GB2511869A - Method of estimating fuel backflow temperature in a fuel injector - Google Patents

Abstract

A method of estimating fuel backflow temperature TEst in a fuel injector 160 of an internal combustion engine 110, the fuel injector being activated by means of a solenoid 34, the method comprising the steps of (i) applying a predetermined voltage V for a predetermined time t to the injector, (ii) reading a current (i) of the injector in a plurality of instants in order to find a current profile i(t) for the injector, (iii) determining a time constant (τ) of the injector as a function of the current profile i(t), of the voltage V and of an electrical resistance value Rinj of the injector, (iv) using the time constant τ to determine a ratio μr/� between the relative permeability μr and the resistivity � of the material of the solenoid 34, and (v) determining the estimated fuel backflow temperature TEst as a function of the ratio μr/�.

Description

METHOD OF ESTIMATING FUEL BACKFLOW TEMPERATURE IN A FUEL

INJECTOR

TEQIIa FIflD The present disclosure relates to a method of estimating fuel backf low temperature in a fuel injector. E3ND

An internal combustion engine for a motor vehicle generally comprises an engine block which defines at least one cylinder accontnodating a reciprocating piston coupled to rotate a crankshaft.

The cylinder is closed by a cylinder head that cooperates with the reciprocating piston to define a combustion chamber. A fuel. and air mixture is cyclically disposed in the combustion chamber and ignited, thereby generating hot expanding exhaust gasses that cause the reciprocating movements of the piston. The fuel is injected into each cylinder by a respective fuel injector. The fuel is provided at high pressure to each fuel injector from a fuel rail in fluid communication with a high pressure fuel piirp that increase the pressure of the fuel received from a fuel source.

The fuel injection system generally comprises a fuel common rail and a plurality of electrically controlled fuel injectors, which are individually located in a respective cylinder of the engine and which are hydraulically connected to the fuel common rail through dedicated feeding conduits.

The fuel in the common rail is maintained at a high pressure by an high pressure pump and enters the injector through a fluid inlet and is directed towards a control chamber in the upper portion of the injector and to a lower portion of the injector where a nozzle and a movable needle are provided.

The needle is connected to an injector rod and is moved with the aid of a dedicated actuator, typically a solenoid actuator controlled by an engine control unit (ECU).

If the solenoid is not activated, the needle is closed because the pressur of the fuel in the control chamber balances the pressure that keeps the needle in the closed position.

The Engine Control Unit (ECU), which rronitors engine operating parameters via various sensors, calculates the appropriate amount of fuel to be injected as a function of various operating conditions of the engine. The ECU determines an appropriate Energizing Time (ET) of the injector as a function of the fuel quantity to be injected.

When a certain quantity of fuel is to be injected, the solenoid is activated and an armature is lifted against the resistance of a spring and fuel pressure is relieved above the needle and a certain quantity of fuel returns to the fuel tank Via an injector backflow port generally positioned on an upper portion of the injector.

This creates a pressure difference above and below the injector rod and the fuel pressure below the needle lifts the needle and the injector opens and fuel is injected into the cylinder.

When the solenoid is deactivated, the pressure in the control chamber increases until the needle closes again the injector.

A problem that may arise in some connon rail injectors is that the injected quantity may change as a function of fuel backf low temperature.

In the prior art there are Imown algorithms that estimate the backif low temperature using the fuel filter terrçerature that, in turn, may be measured by a temperature sensor in the fuel filter. The estimated fuel backflow temperature is then used to correct, by means of maps, the injector energizing time.

However, these known algorithms may have an estimation error of ÷1-15°C. This large estimation error may reduce the reliability of such algorithms.

An object of an embodiment of the invention is to improve the accuracy of the fuel backf low temperature in a fuel injector.

Another object of an embodiment of the invention is to improve the performance of cortinon rail injectors.

Still another o}Sject of an embodiment of the invention is to improve the fuel backflow temperature estimation in such a way to obtain lower engineering margins for performance limitation, since thanks to a more precise estimation, the performance limitation can be started closer to the actual limit.

These objects are achieved by a method, by an engine, by an apparatus, by an automotive system, by a computer program, and by a computer program product having the features recited in the independent claims.

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

StThtRY Pm erthDodixnent of the disclosure provides a method of esti.mating fuel backflow temperature in a fuel injector of an internal combustion engine, the fuel injector being activated by means of a solenoid, the method comprising the steps of: -applying a predetermined voltage for a predetermined time to the injector, -reading a current of the injector in a plurality of instants in order to find a current profile for the injector, -determining a time constant of the injector as a function of the current profile, of the voltage and of an electrical resistance value of the injector, -using the time constant to determine a ratio between the relative permeability and the resistivity of the material of the solenoid, -determining art estimated fuel backflow temperature as a function of the ratio.

