JP5223746B2 - 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 appropriately control the operation of the internal combustion engine, it is necessary to grasp the amount of air charged in the cylinder when the intake valve is closed (hereinafter referred to as “in-cylinder charged air amount”). As a method of grasping the in-cylinder charged air amount, a map for calculating the in-cylinder charged air amount using the output value of the sensor for detecting various parameters of the internal combustion engine as a variable is prepared in advance. A method for estimating the in-cylinder charged air amount from the above and a model equation derived from the model are prepared in advance, and the in-cylinder charged air amount is estimated by numerical values using various parameter values and model equations of the internal combustion engine. A method is considered.

  Among these, as a method using numerical calculation, for example, a throttle model for calculating the throttle valve passage air flow rate based on the throttle valve opening and the intake pipe pressure, and the throttle passage air flow rate and the cylinder inflow air flow rate are used. An in-cylinder inflow air amount model has been proposed, which includes an intake pipe model for calculating the intake pipe pressure and the intake pipe temperature, and an intake valve model for calculating the inflow cylinder flow rate based on the intake pipe pressure and the intake pipe temperature. (Patent Document 1).

JP 2004-197614 A JP 11-336576 A Japanese Patent Laid-Open No. 2004- 211590 Japanese Patent Laid-Open No. 2007-2111747

  By the way, in many internal combustion engines, fuel cut control is performed to stop the supply of fuel to the engine combustion chamber during engine deceleration operation. If the throttle valve is kept open or the intake valve is opened normally during the fuel cut control, air flows into the exhaust purification catalyst provided in the engine exhaust passage. However, when air flows into the exhaust purification catalyst, oxygen poisoning of the so-called exhaust purification catalyst is caused, and the purification performance of the exhaust purification catalyst is lowered. For this reason, in many internal combustion engines, during fuel cut control, the throttle valve is closed or the intake valve is stopped in a closed state in order to prevent oxygen from flowing into the exhaust purification catalyst. Yes.

  Here, if the intake valve is stopped in the closed state during the fuel cut control, the flow of air gradually stops in the engine intake passage. When the flow of air in the engine intake passage stops, the temperature of the air staying in the intake branch pipe near the intake valve, in particular, increases due to the heat of the intake valve and the heat of the cylinder block.

  On the other hand, in the cylinder intake air amount model described above, the cylinder inflow air flow rate is calculated based on the intake pipe pressure in the intake valve model. However, in this intake valve model, the intake valve is stopped in the closed state. The temperature rise of the air in the intake branch pipe due to is not taken into consideration. For this reason, after completion of the fuel cut control, the in-cylinder charged air amount is calculated on the assumption that the temperature of the air staying in the intake branch pipe during the fuel cut control has not increased. Therefore, a large error will occur between the cylinder charge air amount calculated by the cylinder intake air amount model after the end of the fuel cut control and the actual cylinder fill air amount.

  Therefore, in view of the above problems, an object of the present invention is to provide a control device for an internal combustion engine that can accurately estimate the in-cylinder charged air amount even after the end of fuel cut control.

In order to solve the above-described problem, in the first invention, in the control device for an internal combustion engine capable of executing intake valve closing control for stopping the intake valve in a closed state, the flow rate of air passing through the throttle Pressure / temperature calculation means for calculating the intake pipe pressure and intake pipe temperature based on the in-cylinder inflow air flow rate flowing into the cylinder, and the intake pipe pressure and intake pipe temperature calculated by the pressure / temperature calculation means The gas flow rate calculating means for calculating the cylinder inflow air flow rate, the engine control means for controlling the internal combustion engine based on the cylinder inflow air flow rate calculated by the gas flow rate calculation means, and the pressure / temperature calculation means In-cylinder temperature detection means for calculating or detecting the temperature in the intake branch passage, and in-cylinder inflow input to the pressure / temperature calculation means during execution of the intake valve closing control When calculating the in-cylinder inflow air flow rate by the gas flow rate calculation means after the intake valve closing control is finished, the air flow rate is set to zero and is calculated or detected by the branch passage temperature detection means instead of the pressure / temperature calculation means. The in-cylinder inflow air flow rate is calculated based on the temperature in the intake branch passage.
According to the first aspect of the present invention, when the in-cylinder inflow air flow rate is calculated by the gas flow rate calculating means after the intake valve closing / stopping control is completed, the branch passage temperature is not the intake pipe temperature calculated by the pressure / temperature calculating means. The temperature in the intake branch passage calculated or detected by the detection means is used. For this reason, even if the temperature of the air staying in the intake branch pipe rises by executing the intake valve closing control, the air flowing into the cylinder relatively accurately after the intake valve closing control is finished. The temperature can be calculated or detected.

In the second invention, in the first invention, after the intake valve closing stop control is finished, the gas flow rate calculating means calculates or detects Pm by the intake pipe internal pressure and Tmb by the branch passage temperature detecting means. Assuming that the temperature in the intake branch passage, Ta is the outside air temperature, and a and b are values obtained using the engine speed as a variable, the in-cylinder inflow air flow rate mc is calculated based on the following equation (1).

  In a third invention, in the first or second invention, the branch passage temperature detecting means detects the temperature in the intake branch passage by a temperature sensor for detecting the temperature in the intake branch passage.

  In a fourth invention, in the first or second invention, the branch passage temperature detecting means estimates the temperature in the intake branch passage based on an elapsed time from the start of the intake valve closing control.

  According to a fifth invention, in any one of the first to fourth inventions, a pressure sensor for detecting an intake pipe pressure is further provided, which is calculated by the pressure / temperature calculating means during the intake valve closing control. Whether the intake valve is stopped in the closed state during the intake valve closing control based on the difference between the increase rate of the intake pipe pressure and the increase rate of the intake pipe pressure detected by the pressure sensor. Determine whether or not.

  According to a sixth aspect, in the fifth aspect, an increase rate of the intake pipe pressure calculated by the pressure / temperature calculation means and an increase in the intake pipe pressure detected by the pressure sensor during the intake valve closing stop control. Cylinders that are not stopped when the intake valve is closed are determined based on the time when the difference between the ratio and the ratio becomes greater than a certain value.

  In the seventh invention, in the fifth or sixth invention, when it is determined that the intake valve is not stopped in the closed state during the intake valve closing control, the intake valve closing control is terminated. When the in-cylinder inflow air flow rate is calculated later by the gas flow rate calculation means, the gas flow rate calculation means is based on the intake pipe internal pressure detected by the pressure sensor without depending on the intake pipe internal pressure calculated by the pressure / temperature calculation means. To calculate the in-cylinder inflow air flow rate.

  In an eighth invention according to any one of the first to fourth inventions, further comprising an air flow rate detecting means for detecting a flow rate of air passing through the engine intake passage, and during the intake valve closing control. When the air flow rate detected by the air flow rate detection means is not zero, it is determined that the intake valve is closed and not stopped, and the gas flow rate calculation means determines the air flow rate detected by the air flow rate detection means. The in-cylinder inflow air flow rate after completion of the intake valve closing / stopping control is calculated based on the intake pipe pressure at the end of the intake valve closing / closing control calculated based on the above.

  In the ninth invention, in the eighth invention, when it is determined that the intake valve is not stopped in the closed state, the intake valve is in the closed state based on the air flow rate detected by the air flow rate detecting means. The number of cylinders that are not stopped is determined.

  According to the present invention, even if the temperature of the air staying in the intake branch pipe rises by executing the intake valve closing stop control, it flows into the cylinder relatively accurately after the intake valve closing stop control ends. As a result, the in-cylinder inflow air flow rate can be calculated relatively accurately.

