JP4523766B2 - Combustion control device for internal combustion engine - Google Patents

Description

  The present invention relates to a combustion control device for an internal combustion engine that appropriately controls an exhaust gas recirculation amount in accordance with a fuel property such as a cetane number of a fuel used in the internal combustion engine.

  2. Description of the Related Art Conventionally, a combustion control device for an internal combustion engine that appropriately controls the exhaust gas recirculation amount according to the operating state and fuel properties of the internal combustion engine is known (see Patent Document 1).

This is equipped with a means for detecting the ignition timing using an in-cylinder pressure sensor, so that when the target ignition timing differs from the actual ignition timing due to variations in the cetane number of fuel in the market, the target ignition timing will be achieved. The injection timing, EGR rate, etc. are changed.
Japanese Patent Laid-Open No. 11-107820

  However, in the above-described conventional example, since the actual ignition timing is controlled to coincide with the target ignition timing and the EGR rate is corrected, the oxygen amount is changed to realize low-temperature premixed combustion. Although it is recognized that the change in the cetane number affects the actual ignition timing, even if the difference from the actual ignition timing to the target ignition timing includes a delay in the ignition timing due to all disturbances other than the cetane number This is acceptable for control purposes, and does not suppress NOx emissions by optimally controlling the EGR rate in accordance with the fuel properties, particularly the cetane number.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a combustion control device for an internal combustion engine that appropriately controls the exhaust gas recirculation amount in accordance with the fuel properties such as the cetane number of the fuel being used. To do.

The present invention is an exhaust gas recirculation device comprising an EGR passage that recirculates part of exhaust gas of an internal combustion engine to engine intake air and an EGR valve that controls the exhaust gas recirculation rate to the intake air, and detects the cetane number as the property of the fuel used. And calculating the exhaust gas recirculation rate based on the operating state of the internal combustion engine, correcting the exhaust gas recirculation rate according to the cetane number detected by the fuel property detecting unit, and based on the corrected exhaust gas recirculation rate And an exhaust gas recirculation control means for controlling an EGR valve of the exhaust gas recirculation apparatus , wherein the exhaust gas recirculation control means moves the cetane number detected by the fuel property detection means to a side higher and lower than a preset reference cetane number. The exhaust gas recirculation rate is corrected so as to decrease relative to the exhaust gas recirculation rate with respect to the reference cetane number as it deviates .

Therefore, in the present invention, to detect the cetane number as the fuel property of fuel being used by the fuel property detecting means, exhaust recirculation control means, the exhaust gas recirculation rate calculated based on the operating state, the fuel property detecting means The exhaust gas recirculation rate is corrected so as to be relatively decreased with respect to the exhaust gas recirculation rate with respect to the reference cetane number as the cetane number detected in Step 3 deviates to a higher side and a lower side than the preset reference cetane number. Since the EGR valve of the exhaust gas recirculation device is controlled based on the recirculation rate, EGR control suitable for the cetane number as the property of the fuel being used can be performed. That is, appropriate EGR for the slow combustion when the cetane number CN is lower than the reference cetane number CN and the combustion where the ignition delay is shortened and the peak is suppressed when the cetane number CN is higher than the reference cetane number CN Rate.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of an engine system including a combustion control device according to the present invention, which is configured by taking a diesel engine using light oil as fuel as an example.

  In FIG. 1, 1 indicates a diesel engine (hereinafter simply referred to as an engine), and 3 indicates an exhaust passage of the engine 1.

  An exhaust outlet passage 3a constituting an upstream portion of the exhaust passage 3 of the engine 1 is connected to a turbine 3b of a supercharger, and an exhaust aftertreatment device (for example, an oxidation catalyst or a NOx catalyst) is provided in the downstream thereof. The accommodated casing 20 is arranged in series. An air-fuel ratio sensor 37 serving as an actual air-fuel ratio detection unit is provided at the inlet of the casing 20. The air-fuel ratio sensor 37 detects the oxygen concentration in the exhaust gas using, for example, an oxygen ion conductive solid electrolyte, and obtains the air-fuel ratio from the oxygen concentration.

