GB2519165A - Method of controlling a late fuel injection in an internal combustion engine - Google Patents

Abstract

An embodiment of the invention provides a method of controlling a late fuel injection quantity in the exhaust system, 275, of an internal combustion engine, 110, for the regeneration of at least an aftertreatment device, 280, wherein the method performs the steps of determining an oxygen content in the exhaust system, determining a maximum quantity of the late fuel injection based on said oxygen content, an engine speed and an exhaust mass flow. The particular embodiment relate to regeneration of a Lean NOx Trap, Diesel Particulate Filter or Diesel Oxidation Catalyst.

Description

METHOD OF CONTROLLING A LATE FUEL INJECTION

IN AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of controlling a late fuel injection in an internal combustion engine. The method is particularly suitable for controlling the so called "post-injections", which are used during the regeneration phase of the aftertreatment devices.

BACKGROUND

As known, the exhaust gas aftertreatment systems of an internal combustion engine can be provided, among other devices, with a Lean NO Trap (LNT) for trapping nitrogen oxides NO contained in the exhaust gas.

Lean NO Traps (LNT) are subjected to periodic regeneration processes, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NOr) from the LNT.

The LNT are operated cyclically, for example by switching the engine from lean-burn operation to operation whereby an excess amount of fuel is available, referred also as rich operation or regeneration phase. During normal operation of the engine, the NO are stored on a catalytic surface. When the engine is switched to rich operation, the NO stored on the adsorbent site react with the reductants in the exhaust gas and are desorbed and converted to nitrogen and ammonia, thereby regenerating the adsorbent site of the catalyst.

In the art are also known exhaust gas treatment systems for the emissions reduction and in particular of particulates from the diesel engine exhaust gas. These systems are provided with aftertreatment devices installed along the exhaust line of the engine and typically comprise a diesel particulate filter (DPF) for control of particulates.

It is also known in the art, in some exhaust system configuration, to inject a reagent (catalyst) fluid in the exhaust line of the diesel engine in order to reduce emissions by means of the afore-mentioned aftertreatment devices. In particular, hydrocarbon based reagents, generally indicated as HO, like the same diesel fuel used for fuelling the engine, are injected in the exhaust line in order to promote the regeneration of diesel particulate filter (DPF) with the burning of soot accumulated therein.

Both aftertreatment components need to be cleaned by a process called regeneration (DPF and DeSOx regeneration, respectively), during which the exhaust gas temperature is increased substantially to create a condition whereby the soot contained in the DPF is burned (oxidized) and the Sulphur contained in the LNT is removed through rich combustion spikes.

This regeneration can be obtained through late fuel. injections, which oxidize in the LNT, or in a diesel oxidation catalyst (DOG) in case the LNT is not present, providing high temperature inside both the components. For late fuel injections is to be intended fuel injections (so called, post-injections), which do not contribute to the torque forming, since the fuel is injected in the cylinder during the exhaust stroke of the piston, when the exhaust port is already open. Post injection fuel quantities are normally limited through fixed values, that are in general able to cover the standard conditions of an engine point.

Such values are stored in a map, whose input are the engine operating conditions, namely engine speed and load.

Fixed limitation of the post injection quantities can lead to HC slip and white smoke, in case of particular maneuvers. This is due to the fact that a fixed limitation does not use the physical information, which are representative of the actual possibility to oxidize post injection. In fact, a maximum limitation of the late fuel injection quantities, based on load and engine speed gives a constant threshold, that does not take into account transient conditions and combustion characteristics (i.e. amount of air at the exhaust, depending on the air control status).

Therefore a need exists for a method of controlling a late fuel injection, which does not lead to the mentioned inconvenience.

An object of an embodiment of the invention is to provide a method of controlling a late fuel injection, proposing a new approach to estimate the maximum post injection quantity that can be injected.

Another object is to provide an apparatus which allows to perform the above method.

These objects are achieved by a method, by an apparatus, by an engine, by a computer program and computer program product having the features recited in the independent claims.

The dependent claims delineate preferred and/or especially advantageous aspects.

SUMMARY

An erribociiment of the disclosure provides a method of controlling a late fuel injection quantity in an exhaust system of an internal combustion engine, for the regeneration of at least an aftertreatment device, wherein the method performs the following steps: -determining an oxygen content in the exhaust system, -determining a maximum quantity of the late fuel injection, based on said oxygen content, an engine speed and an exhaust mass flow.

Consequently, an apparatus is disclosed for performing the method of controlling a late fuel injection quantity according to any of the preceding claims, wherein the apparatus comprises: -means for determining an oxygen content in the exhaust system, -means for determining a maximum quantity of the late fuel injection, based on said oxygen content, an engine speed and an exhaust mass flow.

