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. A compression end temperature in the combustion chamber is estimated. A target compression end temperature is calculated according to an operating condition of the engine. A main injection and a plurality of pilot injections before the main injection are performed by at least one fuel injection valve. A fuel injection amount in a first-performed pilot injection of the plurality of pilot injections is controlled so that the estimated compression end temperature coincides with the target compression end temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control system for an internal combustion engine in which compression ignition is performed, and particularly to a control system for controlling an amount of fuel injected during a pilot injection of fuel that is performed before a main injection of fuel.

2. Description of the Related Art

Japanese Patent Publication No. 3572435 (JP '435) discloses a control system for an internal combustion engine that estimates a compression end temperature that is a temperature of an air-fuel mixture in a cylinder when a piston is positioned at a compression top dead center. The control system disclosed by JP '435 increases the pilot injection amount of fuel when the estimated compression end temperature becomes relatively high. The control system of JP '435 suppresses a combustion noise by increasing the pilot injection amount of fuel in a high-load operating condition of an engine.

The ignitionability of fuel in the compression-ignition internal combustion engine depends on the compression end temperature during a low temperature condition, e.g., immediately after the cold start of the engine, or in a low load operating condition immediately after starting the engine. If similar control for a high load operating condition is attempted by the control system taught by JP '435, as in the low temperature condition or in the low load operating condition, the ignitionability of fuel is known to degrade.

SUMMARY OF THE INVENTION

The present invention was made in contemplation of the above-described point, and an aspect of the invention is to provide a control system for an internal combustion engine, which appropriately controls an amount of fuel injection during the pilot injection, thereby obtaining stable ignitionability, especially in a low temperature condition, or in a low load operating condition, of the engine.

To attain the above aspect, the present invention provides a control system for an internal combustion engine having a fuel injector for injecting fuel into a combustion chamber of the engine. The control system includes a compression end temperature estimator, a target compression end temperature setter, and a fuel injection controller. The compression end temperature estimator estimates a compression end temperature in the combustion chamber. The target compression end temperature setter sets a target compression end temperature according to an operating condition of the engine. The fuel injection controller performs a plurality of pilot injections via the fuel injection means before performing the main injection. The fuel injection controller controls a fuel injection amount in a first-performed pilot injection of a plurality of pilot injections so that the estimated compression end temperature coincides with the target compression end temperature.

With the above-described structural configuration, the fuel injection amount in the first-performed pilot injection is controlled so that the estimated compression end temperature coincides with the target compression end temperature, which is set according to the engine operating condition. The compression end temperature tends to become higher as the fuel injection amount of the first-performed pilot injection increases. Therefore, by controlling the first-performed pilot injection amount so that the estimated compression end temperature coincides with the target compression end temperature, an appropriate compression end temperature is realized and stabile ignitionability is obtained during the low temperature condition, or during the low load operating condition, of the engine.

Preferably, the control system further includes a pressure detector for detecting the pressure in the combustion chamber, and the compression end temperature estimator estimates the compression end temperature according to the pressure detected by the cylinder pressure detector.

With the above-described structural configuration, the compression end temperature is estimated according to the detected pressure in the combustion chamber. Comparatively, the estimation is performed more accurately, for example, with a method of estimating the compression end temperature, according to the intake air temperature.

The present invention also provides a control system for an internal combustion engine having a fuel injector for injecting fuel into a combustion chamber. The control system includes a cylinder pressure detector, a heat release amount calculator, and fuel injection controller. The cylinder pressure detector detects a pressure in the combustion chamber. The heat release amount calculator calculates a heat release amount in a predetermined crank angular range according to a pressure detected by the cylinder pressure detector. The fuel injection controller performs a main injection and a plurality of pilot injections before the main injection through the fuel injector. The fuel injection controller controls a fuel injection amount in a first-performed pilot injection of the plurality of pilot injections according to the heat release amount calculated by the heat release amount calculator.

