SE1550559A1

SE1550559A1 - A method for operating a compression ignited engine and suchan engine

Info

Publication number: SE1550559A1
Application number: SE1550559A
Authority: SE
Inventors: Tabatabai Ali; Carlgren Magnus; Nordin Mikael
Original assignee: Scania Cv Ab
Priority date: 2015-05-04
Filing date: 2015-05-04
Publication date: 2016-11-05
Also published as: DE102016004791A1; SE538869C2

Abstract

17 ABSTRACT When operating a compression ignited engine (2) having at least onecylinder (5) and for each cylinder a fuel injection nozzle (7) config-ured to inject fuel into the cylinder and connected to a pressurizedfuel accumulator (8) it is determined whether a second position atwhich a start of a main injection of fuel into the cylinder in anoperation cycle thereof requested has a large separation with respectto a first position of a requested pilot injection of fuel into the cylinder.lf this separation is determined to be large a value of a fuel pressuremeasured inside said fuel accumulator is compared with a pre-established table for the type of fuel injection nozzles to which saidfuel injection nozzle belongs stating the minimum amount of fuel inthe form of opening time of said nozzle to be ordered for ensuringthat the pilot injection of fuel will certainly result in a sufficient combustion of pilot injected fuel for a said large separation. (Fig 1).

Description

A METHOD FOR OPERATING A COMPRESSION IGNITED ENGINEAND SUCH AN ENGINE TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for operating a compres- sion ignited engine having at least one cylinder and for each cylinder a fuel injection nozzle configured to inject fuel into said cylinder and connected to a pressurized fuel accumulator, said method comprising the steps of a) determining a second position at which a start of a main injectionof fuel into said cylinder in an operation cycle thereof is to berequested with respect to the position of a piston in said cylinder, b) determining a first position at which a pilot injection of fuel intosaid cylinder with a time gap before said main injection is to berequested with respect to the position of a piston in said cylinder,and c) determining whether a separation of said first and second posi-tions of said pilot injection and main injection, respectively, is con-sidered to be large or not, as well as a compression ignited engine according to the preamble of the appended independent claim directed thereto.

The invention is not restricted to any particular use of a said enginebut relates to injection of fuel into cylinders in compression ignitedengines designed for any type of use, such as industrial applications,in grinding machines and all types of motor vehicles, although theinvention is particularly applicable to utility vehicles, especially wheeled utility vehicles, such as trucks or lorries and buses, and the invention will for that sake hereinafter at some places be discussedfor that field of use for illuminating the invention but accordingly not in any way restricting it thereto.

The position at which a start of a main injection of fuel into a cylinderin an operation cycle in a compression ignited engine is requested isdependent upon various operation parameters of the engine. Thereason for requesting a “late” main injection may for example be adesire to raise the temperature of the exhaust gases resulting fromthe combustion of said fuel in the engine or for influencing the amountof emissions resulting from the combustion to decrease. "Late"means in this context that the piston in said cylinder has at least passed the upper dead point ending a compression stroke thereof.

A said pilot injection of fuel is in such an engine carried out for differ-ent reasons, of which one is to ensure that the fuel injected in a saidmain injection is really combusted when there is a risk that that wouldnot happen without such a pilot injection. A said pilot injection maynot be made to late for ensuring that the pilot injected fuel will becombusted. Said first position has for that sake to be located at acertain distance before the position at which a said piston reachessaid upper dead point in a compression stroke of that piston. Whena said “late” main rejection is requested this means that the separa-tion of said first and second positions of the pilot injection and themain injection will be large resulting in an imminent risk that the fuelinjected according to said main injection will not be combusted evenif a combustion of pilot injected fuel takes place would this combus- tion not be important enough.

BACKGROUND ART US 2008 243358 discloses a method of the type defined in the intro-duction addressing the problem just described by increasing theamount of fuel injected in a said pilot injection when the main injec-tion is late. Said increase is based upon a correction value for the position of the main injection.

