JP5056807B2 - 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 operate the internal combustion engine, it is preferable to make the air-fuel ratio at the time of combustion as close as possible to the target air-fuel ratio. For this purpose, a method is known in which the amount of air charged in the cylinder when the intake valve is closed is estimated, and the fuel injection amount is determined according to the amount of air charged in the cylinder. As a method for estimating the in-cylinder charged air amount, a map for calculating the in-cylinder charged air amount is prepared in advance using the output value of the sensor for detecting various parameters of the internal combustion engine as a variable. From this, a method for estimating the amount of air charged in the cylinder is known. In addition, there is a method in which model calculation formulas derived from models such as a throttle valve and an intake pipe are prepared in advance, and a cylinder charge air amount is estimated by numerical calculation using various parameter values and model calculation formulas of the internal combustion engine. Are known.

  Among these, as a method using numerical calculation, based on the throttle model that calculates the throttle valve passage air flow rate based on the throttle valve opening and the intake pipe pressure, and on the basis of the throttle passage air flow rate and the cylinder inflow air flow rate, There has been proposed an air model including an intake pipe model for calculating the intake pipe pressure and the intake pipe temperature, and an intake valve model for calculating the in-cylinder inflow air flow rate based on the intake pipe pressure and the intake pipe temperature (for example, Patent Documents). 1). In this method, the in-cylinder charged air amount can be calculated based on the calculated in-cylinder inflow air flow rate.

JP-A-2005-69019 JP 2000-87767 A JP 2006-22708 A

  In many internal combustion engines, fuel cut control is performed to stop the supply of fuel to the combustion chamber during engine deceleration operation. If the intake valve or exhaust valve is opened during fuel cut control in the same way as in normal operation, air flows into the exhaust purification catalyst disposed in the engine exhaust passage. 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, many internal combustion engines continue to drive the intake valve during normal operation, and close the intake valve to prevent oxygen from flowing into the exhaust purification catalyst during fuel cut control. It is stopped in the state.

  In an internal combustion engine that stops the intake valve in a closed state in fuel cut control or the like, the actual air flow rate flowing out from the intake pipe becomes zero by stopping the intake valve in the closed state. During the period when the intake valve is stopped in the closed state, the throttle valve is maintained in a slightly open state, and therefore the intake pipe pressure rises. The intake pipe pressure is steady at almost atmospheric pressure.

  In the air model for estimating the in-cylinder inflow air flow rate, the air flow rate that has passed through the throttle valve is estimated. The pressure in the intake pipe from the throttle valve to the intake valve is estimated based on the air flow rate that has passed through the throttle valve before the minute time and the in-cylinder inflow air flow rate that flows into the cylinder before the minute time. A cylinder inflow air flow rate flowing into the cylinder is calculated using the calculated intake pipe pressure.

  In an air model of a control device for an internal combustion engine that stops an intake valve in a closed state, the intake pipe pressure during a period in which the intake valve is stopped in a closed state can be calculated by setting the in-cylinder inflow air flow rate to zero. it can. For example, immediately after the intake valve is closed, the intake pipe pressure gradually rising to atmospheric pressure can be estimated. The actual in-cylinder inflow air flow rate increases as the intake valve goes from fully closed to fully open, and decreases as the intake valve goes from fully open to fully closed. On the other hand, in the air model, the flow rate averaged over time is calculated as the in-cylinder inflow air flow rate. For this reason, the intake pipe pressure calculated at a predetermined time depends on the time at which the in-cylinder inflow air flow rate is switched from the calculated value to zero.

  When the intake valve is re-driven from a state in which the intake valve is stopped in the closed state, the in-cylinder inflow air flow rate is calculated using the intake pipe pressure calculated during the period in which the intake valve is stopped in the closed state. Can do. Using the calculated in-cylinder inflow air flow rate, the in-cylinder charged air amount and the amount of fuel supplied to the cylinder are determined. When the error in the cylinder inflow air flow rate increases, the error in the cylinder charge air amount and the error in the amount of fuel supplied to the cylinder increase. As a result, the air-fuel ratio error when the fuel burns increases. Therefore, it is preferable to accurately estimate the intake pipe pressure during the period in which the intake valve is stopped in the closed state.

  An object of the present invention is to provide a control device for an internal combustion engine that can accurately estimate the pressure in the intake pipe during a period in which the intake valve is stopped in the closed state in the internal combustion engine that is stopped in the closed state. .

  The control apparatus for an internal combustion engine of the present invention can stop the intake valve in a closed state during the operation period of the internal combustion engine, and is based on the in-cylinder inflow air flow rate that is the air flow rate that flows into the cylinder a minute before. The control apparatus for an internal combustion engine calculates an intake pipe internal pressure, which is an air pressure upstream of the intake valve, and calculates a cylinder inflow air flow rate based on the calculated intake pipe internal pressure. When stopping the intake valve in the closed state, the control device sets the in-cylinder inflow air flow rate to zero from the calculated value at a time later than the scheduled time at which the intake valve in the cylinder to be stopped first starts to open. The pressure in the intake pipe is calculated while the intake valve is closed and stopped.

  In the above invention, the time at which the in-cylinder inflow air flow rate is switched from the calculated value to zero is determined based on at least one of the engine speed of the internal combustion engine and the communication delay between the electronic control unit and the engine body. Is preferred. With this configuration, the intake pipe pressure can be calculated with higher accuracy.

