JP2019132262A - Controller of internal combustion engine - Google Patents

Abstract

To provide a controller of an internal combustion engine capable of improving calculation accuracy for suction amount.SOLUTION: A controller 40 of an internal combustion engine is applied to an internal combustion engine having an internal EGR function for causing part of exhaust gas to flow back into a cylinder. The controller comprises a residual gas amount calculation unit 41 configured to calculate a residual gas amount M1, and a backflow gas amount calculation unit 42 configured to calculate a backflow gas amount M2. The controller also comprises: a volume calculation unit 43 configured to add the residual gas amount and the backflow gas amount to calculate an internal EGR gas amount Mrem, calculate an internal EGR gas volume based on the internal EGR gas amount and a suctioned air temperature Tim, and calculate an in-cylinder volume Vdis contributing to suctioned air based on the internal EGR gas volume; and a suctioned air amount calculation unit 44 configured to calculate a suctioned air amount Mcld based on the in-cylinder volume.SELECTED DRAWING: Figure 3

Description

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

  2. Description of the Related Art Conventionally, there is a technique for calculating the amount of intake air charged in a cylinder of an internal combustion engine and controlling the fuel injection amount and ignition timing based on the intake air amount. Here, it is desirable that the intake air amount be an air amount (amount of fresh air gas) actually filled in the cylinder.

  By the way, in recent years, an EGR system that reversely flows a part of exhaust gas may be employed for the purpose of reducing NOx in the exhaust gas. When the EGR system is employed, the capacity of the fresh air intake in the cylinder (net volume in the cylinder, so-called exhaust amount) is substantially reduced by the volume occupied by the EGR gas in the cylinder. If the capacity in the cylinder is substantially reduced, the intake air amount (fresh air amount) is affected and reduced.

  In view of this, the control device disclosed in Patent Document 1 calculates the in-cylinder volume (net in-cylinder volume) that contributes to intake air, and calculates the intake air amount in consideration of the in-cylinder volume, thereby improving the calculation accuracy of the intake air amount. It is improving. In Patent Document 1, the in-cylinder volume (net in-cylinder volume) is calculated based on the compression ratio, specific heat ratio, intake pressure, exhaust pressure, and the like.

JP 2017-40174 A

  By the way, since there is a difference between the temperature of the intake air (intake air temperature) and the temperature of the EGR gas (a part of the exhaust gas), if the intake air and the EGR gas are mixed in the intake stroke, the EGR gas It is conceivable that the volume changes. That is, it is considered that the in-cylinder volume changes depending on the intake air temperature. However, in Patent Document 1, the intake air temperature is not taken into account when calculating the in-cylinder volume. As a result, there is a possibility that the calculation accuracy of the intake air amount is lowered due to the variation in the intake air temperature.

  The present invention has been made in view of the above circumstances, and a main object thereof is to provide a control device for an internal combustion engine capable of improving the calculation accuracy of the intake air amount.

  An internal combustion engine control apparatus that solves the above problems includes an intake valve and an exhaust valve, and an internal EGR that causes a part of the exhaust gas existing in the exhaust passage to flow back into the cylinder during the intake stroke by driving the intake valve and the exhaust valve. In a control device for an internal combustion engine applied to an internal combustion engine having a function, a residual gas amount that is an amount of exhaust gas remaining in the cylinder at the end of an exhaust stroke is determined based on intake pressure, exhaust pressure, and exhaust temperature. A backflow for calculating a backflow gas amount that is a backflow gas amount into the cylinder generated by driving the intake valve and the exhaust valve in the intake stroke after the exhaust stroke is completed, An internal EGR gas amount is calculated by adding a gas amount calculation unit, the residual gas amount and the backflow gas amount, and the intake stroke is completed based on the internal EGR gas amount and the intake air temperature. A volume calculation unit that calculates the volume of the internal EGR gas at the time, calculates a cylinder volume that contributes to intake air based on the volume of the internal EGR gas, and based on the cylinder volume calculated by the volume calculation unit, An intake air amount calculation unit for calculating an intake air amount in the intake stroke.

  When the internal EGR gas and fresh air (intake) are mixed in the intake stroke, the volume of the internal EGR gas at the bottom dead center where the intake stroke ends is changed by the temperature of fresh air (intake air temperature). That is, if the intake air temperature is low, the volume tends to be small, and if the intake air temperature is high, the volume tends to be large. Therefore, by correcting the internal EGR gas amount calculated by adding the residual gas amount and the backflow gas amount based on the intake air temperature, the volume of the internal EGR gas, that is, the cylinder volume that does not substantially contribute to the intake air. The calculation accuracy of can be improved. Then, by subtracting the volume of the internal EGR gas from the maximum value of the in-cylinder volume (in-cylinder volume at the bottom dead center), the in-cylinder volume that contributes to intake (the volume filled with fresh air gas) is accurately determined. Can be calculated. Therefore, the calculation accuracy of the intake air amount can be improved.

