JP2014136994A - Combustion control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion control device capable of realizing appropriate premixed compression ignition combustion even during transient operation of premixed compression ignition combustion or during combustion switching from normal combustion to the premixed compression ignition combustion.SOLUTION: A combustion control device determines a fuel injection quantity on the basis of an engine rotational speed and an accelerator opening, determines fuel injection timing on the basis of the engine rotational speed, the fuel injection quantity, and a combustion method, and then estimates an ignition delay on the basis of an in-cylinder oxygen amount, an in-cylinder gas temperature before fuel injection, the fuel injection timing, the engine rotational speed, a fuel injection pressure, an external temperature, an atmospheric pressure, and a cooling water temperature to obtain an estimated ignition delay τ. A fuel-injection-condition setting unit obtains a target ignition delay τon the basis of the engine rotational speed, the fuel injection quantity, the external temperature, the atmospheric pressure, and the cooling water temperature, calculates an ignition delay deviation Δτbetween the estimated ignition delay τ and the target ignition delay τ, and determines the fuel injection quantity and the fuel injection timing of preliminary injection if the estimated ignition delay τ is shorter than the target ignition delay τby a predetermined amount or more.

Description

  The present invention relates to a combustion control device for an engine that performs premixed compression ignition (PCCI) combustion.

  As an engine combustion control device that performs premixed compression ignition combustion, for example, the one described in Patent Document 1 is known. The combustion control device described in Patent Document 1 detects the actual ignition timing, compares the actual ignition timing with the target ignition timing value in the low temperature premixed combustion region, and the actual ignition timing is the end of injection. The ignition timing is controlled to be the same as the timing or retarded from the injection end timing.

Japanese Patent Laid-Open No. 11-107820

  However, in the above prior art, since the ignition timing is feedback-controlled, there is a control delay at the time of transient operation of premixed compression ignition combustion or when switching from normal combustion (diffusion combustion) to premixed compression ignition combustion. The ignition timing control must be unstable. For this reason, for example, the ignition delay may be shorter than the target value, which may cause deterioration of combustion noise, an increase in NOx emission, torque fluctuation, and the like.

  An object of the present invention is to provide a combustion control device capable of realizing appropriate premixed compression ignition combustion even during transient operation of premixed compression ignition combustion or when switching from normal combustion to premixed compression ignition combustion. Is to provide.

  The present invention relates to a combustion control apparatus for an engine that performs premixed compression ignition combustion, a fuel injection valve that injects fuel into a combustion chamber of the engine, and a fuel that determines a fuel injection amount and fuel injection timing of fuel injection including main injection. Injection condition determining means, ignition delay estimating means for estimating an ignition delay due to fuel injection before fuel is injected from the fuel injection valve, target ignition delay setting means for obtaining a target ignition delay when performing premixed compression ignition combustion, An ignition delay deviation calculating means for calculating an ignition delay deviation between the estimated ignition delay obtained by the ignition delay estimating means and the target ignition delay obtained by the target ignition delay setting means, and the estimated ignition delay is greater than the target ignition delay. Pre-injection additional correction means for determining the fuel injection amount and fuel injection timing of the pre-injection performed before the main injection when the amount is shorter than the fixed amount, Is shall.

  During transient operation of premixed compression ignition combustion or when switching from normal combustion (diffusion combustion) to premixed compression ignition combustion, the ignition delay tends to deviate from the target value, so that combustion noise tends to increase. Therefore, in the combustion control device of the present invention, the ignition delay due to fuel injection is estimated before fuel is injected from the fuel injection valve to obtain the estimated ignition delay, and the target ignition delay when performing premixed compression ignition combustion. An ignition delay deviation between the estimated ignition delay and the target ignition delay is calculated, and when the estimated ignition delay is shorter than the target ignition delay by a predetermined amount or more, the fuel injection amount of the pre-injection performed before the main injection and Determine the fuel injection timing. Therefore, before the main injection is performed, the pre-injection is performed. As a result, combustion noise can be reduced during transient operation of premixed compression ignition combustion or when switching from normal combustion to premixed compression ignition combustion.

  Preferably, the pre-injection additional correction unit determines the fuel injection amount and the fuel injection timing of the pre-injection when the fuel injection amount and the fuel injection timing of the pre-injection are not determined by the fuel injection condition determination unit.

  For example, when the engine load is low, pre-injection may be performed. In such a case, even when the estimated ignition delay is shorter than the target ignition delay by a predetermined amount or more, the pre-injection can be prevented from being performed more than necessary by not performing the pre-injection.

  Preferably, when the estimated ignition delay is shorter than the target ignition delay, the fuel injection timing of the fuel injection determined by the fuel injection condition determining means is determined according to the ignition delay deviation calculated by the ignition delay deviation calculating means. Further provided is an injection timing retard correction means for retarding.

  In this way, when the estimated ignition delay is shorter than the target ignition delay, the fuel injection timing is retarded according to the ignition delay deviation, so that during transient operation of premixed compression ignition combustion or from normal combustion to premixed compression ignition combustion At the time of switching to combustion, combustion noise can be further reduced and an increase in NOx emission can be suppressed.