With the above-described structural configuration, the heat release amount in the predetermined crank angular range is calculated according to the detected pressure in the combustion chamber, and the amount of fuel injected during the first pilot injection of the plurality of pilot injections is controlled according to the calculated heat release amount. The heat release amount from the pilot injection occurring immediately before the main injection is detected by appropriately setting the predetermined crank angular range. Further, by controlling the fuel injection amount of the first-performed pilot injection according to the heat release amount, ignitionability of the fuel injected during the pilot injection immediately before the main injection is improved, and, consequently, ignitionability of the fuel injected during the main injection is also improved. Accordingly, stable ignitionability is obtained, especially in the low temperature condition, or the low load operating condition, of the engine.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

According to one embodiment of the present invention,FIGS. 1 and 2are schematic diagrams of an internal combustion engine and a control system. The internal combustion engine1(hereinafter referred to as “engine”), has four cylinders and is a diesel engine, wherein fuel is injected directly into the cylinders. Each cylinder is provided with a fuel injection valve6electrically connected to an electronic control unit4(hereinafter referred to as “ECU4”). The ECU4controls a valve opening period and a valve opening timing of each fuel injection valve6.

The engine1has an intake pipe22, an exhaust pipe24, and a turbocharger28. The turbocharger28includes a turbine30and a compressor29. The turbine30is driven by the kinetic energy of exhaust gases. The compressor29, which is rotationally driven by the turbine30, compresses the intake air of the engine1.

The turbine30has a plurality of movable vanes (not shown), and is configured so that the rotational speed of the turbine30is adjusted by changing an opening of the movable vanes (hereinafter referred to as “vane opening”). The vane opening of the turbine30is electro-magnetically controlled by the ECU4.

The intake pipe22is provided with an intercooler25on the downstream side of the compressor29for cooling pressurized air.

An exhaust gas recirculation passage26for recirculating exhaust gases to the intake pipe22is provided between the upstream side of the turbine30in the exhaust pipe24and the intake pipe22. The exhaust gas recirculation passage26is provided with an exhaust gas recirculation control valve27(hereinafter referred to as “EGR valve”), that controls the amount of recirculated exhaust gases. The EGR valve27is an electromagnetic valve having a solenoid, wherein a valve opening of the EGR valve27is controlled by the ECU4.

The intake pipe22is provided with an intake air flow rate sensor31for detecting an intake air flow rate GA on the upstream side of the turbine29, and an intake air temperature sensor32for detecting an intake air temperature TIN on the downstream side of an intercooler25. The exhaust pipe24is provided with an exhaust pressure sensor33for detecting an exhaust pressure PEX, and an exhaust gas temperature sensor34for detecting an exhaust gas temperature TEX on the upstream side of the turbine30. The detection signals of sensors31through35are supplied to the ECU4.

Each cylinder of the engine1is provided with a cylinder pressure sensor2for detecting a cylinder pressure (a pressure in the combustion chamber of the engine1). In this embodiment, the cylinder pressure sensor2is configured in one body with the glow plug disposed in each cylinder. The detection signal of the cylinder pressure sensor2is supplied to the ECU4. It is to 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 deg of the crank angle, and 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 engine1, and supplies the cylinder discrimination pulse to the ECU4.

An accelerator sensor35for detecting an operation amount AP of the accelerator pedal of the vehicle driven by the engine1, a coolant temperature sensor36for detecting a coolant temperature TW of the engine1, a boost pressure sensor (not shown) for detecting an intake pressure (boost pressure) PB on the downstream side of the turbocharger28, and a vehicle speed sensor (not shown) for detecting a vehicle speed VP of the vehicle are connected to the ECU4. The detection signals of the above-listed sensors are supplied to the ECU4.

The ECU4provides a control signal of the fuel injection valve6, provided in the combustion chamber of each cylinder of the engine1, to a drive circuit5. The drive circuit5is connected to the fuel injection valves6, and supplies drive signals to the fuel injection valves6according to the control signal from the ECU4. Fuel is thereby injected into the combustion chamber of each cylinder at a fuel injection timing in accordance with the control signal output from the ECU4. The fuel injection amount is controlled to a value in accordance with the control signal from the ECU4.

