JP2016017459A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for properly controlling an amount of intake air and an exhaust gas recirculation rate when a lean operation and a stoichiometric operation are changed over, restricting a variation in engine output and an emission amount of NOx and performing a smooth changing-over operation.SOLUTION: In this invention, an air-fuel ratio transition control operation is carried out when an air-fuel ratio is changed over from a theoretical air-fuel ratio AFST to a lean air-fuel ratio AFLN or vice versa in response to an engine operating state. During the air-fuel ratio transition control operation, a combustion gas layer flow combustion velocity VLF within a combustion chamber is calculated, a throttle valve opening degree TH and EGR valve lift amount LFT are controlled in such a way that the layer flow combustion velocity VLF may be substantially kept constant. An initial layer flow combustion speed VLF0 before changing-over operation is calculated and a target opening degree THCMD of the throttle valve and an EGR valve lift amount instruction value LFTCMD are calculated in such a way that an exhaust gas recirculation rate and an air-fuel ratio after changing-over in which the layer flow combustion speed VLF after changing-over may become the same as the initial layer flow combustion velocity VLFO can be realized.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a control device for an internal combustion engine having an exhaust gas recirculation mechanism, and more particularly to a control device for controlling the air-fuel ratio of an air-fuel mixture in a combustion chamber to a lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. .

  Patent Document 1 discloses a control method for an internal combustion engine that performs a stoichiometric operation that controls the air-fuel ratio to the stoichiometric air-fuel ratio and a lean operation that controls the lean air-fuel ratio leaner than the stoichiometric air-fuel ratio. According to this control method, when switching from the stoichiometric operation to the lean operation, the intake air amount increase control is first started, and then the ignition timing is changed to the retarded side at the timing when the actual increase of the intake air amount is started. Then, the air-fuel ratio is changed to a lean air-fuel ratio, and the ignition timing is changed to the advance side. This makes it possible to switch the operation while suppressing fluctuations in engine output and generation of nitrogen oxides.

Japanese Patent No. 3064782

  Although it is well known to provide an exhaust gas recirculation mechanism to suppress the generation amount of nitrogen oxides, Patent Document 1 shows air-fuel ratio switching control in consideration of the exhaust gas recirculation rate on the premise that exhaust gas recirculation is performed. It has not been.

  The present invention has been made paying attention to this point, and when switching between lean operation and stoichiometric operation, the intake air amount and the exhaust gas recirculation rate are appropriately controlled to prevent fluctuations in engine output and generation of nitrogen oxides. An object of the present invention is to provide a control device that can suppress and perform smooth switching.

  In order to achieve the above object, an invention according to claim 1 is a control device for an internal combustion engine (1), comprising an intake air amount control valve (3) for controlling an intake air amount of the engine, and an exhaust of the engine. An exhaust gas recirculation passage (20) that recirculates air to the intake system, an exhaust gas recirculation mechanism that is provided in the exhaust gas recirculation passage and controls an exhaust gas recirculation amount (21), and sparks of the air-fuel mixture in the combustion chamber In a control apparatus for an internal combustion engine comprising spark ignition means (7, 8) for igniting, the air-fuel ratio of the air-fuel mixture in the combustion chamber is set to a rich air-fuel ratio (AFST) near the stoichiometric air-fuel ratio according to the operating state of the engine. ), An air-fuel ratio control means for controlling the lean air-fuel ratio (AFLN) leaner than the stoichiometric air-fuel ratio, and an air-fuel ratio transition when the air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio or vice versa. Control transient And the transient control means includes laminar combustion speed calculation means for calculating a laminar combustion speed (VLF) of the combustion gas in the combustion chamber of the engine, and the laminar combustion speed (VLF) The air-fuel ratio transition control is executed by controlling the opening amounts of the intake air amount control valve and the exhaust gas recirculation control valve so as to be kept substantially constant.

  According to this configuration, the air-fuel ratio transition control is performed when the air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio or vice versa according to the operating state of the engine. In the air-fuel ratio transition control, the laminar combustion speed of the combustion gas in the combustion chamber of the engine is calculated, and the intake air amount control valve and the exhaust gas recirculation control valve are opened so that the laminar combustion speed is maintained substantially constant. Is controlled. By controlling the intake air amount and the exhaust gas recirculation rate so that the laminar combustion speed is maintained almost constant, the engine output fluctuations and nitrogen oxides are corrected without correcting the ignition timing during the air-fuel ratio transition control. The smooth switching can be performed while suppressing the occurrence of.

  According to a second aspect of the present invention, in the control apparatus for an internal combustion engine according to the first aspect, an air-fuel ratio detection means (17) for detecting an air-fuel ratio of the air-fuel mixture and an ignition timing (IG) by the spark ignition means. In-cylinder pressure calculating means for calculating the in-cylinder pressure (PIG) in the engine and in-cylinder temperature calculating means for calculating the in-cylinder temperature (TIG) at the ignition timing, the laminar combustion speed calculating means includes the air-fuel ratio transition At the start of the air-fuel ratio transition control according to the initial air-fuel ratio (AFLN, AFST) at the start of control, the initial exhaust gas recirculation rate (REGRLN, REGRST) at the start of the air-fuel ratio transition control, the in-cylinder pressure, and the in-cylinder temperature The laminar flow rate (VLF0) is calculated, and the transient control means determines the air-fuel ratio at the end of the air-fuel ratio transition control (AFST, AFLN) and the laminar flow rate (VLF0) according to End exhaust gas recirculation rate calculation means for calculating the final exhaust gas recirculation rate (REGRST, REGRLN) at the end of the fuel ratio shift control is provided, so that the actual exhaust gas recirculation rate (REGR) matches the final exhaust gas recirculation rate (REGRST, REGRLN). And controlling the opening degree of the intake air amount control valve and the exhaust downstream control valve.

