NOx, where nitrogen in the air being supplied to the combustion reacts spontaneously with oxygen at the high temperatures and pressures that arise in the combustion chamber.

Thermal generation of nitric oxides NOxis highly dependent of the temperature of the combustion, where higher temperatures give rise to higher amounts of nitric oxides NOx.

The amount of nitric oxides NOxin the exhaust gas stream may be reduced prior to the exhaust gas stream being released into the surroundings of the vehicle, for example using a Selective Catalytic Reduction (SCR) catalytic converter. Such reduction is not always sufficient, and it is also possible to reduce the nitric oxides by recirculating part of the exhaust gases. Recirculated exhaust gases act as an inert gas during combustion, and hence essentially does not react with the combustion gas (e.g. air) or the fuel present in the combustion chamber. The exhaust gas recirculation (commonly denoted EGR) thereby reduces the maximum temperature that arises during combustion, and therefore also the amount of nitric oxides NOxbeing generated during the combustion.

With regard to EGR recirculation, the exhaust gas stream generated during combustion is usually relatively hot and since the forming of nitric oxides is dependent of the temperature that arises during combustion, recirculated exhaust gases are cooled prior to being recirculated to a combustion chamber.

The cooling makes possible use of higher EGR ratios, while at the same time the gas temperature at the intake side of the combustion chambers is lowered which contributes to a lower maximum temperature and thereby a reduction of the generated nitric oxides.

There exist, however, aftertreatment systems that are capable of reducing nitric oxides to a satisfactory extent using e.g. an efficient SCR catalytic converter without the need for EGR recirculation. The present invention relates in particular to systems of this kind. According to the present invention e.g. means for exhaust gas recirculation, or other suitable means for accomplishing gas flows according to the invention, are used but in a manner different from the prior art.

In particular, the present invention relates to situations that may arise when certain conditions prevail regarding vehicle operation and surroundings. This is accomplished by a method (and system) by means of which a flow of air from the intake side of the internal combustion engine is arranged to mix with exhaust gases resulting from said combustion when the internal combustion engine is delivering at least a first work.

Furthermore, at least part of exhaust gases resulting from said combustion are recirculated to said intake side when the internal combustion engine delivers a second, less than said first, work.

According to the invention, air from the intake side of the internal combustion engine is arranged to bypass the combustion chambers for mixing with the exhaust gases when the work of the internal combustion engine exceeds some first work, e.g. when hot exhaust gases are expected. In this way, hot exhaust gases can be cooled off in situations when hot exhaust gases may damage temperature sensitive components being passed through by the exhaust gases prior to being let out into the surroundings of the vehicle. Such situations may arise in particular at high altitudes and/or when the internal combustion engine load, and hence the produced work, is high at lower internal combustion engine speeds. Lower internal combustion engine speeds in general result in smaller volumes of air being transported through the combustion chambers of the internal combustion engine, thereby providing less cooling. According to one embodiment, the bypass of air is only performed when the altitude of the vehicle exceeds a first altitude. Since the density of air is lower at higher altitudes the mass flow of air through the combustion chambers is reduced at higher altitudes. This, in turn, results in higher exhaust gas temperatures in relation to similar operation at lower altitudes.

The internal combustion engine may comprise a plurality of combustion chambers, which can be divided into groups, or banks, and the flow of air can be arranged to be mixed with exhaust gases from a subset of said plurality of groups of combustion chambers. For example, if the combustion chambers, e.g. cylinders are divided into two or more groups n, the flow of air may be arranged to be mixed with exhaust gases from at most n-1 groups, such as e.g. one group/bank only of said two or more groups. For example, the combustion chambers may be divided into two groups, where the flow of air can be provided to one of said groups, thereby e.g. half of the combustion chambers. Following this mixing, exhaust gases from all combustion chambers may be mixed to form an aggregated exhaust gas stream arranged to pass through at least one component for treating said exhaust gas stream.

As was mentioned, the inventive method not only relates to the adding of a flow of air to the exhaust gas stream, but exhaust gases are also recirculated to the air intake side of the engine when the internal combustion engine delivers a work being equal to or less than said second work. The recirculation of uncooled exhaust gases reduces intake of colder air and in this way, the resulting temperature of the exhaust gases reaching aftertreatment components can be increased in situations when the exhaust gases may otherwise cool off aftertreatment components to an extent where proper operation no longer can be ensured. The recirculation of uncooled exhaust gases also reduces the flow through the aftertreatment components, which is advantageous when the exhaust gases are not hot enough to provide proper heating of aftertreatment components. According to one embodiment, warm exhaust gases are recirculated when an average work delivered by the internal combustion engine is being at most said second work for a first period of time.

According to one embodiment, warm (uncooled) exhaust gases are recirculated when an internal combustion engine is rotating but when there is no combustion in said at least one combustion chamber.

Further characteristics of the present invention and advantages thereof are indicated in the detailed description of exemplary embodiments set out below and the attached drawings.

Brief description of the drawings Fig. 1A illustrates a power train of an exemplary vehicle in which the present invention advantageously can be utilized; Fig. IB illustrates an example of a control unit in a vehicle control system; Fig. 2 illustrates an example of aftertreatment components for treatment of exhaust gases resulting from combustion.

Fig. 3 illustrates an exemplary method according to one embodiment of the present invention.

Fig. 4A illustrates an exemplary system according to one embodiment of the present invention.

Fig. 4B illustrates an exemplary system according to another embodiment of the present invention.

Fig. 5 illustrates bypass of air according to the invention.

Fig. 6 illustrates exhaust gas recirculation according to the invention.

