JP2012255371A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately set a target fresh air volume for achieving a target throttle opening degree in an internal combustion engine into which an external EGR gas can be introduced in a control device of an internal combustion engine.SOLUTION: The control device of an internal combustion engine includes: an EGR path 26 for communicating an exhaust path 14 with an air intake path 12 of the internal combustion engine 10; an EGR valve 28 for operating open and close of the EGR path 26; and a throttle valve 18 disposed in the air intake path 12. The control device of an internal combustion engine calculates a target intake manifold pressure (throttle downstream pressure) Pbased on a target whole aspiration gas volume mthat is a sum of an in-cylinder aspiration EGR gas volume mthat is calculated in consideration of a response delay of an EGR gas, and a target fresh air volume, and then calculates the target throttle opening degree TA required for achieving the calculated target intake manifold pressure P.

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device that calculates a target throttle opening for realizing a target fresh air amount for an internal combustion engine that can introduce external EGR gas.

  Conventionally, for example, Patent Document 1 discloses an intake control device for an internal combustion engine that controls the intake air amount to a target intake air amount by controlling the opening and closing timing of the intake valve. In this conventional intake control device, when the fluctuation amount of the operation time of the intake valve is large and / or when the target intake air amount is small, the target intake pipe pressure is corrected to be smaller. The target throttle opening and the like are set based on the corrected target intake pipe pressure and target intake air amount.

JP 2000-204983 A

  The technique described in Patent Document 1 described above is directed to an internal combustion engine that performs control (so-called external EGR control) for recirculating exhaust gas to the intake passage via an EGR passage that connects the exhaust passage and the intake passage. It is not a thing. For this reason, when the above technique is applied to an internal combustion engine that performs external EGR control, there is a possibility that the target fresh air amount for realizing the target throttle opening cannot be set accurately.

  The present invention has been made to solve the above-described problems, and in an internal combustion engine capable of introducing an external EGR gas, it is possible to accurately set a target fresh air amount for realizing a target throttle opening degree. An object of the present invention is to provide a control device for an internal combustion engine.

A first invention is a control device for an internal combustion engine,
An EGR passage communicating the exhaust passage and the intake passage of the internal combustion engine;
An EGR valve responsible for opening and closing the EGR passage;
A throttle valve disposed in the intake passage;
A target fresh air amount calculating means for calculating a target fresh air amount of the fresh air sucked into the cylinder;
In-cylinder intake EGR gas amount estimation means for estimating the in-cylinder intake EGR gas amount in consideration of a response delay of in-cylinder intake EGR gas sucked into the cylinder with respect to a change in the EGR gas amount passing through the EGR valve When,
Defines the relationship between the target total intake gas amount that is the sum of the target fresh air amount and the in-cylinder intake EGR gas amount, and the throttle downstream pressure that is the pressure of the gas in the intake passage on the downstream side of the throttle valve. A target throttle downstream pressure calculating means for calculating a target throttle downstream pressure according to the relationship information;
Target throttle opening calculating means for calculating a target throttle opening required for realizing the target throttle downstream pressure;
It is characterized by providing.

The second invention is the first invention, wherein
The target fresh air amount calculation means limits the minimum value of the target fresh air amount so that misfire does not occur.

  According to the first aspect of the present invention, the target total air amount that is the sum of the in-cylinder intake EGR gas amount (that is, the EGR gas amount sucked into the cylinder in the course) taking into account the response delay of the EGR gas and the target fresh air amount. A target throttle downstream pressure is calculated from the intake gas amount. Then, based on the calculated target throttle downstream pressure, the target throttle opening is calculated. As a result, even when the in-cylinder intake EGR gas amount is at a time of transition that is significantly different from the steady state, the target fresh air amount for realizing the target throttle opening can be accurately calculated.

  According to the second invention, misfire can be suppressed satisfactorily when the target throttle opening is calculated on the basis of the target total intake gas amount in consideration of the in-cylinder intake EGR gas amount.

