GB2505512A - Method of controlling a rich combustion mode of an internal combustion engine - Google Patents

Abstract

A rich combustion mode of an internal combustion engine (ICE) has a fuel after injection split into at least two pulses. The method of controlling the rich combustion mode comprises obtaining values for fuel injection quantity and injection timing from an engine map 20 for each of the after injection pulses and correcting the obtained values using a coolant temperature correction factor 22 and an environmental (e.g. ambient air) temperature correction factor 21 to give calculated injected fuel quantity and injection timing 23. The engine map is an engine load versus engine speed map dependent on a barometric pressure, which is preferably a 3-baro structure of: sea-level pressure; middle-level pressure and high-level pressure. The method is used in particular by an electronic control unit (ECU) to regulate rich combustion when regenerating a Lean NOx Trap disposed in the exhaust system of the ICE.

Description

METHOD OF ENHANCING THE RICH COMBUSTION MODE WORKING AREA

OF AN INTERNAL COMBUSTION ENGINE

--TECHNICAL FIELD

The present disclosure relates to a method of enhancing the rich combustion mode working area of an internal combustion engine. The method is particularly related to Diesel engines, provides with a Lean NOx Trap device in the exhaust system.

BACKGROUND

It is known that the exhaust gas after-treatment systems of a Diesel engine can be provided, among other devices, with a Lean NO Trap (LNT).

A Lean NO Trap is provided for trapping nitrogen oxides NO contained in the exhaust gas and is located in the exhaust line.

A LNT is a catalytic device containing catalysts, such as Rhodium, Platinum and Palladium, and adsorbents, such as barium based elements, which provide active sites suitable for binding the nitrogen oxides (NOr) contained in the exhaust gas, in order to trap them within the device itself.

Lean NO Traps 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-bum operation to operation whereby an excess amount of fuel is available, referred also as rich operation or regeneration phase (normally, this excess amount of fuel is available by means of an after injection of the fuel). 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.

Unfortunately, the rich combustion working area is limited only in a defined portion of the normal engine working conditions. In particular, the rich combustion working area is severely limited at low load due to an unstable combustion.

Therefore a need exists for a method that could enhance the working area of the diesel engine rich combustion mode, where the rich combustion is stable especially at low load.

An object of this invention is to provide a method which smartly manages the rich injection pattern. As known, modern Diesel engines are equipped with injection systems (e.g. Common Rail System), which are capable to perform multiple injections. In rich combustion mode, the typical injection pattern èould include a pilot injection (which happens well before the Top Death Center, to improve the combustion conditions of the engine combustion chamber for the main injection), a main injection and an after injection. The after injection happens during the engine exhaust stroke, when the exhaust valve is still closed, therefore the injected fuel bums only partially (rich combustion mode). The object of the invention is based on a multi-after injection pulses concept, which allows the rich combustion being more stable especially at low load.

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, and by an electromagnetic signal having the features recited in the independent claims.

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

SUMMARY

An embodiment of the invention provides a method of controlling a rich combustion mode of an internal combustion engine, wherein an after injection is splitted into a number of at least two pulses, and wherein for each of the after injection pulses, an injected quantity and an injection timing is determined, based on an engine load vs. engine speed map structure which is depending on a barometric pressure and is corrected by a coolant temperature and an environmental temperature correction factor.

Consequently, an apparatus is disclosed for controlling a rich combustion mode of an internal combustion engine, the apparatus comprising means for splitting an after injection into a number of at least two pulses and means for determining for each after injection pulse an injected quantity and an injection timing based on an engine load vs. engine speed map structure which is depending on a barometric pressure and is corrected by a coolant temperature and an environmental temperature correction factor An advantage of this embodiment is that it provides a method to optimize the rich combustion modes at low loads, since the after injection split, taking into account both environmental and engine conditions, increases the possibility the fuel is burned by all the oxygen present in the combustion chamber and unbumed hydrocarbons and smoke emissions are reduced.