  Further preferably, when the estimated ignition delay is longer than the target ignition delay, the fuel injection timing of the fuel injection determined by the fuel injection condition determining means is determined in accordance with the ignition delay deviation calculated by the ignition delay deviation calculating means. Further provided is an injection timing advance correction means for advancing.

  Thus, when the estimated ignition delay is longer than the target ignition delay, the fuel injection timing is advanced in accordance with the ignition delay deviation, so that the transient operation of the premixed compression ignition combustion or from the normal combustion to the premixed compression ignition combustion is performed. Misfire can be suppressed when switching to combustion.

  Preferably, the apparatus further includes main injection amount change correction means for changing the fuel injection amount of the main injection determined by the fuel injection condition determining means in accordance with the ignition delay deviation calculated by the ignition delay deviation calculating means.

  For example, when the engine torque is lower than necessary, the engine torque is increased by increasing the fuel injection amount of the main injection according to the ignition delay deviation, and when the engine torque is higher than necessary, according to the ignition delay deviation. The engine torque is lowered by reducing the fuel injection amount of the main injection. Thereby, the fluctuation | variation of an engine torque can be suppressed at the time of the transient operation of premix compression ignition combustion, or the combustion switching from normal combustion to premix compression ignition combustion.

  Further preferably, the ignition delay estimating means includes means for detecting an oxygen amount in the combustion chamber and means for detecting a gas temperature in the combustion chamber, and uses the oxygen amount in the combustion chamber and the gas temperature in the combustion chamber. Estimate the ignition delay.

  During transient operation of premixed compression ignition combustion or when switching from normal combustion to premixed compression ignition combustion, the ignition delay tends to deviate from the target value due to the difference in oxygen amount and gas temperature in the combustion chamber. Therefore, it is possible to obtain a highly accurate estimated ignition delay by detecting the oxygen amount and gas temperature in the combustion chamber and estimating the ignition delay using them. Thereby, correction of fuel injection conditions, such as addition of pre-injection, can be performed more appropriately.

  At this time, it is preferable that the engine further includes a rotation speed detection means for detecting the rotation speed of the engine, and the ignition delay estimation means uses the oxygen amount in the combustion chamber, the gas temperature in the combustion chamber, the fuel injection timing, and the rotation speed of the engine. Estimate the ignition delay.

  The ignition delay is also affected by the fuel injection timing and the engine speed. Therefore, the estimated ignition delay can be obtained with higher accuracy by detecting the engine speed and estimating the ignition delay using the fuel injection timing and the engine speed.

  The fuel injection valve further includes an injection pressure detecting means for detecting an injection pressure of the fuel from the fuel injection valve, and the ignition delay estimating means calculates the oxygen amount in the combustion chamber, the gas temperature in the combustion chamber, and the fuel injection pressure from the fuel injection valve. It may be used to estimate the ignition delay.

  Deviation of the ignition delay from the target value can also be caused by a difference in fuel injection pressure from the fuel injection valve. Accordingly, by detecting the fuel injection pressure from the fuel injection valve and estimating the ignition delay using the injection pressure, it is possible to obtain a more accurate estimated ignition delay.

  Furthermore, it further comprises ambient environment detection means for detecting the ambient environment condition of the engine, and the ignition delay estimation means estimates the ignition delay using the oxygen amount in the combustion chamber, the gas temperature in the combustion chamber, and the ambient environment condition of the engine. May be.

  The estimated ignition delay varies depending on the environment surrounding the engine (outside air temperature, atmospheric pressure, cooling water temperature, etc.). Therefore, it is possible to obtain a more accurate estimated ignition delay by detecting the environment surrounding the engine and estimating the ignition delay using the environment surrounding the engine.

  According to the present invention, appropriate premixed compression ignition combustion can be realized even during transient operation of premixed compression ignition combustion or when switching from normal combustion to premixed compression ignition combustion.

It is a schematic structure figure showing a diesel engine provided with one embodiment of a combustion control device concerning the present invention. It is a block diagram which shows the structure of the combustion control apparatus shown in FIG. It is a flowchart which shows the detail of the fuel injection condition setting process procedure performed by the fuel injection condition setting part shown in FIG. It is a block diagram which shows the function which estimates an ignition delay in procedure S106 shown in FIG. It is a graph which shows an example of the 1st ignition delay sensitivity map showing the ignition delay sensitivity with respect to in-cylinder oxygen amount and in-cylinder gas temperature before fuel injection. It is a graph which shows an example of the 2nd ignition delay sensitivity map showing the ignition delay sensitivity with respect to fuel injection time and an engine speed. It is a graph which shows an example of the relationship between a crank angle and in-cylinder gas temperature. It is a graph which shows an example of the 3rd ignition delay sensitivity map showing the ignition delay sensitivity with respect to fuel injection pressure. It is a graph which shows an example of the heat release rate waveform (combustion waveform) at the time of performing pre-injection. It is a graph which compares and shows an example of the ignition delay sensitivity with respect to the amount of in-cylinder oxygen when pre-injection is performed and when pre-injection is not performed. It is a flowchart which shows the detail of the fuel-injection control processing procedure performed by the fuel-injection control part shown in FIG. FIG. 6 is a timing chart showing an example of in-cylinder gas conditions, ignition delay, and fuel injection conditions when switching from normal combustion (diffusion combustion) to premixed compression ignition combustion. It is a graph which shows an example of the heat release rate waveform (combustion waveform) when the actual ignition delay is shortened from the ignition delay target value.

