JP2017180140A - Control device of internal combustion engine - Google Patents

Abstract

Combustion noise caused by combustion by pilot injection is reduced. A control device for an internal combustion engine that performs main injection and pilot injection, an engine rotational speed calculation unit that calculates the rotational speed of the internal combustion engine, and a temporary pilot injection timing that sets a temporary injection timing of the pilot injection A setting unit, an in-cylinder temperature estimation unit for estimating the temperature in the cylinder when the pilot injection is performed at the temporary injection timing, and the oxygen density in the cylinder when the pilot injection is performed at the temporary injection timing An oxygen density estimation unit, an ignition delay period calculation unit that calculates an ignition delay period from the estimated cylinder temperature, the estimated oxygen density, and the rotational speed of the internal combustion engine, and an ignition timing that calculates the fuel ignition timing When the calculation unit and the ignition delay period are less than the allowable value and the fuel ignition timing is after the time when the in-cylinder pressure change rate is the maximum, the temporary injection timing is set as the pilot injection timing. It includes a lot injection timing setting unit, the. [Selection] Figure 1

Description

  The present invention relates to a control device for an internal combustion engine.

  As a technique for reducing combustion noise of a diesel internal combustion engine, a technique for performing pilot injection prior to main injection, which is main fuel injection, is known. By performing pilot injection, preliminary combustion with pilot injected fuel is performed prior to main injection, and main injection is performed there. Therefore, the main injected fuel burns in a state with little ignition delay, and is moderately overall. Combustion is achieved. As a result, the change in the in-cylinder pressure (combustion chamber pressure) accompanying the combustion of the main injected fuel becomes slow, so that the combustion noise due to the combustion of the main injected fuel is reduced.

  However, even if pilot injection is performed, combustion noise caused by combustion by pilot injection may increase if combustion by pilot injected fuel is not actually performed appropriately.

  In Patent Document 1, a heat generation amount based on pilot injection is calculated, and a fuel injection amount based on pilot injection is corrected based on the calculated heat generation amount, thereby reducing combustion noise caused by combustion by pilot injection. ing.

JP 2009-281143 A

  By the way, the timing of pilot injection also affects the combustion noise resulting from combustion by pilot injection. Therefore, even if the fuel injection amount by pilot injection is corrected as in Patent Document 1, there is a possibility that combustion noise due to combustion by pilot injection may not be sufficiently reduced.

  Therefore, an object of the control device for an internal combustion engine disclosed in this specification is to reduce combustion noise caused by combustion by pilot injection in an internal combustion engine that performs pilot injection.

  In order to solve such a problem, the control device for an internal combustion engine disclosed in the present specification performs a plurality of fuel injections including a main injection and a pilot injection preceding the main injection into the cylinder during one cycle. A control device for an internal combustion engine comprising fuel injection means, a crank angle sensor for detecting a crank angle of the internal combustion engine, and an engine speed calculation unit for calculating the rotational speed of the internal combustion engine from a detection value of the crank angle sensor A temporary pilot injection timing setting unit that sets a temporary injection timing of the pilot injection, an in-cylinder temperature estimation unit that estimates a temperature in the cylinder when the pilot injection is performed at the temporary injection timing, An oxygen density estimator for estimating an oxygen density in the cylinder when the pilot injection is performed at the temporary injection timing; an estimated temperature in the cylinder; and an estimated acid An ignition delay period calculating unit that calculates an ignition delay period from when the fuel is injected by the pilot injection to when the fuel is ignited from the density and the number of revolutions of the internal combustion engine; and an ignition that calculates the ignition timing of the fuel A timing calculation unit, and the in-cylinder pressure change rate in which the ignition delay period is less than or equal to an allowable value and the ignition timing of the fuel is a change in pressure in the cylinder per unit time or unit crank angle is maximum. And a pilot injection timing setting unit that sets the temporary injection timing to the injection timing of the pilot injection.