  According to this configuration, the laminar combustion speed at the start of the air-fuel ratio transition control according to the initial air-fuel ratio at the start of the air-fuel ratio transition control, the initial exhaust gas recirculation rate at the start of the air-fuel ratio transition control, the in-cylinder pressure, and the in-cylinder temperature. Is calculated, the end exhaust gas recirculation rate at the end of the air fuel ratio transition control is calculated according to the end air fuel ratio and the laminar combustion speed at the end of the air fuel ratio transition control, and the actual exhaust gas recirculation rate matches the end exhaust gas recirculation rate Thus, the opening degree of the intake air amount control valve and the exhaust downstream control valve is controlled. This control makes it possible to appropriately control the exhaust gas recirculation rate and switch the air-fuel ratio while maintaining the laminar combustion speed substantially constant.

  According to a third aspect of the present invention, in the internal combustion engine control apparatus according to the second aspect, the in-cylinder pressure (PIG) applied to the calculation of the laminar combustion speed (VLF0) is calculated by the end exhaust gas recirculation rate calculating means. And the end exhaust gas recirculation rate (REGRST) is calculated using the in-cylinder temperature (TIG).

  According to this configuration, since the end exhaust gas recirculation rate is calculated using the in-cylinder pressure and the in-cylinder temperature applied to the calculation of the laminar combustion speed at the start of the air-fuel ratio transition control, the in-cylinder pressure and the in-cylinder temperature are calculated again. Therefore, it is possible to reduce the computation load of the control device.

  According to a fourth aspect of the present invention, in the control apparatus for an internal combustion engine according to the second or third aspect, the transient control means is configured such that the transient air-fuel ratio is 1 or between the initial air-fuel ratio (AFLN or AFST) and the end air-fuel ratio. Two or more intermediate air-fuel ratios (AFMD) are set, and control for shifting from the initial air-fuel ratio to the end air-fuel ratio (AFST or AFLN) via the intermediate air-fuel ratio is performed.

  According to this configuration, one or two or more intermediate air-fuel ratios are set between the initial air-fuel ratio and the end air-fuel ratio, and control for shifting from the initial air-fuel ratio to the end air-fuel ratio via the intermediate air-fuel ratio is performed. Is called. For example, if the amount of change between the initial air-fuel ratio and the end air-fuel ratio is relatively large, the exhaust gas recirculation rate and air-fuel ratio during the transition control may deviate from appropriate values, but the intermediate air-fuel ratio is set. Then, by performing control to shift from the initial air-fuel ratio to the final air-fuel ratio via the intermediate air-fuel ratio, it is possible to prevent the laminar combustion speed, the exhaust gas recirculation rate, and the air-fuel ratio from being shifted during the transition.

  According to a fifth aspect of the present invention, in the control device for an internal combustion engine according to any one of the first to fourth aspects, the fuel injection valve capable of atomizing the fuel and injecting the fuel into the intake passage (2) of the engine. (6), wherein the spark ignition means includes an ignition plug (8) and a plurality of ignition coil pairs (71, 72) for generating a discharge in the ignition plug, and the discharge of the ignition plug is continued. The time (TSKP) can be changed, and when the air-fuel ratio is controlled to the lean air-fuel ratio (AFLN), the ignition timing (IG) is advanced as the lean air-fuel ratio (AFLN) increases. In addition, the discharge duration (TSPK) is set to be long.

  According to this configuration, since the atomized fuel is injected into the intake passage, a relatively homogeneous air-fuel mixture is formed in the intake passage and is further sucked into the combustion chamber, so that the degree of homogeneity is higher. An air-fuel mixture can be formed. Also, since the discharge duration in the spark plug can be changed, the discharge duration can be set longer by setting the ignition timing and discharge duration appropriately, that is, by setting the ignition timing to a relatively advanced angle. Therefore, even if the air-fuel ratio is set to about “30”, it can be surely ignited. In addition, when the target air-fuel ratio is a lean air-fuel ratio, the ignition timing is advanced and the discharge duration is set longer as the lean air-fuel ratio increases, so that ignition is reliably performed even if the target air-fuel ratio changes. be able to.

It is a figure which shows the structure of the internal combustion engine and its control apparatus concerning one Embodiment of this invention. It is a figure for demonstrating arrangement | positioning of the tumble flow control valve (4) provided in an intake passage. It is a figure for demonstrating the operating characteristic of an intake valve. It is a circuit diagram which shows the structure of the ignition circuit unit (7) corresponding to one cylinder. It is a figure for demonstrating the injection state of the fuel injected by a fuel injection valve (6). It is a figure which shows the relationship between an air fuel ratio (AF) and NOx density | concentration (CNOx) in exhaust_gas | exhaustion. It is a figure which shows the relationship between a gas fuel ratio (GF) or an air fuel ratio (AF), and a laminar flow rate (VLF). It is a flowchart for demonstrating air-fuel ratio transfer control. It is a figure which shows the map for a laminar flow velocity (VLF) calculation (exhaust gas recirculation rate = 0). It is a figure which shows the map for a laminar flow rate (VLF) calculation (air-fuel ratio = theoretical air-fuel ratio). It is a figure for demonstrating the example of control operation.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an internal combustion engine (hereinafter referred to as “engine”) and a control device thereof according to an embodiment of the present invention. For example, a throttle valve ( An intake air amount control valve) 3 is arranged. The throttle valve 3 is configured to be driven by an actuator 19, and the actuator 19 is connected to an electronic control unit (hereinafter referred to as “ECU”) 5. The opening degree of the throttle valve 3 is controlled by the ECU 5 via the actuator 19. On the downstream side of the throttle valve 3 in the intake passage 2, a fuel injection valve 6 is provided corresponding to each cylinder, and its operation is controlled by the ECU 5.

  As shown in FIG. 2, a partition wall 2a and a tumble flow control valve 4 disposed in one flow path formed by the partition wall 2a are provided immediately upstream of the intake valve 22 in the intake passage 2. The tumble flow control valve 4 is configured to be opened and closed by an actuator 4a. The actuator 4a is connected to the ECU 5, and its operation is controlled by the ECU 5. The tumble flow control valve 4 generates a tumble flow of the air-fuel mixture in the combustion chamber 1a.

  A spark plug 8 is attached to each cylinder of the engine 1, and the spark plug 8 is connected to the ECU 5 via the ignition circuit unit 7. The ECU 5 controls the discharge start timing CAIG and the discharge duration time TSPK in the spark plug 8 as will be described later. The discharge start timing CAIG may be expressed as “ignition timing IG”.

