Control system for internal combustion engine

A control system for an internal combustion engine having at least one fuel injection valve for injecting fuel into a combustion chamber of the engine, and an exhaust gas recirculation mechanism for recirculating a portion of exhaust gases from the engine to the combustion chamber. The exhaust gas recirculating mechanism includes an exhaust cooler for cooling the recirculated exhaust gases. A target ignition timing of the fuel injected by the fuel injection valve is calculated. An actual compression ignition timing of the fuel injected by the fuel injection valve is detected. Operation of the exhaust cooler is controlled based on the target ignition timing and the actual compression ignition timing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control system for an internal combustion engine and, particularly, to a control system that performs control according to an ignition timing of fuel supplied to the internal combustion engine.

2. Description of the Related Art

Japanese Patent Laid-open No. JP2004-100566 discloses a fuel injection control apparatus in which the cylinder pressure (i.e., pressure in the combustion chamber) is detected by a cylinder pressure sensor. A fuel injection amount, a fuel injection timing, and the like are controlled according to the detected cylinder pressure. According to the disclosed fuel injection control apparatus, a crank angle Cmax, wherein the cylinder pressure has reached a maximum value, is detected, and the fuel injection timing is corrected so that the detected crank angle Cmax coincides with the target value which is previously set according to the engine operating condition.

The cetane number of fuels distributed in the market varies in the range from “40” to “60”. Therefore, it is preferable to perform control suitable for the cetane number of the fuel being used by using a plurality of control maps corresponding to the plurality of cetane numbers of the fuels in the market. Under such control, the fuel injection control is more suitably adapted to the fuel being used as the number of control maps used increases.

However, if the number of control maps used increases too much, the problem of the amount of manpower necessary for setting the control maps increases and/or the memory capacity needed for storing the control maps increases.

SUMMARY OF THE INVENTION

The present invention was attained while contemplating the above-described situation, and an aspect of the present invention is to provide a control system for an internal combustion engine which performs the fuel injection control that is suitable for the fuel in use while also suppressing the number of control maps that need to be used.

In order to attain the above aspect, the present invention provides a control system for an internal combustion engine having fuel injection means for injecting fuel into a combustion chamber of the engine. The control system includes fuel injection control means, exhaust gas recirculating means, exhaust cooling means, target ignition timing calculating means, ignition timing detecting means, and exhaust cooling control means. The fuel injection control means controls the fuel injection means. The exhaust gas recirculating means recirculates a portion of exhaust gases from the engine to the combustion chamber. The exhaust cooling means, which is included in the exhaust gas recirculating means, cools the recirculated exhaust gases. The target ignition timing calculating means calculates a target ignition timing (CAFMM) of the fuel injected by the fuel injection means. The ignition timing detecting means detects an actual ignition timing (CAFM) of the fuel injected by the fuel injection means. The exhaust cooling control means controls an operation of the exhaust cooling means based on the target ignition timing (CAFMM) and the actual ignition timing (CAFM).

With the above-described structural configuration, the operation of the exhaust cooling means is controlled based on the target ignition timing and the actual ignition timing. For example, when the delay of the actual ignition timing with respect to the target ignition timing is rather large or prolonged, the actual ignition timing is advanced to a timing near the target ignition timing by stopping the operation of the exhaust cooling means. Further, when the delay of the actual ignition timing with respect to the target ignition timing is rather small or short, or when the actual ignition timing occurs before the target ignition timing, the actual ignition timing is controlled to be near the target ignition timing by operating the exhaust cooling means. Therefore, the actual ignition timing is made to be closer to the target ignition timing, while at the same time suppressing the number of the control maps corresponding to the cetane numbers of fuels.

Preferably, the fuel injection control means has first and second fuel injection timing maps (CAIMM1, CAIMM2), each of which is set according to an operating condition of the engine. The fuel injection control means uses the first fuel injection timing map (CAIMM1) when the exhaust cooling means is not operating or when the exhaust cooling means is operating and a delay (DCAM) of the actual ignition timing with respect to the target ignition timing is greater than a predetermined threshold value (an ignition delay amount corresponding to CETH2). The fuel injection control means uses the second fuel injection timing map (CAIMM2) when the exhaust cooling means is operating and the delay (DCAM) of the actual ignition timing with respect to the target ignition timing is equal to or less than the predetermined threshold value.

