JP4833924B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine that performs compression ignition, and more particularly to an apparatus that performs a plurality of pilot injections before a main fuel injection.

  Patent Document 1 discloses an internal combustion engine that estimates a compression end temperature that is the temperature of an air-fuel mixture in a cylinder at a compression top dead center and increases the pilot injection amount when the estimated compression end temperature becomes high. The controller is shown. This control is performed for the purpose of suppressing combustion noise by increasing the pilot injection amount during high load operation of the engine.

  Further, as shown in Patent Document 2, in order to improve the ignitability of an internal combustion engine that performs compression ignition, a fuel injection control device that performs pilot injection twice before main injection at the time of engine startup has been conventionally known. ing.

  According to this apparatus, the fuel injection amount in the first pilot injection is set to a value smaller than the fuel injection amount in the second pilot injection. The second pilot injection is executed within a period in which the piston in the cylinder is located between 30 degrees before the compression top dead center and the compression top dead center.

Japanese Patent No. 3572435 Japanese Patent Laid-Open No. 10-274086

  The pilot injection amount control method disclosed in Patent Document 1 is for suppressing combustion noise during high-load operation. Even if it is applied during low-temperature or low-load operation of the engine, the fuel ignitability is improved. It cannot be improved.

  The ignitability of the fuel is considered to be correlated with the amount of heat generated in the combustion chamber, which is the main factor that determines the temperature in the combustion chamber, but it was detected or estimated by detecting or estimating the amount of heat generated in the combustion chamber. The techniques for controlling the pilot injection amount in accordance with the heat generation amount are not shown in Patent Documents 1 and 2 above. For this reason, there is room for improvement in improving the ignitability of the fuel at a low temperature of the engine, for example.

  The present invention appropriately controls the fuel injection amount in the first pilot injection when performing a plurality of pilot injections, and is particularly capable of obtaining stable ignitability when the engine is at a low temperature or during a low load operation. An object of the present invention is to provide a control device.

In order to achieve the above object, an invention according to claim 1 is directed to an in-cylinder pressure detecting means for detecting a pressure (PCYL) in the combustion chamber in a control device for an internal combustion engine having a fuel injection means for injecting fuel into the combustion chamber. A heat generation amount calculation means for calculating a heat generation amount (QHR) in a predetermined crank angle range (TWND) according to the pressure (PCYL) detected by the in-cylinder pressure detection means, and main injection by the fuel injection means Fuel injection control means for executing (INJM) , a first pilot injection (INJP1) before the main injection, and a second pilot injection (INJP2) which is the first pilot injection before the first pilot injection ; And target value calculation means for calculating a target value (QHRCMD) of the heat generation amount according to the operating state of the engine, and the fuel injection control means comprises the heat generation amount ( HR) is controlled so that the fuel injection amount (QIP2) in the second pilot injection matches the target value (QHRCMD), and the predetermined crank angle range (TWND) corresponds to the first pilot injection (INJP1). The heat generation amount to be calculated is set to be calculated.

According to the first aspect of the present invention, the first pilot injection and the second pilot injection are performed before the main injection, and the heat generation amount in the predetermined crank angle range is calculated according to the detected pressure in the combustion chamber. is Rutotomoni, the target value of the heat generation amount is calculated according to the engine operating state. The fuel injection amount in the second pilot injection, which is the first pilot injection , is controlled so that the calculated heat generation amount matches the target value . The predetermined crank angle range is set so that a heat generation amount corresponding to the first pilot injection that is the second pilot injection is calculated. Therefore , the amount of heat generated due to the pilot injection immediately before the main injection can be detected, and the main injection is controlled by controlling the fuel injection amount in the first pilot injection so that the amount of heat generated matches the target value. It is possible to improve the ignitability of the fuel injected in the pilot injection immediately before, and thus the fuel injected in the main injection. As a result, stable ignitability can be obtained particularly when the engine is at a low temperature or during a low load operation.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 and FIG. 2 are diagrams showing the configuration of an internal combustion engine and its control device according to one embodiment of the present invention. The following description will be given with reference to both figures together. An internal combustion engine (hereinafter simply referred to as “engine”) 1 having four cylinders is a diesel engine that directly injects fuel into a cylinder, and a fuel injection valve 6 is provided in each cylinder. The fuel injection valve 6 is electrically connected to an electronic control unit (hereinafter referred to as “ECU”) 4, and the valve opening time and valve opening timing of the fuel injection valve 6 are controlled by the ECU 4.