  In the above invention, there is provided a control device for an internal combustion engine comprising a plurality of cylinders, wherein a period during which an intake valve of one cylinder is open and a period during which an intake valve of another cylinder is open, When stopping in the closed state, the in-cylinder inflow air flow rate can be switched to zero at a time before the time when the intake valve of the last cylinder to be driven is completely closed.

  In the above invention, when the intake valve is to be re-driven from a stopped state, the in-cylinder inflow air flow rate at a time later than the time at which the intake valve of the cylinder to be re-driven first starts to open. It is preferable to calculate the intake pipe pressure when the intake valve is re-driven by switching to a value calculated from zero. With this configuration, the intake pipe pressure can be accurately calculated when the intake valve is driven again.

  ADVANTAGE OF THE INVENTION According to this invention, in the internal combustion engine which an intake valve stops in a closed state, the control apparatus which estimates the intake pipe pressure accurately during the period when the intake valve is stopped in the closed state can be provided.

1 is an overall view of an internal combustion engine equipped with a control device of the present invention. 3 is a block diagram of an air model for calculating an in-cylinder charged air amount according to Embodiment 1. FIG. It is a graph which shows the relationship between a throttle opening and a flow coefficient. It is a graph which shows the relationship between throttle opening and opening cross-sectional area. It is a graph which shows the function (Pm / Pm). 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. 2 is a time chart for explaining an operating state of the internal combustion engine in the first embodiment. It is a block diagram explaining the flow of the parameter of the air model during intake valve stop control. 4 is a time chart when starting intake valve stop control in the first embodiment. 4 is a flowchart when starting intake valve stop control in the first embodiment. 6 is a time chart when the intake valve stop control is terminated and the intake valve is re-driven in the first embodiment. 6 is a time chart when starting intake valve stop control in the second embodiment. In Embodiment 2, it is a flowchart when starting intake valve stop control. 9 is a time chart when the intake valve stop control is terminated and the intake valve is re-driven in the second embodiment.

(Embodiment 1)
With reference to FIGS. 1 to 14, the control apparatus for an internal combustion engine in the first embodiment will be described. In this embodiment, a cylinder injection type spark ignition type internal combustion engine is illustrated, but the present invention is another spark ignition type internal combustion engine such as a port injection type spark ignition type, or a compression self-ignition type internal combustion engine. The present invention can also be applied.

  FIG. 1 is an overall schematic diagram of an internal combustion engine in the present embodiment. The internal combustion engine includes an engine body 1. The engine main body 1 in the present embodiment includes a cylinder block 2, a piston 3 that reciprocates within the cylinder block 2, and a cylinder head 4 that is fixed on the cylinder block 2. A cylinder (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 5. Further, a spark plug 10 is disposed at the center of the inner wall surface of the cylinder head 4. A fuel injection valve 11 that supplies fuel F into the cylinder 5 is disposed around the inner wall surface of the cylinder head 4. A cavity 12 is formed on the top surface of the piston 3 so as to extend from below the injection port of the fuel injection valve 11 to below the spark plug 10.

  The intake port 7 is connected to a surge tank 14 via an intake branch pipe 13 for each cylinder 5. The surge tank 14 is connected to the air cleaner 16 via the 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 the 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 valve timing corresponding to the opening timing or closing timing of the intake valve 6 and the operating angle corresponding to the period during which the intake valve 6 is open. Further, the variable valve mechanism 21 can be stopped while the intake valve 6 is closed. That is, the closed state of the intake valve 6 can be maintained during a period corresponding to the intake process of the combustion cycle.

  The control device for an internal combustion engine in the present embodiment includes an electronic control unit 31. 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 port 36 and an output port 37 are provided.

  The internal combustion engine also includes a throttle opening sensor 43 for detecting the opening of the throttle valve 18. The output signal of the throttle opening sensor 43 is input to the input port 36 via the corresponding AD converter 38. The internal combustion engine includes an atmospheric pressure sensor 45 for detecting the pressure of the atmosphere around the internal combustion engine or the pressure of the air sucked into the upstream side intake pipe 15 through the air cleaner 16 (intake pressure), and the atmospheric pressure around the internal combustion engine. And an atmospheric temperature sensor 44 for detecting the temperature or the temperature of the air sucked into the upstream side intake pipe 15 through the air cleaner 16 (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. An air flow meter 42 for measuring the air flow rate is disposed in the upstream side intake pipe 15. The output signal of the air flow meter 42 is input to the input port 36 via the corresponding AD converter 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 48.

  On the other hand, the output port 37 is connected to the spark plug 10, the fuel injection valve 11, and the step motor 17 for the throttle valve 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 11 (hereinafter referred to as “fuel injection amount”) is determined based on the amount of air charged in the cylinder 5. The fuel ratio is determined to be the target air-fuel ratio. Therefore, in order to set the air-fuel ratio of the air-fuel mixture in the cylinder 5 to the target air-fuel ratio, it is necessary to estimate the amount of air charged in the cylinder 5 (hereinafter referred to as “cylinder charged air amount”). In the present embodiment, the in-cylinder charged air amount is calculated by numerical calculation using a model calculation formula derived from the model of each device.