An advantage of this eitodirnent is that it allows an improved fuel backf low temperature estimation.

Furthermore, the method can be repeated for each injector when it is not activated and improves the measurement of injector-to-injector deviation.

Also, thanks to a more precise fuel backf low temperature estimation a injector performance limitation can be started closer to

the actual limit with respect to the prior art.

This allows lower engineering margins for performance limitation design.

Accordinq to a further embodiment of the invention, the determination of the estinated fuel backflow temperature is performed using a map that correlates said ratio with a fuel temperature.

Ph advantage of this embodiment is that it allows to perform the estimation of the fuel backf low temperature by means of a map determined using Imown physical correlations between the relative permeability and the resistivity of the material and the temperature.

According to a further embodiment of the invention, the time constant of the injector is determined by the following Equation: -t 7. V In ( i -____ \ "inj wherein i is the current in the solenoid and V/R± is the ratio between the voltage V applied to the injector and the electrical resistance R± of the injector.

Advantageously, this embodiment employs a model of the injector as an Ut circuit in order use known mathematical relations for the determination of the time constant of the LR circuit.

According to another embodiment of the invention, the value of the ratio pr/p is determined by the following Equation: Mr t12 NM2 12 MO wherein I is the wire length of the solenoid, N the number of coils of the solenoid, A the wire area of the coils of the solenoid 34 and p is the vacuum permeability.

An advantage of this embodiment is that it uses known mathematical relations of an LR circuit for the determination of the ratio Pr/P.

According to still another embodiment of the invention, the value of the electrical resistance of the injector is determined during an End Of Line procedure.

An advantage of this embodiment is that it allows to determine the electrical resistance of the injector in a very simple and quick way that does not interfere with other End Of Line operations.

According to an embodiment of the invention, the value of the electrical resistance of the injector is determined by applying to the injector a donstant voltage at a constant temperature.

An advantage of this embodiment is that the electrical resistance of the injector is determined in controlled circumstances.

According to still another enilDodiment of the invention, the estimated fuel backf low temperature is used to determine an iterated value R1 of the resistance of the injector (160) using the equation: = R (T0) (1 + a (T -T0)) where T0 is a constant temperature and a is a known coefficient of proportionality, the iterated value R1 of the resistance of the injector being used to determine an iterated value 12 of the time constant that, in turn, is used to determine and iterated value of the fuel backf low temperature T2, the above steps being repeated in order to find successive iterated values of the resistance (R2 of the injector and of the fuel backflow temperature (T2... Ta), until the difference T± -T is equal or less than a predefined error.

An advantage of this err&diment is that it allows to take into account that the resistance of the injector may vary as a function of the temperature.

According to another ertodinent of the invention, a method of operating a fuel injector of an internal cor±'ustion engine is provide, the method comprising the steps of: -determining a nominal Energizing Time for the injector, -correctin the nominal Energizing Time for the injector as a -function of an estimated fuel backf low temperature, in order to obtain a corrected Energizing Time, -energizing the fuel injector for the corrected Energizing Time.

An advantage of this embodiment is that it allows to correct the fuel quantity injected for each injector.

According to another embodiment of the invention, a method of operating an internal corrtustion engine is provided, the method comprising the steps of: -estimating a fuel backflow temperature of an injector, -comparing the baclcflow temperature estimated value to a threshold value thereof, and -if the estimated temperature is higher than the threshold value, start an engine temperature protection lilrLttation procedure.

This embodiment has the advantage that it allows to identify dangerous temperature conditions of the injector and take appropriate action.

According to another eirbodiment of the invention, a method of operating an internal corrbustion engine is provided, the method comprising the steps of: -presetting a maximum resistance value P and a minimum resistance value P of an injector; -determining an actual resistance value R of the injector as function of a backflcw estimated temperature, -turning on a Diagnostic Trouble Code (I7TC) of electrical failure if any of the conditions > R< or R1 < F. is satisfied.

An advantage of this embodiment is that it allows to identify electrical malfunctions of a specific injector.

The invention also comprises an apparatus for estimating fuel backf low temperature in a fuel injector of an internal combustion engine, the fuel injector being activated by means of a solenoid, the apparatus comprising: -means for applying a predetermined voltage for a predetermined time to the injector, -means for reading a current of the injector in a plurality of instants in order to find a current profile for the injector, -means for determining a time constant of the injector as a function of the current profile, of the voltage and of an electrical resistance value of the injector, -means for using the time constant to determine a ratio between

B

the relative permeability and the resistivity of the material of the solenoid, -means for determining an estimated fuel backf low temperature as a function of the ratio.