SUMMARY OF THE INVENTION The object of the present invention is to provide a method and anengine of the type defined in the introduction being improved in atleast some aspect with respect to such methods and engines already known.

This object is with respect to the method obtained by providing sucha method with the features listed in the characterizing part of the ap- pended patent claim 1.

By measuring the fuel pressure inside said fuel accumulator andcomparing the value of said pressure measured with a pre-established table for the type of fuel injection nozzles to which saidfuel injection nozzle belongs stating the minimum amount of fuel inthe form of opening time of said nozzle to be ordered for a certainfuel pressure in a said fuel accumulator for ensuring that the pilotinjection of fuel will result in a sufficient combustion of pilot injectedfuel for a said large separation and determining said minimumamount for said value of the pressure measured, it will be ensured that a proper pilot injection of fuel will automatically always be activated in the case that said separation of said pilot injection andmain injection is large and that the fuel injected according to saidmain injection will really be combusted and no misfiring occur due touncombusted fuel. Thus, it is ensured that always a sufficient amountof pilot injected fuel is introduced in the combustion chamber of thecylinder for ensuring that the main injected fuel will be combusted.Accordingly, said pre-established table has been provided by a cali-bration of a said engine with respect to which amount is the minimumamount allowed for a pilot injection at a certain fuel pressure in saidaccumulator for the type of injection nozzles in question. Such a cal-ibration may then be carried out for one engine and then said pre- established table be used for a plurality of identical engines.

According to an embodiment of the invention said determining in stepc) is carried out by comparing said first and second positions, deter-mining the separation thereof and determining that a large separationthereof exists if said separation exceeds a predetermined separationvalue. Making the determination of the existence of a large separa-tion dependent upon the value of this separation constitutes an ad-vantageous way of ensuring that a sufficient amount of fuel is injectedin a said pilot injection for ensuring that the main injected fuel will be combusted under the conditions prevailing.

According to another embodiment of the invention said determiningin step c) is carried out by comparing a said second position of arequested start of injection of a main injection of fuel with respect tothe position of a piston in said cylinder with a predetermined position of a such start of injection and determining that said separation is to be considered to be large if said second position of said start of in-jection is after said predetermined position of a start of injection. Thisway of determining whether a said separation is considered to belarge may also form a suitable base for the use of a said pre-established table for ensuring that the main injected fuel will certainlybe combusted as a consequence of a sufficient combustion of pilotinjected fuel, i.e. a sufficient temperature raise and pressure increase resulting from a combustion of the pilot injected fuel.

According to another embodiment of the invention said first positionat which a pilot injection of fuel into said cylinder is requested is lo-cated before said piston of the cylinder in a compression stroke thereof reaches the upper dead point ending that stroke.

According to another embodiment of the invention said predeter-mined position considered in step c) is after an upper dead point of said piston of the cylinder ending a compression stroke thereof.

According to another embodiment of the invention the requested po-sition of a start of a main injection is in step a) determined basedupon values of operation parameters of the engine, and according toanother embodiment of the invention said values of operation param-eters is considered when determining said requested position is atleast one of number of revolutions per time unit of a crank shaft ofsaid engine and/or temperature of air injected into said cylinderand/or temperature of engine cooling liquid and/or pressure of turbo charged air and/or fuel pressure and/or amount of inert gas.

The object of the present invention is with respect to the engine ob-tained by providing an engine according to the independent engineclaim. The advantages of such an engine appear clearly from theabove discussion of the method according to the invention and em-bodiments thereof.

The invention also relates to a computer program having the featuresof c|aim 10, a computer program product having the features of c|aim11, an electronic control unit having the features of c|aim 12 and a motor vehicle according to c|aim 13.

Other advantageous features as well as advantages of the present invention appear from the description following below.

BRIEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a specific description of an embodiment of the invention cited as an example. ln the drawings: Fig 1 is a schematic view of an internal combustion engine witha common rail fuel injection system upon which the methodaccording to the present invention is applicable, Fig 2 is a very simplified view illustrating positions of a pilot in- jection and a main injection when a separation thereof is considered to be large, Fig 3 is a flow chart illustrating the steps carried out in a methodaccording to an embodiment of the invention, andFig 4 is a schematic view illustrating an electronic control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF AN EMOBODIMENT OF INVENTION The use of a compression ignited engine according to the presentinvention in a motor vehicle will now by way of example be described,and a drive train 1 of a motor vehicle is for that sake schematicallyillustrated in Fig 1. The drive train 1 comprises a compression ignitedengine 2, for example a diesel engine, which is connected to drivingwheels (not shown) of the vehicle through a clutch 3 and a gearbox4.

The engine comprises a plurality, more exactly four, cylinders 5 sche-matically indicated. However, an engine according to the inventionmay have any suitable number of cylinders. Fuel is fed to the cylin-ders by means of a fuel injection system 6. This fuel injection system6 comprises a number of electrically controlled injection nozzles 7.Each cylinder of the engine 2 is associated with an own such injectionnozzle 7. The injection nozzles 7 are connected to a pressurized fuelaccumulator 8 in the form of a so-called common rail, whichconstitutes an accumulator for accumulating high pressure fuel to befed to the injection nozzles. The fuel accumulator 8 is supplied withpressurized fuel through a high pressure pump 9, which receives fuelfrom a fuel tank 10 of the vehicle 11. The injection nozzles 7 are connected to the fuel accumulator 8 through fuel ducts 12 so as to inject fuel accumulated in the fuel accumulator 8 into the respective cylinder.

Opening times for valves associated with the injection nozzles 7 andby that of the injection nozzles are controlled by a control unit 13,such as an electronic control unit. The control unit 13 is configuredto determine a second position at which a start of a main injection offuel into each cylinder in an operation cycle of the cylinder is to berequested with respect to the position of a piston in said cylinder.This requested position of start of a main injection will by the controlunit 13 be determined based upon values of operation parameters ofthe engine, such as number of revolutions of a crank shaft of theengine, temperature of air injected into the cylinder, temperature of engine cooling liquid and pressure of turbo charged air.

The control unit 13 is also configured to determine a first position atwhich a pilot injection of fuel into said cylinder with a time gap beforesaid main injection is to be requested with respect to the position ofthe piston in said cylinder and to determine whether a separation ofsaid first and second positions of said pilot injection and maininjection, respectively, is considered to be large or not. The enginefurther comprises means 14 configured to measure the fuel pressureinside the fuel accumulator 8 and send information thereabout to thecontrol unit 13. The engine also comprises means 19 included in thecontrol unit 13, configured to compare the value of the pressuremeasured by said means 14, in the case that the control unit hasdetermined that said separation is to be considered to be large, witha pre-established table for the type of fuel injection nozzles to which the fuel injection nozzle 7 belongs stating the minimum amount of fuel in the form of opening time of a said nozzle 7 to be ordered fora certain fuel pressure in a said fuel accumulator ensuring that thepilot injection of fuel will certainly result in a sufficient combustion ofpilot injected fuel for a said large separation. The control unit will bythis determine said minimum amount for said value of the pressuremeasured and control the fuel injection nozzle to inject at least said minimum amount of fuel in said pilot injection of fuel.

Fig 2 illustrates schematically the compression stroke A and the com-bustion stroke B of a piston in an operation cycle of a cylinder andthe location of an upper dead point UDP of the piston separatingthese strokes. A second position at which a start of a main injectionof fuel into said cylinder is requested is indicated at P2, and it isshown that this main injection is rather late by being after said upperdead point of the piston with respect to rotation of a crank shaft ofthe engine. This results in a large separation of a first position P1 ofa pilot injection, since this has to be carried out not later than at leastsome degrees before the UDP. This large separation means that acombustion of pilot injected fuel taken place before said maininjection of fuel will not automatically result in a guarantee of acombustion of the main injected fuel, but it has to be ensured that atleast a certain minimum amount of fuel is injected in said pilotinjection for raising the temperature and increasing the pressure suf-ficiently thereby for ensuring a later combustion of the main injectedfuel. This is also according to the present invention achieved by saidfuel pressure measurement and using the pre-established table ob-tained through calibration of the engine with respect to the minimumamount of fuel to be injected for a specific said fuel pressure for the type of injection nozzles used.

