GB2501923A

GB2501923A - Method of controlling an internal combustion engine

Info

Publication number: GB2501923A
Application number: GB1208262.4A
Authority: GB
Inventors: Alberto Vassallo
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-05-10
Filing date: 2012-05-10
Publication date: 2013-11-13
Also published as: GB201208262D0

Abstract

Disclosed is a method of controlling an internal combustion engine 110 of an automotive system 100. The engine system comprises an exhaust system having at least one after-treatment device 280, an EGR valve 320, a throttle valve 330 and a turbocharger 230 comprising a variable geometry turbine 250 controlled by a VGT actuator 290. When the internal combustion engine 110 is in a cut-off phase, the engine speed is below a speed threshold THR_Spd and a diesel particulate filters 281 inlet temperature DPF_inl temp is lower than a temperature threshold THR_Trnp then the EGR valve 320 duty cycle is set equal to a first speed dependent array, the VGT actuator 290 duty cycle is set equal to a second speed dependent array and the throttle valve 330 duty cycle is set equal to a third speed dependent array. The arrangement is used to provide sufficient heat to regenerate the diesel particulate filter when the engine is in a cut-off or warm-up phase.

Description

METHOD OF CONTROLLING AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method of controlling an internal combustion engine of an automotive system, particularly for improving the aftertreatment warm-up in an exhaust system of the internal combustion engine, which typically could be a highly efficient diesel engine.

BACKGROUND

An internal combustion engine, particularly a highly efficient diesel engine is normally provided with an exhaust gas after-treatment system, for degrading and/or removing the pollutants from the exhaust gas emitted by the Diesel engine, before discharging it in the environment.

The after-treatment system generally comprises an exhaust line for leading the exhaust gas from the Diesel engine to the environment, a Diesel Oxidation Catalyst (DOC) located in the exhaust line, for oxidizing hydrocarbon (HC) and carbon rnonoxides (GO) into carbon dioxide (GO2) and water (H2O), and a Diesel Particulate Filter (DPF) located in the exhaust line downstream the DOG, for removing diesel particulate matter or soot from the exhaust gas.

In order to reduce NO emission, most after-treatment systems further comprises a Selective Reduction Catalyst (SCR), which is located in the exhaust line downstream the DPF. SCR is a catalytic device in which the nitrogen oxides (NOà contained in the exhaust gas are reduced into diatonic nitrogen (N2) and water (1120), with the aid of a gaseous reducing agent, typically ammonia (NI-I3) that can be obtained by urea (GH4N2O) thermo-hydrolysis and that is absorbed inside catalyst. Urea is mixed with the exhaust gas by means of an urea injector that is located in the exhaust line between the DPF and the SCR.

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

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 NQ stored on the adsorbent site react with the reluctants in the exhaust gas and are desorbed and converted to nitrogen and ammonia, thereby regenerating the adsorbent site of the catalyst.

Although these devices are currently the most promising for controlling exhaust emissions, they are not effective until they are heated to a predefined operating or activation temperature.

Nowadays, the need for improving vehicle fuel economy is leading to a widespread reduction of vehicle mass and drag resistance, as well as to usage of highly-efficient intemal combustion engines. The combination of the above mentioned trends will lead to a widespread reduction of exhaust temperature levels, which in turn will slow the warm-up of aftertreatment systems, in particular for cars filled with under-floor SCR.

In order to mitigate this issue, a need exists for a method that, by the employment of EGR recirculation circuit coupled to the engine throttling during cut-off phases, allows to significantly reduce the exhaust flow rate in the aftertreatment during those phases, thus improving the aftertreatment warm-up.

An object of this invention is a method to enhance the aftertreatment warm-up in internal combustion engines, particularly highly-efficient diesel engines, in which the exhaust gases temperature profile during the certification cycle arid under real-world short-commuting urban schedules is quite unfavorable.

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 disclosure provides a method of controlling an internal combustion engine of an automotive system, comprising an exhaust system having at least one after-treatment device, an EGR valve, a throttle valve and a turbocharger comprising a variable geometry turbine controlled by a VGT actuator, wherein the EGR valve duty cycle is set equal to a first speed dependent array, the VGT actuator duty cycle is set equal to a second speed dependent array and the throttle valve duty cycle is set equal to a third speed dependent array, under the conditions that the internal combustion engine is in a cut-off phase, the engine speed is below a speed threshold THR_Spd and a diesel particulate filters inlet temperature DPF_inl temp is lower than a temperature threshold THR_Tmp.

