JP2016014340A - Internal combustion engine control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control unit capable of more appropriately changing air-fuel ratios at a time of switching a stoichiometric operation to a lean operation in an engine including a three-way catalyst in an exhaust system, and suppressing a temporary increase in a NOx concentration downstream of the three-way catalyst.SOLUTION: An internal combustion engine control unit exerts an air-fuel ratio transition control at a time of switching a stoichiometric operation to a lean operation, and exerts an air-fuel ratio rich control to change an air-fuel ratio to a richer air-fuel ratio than a stoichiometric air-fuel ratio in a period before the passage of predetermined rich control time TRICH from start time tS of the air-fuel ratio transition control. The internal combustion engine control unit exerts a control to gradually change the air-fuel ratio to a lean air-fuel ratio AFLN1 after the passage of the predetermined rich control time TRICH. The air-fuel ratio rich control enables an increase in a rate of unoxidized (reduced) noble metal in a three-way catalyst 10 and a temporary increase in a NOx concentration CNOx downstream of the three-way catalyst 10 from being suppressed at a time of switchover of air-fuel ratios.

Description

  The present invention relates to a control device for an internal combustion engine having a three-way catalyst for exhaust purification in an exhaust system. The present invention relates to a control device that controls the 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

  According to the control method disclosed in Patent Document 1, in the transition control when switching from the stoichiometric operation to the lean operation, the air-fuel ratio is initially maintained at the stoichiometric air-fuel ratio, and the lean timing is started from the start of ignition timing advancement. It is gradually changed toward the air-fuel ratio.

  The three-way catalyst provided in the exhaust system contains a noble metal such as palladium. The noble metal is oxidized mainly by purifying NOx during the lean operation, and during the stoichiometric operation, hydrocarbon (HC) and Since carbon monoxide CO acts as a reducing agent, the oxidized noble metal and the reduced noble metal are mixed. Therefore, when the ratio of the reduced noble metal is low when the transition control for switching from the stoichiometric operation to the lean operation is performed by the conventional method, the NOx concentration on the downstream side of the three-way catalyst is temporarily changed during the transition control. There was an increase.

  The present invention has been made paying attention to this point, and in an engine equipped with a three-way catalyst in an exhaust system, the air-fuel ratio is changed more appropriately when switching from stoichiometric operation to lean operation, and on the downstream side of the three-way catalyst. An object of the present invention is to provide a control device capable of suppressing a temporary increase in the NOx concentration.

  In order to achieve the above object, an invention according to claim 1 is directed to a control device for an internal combustion engine (1) having a three-way catalyst (10) in an exhaust system, and mixing in the combustion chamber according to the operating state of the engine. Air-fuel ratio control means for controlling the air-fuel ratio (AF) of the air to a rich air-fuel ratio (AFT) near the stoichiometric air-fuel ratio and a lean air-fuel ratio (AFLN1) leaner than the stoichiometric air-fuel ratio; Transient control means for performing air-fuel ratio transition control when switching from the air-fuel ratio (AFST) to the lean air-fuel ratio (AFLN1), and the transient control means has a predetermined time from the start time (tS) of the air-fuel ratio transition control. (TRICH) The air-fuel ratio is changed to a richer air-fuel ratio than the rich air-fuel ratio in a period until it elapses, and gradually changed toward the lean air-fuel ratio after the predetermined time has elapsed. And wherein the door.

  According to this configuration, the air-fuel ratio shift control is performed when the air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio. Further, the control is performed so that the air-fuel ratio is changed to the rich side and gradually changed toward the lean air-fuel ratio after a predetermined time has elapsed. Thereby, the ratio of the reduced noble metal can be increased, and a temporary increase in the NOx concentration on the downstream side of the three-way catalyst can be suppressed at the time of air-fuel ratio switching.