  FIG. 2 is a block diagram of an air model for estimating the in-cylinder charged air amount in the present embodiment. The air model shown in FIG. 2 is a simple model among many types of air models. The air model M10 includes a throttle model M11 that models a throttle valve, an intake pipe model M12 that models an engine intake passage from the throttle valve to the intake valve, and an intake valve model M13 that models an intake valve. In the throttle model M11, the opening (throttle opening) θt of the throttle valve 18 detected by the throttle opening sensor 43 and the atmospheric pressure detected by the atmospheric pressure sensor 45 (or the intake air upstream of the throttle valve 18). The pressure of air sucked into the pipe) Pa, the atmospheric temperature detected by the atmospheric temperature sensor 44 (or the temperature of air sucked into the intake pipe upstream of the throttle valve 18) Ta, and the intake pipe model M12 The calculated pressure Pm in the engine intake passage from the throttle valve 18 to the intake valve 6 (referred to as “intake pipe pressure” in the present invention) Pm is input, and the values of these input parameters are calculated by the model calculation of the throttle model M11. By substituting into the equation, the flow rate of air passing through the throttle valve 18 per unit time (hereinafter referred to as “throttle valve passing air”). Amount "that) 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). "In-cylinder inflow air flow rate") mc and atmospheric temperature Ta are input. By substituting these input parameter values into the model calculation formula of the intake pipe model M12, the intake pipe pressure Pm and the temperature of the air in the engine intake passage from the throttle valve 18 to the intake valve 6 (hereinafter, “ Tm) ”(referred to as“ intake pipe temperature ”).

  The intake valve model M13 is supplied with the intake pipe pressure Pm, the intake pipe temperature Tm, and the atmospheric temperature Ta calculated in the intake pipe model M12. The in-cylinder inflow air flow rate mc is calculated by substituting these input parameter values into the model calculation formula of the intake valve model M13.

  In this method, the in-cylinder charged air amount Mc, which is the amount of air charged in the cylinder 5 when the intake valve 6 is closed, is calculated using the in-cylinder inflow air flow rate mc.

  In the air model M10, parameter values calculated in each model are used as parameter values input to another model. Therefore, in the entire air model M10, the actually input parameter values are the throttle opening θt and the atmospheric pressure Pa. , And the atmospheric temperature Ta. That is, the in-cylinder charged air amount Mc can be calculated from the three parameters.

  Next, the models M11 to M13 of each device will be described 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 (1), and the throttle valve passing air flow rate mt is calculated by solving this equation. The

In Expression (1), 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 relating 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).

  Further, Φ (Pm / Pa) is a function having Pm / Pa as a variable, as shown in the following equation (2).

  In Expression (2), κ is a specific heat ratio, and is a constant value in the present embodiment.

  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 (2), a map for calculating the function Φ (Pm / Pa) having Pm / Pa as a variable is stored in advance in the ROM 34, and the function Φ (Pm / Pa) is calculated from Pm / Pa and this map. The value of Pa) may be calculated.

These equations (1) and (2) indicate that the pressure of the air upstream of the throttle valve 18 is atmospheric pressure Pa, the temperature of the air upstream of the throttle valve 18 is the atmospheric temperature Ta, and the air passing through the throttle valve 18 With respect to the throttle valve 18 with the pressure as the intake pipe pressure Pm, the law of conservation of mass and the law of conservation of energy between the air upstream of the throttle valve 18 and the air that has passed through the throttle valve 18 are based on the model shown in FIG. , And the relational expression established in the law of conservation of momentum, and the equation of state of gas, the specific expression of 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.

  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 (3) and (4), and by solving these equations, Pm and intake pipe temperature Tm are calculated.

  In Expressions (3) and (4), V is the upstream side 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 (collectively, “intake pipe portion”) The sum of the volumes of

  Note that these equations (3) and (4) are related to the intake pipe portion and the air flowing into the intake pipe portion 23 and the outflow from the intake pipe portion 23 based on the model shown in FIG. It is derived from the relational expression that holds in the law of conservation of mass and the law of conservation of energy with the air flowing into the cylinder.

  Specifically, when the total amount of air in the intake pipe portion is M, the temporal change in the air amount M is caused by the flow rate of air flowing into the intake pipe portion (throttle valve passage air flow rate) mt and the intake pipe portion. Since it is equal to the difference between the flow rate of the air that flows out and flows into the cylinder (cylinder inflow air flow rate) mc, the following equation (5) is established on the law of conservation of mass.

From the equation (5) and the gas equation of state (Pm · V = M · R ^* · Tm), the above equation (3) is derived.

  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 (6) is established.

  Then, the equation (4) is derived from the equation (6) and the above-described gas state equation.

  Next, the intake valve model M13 will be described. In the intake valve model M13, the intake pipe pressure Pm, the intake pipe temperature Tm, and the atmospheric temperature Ta are input to the following equation (7), and by solving this equation, the in-cylinder inflow air flow rate mc is calculated.

  In equation (7), which is a model calculation formula of the intake valve model M13, the constant a is a proportional coefficient, and the constant b is a value representing the amount of gas remaining in the cylinder 5 when the exhaust valve 8 is closed. . In equation (7), constant a and constant 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 (7) ), The constant a and the constant b can be values obtained by using the engine speed NE and the valve timing and / or the phase angle as variables. For example, the constant a and the constant b are stored in the ROM 34 of the electronic control unit 31.