Detailed description of exemplary embodiments In the following detailed description the present invention will be exemplified for a vehicle. The invention is, however, applicable also in other kinds of transportation means, such as air and water crafts. The invention is also applicable in fixed installations.

Fig. 1A schematically depicts a power train of an exemplary vehicle 100. The power train comprises a power source, in the present example an internal combustion engine 101, which, in a conventional manner, is connected via an output shaft of the internal combustion engine 101, normally via a flywheel 102, to a gearbox 103 via a clutch 106. An output shaft 107 from the gearbox 103 propels drive wheels 113, 114 via a final drive 108, such as a common differential, and drive axles 104, 105 connected to said final drive 108.

The internal combustion engine 101 is controlled by the vehicle control system via a control unit 115. The clutch 106 and gearbox 103 are also controlled by the vehicle control system by means of a control unit 116.

Fig. 1A discloses a powertrain of a specific kind, but the invention is applicable for any kind of power train, and also e.g. in hybrid vehicles. The disclosed vehicle further comprises an aftertreatment unit 130 for aftertreatment (purifying) of exhaust gases that results from combustion in the internal combustion engine 101. The functions of aftertreatment unit 130 are controlled by means of a control unit 131.

The aftertreatment unit 130 can be of various kinds and designs. An example of an aftertreatment unit 130 in which the present invention can be utilized is schematically illustrated in figure 2. The exhaust gas stream 201, when encountering the components of the aftertreatment unit 130, first encounters a diesel oxidation catalytic converter (DOC) 203.

The oxidation catalytic converter DOC 202 has different functions, and is, inter alia, used in the aftertreatment to oxidize remaining hydrocarbons and carbon monoxide in the exhaust gas stream to carbon dioxide and water. In the oxidation of hydrocarbons (i.e. oxidation of fuel), heat is also generated, which can be used to increase the temperature of a particle filter DPF 203 during oxidation of soot, socalled regeneration, of the particle filter DPF 203. The oxidation can also in general be used to ensure that aftertreatment components downstream the oxidation catalytic converter 202 maintain a desired minimum temperature.

The oxidation catalytic converter 202 may also oxidize nitrogen monoxides (NO) occurring in the exhaust-gas stream to nitrogen dioxide (N02). This nitrogen dioxide is used, for example, in N02~based regeneration of the diesel particulate filter DPF 203, but also the efficiency of reduction in SCR catalytic converters (see below) is dependent on the ratio between NO and NO2 in the exhaust gas stream, and benefits from NO2 conversion in oxidation catalytic converter DOC 202. Other reactions may also occur in the oxidation catalytic converter DOC 202.

As was mentioned, a diesel particulate filter DPF 203 is arranged downstream the oxidation catalytic converter and basically has the task of collecting particles in the exhaust gas stream, which when the DPF 203 is filled to some suitable extent are processed to less hazardous compositions through regeneration as is known per se.

The disclosed aftertreatment unit 130 also comprises a selective catalytic reduction (SCR) catalytic converter 204 arranged downstream of the DPF 203. SCR catalytic converters in general reduce e.g. nitrous oxides NOxin the exhaust gas stream through the use of an additive in a manner known per se.

The aftertreatment unit 130 finally comprises an ammonia slip catalytic converter ASC 205 arranged downstream of the SCR 204. The ASC oxidises surplus ammonia that may remain in the exhaust gases after passage through the SCR 204. The ASC 205 may also assist the SCR 204 in further NOxreduction.

The components DOC 202, DPF 203, SCR catalytic converter 204, and ASC 205 may be integrated in a single unit 130.

Alternatively, the components can be arranged in any other suitable way manner, and one or more of said components can, for example, consist of separate units. Fig. 2 further discloses temperature sensors 210-212, which can be used e.g. in temperature control of the components. According to the invention, such temperature sensors may or may not be used, and the temperature sensor setup is only exemplary and any suitable sensor, or number of sensors, at any suitable location or locations may be used, or no sensor at all.

The operation of components of the kind disclosed in fig. 2, and perhaps in particular the SCR catalytic converter 204, are highly dependent on the prevailing temperature of the component. If the temperature of the component is too low, desired reactions may not occur and, conversely, if temperature is too high components may instead be damaged. For example, if the oxidation catalytic converter temperature is too low, the oxidation catalytic converter will not be capable of oxidizing remaining hydrocarbons in the exhaust gas stream 201. Similarly, the NOxreduction of the SCR catalytic converter 204 will not occur to a desired extent if the temperature of the SCR catalytic converter 204 is too low.

The temperature of components of the aftertreatment unit 130 is highly dependent of the temperature of the exhaust gas stream 201. Components of this kind are in general relatively well insulated and affected by ambient temperature, e.g. the temperature in the vehicle surroundings, to a much lesser extent when the vehicle is in operation.

The present invention provides a method that influences the exhaust gas temperature of the exhaust gas entering aftertreatment components, and which method at least in some situations controls the exhaust gases by influencing the exhaust gas temperature in a manner that is favourable to the temperature of the aftertreatment components. For example, the present invention may be used for influencing exhaust gas temperatures when driving conditions are such that the resulting exhaust gases (the resulting exhaust gas temperature) may have a detrimental effect of the operation and/or durability of the aftertreatment components.

An exemplary method 300 of the present invention is shown in fig. 3. The method can be implemented at least partly e.g. in the engine control unit 115 for controlling operation of the internal combustion engine 101. The functions of a vehicle are, in general, controlled by a number of control units, and control systems in vehicles of the disclosed kind generally comprise a communication bus system consisting of one or more communication buses for connecting a number of electronic control units (ECUs), or controllers, to various components on board the vehicle. Such a control system may comprise a large number of control units, and the control of a specific function may be divided between two or more of them.