This eSodiment of the invention has basically the same advantages of the method disclosed above, in particular that of obtaining an improved fuel backflow temperature estimation. The estimation can be repeated for each injector when it is not activated and this improves the measurement of injector-to-injector deviation.

According to an aspect of the invention, the means for determining the estimated fuel backflow temperature comprise a map that correlates the ratio with a fuel temperature.

M advantage of this eirbodiment is that it allows to perform the estimation of the fuel backf low temperature by means of a map determined using known physical correlations between the relative permeability and the resistivity of the material and the temperature.

According to another aspect of the invention, the means for determining the time constant t of the injector use the following equation: -t 1. V In -____ \ "titj wherein i is the current in the solenoid and V/Rmjj is the ratio between the voltage V applied to the injector and the electrical resistance Rthji of the injector.

Advantageously, this errbodiment employs a model of the injector as an LR circuit in order use known mathematical relations for the determination of the tine constant of the LR circuit.

According to another aspect of the invention, the means for using the tine constant t to determine a value of the ratio use the following equation: TI2 N2A2 wherein 1 is the wire length of the solenoid, N the number of coils of the solenoid, A the wire area of the coils of the solenoid and Po is the vacuum permeability.

Pn advantage of this embodiment is that it uses known mathematical relations of an LR circuit for the determination of the ratio.

According to still another aspect of the invention, the means for determining a tine constant of the injector use a value of the electrical resistance of the injector determined during an End Of Line procedure.

An advantage of this embodiment is that it allows to determine the electrical resistance of the injector in a very simple and quick way that does not interfere with other End Of Line operations.

According to still another aspect of the invention, the means for determining a tine constant t of the injector use a value of the electrical resistance of the injector determined by applying to the injector a constant voltage at a constant temperature.

Pn advantage of this ertodiment is that the electrical resistance of the injector is determined in controlled circumstances.

According to a further aspect of the invention, the estimated fuel backflow temperature determined by the means for determining an estimated fuel backf low temperature is used to determine an iterated value R1 of the resistance of the injector using the equation: = R(To)*(l + a (Tt -T0)) where T0 is a constant temperature and a is a known coefficient of proportionality, the iterated value R1 of the resistance of the injector being used to determine an iterated value 2 of the time constant that, in turn, is used to determine an iterated value of the fuel backflow temperature T2, the above steps being repeated in order to find successive iterated values of the resistance R2 --R of the injector and of the fuel backf low temperature T2... T, until the difference T11 -T1 is equal or less than a predefined error.

An advantage of this enbodiment is that it allows to take into account that the resistance of the injector may vary as a function of the temperature.

The invention also comprises an apparatus for operating a fuel injector of an internal coribustion engine, the apparatus comprising: -means for determining a nominal Energizing Time for the injector, -means for correcting the nominal Energizing Time for the injector as a function of an estimated fuel backf low temperature in order to obtain a corrected Energizing Tine, and -means for energizing the fuel injector for the corrected Energizing Tine.

An advantage of this embodiment is that it allpws to correct the fuel quantity injected for each injector.

nother embodiment of the invention provides an apparatus for operating an internal combustion engine, the apparatus comprising: -means for estimating a fuel backf low temperature of an injector, -means for comparing the backflow temperature estimated value to a threshold value thereof, and -means for starting an engine temperature protection limitation procedure, if the estimated temperature is higher than the threshold value.

This embodiment has the advantage that it allows to identify dangerous temperature conditions of the injector and take appropriate action - 15.nother embodiment of the invention provides an apparatus for operating an internal combustion engine, the apparatus comprising: -means for presetting a maximum resistance value R and a minimum resistance value R of an injector; -means for determining an actual resistance value of the injector as function of a backf low estimated temperature, -means for turning on a Diaquostic Trouble Code (DTC) of electrical failure if any of the conditions P > R or R < is satisfied..

Pn advantage of this ertodirnent is that it allows to identify electrical malfunctions of a specific injector.

The invention also comprises an automotive system comprising an internal combustion engine managed by an engine Electronic Control Unit, the engine being equipped with a fuel injector, the fuel injector being activated by means of a solenoid, the Electronic Control Unit (ECU) being configured to: -appty a predetermined voltage for a predetermined time to the injector, -read a current of the injector in a plurality of instants in order to find a current profile for the injector, -determine a time constant of the injector as a function of the current profile, of the voltage and of an electrical resistance value of the injector, -use the time constant to determine a ratio between the relative * permeability and the resistivity of the material of the solenoid, -determine an estimated fuel backflow temperature as a function cf the ratio.

This embodiment of the invention has basically the same advantages of the method and of the apparatus disclosed above, in particular that of obtaining an improved fuel backf low temperature estimation. The estimation can be repeated for each injector when it is not activated and this improves the measurement of injector-t0 injector deviation.