It is a figure for demonstrating the system configuration | structure of the internal combustion engine of Embodiment 1 of this invention. It is a block diagram which shows the structure of a torque implementation part. It is the figure which represented the process performed in a torque implementation part with the flowchart in order to calculate the target throttle opening degree TA for implement | achieving a target fresh air amount. Is a diagram showing the relationship between the EGR valve passing gas amount _{m egr} and the intake manifold pressure _{P m.} It is a figure for demonstrating the effect of the calculation of the target throttle opening degree TA in Embodiment 1 of this invention (calculation of the target intake manifold pressure used) in contrast with the conventional calculation method.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining a system configuration of an internal combustion engine 10 according to Embodiment 1 of the present invention. An intake passage 12 and an exhaust passage 14 communicate with each other in the cylinder of the internal combustion engine 10. In the vicinity of the inlet of the intake passage 12, an air flow meter 16 that outputs a signal corresponding to the flow rate of air sucked into the intake passage 12 is provided. A throttle valve 18 for adjusting the amount of air taken into the cylinder is provided downstream of the air flow meter 16. The throttle valve 18 is an electronically controlled throttle valve that can control the throttle opening TA independently of the accelerator opening.

  Each cylinder of the internal combustion engine 10 is provided with a fuel injection valve 20 for injecting fuel into the intake port and an ignition plug 22 for igniting the air-fuel mixture. Further, the internal combustion engine 10 is provided with a variable valve timing mechanism 24 for adjusting the opening / closing timing of intake valves and exhaust valves (not shown) of each cylinder.

  The internal combustion engine 10 also includes an EGR (Exhaust Gas Recirculation) passage 26 that connects the intake passage 12 downstream of the throttle valve 18 and the exhaust passage 14. An EGR valve 28 that opens and closes the EGR passage 26 is provided near the connection port on the intake passage 12 side in the EGR passage 26. By changing the opening degree of the EGR valve 28, the flow rate of the EGR gas (so-called external EGR gas) flowing through the EGR passage 26 can be changed to adjust the EGR rate.

  Further, the system shown in FIG. 1 includes an ECU (Electronic Control Unit) 30. In addition to the air flow meter 16 described above, an internal combustion engine 10 such as a crank angle sensor 32 for detecting the engine speed and an A / F sensor 34 for detecting the air-fuel ratio of the exhaust gas is provided at the input portion of the ECU 30. Various sensors for detecting the driving state are connected. Also, various actuators for controlling the operation of the internal combustion engine 10 such as the throttle valve 18, the fuel injection valve 20, the spark plug 22, the variable valve timing mechanism 24, and the EGR valve 28 are connected to the output portion of the ECU 30. ing.

  The ECU 30 controls the operating state of the internal combustion engine 10 by operating various actuators according to a predetermined program based on the outputs of the various sensors described above. Specifically, a torque achievement unit 36 is virtually configured inside the ECU 30. FIG. 2 is a block diagram showing the configuration of such a torque realization unit 36. Based on the input engine requests (requested torque, required efficiency, and required A / F) and the engine information related to the current operating state of the internal combustion engine 10, the torque achievement unit 36 sets the target throttle opening TA and the target ignition. The time is calculated.

  In the present embodiment, torque, air-fuel ratio, and efficiency are used as control amounts for the internal combustion engine 10. Strictly speaking, the torque here means the indicated torque, and the air-fuel ratio means the air-fuel ratio of the air-fuel mixture used for combustion. The efficiency in this specification means the ratio of the actually output torque to the potential torque that the internal combustion engine 10 can output. The maximum value of efficiency is 1, and at that time, the potential torque that can be output by the internal combustion engine 10 is actually output as it is. When the efficiency is less than 1, the torque that is actually output is smaller than the potential torque that can be output by the internal combustion engine 10, and the margin is mainly output as heat and output from the internal combustion engine 10. .

