GB2498784A

GB2498784A - Method of controlling an internal combustion engine which allows for the delay between the fuel injection and the time at which the fuel burns

Info

Publication number: GB2498784A
Application number: GB1201461.9A
Authority: GB
Inventors: Giuseppe Conte; Vincenzo Alfieri; Alessandro Catanese
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-01-27
Filing date: 2012-01-27
Publication date: 2013-07-31
Also published as: GB201201461D0

Abstract

Disclosed is a method of controlling an internal combustion engine. The method estimates a heat release due to combustion of a quantity of fuel injected in a cylinder of the engine by a fuel injector in an injection pulse. The estimation provides for calculating a heat release rate as a function of a derivative of the energy of the fuel injected quantity. The derivative of the energy of the fuel injected is calculated according to an expression which includes an index representing a delay between the time at which a certain portion of the fuel is injected and the time at which it actually burns. The heat release rate is then integrated in order to estimate the total heat release of the injection pulse and the fuel injection amount and timing are controlled accordingly.

Description

METHOD OF CONTROLL/NG AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present invention relates to a method of controlling an internal combustion engine.

BACKGROUND

Modern internal combustion engines generally comprise a plurality of cylinders, each of which is provided with a dedicated fuel injector for injecting fuel into the cylinder.

The fuel can be injected in the cylinder by means of a single injection pulse per engine cycle, or by means of a plurality of injection pulses per engine cycle according to a multi-injection pattern, typically by means of at least a pilot injection pulse and a following main injection pulse.

A fuel injection is defined by several fuel injection parameters, such as for example a start of injection (SOl), a fuel injected quantity, an energizing time (ET) of the fuel injector for each injection pulses, a dwell time (DT) between two consecutive injection pulses, and an injection pressure. Moreover, the center of combustion (or 50% of mean fraction burned) is generally defined with the acronym MFB5O.

It must be considered that Euro 6 and US emission limits will require from future diesel engines a greater reduction of exhaust emissions in terms of nitrogen oxides (NO) and of particulate matter (PM).

In order to reduce NO and PM, besides using various after-treatment technologies (Selective Catalytic Reduction (SCR), Lean NO Trap (LNT), Diesel Particulate Filter (DPF), etc.), further developments in combustion process are required. In particular, it is required that diesel engines be able to run in different combustion modes (e.g. Conventional Diesel Combustion, Premixed Combustion, After-Treatment Regeneration, etc.), according to the engine operating conditions.

An accurate physics-based model of the combustion process is necessary both for combustion control and simulation purposes.

A control system of the combustion process is needed in order to provide a stable and robust diesel combustion for each combustion modes. The task of combustion control is to adjust injection timing in order to achieve optimal and stable combustion phasing.

According to the state of the art, several physics-based combustion control oriented models have been developed by various sources and can be found in the literature.

For example, a method of estimating the combustion of a quantity of fuel injected in a combustion chamber of a compression ignition internal combustion engine during an engine cycle is known.

This quantity of fuel is injected through at least an injection pulse i, and the known method comprises the step of calculating the heat release rate dQ1(t)Idt, due to the injection pulse I, according to the following equation: d&) = --r1) -Q1(t)] wherein k1 is an index representing the speed of the combustion process during the injection pulse i, Q,(t) is a total heat released up to the time t, QFUEL,(t-r,) is the energy of the fuel injected at the time f-i, by the injection pulse i, Ty is an index representing the delay between the time at which a certain fuel quantity of the injection pulse (is injected and the time at which it actually burns.

However, in some cases the predictive capabilities of this prior art is not completely satisfying.

For example, Figure 3 represents a graph comparing an experimental curve 800 of the heat released in the combustion of an injection with a curve 810 of its values

predicted by the algorithm of the prior art.

Figure 4 represents a graph comparing an experimental curve 820 of the MFBSO parameter with a curve 830 of its values predicted by the algorithm of the prior art.

The MFB5O is a known parameter in the art that represents the position where 50% of fuel mass injected over an engine cycle is burnt. Such parameter provides very important information about the effectiveness of combustion, such as the kind of combustion that is taking place.

It can be seen in both the graphs of Figure 4 and S that there is a certain discrepancy between the experimental data and the prior art model employed.

More specifically, there is a sensible difference in the shape of the model based estimation of the prior art concerning the heat release of an injection.

Also the MFB5O estimated by the prior art model differs sensibly from experimental data, especially during transient conditions of the engine.

