JP5742772B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control apparatus that estimates the ignitability of fuel and performs engine control based on the estimation result.

  A diesel engine ignites and burns injected fuel by compression. Some commercially available diesel oils used as fuel by diesel engines have different components and vary in ignitability. The ignitability of fuel has a great influence on the misfire occurrence status and output. Therefore, to improve the output performance, fuel efficiency, and emission performance of diesel engines, check the ignitability of the fuel in use and adjust the engine control execution mode, such as the timing and amount of fuel injection, according to the results. There is a need to.

  By the way, the ignitability of diesel oil, the fuel for diesel engines, is evaluated by the cetane number. The cetane number of the gas oil used as a sample is expressed as a volume percentage of cetane contained in a mixture of cetane and α-methylnaphthalene that exhibits the same ignitability as the sample.

  Various logics have been proposed for estimating the cetane number of fuel. For example, Patent Document 1 discloses logic for estimating the cetane number of fuel based on the relationship between the rotational fluctuation of a diesel engine after fuel injection, the fuel injection timing, and the engine speed at the time of fuel injection.

JP 2011-256840 A

  By the way, it is conceivable to perform estimation of fuel ignitability using a plurality of different estimation logics. In such a case, a different estimation result may be output for each estimation logic due to a difference in estimation principle. As a result, engine control hunting may occur.

  For example, the estimation by the estimation logic A gives an estimation result that the cetane number of the fuel in use is low, and the estimation by the estimation logic B gives an estimation result that the cetane number of the fuel in use is high. . In this case, after the estimation by the estimation logic A is performed, engine control assuming the use of a low cetane number fuel is performed, and after the estimation by the estimation logic B is performed, an engine assuming the use of a high cetane number fuel is performed. Control will be implemented. Therefore, every time estimation by each estimation logic is performed, the engine control mode is switched, and the control becomes unstable.

  The present invention has been made in view of such circumstances, and the problem to be solved is suitable for a case where a plurality of different estimation logics are employed for estimating the ignitability of fuel without causing control hunting. Another object of the present invention is to provide an engine control apparatus capable of performing engine control.

The engine control equipment for solving the above problems, different estimation logic as the estimation of the cetane number of fuel used, respectively, and the estimation of the cetane number of the fuel based on the occurrence of a misfire, the cetane number of the fuel based on the amount of oil of the estimated, and the estimation of the cetane number of the fuel based on the magnitude of the engine torque produced by combustion of fuel, performs, among the results of those estimates, the engine control based on the cetane number, which is the lowest Like to do.

If the ignitability of the fuel is low, misfiring is likely to occur. Therefore, the ignitability of the fuel in use can be estimated from the misfire occurrence state. Further, after refueling, the composition of the fuel changes and the ignitability of the fuel changes. The maximum change amount of the ignitability at this time can be obtained from the amount of fuel supply. Furthermore, if the ignitability of the fuel decreases, the engine torque generated by the combustion of the unit mass of fuel changes, so the ignitability of the fuel in use should also be estimated from the magnitude of the engine torque generated by the fuel combustion. Can do. Therefore, in the above configuration, the cetane number is estimated as the ignitability of the fuel in use based on the misfire occurrence state, the amount of fuel supply, and the magnitude of the engine torque generated by the combustion of the fuel.

Then, if their estimation result is different, of those estimation result, the engine control based on the cetane number, which is the lowest is performed. Therefore, control hunting does not occur even if different estimation results are output. Further, in order to perform adopted by the engine control cetane most are low contemplated, you are possible to suitably ensure robustness against misfire due to the ignition of low fuel. Therefore, according to the above configuration, even when a plurality of estimation methods are employed for estimating the cetane number of the fuel in use, the engine control can be suitably performed without causing control hunting.
In one example of the engine control device, the estimation of the cetane number of the fuel based on the magnitude of the engine torque is stopped when the cetane number is the same value continuously for a predetermined number of times or more.
Further, in the example of the engine control device, the estimation of the cetane number of the fuel based on the occurrence of the misfire and the estimation of the cetane number of the fuel based on the fuel supply amount may be performed when the cetane number of the fuel is estimated. Fuel injection is not carried out.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows typically the whole structure of the engine control apparatus concerning one embodiment of this invention. Sectional drawing which shows the side part sectional structure of the injector provided in the diesel engine to which the embodiment is applied. The graph which shows an example of the time waveform of a fuel injection rate. The flowchart which shows the process sequence of the torque determination cetane number calculation routine employ | adopted as the said embodiment. (A) is a graph which shows transition of the engine speed before and after execution of fuel injection for cetane number detection, (b) is transition of the rotational speed difference before and after execution of fuel injection for cetane number detection It is a graph which shows. The flowchart which shows the process sequence of the control cetane number setting routine employ | adopted as the said embodiment. The time chart which shows an example of the transition aspect of the misfire detection cetane number, the oil supply determination cetane number, the torque determination cetane number, and the control cetane number in the engine control apparatus of the embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment of an engine control device according to the present invention will be described in detail with reference to FIGS. In addition, the control apparatus of this Embodiment is applied to the vehicle-mounted diesel engine.

