WO2013150350A1

WO2013150350A1 - Method and apparatus for determining the cetane number of a fuel

Info

Publication number: WO2013150350A1
Application number: PCT/IB2013/000342
Authority: WO
Inventors: Makio Tsuchiyama; Hirotaka Kaneko; Mamoru TANIGUCHI; Yuji Takasu
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2012-03-30
Filing date: 2013-03-11
Publication date: 2013-10-10
Also published as: DE112013001833T5; BR112014024318A2; DE112013001833B4; JP5742772B2; BR112014024318B1; CN104204476B; JP2013209941A; CN104204476A; DE112013001833B9

Abstract

An engine control apparatus performs a plurality of estimations of ignition quality of fuel by using a plurality of different estimation logics corresponding one-to-one to the estimations, and performs an engine control based on a result of an estimation that indicates lowest ignition quality among the results of the estimations.

Description

METHOD AND APPARATUS FOR DETERMINING THE CETANE NUMBER OF A FUEL BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to an engine control apparatus and an engine control method that estimate the ignition quality of fuel and perform an engine control on the basis of results of the estimation.

2. Description of Related Art

[0002] A diesel engine burns injected fuel by igniting it through compression. Commercially available light oils that diesel engines use as fuel are different in their components, and vary in the ignition quality. The ignition quality of fuel greatly affects the circumstances of occurrence of misfire, the engine output, etc. Therefore, in order to improve the output performance, the fuel economy performance and the emission performance of a diesel engine, it is necessary to check the ignition quality of the fuel that is presently used and to adjust the manners of execution of engine controls regarding the timing and amount of fuel injection, etc. according to a result of the checking of the ignition quality of the fuel.

[0003] The ignition quality of the light oil used as a fuel of diesel engines is evaluated by the cetane number of the light oil. The cetane number of a specimen light oil is expressed by the volume percentage of the amount of cetane in a mixture of cetane and -methyl naphthalene which exhibits the same ignition quality as the specimen light oil.

[0004] Various logics for estimating the cetane number of fuel have been proposed. For example, Japanese Patent Application Publication No. 2011-256840 (JP 2011-256840 A) discloses a logic in which the cetane number of fuel of a diesel engine is estimated on the basis of a relation among the change in the rotation of the diesel engine that follows fuel injection, the fuel injection timing and the engine rotation speed occurring at the time of fuel injection.

[0005] It is conceivable to estimate the ignition quality of fuel by using different estimation logics. In that case, due to differences in estimation principle, the different estimation logics sometimes provide individually different estimation results. Then, this may result in the hunting of the engine control.

[0006] For example, let it assumed that the estimation based on an estimation logic A provides an estimation result that the cetane number of the presently used fuel is low while the estimation based on an estimation logic B provides an estimation result that the cetane number of the presently used fuel is high. In that case, after the estimation based on the estimation logic A is implemented, an engine control designed on the assumption that a fuel whose cetane number is low is used is implemented; on the other hand, after the estimation based on the estimation logic B is implemented, an engine control designed on the, assumption that a fuel whose cetane number is high is used is implemented. Therefore, every time the estimation based on one of the estimation logics is implemented, the execution mode of the engine control is changed, and therefore the control becomes unstable.

SUMMARY OF THE INVENTION

[0007] The invention provides an engine control apparatus and an engine control method that are capable of restraining occurrence of the control hunting , and therefore suitably performing the engine control even in the case where a plurality of different estimation logics are employed for estimation of the ignition quality of fuel.

[0008] An engine control apparatus according to a first aspect of the invention performs a plurality of estimations of ignition quality of fuel by using a plurality of different estimation logics corresponding one-to-one to the estimations, and performs an engine control based on a result of an estimation that indicates lowest ignition quality among the results of the estimations.

[0009] In the foregoing construction, when the estimations provide different estimation results, the estimation result that indicates the lowest ignition quality of the estimation results is used as a basis for performing the engine control. Therefore, even if different estimation results are output, the control hunting is restrained. Furthermore, since the estimation result that indicates the lowest ignition quality of the estimation results is employed to perform the engine control, robustness against misfire can be suitably secured. Therefore, according to the forgoing construction, even though a plurality of estimation methods are employed to estimate the ignition quality of the presently used fuel, it is possible to restrain the control hunting and suitably perform the engine control.

[0010] In the first aspect, the engine control apparatus may perform the estimation of the ignition quality of the fuel based on a circumstance of occurrence of misfire, the estimation of the ignition quality of the fuel based on amount of refueling and the estimation of the ignition quality of the fuel based on magnitude of engine torque produced by combustion of the fuel.

[0011] If the ignition quality of fuel is low, misfire is likely to occur. Therefore, the ignition quality of the presently used fuel can be estimated from the circumstances of occurrence of misfire. Furthermore, after refueling is performed, the composition of the fuel in the fuel tank usually changes and, therefore, the ignition quality of the fuel changes. The maximum amount of change in the ignition quality of the fuel can be found from the amount of refueling. Still further, if the ignition quality of fuel declines, the engine torque produced by combustion of a unit mass of fuel changes. Therefore, the ignition quality of the presently used fuel can also be estimated from the magnitude of engine torque produced by combustion of the fuel. Therefore, in the foregoing construction, the ignition quality of the presently used fuel is estimated on the basis of the circumstances of occurrence of misfire, the amount of refueling and the magnitude of engine torque produced by combustion of the fuel.