An object of an embodiment of the present invention is to provide a model based combustion estimation strategy capable to estimate the combustion dynamic of an internal combustion engine with good accuracy and acceptable computational

M

requirements, such as to be effectively usable in a control system of an engine.

Another object of an embodiment of the invention is to provide an improved combustion control method without using complex devices and by taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle.

Another object of the present disclosure is to meet these goals by means of a simple, rational and inexpensive solution.

These objects are achieved by a method, 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 an internal combustion engine comprising the steps of: -estimating a heat release due to combustion of a quantity of fuel injected in a cylinder of the engine by a fuel injector in an injection pulse i, wherein the estimation dQChJ(t) provides for calculating a heat release rate c/t as a function of a derivative of the energy of the fuel injected quantity, the derivative of the energy of the fuel injected quantity being calculated according to the following expression: di' wherein r, is an index representing a delay between the time at which a certain portion of the fuel injected quantity is injected and the time at which it actually burns and Qfue/ a-rj is the energy of the fuel injected quantity at the time t-T,, dQ (1) -integrating the heat release rate di' in order to estimate the total heat release of injection pulse i, and -using the total heat release to determine an activation parameter of the fuel injector.

An advantage of this embodiment is that it allows to have a predictive model that matches satisfactorily experimental data. This property make it easy to perform a learning procedure on real data. Furthermore, this embodiment can have a direct positive impact on model-based combustion controls using predictive heat release model and on combustion simulations, providing higher accuracy than previous models. (i)

According to an embodiment of the invention, the heat release rate dt is calculated according to the following equation: dQ1.(t) dQ1,, ((-v.) CI) = K1 (t -v1) + K1, -" --wherein r1 is an index representing a delay between the time at which a certain portion of the fuel injected quantity is injected and the time at which it actually burns, Q,.,1(t-T,) is dQ11(e -z-,) the energy of the fuel injected quantity at the time t-T1, dl' is a derivative of the energy of the fuel injected quantity, Q,(t) is a total heat released up to the time t, and K11, K21, K31 are experimentally determined weighting factors.

An advantage of this embodiment is that it consist in a low throughput predictive model that can be used in current Electronic Control Units of the engine.

According to an embodiment of the invention, the energy of the injected fuel at the time t-r, is calculated according to the following equation: -v,) = Hfrn(t -v3dt wherein [-4, is the lower heating value of the fuel, to is the start of injection and m is the fuei injection rate of the injection pulse i.

An advantage of this embodiment is that it provides a simple way to calculate the energy of the injected fuel, which further reduces the computational and memory efforts.

A further embodiment of the invention, comprises the step of calculating a total heat release of a train of injection pulses iby summing all contributes of each fuel injected quantity of each injection pulse L An advantage of this embodiment is that it takes into account the total heat release due to a train of injection in an engine cycle.

According to a further embodiment of the invention, the activation parameter of the fuel injector is a start of injection timing (Sd).

An advantage of this embodiment is that it allows to control the injection of fuel into the cylinder by operating on a well known injection control parameter.

Another embodiment of the invention provides an apparatus for controlling an ignition internal combustion engine using a strategy for estimating the heat release due to combustion of fuel injected in a cylinder of the engine, wherein the quantity of fuel is injected by a fuel injector in an injection pulse i, the apparatus comprising: -means for estimating a heat release due to combustion of a quantity of fuel injected in a cylinder of the engine by a fuel injector in an injection pulse i, wherein the dQChI (1) estimation provides for calculating a heat release rate dt as a function of a S derivative of the energy of the fuel injected quantity, the derivative of the energy of the fuel injected quantity being calculated according to the following expression: dQfr, (t -v1) dt wherein r1 is an index representing a delay between the time at which a certain portion of the fuel injected quantity is injected and the time at which it actually burns and Q10011(t-T,) is the energy of the fuel injected quantity at the time t-r1, -means for integrating the heat release rate di of injection pulse i in order to estimate the total heat release of injection pulse i and -means for using the total heat release to determine an activation parameter of the fuel injector.

According to an aspect of this embodiment, the apparatus comprises means to tin (t'i calculate the heat release rate dt is calculated according to the following equation: dQChI(t) = K1 f,,d -r1) + K21 dQfiJ(t -r) -K3JQChI(t) wherein r is an index representing a delay between the time at which a certain portion of the fuel injected quantity is injected and the time at which it actually burns, Qiei,(fT,) is dQjueii (t -r1) the energy of the fuel injected quantity at the time t-r1, dt is a derivative of the energy of the fuel injected quantity, Q1(t) is a total heat released up to the time t, and K1, K21, K3 are experimentally determined weighting factors.