  The engine 1 includes an intake pipe 22, an exhaust pipe 24, and a supercharger 28. The supercharger 28 includes a turbine 30 that is driven by exhaust kinetic energy, and a compressor 29 that is rotationally driven by the turbine 30 and compresses intake air.

  The turbine 30 includes a plurality of variable vanes (not shown), and is configured to change the turbine rotational speed (rotational speed) by changing the opening degree of the variable vanes. The vane opening degree of the turbine 30 is electromagnetically controlled by the ECU 4.

An intercooler 25 for cooling the pressurized air is provided in the intake pipe 22 downstream of the compressor 29.
An exhaust gas recirculation passage 26 that recirculates exhaust gas to the intake pipe 22 is provided between the upstream side of the turbine 30 in the exhaust pipe 24 and the intake pipe 22. The exhaust gas recirculation passage 26 is provided with an exhaust gas recirculation control valve (hereinafter referred to as “EGR valve”) 27 for controlling the exhaust gas recirculation amount. The EGR valve 27 is a solenoid valve having a solenoid, and the valve opening degree is controlled by the ECU 4.

  An intake air flow rate sensor 31 for detecting the intake air flow rate GA is provided on the upstream side of the turbine 29 in the intake pipe 22, and an intake air temperature sensor 32 for detecting the intake air temperature TIN is provided on the downstream side of the intercooler 25. . An exhaust pressure sensor 33 for detecting the exhaust pressure PEX and an exhaust temperature sensor 34 for detecting the exhaust temperature TEX are provided on the upstream side of the turbine 30 in the exhaust pipe 24. Detection signals from these sensors are supplied to the ECU 4.

  Each cylinder of the engine 1 is provided with an in-cylinder pressure sensor 2 that detects in-cylinder pressure (pressure in the combustion chamber). In the present embodiment, the in-cylinder pressure sensor 2 is configured integrally with a glow plug provided in each cylinder. A detection signal from the in-cylinder pressure sensor 2 is supplied to the ECU 4. The detection signal of the in-cylinder pressure sensor 2 actually corresponds to a differential signal with respect to the crank angle (time) of the in-cylinder pressure PCYL, and the in-cylinder pressure PCYL is obtained by integrating the in-cylinder pressure sensor output. .

  The engine 1 is provided with a crank angle position sensor 3 that detects a rotation angle of a crankshaft (not shown). The crank angle position sensor 3 generates a pulse every crank angle, and the pulse signal is supplied to the ECU 4. The crank angle position sensor 3 further generates a cylinder identification pulse at a predetermined crank angle position of the specific cylinder and supplies it to the ECU 4.

  The ECU 4 includes an accelerator sensor 35 that detects an operation amount AP of an accelerator pedal of a vehicle driven by the engine 1, a cooling water temperature sensor 36 that detects a cooling water temperature TW of the engine 1, and an intake pipe pressure downstream of the supercharger 28. (Supercharging pressure) A supercharging pressure sensor (not shown) for detecting PB and a vehicle speed sensor (not shown) for detecting the vehicle speed VP of the vehicle are connected, and detection signals from these sensors are sent to the ECU 4. Supplied.