  As an exhaust gas recirculation device, an EGR passage 4 for recirculating a part of the exhaust gas is provided between the intake collector 2c and the exhaust outlet passage 3a of the intake passage 2, and the opening is opened by a stepping motor. Is provided with an EGR valve 5 that can be continuously controlled.

  The intake passage 2 includes an air cleaner 2a at an upstream position, and an airflow meter 7 serving as an intake air amount detection means is provided on the outlet side thereof. A turbocharger compressor 2b is arranged downstream of the air flow overnight 7, and an intake throttle valve that is opened and closed by an actuator (for example, a stepping motor type) between the compressor 2b and the intake collector 2c. 6 is interposed.

  The fuel supply system of the engine 1 includes a fuel tank 60 that stores diesel oil as diesel fuel, a fuel supply passage 16 that supplies fuel to the fuel injection device 10 of the engine 1, and a fuel supply device 16 of the engine 1. And a fuel return passage 19 for returning the return fuel (spill fuel) to the fuel tank 60.

  The fuel injection device 10 of the engine 1 is a known common rail type fuel injection device, and generally includes a supply pump 11, a common rail (accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder. After the fuel pressurized by the supply pump 11 is temporarily stored in the common rail 14 via the fuel supply passage 12, the high-pressure fuel in the common rail 14 is distributed to the fuel injection valves 15 of each cylinder.

  The common rail 14 is provided with a pressure sensor 34 and a temperature sensor 35 in order to detect the pressure and temperature of the fuel in the common rail 14. Further, in order to control the fuel pressure in the common rail 14, a part of the fuel discharged from the supply pump 11 is returned to the fuel supply passage 16 via the overflow passage 17 having the one-way valve 18. Yes. Specifically, a pressure control valve 13 that changes the flow passage area of the overflow passage 17 is provided, and the pressure control valve 13 changes the flow passage area of the overflow passage 17 in accordance with a duty signal from the engine control unit 30. Thereby, the substantial fuel discharge amount from the supply pump 11 to the common rail 14 is adjusted, and the fuel pressure in the common rail 14 is controlled.

  The fuel injection valve 15 is an electronic injection valve that is opened and closed by an ON-OFF signal from the engine control unit 30, and injects fuel into the combustion chamber by the ON signal and stops injection by the OFF signal. The fuel injection amount increases as the period of the ON signal applied to the fuel injection valve 15 increases, and the fuel injection amount increases as the fuel pressure of the common rail 14 increases.

  A water temperature sensor 31 for detecting the cooling water temperature is attached to an appropriate position of the engine 1 as representative of the temperature of the internal combustion engine.

  The engine control unit 30 includes a signal (Qa) from the air flow meter 7 that detects the intake air amount, a signal from the water temperature sensor 31 (cooling water temperature Tw), and a signal from the crank angle sensor 32 for crank angle detection (of the engine speed Ne). Basic crank angle signal), a cylinder discrimination crank angle sensor 33 signal (cylinder discrimination signal Cy1), a pressure sensor 34 signal for detecting fuel pressure in the common rail 14 (common rail pressure PCR), and a temperature sensor for detecting fuel temperature. 35 (fuel temperature TF), an accelerator opening sensor 36 signal (accelerator opening (load) L) for detecting the amount of depression of the accelerator pedal corresponding to the load, and an air fuel ratio sensor 37 signal (02). Entered.

  Next, the contents of the control of the present embodiment executed by the engine control unit 30 will be described based on the flowcharts of FIGS.

  FIG. 8 is a basic control routine related to the control of the entire diesel engine 1.

  In this engine basic control routine, in step S100, the coolant temperature Tw, the engine speed Ne, the cylinder discrimination signal Cyl, the common rail pressure PCR, the signal Qa of the air flow meter 7, the fuel temperature TF, the accelerator opening L, and the air-fuel ratio sensor Each of the signals O2 is read, and the process proceeds to step S200.

  In step S200, fuel property detection control is performed, and in step S300, engine exhaust control is performed, and the process returns.

  FIG. 9 is a flowchart showing details of the control subroutine for fuel property detection in step S200. With this control, the specific gravity of the fuel being used is accurately detected.