  As shown in FIG. 1, a fuel gauge 11 that measures the remaining amount of fuel therein is disposed in a fuel tank 10 of a diesel engine to which the control device of the present embodiment is applied. The fuel tank 10 is connected to a fuel supply passage 12 for sending fuel to be supplied to the diesel engine. A high pressure fuel pump 13 is provided in the middle of the fuel supply passage 12 to pump up the fuel in the fuel tank 10 and then pressurize and discharge the fuel. The downstream end of the oil supply passage 12 is connected to a common rail 14 that stores pressurized fuel. The common rail 14 is connected to an injector 16 of each cylinder of the diesel engine. Each injector 16 is provided with a fuel pressure sensor 17 for detecting the fuel pressure inside the injector 16. Each injector 16 is connected to a return passage 18 for returning surplus fuel to the fuel tank 10.

  Such a diesel engine is controlled by an electronic control unit 19. The electronic control unit 19 includes a microcomputer that performs various arithmetic processes related to engine control. In addition, the electronic control unit 19 is provided with an input circuit to which signals of various sensors that detect the operation status of the diesel engine are input. The fuel gauge 11 and the fuel pressure sensor 17 are connected to this input circuit. The input circuit also includes an intake pressure sensor 20 that detects the intake pressure of the diesel engine, a rotation speed sensor 21 that detects the rotation speed of the diesel engine, a water temperature sensor 22 that detects the cooling water temperature of the diesel engine, and the amount of depression of the accelerator pedal. An accelerator pedal sensor 23 for detecting the vehicle speed and a vehicle speed sensor 24 for detecting the vehicle speed are also connected. Further, the electronic control unit 19 is provided with an actuator drive circuit for driving each part of the diesel engine. Such a drive circuit includes a circuit for driving the injector 16 of each cylinder.

  Then, the more detailed structure of the injector 16 provided in each cylinder of such a diesel engine is demonstrated. The diesel engine employs an electrically driven injector as the injector 16.

  As shown in FIG. 2, the injector 16 includes a housing 30 formed in a hollow cylindrical shape. A needle valve 31 is disposed inside the housing 30 so as to be capable of reciprocating in the vertical direction in the figure. Further, a spring 32 that constantly urges the needle valve 31 downward in the drawing is disposed inside the housing 30 in the upper portion of the needle valve 31 in the drawing.

  In the housing 30, two fuel chambers with the needle valve 31 interposed therebetween, that is, a nozzle chamber 33 positioned below the needle valve 31 in the drawing and a pressure positioned above the needle valve 31 in the drawing. A chamber 34 is formed.

  The nozzle chamber 33 is formed with an injection hole 35 that communicates the inside with the outside of the housing 30. The nozzle chamber 33 is connected to an introduction passage 36 formed inside the housing 30. The introduction passage 36 is connected to the above-described common rail 14 (FIG. 1). The fuel is supplied from the common rail 14 to the nozzle chamber 33 through the introduction passage 36.

  On the other hand, the pressure chamber 34 is connected to the nozzle chamber 33 via the communication passage 37 and to the return passage 18 described above via the discharge passage 38. In addition, a valve body 40 that is driven by a piezoelectric actuator 39 formed by stacking piezoelectric elements such as piezoelectric elements is disposed inside the pressure chamber 34. The pressure chamber 34 is selectively communicated with one of the communication passage 37 and the discharge passage 38 by driving the valve body 40.

  Further, the above-described fuel pressure sensor 17 is integrally provided on the upper portion of the injector 16 in the drawing. The fuel pressure sensor 17 is configured to detect the pressure of the fuel in the introduction passage 36.