With the above-described structural configuration, when the exhaust cooling means is not operating or when the exhaust cooling means is operating and the delay of the actual ignition timing with respect to the target ignition timing is greater than the predetermined threshold value, the ignition timing is controlled using the first fuel injection timing map. When the delay of the actual ignition timing with respect to the target ignition timing is equal to or less than the predetermined threshold value, the ignition timing is controlled using the second fuel injection timing map. Therefore, the actual ignition timing is made to occur closer to the target ignition timing by switching the two fuel injection timing maps and by switching between the operation and stoppage of the exhaust cooling means.

Preferably, the control system further includes pressure detecting means for detecting a pressure in the combustion chamber. The fuel injection control means includes correcting means for correcting a fuel injection timing by the fuel injection means in a retarding direction according to an output (dp/dθ) of the pressure detecting means when the exhaust cooling means is operating.

With the above-described structural configuration, during operation of the exhaust cooling means, the fuel injection timing is corrected in the retarding direction according to the output of the pressure detecting means for detecting the pressure in the combustion chamber. When using the fuel of a high cetane number, there is a possibility that combustion noise may increase if the fuel injection timing is set to a value suitable for the fuel of a lower cetane number. Therefore, such a problem can be avoided by correcting the fuel injection timing in the retarding direction when the output of the pressure detecting means becomes rather large or great.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIGS. 1 and 2are schematic diagrams showing a configuration of an internal combustion engine and a control system therefor according to one embodiment of the present invention. The internal combustion engine1(hereinafter referred to as “engine”), which is a diesel engine, has four cylinders wherein fuel is injected directly into a combustion chamber. The combustion chamber of each cylinder is provided with a fuel injection valve6that is electrically connected to an electronic control unit4(hereinafter referred to as “ECU”). The ECU4controls a valve opening period and a valve opening timing of each fuel injection valve6. That is, the fuel injection period and fuel injection timing are controlled by the ECU4.

The engine1has an intake pipe7and an exhaust pipe8. An exhaust gas recirculation passage9for recirculating a portion of exhaust gases to the intake pipe7is provided between the exhaust pipe8and the intake pipe7. The exhaust gas recirculation passage9is provided with a recirculated exhaust cooler21for cooling recirculated exhaust gases, a bypass passage23for bypassing the recirculated exhaust cooler21, a switching valve22, and an exhaust gas recirculation control valve20(hereinafter referred to as “EGR valve”) that controls the amount of exhaust gases that are recirculated. The switching valve22switches between a state where the exhaust gas recirculation passage9is connected to the recirculated exhaust cooler21and a state where the exhaust gas recirculation passage9is connected to the bypass passage23. The EGR valve20is an electromagnetic valve having a solenoid. A valve opening of the EGR valve20is controlled by the ECU4. An exhaust gas recirculation mechanism includes the exhaust gas recirculation passage9, the recirculated exhaust cooler21, the bypass passage23, the switching valve22, and the EGR valve20.

Each cylinder of the engine1is provided with a cylinder pressure sensor2that is used for detecting a cylinder pressure (i.e., a pressure in the combustion chamber of the engine1). In this embodiment, the cylinder pressure sensor2is configured in one body together with a grow plug disposed in each cylinder. The detection signal of the cylinder pressure sensor2is supplied to the ECU4. It should be noted that the detection signal of the cylinder pressure sensor2corresponds to a differential signal of the cylinder pressure PCYL with respect to the crank angle (time), and the cylinder pressure PCYL is obtained by integrating the output of the cylinder pressure sensor.

The engine1is provided with a crank angle position sensor3for detecting a rotation angle of the crankshaft (not shown) of the engine1. The crank angle position sensor3generates one pulse at every 1 degree of the crank angle, wherein the pulse is supplied to the ECU4. The crank angle position sensor3further generates a cylinder discrimination pulse at a predetermined crank angle for a specific cylinder of the engine1and supplies the cylinder discrimination pulse to the ECU4.