[0012] If the estimations provide different results, the engine control is performed on the basis of the estimation result that indicates the lowest ignition quality, of the different estimation results. Therefore, even if different estimation results are provided, the control hunting is restrained. Furthermore, since the engine control is performed by using the result of the estimation that indicates the lowest ignition quality, robustness against misfire can be suitably secured. Therefore, according to the foregoing construction, even though a plurality of estimation methods are employed to estimate the ignition quality of the presently used fuel, it is possible to restrain the control hunting and suitably perform the engine control.

[0013] An engine control method according to a second aspect of the invention includes: performing a plurality of estimations of ignition quality of fuel by using a plurality of different estimation logics corresponding one-to-one to the estimations; and performing an engine control based on a result of an estimation that indicates lowest ignition quality among the results of the estimations. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a general diagram schematically showing an overall construction of an engine control apparatus in accordance with an embodiment of the invention;

FIG. 2 is a sectional view showing a structure of a side portion of an injector provided in a diesel engine to which the embodiment is applied;

FIG. 3 is a graph showing an example of a time waveform of a fuel injection rate;

FIG. 4 is a flowchart showing a processing procedure of a torque-based determined cetane number calculation routine employed in the foregoing embodiment;

FIG. 5A is a graph showing transition of the engine rotation speed before and after execution of the fuel injection for detection of the cetane number of the fuel, and FIG. 5B is a graph showing transition of the rotation speed difference before and after execution of the fuel injection for detection of the cetane number;

FIG. 6 is a flowchart showing a processing procedure of a control cetane number setting routine employed in the embodiment; and

FIG. 7 is a time chart showing an example of manners of transition of a misfire detection-based cetane number, a refueling-based determined cetane number, a torque-based determined cetane number and a control cetane number in the engine control apparatus of the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0015] Hereinafter, an embodiment in which an engine control apparatus in accordance with the invention is embodied will be described in detail with reference to FIGS. 1 to 7. Incidentally, the control apparatus of this embodiment is applied to a diesel engine that is to be mounted in a vehicle.

[0016] As shown in FIG. 1, a fuel tank 10 of a diesel engine to which the control apparatus of this embodiment is applied is provided with a fuel gauge 11 that measures the amount of fuel remaining in the fuel tank 10. Furthermore, a fuel supply passageway 12 for sending fuel to be supplied to the diesel engine is connected to the fuel tank 10. An intermediate portion of the fuel supply passageway 12 is provided with a high-pressure fuel pump 13 that pumps up fuel from the fuel tank 10 and then pressurizes it and discharges pressurized fuel. A downstream end of the fuel supply passageway 12 is connected to a common rail 14 that holds pressurized fuel. Injectors 16 for the cylinders of the diesel engine are connected to the common rail 14. Each injector 16 is provided with a fuel pressure sensor 17 that detects fuel pressure in the injector 16. Furthermore, the injectors 16 are connected to a return passageway 18 for returning surplus amounts of fuel to the fuel tank 10.

[0017] The thus-constructed diesel engine is controlled by an electronic control unit 19. The electronic control unit 19 includes a microcomputer that performs various computation processes related to the engine control. Furthermore, the electronic control unit 19 is provided with an input circuit that accepts input of signals from various sensors that detect situations of operation of the diesel engine. The fuel gauge 11 and the fuel pressure sensors 17 are connected to the input circuit. The other sensors connected to the input circuit include an intake pressure sensor 20 that detects the intake air pressure, a rotation speed sensor 21 that detects the rotation speed of the diesel engine, a coolant temperature sensor 22 that detects the temperature of a coolant of the diesel engine, an accelerator pedal sensor 23 that detects the amount of depression of an accelerator pedal, a vehicle speed sensor 24 that detects the vehicle speed, etc. Furthermore, the electronic control unit 19 is provided with drive circuits for actuators that drive various portions of the diesel engine. The drive circuits include circuits that drive the injectors 16 of the cylinders.

[0018] Further details of the construction of each of the injectors 16 provided for the individual cylinders of the diesel engine will be described. This diesel engine employs electrically-driven type injectors as the injectors 16.

[0019] As shown in FIG. 2, each injector 16 has a housing 30 that has a hollow cylindrical shape. Within the housing 30 there is disposed a needle valve 31 for reciprocating movements in the up-down directions in FIG. 2. Furthermore, a spring 32 that always urges the needle valve 31 downward in FIG. 2 is disposed within a portion of the housing 30 which is upward relative to the needle valve 31 in FIG. 2.

[0020] Furthermore, within the housing 30 there are formed two fuel chambers that are separated from each other by the needle valve 31, more specifically, a nozzle chamber 33 located relatively downward in FIG. 2 with respect to the needle valve 31 and a pressure chamber 34 located, relatively upward in FIG. 2 with respect to the needle valve 31.