For the sake of simplicity, Fig. 1A depicts only control units 115-116, 131, but vehicles 100 of the illustrated kind are often provided with significantly more control units, as one skilled in the art will appreciate. Control units 115-116, 131 are arranged to communicate with one another and various components via said communication bus system and other wiring, partly indicated by interconnecting lines in fig. 1A.

The present invention can be implemented in any suitable control unit in the vehicle 100, and hence not necessarily in the control unit 115. The control influencing the resulting exhaust gas temperature according to the present invention will usually depend on signals being received from other control units and/or vehicle components, and it is generally the case that control units of the disclosed type are normally adapted to receive sensor signals from various parts of the vehicle 100. The control unit 115 may, for example, receive signals e.g. from the control unit 131 and various sensors with regard to the control of the internal combustion engine. Also, the control unit 115 may be arranged to receive sensor signals from one or more valves used in the implementation of the present invention according to the below. Control units of the illustrated type are also usually adapted to deliver control signals to various parts and components of the vehicle, e.g. to valves and exhaust brake etc. according to the below, and/or to control units controlling functions of the vehicle used by the present invention. All this is known to the person skilled in the art.

Control of this kind is often accomplished by programmed instructions. The programmed instructions typically consist of a computer program which, when executed in a computer or control unit, causes the computer/control unit to exercise the desired control, such as method steps according to the present invention. The computer program usually constitutes a part of a computer program product, wherein said computer program product comprises a suitable storage medium 121 (see Fig. IB) with the computer program 126 stored on said storage medium 121. The computer program can be stored in a non-volatile manner on said storage medium. The digital storage medium 121 can, for example, consist of any of the group comprising: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk unit etc, and be arranged in or in connection with the control unit, whereupon the computer program is executed by the control unit. The behaviour of the vehicle in a specific situation can thus be adapted by modifying the instructions of the computer program.

An exemplary control unit (the control unit 115) is shown schematically in Fig. IB, wherein the control unit can comprise a processing unit 120, which can consist of, for example, any suitable type of processor or microcomputer, such as a circuit for digital signal processing (Digital Signal Processor, DSP) or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC). The processing unit 120 is connected to a memory unit 121, which provides the processing unit 120, with e.g. the stored program code 126 and/or the stored data that the processing unit 120 requires to be able to perform calculations. The processing unit 120 is also arranged so as to store partial or final results of calculations in the memory unit 121.

Furthermore, the control unit 115 is equipped with devices 122, 123, 124, 125 for receiving and transmitting input and output signals, respectively. These input and output signals can comprise waveforms, pulses or other attributes that the devices 122, 125 for receiving input signals can detect as information for processing by the processing unit 120. The devices 123, 124 for transmitting output signals are arranged so as to convert calculation results from the processing unit 120 into output signals for transfer to other parts of the vehicle control system and/or the component(s) for which the signals are intended. Each and every one of the connections to the devices for receiving and transmitting respective input and output signals can consist of one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Oriented Systems Transport) or any other bus configuration, or of a wireless connection.

Returning to the first exemplary method 300 illustrated in fig. 3, the method starts in step 301, where it is determined whether the exhaust gases are to be controlled according to the invention. The method remains in step 301 for as long as this is not the case. The method continues to step 302 when it is determined that the exhaust gases are to be controlled according to the invention. The transition from step 301 to step 302 can, for example, be initiated according to various criteria. For example, the control can be arranged to be performed at all times. Alternatively, control according to the invention can be arranged to be performed e.g. when conditions, e.g. with regard to vehicle internal operational conditions or conditions regarding the surroundings of the vehicle fulfil some criterion. Such conditions may, for example, relate to the current load of the internal combustion engine, and thereby the amount of work being produced, vehicle speed, ambient temperature, the altitude at which the vehicle is being driven, or any suitable combination of such criteria. Other suitable criteria for performing the transition from step 301 to step 302 may also be applied. As is explained further below such criterion may also include a determination of whether the internal combustion engine work is low or whether there is no fuel injection at all. It is also possible to use the time during which certain conditions have prevailed as criterion.

In step 302 it is determined whether there is a risk that current engine operation may damage aftertreatment components due to high resulting exhaust gas temperature, and air therefore should be supplied to the exhaust gas stream. When this is the case the method continues to step 303, otherwise the method continues to step 306. This is further explained below.

There exist internal combustion engines that are capable of producing exhaust gases that are of such high temperatures that the hot exhaust gases may damage aftertreatment components, and perhaps in particular SCR catalytic converters, which oftentimes are relatively temperature sensitive. The risk for this to occur may perhaps be the greatest at high altitudes where air is thinner, and in particular in combination with low engine speeds while simultaneously a high torque is delivered by the internal combustion engine.

When a vehicle is travelling on high altitudes the same flow of air will be sucked through the air filter, but higher altitudes means less density of the air, and hence a lower mass flow and therefore less air being supplied to the combustion chambers. In these situations, therefore, the total air mass flow may be considerably smaller than the air mass flow on lower altitudes and/or at higher engine speeds. The resulting exhaust gas temperature is dependent on the amount of fuel supplied to the combustion chambers and the amount of air in which the combustion is performed. When there is less air available for the combustion, this will result in higher exhaust gas temperatures. The lower air mass flow results in a smaller amount of air passing through the engine, thereby providing a lesser cooling effect and higher exhaust gas temperatures.

The negative influence of higher altitudes is further increased when the internal combustion engine delivers high loads (high torques) at low engine speeds. This is because the lower engine speeds also reduces the total amount of air mass flowing through the engine per unit of time, thereby providing less cooling. If the internal combustion engine delivers some arbitrary torque at some internal combustion engine speed, this will result in higher temperatures than when the same load/torque is delivered at a higher internal combustion engine speed since in this case higher amounts of air passes through the engine and thereby provide additional cooling.

