GB2530737A

GB2530737A - A method of operating an internal combustion engine

Info

Publication number: GB2530737A
Application number: GB1417211.8A
Authority: GB
Inventors: Luca Gazarella; Roberto Cavallo; Giorgio Nati; Gianmaria Manassero
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2014-09-30
Filing date: 2014-09-30
Publication date: 2016-04-06
Also published as: GB201417211D0

Abstract

The method comprises the steps of measuring (605, figure 4) an air-to-fuel (a/f) ratio in the engine exhaust gas; esÂtimating 600 a value (Texh) of the exhaust gas temperature on the basis of the measÂured value (a/f) of the air-to-fuel ratio; calculating 700 an error between the estimated value (Texh) of the exhaust gas temperature and a target value (Ttar) thereof; adjusting 800 a parameter (ET, FQ) affecting an injected fuel quantity on the basis of the calculated error. An electronic control unit (ECU), in an automotive system, is also configured to perform the above method. These methods can also improve the accuracy of the estimation by including other engine operating parameters such as engine coolant temperature, or manifold pressure, and applying these dedicated factors toe the final temperature estimate (as seen in figure 4). This method allows for a strategy for keeping the temperature of the exhaust gases under control, helping to prevent the exhaust manifold and/or turbine failures while also increasing engine performance. This also allows for a system with fewer sensors as only a lambda sensor can be used instead of a lambda and temperature sensor.

Description

A METHOD OF OPERATING AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present invention relates to a method of operating an internal combustion engine, for example an internal combustion engine of a motor vehicle.

BACKGROUND

It is known that an internal combustion engine conventionally comprises at least one piston arranged inside a corresponding cylinder. An air/fuel mixture is cyclically disposed inside * the cylinder and ignited, thereby generating hot expanding exhaust gas that causes a re-ciprocating motion of the piston.

The air is provided by an intake system that conventionally comprises an intake manifold that receives air from an intake pipe and delivers it into the engine cylinders. On the other side, the exhaust gas is discharged through an exhaust system that likewise comprises an exhaust manifold that receives the exhaust gas from the engine cylinders and directs it into an exhaust pipe.

Some internal combustion engine are equipped with a turbocharger to boost the air pres- sure in the intake manifold. The turbocharger conventionally comprises a compressor lo-cated in the intake pipe and rotationally coupled to a turbine located in the exhaust pipe.

The turbine is rotated by the exhaust gas coming from the exhaust manifold and drives the compressor, which increases the pressure and the temperature of the air in the intake manifold. An intercooler may be located in the intake pipe downstream of the compressor to reduce the air temperature.

The fuel is provided by at least one fuel injector in fluid communication with a fuel rail that receives the fuel from a fuel pump. The fuel injector is operated by an electronic control unit (ECU), which is usually configured to perform several injection pulses per engine cy- cle, according to a predetermined fuel injection pattern. The fuel injection pattern com-prises at least one main fuel injection pulse, which is mainly used to generate torque, and one or more small injection pulses, which are mainly used to reduce noises and/or pollutant emissions.

While the small injection pulses are set to inject a constant fuel quantity, the ECU is con- figured to determine cycle-by-cycle a target fuel quantity to be injected by the main injec-tion pulse, to calculate the time period (usually referred as energizing time -El) that the fuel injector needs to stay open to inject the target fuel quantity, and then to operate the fuel injector accordingly.

However, the variation of the injected fuel quantity may sometimes cause an excessive increase of the exhaust gas temperature, which can lead to exhaust manifold and/or tur-bine failures.

More particularly, the exhaust gas temperature is affected by many engine operating pa-rameters, including the above-mentioned injected fuel quantity, the intake manifold air temperature, the boost pressure, the engine coolant temperature, the engine volumetric efficiency and others.

Under ideal conditions, the values of these parameters should always guarantee that the exhaust gas temperature remains below a safety limit, thereby preventing any intake manifold and/or turbine failures. However, under real operating conditions, the above mentioned parameters may deviate from their expected values, up to the point that the exhaust gas temperature becomes uncontrolled.