Fig 3 illustrates a flow chart of a method according to an embodimentof the present invention carried out for a compression ignited engineof the type shown in Fig 1. The method is carried out for each oper-ation cycle of each cylinder of the engine and starts with a step S1 ofdetermining a second position of a request to start a main injectionof fuel into the cylinder. A first position of a requested pilot injectionof fuel into the cylinder with a time gap before said main injection isthen determined in step S2. lt is after that in a step S3 determinedwhether a separation of said first and second positions is large,whereupon in step S4 the fuel pressure inside said fuel accumulatoris measured. lt is in step S5 asked if said separation is determined tobe large. lf the answer to this question is "yes" the value of the pres-sure measured is in Step S6 compared with a pre-established tablestating how to obtain a minimum amount of fuel in a pilot injection fordifferent such pressure values resulting in a sufficient combustion ofthat fuel for a said large separation, whereupon in a step S7 the fuelinjection nozzle of the cylinder is controlled to inject said minimumamount of fuel in a pilot injection at said first position of the piston. lfthe answer to the question put in step S5 is “no” the fuel injectionnozzle is in step S8 controlled to inject a predetermined amount offuel in a pilot injection. This step S8 may as an alternative involve a decision that no pilot injection is necessary to carry out.

Computer program code for implementing a method according to theinvention is with advantage included in a computer program whichcan be read into the internal memory of a computer, e.g. the internalmemory of an electronic control unit of a motor vehicle. Such a com- puter program is with advantage provided via a computer program 11 product comprising a data storage medium which can be read by acomputer and which has the computer program stored on it. Said datastorage medium is for example an optical data storage medium in theform of a CD ROM disc, a DVD disc etc., a magnetic data storagemedium in the form of a hard disc, a diskette, a cassette tape etc., ora flash memory or a memory of the ROM, PROM, EPROM orEEPROM type. Fig. 4 illustrates very schematically an electronic con-trol unit 13 comprising an execution means 15, e.g. a central proces-sor unit (CPU), for execution of computer software. The executionmeans 15 communicates with a memory 16, e.g. of the RAM type, viaa data bus 17. The control unit 13 comprises also a non-transitorydata storage medium 18, e.g. in the form of a flash memory or amemory of the ROM, PROM, EPROM or EEPROM type. The execu-tion means 15 communicates with the data storage medium 18 viathe data bus 17. A computer program comprising computer programcode for implementing a method according to the invention, e.g. inaccordance with the embodiment illustrated in Fig. 3, is stored on the data storage medium 18.

The invention is of course in no way restricted to the embodimentsdescribed above, since many possibilities for modifications thereofare likely to be obvious to one skilled in the art without having to deviate from the scope of invention defined in the appended claims.

The fuel injected into the cylinders of the engine may be any compression ignited fuel.