  The ECU 5 includes an intake air flow sensor 11 that detects the intake air flow rate GAIR of the engine 1, an intake air temperature sensor 12 that detects the intake air temperature TA, a throttle valve opening sensor 13 that detects the throttle valve opening TH, and an intake pressure PBA. Intake pressure sensor 14 to detect, cooling water temperature sensor 15 to detect engine cooling water temperature TW, and other sensors (not shown) (for example, an accelerator sensor for detecting an accelerator pedal operation amount AP of a vehicle driven by the engine 1, a vehicle speed sensor, etc.) Are connected, and detection signals of these sensors are supplied to the ECU 5.

  A crank angle position sensor 16 that detects a rotation angle of a crankshaft (not shown) of the engine 1 is connected to the ECU 5, and a pulse signal corresponding to the rotation angle of the crankshaft is supplied to the ECU 5. The crank angle position sensor 16 outputs a plurality of pulse signals indicating the crank angle position. These pulse signals are used for various timing controls such as fuel injection timing, ignition timing (discharge start timing of the spark plug 8), and the like. Used to detect the engine speed NE. The engine 1 is provided with a mechanism for continuously changing the intake valve operating phase as will be described later, and based on the pulse signal output from the crank angle position sensor 16, the actual camshaft that drives the intake valve 22 is provided. The operation phase (intake valve operation phase) CAIN can be detected. In the present embodiment, the increase in the intake valve operation phase CAIN corresponds to the advance angle of the phase.

  The exhaust passage 9 is provided with a three-way catalyst 10 containing palladium for exhaust purification. A proportional oxygen concentration sensor 17 (hereinafter referred to as “LAF sensor 17”) is mounted on the upstream side of the three-way catalyst 10 and on the downstream side of the collection portion of the exhaust manifold communicating with each cylinder. 17 outputs a detection signal substantially proportional to the oxygen concentration in the exhaust gas (air-fuel ratio AF). An exhaust pressure sensor 18 for detecting the exhaust pressure PEX is mounted in the vicinity of the LAF sensor 17. The detection signals of these sensors 17 and 18 are supplied to the ECU 5.

  The engine 1 includes an exhaust gas recirculation mechanism. The exhaust gas recirculation mechanism includes an exhaust gas recirculation passage 20 connected to the exhaust passage 9 and the intake air passage 2, and an exhaust gas recirculation control valve that controls the flow rate of the exhaust gas that passes through the exhaust gas recirculation passage 20. (Hereinafter referred to as “EGR valve”) 21. The operation of the EGR valve 21 is controlled by the ECU 5.

  The engine 1 includes a valve operation characteristic variable mechanism 41 that continuously changes the operation phase of the intake valve 22 and a hydraulic control mechanism 42 that drives the valve operation characteristic variable mechanism 41. The operation of the hydraulic control mechanism 42 is controlled by the ECU 5.

  According to the valve operating characteristic variable mechanism 41, the intake valve 22 has the operating characteristic indicated by the solid line L1 in FIG. 3 as the most retarded angle phase, and the most advanced as indicated by the broken line L2 with the advance angle of the cam operating phase (CAIN). It is driven at a phase up to the angular phase. The exhaust valve is driven with a constant operating characteristic indicated by a solid line L3.

  The ECU 5 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, a central processing unit (CPU), It comprises a storage circuit for storing various calculation programs executed by the CPU and calculation results, an output circuit for supplying a drive signal to the fuel injection valve 6, the ignition circuit unit 7, the actuator 4a, and the like.

  The fuel injection amount by the fuel injection valve 6 is controlled by correcting the basic fuel amount calculated according to the intake air flow rate GAIR with the air-fuel ratio correction coefficient KAF corresponding to the air-fuel ratio AF detected by the LAF sensor 17. The The air-fuel ratio correction coefficient KAF is calculated so that the detected air-fuel ratio AF coincides with the target air-fuel ratio AFCMD.

  The ECU 5 calculates the target opening THCMD of the throttle valve 3 in accordance with the accelerator pedal operation amount AP and controls the drive of the actuator 19 so that the detected throttle valve opening TH matches the target opening THCMD.

  FIG. 4 is a circuit diagram showing the configuration of the ignition circuit unit 7 corresponding to one cylinder. The ignition circuit unit 7 includes a first coil pair 71 including a primary coil 71a and a secondary coil 71b, a primary coil 72a, A second coil pair 72 including a secondary coil 72b, a booster circuit 73 that boosts the output voltage VBAT of the battery 30 and outputs a boosted voltage VUP, transistors Q1 and Q2 that control energization of the primary coils 71a and 72a, Diodes D1 and D2 connected between the secondary coils 71b and 72b and the spark plug 8 are provided.

  The bases of the transistors Q1 and Q2 are connected to the ECU 5, and on / off control (primary coil energization control) is performed by the ECU 5. By alternately energizing part of the energization periods of the two primary coils, the discharge duration (discharge duration) TSPK in the spark plug 8 can be changed according to the operating state of the engine 1. . Further, the first energization end timing of the primary coil corresponds to the discharge start timing CAIG, and the discharge start timing CAIG can also be changed according to the operating state of the engine 1.

  The fuel injection valve 6 is capable of atomizing and injecting fuel, and has an SMD (Sauter Mean Diameter) characteristic of about 35 μm (injection at a fuel pressure of 350 kPa and SMD 50 mm below the injection port). Have. FIG. 5 (a) schematically shows the fuel injection state (diffused state of injected fuel) by the fuel injection valve 6, and FIG. 5 (b) shows the fuel by the normal fuel injection valve shown for comparison. The injection state of is shown. In the normal fuel injection valve, the fuel concentration in the peripheral portion of the fuel distributed in a conical shape is high, whereas in the fuel injection valve 6, the reach of the atomized fuel is shortened and the concentration distribution in the diffusion region is reduced. The degree of homogeneity is high (the difference in density is small).

  By using the fuel injection valve 6 capable of atomizing and injecting fuel, an amount of fuel required to make the detected air-fuel ratio AF coincide with the target air-fuel ratio AFCMD is supplied to the combustion chamber, and the air in the combustion chamber is empty. A homogeneous mixture having a substantially uniform fuel ratio distribution (high homogeneity) can be formed.