An accelerator sensor25for detecting an operation amount AP of the accelerator pedal of the vehicle driven by the engine1, a coolant temperature sensor26for detecting a coolant temperature TW of the engine1, and an intake air temperature sensor27for detecting an intake air temperature TA of the engine1are connected to the ECU4. The detection signals of the sensors25-27are supplied to the ECU4.

The ECU4provides a control signal of the fuel injection valve6to a drive circuit5. The drive circuit5is connected to the injection valves6, and supplies drive signals according to the control signal from the ECU4to the fuel injection valves6. Fuel is thereby injected into the combustion chamber of each cylinder at the fuel injection timing in accordance with the control signal output from the ECU4. The fuel injection amount is controlled to the value in accordance with the control signal from the ECU4.

The ECU4includes an amplifier10, an A/D conversion block11, a pulse generation block13, a CPU14(Central Processing Unit), a ROM15(Read Only Memory) for storing programs executed by the CPU14, a RAM16(Random Access Memory) for storing calculation results, and the like, an input circuit17, and an output circuit18. The detection signal of the cylinder pressure sensor2is input to the amplifier10which amplifies the input signal. The signal amplified by the amplifier10is input to the A/D conversion block11. The pulse signal output from the crank angle position sensor3is input to the pulse generation block13.

The A/D conversion block11, which includes a buffer12, converts the cylinder pressure sensor output from the amplifier10to a digital value dp/dθ (hereinafter referred to as “pressure change rate”) and stores the converted digital value dp/dθ in the buffer12. Specifically, a pulse signal PLS1(hereinafter referred to as “one-degree pulse”) having a crank angle period of one degree is supplied to the A/D conversion block11from the pulse generation block13, the cylinder pressure sensor output is sampled at the intervals of the one-degree pulse PLS1to be converted to a digital value, and the digital value is stored in the buffer12.

A pulse signal PLS6having a crank angle period of six degrees is supplied to the CPU14from the pulse generation block13. The CPU14performs a process for reading the digital value stored in the buffer12at intervals of the six-degree pulse PLS6. That is, in the present embodiment, the A/D conversion block11does not request an interrupt to the CPU14, but the CPU14performs the reading process at intervals of the six-degree pulse PLS6.

The input circuit17converts the detection signals from various sensors to digital values and supplies the digital values to the CPU14. An engine rotational speed NE is calculated from the time period of the six-degree pulse PLS6. A demand torque TRQ of the engine1is calculated according to the operation amount AP of the accelerator pedal.

The CPU14calculates a target exhaust gas recirculation amount GEGR according to the engine operating condition and supplies a duty control signal for controlling an opening of the EGR valve20according to the target exhaust gas recirculation amount GEGR to the EGR valve20through the output circuit18. Further, the CPU14determines a cetane number of the fuel in use and performs switching control of the switching valve22according to the determined cetane number. If the switching valve22is switched to the recirculated exhaust cooler21side, a cooling of the recirculated exhaust gases is performed. On the other hand, if the switching valve22is switched to the bypass passage23side, the cooling of the recirculated exhaust gases is not performed.

FIG. 3is a block diagram showing a configuration of a module which calculates a main injection timing CAIM of the fuel injection valve6and the target exhaust gas recirculation amount GEGR (hereinafter referred to as “target EGR amount). The function of the module is realized by the processes executed by the CPU14.

The module shown inFIG. 3includes a main injection timing calculation block31for calculating the main injection timing CAIM, a target EGR flow rate calculation block32for calculating a target exhaust gas recirculation amount GEGR, a cetane number determination block33for estimating a cetane number CET of the fuel in use and outputting a determined cetane number parameter CETD according to the estimated cetane number, and an EGR cooler control block34. In this embodiment, the cetane number of the fuel in use is estimated in view of the cetane number of the fuels distributed in the market. When the estimated cetane number CET is equal to or less than a first threshold value CETH1(for example, 44), a determined cetane number parameter CETD is set to “1”. When the estimated cetane number CET is greater than the first threshold value CETH1and is equal to or less than a second threshold value CETH2(for example, 50), the determined cetane number parameter CETD is set to “2”. When the estimated cetane number CET is greater than the second threshold value CETH2, the determined cetane number parameter CETD is set to “3”.

