GB2500890A

GB2500890A - Method of compensating an injection timing drift in a fuel injection system

Info

Publication number: GB2500890A
Application number: GB1205926.7A
Authority: GB
Inventors: Ignazio Dentici; Michele Bastianelli
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-04-02
Filing date: 2012-04-02
Publication date: 2013-10-09
Also published as: GB201205926D0

Abstract

Disclosed is method of compensating an injection drift of a fuel injector 160 of an internal combustion engine 110. The method comprises the steps of: operating the fuel injector 160 to perform a plurality of test fuel injections, monitoring a signal CSS proporÂtional to a speed of a crankshaft 145 of the internal combustion engine 110 during the test fuel injections, monitoring a signal CAS proportional to an acceleration of the crankshaft 145 during the test fuel injections and integrating the monitored crankshaft acÂceleration signal CAS over a range of crankshaft velocities ranging from a first value CSS0 to a second value CSS1. The result of the integration is compared with an expected value and the energizing time is adjusted if the energizing time differs from the expected value. The steps are repeated until the measured integration value matches the expected integration value.

Description

METHOD OF COMPENSATING A FUEL INJECTION DRIFT OF A FUEL INJECTOR

TECHNICAL FIELD

The present disclosure relates to a method of compensating an injection drift of a fuel in-jector of an internal combustion engine, for example a Diesel engine. :lO

BACKGROD

It is known that an internal combustion engine comprises an engine block defining a plu-rality of cylinders, each of which accommodates a reciprocating piston coupled to rotate a crankshaft. Each piston cooperates with a cylinder head to define a combustion cham- ber, in which an air and fuel mixture is disposed and ignited, thereby producing hot ex-panding exhaust gases that causes the reciprocal movements of the piston.

The fuel is delivered into each of the combustion chambers by means of a dedicated fuel injector, which is usually operated by an engine control unit (ECU) to perform a plurality of separated fuel injections per engine cycle, according to predetermined injection pat-tern. The fuel quantity injected by means of each fuel injection depends on the so called energizing time, namely the time interval between the opening and the closure of the fuel injector.

In order to perform a fuel injection, especially an injection of a small fuel quantity (e.g. a pilot injections), the fuel injector may be controlled by the ECU according to a feed-forward control strategy, which comprises the steps of setting a target value of the fuel quantity to be injected during a fuel injection, of determining a value of the energizing time corresponding to the target value of the fuel quantity, and then of operating the fuel injector according to the determined value of the energizing time.

Notwithstanding, it may happen that the quantity of fuel actually injected by a fuel injec-tor, operated according to this feed-forwards control strategy, does not exactly coincide with the target value thereof. This event is usually referred as injection drift and it is gen-erally caused by production spread and/or aging of the fuel injector.

To solve this drawback, the ECU may implement a fuel delivery compensation strategy, such as for example the so called small quantity adjustment strategy, which corrects the determined value of the energizing time, in order to achieve a better accuracy in the fuel injected quantity. The small quantity adjustment strategy is carried out during engine overruns driving, when the internal combustion engine is working in a cut-off condition To solve this drawback, the ECU may implement a fuel delivery compensation strategy, such as for example the so called small quantity adjustment strategy, which corrects the determined value of the energizing time, in order to achieve a better accuracy in the fuel injected quantity. The small quantity adjustment strategy is carried out during engine overruns driving, when the internal combustion engine is working in a cut-off condition and it is repeated for each fuel injector individually.

In greater details, the small quantity adjustment strategy provides repeating a learning routine, which comprises the step of operating a fuel injector to perform a plurality of test fuel injections having a same predetermined energizing time value, typically the energiz-ing time value nominally corresponding to a given small fuel quantity to be injected (e.g. 1mm3). During these test fuel injections, the small quantity adjustment strategy com-prises the steps of monitoring a signal proportional to an acceleration of the crankshaft, and of comparing the monitored value of the acceleration signal with an empirically de- termined expected value thereof. If the monitored value of the acceleration signal ex- ceeds the expected value thereof, then the predetermined energizing time value is dec-remented of a preset amount. If conversely the monitored value of the acceleration signal is beneath the expected value thereof, then the predetermined energizing time value is incremented of a preset amount.

This learning routine is repeated until the comparison yields that the monitored value of the acceleration signal coincides with the expected value thereof. The energizing time value that has achieved this result is memorized and used to correct the fuel injections performed by the fuel injector so forth during the normal operation of the internal com-bustion engine.

A drawback of this small quantity adjustment strategy is that the crankshaft acceleration signal is very sensitive to noises, such as for example the noises due to driveline clear-ances and resonances, and street noise. All these noise factors make the acceleration signal extremely unstable, so that sometimes the comparison of the monitored accelera- tion signal with a threshold value thereof may be unreliable, thereby releasing wrong in-jected quantity correction and so leading to increase in emission and combustion noise.