The schematic block diagram of an engine system. The figure which shows the lift operation | movement of an intake valve and an exhaust valve. The figure which shows the flow at the time of calculating intake air amount. The figure which shows the relationship between a dead volume coefficient and an engine speed. The figure which shows the relationship between volumetric efficiency, an engine speed, and intake pressure. (A) is a figure which shows the relationship between a fluid friction coefficient and intake temperature, (b) is a figure which shows the relationship between volume force and intake temperature, (c) shows the relationship between volumetric efficiency and intake temperature. Figure. The flowchart which shows the flow of an intake air amount calculation process. The figure which shows the relationship between the coefficient in another example, and an engine speed.

  Hereinafter, an embodiment in which a control device for an internal combustion engine according to the present invention is applied to a multi-cylinder diesel engine provided with a common rail fuel injection device will be described with reference to the drawings. In the following embodiments, the same or equivalent portions are denoted by the same reference numerals in the drawings.

  In the present embodiment, FIG. 1 shows an engine system (an internal combustion engine system). An engine 10 shown in FIG. 1 is mounted on a vehicle as an in-vehicle main engine, and is a four-cycle engine including intake, compression, expansion, and exhaust strokes. The intake passage 11 of the engine 10 is provided with an air flow meter 12 for detecting a mass flow rate of fresh air flowing through the intake passage 11, an intake compressor 16 a of the turbocharger 16, and a throttle valve device 14 in order from the upstream side. . The throttle valve device 14 adjusts the opening degree of the throttle valve 14a by an actuator such as a DC motor.

  A combustion chamber 10 a of each cylinder of the engine 10 is connected to the downstream side of the throttle valve device 14 in the intake passage 11 via a surge tank 15. The combustion chamber 10 a is partitioned by a cylinder 10 b and a piston 17 of the engine 10. The engine 10 is provided with a fuel injection valve 18 having a tip projecting into the combustion chamber 10a. High pressure fuel is supplied to the fuel injection valve 18 from a common rail 19 as a pressure accumulating container. Specifically, high pressure light oil is supplied to the fuel injection valve 18. The fuel injection valve 18 directly injects and supplies the fuel supplied from the common rail 19 into the combustion chamber 10a by being energized. Note that fuel is pumped from the fuel pump 20 to the common rail 19. In FIG. 1, only one cylinder is shown.

  The intake port and the exhaust port of each cylinder of the engine 10 are opened and closed by an intake valve 21 and an exhaust valve 22, respectively. Here, by driving the intake valve 21 and the exhaust valve 22, fresh air or fresh air and an internal EGR gas described later are introduced into the combustion chamber 10a (inside the cylinder). When fuel is injected from the fuel injection valve 18 into the combustion chamber 10a with fresh air or the like being introduced into the combustion chamber 10a, the fuel self-ignites due to compression of the combustion chamber 10a, and energy is generated by combustion. This energy is taken out as rotational energy of the crankshaft 23 of the engine 10 via the piston 17. Burned gas, which is a gas used for combustion, is discharged as exhaust into the exhaust passage 24 by opening the exhaust valve 22. In the present embodiment, the burned gas refers to a gas generated by burning fresh air, fuel, and internal EGR gas in the combustion chamber 10a. A crank angle sensor 25 that detects the rotation angle of the crankshaft 23 is provided in the vicinity of the crankshaft 23.

  The vehicle is provided with a turbocharger 16 as a supercharger. The turbocharger 16 includes an intake air compressor 16a provided in the intake passage 11, an exhaust turbine 16b provided in the exhaust passage 24, and a rotating shaft 16c that connects these. Specifically, the exhaust turbine 16b is rotated by the energy of the exhaust gas flowing through the exhaust passage 24, and the rotational energy is transmitted to the intake compressor 16a via the rotary shaft 16c, and the fresh air is compressed by the intake compressor 16a. That is, fresh air is supercharged by the turbocharger 16. A purification device 26 that purifies the exhaust gas is provided on the downstream side of the turbocharger 16 in the exhaust passage 24.

  The engine 10 of this embodiment is equipped with an internal EGR function that causes a part of the exhaust gas existing in the exhaust passage 24 to flow back into the combustion chamber 10a (cylinder) during the intake stroke by driving the intake valve 21 and the exhaust valve 22. ing. Here, the factors that generate the internal EGR gas will be described.