  Such an injector 16 operates as follows. When the drive voltage is not applied, the piezoelectric actuator 39 is in a state where its entire length is reduced, and the valve body 40 is positioned at a position where the pressure chamber 34 is communicated with the communication passage 37 and the pressure chamber 34 is shut off from the discharge passage 38. Let At this time, the nozzle chamber 33 and the pressure chamber 34 communicate with each other, and the internal pressures thereof are substantially balanced. Therefore, the needle valve 31 at this time is displaced downward in the figure by the urging force of the spring 32 and closes the injection hole 35. Therefore, fuel is not injected from the injector 16 at this time.

  On the other hand, when a driving voltage is applied to the piezoelectric actuator 39, its entire length is extended, the pressure chamber 34 is shut off from the communication path 37, and the valve body 40 is positioned at a position where the pressure chamber 34 communicates with the discharge path 38. At this time, the fuel is discharged from the pressure chamber 34 and the pressure inside the pressure chamber 34 is reduced, so that the pressure in the nozzle chamber 33 becomes higher than the pressure in the pressure chamber 34. Therefore, the needle valve 31 at this time is displaced upward in the figure by the urging force of the spring 32 due to the pressure difference therebetween, that is, away from the position where the injection hole 35 is blocked. Accordingly, fuel is injected from the injector 16 at this time.

  In the present embodiment configured as described above, the electronic control unit 19 performs fuel injection control of the diesel engine. Specifically, the electronic control unit 19 determines the target value (target fuel injection amount) of the fuel injection amount from the engine rotation speed, the amount of depression of the accelerator pedal, and the estimated value (control cetane number) of the cetane number of the fuel in use. Is calculated. The electronic control unit 19 calculates a target value for the fuel injection timing and the fuel injection time from the target fuel injection amount and the engine speed. The electronic control unit 19 controls the fuel injection by applying a driving voltage to the piezoelectric actuator 39 of the injector 16 according to the calculated target value.

  Further, in the present embodiment, in such fuel injection control, the electronic control unit 19 performs the fuel injection rate (injection per unit time) of the injector 16 based on the fuel pressure detected by the fuel pressure sensor 17 installed in the injector 16. Control to form a time waveform of the amount of fuel to be carried out. This control is performed in the following manner.

  When the injector 16 starts to be separated (lifted) from the injection hole 35 of the needle valve 31 in response to application of a driving voltage to the piezoelectric actuator 39, the fuel pressure in the nozzle chamber 33 increases with the increase in the lift amount. Gradually decreases. Further, when the lift amount of the needle valve 31 decreases in accordance with the stop of application of the drive voltage, the fuel pressure in the nozzle chamber 33 gradually increases with the decrease. Therefore, from the fuel pressure detected by the fuel pressure sensor 17, the lift start timing of the needle valve 31 (valve opening drive start timing Tos), the time when the fuel injection rate becomes maximum (maximum injection rate arrival time Toe), the fuel The timing at which the injection rate starts to decrease (injection rate decrease start timing Tcs) and the lift end timing (minimum lift amount arrival timing Tce) of the needle valve 31 can be specified. And the time waveform of a fuel injection rate as shown in FIG. 3 can be calculated | required from those specified time. From the waveform, the actual fuel injection state can be confirmed with extremely high accuracy. In the present embodiment, the electronic control unit 19 obtains the rate of change of the fuel pressure inside the injector 16 (time differential value of the fuel pressure) and obtains each of the above times based on the rate of change.

  In the present embodiment, the electronic control unit 19 estimates the cetane number of the fuel in use, that is, estimates the ignitability of the fuel. Then, by adjusting the control mode such as the fuel injection timing, the fuel injection amount, the EGR amount, and the supercharging rate according to the estimation result, the output performance, fuel consumption performance, and emission performance of the diesel engine are improved. . For example, when the use of fuel with a low cetane number is estimated, changes in the control mode such as increasing the number and amount of pilot injections, accelerating the timing of pilot injection and main injection, reducing the EGR amount, and increasing the supercharging rate Therefore, the occurrence of misfire due to the low ignitability of the fuel is suppressed.

  In the engine control apparatus of the present embodiment, the cetane number is estimated using three estimation logics. That is, there are three types of estimation: cetane number estimation based on misfire, cetane number estimation based on refueling, and cetane number estimation based on engine torque. Hereinafter, details of these three estimation logics will be described.

(Estimation of cetane number based on misfire)
If low cetane number fuel with low ignitability is used, the frequency of misfire increases. Therefore, the cetane number of the fuel in use can be estimated from the misfire occurrence state.