In view of the above, it is an object of an embodiment of the present invention to provide an improved method of compensating the injection drift of a fuel injector, in order to ob-tain precise corrections for the fuel injected quantity (especially but not exclusively for the pilot injections), and thus reduce the polluting emissions and the combustion noises of the internal combustion engine. Another object is that of meeting this goal with a simple, rational and cheap solution.

SUMMARY

These and/or other objects are attained by the characteristics of the embodiments of the invention as reported in independent claims. The dependent claims recite preferred and/or especially advantageous features of the embodiments of the invention.

More particularly, an embodiment of the invention provides a method of compensating an injection drift of a fuel injector of an internal combustion engine, wherein the method comprises the steps of: -operating the fuel injector to perform a plurality of test fuel injections, thereby always using the same energizing time, -monitoring a signal proportional to a speed of a crankshaft of the internal combustion engine during the test fuel injections, -monitoring a signal proportional to an acceleration of the crankshaft during the test fuel injections, -integrating the monitored crankshaft acceleration signal in an interval of values of the monitored speed signal ranging from a first value to a second value, -comparing a result of the integration with an expected value, -adjusting the energizing time, if the comparison yields that the result differs from the expected value, and -repeating the preceding steps, until the comparison yields that the result is equal to the expected value.

This embodiment of the invention is based on the discovery that, for a given fuel quantity injected per engine cycle in the engine cylinder, for a given pressure level in the fuel rail and for a given engaged gear, the crankshaft acceleration signal can be modelled as a curve depending only on the engine speed, namely the rotational speed of the crank-shaft.

As a consequence, the integral of the acceleration signal over the speed signal is a reli-able index of the fuel quantity actually injected in the engine cylinder, which is generally less affected by the external noises than the acceleration signal as such, thereby advan-tageously increasing the robustness of the injection drift compensation strategy.

According to an aspect of the invention, the expected value is determined by -integrating, over the same interval, a balibration function that correlates the acceleration signal to the speed signal.

This aspect of the invention has the advantage of providing a reliable expected value for the integral of the crankshaft acceleration signal. The calibration function may be empiri-cally determined on a test bench.

According to another aspect of the invention, the method comprises the further steps of: -determining a value of a pressure within a fuel rail of the internal combustion engine, and -selecting the calibration function, among a plurality of calibration functions, on the basis of the determined value of the fuel rail pressure.

In other words, this aspect of the invention provides for the compensating method to se-lect the function to be used among a set of different functions correlating the acceleration signal to the speed signal, each of which may be empirically determined on a test bench for a different value of the fuel rail pressure.

As a consequence, this solution has the advantage of allowing the compensating method to be performed under different values of the fuel rail pressure.

According to still another aspect of the invention, the method comprises the further steps 2C of: -determining an engaged gear of a transmission coupled to the internal combustion en-gine, and -selecting the calibration function, among a plurality of calibration functions, on the basis of the determined engaged gear.

In other words, this aspect of the invention provides for the compensating method to se-lect the function to be used among a set of different functions correlating the acceleration signal to the speed signal, each of which may be empirically determined on a test bench fora different engaged gear of the engine transmission.

As a consequence, this solution has the advantage of allowing the compensating method to be performed under different engaged gears of the engine transmission.

Another aspect of the invention provides that the acceleration signal is monitored by monitoring a signal proportional to a timing of the crankshaft, and -processing the monitored timing signal.

This aspect of the invention has the advantage of providing a reliable and easy determi- nation of the acceleration signal, since the crankshaft timing signal may be advanta-geously sensed by a conventional crankshaft position sensor.

According to an aspect of the invention, the processing of the timing signal comprises the step of: -filtering the monitored timing signal with a pass-band filter centred on a fundamental frequency of the monitored timing signal, for example an Infinite Impulse Response (IIR) filter.

In fact, in an internal combustion reciprocating engine, the crankshaft timing signal is linked to the variation of the gas-pressure within each cylinder. Due the thermodynamic cycle (engine cycle), the gas-pressure variation in each cylinder is a periodic function, which depends on the constructional architecture of the internal combustion engine.

In a four-stroke internal combustion engine, each engine cycle is completed in two rota- tions of the engine crankshaft, so that gas-pressure variation has a period of 720 de-grees of Crankshaft rotation (CR). The small quantity adjustment strategy is performed for only one cylinder at a time, which means only one test fuel injection on two rotations of the crankshaft: namely a frequency of 0.5w, wherein w is the crankshaft rotation speed. Therefore, the gas-pressure variation in a four-stroke engine can be expressed by means of a Fourier's series having fundamental frequency 0.5w.

Filtering the crankshaft timing signal with a pass-band filter centred on this fundamental frequenôy has the advantage of removing many of the noises that affect the signal itself, and thus improving the robustness of the subsequent determination of the crankshaft ac-celeration signal.

According to another aspect of the invention, the processing of the timing signal com-prises the step of: -calculating a Root Mean Square (RMS) of the signal resulting from the pass-band filtra-tion.

To calculate the RMS has a double advantage. A first advantage is that of decreasing the noises that still affect the pass-band filtered signal. A second advantage is that of bringing the pass-band filtered signal in "baseband", that means to transform the crank-shaft timing signal into a signal that is directly proportional to the crankshaft acceleration.

