JP4534672B2 - Control device for internal combustion engine - Google Patents

Description

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

  In order to optimize the air-fuel ratio of the air-fuel mixture burned in the combustion chamber of the internal combustion engine, the amount of air filled in the combustion chamber when the intake valve is closed (hereinafter referred to as “cylinder charged air amount”). It is necessary to estimate accurately. Usually, the cylinder air charge amount is estimated from a large number of sensors such as a flow rate sensor (air flow meter) and a large number of maps using output values from these sensors as arguments. Here, when the amount of air charged in the cylinder is estimated using the map, the number of necessary maps and the number of arguments thereof are increased, and accordingly, the number of matching man-hours at the time of creating the map is extremely increased. Therefore, in recent years, it has been studied to calculate the cylinder air charge amount by reducing the number of maps and arguments by using a numerical calculation model represented by a formula based on fluid dynamics.

  Even if the engine operating state such as the engine load and the engine speed is the same, the in-cylinder charged air amount often varies for each cylinder. For this reason, assuming that the in-cylinder charged air amount of all cylinders is the same, the in-cylinder charged air amount is calculated using a numerical calculation model, and the fuel injection amount is determined based on the calculated in-cylinder charged air amount. The fuel ratio will be different. As a result, there arises a problem that torque is uneven between the cylinders, or that the exhaust property is deteriorated in a cylinder where the air-fuel ratio is not appropriate.

  Therefore, in calculating the cylinder air charge amount using the numerical calculation model, it is necessary to consider the variation among the cylinders. In the intake air amount estimation device described in Patent Document 1, the air flow through the throttle detected by the air flow meter and the increase amount of the gas in the intake pipe calculated based on the gas density in the intake pipe are determined for each cylinder. The in-cylinder charged air amount is estimated, and the fuel injection amount is determined for each cylinder based on the estimated in-cylinder charged air amount for each cylinder. As a result, the air-fuel ratio can be precisely controlled for each cylinder so as to eliminate variations in the air-fuel ratio between the cylinders.

JP 2001-234798 A JP 2002-70633 A

  When the cylinder charge air amount is estimated for each cylinder on the basis of the amount of air passing through the throttle and the gas density in the intake pipe or the pressure in the intake pipe as in the intake air amount estimation device of Patent Document 1, it is highly accurate in all operating states. However, it is not possible to estimate the in-cylinder charged air amount. For example, when an internal combustion engine includes an EGR mechanism that allows exhaust gas to flow into an intake pipe, exhaust gas (EGR gas) flows into the intake pipe in addition to air. If an attempt is made to estimate the in-cylinder charged air amount for each cylinder in consideration of such inflow of EGR gas, the numerical expression model becomes complicated and the in-cylinder charged air amount obtained by the numerical calculation is estimated. The accuracy is low.

  Accordingly, an object of the present invention is to provide a control device for an internal combustion engine that can estimate the in-cylinder charged air amount for each cylinder with high accuracy.

In order to solve the above-mentioned problem, the first invention is a control device for an internal combustion engine capable of allowing a fluid other than air that has passed through the throttle valve to flow into an intake pipe portion downstream of the throttle valve. The throttle passage air amount detecting means for detecting the throttle passage air amount passing through the throttle valve, the intake pipe pressure detecting means for detecting the pressure in the intake pipe portion, and the throttle passage air amount detecting means. In-cylinder charged air amount estimating means for estimating the in-cylinder charged air amount for each cylinder based on the throttle passage air amount and the pressure in the intake pipe portion detected by the intake pipe pressure detecting means, and the in-cylinder filling An internal combustion engine control device comprising: engine control means for controlling the internal combustion engine based on an in-cylinder charged air quantity for each cylinder estimated by an air quantity estimation means. Fluid inflow prevention means for preventing fluid other than air that has passed through the throttle valve from flowing into the intake pipe portion is further provided, and the in-cylinder charged air amount estimation means is provided by the fluid inflow prevention means by the intake pipe portion. An estimation is performed when fluid other than air that has passed through the throttle valve is prevented from flowing in and when the pressure in the intake pipe portion is lower than a predetermined pressure .
As described above, if it is attempted to estimate the in-cylinder charged air amount for each cylinder in consideration of the inflow of fluid other than air that has passed through the throttle valve, the model formula of the numerical calculation model becomes complicated and is obtained by numerical calculation. The estimated accuracy of the in-cylinder charged air amount for each cylinder is low. According to the first invention, when the fluid inflow prevention means prevents fluid other than air that has passed through the throttle valve from flowing into the intake pipe portion, the in-cylinder charged air amount for each cylinder is estimated. Therefore, the estimation is performed only when the cylinder charge air amount for each cylinder can be estimated with high accuracy.
Note that the pressure in the intake pipe portion downstream of the intake air detected by the intake pipe pressure detection means means the pressure in the intake pipe (including the surge tank) from the throttle valve to the intake valve. The case where fluid other than air that has passed through the throttle valve flows into the intake pipe includes, for example, the case where EGR gas or purge gas described later flows into the intake pipe.

  According to a second invention, in the first invention, an exhaust gas inflow mechanism for allowing exhaust gas to flow into the intake pipe portion is further provided, and the fluid inflow prevention means has the exhaust gas introduced into the intake air by the exhaust gas inflow mechanism. By preventing the fluid from flowing into the pipe portion, fluid other than air that has passed through the throttle valve does not flow into the intake pipe portion.

  According to a third aspect, in the first or second aspect of the present invention, the apparatus further comprises a purge gas inflow mechanism for causing a gas containing fuel evaporated from a fuel supply system of the internal combustion engine to flow into the intake pipe portion. By preventing the gas containing the fuel from flowing into the intake pipe portion by the purge gas inflow mechanism, fluid other than air that has passed through the throttle valve does not flow into the intake pipe portion. .