It is a figure which shows the whole internal combustion engine provided with the control apparatus of this invention. It is a figure which shows the cylinder inflow air amount model applicable to an internal combustion engine. It is a figure which shows the relationship between a throttle opening and a flow coefficient. It is a figure which shows the relationship between throttle opening and opening cross-sectional area. It is a figure which shows function (PHI) (Pm / Pa). It is a figure which shows the basic concept of a throttle model. It is a figure which shows the basic concept of an intake pipe model. It is a figure which shows the basic concept of an intake valve model. It is a figure regarding the definition of cylinder filling air amount and cylinder inflow air flow volume. It is a figure which shows the flow of the parameter of the cylinder inflow air amount model during intake valve closing stop control. It is a figure which shows the flow of the parameter of the cylinder inflow air amount model after intake valve closing stop control. It is a figure which shows the relationship between the elapsed time from intake valve closing stop control start, and the temperature in an intake branch passage. It is a figure which shows the relationship between the elapsed time from intake valve closing stop control start, and an intake pipe internal pressure. It is a flowchart which shows the control routine of selection control of the intake pipe internal pressure utilized with an intake valve model. It is a figure which shows the relationship between the elapsed time from the intake valve closing stop control start, and the throttle passage air flow rate. The relationship between intake pipe pressure and throttle passage air flow rate when the throttle opening is large and small is shown. It is a figure which shows the relationship between an intake pipe internal pressure, a throttle passage air flow rate, and a cylinder inflow air flow rate. 6 is a flowchart showing a control routine for intake pipe pressure selection control used in the intake pipe model after the intake valve closing control is terminated.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals are assigned to similar components.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an overall view of an internal combustion engine to which the present invention is applied. In the following description, a cylinder injection type spark ignition type internal combustion engine will be described as an example. However, the present invention can be applied to other spark ignition type internal combustion engines and compression self-ignition type internal combustion engines.

  In FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a piston, 4 is a cylinder head, 5 is a cylinder (combustion chamber), 6 is an intake valve, 7 is an intake port, 8 is an exhaust valve, and 9 is an exhaust port. Reference numeral 10 denotes a spark plug, 11 denotes a fuel injection valve, and 12 denotes a cavity.

  The intake port 7 is connected to the surge tank 14 via the intake branch pipe 13 for each cylinder 5. The surge tank 14 is connected to an air cleaner 16 via an upstream side intake pipe 15. A throttle valve 18 driven by a step motor 17 is disposed in the upstream side intake pipe 15. On the other hand, the exhaust port 9 is connected to an exhaust pipe 19. The exhaust pipe 19 is connected to the exhaust purification catalyst 20.

  The intake valve 6 is provided with a variable valve mechanism 21 that can change the phase angle and the operating angle of the intake valve 6. The variable valve mechanism 21 can freely change the phase angle and operating angle of the intake valve 6 and can also stop the intake valve 6 in a closed state.

  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.

  An intake pipe pressure sensor 40 for detecting the pressure in the surge tank 14 (hereinafter referred to as “intake pipe pressure”) is attached to the surge tank 14. The intake pipe pressure sensor 40 generates an output voltage proportional to the intake pipe pressure, and this output voltage is input to the input port 36 via the corresponding AD converter 38. The intake pipe pressure sensor 40 does not necessarily have to be attached to the surge tank 14 and may be attached anywhere in the intake passage on the intake downstream side of the throttle valve 18. Similarly, the “intake pipe pressure” means the pressure at any position in the intake passage on the intake downstream side of the throttle valve 18.

  A temperature sensor 41 for detecting the temperature inside the intake branch pipe 13 is attached to the intake branch pipe 13. The temperature sensor 41 generates an output voltage proportional to the intake pipe internal temperature, and this output voltage is input to the input port 36 via the corresponding AD converter 38.

  The internal combustion engine also has a throttle opening sensor 43 for detecting the opening of the throttle valve 18, the atmospheric pressure around the internal combustion engine, or the pressure of the air taken into the upstream intake pipe 15 (intake pressure). And an atmospheric temperature sensor 45 for detecting the temperature of the atmosphere around the internal combustion engine or the temperature of the air taken into the upstream side intake pipe 15 (intake air temperature). . These sensors 44 and 45 generate output voltages proportional to the atmospheric pressure and the atmospheric temperature, respectively, and these output voltages are input to the input port 36 via the corresponding AD converters 38.

  A load sensor 47 that generates an output voltage proportional to the amount of depression of the accelerator pedal 46 is connected to the accelerator pedal 46. The output voltage of the load sensor 47 is input to the input port 36 via the corresponding AD converter 38. The internal combustion engine includes a crank angle sensor 48. For example, the crank angle sensor 48 generates an output pulse every time the crankshaft rotates 30 degrees, and the 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 45. On the other hand, the output port 37 is connected to the spark plug 10, the fuel injection valve 11, and the throttle valve step motor 17 via a corresponding drive circuit 39.

  By the way, the amount of fuel to be injected into the cylinder 5 from the fuel injection valve 10 (hereinafter simply referred to as “fuel injection amount”) is mixed in the cylinder 5 based on the amount of air charged in the cylinder 5. The air / fuel ratio of the air is determined to be the target air / fuel ratio. Therefore, in order to accurately set the air-fuel ratio of the air-fuel mixture in the cylinder 5 to the target air-fuel ratio, the amount of air charged in the cylinder 5 (hereinafter referred to as “cylinder charged air amount”) is accurately grasped. There is a need.

  As a method of estimating the in-cylinder charged air amount, there is a method of calculating the in-cylinder charged air amount by numerical calculation using an expression derived from a model. FIG. 2 shows the simplest model among such models. In the following, the simplest model shown in FIG. 2 will be described as an example. However, the control device of the present invention can be applied to various methods for calculating the in-cylinder charged air amount using the model.

  The cylinder inflow air amount model M10 shown in FIG. 2 includes a throttle model M11, an intake pipe model M12, and an intake valve model M13.

  In the throttle model M11, the opening degree (throttle opening degree) θt of the throttle valve 18 detected by the throttle opening degree sensor 43 and the atmospheric pressure detected by the atmospheric pressure sensor 45 (or the air sucked into the intake pipe 15). Pressure) Pa, the atmospheric temperature detected by the atmospheric temperature sensor 44 (or the temperature of the air sucked into the intake pipe 15) Ta, and the pressure in the surge tank 14 calculated in the intake pipe model M12 (hereinafter, Pm) (referred to as “intake pipe pressure”) is input, and the value of each of these input parameters is substituted into a model formula of a throttle model M11 to be described later, whereby the flow rate of air passing through the throttle valve 18 per unit time ( In the following, mt is calculated.

  Further, the intake pipe model M12 includes a throttle valve passage air flow rate mt calculated in the throttle model M11 described above and a flow rate of air flowing into the cylinder 5 per unit time calculated in the intake valve model M13 (hereinafter referred to as the following). The definition of the in-cylinder inflow air flow rate mc will be described in detail in the intake valve model M23.) Mc and the atmospheric temperature Ta are input, and each of these input parameters is input. By substituting the value into a model expression of an intake pipe model M12 to be described later, the intake pipe pressure Pm and the temperature of the air in the surge tank 14 (hereinafter referred to as “intake pipe temperature”) Tm are calculated.

  The intake valve model M13 receives the intake pipe pressure Pm, the intake pipe temperature Tm, and the atmospheric temperature Ta calculated in the intake pipe model M12. The values of these input parameters will be described later. By substituting into the model equation of the intake valve model M13, the in-cylinder inflow air flow rate mc is calculated.

  In this method, as will be described later, the amount of gas filled in the cylinder 5 when the intake valve 6 is closed using the in-cylinder inflow air flow rate mc (hereinafter referred to as “in-cylinder charged air amount”). Mc is calculated.