According to an aspect of the invention, the ECU is configured to determine the estimated fuel backflow temperature by using a map that correlates the ratio with a fuel temperature.

Pn advantage of this embodiment is that it allows to perform the estimation of the fuel backf low temperature by means of a map determined using known physical correlations between the relative permeability and the resistivity of the material and the temperature.

According to another aspect of the invention, the ECU is configured to determine the tine constant i of the injectdr by using the following equation: -t t= 1. V l1ttR -wherein i is the current in the solenoid and V/Ri is the ratio between the voltage V applied to the injector and the electrical resistance Rm1 of the injector.

Advantageously, this embodiment employs a model of the injector as an LR circuit in order use known mathernaticai relations for the determination of the time constant of the LR circuit.

According to another aspect of the invention, the ECU is confiqured to use the time constant t to determine a value of the ratio by using the following equation: Mr r12 J NA2 12 Mo wherein 1 is the wire length of the solenoid, N the number of coils of the solenoid, A the wire area of the coils of the solenoid and Mo is the vacuum permeability.

An advantage of this embodiment is that it uses known mathematical relations of an LR circuit for the determination of the ratio.

According to still another aspect of the invention, the ECU is configured to detennine a time constant i of the injector by using a value of the electrical resistance of the injector determined during an End Of Line procedure.

An advantage of this eitodiment is that it allows to determine the electrical resistance of the injector in a very simple and quick way that does not interfere with other End Of Line operations.

According to still another aspect of the invention, the ECU is configured to determine a time constant T of the injector by using a value of the electrical resistance of the injector determined by applying to the injector a constant voltage at a constant temperature.

An advantage of this entodiment ith that the electrical resistance of the injector is determined in controlled circumstances.

According to a further aspect of the invention, the estimated fuel backf low temperature determined by the ECU is used to determine an iterated value R1 of the resistance of the injector using the equation: = R(To)*(l + cx (T -To)) where T0 is a constant temperature and a is a known coefficient of proportionality, the iterated value R1 of the resistance of the injector being used to determine an iterated value 12 of the time constant that, in turn, is used to determine an iterated value of the fuel backflow temperature T2, the above steps being repeated in order to find successive iterated values of the resistance R2 P-of the injector and of the fuel backf low temperature T2... T, until the difference T11 -T1 is equal or less than a predefined error.

Pn advantage of this embodiment is that it allows to take into account that the resistance of the injector may vary as a function of the temperature.

The invention also comprises an automotive system comprising an internal contust ion engine managed by an engine Electronic Control Unit, the engine being equipped with a fuel injector, the fuel injector being activated by means of a solenoid, the Electronic Control Unit (ECU) being configured to: -detentiine a nominal Energizing Time for the injector, -correct the nominal Energizing Time for the injector as a function of an estimated fuel backflow temperature in order to obtain a corrected Energizing Tine, and -energize the fuel injector for the corrected Energizing Time.

Pn advantage of this embodiment is that it allows to correct the fuel quantity injected for each injector.

The invention also comprises an automotive system comprising an internal combustion engine managed by an engine Electronic Control Unit, the engine being equipped with a fuel injector, the fuel injector being activated by means of a solenoid, the Electronic Control Unit (ECU) being configured to: -estimate a fuel backf low temperature of an injector, -compare the backflow temperature estimated value to a threshold value thereof, and -start an engine temperature protection limitation procedure, if the estimated temperature is higher than the threshold value.

This errbodixnent has the advantage that it allows to identify dangerous temperature conditions of the injector and take appropriate action.

The invention also comprises an automotive system comprising an internal contustion engine managed by an engine Electronic Control Unit, the engine being equipped with a fuel injector, the fuel injector being activated by means of a solenoid, the Electronic Control Unit (ECU) being configured to: -preset a maximum resistance value B and a minimum resistance value P of an injector; -determine an actual resistance value R of the injector as function of a backflow estimated temperature, and -turn on a Diaqnostic Trouble Code (OTC) of electrical failure if any of the conditions R > R or P C R is satisfied.

An dvantage of this embodiment is that it allows to identify electrical malfunctions of a specific injector.

The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.

The computer program prcduct can be ertodied as a control apparatus for an internal contustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case, when the control apparatus executes the computer program all the steps of the method described above are carried out.

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

BRIEF DEScRIPTIQ OF THE DR2% WINGS The various embodiments will now be described, by way of example, with reference to the accompanying drawings, wherein like numerals denote like elements, and in which: Figure 1 shows an automotive system; Figure 2 is a cross-section of an internal combustion engine belonging to the automotive system f figure 1; Figure 3 is a schematic representation of a solenoid fuel injector and of its main electrical parameters; Figure 4 is a flowchart representing an embodiment of the method of the invention; Figure 5 is a flowchart representing another embodiment of the method of the invention; and Figure 6 is a flowchart representing still another embodiment of the method of the invention.