  Specifically, the electronic control unit 19 detects the occurrence of misfire from the fluctuation of the engine speed. When the number of misfire detections reaches a predetermined value, the electronic control unit 19 decreases the estimated cetane number based on the misfire occurrence state, that is, the misfire detection cetane number. The misfire detection cetane number is reset to the initial value when refueling is performed. The number of misfire detections is cleared to “0” for each refueling.

(Estimation of cetane number based on refueling)
After refueling, the composition of the fuel in the fuel tank 10 changes and the cetane number of the fuel also changes. The maximum value of the change can be obtained from the cetane number of the fuel before fueling, the amount of fueling, and the like.

  Specifically, when it is confirmed that refueling has been performed from the increase in the remaining amount of fuel in the fuel tank 10, the electronic control unit 19 determines that the fuel that has been refueled has a cetane number of the assumed fuel used. Assuming the lowest fuel, the cetane number of the fuel after refueling is estimated. The cetane number estimated here, that is, the oil supply determination cetane number Cr is calculated based on the following equation (1). In the following equation (1), “Fb” represents the remaining amount of fuel in the fuel tank 10 before refueling (the remaining amount of fuel before refueling), “Fr” represents the amount of fuel that has been refueled (refueling amount), and “Fa” represents The fuel remaining amount (fuel remaining amount after refueling) in the fuel tank 10 after refueling is shown. “Cb” is an estimated value of the cetane number of the fuel in the fuel tank 10 before refueling (the cetane number before refueling), and “Cm” is an assumed minimum value of the cetane number of the fuel used (the minimum cetane number). Each is shown.

Cr = (Cb × Fa + Cm × Fr) / Fa (1)

The refueling determination cetane number is calculated when refueling is confirmed. Then, the value of the fuel supply determination cetane number is reset to the initial value when an estimation result of the cetane number based on the magnitude of the engine torque generated after fuel injection is obtained.

(Estimation of cetane number based on engine torque)
The higher the ignitability of the fuel, the less unburned fuel remains, and the engine torque generated after fuel injection increases. Therefore, the electronic control unit 19 performs a small amount of fuel injection when the execution condition described later is satisfied, obtains the magnitude of the engine torque (generated torque) generated by the combustion of the injected fuel, and determines the magnitude from that magnitude. Estimated cetane number of fuel.

  Specifically, the estimation of the cetane number (torque determination cetane number) based on the magnitude of the generated torque after fuel injection is performed through the processing of the torque determination cetane number calculation routine shown in FIG. The processing of this routine is repeatedly executed at regular control cycles by the electronic control unit 19 during operation of the diesel engine.

When the processing of this routine is started, first, in step S100, it is determined whether or not an execution condition for torque determination cetane number calculation is satisfied. As the execution condition, all of the following (A) to (C) are satisfied.
(A) The fuel cut at the time of deceleration of the diesel engine, which is performed in response to the release of the accelerator operation (depressing the accelerator pedal) while the vehicle is running, is being executed.
(B) The total fuel injection amount after refueling is equal to or greater than the specified value α. The prescribed value α is set to a value larger than the total amount of fuel that can be filled in the fuel path from the fuel tank 10 to the injector 16. That is, the establishment of this condition (b) means that after refueling, the fuel in the fuel path is replaced with new fuel from the fuel tank 10 after refueling.
(C) The torque determination cetane number calculated by this routine is not the same value continuously for the specified number of times. If the calculated value of the torque determination cetane number according to this routine is the same value continuously for a certain number of times or more, it is considered that the calculated value of the torque determination cetane number will not change thereafter. Therefore, in this embodiment, in such a case, calculation of the torque determination cetane number is stopped. The count of the number of times that the calculated torque determination cetane number is continuously the same is cleared when refueling is confirmed.

  If the execution condition is not satisfied (NO), the process of this routine is terminated as it is, and if it is satisfied (YES), the process proceeds to step S101. In step S101, the fuel injection timing for cetane number detection is set based on the engine speed, the engine coolant temperature, and the intake pressure. The reason why the engine speed, the engine coolant temperature, and the intake pressure are used for calculating the fuel injection timing here is as follows.

  The amount of unburned fuel varies depending on the fuel injection timing in addition to the ignitability of the fuel. If the fuel injection timing is earlier, the time from when the fuel is injected until the in-cylinder pressure or the in-cylinder temperature decreases and combustion is no longer established becomes longer. Therefore, if the fuel injection timing is earlier, the combustion will continue for a longer time, and the remaining unburned fuel will be reduced. On the other hand, if the fuel injection timing is late, the above time is shortened and the duration of combustion is also shortened, so that the amount of unburned fuel increases. On the other hand, the time from when the fuel is injected until the in-cylinder pressure or in-cylinder temperature decreases decreases as the engine speed increases. Therefore, in order to make the combustion conditions uniform, it is necessary to advance the fuel injection timing for detecting the cetane number as the engine speed increases.

