JP2019108839A - Control device for internal combustion engine - Google Patents

Abstract

To provide a control device for an internal combustion engine which can suitably estimate a variety of flow rates.SOLUTION: An ECU (40) of an engine comprises an intake pressure acquisition part (41) for acquiring intake pressure, a back pressure acquisition part (42) for acquiring back pressure of an exhaust turbine, and an intake amount acquisition part (43) for acquiring a cylinder intake amount. The ECU also comprises a setting part (44) for setting a temporary value as exhaust pressure, an EGR amount calculation part (45) for calculating first differential pressure between upstream and downstream of an EGR valve from the intake pressure and the temporary value, and calculating an EGR amount on the basis of the first differential pressure, and a turbine passage amount calculation part (46) for calculating second differential pressure between upstream and downstream of the exhaust turbine from the back pressure and the temporary value, and calculating a turbine passage amount on the basis of the second differential pressure. The ECU further comprises a search part (47) for searching a true value of the exhaust pressure at which a value obtained by subtracting the EGR amount from a cylinder intake amount coincides with the turbine passage amount by setting a temporary value once or a plurality of times.SELECTED DRAWING: Figure 2

Description

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

  Conventionally, an EGR passage is provided that connects the exhaust pipe of the internal combustion engine upstream of the exhaust turbine of the turbocharger and the intake pipe of the internal combustion engine downstream of the compressor of the supercharger. An internal combustion engine is known in which the engine is circulated as EGR gas. In such an internal combustion engine, ignition timing control is performed according to a cylinder intake air amount sucked into a cylinder of the internal combustion engine, an EGR amount (more specifically, an EGR rate calculated based on the EGR amount), and the like. Therefore, various methods have been proposed to accurately calculate the EGR amount.

  For example, in Patent Document 1, the intake pressure, the exhaust pressure, the sound velocity in the exhaust pipe, the density in the exhaust pipe, and the EGR amount are acquired under predetermined conditions, and the EGR valve opening degree is obtained based on these various parameters. The relationship with the EGR effective opening area is learned. Then, by estimating the amount of EGR based on the relationship between the learned EGR valve opening degree and the EGR effective opening area, the exhaust pipe valve does not operate normally when the flow rate characteristics change due to deposits, or due to aged deterioration. Even in this case, the EGR amount can be calculated (estimated) with high accuracy.

JP, 2015-17569, A

  By the way, when adopting the above method, it is necessary to measure the exhaust pressure or to estimate it by map calculation. In order to measure the exhaust pressure, it is necessary to provide a sensor in the exhaust pipe which is high temperature and high pressure. On the other hand, in the case of estimating the exhaust pressure by the map, it is necessary to obtain a map showing the relationship between the engine rotational speed, the intake pressure, and the exhaust pressure according to the state of the post-processing. However, in order to obtain this map, a great deal of adaptation time is required. As mentioned above, in the said method, there existed a problem that it was difficult to measure exhaust pressure or to estimate with a map.

  The present invention has as its main object to provide a control device of an internal combustion engine capable of suitably estimating various flow rates in view of the above-mentioned situation.

  A control device for an internal combustion engine that solves the above problems is provided between a supercharger that supercharges intake air by exhaust gas of the internal combustion engine, and an intake passage and an exhaust passage connected to the internal combustion engine, and the exhaust passage The EGR passage connecting the upstream side of the exhaust turbine of the turbocharger and the downstream side of the compressor of the intake passage among the intake passage and the EGR passage are recirculated to the intake passage via the EGR passage. An intake pressure acquisition unit that is applied to an internal combustion engine system including an EGR valve that controls an EGR amount, and that acquires an intake pressure downstream of a junction with the EGR passage in the intake passage; And a setting unit configured to set a temporary value as exhaust pressure upstream of the exhaust turbine in the exhaust passage, and a cylinder sucked into a cylinder of the internal combustion engine. A first differential pressure before and after the EGR valve is calculated from an intake amount acquisition unit that acquires an intake amount, and the intake pressure and the temporary value, and the EGR amount is calculated based on the first differential pressure. A second differential pressure before and after the exhaust turbine is calculated from the calculation unit, the back pressure, and the temporary value, and a turbine passing amount passing through the exhaust turbine is calculated based on the second differential pressure. Search for setting the temporary value one or more times by the calculation unit and the setting unit, and searching for the true value of the exhaust pressure in which the value obtained by subtracting the EGR amount from the cylinder intake amount matches the turbine passing amount The subject matter is to provide a part.