The reasons of this deviation are multiple and may include (but are not limited to) differ-ent fuel injector efficiency (due for example to injector aging and/or injector-to-injector production spread), different fuel conditions (for example different fuel pressure and/or temperature), different intercooler efficiency (due for example to intercooler aging and/or intercooler-to-intercooler production spread), different efficiency of the engine cooling system and/or different engine volumetric efficiency (due for example to engine aging and/or engine-to-engine production spread).

For all these reasons, the lack of a dedicated control may potentially allow the exhaust gas temperature to become too hot and to damage the cylinder head and/or the turbine.

SUMMARY

An object of an embodiment of the present invention is that of providing a strategy for keeping the exhaust gas temperature under control, thereby solving or at least positively reducing the above mentioned drawback.

Another object is that of achieving this goac with a simple, rational and rather inexpensive solution.

These and other objects are achieved by the embodiments of the invention having the features recited in the independent claims. The dependent claims delineate secondary aspects of the invention.

More particularly, an embodiment of the invention provides a method of operating an in-ternal combustion engine comprising the steps of: -measuring an air-to-fuel ratio in the engine exhaust gas, -estimating a value of the exhaust gas temperature on the basis of the measured value of the air-to-fuel ratio, -calculating an error between the estimated value of the exhaust gas temperature and a target value thereof, -adjusting a parameter affecting an injected fuel quantity on the basis of the calculated error.

As a mailer of fact, this embodiment of the invention provides a closed-loop control strat-egy of the exhaust gas temperature, wherein the exhaust gas temperature is not directly measured but estimated as a function of the measured value of the air fuel ration in the exhaust gas.

Thanks to this solution, the proposed strategy does not require any sensor to measure the exhaust gas temperature but can simply use the lambda sensor that is usually locat-ed in the exhaust pipe of the internal combustion engines, thereby allowing a reliable control of the exhaust gas temperature in a simple and effective way, without additional costs.

Keeping the exhaust gas temperature under control, the proposed strategy is particularly able to prevent the exhaust manifold and!or turbine failures, while allowing an increase in the engine performance.

In particular, if the estimated value of the exhaust gas temperature is too high, the pro- * posed strategy will adjust the injected fuel quantity to decrease the exhaust gas tempera-ture, thereby guaranteeing the right performance of the engine in terms of maximum power.

On the other side, if the estimated value of the exhaust gas temperature is too low, the proposed strategy will allow the engine to generate the right power by properly adjusting the fuel injected quantity.

The global effect of this approach is that the proposed strategy guarantees that all the engines of the same family can generate the same power and show the same behavior under the various operating conditions, irrespective from the production spread and the aging of the components.

According to an aspect of the invention, the value of the exhaust gas temperature is es- timated also on the basis of a measured value (CT, AT, BP) of at least an additional en-gine operating parameter chosen among: a boost pressure, an intake manifold pressure and an engine coolant temperature.

This solution improves the reliability of the exhaust gas temperature estimation and thus of the entire control strategy.

Moreover, the internal combustion engines are usually already equipped with sensors configured to measure these additional parameters, so that no additional costs are intro-duced.

According to another aspect of the invention, the value of the exhaust gas temperature may be estimated (not only on the basis of the measured value of the air-to-fuel ratio and possibly of the additional parameters set forth above but) also on the basis of a meas-ured value of an engine speed.

This solution further improves the reliability of the exhaust gas temperature estimation and thus of the entire control strategy.

Also this aspect of the invention does not imply additional costs, because the internal combustion engines are usually already equipped with an engine speed sensor.

A specific aspect of the invention provides that the estimation of the exhaust gas tem-perature value may comprise the steps of: -multiplying the measured value of the air-to-fuel ratio by a dedicated factor to calculate a temperature contribution, -multiplying the measured value of each one of the additional engine operating parame-ters by a dedicated factor to calculate an additional temperature contribution, -adding the calculated temperature contributions to a predetermined temperature base value to calculate the estimated value of the exhaust gas temperature, wherein the temperature base value and each one of the factors are determined on the basis of the measured value of the engine speed.

This aspect of the invention provides a reliable mathematical model that allows the esti-mation of the exhaust gas temperature with a little computational effort.

According to another aspect of the invention, the method may comprise the step of filter-ing the estimated value of the exhaust gas temperature.

This solution has the effect of smoothing the estimated value of the exhaust gas temper- ature, thereby eliminating the unreliable values that may be caused for example by ex-ternal noises that affect the sensors' signals.