  As can be seen from FIG. 2, in the in-cylinder inflow air amount model M10, the parameter value calculated in each model is used as a parameter value input to another model. The only parameter values that are actually input are the three parameters of the throttle opening θt, the atmospheric pressure Pa, and the atmospheric temperature Ta. That is, according to this method, it can be said that the in-cylinder charged air amount Mc is calculated from the three parameters.

式（２）において、μｔはスロットル弁における流量係数であり、スロットル開度θｔの関数であって、図３に示したマップから定まる。また、Ａｔはスロットル弁１８の開口断面積であり、スロットル開度θｔの関数であって、図４に示したマップから定まる。なお、これら流量係数μｔおよび開口断面積Ａｔをまとめたμｔ・Ａｔをスロットル開度θｔの関数として１つのマップから求めるようにしてもよい。また、Ｒは気体定数に関する定数であり、いわゆる気体定数Ｒ^*を１モル当たりの空気の質量Ｍａで除算した値である（Ｒ＝Ｒ^*／Ｍａ） Next, each model M11-M13 is demonstrated in detail.
In the throttle model M11, the atmospheric pressure Pa, the atmospheric temperature Ta, the intake pipe pressure Pm, and the throttle opening θt are input to the following equation (2), and the throttle valve passing air flow rate mt is calculated by solving this equation. .

In Expression (2), μt is a flow coefficient in the throttle valve, which is a function of the throttle opening θt, and is determined from the map shown in FIG. At is the opening cross-sectional area of the throttle valve 18, which is a function of the throttle opening θt, and is determined from the map shown in FIG. The flow rate coefficient μt and the opening cross-sectional area At may be obtained from one map as a function of the throttle opening θt. R is a constant related to the gas constant, and is a value obtained by dividing the so-called gas constant R ^* by the mass of air Ma per mole (R = R ^* / Ma).

式（３）において、κは比熱比であり、この方法では、一定値としている。 Further, Φ (Pm / Pa) is a function having Pm / Pa as a variable, as shown in the following equation (3).

In the equation (3), κ is a specific heat ratio, and is a constant value in this method.

  Note that there is a relationship as shown in FIG. 5 between the function Φ (Pm / Pa) and Pm / Pa. Therefore, instead of the equation (3), a map for calculating the function Φ (Pm / Pa) having Pm / Pa as a variable is stored in the ROM 34 in advance, and the function Φ (Pm / Pa) is calculated from Pm / Pa and this map. The value of Pa) may be calculated.

These formulas (2) and (3) indicate that the pressure of the air upstream of the throttle valve 18 is the atmospheric pressure Pa, the temperature of the air upstream of the throttle valve 18 is the atmospheric temperature Ta, and the pressure of the air that has passed through the throttle valve 18 Is the intake pipe pressure Pm, and the throttle valve 18 is based on the model as shown in FIG. 6, the mass conservation law, the energy conservation law between the air upstream of the throttle valve 18 and the air that has passed through the throttle valve 18, And it is derived using the relational expression established in the momentum conservation law, the equation of state of the gas, the specific expression of the specific heat ratio (κ = Cp / Cv), and the Mayer relational expression (Cp = Cv + R ^* ). Here, Cp is a constant pressure specific heat, Cv is a quantitative specific heat, and R ^* is a so-called gas constant.

式（４）および（５）において、Ｖはスロットル弁１８から吸気弁６までの吸気管１５、サージタンク１４、吸気枝管１３、および、吸気ポート７（以下、これらまとめて、「吸気管部分」という）のトータルの容積であり、通常、一定値である。 Next, the intake pipe model M12 will be described. In the intake pipe model M12, the throttle valve passage air flow rate mt, the in-cylinder inflow air flow rate mc, and the atmospheric temperature Ta are input to the following equations (4) and (5), and by solving these equations, the intake pipe pressure Pm and The intake pipe temperature Tm is calculated.

In the equations (4) and (5), V is the intake pipe 15 from the throttle valve 18 to the intake valve 6, the surge tank 14, the intake branch pipe 13, and the intake port 7 (hereinafter collectively referred to as “intake pipe portion”). )), And is usually a constant value.

  Note that these equations (4) and (5) relate to the intake pipe portion, based on the model shown in FIG. 7, and the air flowing into the intake pipe portion and out of the intake pipe portion and into the cylinder It is derived from the relational expression that holds in the law of conservation of mass and the law of conservation of energy.

そして、この式（６）と、気体の状態方程式（Ｐｍ・Ｖ＝Ｍ・Ｒ^*・Ｔｍ）とから、上記式（４）が導き出される。 Specifically, if the total air amount in the intake pipe portion is M, the temporal change in the total air amount M is the flow rate of air flowing into the intake pipe portion (that is, the throttle valve passing air flow rate) mt. Since it is equal to the difference between the flow rate of air flowing out of the intake pipe portion and flowing into the cylinder (that is, the in-cylinder inflow air flow rate) mc, the following equation (6) is established in terms of mass conservation.

From the equation (6) and the gas equation of state (Pm · V = M · R ^* · Tm), the above equation (4) is derived.

そして、この式（７）と、上述した気体の状態方程式とから、上記式（５）が導き出される。 Further, the amount of time change of the energy amount M · Cv · Tm of the air in the intake pipe portion is the energy amount of air flowing into the intake pipe portion and the energy amount of air flowing out of the intake pipe portion and into the cylinder. Therefore, if the temperature of the air flowing into the intake pipe portion is the atmospheric temperature Ta, and the temperature of the air flowing out of the intake pipe portion and flows into the cylinder is the intake pipe temperature Tm, The following equation (7) is established.

Then, the equation (5) is derived from the equation (7) and the gas state equation described above.

式（８）において、ａおよびｂは、機関回転数ＮＥを変数として求まる値である。また、内燃機関において、吸気弁６の開弁タイミングまたは閉弁タイミングに相当するバルブタイミング、および、開弁時間に相当する作用角の少なくとも一方が変更可能となっている場合には、式（８）において、ａおよびｂは、機関回転数ＮＥとバルブタイミングまたは位相角またはこれら両方とを変数として求まる値である。別の云い方をすれば、式（８）において、ａは比例係数であり、ｂは排気弁８の閉弁時に気筒５内に残存していたガスの量を表す値である。 Next, the intake valve model M13 will be described. In the intake valve model M13, the intake pipe internal pressure Pm, the intake pipe internal temperature Tm, and the atmospheric temperature Ta are input to the following equation (8), and by solving this equation, the cylinder inflow air flow rate mc is calculated.

In Expression (8), a and b are values obtained using the engine speed NE as a variable. In the internal combustion engine, when at least one of the valve timing corresponding to the valve opening timing or the valve closing timing of the intake valve 6 and the operating angle corresponding to the valve opening time can be changed, the equation (8) ), A and b are values obtained by using the engine speed NE and the valve timing and / or the phase angle as variables. In other words, in equation (8), a is a proportional coefficient, and b is a value representing the amount of gas remaining in the cylinder 5 when the exhaust valve 8 is closed.

  Further, in the equation (8), when the engine operating state is changing, that is, during transient operation, the intake pipe internal temperature Tm may change greatly, so that this change in the intake pipe internal temperature Tm is compensated. Ta / Tm derived from theory and empirical rule is used as the correction coefficient.

  It should be noted that the expression (8) relates to the intake valve 6 on the basis of the model as shown in FIG. 8 and assumes that the in-cylinder inflow air flow rate mc is proportional to the intake pipe pressure Pm as described in detail below. And derived from theory and empirical rules.