The ECU4includes an amplifier10, an A/D converter11, a pulse generator13, 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, etc., an input circuit17, and an output circuit18. The detection signal of the cylinder pressure sensor2is input to the amplifier10. The amplifier10amplifies the input signal. The signal amplified by the amplifier10is input to the A/D converter11. The pulse signal output from the crank angle position sensor3is input to the pulse generator13.

The A/D converter11, which includes a buffer12, converts the cylinder pressure sensor output from the amplifier10to a digital value (hereinafter referred to as “pressure change rate”) dp/dθ, and stores the converted digital value 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 converter11from the pulse generator13, the cylinder pressure sensor output is sampled at 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 PLS6, having a crank angle period of six degrees, is supplied to the CPU14from the pulse generator13. 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 converter11does not request an interrupt from 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 intake air flow rate GACMD, according to the engine operating condition, and supplies a duty control signal for controlling an opening of the EGR valve27to the EGR valve27through the output circuit18. The duty control signal is generated so that the detected air flow rate GA coincides with the target intake air flow rate GACMD.

In this embodiment, the pilot injection of fuel is performed twice before the main injection of fuel with the fuel injection valve6(double pilot injection mode) in a predetermined operating condition of the engine1in order to secure stable combustion. Normally, one pilot injection INJP is performed before the main injection INJM (single pilot injection mode), as shown inFIG. 3A. In the double pilot injection mode, the pilot injection, which is performed at a timing near compression top dead center, is referred to as “first pilot injection INJP1”, and the other pilot injection, which is performed before the first pilot injection INJP1, is referred to as “second pilot injection INJP2”. In the single pilot injection mode, only one pilot injection INJP, corresponding to the first pilot injection INJP1, is performed.

For example, the main injection INJM is performed at a timing substantially equal to the compression top dead center (CA=0), the first pilot injection INJP1is performed at a timing of about 13 degrees (CA=−13) before the top dead center, and the second pilot injection INJP2is performed at a timing of about 20 degrees (CA=−20) before the top dead center. Further, if a pilot injection amount QIP in the single pilot injection mode is set to about 4 mg per one injection, a first pilot injection amount QIP1and a second pilot injection amount QIP2in the double pilot injection mode is set, respectively, to about 2 mg.

FIGS. 4A and 4Bare time charts showing changes in a heat release rate ROHR. The solid line L1and the dashed line L2, respectively, correspond to examples in which the pilot injection amount is set to 4 mg and 6 mg in the single pilot injection mode. The dot-and-dash line L3corresponds to an example in which the first pilot injection amount QIP1and the second pilot injection amount QIP2are set to 2 mg (i.e., the total amount is 4 mg), in the double pilot injection mode.FIG. 4Bshows an expanded portion ofFIG. 4Ain the vicinity of the compression top dead center (CA=0 deg).

According toFIGS. 4A and 4B, it is confirmed that an ignition timing CAIGSP at which the heat release rate ROHR begins to increase in response to the pilot injection, hardly changes, even if the pilot injection amount changes in the single pilot injection mode. On the other hand, the ignition timing CAIGDP in the double pilot injection mode advances from the ignition timing CAIGSP.

FIGS. 5A and 5Bare time charts showing changes in a temperature TCYL in the cylinder. The solid line L4and the dashed line L5ofFIGS. 5A and 5B, respectively, correspond to examples in which the pilot injection amount is set to 4 mg and 6 mg in the single pilot injection mode. The dot-and-dash line L6corresponds to an example in which both of the first pilot injection amount QIP1and the second pilot injection amount QIP2are set to 2 mg (e.g., the total amount is 4 mg) in the double pilot injection mode.FIG. 5Bshows an expanded part ofFIG. 5Ain the vicinity of the compression top dead center (CA=0 deg).

As clearly seen fromFIGS. 5A and 5B, the temperature in the cylinder, when the piston is positioned at the compression top dead center, i.e., the compression end temperature TCMP in the double pilot injection mode, becomes higher than the temperature in the cylinder in the single pilot injection mode. Therefore, it is confirmed that the ignition timing CAIGDP in the double pilot injection mode advances from the ignition timing CAIGSP in the single pilot injection mode since the compression end temperature TCMP becomes higher.