  FIG. 2 shows the lift operation of the intake valve 21 and the exhaust valve 22. In FIG. 2, EVO is an exhaust valve opening timing, EVC is an exhaust valve closing timing, IVO is an intake valve opening timing, IVC is an intake valve closing timing, and OL is a valve overlap amount. In the present embodiment, as shown in FIG. 2, a valve overlap is generated in which both the intake valve 21 and the exhaust valve 22 are opened. In general, since the exhaust pressure is larger than the intake pressure, when the intake valve 21 and the exhaust valve 22 are simultaneously opened, the burned gas in the exhaust passage 24 is blown back (reverses) to the intake side. Thereby, in the subsequent intake stroke, the burned gas flows again into the combustion chamber 10a (inside the cylinder). This backflow gas becomes a part of the internal EGR gas.

  Further, when the exhaust stroke ends (when the piston 17 exists at the top dead center (TDC)), a gap is generated in the combustion chamber 10a. Since the burned gas remains in the gap in the combustion chamber 10a, the remaining gas becomes a part of the internal EGR gas.

  That is, the internal EGR gas is an exhaust gas (remaining gas) remaining in the gap in the combustion chamber 10a at the end of the exhaust stroke, and an exhaust gas (back flow gas) that has flowed back from the exhaust passage 24 in the subsequent intake stroke. , Are combined.

  Next, the ECU 40 that is an electronic control device that controls the engine system will be described. The ECU 40 is mainly composed of a microcomputer including a known CPU, ROM, RAM, and the like. The detected values of the intake pressure sensor 31, the intake temperature sensor 32, the exhaust temperature sensor 33, and the exhaust pressure sensor 34 are input to the ECU 40, respectively. Further, the detected values of the accelerator sensor 37, the exhaust oxygen concentration sensor 38, the atmospheric pressure sensor 39, the air flow meter 12, and the crank angle sensor 25 are input to the ECU 40, respectively.

  The intake pressure sensor 31 detects the gas pressure (intake pressure Pim) in the surge tank 15, and the intake temperature sensor 32 detects the gas temperature (intake temperature Tim) in the surge tank 15. The exhaust temperature sensor 33 detects the temperature (exhaust temperature Tex) of the exhaust discharged from the combustion chamber 10a. The exhaust pressure sensor 34 detects a gas pressure (exhaust pressure Pex) between the combustion chamber 10a and the exhaust turbine 16b in the exhaust passage 24. The accelerator sensor 37 detects the accelerator operation amount of the accelerator operation member of the driver, and specifically detects the depression amount of the accelerator pedal. The exhaust oxygen concentration sensor 38 detects the oxygen concentration in the exhaust. The atmospheric pressure sensor 39 detects atmospheric pressure. The crank angle sensor 25 outputs a rectangular crank angle signal at every predetermined crank angle (for example, at a cycle of 10 ° CA). The ECU 40 detects the engine speed Ne as the engine speed based on the crank angle signal.

  The ECU 40 calculates an intake amount (in-cylinder charged air amount) that is a mass flow rate of the intake air introduced into the combustion chamber 10a based on the detection values of the various sensors described above, and based on the intake amount, the fuel injection valve Combustion control of the engine 10 such as 18 fuel injection control is performed.

  By the way, in the combustion control, the amount of oxygen that contributes to combustion in the cylinder (intake amount × oxygen concentration) is used, and the amount of air actually taken into the cylinder (external EGR gas if it has an external EGR function). It is desirable that the amount of air including However, the volume in the combustion chamber 10a is substantially reduced by the volume occupied by the internal EGR gas in the combustion chamber 10a. If the volume in the combustion chamber 10a is substantially reduced, the intake air amount is affected. Specifically, it will decrease. Therefore, in order to improve control accuracy such as fuel injection amount control, it is necessary to accurately grasp the amount of air (the amount of fresh air) that is actually charged into the combustion chamber 10a.

  Therefore, the ECU 40 according to the present embodiment accurately calculates the in-cylinder volume Vdis contributing to intake air by the method described below, and calculates the intake air amount Mcld in consideration of the in-cylinder volume Vdis, whereby the intake air amount Mcld. The calculation accuracy is improved. The in-cylinder volume Vdis that contributes to intake air is the substantial capacity of the combustion chamber 10a after considering the volume of the internal EGR gas (after excluding the volume) when the piston 17 is at bottom dead center. is there. Hereinafter, a method for calculating the intake air amount Mcld will be described in detail.