In order to solve the above-mentioned problem, in the fourth invention, a throttle passage air amount detecting means for detecting a throttle passage air amount passing through the throttle valve, and a pressure in an intake pipe portion downstream of the throttle valve are detected. In-cylinder for each cylinder based on the intake pipe pressure detecting means, the throttle passing air quantity detected by the throttle passing air quantity detecting means, and the pressure in the intake pipe portion detected by the intake pipe pressure detecting means. In-cylinder charged air amount estimating means for estimating the charged air amount; and engine control means for controlling the internal combustion engine based on the in-cylinder charged air amount for each cylinder estimated by the in-cylinder charged air amount estimating means. The in-cylinder charged air amount estimation means estimates when the pressure in the intake pipe portion is lower than a predetermined pressure.
If the pressure in the intake pipe is the same as the pressure in the intake pipe portion upstream of the throttle valve, the flow rate of air passing through the throttle valve is affected by the pulsation of the pressure in the intake pipe. It is difficult to detect the pulsation of the air flow through the throttle valve with high accuracy using an air flow meter with low responsiveness, and the pulsation of the air flow through the throttle valve with high accuracy using an air flow meter with low responsiveness. Even if it can be detected, if it is attempted to estimate the in-cylinder charged air amount for each cylinder in consideration of the pulsation of the air flow rate through the throttle valve, the model formula of the numerical calculation model becomes complicated and each numerical value obtained by numerical calculation The estimation accuracy of the in-cylinder charged air amount for each cylinder is low. According to the fourth aspect of the invention, when the pressure in the intake pipe portion is lower than the predetermined pressure, the cylinder charge air amount for each cylinder is estimated. As a result, estimation is performed only when the cylinder air charge amount for each cylinder can be estimated with high accuracy.
The “predetermined pressure” is a pressure lower than the pressure in the intake pipe portion upstream of the intake of the throttle valve, and preferably a pressure that is low enough that the throttle passage air flow rate is hardly affected by the pulsation of the intake pipe pressure. It is.

  In a fifth aspect of the present invention, in any one of the first to fourth aspects, the intake valve has an in-cylinder calculated by the in-cylinder charged air amount calculating means in which an operating angle is changed according to an engine operating state. A working angle estimating means for estimating an actual working angle in each cylinder based on the amount of charged air is further provided.

According to the first to third aspects of the invention, when the fluid inflow prevention means prevents fluid other than air that has passed through the throttle valve from flowing into the intake pipe portion, Since the estimation is performed, the estimation is performed only when the cylinder air charge amount for each cylinder can be estimated with high accuracy. Therefore, the cylinder air charge amount for each cylinder can be estimated with high accuracy.

  According to the fourth and fifth aspects of the present invention, the cylinder charge air amount is estimated when the pressure in the intake pipe portion is lower than the predetermined pressure, so that the pulsation of the air flow rate through the throttle valve is suppressed, and as a result, The estimation is performed only when the cylinder air charge amount for each cylinder can be estimated with high accuracy. Therefore, the cylinder air charge amount for each cylinder can be estimated with high accuracy.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. The engine body 1 schematically shown in FIG. 1 represents a direct injection spark ignition type internal combustion engine. However, the present invention may be applied to another spark ignition internal combustion engine or a compression self-ignition internal combustion engine.

  As shown in FIG. 1, in the first embodiment of the present invention, the engine body 1 includes a cylinder block 2, a piston 3 that reciprocates within the cylinder block 2, and a cylinder head 4 fixed on the cylinder block 2. It has. A combustion chamber 5 is formed between the piston 3 and the cylinder head 4. In the cylinder head 4, an intake valve 6, an intake port 7, an exhaust valve 8, and an exhaust port 9 are arranged for each cylinder. Further, as shown in FIG. 1, a spark plug 10 is disposed at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is disposed around the inner wall surface of the cylinder head 4. A cavity 12 extending from the lower side of the fuel injection valve 11 to the lower side of the spark plug 10 is formed on the top surface of the piston 3. A variable valve mechanism 13 is attached to the intake valve 6, whereby the phase angle and operating angle of the intake valve 6 are changed.

  The intake port 7 of each cylinder is connected to a surge tank 15 via an intake branch pipe 14, and the surge tank 15 is connected to an air cleaner 17 via an intake pipe 16. A throttle valve 19 driven by a step motor 18 is disposed in the intake pipe 16. An air flow meter 20 for detecting the flow rate of air (intake gas) passing through the intake pipe 16 is disposed in the intake pipe 16 upstream of the throttle valve 19. On the other hand, the exhaust port 9 of each cylinder is connected to an exhaust pipe 21, which is connected to an exhaust purification device 22. A fuel tank (not shown) or the like is connected to a canister 23 for storing evaporated fuel in the fuel tank or the like. The canister 23 is connected to the intake pipe 16 downstream of the throttle valve 19 via a purge control valve 24.

  The electronic control unit (ECU) 31 comprises a digital computer, and is connected to each other via a bidirectional bus 32, a RAM (random access memory) 33, a ROM (read only memory) 34, a CPU (microprocessor) 35, an input. A port 36 and an output port 37 are provided. The surge tank 15 is provided with an intake pipe pressure sensor 40 for detecting the pressure of air (intake gas) in the intake pipe and an intake pipe temperature sensor 41 for detecting the temperature of the air in the intake pipe. The intake pipe internal pressure sensor 40 and the intake pipe internal temperature sensor 41 generate output voltages proportional to the intake pipe internal pressure and the intake pipe internal temperature, and these output voltages are input to the input port 36 via the corresponding AD converters 38.

  In addition, a throttle opening sensor 42 for detecting the opening of the throttle valve 19 and an atmospheric temperature around the internal combustion engine or an air temperature for detecting the temperature of the air taken into the intake pipe 16 (intake air temperature). A sensor 43 and an atmospheric pressure sensor 44 for detecting the atmospheric pressure around the internal combustion engine or the pressure of the air sucked into the intake pipe 16 (intake pressure) are provided, and the output voltage of these sensors corresponds to the corresponding AD. The signal is input to the input port 36 via the converter 38. A load sensor 46 that generates an output voltage proportional to the amount of depression of the accelerator pedal 45 is connected to the accelerator pedal 45, and the output voltage of the load sensor 46 is input to the input port 36 via the corresponding AD converter 38. The For example, the crank angle sensor 47 generates an output pulse every time the crankshaft rotates 30 degrees, and this output pulse is input to the input port 36. The CPU 35 calculates the engine speed from the output pulse of the crank angle sensor 47. On the other hand, the output port 37 is connected to the spark plug 10, the fuel injection valve 11, the throttle valve control step motor 18, and the EGR control valve control step motor 24 via corresponding drive circuits 39.

