JP2006200460A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine inhibiting a torque variation on changing of an air-fuel ratio by suitably controlling an injector for injecting fuel into a cylinder. <P>SOLUTION: A cylinder oxygen amount mo2 is estimated according to an engine operation state and a fuel injection parameter Q* is calculated according to the in-cylinder oxygen amount mo2. Fuel injection by the injector is controlled according to the fuel injection parameter Q*. When the air-fuel ratio is changed from a lean air-fuel ratio to a rich air-fuel ratio or when it is changed vice versa, the fuel injection parameter Q* in the transition of the air-fuel ratio is set to smoothly change according to an objective fuel injection parameter Q*tgt and an objective in-cylinder oxygen amount mo2tgt after the change of the air-fuel ratio and to an initial fuel injection parameter Q*ini and an initial in-cylinder oxygen amount mo2ini before the change (S97-S99). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for an internal combustion engine provided with an exhaust gas recirculation device that recirculates a part of exhaust gas to an intake system, and more particularly to a device that controls fuel injection by an injector.

  Patent Document 1 discloses a lean NOx that absorbs NOx in exhaust gas when performing a lean burn operation in which the air-fuel ratio of an air-fuel mixture combusted in an internal combustion engine is set to a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio. An exhaust gas purification device with a catalyst is shown. In this apparatus, if the lean burn operation is continued, the amount of NOx absorbed by the lean NOx catalyst increases. Therefore, before the NOx amount exceeds the allowable limit, the air / fuel ratio is made richer than the stoichiometric air / fuel ratio, thereby reducing the lean NOx. Reduction of NOx absorbed by the catalyst is performed. Such enrichment of the air-fuel ratio is hereinafter referred to as “NOx reduction enrichment”.

Japanese Patent No. 2600492

  In the apparatus disclosed in Patent Document 1, when performing NOx reduction enrichment, the air-fuel ratio is first switched stepwise from the lean air-fuel ratio to the rich air-fuel ratio, and when the NOx reduction is completed, the rich air-fuel ratio is changed. The air-fuel ratio is returned stepwise from the fuel ratio. Therefore, there has been a problem that the engine output torque fluctuates when the air-fuel ratio is switched.

  The present invention has been made paying attention to this point, and provides a control device for an internal combustion engine capable of appropriately controlling an injector that injects fuel into a cylinder at the time of air-fuel ratio switching and suppressing torque fluctuations. The purpose is to do.

  In order to achieve the above object, according to the first aspect of the present invention, air is sucked into the cylinder (3a) through the intake system (4), and the fuel injected from the injector (6) is put into the cylinder (3a). In the control device for an internal combustion engine that supplies and recirculates a part of the exhaust gas discharged from the internal combustion engine (3) to the intake system (4) as recirculated exhaust gas by the exhaust gas recirculation device (14), the intake system (4) Intake air amount control means (2, 7) for controlling the amount of intake air sucked into the cylinder (3a) via the intake air amount detection means (27) for detecting the intake air amount (Fa), Based on the recirculated exhaust gas flow rate estimating means for estimating the flow rate (Fe) of the recirculated exhaust gas from the exhaust gas recirculation device (14), the detected intake air amount (Fa), and the estimated recirculated exhaust gas flow rate (Fe). In the cylinder In-cylinder oxygen amount estimating means (2) for estimating the amount of oxygen present (mo2), rotation speed detecting means (22) for detecting the rotation speed (Ne) of the internal combustion engine, and the detected rotation of the internal combustion engine A fuel injection parameter determination means (2) for determining a fuel injection parameter (Q *) based on the number (Ne) and the estimated in-cylinder oxygen amount (mo2); and the determined fuel injection parameter (Q *) Based on the injector control means (2) for controlling the injector (6) and switching the air-fuel ratio of the air-fuel mixture combusting in the cylinder from the lean air-fuel ratio to the rich air-fuel ratio, or from the rich air-fuel ratio. Switching command means (2) for instructing switching to a lean air-fuel ratio, and the fuel injection parameter determining means, when commanded to switch the air-fuel ratio by the switching command means, According to the in-cylinder oxygen amount (mo2ini), and switching the target cylinder oxygen amount of 換後 and (mo2tgt), and determines to smoothly change the fuel injection parameter (Q *).

  Specifically, the fuel injection parameter determining means is configured to switch a command for a difference (| mo2ini−mo2tgt |) between the estimated in-cylinder oxygen amount (mo2ini) before switching and the target cylinder oxygen amount (mo2tgt) after switching. Ratio calculation means for calculating the ratio (| mo2v−mo2ini |) of the estimated change in oxygen amount (| mo2v−mo2ini |) later, and a ratio parameter (Q * ratio) that increases as the ratio (Oxyratio) increases. Ratio parameter setting means for setting the fuel injection parameter value before switching (Q * ini), the target value (Q * tgt) of the fuel injection parameter after switching, and the ratio parameter (Q *) The fuel injection parameter (Q *) is preferably determined using the ratio).

  When the air-fuel ratio is switched from a lean air-fuel ratio to a rich air-fuel ratio, the ratio parameter setting means has a change rate (dQ * ratio / dOxyratio) of the ratio parameter (Q * ratio) with respect to a change in the ratio (Oxyratio). When the ratio parameter (Q * ratio) is set so that the ratio (Oxyratio) increases gradually as the ratio (Oxyratio) increases, and the air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio, the rate of change (dQ * It is desirable to set the ratio parameter (Q * ratio) so that ratio / dOxyratio) gradually decreases as the ratio (Oxyratio) increases.

  The ratio parameter setting means preferably corrects the ratio parameter (Q * ratio) according to the lean air-fuel ratio. Specifically, when the air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio, the ratio parameter (Q * ratio) is corrected so as to decrease as the lean air-fuel ratio decreases, and the air-fuel ratio is adjusted to the rich air-fuel ratio. When switching from an air-fuel ratio to a lean air-fuel ratio, it is desirable to correct so that the ratio parameter (Q * ratio) decreases as the lean air-fuel ratio decreases.

  According to the first aspect of the present invention, when it is instructed to switch the air-fuel ratio from the lean air-fuel ratio to the rich air-fuel ratio or from the rich air-fuel ratio to the lean air-fuel ratio, the estimated in-cylinder oxygen before switching is instructed. Since the fuel injection parameter is determined so as to change smoothly according to the amount and the target cylinder oxygen amount after switching, torque shock at the time of air-fuel ratio switching can be suppressed.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
An internal combustion engine (hereinafter referred to as “engine”) 3 shown in FIG. 1 is a diesel engine of, for example, four cylinders (only one is shown) mounted on a vehicle (not shown). A combustion chamber 3d is formed between the piston 3b and the cylinder head 3c of each cylinder 3a. An intake pipe 4 (intake system) and an exhaust pipe 5 are connected to the combustion chamber 3d, and an intake valve and an exhaust valve (both not shown) are provided in the intake port and the exhaust port, respectively. Yes. A fuel injection valve (hereinafter referred to as “injector”) 6 and an in-cylinder pressure sensor 21 are attached to the cylinder head 3c so as to face the combustion chamber 3d.