  Hereinafter, a preferred embodiment of a combustion control device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing a diesel engine provided with an embodiment of a combustion control device according to the present invention. In the figure, a diesel engine 1 according to the present embodiment is a common rail type four-cylinder in-line diesel engine. The diesel engine 1 includes an engine body 2, and the engine body 2 is provided with four cylinders (cylinders) 3.

  Each cylinder 3 is provided with an injector (fuel injection valve) 5 for injecting fuel into the combustion chamber 4. Each injector 5 is connected to a common rail 6, and high-pressure fuel stored in the common rail 6 is constantly supplied to each injector 5.

  An intake passage 7 for sucking air into the combustion chamber 4 is connected to the engine body 2 via an intake manifold 8. In addition, an exhaust passage 9 for discharging exhaust gas after combustion is connected to the engine body 2 via an exhaust manifold 10.

  In the intake passage 7, an air cleaner 11, a compressor 13 of the turbocharger 12, an intercooler 14, and a throttle valve 15 are provided from the upstream side toward the downstream side. The exhaust passage 9 is provided with a turbine 16 of the turbocharger 12 and a catalyst 17 with a DPF from the upstream side toward the downstream side.

  The diesel engine 1 also includes an exhaust gas recirculation (EGR) unit 18 that recirculates a part of the exhaust gas after combustion into the combustion chamber 4 as exhaust gas recirculation gas (EGR gas). The EGR unit 18 is provided so as to connect the intake passage 7 and the exhaust manifold 10, and an EGR passage 19 that recirculates the EGR gas, and an EGR that adjusts the recirculation amount of the EGR gas from the exhaust manifold 10 to the intake passage 7. The EGR cooler 21 that cools the EGR gas that passes through the valve 20, the EGR passage 19, the bypass passage 22 that is connected to the EGR passage 19 so as to bypass the EGR cooler 21, and the EGR gas passage on the EGR cooler 21 side Or it has the switching valve 23 switched to the bypass channel | path 22 side.

  Furthermore, as shown in FIG. 2, the diesel engine 1 includes a rotation speed sensor 24, an accelerator opening sensor 25, an air flow meter 26, an intake manifold pressure sensor 27, an injection pressure sensor 28, an outside air temperature sensor 29, An atmospheric pressure sensor 30, a water temperature sensor 31, and an electronic control unit (ECU) 32 are provided.

  The rotational speed sensor 24 is a sensor (rotational speed detection means) that detects the rotational speed of the engine body 2 (engine rotational speed). The rotation speed sensor 24 detects the engine rotation speed by detecting the rotation angle (crank angle) of a crankshaft (not shown), for example.

  The accelerator opening sensor 25 is a sensor that detects the depression angle of the accelerator pedal (accelerator opening) as an alternative value for the load (engine load) of the engine body 2. In addition, in the diesel engine 1 provided with the common rail type fuel injection device as in the present embodiment, the fuel injection amount is electronically controlled, and the fuel injection amount can be used as an alternative value of the engine load.

  The air flow meter 26 is a sensor that detects the amount of air (fresh air amount) taken into the combustion chamber 4 from the intake passage 7. The intake manifold pressure sensor 27 is a sensor that detects the pressure (intake manifold pressure) of the intake manifold 8, that is, the supercharging pressure. The injection pressure sensor 28 is a sensor (injection pressure detection means) that detects the injection pressure of fuel from each injector 5. The injection pressure sensor 28 detects, for example, the pressure of the common rail 6 (common rail pressure) as the injection pressure.

  The outside air temperature sensor 29 is a sensor that detects the outside air temperature. The atmospheric pressure sensor 30 is a sensor that detects atmospheric pressure. The water temperature sensor 31 is a sensor that detects the temperature (cooling water temperature) of the cooling water flowing in the engine body 2. The outside air temperature sensor 29, the atmospheric pressure sensor 30, and the water temperature sensor 31 constitute an ambient environment detection unit that detects an ambient environment state of the engine 1.

  The ECU 32 includes a fuel injection condition setting unit 33 and a fuel injection control unit 34. The fuel injection condition setting unit 33 performs a predetermined process based on the detection values of the sensors 24 to 31 and sets the fuel injection condition. The fuel injection control unit 34 controls fuel injection into each combustion chamber 4 by controlling each injector 5 in accordance with the fuel injection condition set by the fuel injection condition setting unit 33. Specific processing procedures of the fuel injection condition setting unit 33 and the fuel injection control unit 34 will be described in detail later.

  Here, each injector 5, the sensors 24-31, and ECU32 comprise the combustion control apparatus 35 of this embodiment. Such a combustion control device 35 is configured to perform premixed compression ignition combustion of split injection in which fuel is injected from each injector 5 in a plurality of times in one cycle of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. Control.

  FIG. 3 is a flowchart showing details of the fuel injection condition setting processing procedure executed by the fuel injection condition setting unit 33 of the ECU 32. This process is executed for each cylinder 3.