[0021] The nozzle chamber 33 is provided with injection holes 35 that provide communication between the inside of the the nozzle chamber 33 and the outside of the housing 30. The nozzle chamber 33 is connected with an introduction passageway 36 that is formed within the housing 30. The introduction passageway 36 is connected to the common rail 14 (FIG. 1). Fuel is supplied into the nozzle chamber 33 from the common rail 14 via the introduction passageway 36.

[0022] On another hand, the pressure chamber 34 is connected to the nozzle chamber 33 through a communication passageway 37, and to the aforementioned return passageway 18 through a discharge passageway 38. Furthermore, within the pressure chamber 34 there is provided a valve body 40 that is driven by a pressure-electric actuator 39 that is formed by laminating pressure-electric elements, for example, piezoelectric elements. Thus, the pressure chamber 34 is selectively caused to communicate with one of the communication passageway 37 and the discharge passageway 38 by driving the valve body 40.

[0023] A fuel pressure sensor 17 as described above is provided integrally with an upper portion of the injector 16 in FIG. 2. The fuel pressure sensor 17 is constructed so as to detect the pressure of fuel within the introduction passageway 36.

[0024] Each of the thus-constructed injectors 16 operates as follows. The pressure-electric actuator 39, when not energized with drive voltage, assumes a contracted state in which the entire length of the pressure-electric actuator 39 is reduced, so as to position the voltage body 40 at such a position that the pressure chamber 34 communicates with the communication passageway 37 and is shut off from the discharge passageway 38. At this time, the nozzle chamber 33 and the pressure chamber 34 communicate with each other, so that the pressures in the two chambers are substantially equal. Therefore, at this time, the needle valve 31 has been disposed downward in FIG. 2 by the spring force of the spring 32 so that the injection holes 35 are closed. Hence, at this time, fuel is not injected from the injector 16.

[0025] On another hand, when the pressure-electric actuator 39 is energized with drive voltage, the entire length thereof increases so as to position the valve body 40 at such a position that the pressure chamber 34 is shut off from the communication passageway 37 and communicates with the discharge passageway 38. At this time, fuel is discharged from the pressure chamber 34 and the pressure in the pressure chamber 34 declines. Therefore, the pressure in the nozzle chamber 33 becomes greater than the pressure in the pressure chamber 34. Due to the pressure difference, at this time, the needle valve 31 is displaced upward in FIG. 2 by the spring force of the spring 32, that is, displaced thereby so as to move away from the position at which the needle valve 31 closes the injection holes 35. Therefore, at this time, the injector 16 injects fuel.

[0026] In the embodiment constructed as described above, the electronic control unit 19 performs a fuel injection control of the diesel engine. Concretely, the electronic control unit 19 calculates a target value of the amount of fuel injection (target fuel injection amount) from the engine rotation speed, the amount of depression of the accelerator pedal and an estimated value of the cetane number (control cetane number) of the fuel in use. Furthermore, the electronic control unit 19 calculates target values of the fuel injection timing and of the fuel injection duration from the target fuel injection amount and the engine rotation speed. Then, according to these calculated target values, the electronic control unit 19 applies the drive voltage to the pressure-electric actuator 39 of each injector 16 so as to control the fuel injection.

[0027] Furthermore, in this embodiment, in conjunction with the above-described fuel injection control, the electronic control unit 19 implements a control of forming a time waveform of the fuel injection rate of each injector 16 (the amount of fuel injected per unit time) on the basis of the fuel pressure detected by the fuel pressure sensors 17 provided for the individual injectors 16. This control is performed in the following manner.

[0028] After the needle valve 31 of an injector 16 starts to lift from the injection holes 35 according to the drive voltage applied to the pressure-electric actuator 39, the fuel pressure in the nozzle chamber 33 gradually decreases with the increasing lift of the needle valve 31. Then, the application of the drive voltage stops and the lift of the needle valve 31 decreases. With the decreasing lift of the valve, the fuel pressure in the nozzle chamber 33 gradually rises. Therefore, from the fuel pressure detected by the fuel pressure sensor 17 of the injector 16, it is possible to specifically determine the timing at which the needle valve 31 starts to lift (valve opening-drive start timing Tos), the timing at which the fuel injection rate- becomes maximum (maximum injection rate attainment timing Toe), the timing at which the fuel injection rate starts to decrease (fuel injection rate decrease start timing Tcs) and the timing at which the lifting of the needle valve 31 ends (minimum lift attainment timing Tee). Then, from these determined timings, a time waveform of the fuel injection rate as shown in FIG. 3 can be found. From that waveform, it is possible to check the actual situation of fuel injection with very high accuracy. Incidentally, in this embodiment, the electronic control unit 19 finds the rate of change of the fuel pressure (the time derivative of the fuel pressure) within each injector 16, and finds the aforementioned timings on the basis of the rate of change: [0029] Furthermore, in this embodiment, the electronic control unit 19 estimates the cetane number of the presently used fuel, that is, estimates the ignition quality of the fuel. Then, according to results of the estimation, the electronic control unit 19 adjusts the manners of control of the fuel injection timing, the amount of fuel injection, the EGR amount, the supercharge rate, etc. This improves the the output performance, the fuel economy performance and the emission performance of the diesel engine. For example, when the cetane number of the presently used fuel is estimated to be low, the electronic control unit 19 changes the manners of control, for example, increases the number of performances of pilot injection or the amount of pilot injection, advances the timing of pilot injection and the timing of main injection, decreases the EGR amount, heightens the supercharge rate, etc., so as to restrain occurrence of misfire that results from low ignition quality of fuel.