The main injection timing calculation block31includes a first main injection timing map value calculation block41, a second main injection timing map value calculation block42, and a switching block43. The first main injection timing map value calculation block41retrieves a CAIMM1map, which is previously set according to the engine rotational speed NE and the demand torque TRQ, to calculate a first main injection timing map value CAIMM1. The CAIMM1map is set based on the fuel of the cetane number CET3(for example, 57) being greater than the second threshold value CETH2. The second main injection timing map value calculation block42retrieves a CAIMM2 map, which is previously set according to the engine rotational speed NE and the demand torque TRQ, to calculate a second main injection timing map value CAIMM2. The CAIMM2map is set based on the fuel of the cetane number CET2(for example, 46) which is between the first threshold value CETH1and the second threshold value CETH2. The cetane number CET2is an average cetane number of the fuels distributed in the market.

The switching block43selects the first main injection timing map value CAIMM1or the second main injection timing map value CAIMM2according to the determined cetane number parameter CETD and outputs the selected map value as a main injection timing CAIM. Specifically, when the determined cetane number parameter CETD is equal to “1” or “2”, the second main injection timing map value CAIMM2is selected. When the determined cetane number parameter CETD is equal to “3”, the first main injection timing map value CAIMM1is selected.

The target EGR flow rate calculation block32includes a first target EGR amount map value calculation block51, a second target EGR amount map value calculation block52, and a switching block53. The first target EGR amount map value calculation block51retrieves a GEGRM1 map, which is previously set according to the engine rotational speed NE and the demand torque TRQ, to calculate a first target EGR amount map value GEGRM1. The GEGRM1map is set based on the fuel of the cetane number CET3. The second target EGR amount map value calculation block52retrieves GEGRM2map, which is previously set according to the engine rotational speed NE and the demand torque TRQ, to calculate a second target EGR amount map value GEGRM2. The GEGRM2map is set based on the fuel of the cetane number CET2.

The switching block53selects the first target EGR amount map value GEGRM1or the second target EGR amount map value GEGRM2according to the determined cetane number parameter CETD and outputs the selected map value as a target EGR flow rate GEGR. Specifically, when the determined cetane number parameter CETD is equal to “1” or “2”, the second target EGR amount map value GEGRM2is selected. When the determined cetane number parameter CETD is equal to “3”, the first target EGR amount map value GEGRM1is selected.

The cetane number determination block33includes a target main injection ignition timing calculation block61, an ignition timing detection block62, a subtracting block63, a filtering block64, a switching block65, a cetane number estimation block66, and a determination parameter setting block67.

The target main injection ignition timing calculation block61retrieves a CAFMM map, which is previously set according to the engine rotational speed NE and the demand torque TRQ, to calculate a target main injection ignition timing CAFMM. The CAFMM map is set based on the fuel of the above-described cetane number CET2(for example, 46).

The ignition timing detection block62detects a main injection ignition timing CAFM according to the pressure change rate dp/dθ obtained by converting the output signal of the cylinder pressure sensor2to a digital value. The detection method thereof will be described later with reference toFIGS. 5-7C. The subtracting block63subtracts the main injection ignition timing CAFM from the target main injection ignition timing CAFMM to calculate an ignition delay angle DCAM.

The filtering block64performs filtering using the least-squares calculation method or the moving averaging calculation of data of the ignition delay angle DCAM obtained in a comparatively long time period (e.g., 10-60 seconds) to calculate a filtered ignition delay angle DCAMF. The switching block65is on/off controlled by a switching control signal SCTL set by a process shown inFIG. 4which is described below. The switching block65is turned off when the switching control signal SCTL is “0”, and turned on when the switching control signal SCTL is “1”. The switching control signal SCTL is set to “1” when an execution condition of the cetane number estimation is satisfied.

The cetane number estimation block66converts the ignition delay angle DCAMF to an ignition delay time period TDFM using the engine rotational speed NE and retrieves a CET table shown inFIG. 8according to the ignition delay time period TDFM to calculate the cetane number CET. The cetane number estimation block66applies the cetane number CET to equation (1) to calculate a cetane number learning value CETLRN.
CETLRN=α×CET+(1−α)×CETLRN(1)
where α is an averaging coefficient set to a value between “0” and “1”, and the CETLRN on the right side is a preceding calculated value.