  According to the control device for an internal combustion engine disclosed in this specification, in an internal combustion engine that performs pilot injection, combustion noise caused by combustion by pilot injection can be reduced.

FIG. 1 is a schematic diagram illustrating a configuration of an engine system to which a control device for an internal combustion engine according to an embodiment is applied. FIG. 2 is a flowchart showing an example of pilot injection timing control executed by the ECU. FIG. 3A is an example of an equal ignition delay diagram showing the relationship between the oxygen density during pilot injection, the in-cylinder temperature during pilot injection, and the ignition delay period when the engine speed is 1000 rpm. FIG. 3B is an example of an equal ignition delay diagram showing the relationship between the oxygen density during pilot injection, the in-cylinder temperature during pilot injection, and the ignition delay period when the engine speed is 2000 rpm. is there. FIG. 4 is a flowchart showing an example of pilot injection amount control executed by the ECU. It is a map which shows the relationship between the oxygen density at the time of pilot injection, the cylinder temperature at the time of pilot injection, and the calorific value per 1 mm ³ / st.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions, ratios, and the like of each part may not be shown so as to completely match the actual ones. In some cases, details are omitted in some drawings.

  First, an engine system to which a control device for an internal combustion engine according to an embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic diagram illustrating a configuration of an engine system 10 to which a control device for an internal combustion engine according to an embodiment is applied.

  The engine system 10 includes an engine 100 as an internal combustion engine that is a diesel engine. Although FIG. 1 illustrates a four-cylinder engine, the present invention can be applied to an internal combustion engine having an arbitrary number of cylinders. Each cylinder of the engine 100 includes a fuel injection valve 12, an intake valve 14, an exhaust valve 16, and the like that inject fuel into a combustion chamber (inside the cylinder). The engine 100 also includes an intake passage 18 that sucks intake air into each cylinder, and an exhaust passage 20 that discharges exhaust gas from each cylinder. The intake passage 18 is provided with a throttle valve 22 that adjusts the amount of intake air. A catalyst 24 for purifying exhaust gas is provided in the exhaust passage 20.

  The engine 100 includes an EGR mechanism 26 that recirculates a part of the exhaust gas as EGR gas to the intake system. The EGR mechanism 26 includes an EGR passage 28 that connects the intake passage 18 and the exhaust passage 20, and an EGR valve that adjusts the recirculation amount (EGR amount) of EGR gas recirculated from the exhaust system to the intake system via the EGR passage 28. 30. The engine 100 is equipped with a supercharger 32 that supercharges intake air using exhaust pressure. The present invention is also applicable to an internal combustion engine that is not equipped with the supercharger 32.

  The engine system 10 includes an ECU (Electronic Control Unit) 200. The ECU 200 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a storage device. ECU 200 executes pilot injection timing control, which will be described later, by executing a program stored in a ROM or a storage device. ECU 200 is an example of an engine speed calculation unit, a temporary pilot injection timing setting unit, an in-cylinder temperature estimation unit, an oxygen density estimation unit, an ignition delay period calculation unit, an ignition timing calculation unit, and a pilot injection timing setting unit.

  Various actuators such as the fuel injection valve 12, the throttle valve 22, and the EGR valve 30 are connected to the output side of the ECU 200.

  On the input side of the ECU 200, a crank angle sensor 41 that detects the crank angle of the engine 100, an air flow meter 42 that detects the intake air amount, and a boost pressure sensor 43 that measures the boost pressure acting upstream of the throttle valve 22. Is connected. Further, on the input side of the ECU 200, an exhaust manifold pressure sensor 44 that detects an exhaust manifold pressure that is an exhaust pressure in the exhaust manifold, an exhaust manifold temperature sensor 45 that detects an exhaust manifold temperature that is an exhaust temperature in the exhaust manifold, and an intake air An intake manifold pressure sensor 46 for detecting the pressure in the manifold is connected. Further, an air-fuel ratio sensor 47 that detects the air-fuel ratio of the engine 100 and an engine water temperature sensor 48 that detects the engine water temperature are connected to the input side of the ECU 200.