  When the cylinder wall temperature is low, the maximum value (peak temperature) of the in-cylinder temperature in the engine compression stroke is low. Further, when the intake pressure is low, the maximum value (peak pressure) of the in-cylinder pressure in the engine compression stroke is low. As the peak temperature or peak pressure is lower, the time during which the cylinder is in a high temperature and high pressure state is shortened, and the duration of combustion is shortened. Therefore, in order to make the combustion conditions uniform, it is necessary to advance the timing of fuel injection for cetane number detection as the cylinder wall temperature is lower or the intake pressure is lower.

  Therefore, in this embodiment, in order to make the combustion conditions of the injected fuel uniform when detecting the cetane number, the fuel injection timing is adjusted according to the engine rotational speed, the cylinder wall temperature, and the intake pressure at that time. I am doing so. Specifically, in this embodiment, the higher the engine speed, the earlier the fuel injection timing for cetane number detection. Similarly, in the present embodiment, the lower the engine coolant temperature that is the index value of the cylinder wall temperature, the earlier the fuel injection timing for cetane number detection. Furthermore, in this embodiment, the lower the intake pressure, the earlier the fuel injection timing for cetane number detection.

  When the fuel injection timing is set in this way, a prescribed amount of fuel injection is performed at the set timing in the subsequent step S102. In step S103, the magnitude of torque generated by the injection is obtained.

  Calculation of the generated torque in step S103 is performed in the following manner. The electronic control unit 19 obtains the engine rotation speed every predetermined period, and obtains a difference (rotation speed difference ΔNE) between the obtained engine rotation speed and the engine rotation speed obtained before the specified period.

  FIG. 5A shows the transition of the engine speed before and after execution of fuel injection for cetane number detection, and FIG. 5B shows the transition of the rotational speed difference ΔNE at that time. When fuel injection for detecting the cetane number is executed, and engine torque is thereby generated, the engine rotational speed increases or decreases, and the rotational speed difference ΔNE increases. The time integral value (corresponding to the area of the hatched portion in FIG. 5B) of the increase in the rotational speed difference ΔNE increases as the generated torque increases. Therefore, in the present embodiment, the time integral value of the increase in the rotational speed difference ΔNE is calculated as the rotational fluctuation amount ΣΔNE, and the value is used as an index value of the generated torque.

  Next, in step S104, the actual fuel injection timing and fuel injection amount are obtained from the time waveform of the injection rate in the fuel injection in step S102, and the command value and actual value of the fuel injection timing and fuel injection amount are calculated. Errors (injection timing error, injection amount error) are respectively calculated. Based on the injection timing error and the injection amount error, the rotational fluctuation amount ΣΔNE is corrected. This correction is performed in order to reduce the influence of the injection timing error or the injection amount error on the cetane number estimation result by correcting the amount corresponding to the change in the engine torque caused by the injection timing error or the injection amount error. Is called. Specifically, the greater the injection timing error toward the advance side (the side at which the injection timing is advanced), the greater the generated torque, so the rotational fluctuation amount ΣΔNE is largely corrected to decrease. Further, since the generated torque increases as the injection amount error to the increase side increases, the rotational fluctuation amount ΣΔNE is largely corrected to decrease.

  In subsequent step S105, a torque determination cetane number is calculated based on the corrected rotational fluctuation amount ΣΔNE and the engine rotational speed at the time of fuel injection execution. The microcomputer of the electronic control unit 19 stores the rotational fluctuation amount ΣΔNE and the relationship between the engine rotational speed and the cetane number of the fuel, which are obtained in advance by experiments, and the calculation here is based on the stored relationship. Based on. Then, after the calculation of the torque determination cetane number, the current processing of this routine is terminated.

(Setting of control cetane number)
As described above, in this embodiment, the cetane number of the fuel in use is estimated using three different estimation logics. Since these estimation logics have different estimation principles, discrepancies may occur in the cetane number estimation results. In this embodiment, the estimated value of cetane number actually used for engine control, that is, the control cetane number is set in the following manner so that control hatching does not occur even in such a case.

  The setting of the control cetane number in the present embodiment is performed through the processing of the control cetane number setting routine shown in FIG. The processing of this routine is repeatedly executed at regular control intervals by the electronic control unit 19 during operation of the diesel engine.