  The EGR amount can be calculated (estimated) from the first differential pressure before and after the EGR valve, and the turbine passing amount can be calculated (estimated) from the second differential pressure before and after the exhaust turbine. And from the law of mass conservation, the value obtained by subtracting the EGR amount from the cylinder intake amount should match the turbine passing amount, so the setting unit sets the temporary value as the exhaust pressure one or more times, and such Search for the true value of the exhaust pressure that satisfies the conditions. Then, various flow rates such as the EGR amount can be suitably calculated based on the exhaust pressure which is the true value specified by the search. That is, even if the exhaust pressure is not measured or estimated by a map, the true value of the exhaust pressure can be specified, and various flow rates such as the EGR amount can be suitably calculated.

FIG. 1 is a block diagram showing an engine system. The functional block diagram which shows the presumed process of exhaust pressure. The figure which shows the relationship between the command value with respect to an exhaust turbine, and a nozzle opening degree. The figure which shows the relationship between a branch amount or turbine passing amount, and a temporary value. The flowchart which shows exhaust pressure estimation processing. The flowchart which shows the abnormality determination processing of a sensor.

  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, parts identical or equivalent to each other are denoted by the same reference numerals in the drawings.

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

  The 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 the 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 whose tip end projects into the combustion chamber 10a. The fuel injection valve 18 is supplied with high-pressure fuel from a common rail 19 as a pressure accumulation container. Specifically, high pressure light oil is supplied to the fuel injection valve 18. The fuel injection valve 18 injects and supplies the fuel supplied from the common rail 19 directly into the combustion chamber 10a by being energized. The fuel is pumped from the fuel pump 20 to the common rail 19. Further, FIG. 1 shows only one cylinder.

  Each of the intake port and the exhaust port of each cylinder of the engine 10 is opened and closed by each of the intake valve 21 and the exhaust valve 22. Here, fresh air or fresh air and an external EGR gas described later are introduced into the combustion chamber 10a by opening the intake valve 21. When fuel is injected from the fuel injection valve 18 to the combustion chamber 10a while fresh air or the like is introduced into the combustion chamber 10a, the fuel is self-ignited by the 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. The burned gas, which is a gas used for combustion, is discharged as exhaust gas into the exhaust passage 24 by opening the exhaust valve 22. In the present embodiment, the burnt gas refers to a gas generated by burning fresh air, fuel and external EGR gas in the combustion chamber 10a. In the vicinity of the crankshaft 23, a crank angle sensor 25 for detecting the rotation angle of the crankshaft 23 is provided.

  The vehicle is provided with a turbocharger 16 as a supercharger. The turbocharger 16 includes an intake compressor 16 a provided in the intake passage 11, an exhaust turbine 16 b provided in the exhaust passage 24, and a rotary shaft 16 c connecting the two. Specifically, the energy of the exhaust flowing through the exhaust passage 24 rotates the exhaust turbine 16b, and the rotational energy is transmitted to the intake compressor 16a via the rotation shaft 16c, and the fresh air is compressed by the intake compressor 16a. That is, the fresh air is supercharged by the turbocharger 16.

  In the present embodiment, it is assumed that, in addition to a normal turbocharger, the turbocharger 16 can adjust the supercharging pressure of fresh air by the energization operation. Further, as the turbocharger 16, a variable nozzle turbocharger (VNT) capable of adjusting the supercharging state by adjusting the blade angle (nozzle opening degree) of the turbine wheel is also assumed.

  A purification device 26 is provided downstream of the turbocharger 16 in the exhaust passage 24 to purify the exhaust gas.

  A portion of the exhaust discharged to the exhaust passage 24 is recirculated to the intake passage 11 via the EGR passage 27. Specifically, the upstream side of the exhaust turbine 16 b in the exhaust passage 24 is connected to the surge tank 15 via the EGR passage 27. An EGR valve device 28 is provided in the EGR passage 27. The EGR valve device 28 adjusts the opening degree of the EGR valve 28 a by an actuator such as a DC motor. Depending on the degree of opening of the EGR valve 28a, part of the exhaust gas discharged to the exhaust passage 24 is cooled by the EGR cooler 29 and then supplied to the surge tank 15 as external EGR gas.

  The ECU 40, which is an electronic control unit that controls an engine system, is mainly configured by a microcomputer including a known CPU, a ROM, a RAM, and the like. Detection values of the intake pressure sensor 31, the intake temperature sensor 32, the exhaust temperature sensor 33, and the back pressure sensor 34 are input to the ECU 40, respectively. Further, detection 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 in the surge tank 15, and the intake temperature sensor 32 detects the gas temperature in the surge tank 15. The exhaust temperature sensor 33 detects the temperature of the exhaust discharged from the combustion chamber 10a. The back pressure sensor 34 detects a gas pressure downstream of the exhaust turbine 16 b in the exhaust passage 24 and on the upstream side of an aftertreatment device such as the purification device 26. The accelerator sensor 37 detects an accelerator operation amount of an accelerator operation member of a driver, and specifically detects a depression amount of an accelerator pedal. The exhaust oxygen concentration sensor 38 detects the oxygen concentration in the exhaust gas. The atmospheric pressure sensor 39 detects the pressure of the atmosphere.