  The injector 6 is disposed at the center of the cylinder head 3c and is connected to a high-pressure pump (both not shown) via a common rail. Fuel in a fuel tank (not shown) is boosted by a high-pressure pump, then sent to the injector 6 through the common rail, and injected from the injector 6 into the combustion chamber 3d. The injection pressure Pe, injection time (valve opening time) De, and injection timing (valve opening timing) TMe of the injector 6 are controlled by control signals from an electronic control unit (hereinafter referred to as “ECU”) 2 shown in FIG. . In the following description, FIG. 2 is also referred to.

  The in-cylinder pressure sensor 21 (combustion state detection means) is, for example, of the piezoelectric element type, and a piezoelectric element (not shown) is provided in accordance with a change in pressure (hereinafter referred to as “in-cylinder pressure”) P in the combustion chamber 3d. By displacing, a detection signal indicating the change amount ΔP of the in-cylinder pressure P is output to the ECU 2. The ECU 2 obtains the in-cylinder pressure P by integrating this detection signal.

  A magnet row 22a is attached to the crankshaft 3e of the engine 3. The magnet rotor 22a and the MRE pickup 22b constitute a crank angle sensor 22 (rotational speed detection means). The crank angle sensor 22 outputs a CRK signal and a TDC signal, which are pulse signals, to the ECU 2 as the crankshaft 3e rotates.

  The CRK signal is output every predetermined crank angle (for example, 30 degrees). The ECU 2 obtains the rotational speed Ne (hereinafter referred to as “engine rotational speed”) Ne of the engine 3 based on the CRK signal. The TDC signal is a signal indicating that the piston 3b of each cylinder is at a predetermined crank angle position near the TDC (top dead center) at the start of the intake stroke, and in this example of the four-cylinder type, every crank angle of 180 degrees. Is output.

  A throttle valve 7 (intake amount control means) is provided on the upstream side of the intake manifold 4a of the intake pipe 4 and an actuator 8 for driving the throttle valve 7 is connected to the throttle valve 7. The actuator 8 is composed of a motor, a gear mechanism (not shown) or the like, and the operation of the actuator 8 is controlled by a control signal from the ECU 2 so that the opening of the throttle valve 7 (hereinafter referred to as “throttle valve opening”). TH) changes, and the amount of intake air taken into the combustion chamber 3d is controlled accordingly. The throttle valve opening TH is detected by a throttle valve opening sensor 23, and the detection signal is output to the ECU 2.

  The intake manifold 4a is provided with an intake pressure sensor 24 and an intake air temperature sensor 25. The intake pressure sensor 24 detects the pressure in the intake manifold 4a (hereinafter referred to as “in manifold pressure”) Pi, and the intake air temperature sensor 25 includes a thermistor and the like, and the temperature in the intake manifold 4a (hereinafter referred to as “in manifold temperature”). ) Ts is detected, and those detection signals are output to the ECU 2. An engine water temperature sensor 26 is attached to the main body of the engine 3. The engine water temperature sensor 26 is composed of a thermistor or the like, detects the temperature (hereinafter referred to as “engine water temperature”) Tw of the coolant circulating in the main body of the engine 3, and outputs a detection signal to the ECU 2.

  The intake pipe 4 is provided with a supercharging device 9. The supercharger 9 includes an evening charger-type supercharger 10, an actuator 11 connected thereto, and a vane opening control valve 12. The supercharger 10 includes a rotatable compressor blade 10a provided upstream of the throttle valve 7 of the intake pipe 4, a turbine blade 10b provided in the middle of the exhaust pipe 5, and a plurality of rotatable variable vanes. 10c (only two are shown) and a shaft 10d for integrally connecting these blades 10a and 10b. The supercharger 10 performs a supercharging operation by rotating the compressor blade 10a integrally therewith as the turbine blade 10b is rotationally driven by the exhaust gas in the exhaust pipe 5.

  Each variable vane 10 c is connected to the actuator 11, and its opening degree (hereinafter referred to as “vane opening degree”) VO is controlled via the actuator 11. The actuator 11 is of a diaphragm type that operates by negative pressure, and is connected to a negative pressure pump (not shown), and the vane opening control valve 12 is provided in the middle thereof. The negative pressure pump operates using the engine 3 as a power source and supplies the generated negative pressure to the actuator 11. The vane opening degree control valve 12 is configured by an electromagnetic valve, and the negative pressure supplied to the actuator 11 changes when the valve opening degree is controlled by a control signal from the ECU 2. The supercharging pressure is controlled by changing the vane opening VO of the engine 10c.

An air flow sensor 27 (intake air amount detection means) is provided upstream of the supercharger 10 in the intake pipe 4. The air flow sensor 27 detects the intake air amount Fa flowing in the intake pipe 4 and outputs a detection signal to the ECU 2.
Further, the intake manifold 4a of the intake pipe 4 is divided into a swirl passage 4b and a bypass passage 4c from the collecting portion to the branch portion. The bypass passage 4c is provided with a swirl device 13 for generating a swirl in the combustion chamber 3d. The swirl device 13 includes a swirl valve 13a, an actuator 13b for driving the swirl valve 13a, and a swirl control valve 13c. The actuator 13b and the swirl control valve 13c are respectively configured similarly to the actuator 11 and the vane opening control valve 12 of the supercharging device 9, and the swirl control valve 13c is connected to the negative pressure pump. With the above configuration, when the valve opening degree of the swirl control valve 13c is controlled by the control signal from the ECU 2, the negative pressure supplied to the actuator 13b changes, and the opening degree SVO of the swirl valve 13a changes. The strength of the swirl is controlled.

  Further, an exhaust gas recirculation pipe (hereinafter referred to as “EGR pipe”) 14a is connected between the portion of the collecting portion of the swirl passage 4b of the intake manifold 4a and the downstream side of the oxidation catalyst 15 described later of the exhaust pipe 5. The EGR pipe 14a and the exhaust gas recirculation control valve (hereinafter referred to as “EGR control valve”) 14b provided in the middle thereof constitute an exhaust gas recirculation device (hereinafter referred to as “EGR device”) 14. A part of the exhaust gas from the engine 3 is recirculated to the intake pipe 4 as recirculated exhaust gas through the EGR pipe 14a. The EGR control valve 14b is composed of a linear electromagnetic valve, and its opening degree (hereinafter referred to as “EGR valve opening degree”) LE is controlled in accordance with a control signal from the ECU 2, whereby the recirculated exhaust gas flow rate Fe is reduced. Be controlled. The EGR valve opening degree LE is detected by the EGR valve opening degree sensor 28, and the detection signal is output to the ECU 2.

  Further, an oxidation catalyst 15 and a NOx absorption catalyst 16 are provided in order from the upstream side of the exhaust pipe 5 on the downstream side of the supercharger 10. The oxidation catalyst 15 oxidizes HC and CO in the exhaust gas and purifies the exhaust gas. Further, the NOx absorption catalyst 16 absorbs NOx in the exhaust gas in a lean oxidizing atmosphere and reduces the absorbed NOx in a rich reducing atmosphere.

  Further, an oxygen concentration sensor 29 is provided between the supercharger 10 and the oxidation catalyst 15 in the exhaust pipe 5. The oxygen concentration sensor 29 linearly detects the oxygen concentration λ in the exhaust gas and outputs the detection signal to the ECU 2. The ECU 2 calculates the air-fuel ratio A / F of the gas burned in the combustion chamber 3d based on the oxygen concentration λ. The ECU 2 further detects from the accelerator opening sensor 30 (accelerator depression amount detection means) the depression amount (hereinafter referred to as “accelerator opening”) AP of the accelerator pedal (not shown) of the vehicle driven by the engine 3. A signal is output.