  In the figure, first, based on the crank angle detected by the rotational speed sensor 24, it is determined whether it is time to set the fuel injection condition (step S101). When it is determined that it is time to set the fuel injection condition, the injector 5 is based on the engine speed detected by the speed sensor 24 and the accelerator opening (engine load) detected by the accelerator opening sensor 25. The total amount of fuel injected from the fuel (the total amount of fuel injection) is determined (step S102).

  Subsequently, the combustion method to be performed is determined based on the engine speed and the accelerator opening (step S103). As the combustion method, one of premixed compression ignition combustion and normal combustion (diffusion combustion) is selected.

  Subsequently, the injection amount (fuel injection amount) and timing (fuel injection timing) of each divided injection are determined based on the engine speed, the fuel injection amount, and the combustion method (step S104). More specifically, for example, when premixed compression ignition combustion is selected, the fuel injection amount and fuel injection timing of the first main injection and the second main injection performed thereafter are determined. At this time, when the accelerator opening is smaller than the predetermined amount, the pre-injection is performed before the first main injection, so the fuel injection amount and fuel injection timing of the pre-injection are also determined. Further, if necessary, the fuel injection amount and fuel injection timing of after-injection performed after the second main injection are also determined. Note that the fuel injection amounts for pre-injection and after-injection are set to be smaller than the fuel injection amount for main fuel injection.

  Subsequently, it is determined whether or not the combustion method is premixed compression ignition combustion (step S105). When it is determined that the combustion method is not the premixed compression ignition combustion but the normal combustion, this processing is terminated. When it is determined that the combustion method is premixed compression ignition combustion, an ignition delay corresponding to the current state of the engine 1 is estimated to obtain an estimated ignition delay τ (step S106). The ignition delay refers to a period from the start of fuel injection to ignition (see FIGS. 9 and 13).

  FIG. 4 is a block diagram illustrating a function for estimating the ignition delay in step S106. In the figure, the functions of step S106 are as follows: in-cylinder gas amount detection unit 36, combustion efficiency detection unit 37, in-cylinder oxygen amount detection unit 38, in-cylinder gas temperature detection unit 39, and base term generation unit 40. And a first correction term generation unit 41, a second correction term generation unit 42, a third correction term generation unit 43, and addition units 44 to 46.

  The in-cylinder gas amount detection unit 36 determines the amount of gas in the combustion chamber 4 (in-cylinder) based on the engine speed detected by the speed sensor 24 and the intake manifold pressure (supercharging pressure) detected by the intake manifold pressure sensor 27. Gas amount) is detected. Specifically, the in-cylinder gas amount detection unit 36 obtains the in-cylinder gas amount using a map that represents the relationship between the engine speed, the intake manifold pressure, and the in-cylinder gas amount.

  The combustion efficiency detector 37 determines the combustion efficiency based on the engine speed detected by the speed sensor 24, the fresh air amount detected by the air flow meter 26, and the fuel injection amount determined in step S102 shown in FIG. To detect. Specifically, the in-cylinder gas amount detection unit 37 obtains the combustion efficiency using a map that represents the relationship between the engine speed, the fresh air amount, the fuel injection amount, and the combustion efficiency.

  The in-cylinder oxygen amount detection unit 38 includes the fresh air amount detected by the air flow meter 26, the in-cylinder gas amount obtained by the in-cylinder gas amount detection unit 36, the combustion efficiency obtained by the combustion efficiency detection unit 37, and the above-mentioned Based on the fuel injection amount determined in step S102, an oxygen amount (in-cylinder oxygen amount) in the combustion chamber 4 is obtained. Specifically, in addition to the amount of fresh oxygen contained in the in-cylinder gas, it is necessary to determine the amount of oxygen in the EGR gas contained in the in-cylinder gas. First, the EGR gas amount itself can be obtained as a difference between the in-cylinder gas amount and the fresh air amount. Next, the ratio of the oxygen amount in the EGR gas amount can be obtained from the in-cylinder oxygen amount, the fuel injection amount, and the combustion efficiency before the EGR gas recirculation delay. Therefore, the in-cylinder oxygen amount detection unit 38 obtains the in-cylinder oxygen amount by calculation from the fresh air amount, the in-cylinder gas amount, the combustion efficiency, and the fuel injection amount.

  The in-cylinder gas temperature detection unit 39 includes the intake manifold pressure detected by the intake manifold pressure sensor 27, the in-cylinder gas amount obtained by the in-cylinder gas amount detection unit 36, and the in-cylinder oxygen amount obtained by the in-cylinder oxygen amount detection unit 38. Based on the amount and the fuel injection timing determined in step S104 shown in FIG. 3, the gas temperature (in-cylinder gas temperature) in the combustion chamber 4 before fuel injection is detected. Specifically, the in-cylinder gas temperature detection unit 39 uses the map representing the relationship between the intake manifold pressure, the in-cylinder gas amount, the in-cylinder oxygen amount, and the fuel injection timing and the in-cylinder gas temperature. Find the in-cylinder gas temperature.