When refueling, the cetane number learning value CETLRN is initialized to the cetane number CET2that corresponds to the average cetane number of the fuels distributed in the market and converges to the value indicative of the cetane number of the fuel in use upon subsequent learning.

The cetane number learning value CETLRN described above is calculated using all of the cylinder pressure sensor outputs corresponding to four cylinders. Therefore, an averaging of the cetane number CET detected in each cylinder and the cetane numbers CET, whose detection timings are different from each other, is performed by equation (1). When the cetane number estimation process is not executed, the latest cetane number learning value CETLRN of the stored learning values is output from the cetane number estimation block66.

The EGR cooler control block34outputs a switching control signal BVCMD to the switching valve22according to the determined cetane number parameter CETD. Specifically, the switching control signal BVCMD, which switches the switching valve22to the bypass passage23side, is output when the determined cetane number parameter CETD is equal to “1”. The switching control signal BVCMD, which switches the switching valve22to the recirculated exhaust cooler21side, is output when the determined cetane number parameter CETD is equal to “2” or “3”.

Next, the setting of the switching control signal SCTL is explained with reference toFIG. 4. The switching control signal setting process shown inFIG. 4is executed at predetermined time intervals in the CPU14.

In step S11, it is determined whether any failure of the sensors (e.g., the crank angle position sensor3, the accelerator sensor21, the cylinder pressure sensor2) necessary for the cetane number estimation process is detected. If the answer to step S11is affirmative (YES), the switching control signal SCTL is set to “0” (step S15). If no failure of the sensors is detected, it is determined whether the engine operating condition is in a predetermined operating region (for example, a region where the engine rotational speed NE is within the range from 1000 to 3000 rpm and the demand torque TRQ is within the range from 0 to 250 Nm) in which the cetane number estimation is performed (step S12). If the answer to step S12is negative (NO), the process proceeds to step S15described above. If the engine operating condition is in the predetermined operating region, it is determined whether the cetane number estimation is completed (step S13). Since the answer to step S13is negative (NO) at first, the cetane number estimation process is permitted, i.e., the switching control signal SCTL is set to “1” (step S14). Thereafter, when the estimation process is completed, the process proceeds to step S15from step S13.

FIG. 5is a block diagram showing a configuration of the ignition timing detection block62. The ignition timing detection block62includes a band pass filtering block71, a phase delay correction block72, and an ignition timing determination block73. The pressure change rate dp/dθ output from the cylinder pressure sensor2is input to the band pass filtering block71. InFIG. 6, the waveform W1shows an input waveform, and the waveform W2shows an output waveform. The phase delay occurring in the band pass filtering block71is corrected in the phase delay correction block72.

The ignition timing determination block73determines a crank angle position CAFP (hereinafter referred to as “pilot injection ignition timing”) at which the pressure change rate dp/dθ takes a peak value corresponding to the pilot injection and a crank angle position CAFM (hereinafter referred to as “main injection ignition timing”) at which the pressure change rate dp/dθ takes another peak value corresponding to the main injection. Specifically, as shown inFIG. 7C, the crank angle position at which the pressure change rate dp/dθ output from the phase delay correction block72exceeds a pilot detection threshold value DPP is determined to be the pilot injection ignition timing CAFP, and the crank angle position at which the pressure change rate dp/dθ exceeds a main detection threshold value DPM is determined to be the main injection ignition timing CAFM. In this embodiment, only the main injection ignition timing CAFM is used for estimating the cetane number CET.

InFIGS. 7A and 7B, a pilot injection pulse INJP started from a crank angle position CAIP and a main injection pulse INJM started from a crank angle position CAIM are shown. InFIG. 7C, an angle position range RDET (for example, 10 degrees), where the ignition timings CAFP and CAFM are detected, is shown. By limiting the detection angle position range RDET to a comparatively narrow range, as shown inFIG. 7C, the ignition timing is accurately determined without increasing calculation load on the CPU14.