  By the way, in the control device for the internal combustion engine, in order to set the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 5 of the internal combustion engine to the target air-fuel ratio, the combustion chamber 5 is filled when the intake valve 6 is closed. The amount of air (intake gas) that has been performed (hereinafter referred to as “cylinder charged air amount Mc”) is estimated, and the air-fuel ratio of the air-fuel mixture is determined to be the target air-fuel ratio based on the estimated cylinder charged air amount Mc. The amount of fuel injected from the fuel injection valve 11 into the combustion chamber 5 (or intake passage) of the internal combustion engine (hereinafter referred to as “fuel injection amount”) is determined. Therefore, in order to accurately set the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber 5 of the internal combustion engine to the target air-fuel ratio, it is necessary to accurately estimate the cylinder charge air amount Mc.

  Usually, the in-cylinder charged air amount Mc is estimated from a large number of sensors such as a flow rate sensor (air flow meter), an atmospheric temperature sensor, and an atmospheric pressure sensor, and a large number of maps using output values from these sensors as arguments. However, when the in-cylinder charged air amount Mc is estimated using the map in this way, in order to make the estimated value of the in-cylinder charged air amount Mc more accurate, the number of necessary maps and their arguments are required. The number of will increase. If the number of maps increases in this way, the ROM of the ECU for storing the maps must have a large storage capacity, which increases the manufacturing cost of the control device for the internal combustion engine. Furthermore, in order to create each map, a calibration operation must be performed for each type of internal combustion engine in which the map is used, but the number of measurement points in this calibration operation increases according to the number of maps and the number of arguments thereof. If the number of maps and the number of arguments increase, the number of man-hours for fitting work will increase.

  In view of this, a control device for an internal combustion engine that calculates the in-cylinder charged air amount Mc by numerical calculation using various models without using a map has been studied. In such a control apparatus, the number of necessary maps is reduced as much as possible by using a lot of numerical calculations. This greatly reduces the number of man-hours for performing the fitting work, but also the in-cylinder charged air amount Mc Can be calculated accurately.

  In many of these models, if the engine operating state is the same, the cylinder charge air amount Mc is calculated assuming that the cylinder charge air amount Mc is the same in all cylinders. However, in actuality, the cylinder charge air amount differs between the cylinders even if the engine operating state is the same, for example, because the opening / closing valve timing of the intake valve differs among the cylinders due to manufacturing errors or the like.

  In this way, the cylinder charge air amount is calculated assuming that the cylinder charge air amount is the same in all the cylinders even though the cylinder charge air amount is actually different among the cylinders. If the fuel injection amount is determined based on the charge air amount, the air-fuel ratio of the air-fuel mixture becomes different for each cylinder. When the internal combustion engine is operated in such a state, there are problems that the torque generated for each cylinder differs, or that the exhaust property deteriorates in a cylinder where the air-fuel ratio is not appropriate.

  Therefore, in the present embodiment, taking into consideration that the cylinder charge air amount differs for each cylinder, the flow rate of air passing through the throttle valve 19 per unit time (hereinafter referred to as “throttle valve passage air flow rate mt”). ) And the pressure (hereinafter referred to as “intake pipe pressure Pm”) of air (intake gas) existing in a portion of the intake pipe 16 and the like from the throttle valve 19 to the intake valve 6 (hereinafter referred to as “intake pipe portion”). In-cylinder charged air amount Mc is calculated for each cylinder.

  Hereinafter, with reference to FIG. 2 and FIG. 3, a method of calculating the in-cylinder charged air amount will be described. FIG. 2 shows a basic concept of a model in the intake pipe portion (hereinafter referred to as “intake pipe model”). FIG. 3A shows a change in the flow rate with respect to the crank angle. The solid line mt in FIG. 3 indicates the throttle valve passing air flow rate, and the solid line mc indicates the in-cylinder intake air flow rate to all the cylinders. FIG. 3B shows a change in the intake pipe pressure with respect to the crank angle.

ここで、Ｔｍは吸気管部分内に存在する空気の温度（以下、「吸気管内温度」と称す）、Ｖｍは吸気管部分の容積、Ｒａは気体定数を空気の平均分子量で除算した値である。したがって、時刻ｔからΔｔ秒間における吸気管内圧力の変化量ΔＰｍは、式（１）を積分することによって下記式（２）のように表すことができる。

First, consider the intake pipe model shown in FIG. When the law of conservation of mass is applied to the intake pipe portion, the intake pipe pressure Pm, the air flow rate flowing into the intake pipe portion (ie, the throttle valve passage air flow rate mt), and the flow rate of intake gas flowing out from the intake pipe portion (ie, The in-cylinder intake air flow rate mci) to the i-th cylinder holds the relationship of the following formula (1).

Here, Tm is the temperature of air existing in the intake pipe portion (hereinafter referred to as “intake pipe temperature”), Vm is the volume of the intake pipe portion, and Ra is a value obtained by dividing the gas constant by the average molecular weight of air. . Therefore, the amount of change ΔPm in the intake pipe pressure from time t to Δt seconds can be expressed as the following formula (2) by integrating the formula (1).