  The torque realization unit 36 shown in the block diagram of FIG. 2 includes a combustion guarantee guard unit 38, a new air amount control torque calculation unit 40, a target new air amount calculation unit 42, a throttle opening calculation unit 44, The estimated torque calculation unit 46, the ignition timing control torque efficiency calculation unit 48, the combustion guarantee guard unit 50, the ignition timing calculation unit 52, the combustion guarantee guard unit 54, and the in-cylinder intake EGR gas amount calculation unit 56 can be divided. Hereinafter, functions of the elements 38 to 56 will be described.

  First, the required torque, the required efficiency, and the required air-fuel ratio (requested A / F) are input to the torque realization unit 36 as requests for the control amount of the internal combustion engine 10. These requests are supplied from a powertrain manager positioned above the torque realizing unit 36. The required torque is set according to the operating condition and operating state of the internal combustion engine 10, specifically based on the amount of operation of the accelerator pedal by the driver and a signal from a vehicle control system such as VSC or TRC. . The required efficiency is set to a value smaller than 1 when it is desired to increase the temperature of the exhaust gas or to create a reserve torque. The required air-fuel ratio is changed so that the oxygen storage amount of the catalyst is properly maintained centering on the stoichiometry. Specifically, the required air-fuel ratio is actively changed by open loop control, or the required air-fuel ratio is changed by air-fuel ratio feedback control.

  The required torque and the required efficiency received by the torque realization unit 36 are input to the new air amount control torque calculation unit 40. The new air amount control torque calculation unit 40 calculates the new air amount control torque by dividing the required torque by the required efficiency. When the required efficiency is smaller than 1, the new air amount control torque is raised more than the required torque. This means that the throttle valve 18 is required to potentially output a torque larger than the required torque. However, with respect to the required efficiency, the value that has passed through the combustion guarantee guard unit 38 is input to the new air amount control torque calculation unit 40. The combustion guarantee guard unit 38 limits the minimum value and the maximum value of the required efficiency used for calculating the new air amount control torque by a guard value for ensuring proper combustion. As shown in FIG. 2, the minimum value (lower limit) of the required efficiency is limited in this case (that is, when calculating the fresh air amount control torque) in order to avoid misfires and torque fluctuations. The maximum value (upper limit) is limited to avoid knocking.

The fresh air amount control torque is input to the target fresh air amount calculation unit 42. The target fresh air amount calculation unit 42 converts the new air amount control torque into the target fresh air amount (KL) using the new air amount map. The amount of fresh air here means the amount of fresh air sucked into the cylinder (a non-dimensional charging efficiency or load factor can be used instead). The new air amount map assumes that the ignition timing is the optimal ignition timing (the ignition timing on the more retarded side of the MBT and the trace knock ignition timing). It is a map associated with various engine state quantities including the fuel ratio as keys. The actual value and target value of the engine state quantity are used for searching the new air quantity map. Regarding the air-fuel ratio, a target air-fuel ratio described later is used for map search. Therefore, the target fresh air amount calculation unit 42 calculates the fresh air amount necessary for realizing the fresh air amount control torque under the target air-fuel ratio described later as the target fresh air amount of the internal combustion engine 10. The reflection of the in-cylinder intake EGR gas amount m _{egrcyl to} the target fresh air amount calculation unit 42 shown in FIG. 2 is performed when a later-described new air amount lower limit value m _cmin is calculated.

The target fresh air amount is input to the throttle opening calculation unit 44. The throttle opening calculation unit 44 uses a reverse model of the air model to calculate the target total intake gas amount m _cref (the sum of the target fresh air amount input to the throttle opening calculation unit 44 and the in-cylinder intake EGR gas amount m _egrcyl ). ) Is converted into the target throttle opening (TA). Since the air model is a physical model that models the response characteristic of the intake gas amount to the operation of the throttle valve 18, by using the inverse model, the throttle opening required to achieve the target total intake gas amount m _cref is calculated backward. Can do. Since the calculation method of the target throttle opening degree TA is a main characteristic part of the present embodiment, it will be described in detail later with reference to the flowchart of FIG.