The general trend in engine development is towards downspeeding, i.e. the capability of providing high torques at low engine speeds for improved fuel efficiency. This puts further emphasis on low-speed, high-load operation. However, problems of the above kind may result in situations where engines that would be very economical from a manufacturer point of view, and/or fuel efficient from a customer point of view, may not even be built because of the risk of generating too high exhaust temperatures at full load when operating at lower engine speeds.

At least the internal combustion engine may have to be restricted from high loads when operated at lower internal combustion engine speeds to avoid the risk of overheating components being subjected to the exhaust gas stream.

Sometimes, therefore, the amount of fuel supplied to the combustion must be reduced at least in some internal combustion engine speed intervals in order to protect aftertreatment components.

The present invention, inter alia, provide a solution to problems of this kind, and hence makes possible use of engine operation that otherwise may not be possible without the risk of damaging components. In addition, the present invention also addresses problems of other driving conditions, which is explained further below with reference to steps 306-309 of fig. 3.

An exemplary system according to the present invention is disclosed in fig. 4A. The figure shows an exemplary internal combustion engine 101 having six combustion chambers in the form of cylinders il-i6. The internal combustion engine 101 may, of course, comprise any suitable number of cylinders/combustion chambers.

Each combustion chamber il-i6 comprises an inlet (not shown), e.g. controlled by one or more valves, which may be arranged to be individually controlled, acting against the combustion chambers, respectively, for the intake of air for use in the combustion. The engine 101 further comprises an intake conduit 402, e.g. consisting of suitable piping, tubing and/or hosing, for receiving the air for supply to the combustion chambers il-i6. The air in general consists of air from the environment of the vehicle.

According to the disclosed example, ambient air from the vehicle/engine surrounding is drawn trough an air filter 404 from an intake side 404A of the air filter 404 being subjected to ambient air and being drawn through the air filter 404 by means of a compressor 406. The compressor 406 is driven by a turbine 408, the compressor 406 and turbine 408 being interconnected by means of a shaft 410, thereby forming a conventional turbocharger. The compressed air is cooled by a charge air cooler 412 in a manner known per se prior to being supplied to the intake conduit 402 and combustion chambers il i6 of the internal combustion engine 101. Internal combustion engines of the disclosed kind further comprises, in general, at least one fuel injector per combustion chamber (not shown) which in a conventional manner supplies fuel for combustion.

The combustion chambers il-i6 further comprises exhaust outlets, e.g. also controlled by means of valves acting against the combustion chambers il-i6 in a conventional manner, for evacuation of exhaust gases. According to the disclosed embodiment, exhaust gases emanating from cylinders i1-i3 share a common conduit 414 from exhaust outlets to a first inlet 408A of the turbine 408. Correspondingly, exhaust gases emanating from cylinders i4-i6 share a common conduit 416, separate from the conduit 414, from exhaust outlets to a second inlet 408B of the turbine 408. The turbine 408, consequently, comprises separate exhaust gas inlets for receiving the exhaust gas streams from conduits 414 and 416, respectively, e.g. constituting a conventional twin-scroll turbine. The turbine 408 further constitutes a fixed geometry turbine, and a waste gate 418 is connected to either or both conduits 414, 416 for turbine bypass when required.

The exhaust gas stream is discharged by the turbine 408 through a single common outlet 408C and is led, via an exhaust brake 420, to the aftertreatment unit 130 for aftertreatment of exhaust gases according to the above prior to being released into the surroundings of the vehicle 100.

According to the exemplary embodiment, the SCR catalytic converter is in itself capable of reducing nitric oxides to a desired extent and hence no further reduction is required. As was explained above, however, recirculation of actively cooled, through the use of a cooler, exhaust gases is often required in order to be able to fulfil requirements regarding NOxemissions. According to the disclosed example, however, exhaust gas recirculation circuitry is still provided but used in an entirely different context as compared to the prior art, and in a manner contrary to the prior art. According to the invention, there is no such recirculation of cooled exhaust gases. Instead warm (uncooled) exhaust gases are recirculated in situations where there is a desire to increase the exhaust gas temperature. The invention also provides for a gas flow in both directions through the exhaust gas recirculation components, the direction of flow being controlled in dependence of the current operating conditions of the vehicle.

According to the disclosed example, the conduit 416 is connected to an EGR valve 422 by means of a suitable conduit 426 in a manner known per se, and further via a closable valve 424, e.g. a poppet valve, arranged e.g. on a surface, or in close vicinity, of the conduit 416, so that conduit 426 between conduit 416 and EGR valve 422, can be essentially cut off from the exhaust system when conduits 426, 428 are not in use, thereby imposing minimum disturbance on the exhaust gas flow. The EGR valve 422 is further connected to the intake conduit 402 of the internal combustion engine 101 by conduit 428.

As was mentioned, there may exist situations when the exhaust gas stream resulting from combustion in the combustion chambers reaches temperatures that may, at least as time progress, heat aftertreatment components to temperatures where there is a risk of them being damaged. This is valid perhaps in particular for the SCR catalytic converter 204, which in general is highly temperature sensitive with regard to the possibility of suffering physical damage when being subjected to high temperatures.

Further to the method of fig. 3, it can, as was mentioned, be determined in step 302 if there is a risk that a situation of this kind may arise, and when this is the case the method continues to step 303. The determination can be made, e.g. based on signals from an altitude meter or any other suitable means for determining vehicle altitude, e.g. a satellite navigation system.