  Further, the control device for the internal combustion engine uses driving constants a and b to be used during driving of the intake valve with respect to the equation (7), and at the time of re-driving used when re-driving from a state where the intake valve is stopped. The constants a and b may be included. In this case, when the intake valve continues to be driven, the in-cylinder inflow air flow rate is calculated using the constants a and b being driven. When the intake valve is to be redriven from a closed state, the in-cylinder inflow air flow rate can be calculated using the constants a and b at the time of redrive.

  When the drive of the intake valve continues, pulsation appears in the intake pipe pressure. When the intake valve is stopped in the closed state, the pressure is substantially atmospheric pressure. The intake pipe pressure at this time is substantially constant without pulsation. By adopting the constants a and b at the time of re-driving in addition to the constants a and b during driving, it is possible to consider a state without pulsation when the intake valve is stopped in a closed state. For this reason, it is possible to accurately estimate the in-cylinder charged air amount when the intake valve is re-driven from a closed state and stopped.

  Equation (7) relates to the intake valve 6 on the basis of the model as shown in FIG. 8 and regards the in-cylinder inflow air flow rate mc as proportional to the intake pipe pressure Pm, and is 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 internal 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 Equation (7) is derived from theory and empirical rules.

  Furthermore, when the operating state of the internal combustion engine is changing, that is, during transient operation, the intake pipe temperature Tm may change greatly. Therefore, as a correction coefficient for compensating for the change in the intake pipe temperature Tm, And (Ta / Tm) derived from empirical rules.

  Note that the in-cylinder inflow air flow rate mc calculated by the equation (7) is an average value of the flow rate of air flowing out from the intake pipe portion per unit time, so that the in-cylinder inflow air flow rate mc The in-cylinder charged air amount Mc in each cylinder 5 can be calculated by multiplying the time taken for the cycle by the number of cylinders.

  Next, the in-cylinder inflow air flow rate and the in-cylinder charged air amount will be described with reference to FIG. 9, taking an internal combustion engine having four cylinders as an example. The horizontal axis is the crank angle (rotation 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, the third cylinder, the fourth cylinder, and the second cylinder. 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, which is indicated by a one-dot chain line. Therefore, the in-cylinder charged air amount Mc in each cylinder 5 is equal to the in-cylinder inflow air flow rate mc (the dashed line in FIG. 9) and the time required for one cycle of the internal combustion engine (in the example shown in FIG. Is calculated by multiplying the time obtained by dividing the time (degree required for rotation) by the number of cylinders, that is, the time required for the crankshaft to rotate 180 degrees in the example shown in FIG. The in-cylinder charged air amount Mc in each cylinder 5 calculated in this way corresponds to, for example, the hatched portion in FIG.

  Next, a method for calculating the in-cylinder charged air amount Mc when the air model M10 described above is mounted on an internal combustion engine will be described.

  The in-cylinder charged air amount Mc is obtained from the equations (1) to (4) and (7) of each model of the air model M10. These five equations are calculated by the electronic control unit 31 when mounted on the internal combustion engine. Discretized for processing. That is, assuming that the time is t and the calculation interval (calculation period) is Δt, these five equations are discretized as shown in the following equations (8) to (12).

  According to the air model M10 discretized and mounted in the internal combustion engine in this way, the throttle valve passing air flow rate mt (t) at the time t calculated in the throttle model M11 and the time t calculated in the intake valve model M13. The in-cylinder inflow air flow rate mc (t) and the intake pipe internal temperature Tm (t) at time t are input to the expressions (10) and (11) of the intake pipe model M12, and these expressions (10) and ( By solving 11), 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 (8) and (9) 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 (12) of the intake valve model M13, and by solving this expression, the time (t + Δt) The in-cylinder inflow air flow rate mc (t + Δt) at is calculated.

  Thus, the throttle valve passing air flow rate calculated in the previous calculation (throttle valve passing air flow rate before the minute time) and the cylinder inflow air flow rate calculated in the previous calculation (the cylinder inflow air flow rate before the minute time) ) To calculate the current intake pipe pressure. The current in-cylinder inflow air flow rate is calculated using the calculated current intake pipe pressure. By repeating such calculation, the in-cylinder inflow air flow rate mc at any time is calculated. Then, by multiplying the 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, the in-cylinder charged air amount Mc of each cylinder at any time is calculated. Is done.

  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 air model M10 described above, the atmospheric pressure and the atmospheric temperature when the calculation of the air model M10 is started may be always used, or the atmospheric pressure Pa (t at time t ) And the atmospheric temperature Ta (t). Thus, an estimated value can be calculated using the model formula of each device.

  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 5 during engine deceleration operation. When the fuel cut control is executed in this way, if air is circulated in the cylinder 5, that is, air is caused to flow into the cylinder 5 via the intake valve 6, and air is supplied from the cylinder 5 via the exhaust valve 8. When it flows out, 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 and the like of the noble metal decreases (oxygen poisoning).

  For this reason, in the internal combustion engine of the present embodiment, when the fuel cut control is executed, the intake valve stop 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.