  According to a second aspect of the present invention, there is provided the control apparatus for an internal combustion engine according to the first aspect, wherein the engine is capable of retarding a closing timing (CAIVC) of an intake valve of the engine to a timing during a compression stroke. The valve closing timing variable mechanism (41, 42) and the flow generation means (2a, 4) for generating the flow of the air-fuel mixture sucked into the combustion chamber of the engine, the transient control means includes the intake valve The valve closing timing (CAIVC) is controlled to a predetermined retardation timing (CARTDX) within the compression stroke, and the flow generating means is controlled so as to increase the flow strength of the air-fuel mixture.

  The above-mentioned “predetermined retard timing (CARTDX)” has a crank angle (crankshaft rotation phase) within the compression stroke to start the compression stroke in order to ensure the effect of preventing an increase in output fluctuation and the occurrence of knocking. It is desirable to set the angle position on the retard side by 70 degrees or more from the angle position. However, if the amount of retardation is excessive, stable combustion cannot be obtained, so that the angle is set to the advance side from the angular position of, for example, 100 degrees from the compression stroke starting angular position.

  According to this configuration, during the air-fuel ratio transition control, the closing timing of the intake valve is controlled to the predetermined retardation timing within the compression stroke, and is controlled so as to increase the strength of the air-fuel mixture flow. By setting the intake valve closing time to a relatively late time in the compression stroke and reducing the effective compression ratio, it becomes possible to prevent the occurrence of knocking, and further increase the strength of the mixture flow, It is possible to maintain good ignitability of the air-fuel mixture and stabilize combustion during air-fuel ratio transition control that increases the air-fuel ratio. As a result, it is possible to prevent an increase in output fluctuation and occurrence of knocking at the time of air-fuel ratio switching.

  According to a third aspect of the present invention, there is provided the control apparatus for an internal combustion engine according to the first or second aspect, wherein the engine includes an intake air amount control valve (3) for controlling an intake air amount (GA); An exhaust gas recirculation passage (20) that recirculates exhaust gas to an intake system, and an exhaust gas recirculation mechanism that is provided in the exhaust gas recirculation passage and includes an exhaust gas recirculation control valve (21) that controls an exhaust gas recirculation amount, wherein the transient control means includes: The control is performed to increase the intake air amount (GA) by increasing the opening (TH) of the intake air amount control valve and decreasing the opening (LFT) of the exhaust gas recirculation control valve. To do.

  According to this configuration, in the air-fuel ratio transition control, control is performed to increase the intake air amount while increasing the opening degree of the intake air amount control valve and decreasing the opening degree of the exhaust gas recirculation control valve. It is possible to suppress a change in engine output before and after switching and perform smooth switching.

  According to a fourth aspect of the present invention, in the control device for an internal combustion engine according to the third aspect, the engine includes spark ignition means (7, 8) for performing spark ignition of the air-fuel mixture in the combustion chamber, and the transient During the air-fuel ratio shift control, the control means controls the ignition timing (IG) by the spark ignition means according to an exhaust gas recirculation rate (REGR) indicating the ratio of the exhaust gas recirculated through the exhaust gas recirculation mechanism. It is characterized by that.

  According to this configuration, since the ignition timing is controlled according to the exhaust gas recirculation rate during the air-fuel ratio transition control, it is possible to reliably prevent an increase in output fluctuation and the occurrence of knocking during the air-fuel ratio transition control.

  According to a fifth aspect of the present invention, in the control apparatus for an internal combustion engine according to the fourth aspect, the engine is a fuel injection valve (6) capable of atomizing and injecting fuel into an intake passage (2) of the engine. The spark ignition means includes a spark plug (8) and a plurality of ignition coil pairs (71, 72) for generating a discharge in the spark plug, and a discharge duration (TSPK) in the spark plug. ) Can be changed, and when the air-fuel ratio (AF) is controlled to the lean air-fuel ratio (AFLN1), the ignition timing (IG) is advanced and the ignition timing (IG) is advanced as the lean air-fuel ratio increases. Ignition control means for setting a long discharge duration (TSPK) is provided.

  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. Further, as the lean air-fuel ratio increases, the ignition timing is advanced and the discharge duration time is set longer so that the ignition can be reliably performed even if the target air-fuel ratio changes.