  The fuel specific gravity detection control routine will be described below. In step S210, it is determined whether or not the fuel injection amount has been calculated. If it has not been calculated, the process proceeds to step S300 to calculate a fuel injection amount, which will be described later, and if it has been calculated in the previous processing, the process proceeds to step S220. move on.

  In step S220, based on the signal Qa of the air flow meter 7 that detects the intake air amount, the table data of the predetermined intake air amount Qair stored in advance in the ROM of the control unit 30 is retrieved using the value of the signal Qa as a parameter. To do. Then, the process proceeds to step S230.

  In step S230, a fuel injection amount (fuel supply amount) Qmain set using the engine speed Ne and the load L as parameters is obtained by searching a predetermined map stored in advance in the ROM of the control unit 30. Then, the process proceeds to step S240.

  Note that the fuel injection amount (fuel supply amount) Qmain is not the above-described method, but the fuel injection period Mperiod of the fuel injection device that is set with the engine speed Ne and the load L as parameters, and the ROM of the control unit 30. The fuel injection amount (fuel supply amount) Qmain set by using the fuel injection period Mperiod and the common rail pressure PCR as parameters is stored in advance in the ROM of the control unit 30. A predetermined map may be searched for and obtained.

  In step S240, based on the signal O2 of the air-fuel ratio sensor 37, the table data of the actual air-fuel ratio AFreal stored in advance in the ROM of the control unit 30 is retrieved using the value of the signal O2 as a parameter. Then, the process proceeds to step S250.

  In step S250, it is determined whether or not the conditions are suitable for detecting the fuel property. For example, in general, an automobile engine is generally provided with an exhaust gas recirculation device including an EGR valve 5 and the like for NOx reduction. Since the fuel ratio shifts to the rich side, it is necessary to correct the exhaust gas recirculation in order to accurately obtain the actual air fuel ratio. Accordingly, since there is a concern that the detection accuracy of the actual air-fuel ratio deteriorates due to the correction, it is desirable to issue the actual air-fuel ratio detection command only in a region where exhaust gas recirculation is stopped. If it is not suitable for the detection condition in step S250, the process proceeds to step S300 without detecting the fuel property, and if suitable for the detection condition, the process proceeds to step S260.

  In step S260, the actual fuel supply weight Gmain is obtained based on the intake air flow rate Qair obtained in step S220 and the actual air-fuel ratio AFreal obtained in step S240. Specifically, the intake air flow rate Qair is divided by the actual air-fuel ratio AFrea1 to obtain the actual fuel supply weight Gmain (Gmain = Qair ÷ AFrea1). Then, the actual specific gravity Gfuel is obtained based on the obtained actual fuel supply weight Gmain and the fuel injection amount (fuel supply amount) Qmain obtained in step S230. Specifically, the actual fuel supply weight Gmain is divided by the fuel injection amount (fuel supply amount) Qmain to obtain an actual specific gravity Gfue1 (Gfue1 = Gmain ÷ Qmain). Then, the process proceeds to step S270.

  In step S270, the standard specific gravity (reference temperature, for example, specific gravity at a standard temperature of 20 ° C.) Gstd is obtained from the actual specific gravity Gfuel and the fuel temperature TF. Specifically, a map of the standard specific gravity Gstd stored in advance in the ROM of the control unit 30 is searched using the actual specific gravity Gfuel and the fuel temperature TF as parameters, the corresponding value is obtained, and the process proceeds to step S280.

  In step S280, using the standard specific gravity Gstd as a parameter, table data of fuel properties, for example, cetane number Cnumber (hereinafter referred to as cetane number CN) stored in advance in the ROM of the control unit 30 is searched. Then, the process proceeds to step S300.

  Here, the relationship between the standard specific gravity of light oil fuel and the fuel properties of light oil in the market investigated by the present inventors will be described based on the characteristic diagrams shown in FIGS. In light oil, as shown in FIG. 2, the cetane number CN decreases in inverse proportion to the standard specific gravity (hereinafter simply referred to as density). The reason for this is that, as shown in FIG. 3, the higher the density, the lower the cetane number CN (the higher the octane number), the more the aromatic hydrocarbon components having a benzene ring structure that has a low evaporation property. Due to Therefore, it is possible to detect the fuel properties such as cetane number CN, octane number, evaporability, calorific value, and aromatic hydrocarbon content from the standard specific gravity (density) of the fuel. Since the viscosity is proportional to the density, as shown in FIG. 4, the cetane number CN tends to decrease in inverse proportion to the viscosity. Therefore, it is possible to detect the fuel properties such as the cetane number CN from the viscosity of the fuel.