[0030] In the engine control apparatus of the embodiment, the cetane number of fuel is estimated by using three estimation logics. The three estimation logics are estimation of the cetane number of fuel based on misfire, estimation of the cetane number of fuel based on refueling and estimation of the cetane number of fuel based on the engine torque. These three estimation logics will be described in detail below.

[0031] [ESTIMATION OF CETANE NUMBER BASED ON MISFIRE] If a low-cetane number fuel, whose ignition quality is low, is used, the incidence of misfire increases. Therefore, from circumstances of occurrence of misfire, it is possible to estimate the cetane number of the presently used fuel.

[0032] Concretely, the electronic control unit 19 detects occurrence of misfire from changes in the engine rotation speed. Then, when the number of detections of misfire reaches a predetermined value, the electronic control unit 19 decreases the estimated value of the cetane number of the fuel based on the circumstance of occurrence of misfire, that is, the value of the misfire detection-based cetane number. Incidentally, the value of the misfire detection-based cetane number is reset to the initial value when refueling is performed. The number of detections of misfire is cleared to "0" every time refueling is performed. [0033] [ESTIMATION OF CETANE NUMBER BASED ON REFUELING] When the fuel tank 10 is refilled, the composition of the fuel in the fuel tank 10 changes, and the cetane number of the fuel changes. The maximum value of the magnitude of the change in the cetane number can also be found from the cetane number of the fuel prior to the refueling, the amount of the refueling, etc.

[0034] Concretely, when it is recognized that refueling has been performed because of increase in the amount of fuel remaining in the fuel tank 10, the electronic control unit 19 estimates the cetane number of the fuel after the refueling on the assumption that the the fuel having been charged is a fuel whose cetane number is the lowest of all the fuels that are expected to be used. The cetane number estimated at this time, that is, the refueling-based determined cetane number Cr, is calculated on the basis of the following expression (1). In the following expression (1), Fb represents the amount of fuel remaining in the fuel tank 10 prior to refueling (pre-refueling amount of remaining fuel), Fr represents the amount of fuel charged into the tank 10 (amount of tank-charged fuel or amount of refueling), and Fa represents the amount of fuel remaining in the fuel tank 10 after the refueling (post-refueling amount of remaining fuel). Furthermore, Cb represents the estimated value of the cetane number of the fuel in the fuel tank 10 prior to refueling (pre-refueling cetane number), and Cm represents the minimum value of the cetane numbers (minimum cetane number) of the fuels expected to be used.

[0035] Cr = (Cb x Fb + Cm x Fr)/Fa ...(1)

Incidentally, calculation of the refueling-based determined cetane number is performed when refueling is recognized. Then, the value of the refueling-based determined cetane number is reset to the initial value at the time point of obtainment of a result of estimation of the cetane number based on the magnitude of engine torque produced after fuel injection.

[0036] [ESTIMATION OF CETANE NUMBER BASED ON ENGINE TORQUE] As the ignition quality of fuel is higher, the amount of fuel left unburned after combustion is smaller and the engine torque produced following the fuel injection is larger. Therefore, the electronic control unit 19, when an execution condition described below is satisfied, implements injection of a small amount of fuel, finds the magnitude of the engine torque produced (produced torque) by combustion of the small amount of injected fuel, and then estimates the cetane number of fuel from the magnitude of the produced torque.

[0037] Concretely, the estimation of the cetane number based on the magnitude of torque produced following fuel injection (torque-based determined cetane number) is performed through the processing of a torque-based determined cetane number calculation routine shown in FIG. 4. The processing of this routine is executed repeatedly by the electronic control unit 19 at every predetermined control cycle time during operation of the diesel engine.

[0038] When the processing of this routine starts, it is determined firstly in step SlOO whether the condition for execution of the torque-based determined cetane number calculation is satisfied. This execution condition is that all the conditions (A) to (C) stated below are satisfied. (A) The deceleration-time fuel cut of the diesel engine to be implemented according to discontinuation of the accelerator operation (i.e., of the depression of the accelerator pedal) is being executed. (B) The total amount of fuel injection following the previous refilling of the tank 10 is greater than or equal to a predetermined value a. Incidentally, the predetermined value a is set to a value that is greater than a total amount of fuel that can be charged into the fuel channels extending from the fuel tank 10 to the injectors 16. That is, satisfaction of the condition (B) means that after the previous refueling, the fuel in the aforementioned fuel channels has been replaced by the new fuel supplied from the fuel tank 10. (C) It is not the case that the torque-based determined cetane number has been calculated by the routine to be the same as the previously calculated value a predetermined number of times or more in a row. If the torque-based determined cetane number has been calculated by the routine to be the same as the previously calculated value a predetermined number of times or more in a row, the calculated value of the torque-based determined cetane number can be considered to remain unchanged also from the next calculation on. Therefore, in such a case, the embodiment stops calculation of the torque-based determined cetane number. Incidentally, the count of the number of times that the torque-based determined cetane number has been calculated to be the same is cleared at the time point when refueling is detected.