An advantage of this embodiment is that the method improves the limitation of the late fuel injection quantity, by adopting a new approach to estimate the maximum fuel quantity that can be injected by a post-injection, based on the oxygen content in real time conditions. In this way, beneficial limitation of HC slip, HC smell and white smoke can be obtained.

According to another embodiment, the oxygen content is corrected by a first correction factor, which is calculated on the basis of the engine speed and an air mass flow.

Consequently, said means for determining the oxygen content are operating by correcting the oxygen content with a first correction factor, which is calculated on the basis of the engine speed and an air mass flow.

An advantage of this embodiment is that in high load conditions, when the exhaust mass flow is very high, the addition of a contribution of a late fuel injection quantity, higher than the one limited by the available oxygen, can be beneficial to reach a higher temperature, without the occurrence of bad smell and white smoke side effects.

According to a still further embodiment, the oxygen content is corrected by a second correction factor, which is calculated on the basis of an ambient pressure.

Consequently, said means for determining the oxygen content are operating by correcting the oxygen content with a second correction factor, which is calculated on the basis of an ambient pressure.

An advantage of this embodiment is that also in altitude, where the air density is lower, the addition of a contribution of the late fuel injection quantity, higher than the one limited by the available oxygen, can be beneficial to reach a higher temperature, without the occurrence of bad smell and white smoke side effects.

According to still another embodiment, the oxygen content is determined by an oxygen sensor measurement.

Consequently, said means for determining an oxygen content in the exhaust system comprise an oxygen sensor.

An advantage of this embodiment is that the oxygen content can be effectively measured in real time conditions.

Another embodiment of the disclosure provides an internal combustion engine comprising an exhaust system, having an aftertreatment device, wherein a late fuel injection quantity for the regeneration of the aftertreatment device is controlled by a method according to any of the previous embodiments.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program product can be embedded in a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.

Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a plot showing the hydrocarbon slip and the white smoke phenomena.

Figure 4 is a flowchart of the method according to an embodiment of the present invention.

Figure 5 is a more detailed flowchart according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 1001 as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a fixed geometry turbine 250 including a waste gate 290. In other embodiments, the turbocharger 230 may be a variable geometry turbine (VGT) with a VGT actuator arranged to move the vanes to alter the flow of the exhaust gases through the turbine.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust S aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (8CR) systems. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow, pressure, temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including1 but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the waste gate actuator 290, and the cam phaser 155.

Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices.

The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

The program stored in the memory system is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 100 it is normally visible as a computer program product, which is also called computer readable medium or machine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said carrier being transitory or non-transitory in nature with the consequence that the computer program product can be regarded to be transitory or non-transitory in nature.

An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulated technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a WiFi connection to a laptop.

In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

Instead of an ECU 450, the automotive system 100 may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle.

Figure 3 is a plot showing the hydrocarbon slip and the white smoke phenomena. In the diagram the following parameters have been plotted. Data are taken from experimental tests, Curve 500 is the boost pressure [kPa] of the fresh air after the compressor 240, curve 510 is the air mass flow [mg/str] always after the compressor, curve 520 is the 02 concentration [%] upstream the aftertreatment devices 280, curve 530 is the HC concentration [ppm] downstream the aftertreatment devices (in other words, the unburned hydrocarbons which contribute to the vehicle emissions), curve 540 is the late fuel injection quantity Fmm3/str], which is used to regenerate the aftertreatment devices, curve 550 is the measured temperature [°CJ in the exhaust system 270, upfront the diesel particulate filter and finally curve 560 is the desired temperature [°C], always in the exhaust system, upfront the DPF.

The diagram can be divided in three portions: a) is a first portion where the engine is running under standard condition. In this situation, the available oxygen is about 1%, the measured temperature corresponds at the desired value, with low unburned hydrocarbons concentration.

In the second portion b) an under-boost or a transient boost condition is represented. In this case, there is no available oxygen in the exhaust system (since the oxygen is already insufficient for the fuel combustion in the combustion chamber of the engine), the temperature starts to drop, while HC concentration rises. This is the situation during which hydrocarbons slip occurs. For hydrocarbons slip is to be intended the amount of unburned hydrocarbons in the exhaust pipe 275, which contributes to the vehicle emissions.

Finally, in the third portion c) of the plot in Fig. 3, the engine goes back to standard conditions. The available oxygen is again 1%, the cumulated hydrocarbons suddenly burn, causing the white smoke phenomenon and also a temperature overshoot, due to HC cumulated into the catalyst, occurs. As a consequence, such temperature overshoot makes difficult the exhaust temperature control.