  In this embodiment, the ECU 2 includes an intake air amount control means, a recirculated exhaust gas flow rate estimation means, an in-cylinder oxygen amount estimation means, a rotation speed detection means, a fuel injection parameter determination means, an injector control means, a switching command means, a ratio calculation means, And ratio parameter setting means. The ECU 2 is composed of a microcomputer including an I / O interface, CPU, RAM, ROM, and the like, and according to the detection signals from the various sensors 21 to 30 described above, various types of ECU 2 are performed according to a control program stored in the ROM. Perform arithmetic processing. Specifically, the operating state of the engine 3 is determined from the detection signal, and the combustion mode of the engine 3 is determined based on the determination result, and the throttle valve opening TH is determined according to the determined combustion mode. Thus, the intake air amount is controlled, and the fuel injection by the injector 6 is controlled.

  The combustion mode of the engine 3 is roughly divided into a low temperature combustion mode and a normal combustion mode other than that. The low-temperature combustion mode is executed in a low load region after the warm-up of the engine 3 is finished. On the other hand, the normal combustion mode is executed in a higher load region. In both combustion modes, a lean operation in which the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio is normally performed, and NOx absorbed by the NOx absorption catalyst 16 is reduced or attached to the NOx absorption catalyst 16. In order to desorb the sulfur in the fuel, a rich operation for making the air-fuel ratio richer than the stoichiometric air-fuel ratio is appropriately performed. In the low-temperature combustion mode, fuel injection control (hereinafter referred to as “O2 reference LTC control”) mainly based on the in-cylinder oxygen amount and the engine speed Ne described below is executed, and in the normal combustion mode, the throttle valve opening TH and EGR are controlled. On the low load side where the intake air amount can be controlled by changing the valve opening LE, fuel injection control (hereinafter referred to as “O2 standard STD control”) based mainly on the in-cylinder oxygen amount and the engine speed Ne is executed, and the throttle Fuel injection control (hereinafter referred to as “pedal reference STD control”) based on the accelerator opening AP and the engine speed Ne is executed on the high load side where the valve 7 is fully opened and the EGR control valve 14b is fully closed.

  Hereinafter, the process performed by ECU2 is demonstrated. The ECU 2 searches the A * map shown in FIG. 3 according to the engine speed Ne and the accelerator pedal opening AP, and determines the air conditioning parameter A *. The air adjustment parameter A * is a vector whose elements are the target throttle valve opening THR, the target EGR valve opening LER, the target vane opening VOR, and the target swirl valve opening SVOR. A grid point at addresses i and j on the A * map includes a target throttle valve opening degree THR, a target EGR valve opening degree LER, a target vane opening degree VOR and a target that are suitable for the corresponding engine speed Ne and accelerator opening degree AP. A swirl valve opening SVO is set. Then, the ECU 2 drives the corresponding actuator so that the actual throttle valve opening TH, EGR valve opening LE, vane opening VO, and swirl valve opening SVO become the target opening retrieved from the A * map. To do. Thus, the intake air amount, the recirculated exhaust gas flow rate, the supercharging pressure, and the swirl are controlled in accordance with the engine speed Ne and the accelerator pedal opening AP.

  The A * map is provided corresponding to each of the above-described O2 reference LTC control, O2 reference STD control, and pedal reference STD control, and for each of these controls, a normal lean operation map, PM (Particulate Matter) An oxidation map, a NOx reduction map, and a sulfur desorption map are set. The set air-fuel ratio when using the normal lean operation map, PM oxidation map, NOx reduction map, and sulfur desorption map are A / FLN, A / FLP, A / FRN, and A / FRS, respectively. A / FLN> A / FLP> A / FRS> A / FRN is established.

  Next, fuel injection control by the ECU 2 will be described. FIG. 4 shows a calculation process of the in-cylinder state parameter [O2] used for the O2 reference LTC control and the O2 reference STD control. This in-cylinder state parameter [O2] represents the state in the cylinder 3a immediately before fuel injection, and is a total of three parameters: the in-cylinder oxygen amount mo2, the in-cylinder inert gas amount mint, and the actual intake manifold temperature Ti. Composed. The in-cylinder oxygen amount mo2 represents the amount of oxygen existing in the cylinder 3a before fuel injection, and the in-cylinder inert gas amount mint is an inert gas (oxygen) present in the cylinder 3a before fuel injection. The actual intake manifold temperature Ti represents the actual temperature of the intake manifold 4a. Of these, the in-cylinder oxygen amount mo2 is a main parameter that has a major influence on combustion. On the other hand, the in-cylinder inert gas amount mint and the actual intake manifold temperature Ti are sub-parameters that complement the in-cylinder oxygen amount mo2, and in the steady state of the engine 3, are almost uniquely determined according to the in-cylinder oxygen amount mo2. At the same time, in the transient state, it is used to correct the in-cylinder oxygen amount mo2 as described later.

In this process, first, the actual intake manifold temperature Ti is calculated by the following equation (1) from the intake manifold temperature Ts detected by the intake air temperature sensor 25 (step 31).
Ti = Ts (τo · s + 1) (1)
Where τo: intake air temperature sensor time constant
s: Laplace transform operator By such calculation, the actual intake manifold temperature Ti can be correctly estimated in real time while compensating for the response delay based on the detection result of the intake air temperature sensor 25.

  Next, the cylinder oxygen amount mo2 is calculated by estimation (step 32). This calculation is based on the intake air amount Fa detected by the airflow sensor 27, the intake manifold pressure Pi detected by the intake pressure sensor 24, and the actual intake manifold temperature Ti estimated in step 31, and using an EGR model to be described later. The following procedure is performed.

A. B. Estimation of EGR rate Ri Estimation of cylinder oxygen amount mo2 Estimation of EGR Rate Ri The basic equation of the EGR rate Ri is given by the following equation (2).
Ri = Fe_hat / Fi (2)
Here, Fi is the total gas flow rate flowing into the cylinder, Fe_hat is a predicted value of the recirculation exhaust gas flow rate (estimated recirculation exhaust gas flow rate) flowing into the cylinder 3a, and EGR in a transient state between the lean operation and the rich operation. It is obtained in consideration of the response delay of the device 14.

The total gas flow Fi in the equation (2) is calculated by the following equation (3) from a well-known speed density equation.
Fi = Ne · Vd · Pi · ηv / (60 × 2R · Ti) (3)
Where Ne: engine speed (rpm)
Vd: Engine displacement
Pi: In manifold pressure
ηv: Volumetric efficiency of the engine
R: Gas constant
Ti: Intake manifold temperature Note that the volume efficiency ηv is obtained, for example, from a map set in advance based on the experimental result, in accordance with the engine speed Ne and the intake manifold pressure Pi, and the obtained map value is obtained from the actual intake manifold. It is calculated | required by correct | amending according to temperature Ti.