[0039] If the execution condition is not satisfied (NO), the present processing of the routine immediately ends. If the execution condition is satisfied (YES), the process proceeds to step S101. Then, in step S101, the timing of the fuel injection for detecting the cetane number of the fuel is set on the basis of the engine rotation speed, the engine coolant temperature and the intake air pressure. Incidentally, the engine rotation speed, the engine coolant temperature and the intake air pressure are used to calculate the fuel injection timing, for the following reason.

[0040] The amount of fuel left unburned after combustion changes depending on the fuel injection timing as well as the ignition quality of fuel. If the fuel injection timing is relatively early, the time from when fuel is injected until when the in-cylinder pressure and/or the in-cylinder temperature decreases so that combustion is no longer possible is relatively long. Therefore, if the fuel injection timing is earlier, combustion continues for a longer time and the amount of fuel left unburned after combustion is smaller. On another hand, if the fuel injection timing is later, the aforementioned time from when fuel is injected until when combustion is no longer possible is shorter and the duration of combustion is shorter, and therefore the amount of fuel left unburned in the cylinder is larger. The time from when fuel is injected until when the in-cylinder pressure and/or the in-cylinder temperature begins to decrease is shorter as the engine rotation speed is higher. Therefore, in order to uniformalize the combustion condition, the timing of the fuel injection for detection of the cetane number of fuel needs to be further advanced as the engine rotation speed is higher.

[0041] Furthermore, when the cylinder wall temperature is relatively low, the maximum value of the in-cylinder temperature (peak in-cylinder temperature) in the engine compression stroke is relatively low. When the intake air pressure is relatively low, the maximum value of in-cylinder pressure (peak in-cylinder pressure) in the engine compression stroke is relatively low. As the peak in-cylinder temperature or the peak in-cylinder pressure is lower, the duration of a high-temperature and high-pressure state in the cylinder is shorter and the duration of combustion is shorter. Therefore, in order to uniformalize the combustion condition, the timing of the fuel injection for detection of the cetane number needs to be further advanced as the cylinder wall temperature is lower or as the intake air pressure is lower.

[0042] Therefore, in this embodiment, in order to uniformalize the condition of combustion of the fuel injected for detection of the cetane number of the fuel, the injection timing of the fuel is adjusted according to the then engine rotation speed, the then cylinder wall temperature and the then intake air pressure. Concretely, in this embodiment, the timing of the fuel injection for detection of the cetane number of the fuel is further advanced as the engine rotation speed is higher. Likewise, in this embodiment, the timing of the fuel injection for detection of the cetane number of the fuel is further advanced as the engine coolant temperature, which is an index value of the cylinder wall temperature, is lower. Furthermore, in this embodiment, the timing of the fuel injection for detecting the cetane number is further advanced as the intake air pressure is lower.

[0043] After the fuel injection timing is set in the above-described manner, injection of a predetermined amount of fuel is carried out at the set timing in the subsequent step S102. Then, in step S103, the magnitude of the torque produced by that fuel injection is found.

[0044] The calculation of the produced torque in step S103 is performed in the following manner. The electronic control unit 19 acquires the engine rotation speed at every predetermined cycle time, and finds a difference between the acquired engine rotation speed and the engine rotation speed acquired the previous cycle time before (finds a rotation speed difference ΔΝΕ).

[0045] FIG. 5A shows transition of the engine rotation speed before and after execution of the fuel injection for detection of the cetane number of the fuel, and FIG. 5B shows transition of the rotation speed difference ΔΝΕ at that time. As the engine torque is produced due to execution of the fuel injection for detection of the cetane number of the fuel, the engine rotation speed increases or the rate of decrease in the engine rotation speed decreases, so that the rotation speed difference ΔΝΕ increases. The time derivative value of the increase in the rotation speed difference ΔΝΕ (which corresponds to the area of a hatched portion in FIG. 5B) is larger as the produced torque is larger. Therefore, in this embodiment, the time derivative value of the increase in the rotation speed difference ΔΝΕ is calculated as an amount of change in rotation ΣΔΝΕ, and the value of the amount is used as an index value of the produced torque.

[0046] Subsequently, in step S104, the actual fuel injection timing and the actual amount of fuel injection are found from the time waveform of the rate of fuel injection in the fuel injection performed in step S102, and errors between the command values of the fuel injection timing and the amount of fuel injection and the actual values of the fuel injection timing and the amount of fuel injection (the injection timing error and the injection amount error) are calculated. Then, on the basis of the injection timing error and the injection amount error, the amount of change in rotation ΣΔΝΕ is corrected. This correction is a correction of an amount that corresponds to the amount of change in engine torque that is caused by the injection timing error and/or the injection amount error, and is performed to reduce the influence that the injection timing error and the injection amount error have on the result of estimation of the cetane number of the fuel. Concretely, as the injection timing error to the advanced side (the side to which the injection timing becomes further advanced) is larger, the produced torque is larger, so that the amount of change in rotation ΣΔΝΕ is more greatly reduced for correction. Furthermore, as the injection amount error to the side of increased amount is larger, the produced torque is larger, so that the amount of change in rotation ΣΔΝΕ is more greatly reduced for correction.