  FIG. 10 shows a time chart when the fuel cut control is performed in the internal combustion engine in the present embodiment. Until time ts, normal operation in which the intake valve is continuously driven is executed. In the internal combustion engine in the present embodiment, air is continuously flowing into the cylinders until the time ts because the intake valve of any of the cylinders is open. Until the time ts, the actual intake pipe pressure is lower than the atmospheric pressure.

  At time ts, fuel cut control is started. During the fuel cut control period, intake valve stop control is performed to stop the intake valve in a closed state. At time ts, the in-cylinder inflow air flow rate becomes zero. During the intake valve stop control period, the air flow in the intake pipe portion stops. The throttle valve 19 is not completely closed but is maintained in a slightly open state, and air flows therethrough. For this reason, the pressure in the intake pipe gradually increases and becomes a substantially constant value at atmospheric pressure.

  At time te, the fuel cut control is terminated and the intake valve stop control is terminated. The intake valve is driven again at time te. When the intake valve is driven again, the actual pressure in the intake pipe decreases again to a pressure corresponding to the operating state of the engine body.

  FIG. 11 shows a block diagram of an air model when intake valve stop control is performed. When the intake valve stop control is being executed, air does not flow from the intake pipe portion into the cylinder. Therefore, in the present embodiment, during the intake valve stop control, the calculation of the in-cylinder inflow air flow rate by the intake valve model M13 is stopped and the in-cylinder inflow air flow rate mc input to the intake pipe model M12 is zero. It is said. That is, the in-cylinder inflow air flow rate mc is switched from the calculated value to zero.

  In the intake pipe model M12, the following expressions (13) and (14) are derived by substituting mc = 0 into the above expressions (3) and (4). The intake pipe internal pressure Pm and the intake pipe internal temperature Tm are calculated from the equations (13) and (14). Even during the period when the intake valve stop control is being executed, the intake pipe pressure Pm can be continuously calculated.

  After the intake valve has been re-driven, the cylinder charge air amount can be estimated using an air model during normal operation. That is, the in-cylinder inflow air flow rate mc is switched from zero to the calculated value. For example, as shown in FIG. 2, the intake pipe pressure Mm and the intake pipe temperature Tm are calculated by the intake pipe model M12, and the inflow cylinder air amount mc calculated by the intake valve model M13 is used. Mc can be calculated.

  FIG. 12 shows an enlarged view of a time chart when intake valve stop control is performed in the internal combustion engine of the present embodiment. In the example shown in FIG. 12, an internal combustion engine having four cylinders is illustrated. The first cylinder, the third cylinder, the fourth cylinder, and the second cylinder are subjected to the intake process in this order. In the intake process, the intake valve is driven. In the present embodiment, the overlap during the period when the intake valve of each cylinder is open is small.

At time t ₀ , intake valve stop control is started, and a valve stop instruction for stopping the intake valve in a closed state is transmitted. In the air model, for example, a flag for stopping the intake valve is set. A valve stop instruction is transmitted during the intake stroke of the third cylinder.

In the example shown in FIG. 12, the drive of the intake valve is finished in the third cylinder, and the intake valve of the fourth cylinder is stopped in the closed state. The third cylinder corresponds to the final drive cylinder. The fourth cylinder corresponds to a cylinder scheduled to be stopped. Time t ₁ is a scheduled time at which the intake valve in the fourth cylinder that stops first should start opening (IVO). That is, time t ₁ is the time when the intake valve has begun to open when the fourth cylinder is temporarily driven.

  By the way, with reference to FIG. 9, the air model in the present embodiment is an average value model for calculating the time average of the air flow rate sucked into all the cylinders as the in-cylinder inflow air flow rate mc. For example, when the internal combustion engine is in a steady state, the in-cylinder inflow air flow rate mc is substantially constant. As described above, when the intake valve stop control is started, the in-cylinder inflow air flow rate mc input to the intake pipe model M12 is switched from the calculated value of the intake valve model M13 to zero.

Referring to FIG. 12, as the time at which the in-cylinder inflow air flow rate mc is switched from the calculated value to zero, for example, it is conceivable to employ the valve opening time of the cylinder scheduled to stop to stop the intake into the cylinder. That is, it is conceivable to employ the time t ₁ when the fourth cylinder is scheduled to start opening. However, immediately after starting the opening of the cylinder, since the intake valve is in a state of opening, the air flow rate actually flowing into the cylinder is small. That is, the actual amount of change in the in-cylinder inflow air flow rate is small. However, when the in-cylinder inflow air flow rate mc is switched from the calculated value to zero at the time t _{1 when} the opening of the fourth cylinder is scheduled to start, the flow rate when the intake valve of the fourth cylinder operates The amount of change from the flow rate when the intake valve stops increases. In other words, in the air model, the time for switching the in-cylinder inflow air flow rate mc from the calculated value to zero becomes earlier. As a result, the calculated increase in the intake pipe pressure Pm is faster than the actual intake pipe pressure.

  When the intake valve stop control is finished, the in-cylinder inflow air flow rate when the intake valve is re-driven is calculated using the intake pipe pressure calculated during the intake valve stop control period. When the intake valve stop control is completed during the period in which the intake pipe pressure is increasing, the in-cylinder inflow air flow rate is calculated using the intake pipe internal pressure calculated in the transient state.