  As shown in FIG. 3, the ECU 40 calculates a residual gas amount calculation unit 41 that calculates a residual gas amount M1, a backflow gas amount calculation unit 42 that calculates a backflow gas amount M2, and an in-cylinder volume Vdis that contributes to intake air. And a function as an intake air amount calculating unit 44 for calculating the intake air amount Mcld in the intake stroke. These functions are realized by executing programs stored in a storage device (memory for storage) included in the ECU 40. Note that the various functions may be realized by an electronic circuit that is hardware, or may be realized at least in part by software, that is, processing executed on a computer.

  The ECU 40 serving as the residual gas amount calculation unit 41 is configured to perform an exhaust stroke end based on the intake pressure Pim (unit: kPa), the exhaust pressure Pex (unit: kPa), and the exhaust temperature Tex (unit: K). A residual gas amount M1, which is the amount of residual gas in the combustion chamber 10a, is calculated.

Specifically, the ECU 40 first calculates the residual gas density ρrem (unit: g / L) in the combustion chamber 10a at the end of the exhaust stroke (when the piston 17 has reached top dead center) by the following formula. Calculate based on (1). The gas constant (unit: kj / kgK) is “R”.

  Then, the ECU 40 calculates a residual gas amount M1 by multiplying the residual gas density ρrem by the top dead center volume Vdead. The residual gas amount M1 is mass (unit: g). The top dead center volume Vdead is a clearance volume in the combustion chamber 10a when the piston 17 reaches the top dead center. The top dead center volume Vdead is constant and is stored in advance in the storage device of the ECU 40.

  The ECU 40 as the backflow gas amount calculation unit 42 calculates a backflow gas amount M2 that is the amount of backflow gas into the combustion chamber 10a generated by driving the intake valve 21 and the exhaust valve 22 in the intake stroke after the exhaust stroke ends. To do.

More specifically, since the valve overlap becomes longer as the engine speed Ne is lower, the backflow gas amount M2 is increased, and the volume of the top dead center is apparently increased by that amount. Therefore, the ECU 40 calculates the backflow gas amount M2 based on the following formula (2). The backflow gas amount M2 is mass. As shown in FIG. 4, the dead volume coefficient K is a coefficient that is inversely proportional to the engine speed Ne. By multiplying the top dead center volume Vdead by the dead volume coefficient K, it is possible to calculate an apparently increasing volume (that is, the volume of the backflow gas) based on the backflow gas. By multiplying this volume by the residual gas density ρrem, the backflow gas amount M2 can be calculated.

The dead volume coefficient K may be calculated (specified) by a map calculation using an engine rotation speed Ne (unit: rpm) as an argument by obtaining a suitable map by experiments or the like. The matching map may be stored in the storage device of the ECU 40. In addition, you may calculate the dead volume coefficient K based on following Numerical formula (3). Neidle is the engine speed during idling stop, and Kidle is a specified adaptation constant when the engine speed Ne is “Neidle”. Thereby, the ECU 40 has a function as the dead volume coefficient calculation unit 46.

  The ECU 40 as the volume calculation unit 43 calculates the internal EGR gas amount Mrem by adding the residual gas amount M1 and the backflow gas amount M2. The internal EGR gas amount Mrem is a mass. Based on the internal EGR gas amount Mrem and the intake air temperature Tim, the ECU 40 calculates a volume Vegr of the internal EGR gas when the intake stroke ends (when the piston 17 reaches bottom dead center), and the internal EGR gas is calculated. Based on the gas volume Vegr, an in-cylinder volume Vdis that contributes to intake air is calculated.

More specifically, it can be assumed that the inhaled fresh air and the internal EGR gas are mixed at a uniform temperature at the bottom dead center. Therefore, the heat balance before and after mixing can be expressed as shown in Equation (4). “Mair” is the mass of inhaled fresh air (air), “Cair” is the specific heat of inhaled fresh air (air), and “T” is the temperature of the mixed gas at the bottom dead center. “Cex” is the specific heat of the exhaust. “V” is the volume (bottom dead center volume) of the combustion chamber 10a when the piston 17 has reached bottom dead center. In addition, since the law of conservation of mass is established before and after mixing, Equation (5) is established.

In the present embodiment, it is assumed that the specific heat Cair of the intake air (air) and the specific heat Cex of the exhaust are the same in order to simplify the calculation. Thus, the unknowns are the temperature T of the mixed gas and the mass Mair of the sucked fresh air. Therefore, the following mathematical formulas (6) and (7) can be derived by solving the mathematical formulas (4) and (5).

  From the above, the ECU 40 determines from the intake air temperature Tim, the intake air pressure Pim, the internal EGR gas amount Mrem, the exhaust gas temperature Tex, the gas constant R, and the bottom dead center volume V at the end of the intake stroke ( When the piston 17 reaches bottom dead center), the mass Mair of fresh air sucked into the combustion chamber 10a is calculated.