FIG. 10is a diagram illustrating a fuel injection control, an exhaust gas recirculation amount control, and a recirculated exhaust cooling control in this embodiment. Region1ofFIG. 10shows a cetane number region where the determined cetane number parameter CETD is equal to “1”, Region2shows a cetane number region where the determined cetane number parameter CETD is equal to “2”, and Region3shows a cetane number region where the determined cetane number parameter CETD is equal to “3”.

In Region1, the fuel injection control and the exhaust gas recirculation amount control are performed using maps for low cetane numbers, i.e., using the second main injection timing map value CAIMM2and the second target EGR amount map value GEGRM2, and cooling of the recirculated exhaust gases is not performed. By stopping the cooling of the recirculated exhaust gases, ignitionability of the fuel of a cetane number lower than the cetane number CET2, which is a reference for setting the maps for fuels of low cetane numbers, is improved.

In Region2, the fuel injection control and the exhaust gas recirculation amount control are performed using the maps for fuels of low cetane numbers, i.e., the second main injection timing map value CAIMM2and the second target EGR amount map value GEGRM2, and the cooling of recirculated exhaust gases is performed. In Region2, the cetane number CET2used as the reference for setting the maps for fuels of low cetane numbers (CAIMM2map and GEGRM2map) is included. By using the maps for fuels of low cetane numbers and performing the cooling of recirculated exhaust gases, optimal fuel injection control and exhaust gas recirculation amount control is performed.

In Region3, the fuel injection control and the exhaust gas recirculation amount control are performed using the maps for fuels of high cetane numbers, i.e., the first main injection timing map value CAIMM1and the first target EGR amount map value GEGRM1, and the cooling of recirculated exhaust gases is performed. In Region3, the cetane number CET3used as the reference for setting the maps for fuels of high cetane numbers (CAIMM1map and GEGRM1map) is included. By using the maps for fuels of high cetane numbers and performing the cooling of recirculated exhaust gases, optimal fuel injection control and exhaust gas recirculation amount control is performed.

As described above, in this embodiment, the controls corresponding to the three regions of fuel are performed using the two maps and according to whether the cooling of recirculated exhaust gases is performed or not. Consequently, the actual ignition timing is made closer to the target ignition timing, and the exhaust gas recirculation amount control is appropriately performed, while suppressing the number of control maps corresponding to the cetane number of fuels.

In this embodiment, the fuel injection valve6corresponds to the fuel injection means; the recirculated exhaust cooler21and the switching valve22correspond to the exhaust cooling means; the exhaust gas recirculation passage9, the exhaust gas recirculation control valve20, the recirculated exhaust cooler21, the bypass passage23, and the switching valve22define the exhaust gas recirculating means; and the ECU4forms the fuel injection control means, the target ignition timing calculating means, a portion of the ignition timing detecting means, and the exhaust cooling control means. Specifically, the main injection timing calculation block31ofFIG. 3corresponds to the fuel injection control means. The target main injection ignition timing calculation block61corresponds to the target ignition timing calculating means. The ignition timing detection block62corresponds to a portion of the ignition timing detecting means, and the EGR cooler control block34corresponds to the exhaust cooling control means. The state where the switching valve22is switched to the recirculated exhaust cooler21side corresponds to the state where the exhaust cooling means is operating, and the state where the switching valve22is switched to the bypass passage23side corresponds to the state where the exhaust cooling means is not operating.

Second Embodiment

This embodiment is obtained by replacing the main injection timing calculation block31shown inFIG. 3with a main injection timing calculation block31ashown inFIG. 11. Except for this difference, the structure of the second embodiment is the same as in the first embodiment. The main injection timing calculation block31ashown inFIG. 11includes a main injection timing map value calculation block44, a target pressure change rate calculation block45, a subtracting block46, a PI control block47, a switching block48, and an adding block49.

The main injection timing map value calculation block44, like the second main injection timing map value calculation block42shown inFIG. 3, retrieves the CAIMM map, which is set based on the cetane number CET2(for example, 46) according to the engine rotational speed NE and the demand torque TRQ, to calculate a main injection timing map value CAIMM.