According to another aspect of the invention, the processing of the timing signal com-prises the further step of: -filtering the signal resulting from the root mean square calculation with a low pass filter, for example an IIR filter.

This aspect of the invention has the advantage of eliminating high frequency noises that may still affect the signal, thereby further increasing the robustness of the determination of the acceleration signal.

Another aspect of the invention provides that the adjustment of the energizing time com-prises the steps of: -increasing the energizing time by a preset amount, if the comparison yields that the re-suit of the integration is smaller than the expected value, -decreasing the energizing time by a preset amount, if the comparison yields that the re-sult is larger than the expected value.

This aspect of the invention has the advantage of increasing the rapidity of the compen-sating method to converge on a final value of the energizing time.

Still another embodiment of the invention provides that the comparison between the re-sult of the integration and the expected value comprises the step of calculating a ratio between the result and the expected value.

This aspect of the invention has the advantage of providing a reliable index of the devia-tion between the integral of the acceleration signal and the expected value thereof.

Another embodiment of the invention provides a method of operating an internal com-bustion engine, comprising the steps of: -performing the injection drift compensating method disclosed above, -memorizing the energizing time for which the result of the integration is equal to the ex-pected value, and -using the memorized energizing time to correct subsequent fuel injections performed by the fuel injector.

This embodiment of the invention takes advantage of the reliability and effectiveness of the compensating method explained above, in order to improve the performances of the internal combustion engine, for example in terms of engine noise, polluting emissions and fuel consumption.

The methods according to 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 methods de-scribed above, and in the form of a computer program product on which the computer program is stored. 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 pro-gram to carry out all steps of the method.

By way of example, the computer program product may be embodied as an internal combustion engine comprising an engine block defining a cylinder, a reciprocating piston accommodated inside the cylinder and coupled to rotate a crankshaft, a fuel injector lo-cated in the cylinder for injecting fuel therein, an electronic control unit (ECU) connected to the fuel injector, a memory system connected to the electronic control unit, and the computer program stored in the memory system.

Another embodiment of the invention provides an apparatus for compensating an injec- tion drift of a fuel injector of an internal combustion engine, wherein the apparatus com-prises: -means for operating the fuel injector to perform a plurality of test fuel injections, thereby always using the same energizing time, -means for monitoring a signal proportional to a speed of a crankshaft of the internal combustion engine during the test fuel injections, -means for monitoring a signal proportional to an acceleration of the crankshaft during the test fuel injections, -means for integrating the monitored crankshaft acceleration signal in an interval of val-ues of the monitored speed signal ranging from a first value to a second value, -means for comparing a result of the integration with an expected value, -means for adjusting the energizing time, if the comparison yields that the result differs from the expected value, and -means for repeating the preceding steps, until the comparison yields that the result is equal to the expected value.

This embodiment of the invention has the same advantages of the method described above, including that of improving the reliability and effectiveness of the compensation of the injection drift of the fuel injector.

According to an aspect of this embodiment, the apparatus comprises means for deter-mining the expected value by integrating, over the same interval, a calibration function that correlates the acceleration signal to the speed signal.

This aspect has the advantage of providing a reliable expected value for the integral of the crankshaft acceleration signal.

According to another aspect of the embodiment, the apparatus further comprises: -means for determining a value of a pressure within a fuel rail of the internal combustion engine, and -means for selecting the calibration function, among a plurality of calibration functions, on the basis of the determined value of the fuel rail pressure.

In other words, this aspect of the invention provides for the apparatus to select the func-tion to be used among a set of different functions correlating the acceleration signal to the speed signal, each of which may be empirically determined on a test bench for a dif-ferent value of the fuel rail pressure.

As a consequence, this solution has the advantage of allowing the apparatus to compen-sate the injection drifts under different values of the fuel rail pressure.

According to still another aspect of the embodiment, the apparatus further comprises: -means for determining an engaged gear of a transmission coupled to the internal com-bustion engine, and -means for selecting the calibration function, among a plurality of calibration functions, on the basis of the determined engaged gear.

In other words, this aspect of the invention provides for the apparatus to select the func-tion to be used among a set of different functions correlating the acceleration signal to the speed signal, each of which may be empirically determined on a test bench for a dif-ferent engaged gear of the engine transmission.

As a consequence, this solution has the advantage of allowing the apparatus to compen-sate the injection drifts under different engaged gears of the engine transmission.

Another aspect of the embodiment provides that the means for monitoring the crankshaft acceleration signal comprise: -means for monitoring a signal proportional to a timing of the crankshaft, and -means for processing the monitored timing signal.

According to an aspect of the embodiment, the means for processing the timing signal comprise: -a pass-band filter centred on a fundamental frequency of the monitored timing signal.

for example an Infinite Impulse Response (lIR) filter.

Filtering the crankshaft timing signal with a pass-band filter centred on this fundamental frequency has the advantage of removing many of the noises that affect the signal itself, and thus improving the robustness of the subsequent determination of the crankshaft ac-celeration signal.