  Further, the ECU 40 determines that the intake stroke ends (the piston 17 reaches the bottom dead center) from the intake pressure Pim, the fresh air mass Mail, the internal EGR gas amount Mrem, and the bottom dead center volume V based on the equation (7). The temperature T of the mixed gas in the combustion chamber 10a is calculated.

Then, the ECU 40 calculates the volume Vegr of the internal EGR gas at the end of the intake stroke from the calculated temperature T of the mixed gas based on the formula (8). In addition, Formula (8) is derived | led-out from the state equation of gas.

  Then, the ECU 40 calculates the in-cylinder volume Vdis (= V−Vegr) that contributes to the intake air by subtracting the volume Vegr of the internal EGR gas from the bottom dead center volume V.

  The ECU 40 as the intake air amount calculating unit 44 calculates the intake air amount Mcld in the intake stroke based on the in-cylinder volume Vdis calculated by the volume calculating unit 43.

More specifically, the ECU 40 calculates the intake air amount Mcld (unit: rpm) from the volume efficiency η, the intake air (air) density ρim, the in-cylinder volume Vdis and the engine speed Ne (unit: rpm) based on the equation (9). g / s). At this time, “η” indicates volumetric efficiency.

  The ECU 40 obtains the volume efficiency η by map calculation using the intake pressure Pim and the engine speed Ne as arguments. For this reason, the ECU 40 has a function as the volumetric efficiency calculation unit 45. The volumetric efficiency η indicates the ease of inhaling air. The amount of gas that actually enters the combustion chamber 10a is the maximum gas that can theoretically enter the combustion chamber 10a under the conditions of the intake pressure Pim and the intake air temperature Tim. It is divided by the quantity. As shown in FIG. 5, the volumetric efficiency η decreases as the intake pressure Pim increases. Further, the volumetric efficiency η decreases as the engine speed Ne increases. In order to calculate the volumetric efficiency η, the matching map used by the map calculation is specified by an experiment or the like and stored in the storage device of the ECU 40.

  By the way, the inventors have found that the volumetric efficiency η varies depending on the intake air temperature Tim. For this reason, it is desirable to create a map in consideration of the intake air temperature Tim. However, when an arithmetic map is created using the intake air temperature Tim as an argument in addition to the intake pressure Pim and the engine speed Ne, there is a problem that the number of man-hours for the map increase. Therefore, a method for accurately correcting the volumetric efficiency η without using an experiment was derived as follows. This will be described in detail below.

  The intake air is sucked into the combustion chamber 10a from the intake passage 11 through the suction hole of the combustion chamber 10a. For this reason, it can be considered that the air moves through the throttle (the suction hole of the combustion chamber 10a) in the space of the pressure difference ΔP (= Pim). In this assumption, the pressure difference ΔP between the intake passage 11 and the combustion chamber 10a at the start of the intake stroke can be regarded as the intake pressure Pim. This is because the piston 17 has reached the top dead center at the start of the intake stroke, and intake is performed due to the occurrence of decompression as the piston 17 descends.

Based on the above assumption, the fluid friction coefficient λ of the intake air can be expressed as Equation (10) based on the Blasius equation (flow velocity and friction equation). Ink (air) kinematic viscosity (unit: m ^ 2 / s) is “ν”, flow velocity (unit: m / s) is “Um”, and representative length (unit: m) is “d”. " “Re” is the Reynolds number (a dimensionless number representing the ratio of the inertial force to the viscous force of the fluid).

Then, based on Darcy-Weissbach's equation, the relational expression shown in Equation (11) can be derived. Moreover, the relational expression shown in Formula (12) can be derived from the gas state equation. By arranging these mathematical formulas, the relationship among the flow velocity Um, the intake air temperature Tim, and the fluid friction coefficient λ is shown in the mathematical formula (13).

Further, the kinematic viscosity ν is proportional to the square of the intake air temperature Tim as shown in Equation (14) if the pressure is constant. By arranging the equations (11) to (14), it can be seen that the fluid friction coefficient λ is proportional to the third power of the intake air temperature Tim, as shown in the equation (15).

Next, a relational expression between the pressure difference ΔP and the flow velocity Um can be derived based on the Darcy-Weissbach equation as shown in Equation (16). Equation (17) shows a relational expression between the intake air amount Mcld and the flow velocity. By organizing these equations (16) and (17), as shown in equation (18), the relationship among the intake air amount Mcld, the intake air density ρim, the intake air pressure Pim, and the fluid friction coefficient λ is derived.

The volume efficiency η can be expressed by the following equation (19) based on the equations (9), (15), and (18).