According to the present example, the exhaust gases resulting from combustion are cooled by supplying air from the intake side of the internal combustion engine to the exhaust gases, thereby bypassing the combustion chambers. In step 303 it is therefore determined a suitable control of the bypass of air from intake conduit 402 to exhaust evacuation conduit 416, bypassing combustion chambers il-i6. This determination can, for example, be determined based on the altitude of the vehicle, which can be determined by any suitable sensor, topographical data or the like. The determination in step 303 can also, alternatively or in addition, be arranged to be based e.g. on the current internal combustion engine load and/or current vehicle speed etc. The determination can also be based e.g. on the time during which such conditions has prevailed.

The control of the bypass of air can e.g. consist of a determination of a bypass flow of the air and/or a suitable control/opening of the EGR valve 422. For example, the flow and/or opening of EGR valve can be determined using a lookup table comprising e.g. altitudes, loads, internal combustion engine speeds, time periods and suitable bypass setting and/or flow for various situations, which table can be determined e.g. empirically. Alternatively, a suitable algorithm can be used. According to one embodiment, signals from one or more temperature sensors, e.g. temperature sensors 210-212 of fig. 2, can be used to continuously or at intervals control the bypass flow on the basis of the resulting exhaust gas temperature so that a suitable temperature is obtained.

When a suitable control has been determined, the method continues to step 304 where the control is commenced by opening valve 424, which in normal operation is closed, and the EGR valve 422 is controlled to open to a determined extent to obtain the desired control of the flow from intake conduit 402 to exhaust conduit 416. According to one embodiment, schematically shown in fig. 4B, the EGR valve 422 is completely omitted and only a valve 424 is used. That is, valve 424 can be arranged to control the flow of air, e.g. by suitable throttling. In a simplest form from fully open to fully closed position and vice versa. The invention is explained below in relation to the embodiment shown in fig 4A, but the effect accomplished by EGR valve 422 can consequently be accomplished by valve 424 instead.

Fig. 5, which is similar to fig. 4A, illustrates the direction of flow of air from intake side 402 to conduit 416 by arrows 502, 504, 506. With regard to the flow, this can be arranged to be controlled using e.g. a flow meter in the EGR circuit, but a control using suitable setting of the EGR valve 422 is in general sufficient. According to one embodiment, the EGR valve 422 is opened completely in the control according to the invention to allow the resulting flow to be whatever the resulting flow becomes, the actual flow thereby depending on prevailing pressures in the system. According to one embodiment, the EGR valve can be alternately opened and closed to obtain a suitable average flow over time. According to one embodiment the control of the valve 424 and/or EGR valve 422 is performed based on one or more temperatures, e.g. measured by any of temperature sensors 210-212.

Consequently, according to the invention, a conventional EGR circuit is used but in a manner contrary to the prior art, i.e. air is passed from intake side to exhaust side of the internal combustion engine when the load is high instead of the other way around. According to the embodiment shown in fig. 4A, air from the intake conduit 402 is arranged to bypass the combustion chambers il-i6 for mixture with exhaust gases from one bank only (cylinders i4-i6) of the cylinders.

However, since the exhaust gas streams from conduits 412 and 416, respectively, will be united at the turbine outlet 408C, the bypass of air will have a cooling effect on the aggregated exhaust gas stream reaching the aftertreatment components, and hence reducing negative temperature impact of the current operating conditions of the internal combustion engine.

According to one embodiment, air from the intake conduit 402 is arranged to bypass the combustion chambers il-i6 for mixture with exhaust gases from any number of cylinders, or all of the cylinders.

In order to ensure proper operation, the described method requires that the pressure in the intake conduit is higher than on the exhaust side in order to obtain a desired direction of flow. This, however, is generally the case in internal combustion engine operation, in particular with regard to internal combustion engines equipped with a turbocharger. The effect can, however, be accomplished also when the pressure relationship does not fulfil this criteria, e.g. through the use of a Venturi tube. Such creation of a flow from a lower pressure side to a higher pressure side is well known per se, and therefore not described more in detail herein. However, as was mentioned, in general pressure relationships are such that no Venturi tube is required in the installation.

Also, a control according to the invention further has the result that a higher total flow will reach the turbine 408. This, in turn, means that the rotational speed of the turbine increases, with the further result that the compressor 406 further increases compression of intake air. This, in turn, means that control according to the present invention not necessarily decreases the pressure level in the intake conduit 402 but rather maintains or increases the prevailing pressure level.

The opening of the EGR valve 422 will further give rise to a pressure increase on the exhaust side of the internal combustion engine, which in turn forces the internal combustion engine 101 to work somewhat harder due to the increased back-pressure when evacuating exhaust gases from the cylinders, with a corresponding increase in fuel consumption as a result. Consequently, the present invention provides a solution that although giving rise to a slight increase in fuel consumption, results in the exhaust gases still being cooled.

In step 305 it is checked whether control according to the invention is to be ended and the bypass of air be stopped. This can, for example, be the case when internal combustion engine operating conditions have improved from an exhaust gas temperature point of view. The method returns to step 304 for as long as this is not the case. Alternatively the method may return to step 303 for an adjustment of the bypass flow of air e.g. if conditions have changed. When it is determined that the bypass of air no longer is needed the method can be arranged to return to step 301, waiting for a next occasion when control according to the above is required. In this case, valve 424 can be closed so as to minimise additional and undesired volumes for undesired exhaust gas expansion, and thereby associated loss of energy for driving the turbine, upstream the turbine 408 from the EGR circuitry when this circuitry is not in operation.

The control performed according to fig. 5 can consequently be arranged to be activated when required, e.g. in driving situations where undesired exhaust gas temperatures arise. Since the present invention is capable of cooling the exhaust gases, manufacture of engines being capable of being subjected to high loads at low engine speeds is facilitated, since problems with high exhaust gas temperatures can be at least mitigated.