  From equation (2), if the inflow air flow rate (mt) to the intake pipe portion is larger than the outflow air flow rate (mci), the intake pipe pressure increases, if it is less, the intake pipe pressure decreases, and if equal, the intake pipe pressure decreases. It can be seen that the amount of change ΔPm in the intake pipe pressure during Δt seconds corresponds to the change in the amount of air in the intake pipe portion. When the engine operating state is in a steady state as will be described later, the outflow air flow rate (mci) from the intake pipe portion is intermittent depending on the opening and closing of the intake valve 6, whereas from the intake pipe portion The inflow air flow rate (mt) is buffered in the intake pipe portion and its change is gentle. For this reason, the magnitude relationship between the outflow air flow rate (mci) and the inflow air flow rate (mt) is repeatedly reversed (see FIG. 3A). This means that the value in parentheses on the right side of the above equation (2) repeats positive and negative inversions at a constant cycle, that is, the intake pipe pressure repeatedly rises and falls at a constant cycle, and represents the pulsation of the intake pipe pressure. .

  Here, it is assumed that the valve opening periods of the intake valves 6 of the cylinders do not overlap as shown in FIG. In this case, regarding the intake to the i-th cylinder, the intake pipe pressure takes the maximum value Pmmax when the time (crank angle) differential value of the intake pipe pressure is zero (dPm / dt = 0), that is, through the throttle valve. When the magnitude of the air flow rate mt and the in-cylinder intake air flow rate mci to the i-th cylinder are balanced (mt = mci) and the in-cylinder intake gas amount mci increases, that is, the magnitude Is the time when the throttle valve passage air flow rate mt is larger until the two are balanced (this time is set as the maximum time tmax). On the other hand, regarding the intake to the i-th cylinder, the intake pipe pressure takes the minimum value Pmmin when the time differential value of the intake pipe pressure is zero and the in-cylinder intake gas amount mci is decreased. That is, the cylinder intake gas amount mci is larger until the above-mentioned magnitude is balanced (the time at this time is set as the minimum value time tmin).

Therefore, the amount of decrease in the intake pipe pressure caused by intake of intake gas into the i-th cylinder (hereinafter referred to as “intake pipe pressure drop amount”) ΔPmdwn (that is, the difference between the maximum value Pmmax and the minimum value Pmmin of the intake pipe pressure) ) Can be expressed as in the following formula (3). In addition, it turns out that the integral term of Formula (3) is corresponded to the area A of Fig.3 (a), and (DELTA) Pmdwn is proportional to the area A. FIG. Therefore, the air amount corresponding to the area A can be referred to as the excess air amount to the i-th cylinder corresponding to the amount of decrease in the intake pipe pressure due to the opening of the intake valve corresponding to the i-th cylinder.

ここで、式（４）中のスロットル弁通過空気流量ｍｔの積分項は、図３（ａ）の面積Ｂに相当し、Ｍｃｉは図３の面積Ａと面積Ｂとを加算した値となっている。したがって、Ｍｃｉは第ｉ気筒に対応する吸気弁６の開弁期間中に第ｉ気筒の燃焼室５内に充填されたガス量、すなわち筒内充填空気量に相当する。ただし、厳密に言えば、実際の筒内充填空気量は図３の面積Ａおよび面積Ｂに面積Ｃを加えた量に相当するため、上記Ｍｃｉは面積Ｃに相当するガス量を微少として無視した近似値となっている。 From the assumption that the valve opening periods of the intake valves 6 of the respective cylinders do not overlap, the above equation (3) can be transformed into the following equation (4).

Here, the integral term of the throttle valve passing air flow rate mt in the equation (4) corresponds to the area B in FIG. 3A, and Mci is a value obtained by adding the area A and the area B in FIG. Yes. Therefore, Mci corresponds to the amount of gas charged into the combustion chamber 5 of the i-th cylinder during the valve opening period of the intake valve 6 corresponding to the i-th cylinder, that is, the amount of in-cylinder charged air. Strictly speaking, however, the actual cylinder air filling amount corresponds to the amount obtained by adding area C to area A and area B in FIG. 3, and thus Mci ignores the gas amount corresponding to area C as a small amount. It is an approximate value.

  Accordingly, when the engine operating state is in a steady state and the valve opening periods of the intake valves 6 of the respective cylinders do not overlap, the throttle valve passage air flow rate mt, the intake pipe temperature Tm, and the intake pipe pressure drop amount ΔPmdwn are detected or By calculating, the in-cylinder charged air amount Mci to the i-th cylinder can be calculated from the above equation (4).

式（５）において、Δｔｄｗｎは最大値時刻ｔｍａｘから最小値時刻ｔｍｉｎまでの間の時間であって、吸気管内圧力の降下時間を表す。また、式（５）におけるスロットル弁通過空気流量ｍｔは、最大値時刻ｔｍａｘから最小値時刻ｔｍｉｎまでの期間、または吸気弁６の開弁期間中にエアフロメータ２０の検出値を平均した値である。あるいは、最大値時刻ｔｍａｘから最小値時刻ｔｍｉｎまでの期間、または吸気弁６の開弁期間中における実際のスロットル弁通過空気流量の変動が小さいことから、これら期間中の特定の時刻におけるエアフロメータ２０の検出値であってもよい。同様に、式（５）における吸気管内温度Ｔｍも、上記期間中における吸気管内温度センサ４１の検出値を平均した値、または上記期間中の特定の時刻における吸気管内温度センサ４１の検出値である。 Note that when the expression (4) is mounted, the expression (4) may be modified as the following expression (5).

In equation (5), Δtdwn is the time between the maximum value time tmax and the minimum value time tmin, and represents the pressure drop time of the intake pipe pressure. Further, the throttle valve passing air flow rate mt in the equation (5) is a value obtained by averaging the detected values of the air flow meter 20 during the period from the maximum value time tmax to the minimum value time tmin or during the valve opening period of the intake valve 6. . Alternatively, since the variation in the actual throttle valve passage air flow rate during the period from the maximum value time tmax to the minimum value time tmin or during the valve opening period of the intake valve 6 is small, the air flow meter 20 at a specific time during these periods. May be a detected value. Similarly, the intake pipe temperature Tm in the equation (5) is also an average value of detection values of the intake pipe temperature sensor 41 during the period, or a detection value of the intake pipe temperature sensor 41 at a specific time during the period. .