An aspect of the invention provides that the estimated value of the exhaust gas tempera-ture may be filtered by means of a first-order low-pass filter.

Provided that the time constant of this first-order low-pass filter is properly selected, this aspect of the invention provides a simple solution to achieve a reliable estimated value of the exhaust gas temperature..

According to another aspect of the invention, the parameter affecting the injected fuel quantity may be adjusted by means of the controller that uses the calculated exhaust gas temperature error as input.

This aspect of the invention provides a simple solution to implement the proposed closed-loop control strategy.

An aspect of the invention particularly provides that the controller may be a proportional-integrative-derivative (PID) controller.

The PID controller is quite effective in adjusting the injected fuel quantity parameter to reach the target value of the exhaust gas temperature.

According to a further aspect of the invention, the parameter affecting the injected fuel quantity may be either an energizing time of a fuel injector or a target value of a fuel quantity to be injected by a fuel injector.

In other words, the proposed closed-loop control strategy may act directly on the duration of the injection pulse (i.e. the main injection pulse) or on the target value of the injected fuel quantity which will be subsequently used to determine the duration of the injection pulse.

The method of the invention 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 a computer program prDduct* comprising the computer program. The method can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out all steps of the method.

Another embodiment of the invention provides an automotive system comprising an in-ternal combustion engine and an electronic control unit configured to: -measure an air-to-fuel ratio in the engine exhaust gas, -estimate a value of the exhaust gas temperature on the basis of the measured value of the air-to-fuel ratio, -calculate an error between the estimated value of the exhaust gas temperature and a target value thereof, -adjust a parameter affecting an injected fuel quantity on the basis of the calculated er-ror.

This embodiment of the invention achieve essentially the same effects of the method above, particularly that of keeping the exhaust gas temperature under control to prevent the exhaust manifold andor turbine failures.

According to an aspect of the invention, the electronic control unit may be configured to estimate the exhaust gas temperature value also on the basis of a measured value of at least one additional engine operating parameter chosen among: a boost pressure, an in-take manifold pressure and an engine coolant temperature.

According to another aspect of the invention, the electronic control unit may be config- ured to estimate the exhaust gas temperature value also on the basis of a measured val-ue of an engine speed.

A specific aspect of the invention provides that the electronic control unit may be config-ured to estimate the exhaust gas temperature value with the steps of: -multiplying the measured value of the air-to-fuel ratio by a dedicated factor to calculate a temperature contribution, -multiplying the measured value of each one of the additional engine operating parame-ters by a dedicated factor to calculate an additional temperature contribution, -adding the calculated temperature contributions to a predetermined temperature base value to calculate the estimated value of the exhaust gas temperature, wherein the temperature base value and each one of the factors are determined on the basis of the measured value of the engine speed.

According to another aspect of the invention, the electronic control unit may be further configured to filter the estimated value of the exhaust gas temperature.

An aspect of the invention provides that the electronic control unit may be configured to filter the estimated value of the exhaust gas temperature means of a first-order low-pass filter.

Provided that the time constant of this first-order low-pass filter is properly selected, this aspect of the invention provides a simple solution to achieve a reliable estimated value of the exhaust gas temperature.

According to another aspect of the invention, the electronic control unit may be config- ured to adjust the parameter affecting the injected fuel quantity by means of the control-ler that uses the calculated exhaust gas temperature error as input.

Still another embodiment of the invention provides an automotive system comprising an internal combustion engine and; -means for measuring an air-to-fuel ratio in the engine exhaust gas, -means for estimating a value of the exhaust gas temperature on the basis of the meas-ured value of the air-to-fuel ratio, -means for calculating an error between the estimated value of the exhaust gas temper-ature and a target value thereof, -means for adjusting a parameter affecting an injected fuel quantity on the basis of the calculated error.

This embodiment of the invention achieve essentially the same effects of the method above, particulaily that of keeping the exhaust gas temperature under control to prevent the exhaust manifold and/or turbine failures.

According to an aspect of the invention, the estimating means may be configured to es-timate the exhaust gas temperature value also on the basis of a measured value of at least one additional engine operating parameter chosen among: a boost pressure, an in-take manifold pressure and an engine coolant temperature.

According to another aspect of the invention, the estimating means may be configured to estimate the exhaust gas temperature value also on the basis of a measured value of an engine speed.