  The ECU 40 performs combustion control of the engine 10 including fuel injection control of the fuel injection valve 18, drive control of the EGR valve device 28, and supercharging pressure control by the turbocharger 16 based on detection values of the various sensors described above.

  In the drive control of the EGR valve device 28, the ECU 40 determines a target EGR amount that matches the estimated value of the exhaust oxygen concentration to the target value, and the opening degree of the EGR valve 28a so that the EGR amount matches the target EGR amount. Feedback control.

  Incidentally, when the EGR amount is too small, a sufficient NOx reduction effect can not be obtained, and when the EGR amount is too large, oxygen in the cylinder runs short and particulates (especially smoke) increase. Therefore, the drive control of the EGR valve device 28 aims to reduce NOx by increasing the amount of EGR to the limit (smoke limit) where the amount of smoke generation increases rapidly. Therefore, the exhaust oxygen concentration having a strong correlation with the amount of smoke generation is used as a control index, and the exhaust oxygen concentration of the smoke limit is set to the above-mentioned target exhaust oxygen concentration. Further, the target exhaust oxygen concentration is also set according to the state of the purification device 26.

  However, when the exhaust oxygen concentration is directly detected by the exhaust oxygen concentration sensor 38 mounted in the exhaust passage 24 and used for the drive control, the exhaust flows through the exhaust passage 24 and reaches the exhaust oxygen concentration sensor 38 And the reaction time from the detection of the exhaust oxygen concentration by the exhaust oxygen concentration sensor 38 to the output of the signal. Therefore, it is difficult to directly use the detected value of the exhaust oxygen concentration sensor 38 for the above feedback control.

  Therefore, the ECU 40 substitutes the detection value of an intake system sensor (for example, the air flow meter 12, the intake pressure sensor 31, and the intake temperature sensor 32) for detecting the state quantity of intake, the required injection amount of fuel, and the rotational speed into a model arithmetic expression. The exhaust oxygen concentration is estimated.

  Further, when the internal combustion engine is in steady operation, the concentration of exhaust oxygen exhausted from the engine 10 is constant. Therefore, the detected value of the exhaust oxygen concentration sensor 38 can be regarded as the exhaust oxygen concentration at the present time when the delay time is eliminated. Therefore, the amount of error between the detected value of the exhaust oxygen concentration sensor 38 and the estimated value during steady operation is learned (learned at steady time), and the exhaust oxygen concentration estimated value is corrected based on the learned value.

  For this reason, in the drive control of the EGR valve device 28, it is necessary to suitably calculate the calculation (estimate) of the EGR amount. Hereinafter, the configuration in the present embodiment for suitably calculating the EGR amount will be described in detail.

  As shown in FIG. 2, the ECU 40 includes an intake pressure acquisition unit 41, a back pressure acquisition unit 42, an intake amount acquisition unit 43, a setting unit 44, an EGR amount calculation unit 45, and a turbine passing amount calculation unit 46. , And a function as the search unit 47. Various functions are realized by executing a program stored in a storage device (memory for storage) included in the ECU 40 for these functions. The various functions may be realized by an electronic circuit that is hardware, or at least a part may be realized by software, that is, a process executed on a computer.

  The ECU 40 as the intake pressure acquisition unit 41 acquires the intake pressure Pim downstream of the junction with the EGR passage 27 in the intake passage 11 based on the detection value from the intake pressure sensor 31.

  The ECU 40 as the back pressure acquisition unit 42 acquires the back pressure Ptb (the exhaust pressure downstream of the exhaust turbine 16 b) of the exhaust turbine 16 b based on the detection value from the back pressure sensor 34. Although the back pressure sensor 34 is provided, the back pressure Ptb may be acquired from the atmospheric pressure acquired from the atmospheric pressure sensor 39 and the differential pressure generated by the post-processing device such as the purifying device 26.

  The ECU 40 as the intake amount acquisition unit 43 acquires a cylinder intake amount Mcld to be taken into the cylinder 10b. Specifically, the ECU 40 maps the volume efficiency from the intake pressure Pim and the rotational speed Ne. Then, the cylinder intake air amount Mcld is calculated (obtained) from the equation of state of gas using the intake air temperature Tim, the exhaust gas temperature Tex, the intake air pressure Pim and the volumetric efficiency. The cylinder intake air amount Mcld may be calculated (acquired) by map calculation from the intake air temperature Tim, the exhaust gas temperature Tex, the intake pressure Pim and the rotational speed Ne, or may be calculated (acquired) by a model calculation equation. The rotational speed Ne (engine rotational speed) may be calculated based on the detected value from the crank angle sensor 25.