  That is, the cylinder charge air amount Mc is determined when the intake valve 6 is closed and is proportional to the pressure in the cylinder 5 when the intake valve 6 is closed. Here, since the pressure in the cylinder 5 when the intake valve 6 is closed can be regarded as being equal to the pressure of the air upstream of the intake valve 6 (that is, the intake pipe pressure) Pm, the cylinder charge air amount Mc is the intake pipe pressure. It can be approximated to be proportional to Pm.

  On the other hand, the in-cylinder charged air amount Mc is obtained by integrating the air flow rate (cylinder inflow air flow rate) mc flowing into the cylinder 5 during the valve opening period of the intake valve 6 over the valve opening period of the intake valve 6. It is obtained by doing. That is, there is a relationship between the in-cylinder charged air amount Mc and the in-cylinder inflow air flow rate mc that the time integral value of the in-cylinder inflow air flow rate mc is the in-cylinder charged air amount Mc.

  In this way, the cylinder charge air amount Mc is proportional to the intake pipe pressure Pm, and the time integral value of the cylinder inflow air flow rate mc is between the cylinder charge air amount Mc and the cylinder inflow air flow rate mc. Since there is a relationship that the in-cylinder charged air amount Mc, the in-cylinder inflow air flow rate mc can be regarded as being proportional to the intake pipe pressure Pm.

Therefore, in this method, it is assumed that the in-cylinder inflow air flow rate mc is proportional to the intake pipe pressure Pm, and the equation (8) is derived from the theory and empirical rules.
Note that the in-cylinder inflow air flow rate mc calculated by the equation (8) is an average value of the flow rate of air flowing out from the intake pipe portion per unit time. The in-cylinder charged air amount Mc in each cylinder 5 is calculated by multiplying the time required for the cycle by the number of cylinders.

Next, this will be described with reference to FIG. 9, taking an internal combustion engine having four cylinders as an example.
In FIG. 9, the horizontal axis is the crank angle, and the vertical axis is the amount of air flowing from the intake pipe portion into the cylinder 5 per unit time. In the example shown in FIG. 9, the intake stroke is performed in the order of the first cylinder # 1, the third cylinder # 3, the fourth cylinder # 4, and the second cylinder # 2. When the intake stroke is performed in this way, the flow rate of air flowing into each cylinder 5 from the intake pipe portion changes as indicated by the broken line in FIG. 9, and as a result, the flow rate of air flowing out from the intake pipe portion is 9 will change as indicated by the solid line in FIG.

  The average value of the flow rate of air flowing out from the intake pipe portion (solid line in FIG. 9) is the in-cylinder inflow air flow rate mc, and is indicated by a broken line in FIG. Accordingly, the in-cylinder charged air amount Mc in each cylinder 5 is equal to the in-cylinder inflow air flow rate mc (broken line in FIG. 9) and the time taken for one cycle of the internal combustion engine (in the example shown in FIG. (Time required for rotation) divided by the number of cylinders (four in the example shown in FIG. 9), that is, in the example shown in FIG. 9, it takes time required for the crankshaft to rotate 180 °. It is calculated by this. Then, the in-cylinder charged air amount Mc in each cylinder 5 thus calculated coincides with, for example, the hatched line in FIG.

Next, a method for calculating the in-cylinder charged air amount Mc when the in-cylinder inflow air amount model M10 described above is mounted on the internal combustion engine will be described.
The in-cylinder charged air amount Mc is obtained from the equations (2) to (5) and (8) of each model of the in-cylinder inflow air amount model M10. When these five equations are mounted on the internal combustion engine, It is discretized so that it can be processed by the ECU 31. That is, assuming that the time is t and the calculation interval (calculation cycle) is Δt, these five expressions are discretized into the following expressions (9) to (13).

  According to the in-cylinder inflow air amount model M10 discretized and mounted in the internal combustion engine in this way, the throttle valve passage air flow rate mt (t) calculated at the time t calculated in the throttle model M11 and the intake valve model M13 The calculated in-cylinder inflow air flow rate mc (t) at the time t and the intake pipe internal temperature Tm (t) at the time t are input to the expressions (11) and (12) of the intake pipe model M12, and these expressions (11 ) And (12), the intake pipe pressure Pm (t + Δt) and the intake pipe temperature Tm (t + Δt) at time (t + Δt) are calculated.

  Then, the intake pipe pressure Pm (t + Δt) calculated in the intake pipe model M12 and the throttle opening θt (t) at time t are input to the equations (9) and (10) of the throttle model M11, and these equations are solved. Thus, the throttle valve passing air flow rate mt (t + Δt) at time (t + Δt) is calculated.

  Further, the intake pipe pressure Pm (t + Δt) and the intake pipe temperature Tm (t + Δt) calculated in the intake pipe model M12 are input to the expression (13) of the intake valve model M13, and the time (t + Δt) is obtained by solving this expression. The in-cylinder inflow air flow rate mc (t + Δt) at is calculated.

  By repeating such calculation, the in-cylinder inflow air flow rate mc at any time is calculated. Then, as described above, the in-cylinder inflow air amount Mc of each cylinder at an arbitrary time is obtained by multiplying the thus calculated in-cylinder inflow air flow rate mc by the time obtained by dividing the time required for one cycle by the number of cylinders as described above. Calculated.

  At the time of starting the internal combustion engine, that is, at time t = 0, the intake pipe pressure Pm is equal to the atmospheric pressure Pa (Pm (0) = Pa), while the intake pipe temperature Tm is equal to the atmospheric temperature Ta. (Tm (0) = Ta) and calculation in each of the models M11 to M13 is started.

  Further, as the atmospheric pressure Pa and the atmospheric temperature Ta used in the in-cylinder inflow air amount model M10 described above, the atmospheric pressure and the atmospheric temperature when the calculation of the in-cylinder inflow air amount model M10 is started may be always used. The atmospheric pressure Pa (t) and the atmospheric temperature Ta (t) at time t may be used.

  By the way, in the internal combustion engine of the present embodiment, fuel cut control is executed to stop the supply of fuel to the cylinder during engine deceleration operation. When air is circulated in the cylinder when the fuel cut control is performed in this way, that is, when air is caused to flow into the cylinder via the intake valve 6 and air is caused to flow out from the cylinder via the exhaust valve 8. A large amount of air flows into the exhaust purification catalyst 20.

  When air, particularly oxygen, flows into the exhaust purification catalyst 20, oxygen is adsorbed on the surface of the exhaust purification catalyst 20. Further, the noble metals supported on the exhaust purification catalyst 20 are combined with each other at a high temperature to become large particles, and this binding reaction is promoted by oxygen adsorbed on the surface of the exhaust purification catalyst 20. For this reason, when a large amount of air flows into the exhaust purification catalyst 20 and the amount of oxygen retained on the surface of the exhaust purification catalyst 20 increases, the oxidation ability of the noble metal is reduced (oxygen poisoning). Therefore, it is necessary to prevent oxygen from flowing into the exhaust purification catalyst 20 during fuel cut control.

  For this reason, in the internal combustion engine of the present embodiment, when the fuel cut control is executed, the intake valve closing control for stopping the intake valve 6 in the closed state is executed. As a result, oxygen is suppressed from flowing into the exhaust purification catalyst 20 even during fuel cut control, and as a result, oxygen poisoning of the exhaust purification catalyst 20 is suppressed.

  Thus, when the intake valve closing control is being executed, air does not flow into the cylinder from the intake pipe portion. Therefore, in the present embodiment, during the intake valve closing control, the calculation of the cylinder inflow air flow rate by the intake valve model M13 is stopped and the cylinder inflow air flow rate mc input to the intake pipe model M12 is stopped. The value of is set to zero.