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

Some entodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal carbustion engine (ICE) having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chanter 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 corunication with a high pressure fuel pump 180 that increases the pressure of the fuel received from a fuel source, such as a tank 190.

A certain guantity of fuel returns to the fuel tank 190 via an injector backflow line 195 starting from an injector backf low port on an upper portion of the injector 160.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in tinie 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. 1n air intake duct 205 may provide air from the arrbient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other ertodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. Pn intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other entodiments, 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 NQ< traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other enbodiments 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. Jn EGS valve 320 regulates a flow of exhaust gases in the EGR system 300.

The autcmotive system 100 may further include an electronic control unit (ECU) 450 in coirniunication 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 coirbustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cain phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

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

More specifically, Figure 3 is a schematic representation of a solenoid fuel injector 160 and of its main electrical parameters, the injector 160 having a body 10 that extends longitudinally and a side inlet 12 for connection to the fuel rail 170 of a fuel-supply system.

Fuel entering the injector 160 through fuel inlet 12 is directed towards a control chanter 46 in the upper portion of the injector 160 and to a lower portion of the injector where a nozzle 14 and a movable needle 24 are provided.

The needle 24 is connected to an injector rod 50 and is moved with the aid of a dedicated actuator, typically a solenoid actuator 34 controlled by the engine control unit (ECU) 450.

If the solenoid 34 is not activated, the needle 24 is closed because the pressure of the fuel in the control chamber 46 balances the pressure that keeps the needle 24 in the closed position.

The Engine Control Unit (ECU) 450 monitors engine operating parameters via various sensors, as described above, and calculates the appropriate amount of fuel to be injected as a function of various operating conditions of the engine 110. The ECU 450 determines an appropriate Energizing Time (ET) of the injector 160 as a function of the fuel quantity to be injected.

when a certain quantity of fuel is to be injected, solenoid 34 is activated and an armature 36 is lifted against the resistance of a spring 38 and fuel pressure is relieved above the needle 24 and a certain quantity of fuel returns to the fuel tank 190 via an injector backf low port 90 on an upper portion of the injector 160.

This creates a pressure difference above and below the injector rod 50 and fuel pressure below the needle 24 lifts the needle 24 and the injector 160 opens and fuel is injected into the cylinder 125.

When the solenoid 34 is deactivated, the pressure in the control charrber 46 increases until the needle 24 closes again the injector 160.

However the injector's performance, and in particular the injected quantity, may be influenced by fuel backf low temperature.

Eirodirnents of the method of the present invention for estimating fuel backf low temperature Tt are herebelow disclosed.

As a prerequisite to understanding the various eritodiments of the invention, the relationships to the various physical and electrical parameters involved in the fuel backflow temperature estimation is illustrated, also with reference to Figure 3.

-The injector's 160 electrical characteristics can *be schematized by an equivalent electrical circuit 500, namely an LR circuit comprising a resistor R in series with an inductor L and driven by a voltage source V (Fig. 3) Under these assumptions, applying a constant voltage V to the injector 160, an electrical current I is generated and said current evolves as shown in the graph of the rightmost portion of Figure 3.

I1⁄2pplying such constant voltage V, for example the battery voltage, allows to acquire a value of the ratio V/R, as shown in Figure 3.

In particular, the current i under constant voltage V can be measured at different intervals of tine such as 50 ps, 100 pa, and so pn for a certain length of tine, such as 15 ma, to perform a learning of the current profile i (t).

Since an LR circuit model is used, it can be observed that as an effect of the application of voltage V, the current I increases exponentially up to the asymptotic value V/R.

As is known, the current i of the LR circuit 500 is given by Equation (1): (1) = + 1? where V is the constant voltage applied, R is the resistance of the circuit 500, t is the tine and i is the time constant.

Therefore, knowing the current profile 1(t) over time due to constant voltage V, it is possible to evaluate the ratio V/R, as shown in the rightmost portion of Figure 3, and therefore the resistance R of the circuit that schematizes the electrical parameters of injector 160.

Knowing the current profile 1(t) due to constant voltage V and the ratio V/R it is also possible to evaluate the time constant t of the LR circuit 500 and, from the time constant T, it is possible to estimate the fuel backf low temperature as will be explained herebelow.

As a general rule, the time constant T can be evaluated by solving Equation (1) above for t, namely: By definition, the tine constant t of an LR circuit is also expressed as i = L/R, where L is the inductance of circuit 500, therefore the following Equation (2) can be written: (2) L /10 MrN24 A Itr N2A2 1 p1p'° L2 where Po is the vacuum permeability, Pr is the relative permeability of the material of the solenoid, N is the number of coils of the solenoid, A is the wire area of the coils of the solenoid, 1 is the wire length of the solenoid and p is the resistivity of the material of the solenoid.