According to another embodiment, said dependency on a barometric pressure is realized by correcting said engine load vs. engine speed map structure with a sea level, a middle level and a high level correction factor.

An advantage of this embodiment is that the engine maps, load vs. speed, which are the starting point to determine the fuel quantities and the timing of the after injection pulses, are corrected taking into account the actual altitude of the vehicle and consequently the barometric pressure.

According to a further embodiment said coolant temperature and environmental temperature correction factors are also depending on a barometric pressure and wherein the dependency is also realized by correcting them with a sea level, a middle level and a high level correction factor.

An advantage of this embodiment is that the engine maps, load vs. speed, which are the starting point to determine the fuel quantities and the timing of the after injection pulses, are corrected also taking into account the actual values of the air and coolant temperature.

According to a still further embodiment, the air/fuel ratio closed-loop control acts on a calibratable number of after-injection pulses, minor or equal to the total number of after injection pulses, and determines the corrected quantity in a proportional way respect to the open-loop quantity ratio.

An advantage of this embodiment is that by using a calibrated number of after injection pulses in the routine of the air/fuel ratio closed loop control allows to optimize the trade-off combustion stability vs. torque neutrality and emissions containment.

According to another embodiment, the method according to one of the previous embodiments, once detected a rich combustion valid mode, further comprises: -evaluating the engine operating conditions, load and speed, and the number of the after injection pulses, -determining in open loop the injected quantity and the timing for each after injection pulse, -evaluating the number of after injection pulses to be used for the air/fuel ratio closed loop control, -splitting the control action over the fuel quantities of the selected after injection pulses in a proportional way respect to the open-loop quantity ratio, -calculating the final fuel quantities, both open loop and closed loop contribution, for each after injection pulses.

An advantage of this embodiment is that the fuel quantities of each after injection pulses are determined not only in open loop controls, based on the engine and the environmental conditions, but also in closed loop control, determined by keeping a constant air/fuel ratio.

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 embodied as 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.

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.

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 schematic view of the after-treatment system according to the invention.

Figure 4 is a graph schematizing the rich combustion working area according to a known control strategy.

Figure 5 is a graph schematizing in the lower part the enhanced working area for rich combustion modes according to a new control strategy and in the upper part the related injection pattern.

Figure 6 is a block diagram showing the strategy to estimate the after injection pulses both in term of fuel quantity and timing.

Figure 7 is a block diagram showing the structure of the base set point map.

Figure 8 is a flowchart of a method of enhancing the rich combustion working area, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 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 by 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 rotétionally 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 variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust 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 281, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, particulate filters (DPF) 282 or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate filter (SCRF). 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 30O 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 and 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, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VOl 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.

Turning back to the exhaust system 270, the proposed invention relies on a method which evaluates the NOx storage efficiency of an Lean NOx Trap after-treatment device 281 (Fig. 3). Advantageously, the after treatment system could also comprise a particulate filter (DPE) 282 to trap particulate emitted in case of a Diesel engine. An upstream LNT NOx sensor 283 can be provided, a NOx temperature sensor 285 can be provided, as well.

Preferably, the LNT 281 could be positioned as close as possible to the exit of the turbocharger 230 to take advantage of the high temperature conditions which are beneficial for it.

The LNT reduces engine-out exhaust gas constituents (CO and HC) with high efficiency and stores NOx during lean operating conditions. During rich operating conditions, i.e. LNT regeneration phase, the NOx is released and converted.

Rich combustionmodes are operation whereby an excess amount of fuel is available. As known modern Diesel engines are equipped with injection systems (e.g. Common Rail System), which are capable to perform multiple injections. In rich combustion mode, the typical injection pattern could include a pilot injection (which happens well before the Top Death Center, to improve the combustion conditions of the engine combustion chamber for the main injection), a main injection and an after injection. The after injection happens during the engine exhaust stroke, when the exhaust valve is still closed, therefore the injected fuel burns only partially (rich combustion mode).

When the engine is switched to rich operation, the NQ 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.

