SE538870C2

SE538870C2 - A method for operating a compression ignited engine and suchan engine

Info

Publication number: SE538870C2
Application number: SE1550557A
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: 2017-01-17
Also published as: DE102016005521A1; SE1550557A1

Abstract

16 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 position at which astart of a main injection of fuel into a cylinder in an operation cyclethereof requested is to be considered to be late. lf it is determinedthat the main injection requested will be late the fuel pressure insidesaid fuel accumulator is measured and the value of that pressure iscompared with a pre-established table for the type of fuel injectionnozzles to which said fuel injection nozzle belongs stating the mini-mum amount of fuel in the form of opening time of said nozzle to beordered for a certain fuel pressure in a said fuel accumulator for en-suring that a pilot injection of fuel with a time gap before said main injection will certainly result in a combustion of pilot injected fuel. (Fig 1).

Description

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 position at which a start of a main injection offuel into said cylinder in an operation cycle thereof is to berequested with respect to the position of a piston in said cyl-inden comparing said position of said requested start with a prede-termined such position for determining that the start of saidmain injection is considered to be late if it is after said prede-termined position, controlling the fuel injection nozzle for said cylinder to injectfuel according to a pilot injection with a time gap before saidmain injection provided that it in step b) has been determinedthat the main injection requested will be late for a combustionof said pilot injected fuel in the cylinder prior to the combus- tion of the fuel injected according to said main injection, 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.

The position at which a start of a main injection of fuel into the cylin-der in an operation cycle in a compression ignited engine is re-quested is dependent upon various operation parameters of the en-gine. The reason for requesting a “late” main injection may for exam-ple be a desire to raise the temperature of the exhaust gases result-ing from the combustion of said fuel in the engine or for influencingthe amount of emissions resulting from the combustion to decrease."Late" means in this context that the piston in said cylinder has atleast passed the upper dead point ending a compression strokethereof. ln case of such a late main injection of fuel into the cylinderthere is under some circumstances an imminent risk that the fuel in-jected will not be combusted, for example as a consequence of a coldcombustion chamber or for other reasons related to the combustion, such as low quality fuel or a low pressure of turbo charged air.

A proper pilot injection of fuel with a time gap before said main injec-tion ensuring that the pilot injected fuel will be combusted would then ensure that the fuel of the main injection will be combusted thanks to the temperature raise and pressure increase resulting in the combus-tion chamber by the combustion of the pilot injected fuel. Accordingly,it is desired to ensure that a proper pilot injection of fuel combustedin said combustion chamber really takes place automatically each time a said late main injection is requested.

BACKGROUND ART US 6 378 297 B1 discloses a method in which a pilot injection of fuelis carried out for avoiding misfiring of cylinders of an internal com- bustion 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 ap- pended patent claim 1.

By said measuring of the fuel pressure inside the fuel accumulatorand the comparing of the value of the pressure measured with a pre-established table for the type of fuel injection nozzles to which thefuel injection nozzle in question belongs stating the minimum amountof fuel in the form of opening time of the nozzle to be ordered for a certain fuel pressure in said fuel accumulator for ensuring that the pilot injection of fuel will certainly result in a combustion of pilot in-jected fuel, it will be ensured that a proper pilot injection of fuel willautomatically always be activated in the case that said requested po-sition of the main injection of fuel is considered to be late. This willensure that no misfiring due to uncombusted fuel will occur, and acalibration of said minimum amount of fuel at a specific injection pres-sure for the type of injection nozzle will be easy to carry out, and thiscalibration may then be the same for a plurality of identical engines,so that it has not to be carried out for each individual engine. Thus,it is ensured that a proper pilot injection of fuel is activated in thecase that the main injection of fuel is requested that late that there isa risk that the main injected fuel will not be combusted through whichit is ensured that the main injected fuel will be combusted thanks tothe temperature raise and pressure increase in the combustion chamber resulting from the combustion of the pilot injected fuel.

According to an embodiment of the invention said pilot injection offuel is carried out 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 b) is after an upper dead point ofsaid piston of the cylinder ending a compression stroke thereof. Thus,a risk of misfiring or no combustion of the main injected fuel in thecombustion stroke is then considered to not exist in the case thatsaid main injection is requested to be at a position reached beforesaid predetermined position. However, it is pointed out that a pilot injection may then still be carried out for other reasons.