  The ECU 30 operates the throttle valve 18 in accordance with the target throttle opening calculated by the throttle opening calculation unit 44. When the delay control is performed, the throttle opening (target throttle opening) calculated by the throttle opening calculation unit 44 and the actual throttle opening realized by the operation of the throttle valve 18 are calculated. In the meantime, there is a delay corresponding to the delay time.

  In parallel with the above processing, the torque realizing unit 36 calculates the estimated torque based on the actual throttle opening by the estimated torque calculating unit 46. The estimated torque calculation unit 46 converts the throttle opening to the estimated fresh air amount using the forward model of the air model described above, and then converts the estimated fresh air amount to the estimated torque using the torque map. The estimated fresh air amount is a fresh air amount estimated to be realized by the operation of the throttle valve 18 by the ECU 30. The estimated torque in this specification is an MBT torque that can be output when the ignition timing is set to the optimal ignition timing under the current throttle opening, that is, an estimated value of the torque that the internal combustion engine 10 can potentially output. is there. The torque map is an inverse map of the above-described new air amount map, and is a map associated with the new air amount, torque, and various engine state quantities as keys on the assumption that the ignition timing is the optimal ignition timing. It is. In this torque map search, a target air-fuel ratio described later is used for map search. Therefore, the estimated torque calculation unit 46 calculates the torque estimated to be realized by the estimated fresh air amount under the target air-fuel ratio described later.

The estimated torque is input to the ignition timing control torque efficiency calculation unit 48 together with the duplicated required torque. The ignition timing control torque efficiency calculation unit 48 calculates the ratio of the required torque to the estimated torque as the ignition timing control torque efficiency. The calculated ignition timing control torque efficiency is input to the ignition timing calculation section 52 after passing through the combustion guarantee guard section 50. The combustion guarantee guard unit 50 limits the ignition timing control torque efficiency minimum value and maximum value) by a guard value that guarantees combustion. As shown in FIG. 2, the minimum value (lower limit) of the required efficiency is limited in this case (that is, when calculating the target ignition timing) in order to avoid misfire and torque fluctuation, and the maximum value (upper limit). This is for avoiding knock and for avoiding misfire (EGR misfire upper limit) associated with execution of control of the fresh air amount using the in-cylinder intake EGR gas amount m _egrcyl of the present embodiment.

  The ignition timing calculation unit 52 calculates the ignition timing (SA) from the input ignition timing control torque efficiency. Specifically, the optimal ignition timing is calculated based on the engine state quantity such as the engine speed, the required torque, the target air-fuel ratio, and the like, and the retard amount with respect to the optimal ignition timing is calculated from the input ignition timing control torque efficiency. Then, the sum of the retard amount and the optimum ignition timing is calculated as the final target ignition timing. For the calculation of the optimum ignition timing, for example, a map that associates the optimum ignition timing with various engine state quantities can be used. For the calculation of the retard amount, for example, a map that associates the retard amount with the ignition timing control torque efficiency and various engine state quantities can be used. If the ignition timing control torque efficiency is 1, the retard amount is zero, and the smaller the ignition timing control torque efficiency is, the larger the retard amount is.

  The ECU 30 operates the spark plug 22 according to the target ignition timing calculated by the ignition timing calculation unit 52.

  The required air-fuel ratio input to the torque achievement unit 36 passes through the combustion guarantee guard unit 54 and is then supplied to the target fresh air amount calculation unit 42 and the ignition timing calculation unit 52 as the target air-fuel ratio. The combustion guarantee guard unit 54 limits the maximum value and the minimum value of the target air-fuel ratio with a guard value for ensuring proper combustion.

  By the way, in the internal combustion engine capable of introducing external EGR gas, such as the internal combustion engine 10 of the present embodiment, the amount of EGR gas sucked into the cylinder at the time of transition when the operating state of the internal combustion engine is changing is It is very different from the amount of EGR gas sucked in. Therefore, the target fresh air amount is calculated using the relationship assuming the fresh air amount under the steady EGR gas amount, and the target throttle opening for realizing the target fresh air amount is calculated. This makes it difficult to accurately control the amount of fresh air drawn into the cylinder to the target amount of fresh air.