  ECU 200 calculates the rotational speed of engine 100 (engine rotational speed) from the detected value of the crank angle sensor. Furthermore, the ECU 200 executes the following pilot injection timing control in order to reduce combustion noise caused by pilot injection based on various information and signals regarding the operating state and operating conditions of the engine input from each sensor. .

  FIG. 2 is a flowchart showing an example of pilot injection timing control executed by the ECU 200. The process in FIG. 2 is executed at predetermined time intervals (for example, 8 msec).

  ECU 200 first sets a temporary pilot injection timing (step S11). In the present embodiment, at the start of the process of FIG. 2, ECU 200 sets a default value for the temporary pilot injection timing. The default value is, for example, main injection timing−α−β (for example, α = 3, β = 8).

  Next, the ECU 200 calculates the in-cylinder temperature and oxygen density at the time of pilot injection when pilot injection is performed at the temporary pilot injection timing (step S13). For example, the ECU 200 calculates the in-cylinder temperature at the time of pilot injection based on an example of a calculation model represented by the following equations 1 to 3. More specifically, first, the bottom dead center in-cylinder temperature is calculated based on the bottom dead center pressure, the bottom dead center volume, the total cylinder gas amount, and the gas constant using the formula (1). In this embodiment, the supercharging pressure acquired from the supercharging pressure sensor 43 is used as the bottom dead center pressure. However, the bottom dead center pressure may be acquired from a pressure sensor provided in the cylinder. The total cylinder gas amount is calculated based on, for example, the intake air amount, the exhaust manifold pressure, the TDC capacity, the exhaust manifold temperature, and the like.

  Next, the polytropic index is calculated based on the compression end in-cylinder temperature, the bottom dead center in-cylinder temperature, and the compression ratio, using the equation (2). Formula 2 shows an example of a method for calculating the polytropic index. Note that the compression end in-cylinder temperature is calculated based on the compression end in-cylinder temperature, the bore wall temperature, and the like at the time of adiabatic change. The compression end in-cylinder temperature at the time of adiabatic change is calculated based on, for example, the adiabatic compression end pressure, the TDC volume, the cylinder gas total amount, the gas constant, and the like. The adiabatic compression end pressure is calculated based on, for example, the bottom dead center pressure and the compression ratio. In this embodiment, the engine water temperature acquired from the engine water temperature sensor 48 is used as the bore wall temperature. However, the bore wall temperature may be obtained from a temperature sensor that directly detects the cylinder wall temperature. Alternatively, the temperature of the lubricating oil may be substituted.

  Next, the in-cylinder temperature at the time of pilot injection is calculated by the following equation using the bottom dead center in-cylinder temperature and the polytropic index, the bottom dead center volume, and the pilot injection volume.

  The oxygen density at the time of pilot injection is calculated by, for example, the following equation (4). In Equation 4, the oxygen density at the time of pilot injection is calculated based on the total amount of cylinder gas, the oxygen mass ratio in the cylinder, and the cylinder volume at the time of pilot injection.

The oxygen mass ratio in the cylinder is calculated based on the exhaust CO ₂ mass per molecule of fuel, the EGR rate, and the total mass in cylinder per molecule of fuel. The in-cylinder total mass per fuel molecule is calculated based on the intake gas mass per fuel molecule, the EGR rate, and the exhaust gas mass per fuel molecule. The intake gas mass is calculated based on the pressure in the intake manifold detected by the intake manifold pressure sensor 46, for example. The exhaust gas mass is calculated based on the intake air mass and the air-fuel ratio of the engine 100, for example.