  In the present embodiment, the target air-fuel ratio AFCMD after completion of warm-up is set according to the operating state of the engine 1 (mainly required torque and engine speed NE). Normally, lean operation is performed in which the target air-fuel ratio AFCMD is set to a range of, for example, “24” to “35” (hereinafter referred to as “ultra-lean air-fuel ratio range”). In a state or the like, stoichiometric operation is performed to set the target air-fuel ratio AFCMD to the theoretical air-fuel ratio (14.7).

  The minimum air-fuel ratio AFL1 (for example, “24”) during lean operation is set so that the NOx emission amount from the engine 1 is equal to or less than the allowable upper limit value CNOxHL (for example, 120 ppm). The maximum air-fuel ratio AFL2 (eg, “35”) is an air-fuel ratio set as a limit value for obtaining a necessary engine output.

  FIG. 6 is a diagram showing the relationship between the air-fuel ratio AF and the NOx concentration CNOx in the exhaust gas. When the air-fuel ratio AF is “16” or more, the NOx increases as the air-fuel ratio AF increases (lean). The concentration CNOx decreases. Therefore, the minimum air-fuel ratio AFL1 during the lean operation needs to be set so as to increase as the allowable upper limit value CNOxHL decreases.

  The discharge start timing CAIG in the spark plug 8 is set to a range of 50 degrees to 15 degrees before top dead center corresponding to the target air-fuel ratio AFCMD in the ultra-lean air-fuel ratio range, and the discharge duration TSPK is a homogeneous lean mixture. In order to ensure ignition, it is set to 1.8 to 3 msec. The boost voltage VUP is set so that the discharge energy when the discharge duration time TSPK is set in this way is 150 to 600 mJ. Conventional lean mixture combustion by spark ignition is stratified mixture combustion realized by generating a flow in the combustion chamber so that the air-fuel ratio in the vicinity of the spark plug becomes relatively small. In the homogeneous lean mixture combustion, the discharge start time CAIG is set from the ignition timing (for example, 8.0 degrees) of the stratified mixture combustion so that the discharge duration TSPK is set relatively long and the discharge duration TSPK can be secured. Set to the advance side. In the ultra lean air-fuel ratio range, the discharge start timing CAIG is advanced and the discharge duration time TSPK is set longer as the target air-fuel ratio AFCMD increases.

  Furthermore, the geometrical compression ratio of the engine 1 (ratio of the combustion chamber volume when the piston is located at the bottom dead center and the combustion chamber volume when the piston is located at the top dead center) has a minimum effective compression ratio of 9.0. In order to achieve this, it is set slightly larger than the geometric compression ratio of a normal spark ignition engine.

  Further, by changing the opening degree of the tumble flow control valve 4, tumble flow generation control for generating tumble flow with a flow rate of about 5 to 15 m / sec (flow rate when the engine speed NE is 1500 rpm) is performed.

  By setting the discharge duration TSPK to be relatively long and generating a tumble flow in the combustion chamber, a strong initial flame kernel is formed in the lean mixture combustion, and the flame kernel is grown, thereby compressing top dead center. By raising the temperature of the unburned air-fuel mixture to a temperature of 1000 ° K or higher, combustion can be reliably completed after compression top dead center.

  As described above, when the lean operation is performed, the NOx emission amount can be set to the allowable upper limit value or less without performing the exhaust gas recirculation, so that the exhaust gas recirculation rate indicating the ratio of the exhaust gas recirculated through the exhaust gas recirculation passage 20 REGR is set to “0”. On the other hand, when the stoichiometric operation is performed, the exhaust gas recirculation rate REGR is set to a value according to the engine operating state in order to reduce the NOx emission amount, and the intake gas and the fuel mixed with the recirculated exhaust gas and the air are mixed. An air-fuel mixture is supplied to the combustion chamber.

Therefore, in the following description, in addition to the air-fuel ratio AF, a parameter called a gas fuel ratio GF is introduced. The gas fuel ratio GF is defined by the following formula (1). In the formula (1), MAIR is an intake air amount, MEGR is a recirculation exhaust amount, and MFUEL is a fuel amount (both are expressed by mass converted per unit time (for example, one intake stroke)). Since equation (1) can be transformed into equation (2), when the exhaust gas recirculation rate REGR is “0”, the gas fuel ratio GF is equal to the air-fuel ratio AF.
GF = (MAIR + MEGR) / MFUEL (1)
GF = MAIR / MFUEL + MEGR / MFUEL
= AF + MEGR / MFUEL (2)

FIG. 7 shows the relationship between the laminar combustion velocity VLF of the combustion gas and the gas fuel ratio GF when the air-fuel mixture in the combustion chamber burns (when the engine speed NE and the engine output are constant). A solid line L11 shows the relationship between the gas fuel ratio GF (= air-fuel ratio AF) and the laminar combustion velocity VLF in a state where the exhaust gas recirculation rate REGR is “0”, and a broken line L12 shows the air-fuel ratio AF and the stoichiometric air-fuel ratio AFST (= 14). .7) shows the relationship between the gas fuel ratio GF and the laminar combustion velocity VLF when the exhaust gas recirculation rate REGR is changed. Since the air-fuel ratio AF is constant, the gas fuel ratio GF increases as the exhaust gas recirculation rate REGR is increased. As is clear from FIG. 7, the laminar combustion velocity VLF decreases as the gas fuel ratio GF (air fuel ratio AF) increases.
The laminar combustion speed VLF is a combustion speed in a laminar flow state of the combustion gas, and a simple calculation method is disclosed in, for example, Japanese Patent No. 4066866.

  In the present embodiment, when switching from lean operation to stoichiometric operation or vice versa, air-fuel ratio transition control is performed to switch the air-fuel ratio while keeping the laminar combustion velocity VLF substantially constant. For example, in FIG. 7, the transition from the lean operation point PLN (AF≈29, REGR = 0) to the stoichiometric operation point PST (AF = 14.7, REGR≈39%) is indicated by an arrow line (line with an arrow) AR. By performing as shown, it is possible to shift from lean operation to stoichiometric operation with exhaust gas recirculation while keeping the laminar combustion velocity VLF constant. Further, if the direction of the arrow line AR is reversed, it is possible to shift from the stoichiometric operating point PST to the lean operating point PLN while keeping the laminar combustion velocity VLF constant. In the following description, the operating point before the transition is referred to as the “initial operating point”, the operating point after the transition is referred to as the “target operating point”, and the parameters indicating the gas amount are all expressed in mass per unit time.