  Next, FIG. 10 is a subroutine related to engine exhaust control performed in step S300 of FIG. Here, first, common rail pressure control is performed in step S310 so that the defined engine exhaust emission performance is obtained. In this common rail pressure control, the fuel injection amount is searched by searching a predetermined map stored in advance in the ROM of the control unit 30 using the engine speed Ne and the load L as parameters. Therefore, the target reference pressure PCRO of the common rail 14 is obtained, and feedback control of the pressure control valve 13 is executed so that the target reference pressure PCRO is obtained.

  Next, in step S315, fuel injection control is performed. In this fuel injection control, for example, the engine speed Ne and the load L are used as parameters, and the fuel injection amount Qmain, the fuel injection period Mperiod, the fuel injection start timing Mstart, and the like are stored in the ROM of the control unit 30 in advance. Search map data and find each. Then, based on the crank angle signal of the crank angle detection crank angle sensor 32 and the cylinder discrimination signal Cyl of the cylinder discrimination crank angle sensor 33, the fuel injection valve of the cylinder to be injected is supplied so that the fuel injection amount Qmain is supplied. 15 is driven to open.

  In step S320, EGR control is performed. In this EGR control, for example, a fuel injection amount Qmain set with the engine speed Ne and the load L as parameters is obtained by searching a predetermined map stored in advance in the ROM of the control unit 30, and the fuel injection amount is determined. A predetermined map stored in advance in the ROM of the control unit 30 is searched using the amount Qmain and the engine speed Ne as parameters, and the intake throttle valve drive signal (meaning the opening of the intake throttle valve 6) THduty and An EGR drive signal (opening signal of the EGR valve 5) EGRduty serving as a reference EGR control signal is obtained, and the intake throttle valve 6 and the EGR valve 5 are driven based on the respective drive signals. The details of the EGR control will be described later based on the EGR control subroutine of FIG.

  In step S360, exhaust aftertreatment control is performed. This exhaust aftertreatment control is performed by, for example, a known NOx trap catalyst that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases NOx when the oxygen concentration of the inflowing exhaust gas is reduced. The intake throttle is strengthened (inlet throttle valve 6 is small), exhaust gas recirculation is strengthened, or post-injection (a small amount of fuel is injected after the main injection) at the regeneration timing of the NOx trap catalyst. Are executed alone or in combination so that the air-fuel ratio of the exhaust gas discharged from the engine is made rich to perform NOx regeneration.

  FIG. 11 is a subroutine related to EGR control of the diesel engine performed in step S320.

  In this EGR control routine, in step S321, a fuel injection amount Qmain set with the engine speed Ne and the load L as parameters is obtained by searching a predetermined map stored in the ROM of the control unit 30 in advance. Proceed to step S322.

  In step S322, using the fuel injection amount Qmain and the engine speed Ne as parameters, a predetermined map stored in advance in the ROM of the control unit 30 is searched for an intake throttle valve drive signal (opening of the intake throttle valve 6). TH duty is calculated, and the process proceeds to step S323. The opening degree of the intake throttle valve 6 is preferably set so that the opening degree is increased (the intake throttle degree is decreased) as the engine load L is higher and the engine speed Ne is higher.

  In step S323, a predetermined map stored in advance in the ROM of the control unit 30 is searched using the engine speed Ne and the fuel injection amount Qmain as parameters, and an EGR drive signal (EGR valve 5) serving as a reference EGR control signal is searched. The opening degree signal) EGRduty is obtained. Then, the process proceeds to step S324. It is desirable that the opening of the EGR valve 5 is set so that the opening of the EGR valve 5 is largely increased (the amount of EGR is increased) as the engine load L is lower.