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 engine operation area | region (RLN) which sets an air fuel ratio to the value of the lean side from a theoretical air fuel ratio, and the engine operation area | region (RST) which sets an air fuel ratio to a theoretical air fuel ratio. It is a figure which shows the relationship between an air fuel ratio (AF) and NOx density | concentration (CNOxF) in exhaust_gas | exhaustion. 6 is a time chart for explaining setting of control parameters in air-fuel ratio transition control (theoretical air-fuel ratio → lean air-fuel ratio). FIG. 9 is a time chart showing changes in air-fuel ratio (AF), intake air amount (GA)), NOx concentration (CNOx), and HC concentration (CHC) when the control shown in FIG. 8 is performed. It is a figure which shows the relationship between an exhaust gas recirculation rate (REGR) and ignition timing (IG). It is a figure for demonstrating exhaust gas purification by a three-way catalyst. It is a flowchart of the process which performs air-fuel ratio transfer control (switching from stoichiometric operation to lean operation). It is a time chart for demonstrating the air fuel ratio rich control performed by the process of FIG. It is a time chart for demonstrating the effect of the air fuel ratio rich control performed by the process of FIG.

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 (air-fuel ratio AF) in the exhaust gas and supplies it 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 first valve operating characteristic variable mechanism 41 that mechanically switches a valve lift amount and an opening angle (an angle period in which the lift amount is greater than “0”) of the intake valve 22 to two stages, and an operation phase of the intake valve 22. Is provided with a variable valve operating characteristic device 40 having a second valve operating characteristic variable mechanism 42 for continuously changing the valve operating characteristic. By adopting the first valve operating characteristic variable mechanism 41 that mechanically switches between two stages, the intake valve operating characteristic can be quickly changed. The first valve operating characteristic variable mechanism 41 switches the lift amount and the opening angle of the intake valve 22 between the first operating characteristic VT1 and the second operating characteristic VT2. The valve operating characteristic variable device 40 includes a hydraulic control mechanism 43 for driving the first valve operating characteristic variable mechanism 41 and a hydraulic control mechanism 44 for driving the second valve operating characteristic variable mechanism 42. The operation of the hydraulic control mechanism 43 and the hydraulic control mechanism 44 is controlled by the ECU 5. In the following description, the operation characteristic switched by the first valve operation characteristic variable mechanism 41 is referred to as “intake valve operation characteristic VT”.

  According to the valve operating characteristic variable device 40, the intake valve 22 has the cam operating phase with the first operating characteristic VT1 indicated by the solid line L1 and the second operating characteristic VT2 indicated by the solid line L2 in FIG. Driven by the phase up to the most advanced angle phase indicated by the broken lines L3 and L4 with the advance angle of (CAIN). The exhaust valve is driven with a constant operating characteristic indicated by a solid line L5. As is apparent from FIG. 3, in this embodiment, the closing timing CAIVC of the intake valve is set to be after the start of the compression stroke, and the Atkinson cycle operation is performed. Further, the valve closing timing CAIVC1 of the intake valve 22 in the first operating characteristic VT1 is on the more retarded side than the valve closing timing CAIVC2 in the second operating characteristic VT2.

  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, for example, as shown in FIG. 6 according to the engine speed NE and the required torque TRQCMD. In the region RLN shown in FIG. 6, a lean operation is performed in which the target air-fuel ratio AFCMD is set to a range of about “24” to “35” (hereinafter referred to as “ultra-lean air-fuel ratio range”). A stoichiometric operation for setting the AFCMD to the stoichiometric air-fuel ratio (14.7) is performed. The solid line indicating the boundary between the region RLN and the region RST shown in FIG. 6 corresponds to the boundary when switching from lean operation to stoichiometric operation, and the broken line corresponds to the boundary when switching from stoichiometric operation to lean operation.