According to another embodiment of the invention the requested po-sition of start of a main injection is in step a) determined based uponvalues of operation parameters of the engine, and according to an-other embodiment of the invention said values of operation parame-ters considered when determining said requested position is at leastone of number of revolutions per time unit of a crank shaft of saidengine and/or temperature of air injected into said cylinder and/ortemperature 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 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 is a schematic view of an internal combustion engine witha common rail fuel injection system upon which themethod according to the present invention is applicable, Fig 2 is a flow chart illustrating the steps carried out in a methodaccording to an embodiment of the invention, and Fig 3 is a schematic view illustrating an electronic control unit for implementing a method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE 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 injection nozzle 7. The injection nozzles 7 are connected to a pressurized fuel accumulator 8 in the form of a so-called common rail, which consti-tutes an accumulator for accumulating high pressure fuel to be fed tothe injection nozzles. The fuel accumulator 8 is supplied with pres-surized fuel through a high pressure pump 9, which receives fuel froma fuel tank 10 of the vehicle 11. The injection nozzles 7 are connectedto 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 position at which a start of a main injection of fuel intoeach cylinder in an operation cycle of the cylinder is to be requestedwith respect to the position of a piston in said cylinder. This requestedposition of start of a main injection will by the control unit 13 be de-termined based upon values of operation parameters of the engine,such as number of revolutions of a crank shaft of the engine, temper-ature of air injected into the cylinder, temperature of engine cooling liquid and pressure of turbo charged air.

The engine further comprises means 14 configured to measure thefuel pressure inside the fuel accumulator 8 and send informationthereabout to the control unit 13. The control unit is configured tocompare said position of said requested start of a main injection offuel into a cylinder with a predetermined such position for determiningthat the start of said main injection is considered to be late if it is aftersaid predetermined position and to control the fuel injection nozzle 7for that cylinder to inject fuel according to a pilot injection with a time gap before said main injection provided that it has been determined that the main injection requested will be late for a combustion of saidpilot injected fuel in the cylinder prior to the combustion of the fuelinjected according to said main injection. The engine further com-prises means 19 included in the control unit 13, configured to com-pare the value of the pressure measured by said means 14, in casethe control unit has determined that the requested main injection isto be considered to be late, with a pre-established table for the typeof fuel injection nozzles to which the fuel injection nozzle 7 belongsstating the minimum amount of fuel in the form of opening time of asaid nozzle 7 to be ordered for a certain fuel pressure in a said fuelaccumulator 8 for ensuring that the pilot injection of fuel will certainlyresult in a combustion of pilot injected fuel. The control unit 13 willby this 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.

Said predetermined position for considering whether a start of a maininjection is considered to be late may be located at a suitable positionafter an upper dead point of a piston of a cylinder ending a compres-sion stroke thereof with respect to rotation of a crank shaft of theengine. Thus, when said requested start of a main injection is aftersaid predetermined position the control unit 13 shall ensure that apilot injection is automatically activated and that it involves a saidminimum amount of fuel resulting in a combustion thereof raising thetemperature and increasing the pressure in the combustion chamberof the cylinder. This is ensured by utilising the result of a previouscalibration of the injection nozzles with respect to the fuel accumula- tor for establishing said table. Accordingly, said minimum amount of fuel will be injected by said pilot injection into the cylinder inde- pendently of the value of the fuel pressure measured.

Fig 2 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 the position of a request to start a main injection of fuelinto the cylinder. Said determined position is then in a step S2 com-pared with a predetermined position and it is in a following step Se,asked whether the determined position is after said predeterminedposition. When the answer to this question is “No” the method is re-started with the step S1 for the next operation cycle of the cylinder.However, if the answer to said question is "Yes" the fuel pressureinside the fuel accumulator is measured in step S4. The value of thefuel pressure measured is in step S5 then compared with a pre-es-tablished table stating how to obtain minimum amount of fuel in apilot injection for certain said pressures, whereupon in a step S6 thefuel injection nozzle of the cylinder is controlled to inject said mini-mum amount of fuel in a pilot injection with a time gap before said main injection.