  However, the in-cylinder charged air amount can be calculated using the equations (4) and (5) only when the opening timings of the intake valves 6 of the respective cylinders do not overlap. This is because, when the control device of the first embodiment is used in the case where the opening timing of the intake valve 6 of each cylinder overlaps, the error of the calculated cylinder air charge amount Mci for each cylinder becomes large. It is because it ends. That is, as described with reference to FIG. 3A, when the cylinder charge air amount is calculated using the equation (4) or the equation (5), the cylinder fill air amount is a gas amount corresponding to the area C. Is an approximate value neglected as a small amount. However, when the valve opening timings of the intake valves 6 between the cylinders overlap, the throttle valve passing air flow rate mt is large as shown in FIG. 4, and therefore the gas amount corresponding to the area C is so large that it cannot be ignored.

Therefore, when the valve opening timing of the intake valve 6 of each cylinder overlaps, among the in-cylinder charged air amount Mci for each cylinder, the gas amount other than the gas amount corresponding to the area A is as shown in FIG. Instead of obtaining the area of a rectangle, the area of a trapezoid is obtained. That is, mt · (Δtdwn + Δtioc) / 2 is used instead of mt · Δtdwn in the above formula (5). Here, Δtdwn is the time between the maximum value time tmax when the intake pipe pressure takes the maximum value Pmmax and the minimum value time tmin when the minimum value Pmmin is taken (Δtdwn = tmin−tmax). , Δtioc is the time between the time when the intake valve 6 of the i-th cylinder opens (valve opening time) tio and the time when the intake valve 6 closes (valve closing time) tic, that is, the intake valve 6 of the i-th cylinder. Is the time during which the valve is open (Δtioc = tic-tio). Therefore, in the present embodiment, the above formula (5) is rewritten and used as the following formula (6).

  In Expression (6), a term including ΔPmdwn represents a gas amount corresponding to the area A in FIG. 5B, and a term including mt represents a gas amount corresponding to the area B in FIG. The in-cylinder charged air amount Mci to the i-th cylinder is a value obtained by adding the area A and the area B in FIG. As can be seen from FIG. 5 (a), by obtaining a gas amount other than the gas amount corresponding to the area A as a trapezoid, most of the gas amount corresponding to the area C shown in FIG. Can be included. Therefore, according to the equation (6), the in-cylinder charged air amount Mci more accurately represents the amount of gas charged in the combustion chamber 5 of the i-th cylinder during the opening period of the intake valve 6 of the i-th cylinder. Even when the opening timing of the intake valve 6 of each cylinder overlaps, the calculation error of the in-cylinder charged air amount Mci can be suppressed to a small value.

  In the above-described embodiment, the intake pipe temperature sensor 41 is attached to the surge tank 15 to detect the temperature of the intake gas in the intake pipe portion, but the temperature sensor is attached to the intake upstream side of the throttle valve 19 or A temperature sensor may be provided integrally with the air flow meter 20, and the temperature detected by the temperature sensor may be used as the intake pipe temperature. This is because the intake pipe temperature can be approximated to be substantially equal to the temperature of the air upstream of the intake of the throttle valve 19, particularly when the engine operating state is in a steady state, and in this embodiment, the cylinder to the i-th cylinder is approximated. The calculation of the internal charge air amount Mci is performed when the engine operating state is in a steady state.

  Thus, by calculating the in-cylinder charged air amount for each cylinder when the engine operating state is in a steady state, the relative deviation of the in-cylinder charged air amount for each cylinder can be obtained. Therefore, for example, if the average value of the in-cylinder charged air amount to all the cylinders can be calculated from the throttle valve opening etc. by a model different from the above numerical calculation model, The in-cylinder charged air amount for each cylinder is calculated by multiplying the average value of the in-cylinder charged air amount by the relative deviation of the in-cylinder charged air amount for each cylinder calculated by the numerical calculation model. In this case, if the model for calculating the average value of the in-cylinder charged air amount to all cylinders from the throttle valve opening etc. is a model corresponding to when the engine operating state is in the transient state, the engine operating state is in the transient state. Even in this case, the in-cylinder charged air amount for each cylinder can be calculated.

  By the way, the calculation of the in-cylinder charged air amount Mci for each cylinder as described above is not always accurate if the engine operating state is in a steady state. There is an engine operating state in which the calculation accuracy of the in-cylinder charged air amount Mci is low. Examples of such engine operating states include the following.

The first operating state includes a state in which internal EGR is performed. In many internal combustion engines, an intake valve is used to reduce the NO _x concentration in the exhaust gas discharged from the combustion chamber 5 or to reduce the pumping loss due to the throttle valve 19 when performing stratified combustion in the combustion chamber 5. 6 has an internal EGR mechanism in which a part of the exhaust gas in the combustion chamber 5 is returned to the intake port 7 via 6 and flows into the combustion chamber 5 again. In this embodiment, the internal EGR mechanism is a mechanical variable valve mechanism that changes the phase angle and operating angle of the intake valve 6 and the like by changing the rotation angle of the camshaft relative to the rotation angle of the crankshaft. The amount of exhaust gas (EGR gas) returned from the combustion chamber 5 to the intake port 7 varies depending on the phase angle and operating angle of the intake valve 6. That is, by extending the period during which the intake valve 6 is open during the exhaust stroke of each cylinder, in other words, the period during which the exhaust valve 8 and the intake valve 6 are simultaneously open (valve overlap) is increased. As a result, the EGR gas increases. Conversely, if the intake valve 6 is not opened at all during the exhaust stroke, or if there is no valve overlap period between the exhaust valve 8 and the intake valve 6, the amount of EGR gas returned to the intake port 7 is zero. Become.