From the above Equation (2), the ratio: Pr p can be extracted, since po is a constant and, for any given injector 160, parameters I (wire length of the solenoid), N (number of coils of the solenoid), A (wire area of the coils of the solenoid) are also all constant.

This observation shows that the time constant t is a function of the ratio Pr/P of the relative permeability Pr and the resistivity of the material of the coils of the solenoid.

Both these material characteristics have values that may change as a function of temperature T. In the technical literature maps are known that express the relative permeability Pr of a material as a function of temperature T and maps that express the resistivity p of the material as a function of temperature T. Therefore, with information from these maps, a further map can be obtained that correlates the ratio Pr/P to fuel temperature T, as shown in Table 1 below:

TABLE 1 Pr

Temperature T -30°C ______ 0°c _____ + 10 °C ___________ +150°C xn where X1 represents the value of the ratio Pr/P at temperature T. Figure 4 is a flowchart representing an embodiment of the method of the invention.

At the start of this embodiment of the method, a check is made to S verify if the vehicle is performing End Of Line (EOL) procedures (block 600), namely the quality control procedures usually performed at the end of the assembly line of a vehicle. If this check is negative, the vehicle is considered to be in normal running operation (block 610) and certain steps will then be performed, as will be explained hereinafter.

If, on the contrary, it is determined that the vehicle is performing End Of Line (EOL) procedures, each injector 160 is subjected to a voltage actuation for a predetermined interval of time when the injector 160 is not activated, for example 15 ms, (block 620). A predetermined voltage V is applied, for example, the voltage of the battery. An exemplary value of this constant voltage V at the EOL stage is SV. This learning may have a duration, in a worst case of 60 ins, therefore it does not affect EOL operation timing.

Resistance of each injector is measured (block 630) by following the current sampling procedure above explained to find the value of V/R1t and thus Rt for each injector.

These values of R± and V/R are evaluated at a constant temperature TMr that can be read with the air sensor 340 and are stored in the data carrier 460 asscciated to the ECU 450 (block 640).

Therefore this procedure allows to determine resistance values Rthjj at * temperature TMr for each of the injectors 160.

If the vehicle is considered to be in normal running operation (block 610), each injector is subjected to a predetermined voltage for a predetermined time (block 650), such as 100 ps, and the current i is read.in three points i, i1 and i2 (block 660) in order to find the correspondent current profile for each injector 160.

This operation may be performed on each injector 160 when the injector 160 is net activated.

At this stage, a time constant t for each injector 160 is evaluated using Equation (1) in the form of block 670, namely: -t 1= * __ my [n particular, i is known by the above procedure and the ratio V/R is known from the EOL procedure.

The value of the time constant -t is then used in Equation (2) with its terms rearranged in the form of block 680, namely: t12__Pr N2A2 --12 Mo This Equation allows to find the value of the ratio pr/p since tine constant -r has been determined in the previous step and I (wire length of the solenoid), N (number of coils of the solenoid), A (wire area of the coils of the solenoid) are all fixed characteristics of the injector and Mo is the vacuum permeability.

Finally, since the ratio hr/P has been determined, the value of the temperature Tt of the fuel backf low can be estimated by using the information in the map of Table 1 (block 690).

The fuel backf low temperature estimated with the previously described method can be used in several different ways, as represented in Figure 5, A first use of the fuel backflcw temperature Tt is to correct the injector performance as a function of the estimated fuel backf low temperature (block 700). Correction of the performance can be done, for example, by correcting a nominal Energizing Time ET for the injector 160 as a function of the estimate fuel backf low temperature namely by determining a corrected Energizing Time EToorr using Imown maps that correlate the Energizing Tine to the backflow temperature. Then the injector 160 may be actuated with a corrected Energizing Tine ET (block 710).

This procedure can be performed, if necessary, for each injector of the engine 110.

another way to use the fuel backf low temperature estimated value Tt is to check if such value TESt is higher than a threshold value T thereof (block 720). If this condition is satisfied, a temperature protection limitation of the engine may be started. The threshold value T may vary depending on the engine systems and other factors.

Exemplary values of Tmay be around 145 00.

Still another way to use the backflow temperature estimated value is to perform an injector resistance check, namely to predefine a maximum resistance value R and a minimum resistance value R4±± and then to check if a calculated resistance value R that is a function of the fuel backf low estimated temperature Tt is inside the predefined range P-R<. On the contrary, if any of the conditions > R or P < R is satisfied, a Diagnostic Trouble Code (DTC) of electrical failure may be turned on.