The target pressure change rate calculation block45retrieves a dp/dθM map according to the engine rotational speed NE and the demand torque TRQ to calculate a target pressure change rate dp/dθM. The dp/dθM map is set so that the combustion noise does not become excessively large in a high load operating condition. The subtracting block46subtracts the pressure change rate dp/dθ from the target pressure change rate dp/dθM to calculate a pressure change rate deviation Ddp/dθ.

The PI control block47calculates a correction amount CAD of the main injection timing with the PI (proportional/integral) control method so that the pressure change rate deviation Ddp/dθ may become “0”. The switching block48selects the correction amount CAD or “0” according to the determined cetane number parameter CETD. Specifically, if the determined cetane number parameter CETD is equal to “1” or “2”, the value “0” is output. If the determined cetane number parameter CETD is equal to “3”, the correction amount CAD is output.

The adding block49adds the correction amount CAD to the main injection timing map value CAIMM to calculate the fuel injection timing CAIM. For example, if the detected pressure change rate dp/dθ becomes greater than the target pressure change rate dp/dθM, the pressure change rate deviation Ddp/dθ takes a negative value and the absolute value of the pressure change rate deviation Ddp/dθ increases. The correction amount CAD is then set to a negative value corresponding to the pressure change rate deviation Ddp/dθ. The absolute value of the correction amount CAD is controlled to increase as the absolute value of the pressure change rate deviation Ddp/dθ increases. As such, the main injection timing map value CAIMM is corrected in the retarding direction, i.e., the direction in which the pressure change rate dp/dθ decreases, and the pressure change rate dp/dθ is controlled to converge to the target pressure change rate dp/dθM.

FIG. 12is a diagram showing the fuel injection control and recirculated exhaust cooling control in this embodiment. In this embodiment, the CAIMM map is a map for fuels of low cetane numbers (i.e., a map based on the fuel of the cetane number CET2). The controls in Regions1and2are substantially the same as those of the first embodiment.

In Region3, the fuel injection control is performed using the CAIMM map (the map for fuels of low cetane numbers). Further, the control (NV control) for reducing the combustion noise is performed by controlling the pressure change rate dp/dθ in a feedback manner to the target pressure change rate dp/dθM. Therefore, the combustion noise is suppressed even if the maps for fuels of low cetane numbers are used.

As described above, in this embodiment, only one map for calculating the fuel injection timing is used, and the control (NV control) for reducing the combustion noise is performed with respect to the high cetane number fuel of which the determined cetane number parameter CETD is “3”. Consequently, the number of the control maps is further reduced compared with the first embodiment, while suppressing the problem of combustion noise.

In this embodiment, the main injection timing calculation block31acorresponds to the fuel injection control means.

The present invention is not limited to the embodiments described above, and various modifications may be made thereto. For example, in the embodiments described above, the estimated cetane number CET of the fuel in use is calculated according to the ignition delay angle DCAM obtained by subtracting the detected ignition timing CAFM from the target main injection ignition timing CAFMM. Further, the fuel injection control, the exhaust gas recirculation control, and the recirculated exhaust cooling control are performed according to the estimated cetane number CET. Alternatively, the fuel injection control, the exhaust gas recirculation control, and the recirculated exhaust cooling control may be performed according to the ignition delay time period TDFM.

Further, in the above-described second embodiment, the NV control is performed by controlling the pressure change rate dp/dθ in a feedback manner to the target pressure change rate dp/dθM. Alternatively, a more simplified control method may be adopted. That is, the fuel injection timing may be corrected in the retard direction when the detected pressure change rate dp/dθ exceeds a predetermined change rate dp/dθX (for example, 0.5 MPa/deg).

Further, in the above-described embodiments, the actual ignition timing CAFM is detected as a timing at which the pressure change rate dp/dθ detected by the cylinder pressure sensor2exceeds the detection threshold value DPM. Alternatively, the actual ignition timing CAFM may be determined as a timing at which the heat release rate reaches a value of 50% of the maximum value.

In the above-described embodiments, the present invention is described with regard to a 4-cylinder diesel internal combustion engine. However, the present invention can be implemented in a diesel internal combustion engine having another number of cylinders, or a watercraft propulsion engine, such as an outboard engine having a vertically extending crankshaft.