The physical limit for the oxidation of the fuel, which is injected by late injections, inside the LNT/DOC is the amount of oxygen that is available at its inlet. The oxygen content multiplied by the stoichiometric ratio fuellO2, determines the maximum fuel quantity which should be provided by the late injections. Therefore, according to an embodiment of the present invention, the oxygen content is used as the input of the fuel quantity limitation of the late injections. The information can be taken from an oxygen sensor 435 or from an exhaust oxygen model, depending on the sensitivity to the post injection itself of the sensor and the availability of the model. With oxygen based Pate injection limitation, the HC slip, as in portion b) of the diagram, is eliminated because of optimized late injection limitation. Moreover, no hydrocarbons would be cumulated into the catalyst (see portion c)), avoiding, when burnt, white smoke and temperature overshoot.

Fig. 4 shows a flowchart of an embodiment of the present invention: at first the oxygen content 02 in the exhaust system is determined 3410 and then the maximum quantity of the late fuel injection Qpost_max is calculated 3420, based on said oxygen content, the engine speed n and the exhaust mass flow me,d,.

Fig. 5 is a more detailed flowchart showing further embodiments of the present invention.

According to this flowchart, the oxygen content 02 can be corrected S51O by a first correction factor ki, which is calculated on the basis of the engine speed n and the. air mass flow m211. Alternatively or in addition, the oxygen content 02 can be corrected 3520 by a second correction factor k2, which is calculated on the basis of an ambient pressure Pamb.

In fact, although the limitation of the late injections fuel quantity, based on the theoretical chemistry of the system, can be satisfactory, it has been observed that in high load conditions, when the exhaust mass flow is very high, or in altitude, when the air density is lower, the addition of a contribution of the late fuel injection quantity higher than the one limited by the available oxygen (according to stoichiometry) can be beneficial from the point of view of the temperature. In other words, a higher temperature in the exhaust system can be reached, without causing bad smell and white smoke side effects. This is due to the fact that in those conditions, even if the hydrocarbons slip depends on the available oxygen in the exhaust system 270, an additional fuel quantity can be injected by a post-injection resulting advantageous for the temperature control, while the HC slip is not high enough to be critical from the point of view of smell and white smoke.

Summarizing the present method controls the limitation of the late fuel injections quantity for aftertreatment devices regeneration and is based on the determination of the oxygen content and consequently through chemical balance equations and evidence based phenomena. The method requires limited software change and usage of inputs already used by other systems. Moreover, such method has a neutral or positive impact on the ECU memory (combustion mode specific maps can be removed, just one map and two arrays should be added). On the other hand, the method reaches a significant reduction of HC slip, HC smell and white smoke, thanks to the optimized maximum fuel quantity of the late injections, which can be injected.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS

data carrier automotive system 110 internal combustion engine engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector 165 fuel injection system fuel rail fuel pump fuel source intake manifold 205 air intake duct 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine * 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 waste gate valve 295 waste gate actuator 9r electric pressure valve or boost pressure control valve 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow, pressure, temperature and humidity sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 435 oxygen sensor 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 boost pressure (kPa] 510 air mass flow [mg/strI 520 02 Concentration [%] 530 HC Concentration [ppml 540 late fuel injection quantity [mm3/strJ 550 measured temperature [°C] in the exhaust line 560 is the desired temperature [°C] in the exhaust line 8410 step 8420 step 8510 step 8520 step 02 oxygen content Qpost_max maximum quantity of the late fuel injection n engine speed exhaust mass flow air mass flow ki first correction factor k2 second correction factor Pamb ambient pressure

Claims (10)

1 0

2. Method according to claim 1. wherein the oxygen content (02) is corrected by a first correction factor (kl), which is calculated on the basis of the engine speed (n) and an air mass flow (mair).

3. Method according to claim 1 or 2, wherein the oxygen content (02)is corrected by a second correction factor (k2), which is calculated on the basis of an ambient pressure (Pamb).

4. Method according to any of the preceding claims, wherein the oxygen content (02) is determined by an oxygen sensor (435) measurement.

5. Apparatus for carrying out a method of controlling a late fuel injection quantity according to any of the preceding claims, wherein the apparatus comprises: -means for determining an oxygen content (02) in the exhaust system, -means for determining a maximum quantity of the late fuel injection (Qpostniax), based on said oxygen content, an engine speed (n) and an exhaust gas flow (m).

6. Apparatus according to claim 5, wherein said means for determining an oxygen content (02) in the exhaust system comprise an oxygen sensor (435).

7. Internal combustion engine (110) comprising an exhaust system (270), having an aftertreatment device (280), wherein a late fuel injection quantity for the regeneration of the aftertreatment device (280) is controlled by a method according to any of the claims from Ito 4.

8. A non-transitory computer program comprising a computer-code suitable for performing the method according to any of the claims 1-4.

9. Computer program product on which the non-transitory computer program according to ciajm 8 is stored.

10. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a non-transitory computer program according to claim 8 stored in a memory system (460).