GB2505917A

GB2505917A - Method of calculating leakage in a common rail fuel injection system taking into account a predetermined leakage quantity.

Info

Publication number: GB2505917A
Application number: GB201216442A
Authority: GB
Inventors: Massimiliano Melis; Angelo Cancellieri
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-09-14
Filing date: 2012-09-14
Publication date: 2014-03-19
Also published as: GB201216442D0

Abstract

The method comprises calculating an injector leakage quantity as a function of a set of input variables and a predetermined leakage quantity. The variables may comprise values for rail pressure, fuel density and electric command duration. The variables may also comprise an operating condition coefficient, mapped as a function of rail pressure, command duration and a ratio between a first injector equivalent area corresponding to the working condition of the leakage quantity and a second area corresponding to the generic condition where the leakage quantity is estimated. The operating condition coefficient may depend on injector design and is evaluated across a batch of injectors. The input variables may further comprise a value for fuel density, based on fuel temperature and rail pressure. The fuel injector may comprise a solenoid or piezoelectric actuator. The method may be carried out by an electronic control unit using a computer program.

Description

METHOD OF CALCULATING THE INJECTOR LEAKAGE

OF A FUEL INJECTION SYSTEM

TECHNICAL FIELD

The present disclosure relates to a method of calculating the injector leakage of a fuel injection system Particularly, the method is related to fuel injectors for internal combustion engines and, more particularly, to fuel injectors of a Common Rail System (CRS).

BACKGROUND

It is known that modem engines are provided with a fuel injection system for directly injecting the fuel into the cylinders of the engine. 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 rail through dedicated injection pipes.

Each fuel injector, particularly injectors of a Common rail system, generally comprises an injector housing, a nozzle and a movable needle which repeatedly opens and closes this nozzle; the fuel, coming from the rail and passing through the injection pipe and, inside the injector housing1 a delivery channel, reaches the nozzle and can thus be injected into the cylinder giving rise to single or multi-injection patterns at each engine cycle.

The needle is moved with the aid of a dedicated actuator, typically a solenoid actuator or a piezoelectric actuator, which is controlled by an electronic control unit (ECU). The ECU operates each fuel injection by generating an electric opening command, causing the actuator to open the fuel injector nozzle for a predetermined amount of time, and a subsequent electric closing command, causing the actuator to close the fuel injector nozzle.

The time between the electric opening command and the electric closing command is generally referred as energizing time of the fuel injector, and it is determined by the ECU as a function of a desired quantity of fuel to be injected.

Considering the fuel quantity coming from the common rail and entering the injector, only a first portion of this is injected in the engine combustion chamber. A remaining portion of this fuel amount is recirculated from an injector outlet and is generally called as injector leakage or, simply, leakage.

As known, one of the main problem of controlling an injection system and in particular the pressure control of a common rail system is related to the evaluation of the injector leakage. In fact, to establish a well defined pressure value in the rail, the electronic control unit should calculate the so called quantity balance. The quantity balance means the mass balance between the fuel coming from the injection pump and entering the rail and the fuel exiting the rail and flowing towards the injectors. The fuel amount entering the rail is determined by the feed forward control strategy of the high pressure pump. The fuel amount exiting the rail is the sum of the injected portion (as well, established by the ECU control strategies) and the injector leakages amount-The injector leakage is a characteristic of the single injector, depending on some physical parameters, as will be better explained later Up today, the injector leakage is taken into account by using a map, function of pressure and temperature conditions.

Unfortunately, up today, injector to injector leakages deviation is not corrected and the spread between injector to injector is really remarkable. This problem negatively influences the feed forward control of the high pressure pump, and consequently, the rail pressure, in other words the injection pressure. Furthermore, this uncertainty in the rail quantity balance does not allow to properly control the Electronic Returnless Fuel System (ERFS), i.e. a variable displacement feeding pump, which would increase the global efficiency of the common rail system.

Therefore a need exists for a new method of better estimating the injector leakages taking into account the spread injector to injector, thus improving feed forward control capability of the fuel injection pump and the ERFS control.

An abject of an embodiment of the invention is to provide a method which calculated the leakages of each single injector, based an supplier measurements and taking into account the parameters, which influence the spread between injector to injector.

These objects are achieved by a method, by an apparatus, by an internal combustion engine and by an automotive system provided with an electronic control unit able to control the fuel injections, having the features recited in the independent claims.

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

SUMMARY

An embodiment of the disclosure provides a method of estimating a current injector leakage quantity of a common rail fuel injector, wherein injector leakage quantity is calculated as a function of a set of input variables and a predermined leakage quantity.