According to another aspect of the embodiment, the means for processing the timing signal comprise: -means for calculating a Root Mean Square (RMS) of the signal resulting from the pass-band filtration.

According to another aspect of the embodiment, the means for processing the timing signal comprise: -a low pass filter for filtering the signal resulting from the root mean square calculation.

Another aspect of the embodiment provides that the means for adjusting the predeter-mined energizing time comprise: -means for increasing the energizing time by a preset amount, if the comparison yields that the result of the integration is smaller than the expected value, -means for decreasing the energizing time by a preset amount, if the comparison yields that the result is larger than the expected value.

This aspect of the invention has the advantage of increasing the rapidity of the apparatus to converge on a final value of the energizing time.

Still another embodiment of the embodiment provides that the means for comparing the result of the integration and the expected value comprise means for calculating a ratio between the result and the expected value.

Another embodiment of the invention provides an apparatus for operating an internal combustion engine, comprising: -the apparatus for compensating an injection drift disclosed above, -means for memorizing the energizing time for which the result of the integration is equal to the expected value, and -means for using the memorized energizing time to correct subsequent fuel injections performed by the fuel injector.

This embodiment of the invention takes advantage of the reliability and effectiveness of the compensating apparatus described above, in order to improve the performances of the internal combustion engine, for example in terms of engine noise, polluting emissions and fuel consumption.

Still another embodiment of the invention provides an automotive system comprising an internal combustion engine, wherein the internal combustion engine comprises an engine block defining a cylinder accommodating a reciprocating �iston coupled to rotate a crankshaft, a fuel injector located in the cylinder for injecting fuel therein, and an elec- tronic control unit connected to the fuel injector, wherein the electronic control unit is con-figured to: -operate the fuel injector to perform a plurality of test fuel injections, thereby always us-ing the same energizing time, -monitor a signal proportional to a speed of a crankshaft of the internal combustion en-gine during the test fuel injections, -monitor a signal proportional to an acceleration of the crankshaft during the test fuel in-jections, -integrate the monitored crankshaft acceleration signal in an interval of values of the monitored speed signal ranging from a first value to a second value, -compare a result of the integration with an expected value, -adjust the energizing time, if the comparison yields that the result differs from the ex-pected value, and -repeat the preceding steps, until the comparison yields that the result is equal to the expected value.

Also this embodiment of the invention has the same advantages of the method described above, including that of improving the reliability and effectiveness of the compensation of the injection drift of the fuel injector S According to an aspect of this embodiment, the electronic control unit is configured to de-termine the expected value by -integrating! over the same interval, a calibration function that correlates the acceleration signal to the speed signal.

This aspect of the invention has the advantage of providing a reliable expected value for the integral of the crankshaft acceleration signal.

According to another aspect of the embodiment, the electronic control unit is further con-figured to: -determine a value of a pressure within a fuel rail of the internal combustion engine, and -select the calibration function, among a plurality of calibration functions, on the basis of the determined value of the fuel rail pressure.

In other words, this aspect of the invention provides for the electronic control unit to se-lect the function to be used among a set of different functions correlating the acceleration signal to the speed signal, each of which may be empirically determined on a test bench for a different value of the fuel rail pressure.

As a consequence, this solution has the advantage of allowing the electronic control unit to compensate injection drifts under different values of the.fuel rail pressure.

According to still another aspect of the embodiment, the electronic control unit is further configured to: -determine an engaged gear of a transmission coupled to the internal combustion en-gine, and -select the calibration function, among a plurality of calibration functions, on the basis of the determined engaged gear.

In other words, this aspect of the invention provides for the electronic control unit to se-lect the function to be used among a set of different functions correlating the acceleration signal to the speed signal, each of which may be empirically determined on a test bench for a different engaged gear of the engine transmission.

As a consequence, this solution has the advantage of allowing the electronic control unit to compensate injection drifts under different engaged gears of the engine transmission.

Another aspect of the embodiment provides that the electronic control unit is configured to monitor the acceleration signal by -monitoring a signal proportional to a timing of the crankshaft, and -processing the monitored timing signal.

According to an aspect of the embodiment, the electronic control unit is configured to process the timing signal with the step of: -filtering the monitored timing signal with a pass-band filter centred on a fundamental frequency of the monitored timing signal, for example an Infinite Impulse Response (lIR) filter.

According to another aspect of the embodiment, the electronic control unit is configured to process the timing signal with the step of: -calculating a Root Mean Square (RMS) of the signal resulting from the pass-band filtra-tion.

According to another aspect of the embodiment, the electronic control unit is configured to process the timing signal with the further step of: -filtering the signal resulting from the root mean square calculation with a low pass filter, for example an IIR filter.

Another aspect of the embodiment provides that the electronic control unit is configured to adjust the predetermined energizing time with the steps of: -increasing the energizing time by a preset amount, if the comparison yields that the re-sult of the integration is smaller than the expected value, -decreasing the energizing time by a preset amount, if the comparison yields that the re-sult is larger than the expected value.