  The ECU 40 as the setting unit 44 sets a temporary value Pex1 as the exhaust pressure Pex upstream of the exhaust turbine 16b in the exhaust passage 24. Specifically, at the time of initial setting, an intermediate value in a predetermined search range is set as an initial value of the temporary value Pex1. On the other hand, from the first time until the true value Pex2 of the exhaust pressure Pex is determined (until the search ends), it is calculated (specified) as a search result (previous search result) by the search unit 47 described later The exhaust pressure Pex is set as a temporary value Pex1.

  The ECU 40 as the EGR amount calculation unit 45 (corresponding to a first calculation unit) calculates a first differential pressure ΔP1 (= Pex1-Pim) before and after the EGR valve 28a from the intake pressure Pim and the temporary value Pex1. The EGR amount Megr is calculated based on the first differential pressure ΔP1. The EGR amount Megr is the mass flow rate of the external EGR gas passing through the EGR passage 27.

  More specifically, the ECU 40 substitutes the first differential pressure ΔP1, the valve opening degree Regr of the EGR valve 28a, and the argument C1 calculated based on the EGR gas density eegr in the EGR passage 27 into the function F1 to set the EGR amount Megr Calculate The valve opening degree Regr in the EGR valve 28a is a ratio of the opening area to the cross-sectional area of the EGR passage 27, and may be a measured value or a command value. The EGR gas density eegr may be estimated by a model calculation equation based on the intake pressure Pim and the intake temperature Tim, or may be estimated by map calculation.

Here, the argument C1 is calculated based on the first differential pressure ΔP1, the valve opening degree Regr, and the EGR gas density eegr by Equation (1). Further, the function F1 shown in the equation (2) is an approximation equation (model operation equation) conforming to the physical equation, and when substituting the argument C1 into the function F1 to calculate the EGR amount Megr, the EGR amount Megr is It has a net increase characteristic with respect to the argument C1.

The function F1 will be described in detail as to how it is derived. From the relationship between the flow velocity and the differential pressure, the flow velocity Vegr of the EGR gas and the first differential pressure ΔP1 before and after the EGR valve 28a satisfy the equation (3). The coefficient of friction is "λ". Then, assuming that the cross-sectional area (opening area) of the EGR valve 28 a is “A”, the EGR amount Megr has a relationship as shown in the equation (4).

  Since the cross-sectional area A of the EGR valve 28a has the property of increasing purely with respect to the valve opening degree Regr, the coefficient R can be regarded as a pure increase with respect to the valve opening degree Regr in Equation (4). Therefore, it can be said that the EGR amount Megr has a net increase characteristic with respect to the argument C1.

  In the present embodiment, the EGR amount Megr is calculated (acquired) by the model operation expression based on the argument C1, but the EGR amount Megr is calculated (acquired) by map operation based on the argument C2. It is also good.

  The ECU 40 as the turbine passing amount calculation unit 46 (corresponding to a second calculation unit) calculates a second differential pressure ΔP2 (= Pex1−Ptb) before and after the exhaust turbine 16b from the back pressure Ptb and the temporary value Pex1. Then, the ECU 40 calculates a turbine passing amount Mtb, which is a mass flow rate of air that has passed through the exhaust turbine 16b, based on the second differential pressure ΔP2.

  More specifically, the ECU 40 substitutes, for the function F2, the argument C2 calculated based on the second differential pressure ΔP2, the nozzle opening degree Rvnt in the exhaust turbine 16b, and the exhaust gas density 24ex in the exhaust passage 24. Calculate Mtb. The exhaust gas density ρex may be estimated by a model calculation equation based on the back pressure Ptb and the exhaust temperature Tex (or the gas temperature in the aftertreatment device), or may be estimated by map calculation. The nozzle opening degree Rvnt corresponds to the opening degree of the turbocharger 16, and is the ratio of the opening area to the cross-sectional area of the exhaust passage 24 provided with the exhaust turbine 16b.

Here, the argument C2 is calculated on the basis of the second differential pressure ΔP2, the nozzle opening degree Rvnt, and the exhaust gas density に よ り ex by the equation (5). Moreover, the function F2 shown to Numerical formula (6) is an approximation formula (model calculation formula) based on a physical formula similarly to the function F1.