FIG. 8 is a flowchart for explaining the air-fuel ratio shift control in the present embodiment.
In step S11, an intake gas amount MGAS in the combustion chamber at the intake valve closing timing CAIVC is calculated. Specifically, the combustion chamber volume (hereinafter referred to as “compression start volume”) V0 at the intake valve closing timing CAIVC is calculated by searching the combustion chamber volume table, and the compression start volume V0 is applied to the following equation (3). By doing so, the intake gas amount MGAS is calculated.
MGAS = P0 × V0 / (R × TAK) (3)

  P0 in equation (3) is the compression start cylinder pressure, and is approximated to be equal to the detected intake pressure PBA. R is a gas constant, and TAK is an absolute temperature conversion value of the intake air temperature TA. The combustion chamber volume table is a table for calculating the combustion chamber volume according to the crank angle, and is preset according to the specifications of the engine 1.

  In step S12, a specific heat ratio map in which the specific heat ratio κ is set according to the air-fuel ratio and the exhaust gas recirculation rate is searched according to the detected air-fuel ratio AF and the exhaust gas recirculation rate REGR, and the specific heat ratio κ of the intake gas is determined. calculate. The actual exhaust gas recirculation rate REGR can be calculated using, for example, the technique disclosed in Japanese Patent No. 5270008. When the initial operating point is the lean operating point PLN, the exhaust gas recirculation rate REGR is “0”.

In step S13, the in-cylinder pressure PIG at the ignition timing IG is calculated by applying the compression start in-cylinder pressure P0, the compression start volume V0, and the specific heat ratio κ to the following equation (4), and the in-cylinder pressure PIG and the intake gas amount MGAS are further calculated. The in-cylinder temperature TIG at the ignition timing IG is calculated by applying to the following equation (5).
PIG = P0 × (V0 / VIG) ^κ (4)
TIG = PIG × VIG / (R × MGAS) (5)
Here, VIG is the combustion chamber volume at the ignition timing IG, and is calculated using the combustion chamber volume table.

  In step S14, a laminar combustion velocity (hereinafter referred to as “initial laminar combustion velocity”) VLF0 at the initial operating point is calculated. Specifically, by searching a VLF map set as shown in FIGS. 9 and 10 according to the detected air-fuel ratio AF, exhaust gas recirculation rate REGR, in-cylinder pressure PIG, and in-cylinder temperature TIG, the initial value is obtained. A laminar combustion velocity VLF0 is calculated.

  FIG. 9 corresponds to the state where the exhaust gas recirculation rate REGR is “0”, and FIG. 9A shows the in-cylinder temperature TIG and the layer when the in-cylinder pressure PIG is the first pressure value P1 (for example, 500 kPa). FIG. 9B shows the relationship between the in-cylinder temperature TIG and the laminar combustion rate VLF when the in-cylinder pressure PIG is the second pressure value P2 (for example, 1000 kPa), The plurality of curves correspond to a state where the equivalence ratio Φ is “1.0”, “0.9”,..., “0.4”. The equivalence ratio Φ is a parameter in which “1.0” corresponds to the theoretical air-fuel ratio AFST and is proportional to the reciprocal of the air-fuel ratio AF. That is, the equivalent ratio Φ = 0.4 corresponds to the air-fuel ratio AF = 36.75, and Φ = 0.5 corresponds to AF = 29.4.

  FIG. 10 corresponds to the state where the air-fuel ratio AF is the stoichiometric air-fuel ratio AFST (Φ = 1.0), and FIG. 10A shows the in-cylinder temperature TIG when the in-cylinder pressure PIG is the first pressure value P1. FIG. 10B shows the relationship between the in-cylinder temperature TIG and the laminar combustion rate VLF when the in-cylinder pressure PIG is the second pressure value P2. This curve corresponds to a state where the exhaust gas recirculation rate REGR is 0, 10,..., 50%.

  For example, in the case where the initial operating point is the lean operating point PLN and the in-cylinder pressure PIG is the first pressure value P1, according to the in-cylinder temperature TIG and the air-fuel ratio AF (equivalent ratio Φ), FIG. The initial laminar combustion velocity VLF0 is calculated by searching the VLF map shown (and interpolation calculation). FIG. 9A shows an example in which the in-cylinder temperature is the temperature TIG0 and the equivalence ratio Φ is 0.5. Further, when the initial operating point is the stoichiometric operating point PST, for example, a VLF map search (and interpolation calculation) shown in FIG. 10A is performed according to the exhaust gas recirculation rate REGR, the in-cylinder pressure PIG, and the in-cylinder temperature TIG. ) To calculate the initial laminar combustion velocity VLF0.

  In step S15, it is determined whether or not the operation is switched from the lean operation to the stoichiometric operation. If the answer is affirmative (YES), the stoichiometric operation point PST (AF = AFST) is determined according to the initial laminar combustion speed VLF0. The stoichiometric exhaust gas recirculation rate REGRST, which is the exhaust gas recirculation rate REGR, is calculated (step S16). The initial laminar combustion velocity VLF0 calculated in step S14 and the same in-cylinder temperature TIG as in step S14 are applied to, for example, the map shown in FIG. 10A where the in-cylinder pressure PIG is the first pressure value P1, and the stoichiometric operation is performed. The exhaust gas recirculation rate REGRST is calculated. The stoichiometric exhaust gas recirculation rate REGRST is calculated, for example, as an exhaust gas recirculation rate (about 25%) corresponding to the operating point PX0 in FIG.