Steps 303-305 and fig. 5 relates to a situation where the resulting exhaust gases are too hot for one or more components being subjected to the exhaust gas stream. However, it is also possible that the situation is the other way around. This is exemplified with further reference to steps 306-309 and fig. 6. As was mentioned above, aftertreatment components may be sensitive to high temperatures. However, the processes that occur in such components during operation of the vehicle in general require that the components maintain a minimum temperature in order to ensure proper operation. For example, an SCR catalytic converter requires a minimum temperature to ensure that the reduction occurs to a desired extent. Also, the oxidation catalytic converter needs to maintain a certain temperature, otherwise there will be no or insufficient oxidation. If the temperature becomes too low, consequently, desired reactions occurring in the aftertreatment components may be reduced to a level where the vehicle no longer fulfils e.g. legislative requirements with regard to emissions. The desired reaction may also stop completely.

Consequently, it is also desirable to ensure that aftertreatment components maintain a desired minimum temperature. With regard to the temperature of the aftertreatment components, the temperature is almost completely controlled by the exhaust gas temperature/flow. Cooling of aftertreatment components by surrounding ambient air has less impact due to the aftertreatment components oftentimes being relatively well insulated.

For example, if the internal combustion engine is subjected to low loads it is not uncommon that the resulting exhaust gas temperatures becomes so low that in time aftertreatment components are cooled off to an extent where proper operation no longer can be ensured or maintained. Situations of this kind must in general be attended to, and according to conventional solutions this is accomplished e.g. by restricting air being supplied to the combustion. This can be accomplished, for example, through the use of an intake throttle, illustrated by 606 and dashed lines in fig. 6. Use of such intake throttle is not required according to the present invention.

Furthermore, if the amount of intake air is reduced through the use of an intake throttle, a pressure below current atmospheric pressure is created in the intake manifold and hence also in the combustion chambers. This may cause engine lubricant to pass the cylinder piston and accumulate on the top of the piston. This, in turn, may lead to coking of the top land region of the piston, in the end causing cylinder failure. Consequently, use of such technology is highly undesirable. Another measure that can be taken in low-load situations is to reduce intake air by opening the waste gate 418, thereby reducing turbine 408 speed and hence compressor speed and thereby intake air pressure.

The work being produced by the internal combustion engine can also be increased using e.g. the exhaust brake 420 to increase the back pressure and thereby the load of the internal combustion engine 101. The efficiency of the internal combustion engine may also be reduced, e.g. through the use of retarded ignition/fuel supply. These methods result in poor fuel economy.

However, exhaust gas temperature increasing actions of these kinds oftentimes are still not sufficient, with the result that the resulting exhaust gases are still too cold to ensure proper heating of the aftertreatment components. For example, if the work being produced by the internal combustion engine is small there may no longer be any significant intake air pressure to reduce, i.e. there is no longer a compression. When this is the case, an opening of the waste gate 418 will have essentially no effect.

The above is also valid to an even further extent when the vehicle is coasting, in particular when coasting with the engine rotating and the transmission in gear without fuel supply. During coasting cold air will be flushed through the engine and thereby also the aftertreatment components without undergoing substantially any heating. This flushing of cold air through the engine will subject the aftertreatment components to substantial cooling. With regard to coasting, the available measures to be taken to reduce the negative impact of the cool exhaust gases are even more limited since in general there is no combustion. The intake air may be throttled, but, again, this may result in cylinder failure.

Oftentimes, at least in hilly terrain, downhill sections of road are of such length that the aftertreatment components will be cooled off to an extent where the resulting emissions no longer will fulfil legislative requirements when the driving resistance, and thereby load of the internal combustion engine, again increases following the downhill section of road. The vehicle fulfilment of exhaust emission legislation is oftentimes controlled by onboard diagnostics, and when the vehicle control system determines that aftertreatment is not working properly measures are being taken to as quickly as possible ensure proper operation of the aftertreatment again. This may have the effect that the vehicle may be driven uphill at a substantial internal combustion engine load due to the driving resistance imposed by the road inclination, but where e.g. the exhaust brake in spite of this is still being activated to further increase the internal combustion engine load to thereby quicker reach desired temperatures in the aftertreatment components.

According to the invention, negative effects caused by undesired cooling of aftertreatment components are reduced by uncooled (warm) exhaust gas recirculation. As was mentioned, in step 301 it is determined whether the exhaust gas stream is to be controlled according to the invention where the transition from step 301 to step 302 can be initiated according to the various criteria stated above, which can include e.g. low/zero-load and/or coasting situations. In this case, it is determined in step 302 that there is no risk that current engine operation may damage aftertreatment components due to excessive heating, and hence the method continues to step 306.

In step 306 it is determined whether exhaust gases are to be recirculated from exhaust conduit 416 to intake conduit 402 using the same EGR circuitry as is used above. This determination can, for example, be performed in a manner similar to the above and be determined based e.g. on the current internal combustion engine load and/or current vehicle speed, the time during which various conditions have prevailed etc. If recirculation is to be performed, the method continues to step 307 for determining a suitable control of the exhaust gas stream recirculation.

The control of the recirculation flow of exhaust gases can e.g. consist of a determination of a suitable control/opening of the EGR valve 422. For example, the flow and/or opening of EGR valve 422 can be determined using a lookup table in a manner similar to the above, which table can be determined e.g. empirically. It is also possible to use any suitable conventional EGR mechanism described in the art.

Alternatively, a suitable algorithm can be used. According to one embodiment, the control consists of opening valve 424 and EGR valve 422 while simultaneously a suitable back pressure for ensuring the recirculation is established.

