SE539418C2

SE539418C2 - A method for operating a compression ignited engine and such engine

Info

Publication number: SE539418C2
Application number: SE1550555A
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: 2017-09-19
Also published as: BR102016009888A2; DE102016004732A1; DE102016004732B4; SE1550555A1

Abstract

17 ABSTRACT When Operating a compression ignited engine (2) having at least onecylinder (5) and for each cylinder a fuel injection nozzle (7)configured to inject fuel into the cylinder the quotient (start ofcombustion - start of injection/end of injection - start of injection) iscalculated for a main injection of fuel to be carried out in a saidcylinder based upon existing operation parameters of the engine. Acontrol unit (13) compares the value of this quotient with apredetermined value and controls a said nozzle (7) to carry out a pilotinjection of fuel prior to said main injection in case said quotient ishigher than said predetermined value considered as an existence ofa need to carry out such a pilot injection for reducing otherwisepowerful combustion noises created at the start of combustion of the fuel injected into the cylinder according to the main injection. (Fig 1).

Description

The present invention relates to a method for operating a compression ignited engine having at least one cylinder and for each cylinder a fuel injection nozzle configured to inject fuel into said cylinder, said method comprising the steps of a) determining a desired position of a start of combustion of fuel injected by a main injection of fuel into said cylinder in anoperation cycle thereof with respect to the position of a pistonin said cylinder based upon existing operation parameters of the engine, b) determining a position at which a start of a said main injection of fuel into said cylinder is to be requested with respect to theposition of said piston in said cylinder based upon existingoperation parameters of the engine and said desired positiondetermined for said start of combustion, determining a position at which said main injection of fuel intosaid cylinder is to be ended with respect to the position of thepiston in said cylinder based upon existing operation parameters of the engine, d) determining whether there is a need to inject fuel in the form of a pilot injection with a time gap before said main injectionfor a combustion of said pilot injected fuel in the cylinder priorto the combustion of the fuel injected according to said main injection for reducing combustion noises created at said start of combustion of the fuel injected according to said maininjection, and e) controlling the fuel injection nozzle for said cylinder to injectfuel according to a pilot injection in case it has in step d) beendetermined that said need exists, 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, especiallywheeled utility vehicles, such as trucks or lorries and buses, and theinvention 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.

A said pilot injection of fuel is in such an engine carried out fordifferent reasons, such as to use a combustion of pilot injected fuelprior to a main injection of fuel into the cylinder to raise thetemperature of the exhaust gases resulting from the combustion ofthe fuel in the engine, for influencing the amount of emissionsresulting from the combustion to decrease or for reducing combustionnoises created at a start of combustion of the fuel injected accordingto a main injection. The present invention is directed to addressingproblems with said combustion noises through pilot injection of fuelin a cylinder prior to combustion of the main injection. The result of a pilot injection and combustion of the pilot injected fuel prior to said main injection and combustion of the main injected fuel will be a raiseof temperature and an increase of pressure inside the combustionchamber of said cylinder, which will counteract a powerfulinstantaneous combustion resulting in loud combustion noises whenthe combustion of the main injected fuel starts. However, the pilotinjection of fuel may under some conditions also have some negativeconsequence, such as negatively influencing the fuel consumption ofthe engine and/or the formation of emissions. Thus, it is desired toonly carry out a pilot injection of fuel with the aim to reduce powerfulsaid combustion noises when a need to reduce such noises really exists.

BACKGROUND ART JP 2008 08 2244 discloses a method using pilot injection of fuel intoa cylinder of an engine for reducing powerful combustion noisescreated at a start of combustion of fuel injected according to a maininjection. This method addresses the problem to determine whethera pilot injection is really needed for reduction of powerful combustionnoises by estimating and measuring the combustion condition of fuelinjected into the cylinder. lt is also known to use different mapsincluding numbers of revolutions and loads on axles of an engine forestimating said need. However, a calibration with numbers ofrevolutions of the engine and loads on axles in different maps resultsin problems since the dynamic of the engine with respect to differenttemperatures and pressures is not considered. There is also aproblem in transitional regions of either activating a pilot injection ordeactivating such a pilot injection which may result in a fluttering or flickering behaviour of the engine.