Therefore, in the intake valve model M12, by substituting mc = 0 into the above expressions (4) and (5), the intake pipe pressure Pm and the intake pipe temperature Tm are calculated by the following expressions (14) and (15). . As a result, the intake pipe pressure Pm can be calculated relatively accurately even when the intake valve closing control is being executed. This is shown in FIG.

  By the way, when the intake valve closing control is being executed, the air flowing into the intake pipe portion via the throttle valve 18 stays in the intake pipe portion. At this time, the temperatures of the wall surfaces of the intake valve 6 and the intake port 7 are relatively high. Therefore, of the air staying in the intake pipe portion, the air contacting the wall surfaces of the intake valve 7 and the intake port 7 That is, the air in the intake port 7 and the intake branch pipe 13 (hereinafter collectively referred to as “intake branch passage”) is heated.

  However, in the intake pipe model M12 described above, as described above, the mass conservation law and the energy conservation law established between the air flowing into the intake pipe portion and the air flowing out of the intake pipe portion and into the cylinder. Based on this, equations (4) and (5) are derived. In other words, in the intake pipe model M12, the temperature rise of the air in the intake branch passage due to contact with the wall surfaces of the intake valve 6 and the intake port 7 is not considered.

  However, when the intake valve closing stop control is not executed, the influence of the temperature rise of the air in the intake branch passage due to contact with the wall surface of the intake valve 6 or the intake port 7 is small. Even if the calculation is performed while ignoring, the error generated between the intake pipe temperature Tm calculated by the intake pipe model M12 and the actual temperature of the air in the intake branch passage is so small that it can be ignored. However, when the intake valve closing / stopping control is executed, if the influence of such a temperature rise is ignored, the intake pipe temperature Tm calculated by the intake pipe model M12 and the actual temperature of the air in the intake branch passage The error that occurs during this period becomes so large that it cannot be ignored.

  Here, since the calculation of the in-cylinder inflow air flow rate by the intake valve model M13 is stopped during the execution of the intake valve closing stop control, the calculated intake pipe internal temperature Tm becomes the other intake pipe model M12. Will not be used. Therefore, even if an error occurs between the intake pipe temperature Tm calculated by the intake pipe model M12 and the actual temperature of the air in the intake branch passage, the calculation of the in-cylinder inflow air flow rate mc, The calculation with the inflow air amount model M10 has little influence.

  On the other hand, after the intake valve closing stop control is finished, the calculation of the in-cylinder inflow air flow rate by the intake valve model M13 is resumed. In particular, immediately after the end of the intake valve closing control, the intake pipe temperature and the intake pipe pressure at the end of the intake valve closing stop control are used to calculate the in-cylinder inflow air flow rate mc by the intake valve model M13. become. However, as described above, since there is an error in the intake pipe temperature Tm calculated by the intake pipe model M12 at the end of the intake valve closing control, the in-cylinder calculated immediately after the intake valve closing control is ended. An error occurs in the inflow air flow rate mc. For this reason, the cylinder inflow air flow rate mc cannot be accurately calculated immediately after the intake valve closing stop control ends, and as a result, the cylinder charge air amount Mc cannot be accurately calculated.

  Therefore, in the embodiment according to the present invention, when the fuel cut control is performed and the intake valve closing / stopping control is executed, the intake branch flow is calculated in calculating the in-cylinder inflow air flow immediately after the intake valve closing / stopping control is finished. The temperature detected by the temperature sensor 41 that detects the temperature in the passage is used.

  That is, in the embodiment according to the present invention, when the intake valve closing control is started, as shown in FIG. 10, the calculation of the cylinder inflow air flow rate by the intake valve model M13 is stopped and the intake pipe model is stopped. In M12, the intake pipe pressure Pm and the intake pipe temperature Tm are calculated by the above equations (14) and (15).

Thereafter, when the intake valve closing control is terminated, the opening and closing of the intake valve 6 is resumed. Along with this, the calculation of the in-cylinder inflow air flow rate by the intake valve model M13 is also resumed. At this time, the intake valve model M13 includes model equations (4), (5) or (14) of the intake pipe model M12, The intake branch passage internal temperature Tmb detected by the temperature sensor 41 is used instead of the intake pipe internal temperature Tm calculated by (15). That is, after the intake valve closing stop control is finished, the cylinder inflow air flow rate mc is calculated by the following equation (16). This is shown in FIG.

  Thereafter, as the elapsed time from the end of the intake valve closing control becomes longer, the actual temperature in the intake branch passage decreases and gradually approaches the intake pipe temperature Tm calculated by the model expression of the intake pipe model M12. It becomes. Therefore, when the elapsed time from the end of the intake valve closing stop control becomes a certain time or more, or the intake branch passage temperature detected by the temperature sensor 41 and the intake pipe temperature Tm calculated by the intake pipe model M12. When the difference becomes a certain value or less, the intake valve model M13 uses the intake pipe temperature Tm calculated by the model expression of the intake pipe model M12.

  As described above, at the end of the intake valve closing / stopping control, not the intake pipe temperature Tm calculated by the intake pipe model M12 but the intake branch passage temperature Tmb detected by the temperature sensor 41 is used. By performing the calculation, even if the temperature of the air in the intake branch passage rises due to contact with the wall surface of the intake valve 6 or the intake port 7, the intake air flow rate mc in the cylinder is relatively accurately determined by the intake valve model M13. Can be calculated.

  In the above-described embodiment, the intake branch passage temperature Tmb detected by the temperature sensor 41 is used when the intake valve closing control is terminated. However, the temperature in the intake branch passage does not necessarily have to be detected by the temperature sensor 41. For example, in the intake branch passage at the end of the intake valve closing stop control, depending on the elapsed time from the start of the intake valve closing stop control. The temperature may be calculated.

  FIG. 12 is a diagram illustrating the relationship between the elapsed time from the start of the intake valve closing control and the intake branch passage temperature Tmb. As shown in FIG. 12, the intake branch passage temperature Tmb increases as the elapsed time from the start of the intake valve closing stop control becomes longer. Therefore, if the temperature in the intake branch passage at the start of the intake valve closing stop control is known, the temperature sensor 41 is not used, and the inside of the intake branch passage during the execution of the intake valve close stop control and at the end of the intake valve close stop control is terminated. The temperature can be estimated. Further, when the intake valve closing control is started, the temperature of the air in the intake branch passage substantially matches the temperature of the air in the entire intake pipe portion. The in-passage temperature is equal to the intake pipe temperature Tm calculated by the intake pipe model M12.

  Therefore, based on the intake pipe temperature Tm calculated by the intake pipe model M12 at the start of the intake valve closing stop control and the map as shown in FIG. 12, the inside of the intake branch passage at the end of the intake valve closing stop control is determined. The temperature can be estimated relatively accurately, and the calculation in the intake valve model M13 is performed at the end of the intake valve closing / stopping control by using the intake branch passage temperature estimated in this manner, so that the temperature is relatively accurate. In-cylinder inflow air flow rate can be calculated. Thereby, it is not necessary to provide a temperature sensor for detecting the temperature in the intake branch passage, and the manufacturing cost can be reduced.

  The map shown in FIG. 12 shows the temperature of the intake valve, the wall surface temperature of the intake port 7, the temperature in the intake branch passage at the start of the intake valve closing control (ie, the intake pipe at the start of the intake valve closing control). Change based on the temperature in the part). The temperature of the intake valve, the wall surface temperature of the intake port 7 and the like change based on the temperature of the engine cooling water. Therefore, the map shown in FIG. 12 may be changed according to the temperature of the engine coolant or the temperature in the intake pipe portion at the start of the intake valve closing control.