According to another aspect of this embodiment of the invention, the energy of the injected fuel quantity at the time t-r, is calculated according to the following equation: QfidIO-rI)= wherein H0 is the lower heating value of the fuel, t0 is the start of injection and m the fuel injection rate of the injection pulse /.

According to another aspect of this embodiment of the invention, the apparatus is provided with means for calculating a total heat release of a train of injection pulses i by summing all contributes Qh_,(t) of each fuel injected quantity of each injection pulse i.

An advantage of this embodiment is that it takes into account the total heat release due to a train of injection in an engine cycle.

According to another aspect of this embodiment of the invention, the activation parameter of the fuel injector is a start of injection timing (SOP).

Another embodiment of the invention provides an automotive system comprising an internal combustion engine, managed by an engine Electronic Control Unit, the internal combustion engine comprising a fuel injector to inject a quantity of fuel in an injection pulse i, wherein the Electronic Control Unit is configured to: -estimate a heat release due to combustion of a quantity of fuel injected in a cylinder of the engine by a fuel injector in an injection pulse i, wherein the estimation dQChI (I) provides for calculating a heat release rate at as a function of a derivative of the energy of the fuel injected quantity, the derivative of the energy of the fuel injected quantity being calculated according to the following expression: di wherein T1 is an index representing a delay between the time at which a certain portion of the fuel injected quantity is injected and the time at which it actually burns and Q.,ei,(tTj is the energy of the fuel injected quantity at the time t-71, (t) -integrate the heat release rate di of injection pulse i in order to estimate the total heat release of injection pulse i and -use the total heat release to determine an activation parameter of the fuel injector.

Both these last two embodiments have the same advantage of the method disclosed above.

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 forni 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, wherein like numerals denote like elements, and in which: Figure 1 shows an automotive system; Figure 2 is a cross-section of an internal combustion engine belonging to the automotive system of figure 1; Figure 3 is a graph comparing an experimental curve of the heat released in the combustion of an injection with a curve of its values predicted by an algorithm of the prior art; Figure 4 is a graph comparing an experimental curve of the MFB5O parameter on transient conditions with a curve of its values predicted by an algorithm of the prior ad; Figure 5 is a graph that represents the effect of a train of injections on the cumulative heat generated in a cylinder; Figure 6 is a schematical representation of the main steps of an estimation of total het release according to an embodiment of the invention; Figure 7 is a schematical representation of the main steps of an embodiment of the invention; Figure 8 is a graph comparing an experimental curve of the heat released in the combustion of an injection with a curve of its values predicted by an algorithm according to an embodiment of the invention; and Figure 9 is a graph comparing an experimental curve of the MFB5O parameter on transient conditions with a curve of its values predicted by an algorithm according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses.

Some embodiments may include an automotive system loop 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 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 variable geometry turbine (VOT) 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 NO. traps 265, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems, and particulate filters. 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 30ft 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.

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 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, or data carrier 460, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals totfrom 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.

More specifically, Figure 5 is a graph that represents the effect of a train of injections on the cumulative heat generated in a cylinder & In particular, a pilot and a main injection are represented. The fuel quantity injected in the pilot injection is represented by a triangular curve 600 and the fuel quantity injected in the main injection is represented by a triangular curve 610.

After a time interval 1j from the Start of Injection of the pilot injection, the heat released by the combustion of the pilot injection's fuel Qch_p(t) starts to increase as represented by curve 620.

In a similar fashion, after a time interval Tmam from the Start of Injection of the main injection the heat released by the combustion of the main injection's fuel Qch_majn(t) starts to grow as represented by curve 630. The sum of the heat released by the combustion of the pilot and of the main injection Qth(t) is represented by curve 640.

An embodiment of the invention provides for an estimation of the variation of the quantity of heat released in a generic injection pulse i, wherein the estimating strategy -(1) comprises the step of calculating the heat release rate dt as a function of the derivative of the energy of the fuel injected by the injection pulse the method further Jfl. (t comprising a step of integrating the heat release rate dt of injection pulse i in order to estimate the total heat release of injection pulse i and a step of using the total heat release to determine an activation parameter of the fuel injector (160).

The derivative term allows to have an improvement in term of dynamics by better matching the shape of real data.

The direct correlation between the heat release and the fuel injection rates has a physical meaning. In fact, during the combustion process, the turbulence generation due to the momentum transfer from high-pressure fuel injection into the cylinder 125 enhances the speed of the heat release.