When a suitable control has been determined in step 307, the method continues to step 308 where the control is commenced by opening valve 424 and the EGR valve 422 is controlled to open to a determined extent to obtain the desired control of the flow from exhaust conduit 416 to intake conduit 402. This is disclosed in fig. 6 by arrows 602, 604. In order to ensure a flow in the desired direction, i.e. from exhaust conduit to intake conduit, the exhaust brake, for example, can be at least partially closed to increase the engine back pressure so that the pressure prevailing in the exhaust conduit 416 will exceed the pressure in the intake conduit 402. The created pressure difference must also take into account possible pressure drop through the EGR circuit to ensure proper direction of flow through the EGR circuit. If the turbo charger is of a variable geometry turbine (VGT) type, the turbo charger can, instead, be used to increase back pressure. It is also possible to use e.g. a Venturi valve in this control as well, or e.g. an exhaust compressor. It is also possible to e.g. close the exhaust conduit 416 passage to the turbocharger to thereby force the exhaust gases to the intake conduit 402. In principle, as is appreciated by a person skilled in the art, any suitable means can be used as throttle device for throttling the exhaust gas stream, if necessary, e.g. to increase the back pressure of the engine to ensure a desired flow in a desired flow direction according to the above. Also, the pressure difference can be accomplished, for example, through the use of an intake throttle, such as intake throttle 606, although possible resulting pressures below atmospheric pressure should be paid attention to.

The EGR valve 422 can be arranged to be opened e.g. completely and recirculation according to the invention be controlled by means according to the above. In principle, if the back pressure is controlled to a pressure exceeding the intake pressure, substantially all of the exhaust gas flow from cylinders i4-i6 may be recirculated to the internal combustion engine intake side. According to one embodiment, the EGR valve can be alternately opened and closed to obtain a suitable average exhaust recirculation over time.

Consequently, the EGR circuit is used also for exhaust gas recirculation according to the invention, but not as in the conventional sense where actively cooled exhaust gases are recirculated during high engine loads, but instead warm exhaust gases are recirculated when the load is small or when there is no fuel injection at all. The recirculated exhaust gases are in general of a higher temperature than the intake air, and will hence increase the temperature in the combustion chambers in comparison to a situation when there is no exhaust gas recirculation. In general, an increase of a first number of degrees of the temperature of the gas being supplied to the combustion will result in an essentially corresponding increase in temperature of the resulting exhaust gases.

In general, recirculated exhaust gases are actively cooled before reaching the intake side of the engine to minimise the increasing impact of the temperature in the combustion chamber and thereby minimising N0Xformation during combustion.

According to the invention, it is, on the contrary, desirable that the exhaust gases are as warm as possible to minimise the cooling effect during low/no load conditions. Therefore, recirculated exhaust gases are not actively cooled according to the invention. In addition, since, according to the disclosed example, half of the exhaust gases can be recirculated to the intake side of the internal combustion engine, the resulting exhaust gas flow will be reduced to half the flow that would otherwise be passing the aftertreatment, and still having a higher temperature than would otherwise be the case. Consequently, the present invention provides a solution that significantly may reduce the negative impact of cold exhaust gases on the operation of aftertreatment components.

According to the embodiment shown in figs. 4,6, exhaust gases from one bank only (cylinders i4-i6) of the cylinders are arranged to be recirculated to the intake side, and in this case half the cylinders. However, the recirculation can be arranged to be performed from any number of the cylinders/combustion chambers, i.e. more or less than exemplified above. This applies to internal combustion engines having any number of cylinders. It is also possible to perform the recirculation from a position downstream the turbine 408, e.g. upstream the exhaust brake.

In step 309 it is checked whether recirculation according to the invention is to be ended. This can, for example, be the case when internal combustion engine operating conditions has changed and exhaust gases of sufficient temperature may be produced without recirculation. The method returns to step 308 for as long as this is not the case. Alternatively, the method may return to step 307 in case control parameters are to be changed. When it is determined that the recirculation of exhaust gases no longer is needed the method can be arranged to return to step 301, waiting for a next occasion when control according to the above is required. Similar to the above, valve 424 can be closed so as to influence exhaust gas flow as little as possible in normal engine operation, in particular in order to minimise additional and undesired volumes for exhaust gas expansion upstream the turbine 408 according to the above.

The control performed according to fig. 5 can consequently be arranged to be activated when required e.g. in driving situations when there may be an undesired cooling of aftertreatment components.

According to the above disclosed embodiments only one bank of cylinders il-i6, i.e. the bank consisting of cylinders i4-i6, take part in the gas exchange from intake conduit 402 to exhaust conduit 416 and vice versa. Although a design of this kind provides advantages it is also contemplated that according to one embodiment the other or both cylinder banks take part in the gas exchange, in either of the described directions, according to the present invention. Furthermore, the use of a twin-scroll turbine is not necessary but exhaust gases from all combustion chambers of the internal combustion engine can be arranged to be conducted through a single conduit prior to reaching the turbine. It is also possible to direct the flow of air from engine intake side to a position downstream the turbo charger, or even downstream one or more of the aftertreatment components but upstream at least one such component.

Furthermore, according to the above embodiments, a single EGR circuit is used for gas flow in both directions. This is highly advantageous. However, according to one embodiment, separate circuitry can be used for the bypass of air, and recirculation of exhaust gases, respectively.

Finally, the present invention has been exemplified for a vehicle. The invention is, however, applicable in any kind of craft, such as, e.g., aircrafts and watercrafts. The invention is also applicable for use in combustion plants. Also, the aftertreatment may comprise further components such as one or more particle filters, one or more oxidation catalytic converters as is known per se. It is also contemplated that the aftertreatment may comprise no or more than one SCR catalytic converter and/or more than one or no ammonia slip catalytic ASC converter.