  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. 7 is a diagram showing the relationship between the air-fuel ratio AF and the NOx concentration CNOxF in the exhaust gas upstream of the three-way catalyst 10. In the range where the air-fuel ratio AF is “16” or more, the air-fuel ratio AF increases. The NOx concentration CNOxF decreases (the more lean it is). 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. Increase the temperature of the unburned gas mixture to 1000 ° K or higher and change the elementary reaction that governs the laminar combustion rate into a reaction in which hydrogen peroxide decomposes to generate OH radicals, and compression top dead center It becomes possible to complete the combustion with certainty later.

Next, an outline of air-fuel ratio transition control when switching from stoichiometric operation to lean operation in the present embodiment will be described with reference to FIGS.
FIG. 8 is a time chart for explaining the air-fuel ratio transition control at the time of switching from stoichiometric operation to lean operation. FIGS. 8A to 8G show the throttle valve opening TH and the EGR valve lift amount, respectively. Changes in LFT, intake valve operation phase CAIN, intake valve operation characteristic VT, opening TCV of the tumble flow control valve 4, fuel injection time (fuel injection amount) TI, and ignition timing IG are shown. Time tS is the transition control start time, and time tE is the transition control end time. The broken lines shown in FIGS. 8A, 8B, 8C, and 8E indicate the target opening THCMD, the EGR valve lift amount command value LFTCMD, the intake valve operation phase command value CAINCMD, and the tumble flow control valve, respectively. The opening command value TCVCMD is indicated. Each control parameter is controlled as follows.

  Throttle valve target opening THCMD: gradually increases from time tS toward the lean operation opening THLN, and after time t11 when the lean operation opening THLN is reached, the lean operation opening THLN is maintained.

Command value LFTCMD of EGR valve lift amount LFT: At time tS, it is decreased stepwise to “0” which is the lean operation lift amount, and thereafter maintained at “0”. During the lean operation, the exhaust gas recirculation rate REGR is set to “0” because the NOx emission amount from the engine 1 is small.
Intake valve operation phase command value CAINCMD: The time is advanced stepwise to the initial phase CAINI at time tS, and then gradually advanced to time t12 when the lean operation phase CALN is reached. After time t12, the lean operation phase CALN is maintained.

Intake valve operating characteristic VT: maintained at the first operating characteristic VT1 from time tS to tE, and switched to the second operating characteristic VT2 at time tE.
Opening command value TCVCMD of the tumble flow control valve 4: At time tS, it is decreased stepwise to 0 degree (strong flow control value), and thereafter maintained at 0 degree.

  Fuel injection time TI: Since the air-fuel ratio AF is changed mainly by changing the intake air amount, the fuel injection time TI is held at a substantially constant value from time tS to tE. However, fine adjustment by feedback control is performed so that the detected air-fuel ratio AF coincides with the target air-fuel ratio AFCMD, and the fuel injection time TI (fuel injection amount) is set over the predetermined rich control time TRICH immediately after the start of the air-fuel ratio transition control. The air-fuel ratio rich control is slightly increased.

  Ignition timing IG: set according to the table shown in FIG. 10, for example, according to the actual exhaust gas recirculation rate REGR. As a result, the angle is retarded at a relatively high speed immediately after time tS, and then gradually advanced toward a value suitable for lean operation.

According to the table shown in FIG. 10, the ignition timing IG is set to advance as the exhaust gas recirculation rate REGR increases. The actual exhaust gas recirculation rate REGR is calculated by a known method (for example, the method disclosed in Japanese Patent No. 5270008).
The transition control end time tE is the time when the air-fuel ratio AF reaches the lean air-fuel ratio AFLN1.

  9A to 9D show the air-fuel ratio AF, the intake air amount GA, the NOx concentration CNOx in the exhaust (downstream of the three-way catalyst 10), and the air-fuel ratio AF when the air-fuel ratio transition control shown in FIG. The transition of the HC concentration CHC in the exhaust (downstream of the three-way catalyst 10) is shown, and the broken line in FIG. 9A shows the transition of the target air-fuel ratio AFCMD. The HC concentration CHC indicates the concentration of the plurality of hydrocarbon components contained in the fuel as a whole. The target air-fuel ratio AFCMD is gradually changed from the stoichiometric air-fuel ratio toward the lean air-fuel ratio so as not to deviate from the controllable range of the air-fuel ratio AF during the air-fuel ratio transition control. At this time, the target air-fuel ratio AFCMD is set according to the intake air amount GA and the exhaust gas recirculation rate REGR.