[0047] Subsequently, in step S 105, an estimated cetane number of the fuel is calculated on the basis of the post-correction amount of change in rotation ΣΔΝΕ and the engine rotation speed occurring at the time of execution of the fuel injection. The microcomputer of the electronic control unit 19 pre-stores empirically predetermined^■- ·- relations of the cetane number of fuel with the amount of change in rotation ΣΔΝΕ and the engine rotation speed. The calculation in step S105 is performed on the basis of the pre-stored relations. After the torque-based determined cetane number is calculated, the present processing of the routine ends.

[0048] [SETTING OF CONTROL CETANE NUMBER] As described above, the cetane number of the presently used fuel is estimated by using three different estimation logics. These estimation logics are different from each other in the estimation principle, and therefore sometimes produce different results of estimation of the cetane number. In this embodiment, in order to prevent control hunting from occurring even in such a case, an estimated value of the fuel's cetane number that is actually used in the engine control, that is, a control cetane number, is set in the following manner.

[0049] The setting of the control cetane number in this embodiment is performed through the process of a control cetane number setting routine shown in FIG. 6. The process of this routine is repeatedly executed at every predetermined control cycle time by the electronic control unit 19 during operation of the diesel engine.

[0050] When the process of the routine starts, it is firstly determined in step S200 whether any one of the three estimated values of the cetane number, that is, the misfire detection-based cetane number, the refueling-based determined cetane number and the toque determination cetane number, has been updated. If none of the three estimated values has been updated (NO), the present process of the routine immediately ends. In that case, the control cetane number is maintained at the current value.

[0051] On the other hand, if any one of the three estimated values of the cetane number of the fuel has been updated (YES in S200), the control cetane number is set to the smallest one of the misfire detection-based cetane number, the refueling-based determined cetane number and the torque-based determined cetane number, that is, the result of estimation that indicates the lowest cetane number of the results of estimation of the cetane number provided by the three estimation logics. After that, the present process of the routine ends. [0052] Now, operation of the foregoing embodiment will be described with reference to FIG. 7. FIG. 7 shows an example of manners of transition of the misfire detection-based cetane number, the refueling-based determined cetane number, the torque-based determined cetane number and the control cetane number in the engine control apparatus of the embodiment.

[0053] Up to time tl, the torque-based determined cetane number is the least value among the misfire detection-based cetane number, the refueling-based determined cetane number and the torque-based determined cetane number. Therefore, during the period till time tl, the value of the torque-based determined cetane number is set as the value of the control cetane number.

[0054] When refueling is carried out at time tl, the value of the refueling-based determined cetane number is updated, so that the value of the refueling-based determined cetane number becomes less than the value of the torque-based determined cetane number, which, until that time point, is the smallest of the estimated values of the cetane number of the fuel. Therefore, from time tl, the value of the refueling-based determined cetane number is set as the value of the control cetane number.

[0055] Then, at time t2, the foregoing execution condition is satisfied, and the estimation of the cetane number of the fuel based on the engine torque produced by combustion of the fuel (the calculation of the torque-based determined cetane number) is performed. In this estimation, the torque-based determined cetane number is calculated to be the same value as that previously calculated, and therefore the value of the torque-based determined cetane number does not change. Depending on the value of the torque-based determined cetane number calculated at this time, the value of the refueling-based determined cetane number updated due to the refueling performed at time tl is reset to an initial value. As a result, the value of the refueling-based determined cetane number becomes larger than the value of the torque-based determined cetane number, so that the torque-based determined cetane number is the least value of the three estimated values of the cetane number. Therefore, from time t2, the value of the torque-based determined cetane number is set as the value of the control cetane number. [0056] Then, when at time t3 occurrence of misfire is detected, the value of the misfire detection-based cetane number is decreased. As a result, the value of the misfire detection-based cetane number is less than the value of the torque-based determined cetane number, which is, until that time point, the smallest of the three estimated values of the cetane number of the fuel. Therefore, from time t3, the value of the misfire detection-based cetane number is set as the value of the control cetane number.

[0057] After that, when refuel is performed at time t4, the value of the refueling-based determined cetane number is updated. On another hand, the value of the misfire detection-based cetane number is reset to the initial value in response to the refueling. As a result, the value of the refueling-based determined cetane number becomes less than the value of the misfire detection-based cetane number and the value of the torque-based determined cetane number, so that, from time t4, the presently updated value of the refueling-based determined cetane number is set as the value of the control cetane number.

[0058] Then, at time t5, the aforementioned execution condition is satisfied, and the process of calculating the torque-based determined cetane number is carried out. In this calculation process, the torque-based determined cetane number is calculated to be the same as that previously calculated. Depending on the value of the torque-based determined cetane number that is calculated at this time, the value of the refueling-based determined cetane number updated due to the refueling performed at the time t4 is reset to the initial value. Then, as a result, the value of the refueling-based determined cetane number becomes larger than the value of the torque-based determined cetane number, so that the value of the torque-based determined cetane number is the least of the three estimated values of the cetane number. Therefore, from time t5, the value of the torque-based determined cetane number is set as the value of the control cetane number.