  When the calculated increase in the intake pipe pressure Pm is faster than the actual increase in the intake pipe pressure, the intake pipe pressure Pm calculated by the air model is higher than the actual intake pipe pressure. The calculated in-cylinder charged air amount Mc becomes larger than the actual amount. The amount of fuel supplied to the combustion chamber increases, and the air-fuel ratio in the combustion chamber shifts to a richer side than the target air-fuel ratio. Thus, an error may occur in the air-fuel ratio at the time of combustion.

In the present embodiment, the in-cylinder inflow air flow rate mc is switched from the calculated value of the intake valve model M13 to zero at a time after the scheduled time t _{1 at} which the intake valve of the fourth cylinder to be stopped first starts to open. Yes. The time at which the in-cylinder inflow air flow rate mc is switched from the calculated value to zero is delayed from the time t ₁ by the time dt _IVO . In time t _2, the are switched to zero cylinder flow-in air flow rate mc from the calculated values. By performing this control, it is possible to improve the estimation accuracy of the intake pipe pressure Pm calculated by the air model. In particular, the intake pipe pressure can be accurately estimated from when the intake valve is stopped in the closed state until the intake pipe pressure becomes almost steady. Therefore, the cylinder inflow air flow rate mc can be accurately estimated even when the intake valve is re-driven while the intake pipe pressure is in a transient state. The air-fuel ratio at the time of re-driving can be brought close to the target air-fuel ratio with high accuracy.

FIG. 13 shows a flowchart of the control of the internal combustion engine in the present embodiment. The flowchart shown in FIG. 13 is a flowchart when starting intake valve stop control. In step 101, an instruction to stop the intake valve is detected. Next, in step 102, first determine the scheduled stop cylinder to be stopped to detect the expected time t ₁ should begin opening the intake valve of the expected stop cylinder.

Next, in step 103, a correction time dt _IVO for switching the in-cylinder inflow air flow rate mc in the air model from the calculated value to zero is determined. The time for switching the in-cylinder inflow air flow rate mc depends on the crank angle when the cylinder to be stopped is driven. The correction time depends on, for example, the engine speed NE of the internal combustion engine. By increasing the engine speed NE, the rate of increase in the in-cylinder inflow air flow rate when the intake valve starts to open increases. In this case, it is preferable to advance the time at which the in-cylinder inflow air flow rate mc is switched from the calculated value to zero. That is, it is preferable to reduce the correction time dt _IVO .

In the present embodiment, the value of the correction time dt _IVO that is a function of the engine speed NE is stored in the ROM 34 of the electronic control unit 31. When the intake valve stop control should be started, the engine speed NE can be detected in step 103, and the correction time dt _IVO can be determined from the detected engine speed NE.

Next, in step 104, the in-cylinder inflow air flow rate mc input to the intake pipe model M12 is switched to zero at time (t ₁ + dt _IVO ) based on the calculated correction time dt _IVO .

In the present embodiment, the correction time dt _IVO is determined based on the engine speed. However, the correction time dt _IVO is not limited to this mode, and the correction time dt _IVO takes into account the communication delay between the electronic control unit 31 and the engine body. Can be determined. For example, as the communication delay from the sensor such as the crank angle sensor 48 to the electronic control unit 31 is longer, the correction time dt _IVO can be controlled to be shorter. The correction time can be determined using the communication delay between the electronic control unit 31 and the engine body 1 as a function.

  Thus, by determining the time at which the in-cylinder inflow air flow rate is switched from the calculated value to zero based on at least one of the engine speed of the internal combustion engine and the communication delay between the electronic control unit and the engine body, The intake pipe pressure can be estimated more accurately.

The correction time dt _IVO in the present embodiment is a function such as the engine speed of the internal combustion engine. However, the correction time dt _IVO is not limited to this form, and the correction time dt _IVO may be a predetermined fixed value. I do not care.

  Next, the control when the intake valve stop control in the present embodiment is finished and the intake valve is re-driven will be described.

FIG. 14 is an enlarged view of a time chart when the intake valve stop control is ended and the intake valve is re-driven. At time t ₀ , a signal for re-driving the intake valve is transmitted. The first cylinder is the final cylinder that stops when the intake valve is closed. The first cylinder corresponds to the final stop cylinder. The third cylinder is the first cylinder when the intake valve is redriven. The third cylinder corresponds to a redrive start cylinder. The fourth cylinder is driven following the third cylinder. In the example shown in FIG. 14, the intake valve is redriven from a state in which the intake pipe pressure is substantially atmospheric pressure. That is, the intake valve is re-driven in a state where the intake pipe pressure after the intake valve stops is substantially constant.

When the intake valve is driven again, the in-cylinder inflow air flow rate mc in the air model is switched from zero to the calculated value of the intake valve model M13. When the drive of the intake valve is resumed, the in-cylinder inflow air flow rate mc is switched from zero to the calculated value at time t _{2 when the} correction time dt _IVO is delayed from time t ₁ when the intake valve of the third cylinder starts to open. Is preferred. Immediately after the intake valve starts to open, the air flow rate actually flowing into the cylinder is small. For this reason, the intake pipe pressure can be accurately estimated by setting the time for switching the in-cylinder inflow air flow rate in the air model to a time after the time when the intake valve starts to open. When the intake valve is driven again, the in-cylinder inflow air flow rate can be accurately estimated. As a result, the air-fuel ratio during combustion in the combustion chamber can be accurately controlled.