Consequently, an apparatus is disclosed for estimating an injector leakage quantity, the apparatus comprising means for calculating an injector leakage quantity as a function of a set of input variables and a predetermined leakage quantity.

An advantage of this embodiment is that the corrected injection leakage quantity can be used in the already existing routines of the variable displacement feeding pump, to determine its quantity balance, and the rail pressure feed-forward control, to determine the fuel pump flowrate, thus improving such control strategies.

According to an aspect of the invention, the set of input variables comprises a value of a rail pressure and an electric command duration.

According to another aspect, the set of input variables comprises an operating condition coefficient, wherein said operating condition coefficient is mapped as function of the rail pressure, the electric command duration and a ratio between a first injector equivalent area, corresponding to the working condition of said predetermined leakage quantity and a second injector equivalent area, corresponding to the generic condition where the injector leakage quantity is estimated.

An advantage of this aspect is that said operating condition coefficient takes into account the parameters, which influence the injector leakage, namely, the gap between needle and nozzle, the characteristic areas of the control volume, the rail pressure and the electric command duration.

According to a further aspect, said operating condition coefficient depends on the injector design and is evaluated as function of said rail pressure and said electric command duration on a batch of injectors.

An advantage of this aspect is that the function between the operating condition coefficient and its characteristic parameters is determined on a wide statistical base.

According to a still further aspect, the set of input variables further comprises a value of a fuel density, wherein fuel density is calculated as a function of the rail pressure and a fuel temperature.

According to a further embodiment, said injector leakage quantity is calculated by using the following equation:

Q -

teak-P/i -k(,p, Er, AFOL /A,1)apO, pp,l /App,1 PEOL ETEOL /EI1 An advantage of this embodiment, is that the method can be simplified by considering the fuel as incompressible and therefore applying the Bernoulli equation.

According to another embodiment, said method of estimating injector leakage quantity is applied to a fuel injector, comprising a solenoid actuator.

An advantage of this embodiment is the fact that the new method is applicable to any solenoid injector, which is, as known, the standard in the majority of common rail systems.

According to still another embodiment, said method of estimating injector leakage quantity is applied to a fuel injector, comprising a piezoelectric actuator.

An advantage of this embodiment is the fact that the new method is also applicable to any piezoelectric injector, which represents the "premium" application in common rail systems.

A further aspect of the disclosure provides an internal combustion engine of an automotive system equipped with one or more fuel injectors according to one of the previous embodiments.

A still further aspect of the disclosure provides an automotive system comprising an electronic control unit configured for carrying out the above method according to one of the previous embodiments.

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

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

The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.

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

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to 20. the accompanying drawings, in which: Figure 1 shows an automotive system.

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

Figure 3 is an external view cia fuel injector Figure 4 is a flowchart of a method of estimating the injector leakage quantity, according to the present invention

DETAILED DESCRIPTION OF THE DRAWINGS

Some embodiments may include an automotive system 100, as shown in Figures land 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.

A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.

A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190. The fuel injection system with the above disclosed components is known as Common Rail Diesel Injection System (CR System). It is a relative new injection system for passenger cars. The main advantage of this injection system, compared to others, is that due to the high pressure in the system and the electromagnetically controlled injectors it is possible to inject the correct amounts of fuel at exactly the right moment. This implies lower fuel consumption and less emissions.

Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200.

An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aItertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (8CR) 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 system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals ta/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 embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

Turning back to the fuel injection, in Fig. 3, the fuel injector 160 comprises an actuator controlled by the ECU 450 (solenoid actuator 161 or piezoelectric actuator), an injector fuel inlet 169 an injection housing 162, comprising means for feeding and discharge the injector, a nozzle 164, provided with a needle which, with its controlled movement, covers and uncovers the injection holes, and an injector outlet 163 for the leakage discharge. The ECU 450 operates each fuel injection by generating an electric opening command, causing the actuator to open the fuel injector nozzle 164 (up movement of the needle) for a predetermined amount of time, and a subsequent electric closing command, causing the actuator to close the fuel injector nozzle (down movement of the needle).

Considering the fuel quantity coming from the common rail and entering the injector, only a first portion of this is injected in the engine combustion chamber. A remaining portion of this fuel amount is recirculated from an injector outlet and is generally called as injector leakage or, simply, leakage. The leakage of the injector can be divided in two parts: a first part, also called intrinsic leakage, derives from the coupling between the nozzle and the needle, while a second part, called functional leakage, is due to the function of the injector itself. In fact, as known, to open the injector, the actuator should discharge a control volume on top of the needle, causing the up movement of the needle itself.