[0059] Then, at time t6, the execution condition is satisfied again, and the process of calculating the torque-based determined cetane number is performed again. As a result, the value of the torque-based determined cetane number is increased. Then, from time t6, the increased value of the torque-based determined cetane number is set as the value of the control cetane number.

[0060] According to the engine control apparatus of the embodiment described above, the following effects can be achieved. In the embodiment, the control cetane number for use in the engine control is set to the estimated value of the cetane number which indicates the least of the three estimated values of the cetane value (the misfire detection-based cetane number, the refueling-based determined cetane number and the torque-based determined cetane number) found by using the individually different estimation logics. Therefore, even if the estimated values of the cetane number of the fuel differ from each other, the control hunting is restrained. Furthermore, since the estimated value of the cetane number that indicates the least of the estimated values of the cetane number, it is possible to secure a certain robustness against the occurrence of misfire resulting from low ignition quality of fuel. Hence, according to the embodiment, even in the case where a plurality of estimation methods are employed to estimate the ignition quality of the presently used fuel, it is possible to restrain the control hunting and suitably perform the engine control.

[0061] In the embodiment, if the torque-based determined cetane number has been calculated to be the same value consecutively a predetermined number of times, detection of the torque-based determined cetane number is stopped from being further performed. The detection of the torque-based determined cetane number is performed by injecting fuel during a deceleration-time fuel cut during which fuel injection is normally not performed, and therefore results in consumption of fuel that is normally not needed and production of white smoke. In the embodiment, at the time point when it is determined that the value of the torque-based determined cetane number has become substantially fixed, the detection of the torque-based determined cetane number is stopped being performed. Therefore, the fuel consumption for the detection and the production of white smoke associated with the detection can be suitably restrained.

[0062] In the embodiment, the value of the misfire detection-based cetane number is decreased according to detection of misfire, and the value of the control cetane number is set to a value that is less than or equal to the value of the misfire detection-based cetane number. Then, the decreased value of the misfire detection-based cetane number is maintained until refueling is performed. Therefore, in the embodiment, even in the case where the value of the refueling-based determined cetane number and/or the value of the torque-based determined cetane number is large, the control cetane number is set small if misfire occurs. Hence, even when the destabilization of combustion that has resulted in misfire is not a result of low ignition quality of fuel, the engine control can be performed so that occurrence of misfire can be suitably restrained. On another hand, if refueling is performed, the value of the misfire detection-based cetane number is reset in response to the refueling since it is expected that the refueling may dissolve a factor of misfire. Due to this, it is possible to perform an appropriate engine control commensurate with actual circumstances regarding combustion stability.

[0063] In this embodiment, on the basis of the time waveform of the fuel injection rate found from results of detection of the fuel pressure in the injectors 16, the control apparatus finds the actual fuel injection timing and the actual amount of fuel injection, and corrects the produced torque (the amount of change in rotation ΣΔΝΕ). Since the amount of fuel injection for detection of the cetane number of the fuel is small, even a slight Shift in the fuel injection timing and/or the fuel injection amount greatly affects the results of estimation of the cetane number. In the embodiment, however, the actual fuel injection timing and the actual amount of fuel injection are accurately found, and the results of computation of the produced torque are corrected. Therefore, the estimation of the cetane number based on the magnitude of the engine torque produced by combustion of fuel can be more accurately performed.

[0064] In the embodiment, the timing of the fuel injection for detecting the cetane number of the fuel is adjusted according to the engine rotation speed. Concretely, the timing of the fuel injection for detecting the cetane number is further advanced as the engine rotation speed is higher. Therefore, it is possible to suitably restrain the influence that the change in the produced torque depending on the engine rotation speed has on the results of estimation of the cetane number of fuel. [0065] In the embodiment, the timing of the fuel injection for detecting the cetane number of the fuel is adjusted according to the cylinder wall temperature. Concretely, the timing of the fuel injection for detecting the cetane number is further advanced as the engine coolant temperature, which is an index value of the cylinder wall temperature, is lower. Therefore, it is possible to suitably restrain the influence that the change in the produced torque depending on the cylinder wall temperature has on the results of estimation of the cetane number of fuel.

[0066] In the embodiment, the timing of the fuel injection for detecting the cetane number of the fuel is adjusted according to the intake air pressure. Concretely, the timing of the fuel injection for detecting the cetane number is further advanced as the intake air pressure is lower. Therefore, it is possible to suitably restrain the influence that the change in the produced torque depending on the intake air pressure has on the results of estimation of the cetane number of fuel.

[0067] Incidentally, the foregoing embodiment can also be carried out with the following modifications. Although in the foregoing embodiment, it is detected that refueling has been performed on the basis of an increase in the amount of fuel remaining in the tank 10 which is detected by the fuel gauge 11, performance of refueling may also be detected in other manners, for example, by monitoring the open/closure of the fuel cap.

[0068] Although in the embodiment, the magnitude of the engine torque produced by combustion of the fuel is found from the amount of change in the engine rotation speed, the magnitude of the engine torque produced by combustion of the fuel may also be found from other parameters, such as the amount of increase in the in-cylinder pressure that is associated with the combustion, or the like.