  The ECU 4 supplies a control signal for the fuel injection valve 6 provided in the combustion chamber of each cylinder of the engine 1 to the drive circuit 5. The drive circuit 5 is connected to the fuel injection valve 6, and supplies a drive signal corresponding to the control signal supplied from the ECU 4 to the fuel injection valve 6. Thus, at the fuel injection timing corresponding to the control signal output from the ECU 4, fuel is injected into the combustion chamber of each cylinder by the fuel injection amount corresponding to the control signal.

  The ECU 4 includes an amplifier 10, an A / D converter 11, a pulse generator 13, a CPU (Central Processing Unit) 14, a ROM (Read Only Memory) 15 that stores a program executed by the CPU 14, and a CPU 14. A RAM (Random Access Memory) 16 for storing calculation results and the like, an input circuit 17, and an output circuit 18 are provided. A detection signal of the in-cylinder pressure sensor 2 is input to the amplifier 10. The amplifier 10 amplifies an input signal. The signal amplified by the amplifier 10 is input to the A / D converter 11. The pulse signal output from the crank angle position sensor 3 is input to the pulse generator 13.

  The A / D conversion unit 11 includes a buffer 12, converts the in-cylinder pressure sensor output input from the amplifier 10 into a digital value (hereinafter referred to as “pressure change rate”) dp / dθ, and stores the converted value in the buffer 12. More specifically, the A / D converter 11 is supplied with a pulse signal PLS1 (hereinafter referred to as “1 degree pulse”) PLS1 having a crank angle of 1 degree from the pulse generator 13, and this 1 degree pulse PLS1. The in-cylinder pressure sensor output is sampled at a period of ## EQU2 ## and converted into a digital value and stored in the buffer 12.

  On the other hand, the pulse signal PLS6 with a crank angle of 6 degrees is supplied from the pulse generator 13 to the CPU 14, and the CPU 14 performs a process of reading the digital value stored in the buffer 12 with the period of the 6 degrees pulse PLS6. . That is, in this embodiment, the A / D conversion unit 11 does not issue an interrupt request to the CPU 14, but the CPU 14 performs a reading process at a cycle of the 6-degree pulse PLS6.

  The input circuit 17 converts detection signals from various sensors into digital values and supplies them to the CPU 14. The engine speed NE is calculated from the cycle of the 6-degree pulse PLS. Further, the required torque TRQ of the engine 1 is calculated according to the accelerator pedal operation amount AP.

  The CPU 14 calculates a target intake air flow rate GACMD according to the engine operating state, and outputs a duty control signal for controlling the opening degree of the EGR valve 27 so that the detected intake air flow rate GA matches the target intake air flow rate GACMD. The EGR valve 27 is supplied via the output circuit 18.

  In the present embodiment, in order to ensure combustion stability, pilot injection is executed twice before the main injection of fuel by the fuel injection valve 6 in a predetermined operation state of the engine 1 (double pilot injection mode). Normally, as shown in FIG. 3A, one pilot injection INJP is executed before the main injection INJM (single pilot injection mode). Hereinafter, the pilot injection in which the execution timing of the pilot injection in the double pilot injection mode is closer to the compression top dead center is referred to as the first pilot injection INJP1, and the pilot injection executed before the first pilot injection INJP1 is the second pilot injection. It is called pilot injection INJP2. In the single pilot injection mode, only pilot injection corresponding to the first pilot injection INJP1 is performed.

  For example, the main injection INJM is executed substantially at the compression top dead center (CA = 0), and the first pilot injection INJP1 is executed at a timing of about 13 degrees (CA = −13) before the top dead center. INJP2 is executed at a timing of about 20 degrees (CA = −20) before top dead center. In addition, when the pilot injection amount QIP in the single pilot injection mode is about 4 mg per injection, the first pilot injection amount QIP1 and the second pilot injection amount QIP2 in the double pilot injection mode are each about 2 mg.

  FIG. 4 is a time chart showing the transition of the heat generation rate ROHR. The solid line L1 and the broken line L2 in this figure correspond to the example in which the pilot injection amount is 4 mg and 6 mg in the single pilot injection mode, respectively, and the alternate long and short dash line L3 is the first pilot injection amount QIP1 and the second pilot injection amount in the double pilot injection mode. This corresponds to an example in which both QIP2 are 2 mg (4 mg in total). FIG. 4B is an enlarged view of the vicinity of the compression top dead center (CA = 0 deg) of FIG.