  According to FIG. 9, the intake air amount GA increases as the throttle valve opening TH increases, and the air-fuel ratio AF smoothly transitions from the stoichiometric air-fuel ratio AFST to the lean air-fuel ratio AFLN1 (about “24”). It can be confirmed that the NOx concentration CNOx and the HC concentration CHC are suppressed to be relatively small during the transition control.

FIG. 11 is a diagram for explaining the purification of exhaust gas in the three-way catalyst 10, and shows an example in which palladium Pd is used as a noble metal. As described above, during the stoichiometric operation, palladium oxide PdO and non-oxidized (reduced) palladium Pd are mixed. Nitric oxide NO in the exhaust gas changes to nitrogen N ₂ by oxidizing palladium Pd, and hydrocarbon (HC) and carbon monoxide CO reduce carbon dioxide CO ₂ and water by reducing palladium oxide PdO. Change to H ₂ O. Therefore, when the ratio of the reduced palladium Pd is low, there is a high possibility that the NOx concentration CNOx on the downstream side of the three-way catalyst 10 increases.

  Therefore, in the present embodiment, the ratio of the reduced palladium Pd is increased by temporarily enriching the air-fuel ratio AF immediately after the start of the air-fuel ratio transition control at the time of switching from stoichiometric operation to lean operation. CNOx is prevented from temporarily increasing.

  FIG. 12 is a flowchart showing a procedure of processing for executing air-fuel ratio transition control executed when switching from stoichiometric operation to lean operation. This process is executed, for example, every predetermined time.

  In step S11, it is determined whether or not the switch request flag FSTLN from stoichiometric operation to lean operation is “1”, and when this answer is affirmative (YES), the processing of steps S12 to S16 is executed. Switching request flag FASTLN is set to “1” when the engine operating state changes from region RST to region RLN shown in FIG. 6. If the answer to step S11 is negative (NO), the air-fuel ratio transition control from the lean operation to the stoichiometric operation or the normal control is performed by other processing (not shown) without executing this processing.

  In step S12, it is determined whether or not a predetermined rich control time TRICH (for example, 0.5 seconds) has elapsed since the time when the answer to step S11 became affirmative (YES) (the time when air-fuel ratio transition control starts). Initially, this answer is negative (NO), so air-fuel ratio rich control is executed to decrease the air-fuel ratio AF by about 0.5 by increasing the fuel injection time TI (step S13). The predetermined rich control time TRICH is desirably set according to the mass MPd of palladium contained in the three-way catalyst 10. That is, it is desirable to set the predetermined rich control time TRICH longer as the mass MPd of palladium is larger.

  When the predetermined rich control time TRICH has elapsed from the start of the air-fuel ratio transition control, the answer to step S12 becomes affirmative (YES), and thereafter, the process immediately proceeds from step S12 to step S14.

  In step S14, the air-fuel ratio transition control from the stoichiometric operation to the lean operation described with reference to FIGS. 8 and 9 is executed. In step S15, it is determined whether or not the air-fuel ratio shift control has ended. If the answer to step S15 is affirmative (YES), the switching request flag FSTLN is returned to "0" (step S16). The air-fuel ratio shift control ends when the air-fuel ratio AF reaches the post-shift air-fuel ratio (tE).

  FIG. 13 is a time chart for explaining the air-fuel ratio rich control in step S13 of FIG. 12, and shows the transition of the addition time DTI applied to the calculation of the fuel injection time TI during the air-fuel ratio rich control. The addition time DTI is set to increase stepwise to the rich control value DTIR at time tS and decrease stepwise to “0” at time tRE. The rich control value DTIR is a value that enriches the air-fuel ratio 14.7 to about 14.2, and corresponds to about 3 to 4% of the fuel injection time TI. The air-fuel ratio rich control is terminated at time tRE.