[0069] Although in the embodiment, the timing of the fuel injection for detection of the cetane number of the fuel is adjusted according to the intake air pressure, the adjustment of the fuel injection timing may be omitted if the intake air pressure at the time of detection of the cetane number can be assumed to be substantially constant or if the changes in the produced torque that are caused by differences in the intake air pressure are sufficiently small.

.[0070] Although in the embodiment, the timing of the fuel injection for detection of the cetane number of the fuel is adjusted according to the cylinder wall temperature, the adjustment of the fuel injection timing may be omitted if the cylinder wall temperature at the time of detection of the cetane number can be assumed to be substantially constant or if the changes in the produced torque that are caused by differences in the cylinder wall temperature are sufficiently small.

[0071] Although in the embodiment, the timing of the fuel injection for detection of the cetane number of the fuel is adjusted according to the engine rotation speed, the adjustment of the fuel injection timing may be omitted if the engine rotation speed at the time of detection of the cetane number can be assumed to be substantially constant or if the changes in the produced torque that are caused by differences in the engine rotation speed are sufficiently small.

[0072] In the foregoing embodiment, change in the fuel pressure in each injector 16 at the time of the fuel injection for detecting the cetane number is detected, and, from a result of the detection, the actual fuel injection timing and the actual amount of fuel injection are found. Then, the magnitude of the engine torque produced by combustion of the fuel (the amount of change in rotation ΣΔΝΕ) is corrected according to the actual fuel injection timing and the actual fuel injection amount that are found in the foregoing manner, before being used for estimation of the cetane number. However, in the case where the amount of fuel injection or the fuel injection timing can be controlled with sufficiently high accuracy or the case where the change in the produced torque due to a shift in the amount and/or timing of fuel injection is sufficiently small, it is possible to more accurately perform the estimation of the cetane number of the fuel based on the magnitude of the engine torque produced by combustion of the fuel without a need to perform the foregoing correction.

[0073] In the foregoing embodiment, when the value of the misfire detection-based cetane number of the fuel is temporarily decreased in response to detection of misfire, the decreased value of the misfire detection-based cetane number is maintained until refueling is performed, so that robustness against misfire is suitably secured. In the case where instead of the robustness against misfire, other engine performances, such as fuel economy performance or output performance, are given priority, it is permissible to increase the value of the misfire detection-based cetane number when detection of misfire stops.

[0074] In the foregoing embodiment, if the torque-based determined cetane number of fuel has been calculated to be the same value consecutively a predetermined number of times, detection of the torque-based determined cetane number is stopped from being further performed. However, when the fuel consumption by the fuel injection for detecting the cetane number of the fuel and the production of white smoke associated with that fuel injection can be sufficiently ignored, detection of the torque-based determined cetane number may be continued even if the torque-based determined cetane number has been calculated to be the same value consecutively a predetermined number of times.

[0075] Although in the embodiment, the torque-based determined cetane number is detected during a deceleration-time fuel cut, the torque-based determined cetane number may also be detected during a period other than the deceleration-time fuel cut.

[0076] Although the embodiment employs the injectors 16 each of which contains the fuel pressure sensor 17 and operates by using the pressure-electric actuator 39, it is also permissible to employ injectors that use another actuating (or driving) method or injectors that do not have the fuel pressure sensors 17.

[0077] Next, technical ideas that can be conceived or grasped from the foregoing embodiment and its modifications will be described below along with effects of the technical ideas. The estimation of the ignition quality of fuel based on the amount of refueling may also be performed on an assumption that the fuel supplied by refueling has the lowest ignition quality of all the fuels that are considered to be used.

[0078] The estimation of the ignition quality of the fuel based on the magnitude of the engine torque may also be performed by computing an estimated value of an index value of the ignition quality on the basis of a relation among the engine rotation speed at the time of the fuel injection performed for the estimation, the magnitude of the engine torque produced by combustion of the fuel injected by the aforementioned fuel injection, and the timing of that fuel injection.

[0079] The estimation of the ignition quality of fuel based on the magnitude of the engine torque may also be performed by using the amount of change in the engine rotation speed caused by combustion of the fuel as an index value of the magnitude of the engine torque.

Claims

1. An engine control apparatus characterized in that the engine control apparatus performs a plurality of estimations of ignition quality of fuel by using a plurality of different estimation logics corresponding one-to-one to the estimations, and performs an engine control based on a result of an estimation that indicates lowest ignition quality among the results of the estimations.

2. The engine control apparatus according to claim 1, wherein the engine control apparatus performs the estimation of the ignition quality of the fuel based on a circumstance of occurrence of misfire, the estimation of the ignition quality of the fuel based on amount of refueling and the estimation of the ignition quality of the fuel based on magnitude of engine torque produced by combustion of the fuel.

3. An engine control method characterized by comprising:

performing a plurality of estimations of ignition quality of fuel by using a plurality of different estimation logics corresponding one-to-one to the estimations; and

performing an engine control based on a result of an estimation that indicates lowest ignition quality among the results of the estimations.