FIG. 6shows a relationship between the second pilot injection amount QIP2and the compression end temperature TCMP. If the second pilot injection amount QIP2increases, the compression end temperature TCMP becomes high. Therefore, the compression end temperature TCMP is controlled by changing the second pilot injection amount QIP2in the double pilot injection mode.

Therefore, in this embodiment a target compression end temperature TCMPCMD is set according to the engine operating condition, and a feedback control is performed so that an estimated compression end temperature TCMPE, which is estimated based on the engine operating condition, coincides with the target compression end temperature TCMPCMD. Accordingly, the actual compression end temperature TCMP is appropriately controlled, thereby obtaining stable ignitionability.

FIG. 7is a block diagram showing a configuration of an injection amount calculation module for calculating a main injection amount QIM, the first pilot injection amount QIP1, and the second pilot injection amount QIP2of fuel injected by the fuel injection valve6. The function of the injection amount calculation module is realized by the process executed by the CPU14.

The injection amount calculation module shown inFIG. 7includes a demand torque calculator41, a total injection amount calculator42, a first pilot injection amount calculator43, a second pilot injection amount map value calculator44, subtracting blocks45and46, a target compression end temperature calculator47, an estimated compression end temperature calculator48, a subtracting block49, a correction amount calculator50, and an adding block51.

The demand torque calculator41calculates a demand torque TRQ of the engine1according to the accelerator pedal operation amount AP. The demand torque TRQ is calculated to be substantially proportional to the accelerator pedal operation amount AP. However, when the accelerator pedal operation amount AP rapidly increases, the increase in the demand torque TRQ is limited in order to suppress smoke.

The total injection amount calculator42retrieves a total injection amount map (not shown), which is previously set according to the demand torque TRQ and the engine rotational speed NE, to calculate a total injection amount QIT. The subtracting blocks45and46subtract the first pilot injection amount QIP1and the second pilot injection amount QIP2from the total injection amount QIT to calculate the main injection amount QIM. The total injection amount map is set so the total injection amount QIT increases as the demand torque TRQ, and/or the engine rotational speed NE, increase(s).

The first pilot injection amount calculator43retrieves a first pilot injection amount map (not shown), which is previously set according to the demand torque TRQ and the engine rotational speed NE, to calculate the first pilot injection amount QIP1.

The second pilot injection amount map value calculator44retrieves a second pilot injection amount map (not shown), which is previously set according to the demand torque TRQ and the engine rotational speed NE, to calculate a second pilot injection amount map value QIP2M.

The target compression end temperature calculator47retrieves a target compression end temperature map (not shown), which is previously set according to the demand torque TRQ and the engine rotational speed NE, to calculate the target compression end temperature TCMPCMD.

The estimated compression end temperature calculator48calculates the estimated compression end temperature TCMPE according to the detected cylinder pressure PCYL. Specifically, a cylinder pressure PCYL0, when the piston is positioned at the compression top dead center, is applied to equation (1). By using the detected cylinder pressure PCYL, an accurate value of the estimated compression end temperature TCMPE is obtained.
TCMPE=KC×PCYL0×VCYL0/(GT0×R0)  (1)

In equation (1), “KC” is a constant set to a predetermined value, “VCYL0” is a cylinder volume when the piston is positioned at the compression top dead center, “GT0” is a weight kg/cycle of total gases which exist in the cylinder, and “R0” is a modified gas constant.