  FIG. 14 is a time chart for explaining the effect of executing the above-described air-fuel ratio rich control. FIG. 14A shows an enlarged view of the detected air-fuel ratio AF, and FIG. b) shows the transition of the NOx concentration CNOx on the downstream side of the three-way catalyst 10. The broken lines shown in FIGS. 14A and 14B correspond to the case where the air-fuel ratio rich control is not performed.

  The air-fuel ratio rich control is executed in a period from the time tS until the predetermined rich control time TRICH elapses. The change of the detected air-fuel ratio AF in the exhaust passage by the rich control is slightly delayed and shown in FIG. And is minimized at time t21. When the air-fuel ratio rich control is not performed, the increase amount of the NOx concentration CNOx increases as shown by the broken line in FIG. 14B, but the air-fuel ratio rich control is improved to the extent indicated by the solid line by performing the air-fuel ratio rich control. be able to.

  As described above, in the present embodiment, the air-fuel ratio shift control is performed when switching from the stoichiometric operation to the lean operation, and the air-fuel ratio is set in the period from the start time tS of the air-fuel ratio shift control until the predetermined rich control time TRICH elapses. The air-fuel ratio is changed to a richer air-fuel ratio (for example, about 14.2) than the stoichiometric air-fuel ratio, and control is gradually performed toward the lean air-fuel ratio AFLN1 after a predetermined rich control time TRICH has elapsed. As a result, the ratio of reduced palladium Pd is increased, and a temporary increase in the NOx concentration CNOx on the downstream side of the three-way catalyst 10 is suppressed at the time of air-fuel ratio switching (when switching from stoichiometric operation to lean operation). be able to.

  During the air-fuel ratio transition control, the intake valve operating characteristic VT is set to the first operating characteristic VT1, and the intake valve operating phase CAIN is set to a relatively small value so that the closing timing CAIC of the intake valve 22 is compressed. The tumble flow control valve 4 is controlled so as to increase the strength of the air-fuel mixture flow in the combustion chamber while being controlled to a predetermined retard timing CARTDX (70 degrees in the example shown in FIG. 8) in the stroke. By setting the intake valve closing timing CAIVC to a relatively late timing within the compression stroke and reducing the effective compression ratio, it becomes possible to prevent the occurrence of knocking and further increase the strength of the mixture flow. During the air-fuel ratio transition control that increases the air-fuel ratio, good ignitability of the air-fuel mixture can be maintained and combustion can be stabilized. As a result, it is possible to prevent an increase in output fluctuation and occurrence of knocking at the time of air-fuel ratio switching.

  When switching from stoichiometric operation to lean operation, control is performed to increase the intake air amount by increasing the throttle valve opening TH and decreasing the EGR valve lift amount LFT. By controlling the intake air amount and the exhaust gas recirculation amount as described above, it is possible to suppress a change in the engine output before and after the air-fuel ratio switching and perform a smooth switching.

  Further, since the ignition timing IG is controlled according to the exhaust gas recirculation rate REGR during the air-fuel ratio transition control, it is possible to reliably prevent an increase in output fluctuation and occurrence of knocking during the air-fuel ratio transition control.

  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, the discharge start timing CAIG (= ignition timing IG) and the discharge duration time TSPK are appropriately set, that is, the discharge start timing CAIG is relatively advanced. By setting to the side, it is possible to set the discharge duration time TSPK longer, and even if the air-fuel ratio AF is set to about “30”, the ignition can be surely performed. Further, when the target air-fuel ratio AFCMD is a lean air-fuel ratio, the target air-fuel ratio AFCMD is changed by advancing the discharge start timing CAIG and setting the discharge duration time TSPK longer as the lean air-fuel ratio increases. Can be surely ignited.