This aspect of the invention has the advantage of increasing the rapidity of the electronic control unit to converge on a final value of the energizing time.

Still another aspect of the embodiment provides that the electronic control unit is contig- ured to compare the result of the integration and the expected value with the step of cal-culating a ratio between the result and the expected value.

This aspect of the invention has the advantage of providing a reliable index of the devia-tion between the integral of the acceleration signal and the expected value thereol.

According to another aspect of the embodiment, the electronic control unit is further con-figured to: -memorize the energizing time for which the result of the integration is equal to the ex-pected value, and -use the memorized energizing time to correct subsequent fuel injections performed by the fuel injector.

This aspect has the advantage of improving the performances of the internal combustion engine, for example in terms of engine noise, polluting emissions and luel consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is schematic representation of a motor vehicle.

Figure 2 shows an automotive system included in the motor vehicle of figure 1.

Figure 3 is a schematic representation of the section A-A of an internal combustion en-gine included in the automotive system of figure 2.

Figure 4 is a flowchart of a strategy for compensating a fuel injection drift of a fuel njec-tion according to an embodiment of the present invention.

Figure 5 is a flowchart representing a signal processing chain involved in the compensat-ing strategy of figure 4.

Figure 6 shows in comparison two graphs representing the variation of a crankshaft ac-celeration signal over a crankshaft speed signal.

Figure 7 is a flowchart of a strategy for operating a fuel injector during normal operation of the motor vehicle.

DETAILED DESCRIPTION

Some embodiments may include a motor vehicle 100, as shown in figure 1, that includes an automotive system 105. The automotive system 105 basically comprises an internal combustion engine (ICE) 110 having a crankshaft 145 coupled to rotate a wheel drive 111. By way of example, the crankshaft 145 may be coupled to the wheel drive 111 through a transmission 112 (also referred as gearbox), which is provided for changing the gear ratio between the crankshaft 145 and the wheel drive 111, a clutch 113 connect-ing the crankshaft 145 to the transmission 112, and a differential 114 connecting the transmission 112 to the wheel drive 111. A manual shifter 115, for example a shift lever.

is coupled to the transmission 112, in order to allow a human driver of the motor vehicle to change the gears of the transmission 112.

As shown in figures 2 and 3, the ICE 110 comprises an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate the crankshaft 145. A cylin-der 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, re-sulting in hot expanding exhaust gasses causing reciprocal movements of the piston 140.

The fuel is provided in each of the cylinder 125 by at least one respective 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 increases 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 rotat- ing in time with the crankshaft 145. The valves 215 selectively allow air into the combus-tion chamber 150 from the port 210 and alternately allow exhaust gases to exit through at least one exhaust 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 pipe 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 intake pipe 205 and manifold 200. An intercooler 260 disposed in the intake pipe 205 may reduce the temperature of the air. The turbine 250 rotates by receiving ex-haust 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. 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 gases exit the turbine 250 and are directed into an exhaust system 270.

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, hydrocarbon adsorbers, selective catalytic reduction (SCR) 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 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR sys-tem 300.

The automotive system 105 may further include an electronic control unit (ECU) 450 in communication with one or more sensors andlor 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 camshaft position sensor 410, a crankshaft position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, an accelerator pedal posi-tion sensor 445, and a gear sensor 446 for sensing the gear actually engaged in the transmission 112. 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 commu- nication between the ECU 450 and the various sensors and devices, but some are omit-ted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system 460 and an interface bus. The memory system 460 may include various storage types including optical storage, magnetic stor- age, solid state storage, and other non-volatile memory. The interface bus may be con-figured to send, receive, and modulate analog and/or digital signals tolfrom the various sensors and control devices. The CPU is configured to execute instructions stored as a program in the memory system 460, and send and receive signals to/from the interface bus. The program may embody the methods disclosed hereinafter, allowing the CPU to carryout out the steps of such methods and control the ICE 110 accordingly.

The ECU 450 may be particularly configured to perform a strategy for compensating an injection drift of the fuel injectors 160. This injection drift compensating strategy may be performed during overruns of the motor vehicle, when the ICE 110 is working in a cut-off condition, namely in a condition in which no fuel would be normally requested to be in-jected into the engine cylinders 125. In this condition, the injection drift compensating strategy is performed for each fuel injector 160 one at the time, while the remaining fuel injectors 160 remain closed in order to not inject any fuel.

As shown in figure 4, the injection drift compensating strategy firstly provides for initializ- ing (block 600) a test value ET of an energizing time. The initial test value ET1 is deter- mined as the value of the energizing time that would correspond to a predetermined tar-get value of a fuel quantity to be injected by the fuel injector 160, if the fuel injector 160 were in nominal condition. The fuel quantity target value may be a small value, for exam-ple 1mm3. The initial test value ET, of the energizing time, corresponding to this fuel quantity target value, may be an empirically determined calibration value, which is stored in the memory system 460 and which the ECU 450 reads therefrom.