Therefore, in the present embodiment, when the target throttle opening for realizing the target fresh air amount is calculated by the throttle opening calculation unit 44, the target total value that is the target value of the total gas amount sucked into the cylinder is calculated. In-cylinder intake (external) EGR calculated by taking the intake gas amount (total gas amount passing through the intake valve) m _cref into consideration the target fresh air amount and intake behavior (more specifically, response delay of EGR gas) It was calculated as the sum of the amount of gas (that is, the amount of EGR gas that is inhaled in the _event ) m _egrcyl . The target intake manifold pressure (throttle downstream pressure) P _mref is calculated based on the target total intake gas amount (total intake valve passage total gas amount) m _cref .

Even when a target fresh air amount that does not misfire is instructed at the steady state, a situation in which the in-cylinder intake EGR gas amount m _egrcyl becomes larger than the steady state value is likely to occur particularly during deceleration. For this reason, even if the target total intake gas amount m _cref calculated as described above is used, if the target fresh air amount is small with respect to the cylinder intake EGR gas amount m _egrcyl , the EGR rate increases. There is a risk of misfire. Therefore, in the present embodiment, the minimum value of the target fresh air amount is limited using the fresh air lower limit value m _cmin calculated as in the following equation (1).
m _cmin = in-cylinder intake EGR gas amount m _egrcyl × (1−upper limit EGR rate) ÷ upper limit EGR rate (1)
Here, the EGR rate is (m _egrcyl / (fresh air amount + m _egrcyl )).

However, if the minimum value of the target fresh air amount is limited by the fresh air lower limit value m _cmin as described above, the torque cannot be controlled according to the target value (specifically, the torque will increase). is assumed. The reason is that the amount of fresh air is increased so as not to misfire. Therefore, in the present embodiment, when the minimum value of the target fresh air amount is limited using the fresh air lower limit value m _cmin (that is, when the target fresh air amount is smaller than the new air amount lower limit value m _cmin ). In this case, the upper limit value of the ignition timing control torque efficiency is set to a value equal to a value obtained by dividing the target fresh air amount before the restriction by the new air amount lower limit value m _cmin (EGR misfire shown in FIG. 2). Equivalent to setting an upper limit).

FIG. 3 is a flowchart showing a process performed by the torque realizing unit 36 in order to calculate the target throttle opening degree TA for realizing the target fresh air amount.
The processes in steps S1 and S2 in this flowchart are processes performed by the in-cylinder intake EGR gas amount calculation unit 56. In the first step S1, the EGR valve passage gas amount m _egr (t) in the current control cycle t is calculated. The EGR valve passage gas amount m _egr can be calculated based on the EGR valve opening degree and the intake manifold pressure (in manifold pressure). FIG. 4 is a diagram showing the relationship between the EGR valve passing gas amount m _egr and the intake manifold pressure P _m . The ECU 30 stores, as a map, a relationship that defines the EGR valve passage gas amount _megr and the intake manifold pressure as shown in FIG. 4 for each predetermined EGR valve opening. In step S1, an EGR valve passage gas amount m _egr (t) is calculated by referring to a map corresponding to the current EGR valve opening degree and inputting the previous value P _mrefo of the target intake manifold pressure.

Next, in step S2, in-cylinder intake EGR gas amount m _egrcyl (t) in the current control cycle t is calculated according to the following equation (2).
m _egrcyl (t) = m _egrcyl (t−Δt) + (m _egr (t−muda) −m _egrcyl (t−Δt)) / n (2)
However, in the above equation (2), Δt is a control cycle, muda is a dead time determined according to the engine operating state (engine speed, etc.), and n is the engine operating state (engine speed, etc.). The reflection rate is determined accordingly. More specifically, the dead time is the delay (transportation delay) time to changes in the EGR valve passing gas amount _{m egr} is reflected in the cylinder intake EGR gas amount _{m egrcyl.} Further, the gas that has passed through the EGR valve 28 during the transition does not simply flow into the cylinder at the same flow rate as when the EGR valve 28 passes, but diffuses into the fresh air in the intake passage 12 on the downstream side of the throttle valve 18. After that, it flows into the cylinder. The reflection rate is a value that determines the rate at which the gas that has passed through the EGR valve 28 flows into the cylinder due to the influence of such diffusion.