  When the processing of this routine is started, first, in step S200, it is determined whether or not any of the three cetane number estimated values, that is, any of the misfire detection cetane number, the fuel supply determination cetane number, and the torque determination cetane number is updated. Determined. Here, if none of the values has been updated (NO), the processing of this routine is terminated as it is. In this case, the control cetane number is maintained at the previous value.

  On the other hand, if any of the values has been updated (S200: YES), in step S201, the smallest value among the misfire detection cetane number, the fuel supply determination cetane number, and the torque determination cetane number, that is, 3 Of the estimation results of the cetane number by the two estimation logics, the estimation result having the lowest cetane number is set as the control cetane number. Thereafter, the processing of this routine is terminated.

  Next, the operation of this embodiment will be described with reference to FIG. The figure shows an example of transition modes of misfire detection cetane number, oil supply determination cetane number, torque determination cetane number, and control cetane number in the engine control apparatus of the present embodiment.

  Prior to time t1, the torque determination cetane number is the lowest value among the misfire detection cetane number, the fuel supply determination cetane number, and the torque determination cetane number. Therefore, during this period, the value of the torque determination cetane number is set to the value of the control cetane number.

  When refueling is performed at time t1, the value of the oil supply determination cetane number is updated. As a result, the value of the oil supply determination cetane number is the torque determination cetane number that has been the smallest value among the estimated cetane numbers so far. Is below the value of. Therefore, from this time t1, the value of the fuel supply determination cetane number is set to the value of the control cetane number.

  At the subsequent time t2, the execution condition described above is satisfied, and the estimation of the cetane number (calculation of the torque determination cetane number) is performed based on the engine torque generated by the fuel combustion. Here, the same value as before is calculated as the value of the torque determination cetane number, and there is no change in the value of the torque determination cetane number. On the other hand, depending on the calculation of the torque determination cetane number at this time, the value of the fuel supply determination cetane number updated by the fuel supply at time t1 is reset to the initial value. As a result, the value of the oil supply determination cetane number exceeds the value of the torque determination cetane number, and the torque determination cetane number is the lowest value among the three estimated cetane numbers. Therefore, from this time t2, the value of the torque estimation cetane number is set to the value of the control cetane number.

  When the occurrence of misfire is detected at time t3 thereafter, the value of the misfire detection cetane number is decreased. As a result, the misfire detection cetane number value is lower than the torque estimation cetane number value that has been the smallest among the cetane number estimated values so far. Therefore, from this time t3, the misfire detection cetane number value is set to the control cetane number value.

  Furthermore, when refueling is performed at time t4 thereafter, the value of the refueling determination cetane number is updated. On the other hand, the value of the misfire detection cetane number is reset to an initial value in accordance with refueling. As a result, the value of the fuel supply determination cetane number falls below the value of the misfire detection cetane number and the value of the estimated torque cetane number. From this time t4, the value of the oil supply determination cetane number updated here is controlled. Set to the value of cetane number.

  At the subsequent time t5, the above-described execution condition is satisfied, and the torque determination cetane number calculation process is performed. In the calculation process at this time, the same value as before is calculated as the value of the torque determination cetane number. On the other hand, by calculating the torque determination cetane number at this time, the value of the fuel supply determination cetane number updated by the fuel supply at time t4 is reset to the initial value. As a result, the value of the oil supply determination cetane number exceeds the value of the torque determination cetane number, and the torque determination cetane number is the lowest value among the three estimated cetane numbers. Therefore, from this time t5, the value of the torque estimation cetane number is set to the value of the control cetane number.

  At the subsequent time t6, the above execution condition is satisfied again, and the torque determination cetane number calculation process is performed again. As a result, the value of the torque determination cetane number is increased. Then, after this time t6, the increased torque estimated cetane number value is set as the control cetane number value.

According to the engine control apparatus of the present embodiment described above, the following effects can be obtained.
(1) In the present embodiment, when the cetane number is the lowest among the three cetane number estimated values (misfire detection cetane number, refueling determination cetane number, torque determination cetane number) obtained using different estimation logics, The estimated value is set as the control cetane number used for engine control. Therefore, even if the values of the cetane number estimated values are different, control hatching does not occur. Moreover, since the estimated value with the lowest cetane number is used for engine control, robustness against misfire due to low ignitability of fuel can be suitably ensured. Therefore, according to the present embodiment, even when a plurality of estimation methods are employed for estimating the ignitability of the fuel in use, the engine control can be suitably performed without causing control hunting.