  By the way, the turbocharger 16 assumes the variable nozzle type turbocharger other than the turbocharger without the variable nozzle. The variable nozzle turbocharger has a predetermined opening area even when the exhaust turbine 16 b is commanded to be fully closed. For this reason, when adopting a variable nozzle type turbocharger, it can not be said that the opening area (cross-sectional area) of the nozzle has the property of increasing purely with respect to the command value for the exhaust turbine 16b. That is, when the variable nozzle turbocharger is employed, the command value for the exhaust turbine 16b can not be handled in the same manner as the valve opening degree Regr.

  Therefore, in the case of adopting a variable nozzle turbocharger, a predetermined value in the case where the command value for the exhaust turbine 16b is a fully closed command so that the command value for the exhaust turbine 16b can be handled similarly to the valve opening Regr. Correction (correction) is made based on the opening area. And the value after correction is made into nozzle-opening degree Rvnt.

  Specifically, as shown in FIG. 3, when the command value for the exhaust turbine 16b is a full open command (100 percent), the nozzle opening degree Rvnt is made 100 percent while the full close command (0 percent) In some cases, the command value is corrected so that the opening degree (α percent) calculated based on the predetermined opening area becomes the nozzle opening degree Rvnt. At that time, the nozzle opening degree Rvnt is corrected so as to have a property that the opening area of the nozzle is purely increased.

  Thus, the nozzle opening degree Rvnt has a pure increase relation to the opening area of the nozzle, and when substituting the argument C2 for the function F2 to calculate the turbine passing amount Mtb, the turbine passing amount Mtb is the same as the EGR amount Megr In addition, for the argument C2, it has a net increase characteristic.

  In the present embodiment, the turbine passing amount Mtb is calculated (acquired) by the model operation expression based on the argument C2, but the turbine passing amount Mtb is calculated (acquired) by map operation based on the argument C2. You may

  The ECU 40 as the search unit 47 searches for the true value Pex2 of the exhaust pressure Pex. That is, as shown in FIG. 1, the value obtained by subtracting the EGR amount Megr from the cylinder intake amount Mcld from the law of mass conservation (hereinafter, referred to as a branch amount Mex) should coincide with the turbine passing amount Mtb. Therefore, the ECU 40 searches for a true value Pex2 of the exhaust pressure Pex such that a value obtained by subtracting the EGR amount Megr from the cylinder intake amount Mcld matches (approximates) the turbine passing amount Mtb.

  By the way, as described above, the EGR amount Megr has a characteristic that the net increase with respect to the argument C1. Then, the argument C1 is purely increased with respect to the temporary value Pex1 of the exhaust pressure Pex, as shown in Formula (1). Therefore, as shown by the solid line in FIG. 4, the branch amount Mex calculated by subtracting the EGR amount Megr from the cylinder intake amount Mcld is reduced netly with respect to the temporary value Pex1 of the exhaust pressure Pex. .

  On the other hand, the turbine passing amount Mtb has a net increase characteristic with respect to the argument C2. Then, the argument C2 is purely increased with respect to the temporary value Pex1 of the exhaust pressure Pex, as shown in the equation (5). Therefore, as indicated by a broken line in FIG. 4, the turbine passing amount Mtb is purely increased with respect to the temporary value Pex1 of the exhaust pressure Pex.

  Therefore, as shown in FIG. 4, when searching for the true value Pex2 of the exhaust pressure Pex that matches the branch amount Mex and the turbine passing amount Mtb, it is physically ensured that there is no local solution. That is, there is only one optimal solution, and by performing a predetermined number of calculations (for example, five times), it becomes possible to complete the search for a solution (true value) with a predetermined accuracy.

  In the present embodiment, the ECU 40 employs a binary search when searching for the true value Pex2 of the exhaust pressure Pex. Specifically, the ECU 40 calculates a branch amount Mex (= between Mcld-Megr). Then, if the value (Mex−Mtb) obtained by subtracting the turbine passing amount Mtb from the branch amount Mex is larger than 0, the ECU 40 is more true than the present exhaust pressure (Pex1 (n)) based on the equation (7). Exhaust pressure (Pex1 (n + 1)) close to the value is calculated. On the other hand, if the value obtained by subtracting the turbine passing amount Mtb from the branch amount Mex is smaller than 0, the exhaust pressure (Pex1 (n)) closer to the true value than the current exhaust pressure (Pex1 (n)) based on the equation (8). Calculate n + 1)).

In Equations (7) and (8), “n” indicates the number of operations (the number of searches), the initial value is 1, and one is added each time the operation (search) is performed. Further, in Equations (7) and (8), “Pex1 (n)” is a value corresponding to the temporary value Pex1 in this time. “Pex1 (n + 1)” is the exhaust pressure closer to the true value than the present exhaust pressure, and the true value Pex2 (when the predetermined number of calculations is performed) or the temporary value Pex1 at the next time (If not done). “Pexmax” indicates the maximum value of the exhaust pressure Pex in the search range, and “Pexmin” indicates the minimum value of the exhaust pressure Pex in the search range.