  From FIG. 4, in the single pilot injection mode, the ignition timing CAIGSP where the heat generation rate ROHR begins to increase corresponding to the pilot injection hardly changes even if the pilot injection amount is changed, whereas in the double pilot injection mode. It can be confirmed that the ignition timing CAIGDP is advanced from the ignition timing CAIGSP.

  FIG. 5 is a time chart showing the transition of the in-cylinder temperature TCYL. The solid line L4 and the broken line L5 in this figure correspond to an example in which the pilot injection amount is 4 mg and 6 mg in the single pilot injection mode, respectively, and the alternate long and short dash line L6 is the first pilot injection amount QIP1 and the second pilot injection amount in the double pilot injection mode. This corresponds to an example in which both QIP2 are 2 mg (4 mg in total). FIG. 5B is an enlarged view of the vicinity of the compression top dead center (CA = 0 deg) of FIG.

  As is apparent from FIG. 5, the in-cylinder temperature at the compression top dead center, that is, the compression end temperature TCMP, is higher in the double pilot injection mode than in the single pilot injection mode. Therefore, it can be confirmed that the ignition timing CAIGDP in the double pilot injection mode is earlier than the ignition timing CAIGSP in the single pilot injection mode because the compression end temperature TCMP becomes higher.

  By adopting the double pilot injection mode in this way, the compression end temperature TCMP can be increased and the ignitability of the fuel can be improved. More specifically, the combustion (or low-temperature oxidation reaction) of the fuel injected by the second pilot injection INJP2 increases the compression end temperature TCMP, thereby promoting the ignition of the fuel injected by the first pilot injection INJP1. As a result, it is considered that the ignitability of the fuel injected by the main injection INJM is improved.

  FIG. 6A is a diagram showing the transition of the heat generation rate ROHR in the double pilot injection mode, and FIG. 6B shows the execution timing of the two pilot injections INJP1 and INJP2 and the main injection. As is apparent from the figure, the heat generation rate ROHR increases corresponding to each fuel injection.

  In the present embodiment, the heat generation amount QHR (that is, the heat generation amount corresponding to the first pilot injection INJP1) in the window period TWND shown in FIG. 6 is calculated based on the detected pressure change rate dp / dθ and the in-cylinder pressure PCYL. Then, the second pilot injection amount QIP2 is controlled so that the calculated heat generation amount QHR matches the target heat generation amount QHRCMD set according to the engine operating state. Thus, the second pilot injection amount QIP2 can be appropriately controlled, and stable ignitability can be obtained particularly when the engine 1 is at a low temperature or during a low load operation.

  FIG. 7 is a block diagram showing a configuration of an injection amount calculation module for calculating the main injection amount QIM, the first pilot injection amount QIP1, and the second pilot injection amount QIP2 by the fuel injection valve 6. The function of this module is realized by arithmetic processing executed by the CPU 14.

  The injection amount calculation module shown in FIG. 7 includes a required torque calculation unit 41, a total injection amount calculation unit 42, a first pilot injection amount calculation unit 43, a second pilot injection amount map value calculation unit 44, subtraction units 45 and 46, a target. A heat generation amount calculation unit 47, a heat generation amount calculation unit 48, a window setting unit 49, a subtraction unit 50, a correction amount calculation unit 51, and an addition unit 52 are provided.

  The required torque calculation unit 41 calculates the required torque TRQ of the engine 1 according to the accelerator pedal operation amount AP. The required torque TRQ is calculated so as to be substantially proportional to the accelerator pedal operation amount AP. However, in order to suppress smoke, when the accelerator pedal operation amount AP increases rapidly, the increase in the required torque TRQ is limited. .