  The fluid friction coefficient λ is proportional to the 3 / 7th power of the intake air temperature Tim as shown in Expression (15). Therefore, the fluid friction coefficient λ (that is, the viscosity and the difficulty in movement) and the intake air temperature Tim have a relationship as shown in FIG. Further, Pim / ρim (volume force, that is, ease of movement) is proportional to the intake air temperature Tim, as shown in Equation (12). Therefore, Pim / ρim and the intake air temperature Tim have a relationship as shown in FIG. Pim / ρim has a larger slope with respect to the intake air temperature Tim than the fluid friction coefficient λ. For this reason, the volumetric efficiency η is proportional to the intake air temperature Tim, as shown in FIG. Specifically, the volumetric efficiency η is proportional to the 2 / 7th power of the intake air temperature Tim.

  From the above, it was possible to derive that the volume efficiency η specified by using the engine speed Ne and the intake pressure Pim as an argument is proportional to the 2 / 7th power of the intake air temperature Tim.

Therefore, the ECU 40 corrects the volume efficiency η specified by using the following equation (20) with the engine speed Ne and the intake pressure Pim as arguments based on the intake air temperature Tim. “Ηc” is the corrected volumetric efficiency after correction, and “Tb” is the intake air temperature (reference intake air temperature) set when acquiring the conformity map of the volumetric efficiency η. A compatible map that can specify the reference intake air temperature Tb using the engine speed Ne and the intake pressure Pim as arguments is stored in the storage device of the ECU 40. The ECU 40 calculates the engine speed Ne by map calculation. The reference intake air temperature Tb is specified (calculated) using the intake air pressure Pim as an argument.

  Therefore, when calculating the intake air amount Mcld based on Equation (9), the ECU 40 calculates the intake air amount Mcld using the volume efficiency η in Equation (9) as the modified volume efficiency ηc. As a result, even if the intake air temperature Tim varies, it can be taken into account, and the intake air amount Mcld can be prevented from varying.

  Next, an intake air amount calculation process executed when calculating the intake air amount Mcld will be described with reference to FIG. The intake air amount calculation process is executed by the ECU 40 at a predetermined timing (for example, at the start of the intake stroke).

  First, the ECU 40 obtains various information (intake pressure Pim, intake air temperature Tim, exhaust pressure Pex, exhaust temperature Tex, engine speed Ne, etc.) from various sensors (step S100).

  Next, the ECU 40 calculates a residual gas amount M1 at the end of the exhaust stroke (step S101). Specifically, as described above, the ECU 40 calculates the residual gas density ρrem in the combustion chamber 10a at the end of the exhaust stroke based on Equation (1), and sets the top dead center volume Vdead to the residual gas density ρrem. By multiplying, the residual gas amount M1 is calculated.

  Next, the ECU 40 calculates a backflow gas amount M2 (step S102). Specifically, as described above, the ECU 40 calculates the backflow gas amount M2 based on Expression (2). At that time, the ECU 40 corrects (specifies) the dead volume coefficient K based on the engine speed Ne.

  Then, the ECU 40 calculates a mass Mair of inhaled fresh air (step S103). Specifically, as described above, the ECU 40 calculates the intake air temperature Tim, the intake pressure Pim, the internal EGR gas amount Mrem, the exhaust gas temperature Tex, the gas constant R, and the bottom dead center volume V based on the equation (6). The mass Mair of air (fresh air) is calculated.

  The ECU 40 calculates the temperature T of the mixed gas at the end of the intake stroke (step S104). Specifically, as described above, the ECU 40 calculates the temperature T of the mixed gas from the intake pressure Pim, the intake air mass Mail, the internal EGR gas amount Mrem, and the bottom dead center volume V based on the equation (7). Is calculated.

  The ECU 40 calculates the in-cylinder volume Vdis (step S105). Specifically, the ECU 40 calculates the volume Vegr of the internal EGR gas from the calculated temperature T of the mixed gas based on the mathematical formula (8). Then, the ECU 40 calculates the in-cylinder volume Vdis (= V−Vegr) that contributes to the intake air by subtracting the volume Vegr of the internal EGR gas from the bottom dead center volume V.

  Next, the ECU 40 calculates volumetric efficiency η (step S106). In step S106, the ECU 40 specifies the volume efficiency η by map calculation using the engine speed Ne and the intake pressure Pim as arguments. In addition, the ECU 40 specifies the reference intake air temperature Tb by using the map rotation, with the engine speed Ne and the intake pressure Pim as arguments. Then, the ECU 40 corrects the specified volume efficiency η based on the reference intake air temperature Tb and the intake air temperature Tim according to the mathematical formula (20), and calculates a corrected volume efficiency ηc.