At time t ₀ , a signal for re-driving the intake valve is transmitted, and the time t _{1 at} which the opening of the third cylinder where the intake valve is re-driven first starts is detected. Next, the correction time dt _IVO is determined. The correction time dt _IVO for re-driving the intake valve is the same as the switching of the in-cylinder inflow air flow when the intake valve is stopped, the communication speed between the engine speed of the internal combustion engine and the electronic control unit and the engine body. It is preferable to determine based on at least one of them. Next, at time t ₂ , that is, at time (t ₁ + dt _IVO ), the in-cylinder inflow air flow rate mc is switched from zero to a calculated value.

  The internal combustion engine in the present embodiment has been described by taking a four-cylinder internal combustion engine having four cylinders as an example, but is not limited to this form, and the present invention can be applied to an internal combustion engine having an arbitrary number of cylinders. . For example, the present invention can also be applied to an internal combustion engine that is a single-cylinder internal combustion engine and that does not overlap when the intake valve is open.

  In the present embodiment, the air model shown in FIG. 2 has been described as an example. However, the present invention is not limited to this mode, and the intake air flow rate in the cylinder that flows into the cylinder is used in the intake pipe upstream of the intake valve. The present invention can be applied to a control device for an internal combustion engine that estimates pressure.

(Embodiment 2)
With reference to FIGS. 15 to 17, the control apparatus for an internal combustion engine in the second embodiment will be described. In the control device for an internal combustion engine, the amount of air charged in the cylinder is estimated by the air model M10 as in the first embodiment (see FIG. 2). The intake valve stop control for stopping the intake valve in the closed state during the operation period of the internal combustion engine is the same as in the first embodiment.

  The internal combustion engine in the present embodiment has a plurality of cylinders, and has an overlap during a period in which the intake valve in each cylinder is open. That is, in the internal combustion engine in the present embodiment, the period during which the intake valve of one cylinder is open overlaps with the period during which the intake valve of another cylinder is open. In the present embodiment, a six-cylinder internal combustion engine will be described as an example of an internal combustion engine having a plurality of cylinders.

FIG. 15 shows an enlarged view of a time chart when the intake valve stop control is started. In the present embodiment, the first cylinder, the fifth cylinder, the third cylinder, the sixth cylinder, the second cylinder, and the fourth cylinder are subjected to the intake process in this order. In the example shown in FIG. 15, a valve stop instruction is transmitted at time t ₀ . The first cylinder and the fifth cylinder are driven, and a valve stop instruction is transmitted during the intake process of the fifth cylinder. The fifth cylinder corresponds to the final drive cylinder. The third cylinder corresponds to a scheduled stop cylinder in which the intake valve first stops.

Time t ₁ is a scheduled time at which the intake valve in the third cylinder that stops first should start to open. Time t ₃ is the time when the intake valve of the fifth cylinder is completely closed (IVC). By performing the intake valve stop control, the in-cylinder air flow rate mc input to the intake pipe model M12 of the air model M10 is switched from the calculated value to zero. In the present embodiment, in-cylinder inflow air flow rate mc is switched from the calculated value to zero at time t ₂ before time t ₃ when the intake valve of the fifth cylinder, which is the final drive cylinder, is completely closed.

The time to switch the cylinder flow-in air flow rate, the fifth cylinder intake valve is the final drive cylinder is conceivable to employ a time t ₃ when fully closed. However, in an internal combustion engine in which the intake valve opening period of each cylinder overlaps, the scheduled time at which the intake valve of the cylinder to be stopped should start to open becomes earlier. For this reason, the influence of the amount of air that was scheduled to flow into the third cylinder, which is the first cylinder to be stopped, increases. The actual intake pipe internal pressure rises at a time earlier than time t ₃ when the closing of the fifth cylinder, which is the final drive cylinder, is completed.

Referring to FIG 15, when switching the cylinder flow-in air flow rate mc from the calculated value to zero at time t _3, increase of the calculated intake pipe pressure becomes slower than the actual increase of the intake pipe pressure End up. In the present embodiment, the correction time dt _IVC earlier time t ₂ than closing is completed the time t ₃ of the final drive cylinders are switched to zero cylinder flow-in air flow rate mc from the calculated values.

FIG. 16 shows a flowchart of the control of the internal combustion engine in the present embodiment. The flowchart shown in FIG. 16 is a flowchart when starting the intake valve stop control. In step 111, an instruction to stop the intake valve is detected. Next, at step 112, after defining the first expected stop cylinder to be stopped, the intake valve of the final drive cylinder to detect the time t ₃ when fully closed.

Next, in step 113, a correction time dt _IVC is determined. In the present embodiment, the correction time dt _IVC is determined based on the engine speed of the internal combustion engine. As in the first embodiment, by determining the correction time dt _IVC based on at least one of the engine speed of the internal combustion engine and the communication delay between the electronic control unit and the engine body, the intake pipe pressure can be accurately determined. Can be estimated.