  Based on the in-cylinder oxygen amount obtained by the in-cylinder oxygen amount detection unit 38 and the in-cylinder gas temperature before fuel injection obtained by the in-cylinder gas temperature detection unit 39, the base term generation unit 40 detects the estimated ignition delay. Generate a base term. Specifically, the base term generation unit 40 obtains a base term of the estimated ignition delay using a first ignition delay sensitivity map as shown in FIG. The first ignition delay sensitivity map is a map representing the ignition delay sensitivity with respect to the in-cylinder oxygen amount and the in-cylinder gas temperature before fuel injection. The first ignition delay sensitivity map is set so that the ignition delay decreases as the in-cylinder oxygen amount increases, and the ignition delay decreases as the in-cylinder gas temperature before fuel injection increases.

  The first correction term generation unit 41 generates a first correction term for the estimated ignition delay based on the fuel injection timing determined in step S104 shown in FIG. 3 and the engine speed detected by the rotation speed sensor 24. Specifically, the first correction term generating unit 41 obtains a first correction term of the estimated ignition delay using a second ignition delay sensitivity map as shown in FIG. The second ignition delay sensitivity map is a map representing the ignition delay sensitivity with respect to the fuel injection timing and the engine speed.

  As shown in FIG. 7, as the fuel injection timing (black point X) is retarded, the in-cylinder gas temperature decreases from the fuel injection to the ignition with the expansion of the in-cylinder volume after the fuel injection. Therefore, as shown in FIG. 6, the second ignition delay sensitivity map is set so that the ignition delay is extended as the fuel injection timing is retarded under the condition after compression top dead center (TDC). . Further, as the engine speed increases, the in-cylinder gas temperature decreases as the in-cylinder volume increases. For this reason, as shown in FIG. 6, the second ignition delay sensitivity map is set so that the ignition delay is extended as the engine speed increases.

  The second correction term generating unit 42 generates a second correction term with an estimated ignition delay based on the fuel injection pressure detected by the injection pressure sensor 28. Specifically, the second correction term generation unit 42 obtains a second correction term for the estimated ignition delay using a third ignition delay sensitivity map as shown in FIG. The third ignition delay sensitivity map is a map representing the ignition delay sensitivity with respect to the fuel injection pressure. As the fuel injection pressure becomes higher, fuel evaporation is promoted by atomization of the fuel. For this reason, as shown in FIG. 8, the third ignition delay sensitivity map is set so that the ignition delay decreases as the fuel injection pressure increases.

  Based on the outside air temperature detected by the outside air temperature sensor 29, the air pressure detected by the air pressure sensor 30, and the cooling water temperature detected by the water temperature sensor 31, the third correction term generating unit 43 is a third correction term for the estimated ignition delay. Is generated. Specifically, the third correction term generation unit 43 uses the fourth ignition delay sensitivity map (not shown) representing the ignition delay sensitivity with respect to the outside air temperature, the atmospheric pressure, and the cooling water temperature to perform the third correction of the estimated ignition delay. Find the term.

  The base term, the first correction term, and the second correction term respectively generated by the base term generation unit 40, the first correction term generation unit 41, and the second correction term generation unit 42 are under standard environmental conditions (for example, an air temperature of 25 ° C., This is a term for obtaining an estimated ignition delay at an atmospheric pressure of 101 KPa and a water temperature of 80 ° C. On the other hand, the third correction term generated by the third correction term generation unit 43 is a term for obtaining the estimated ignition delay in consideration of changes in the environmental conditions.

  The adding unit 44 adds the base term of the estimated ignition delay generated by the base term generating unit 40 and the first correction term of the estimated ignition delay generated by the first correction term generating unit 41 to obtain a primary estimated ignition delay. Is calculated. The adding unit 45 calculates the secondary estimated ignition delay by adding the second correction term of the estimated ignition delay generated by the second correction term generating unit 42 to the primary estimated ignition delay calculated by the adding unit 44. The adding unit 46 adds the third correction term of the estimated ignition delay generated by the third correction term generating unit 43 to the secondary estimated ignition delay calculated by the adding unit 45 to obtain the final estimated ignition delay τ. calculate.

  Here, as shown in FIG. 9, when the pre-injection is not performed, the reference for the ignition delay is the start timing of the main injection. On the other hand, when pre-injection is performed, the reference for the ignition delay is the start time of pre-injection. Under the conditions for performing the pre-injection, the pre-mixture of fuel and air by the pre-injection and the pre-mixture of fuel and air by the main injection burn almost simultaneously. Therefore, when performing the pre-injection, the reference of the ignition delay is set as the start timing of the pre-injection, and the relationship between the in-cylinder oxygen amount and the ignition delay is not performed as shown in FIG. The ignition delay sensitivity equivalent to the condition (see the broken line P in the figure) is obtained, and the ignition delay can be estimated. In FIG. 10, a square mark Q indicates the ignition delay sensitivity when the pre-injection start timing is set as the ignition delay reference in the pre-injection conditions, and the round mark R indicates the pre-injection conditions. Shows the ignition delay sensitivity when the ignition delay criterion is the start timing of the main injection. Therefore, since an ignition delay sensitivity map under conditions where pre-injection is not performed can be used, it is not necessary to add an ignition delay sensitivity map under conditions where pre-injection is performed.