  In step S324, it is determined whether or not the cetane number CN of the fuel being used has been detected. If the cetane number CN of the fuel has not been detected yet, the process proceeds to step S325, and if it has been detected, the process proceeds to step S326. This is because, as described above, after the fuel injection amount (fuel supply amount) is calculated and the intake air amount Qair and the actual air-fuel ratio AFreal in the engine operating state are detected, the cetane number CN detection steps S260 to S280 are performed. Is executed.

  In step S325, table data of a predetermined intake throttle valve drive signal correction coefficient KTWTH and an EGR valve drive signal correction coefficient KTWEGR stored in advance in the ROM of the control unit 30 is searched using the coolant temperature as a parameter, The process proceeds to step S327. Here, as shown in FIG. 5B, the correction coefficient KTWTH of the intake throttle valve drive signal based on the cooling water temperature is set such that the intake throttle degree decreases as the cooling water temperature decreases (the correction coefficient KTWTH decreases). It is set. Further, as shown in FIG. 5A, the correction coefficient KTWEGR of the EGR valve drive signal is such that the EGR opening is decreased (the correction coefficient KTWEGR is decreased) and the amount of EGR is decreased as the coolant temperature is lower. It is set.

In step S327, the intake throttle valve drive signal THduty is corrected by multiplying by the intake throttle valve drive signal correction coefficient KTWTH (THduty × KTWTH → THduty), and the above EGR valve drive signal correction coefficient KTWEGR is multiplied. To correct the EGR valve drive signal EGRduty (EGRduty × KTWEGR → EGRduty). And it progresses to step S328 In addition, in said example, although correction with respect to cooling water temperature is performed by multiplying a correction coefficient, each correction value is calculated | required based on cooling water temperature, and this is taken as an intake throttle valve drive signal. You may make it add to THduty and EGR valve drive signal EGRduty.

  In step S328, the intake throttle valve 6 and the EGR valve 5 are driven based on the respective drive signals, and the process proceeds to step 360 of the exhaust aftertreatment control.

  Further, in step S326, which proceeds when the cetane number CN of the fuel has already been detected in step S324, the predetermined intake air previously stored in the ROM of the control unit 30 using the cooling water temperature and the cetane number CN of the fuel as parameters. The map data (see FIG. 7) of the correction coefficient KCNTH of the throttle valve drive signal and the correction coefficient KCNNEGR of the EGR valve drive signal are respectively searched, and the process proceeds to step S327.

  In step S327, as described above, the intake throttle valve drive signal THduty and the EGR valve drive signal EGRduty are corrected by multiplying these correction coefficient KCNTH and correction coefficient KCNEGR, respectively.

  Here, as shown in FIG. 6, the required EGR rate for obtaining an equal NOx reduction rate for each cetane number CN is 60 even if the cetane number CN is 60 or more, centering on the reference cetane number CN1 (for example, CN = 60). In the following, the required EGR rate (%) is basically reduced. This is because the low cetane number CN fuel is too ignitable and the combustion is slow and delayed, whereas the high cetane number CN fuel has good ignitability and therefore the ignition delay is shortened. This is because the combustion peak is suppressed.

  Then, the map data of the correction coefficient KCNTH of the intake throttle valve drive signal and the correction coefficient KCNEGR of the EGR valve drive signal using the cooling water temperature as a parameter, as shown in FIG. 7, is the reference cetane number CN1 (= 60) at the reference temperature. If the cetane number CN is constant, the EGR rate is decreased (the intake throttle degree is decreased and the EGR opening is decreased) as the cetane number CN moves up and down from the reference cetane number CN1. For example, the EGR rate is decreased as the cooling water temperature is lower (the intake throttle degree is weakened and the EGR valve opening is decreased). In addition, the lower the cooling water temperature than the reference temperature, the higher the point of EGR rate shifts to the cetane number CN higher than the reference cetane number CN1, and conversely, the higher the cooling water temperature than the reference temperature, the highest EGR rate. The larger point moves to a cetane number CN lower than the reference cetane number CN1. This is because, when the cooling water temperature is low, even if the fuel has a high cetane number CN, the ignitability is reduced, the combustion peak due to the ignition delay is increased, and the NOx generation is promoted. . On the contrary, when the cooling water temperature is high, the ignitability is recovered even if the fuel has a low cetane number CN, and the combustion that was slow and delayed due to the poor ignitability has a combustion peak as well as the reference cetane number CN1. This is to prevent the NOx generation from being promoted greatly and rapidly.