In this case, to perform the evaluation of the resistance Rr, the resistivity PUL of the material of the solenoid, may be calculated starting from and from the calculated resistivity pt and using known maps.

The actual resistance R can be determined with the formula: R= (pt* 14 /A where I is the length of the wire of the solenoid and A the area of the wire of the solenoid.

A further refinement of the method of the invention considers the fact that the resistance R of the solenoid of the injector 160 varies as a function of the temperature T of the fuel backflow.

Due to the above phenomenon, the estimation of the fuel backflow temperature by means of the calculation of the time constant i using the fixed resistance value R± of each injector measured at a constant temperature TMr can be thus affected by a systematic error.

Generally speaking the resistance R of the solenoid of the injector 160 may be considered to vary as a linear function of the temperature T, namely according to the following Equation (3): (3) R = R(To)*(1 + a (T -To)) where T0 is a specified temperature, for example 20 CC, and a is a known proportionality coefficient.

Pn iterative method, such as the one schematically represented in Figure 6, can be used to provide a better estimate of the backf low temperature Tt.

The iteration procedure starts from the value of the resistance Rmj at the temperature T measured during the End Of Line (EOL) phase.

The value Ri of the resistance can be used to find a first value t of the time constant i, namely c1 = f (Rthj) (block (800) This operation can be done using the Equation: -t Ti The value t of the time ccnstant calculated at this first iteration is then inputted into Equation (2), namely r112 (2) N2A2 -.P 1 that gives a value (pr/ph of the ratio Pr/P (block 810), since all other terms apart from i are known material characteristics of the solenoid.

The map of Table 1 can then be used in order to find a value T1 of the temperature that corresponds to the ratio (r/p)1 (block 820).

At this point, a second iteration can then be performed in which Equation (3) is used, namely: (3) R=R (T0)(l+a (T-T0)) with T = T1 to find R1 = S (T0) (1 + a (T1 -Ta)) (block 830).

This iterated value R1 of the resistance is then used in the Equation: 12 1n(i _V/R) to find a second iterated value t2 of the tine constant -t, nathely = f (R1) (block 840) In analogy to the steps above described, the value t2 of the tine constant calculated at this second iteration is then inputted into Equation (2), namely: 2 2 - N2A2 -12 Io that gives a value (Pr/P)2 of the ratio pr/p.

The map of Table 1 can then be used in order to find a value I of the temperature that corresponds to the ratio (Pr/P)2.

The above described iterations can then be performed a number i of tines (blocks 850,860) to find successive values of the resistance R2,R3, R0 of the injector (160) and successive values of the temperature T, namely T2, T3, T1... T, until the difference T11 -T1 is equal or less than a predefined error Te (block 870), for exarrple until, T1.1 -T1 <= 5 °C.

In general four of five iterations may be sufficient to arrive at an acceptable value of the temperature.

Since the battery voltage changes between End Of Line (EOL) and running conditions, the method may provide for a phase of storing the voltage value V at which the resistance Rmj is evaluated.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary enbodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

* BEFERENcE injector body 12 fuel inlet 5, 14 nozzle 24 movable needle 34 solenoid actuator 36 armature 38 spring 46 control chamber injector rod backflow port automotive system internal combustion engine (ICE) 120. engine block cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phaser fuel injector fuel rail 180 fuel pump fuel tank backf low line intake manifold 205 air intake duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 exhaust aftertreatment device 290 VGT actuator 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensor 445 accelerator pedal position sensor 450 electronic control unit (ECU) 460 data carrier 500 circuit 600 block 610 block 620 block 630 block 640 block 650 block 660 block 670 block 680 block 690 block 700 block 710 block 720 block 730 block BOO block 810 block 820 block 830 block -36 840 block 850 block 860 block 870 block aaD4S

Claims (15)

1. A method of estimating fuel backf low temperature (Tt) in a fuel injector (160) of an internal combustion engine (110), the fuel injector (160) being activated by means of a solenoid (34), the method comprising the steps of: -applying a predetermined voltage (V) for a predetermined time (t) to the injector (160), -reading a current (i) of the injector (160) in a plurality of instants in order to find a current profile (i(t)) for the injector (160), -determining a time constant (i) of the injector (160) as a function of the current profile (i(t)), of the voltage (V) and of an electrical resistance value (Ri) of the injector (160), -using the time constant (T) to determine a ratio (pr/p) between the relative permeability (Pr) and the resistivity (p) of the material of the solenoid (34), -determining an estimated fuel backflow temperature (T) as a function of the ratio (pr/p).

2. A method according to claim 1, wherein the determination of the estimated fuel backflow temperature (T) is performed using a map that correlates the ratio (pr/p) with a fuel temperature (T).