In step S17, the stoichiometric operation gas amount MGASSST, which is the intake gas amount at the target operating point, is calculated as follows. Since the fuel amount MFUEL is determined according to the required output TRQCMD of the engine 1, the stoichiometric operation air amount AIRRST is calculated by applying the fuel amount MFUEL to the following equation (6), and the calculated stoichiometric operation air amount MAINST Further, the stoichiometric operation exhaust gas recirculation rate REGRST is applied to the equation (7) to calculate the stoichiometric operation recirculation exhaust amount MEGRST, and the stoichiometric operation gas amount MGASSST is calculated from the equation (8). Note that “REGRST” in the equation (7) is not [%] but a ratio itself having a value from “0” to “1”.
MAIRST = MFUEL × AFST (6)
MEGRST = REGRST × MAIRST / (1-REGRST) (7)
MGASST = MAIRST + MEGRST (8)

  In step S18, a PBA map set in advance for calculating the intake pressure PBA according to the intake gas amount MGAS and the engine speed NE is searched according to the stoichiometric operation gas amount MGASSST and the engine speed NE. Thus, the stoichiometric operation intake pressure PBAST is calculated.

  In step S19, a TH map set in advance for calculating the throttle valve opening TH according to the intake pressure PBA and the engine speed NE is searched according to the stoichiometric operation intake pressure PBAST and the engine speed NE. Then, the stoichiometric operation target opening degree THCMDST is calculated.

  In step S20, an LFT map for calculating the EGR valve lift amount LFT according to the exhaust gas recirculation rate REGR and the differential pressure DP between the upstream side and the downstream side of the EGR valve 21 is obtained as a stoichiometric operation exhaust gas recirculation rate REGRST and a differential pressure DP. A search is performed according to (= exhaust pressure PEX−intake pressure PBA), and a stoichiometric operation lift amount command value LFTCMDST is calculated.

In step S21, the throttle valve target opening THCMD is set to the stoichiometric operation target opening THCMDST, and the EGR valve lift amount command value LFTCMD is set to the stoichiometric operation lift amount command value LFTCMDST. At this time, the target opening THCMD is gradually changed from the current value toward the stoichiometric operation target opening THCMDST, and the EGR valve lift amount command value LFTCMD is changed from the current value (= 0) to the stoichiometric operation lift amount command value LFTCMDST. It is desirable to change gradually.
In step S27, the throttle valve 3 and the EGR valve 21 are driven so that the throttle valve opening TH and the EGR valve lift amount LFT coincide with the stoichiometric operation target opening THCMDST and the stoichiometric operation lift amount command value LFTCMDST, respectively.

If the answer to step S15 is negative (NO) and switching from stoichiometric operation to lean operation, the process proceeds to step S22, in which the lean operation exhaust gas recirculation rate REGRLN is set to “0”, and the EGR valve lift amount The command value LFTCMD is set to “0”.
It is desirable that the EGR valve lift amount command value LFTCMD is gradually changed from the current value toward “0”.

In step S23, the lean operation gas amount MGASLN, which is the intake gas amount at the target operating point (air-fuel ratio = AFLN), is calculated using the following equations (6a) to (8a). Since the exhaust gas recirculation is not performed in the lean operation, the lean operation gas amount MGASLN becomes equal to the lean operation air amount MAIRLN.
MAIRLN = MFUEL × AFLN (6a)
MEGRLN = 0 (7a)
MGASLN = MAIRLN (8a)

In step S24, a lean operation intake pressure PBALN is calculated by searching a PBA map according to the lean operation gas amount MGASNL (= MAIRLN) and the engine speed NE, and in step S25, the lean operation intake pressure PBALN and the engine rotation are calculated. The TH map is searched according to the number NE, and the lean operation target opening THCMDLN is calculated. In step S26, the target opening degree THCMD is set to the lean operation target opening degree THCMDLN. Thereafter, the process proceeds to step S27.
It is desirable that the target opening degree THCMD is gradually changed from the current value toward the lean operation target opening degree THCMDLN.

  Normally, since the fuel amount MFUEL is the same before and after the operation switching, the throttle valve opening TH is controlled in the decreasing direction and the EGR valve lift amount LFT is controlled in the increasing direction when switching from the lean operation to the stoichiometric operation. Is done. Conversely, when switching from stoichiometric operation to lean operation, the throttle valve opening TH is controlled in the increasing direction, and the EGR valve lift amount LFT is controlled in the decreasing direction.

Although not shown in FIG. 8, the target air-fuel ratio AFCMD is gradually changed from the lean air-fuel ratio AFLN toward the stoichiometric air-fuel ratio AFST or vice versa. The changing speed of each control parameter (THCMD, LFTCMD, AFCMD) is set so that the execution time of the air-fuel ratio transition control becomes a predetermined transition time TTR (for example, about 2 to 3 seconds). With the control described above, the intake air amount is gradually decreased and the exhaust gas recirculation rate is gradually increased while maintaining the laminar combustion velocity VLF substantially constant, so that the transition from the lean operation to the stoichiometric operation can be performed smoothly. In addition, the intake air amount can be gradually increased and the exhaust gas recirculation rate can be gradually decreased while maintaining the laminar combustion speed VLF substantially constant, so that the transition from the stoichiometric operation to the lean operation can be performed smoothly.
During the air-fuel ratio transition control, it is desirable to set the opening degree of the tumble flow control valve 4 so that the flow strength becomes high. This makes it possible to further stabilize the combustion during the transition control.

  FIG. 11 is a diagram for explaining an example of the switching operation from the lean operation to the stoichiometric operation. FIG. 11A shows a lean operating point PLF by performing the above-described cooperative control of the throttle valve opening TH and the EGR valve lift amount LFT under the condition that the engine speed NE and the engine output (IMEP) are constant. The relationship between the air-fuel ratio AF and the exhaust gas recirculation rate REGR when the transition from the AF = 28, REGR = 0% to the stoichiometric operating point PST (AF = 14.7, REGR = 35%) is performed, 11 (b) to 11 (f) respectively show the throttle valve opening TH during the transition control, the exhaust gas recirculation rate REGR, the indicated thermal efficiency ηi, the ignition timing IG, the combustion angle period MBF10-90, and the combustion fluctuation rate COV. The relationship is shown.