On the other hand, when the ideal gas law is applied to the intake manifold 4a under a constant temperature condition, the following equation (4) is established between the recirculated exhaust gas flow rate Fe, the intake air amount Fa, and the total gas flow rate Fi. A relationship is established.
dPi / dt = (R · Ti / Vi) · (Fe + Fa−Fi) (4)
When Vi: intake manifold volume equation (4) is solved for the recirculated exhaust gas flow rate Fe, the following equation (5) is obtained.
Fe = (dPi / dt) · Vi / (R · Ti) −Fa + Fi (5)

Further, when the Laplace transform operator s is introduced (dPi / dt = sPi) and the equation (5) is rewritten, the following equation (6) is obtained.
Fe = s · Pi · Vi / (R · Ti) −Fa + Fi (6)
On the other hand, the predicted value Fe_hat of the recirculated exhaust gas flow rate is expressed by the following equation (7) in consideration of the first-order lag of the response of the EGR device 14.
Fe_hat = (1 / (τs + 1)) · Fe (7)

Therefore, the predicted value Fe_hat of the recirculated exhaust gas flow rate is obtained from both equations (6) and (7) as in the following equation (8).
Fe_hat = (s · Pi / (τs + 1)) (Vi / (R · Ti))
− (1 / (τs + 1)) · Fa + (1 / (τs + 1)) · Fi
(8)
Here, s · Pi / (τs + 1) is an approximate value of dPi / dt using the numerical difference filter s / (τs + 1), and the time constant τ is determined based on experimental results.

Therefore, by substituting the total gas flow rate Fi calculated by the equation (3) and the predicted value Fe_hat of the recirculated exhaust gas flow rate in the transient state calculated by the equation (8) into the equation (2), the EGR in the transient state is obtained. The rate Ri can be calculated.
In the steady state, the following equation (9) holds, so
Fe_hat = Fe = Fi-Fa (9)
From the equations (9) and (2), the EGR rate Ri in the steady state is calculated by the following equation (10).
Ri = (Fi−Fa) / Fi (10)

B. Estimation of In-Cylinder Oxygen Mo2 Next, the in-cylinder oxygen amount mo2 is estimated based on the total gas flow rate Fi and the EGR rate Ri obtained as described above.

The basic equation of the cylinder oxygen amount mo2 is given by the following equation (11).
mo2 = ma × φ (O2) a + me × φ (O2) e (11)
Where ma is the amount of air flowing into the cylinder in each combustion cycle
me: Amount of recirculated exhaust gas flowing into the cylinder in each combustion cycle
φ (O2) a: oxygen concentration in air (constant)
φ (O2) e: Oxygen concentration in the recirculated exhaust gas The air amount ma and the recirculated exhaust gas amount me in the equation (11) are calculated from the total gas flow rate Fi and the EGR rate Ri by the following equations (12) and (13), respectively. .
ma = (Fi × (1-Ri) × 60 × 2) / (Ne × ncyl) (12)
me = (Fi × Ri × 60 × 2) / (Ne × ncyl) (13)
Where ncyl: number of engine cylinders

ここで、ｉは燃焼サイクルを表す添え字であり（累乗を意味するものではない）、ａ0，ａ1，ａ2，…ａnは、実験結果に基づき、エンジン３の運転状態および排気マニホルドの容積によって決定される重み係数である。 Further, the oxygen concentration φ (O2) e in the recirculated exhaust gas can be calculated by the following equation (14) in consideration of the response delay of the EGR device 14.

Here, i is a subscript representing the combustion cycle (not meaning a power), and a0, a1, a2,..., An are determined by the operating state of the engine 3 and the volume of the exhaust manifold based on the experimental results. Weighting factor.

ここで、ｍf は気筒に噴射される燃料量、Ｌstは、燃料のタイプに応じて決定される理論空燃比である。すなわち、式（１５）中のｍf×Ｌst×φ(Ｏ２)a は、リーン運転において噴射燃料量ｍf の完全燃焼により消費される酸素量に相当する。なお、式（１４）（１５）によれば、還流排ガス中の酸素濃度φ(Ｏ２)e を算出するには、排ガス中の酸素濃度φ(Ｏ２)exh の初期値が必要である。このφ(Ｏ２)exh の初期値は、例えば、エンジン３の始動直後にＥＧＲ動作を停止するという条件が設定されている場合には、φ(Ｏ２)e ＝０であることから、そのときの吸入空気量Ｆａおよび燃料噴射量ｍf などに応じ、式（１４）などを用いて求めることができる。 Φ (O2) exh is the oxygen concentration in the exhaust gas, and is calculated by the following equation (15) in the lean operation.

Here, mf is the amount of fuel injected into the cylinder, and Lst is the stoichiometric air-fuel ratio determined according to the type of fuel. That is, mf × Lst × φ (O2) a in the equation (15) corresponds to the amount of oxygen consumed by complete combustion of the injected fuel amount mf in the lean operation. According to the equations (14) and (15), in order to calculate the oxygen concentration φ (O2) e in the recirculated exhaust gas, the initial value of the oxygen concentration φ (O2) exh in the exhaust gas is required. The initial value of φ (O2) exh is, for example, φ (O2) e = 0 when the condition that the EGR operation is stopped immediately after the start of the engine 3 is set. Depending on the intake air amount Fa, the fuel injection amount mf and the like, it can be obtained using the equation (14).

  Therefore, the oxygen concentration φ (O2) e in the recirculated exhaust gas calculated by the equation (14), the air amount ma and the recirculated exhaust gas amount me calculated by the equations (12) and (13) are substituted into the equation (11). Thus, the in-cylinder oxygen amount mo2 in the lean operation can be calculated. Further, in the rich operation, since the in-cylinder oxygen is completely consumed by the combustion, φ (O2) exh = 0, so that by substituting this into the equation (14), the oxygen concentration φ in the recirculated exhaust gas (O2) e is obtained, and the in-cylinder oxygen amount mo2 can be calculated.

Returning to FIG. 4, in step 33 following step 32, an in-cylinder inert gas amount mint is calculated. As described above, since the in-cylinder inert gas is a gas other than oxygen among the gases present in the cylinder 3a, the in-cylinder inert gas amount mint is the in-cylinder oxygen amount mo2 obtained in step 32. Is calculated by the following equation (16).
mint = (ma + me) -mo2 (16)

  Next, the in-cylinder state parameter [O2] is determined by setting the actual intake manifold temperature Ti, the in-cylinder oxygen amount mo2 and the in-cylinder inert gas amount mint estimated in steps 31 to 33, respectively (step 34), and the present process. Exit.

  As is apparent from the above, in the calculation process of the in-cylinder state parameter [O2], the intake air amount Fa detected by the airflow sensor 27, the intake manifold pressure Pi detected by the intake pressure sensor 24, and the intake air temperature sensor 25 are detected. The in-cylinder oxygen amount mo2, the in-cylinder inert gas amount mint, and the actual intake manifold temperature Ti are estimated in all operating states including a transient state using the intake manifold temperature Ts and the EGR model. Then, with these three parameters as one set, an in-cylinder state parameter [O2] representing a state in the cylinder 3a immediately before fuel injection is determined. Since the in-cylinder state parameter [O2] represents the state in the cylinder 3a immediately before fuel injection as described above, the engine water temperature Tw may be included in this.