3. A method according to claim 1, wherein the time constant t of the injector (160) is determined by the following equation: -t r v In -____ wherein i is the current in the solenoid (34) and V/R1 is the ratio between the voltage (V) applied to the injector (160) and the electrical resistance (R1t) of the injector (160)

4. A method according to claim 1, wherein the value of the ratio (Pr/P) is determined by the following equation: Pr it2 N2A2 12 Mo wherein.1 is the wire length of the solenoid (34), N the number of coils of the solenoid (34), A the wire area of the coils of the solenoid (34) and p, is the vacuum permeability.

5. A method according to claim 1, wherein the value of the electrical resistance (R) of the injector (160) is determined during an End Of Line procedure.

6. A method according to claim 1, wherein the value of the electrical resistance (Rj±) of the injector (160) is determined by applying to the injector (160) a constant voltage (V) at a constant temperature (TMr).

7. A method according to claim 1, wherein the estimated fuel backflow temperature (T) is used to determine an iteratedvalue (R1) of the resistance of the injector (i60) using the equation: R(To)*(1 + a (T -T0)) where T0 is a constant temperature and a is a known coefficient of proportionality, the iterated value (R1) of the resistance of the injector (160) being used to determine an iterated value (2) of the time constant that, in turn, is used to determine an iterated value of the fuel backflow temperature (T2), the above steps being repeated in order to find successive iterated values of the resistance (R2 R) of the injector (160) and of the fuel backflow temperature (T2...Ta), until the difference T-1 -T1 is equal or less than a predefined error (Terr).

8. A method of operating a fuel injector (160) of an internal cortustion engine (110), the method comprising the steps of: -determining a nominal Energizing Time (ET) for the injector (160), -correcting the nominal Energizing Time (ETN0i for the injector (160) as a function of a fuel backflcw temperature (T) estimated according to one of the claims 1 to 6 in order to obtain a corrected Energizing Time (ETcorr), -energizing the fuel injector (160) for the corrected Energizing Time (ETrr).

9. A method of operating an internal corrustion engine (110), the method comprising the steps of: -estimating a fuel backflow temperature (T) of an injector (160) according to one of the claims 1 to 6, -comparing the backf low temperature estimated value (T) to a threshold value thereof (Tn), and -if the estimated temperature (T) is higher than the threshold value (Tj, start an engine (110) temperature protection limitation procedure.

10. A method of operating an internal combustion engine (110), the method comprising the steps of: -presetting a maximum resistance value P and a minimum resistance value R of an injector (160); -determining an actual resistance value R of the injector (160) as function of a backflow estimated temperature (T) estimated according to one of the claims 1 to 6, -turning on a Diagnostic Trouble Code (DTC) of electrical failure if any of the conditions R > R or < R is satisfied.

11. An apparatus for estimating fuel backflow temperature (T) in a fuel injector (160) of an internal combustion engine (110), the fuel injector (160) being activated by means of a solenoid (34), the apparatus comprising: -means for applying a predetermined voltage (V) for a predetermined time (t) to the injector (160), -means for reading a current (i) of the injector (160) in a plurality of instants in order to find a current profile (i (t)) for the injector (160), means for determining a time constant (t) of the injector (160) as a function of the current profile (i(t)), of the voltage (V) and of an electrical resistance value (Rj) of the injector (160), -means for using the time constant (i) to determine a ratio (Pr/P) between the relative permeability (jir) and the resistivity (p) of the material of the solenoid (34), -means for determining an estimated fuel backflow temperature (T) as a function of the ratio (pr/p).

12. An automotive system comprising an internal combustion engine (110), managed by an engine Electronic Control Unit (450), the engine (110) being equipped with a fuel injector (160), the fuel injector (160) being activated by means of a solenoid (34), the Electronic Control Unit (450) being configured to: -apply a predetermined voltage (V) for a predetermined time (t) to the injector (160), -read a current (i) of the injector (160) in a plurality of instants in order tb find a current profile (i(t)) for the injector (160), -determine a time constant (t) of the injector (160) as a function of the current profile (i(t)), of the voltage (V) and of an electrical resistance value (R) of the injector (160), -use the time constant (i) to determine a ratio (pr/p) between the relative permeability (Pr) and the resistivity (p) of the material of the solenoid (34), -determine an estimated fuel backflo temperature (TEst) as a function of the ratio (pr/p)-

13. An internal combustion engine (110) equipped with a fuel injector (160), the fuel injector (160) being activated by means of a solenoid (34), the engine (110) being controlled by an Electronic control Unit (450) configured for carrying out the methods according to any of the claims 1-10.

14. A computer program comprising a computer-code suitable for perfoxminq the methods according to any of the claims 1-10.

15. Computer program product on which the computer program according to claim 14 is stored.