Consequently, an apparatus is disclosed for controlling an internal combustion engine of an automotive system, the apparatus comprising means for setting the EGR valve duty cycle equal to a first speed dependent array, means foe setting the VGT actuator duty cycle equal to a second speed dependent array and means for setting the throttle valve duty cycle to a third speed dependent array, under the conditions that the internal combustion engine is in a cut-off phase, the engine speed is below a speed threshold THR_Spd and a diesel particulate filters inlet temperature DPF_inl temp is lower than a temperature threshold THR_Tmp.

An advantage of this embodiment is that it provides a quicker aftertreatment warm-up. In addition, the coordination of EGR valve, throttle valveand VGT actuator improves the tip-in performance with respect to a pure throttle-based strategy as the pressure level in the intake manifold is kept at high values. Another potential benefit is that back-flow air recirculation through the EGR module could help removing deposed soot, thus reducing the fouling risk.

According to an aspect of this embodiment, said first, second and third speed dependent arrays are respectively a set-point HP-EGR_SP value for the EGR valve duty cycle, a set-point value VGT_SP for the VGT actuator duty cycle and a set-point value THR_SP for the throttle valve duty cycle.

An advantage of this aspect is that the use of a specific set-point value instead of an array of engine speed dependent values would simplify the engine calibration procedures.

According to a further embodiment of the invention, in case of low pressure EGR recirculation system, the internal combustion engine further comprises a low pressure EGR valve and the method ultimate step further comprises the followings: -setting the low pressure EGR valve duty cycle equal to a fourth speed dependent array.

An advantage of this embodiment is that it provides a quicker aftertreatment warm-up even in case of low pressure EGR recirculation systems.

According to an aspect of this embodiment, said fourth speed dependent array is a set-point value LP-EGR_SP for the low pressure EGR valve duty cycle.

According to a further embodiment of the invention, in case of low pressure EGR recirculation system, the internal combustion engine further comprises an exhaust throttle valve and the method ultimate step further comprises the followings: -setting the exhaust throttle valve duty cycle equal to a fifth speed dependent array.

An advantage of this embodiment is that it also provides a quicker aftertreatment warm-up even in case of low pressure EGR recirculation systems.

According to an aspect of this embodiment, said fifth speed dependent array is a set-point value EXH_THR-SP for the exhaust throttle EGR valve duty cycle.

S

The method according to one of its embodiments or aspects can be carried out on an internal combustion engine of an automotive system, which is equipped with an exhaust system comprising at least one after-treatment devices, while the internal combustion S engine also comprises an EGR valve, a throttle valve (330) and a turbocharger, the turbocharger comprising a variable geometry turbine (250) with a VGT actuator (290), and the automotive system comprises an electronic control unit (450) configured for carrying out the above method.

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 wiU 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 flowchart of a method for improving the after treatment warm-up according to a first embodiment of the invention.

Figure 4 is a flowchart of a method for improving the after treatment warm-up according to a second embodiment of the invention.

Figure 5 is a simplified scheme of the internal combustion engine of figure 2 according to the first embodiment of the invention.

Figure 6 is a simplified scheme of the internal combustion engone of figure 2 according to the second 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 ISO that increase the pressure of the fuel received 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 valve 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 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)1 oxidation catalysts, lean NOx traps 284, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems 282, particulate filters (DPF) 281 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 300. Still other embodiments (Fig. 6) may include an EGR system characterized by a "long route" of the exhaust gases. In this case an additional low pressure EGR valve 325 will recirculate the exhaust gases downstream the aftertreatment devices towards the compressor 240 inlet. In alternative, instead of the low pressure EGR valve 325, an exhaust throttle valve 335 is provided.