  As described above, the ignition delay under the standard environmental conditions is estimated based on the in-cylinder oxygen amount, the in-cylinder gas temperature before fuel injection, the fuel injection timing, the engine speed and the fuel injection pressure, and the outside air temperature, Since the ignition delay is corrected in consideration of changes in environmental conditions such as the atmospheric pressure and the cooling water temperature, a highly accurate estimated ignition delay τ can be obtained.

Returning to FIG. 3, after obtaining the estimated ignition delay τ in step S106, the target ignition delay τ _tp during premixed compression ignition combustion is obtained (step S107). At this time, the engine speed detected by the speed sensor 24, the fuel injection amount determined in the above step S102, the outside air temperature detected by the outside air temperature sensor 29, the atmospheric pressure and water temperature sensor 31 detected by the air pressure sensor 30. Based on the coolant temperature detected by the above, the target ignition delay τ _tp is obtained using a preset target ignition delay map. The target ignition delay τ _tp is an ignition delay for obtaining a target combustion waveform corresponding to the engine speed, the fuel injection amount, the outside air temperature, the atmospheric pressure, and the cooling water temperature.

Subsequently, a deviation (ignition delay deviation Δτ _tp ) between the estimated ignition delay τ and the target ignition delay τ _tp is calculated from the following formula (step S108).
Ignition delay deviation Δτ _tp = Estimated ignition delay τ−Target ignition delay τ _tp

It is determined whether the estimated ignition delay τ is shorter than the target ignition delay τ _tp by a predetermined amount or more, that is, whether the ignition delay deviation Δτ _tp ≦ the predetermined amount A (A <0) (step S109). When it is determined that the estimated ignition delay τ is shorter than the target ignition delay τ _tp by a predetermined amount or more, it is subsequently determined whether pre-injection is not performed in the previous procedure (procedure S102) (procedure S110). . When it is determined that pre-injection is not performed in the previous procedure, the fuel injection amount and fuel injection timing of pre-injection are determined (procedure S111). At this time, the fuel injection amount of the pre-injection is reduced from the fuel injection amount of the first main injection or the fuel injection amount of the second main injection.

When it is determined in step S109 that the estimated ignition delay τ is not shorter than the target ignition delay τ _tp by a predetermined amount or when it is determined in step S110 that pre-injection is to be performed, step S111 is executed. do not do. When pre-injection has already been determined because the engine load is low in this way, new pre-injection is not additionally performed, so that the number of pre-injections need not be increased more than necessary.

Subsequently, it is determined whether the estimated ignition delay τ is shorter than the target ignition delay τ _tp , that is, whether the ignition delay deviation Δτ _tp <0 (step S112). When it is determined that the estimated ignition delay τ is shorter than the target ignition delay τ _tp , the fuel injection timings of all the fuel injections are retarded according to the ignition delay deviation Δτ _tp (step S113). At this time, when pre-injection is performed, misfire resistance is improved by the pre-injection, so that a sufficient amount of retardation can be ensured.

Subsequently, the fuel injection amount of the main injection is changed according to the ignition delay deviation Δτ _tp (step S114). At this time, the fuel injection amount of the main injection is increased or decreased depending on the operation region (engine speed, engine load, etc.). For example, when the engine torque is low, depending on the ignition delay deviation .DELTA..tau _tp increasing the amount of fuel injection amount of main injection, at high engine generated torque, the fuel injection amount of main injection according to the ignition delay deviation .DELTA..tau _tp To lose weight.

On the other hand, when it is determined in step S112 that the estimated ignition delay τ is _{equal to} or greater than the target ignition delay τ _tp , that is, the ignition delay deviation Δτ _tp ≧ 0, the fuel of all fuel injections according to the ignition delay deviation Δτ _tp The injection timing is advanced (step S115).

Subsequently, the fuel injection amount of the main injection is changed according to the ignition delay deviation Δτ _tp (step S116). At this time, the fuel injection amount of the main injection is increased or decreased depending on the operation region (engine speed, engine load, etc.) as in the above step S114.

  FIG. 11 is a flowchart showing details of the fuel injection control processing procedure executed by the fuel injection control unit 34 of the ECU 32. This process is also executed for each cylinder 3.

  In the figure, first, it is determined whether or not there is pre-injection in the fuel injection condition set by the fuel injection condition setting unit 33 (step S121). When it is determined that the fuel injection condition includes pre-injection, pre-injection is performed according to the fuel injection amount and fuel injection timing set by the fuel injection condition setting unit 33 (step S122). When it is determined that pre-injection is not performed under the fuel injection conditions, step S122 is not performed.

  Subsequently, the first main injection is performed according to the fuel injection amount and fuel injection timing set by the fuel injection condition setting unit 33 (step S123). Then, the second main injection is performed in accordance with the fuel injection amount and fuel injection timing set by the fuel injection condition setting unit 33 (step S124). Thereafter, when there is after injection in the fuel injection condition set by the fuel injection condition setting unit 33, the after injection is performed.