The total gas weight GT0is a sum of an intake fresh air weight GAW kg/cycle and a residual gas weight GR kg/cycle in the cylinder, as shown in equation (2). The intake fresh air weight GAW is obtained by integrating the intake air flow rate GA.
GT0=GAW+GR(2)

The residual gas weight GR is calculated by applying an average intake gas temperature TINAV, an average exhaust pressure PEXAV, and an average exhaust gas temperature TEXAV to equations (3) and (4). The average intake gas temperature TINAV, the average exhaust pressure PEXAV, and the average exhaust gas temperature TEXAV are calculated as average values in one combustion cycle. In equation (3), “α” is a temperature coefficient which is calculated by equation (4), “VST” is a cylinder capacity, “Rr” is a corrected gas constant, and “ε” is a compression ratio. It is to be noted that the temperature coefficient α is set to “0.9” when the temperature coefficient α, calculated by equation (4), is greater than “0.9”. Further, in equation (3), the corrected gas constant “Rr” is applied, instead of the gas constant “R”, since the constitution of the air-fuel mixture in the combustion chamber changes depending on a flow rate of recirculated exhaust gases. The corrected gas constant “Rr” is obtained by correcting the gas constant “R” for every combustion cycle according to the recirculated exhaust gas flow rate and the intake air flow rate.

The modified gas constant R0in equation (1) is calculated by equation (5). In equation (5), “R” is a gas constant and “λAV” is an average excessive air ratio calculated by equation (6).
R0=R−(0.14/λAV)  (5)
λAV=Gab/(Thair×Grb)  (6)

In equation (6), “Gab” is a modified air weight calculated by equation (7), “Grb” is a modified residual gas weight calculated by equation (8), and “Thair” is a theoretical air amount (=14.512).
Gab=Ga+Gr×(1−Gf/Ga)  (7)
Grb=Gr×Gf/Ga(8)
where “Gf” is a fuel weight kg/cycle injected per 1 cycle, which corresponds to the total injection amount QIT in this embodiment.

The subtracting block49subtracts the estimated compression end temperature TCMPE from the target compression end temperature TCMPCMD to calculate a temperature difference DTCMP. The correction amount calculator50calculates a correction amount QIP2C so the temperature difference DTCMP becomes “0” with the PID (proportional, integral and differential) control. The correction amount QIP2C is calculated to increase as the temperature difference DTCMP increases.

FIG. 8is a block diagram showing a configuration of an injection timing calculation module which calculates execution timings of the fuel injection with the fuel injection valve6, i.e., a main injection timing CAM, a first pilot injection timing CAP1, and a second pilot injection timing CAP2. The function of the injection timing calculation module is realized by the operation process executed by the CPU14.

The injection timing calculation module includes a main injection timing calculator61, a first pilot injection timing calculator62, and a second pilot injection timing calculator63. The injection timing calculators61to63, respectively, retrieve a main injection timing map, a first pilot injection timing map, and a second pilot injection timing map, which are previously set according to the demand torque TRQ and the engine rotational speed NE, to calculate the main injection timing CAM, the first pilot injection timing CAP1, and the second pilot injection timing CAP2.

As described above, in this embodiment the second pilot injection amount QIP2is controlled so that the estimated compression end temperature TCMPE coincides with the target compression end temperature TCMPCMD, which is set according to the demand torque TRQ and the rotational speed NE. The compression end temperature TCMP tends to become higher as the second pilot injection amount QIP2, which is an injection amount of the first pilot injection, increases. Accordingly, by controlling the second pilot injection amount QIP2so the estimated compression end temperature TCMPE coincides with the target compression end temperature TCMPCMD, an appropriate value of the compression end temperature is secured to obtain stable ignitionability.

In this embodiment, the fuel injection valve6corresponds to the fuel injection means, and the cylinder pressure sensor2corresponds to the cylinder pressure detecting means. Further, the cylinder pressure sensor2, the intake air flow rate sensor31, the intake air temperature sensor32, the exhaust gas temperature sensor33, and the exhaust pressure sensor34constitute a part of the compression end temperature estimating means. Further, the ECU4constitutes a part of the compression end temperature estimating means, the target compression end temperature setting means, and the fuel injection control means. Specifically, the total injection amount calculator42, the first pilot injection amount calculator43, the second pilot injection amount map value calculator44, the subtracting blocks45,46, and49, the correction amount calculator50, and the adding block51inFIG. 7, the main injection timing calculator61, the first pilot injection timing calculator62, and the second pilot injection timing calculator63inFIG. 8, correspond to the fuel injection control means. The target compression end temperature calculator47corresponds to the target compression end temperature setting means. The estimated compression end temperature calculator48corresponds to the compression end temperature estimating means.