  Then, the ECU 40 calculates the intake air amount Mcld (step S107). In step S107, the ECU 40 calculates the intake air amount Mcld from the volume efficiency η (= corrected volume efficiency ηc), the intake (air) density ρim, the in-cylinder volume Vdis, and the engine speed Ne based on the mathematical formula (9). .

  According to the embodiment described above in detail, the following excellent effects can be obtained.

  When the internal EGR gas and fresh air (intake) are mixed in the intake stroke, the volume Vegr of the internal EGR gas at the bottom dead center where the intake stroke ends is changed by the temperature of fresh air (intake air temperature Tim). That is, if the intake air temperature Tim is low, the volume Vegr tends to be small, and if the intake air temperature Tim is high, the volume Vegr tends to be large. Therefore, the ECU 40 corrects the internal EGR gas amount Mrem calculated by adding the residual gas amount M1 and the backflow gas amount M2 based on the intake air temperature Tim, so that the volume Egr of the internal EGR gas, that is, substantially In addition, it is possible to improve the calculation accuracy of the in-cylinder volume that does not contribute to the intake air. By subtracting the volume Vegr of the internal EGR gas from the maximum volume (bottom dead center volume V) of the combustion chamber 10a, the in-cylinder volume Vdis contributing to intake air (the volume filled with fresh air) is accurately calculated. can do. Therefore, the calculation accuracy of the intake air amount Mcld can be improved.

  The faster the engine speed Ne, the shorter the time for the intake valve 21 and the exhaust valve 22 to overlap, and the smaller the amount of gas flowing back. Therefore, the ECU 40 corrects the backflow gas amount M2 based on the engine speed Ne. Specifically, the ECU 40 specifies the dead volume coefficient K from the formula (3) based on the engine speed Ne, and calculates the backflow gas amount M2 from the formula (2) based on the specified dead volume coefficient K. . Thereby, the calculation accuracy of the backflow gas amount M2 can be improved.

  The ECU 40 specifies (calculates) the volumetric efficiency η by map calculation based on the engine speed Ne and the intake pressure Pim. Then, the ECU 40 corrects the specified volume efficiency based on the intake air temperature Tim. Specifically, the ECU 40 corrects the volumetric efficiency η as being proportional to the 2 / 7th power of the intake air temperature Tim.

  Thereby, the calculation precision of volumetric efficiency (eta) can be improved. As a result, the calculation accuracy of the intake air amount Mcld can be improved. The fact that the volumetric efficiency η is proportional to the 2 / 7th power of the intake air temperature Tim is not based on an experiment but derived based on a theoretical formula. For this reason, it is not necessary to adapt for every engine, and man-hours, such as an experiment which specifies the adaptation coefficient required for performing map calculation, can be reduced.

(Other embodiments)
The present invention is not limited to the above embodiment, and may be implemented as follows, for example. In the following, parts that are the same or equivalent to each other in the respective embodiments are denoted by the same reference numerals, and the description of the same reference numerals is used.

  In the above embodiment, the specific heat Cex of the exhaust (that is, the internal EGR gas) varies depending on the oxygen concentration in the exhaust. If the specific heat Cex of the internal EGR gas is different, the temperature T of the mixed gas at the bottom dead center is affected even at the same intake air temperature Tim. As a result, the volume Vegr of the internal EGR gas at the bottom dead center is also affected. Therefore, the ECU 40 may correct the volume Vegr of the internal EGR gas based on the exhaust oxygen concentration acquired from the exhaust oxygen concentration sensor 38, and improve the calculation accuracy of the volume Vegr of the internal EGR gas in the intake stroke.

  Specifically, in the above embodiment, the specific heat Cair of air and the specific heat Cex of exhaust are the same, but the specific heat Cex of exhaust may be specified (estimated). The specific heat Cex of the exhaust has a relationship that is inversely proportional to the exhaust oxygen concentration. Therefore, the ECU 40 specifies the specific heat Cex of the exhaust based on the oxygen concentration of the exhaust acquired from the exhaust oxygen concentration sensor 38 by map calculation or the like. And ECU40 should just calculate the temperature T of mixed gas based on Numerical formula (4), (5). The specific heat Cair of air is constant. By doing so, the ECU 40 corrects the volume Vegr of the internal EGR gas based on the oxygen concentration in the exhaust gas, and can improve the calculation accuracy of the intake air amount Mcld.

  In the above-described embodiment, the internal EGR gas amount Mrem (particularly the backflow gas amount M2) may be configured to be controllable. For example, a variable valve mechanism that makes the opening / closing timing or lift amount of at least one of the intake valve 21 and the exhaust valve 22 variable is provided, and the internal EGR gas amount Mrem can be controlled by controlling the valve overlap amount. Also good. Further, the exhaust valve 22 may be retarded so that the exhaust flows backward and the internal EGR gas amount Mrem can be controlled. In this case, it is desirable to change the dead volume coefficient K according to the control amounts of the intake valve 21 and the exhaust valve 22.