According to the above equation (2), the response delay of the EGR gas (more specifically, the transport delay of the gas that has passed through the EGR valve 28, and the fresh air in the intake passage 12 on the downstream side of the throttle valve 18) In consideration of the influence of EGR gas diffusion), the in-cylinder intake EGR gas amount m _egrcyl (t) to be inhaled in the course of a transition can be calculated.

The processing in steps S3 to S5 is processing performed by the target fresh air amount calculation unit 42. In step S3, the new air amount lower limit value m _cmin (t) in the current control cycle t is determined based on the in-cylinder intake EGR gas amount m _egrcyl (t) calculated in step S2 and a predetermined upper limit EGR rate (misfire occurs). And a value set in advance as the upper limit EGR rate that is not present) is calculated according to the above equation (1).

In step S4, it is determined whether or not the target fresh air amount calculated by the target fresh air amount calculation unit 42 is smaller than the new air amount lower limit m _cmin (t) calculated in step S3. As a result, when this determination is not established, the process directly proceeds to step S7. On the other hand, when this determination is satisfied, the fresh air lower limit value m _cmin (t) is used as the target fresh air amount (step S5). By such processing, the target fresh air amount is limited as necessary so as not to fall below the new air amount lower limit value m _cmin (t).

The process of step S6 is a process performed by the combustion guarantee guard unit 50. In step S6, the upper limit value of the ignition timing control torque efficiency is set to a value equal to the value obtained by dividing the target fresh air amount before replacement in step S5 by the new air amount lower limit value m _cmin (t).

The processing of steps S7 to S10 is processing performed by the throttle opening calculation unit 44. In step S7, the target total intake gas amount m _cref , which is the target value of the total gas amount sucked into the cylinder, is set to the target fresh air amount (if the determination in step S4 is satisfied, the new air amount lower limit value). m _cmin (t)) and the sum of in-cylinder intake EGR gas amount m _egrcyl .

Next, in step S8, the target intake manifold pressure P _mref is calculated from the target total intake gas amount m _cref . More specifically, an intake characteristic map (a _total , b) defining a relationship indicated by a solid line in FIG. 5B described later, that is, a relationship between the target total intake gas amount m _cref and the target intake manifold pressure P _{mref. The} target intake manifold pressure P _mref is calculated using a _total map).

Next, in step S9, in accordance with the following equation (3), the target intake manifold pressure _{P mref} and the target total intake gas amount _{m cref} and the target throttle valve from the EGR valve passing gas amount _{m egr} passing gas amount _{m t} is calculated .
_{m t = (P mref -P mrefo} ) / Δt × V m / κ / R / T m + m cref -m egr ··· (3)
However, in the above equation (3), P _mref is the previous value of the target intake manifold pressure, V _m is the internal volume of the intake passage 12 from the throttle valve 18 to the intake valve, κ is the specific heat ratio, and R is the gas constant. _Tm is the gas temperature in the intake passage 12, and here is a constant value approximated by the atmospheric temperature.

Next, in step S10, in accordance with the following equation (4), the target throttle opening degree TA is calculated from the target throttle valve passing gas amount m _{t.
^{TA = A t -1 × (μ}} × √ (R × T a) / P a / φ (P mref, P a)) ··· (4)
However, in the above (4), the opening area of _{A t} is the throttle valve 18, mu is the flow coefficient of the opening of the throttle valve 18, _{T a} is the ambient temperature, _{P a} is atmospheric pressure.

