JP6010642B2 - Combustion control device for internal combustion engine - Google Patents

Description

  The present invention relates to a combustion control apparatus for an internal combustion engine having a three-way catalyst for exhaust purification, and more particularly, to a combustion control apparatus that performs catalyst temperature increase promotion control for accelerating the activation of the three-way catalyst during a cold start of the internal combustion engine. .

  Patent Document 1 discloses a combustion control device that performs catalyst temperature increase promotion control at the time of cold start of an internal combustion engine having a three-way catalyst in an exhaust passage. According to this device, the intake air amount of the engine is increased, the air-fuel ratio of the air-fuel mixture in the combustion chamber is controlled to be leaner than the stoichiometric air-fuel ratio, and the ignition timing is optimally ignited (ignition timing at which the engine output becomes maximum) By setting the ignition timing to a more retarded angle, the temperature increase of the three-way catalyst is promoted.

JP 2002-188500 A

  When the engine is cold started, if the ignition timing is retarded by setting the air-fuel ratio to a lean air-fuel ratio, the combustion tends to become unstable, so the ignition timing is retarded so that the combustion does not become unstable. It is necessary to set the amount relatively small. As a result, the temperature increase promotion control disclosed in Patent Document 1 cannot sufficiently raise the temperature of the exhaust gas discharged from the engine and flowing into the three-way catalyst. 100 seconds or more), and it was a factor that deteriorated fuel consumption.

  The present invention has been made paying attention to this point, and it is an object of the present invention to provide a combustion control device that can more appropriately execute catalyst temperature increase control during cold start of an engine and improve fuel efficiency. To do.

In order to achieve the above object, the invention according to claim 1 is directed to a combustion control device for an internal combustion engine in which a three-way catalyst (10) containing platinum is provided in an exhaust passage (9), and a combustion chamber (1a) of the engine. Spark ignition means (7, 8) for spark ignition of the air-fuel mixture, homogeneous lean mixture formation means (5, 6) for forming a homogeneous and lean air-fuel mixture in the combustion chamber, and immediately after starting the engine In the first three-way catalyst (10), the first temperature-rise promotion control means for executing the first temperature-rise promotion control until the control switching timing (t1), and the three-way catalyst (10) A second temperature rise promotion control means for executing a second temperature rise promotion control for promoting temperature rise after the control switching timing (t1), the spark ignition means comprising: an ignition plug (8); A plurality of ignition coil pairs (71, 72) for generating a discharge in the spark plug The discharge start timing (CAIG) and duration (TSPK) of the spark plug (8) can be changed, and the first temperature rise promotion control means increases the intake air amount of the engine. The air-fuel ratio (AF) of the air-fuel mixture is controlled to the first lean air-fuel ratio (AFTRA1) leaner than the stoichiometric air-fuel ratio, and the discharge start timing (CAIG) of the spark plug is retarded from the optimal ignition timing. The first temperature increase promotion control is executed by setting to a predetermined retarded ignition timing (CATRA1), and the second temperature increase promotion control means converts the air-fuel ratio (AF) to the first lean air-fuel ratio (AFTRA1). Furthermore, the lean side second lean air-fuel ratio (AFTRA2) is controlled, and the discharge start timing (CAIG) is further retarded from the predetermined retarded ignition timing (CATRA1). Wherein the increasing the serial spark plug of the discharge duration (TSPK).