Second Embodiment

In a second embodiment according to the present invention, a heat release amount in a predetermined crank angular range is calculated according to the detected cylinder pressure PCYL, and the fuel injection amount of the first pilot injection is controlled according to the calculated heat release amount when performing a plurality of pilot injections. The points in this embodiment, which are comparatively different from the first embodiment, will be described below.

As shown inFIG. 5, by adopting the double pilot injection mode, the compression end temperature TCMP is raised to improve the ignitionability of the fuel. Specifically, it is considered that the compression end temperature TCMP is raised by a combustion, or a low-temperature oxidation, of the fuel injected by the second pilot injection INJP2to accelerate ignition of the fuel injected in the first pilot injection INJP1, which consequently improves ignitionability of the fuel injected by the main injection INJM.

FIG. 9Ashows changes in the heat release rate ROHR in the double pilot injection mode, andFIG. 9Bshows execution timings of two pilot injections INJP1and INJP2. and the main injection INJM. As shown inFIGS. 9A and 9B, the heat release rate ROHR increases in accordance with each fuel injection.

As shown inFIG. 9A, in this embodiment a heat release amount QHR in a window period TWND (i.e., a heat release amount corresponding to the first pilot injection INJP1) is calculated based on the detected pressure change rate dp/dθ and cylinder pressure PCYL, and the second pilot injection amount QIP2is controlled so that the calculated heat release amount QHR coincides with a target heat release amount QHRCMD, which is set according to the engine operating condition. With such control, the second pilot injection amount QIP2is appropriately controlled to obtain stable ignitionability of the fuel, especially in a low temperature condition or in a low load operating condition of the engine1.

FIG. 10is a block diagram showing a configuration of an injection amount calculation module, which calculates the main injection amount QIM, the first pilot injection amount QIP1, and the second pilot injection amount QIP2of fuel injected with the fuel injection valve6. The function of the injection amount calculation module is realized by the operation process executed by the CPU14.

The injection amount calculation module shown inFIG. 10includes the demand torque calculator41, the total injection amount calculator42, the first pilot injection amount calculator43, the second pilot injection amount map value calculator44, the subtracting blocks45and46, a target heat release amount calculator71, a heat release amount calculator72, a window setter73, a subtracting block74, a correction amount calculator75, and the adding block51. Subsequently, the module shown inFIG. 10is obtained by deleting the target compression end temperature calculator47, the estimated compression end temperature calculator48, the subtracting block49, and the correction amount calculator50in the injection amount calculation module shown inFIG. 7, and by adding the target heat release amount calculator71, the heat release amount calculator72, the window setter73, the subtracting block74, and the correction amount calculator75.

The target heat release amount calculator71retrieves a target heat release amount map (not shown), which is previously set according to the demand torque TRQ and the engine rotational speed NE, to calculate the target heat release amount QHRCMD in the window period TWND.

The heat release amount calculator72calculates the heat release rate ROHR J/deg according to the detected pressure change rate dp/dθ and cylinder pressure PCYL, and calculates the heat release amount QHR by integrating the heat release rate ROHR in the window period TWND. The heat release rate ROHR is calculated by equation (11).
ROHR=κ/(κ−1)×PCYL×dV/dθ+1/(κ−1)×VCYL×dp/dθ(11)

In equation (11), “κ” is a specific heat ratio of the air-fuel mixture, “PCYL” is a detected pressure in the cylinder, “dV/dθ” is a cylinder volume increase rate m3/deg, “VCYL” is a cylinder volume, and “dp/dθ” is a pressure change rate kPa/deg.