In step 114, the in-cylinder inflow air flow rate mc is switched from the calculated value to zero at time (t ₃ -dt _IVC ). By performing this control, the intake pipe pressure can be estimated with high accuracy. For example, even when the intake valve is re-driven during a transition period in which the intake pipe pressure is increasing, the cylinder charge air amount can be accurately estimated. As a result, the air-fuel ratio at the time of combustion can be accurately controlled.

  The control device in the present embodiment is suitable for an internal combustion engine having a large overlap during a period when the intake valve is open. That is, it is suitable for an internal combustion engine having a large crank angle in which the period during which the intake valve is open overlaps. For example, it is suitable for an internal combustion engine having six or more cylinders. Or, for example, it is suitable for an internal combustion engine in which the angle range of the crank angle in which the periods during which the intake valve is open overlaps is 60 ° or more. Furthermore, in an internal combustion engine using an Atkinson cycle provided in a hybrid vehicle or the like, there may be a large overlap during a period in which the intake valve of each cylinder is open. Thus, it is suitable for an internal combustion engine in which the overlap of the open periods of the intake valves of different cylinders is large.

  Next, the control when the intake valve stop control in the present embodiment is finished and the intake valve is re-driven will be described.

  FIG. 17 is an enlarged view of a time chart when the intake valve stop control is terminated and the intake valve is re-driven in the present embodiment. In the example shown in FIG. 17, the first cylinder is the final cylinder that stops in the closed state, and corresponds to the final stopped cylinder. The fifth cylinder is a cylinder that has restarted driving first, and corresponds to a re-driving start cylinder. The third cylinder is driven following the fifth cylinder.

In the present embodiment, as described above, the time for switching to the zero cylinder flow-in air flow rate from the calculated value at the start of the intake valve stop control is based on the time t ₃ when the intake valve of the final drive cylinders are fully closed (See FIG. 15). However, when the intake valve is redriven, the influence of the air flow rate flowing into the cylinder that is redriven first increases. The influence of the air flow rate flowing into the fifth cylinder increases. Therefore, the time to re-drive the intake valve, likewise, at time t ₂ from time t ₁ the cylinder starts opening delayed a predetermined time to first re-drive, the cylinder incoming air flow in the first embodiment It is preferable to switch mc from zero to a calculated value.

At time t ₀ , a signal for re-driving the intake valve is transmitted. First, a time t _{1 at} which the opening of the fifth cylinder in which the intake valve is redriven is started is detected. Next, the correction time dt _IVO is determined. The correction time dt _IVO is preferably determined based on at least one of the rotational speed of the internal combustion engine and the communication delay between the electronic control unit and the engine body, as in the first embodiment. Next, at time t ₂ , that is, at time (t ₁ + dt _IVO ), the in-cylinder inflow air flow rate mc is switched from zero to a calculated value.

  As described above, when the intake valve stop control in the present embodiment is terminated and the intake valve is re-driven, the in-cylinder inflow air flow rate is determined based on the time when the re-driven intake valve starts to open first. It is preferable to determine the time for switching from zero to the calculated value. By performing this control, the intake pipe pressure can be accurately estimated when the intake valve is re-driven, and the in-cylinder charged air amount can be accurately calculated. As a result, the air-fuel ratio at the time of combustion can be accurately controlled.

  Other configurations, operations, and effects are the same as those in the first embodiment, and thus description thereof will not be repeated here.

  The above embodiments can be combined as appropriate. In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. Further, in the embodiment, changes included in the scope of claims are intended.

1 Engine Body 5 Cylinder 6 Intake Valve 7 Intake Port 11 Fuel Injection Valve 23 Intake Pipe Part 18 Throttle Valve M10 Air Model M11 Throttle Model M12 Intake Pipe Model M13 Intake Valve Model

Claims (4)

The air pressure on the upstream side of the intake valve can be stopped in the closed state during the operation period of the internal combustion engine, based on the in-cylinder inflow air flow rate that is the air flow rate that flows into the cylinder a minute before. A control device for an internal combustion engine that calculates an intake pipe internal pressure and calculates a cylinder inflow air flow rate based on the calculated intake pipe internal pressure,
When stopping the intake valve in the closed state, the inflow flow rate in the cylinder is switched from the calculated value to zero at a time later than the scheduled time at which the intake valve in the cylinder to be stopped first starts to open. A control apparatus for an internal combustion engine, characterized by calculating an intake pipe pressure during a period in which the valve is stopped in a closed state.   The time for switching the in-cylinder inflow air flow rate from the calculated value to zero is determined based on at least one of the engine speed of the internal combustion engine and a communication delay between the electronic control unit and the engine body, The control apparatus for an internal combustion engine according to claim 1. A control device for an internal combustion engine comprising a plurality of cylinders, wherein a period during which the intake valve of one cylinder is open and a period during which the intake valve of another cylinder is open,
The in-cylinder inflow air flow rate is switched to zero at a time before the time when the intake valve of the last cylinder to be driven is completely closed when the intake valve is stopped in a closed state. 3. The control device for an internal combustion engine according to 2.   When the intake valve is to be restarted from a closed state, the in-cylinder inflow air flow rate is calculated from zero at a time later than the time when the intake valve of the cylinder to be redriven first starts to open. The internal combustion engine control device according to any one of claims 1 to 3, wherein the pressure in the intake pipe is calculated when the intake valve is re-driven by switching to the above value.

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