  FIG. 5 shows the Q * i, j map setting process. This Q * i, j map defines the optimum fuel injection parameter Q * i, j for the in-cylinder state parameter [O2] and the engine speed Ne in a steady state. The fuel injection parameter Q * i, j is composed of a total of three control parameters: the injection pressure Pe of the injector 6, the injection time De, and the injection timing TMe. The subscript i indicates the address of the engine speed Ne and the subscript j. Represents the address of the in-cylinder state parameter [O2]. This setting process is executed in advance in a bench test (benchmark test).

  In this process, first, the fuel injection parameter Q *, that is, the injection pressure Pe, the injection time Te, is controlled while the accelerator opening AP, the opening of the vane opening control valve 12, the EGR valve opening LE, and the like are controlled to certain values. Then, the injection timing TMe is tuned (adjusted) (step 41). Next, in this state, it is determined whether or not the combustion state has become optimal (step 42). This determination is performed based on one appropriate predetermined criterion, for example, a criterion such as a minimum NOx emission amount (NOx best), a best fuel consumption (fuel consumption best), or a maximum output (output best). Alternatively, determination may be made for each of the plurality of criteria, and the fuel injection parameter Q * may be set.

  When the answer to step 42 is YES and the combustion state becomes optimum, the fuel injection parameter Q * at that time is assigned to the addresses i and j corresponding to the engine speed Ne and the in-cylinder state parameter [O2] at that time. Is assigned (step 43). Thereby, one fuel injection parameter Q * i, j is determined. Next, it is determined whether or not the assignment of the fuel injection parameter Q * has been completed for all addresses i and j of the Ne value and the [O2] value (step 44). When the answer is NO, the steps 41 to 43 are repeated, and when the answer is YES, the process is terminated. As a result, a Q * i, j map as shown in FIG. 6 is obtained, and the fuel injection parameter Q * i for all addresses i, j corresponding to the engine speed Ne and the in-cylinder state parameter [O2]. , j is assigned.

  Accordingly, if the engine speed Ne and the in-cylinder state parameter [O2] are obtained in the steady state of the engine 3, the fuel injection parameters Q * i, j corresponding to the addresses i, j are represented in the Q * i, j map. By reading from, it is possible to uniquely determine the optimum fuel injection parameter Q * for the state of the combustion chamber 3d at that time, that is, the injection pressure Pe, the injection time Te, and the injection timing TMe. When the fuel injection parameter Q * i, j is determined, the torque T of the engine 3 obtained at that time is also uniquely determined using the address i, j as a function. The determined torque Ti, j is Ti , j map (not shown).

  The Q * i, j map and Ti, j map are set separately for lean operation and rich operation. As the lean operation map, a normal lean operation map and a PM (Particulate Matter) oxidation map are provided, and as the rich operation map, a NOx reduction map and a sulfur desorption map are provided. The set air-fuel ratio when using the normal lean operation map, PM oxidation map, NOx reduction map, and sulfur desorption map are A / FLN, A / FLP, A / FRN, and A / FRS, respectively. A / FLN> A / FLP> A / FRS> A / FRN is established.

Further, in the engine control of the present embodiment, all control parameters including the fuel injection parameter Q * and the torque T are set based on the addresses i and j.
The above Q * i, j map is set on the assumption that the engine 3 is in a steady state. This is because, in a steady state, the in-cylinder inert gas amount mint and the actual intake manifold temperature Ti are determined almost uniquely with respect to a certain cylinder oxygen amount mo2, and the relationship between the three components can be regarded as substantially constant. This is because the optimum fuel injection parameter Q * is also uniquely determined for the state of the combustion chamber 3d represented by these three parties. However, in the transient state, the relationship between the three is shifted from the steady state. For example, even if the in-cylinder oxygen amount mo2 is the same, the in-cylinder inert gas amount mint and the actual intake manifold temperature Ti are not in the steady state. Since the values are different, the combustion state changes accordingly. For this reason, in the transient state, the optimum fuel injection parameter Q * cannot be obtained only by referring to the Q * i, j map.

From the above viewpoint, in order to quantitatively compensate for the influence of the deviation of the in-cylinder inert gas amount mint and the actual intake manifold temperature Ti on the combustion in the transient state, the correction function f (α , Β) i, j is introduced.
f (α, β) i, j = (mint / mints) ^{−αi, j} × (Ti / Tis) ^{βi , j} (17)
This correction function f (α, β) i, j is obtained by changing the actual in-cylinder oxygen amount mo2 in the transient state to the in-cylinder oxygen amount (hereinafter ““ It is used to convert to mo2v (referred to as “virtual cylinder oxygen amount”).
mo2v = mo2 × f (α, β) i, j (18)

In the equation (17), mints and Tis are the in-cylinder inert gas amount and the actual intake manifold temperature in the steady state, respectively. Further, mint and Ti in the equation are the actual in-cylinder inert gas amount and the actual intake manifold temperature in the transient state calculated by the above-described method, respectively. That is, the first term (mint / mints) ^{-αi, j} in the ^equation represents the degree of influence on combustion due to the displacement of the in-cylinder inert gas amount, and the second term (Ti / Tis) ^{βi, j} is This represents the degree of influence on combustion due to the intake manifold temperature difference. Αi, j and βi, j are correction variables for defining the degree of influence. For this reason, the correction variable α is set to the value 0 in the operating state in which the EGR device 14 is stopped and it is considered that there is no influence of the in-cylinder inert gas amount.

  FIG. 7 shows a process for setting correction variables αi, j, βi, j. This process is executed in advance in the bench test in the same manner as the Q * i, j map setting process described above. In this process, first, the opening degree of the vane opening degree control valve 12 and / or the EGR valve opening degree LE is changed from a steady state in which the engine 3 is operated at a constant engine speed Ne and in-cylinder state parameter [O2]. By doing so, only the in-cylinder inert gas amount mint is offset (a small amount is changed) (step 61). Next, in this offset state, it is determined whether or not the combustion state has become optimal while tuning the fuel injection parameter Q * (step 62). This determination is made based on the same standard as the above-described standard used for setting the Q * i, j map.

  When the answer to step 62 is YES, the combustion state in the steady state closest to the combustion state at that time is selected as the virtual combustion state from the Q * i, j map (step 63). For this selection, for example, an approximate function of the heat generation rate at each address i, j on the Q * i, j map is obtained in advance, and the address i at that time corresponds to the engine speed Ne before the offset. This is done by specifying an address j having an approximate function value closest to the heat release rate. When the addresses i and j are specified in this manner, the in-cylinder state parameter [O2] is also specified, and the in-cylinder oxygen amount mo2 is obtained as the virtual cylinder oxygen amount mo2v.