By the way, when the intake valve closing control is executed, the actual intake pipe pressure increases as shown by a solid line in FIG. 13 according to the elapsed time from the start of the intake valve closing control (in FIG. 13, intake valve closing stop control is started at time t _0). This is because when the intake valve 6 is stopped in the closed state, air flows into the intake pipe portion via the throttle valve 18, but air does not flow out from the intake pipe portion via the intake valve 6. is there.

  On the other hand, the intake pipe pressure Pm during the intake valve closing control is calculated by the above equation (15). If the intake valve closing control is normally performed, the intake pipe pressure Pm calculated in this way changes in the same manner as the actual intake pipe pressure, that is, as shown by the solid line in FIG. Therefore, when the calculation of the in-cylinder inflow air flow rate by the intake valve model M13 is resumed after the intake valve closing control is finished, the intake pipe pressure calculated by the intake pipe model M12 is input to the intake valve model M13. The in-cylinder inflow air flow rate can be calculated relatively accurately.

  However, if a malfunction or the like occurs in the variable valve mechanism, and the intake valve 6 is not stopped in a closed state for some cylinders during the execution of the intake valve close / stop control, the intake valve 6 opens. The actual intake pipe pressure does not change as shown by the solid line in FIG. In FIG. 13, # 1 to # 4 indicate the numbers of the cylinders during the intake stroke. For example, when the intake valve 6 of the fourth cylinder is not closed and is not stopped, the actual intake pipe pressure is as shown in FIG. It will change as indicated by the broken line inside. For this reason, when a failure or the like occurs in the variable valve mechanism, an error occurs in the intake pipe pressure calculated by the intake pipe model M12 with respect to the actual intake pipe pressure.

  For this reason, when a failure or the like occurs in the variable valve mechanism, when the calculation of the in-cylinder inflow air flow rate by the intake valve model M13 is resumed after the intake valve closing control is terminated, the intake air calculated by the intake pipe model M12 is restored. If the in-pipe pressure Pm is input to the intake valve model M13, the in-cylinder inflow air flow rate cannot be accurately calculated.

  Therefore, in the embodiment according to the present invention, it is determined whether or not the variable valve mechanism has failed, and when it is determined that the variable valve mechanism has failed, the intake valve closing control is terminated. When the calculation of the in-cylinder inflow air flow rate by the intake valve model M13 is resumed later, the intake valve model M13 is calculated using other values without using the intake pipe pressure calculated by the intake pipe model M12. I am going to do that.

  First, the determination of the presence or absence of a failure of the variable valve mechanism will be described. As described above, when the intake valve 6 of the fourth cylinder is not stopped in the closed state, the actual intake pipe pressure changes as shown by the broken line in FIG. That is, when the intake valve 6 opens during the intake stroke of the fourth cylinder, air flows out from the intake pipe portion into the cylinder via the intake valve 6 during the intake stroke of the fourth cylinder. Therefore, in this case, during the intake stroke of the fourth cylinder, the intake pipe pressure Pm (solid line in FIG. 13) calculated by the intake pipe model M12 is higher than the actual intake pipe pressure (broken line in FIG. 13). It will be low. When the intake valve 6 of the fourth cylinder is opened, the rate of increase of the intake pipe pressure Pm (solid line in FIG. 13) calculated by the intake pipe model M12 during the intake stroke of the fourth cylinder is actually This is higher than the rate of increase in the intake pipe pressure (broken line in FIG. 13).

  Therefore, in the embodiment according to the present invention, the actual intake pipe pressure is detected by the pressure sensor 40 that detects the intake pipe pressure, and the increase rate of the intake pipe pressure detected by the pressure sensor 40 is calculated by the intake pipe model M12. When the difference in the increase rate of the intake pipe pressure becomes a certain value or more, the intake pipe pressure Pm is compared when the difference in the increase rate of the intake pipe pressure becomes a certain value or more. It is determined that the valve operating mechanism of the intake valve 6 of the cylinder in the stroke is out of order. Thereby, it becomes possible to accurately determine the failure of the variable valve mechanism of the intake valve 6.

  In the embodiment according to the present invention, when it is determined that there is a failure in the variable valve mechanism, the intake valve model M13 is calculated by the intake pipe model M12 at the end of the intake valve closing control. The intake pipe pressure detected by the pressure sensor 40 is input instead of the intake pipe pressure. Even if there is a failure in the variable valve mechanism, the pressure sensor 40 can detect the pressure in the intake pipe relatively accurately. Therefore, even when the intake valve closing control is terminated, the intake valve is relatively accurately detected. The in-cylinder inflow air flow rate can be calculated by the model M13.

  In the embodiment according to the present invention, the output of the pressure sensor 40 is basically not used in the intake valve model M13 even though the pressure sensor 40 for detecting the pressure in the intake pipe is provided. Hereinafter, this reason will be described.

  The in-cylinder inflow air amount model M10 described above is the simplest model. By inputting the current throttle opening to the throttle model M11, the current in-cylinder charged air amount is calculated by the intake valve model M13. Yes. However, by using the in-cylinder inflow air amount model M10, it is also possible to predict a future in-cylinder charged air amount as shown in Patent Document 3, for example.

  That is, in the internal combustion engine equipped with the electronically controlled throttle valve 18, the in-cylinder charged air amount is calculated by the in-cylinder inflow air amount model M10 based on the target throttle opening corresponding to the depression amount of the accelerator pedal. The drive start of the throttle valve 18 to the target throttle opening can be delayed for a predetermined time. In this case, the in-cylinder charged air amount calculated by the in-cylinder inflow air amount model M10 can predict the previous (future) in-cylinder charged air amount for the predetermined time.

  Thus, when predicting the future in-cylinder charged air amount by the in-cylinder inflow air amount model M10, the values of the various parameters input to the in-cylinder inflow air amount model M10 are the values of the current parameters detected by the various sensors. If the value is used, it will be difficult to accurately predict the future in-cylinder charged air amount. Therefore, when predicting the future in-cylinder charged air amount in this way, basically, the current parameter values detected by various sensors are used as the parameter values input to the in-cylinder inflow air amount model M10. Therefore, in the embodiment according to the present invention, the intake valve model M13 basically does not use the output of the pressure sensor 40.

  However, if there is a failure in the variable valve mechanism, the error between the intake pipe pressure calculated by the intake pipe model M12 and the actual intake pipe pressure is large at the end of the intake valve closing stop control. The intake pipe pressure detected by the pressure sensor 40 is input to the intake valve model M13.

  FIG. 14 is a flowchart showing a control routine of intake pipe pressure selection control used in the intake valve model M13. The illustrated control routine is performed by interruption at regular time intervals.

  First, as shown in step S11 in FIG. 14, it is determined whether or not the valve stop control flag Xv is 1. The valve stop control flag Xv is a flag that becomes 1 during the execution of the intake valve closing stop control and becomes 0 when the control is finished. If it is determined in step S11 that the intake valve closing control is being executed and the valve stop control flag Xv is 1, the process proceeds to step S12. In step S12, a difference ΔdPm / dt between the change rate of the intake pipe pressure (change amount per unit time) calculated by the intake pipe model M12 and the change rate of the intake pipe pressure detected by the pressure sensor 40 is calculated in advance. It is determined whether or not the value is equal to or greater than a predetermined value A. If it is determined that the difference ΔdPm / dt is smaller than the constant value A, there is no failure in the variable valve mechanism, and the control routine is terminated. On the other hand, if it is determined that the difference ΔdPm / dt is greater than or equal to the constant value A, a failure or the like exists in the variable valve mechanism, and therefore the valve stop fail flag Xf is set to 1 in step S13. The valve stop fail flag Xf is a flag that is set to 1 when some or all of the intake valves 6 are not stopped in the closed state even if the intake valve closing control is executed, and is set to 0 otherwise. .