A further embodiment of the invention provides for an estimation of the variation of the quantity of heat released in a generic injection pulse i, according to the following Equation (1): dQ *(t) dQ, (i-v.) C/I_I = K1, Q1 i (1 -r/) + K2 -, -K3 IQCh,(t) di' --cit --(1) wherein T1 is an index representing a delay between the time at which a certain fuel quantity of the injection pulse i is injected and the time at which it actually burns1 Qruei,(t-dQ1,0,, (t -v) r1) is the energy of the fuel injected at the time t-r, by the injection pulse I, di S is a derivative of the energy of the fuel injected at the time t-T1 by the injection pulse i and QchI(t) is a total heat released up to the time t, and I<ii, <2i, K3j are experimentally determined weighting factors.

The same relation structure can be used for each injection pulse assuming, in an exemplary embodiment of the invention a pilot injection and a main injection. In the case Equation (1) can be rewritten, for the pilot and the main injection, in the following form: dQa,pj, (1) = K]f/Qfi,,/ 11 (1 -+ K21, dQiuei pu0 -re,,) -K3P,,QCh (t) dQCh HO/Il (I) = Ah,,oi,,Qtae! JJU1 (1 -vfllQh,) + K2111011, dQfilOt_ThU/flQ - -K3 n,th,, 2.1,,Wh,(t) Figure 6 represents the steps involved in a preferred embodiment of the invention, in order to estimate the cumulative heat release due to a train of i injections, where each njectbr, may be a pot of a 11 Sin Or an after injection and so on.

First for each injection, an injection profile is defined (block 500) in terms of a total quantity of fuel q1to be injected employing an energizing time ET.

Then a quantity of heat released by injection i is calculated (block 510) by the formula: = HJrn(t-vJdi where H is the lower heating value of the fuel and m is the fuel injection rate of the injection pulse i. This quantity of heat is released after a delay from the start of injection.

A derivative with respect to timet is calculated of the Qfi,0/_/(tT1) term (block 520) dQfi,.(( (t -v1) and the derivative term di is then used along with the r1_1" -r) term to dQd,J (t) calculate the heat release rate di' of injection 7' (block 530), leading to Equation (1): -K -K dQ(t-r,) K -1Q1., ( r3+ 21 -3 1Q,() dl ---dt --(1) dQ.,,1 (I) Then the heat release rate dt of injection "1" is integrated (block 540) in order to estimate the total heat release of injection "/ (block 540).

The total heat release of the train of injection is then estimated by summing all contributes _1() of each injection "I' (block 550).

Figure 7 is a schematical representation of the main steps of an embodiment of the invention and with reference to a train of injections in an engine cycle.

The ECU 450 uses the estimation strategy (block 960) as above described with reference to Figure 6 in order to determine the total heat release of the train of injection.

The total heat release of the train of injection is then used to estimate a MFB5D parameter of the combustion. This combustion index may be used to control the engine 110 in closed loop (block 970), for example by correcting an activation parameter of the fuel injector 160 such as a start of injection timing (SQl).

This strategy is merely n exmp!e of use of the estimation strategy described since this estimation strategy can be used in any model based combustion control strategy be it a closed loop control or a feed forward control strategy.

In Figure 8 a graph comparing an experimental curve 900 of the heat released in the combustion of an injection with a curve 910 of its values predicted by the algorithm of the

prior art is represented.

Figure 9 represents a graph comparing an experimental curve 920 of the MFB5O parameter with a curve 930 of its values predicted by the algorithm of the prior art.

It can be seen in both the graphs of Figure 6 and 7 that the model of the present invention gives a very good correlation with experimental data.

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

automotive system internal combustion engine (ICE) 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 duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 240 compressor 244 exhaust line portion 250 turbine 260 intercooler 270 exhaust system 275 exhaust line 280 exhaust aftertreatment device 285 LNltrap 290 VOT actuator 300 EGR 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 and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 460 data carrier 500 block 510 block 520 block 530 block 540 block 550 block 600 fuel quantity injected in a pilot injection 610 fuel quantity injected in a main injection 620 heat release by a pilot injection 630 heat release by a main injection 640 cumulative heat release 800 heat release curve

810 prior art heat release estimation

820 MFB5O parameter curve

830 prior art MFB5O parameter estimation

900 heat release curve 910 heat release estimation 920 MFBSO parameter curve 930 MFBSO parameter estimation 960 block 970 block