  FIG. 5 is a diagram for explaining the effect of the method of calculating the target throttle opening degree TA (calculating the target intake manifold pressure) in the first embodiment of the present invention in comparison with the conventional calculation method. More specifically, FIG. 5 (B) is a diagram corresponding to the calculation method of the present embodiment, and FIG. 5 (A) is a diagram corresponding to a conventional calculation method referred to for comparison.

A waveform indicated by a broken line in FIG. 5A (the same applies to FIG. 5B) is drawn into the cylinder using the in-cylinder intake EGR gas amount m _egrcyl (= EGR valve passing gas amount m _egr ) at the steady state. 3 shows “steady fresh air quantity characteristics” (so-called a and b maps) that define the relationship between the fresh air quantity to be generated and the intake manifold pressure (throttle downstream pressure). This relationship is determined by the engine speed, the valve timing of the intake and exhaust valves, and the EGR valve opening. On the other hand, the instantaneous fresh air amount characteristic at the time of transition varies depending on the in-cylinder intake EGR gas amount m _egrcyl at the time of transition, which is greatly different from that at the time of steady state. An example is shown in FIG. The waveform is shown by the dotted line. Therefore, when the target intake manifold pressure P _mref is calculated from the target fresh air amount using the broken line relationship in FIG. 5 (A), it is sucked into the cylinder as shown in FIG. 5 (A). It becomes difficult to control the fresh air amount to the target fresh air amount (in the example of FIG. 5A, the actual fresh air amount is smaller than the target fresh air amount).

On the other hand, the waveform indicated by the solid line in FIG. 5B shows the in-cylinder intake EGR gas amount (the amount of EGR gas sucked into the cylinder in the course) m _egrcyl taking into account the intake behavior (response delay of EGR gas). “Intake characteristics of intake valve passage gas” (a _total , b) defining the relationship between the target total intake gas amount (target intake valve passage gas amount) m _cref which is the sum of the fresh air amount and the target intake manifold pressure P _{mref total} map). This relationship is uniquely determined by the engine speed and the valve timing of the intake / exhaust valves, and hardly depends on the EGR gas amount.

In the calculation method of the present embodiment, as shown in FIG. 5 (B), the target intake manifold pressure P _mref is calculated from the target total intake gas amount m _cref using the relationship of the intake valve passing gas intake characteristics (solid line). Is done. In FIG. 5B, the difference between the solid line and the broken line for the intake gas amount corresponds to the EGR gas amount at the steady state. Further, the “difference from the steady state fresh air amount characteristic” in FIG. 5B differs from the steady state due to the effect of the fresh air amount calculated from the steady state fresh air amount characteristic and the response delay of the EGR gas. This is equivalent to the difference from the fresh air volume during the transition.

According to the calculation method of the present embodiment described above, by calculating the target intake manifold pressure P _mref from the target total intake gas amount m _cref , the influence of the response delay of the EGR gas at the time of transition is taken into account, and the target intake manifold pressure P _mref can be calculated. Then, the target throttle opening degree TA can be calculated based on the calculated target intake manifold pressure P _mref . As a result, even when the in-cylinder intake EGR gas amount m _egrcyl is in a transient state that is significantly different from the steady state, the target fresh air amount for realizing the target throttle opening degree TA can be accurately calculated.

Further, according to the process of the flowchart shown in FIG. 3, when the target fresh air amount is smaller than the fresh air amount lower limit m _cmin is fresh air amount lower limit m _cmin is set as the target fresh air amount. According to the above equation (1), the ratio of the target fresh air amount to the in-cylinder intake EGR gas amount m _egrcyl is not smaller than the ratio of the fresh air amount to the EGR gas amount under the upper limit EGR rate at which misfire does not occur. Thus, the minimum value of the target fresh air amount is limited. Thus, the target throttle opening degree TA is calculated based on the target total intake gas amount m _cref in consideration of the EGR gas amount (in-cylinder intake EGR gas amount m _egrcyl ) that is inhaled by the calculation method of the present embodiment described above. In this case, misfire can be suppressed well.