  The ECU 40 as the search unit 47 repeats the calculation a predetermined number of calculations (the number of searches, for example, five times), and sets Pex1 (n + 1) calculated thereafter to a true value Pex2. The predetermined number of operations is a fixed number, and is determined by the calculation accuracy of the true value Pex2. That is, when it is necessary to calculate with high accuracy, the number of operations may be increased. Further, if the branch amount Mex and the turbine passing amount Mtb coincide with each other, the temporary value Pex1 is specified as the true value Pex2.

  When the ECU 40 identifies the true value Pex2 of the exhaust pressure Pex, the ECU 40 identifies the true value of various flow rates such as the EGR amount Megr based on the identified true value Pex2, and executes various controls such as drive control of the EGR valve device 28. Do.

  Next, an exhaust pressure estimation process executed by the ECU 40 to estimate the exhaust pressure Pex will be described based on FIG. The exhaust pressure estimation process is performed at predetermined intervals. In the present embodiment, although the process is performed at a predetermined cycle, the process may be performed at a predetermined timing (for example, the timing of starting intake).

  The ECU 40 acquires various information (intake pressure Pim, back pressure Ptb, intake temperature Tim, exhaust temperature Tex, etc.) (step S101). Then, the ECU 40 calculates and acquires the cylinder intake air amount Mcld, other gas density (EGR gas density eegr, exhaust gas density exex) and the like based on the acquired various information (step S102).

  Next, the ECU 40 sets a temporary value Pex1 of the exhaust pressure Pex (step S103). After the exhaust pressure estimation process is performed, when step S103 is performed first, an intermediate value in the search range of the exhaust pressure Pex determined in advance is set as an initial value. The search range has a minimum value that can be taken as the exhaust pressure Pex as a lower limit and a maximum value as an upper limit.

  On the other hand, after the exhaust pressure estimation process is performed, when the number of times of execution of step S103 is the second or later, the ECU 40 determines the exhaust pressure Pex specified as a search result (previous search result) in step S107 described later. Is set as a temporary value Pex1.

  Then, the ECU 40 calculates a first differential pressure ΔP1 before and after the EGR valve 28a from the intake pressure Pim and the temporary value Pex1, and calculates (acquires) an EGR amount Megr based on the first differential pressure ΔP1 (step S104) ). More specifically, the ECU 40 calculates an argument C1 based on the first differential pressure ΔP1, the valve opening degree Regr, and the EGR gas density eegr, and calculates an EGR amount Megr based on the argument C1.

  The ECU 40 calculates (acquires) the branch amount Mex by subtracting the EGR amount Megr calculated (acquired) in step S104 from the cylinder intake amount Mcld calculated (acquired) in step S102 (step S105).

  Then, the ECU 40 calculates a second differential pressure ΔP2 before and after the exhaust turbine 16b from the back pressure Ptb and the temporary value Pex1, and calculates (acquires) the turbine passing amount Mtb based on the second differential pressure ΔP2 (step) S106). More specifically, the ECU 40 calculates the argument C2 based on the second differential pressure ΔP2, the nozzle opening degree Rvnt, and the exhaust gas density exex, and calculates the turbine passing amount Mtb based on the calculated argument C2.

  The ECU 40 searches for the exhaust pressure Pex such that the branch amount Mex matches (closes) the turbine passing amount Mtb (step S107). Specifically, if the value (Mex−Mtb) obtained by subtracting the turbine passing amount Mtb from the branch amount Mex is larger than 0, the ECU 40 uses the present exhaust pressure (Pex1 (n)) based on the equation (7). The exhaust pressure (Pex1 (n + 1)) closer to the true value is calculated. On the other hand, if the value obtained by subtracting the turbine passing amount Mtb from the branch amount Mex is smaller than 0, the exhaust pressure (Pex1 (n)) closer to the true value than the current exhaust pressure (Pex1 (n)) based on the equation (8). Calculate n + 1)).

  The ECU 40 determines whether the calculation is completed (step S108). Specifically, after the exhaust pressure estimation process is performed, it is determined whether the number of executions of step S107 has reached a predetermined number of operations (for example, five times). If the determination result is negative, the process proceeds to step S103, and the processes after step S103 are performed again. In the next step S103, the exhaust pressure (Pex1 (n + 1)) calculated (specified) by the search result of the current step S107 is set as a new temporary value Pex1.