  In this embodiment, the throttle valve 3 corresponds to an intake air amount control valve, the first and second valve operating characteristic variable mechanisms 41 and 42 constitute an intake valve closing timing variable mechanism, an ignition circuit unit 7 and an ignition plug Reference numeral 8 corresponds to spark ignition means, and the partition wall 2a and the tumble flow control valve 4 correspond to flow generation means. The ECU 5 constitutes air-fuel ratio control means, transient control means, and ignition control 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 intake valve closing timing variable mechanism is configured by the first and second valve operating characteristic variable mechanisms 41 and 42, but the intake valve closing timing is only configured by the second valve operating characteristic variable mechanism 42. A variable mechanism may be configured. The invention of claim 1 can also be applied to a control device for an internal combustion engine that does not include an intake valve closing timing variable mechanism and a mechanism for generating a mixture flow in the combustion chamber.

  In the embodiment described above, a mechanism for generating a tumble flow is used as the flow generation means. However, a mechanism for generating a swirl flow may be employed. Moreover, you may comprise the shape of the combustion chamber 1a and the piston top part so that a squish flow may be produced | generated.

  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, in the present invention, the air-fuel ratio AF in the lean operation is closer to the theoretical air-fuel ratio. The present invention is also applicable to a control device that sets values (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 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.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Intake passage 2b Partition (flow production | generation means)
3 Throttle valve (intake air amount control valve)
4 Tumble flow control valve (flow generation means)
5 Electronic control unit (air-fuel ratio control means, transient control means, ignition control means)
6 Fuel injection valve 7 Ignition circuit unit (spark ignition means)
8 Spark plug (spark ignition means)
41 First valve operating characteristic variable mechanism (intake valve closing timing variable mechanism)
42 Second valve operating characteristic variable mechanism (intake valve closing timing variable mechanism)
AF air fuel ratio TH throttle valve opening LFT EGR valve lift amount CAIN intake valve operating phase VT intake valve operating characteristic TCV tumble flow control valve opening TI fuel injection time IG ignition timing

Claims (5)

In a control device for an internal combustion engine having a three-way catalyst in an exhaust system,
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;
The transient control means changes the air-fuel ratio to a richer air-fuel ratio than the rich air-fuel ratio in a period from the start of the air-fuel ratio transition control to a predetermined time, and after the predetermined time has elapsed, A control device for an internal combustion engine, which is gradually changed toward the fuel ratio. The engine includes an intake valve closing timing variable mechanism capable of delaying a closing timing of the intake valve of the engine to a timing during a compression stroke, and a flow that generates a flow of an air-fuel mixture sucked into a combustion chamber of the engine Generating means,
The transient control means controls the flow generation means to control the closing timing of the intake valve to a predetermined retardation timing within a compression stroke and to increase the flow strength of the air-fuel mixture. The control device for an internal combustion engine according to claim 1. The engine includes an intake air amount control valve that controls the amount of intake air, an exhaust gas recirculation passage that recirculates the exhaust of the engine to an intake system, and an exhaust gas recirculation control valve that is provided in the exhaust gas recirculation passage and controls the exhaust gas recirculation amount An exhaust gas recirculation mechanism comprising
2. The transient control unit performs control to increase the intake air amount by increasing the opening degree of the intake air amount control valve and decreasing the opening degree of the exhaust gas recirculation control valve. Or the control apparatus for an internal combustion engine according to 2; The engine includes spark ignition means for performing spark ignition of an air-fuel mixture in the combustion chamber,
The transient control means controls the ignition timing by the spark ignition means in accordance with an exhaust gas recirculation rate indicating a ratio of an exhaust gas recirculated through the exhaust gas recirculation mechanism during the air-fuel ratio transition control. The control apparatus for an internal combustion engine according to claim 3. The engine includes a fuel injection valve capable of atomizing and injecting fuel in an intake passage of the engine, and the spark ignition means includes a spark plug and a plurality of ignition coil pairs for generating discharge in the spark plug. It is possible to change the duration of discharge in the spark plug,
When the air-fuel ratio is controlled to the lean air-fuel ratio, the ignition control means is provided to advance the ignition timing and set the discharge duration time longer as the lean air-fuel ratio increases. Item 5. The control device for an internal combustion engine according to Item 4.

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