Next, a correction variable α is calculated (step 64). This calculation is performed as follows. That is, in step 63, the virtual cylinder oxygen amount mo2v is obtained, and the cylinder oxygen amount mo2 is calculated from Equation (11) at any time. Therefore, from these mo2v value, mo2 value and Equation (18), The correction function f (α, β) i, j is obtained by the equation (19).
f (α, β) i, j = mo2v / mo2 (19)

On the other hand, the in-cylinder inert gas amount mint in the equation (17) is calculated at any time by the equation (16), and the in-cylinder inert gas amount mints in the steady state is known from the address j before the offset, Ti / Tis is equal to the value 1 because the actual intake manifold temperature Ti is not offset. Therefore, the following equation (20) is established, and the correction variable α can be calculated from the equations (20) and (19).
f (α, β) i, j = (mint / mints) ^{−αi, j} (20)

  Subsequently, in order to calculate the correction variable β, only the actual intake manifold temperature Ti is offset by changing the opening degree of the vane opening degree control valve 12 and / or the EGR valve opening degree LE from the steady state (step) 65). Thereafter, similarly to steps 62 to 64, it is determined whether or not the combustion state has become optimum (step 66), and the steady state combustion state closest to the optimum combustion state is selected as the virtual combustion state (step 67). ) And a correction variable β is calculated from the selected virtual combustion state and equations (17) and (18) (step 68). As described above, the correction functions α and β are set for one address i and j. Next, it is determined whether or not the calculation of the correction functions α and β is completed for all addresses i and j of the Ne value and the [O2] value (step 69). When this answer is NO, the above steps 61 to 68 are repeated, and when it becomes YES, this processing is ended. As described above, the correction variables α and β are set for all the addresses i and j, stored as α i, j map and β i, j map, and the correction function f according to α i, j and β i, j. (Α, β) i, j is set.

  FIG. 8 determines the fuel injection parameter Q * i, j during operation of the engine 3 using the Q * i, j map and the correction function f (α, β) i, j set in advance as described above. Indicates processing. First, it is determined whether or not the engine 3 is in a transient state (step 71). When the answer is NO and the engine 3 is in a steady state, the above-described method is applied to the in-cylinder state parameter [O2] s (in-cylinder oxygen amount mo2s, in-cylinder inert gas amount mints, and actual intake manifold temperature Tis in the steady state. ) Is calculated (step 72). Next, an address i, j corresponding to the engine speed Ne and the calculated in-cylinder state parameter [O2] is determined (step 73), and a fuel injection parameter Q * i, j corresponding to the determined address i, j is determined. Is determined from the Q * i, j map and determined as the fuel injection parameter Q * (step 74). Further, the correction variables α and β are determined by searching the α i, j map and β i, j (step 75).

  If the answer to step 71 is YES and the engine 3 shifts from the steady state to the transient state, the in-cylinder state parameters [O2] (mo2, mint and Ti) in the transient state are calculated (step 76). Then, using the calculated mint value and Ti value, the mints value and Tis value in the steady state calculated in step 72, and the correction variables α and β determined in step 75, the correction function f (α , Β) is calculated (step 77). Next, using the calculated correction function f (α, β) and the in-cylinder oxygen amount mo2 calculated in step 76, the virtual in-cylinder oxygen amount mo2v is calculated by equation (18) (step 78). As a result, the actual in-cylinder oxygen amount mo2 in the transient state is converted into the virtual in-cylinder oxygen amount mo2v in the steady state. Next, on the same address i, an in-cylinder state parameter [O2] including the in-cylinder oxygen amount mo2 closest to the calculated virtual cylinder oxygen amount mo2v is selected, and the corresponding addresses i and j are assigned to the virtual address i, It is determined as jv (step 79). As a result, as shown in FIG. 9, the address of the in-cylinder state parameter [O2] moves from j in the steady state to the virtual address jv on the Q * i, j map. Then, the fuel injection parameter Q * i, jv corresponding to the virtual address i, jv is read from the Q * i, j map and determined as the fuel injection parameter Q * (step 80). When the fuel injection parameter Q * i, jv is determined, the torque T of the engine 3 obtained at that time can be determined as T = Ti, jv from the Ti, j map.

Next, fuel injection control (hereinafter referred to as “air-fuel ratio switching control”) at the time of transition from lean operation to rich operation and at the time of transition from rich operation to lean operation will be described.
FIG. 10 is a state transition diagram of the air-fuel ratio switching control. Four states, that is, a lean state, a lean → rich state (a transition state from a lean state to a rich state), a rich state, and a rich → lean state (rich state). Transition state from lean to lean). The target in-cylinder oxygen amount mo2tgtL in the lean state and the target in-cylinder oxygen amount mo2tgtR in the rich state are determined using a map set in advance by a bench test according to the accelerator opening AP and the engine speed Ne.

The air-fuel ratio switching control is generally executed as follows.
1) During normal operation, the engine 3 operates in a lean state. For example, when NOx reduction enrichment is required and a rich request (air-fuel ratio switching command to rich air-fuel ratio) is made, the engine combustion mode shifts from lean to rich.
2) In the lean-to-rich state, when the virtual cylinder oxygen amount mo2v reaches the target cylinder oxygen amount mo2tgtR in the rich state, or when the rich request disappears, the engine combustion mode shifts to the rich state. When there is no rich request, the rich state is immediately shifted to the rich to lean state.
3) When the rich request is lost in the rich state (the air-fuel ratio switching command to the lean air-fuel ratio is issued), the rich-to-lean state is entered.
4) In the rich to lean state, when the virtual cylinder oxygen amount mo2v reaches the target cylinder oxygen amount mo2tgtL in the lean state, or when a rich request is made, the engine combustion mode shifts to the lean state. When a rich request is made, the lean state is immediately shifted to the lean to rich state.

  In the lean state, the air conditioning parameter A * and the fuel injection parameter Q * are set using the map for lean operation, that is, the map for normal lean operation or the map for PM oxidation. In the rich state, the rich operation described above is set. The air conditioning parameter A * and the fuel injection parameter Q * are set using the map for NOx, that is, the NOx reduction map or the sulfur desorption map.

In the lean-> rich state or the rich-> lean state, the air conditioning parameter A * is calculated using the corresponding map of the transition destination, so that the in-cylinder oxygen amount mo2 becomes the target cylinder oxygen amount mo2tgtR or mo2tgtL. The throttle valve opening TH is controlled. The fuel injection parameter Q * is calculated as follows. First, the oxygen ratio Oxyratio is calculated by the following formula (21). The oxygen ratio Oxyratio is a parameter having a value “0” at the start of the air-fuel ratio transition and a value “1” at the completion of the transition, and indicates the progress of the air-fuel ratio switching.
Oxyratio = | mo2v−mo2ini | / | mo2ini−mo2tgt | (21)
Where mo2v: virtual cylinder oxygen amount
mo2ini: In-cylinder oxygen amount immediately before switching
mo2tgt: Target cylinder oxygen after switching

Next, as shown in the following formula (22), a ratio parameter Q * ratio is calculated according to the oxygen ratio Oxyratio. The function f (Oxyratio) will be described later. Then, the ratio parameter Q * ratio is applied to the following equation (23) to calculate the fuel injection parameter Q *.
Q * ratio = f (Oxyratio) (22)
Q * = Q * ini + Q * ratio × (Q * tgt−Q * ini) (23)
Where Q * ini: fuel injection parameters just before switching
Q * tgt: Target fuel injection parameter after switching

  The calculation of the fuel injection parameter Q * using the equations (21) to (23) is performed in order to suppress the torque shock accompanying the switching of the air-fuel ratio. Hereinafter, how to set the function f (Oxyratio) will be described.

  FIG. 11 shows changes in engine output torque when the air-fuel ratio is changed by changing the intake air amount with the fuel supply amount kept constant. When the air-fuel ratio is enriched by reducing the intake air amount from the lean state of the air-fuel ratio A / F = 28, the output torque initially decreases with a small slope, and with a larger slope as the air-fuel ratio decreases. Decrease. That is, this change characteristic is not linear but exponential.