  When controlling the internal EGR gas amount Mrem, the ECU 40 determines a target EGR gas amount that matches the estimated value of the exhaust oxygen concentration with the target value, for example, and the internal EGR gas amount Mrem matches the target EGR gas amount. As such, the intake valve 21 and the exhaust valve 22 may be controlled.

In the above embodiment, the residual gas amount M1 and the backflow gas amount M2 are calculated, respectively, but may be calculated collectively. For example, the ECU 40 may calculate the internal EGR gas amount Mrem based on the mathematical formulas (21) and (22). As shown in FIG. 8, the coefficient K2 is a coefficient that is inversely proportional to the engine speed Ne. The coefficient K2 may be calculated (specified) by map calculation using an engine rotation speed Ne as an argument by obtaining a suitable map by experiment or the like. In this case, the ECU 40 has the functions of the residual gas amount calculation unit 41 and the backflow gas amount calculation unit 42.

  In the above embodiment, a gasoline engine may be adopted as the internal combustion engine.

  In the above embodiment, the exhaust pressure Pex may not be a measured value, but may be an estimated value, for example.

  In the above embodiment, a variable valve mechanism that makes the opening / closing timing or the lift amount of at least one of the intake valve 21 and the exhaust valve 22 variable may be provided. Then, the valve opening / closing timing may be appropriately adjusted by the variable valve mechanism according to the accelerator opening degree, the engine operating state, and the like each time.

  DESCRIPTION OF SYMBOLS 21 ... Intake valve, 22 ... Exhaust valve, 24 ... Exhaust passage, 40 ... ECU, 41 ... Residual gas amount calculation part, 42 ... Backflow gas amount calculation part, 43 ... Volume calculation part, 44 ... Intake amount calculation part, M1 ... Residual gas amount, M2 ... backflow gas amount, Mcld ... intake amount, Mrem ... internal EGR gas amount, Pex ... exhaust pressure, Pim ... intake pressure, Tex ... exhaust temperature, Tim ... intake temperature, Vdis ... in-cylinder volume, Vegr ... volume.

Claims (5)

An internal EGR that includes an intake valve (21) and an exhaust valve (22) and causes a part of the exhaust gas existing in the exhaust passage (24) to flow back into the cylinder (10a) in the intake stroke by driving the intake valve and the exhaust valve. In the internal combustion engine control device (40) applied to the internal combustion engine (10) having a function,
Based on the intake pressure (Pim), the exhaust pressure (Pex), and the exhaust temperature (Tex), the residual gas amount that calculates the residual gas amount (M1) that is the amount of exhaust gas remaining in the cylinder when the exhaust stroke ends. A calculation unit (41);
A backflow gas amount calculation unit (42) that calculates a backflow gas amount (M2) that is a backflow gas amount into the cylinder generated by driving the intake valve and the exhaust valve in the intake stroke after the exhaust stroke is finished. )When,
The internal EGR gas amount (Mrem) is calculated by adding the residual gas amount and the backflow gas amount, and the internal EGR gas when the intake stroke ends based on the internal EGR gas amount and the intake air temperature (Tim). A volume calculation unit (43) that calculates a volume (Vegr) of the cylinder and calculates an in-cylinder volume (Vdis) that contributes to intake air based on the volume of the internal EGR gas;
An internal combustion engine control device comprising: an intake air amount calculating unit (44) that calculates an intake air amount (Mcld) in the intake stroke based on the in-cylinder volume calculated by the volume calculating unit.   2. The control device for an internal combustion engine according to claim 1, wherein the backflow gas amount calculation unit corrects the backflow gas amount based on a rotation speed (Ne) of the internal combustion engine.   The internal combustion engine control device according to claim 1, wherein the volume calculation unit corrects the volume of the internal EGR gas based on an oxygen concentration in exhaust gas. A volume efficiency calculation unit (45) for calculating volume efficiency (η) based on the rotational speed and intake pressure of the internal combustion engine;
The intake air amount calculation unit is configured to calculate the intake air amount based on the in-cylinder volume and the volume efficiency,
The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the volumetric efficiency calculation unit corrects the volumetric efficiency based on intake air temperature.   The control apparatus for an internal combustion engine according to claim 4, wherein the volumetric efficiency calculation unit corrects the volumetric efficiency on the assumption that the volumetric efficiency calculation unit is proportional to the 2 / 7th power of the intake air temperature.

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