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, including1 but not limited to, the fuel injectors 160, the throttle valve 330, the EGR Valve 320, the VGT 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 toffrom 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 andfor 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 exhaust system 270, the proposed invention relies on the optimization of the warm-up phase of the after-treatment devices. In particular, the usage of highly-efficient leads to a widespread reduction of exhaust temperature levels, which in turn will slow the warm-up of aftertreatment systems, in particular for cars fitted with under-floor SCR. In order to mitigate this issue the present ROI proposes the employment of EGR recirculation coupled to engine throttling during cut-off phases, in order to significantly reduce the exhaust flow rate in the aftertreatment during those phases.

More in detail, Fig. 3 shows a flowchart illustrating the method according to the invention, while Fig. 5 shows the simplified engine scheme, associated with the present method.

Considering Figs. 1, 2 and 5, the internal combustion engine 110 of an automotive system 100 comprises an exhaust system 270, which in turn comprises at least one after-treatment devices (280). preferably at least a diesel particulate fitter (DPF) 281. In the example of Fig. 5 there are a close coupled diesel oxidation catalyst (DOC) 283 and a DPF 281 in one brick and then an underfloor selective catalyst reduction (8CR) system 282. The internal combustion engine 110 also comprises an EGR valve 320, a throttle valve 330 and a turbocharger 230, the turbocharger comprising a variable geometry turbine 250 with a VGT actuator 290. The method, according to the invention, comprises the following steps: -detecting 20 if the engine 110 is in a cut-off phase, with fuel supply equal to 0, and, if yes, -detecting 21 if the engine speed is lower than a speed threshold THR_Spd and, if yes, -detecting 22 if the diesel particulate filter 281 inlet temperature DPF_inl temp is lower than a temperature threshold Tl-IR_Tmp and, if yes, -setting 23 the EGR valve 320 duty cycle equal to a first speed dependent array, the VOT actuator 290 duty cycle equal to a second speed dependent array and the throttle valve 330 duty cycle equal to a third speed dependent array.

The threshold on engine speed THR_Spd, which can be calibrated, limits the application of the present method to low engine speed, thus avoiding its usage for improper operation (e.g. at high speed cut-off, which are typical of sporty driving). The threshold on DPF inlet temperature (THR_Tmp, also calibrated) activates the technique only in case of need for aftertreatment warm-up or for improving temperature stability during DPF regeneration events.

The set of speed-dependent arrays for the valve actuators can also be set-points values, respectively HP-EGR_SP for the EGR valve 320, VGT_SP for the VGT actuator 290 and THR_SP for the throttle valve 330, in order to simplify the engine calibration. Preferably, such set-points values, in order to reduce the airflow, are suitable to let the EGR valve 320 open, and the throttle valve 330 and the VGT actuator 290 closed in order to increase the recirculation, The proposed technique involves, therefore, the recognition of cut-off conditions for reducing inducted airflow (based on zero fuelling, engine speed and exhaust temperature downstream of DOC); the set-up of an operating mode with a specific set-of EGR, throttle and VOT valve positions. EGR valve should be fully open in order to recirculate as much as possible air, while throttle and VGT closed in order to further limit the suction of fresh air. The backflow created in the EGR cooler, in addition to reducing intake flow rate, would be also helpful in removing looser deposits in the cooler itself, therefore limiting the fouling risk to a significant extent.

The strategy applies well to both high-pressure and low-pressure EGR systems. A high pressure EGR system 300, also called "short route" EGR system, is the one showed in Fig. 5. The term high pressure, as known, means the exhaust gases are recirculated from the exhaust manifold 270 (upstream the turbine 250) to the intake manifold 200, downstream the compressor 240.

A low pressure EGR system, also called long route" EGR system, is the one showed in Fig. 6. In this example the exhaust system 280 comprises a close coupled lean NOx trap (LNT) 254 and a DPF 281. The term low pressure, as known, means that the exhaust gases are also recirculated downstream the aftertreatment devices through, alternatively, a low pressure EGR valve 325 or an exhaust throttle valve 325, to the inlet system, upstream the compressor 240.

In case of a low pressure EGR system, the present method (see flow-chart in Fig. 4) operates in the same way. In addition, step 23 will also set either the low pressure EGR valve 325 duty cycle or the exhaust throttle valve 335 duty cycle respectively equal to a fourth or a fifth speed dependent array.