  In the above example, the correction for the cooling water temperature and the fuel property is performed by multiplying the correction coefficient. However, the respective correction values are obtained based on the cooling water temperature and the fuel property, and this is calculated as the intake throttle valve. You may make it add to drive signal THduty and EGR valve drive signal EGRduty.

  In the present embodiment, the following effects can be achieved.

  (A) An exhaust gas recirculation device comprising an EGR passage 4 for recirculating part of the exhaust gas of the internal combustion engine 1 to the intake air of the internal combustion engine and an EGR valve 5 for controlling the exhaust gas recirculation rate to the intake air, and the cetane number of the fuel used , Octane number, evaporability, calorific value, aromatic hydrocarbon content, fuel property detection means (S200) for detecting at least one fuel property, and exhaust gas recirculation rate calculated according to the operating state of the internal combustion engine 1 The exhaust gas recirculation control means (S320) corrects the exhaust gas recirculation rate according to the fuel property detected by the fuel property detection means (S200), and controls the EGR valve 5 of the exhaust gas recirculation device according to the corrected exhaust gas recirculation rate. ). For this reason, the exhaust gas recirculation rate according to the operating state can be corrected according to the fuel properties, and the EGR valve 5 of the exhaust gas recirculation device can be controlled, and EGR control suitable for the properties of the fuel being used can be performed.

  (A) The exhaust gas recirculation control means (S320) is configured to control the exhaust gas recirculation rate with respect to the reference cetane number CN as the cetane number CN detected by the fuel property detection means (S200) deviates from a preset reference cetane number CN. In order to correct the exhaust gas recirculation rate to be relatively decreased, the slow combustion when the cetane number CN is lower than the reference cetane number CN and the ignition delay when the cetane number CN is higher than the reference cetane number CN are shortened and peaked. It is possible to obtain an appropriate EGR rate with respect to the combustion with suppressed.

  (C) Further, the exhaust gas recirculation control means (S320) decreases the EGR rate as the cooling water temperature is lower, but the cetane number CN detected by the fuel property detection means (S200) is greater than the preset reference cetane number CN. When the temperature is high, the exhaust gas recirculation rate is increased and corrected with respect to the set value of the reference cetane number CN as the temperature of the internal combustion engine 1 detected by the temperature detecting means 31 moves away from the preset temperature to the low temperature side. In the case of fuel having a high cetane number CN when the water temperature TW is low, the ignitability is reduced, the combustion peak due to the ignition delay is increased, and the generation of NOx is suppressed.

  (D) Intake air amount detection means (S220) for detecting the intake air amount Qair of the engine 1, fuel supply amount detection means (S230) for detecting the fuel supply amount Qmain to the engine 1, and the actual air-fuel ratio AFreal An actual air-fuel ratio detection means (S240) for detecting the fuel, and the specific gravity detection means (S260) detects the specific gravity of the fuel by the detected intake air amount Qair, fuel supply amount Qmain, and actual air-fuel ratio AFreal. The fuel property can be accurately determined by a practical method, and the fuel supply amount detection means (S230) obtains the fuel injection amount Qmain as map data from the detected engine speed Ne and the load L. Thus, the function originally provided in the engine can be diverted, and the cost is not increased. Further, the actual fuel supply weight is obtained by dividing the intake air flow rate Qair by the actual air-fuel ratio AFreal, and the actual specific gravity Gfuel is obtained by dividing the actual fuel supply weight by the main fuel injection amount (fuel supply amount). The air-fuel ratio AFreal can be detected with high accuracy and without an increase in cost, and the fuel property is obtained after taking the standard specific gravity in consideration of the fuel temperature, so that the fuel property can be detected with higher accuracy.