  The total injection amount calculation unit 42 searches a total injection amount map (not shown) set in advance according to the required torque TRQ and the engine speed NE, and calculates the total injection amount QIT. The subtracting units 45 and 46 calculate the main injection amount QIM by subtracting the first pilot injection amount QIP1 and the second pilot injection amount QIP2 from the total injection amount QIT. The total injection amount map is set so that the total injection amount QIT increases as the required torque TRQ increases and the engine speed NE increases.

  The first pilot injection amount calculation unit 43 searches a first pilot injection amount map (not shown) set in advance according to the required torque TRQ and the engine speed NE, and calculates the first pilot injection amount QIP1.

  The second pilot injection amount map value calculation unit 44 searches a second pilot injection amount map (not shown) set in advance according to the required torque TRQ and the engine speed NE, and the second pilot injection amount map value QIP2M. Is calculated.

  The target heat generation amount calculation unit 47 searches a target heat generation amount map (not shown) set in advance according to the required torque TRQ and the engine speed NE, and calculates the target heat generation amount QHRCMD in the window period TWND. .

The heat generation amount calculation unit 48 calculates a heat generation rate ROHR [J / deg] according to the detected pressure change rate dp / dθ and in-cylinder pressure PCYL, and integrates the heat generation rate ROHR in the window period TWND. The amount of heat generation QHR is calculated. The heat release rate ROHR is calculated by the following formula (1).
ROHR = κ / (κ−1) × PCYL × dV / dθ
+ 1 / (κ−1) × VCYL × dp / dθ (1)

Here, κ is the specific heat ratio of the air-fuel mixture, PCYL is the detection cylinder pressure, dV / dθ is the cylinder volume increase rate [m ³ / deg], VCYL is the cylinder volume, dp / dθ is the pressure change rate [kPa / deg]. It is.

  The window setting unit 49 sets the window period TWND shown in FIG. 6 according to the first pilot injection timing CAP1 calculated by a fuel injection timing calculation module (FIG. 8) described later. Specifically, for example, the first pilot injection end timing CAP1E is calculated according to the first pilot injection timing CAP1 and the first pilot injection amount QIP1, the window start timing CAWS is set to the first pilot injection end timing CAP1E, and the window The end time CAWE is set to a time obtained by adding a predetermined angle DCAW (for example, 13 degrees) to the window start time CAWS. Alternatively, the window end timing CAWE may be set according to the heat generation rate ROHR. For example, after the window start time CAWS, the time when the heat generation rate ROHR first becomes “0” may be set as the window end time CAWE.

  The subtraction unit 50 subtracts the heat generation amount QHR from the target heat generation amount QHRCMD to calculate a heat generation amount deviation DQHR. The correction amount calculation unit 51 calculates the correction amount QIP2C by PID (proportional integral differentiation) control so that the heat generation amount deviation DQHR becomes “0”. The correction amount QIP2C is calculated so as to increase as the heat generation amount deviation DTCMP increases.

  Since the heat generation amount QHR within the window period TWND changes depending on not only the first pilot injection amount QIP1 but also the second pilot injection amount QIP2, the first pilot is in a substantially steady state. The injection amount QIP1 is substantially constant, and the heat generation amount QHR can be matched with the target heat generation amount QHRCMD by calculating the second pilot injection amount QIP2 using the correction amount QIP2C.

  FIG. 8 is a block diagram showing a configuration of an injection timing calculation module that calculates the fuel injection execution timing by the fuel injection valve 6, that is, the main injection timing CAM, the first pilot injection timing CAP1, and the second pilot injection timing CAP2. The function of this module is realized by arithmetic processing executed by the CPU 14.

  The injection timing calculation module includes a main injection timing calculation unit 61, a first pilot injection timing calculation unit 62, and a second pilot injection timing calculation unit 63. These injection timing calculation units 61 to 63 search a main injection timing map, a first pilot injection timing map, and a second pilot injection timing map that are preset according to the required torque TRQ and the engine speed NE, respectively. A main injection timing CAM, a first pilot injection timing CAP1, and a second pilot injection timing CAP2 are calculated.