  In the above, the fuel injection condition setting unit 33 is the fuel injection condition determining means for determining the fuel injection amount and fuel injection timing of the fuel injection including the main injection, and the ignition by the fuel injection before the fuel is injected from the fuel injection valve 5. The ignition delay estimation means for estimating the delay, the target ignition delay setting means for obtaining the target ignition delay when performing the premixed compression ignition combustion, the estimated ignition delay obtained by the ignition delay estimation means and the target ignition delay setting means. An ignition delay deviation calculating means for calculating an ignition delay deviation from the target ignition delay, and a fuel injection amount of pre-injection performed before the main injection when the estimated ignition delay is shorter than the target ignition delay by a predetermined amount or more And pre-injection additional correction means for determining the fuel injection timing. Further, the fuel injection condition setting unit 33 determines the fuel injection determined by the fuel injection condition determining means according to the ignition delay deviation calculated by the ignition delay deviation calculating means when the estimated ignition delay is shorter than the target ignition delay. Injection timing delay correction means for delaying the fuel injection timing, and when the estimated ignition delay is longer than the target ignition delay, fuel injection condition determination means according to the ignition delay deviation calculated by the ignition delay deviation calculation means The injection timing advance correction means for advancing the fuel injection timing determined by the fuel injection timing, and the ignition delay deviation calculated by the ignition delay deviation calculation means, and the main injection determined by the fuel injection condition determination means Main injection amount change correction means for changing the fuel injection amount is configured.

  In the fuel injection condition setting unit 33, steps S102 to S104 shown in FIG. 3 function as fuel injection condition determination means, the procedure S106 functions as ignition delay estimation means, and the procedure S107 functions as target ignition delay setting means. The procedure S108 functions as an ignition delay deviation calculating means, the procedures S109 to S111 function as pre-injection additional correction means, the procedures S112 and S113 function as injection timing retardation correction means, and the procedures S112 and S115. Functions as injection timing advance correction means, and the steps S114 and S116 function as main injection amount change correction means.

  Here, at the time of combustion switching from normal combustion (diffusion combustion) to premixed compression ignition combustion, as shown in FIG. 12, in-cylinder gas conditions (for example, in-cylinder oxygen amount) and fuel injection conditions (for example, fuel injection of main injection) (Time) is changed all at once. At this time, within the predetermined period W from the combustion switching timing, the in-cylinder gas condition and the ignition delay gradually change to coincide with the target value for premixed compression ignition combustion (see broken line).

At this time, as described above, by delaying or advancing the fuel injection timing in accordance with the ignition delay deviation Δτ _tp between the estimated ignition delay τ and the target ignition delay τ _tp , the fuel injection condition is set simultaneously with the combustion switching timing. It is not changed from the fuel injection timing of normal combustion to the fuel injection timing of premixed compression ignition combustion (see the broken line), but gradually changed from the combustion switching timing (see the solid line).

  By the way, during the transition operation of premixed compression ignition combustion such as when fuel cuts such as deceleration or shift change or when supercharging is delayed during acceleration, combustion occurs when switching from normal combustion (diffusion combustion) to premixed compression ignition combustion Problems such as increased noise, increased NOx emissions, misfire, and fluctuations in engine torque occur. Such a problem is caused by the fact that the actual ignition delay deviates from the target value of the ignition delay due to the delay in the EGR recirculation due to the deviation in the in-cylinder oxygen amount, the in-cylinder gas temperature, or the like, or the delay in following the fuel injection pressure. . For example, as shown in FIG. 13, when the in-cylinder oxygen amount, the in-cylinder gas temperature, and the fuel injection pressure become higher than necessary, the actual combustion waveform (see the solid line M) becomes the target combustion waveform (one-dot chain line N If the actual ignition delay from the start of the first main injection is shorter than the ignition delay target value, combustion noise increases, NOx emission increases, and engine torque decreases.

On the other hand, in this embodiment, after determining the fuel injection amount and the fuel injection timing, the estimated ignition delay τ is obtained and the target ignition delay τ _tp is obtained, and the ignition delay deviation between the estimated ignition delay τ and the target ignition delay τ _tp is determined. Δτ _tp is calculated, and pre-injection is additionally performed when the estimated ignition delay τ is shorter than the target ignition delay τ _tp by a predetermined amount or more. Therefore, when the fuel is cut or when the combustion is switched from normal combustion to premixed compression ignition combustion, sudden heat generation can be suppressed, so that combustion noise can be reduced.

Further, when the estimated ignition delay τ is shorter than the target ignition delay τ _tp , the fuel injection timing is retarded according to the ignition delay deviation Δτ _tp , so that the premixed compression ignition combustion is performed from the time of fuel cut or normal combustion Excessive combustion is further suppressed when switching to combustion. As a result, combustion noise can be further reduced, and an increase in NOx emission can be suppressed.

Further, when the estimated ignition delay τ is greater than or equal to the target ignition delay τ _tp , the fuel injection timing is advanced in accordance with the ignition delay deviation Δτ _tp , so that the combustion stability is stabilized at the time of supercharging delay during acceleration. Increases nature. Thereby, misfire and smoke discharge | emission can be suppressed.

In addition, since the fuel injection amount of the main injection is increased or decreased according to the ignition delay deviation Δτ _tp , combustion from normal combustion to premixed compression ignition combustion at the time of supercharging delay at the time of fuel cut or acceleration At the time of switching, fluctuations in engine torque can be suppressed.