Shown inFIG. 9A, the window setting block73sets the window period TWND according to the first pilot injection timing CAP1calculated by the fuel injection timing calculation module shown inFIG. 8. Specifically, as an example, a first pilot injection end timing CAP1E is calculated according to the first pilot injection timing CAP1and the first pilot injection amount QIP1; a window start timing CAWS is set to the first pilot injection end timing CAP1E; and a window end timing CAWE is set to a timing obtained by adding a predetermined angle DCAW (for example, 13 degrees) to the window start timing CAWS. Alternatively, the window end timing CAWE may be set according to the heat release rate ROHR. For example, the window end timing CAWE may be set to a timing at which the heat release rate ROHR first reaches “0” after the window start timing CAWS.

The subtracting block74subtracts the heat release amount QHR from the target heat release amount QHRCMD to calculate a heat release amount difference DQHR. The correction amount calculator75calculates a correction amount QIP2Ca so the heat release amount difference DQHR becomes “0” with the PID (proportional, integral and differential) control. The correction amount QIP2Ca is calculated to increase as the heat release amount difference DTCMP increases.

Since the heat release amount QHR in the window period TWND changes depending not only on the first pilot injection amount QIP1, but also on the second pilot injection amount QIP2, the first pilot injection amount QIP1becomes substantially constant if the engine operating condition is substantially steady. Therefore, by calculating the second pilot injection amount QIP2using the correction amount QIP2Ca, the heat release amount QHR is made to coincide with the target heat release amount QHRCMD.

As described above, in this embodiment the second pilot injection amount QIP2is controlled so the heat release amount QHR corresponding to the first pilot injection INJP1coincides with the target heat release amount QHRCMD, which is set according to the demand torque TRQ and the engine rotational speed NE. The window period TWND is set so the heat release amount QHR after execution of the first pilot injection INJP1is obtained. Therefore, the fuel injection amount QIP2in the second pilot injection INJP2(the pilot injection which is performed prior to the first injection INJP1) is controlled so the heat release amount QHR due to the first pilot injection INJP1, which is performed immediately before the main injection INJM, coincides with the target heat release amount QHRCMD. According to this control, ignitionability of the fuel injected in the first pilot injection INJP1, and consequently of the fuel injected in the main injection INJM, is improved. As a result, stable ignitionability is obtained, especially in the low temperature condition, or in the low load operating condition, of the engine1.

In this embodiment, the fuel injection valve6corresponds to the fuel injection means, and the cylinder pressure sensor2corresponds to the cylinder pressure detecting means. Further, the ECU4constitutes the heat release amount calculation means and the fuel injection control means. Specifically, the total injection amount calculator42, the first pilot injection amount calculator43, the second pilot injection amount map value calculator44, the target heat release amount calculator71, the subtracting blocks45,46, and74, the correction amount calculator75, and the adding block51inFIG. 7, and the main injection timing calculator61, the first pilot injection timing calculator62, and the second pilot injection timing calculator63inFIG. 8, correspond to the fuel injection control means. The heat release amount calculator72and the window setter73correspond to the heat release amount calculation means.

The present invention is not limited to the embodiments described above, and various modifications may be made thereto without departing from the spirit and/or scope thereof. For example, in the above-described first embodiment, the estimated compression end temperature TCMPE is calculated according to the detected cylinder pressure PCYL. Alternatively, the estimated compression end temperature TCMPE may be calculated using equation (9).
TCMPE=TIN×εκ-1(9)
where “ε” is a compression ratio, and “K” is a polytropic index which is calculated, for example, according to the intake air temperature TIN, the engine coolant temperature TW, and the engine rotational speed NE.

Further, the estimated compression end temperature TCMPE may be calculated with the method shown in JP '435.

Further in the embodiments described above, the first pilot injection amount QIP1is calculated using the first pilot injection amount map. Alternatively, a total pilot injection amount QITP, which is a sum of the first pilot injection amount QIP1and the second pilot injection amount QIP2, may be calculated according to the demand torque TRQ and the engine rotational speed NE, and the first pilot injection amount QIP1may be calculated by subtracting the second pilot injection amount QIP2from the total pilot injection amount QITP.

The present invention can also be applied to a control system for a watercraft propulsion engine, such as an outboard engine having a vertically extending crankshaft.