Afterwards, the injection drift compensating strategy provides for the ECU 450 to perform a learning routine, which comprises the initial step of commanding the fuel injector 160 to perform (block 605) a plurality of subsequent test fuel injections (typically one test fuel injection per engine cycle), each of which by activating the fuel injector 160 for the test value ET of the energizing time.

During these engine cycles, the learning routine provides for the ECU 450 to monitor (block 610) a signal CSS proportional to the engine speed, namely to the rotational speed of the crankshaft 145. This crankshaft speed signal CSS may be monitored by the ECU 450 through the crankshaft position sensor 420. It should be observed that, being the ICE 110 in overrun and in cut-off condition, the crankshaft speed signal CSS is gen-erally decreasing during the learning routine.

Contemporaneously, the learning routine provides for the ECU 450 to monitor (block 615) a signal CAS proportional to an acceleration of the crankshaft 145.

As shown in figure 5, this crankshaft acceleration signal CAS may be monitored by the ECU 450 through the steps of monitoring a signal CTS proportional to a timing of the crankshaft 145, and then of processing the monitored timing signal CTS, in order to ob-tain the signal CAS proportional to the crankshaft acceleration. The crankshaft timing signal CTS may be monitored by the ECU 450 through the crankshaft position sensor 420.

Since the crankshaft timing signal CTS is very sensitive to noises, the signal processing chain of the this example firstly provides for the ECU 450 to filter (block 700) the crank-shaft timing signal CTS with a pass-band filter centred on a fundamental frequency of the crankshaft timing signal CTS itself. The ICE 110 of the present example is a four-stroke reciprocating engine, so that any engine cycle takes two rotations of the crankshaft 145 to be completed. The small quantity adjustment strategy is performed for only one cylin-der at a time, which means only one test fuel injection on two rotations of the crankshaft, which means that the fundamental frequency of the crankshaft timing signal CTS is 0.5w, wherein w is the crankshaft rotation speed. The step of filtering the crankshaft timing sig-nal CTS with a pass-band filter centred on this fundamental frequency has the advantage of removing many of the noises that affect the signal CTS itself. The pass-band filter may be an IIR filter of the second or the forth order. This filter may be modelled for this spe-cific filtration step and empirically optimized on a test bench, in order to obtain the best performances in terms of noise removal and group delay. This empirically optimized filter may be stored in the memory system 460, in order to be used by the ECU 450 for per-forming this filtration.

S Afterwards, the signal processing chain provides for the ECU 450 to calculate (block 705) a Root Mean Square (RMS) of the band-pass filtered signal. The RMS is an arith-metic operation that has the effect of decreasing the noises that might be still present in the band-pass filtered signal, and also the effect of bringing the band-pass filtered signal in "baseband", namely of transforming the crankshaft timing signal into a signal that is di-rectly proportional to the crankshaft acceleration.

As a final step, the signal processing chain may provide for the ECU 450 to filter (block 710) the RMS signal with low-pass filter, in order to remove high-frequency noises that might be still present in the signal. The low-band filter may be an IIR filter of the second order. This filter may be modelled for this specific filtering step and empirically optimized on a test bench. This empirically optimized filter may be stored in the memory system 460, in order to be used by the ECU 450 for performing this filtration.

After this last low-pass filtering step, the resulting crankshaft acceleration signal CAS may be directly used in the learning routine involved in the fuel injection compensating strategy, as illustrated in figure 4.

2 C More particularly, the learning routine may provide for the ECU 450 to plot (block 620) the monitored crankshaft acceleration signal CAS over the monitored crankshaft speed signal CSS. In other words, each monitored value of the crankshaft acceleration signal CAS is correlated to a corresponding value of the crankshaft speed signal CSS, wherein the corresponding value of the crankshaft speed signal CSS is the value of the crank-shaft speed signal CSS monitored at the same instant of the monitored value of the crankshaft speed signal CSS. In this way, the plotting step obtains an actual graph C representing the variation of the monitored crankshaft acceleration signal CAS over the monitored crankshaft speed signal CSS, as shown for example in figure 6.

At this point, the learning routine provides for the ECU 450 to integrate (block 625) the graph C on an interval CSS0-CSS1 of monitored values of the crankshaft speed signal CSS, wherein the initial value CSS0 is generally lower than the final value CSS1.

The resultant value I of this integration is then divided by an expected value thereof (block 630), thereby obtaining a ratio R between this two values.

The expected value lex of the integration may be determined through the step of integrat-ing (block 635), on the same interval CSS3-CSS1 of monitored values of the crankshaft speed signal CSS, a predetermined target function TF that correlates the crankshaft ac-celeration signal CAS to the crankshaft speed signal CSS in case of a fuel injector 160 in nominal condition. An example of target function TF is represented in figure 6.