  Furthermore, since the ignition delay is estimated using the in-cylinder oxygen amount, the in-cylinder gas temperature, and the fuel injection pressure that affect the deviation from the target ignition delay value, a highly accurate estimated ignition delay τ can be obtained. Therefore, it is possible to appropriately correct the fuel injection conditions such as the additional execution of the pre-injection, the delay or advance of the fuel injection timing, and the change of the fuel injection amount of the main injection.

  As described above, according to the present embodiment, an increase in combustion noise, an increase in NOx emission, misfire, engine torque generated during transient operation of premixed compression ignition combustion or when switching from normal combustion to premixed compression ignition combustion is performed. Fluctuations and the like can be suppressed. As a result, excellent premixed compression ignition combustion can be realized.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the estimated ignition delay τ is obtained based on the in-cylinder oxygen amount, the in-cylinder gas temperature before fuel injection, the fuel injection timing, the engine speed, the fuel injection pressure, the outside air temperature, the atmospheric pressure, and the cooling water temperature. However, the present invention is not particularly limited thereto, and the estimated ignition delay τ may be obtained using at least the in-cylinder oxygen amount and the in-cylinder gas temperature before fuel injection.

  Further, in the above embodiment, the main injection is performed twice, but the number of main injections is not particularly limited to two, and may be only one, or three or more times. It may be.

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 4 ... Combustion chamber, 5 ... Injector (fuel injection valve), 24 ... Revolution sensor (revolution number detection means), 28 ... Injection pressure sensor (injection pressure detection means), 29 ... Outside temperature sensor (ambient) (Environment detection means), 30 ... atmospheric pressure sensor (ambient environment detection means), 31 ... water temperature sensor (ambient environment detection means), 32 ... ECU, 33 ... fuel injection condition setting unit (fuel injection condition determination means, ignition delay estimation means, Target ignition delay setting means, ignition delay deviation calculating means, pre-injection additional correction means, injection timing delay angle correcting means, injection timing advance angle correcting means, main injection amount change correcting means), 34 ... fuel injection control section, 35 ... combustion Control device, 38 ... in-cylinder oxygen amount detection unit, 39 ... in-cylinder gas temperature detection unit.

Claims (9)

In an engine combustion control device that performs premixed compression ignition combustion,
A fuel injection valve for injecting fuel into the combustion chamber of the engine;
Fuel injection condition determining means for determining a fuel injection amount and fuel injection timing of fuel injection including main injection;
An ignition delay estimating means for estimating an ignition delay due to the fuel injection before injecting fuel from the fuel injection valve;
A target ignition delay setting means for obtaining a target ignition delay when performing the premixed compression ignition combustion;
An ignition delay deviation calculating means for calculating an ignition delay deviation between the estimated ignition delay obtained by the ignition delay estimating means and the target ignition delay obtained by the target ignition delay setting means;
Pre-injection additional correction means for determining a fuel injection amount and fuel injection timing of pre-injection performed before the main injection when the estimated ignition delay is shorter than the target ignition delay by a predetermined amount or more. A characteristic combustion control device.   The pre-injection additional correction means determines the pre-injection fuel injection amount and fuel injection timing when the fuel injection condition determination means has not determined the fuel injection amount and fuel injection timing of the pre-injection. The combustion control device according to claim 1, characterized in that:   When the estimated ignition delay is shorter than the target ignition delay, the fuel injection timing of the fuel injection determined by the fuel injection condition determining means according to the ignition delay deviation calculated by the ignition delay deviation calculating means The combustion control apparatus according to claim 1 or 2, further comprising injection timing delay angle correction means for delaying the angle.   When the estimated ignition delay is longer than the target ignition delay, the fuel injection timing of the fuel injection determined by the fuel injection condition determining means according to the ignition delay deviation calculated by the ignition delay deviation calculating means The combustion control apparatus according to any one of claims 1 to 3, further comprising an injection timing advance correction means for advancing the angle.   The apparatus further comprises main injection amount change correcting means for changing the fuel injection amount of the main injection determined by the fuel injection condition determining means in accordance with the ignition delay deviation calculated by the ignition delay deviation calculating means. The combustion control device according to any one of claims 1 to 4.   The ignition delay estimating means includes means for detecting an oxygen amount in the combustion chamber and means for detecting a gas temperature in the combustion chamber, and uses the oxygen amount in the combustion chamber and the gas temperature in the combustion chamber. The combustion control device according to claim 1, wherein the ignition delay is estimated. A rotation speed detecting means for detecting the rotation speed of the engine;
7. The ignition delay estimating means estimates the ignition delay using an oxygen amount in the combustion chamber, a gas temperature in the combustion chamber, the fuel injection timing, and the engine speed. Combustion control device. An injection pressure detecting means for detecting an injection pressure of fuel from the fuel injection valve;
7. The ignition delay estimation means estimates the ignition delay using an oxygen amount in the combustion chamber, a gas temperature in the combustion chamber, and an injection pressure of fuel from the fuel injection valve. Combustion control device. It further comprises ambient environment detection means for detecting the ambient environment condition of the engine,
7. The combustion control apparatus according to claim 6, wherein the ignition delay estimation means estimates the ignition delay using an oxygen amount in the combustion chamber, a gas temperature in the combustion chamber, and an environment surrounding the engine. .

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