A specific aspect of the invention provides that the estimating means may comprise: -means for multiplying the measured value of the air-to-fuel ratio by a dedicated factor to calculate a temperature contribution, -means for multiplying the measured value of each one of the additional engine operat-ing parameters by a dedicated factor to calculate an additional temperature contribution, -means for adding the calculated temperature contributions to a predetermined tempera-ture base value to calculate the estimated value of the exhaust gas temperature, wherein the temperature base value and each one of the factors are determined on the basis of the measured value of the engine speed.

According to another aspect of the invention, the automotive system may comprise means for filtering the estimated value of the exhaust gas temperature.

An aspect of the invention provides that the filtering means may comprise a first-order low-pass filter.

According to another aspect of the invention, the means for adjusting the parameter af- fecting the injected fuel quantity may comprise a controller that uses the calculated ex-haust gas temperature error as input.

The PlO controller is quite effective in adjusting the injected fuel quantity parameter to reach the target value of the exhaust gas temperature.

According to a further aspect of the invertion, the parameter affecting the injected fuel quantity may be either an energizing time of a fuel injector or a target value of a fuel quantity to be injected by a fuel injector.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 schematically shows an automotive system according to an embodiment of the invention.

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

Figure 3 is a flowchart representing a control strategy of the exhaust gas temperature according to an embodiment of the invention.

Figure 4 is a flowchart representing a method for estimating the exhaust gas temperature within the control strategy of figure 3.

DETAILED DESCRIPTION

Some embodiments may include an automotive system 100, as shown in figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 de-fining 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 mani-fold 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 tur-bocharger 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 dud 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, hydrocarbon adsorbers, selective catalytic reduction (5CR) systems, and particulate filters. Other embodiments may include an exhaust gas recircu- lation (EGR) system 300 coupled between the exhaust manifold 225 and the intake man- ifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the tempera-ture 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 engine cooling circuit 500 for cooling the internal combustion engine 110. The engine cooling circuit 500 schematically com- prises a coolant pump 505 that delivers a coolant, typically a mixture of water and anti-freeze, from a coolant tank 510 to a plurality of cooling channels internally defined by the engine block 120 and by the cylinder head 130, and a radiator 520 for cooling down the coolant, once it has passed through the cooling channels and before it returns to the coolant tank 510.

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 temperature and level sensor 360, an oil temperature and level sensor 385, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, a lambda sensor (i.e. oxygen sensor) 435, 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 VOT 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 con-figured to execute instructions stored as a program in the memory system 460, and send and receive signals to/from the interlace bus. The memory system 460 may include van-ous 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 460 is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 100 it is normally visible as a com-puter 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 canler 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 modulation technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electro-magnetic 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 em- bodied in a tangible storage medium. The storage medium is then the non-transitory car- rier 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 medi-um 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 proces-sor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle.

One of the tasks of the ECU 450 is that of operating the fuel injector 160 according to a predetermined fuel injection pattern, which generally provides for performing several in-jection pulses per engine cycle, including a main fuel injection pulse and one or more small injection pulses.

While performing this task, the ECU 450 is generally configured to determine a target fuel quantity FQ to be injected by means of the main injection pulse, to calculate the time period (usually referred as energizing time) ET that the fuel injector 160 needs to stay open in order to inject the target fuel quantity FQ, and then to operate the fuel injector accordingly.

During these operations, the ECU 450 may be also configured to keep the temperature of the exhaust gases under control by implementing the closed-loop control strategy rep-resented in figure 3.

This closed-loop control strategy provides for the ECU 450 to estimate (block 600) a val- ue Texh of the temperature of the exhaust gases generated by the operations of the inter-nal combustion engine 110. The estimation of the exhaust gas temperature value Te,m may be performed through a mathematical model of the engine system, as it will be ex-plained later on.

The ECU 450 is then configured to calculate (block 700) an error E (i.e. the difference) between the estimated value T of the exhaust gas temperature and a target value Tta.r thereof. The target value Tr of the exhaust gas temperature may be determined by the ECU 450 on the basis of the operating conditions of the engine 110, by means of a dedi-cated strategy. In particular, the target value Tr of the exhaust gas temperature should be smaller than a temperature threshold value, above which the exhaust manifold 225 and/or the turbine 250 can be damaged.