  According to this configuration, the first temperature increase promotion control for promoting the temperature increase of the three-way catalyst is executed immediately after the start of the engine until the control switching timing, and after the control switching timing, the temperature increase of the three-way catalyst is accelerated. The second temperature increase promotion control is performed for this purpose. In the first temperature increase promotion control, the intake air amount of the engine is increased, the air-fuel ratio is controlled to the first lean air-fuel ratio leaner than the stoichiometric air-fuel ratio, and the discharge start timing of the spark plug is retarded from the optimal ignition timing. In the second temperature increase promotion control, the air-fuel ratio is controlled to a second lean air-fuel ratio that is leaner than the first lean air-fuel ratio, and the discharge start timing is delayed by a predetermined delay. Control is performed to further retard the angular ignition timing and increase the discharge duration of the spark plug. The three-way catalyst containing platinum is activated at a lower temperature by setting the air-fuel ratio to a leaner side (for example, about “22”) than the set air-fuel ratio (for example, “16”) in the conventional catalyst temperature increase promotion control. The activation of the three-way catalyst can be accelerated by performing the second temperature increase promotion control after the control switching time when the temperature of the three-way catalyst becomes higher to some extent. Therefore, the fuel efficiency can be improved by making the air-fuel ratio leaner and shortening the execution time of the catalyst acceleration control.

  According to a second aspect of the present invention, in the combustion control apparatus for an internal combustion engine according to the first aspect, the temperature parameter acquisition means for acquiring the catalyst temperature parameter (TCAT) correlated with the temperature (TCAT) of the three-way catalyst. The control switching time (t1) is a time when the catalyst temperature parameter (TCAT) reaches a predetermined temperature (TCATL).

  According to this configuration, the control switching time is set to the time when the catalyst temperature parameter reaches the predetermined temperature. Since the second temperature increase promotion control is effective after the time when the temperature of the three-way catalyst reaches the predetermined temperature, the second temperature increase promotion control is executed from the time when the catalyst temperature parameter exceeds the predetermined temperature. As a result, a remarkable temperature increase promoting effect can be obtained.

The invention according to claim 3, in the combustion control device for an internal combustion engine according to claim 2, wherein the second temperature increase promotion control means, the higher the catalyst temperature parameter (TCAT) is high the air-fuel ratio (AF) The discharge start time (CAIG) is advanced, and the discharge duration (TSPK) is decreased.

  According to this configuration, as the catalyst temperature parameter increases, the air-fuel ratio is decreased, the discharge start timing is advanced, and the discharge duration time is decreased. Since the three-way catalyst containing platinum has a characteristic that the purification performance becomes higher as the air-fuel ratio becomes closer to the theoretical air-fuel ratio when the catalyst temperature becomes higher, the higher the catalyst temperature parameter, the lower the air-fuel ratio. Performance can be obtained. In addition, by reducing the air-fuel ratio, stable combustion can be obtained even if the advance angle of the discharge start time and the discharge duration time are shortened. Therefore, the discharge start time is advanced as much as possible and the discharge duration time is reduced. As a result, the engine output can be increased and the energy efficiency can be increased.

  According to a fourth aspect of the present invention, in the combustion control device for an internal combustion engine according to any one of the first to third aspects, the flow generating means (2a, 2) for generating a flow of the air-fuel mixture sucked into the combustion chamber. 4), and the second temperature rise promotion control means controls the flow intensity to be relatively high at the start of the second temperature rise promotion control, and the air-fuel ratio is set to the first lean air-fuel ratio ( AFTRA1) The flow strength is gradually reduced from the time point (t2) when the pressure is reduced to the vicinity.

  According to this configuration, at the start of the second temperature increase promotion control, the flow strength is controlled to be relatively high, and the flow strength is gradually increased from the time when the air-fuel ratio is reduced to the vicinity of the first lean air-fuel ratio. The control to decrease is performed. By controlling the air-fuel ratio to be reduced, combustion does not become unstable even if the flow intensity is reduced, so the flow intensity can be reduced, heat loss during combustion can be reduced, and thermal efficiency can be improved. it can.

  According to a fifth aspect of the present invention, in the combustion control device for an internal combustion engine according to any one of the first to fourth aspects, the homogeneous lean air-fuel mixture forming means is a fuel injection valve capable of atomizing and injecting fuel. (6) is used to inject fuel into the intake passage (2) of the engine.

  According to this configuration, since the fuel is injected into the intake passage of the engine using the fuel injection valve capable of atomizing and injecting the fuel, a highly homogenous mixture is formed, and the homogeneous lean mixture is It is possible to ignite reliably by spark ignition and realize high-efficiency combustion with little NOx emission.