  Thereafter, when the intake valve closing control is terminated, in the next control routine, the valve stop control flag Xv is set to 0, and it is determined in step S11 that the valve stop control flag Xv is not 1, and the process proceeds to step S14. In step S14, it is determined whether it is immediately after the end of the intake valve closing stop control. If it is determined that the intake valve closing control has just ended, the process proceeds to step S15. In step S15, it is determined whether or not the valve stop fail flag Xf is 1. When it is determined that the valve stop fail flag Xf is 1, that is, when it is determined that a failure or the like exists in the variable valve mechanism. Then, the process proceeds to step S16. In step S16, the intake pipe pressure detected by the pressure sensor 40 is input to the intake valve model M13. On the other hand, if it is determined that the valve stop fail flag Xf is 0, that is, if it is determined that no failure or the like exists in the variable valve mechanism, the process proceeds to step S17. In step S17, the intake pipe pressure calculated by the intake pipe model M12 is input to the intake valve model M13. Thereafter, in step S18, the valve stop fail flag Xf is reset to 0, and the control routine is ended.

Next, a second embodiment of the present invention will be described.
In the above embodiment, the pressure sensor 40 is used to determine the presence or absence of a failure or the like of the variable valve mechanism. However, normally, when the in-cylinder charged air amount is calculated using the in-cylinder inflow air amount model M10, it is not necessary to detect the intake pipe pressure with the pressure sensor 40. Therefore, in the above-described embodiment, the pressure sensor 40 is provided to determine whether or not the variable valve mechanism has failed. The provision of the pressure sensor 40 increases the manufacturing cost.

  On the other hand, even when the in-cylinder inflow air amount model M10 is used, the internal combustion engine is provided with the air flow meter 42 for detecting the flow rate of the air flowing in the intake pipe upstream of the throttle valve 18. Therefore, in the second embodiment of the present invention, the air flow meter 42 is used to determine whether or not the variable valve mechanism has failed.

Here, when the intake valve closing / stopping control is executed, the actual throttle passage air flow rate gradually decreases and finally converges to almost zero as shown by the solid line in FIG. , the intake valve closing stop control is started at time t _0). This is because when the intake valve 6 is stopped in a closed state, air does not flow into the cylinder, and therefore air does not flow into the intake pipe portion.

  On the other hand, the throttle passage air flow rate mt during the intake valve closing stop control is calculated by the above equation (2), and the intake pipe pressure Pm used in the equation (2) is the intake air calculated by the above equation (15). In-pipe pressure is substituted. The throttle passage air flow rate mt calculated in this way changes in the same manner as the actual throttle passage air flow rate, that is, as shown by the solid line in FIG. 15, if the intake valve closing control is normally performed. To do.

  However, if a malfunction or the like occurs in the variable valve mechanism, and the intake valve 6 is not stopped in a closed state for some cylinders during the execution of the intake valve close / stop control, the intake valve 6 opens. The actual throttle passage air flow rate does not change as shown by the solid line in FIG. For example, when the intake valve 6 is opened even during the execution of the intake valve closing / stopping control for only one cylinder, the actual throttle passage air flow rate is as shown by the broken line in FIG. It will change. For this reason, when a failure or the like occurs in the variable valve mechanism, the actual throttle air flow rate, that is, the air flow rate detected by the air flow meter 42 (hereinafter referred to as “air flow detection air flow rate”) and the throttle model M11 are calculated. It becomes a value different from the throttle passage air flow rate.

Therefore, in the present embodiment, when the throttle passage air flow calculated by the throttle model M11 converges to almost zero (that is, after time t _{1 in} FIG. 15), the air flow is detected by the air flow meter 42. If the detected airflow detected air flow rate is almost zero, it is determined that the variable valve mechanism has not failed, and the detected airflow detected air flow rate is not zero. In this case, it is determined that no failure or the like has occurred in the variable valve mechanism. As a result, a failure of the variable valve mechanism of the intake valve 6 can be accurately determined.

  By the way, in the first embodiment, when it is determined that there is a failure in the variable valve mechanism, the intake pipe pressure detected by the pressure sensor 40 is detected in the intake model M13 at the end of the intake valve closing control. I am going to enter. However, in this embodiment, the pressure sensor 40 is not provided, and therefore the intake pipe pressure detected by the pressure sensor 40 cannot be input. Therefore, in the present embodiment, the in-cylinder inflow air flow rate is calculated using the air flow rate detected by the air flow meter 42.

  FIG. 16 shows the relationship between the intake pipe pressure and the throttle passage air flow rate (that is, the air flow rate detected by the air flow meter 42) when the throttle opening is large and small. As can be seen from FIG. 16, since the airflow detection air flow rate and the intake pipe internal pressure have a fixed relationship for each throttle opening, if the throttle opening and the airflow detection air flow rate are known, the intake pipe internal pressure is estimated. be able to. In the example shown in FIG. 16, when the throttle opening is large and the airflow detection air flow rate is mt1, the intake pipe pressure is Pm1, the throttle opening is small and the airflow detection air flow rate is mt2. In this case, the intake pipe pressure is Pm2.

  Therefore, in this embodiment, the relationship between the throttle valve passage air flow rate (that is, the airflow detection air flow rate), the throttle opening degree, and the intake pipe pressure is obtained in advance as a map, and the actual airflow detection air flow rate and the throttle opening degree Based on this, the intake pipe pressure is calculated using a map. Thus, by calculating the intake pipe pressure based on the actually measured value of the air flow meter 42, it is possible to calculate the intake pipe pressure relatively accurately even when the variable valve mechanism has a failure.

  The calculation of the intake pipe pressure is not necessarily performed using a map. For example, the above equation (2) is modified to obtain an equation for calculating the intake pipe pressure Pm by inputting the throttle passage air flow rate mt and the throttle opening θt, and the airflow detection air is calculated using the equation. The intake pipe pressure may be calculated based on the flow rate and the throttle opening.

  FIG. 17 is a graph showing the relationship between the intake pipe pressure, the throttle passage air flow rate mt, and the cylinder inflow air flow rates a to d. In the figure, mt indicates the transition of the throttle passage air flow rate with respect to the intake pipe pressure at a specific throttle opening. Further, a in the figure is the in-cylinder inflow air flow rate when the intake valve closing / stopping control is not being executed, and b is the intake valve closing / stopping control being executed and the intake valves are closed for all the cylinders. In-cylinder inflow air flow rate when stopped, c is in-cylinder inflow air flow rate when intake valve closing control is being executed and the intake valve is not stopped in a closed state for only one cylinder, d is intake air The in-cylinder inflow air flow rate when the valve closing control is being executed and the two-cylinder intake valves are not stopped in the closed state is shown.

  Here, in the steady state (when the intake valve closing / stopping control is being executed, after the intake valve closing / stopping control is started, the throttle passing air flow rate and the in-cylinder inflow air flow rate converge to a constant value), the throttle passes. The air flow rate mt is equal to the in-cylinder inflow air flow rate mc. Therefore, in the steady state, the intersection of the curve of the throttle passage air flow rate and the straight line of the cylinder inflow air flow rate in FIG. 17 becomes the actual throttle passage air flow rate and the cylinder inflow air flow rate. Therefore, when the intake valve closing stop control is not being executed, the throttle passage air flow rate becomes mt3 which is the throttle passage air flow rate at the intersection of the throttle passage air flow rate curve and the straight line a in the steady state. On the other hand, when the intake valve closing control is being executed and the intake valves are stopped in the closed state for all the cylinders, the throttle passage air flow rate becomes the throttle passage air flow rate in FIG. This is 0, which is the flow rate of air passing through the throttle at the intersection of this curve and the straight line b. Similarly, when the intake valve closing / stopping control is being executed and the intake valve has not been stopped in a closed state for only one cylinder, the throttle passing air flow rate in FIG. When mt5 is the flow rate of air passing through the throttle at the intersection of the flow rate curve and the straight line c and the intake valve closing control is being executed and the two-cylinder intake valves are not stopped in a closed state, In this state, the throttle passage air flow rate becomes mt4 which is the throttle passage air flow rate at the intersection of the throttle passage air flow rate curve and the straight line d in FIG.