  On the other hand, if the determination result is affirmative, the ECU 40 ends the exhaust pressure estimation process. When the process ends, the ECU 40 specifies the exhaust pressure (Pex1 (n + 1)) calculated in the last step S107 as the true value Pex2. Further, the ECU 40 estimates various flow rates such as the EGR amount Megr based on the identified true value Pex2 of the exhaust pressure Pex. The method of calculating the EGR amount Megr is the same as the method of calculating in step S104.

  According to the above configuration, the following effects can be obtained.

  The EGR amount Megr can be calculated (estimated) from the first differential pressure ΔP1 before and after the EGR valve 28a, and the turbine passing amount Mtb can be calculated (estimated) from the second differential pressure ΔP2 before and after the exhaust turbine 16b. . Then, from the law of mass conservation, the value (branching amount Mex) obtained by subtracting the EGR amount Megr from the cylinder intake amount Mcld should be equal to the turbine passing amount Mtb. The ECU 40 sets the temporary value Pex1 as the exhaust pressure Pex one or more times, and searches for the true value Pex2 of the exhaust pressure Pex that satisfies such conditions. Then, on the basis of the true value Pex2 specified by the search, true values of various flow rates such as the EGR amount Megr can be suitably calculated. That is, even if the exhaust pressure Pex is not measured or estimated by a map, the true value Pex2 of the exhaust pressure Pex can be specified, and various flow rates (true values) such as the EGR amount Megr can be suitably calculated.

  The ECU 40 calculates the EGR amount Megr based on the first differential pressure ΔP1, the valve opening degree Regr of the EGR valve 28a, and the argument C1 calculated by the EGR gas density eegr in the EGR passage 27. Further, the ECU 40 calculates the turbine passing amount Mtb based on the second differential pressure ΔP2, the nozzle opening degree Rvnt in the exhaust turbine 16b, and the argument C2 calculated by the exhaust gas density exex downstream of the exhaust turbine 16b. In this case, as shown in FIG. 4, the branch amount Mex is purely reduced with respect to the exhaust pressure Pex (provisional value Pex1), and the turbine passing amount Mtb is against the exhaust pressure Pex (provisional value Pex1). Net increase. Therefore, there is no local solution, and it is possible to specify the exhaust pressure Pex (true value Pex2) with desired accuracy by setting (calculating) the fixed number of times.

  In the case of a variable nozzle type turbocharger, the command value for the exhaust turbine 16b is corrected based on a predetermined opening area that occurs when the command value for the exhaust turbine 16b is a fully closed command, and the nozzle opening degree Rvnt is set. That is, when the command value is the full open command, the nozzle opening degree Rvnt is set to 100%, and when the full close command is given, the opening degree (α percent) calculated based on the predetermined opening area is obtained. As such, the command value is corrected, and the nozzle opening degree Rvnt is set. Therefore, even when the variable nozzle turbocharger in which a predetermined opening area is generated when the fully closed command is employed, the turbine passing amount Mtb is appropriate for the exhaust pressure Pex (provisional value Pex1). It is possible to secure that there is no local solution.

  The ECU 40 searches for a true value Pex2 of the exhaust pressure Pex by binary search in a search range set in advance. In the binary search, the search range is determined in advance, and the center of the section including the true value (solution) is repeatedly found to approach the true value, so the accuracy of the search result is uniquely determined by the number of searches. Therefore, under any condition, the true value (solution) can be found by the fixed number of operations.

(Other embodiments)
The present invention is not limited to the above embodiment, and may be implemented, for example, as follows. In addition, below, the same code | symbol is attached | subjected to the part which is mutually the same or equal in each embodiment, and the description is used about the part of the same code | symbol.

Although binary search is adopted in the above-mentioned embodiment, other search methods may be adopted. For example, a linear search may be employed.
In the above embodiment, as the nozzle opening degree, one obtained by correcting the command value is used, but it may be a measured value (including an estimated value) of the nozzle opening degree.

  In the above embodiment, at least one of the intake passage 11, the exhaust passage 24, and the EGR passage 27 may be provided with a sensor for detecting the amount of air (the amount of gas) passing therethrough. In this case, the ECU 40 may have a function as an abnormality detection unit that detects an abnormality in the sensor. For example, as shown in FIG. 6, the ECU 40 estimates (calculates) an air amount (estimated value of the sensor) to be detected by the sensor based on the true value Pex2 of the exhaust pressure Pex searched for (step S201) . Thereafter, the ECU 40 compares the estimated air amount (calculation result) with the air amount (input result) detected by the sensor (step S202). And ECU40 determines abnormality of a sensor based on the comparison (step S203). That is, the ECU 40 determines an abnormality based on whether the difference is equal to or more than a threshold. If there is a sensor abnormality, the ECU 40 notifies of the abnormality (step S204), and if there is no abnormality, the process ends.