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 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 valve opening time of a fuel injection valve (6), valve opening time (TFI), and the lift amount (LFT) at the time of valve opening. It is a figure which shows transition of the cylinder pressure (PCYL) in a compression stroke and a combustion stroke. It is a figure which shows the relationship between an air fuel ratio (AF) and the activation temperature (TACT) of a three-way catalyst. It is a figure which shows the relationship between the temperature (TCAT) of a three-way catalyst, and HC purification rate ((eta) HC). It is a flowchart of the temperature increase promotion control process of a three-way catalyst. It is a figure which shows the table referred by the process of FIG. 10 is a time chart illustrating an operation example of temperature increase promotion control in FIG. 9.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing the configuration of an internal combustion engine (hereinafter referred to as “engine”) and its control device according to an embodiment of the present invention. For example, a throttle valve 3 is placed in the middle of an intake passage 2 of a four-cylinder engine 1. 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 21 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 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 exhaust passage 9 is provided with a three-way catalyst 10 containing platinum for exhaust purification. The three-way catalyst 10 is equipped with a catalyst temperature sensor 18 for detecting the temperature of the three-way catalyst 10 (hereinafter referred to as “catalyst temperature”) TCAT, and the detection signal is supplied to the ECU 5. 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 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. 3 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. It is possible to change the discharge duration (discharge duration) TSPK in the spark plug 8 according to the operating state of the engine 1 by alternately conducting energization while overlapping a part of the energization periods of the two primary coils. it can. 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). And a valve that can change the opening degree (lift amount) of the valve in at least two stages. FIG. 4A schematically shows a fuel injection state (a state in which the injected fuel is diffused) by the fuel injection valve 6, and FIG. 4B shows a fuel by a 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).

  FIG. 5 is a diagram showing the valve opening timing, the valve opening time TFI, and the lift amount LFT when the fuel injection valve 6 is opened, and the horizontal axis is the crank angle CRA. In the present embodiment, the first fuel injection FI1 is executed in the compression stroke within one combustion cycle, and the second fuel injection FI2 is executed in the intake stroke. Moreover, the first fuel injection FI1 is a fuel injection having a relatively large lift amount LFT1 and a relatively short valve opening time TFI1, and the second fuel injection FI2 has a lift amount LFT2 smaller than the lift amount LFT1 and a valve opening time. Let TFI2 be the fuel injection set longer than the valve opening time TFI1. The lift amounts LFT1, LFT2 and the valve opening times (fuel injection times) TFI1, TFI2 are set so that the total fuel injection amount in the first and second fuel injections FI1, FI2 becomes the fuel injection amount corresponding to the target air-fuel ratio AFCMD. Is set.

A fuel injection valve 6 capable of atomizing and injecting fuel is opened as shown in FIG. 5 to form a relatively homogeneous air-fuel mixture in the intake passage 2 by the first fuel injection FI1, By executing the second fuel injection FI2, 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-fuel ratio distribution in the combustion chamber is substantially uniform. It is possible to form a homogeneous (high homogeneity) homogeneous lean mixture.
It is desirable that the first fuel injection FI1 is executed in the compression stroke of the target cylinder, and the end timing of the second fuel injection FI2 is set immediately before the end timing of the intake stroke.

  In the present embodiment, the target air-fuel ratio AFCMD after completion of warm-up is set to a range of, for example, about “24” to “35” (hereinafter referred to as “ultra-lean air-fuel ratio range”). The air-fuel ratio “24” (lean side predetermined air-fuel ratio) is set so that the NOx emission amount from the engine 1 is equal to or less than an allowable upper limit value (for example, 120 ppm). The air / fuel ratio “35” is an air / fuel ratio set as a limit value for obtaining a necessary engine output.

  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.

  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, and the flame kernel is grown, so that an unburned mixture at the compression top dead center. By raising the temperature to 1000 ° K or higher, the elementary reaction that governs the combustion laminar flow rate is changed to a reaction in which hydrogen peroxide decomposes to generate OH radicals, ensuring combustion after compression top dead center Can be completed.