  (2) In the present embodiment, when the calculated value of the torque determination cetane number is the same value continuously for a specified number of times, the detection of the torque determination cetane number thereafter is stopped. The detection of the torque determination cetane number is originally performed by injecting fuel during fuel cut during deceleration when fuel injection is not performed, and thus causes unnecessary consumption of fuel and generation of white smoke. In this respect, in the present embodiment, when it is determined that the value of the torque determination cetane number is almost confirmed, the subsequent detection of the torque determination cetane number is terminated, so that fuel consumption for the detection and white Smoke generation can be suitably suppressed.

  (3) In the present embodiment, the value of the misfire detection cetane number is decreased in accordance with the detection of the misfire, and the value of the control cetane number is made equal to or less than the value of the misfire detection cetane number. And the value of the reduced misfire detection cetane number is maintained until refueling is performed. In this embodiment, even if the fuel supply determination cetane number and the torque determination cetane number are large, the control cetane number is reduced if a misfire occurs. Therefore, even when the instability of combustion that causes misfire is not caused by the low ignitability of the fuel, the engine control can be performed so as to suppress the occurrence of a suitable misfire. On the other hand, if refueling is performed, it is expected that the cause of misfire will be eliminated, so by resetting the misfire detection cetane number according to refueling, appropriate engine control according to the actual situation of combustion stability It can be performed.

  (4) In the present embodiment, the actual fuel injection timing and the fuel injection amount are obtained based on the time waveform of the fuel injection rate obtained from the detection result of the fuel pressure in the injector 16, and the generated torque (rotational fluctuation amount) is obtained. (ΣΔNE) is corrected. Since the fuel injection amount for detecting the cetane number is very small, a slight shift in the fuel injection timing and the fuel injection amount greatly affects the estimation result of the cetane number. In this respect, in the present embodiment, the actual fuel injection timing and the fuel injection amount are accurately obtained and the calculation result of the generated torque is corrected. Therefore, the cetane number based on the magnitude of the engine torque generated by the combustion of the fuel Can be estimated more accurately.

  (5) In this embodiment, the fuel injection timing for detecting the cetane number is adjusted according to the engine speed. Specifically, the higher the engine speed, the earlier the fuel injection timing for cetane number detection. Therefore, it is possible to suitably suppress the influence of the change in the generated torque due to the engine speed on the estimation result of the cetane number.

  (6) In this embodiment, the fuel injection timing for detecting the cetane number is adjusted according to the cylinder wall temperature. Specifically, the lower the engine coolant temperature, which is the index value of the cylinder wall temperature, the earlier the fuel injection timing for cetane number detection. Therefore, it is possible to suitably suppress the influence of the change in the generated torque due to the cylinder wall temperature on the estimation result of the cetane number.

  (7) In this embodiment, the fuel injection timing for cetane number detection is adjusted according to the intake pressure. Specifically, the lower the intake pressure, the earlier the fuel injection timing for cetane number detection. Therefore, it is possible to suitably suppress the influence of the change in the generated torque due to the intake pressure on the estimation result of the cetane number.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, it has been confirmed that refueling has been performed from the increase in the remaining amount of fuel detected by the fuel gauge 11, but refueling may be confirmed by other methods such as opening and closing the fuel cap. Anyway.

  In the above embodiment, the magnitude of the engine torque generated by the combustion of fuel is obtained from the fluctuation amount of the engine rotation speed, but it is obtained from other parameters such as the increase in in-cylinder pressure accompanying combustion. Also good.

  In the above embodiment, the fuel injection timing for detecting the cetane number is adjusted according to the intake pressure. However, when the intake pressure at the time of detecting the cetane number is considered to be substantially constant, When the change in the generated torque due to the difference is sufficiently small, such adjustment of the injection timing may be omitted.

  In the above embodiment, the fuel injection timing for cetane number detection was adjusted according to the cylinder wall temperature, but it can be assumed that the cylinder wall temperature at the time of cetane number detection is substantially constant, If the change in the generated torque due to the difference in cylinder wall temperature is sufficiently small, such adjustment of the injection timing may be omitted.

  In the above embodiment, the fuel injection timing for detecting the cetane number is adjusted according to the engine rotation speed, but it can be assumed that the engine rotation speed at the time of cetane number detection is substantially constant, If the change in the generated torque due to the difference in engine speed is sufficiently small, the adjustment of the injection timing may be omitted.