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 appended patent claim 1. lt has turned out that the value of said quotient is a useful and reliablemeasure of the need to carry out a pilot injection of fuel for reducingpowerful combustion noises created at combustion of fuel injectedaccording to a main injection in a cylinder. Thus, the relationshipbetween uncombusted fuel before the start of combustion of fuel andthe total amount of fuel injected is realized to be a good measure ofhow much noise a combustion will really cause. Accordingly, theactivating of a pilot injection is only made if a value so calculated ofthe need of a pilot injection exceeds a calibrated maximum value fornot carrying out such an injection for the conditions of the enginedetermined by the value of existing operation parameters thereof.This is a dynamical way of approaching the problem of powerfulcombustion noises of a said engine. Furthermore, a said calibrationwill probably only be necessary to carry out for one engine and then be used for a plurality of identical engines.

According to an embodiment of the invention said positionsdetermined in steps a), b) and c) are determined in the form of angles of a crank shaft of the engine.

According to another embodiment of the invention said existingoperation parameters based upon which said determinations arecarried out comprise number of revolutions per time unit of a crankshaft of said engine and/or temperature of air injected into saidcylinder and/or temperature of an engine coo|ing liquid and/orpressure of turbo charged air and/or fuel pressure and/or amount of inert gas.

According to another embodiment of the invention said fuel injected by said fuel injection nozzle is compression ignited fuel.

The object of the present invention is with respect to the engineobtained 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 embodiments thereof.

The invention also relates to a computer program having the featuresof claim 8, a computer program product having the features of claim9, an electronic control unit having the features of claim 10 and a motor vehicle according to claim 11.

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 Fig 2 Fig 3 Fig 4 is a schematic view of an internal combustion engine witha common rai| fuel injection system upon which the method according to the present invention is applicable, is a simplified graph illustrating the pressure P inside acylinder of a compression ignited engine of the type towhich the present invention belongs, injection nozzlesignal l, start of injection SOI, start of combustion SOC aswell as end of injection EOI of fuel F injected according toa main injection versus a crank shaft angle C, in which C= O corresponds to a position of a piston in said cylinder atthe upper dead point ending a compression stroke and starting a combustion stroke thereof, is a graph illustrating pressure P and heat release Hversus said crank shaft angle C in case of carrying out nopilot injection when a method according to the present invention has determined that such a need really exists, is a graph corresponding to Fig 3 for the case that it hasbeen listened to said need and a pilot injection has been carried out, Fig 5 is flow chart illustrating the steps carried out in a methodaccording to an embodiment of the invention, andFig 6 is a schematic view illustrating an electronic control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THEINVENTION 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 an injection system 6. This fuel injection system 6comprises 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, which constitutes an accumulator for accumulatinghigh pressure fuel to be fed to the injection nozzles. The fuelaccumulator 8 is supplied with pressurized fuel through a pump 9, which receives fuel from a fuel tank 10 ofthe vehicle 11. The injection nozzles 7 are connected to the fuel accumulator 8 through fuel ducts12 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 desired position of a start of combustion SOC (see Fig2) of fuel injected by a main injection of fuel into a said cylinder in anoperation cycle thereof, a position SOI at which a start of a said maininjection of fuel into said cylinder is to be requested and a positionEOI at which said main injection of fuel into said cylinder is to beended. These determinations are based upon existing operationparameters of the engine. lt is shown in Fig 2 by the area F1 howmuch fuel is injected into the cylinder between SOI and SOC, whichaccordingly constitutes an ignition delay. This amount of fuel Fi willbe uncombusted when said combustion starts at SOC. Therelationship of Fl to F (the total amount of fuel injected) will besubstantially the same as the relationship of the ignition delay, i.e.SOI-SOC, to SOI-EOI. lt has been found that the level of combustionnoises created at a start of combustion SOC through aninstantaneous combustion of the uncombusted fuel already presentin the cylinder is dependent upon the value of said relationship and increases when the value of this relationship increases.