FIG. 6 is a diagram showing the transition of the in-cylinder pressure PCYL in the compression stroke and the combustion stroke. The solid line L1 corresponds to the present embodiment, the thick broken line L2 corresponds to HCCI (homogeneous mixture compression ignition) combustion, and the thin broken line Corresponds to stoichiometric combustion (combustion when the air-fuel ratio is set to the stoichiometric air-fuel ratio). In this figure, the crank angle CRA of 0 degrees corresponds to the compression top dead center. It should be noted that the ignition timing in the case of stoichiometric combustion is set slightly ahead of the compression top dead center (for example, a range within a crank angle of 10 degrees).
It can be confirmed that highly efficient and stable combustion can be obtained by the combustion of the homogeneous lean air-fuel mixture of the present embodiment by spark ignition.

In this embodiment, immediately after the cold start of the engine 1, the temperature increase promotion control of the three-way catalyst 10 is executed. Hereinafter, the temperature increase promotion control will be described in detail.
FIG. 7 is a diagram showing the relationship between the air-fuel ratio AF and the activation temperature TACT of the three-way catalyst 10. The solid line corresponds to the three-way catalyst 10 containing platinum in the present embodiment, and the broken line is for comparison. The relationship between the activation temperature TACT of the three-way catalyst containing palladium and the air-fuel ratio AF is shown. The activation temperature TACT is defined as a temperature at which the purification rate (HC purification rate) of hydrocarbon components in the exhaust gas becomes 10%.

  According to FIG. 7, in the three-way catalyst containing palladium, the activation temperature TACT is lowest (activation is accelerated) when the air-fuel ratio AF is in the range of about “17” to “18”, but the three-way catalyst containing platinum. In the catalyst 10, it can be confirmed that the activation temperature TACT decreases as the air-fuel ratio AF increases. Therefore, in order to activate the three-way catalyst 10 at an early stage, it is effective to perform the temperature rise promotion control with lean air-fuel ratio combustion of the air-fuel ratio “20” to “22”.

  FIG. 8 is a graph showing the relationship between the temperature of the three-way catalyst 10, that is, the catalyst temperature TCAT, and the HC purification rate ηHC, and the curves L11 to L15 correspond to the air-fuel ratio AF shown in the figure. From this figure, when the catalyst temperature TCAT is about 250 ° C., a high purification rate is obtained when the air-fuel ratio AF is “22.5”, and as the catalyst temperature TCAT rises, the air-fuel ratio AF is decreased to always reduce the air-fuel ratio AF. It can be confirmed that the rate is obtained.

  Therefore, in the temperature increase promotion control of this embodiment, the air-fuel ratio AF is controlled in accordance with the catalyst temperature TCAT from the time when the catalyst temperature TCAT has risen to some extent (for example, when the catalyst temperature TCAT has increased to 220 ° C.). The relationship between the catalyst temperature TCAT and the HC purification rate ηHC as indicated by L10 is realized.

FIG. 9 is a flowchart of the temperature increase promotion control process. This process is executed in the ECU 5 every predetermined time (for example, 10 msec).
In step S11, it is determined whether or not the catalyst temperature TCAT is lower than a predetermined upper temperature TCATH (eg, 350 ° C.). If the answer is negative (NO), that is, if the catalyst temperature TCAT is sufficiently high, the temperature increase promotion control is unnecessary. Therefore, the process is immediately terminated. If the answer to step S11 is affirmative (YES), it is determined whether or not the catalyst temperature TCAT is higher than a predetermined lower temperature TCATL (eg, 220 ° C.) (step S12). Immediately after the cold start of the engine 1, this answer is initially negative (NO), and the first temperature increase promotion control is executed in steps S13 to S16. The predetermined lower temperature TCATL corresponds to the lowest temperature at which the above-described temperature increase promotion control by the lean air-fuel ratio combustion (second temperature increase promotion control) is effective.