  When the internal EGR is performed and the exhaust gas is returned into the intake port 7, that is, when there is a valve overlap, the EGR gas flows into the intake pipe portion in addition to the air flowing in through the throttle valve 19. I'm damned. As shown in FIG. 2, in the intake pipe model, the numerical calculation model is created by using only the air passing through the throttle valve as the gas flowing into the intake pipe. Therefore, in the intake pipe model, EGR gas flows into the intake pipe portion. If the intake pipe model is used when EGR gas is allowed to flow into the intake pipe portion, the calculation accuracy of the in-cylinder charged air amount for each cylinder calculated by the intake pipe model is not supported. Is low. On the other hand, when a numerical calculation model is created so as to correspond to the case where EGR gas is caused to flow into the intake pipe portion, the model becomes complicated and the load on the ECU 31 increases, and the operation used for calculation in the numerical calculation model The parameter increases and the calculation accuracy of the in-cylinder charged air amount for each cylinder decreases. Therefore, when the internal EGR is performed, that is, when there is a valve overlap, the accuracy of calculation of the in-cylinder charged air amount Mci for each cylinder is low even if the engine operating state is in a steady state. End up.

  The second operating state includes a state where purge control is performed. In the present embodiment, a canister 23 is provided for temporarily storing fuel vapor evaporated from a fuel supply system such as a fuel tank. The canister 23 accommodates activated carbon having a property of adsorbing fuel vapor and releasing the fuel vapor again when air is flown. For example, the canister 23 traps the evaporated fuel when the fuel is actively evaporated, such as when the engine is stopped. During engine operation, air is taken from the outside of the canister, the evaporated fuel adsorbed on the activated carbon is released, and is sucked into the intake pipe 16 downstream of the throttle valve 19 for purging (purge control). The purge control valve 24 distributes air containing evaporated fuel (hereinafter referred to as “purge gas”) from the canister 23 to the intake pipe 16. The opening and closing of the purge control valve 24 is performed according to the engine operating state. Basically, the larger the opening of the purge control valve 24, the larger the flow rate of the purge gas that flows into the intake pipe 16.

  When purge control is being performed and purge gas is flowing into the intake pipe 16, that is, when the purge control valve 24 is open, in addition to the air flowing into the intake pipe portion via the throttle valve 19, Purge gas flows in. As described above, in the intake pipe model, since the above numerical calculation model is created by setting the gas flowing into the intake pipe only as the amount of air passing through the throttle valve, when the purge gas is caused to flow into the intake pipe portion, the intake pipe model The calculation accuracy of the in-cylinder charged air amount calculated for each cylinder is low. On the other hand, when the numerical calculation model is created so as to correspond to the case where the purge gas is caused to flow into the intake pipe portion, the model becomes complicated and the load on the ECU 31 increases, and the operation parameters used for the calculation in the numerical calculation model Increases and the calculation accuracy of the in-cylinder charged air amount for each cylinder decreases. Therefore, when the purge control is performed, that is, when the purge control valve 24 is opened, the calculation accuracy of the in-cylinder charged air amount Mci for each cylinder even if the engine operating state is in a steady state. Will be low.

  The third operating state includes a case where the intake pipe negative pressure is low, that is, a case where the pressure in the intake pipe portion is high. As described above, in the intake pipe model using the equation (6), it is approximated that the throttle passage air flow rate mt is substantially constant over the period from the maximum value time tmax to the minimum value time tmin. The in-cylinder charged air amount is calculated, and the throttle passage air flow rate mt used in the equation (6) is, for example, during the period from the maximum value time tmax to the minimum value time tmin or during the valve opening period of the intake valve 6 The flow rate of air passing through the throttle detected by the air flow meter 20 is averaged.

  However, in actuality, the throttle passage air flow rate pulsates, and if the pulsation of the throttle passage air flow rate is large, an error from the throttle passage air flow rate mt approximately used in the equation (6) increases. In addition, the calculation accuracy of the cylinder air charge amount Mci for each cylinder calculated by the intake pipe model is low.

  Examples of the case where the actual pulsation of the throttle passage air flow rate is large include a case where the throttle opening of the throttle valve 19 is large and a case where the operating angle of the intake valve 6 is small. When the throttle opening is large, air easily flows into the intake pipe portion via the throttle valve 19. For this reason, the negative pressure in the intake pipe portion is low, that is, the intake pipe internal pressure is high. The differential pressure is small. Similarly, when the operating angle of the intake valve 6 is small, the amount of air flowing out from the intake pipe portion into the combustion chamber 5 via the intake valve 6 is small. For this reason, the intake pipe pressure is unlikely to decrease, and the differential pressure between the upstream intake pipe pressure and the intake pipe pressure is small.

  Here, the pulsation of the intake pipe pressure caused by opening and closing of the intake valve 6 exceeds the intake pipe portion as the differential pressure between the intake pipe pressure and the upstream intake pipe pressure increases, that is, as the negative pressure in the intake pipe portion increases. Therefore, the air flow rate through the throttle is less likely to pulsate. Conversely, the smaller the pressure difference between the intake pipe pressure and the upstream intake pipe pressure, that is, the smaller the negative pressure in the intake pipe portion, the more the pressure is transmitted across the intake pipe portion, and therefore the throttle passage air flow rate is more likely to pulsate. Therefore, when the throttle opening of the throttle valve 19 is large and when the operating angle of the intake valve 6 is small, the calculation accuracy of the in-cylinder charged air amount Mci for each cylinder calculated by the intake pipe model is low. .

  Thus, when the engine operating state is in the three operating states described above, the calculation accuracy of the in-cylinder charged air amount Mci for each cylinder is low even if the engine operating state is in a steady state. Therefore, in the present invention, when the engine operating state is the above-described three operating states, the cylinder charge air amount Mci for each cylinder is not calculated. This prevents the calculation of the cylinder charge air amount Mci for each cylinder in a state where the calculation accuracy is low, so that the calculation of the cylinder charge air amount Mci for each cylinder is always performed with high accuracy. As a result, the relative deviation of the in-cylinder charged air amount for each cylinder can always be accurately obtained.