As known, one of the main problem of controlling an injection system and in particular the pressure control of a common rail system is related to the evaluation of the injector leakage. In fact, to establish a well defined pressure value in the rail, the electronic control unit should calculate the so called quantity balance. The quantity balance means the mass balance between the fuel coming from the injection pump and entering the rail and the fuel exiting the rail and flowing towards the injectors. The fuel amount entering the rail is determined by the feed forward control strategy of the high pressure pump. The fuel amount exiting the rail is the sum of the injected portion (as well, established by the ECU control strategies) and the injector leakages amount. The injector leakage is a characteristic of the single injector, depending on some physical parameters: these are mainly the gap between needle and nozzle, determining the intrinsic leakage, the characteristic areas of the control volume and the electric command duration causing the functional leakage. Up today, the injector leakage is taken into account by using a map function of pressure and temperature conditions.

Unfortunately, up today, injector to injector leakages deviation is not corrected and the spread between injector to injector is really remarkable. This problem negatively influences both the feed forward control of the high pressure pump and, consequently, the rail pressure, in other words the injection pressure. Furthermore this uncertainty in the rail quantity balance does not allow to properly control the Electronic Returnless Fuel System (ERFS), i.e. a variable displacement feeding pump, which would increase the global efficiency of the common rail system.

The method according to the present invention aims to take into account the injector leakage not from a statistical point of view, but taking into account the influencing parameters of each injector. The method is based on the fact that, currently, fuel injection system (FIS) suppliers are measuring injector leakages at the end of production line (EOL) to detect potential failures in the process. Normally, this measurement is done in full load condition (i.e. at the maximum injection pressure) and at a predetermined temperature. Therefore, this information is available and could be introduced in the injector datamatrix.

By using this new information, it is possible to build up the new method, taking, as input variables 10, 11, 12, 13, the rail pressure p, the fuel temperature T, which has to be used to evaluate 20 the fuel density, the electric command duration ET and of course the end of line injector leakage measurement Qleak.EOL. The output variable will be the corrected leakage quantity available for each injector and each working condition.

The injector leakages can be modeled as follow, by. using the well known Bernoulli equation: Qleak = Aequivaient i(2ApIp) ET (1) where: Qleak is the generic injector leakage Aequiaient is an equivalent injector section, taking into account both control volume characteristic areas and nozzlelneedle gap.

p is the rail pressure p is the fuel density ET is the electric command duration.

Using the Bernoulli formula is possible to estimate the leakage at different pressures and Els. In order to take into account the dynamic effect (injector actuator opening/closing) of the specific operating condition, an additional coefficient k (p, El, AFOL/Apti) has to be introduced 21. It can be defined as an operating condition coefficient k and is function of the rail pressure, the electric command duration and the ratio between the equivalent area corresponding to the condition of the end of line measurement (AEOL) and the equivalent area corresponding the generic condition where the injector leakage has to be calculated (Ap1). Therefore this operating condition coefficient k depends on the injector design and has to be evaluated experimentally as function of rail pressure and ET on a representative batch of injectors, during the development phase.

The following equation: QICOk-FOL -k ET A A 2ApftQJ/pEQL ETFOL/ - LOL I P/I / (2) can be applied, where the variables have been already defined and the subscripts EOL and Pti are respectively referred to the variables corresponding to the condition of the end of line measurement and the variables corresponding to the generic point (working condition), where the injector leakage has to be evaluated-More precisely1 Qtealc-ptl is the estimated leakage quantity, QIeaIc.EOL is the measured, i.e predetermined leakage quantity, k is the operating condition coefficient, p is the rail pressure, ET is the electric command duration, AEOL is the first injector equivalent area, Ap1 is the second injector equivalent area, PEOL is the rail pressure corresponding to the predetemined leakage quantity, PPt1 is the rail pressure corresponding to the estimated leakage quantity, PEOL S the density corresponding to the predetermined leakage quantity, ppti is the density corresponding to the estimated leakage quantity, ETEOL is the electric command duration corresponding to the predetermined leakage quantity, ETpi is the electric command duration corresponding to the estimated leakage quantity.

Starting from equation (2), it is possible, knowing QIeak.E0L, to calculate the leakage at the generic point (Qleak-Pti) as follows: -3 Qieat-cot Q/CQk_PII -k, ET, AEQL /A,3 IAp0 Pmi /aP, PROL ETEOL /ET,, A simple block diagram is shown in fig. 4. The method of calculating the injector leakage starts acquiring, as input variables 10, 11, 12, 13, the rail pressure p, the electric command duration El, the fuel temperature T (normally, the temperature before the fuel enters the high pressure pump) and leakage quantity as measured at the EOL (Qleak-E0L).