  In the above embodiment, the actual fuel supply weight Gmain is obtained by dividing the intake air flow rate Qair by the actual air-fuel ratio AFreal, and this actual fuel supply weight Gmain is divided by the fuel injection amount (fuel supply amount) Qmain. Gfue1 is obtained, and this is corrected with the fuel temperature TF to obtain the standard specific gravity Gstd. Instead of such a method, the fuel injection period Mperiod and the common rail pressure PCR in the fuel injection device 10 of the engine 1 are used. The fuel injection amount Qmain is obtained, the reference fuel injection weight Gmain is obtained from the fuel injection amount Qmain, the preset reference fuel specific gravity γstd, and the fuel temperature TF, and the air detected by the reference fuel injection weight Gmain and the air flow meter 7 is obtained. The reference air-fuel ratio AFstd is obtained from the weight Gair, and the reference air-fuel ratio AFstd is obtained. By comparing the actual air-fuel ratio AFreal detected by the air-fuel ratio sensor 37 can be made to determine the actual fuel specific gravity Ganmarea1.

The system block diagram of the diesel engine provided with the combustion control apparatus of this invention. The characteristic view which shows the relationship between the density of light oil, and a cetane number. The characteristic view which shows the relationship between the density of light oil, and aromatic hydrocarbon component content. The characteristic view which shows the relationship between the viscosity of light oil, and a cetane number. The figure which shows the correction coefficient (A) of the EGR valve drive signal for every cooling water temperature, and the correction coefficient (B) of an intake throttle valve drive signal. The figure which shows the characteristic of the request | required EGR rate which obtains the equal NOx reduction rate for every cetane number. FIG. 6 is a characteristic diagram of an intake throttle valve correction coefficient and an EGR valve correction coefficient using the cetane number of light oil and the coolant temperature as parameters. The flowchart which shows the basic control routine of a diesel engine. The flowchart which shows the control routine for fuel specific gravity detection. The flowchart which shows an engine exhaust control routine. The flowchart which shows an EGR control routine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 5 EGR valve 6 Intake throttle valve 10 Fuel injection apparatus 30 Engine control unit 31 Water temperature sensor

Claims (4)

An exhaust gas recirculation device comprising an EGR passage for recirculating part of the exhaust gas of the internal combustion engine to the engine intake air and an EGR valve for controlling an exhaust gas recirculation rate to the intake air;
Fuel property detecting means for detecting the cetane number as the property of the fuel being used;
Calculate the exhaust gas recirculation rate based on the operating state of the internal combustion engine,
Correct the exhaust gas recirculation rate according to the cetane number detected by the fuel property detection means,
An exhaust gas recirculation control means for controlling the EGR valve of the exhaust gas recirculation apparatus based on the corrected exhaust gas recirculation rate.
The exhaust gas recirculation control means makes the exhaust gas recirculation rate relative to the exhaust gas recirculation rate relative to the reference cetane number as the cetane number detected by the fuel property detection means deviates to a higher side and a lower side than a preset reference cetane number. A combustion control apparatus for an internal combustion engine, wherein the correction is performed so as to decrease the engine. The combustion control device for an internal combustion engine includes temperature detection means for detecting the temperature of the internal combustion engine,
When the cetane number detected by the fuel property detection means is higher than a preset reference cetane number, the exhaust gas recirculation control means has a temperature lower than the preset temperature detected by the temperature detection means. 2. The combustion control apparatus for an internal combustion engine according to claim 1 , wherein the exhaust gas recirculation rate is corrected to increase as it moves away from the engine . The fuel property detection means includes specific gravity detection means for detecting the specific gravity of the fuel being used,
The combustion control device for an internal combustion engine according to claim 1 or 2, wherein a cetane number as a fuel property is detected based on the specific gravity detected by the specific gravity detection means . The combustion control device for an internal combustion engine includes an intake air amount detection unit that detects an intake air amount of the internal combustion engine, a fuel supply amount detection unit that detects a fuel supply amount to the internal combustion engine, and an actual air fuel ratio that detects an actual air-fuel ratio. And a fuel ratio detecting means,
4. The combustion control apparatus for an internal combustion engine according to claim 3, wherein the specific gravity detecting means detects the specific gravity of the fuel based on the detected intake air amount, fuel supply amount, and actual air-fuel ratio .

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