The electronic control unit 13 in the engine according to the inventionhas through prior calibration been provided with predetermined values of Fl/F for different existing operation parameters of the engine stating that there is a need to carry out a pilot injection when this quotient has a value exceeding a said predetermined value.

Fig 3 illustrates how the pressure P and the heat release H in anengine according to the invention may vary with a crank shaft angleC in connection with a main injection of fuel into a cylinder when nopilot injection is carried out but the value of said quotient is higherthan said predetermined value. The uncombusted fuel present in saidcylinder at start of combustion SOC will then be instantaneouslycombusted resulting in a powerful increase of the heat release H inits turn resulting in a considerable annoying noise. Fig 4 shows whathappens when instead a pilot injection is carried out before said maininjection the pilot injected fuel will then be combusted at PSOC. Thiswill result in a raise of the temperature and an increase of thepressure in the cylinder before a start of combustion SOC of the maininjected fuel, which will then result in a much less steep increase ofthe heat release H at the start of said combustion and by that asubstantial reduction of the combustion noises then created to a levelbeing acceptable and for instance not noticed by a driver of a vehicle having the engine according to the invention.

Fig 5 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 eachoperation cycle of each cylinder of the engine and starts with a stepS1 of determining a desired position of start of combustion of fuelinjected by a main injection of fuel into the cylinder and thencontinued with the step S2 of determining a position at which a start of an injection of fuel is to take place. The position at which said injection of fuel into the cylinder is to be ended is then determined inthe step S3. The quotient (SOC-SOI)/(EOI-SOI) is then calculated instep S4. The method is continued with comparing the value of saidquotient calculated with a predetermined value for existing operationparameters of the engine in step S5, whereupon in the step S6 thequestion is asked whether the value of said quotient is higher thansaid predetermined value. lf the answer to this question is “yes” themethod is continued with the step S7 of controlling the nozzle of thecylinder to carry out a pilot injection of fuel prior to said main injectionso as to reduce combustion noises created at the start of combustionSOC.

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 programproduct 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. 6 illustrates very schematically an electronic con-trol unit 13 comprising an execution means 14, e.g. a central proces-sor unit (CPU), for execution of computer software. The executionmeans 14 communicates with a memory 15, e.g. of the RAM type, viaa data bus 16. The control unit 13 comprises also a non-transitory data storage medium 17, e.g. in the form of a flash memory or a 11 memory of the ROM, PROM, EPROM or EEPROM type. The execu-tion means 14 communicates with the data storage medium 17 viathe data bus 16. A computer program comprising computer programcode for implementing a method according to the invention, e.g. inaccordance with the embodiment illustrated in Fig. 5, is stored on the data storage medium 17.

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 anycompression 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, said method comprising the steps of a) b) d) determining a desired position (SOC) of a start of combustionof fuel injected by a main injection of fuel into said cylinder (5)in an operation cycle thereof with respect to the position of apiston in said cylinder based upon existing operationparameters of the engine, determining a position (SOI) at which a start of a said maininjection of fuel into said cylinder is to be requested withrespect to the position of said piston in said cylinder (5) basedupon existing operation parameters of the engine and saiddesired position determined for said start of combustion,determining a position (EOI) at which said main injection offuel into said cylinder (5) is to be ended with respect to theposition of the piston in said cylinder based upon existingoperation parameters of the engine, determining whether there is a need to inject fuel in the formof a pilot injection with a time gap before said main injectionfor a combustion of said pilot injected fuel in the cylinder priorto the combustion of the fuel injected according to said maininjection for reducing combustion noises created at said startof combustion of the fuel injected according to said main injection, and 13 e) controlling the fuel injection nozzle for said cylinder to injectfuel according to a pilot injection in case it has in step d) beendetermined that said need exists, characterized in that step d) is carried out by using the results obtained through the steps a) - c) to calculate a value of the difference of said positions of start of combustion and start ofinjection divided by the difference of end of injection and start of injection for said main injection and consider this value to be a measure of said need of a pilot injection, comparing said value with a predetermined value of this quotient ((SOC-SOl)/(EOl- SOl)) for said existing operation parameters of the engine and determining that said need exists if said value is higher than said predetermined value.