The target function TF may be a calibration function, which is empirically determined dur-ing an experimental activity performed on a test bench. During this experimental activity the crankshaft acceleration signal is determined according to the same signal processing chain described above and depicted in figure 5. Once the experimental activity is over, the resultant target function TE may be stored in the memory system 460 to be used by the ECU 450 during the learning routine. In some embodiments, the memory system 460 may contain several target functions TF, each of which has been empirically determined as explained above, but under different values of the pressure within the fuel rail and un-der different gears engaged in the transmission that connects the engine to the wheel drive.

In this cases, the learning routine may provide for the ECU 450 to sense an actual value FRP of the pressure within the fuel rail 170, for example through the pressure sensor 400, to sense the gear GE actually engaged in the transmission 112, for example through the gear sensor 446, to select (block 640), among the target functions stored in the memory system 460, the target function TF that corresponds to the sensed pressure value FP and the sensed engaged gear GE, and then to use the selected target function FP to calculate the expected value ex* The ratio R between the resultant value I of the integration and the expected value 1ex thereof is then applied to a first condition block 645, which checks if the ratio R is lower than I (possibly allowing a little tolerance).

If the first condition block 645 yields positive, it means that the fuel injector 160 operated for the test value ET of the energizing time has injected a fuel quantity lower than ex- pected (e.g. lower than 1mm3). In this case, the compensating strategy provides for in-crementing (block 650) the test energizing time value ET of a preset amount X, and then of repeating the learning routine using this incremented energizing time value.

If conversely the first condition block 645 yields negative, the ratio R between the resuL tant value I of the integration and the expected value L thereof is applied to a second condition block 655, which checks if the ratio R is greater than 1 (possibly allowing a little tolerance).

If the second condition block 655 yields positive, it means that the fuel injector 160 oper-ated for the test value ET of the energizing time has injected a fuel quantity greater than expected (e.g. greater than 1mm3). In this case, the compensating strategy provides for decrementing (block 660) the predetermined energizing time value ET of a preset amount Y, and then of repeating the learning routine using this decremented energizing time value.

As a matter of fact, the energizing time test value ET is adjusted and the learning routine is repeated, until an energizing time test value ET1 is found for which both the condition blocks 645 and 655 yield negative.

When both the condition blocks 645 and 655 yield negative, it means that the ratio R be-tween the resultant value I of the integration and the expected value thereof is equal to 1 (or within a little range of tolerances across 1), and that the fuel injector 160 oper- ated with the last used test value ET of the energizing time has injected exactly the ex-pected fuel quantity (e.g. 1mm3).

The energizing time value ET for which both the condition blocks 645 and 655 yield negative is then memorized (block 665) in the memory system 460 and the compensat-ing strategy is ended.

Afterwards, the memorized test value El1 of the energizing time may be used to correct other fuel injections performed by the fuel injector 160 during the normal operation of the ICE 110.

More particularly, during the normal operation of the ICE 110, the ECU 450 may control the fuel injector 160 to perform some fuel injection using the strategy schematically illus-trated in figure 7. This strategy firstly provides for the ECU 450 to determine (block 800) a nominal value ET of the energizing time for the fuel injector 160. This nominal value ET of the energizing time is determined as the value that would correspond to a desired quantity of fuel to be injected, if the fuel injector 160 were in nominal condition. The strat-egy further provides for the ECU 450 to determine (block 805) a correction factor CF as a function of the memorized test value ET of the energizing time resulting at the end of the compensating strategy explained above. The correction factor CF is then subtracted (block 810) from the nominal value ET of the energizing time, thereby obtaining a CON rected value ET0 of the energizing time. Finally, the strategy provides for the ECU 450 to activate (block 815) the fuel injector 160 for the corrected value ET of the energizing time.

White 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 forgoing 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 in their legal equivalents.

REFERENCES

motor vehicle automotive system 110 internal combustion engine 111 wheel drive 112 transmission 113 clutch 114 differential 115 manualshifter engine block cylinder cylinder head camshaft 140 piston crankshaft combustion chamber cam phaser fuel injector 170 fuel rail fuel pump fuel source intake manifold 205 air intake pipe 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 altertreatment devices 290 VOl 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 in-cylinder pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 camshaft position sensor 420 crankshaft position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator pedal position sensor 446 gear sensor 450 ECU 460 memory system 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 block 700 block 705 block 710 block 800 block 805 block 810 block 815 block ET test value of the energizing time ET nominal value of the energizing time ET corrected value of the energizing time CSS crankshaft speed signal CAS crankshaft acceleration signal CIS crankshaft timing signal C actual graph 8S0-CSS1 interval of monitored values of CAS result of the integration lex expected value of the result of the integration TF target function FRP actual value of fuel rail pressure GE gear engaged R ratio X preset amount Y preset amount CF correction factor