The calculated error E is used by the ECU 450 as input of a controller 800, for example a proportional-integrative (PID) controller, which is configured to automatically adjust a val- ue of a parameter that is able to affect (i.e. change) the fuel quantity injected into the in-ternal combustion engine 110, in order to minimize the error E. The parameter affecting the injected fuel quantity may be either the energizing time ET of the main injection pulse or the target fuel quantity FQ to be injected during the main in-jection pulse.

This close-loop control cycle is periodically repeated at high frequency during the engine operations, so that the PID controller 800 continuously determines a corrective action on the injected fuel quantity that leads the system (i.e. the engine 110) to generate exhaust gases having the desired temperature target value The corrective action may be ei-ther negative (fuel reduction), in case the estimation yields a value Te,ti of the exhaust gas temperature that exceeds the target value Tthr, or positive (fuel increase), in case the estimation yields a value a value Texh of the exhaust gas temperature that is lower than the target value Referring now to the flowchart of figure 4, the estimation of the exhaust gas temperature may be made by measuring (block 605) a value A of the air-to-fuel ratio (lambda ratio) in the exhaust gas and the values of several additional engine operating parameters, in- cluding a value CT of the coolant temperature (block 610), a value AT of the air tempera-ture in the intake manifold 200 (block 615), a value BP of the air pressure in the intake manifold 200 (also referred as boost pressure) (block 620), and a value ES of the engine speed (block 625).

The air-to-fuel ratio value A may be measured by means of the lambda sensor 435. The coolant temperature value CT may be measured by means of the coolant temperature sensor 380. The air temperature value AT and the air pressure value BP may be meas-ured by means of manifold pressure and temperature sensor 350. The engine speed value ES may be measured by means of the crank position sensor 420.

The engine speed value ES may be used to determine a base value To of the exhaust gas temperature (block 630). The temperature base value To may be a calibration pa-rameter that depends of the current value ES of the engine speed. The temperature base values T0 may be determined with an experimental activity on a test bench, and then memorized in the memory system 460 in the form of a table or map that correlates each value of the engine speed with a corresponding base value Io of the exhaust gas tem-perature. As a consequence, the ECU 450 may be simply configured to retrieve from said table or map the base value T0 of the exhaust gas temperature corresponding to the current value ES of the engine speed.

The engine speed value ES may be further used to determine several factors (block 635), including an air-to-fuel ratio factor Fx, a coolant temperature factor Fci, an air tem-perature factor FAT and an air pressure factor FBP. Also these factors FA, FCT, FAT and FBP may be calibration parameters that depends of the current value ES of the engine speed.

These factors Fx, FCT, FAT and FBP may be determined with an experimental activity on a test bench, and then memorized in the memory system 460 in the form of a table or map that correlates each value of the engine speed with a corresponding group of factors FA, Fcr, FAT and Fp, As a consequence, also in this case the ECU 450 may be simply con-figured to retrieve from said table or map the factors FA, FOT, FAT and FBP corresponding to the current value ES of the engine speed.

The air-to-fuel ratio factor FA is multiplied by the measured value A of the air-to-fuel ratio (block 640), thereby calculating a first contribution Ti of the exhaust gas temperature ac-cording to the following equation: Ti=l3çA.

The coolant temperature factor Fcr is multiplied by the measured value CT of the coolant temperature (block 645), thereby calculating a second contribution 12 of the exhaust gas temperature according to the following equation: = CT CT.

The air temperature factor FAT is multiplied by the measured value AT of the air tempera- ture (block 650), thereby calculating a third contribution T3 of the exhaust gas tempera-ture according to the following equation: = AT. AT.

The air pressure factor Fap is finally multiplied by the measured value BP of the air pres- sure (block 655), thereby calculating a fourth contribution T4 of the exhaust gas tempera-ture according to the following equation: = FBP'BP.

These four contributions Th, T2, T3 and T4 are then added to the temperature base value T0 to calculate (block 660) a rough value rexi, of the exhaust gas temperature as follows: T*exh = 0 + 1 + T2 + T3 ÷ T4.

The ECU 450 may be finally configured to apply the rough value T* of the exhaust gas temperature as input of a filter 665, for example a first-order low-pass filter having a proper time constant, which yields as output the final estimated value Te,ji of the exhaust gas temperature that will be used in the closed-loop control strategy that has been previ-ously described and represented in figure 3.