  According to FIG. 11B, it can be confirmed that the throttle valve opening TH is decreased from about 35 degrees to about 11 degrees. The combustion angle period MBF10-90 is a crank angle period in which the combustion mass ratio of the air-fuel mixture ranges from 10% to 90%, and is a parameter correlated with the laminar combustion velocity VLF. That is, from FIG. 11 (e), it can be confirmed that the laminar combustion velocity VLF is maintained substantially constant at the time of switching from the lean operation point PLF to the stoichiometric operation point PST, and the ignition timing IG is also controlled to be substantially constant. In this state (FIG. 11 (d)), the combustion fluctuation rate COV is kept at a low value (FIG. 11 (f)), and the indicated thermal efficiency ηi is also kept at a relatively good value (FIG. 11 (c)). ) Can be confirmed. Further, as described above, in lean operation, the air-fuel ratio AF is set to the ultra-lean air-fuel ratio range, so the NOx emission amount is kept low, and the exhaust gas recirculation rate REGR is set in the transition control for shifting the air-fuel ratio AF to the stoichiometric air-fuel ratio AFST. Since it is controlled so as to gradually increase, an increase in the NOx emission amount can be suppressed.

  As described above, in the present embodiment, the air-fuel ratio transition control is performed when the air-fuel ratio AF is switched from the stoichiometric air-fuel ratio AFST to the lean air-fuel ratio AFLN or vice versa according to the engine operating state. In the air-fuel ratio transition control, the laminar combustion speed VLF of the combustion gas in the combustion chamber is calculated, and the throttle valve opening TH and the EGR valve lift amount LFT are controlled so that the laminar combustion speed VLF is maintained substantially constant. The By controlling the throttle valve opening TH and the EGR valve lift amount LFT so that the laminar combustion speed VLF is maintained substantially constant, the engine output is corrected without correcting the ignition timing IG during the air-fuel ratio transition control. Thus, smooth switching can be performed while suppressing fluctuations in NOx and NOx emissions.

  In addition, the initial air-fuel ratio detected at the start of the air-fuel ratio shift control, the initial exhaust gas recirculation rate at the start of the air-fuel ratio shift control, the in-cylinder pressure PIG at the ignition timing IG and the in-cylinder temperature TIG, the initial layer at the start of the air-fuel ratio shift control When the flow combustion speed VLF0 is calculated and switching from the lean operation to the stoichiometric operation, the stoichiometric operation exhaust gas recirculation rate REGRST is calculated according to the stoichiometric air-fuel ratio AFST and the initial laminar combustion speed VLF0, and the actual exhaust gas recirculation rate REGR is calculated. The throttle valve opening TH and the EGR valve lift amount LFT are controlled so as to coincide with the stoichiometric exhaust gas recirculation rate REGRST. Further, when switching from stoichiometric operation to lean operation, the lean operation exhaust gas recirculation rate REGRLN is set to “0”, and the exhaust gas recirculation rate REGR is stoichiometric while maintaining the laminar combustion velocity VLF at the initial laminar combustion velocity VLF0. The throttle valve opening TH and the EGR valve lift amount LFT are controlled so as to gradually decrease from the operating exhaust gas recirculation rate REGRST toward “0”. With this control, it is possible to appropriately control the intake air amount and the exhaust gas recirculation rate REGR, and to switch the air-fuel ratio while maintaining the laminar combustion speed VLF substantially constant.

  Further, since the stoichiometric exhaust gas recirculation rate REGRST which is the end exhaust gas recirculation rate is calculated using the in-cylinder pressure PIG and the in-cylinder temperature TIG applied to the calculation of the initial laminar combustion speed VLF0 at the start of the air-fuel ratio transition control, the in-cylinder pressure It is not necessary to recalculate the PIG and the in-cylinder temperature TI, and the calculation load on the control device can be reduced.

  Further, since the fuel atomized by the fuel injection valve 6 is injected into the intake passage 2, a relatively homogeneous air-fuel mixture is formed in the intake passage 2 and further sucked into the combustion chamber, so that the degree of homogeneity is increased. A high air-fuel mixture can be formed. Further, since the discharge duration time TSPK in the spark plug 8 can be changed, by appropriately setting the ignition timing IG (discharge start timing CAIG) and the discharge duration time TSPK, that is, the ignition timing IG is relatively advanced. By setting, it is possible to set the discharge duration time TSPK to be long, and even if the air-fuel ratio is set to about “30”, ignition can be ensured. When the target air-fuel ratio AFCMD is the lean air-fuel ratio AFLN, the ignition timing IG is advanced and the discharge duration time TSPK is set longer as the lean air-fuel ratio AFLN increases, so that the target air-fuel ratio AFCMD changes. However, it can be ignited reliably.

  In this embodiment, the throttle valve 3 corresponds to an intake air amount control valve, the ignition circuit unit 7 and the spark plug 8 constitute spark ignition means, the oxygen concentration sensor 17 corresponds to air-fuel ratio detection means, and the ECU 5 An in-cylinder pressure calculating unit, an in-cylinder temperature calculating unit, a laminar combustion speed calculating unit, an air-fuel ratio control unit, a transient control unit, and an end exhaust gas recirculation rate calculation unit are configured.

[Modification]
In the above-described embodiment, the lean operation in which the air-fuel ratio is set to the ultra-lean air-fuel ratio range and the stoichiometric operation are switched. However, when the air-fuel ratio change amount before and after the transition is large, the lean operation is performed. Operation switching is performed between the air-fuel ratio AFST and the stoichiometric air-fuel ratio AFST via one or more intermediate air-fuel ratios AFMD (for example, air-fuel ratios “20” and “24”) and the intermediate air-fuel ratio AFMD. You may do it. When the air-fuel ratio change amount is relatively large, the exhaust gas recirculation rate REGR and the air-fuel ratio AF during the transition control may deviate from appropriate values (for example, values as shown in FIG. 11A). By setting the air-fuel ratio and controlling the transition from the initial air-fuel ratio to the final air-fuel ratio via the intermediate air-fuel ratio, the shift of the laminar combustion speed VLF, the exhaust gas recirculation rate REGR, and the air-fuel ratio AF during the transition is prevented can do.