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 a computer and which has the computer program stored on it. Said data storage 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. 3 i||ustrates 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. 2, 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 com- pression ignited fuel.

Claims

Claims 11

1. A method for operating a compression ignited engine 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) determining a position at which a start of a main injection offuel into said cylinder (5) in an operation cycle thereof is to berequested with respect to the position of a piston in said cyl-inden comparing said position of said requested start with a prede-termined such position for determining that the start of saidmain injection is considered to be late if it is after said prede-termined position, controlling the fuel injection nozzle (7) for said cylinder (5) toinject fuel according to a pilot injection with a time gap beforesaid main injection provided that it in step b) has been deter-mined that the main injection requested will be late for a com-bustion of said pilot injected fuel in the cylinder prior to thecombustion of the fuel injected according to said main injec- tion, characterized in that it comprises an additional step of d) e) measuring the fuel pressure inside said fuel accumulator (8)and when it in step b) is determined that the requested maininjection is to be considered to be late the step of comparing the value of said pressure measured in step g) with a pre-established table for the type of fuel injection nozzles 12 (7) to which said fuel injection nozzle belongs stating the min-imum amount of fuel in the form of opening time of said nozzleto be ordered for a certain fuel pressure in a said fuel accu-mulator (8) for ensuring that the pilot injection of fuel will cer-tainly result in a combustion of pilot injected fuel, and deter-mining said minimum amount for said value of the pressuremeasured, and that in step c) the fuel injection nozzle (7) is controlled to inject at least said minimum amount of fuel determined in step e).

2. A method according to claim 1, characterized in that said pilotinjection of fuel is carried out before said piston of the cylinder(5) in a compression stroke thereof reaches the upper dead point ending that stroke.

3. A method according to claim 1 or 2, characterized in that saidpredetermined position considered in step b) is after an upperdead point of said piston of the cylinder (5) ending a compression stroke thereof.

4. A method according to any of the preceding claims, character-ized in that the requested position of start of a main injection isin step a) determined based upon values of operation parame- ters of the engine (2).

5. A method according to claim 4, characterized in that said valuesof operation parameters considered when determining said re- quested position is at least one of number of revolutions per time 13 unit of a crank shaft of said engine and/or temperature of air in-jected 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 gas.

6. 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 position at which a start of a main injection of fuelinto said cylinder in an operation cycle thereof is to be requestedwith respect to the position of a piston in said cylinder, to com-pare said position of said requested start with a predeterminedsuch position for determining that the start of said main injectionis considered to be late if it is after said predetermined positionand to control the fuel injection nozzle (7) for said cylinder toinject fuel according to a pilot injection with a time gap beforesaid main injection provided that it has determined that the maininjection requested will be late for a combustion of said pilot in-jected fuel in the cylinder prior to the combustion of the fuel in-jected according to said main injection, and means (14) config-ured to measure 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 the re-quested main injection is to be considered to be late, with a pre- established table for the type of fuel injection nozzles (7) to 10. 14 which said fuel injection nozzle belongs stating the minimumamount of fuel in the form of opening time of said nozzle to beordered for a certain fuel pressure in a said fuel accumulator forensuring that the pilot injection of fuel will certainly result in acombustion of pilot injected fuel, and determine said minimumamount for said value of the pressure measured, and that saidcontrol unit (13) is configured to control the fuel injection nozzle(7) to inject at least said minimum amount of fuel determined by said means in said pilot injection of fuel.

7. An engine according to claim 6, characterized in that it is a die- sel engine.

8. A computer program comprising a computer program code forcausing a computer to implement a method according to any ofclaims 1-5 when the computer program is executed in the com- puter.

9. A computer program product comprising a non-transitory datastorage medium which can be read by a computer and on whichthe program code of a computer program according to claim 8 is stored.

10. An electronic control unit comprising an execution means (15), amemory (16) connected to the execution means and a non-tran-sitory data storage medium (18) which is connected to the exe-cution means (15) and on which the computer program code of a computer program according to claim 8 is stored.

11. A motor vehicle, especially a wheeled vehicle such as a truck orbus, characterized in that it comprises an engine according to claim 6 or 7.