  In step S13, the target opening THCMD of the throttle valve 3 is set to the temperature increase promoting idle opening THFIDL, and the intake air amount of the engine 1 is increased. In step S14, the target air-fuel ratio AFCMD is set to a first predetermined air-fuel ratio AFTRA1 (eg, “16”), and in step S15, the discharge start timing CAIG of the spark plug 8 is set to a first predetermined timing that is retarded from the optimal ignition timing. While setting to CATRA1 (for example, 3 degrees), the discharge duration TSPK is set to a first predetermined time TTRA1 (for example, 2.0 msec (equivalent value of 180 mJ for discharge energy)). In step S16, the opening command value TCVCMD of the tumble flow control valve 4 is set to a relatively small first predetermined opening TCVTRA1, and the opening is set to correspond to a state where the flow intensity is relatively high. In the present embodiment, the discharge start timing CAIG is defined by the advance amount from the compression top dead center. An increase in the opening command value TCVCMD corresponds to a decrease in the strength of the tumble flow.

  The target opening THCMD, the target air-fuel ratio AFCMD, the discharge duration time TSPK, and the opening command value TCVCMD are gradually changed from the initial values at the start of the engine 1 to the set values.

  If the catalyst temperature TCAT exceeds the predetermined lower temperature TCATL by the first temperature increase promotion control, the answer to step S12 becomes affirmative (YES), and the second temperature increase promotion control by steps S21 to S24 is executed.

  In step S21, the AFCMD table shown in FIG. 10A is retrieved according to the catalyst temperature TCAT, and the target air-fuel ratio AFCMD is set. The AFCMD table is set to the first predetermined air-fuel ratio AFTRA1 when the catalyst temperature TCAT is lower than the predetermined lower temperature TCATL. When the catalyst temperature TCAT is higher than the predetermined lower temperature TCATL, the target air-fuel ratio AFCMD becomes higher. It is set to decrease. The second and third predetermined air-fuel ratios AFTRA2 and AFTRA3 in FIG. 10A are set to “22.5” and “14.7”, for example.

  In step S22, the discharge start timing CAIG and the discharge duration time TSPK are set according to the target air-fuel ratio AFCMD. Specifically, the CAIG table shown in FIG. 10B is searched according to the target air-fuel ratio AFCMD, the discharge start timing CAIG is calculated, and the TSPK table shown in FIG. 10C according to the target air-fuel ratio AFCMD. And the discharge duration TSPK is calculated.

  The CAIG table is set so that the discharge start timing CAIG decreases as the target air-fuel ratio AFCMD increases. The second and third predetermined times CATRA2 and CATRA3 in FIG. 10B are set to, for example, “0 degree” and “10 degrees”, respectively. The second predetermined timing CATRA2 is set to be retarded from the optimal ignition timing and further retarded from the first predetermined timing CATRA1.

  The TSPK table is set so that the discharge duration TSPK increases as the target air-fuel ratio AFCMD increases. The second and third predetermined times TTRA2 and TTRA3 in FIG. 10C are set to, for example, “5.0 msec” and “1.5 msec”, respectively.

  In step S23, it is determined whether or not the target air-fuel ratio AFCMD is equal to or less than a first predetermined air-fuel ratio AFTRA1. If this answer is negative (NO), the processing is immediately terminated. If the answer is positive (YES), the opening command value TCVCMD of the tumble flow control valve 4 is changed from the first predetermined opening TCVTRA1 to the second predetermined opening. A process of gradually increasing is performed until TCVTRA2 (> TCVTRA1) is reached (step S24).

  Note that at the beginning of the second temperature increase promotion control, the target air-fuel ratio AFCMD, the discharge start timing CAIG, and the discharge duration time TSPK are calculated in steps S21 and S22 from the set values in the first temperature increase promotion control. Transient control that gradually changes to the first set value is performed.