  Thus, when the throttle opening is a specific opening, the amount of air passing through the throttle in the steady state depends on the number of cylinders in which the intake valve 6 is not stopped while the intake valve closing control is being executed. Determined. In other words, it is possible to calculate the number of cylinders in which the intake valve is not stopped in the closed state during the execution of the intake valve closing stop control based on the airflow detection air flow rate and the throttle opening. For example, in the example shown in FIG. 17, when the throttle opening is at a certain opening, and the airflow detection air flow rate is in the vicinity of mt5, the intake valve 6 is not stopped in the closed state. When it is determined that the number of cylinders is 1, and the airflow detection air flow rate is in the vicinity of mt4, it is determined that the number of cylinders that are not stopped when the intake valve 6 is closed is 2.

  FIG. 18 is a flowchart showing a control routine of intake pipe pressure selection control used in the intake pipe model M12 after the intake valve closing stop control is completed. The illustrated control routine is performed by interruption at regular time intervals.

  First, as shown in step S21 in FIG. 18, it is determined whether or not the valve stop control flag Xv is 1. In step S21, when it is determined that the intake valve closing control is not executed and the valve stop control flag Xv is 0, the control routine is ended. On the other hand, if it is determined in step S21 that the intake valve closing stop control is being executed and the valve stop control flag Xv is 1, the process proceeds to step S22.

  In step S22, it is determined whether or not the throttle passing air flow rate mt calculated by the throttle model M11 is substantially zero, that is, whether or not the throttle passing air flow rate has converged to zero. When it is determined that the throttle passage air flow rate mt calculated by the throttle model M11 is not zero, the control routine is terminated. On the other hand, if it is determined in step S22 that the throttle passing air flow rate mt calculated by the throttle model M11 is zero, the process proceeds to step S23. In step S23, it is determined whether or not the air flow rate mtafm detected by the air flow meter 42 is substantially zero, that is, whether or not the actual air flow rate flowing through the intake pipe 15 has converged to zero. If it is determined in step S23 that the air flow rate mtafm detected by the air flow meter 42 is also substantially zero, no failure or the like has occurred in the variable valve mechanism, and the process proceeds to step S24. In step S24, the in-cylinder inflow air flow rate mc at the end of the intake valve closing control is calculated by the intake valve model M13 using the intake pipe pressure Pm calculated by the intake pipe model M12.

  On the other hand, if it is determined in step S23 that the air flow rate mtafm detected by the air flow meter 42 is not zero, a failure or the like has occurred in the variable valve mechanism, and the process proceeds to step S25. In step S25, the intake pipe pressure Pm is calculated as described above based on the air flow rate mtafm detected by the air flow meter. Next, in step S26, based on the air flow rate mtafm detected by the air flow meter 42, the number of cylinders in which the intake valve 6 is not stopped in the closed state is calculated as described above. Next, in step S27, the in-cylinder inflow air flow rate mc at the end of the intake valve closing control is calculated based on the intake pipe pressure Pm calculated in step S25.

DESCRIPTION OF SYMBOLS 1 Engine body 5 Combustion chamber 6 Intake valve 7 Intake port 8 Exhaust valve 11 Fuel injection valve 13 Intake pipe 18 Throttle valve 22 EGR control valve M10 In-cylinder inflow air amount model M11 Throttle model M12 Intake pipe model M13 Intake valve model

Claims (9)

In a control device for an internal combustion engine capable of executing intake valve closing control for stopping an intake valve in a closed state,
Pressure / temperature calculating means for calculating the pressure in the intake pipe and the temperature in the intake pipe based on the flow rate of air passing through the throttle valve and the flow rate of in-cylinder air flowing into the cylinder;
A gas flow rate calculating means for calculating a cylinder inflow air flow rate based on the intake pipe pressure and the intake pipe temperature calculated by the pressure / temperature calculating means;
Engine control means for controlling the internal combustion engine based on the in-cylinder inflow air flow rate calculated by the gas flow rate calculation means;
In addition to the pressure / temperature calculation means, a branch passage temperature detection means for calculating or detecting the temperature in the intake branch passage,
When the intake air valve closing / stopping control is being executed, the cylinder inflow air flow rate input to the pressure / temperature calculating means is set to zero, and the inflow air flow rate in the cylinder is calculated by the gas flow rate calculating means after the intake valve closing / stopping control ends. A control device for an internal combustion engine, which calculates the inflow air flow rate in the cylinder based on the temperature in the intake branch passage calculated or detected by the temperature detection means in the branch passage without using the pressure / temperature calculation means. . After completion of the intake valve closing stop control, the gas flow rate calculation means is configured such that Pm is the pressure in the intake pipe, Tmb is the temperature in the intake branch passage calculated or detected by the temperature detection means in the branch passage, and Ta is the outside air temperature. The control device for an internal combustion engine according to claim 1, wherein a cylinder inflow air flow rate mc is calculated based on the following formula (1), where a, b are values obtained by using the engine speed as a variable.

  3. The control device for an internal combustion engine according to claim 1, wherein the branch passage temperature detecting means detects the temperature in the intake branch passage by a temperature sensor that detects the temperature in the intake branch passage.   3. The control device for an internal combustion engine according to claim 1, wherein the branch passage temperature detecting means estimates the temperature in the intake branch passage based on an elapsed time from the start of the intake valve closing control. A pressure sensor for detecting the pressure in the intake pipe;
The intake air based on the difference generated between the rate of increase of the intake pipe pressure calculated by the pressure / temperature calculation means and the rate of increase of the intake pipe pressure detected by the pressure sensor during the intake valve closing control. The control device for an internal combustion engine according to any one of claims 1 to 4, wherein it is determined whether or not the intake valve is stopped in a closed state during the valve closing stop control.   The difference generated between the rate of increase in the intake pipe pressure calculated by the pressure / temperature calculating means and the rate of increase in the intake pipe pressure detected by the pressure sensor during the intake valve closing / stopping control is greater than a certain value. 6. The control device for an internal combustion engine according to claim 5, wherein a cylinder that is not stopped in a closed state of the intake valve is determined based on a time when the intake valve becomes large.   When it is determined that the intake valve is not stopped in the closed state during the intake valve closing control, when the in-cylinder inflow air flow rate is calculated by the gas flow rate calculation means after the intake valve closing control is ended The gas flow rate calculation means calculates the in-cylinder inflow air flow rate based on the intake pipe internal pressure detected by the pressure sensor without depending on the intake pipe internal pressure calculated by the pressure / temperature calculation means. The control apparatus of the internal combustion engine described in 1. An air flow rate detecting means for detecting a flow rate of air passing through the engine intake passage;
When the air flow rate detected by the air flow rate detecting means during the intake valve closing control is not zero, it is determined that the intake valve is not closed and the gas flow rate calculating means The in-cylinder inflow air flow rate after the end of the intake valve closing stop control is calculated based on the intake pipe pressure at the end of the intake valve closing stop control calculated based on the air flow rate detected by the detecting means. The control apparatus of the internal combustion engine of any one of -4.   When it is determined that the intake valve is closed and not stopped, the number of cylinders that are not stopped when the intake valve is closed is determined based on the air flow detected by the air flow detection means. The control apparatus for an internal combustion engine according to claim 8.

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