Thus, since the change in torque with respect to the change in air-fuel ratio is non-linear, in order to suppress the change in torque at the time of air-fuel ratio switching, it is necessary to adjust the non-linear fuel amount. That is, when shifting from the lean state to the rich state, the fuel amount must be gradually increased at first, and as the air-fuel ratio decreases, it needs to be increased more quickly, while when shifting from the rich state to the lean state First, the amount of fuel must be decreased rapidly, and the rate of decrease must be reduced as the air-fuel ratio increases.
In addition, at the time of air-fuel ratio switching, the fuel injection timing TMe and the fuel injection pressure Pe must also be changed nonlinearly.

  Further, the target air-fuel ratio in the rich state is substantially fixed, but the air-fuel ratio in the lean state changes according to the engine load. For example, if the lean air-fuel ratio (lean air-fuel ratio) is set to decrease as the engine load increases, it is necessary to increase the fuel amount more quickly as the engine load increases in the lean to rich state. is there. Further, in the rich-to-lean state, it is necessary to decrease the fuel amount at a lower speed as the engine load increases.

  From the above examination results, in the present embodiment, the ratio parameter Q * ratio is calculated using the function f (Oxyratio) as shown in FIG. 12A in the lean → rich state, and in the rich → lean state, The ratio parameter Q * ratio is calculated using a function f (Oxyratio) as shown in FIG. The curve L1 in FIG. 12A shows the characteristics when the lean air-fuel ratio is large, and the curve L2 shows the characteristics when the lean air-fuel ratio is small. Similarly, a curve L3 in FIG. 12B shows characteristics when the lean air-fuel ratio is large, and a curve L4 shows characteristics when the lean air-fuel ratio is small.

The function f (Oxyratio) shown in FIG. 12 (a) increases gradually as the oxygen ratio Oxyratio increases, that is, the rate of change dQ * ratio / dOxyratio of the ratio parameter Q * ratio with respect to the change of the oxygen ratio Oxyratio. It is set to be. On the other hand, the function f (Oxyratio) shown in FIG. 12B is set such that the change rate dQ * ratio / dOxyratio gradually decreases as the oxygen ratio Oxyratio increases. This tendency becomes more prominent as the lean air-fuel ratio is larger, and when it is smaller, the change rate dQ * ratio / dOxyratio is less changed. In the lean → rich state (FIG. 12 (a)), it is desirable to correct the ratio parameter Q * ratio to increase as the lean air-fuel ratio becomes smaller with reference to the curve L1, and the rich → lean state (FIG. 12). In (b)), it is desirable that correction is performed so that the ratio parameter Q * ratio decreases as the lean air-fuel ratio decreases with the curve L3 as a reference.
By using the function f (Oxyratio) shown in FIG. 12, torque fluctuation at the time of air-fuel ratio switching can be appropriately suppressed.

Next, a fuel injection control process executed by the ECU 2 at the time of air-fuel ratio switching will be described with reference to FIGS.
FIG. 13 shows a control process including fuel injection control that is executed at the time of transition from lean operation to rich operation. In this process, first, it is determined whether or not this time is a loop immediately after a command for switching from lean operation to rich operation is made (step 91). If the answer is YES and immediately after the switching command, the target torque TRi, j, the target fuel injection parameter Q * tgt, and the target in-cylinder oxygen amount mo2tgt in the rich operation are determined (step 92). Specifically, on the TRi, j map for rich operation, the address i, j having the same torque value as the torque TLi, jv immediately before the transition and the engine speed Ne is the same as that immediately before the transition is specified. The torque TRi, j (= TLi, jv) at the address i, j is set as the target torque at the transfer destination. When the destination addresses i and j are specified in this way, the target fuel injection parameter Q * tgt and the target cylinder oxygen amount mo2tgt (mo2tgtR) are automatically determined accordingly. Further, the in-cylinder oxygen amount mo2 and the fuel injection parameter Q * at this time are stored as the initial cylinder oxygen amount mo2ini and the initial fuel injection parameter Q * ini, respectively.

  Next, the target throttle opening degree THR and the overshoot time TMos corresponding to the transition period are set according to the target torque TRi, j set at step 92 (step 93), and the throttle valve 7 is set according to these settings. After driving, the process proceeds to step 94. If the answer to step 91 is NO, not immediately after the transition, steps 92 and 93 are skipped and the process proceeds to step 94. In this step 94, the actual in-cylinder oxygen amount mo2 is calculated, and then the calculated in-cylinder oxygen amount mo2 is corrected with the correction function f (α, β) i, j, thereby obtaining the virtual in-cylinder oxygen amount mo2v. Calculate (step 95).

  Next, it is determined whether or not the calculated virtual cylinder oxygen amount mo2v is substantially equal to the target cylinder oxygen amount mo2tgt obtained in step 92 (step 96). When this answer is NO, since the shift to the rich operation is in progress, the virtual cylinder oxygen amount mo2v, the initial cylinder oxygen amount mo2ini, and the target cylinder oxygen amount mo2tgt are applied to the equation (21), and the oxygen ratio Oxyratio is calculated (step 97). In step S98, a Q * ratio table corresponding to the curves L1 and L2 shown in FIG. 12A is retrieved according to the oxygen ratio Oxyratio, and the engine load (specifically, torque TRi, j or accelerator pedal opening AP) is obtained. A corresponding interpolation calculation is performed to calculate the ratio parameter Q * ratio. In step S99, the ratio parameter Q * ratio, the initial fuel injection parameter Q * ini, and the target fuel injection parameter Q * tgt are applied to the equation (23) to calculate the fuel injection parameter Q *.

  On the other hand, if the answer to step 96 is YES and the virtual cylinder oxygen amount mo2v is substantially equal to the target cylinder oxygen amount mo2tgt, it is determined that the transition period has ended, and the throttle opening TH is set to the target throttle opening THR. (Step 100) and the fuel injection parameter Q * is set to the target fuel injection parameter Q * tgt (step 101). Next, the air-fuel ratio A / F is adjusted by finely adjusting the throttle opening TH, the supercharging pressure, etc. according to the detection result of the oxygen concentration sensor 29 (step 102), and this process is terminated. After the transition period ends, fuel injection control in a steady state according to the engine speed Ne and the in-cylinder state parameter [O2] is performed based on the Q * Ri, j map for rich operation.

  FIG. 14 shows a control process including fuel injection control that is executed at the time of transition from rich operation to lean operation. This process is performed basically in the same manner as the process of FIG. 13 except that the rich / lean relationship is reversed. That is, immediately after the switching command from the rich operation to the lean operation (step 111: YES), the target torque TLi, j, the target fuel injection parameter Q * tgt, and the target in-cylinder oxygen amount mo2tgt in the lean operation are determined (step 112). ). Specifically, on the TLi, j map for lean operation, an address i, j having the same torque value as the torque TRi, jv immediately before the transition and the engine speed Ne is identified, The torque TLi, j (= TRi, jv) at the address i, j is set as the target torque at the transfer destination. Further, the target fuel injection parameter Q * tgt and the target cylinder oxygen amount mo2tgt (mo2tgtL) are determined according to the destination addresses i and j. Further, the in-cylinder oxygen amount mo2 and the fuel injection parameter Q * at this time are stored as the initial cylinder oxygen amount mo2ini and the initial fuel injection parameter Q * ini, respectively.