If the efficiency of the torque is considered to be substantially equal to the efficiency of the air amount, when to limit the minimum value of the target fresh air amount as described above in the fresh air amount lower limit m _cmin, the fresh air amount lower limit m _cmin The torque increases by the ratio obtained by dividing by the target fresh air volume before the limit (the increased fresh air volume to prevent misfire). According to the processing of the flowchart shown in FIG. 3, for the purpose of suppressing such torque increase, when the target fresh air amount is smaller than the fresh air lower limit value m _cmin , the upper limit value of ignition timing control torque efficiency. Is set to a value equal to the value obtained by dividing the target fresh air amount by the new air amount lower limit value m _cmin . Thus, by limiting the upper limit value of the ignition timing control torque efficiency (corresponding to the EGR misfire upper limit guard in FIG. 2), the target ignition timing is set so as to cancel the torque increase corresponding to the increase in the fresh air amount. Is set (retarded). Thus, the target throttle opening degree TA is calculated based on the target total intake gas amount m _cref in consideration of the EGR gas amount (in-cylinder intake EGR gas amount m _egrcyl ) that is inhaled by the calculation method of the present embodiment described above. In this case, misfire can be suppressed well while obtaining a target torque that satisfies the required torque and the required efficiency.

  In the first embodiment described above, the target fresh air amount calculation unit 42 calculates the target fresh air amount according to the required torque and the required efficiency, so that the “target fresh air amount calculating means” in the first aspect of the invention is When the in-cylinder intake EGR gas amount calculation unit 56 executes the processing of steps S1 and S2, the “in-cylinder intake EGR gas amount estimation means” in the first aspect of the invention is the throttle opening calculation unit 44 and the step S7 By executing the processes of steps S9 and S10, the “target throttle downstream pressure calculating means” in the first aspect of the invention is executed by the throttle opening calculation unit 44 executing the processes of steps S9 and S10. “Target throttle opening calculation means” is realized.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake passage 14 Exhaust passage 16 Air flow meter 18 Throttle valve 20 Fuel injection valve 22 Spark plug 24 Variable valve timing mechanism 26 EGR passage 28 EGR valve 30 ECU (Electronic Control Unit)
32 Crank angle sensor 34 A / F sensor 36 Torque realization unit 38 Combustion protection guard unit 40 New air amount control torque calculation unit 42 Target new air amount calculation unit 44 Throttle opening calculation unit 46 Estimated torque calculation unit 48 For ignition timing control Torque efficiency calculation unit 50 Combustion security guard unit 52 Ignition timing calculation unit 54 Combustion security guard unit 56 In-cylinder intake EGR gas amount calculation unit m _cmin fresh air amount lower limit m _cref target total intake gas amount (target intake valve passing gas amount)
m _egr EGR valve passage gas amount m _{egrcyl in-} cylinder intake EGR gas amount m _t target throttle valve passage gas amount P _mref target intake manifold pressure

Claims (2)

An EGR passage communicating the exhaust passage and the intake passage of the internal combustion engine;
An EGR valve responsible for opening and closing the EGR passage;
A throttle valve disposed in the intake passage;
A target fresh air amount calculating means for calculating a target fresh air amount of the fresh air sucked into the cylinder;
In-cylinder intake EGR gas amount estimation means for estimating the in-cylinder intake EGR gas amount in consideration of a response delay of in-cylinder intake EGR gas sucked into the cylinder with respect to a change in the EGR gas amount passing through the EGR valve When,
Defines the relationship between the target total intake gas amount that is the sum of the target fresh air amount and the in-cylinder intake EGR gas amount, and the throttle downstream pressure that is the pressure of the gas in the intake passage on the downstream side of the throttle valve. A target throttle downstream pressure calculating means for calculating a target throttle downstream pressure according to the relationship information;
Target throttle opening calculating means for calculating a target throttle opening required for realizing the target throttle downstream pressure;
A control device for an internal combustion engine, comprising:   2. The control apparatus for an internal combustion engine according to claim 1, wherein the target fresh air amount calculation means limits a minimum value of the target fresh air amount so that misfire does not occur.

Images