  Next, ECU 200 calculates the ignition delay period based on the in-cylinder temperature at the time of pilot injection calculated at step S13, the oxygen density at the time of pilot injection, and the current engine speed (step S15). Specifically, the ECU 200 obtains the ignition delay period from the in-cylinder temperature and the oxygen density at the time of pilot injection, which is prepared for each engine speed, as shown in FIGS. 3 (a) and 3 (b). The ignition delay time is calculated using the delay diagram.

  Next, the ECU 200 calculates the ignition timing by adding the ignition delay period to the temporary pilot injection timing (step S17).

  Next, the ECU 200 determines whether or not the ignition delay period is equal to or less than an allowable value and the ignition timing is on the retard side with respect to the timing at which the in-cylinder pressure change rate dp / dθ takes a peak value ( Step S19). In addition, if the ignition delay period is equal to or less than the allowable value, the allowable value is set such that the fuel by the pilot injection can be combusted before the main injection.

  If the determination in step S19 is affirmative, the ECU 200 sets the temporary pilot injection timing set in step S11 as the pilot injection timing (step S21), and ends the process of FIG.

  On the other hand, if the determination in step S19 is negative, the ECU 200 resets the temporary pilot injection timing in step S11 and executes the processing from step S13. For example, when the ignition delay time is equal to or less than the allowable value in step S19, the ECU 200 sets the temporary pilot injection time to an advance side with respect to the current temporary pilot injection time, in which the ignition delay becomes longer, and the ignition delay time. Is larger than the allowable value, the temporary pilot injection timing is set to the retard side of the current temporary pilot injection timing at which the ignition delay is shortened.

  If the timing at which the in-cylinder pressure change rate dp / dθ takes a peak value and the pilot combustion overlap, the increase in the in-cylinder pressure increases and the combustion noise increases. However, according to the pilot injection timing control described above, pilot injection Can be burned after the time when the in-cylinder pressure change rate dp / dθ takes a peak value, so that combustion noise can be reduced. Further, if the pilot ignition delay period is long, the combustion noise increases. However, in the above pilot injection timing control, the ignition delay period is set to the allowable value or less, so the combustion noise can be reduced.

  As is apparent from the above description, the engine system 10 includes an engine 100 including a fuel injection valve 12 that performs a plurality of fuel injections, including main injection and pilot injection preceding the main injection, in a cylinder during one cycle. A crank angle sensor 41 that detects the crank angle and an ECU 200 are provided. ECU 200 calculates the rotational speed of engine 100 from the detected value of the crank angle sensor, sets a temporary injection timing for pilot injection, and the temperature in the cylinder at the time of pilot injection when pilot injection is performed at the temporary injection timing , And the oxygen density in the cylinder at the time of pilot injection when pilot injection is performed at the temporary injection timing is estimated. ECU 200 determines the ignition delay from when the fuel is injected by pilot injection until the fuel is ignited based on the estimated temperature in the cylinder at the time of pilot injection, the estimated oxygen density at the time of pilot injection, and the rotational speed of engine 100. When the ignition timing of the fuel is calculated based on the ignition delay period, the ignition delay period is less than the allowable value, and the fuel ignition timing is after the period when the in-cylinder pressure change rate is maximum The temporary injection timing is set as the pilot injection timing. Thereby, fuel by pilot injection can be burned after the time when the in-cylinder pressure change rate dp / dθ takes a peak value, so that combustion noise can be reduced. Further, if the pilot ignition delay period is long, the combustion noise increases. However, since the ignition delay period is set to an allowable value or less, the combustion noise can be reduced.

  As described above, the combustion noise increases as the in-cylinder pressure change rate (dp / dθ) increases. There are two types of combustion: premixed combustion and diffusion combustion. Premixed combustion is a combustion that has a long ignition delay period and burns rapidly when the ignition temperature is reached. The sound becomes louder. On the other hand, if fuel is supplied to a high temperature field, diffusion combustion has a short ignition delay period, so that the in-cylinder pressure change rate is small and the combustion noise is small. Therefore, the ECU 200 controls the pilot injection amount in addition to the pilot injection timing control, thereby reducing the combustion noise by setting the in-cylinder temperature at the time of main injection to a temperature at which fuel from the main injection can be diffusely burned. Pilot injection amount control may be performed.