  Next, the target throttle opening degree THL and the overshoot time TMos are set according to the target torque TLi, j (step 113), and the throttle valve 7 is driven according to these settings. Next, the actual in-cylinder oxygen amount mo2 is calculated (step 114), and the calculated in-cylinder oxygen amount mo2 is converted into a correction function f (α, β) i. Corrected by j, the virtual cylinder oxygen amount mo2v is calculated (step 115).

  When the virtual cylinder oxygen amount mo2v has not reached the target cylinder oxygen amount mo2tgt (step 116: NO) and the transition is in progress, the virtual cylinder oxygen amount mo2v, the initial cylinder oxygen amount mo2ini, and the target cylinder oxygen amount The oxygen ratio Oxyratio is calculated from mo2tgt (step 117). Next, a Q * ratio table corresponding to the curves L3 and L4 shown in FIG. 12B is retrieved according to the oxygen ratio Oxyratio, and according to the engine load (specifically, the torque TLi, j or the accelerator pedal opening AP). Interpolation is performed to calculate the ratio parameter Q * ratio (step 118). In step 119, the ratio parameter Q * ratio, the initial fuel injection parameter Q * ini, and the target fuel injection parameter Q * tgt are applied to the equation (23) to calculate the fuel injection parameter Q *.

  On the other hand, when the virtual cylinder oxygen amount mo2v is substantially equal to the target cylinder oxygen amount mo2tgt (step 116: YES) and the transition period ends, the throttle opening TH is controlled to the target throttle opening THL (step 120). At the same time, the fuel injection parameter Q * is set to the target fuel injection parameter Q * tgt (step 121), and this process ends. After the transition period ends, fuel injection control in a steady state according to the engine speed Ne and the in-cylinder state parameter [O2] is performed based on the Q * Li, j map for lean operation.

  As described above, in the present embodiment, when the air-fuel ratio is switched, the fuel injection parameter Q * is smoothly changed according to the initial cylinder oxygen amount mo2ini before switching and the target cylinder oxygen amount mo2tgt after switching. As a result, torque fluctuations at the time of air-fuel ratio switching can be suppressed. More specifically, the oxygen ratio Oxyratio indicating the progress of the air-fuel ratio switching is calculated, the ratio parameter Q * ratio is calculated according to the oxygen ratio Oxyratio, and the fuel injection parameter Q * is smoothly set by the ratio parameter Q * ratio. I try to change it. Then, the ratio parameter Q * ratio is set according to operating conditions such as the oxygen ratio Oxyratio and the engine load, as shown in FIG. 12, taking into consideration the characteristics of the torque change with respect to the air-fuel ratio change shown in FIG. Therefore, torque fluctuation can be sufficiently suppressed regardless of the engine load at the time of air-fuel ratio switching.

  In the present embodiment, the ECU 2 performs an air-fuel ratio enrichment timing for NOx reduction or sulfur desorption, that is, a timing for switching from lean operation to rich operation, and an end timing of the air-fuel ratio enrichment, that is, rich operation to lean operation. Is determined, the air-fuel ratio switching command is issued, and the intake air amount control and the fuel injection control process corresponding to the switching command are executed. Therefore, the ECU 2 constitutes a switching command means, a part of the intake air amount control means, a fuel injection parameter determination means, a ratio calculation means, and a ratio parameter setting means. More specifically, the processes in FIGS. 8, 13 and 14 correspond to the fuel injection parameter determination means, step 97 in FIG. 13 and step 117 in FIG. 14 correspond to the ratio calculation means, and the steps in FIG. 98 and step 118 in FIG. 14 correspond to the ratio parameter setting means.

  The present invention is not limited to the embodiment described above, and various modifications can be made. For example, in the above-described embodiment, the fuel injection parameter Q * is configured by the injection time De, the injection timing TMe, and the injection pressure Pe, but may be one or two of these. Furthermore, although the example which applied this invention to control of the diesel engine was shown in embodiment mentioned above, this invention is applicable also to control of a gasoline engine.

  The present invention can also be applied to control of a marine vessel propulsion engine such as an outboard motor having a crankshaft as a vertical direction.

It is a figure which shows roughly the control apparatus to which this invention is applied with an internal combustion engine. It is a block diagram which shows a control apparatus. It is a figure which shows an A * map. It is a flowchart which shows the calculation process of an in-cylinder state parameter. It is a flowchart which shows the setting process of a Q * i, j map. It is a figure which shows Q * i, j map. It is a flowchart which shows the setting process of correction variable (alpha) i, j and (beta) i, j. It is a flowchart which shows the setting process of fuel parameter Q *. It is a figure explaining the method of calculating | requiring the virtual address i and jv. It is a state transition diagram concerning air-fuel ratio switching control. It is a figure for demonstrating the change of the engine output torque when changing an air fuel ratio. It is a figure which shows the function (table) for calculating a ratio parameter (Q * ratio) from oxygen ratio (Oxyratio). It is a flowchart which shows the control processing performed at the time of transfer from lean operation to rich operation. It is a flowchart which shows the control processing performed at the time of transfer from rich operation to lean operation.

Explanation of symbols

2 Electronic control unit (intake air amount control means, recirculation exhaust gas flow rate estimation means, in-cylinder oxygen amount estimation means, fuel injection parameter determination means, injector control means, switching command means, ratio calculation means, ratio parameter setting means)
3 Internal combustion engine 3a Cylinder 4 Intake pipe (intake system)
6 Injector 7 Throttle valve (intake air amount control means)
14 Exhaust gas recirculation device 22 Crank angle sensor (rotational speed detection means)
27 Air flow sensor (intake air volume detection means)

Claims (1)

Air is sucked into the cylinder through the intake system, fuel injected from the injector is supplied into the cylinder, and part of the exhaust gas discharged from the internal combustion engine is returned to the intake system as recirculated exhaust gas by the exhaust gas recirculation device. In a control device for an internal combustion engine,
Intake air amount control means for controlling the amount of intake air taken into the cylinder via the intake system;
An intake air amount detection means for detecting the intake air amount;
Recirculation exhaust gas flow rate estimating means for estimating the flow rate of recirculated exhaust gas by the exhaust gas recirculation device;
In-cylinder oxygen amount estimation means for estimating the amount of oxygen present in the cylinder based on the detected intake air amount and the estimated recirculated exhaust gas flow rate;
A rotational speed detection means for detecting the rotational speed of the internal combustion engine;
Fuel injection parameter determination means for determining a fuel injection parameter based on the detected rotational speed of the internal combustion engine and the estimated in-cylinder oxygen amount;
Injector control means for controlling the injector based on the determined fuel injection parameter;
Switching command means for commanding switching the air-fuel ratio of the air-fuel mixture combusting in the cylinder from the lean air-fuel ratio to the rich air-fuel ratio, or switching from the rich air-fuel ratio to the lean air-fuel ratio,
The fuel injection parameter determining means, when the switching command means is instructed to switch the air-fuel ratio, according to the estimated cylinder oxygen amount before switching and the target cylinder oxygen amount after switching, A control apparatus for an internal combustion engine, wherein an injection parameter is determined so as to change smoothly.

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