Operating in rich combustion mode, the engine can support it only in a defined portion of the normal working conditions, since the rich combustion working area is severely limited at low load due to an unstable combustion. More in detail, managing the rich combustion mode with a typical injection pattern, composed of a pilot, a main and an after injection, leads to a rich engine map where at high load and speed the main limitation is the inlet turbine temperature while at low load the combustion instability limits severely the usage of the rich modes. The absolute values of engine speed and load of course is than related to the HW, to the emission strategy and engine noise target. Fig. 4 shows the above limitations and rich combustion working area 500.

The problem to be solved by the invention is to enlarge the rich combustion mode working area, above all at low load conditions, in other words, try to better stabilize the combustion in such conditions. As known, while working in rich conditions (air/fuel ratio C 1), at the normal operating fuel injections (pilot and main), an after injection is added.

After injection means a late fuel injection, happening during the exhaust stroke, while the exhaust port is still closed. Therefore this injection is still capable to contribute to the combustion whenever sufficient oxygen is available. The idea behind the invention is to split the after injection in several pulses (being almost equal the total amount of injected fuel), to optimize the combustion at low loads: in fact each smaller fuel amount has higher probability to be surrounded by the oxygen and then burned. Therefore, this after injection split will increase the possibility the fuel is burned by all the oxygen present in the combustion chamber, thus reducing the HC, to keep the combustion stable and respecting temperature and emission limits. Fig. 5, upper part, shows this new injection pattern rich combustion mode: the after injection has been splitted in four pulses: after injection 1, after injection 2, and so on. Of course the number of pulses is calibratable even if first tests have demonstrated that a maximum number of four pulses is adequate.

The results in term of increased engine working area during rich combustion mode are schematized in the lower part of Fig. 5, wherein, together with the previous working area 500, an additional working area 510 is available.

Of course the after injection pulses must be defined both in term of single fuel quantity and timing, that is to say, time distance between two consecutive pulses. Fig. 6 is a block diagram showing the strategy to estimate the after injection pulses and timing: a fuel quantity, specific for each after injection pulse, is calibrated in the ECU, mainly on the base of engine speed and engine torque. Quantity corrections for environmental and engine conditions have to be applied (barometric pressure, environmental air temperature and coolant temperature). A maximum number of four after pulses has been chosen in this example, as function of the engine operating point.

Also calibratable are the different timings (time distance between two consecutive pulses) for this new injection pattern. Timing corrections for environmental and engine conditions have to be applied as well: as for fuel quantities, barometric pressure, environmental air temperature and coolant temperature. Therefore in Fig. 6, block 20 is the base set point map with a structure, as will be seen soon after, of three barometric conditions, while block 21 and 22 respectively represent the map corrections due to air and coolant temperature. From all three map structures, the outcome will be fuel quantities and timing. base values from block 20, correction values (offset) from blocks 21and22.

As an example, in Fig. 7 is shown the detail of block 20, but similar details are also available for the map structure& in block 21 and 22. More in detail, the figure shows the map structure taking into account the barometric conditions. Three engine maps 24, 25, 26 (engine load vs. engine speed) are defined for, respectively, see level, middle level and high level. Respectively, sea level condition means a barometric pressure of about 98-100 kPa, middle level means barometric pressure ranging in 80-85 kPa and high level means barometric pressure of about 75 kPa. Each of this map is multiplied 27, 26, 29 per a correction factor (ci c2, c3, ranging between 0 and 1) and then summed according to following equation: Base set point map = Mapl x ci + Map2 x c2 + Map3 x c3 And ci + c2 +c3 =1 where: Map I and ci are the map and correction factor at sea level condition Map 2 and c2 are the map and correction factor at middle level condition Map 3 and c3 are the map and correction factor at high level condition Same map structures are defined to take into account the contribution of the air temperature and the coolant temperature: for each of these parameters the three engine maps are corrected with a specific factor, function of the actual value of the air or coolant temperature.