Claims

CLAIMS1. A method of compensating an injection drift of a fuel injector (160) of an internal combustion engine (110), wherein the method comprises the steps of: -operating the fuel injector (160) to perform a plurality of test fuel injections, thereby al-ways using the same energizing time (ET), -monitoring a signal (CSS) proportional to a speed of a crankshaft (145) of the internal combustion engine (110) during the test fuel injections, -monitoring a signal (CAS) proportional to an acceleration of the crankshaft (145) during the test fuel injections, -integrating the monitored crankshaft acceleration signal (GAS) in an interval of values of the monitored speed signal (CSS) ranging from a first value (GSS0) to a second value (CSS1), -comparing a result (I) of the integration with an expected value (lex), -adjusting the energizing time (ET), if the comparison yields that the result differs from the expected value (l), and -repeating the preceding steps, until the comparison yields that the result is equal to the expected value (lex).
2. A method according to claim 1, wherein the expected value (lex) is determined by -integrating, over the same interval (CSS0-C551), a calibration function (IF) that corre-lates the acceleration signal (GAS) to the speed signal (CSS).
3. A method according to claim 2, comprising the further steps of: -determining a value (FRP) of a pressure within a fuel rail (170) of the internal combus-tion engine (110), and -selecting the calibration function (TF), among a plurality of calibration functions, on the basis of the determined value (FRP) of the fuel rail pressure.
4. A method according to claim 2 or 3, comprising the further steps of: -determining an engaged gear (GE) of a transmission (112) coupled to the internal com-bustion engine (110), and -selecting the calibration function (TF), among a plurality of calibration functions, on the basis of the determined engaged gear (GE).
5. A method according to any of the preceding claims, wherein the acceleration signal (GAS) is monitored by -monitoring a signal (CTS) proportional to a timing of the crankshaft (145), and -processing the monitored timing signal (CIS).
6. A method according to claim 5, wherein the processing of the timing signal (CTS) comprises the step of: -filtering the monitored timing signal (CTS) with a pass-band filter centred on a funda-mental frequency of the monitored timing signal (CTS).
7. A method according to claim 6, wherein the processing of the timing signal (CTS) comprises the step of: -calculating a root mean square of the signal resulting from the pass-band filtration.
8. A method according to claim 7, wherein the processing of the timing signal (CTS) comprises the further step of: -filtering the signal resulting from the root mean square calculation with a low pass filter.
9. A method according to any of the preceding claims, wherein the adjustment of the energizing time (ET) comprises the steps of: -increasing the energizing time by a preset amount (X), if the comparison yields that the result of the integration is smaller than the expected value (lex), -decreasing the energizing time by a preset amount (Y), if the comparison yields that the result is larger than the expected value (lex)
10. A method according to any of the preceding claims, wherein the comparison be- tween the result of the integration and the expected value (la) comprises the step of cal-culating a ratio between the result and the expected value (Lx).
11. A method of operating an internal combustion engine (110), comprising the steps of: -performing an injection drift compensating method according to any of the preceding claims, -memorizing the energizing time for which the result of the integration is equal to the ex-pected value (lex), and -using the memorized energizing time to correct subsequent fuel injections performed by the fuel injector (160).
12. A computer program comprising a computer code suitable for performing the method according to any of the preceding claims.
13. A computer program product on which the computer program of claim 12 is stored.
14. An apparatus for compensating an injection drift of a fuel injector (160) of an inter-nal combustion engine (110), wherein the apparatus comprises: -means (450) for operating the fuel injector (160) to perform a plurality of test fuel injec-tions, thereby always using the same energizing time (EL), -means (420, 450) for monitoring a signal (CSS) proportional to a speed of a crankshaft (145) of the internal combustion engine (110) during the test fuel injections, -means (420, 450) for monitoring a signal (CAS) proportional to an acceleration of the crankshaft (145) during the test fuel injections, -means (450) for integrating the monitored crankshaft acceleration signal (CAS) in an interval of values of the monitored speed signal (CSS) ranging from a first value (CSS0) to a second value (CSS1), -means (450) for comparing a result (I) of the integration with an expected value (lex), -means (450) for adjusting the energizing time (ETj, if the comparison yields that the re-sult differs from the expected value (l), and -means (450) for repeating the preceding steps, until the comparison yields that the re-sult is equal to the expected value (lex).
15. An automotive system (105) comprising an internal combustion engine (110), wherein the internal combustion engine (110) comprises an engine block (120) defining a cylinder (125) accommodating a reciprocating piston (140) coupled to rotate a crankshaft (145), a fuel injector (160) located in the cylinder (125) for injecting fuel therein, and an electronic control unit (450) connected to the fuel injector (160), wherein the electronic control unit (450) is configured to: -operate the fuel injector (160) to perform a plurality of test fuel injections, thereby al-ways using the same energizing time (ET), -monitor a signal (CSS) proportional to a speed of a crankshaft (145) of the internal combustion engine (110) during the test fuel injections, -monitor a signal (CAS) proportional to an acceleration of the crankshaft (145) during the test fuel injections, -integrate the monitored crankshaft acceleration signal (CAS) in an interval of values of the monitored speed signal (CSS) ranging from a first value (CSS0) to a second value (CSS1), -compare a result (I) of the integration with an expected value (Lx), -adjust the energizing time (ET), if the comparison yields that the result differs from the expected value (lex), and -repeat the preceding steps, until the comparison yields that the result is equal to the expected value (lex).