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 r ad map for implementing at least one exemplary em- bodiment, it being understood that various changes may be made in the function and ar-rangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERBS

100 automotive system internal combustion engine engine block cylinder cylinder head 135 camshaft piston crankshaft combustion chamber cam phaser 160 fuel injector fuel rail fuelpump fuelsource intake manifold 205 airintakeduct 210 intake port 215 valves 220 exhaust port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 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 sensor 385 oil temperature and level sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 435 lambda sensor 440 EGR temperature sensor 445 accelerator pedal position sensor 450 ECU 460 memory system 500 engine cooling circuit 505 coolant pump 510 coolant tank 520 radiator 600 block 605 block 610 block 615 block 620 block 625 block 630 block 635 block 640 block 645 block 650 block 655 block 660 block 665 filter 700 block 800 controller

Claims

CLAIMSI. A method of operating an internal combustion engine (110) comprising the steps of: -measuring (605) an air-to-fuel ratio (A) in the engine exhaust gas, -estimating (600) a value (Teith) of the exhaust gas temperature on the basis of the measUred value (A) of the air-to-fuel ratio, -calculating (700) an error (E) between the estimated value (Th) of the exhaust gas temperature and a target value (Tthr) thereof, -adjusting (800) a parameter (ET, FQ) affecting an injected fuel quantity on the basis of the calculated error (E).
2. A method according to claim 1, wherein the value (Texh) of the exhaust gas temper- ature is estimated also on the basis of a measured value (CT, AT, BP) of at least an ad-ditional engine operating parameter chosen among: a boost pressure, an intake manifold pressure and an engine coolant temperature.
3. A method according to claim 1 or 2, wherein the value (Tsi) of the exhaust gas temperature is estimated also on the basis of a measured value (ES) of an engine speed.
4. A method according to claim 3, wherein the estimation of the exhaust gas tempera-ture value (Te,.±,) comprises the steps of: -multiplying (640) the measured value (A) of the air-to-fuel ratio by a dedicated factor (FA) to calculate a temperature contribution (Ii), -multiplying (645, 650, 655) the measured value (CT, AT, BP) of each one of the addi-tional engine operating parameters by a dedicated factor (FCT, FAT, FBP) to calculate an additional temperature contribution (12, T3, T4), -adding the calculated temperature contributions (Ti, T2, T3, T4) to a predetermined tem- perature base value (To) to calculate the estimated value (T) of the exhaust gas tem-perature, wherein the temperature base value (To) and each one of the factors (Fcr, FAT, FBP) are determined on the basis of the measured value (ES) of the engine speed.
5. A method according to any of the preceding claims, comprising the step of filtering (665) the estimated value of the exhaust gas temperature.
6. A method according to claim 5, wherein the estimated value (Te,) of the exhaust gas temperature is filtered by means of a first order filter.
7. A method according to any of the preceding claims, wherein the parameter affect- ing the injected fuel quantity is adjusted by means of a controller (800) that uses the cal-culated exhaust gas temperature error (E) as input.
8. A method according to claim 7, wherein the controller (800) is a proportional-integrative-derivative controller.
9. A method according to any of the preceding claims, wherein the parameter affect-ing the injected fuel quantity is either an energizing time (ET) of a fuel injector (160) or a target value (FO) of a fuel quantity to be injected by a fuel injector (160).
10. A computer program comprising a program-code for carrying out the method of any of the preceding claims.
11. A computer program product comprising the computer program of claim 10.
12. An electromagnetic signal modulated to carry a sequence of data bits which repre-sents the computer program of claim 10.
13. Another embodiment of the invention provides an automotive system (100) com- prising an internal combustion engine (110) and an electronic control unit (450) config-ured to: -measure (605) an air-to-fuel ratio (A) in the engine exhaust gas, -estimate (600) a value (Te,th) of the exhaust gas temperature on the basis of the meas-ured value (A) of the air-to-fuel ratio, -calculate (700) an error (E) between the estimated value (Te,th) of the exhaust gas tem-perature and a target value (Tr) thereof, -adjust (800) a parameter (ET, FQ) affecting an injected fuel quantity on the basis of the calculated error (E).