  In the above embodiment, a pressure sensor that detects the exhaust pressure Pex may be provided upstream of the exhaust turbine 16b. In this case, the ECU 40 may have a function as an abnormality detection unit that detects an abnormality in the pressure sensor. For example, as shown in FIG. 6, the ECU 40 estimates (calculates) the exhaust pressure (estimated value of the sensor) to be detected by the pressure sensor based on the true value Pex2 of the exhaust pressure Pex searched for (step S201) . Thereafter, the ECU 40 compares the estimated exhaust pressure (calculation result, ie, the true value) with the exhaust pressure (input result, ie, the actual measurement value) detected by the pressure sensor (step S202). Then, the ECU 40 determines that the pressure sensor is abnormal based on the comparison (step S203). That is, the ECU 40 determines an abnormality based on whether the difference is equal to or more than a threshold. If there is an abnormality in the pressure sensor, the ECU 40 notifies of the abnormality (step S204), and if there is no abnormality, the process ends.

  DESCRIPTION OF SYMBOLS 10 ... Engine 11 ... Intake passage, 16 ... Turbocharger, 16b ... Exhaust turbine, 24 ... Exhaust passage, 27 ... EGR passage, 28a ... EGR valve, 40 ... ECU, 41 ... Intake pressure acquisition part, 42 ... Back pressure acquisition The part 43, an intake amount acquisition part 44, a setting part 45, an EGR amount calculation part 46, a turbine passing amount calculation part 47, a search part.

Claims (6)

A turbocharger (16) for supercharging intake air by the exhaust of an internal combustion engine (10), and an intake passage (11) and an exhaust passage (24) connected to the internal combustion engine, the exhaust passage being provided And an EGR passage (27) connecting the upstream side of the exhaust turbine (16b) of the turbocharger and the downstream side of the compressor (16a) of the intake passage, and the EGR passage And a control device (40) for an internal combustion engine applied to an internal combustion engine system comprising: an EGR valve (28a) for controlling an amount of EGR recirculated to the intake passage via:
An intake pressure acquisition unit (41) that acquires an intake pressure downstream of a junction with the EGR passage in the intake passage;
A back pressure acquisition unit (42) for acquiring the back pressure of the exhaust turbine;
A setting unit (44) configured to set a temporary value as an exhaust pressure upstream of the exhaust turbine in the exhaust passage;
An intake amount acquisition unit (43) that acquires a cylinder intake amount that is drawn into a cylinder of the internal combustion engine;
A first calculation unit (45) that calculates a first differential pressure before and after the EGR valve from the intake pressure and the temporary value, and calculates the EGR amount based on the first differential pressure;
A second calculation unit (46) that calculates a second differential pressure before and after the exhaust turbine from the back pressure and the temporary value, and calculates a turbine passing amount passing through the exhaust turbine based on the second differential pressure When,
A search unit (47) for setting the temporary value one or more times by the setting unit, and searching for a true value of the exhaust pressure in which a value obtained by subtracting the EGR amount from the cylinder intake amount matches the turbine passing amount. And a controller for an internal combustion engine. The first calculation unit calculates the EGR amount based on the first differential pressure, the valve opening degree of the EGR valve, and the EGR gas density in the EGR passage.
The internal combustion engine according to claim 1, wherein the second calculation unit calculates the turbine passing amount based on the second differential pressure, the opening degree of the turbocharger, and the exhaust gas density downstream of the exhaust turbine. Control device. The supercharger has a predetermined opening area when a command value for the exhaust turbine is a fully closing command.
The control device for an internal combustion engine according to claim 2, wherein the opening degree of the supercharger is obtained by correcting a command value for the exhaust turbine based on the predetermined opening area.   The control device for an internal combustion engine according to any one of claims 1 to 3, wherein the search unit searches for a true value of the exhaust pressure by binary search in a search range set in advance. At least one of the intake passage, the exhaust passage, and the EGR passage is provided with a sensor that detects an amount of air passing therethrough.
The air amount is estimated based on the true value of the exhaust pressure searched by the search unit, and the abnormality of the sensor is detected based on comparison between the estimated air amount and the air amount detected by the sensor. The control apparatus for an internal combustion engine according to any one of claims 1 to 4, further comprising an abnormality detection unit. A pressure sensor is provided upstream of the exhaust turbine of the turbocharger in the exhaust passage,
The abnormality detection part which detects the abnormality of the said pressure sensor based on the comparison with the true value of the exhaust pressure searched by the said search part and the actual value detected by the said pressure sensor A control device for an internal combustion engine according to any one of the items.

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