Also in this case the set of speed-dependent arrays for the LP EGR valve 325 or the exhaust throttle valve 335 can also be a set-points value (respectively LP-EGR_SP or EXH_THR_SP) in order to simplify the engine calibration. Preferably, also the LP-EGR valve or, alternatively, the exhaust throttle valve should be coordinated in closed position in order to enhance the effect.

With respect to an airflow reduction based only on intake throttling, the usage of HP-EGR and LP-EGR valves is helpful in keeping high intake pressure values for faster tip-in acceleration, as well as for cleaning NP-EGR cooler or LP-EGR filter from the deposits.

Furthermore, the main benefit of this technique is that no additional sensor or actuator is needed, just an optimized operation strategy is involved.

Experimental results have shown that, by applying this method during cut-off, the S temperature drop in front of the DOC 283 is reduced from 60°C to 35°C. Moreover, thanks to the coordination between EGR and throttle, pressure drop in the intake manifold is not significantly increased with respect to an un-throttled case, and pumping is low too, with benefit for kinetic energy recovery.

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 data carrier automotive system internal combustion engine engine block 125 cylinder cylinder head camshaft piston crankshaft 150 combustion chamber cam phaser fuel injector fuel rail fuel pump 190 fuel source 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 diesel particulate filter 282 selective catalytic reduction (SCR) system 283 close coupled diesel oxidation catalyst (DOC) 284 close coupled lean NOx trap (LNT) 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 325 Low pressure EGR valve 330 throttle valve 335 exhaust throttle valve 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 365 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 THR_Spd Engine speed threshold DPFJnI temp DPF inlet temperature THR_Tmp DPF inlet temperature threshold HP-EGR_SP set point of EGR valve duty cycle VGT_SP set point of VGT actuator duty cycle THR_SP set point of throttle valveduty cycle LP-EGR_SP set point of LP-EGR valve duty cycle EXI-IJHR_SP set point of exhaust throttle valve duty cycle

Claims

CLAIMS1. Method of controlling an internal combustion engine (110) of an automotive system (100), comprising an exhaust system having at least one after-treatment device (280), an EGR valve (320), a throttle valve (330) and a turbocharger (230) comprising a variable geometry turbine (250) controlled by a VOl actuator (290), wherein the EGR valve (320) duty cycle is set equal to a first speed dependent array, the VOl actuator (290) duty cycle is set equal to a second speed dependent array and the throttle valve (330) duty cycle is set equal to a third speed dependent array, under the conditions that the internal combustion engine (110) is in a cut-off phase, the engine speed is below a speed threshold (ThR_Spd) and a diesel particulate filters (281) inlet temperature (DPF_inl temp) is lower than a temperature threshold (Tl-IR_Tmp).
2. Method according to claim 1, wherein said first, second and third speed dependent arrays are respectively a set-point value (HP-EGR_SP) for the EGR valve (320) duty cycle, a set-point value (VGT_SP) for the VGT actuator (290) duty cycle and a set-point value (THR_SP) for the throttle valve (330) duty cycle.
3. Method according to claim 1, wherein the iritemal combustion engine further comprises a low pressure EGR valve (325) and the step (23) further comprises the followings: -setting (23) the low pressure EGR valve (325) duty cycle equal to a fourth speed dependent array.
4. Method according to claim 3, wherein said fourth speed dependent array is a set-point value (LP-EGR SP) for the low pressure EGR valve (325) duty cycle.
5. Method according to claim 1, wherein the internal combustion engine further comprises an exhaust throttle valve (335) and the step (23) further comprises the followings: -setting (23) the exhaust throttle valve (335) duty cycle equal to a fifth speed dependent array.
6. Method according to claim 5, wherein said fifth speed dependent array is a set-point value (EXH_THR_SP) for the exhaust throttle valve (335) duty cycle.
7. Internal combustion engine (110) of an automotive system (100) equipped with an exhaust system (270), the exhaust system comprising at least one after-treatment devices (280), the internal combustion engine comprising an EGR valve (320), a throttle valve (330) and a turbocharger (230), the turbocharger comprising a variable geometry turbine (250) with a VGT actuator (290) the automotive system comprising an electronic control unit (450) configured for carrying cut the method according to claims 1-6.
8. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-6.
9. Computer program product on which the computer program according to claim 8is 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 computer program according to claim 8 stored in the data carrier (40).
11. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 8.