2. A method according to claim 1, characterized in that saidpositions (SOC, SOI, EOI) determined in steps a), b) and c) are determined in the form of angles of a crank shaft of the engine.

3. A method according to claim 1 or 2, characterized in that saidexisting operation parameters based upon which saiddeterminations are carried out comprise number of revolutionsper time unit of a crank shaft of said engine and/or temperatureof air injected into said cylinder and/or temperature of an enginecooling liquid and/or pressure of turbo charged air, and/or fuel pressure and/or amount of inert gas.

4. A method according to any of claims 1-3, characterized in that said fuel injected by said fuel injection nozzle (7) is diesel. 14

5. 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, said engine (2) further comprising acontrol unit (13) for controlling said fuel injection nozzle andconfigured to determine a desired position (SOC) of a start ofcombustion of fuel injected by a main injection of fuel into saidcylinder (5) in an operation cycle thereof with respect to theposition of a piston in said cylinder based upon existingoperation parameters of the engine, to determine a position(SOI) at which a start of a said main injection of fuel into saidcylinder is to be requested with respect to the position of saidpiston in said cylinder based upon existing operation parametersof the engine and said desired position determined for said startof combustion, to determine a position (EOI) at which said maininjection of fuel into said cylinder is to be ended with respect tothe position of the piston in said cylinder based upon existingoperation parameters of the engine, to determine whether thereis a need to inject fuel according to a pilot injection with a timegap before said main injection for a combustion of said pilotinjected fuel in the cylinder (5) prior to the combustion of the fuelinjected according to said main injection for reducing combustionnoises created at said start of combustion of the fuel injectedaccording to said main injection, and to control the fuel injectionnozzle (7) for said cylinder to inject fuel according to a pilotinjection in case it has been determined that said need exists, characterized in that said control unit (13) is configured to usethe results of the determinations of positions for start ofcombustion (SOC), start of injection (SOI) and end of injection (EOI) for said main injection of fuel to calculate a value of the difference of said positions of start of combustion and start ofinjection divided by the difference of end of injection and start ofinjection for said main injection and consider this value to be ameasure of said need of a pilot injection, to compare said valuewith a predetermined value of this quotient for said existingoperation parameters of the engine and determine that said need exists if said value is higher then said predetermined value.

6. An engine according to claim 5, characterized in that saidcontrol unit (13) is configured to consider at least one of thefollowing existing operation parameters when carrying out saiddeterminations: number of revolutions per time unit of a crankshaft of said engine and/or temperature of air injected into saidcylinder and/or temperature of engine cooling liquid and/or pressure of turbo charged air.

7. An engine according to claim 5 or 6, characterized in that it is a diesel engine.

8. A computer program comprising a computer program code forcausing a computer to implement a method according to any ofclaims 1-4 when the computer program is executed in the computer.

9. A computer program product comprising a non-transitory datastorage medium (17) which can be read by a computer and onwhich the program code of a computer program according to claim 8 is stored. 16

10. An electronic control unit comprising an execution means (14), a

11. memory (15) connected to the execution means and a non-transitory data storage medium (17) which is connected to theexecution means (15) and on which the computer program code of a computer program according to claim 8 is stored. A motor vehicle, especially a wheeled vehicle such as a truck orbus, characterized in that it comprises an engine according to any of claims 5-7.