  In the above embodiment, the fluctuation of the fuel pressure in the injector 16 at the time of fuel injection for detecting the cetane number is detected, and the actual fuel injection timing and the actual fuel injection amount are obtained from the detection result. Then, after correcting the magnitude of engine torque (rotational fluctuation amount ΣΔNE) generated by fuel combustion according to the obtained actual fuel injection timing and the actual fuel injection amount, the cetane number is estimated. Yes. However, if the fuel injection amount and fuel injection timing can be controlled with sufficiently high accuracy, or if the change in the generated torque due to deviations in the fuel injection amount and fuel injection timing is sufficiently small, the fuel injection amount and fuel injection timing can be corrected without performing such correction. It is possible to more accurately estimate the cetane number based on the magnitude of the engine torque generated by the combustion.

  -In the above embodiment, once the misfire detection cetane number is decreased in response to detection of misfire, the value is maintained until refueling is performed, so that robustness against misfire is suitably ensured. It was. When priority is given to other engine performance such as fuel efficiency and output performance over robustness against misfire, the misfire detection cetane number may be increased when no misfire is detected.

  In the above embodiment, when the calculated value of the torque determination cetane number is the same value continuously for a specified number of times, detection of the torque determination cetane number is stopped thereafter. However, if fuel consumption due to fuel injection for cetane number detection and the generation of white smoke associated therewith are sufficiently negligible, even if the calculated value is the same value for the specified number of times, detection of torque determination cetane number May be continued.

  In the above embodiment, the torque determination cetane number is detected during the fuel cut during deceleration. However, the torque determination cetane number may be detected in addition to the fuel cut during deceleration.

  In the above embodiment, the fuel pressure sensor 17 is built in and the injector 16 that is operated by the piezoelectric actuator 39 is adopted. However, an injector that employs another driving method or an injector that does not incorporate the fuel pressure sensor 17 is used. You may make it adopt.

Next, technical ideas that can be grasped from the above-described embodiment and its modifications will be described below together with their effects.
(A) The engine according to claim 2, wherein the estimation of the ignitability of the fuel based on the refueling amount is performed on the assumption that the refueled fuel is the fuel having the lowest ignitability among the assumed fuels used. Control device.

  (B) The estimation of the ignitability of the fuel based on the magnitude of the engine torque is based on the engine rotation speed at the time of fuel injection performed for the estimation, and the engine generated by the combustion of the fuel injected by the fuel injection The engine control device according to claim 2 or (a), which is performed by calculating an estimated value of the ignitability index value based on a relationship between a magnitude of torque and a fuel injection timing of the fuel injection.

  (C) The estimation of the ignitability of the fuel based on the magnitude of the engine torque is performed by using the fluctuation amount of the engine rotation speed caused by the combustion of the fuel as an index value of the magnitude of the engine torque. The engine control device according to any one of (a) and (b) above.

  DESCRIPTION OF SYMBOLS 10 ... Fuel tank, 11 ... Fuel gauge, 12 ... Refueling passage, 13 ... High pressure fuel pump, 14 ... Common rail, 16 ... Injector, 17 ... Fuel pressure sensor, 18 ... Return passage, 19 ... Electronic control unit, 20 ... Intake pressure sensor , 21 ... Rotational speed sensor, 22 ... Water temperature sensor, 23 ... Accelerator pedal sensor, 24 ... Vehicle speed sensor, 30 ... Housing, 31 ... Needle valve, 32 ... Spring, 33 ... Nozzle chamber, 34 ... Pressure chamber, 35 ... Injection hole , 36 ... introduction passage, 37 ... communication passage, 38 ... discharge passage, 39 ... piezoelectric actuator, 40 ... valve body.

Claims (3)

As an estimate of fuel cetane number using different estimation logics,
Estimating the cetane number of the fuel based on the misfire occurrence,
Estimating the cetane number of the fuel based on the amount of refueling,
Estimating the cetane number of the fuel based on the magnitude of the engine torque generated by the combustion of the fuel;
It performs, among the results of those estimates, the engine control unit and performs engine control based on the cetane number, which is the lowest.   The estimation of the cetane number of the fuel based on the magnitude of the engine torque is stopped when the cetane number is the same value continuously for a predetermined number of times or more.
The engine control apparatus according to claim 1.   In the estimation of the cetane number of the fuel based on the occurrence state of the misfire and the estimation of the cetane number of the fuel based on the fuel supply amount, the fuel injection for the estimation is not performed when the cetane number of the fuel is estimated.
The engine control apparatus according to claim 1 or 2.