  As described above, in the present embodiment, the second heat generation amount QHR corresponding to the first pilot injection INJP1 matches the target heat generation amount QHRCMD set according to the required torque TRQ and the engine speed NE. Pilot injection amount QIP2 is controlled. Since the window period TWND is set so that the heat generation amount QHR after execution of the first pilot injection INJP1 is obtained, the heat generation amount QHR resulting from the first pilot injection INJP1 immediately before the main injection INJM is the target heat generation amount. The fuel injection amount QIP2 in the second pilot injection (pilot injection executed first) INJP2 is controlled so as to coincide with QHRCMD. Thereby, the ignitability of the fuel injected in the first pilot injection INJP1, and consequently the fuel injected in the main injection INJM, can be improved. As a result, stable ignitability can be obtained particularly when the engine is at a low temperature or during a low load operation.

  In the present embodiment, the fuel injection valve 6 corresponds to the fuel injection means, and the in-cylinder pressure sensor 2 corresponds to the in-cylinder pressure detection means. The ECU 4 constitutes a heat generation amount calculation means and a fuel injection control means. More specifically, the total injection amount calculation unit 42, the first pilot injection amount calculation unit 43, the second pilot injection amount map value calculation unit 44, the target heat generation amount calculation unit 47, the subtraction units 45, 46, FIG. 50, the correction amount calculation unit 51, the addition unit 52, the main injection timing calculation unit 61, the first pilot injection timing calculation unit 62, and the second pilot injection timing calculation unit 63 correspond to the fuel injection control means, and calculate the heat generation amount. The unit 48 and the window setting unit 49 correspond to heat generation amount calculation means.

  The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, the first pilot injection amount QIP1 is calculated using the first pilot injection amount map, but all pilots that are the sum of the first pilot injection amount QIP1 and the second pilot injection amount QIP2 are used. The first pilot injection amount QIP1 may be calculated by calculating the injection amount QITP according to the required torque TRQ and the engine speed NE and subtracting the second pilot injection amount QIP2 from the total pilot injection amount QITP. .

  The present invention can also be applied to control of a marine vessel propulsion engine such as an outboard motor having a crankshaft as a vertical direction.

It is a figure which shows the structure of the internal combustion engine and its control apparatus concerning one Embodiment of this invention. FIG. 2 is a diagram specifically showing a partial configuration of the control device shown in FIG. 1. It is a figure for demonstrating fuel-injection mode. It is a figure which shows transition of a heat release rate (ROHR). It is a figure which shows transition of in-cylinder temperature (TCYL). It is a figure which shows transition of the heat generation amount accompanying pilot injection and main injection. It is a figure which shows the structure of a fuel injection amount calculation module. It is a figure which shows the structure of a fuel injection timing calculation module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 In-cylinder pressure sensor (In-cylinder pressure detection means)
4 Electronic control unit (heat generation amount calculation means, fuel injection control means)
6 Fuel injection valve (fuel injection means)

Claims (1)

In a control device for an internal combustion engine provided with fuel injection means for injecting fuel into a combustion chamber,
In-cylinder pressure detecting means for detecting the pressure in the combustion chamber;
Heat generation amount calculation means for calculating a heat generation amount in a predetermined crank angle range according to the pressure detected by the in-cylinder pressure detection means;
Fuel injection control means for executing main injection by the fuel injection means, first pilot injection before the main injection, and second pilot injection that is the first pilot injection before the first pilot injection ;
A target value calculating means for calculating a target value of the heat generation amount according to the operating state of the engine,
The fuel injection control means controls a fuel injection amount in the second pilot injection so that the heat generation amount coincides with the target value, and the predetermined crank angle range has a heat generation corresponding to the first pilot injection. A control device for an internal combustion engine, characterized in that the amount is set to be calculated.

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