  FIG. 6 shows a control routine of calculation timing determination control for determining the timing for calculating the cylinder charge air amount. First, in step 101, it is determined whether or not the engine operating state is in a steady state. If it is determined that the engine operating state is not in a steady state, that is, if it is in a transient state, the control routine is terminated. Calculation of the amount of air charged in the cylinder is not performed. On the other hand, if it is determined that the engine operating state is in a steady state, the routine proceeds to step 102. In step 102, it is determined whether or not there is a valve overlap. If there is a valve overlap, the control routine is terminated. On the other hand, if it is determined in step 102 that there is no valve overlap, the routine proceeds to step 103, where it is determined whether or not the purge control valve 24 is closed. When it is determined that the purge control valve 24 is opened, the control routine is terminated. On the other hand, if it is determined that the purge control valve 24 is closed, the routine proceeds to step 104.

  In step 104, it is determined whether or not the throttle opening Dt is equal to or less than a predetermined throttle opening Dtp. The predetermined throttle opening Dtp is, for example, an opening at which the intake pipe pressure is reduced to such an extent that the throttle-passing air flow rate is hardly affected by the pulsation of the intake pipe pressure. When it is determined that the throttle opening degree Dt is larger than the predetermined throttle opening degree Dtp, the control routine is ended. On the other hand, if it is determined that the throttle opening Dt is equal to or smaller than the predetermined throttle opening Dtp, the routine proceeds to step 105. In step 105, it is determined whether or not the operating angle An is greater than or equal to a predetermined operating angle Anp. The predetermined operating angle Anp is, for example, an operating angle at which the intake pipe pressure is lowered to such an extent that the throttle passage air flow rate is hardly affected by the pulsation of the intake pipe internal pressure. When it is determined that the operating angle An is smaller than the predetermined operating angle Anp, the control routine is ended. On the other hand, if it is determined that the operating angle An is equal to or larger than the predetermined operating angle Anp, the routine proceeds to step 106. In step 106, the in-cylinder charged air amount Mci for each cylinder is calculated based on the throttle passage air flow rate mt and the intake pipe pressure Pm using the above equation (6), and the control routine is terminated.

  In the above embodiment, in addition to the engine operating state being a steady state, there is no valve overlap, the purge control valve is closed, and the throttle opening is equal to or less than a predetermined throttle opening. The cylinder air charge amount Mci is calculated only when all the four conditions that the working angle is equal to or larger than the predetermined working angle are satisfied. However, even if all of these four conditions are not satisfied, the in-cylinder charged air flow rate may be calculated as long as at least one of these conditions is satisfied. In the above embodiment, the variable valve mechanism is mechanical. However, another variable valve mechanism such as an electromagnetically driven intake valve may be used.

  Next, a modified example of the control device according to the first embodiment of the present invention will be described. In this modified example, as shown in FIG. 7, the variable valve mechanism is not provided. Instead, the exhaust pipe 21 and the surge tank 15 are connected via a recirculated exhaust gas (hereinafter referred to as EGR gas) passage 25. Connected to each other. An EGR gas control valve 26 driven by a step motor 27 is disposed in the EGR gas passage 25.

  In this modification, internal EGR by the variable valve mechanism cannot be executed, but external EGR using the EGR gas passage 25 can be performed instead. That is, the EGR gas passage 25, the EGR gas control valve 26, etc. constitute an external EGR mechanism, and this external EGR mechanism is exhaust gas discharged from the combustion chamber 5 to the exhaust port 9 for the same reason as in the case of the internal EGR mechanism. A part of the gas flows into the surge tank 15 and flows into the combustion chamber 5 again. In the external EGR mechanism, the flow rate of the exhaust gas (EGR gas) flowing into the surge tank 15 from the exhaust port 9 changes according to the opening degree of the EGR gas control valve 26.

  When external EGR is performed and exhaust gas is allowed to flow into the surge tank 15, that is, when the EGR gas control valve 26 is opened, the air flowing into the intake pipe portion via the throttle valve 19 In addition, EGR gas is allowed to flow. For this reason, when the external EGR is performed, that is, when the EGR gas control valve 26 is opened, as in the case of the external EGR described above, each engine operation state is in a steady state. The calculation accuracy of the cylinder air charge amount Mci for each cylinder is low.

  Therefore, in this modified example, when the EGR gas control valve 26 is opened, the in-cylinder charged air amount Mci for each cylinder is not calculated. This prevents the calculation of the cylinder charge air amount Mci for each cylinder in a state where the calculation accuracy is low, and as a result, always obtains the relative deviation of the cylinder charge air amount for each cylinder accurately. Can do.

  Next, an internal combustion engine control apparatus according to a second embodiment of the present invention will be described. The control device of the second embodiment is basically the same as the control device of the first embodiment. By the way, when the operating parameters of the internal combustion engine, such as the engine speed, the intake valve phase angle, and the intake pipe pressure, are the same, the in-cylinder charged air amount Mci to the i-th cylinder is the function of the intake valve 6 of the i-th cylinder. It is uniquely determined by the corner. For example, when operating parameters other than the operating angle are fixed, the relationship between the in-cylinder charged air amount Mci and the actual operating angle is a curve as shown in FIG. Therefore, the operation parameters other than the operating angle are fixed to a specific value or a value in the vicinity thereof, and the operation to the i-th cylinder calculated by the operation in the above embodiment (hereinafter referred to as “air amount calculation operation”) is performed. From the in-cylinder charged air amount Mci, the actual operating angle of the intake valve 6 of the i-th cylinder can be estimated based on a map as shown in FIG.

  Specifically, in the present embodiment, when the operating parameters other than the operating angle (for example, the engine speed, the phase angle of the intake valve 6 and the average value of the intake pipe pressure) take a specific value or a value in the vicinity thereof. Curves as shown in FIG. 8 for the cylinder air charge amount and the working angle are obtained in advance experimentally or by calculation, and stored in the ROM 34 of the ECU 31 as a map as shown in FIG. Then, when the operating parameter other than the operating angle takes the specific value or a value in the vicinity thereof during the operation of the internal combustion engine, the in-cylinder charged air amount Mci for each cylinder is calculated by the air amount calculating operation. . The actual operating angle of the intake valve 6 is calculated from the calculated cylinder charge air amount Mci for each cylinder and the map stored in the ROM 34. Thereby, according to this embodiment, the actual operating angle of the intake valve 6 can be calculated relatively accurately.