Claims

Claims 12

1. A method for operating a compression ignited engine (2) having at least one cylinder (5) and for each cylinder a fuel injection nozzle (7) configured to inject fuel into said cylinder and connected to a pressurized fuel accumulator (8), said method comprising the steps of a) b) determining a second position at which a start of a main in- jection of fuel into said cylinder in an operation cycle thereof is to be requested with respect to the position of a piston insaid cylinder, determining a first position at which a pilot injection of fuelinto said cylinder with a time gap before said main injection isto be requested with respect to the position of a piston in saidcylinder, and determining whether a separation of said first and second po-sitions of said pilot injection and main injection, respectively,is considered to be large or not, characterized in that it comprises the step of measuring the fuel pressure inside said fuel accumulator (8)and when it in step c) is determined that said separation is tobe considered to be large the steps e) and f) of comparing the value of said pressure measured in step d) witha pre-established table for the type of fuel injection nozzles(7) to which said fuel injection nozzle belongs stating theminimum amount of fuel in the form of opening time of saidnozzle to be ordered for a certain fuel pressure in a said fuelaccumulator for ensuring that the pilot injection of fuel will result in a sufficient combustion of pilot injected fuel for a said 13 large separation, and determining said minimum amount forsaid value of the pressure measured, and f) controlling the fuel injection nozzle (7) for the cylinder (5) toinject fuel according to said pilot injection of at least said minimum amount determined in step e). A method according to claim 1, characterized in that said deter-mining in step c) is carried out by comparing said first and sec-ond positions, determining the separation thereof and determin-ing that a large separation thereof exists if said separation ex- ceeds a predetermined separation value. A method according to claim 1, characterized in that said deter-mining in step c) is carried out by comparing a said second po-sition of a requested start of injection of a said main injection offuel with respect to the position of a piston in said cylinder (5)with a predetermined position of a such start of injection anddetermining that said separation is to be considered to be largeif said second position of said start of injection is after said predetermined position of a start of injection. A method according to any of the preceding claims, character-í in that said first position at which a pilot injection of fuel intosaid cylinder (5) is requested is located before said piston of thecylinder in a compression stroke thereof reaches the upper dead point ending that stroke. A method according to claim 3, characterized in that said pre- determined position considered in step c) is after an upper dead 14 point of said piston of the cylinder (5) ending a compression stroke thereof. A method according to any of the preceding claims, character-ized in that the requested position of a start of a main injectionis in step a) determined based upon values of operation param- eters of the engine. A method according to claim 6, characterized in that said valuesof operation parameters considered when determining said re-quested position is at least one of number of revolutions per timeunit of a crank shaft of said engine and/or temperature of airinjected into said cylinder and/or temperature of engine coolingliquid and/or pressure of turbo charged air and/or fuel pressure and/or amount of inert air. A compression ignited engine comprising at least one cylinder(5) and for each cylinder a fuel injection nozzle (7) configured toinject fuel into said cylinder and connected to a pressurized fuelaccumulator (8), said engine further comprising a control unit(13) for controlling said fuel injection nozzle and configured todetermine a second position at which a start of a main injectionof fuel into said cylinder in an operation cycle thereof is to berequested with respect to the position of a piston in said cylinder,to determine a first position at which a pilot injection of fuel intosaid cylinder with a time gap before said main injection is to berequested with respect to the position of a piston in said cylinderand to determine whether a separation of said first and second positions of said pilot injection and main injection, respectively, 10. 11. is considered to be large or not, and means (14) configured tomeasure the fuel pressure inside said fuel accumulator (8), characterized in that the engine further comprises means (19)configured to compare the value of said pressure measured, inthe case that the control unit (13) has determined that saidseparation is to be considered to be large, with a pre-establishedtable for the type of fuel injection nozzles (7) to which said fuelinjection nozzle belongs stating the minimum amount of fuel inthe form of opening time of said nozzle to be ordered for a certainfuel pressure in a said fuel accumulator (8) ensuring that the pilotinjection of fuel will certainly result in a sufficient combustion ofpilot injected fuel for a said large separation, and determine saidminimum amount for said value of the pressure measured, andthat said control unit (13) is configured to control the fuelinjection nozzle (7) to inject at least said minimum amount of fuel determined by said means in said pilot injection of fuel. An engine according to claim 8, characterized in that it is a die- sel engine. A computer program comprising a computer program code forcausing a computer to implement a method according to any ofclaims 1-7 when the computer program is executed in the com- puter. A computer program product comprising a non-transitory datastorage medium (18) which can be read by a computer and onwhich the program code of a computer program according to claim 10 is stored. 1

2. 1

3. 16 An electronic control unit comprising an execution means (15), amemory (16) connected to the execution means and a non-transitory data storage medium (18) which is connected to theexecution means (15) and on which the computer program code of a computer program according to claim 10 is stored. A motor vehicle, especially a wheeled vehicle such as a truck orbus, characterized in that it comprises an engine according to claim 8 or 9.