  FIG. 4 is a flowchart showing an example of pilot injection amount control. The process of FIG. 4 is executed every predetermined time (for example, 8 msec).

First, the ECU 200 estimates the in-cylinder temperature at the time of main injection by only compression before performing pilot injection (step S31). The in-cylinder temperature at the time of main injection is calculated by the following equation (5). More specifically, in the equation (5), the in-cylinder temperature during main injection is calculated based on the in-cylinder temperature in bottom dead center, the bottom dead center volume, and the main injection volume.

Subsequently, the ECU 200 calculates a required heat generation amount (step S33). The required calorific value is, for example, the following equation 6 using the total amount of cylinder gas, the constant pressure specific heat at the time of pilot injection, the target temperature that is the target value of the in-cylinder temperature during main injection, and the in-cylinder temperature during main injection estimated in step S31. It is calculated from the following formula. The constant pressure specific heat at the time of pilot injection is calculated based on the constant pressure specific heat of each component (CO ₂ , H ₂ O, N ₂ , O ₂ ) at the cylinder temperature at the time of pilot injection and the mass ratio of each component in the cylinder. The

Subsequently, the ECU 200 calculates a required pilot amount from the heat generation amount per 1 mm ³ / st and the required heat generation amount calculated in step S33 (step S35). This required pilot amount becomes the pilot injection amount. The required pilot amount is calculated by the following equation (7). The ECU 200 can calculate the calorific value per 1 mm ³ / st from, for example, a map that defines the relationship between the pilot injection cylinder temperature and the pilot injection oxygen density shown in FIG.

  By performing pilot injection using the pilot injection amount obtained by the above processing, the in-cylinder temperature at the time of main combustion can be set to a temperature at which main injection can be diffusely burned, so that combustion noise can be further reduced. .

  The above-described embodiments are merely examples for carrying out the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention, and It is apparent from the above description that various other embodiments are possible within the scope.

10. Engine system (control device for internal combustion engine)
41 Crank angle sensor 100 Engine (internal combustion engine)
200 ECU (engine speed calculation unit, provisional pilot injection timing setting unit, in-cylinder temperature estimation unit, oxygen density estimation unit, ignition delay period calculation unit, ignition timing calculation unit, pilot injection timing setting unit)

Claims (1)

A control apparatus for an internal combustion engine comprising fuel injection means for performing a plurality of fuel injections in a cylinder including a main injection and a pilot injection preceding the main injection during one cycle,
A crank angle sensor for detecting a crank angle of the internal combustion engine;
An engine speed calculating unit for calculating the speed of the internal combustion engine from a detection value of the crank angle sensor;
A provisional pilot injection timing setting unit for setting a provisional injection timing of the pilot injection;
An in-cylinder temperature estimation unit that estimates the temperature in the cylinder at the time of pilot injection when the pilot injection is performed at the temporary injection timing;
An oxygen density estimator for estimating the oxygen density in the cylinder at the time of pilot injection when the pilot injection is performed at the temporary injection timing;
From the estimated temperature in the cylinder at the time of the pilot injection, the estimated oxygen density in the cylinder at the time of the pilot injection, and the rotational speed of the internal combustion engine, the fuel is injected by the pilot injection and then the fuel is ignited. An ignition delay period calculation unit for calculating an ignition delay period until
An ignition timing calculation unit for calculating the ignition timing of the fuel;
The ignition delay period is equal to or less than an allowable value, and the ignition timing of the fuel is after the time when the in-cylinder pressure change rate, which is the amount of change in pressure in the cylinder per unit time or unit crank angle, becomes maximum. A pilot injection timing setting unit that sets the temporary injection timing to the injection timing of the pilot injection;
A control device for an internal combustion engine.

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