Then, the fuel, density p (as function of p and T) and the experimental coefficient k (function of p, FT and AEojAptj) are calculated 20 21. Finally, by using the measured, i.e. predetermined EOL leakage and applying the above formula (3), the injector leakage at the generic working condition is calculated 22.

This corrected leakage value 23 will be used in the already existing routines of the variable displacement feeding pump (ERFS,) to determine its quantity balance 24, and the rail pressure feed-forward control 25, to determine the fuel pump flowrate.

A comparison between the current injector leakage spread and the reduced spread available from the new method provides encouraging results. Actually, the injector leakage spread is in between ±45%. By using the new method, the leakage evaluation remains below 20% in almost all the points. The performance of the new method gets worse at lower ETs/pressure but, from one side1 in these points the absolute leakage value is anyhow low and the consequent errors, even if remarkable in percentage, are negligible if taken in absolute value; on the other side, these errors can be further improved during normal calibration work.

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 scope1 applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS block

11 block 12 block 13 block block 21 block 22 block 23 block 24 block block data carrier automotive system internal combustion engine 120 engine block cylinder cylinder head camshaft piston 145 crankshaft combustion chamber cam phaser fuel injector 161 solenoid actuator 162 injector housing 163 injector fuel cutlet 164 injector nozzle 169 injector fuel inlet fuel rail 180 fuel pump fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 turbine 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGS temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU QIeak generic injector leakage Aequivaient equivalent injector section, taking into account both control volume characteristic areas and nozzle/needle gap.

p rail pressure I fuel temperature p fuel density ET electric command duration k operating condition coefficient EOL subscript referring a generic variable to the end of line measurement Pti subscript referring a generic variable to the the generic working condition where the injector leakage has to be calculated

Claims

CLAIMS1. Method of estimating a current injector leakage quantity of a common rail fuel injector, wherein injector leakage quantity is calculated as a function of a set of input variables and a predetermined leakage quantity.
2. Method according to claim 1 wherein the set of input variables comprises a value of a rail pressure and an electric command duration.
3. Method according to claim 1 or 2, wherein the set of input variables comprises an operating condition coefficient, wherein said operating condition coefficient is mapped as function of the rail pressure, the electric command duration and a ratio between a first injector equivalent area, corresponding to the working condition of said predetermined leakage quantity and a second injector equivalent area, corresponding to the generic condition where the injector leakage quantity is estimated.
4. Method according to claim 3, wherein said operating condition coefficient depends on the injector design and is evaluated as function of said rail pressure and said electric command duration on a batch of injectors.
5. Method according to claim 3 or 4, wherein the set of input variables further comprises a value Of a fuel density, wherein fuel density is calculated as a function of the rail pressure and a fuel temperature.
6. Method according to one of the previous claims, wherein said injector leakage quantity is calculated by using the following equation: Q -Qicak_sol, /eak-P/i -k(p, ET, AEOL /A,1) JAPEOL PH I/APP/i PEOL ETEOL /ET,1 wherein Qleak-Ptl is the estimated leakage quantity, QIeak.EOL is the predetermined leakage quantity, k is the operating condition coefficient, p is the rail pressure, ET is the electric command duration, AEOL is the first injector equivalent area, Apti is the second injector equivalent area, PEOL is the rail pressure corresponding to the predetermined leakage quantity, Ppti is the rail pressure corresponding to the estimated leakage quantity, PEOL is the density corresponding to the predetermined leakage quantity, ppti is the density corresponding to the estimated leakage quantity, ETEOL is the electric command duration corresponding to the predetermined leakage quantity, ET1 is the electric command duration corresponding to the estimated leakage quantity.
7. Fuel injector (160) comprising a solenoid actuator, wherein its leakage quantity is estimated according to one of the claims 1-6.
8. Fuel injector (160) comprising a piezoelectric actuator, wherein its leakage quantity is estimated according to one of the claims 1-6
9. Internal combustion engine (110) of an automotive system (100) equipped with one or more fuel injectors (160) according to claim 7 orB.
10. Automotive system (100) comprising an electronic control unit (450) configured for configured for carrying out the method according to claims 1-6.
II. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-6.
12. Computer program product on which the computer program according to claim 11 is stored.
13. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 11 stored in the data carrier (40).
14. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 11.