  When the intake valve 6 is driven by the mechanical variable valve mechanism 13, the target operating angle commanded from the ECU 31 to the variable valve mechanism and the intake valve 6 due to wear of a cam used for the variable valve mechanism or the like. There will be a deviation from the actual operating angle. When a variable valve mechanism (not shown) of the electromagnetic intake valve 6 is provided to drive the intake valve 6, the ECU 31 changes from the ECU 31 to the variable valve mechanism due to deterioration of a spring used in the variable valve mechanism. There is a deviation between the commanded target operating angle and the actual operating angle of the intake valve 6. If such a deviation occurs, the operating angle of the intake valve 6 cannot be controlled appropriately, resulting in deterioration of engine output, fuel consumption, or exhaust properties.

  Therefore, in the present embodiment, when the actual operating angle calculated based on the air amount calculation operation is different from the target operating angle commanded from the ECU 31 to the variable valve mechanism, the calculated actual operating angle and the target By correcting so as to compensate for the difference from the working angle, the actual working angle of the intake valve 6 is always made to coincide with the target working angle.

  For example, when the estimated actual working angle is different from the target working angle, these differences are calculated. Then, after the next cycle, a value obtained by adding the calculated difference to the target operating angle is commanded from the ECU 31 to the variable valve mechanism.

  Therefore, according to the second embodiment, the internal combustion engine is controlled by controlling the actual working angle of the intake valve 6 to always coincide with the target working angle, that is, based on the estimated actual working angle. Thus, deterioration of engine output, fuel consumption, or exhaust properties can be suppressed.

  In this specification, when the engine operating state is in a steady state, the operating parameters of the internal combustion engine (for example, engine speed, engine load, in-cylinder charged air amount, etc.) hardly change and are almost constant. On the other hand, it means that the operating state is maintained, while the case where the engine operating state is in a transient state means an operating state in which the operating parameters of the internal combustion engine vary greatly.

It is a figure which shows the whole internal combustion engine in which the control apparatus of the internal combustion engine of this invention is used. It is a figure which shows the basic concept of the intake pipe model of this invention. It is a figure which shows the change of the flow volume with respect to a crank angle, and the change of the pressure in an intake pipe. It is a figure which shows the change of the flow volume with respect to a crank angle in case the valve opening timing of the intake valve 6 overlaps between cylinders. It is a figure which shows the change of the flow volume with respect to a crank angle. It is a flowchart which shows the control routine of calculation time determination control which determines the time which calculates the cylinder filling air amount. It is a figure which shows the whole internal combustion engine used in the example of a change of the control apparatus of 1st embodiment. It is a figure showing the relationship between cylinder filling air amount and a working angle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine main body 5 Combustion chamber 6 Intake valve 7 Intake port 8 Exhaust valve 11 Fuel injection valve 13 Variable valve mechanism 14 Intake branch pipe 15 Surge tank 16 Intake pipe 19 Throttle valve 20 Air flow meter 23 Canister 31 ECU
40 Intake pipe pressure sensor 41 Intake pipe temperature sensor

Claims (5)

A control device for an internal combustion engine capable of causing a fluid other than air that has passed through the throttle valve to flow into an intake pipe portion downstream of the throttle valve.
A throttle passage air amount detecting means for detecting a throttle passage air amount passing through the throttle valve;
Intake pipe pressure detection means for detecting the pressure in the intake pipe portion;
In-cylinder for estimating the in-cylinder charged air amount for each cylinder based on the throttle-passing air amount detected by the throttle-passing air amount detecting means and the pressure in the intake pipe portion detected by the intake pipe pressure detecting means Filling air amount estimation means;
An internal combustion engine control device comprising engine control means for controlling the internal combustion engine based on the in-cylinder charged air amount for each cylinder estimated by the in-cylinder charged air amount estimating means;
Fluid inflow prevention means for preventing fluid other than air that has passed through the throttle valve from flowing into the intake pipe portion;
The in-cylinder charged air amount estimation means is configured to prevent fluid other than air that has passed through the throttle valve from flowing into the intake pipe portion by the fluid inflow prevention means and in the intake pipe portion. A control device for an internal combustion engine that estimates when the pressure of the engine is lower than a predetermined pressure .   An exhaust gas inflow mechanism for allowing exhaust gas to flow into the intake pipe portion is further provided, and the fluid inflow prevention means prevents the exhaust gas from flowing into the intake pipe portion by the exhaust gas inflow mechanism. 2. The control apparatus for an internal combustion engine according to claim 1, wherein fluid other than air that has passed through the throttle valve does not flow into the intake pipe portion.   A purge gas inflow mechanism for allowing gas containing fuel evaporated from a fuel supply system of the internal combustion engine to flow into the intake pipe portion; and the inflow prevention means causes the gas containing the fuel to be introduced into the intake pipe by the purge gas inflow mechanism. 3. The control device for an internal combustion engine according to claim 1, wherein fluid other than air that has passed through the throttle valve does not flow into the intake pipe portion by preventing the fluid from flowing into the portion. 4. A throttle passage air amount detecting means for detecting a throttle passage air amount passing through the throttle valve;
Intake pipe pressure detection means for detecting the pressure in the intake pipe portion downstream of the throttle valve,
In-cylinder for estimating the in-cylinder charged air amount for each cylinder based on the throttle-passing air amount detected by the throttle-passing air amount detecting means and the pressure in the intake pipe portion detected by the intake pipe pressure detecting means Filling air amount estimation means;
Engine control means for controlling the internal combustion engine based on the in-cylinder charged air amount for each cylinder estimated by the in-cylinder charged air amount estimating means,
The in-cylinder charged air amount estimation means is a control device for an internal combustion engine that performs estimation when the pressure in the intake pipe portion is lower than a predetermined pressure.   The intake valve has a working angle changed according to an engine operating state, and a working angle estimating means for estimating an actual working angle in each cylinder based on the in-cylinder charged air amount calculated by the in-cylinder charged air amount calculating means. The control device for an internal combustion engine according to any one of claims 1 to 4, further comprising:

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