Claims

A method of controlling exhaust gases resulting from combustion in an internal combustion engine (101), said internal combustion engine (101) having at least one combustion chamber (i1-i6) and an inlet side (402) for receiving air compressed by a compressor (101). 406) for use in combustion, wherein said internal combustion engine (101) is further arranged to emit exhaust gases resulting from said combustion in at least one exhaust line (414, 416) arranged between the engine's exhaust emissions and a turbine (408), said compressor (406) is driven by said turbine (408), the method being characterized by: - when said internal combustion engine (101) delivers at least a first job, when an internal combustion engine speed is lower than a first internal combustion engine speed, providing an air flow from said intake side (402) for mixing with the exhaust gases resulting from said combustion, the air stream being led past said at least one combustion chamber (i1-i6) into said min. single exhaust line (414, 416), and - when said internal combustion engine (101) delivers a second work, which is lower said first work, recirculation of at least a part of the exhaust gases resulting from said combustion, from said at least one exhaust line (414,416) to said intake side (402).

The method of claim 1, further comprising: - determining whether the temperature of the exhaust gases resulting from said combustion may be harmful to a component exposed to said exhaust gases, and - providing an air stream for mixing with the exhaust gases when the temperature of the exhaust gases may be harmful to said component.

A method according to any one of claims 1-2, further comprising: - providing said air stream for mixing with the exhaust gases only when an internal combustion engine load is above a first internal combustion engine load.

A method according to any one of claims 1-3, further comprising: - mixing said air stream with said exhaust gases before said exhaust gases reach at least one component (202, 203, 204) for treating said exhaust gases.

A method according to any one of claims 1-4, wherein said internal combustion engine (101) comprises a plurality of combustion chambers (II-i6), said combustion chamber (II-i6) being divided into groups, each group comprising a separate exhaust line for exhaust gases which results from said group, the method further comprising: - providing said air flow to conduits of at most n-1 of said groups.

The method of claim 5, further comprising, downstream of the mixing of said air stream with exhaust gases from said at most n-1 groups of said multiple combustion chambers (i1-i6): - mixing exhaust gases from all of said n groups of combustion chambers to form a total exhaust gas stream, said total exhaust gas stream being arranged to pass through at least one component (202, 203, 204) for processing said exhaust gas stream.

A method according to any one of claims 1-6, further comprising: - recirculating at least a part of the exhaust gases resulting from said combustion to said intake side (402), when said combustion engine (101) has delivered an average work, which is at most said second work, during a first period of time.

A method according to any one of claims 1-7, further comprising: - recirculating at least a part of the exhaust gases resulting from said combustion to said intake side (402), when the second operation is substantially zero, i.e. when there is substantially no combustion in said at least one combustion chamber (i1-i6).

A method according to any one of claims 1-8, further comprising: - recirculating said exhaust gases without cooling said recirculated exhaust gases.

A method according to any one of claims 1-9, wherein said internal combustion engine (101) comprises a plurality of internal combustion chambers (i1-i6), the method further comprising: - recirculating exhaust gases only from a subset of said several internal combustion chambers to said intake side of said internal combustion engine .

A method according to any one of claims 1-10, further comprising: - controlling said recirculation of said exhaust gas stream by throttling of exhaust gases resulting from said combustion and / or throttling of intake air supplied to said combustion.

A method according to any one of claims 1-11, further comprising: - providing said air flow through a first conduit from said intake side to said exhaust gases.

The method of claim 12, further comprising: - recirculating said exhaust gases to said intake side through said first conduit.

A method according to claim 12 or 13, wherein said first conduit has an end facing said intake side and an end facing an exhaust conduit, the method further comprising, when the exhaust gases are not recirculated and no air stream is supplied to said exhaust gases: closing said first conduit near, or substantially at, the end facing the exhaust conduit.

A method according to any one of the preceding claims, wherein said at least one combustion chamber is a combustion chamber in an internal combustion engine of a vehicle (100).

The method of claim 15, further comprising: - providing an air stream for mixing with the exhaust gases only when the height of the vehicle (100) exceeds a first height.

A method according to any one of claims 1-16, further comprising: - controlling said air stream for mixing with the exhaust gases and / or said exhaust gas recirculation, based on the temperature of the exhaust gases and / or one or more after-treatment components.

A computer program comprising program code which, when said program code is executed in a computer, causes said computer to perform the method according to any one of claims 1-17.

A computer program product comprising a computer readable medium and a computer program according to claim 18, wherein said computer program is contained in said computer readable medium.

An exhaust gas control system resulting from combustion in an internal combustion engine (101), said internal combustion engine (101) having at least one combustion chamber (II-16) and an intake side (402) for receiving air from a compressor (406). for use in combustion, wherein said internal combustion engine (101) is further arranged to emit exhaust gases resulting from said combustion in at least one exhaust line (414, 416) arranged between the engine exhaust emissions and a turbine (408), said compressor (406) ) is driven by said turbine (408), the system being characterized by: - means for providing an air stream from said intake side (402) for mixing with the exhaust gases resulting from said combustion, the air stream being led past said at least one combustion chamber (il-i6) into said at least one exhaust line (414,416), when said internal combustion engine (101) delivers at least a first work and means for recirculating at least a part of the exhaust gases which resulted from said combustion, from said at least one exhaust line (414,416) to said intake side (402), when said internal combustion engine (101) delivers a second job, which is lower than said first job.

Vehicle, characterized in that it comprises a system according to claim 21.