  In this modification, initial laminar combustion is performed by using a laminar combustion speed map corresponding to the intermediate air-fuel ratio AFMD, which is set similarly to the laminar combustion speed map corresponding to the stoichiometric air-fuel ratio shown in FIG. An intermediate exhaust gas recirculation rate REGRMD corresponding to the speed VLF0 and the intermediate air-fuel ratio AFMD is calculated.

  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 air-fuel ratio AF in the lean operation is set to an ultra lean air-fuel ratio range (for example, 24 to 35). However, the present invention makes the air-fuel ratio AF in the lean operation more stoichiometric. The present invention is also applicable to a control device that is set to a close value (for example, 16 to 22). In the above-described embodiment, the air-fuel ratio transition control at the time of switching between the stoichiometric operation when the air-fuel ratio is set to the stoichiometric air-fuel ratio and the lean operation that is set to the air-fuel ratio leaner than the stoichiometric air-fuel ratio is shown. The invention can also be applied at the time of switching between a rich operation in which the air-fuel ratio is set to a slightly richer air-fuel ratio in the vicinity of the theoretical air-fuel ratio and a lean operation.

  In the embodiment described above, the in-cylinder pressure PIG and the in-cylinder temperature TIG applied to the calculation of the initial laminar combustion velocity VLF0 are applied as they are to the calculation of the stoichiometric operation exhaust gas recirculation rate REGRST in step S16 in FIG. You may make it perform the correction | amendment corresponding to the change of a state. For example, by detecting the temperature TEGR of the recirculated exhaust gas and correcting the cylinder pressure PIG so that it increases as the exhaust temperature TEGR increases, the corrected cylinder pressure PIGC is calculated, and the corrected cylinder pressure PIGC is expressed by Equation (5). By applying, the corrected in-cylinder temperature TIGC is calculated. Then, the stoichiometric exhaust gas recirculation rate REGRST is calculated using the corrected in-cylinder pressure PIGC and the corrected in-cylinder temperature TIGC. Further, as the recirculation exhaust temperature TEGR increases, the recirculation exhaust volume expands, and the recirculation exhaust amount (mass) MEGR corresponding to the same EGR valve lift amount LFT decreases. Therefore, the stoichiometric operation lift amount command value LFTCMDST is determined as the recirculation exhaust temperature TEGR. It is desirable to correct so that it increases as the value increases.

  In the above-described embodiment, an example of a four-cylinder engine is shown, but the present invention can be applied regardless of the number of cylinders. The present invention can also be applied to a control device such as an engine for a marine propulsion device such as an outboard motor having a vertical crankshaft.

1 Internal combustion engine 3 Throttle valve (intake air amount control valve)
5 Electronic control unit (cylinder pressure calculating means, cylinder temperature calculating means, laminar combustion speed calculating means, air-fuel ratio control means, transient control means, end exhaust gas recirculation rate calculating means)
7 Ignition circuit unit (spark ignition means)
8 Spark plug (spark ignition means)
AF Air-fuel ratio LFT EGR valve lift amount REGR Exhaust gas recirculation rate TH Throttle valve opening VLF Laminar combustion speed IG Ignition timing

Claims (5)

A control device for an internal combustion engine, comprising an intake air amount control valve for controlling an intake air amount of the engine, an exhaust gas recirculation passage for recirculating exhaust gas of the engine to an intake system, and an exhaust gas recirculation passage. In an internal combustion engine control device comprising an exhaust gas recirculation mechanism having an exhaust gas recirculation control valve for controlling a flow rate, and spark ignition means for performing spark ignition of an air-fuel mixture in the combustion chamber,
Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture in the combustion chamber to a rich air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio and a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio according to the operating state of the engine;
Transient control means for performing air-fuel ratio transition control when switching the air-fuel ratio from the rich air-fuel ratio to the lean air-fuel ratio or vice versa,
The transient control means includes laminar combustion speed calculation means for calculating a laminar combustion speed of combustion gas in the combustion chamber of the engine,
In the internal combustion engine, the air-fuel ratio transition control is executed by controlling the opening amounts of the intake air amount control valve and the exhaust gas recirculation control valve so that the laminar combustion speed is maintained substantially constant. Control device. Air-fuel ratio detection means for detecting the air-fuel ratio of the air-fuel mixture;
In-cylinder pressure calculating means for calculating the in-cylinder pressure at the ignition timing by the spark ignition means;
In-cylinder temperature calculation means for calculating the in-cylinder temperature at the ignition timing,
The laminar combustion speed calculating means is configured to change the air-fuel ratio according to an initial air-fuel ratio at the start of the air-fuel ratio transition control, an initial exhaust gas recirculation rate at the start of the air-fuel ratio transition control, the in-cylinder pressure, and the in-cylinder temperature. Calculate the laminar combustion speed at the start of control,
The transient control means has an end exhaust gas recirculation rate calculating means for calculating an end exhaust gas recirculation rate at the end of the air-fuel ratio transition control according to the end air-fuel ratio at the end of the air-fuel ratio transition control and the laminar combustion speed. And
2. The control device for an internal combustion engine according to claim 1, wherein opening amounts of the intake air amount control valve and the exhaust downstream control valve are controlled so that an actual exhaust gas recirculation rate coincides with the end exhaust gas recirculation rate.   The internal combustion engine according to claim 2, wherein the end exhaust gas recirculation rate calculating means calculates the end exhaust gas recirculation rate using the in-cylinder pressure and in-cylinder temperature applied to the calculation of the laminar combustion speed. Control device.   The transient control means sets one or more intermediate air-fuel ratios between the initial air-fuel ratio and the end air-fuel ratio, and transitions from the initial air-fuel ratio to the end air-fuel ratio via the intermediate air-fuel ratio. The control device for an internal combustion engine according to claim 2 or 3, wherein control is performed. A fuel injection valve capable of atomizing the fuel and injecting it into the intake passage of the engine;
The spark ignition means includes an ignition plug and a plurality of ignition coil pairs for generating a discharge in the ignition plug, and is capable of changing a discharge duration in the ignition plug,
5. When the air-fuel ratio is controlled to the lean air-fuel ratio, the ignition timing is advanced and the discharge duration is set longer as the lean air-fuel ratio increases. A control device for an internal combustion engine according to claim 1.

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