The flowchart of this new method of enhancing the engine working area under rich combustion condition is shown in Fig. 8. Once detected 31 a rich combustion valid mode, the method evaluates 32 the engine operating conditions (load and speed) and the number of the after injection pulses; as previously explained, then the method determines in open loop 33 the injected quantity and the timing for each after injection pulse, based on the load/speed engine maps, corrected by barometric pressure, air temperature and coolant temperature. At the same time the separate routine ofthe air/fuel ratio closed loop control 34 requires this method to evaluate 35 the number of after injection pulses to be used for the air/fuel ratio closed loop control. This number will be less or equal to the total number of after injection pulses (as previously established) and calibratable The selected pulses depend on the engine operating point. The method will define the number and their position in the sequence of the after injection pulses. For example, if the pulses are four (1-2-3-4), the strategy can choose two pulses, and specifically No. 2 and No. 4, to contribute to the routine of the air/fuel ratio closed loop control. With this logic, it is possible from one side to keep the combustion stable, due to the presence of multi after injection and from the other side, to guarantee torque neutrality and emissions containment, by selectirig and then correcting with the closed loop control the most appropriate pulses. The air/fuel ratio closed loop control will split 36 the control action over the fuel quantities of the selected after injection pulses in a proportional way respect to the open-loop quantity ratio. At the end, the method calculates 37 the final fuel quantities (both open loop and closed loop contribution) for each after injection pulses.

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 block

21 block 22 block 23 block 24 block block 26 block 27 block 28 block 29 block block 31 block 32 block 33 block 34 block block 36 block 37 block 40 data carrier 50-54 NOx efficiency curves automotive system internal combustion engine engine block 125 cylinder cylinder head camshaft piston crankshaft combustion chamber 155 cam phaser fuel injector fuel rail fuel pump fuel source 200 intake manifold 205 air intake pipe 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 281 lean NOx trap (LNT), fresh catalyst 282 diesel particulate filter (DPF) 283 LNT upstream NOx sensor 285 LNT temperature sensor 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature 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 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 rich combustion working area 510 rich combustion additional working area

Claims (10)

1. CLAIMS1. Method of controlling a rich combustion mode of an internal combustion engine (110), wherein an after injection is splitted into a number of at least two pulses, and wherein for each of the after injection pulses, an injected quantity and an injection timing is determined (23), based on an engine load vs. engine speed map structure which is depending on a barometric pressure (20) and is corrected by a coolant temperature (22) and an environmental temperature (21) correction factor.
2. 2. Method according to claim 1, wherein said dependency on a barometric pressure is realized by correcting said engine load vs. engine speed map structure with a sea level (24), a middle level (25) and a high level (26) correction factor.
3. 3. Method according to claim I or 2 wherein said coolant temperature and environmental temperature correction factors are also depending on a barometric pressure and wherein the dependency is also realized by correcting them with a sea level, a middle level and a high level correction factor.
4. 4. Method according to one of the previous claims, wherein an air/fuel ratio closed-loop control acts on a calibratable number of after-injection pulses, minor or equal to the total number of after injection pulses, and determines the corrected quantity in a proportional way respect to the open-loop quantity ratio.
5. 5. Method according to one of the previous claim, wherein once detected 31 a rich combustion valid mode the method further comprises: -evaluating (32) the engine operating conditions, load and speed, and the number of the after injection pulses -determining in open loop (33) the injected quantity and the timing for each after injection pulse, according to claim ito 3, -evaluating (35) the number of after injection pulses to be used for the air/fuel ratio closed loop control (34), -splitting (36) the control action over the fuel quantities of the selected after injection pulses in a proportional way respect to the open-loop quantity ratio, according to claim 4, -calculating (37) the final fuel quantities, both open loop and closed loop contribution, for each after injection pulses.
6. 6. Internal combustion engine (110) of an automotive system (100) equipped with an fuel injection system the automotive system (100) comprising an electronic control unit (450) configured for carrying out the method according to claims 1-5.
7. 7. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-5.
8. 8. Computer program product on which the computer program according to claim 7 is stored.
9. 9. 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 computer program according to claim 7 stored in the data carrier (40).
10. 10. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 7.