  FIG. 11 is a time chart showing an operation example of the temperature increase promotion control of FIG. 9, and FIG. 11 (a) shows transitions of the catalyst temperature TCAT and the exhaust gas temperature TEXH from the start point of the engine 1 (time t0). 11 (b) to 11 (e) show transitions of the air-fuel ratio AF, the discharge duration time TSPK, the discharge start timing CAIG, and the opening command value TCVCMD of the tumble flow control valve 4 from time t0, respectively.

  The first temperature increase promotion control is executed immediately after the start, and the air-fuel ratio AF, the discharge duration time TSPK, the discharge start timing CAIG, and the opening command value TCVCMD are respectively the first predetermined air-fuel ratio AFTRA1, the first predetermined time TTRA1, 1 predetermined time CATRA1 and first predetermined opening TCVTRA1 are set.

When the catalyst temperature TCAT reaches the predetermined lower temperature TCATL at time t1, the first temperature increase promotion control is shifted to the second temperature increase promotion control. At the beginning of the second temperature increase promotion control, transient control that gradually shifts to the first set value is performed, and the air-fuel ratio AF, the discharge duration time TSPK, and the discharge start timing CAIG are respectively set to the second predetermined air-fuel ratio AFTRA2. The second predetermined time TTRA2 and the second predetermined time CATRA2 are changed. The opening command value TCVCMD is maintained at the first predetermined opening TCVTRA1 until time t2. Time t2 is a time point when the target air-fuel ratio AFCMD decreases to the first predetermined air-fuel ratio AFTRA1 (see step S23 in FIG. 9).
At time t3, the catalyst temperature TCAT reaches the predetermined upper temperature TCATH, and the second catalyst temperature increase promotion control ends. After the end of the second temperature increase promotion control, the routine proceeds to normal control for setting the target air-fuel ratio AFCMD according to the engine operating state.

  As described above, in the present embodiment, the first temperature increase promotion control for promoting the temperature increase of the three-way catalyst 10 immediately after the engine 1 is started is executed until the time t1 when the catalyst temperature TCAT reaches the predetermined lower temperature TCATL. Then, after the time t1, the second temperature increase promotion control is executed. In the first temperature rise promotion control, the intake air amount is increased by increasing the opening degree of the throttle valve 3, the air-fuel ratio AF is controlled to the first predetermined air-fuel ratio AFTRA1 that is leaner than the stoichiometric air-fuel ratio, and the spark plug 8 Is set to a first predetermined timing CATRA1 that is retarded from the optimal ignition timing, and in the second temperature increase promotion control, the air-fuel ratio AF is set further to the lean side than the first predetermined air-fuel ratio AFTRA1. Control is performed to the second predetermined air-fuel ratio AFTRA2, the discharge start timing CAIG is further retarded from the first predetermined timing CATRA1, and the discharge duration time TSPK of the spark plug 8 is increased. The three-way catalyst 10 containing platinum has a lower temperature by setting the air-fuel ratio AF to a leaner side (for example, about “22”) than the set air-fuel ratio (for example, “16”) in the conventional catalyst temperature increase promotion control. The activation of the three-way catalyst 10 can be accelerated by performing the second temperature increase promotion control after time t1 when the catalyst temperature TCAT reaches the predetermined lower temperature TCATL. Therefore, fuel efficiency can be improved by making the air-fuel ratio AF leaner and shortening the execution time of the catalyst acceleration control.

  The second temperature increase promotion control is effective after the time when the temperature TCAT of the three-way catalyst 10 reaches the predetermined lower temperature TCATL, so that the catalyst temperature TCAT exceeds the predetermined lower temperature TCATL. By executing the second temperature increase promotion control, a remarkable temperature increase promotion effect is obtained.

  In the second temperature increase promotion control, the air-fuel ratio AF is decreased as the catalyst temperature TCAT becomes higher, the discharge start timing CAIG is advanced, and the discharge duration time TSPK is decreased. The three-way catalyst 10 containing platinum has a characteristic that when the catalyst temperature TCAT becomes higher, the purification performance becomes higher as the air-fuel ratio AF is closer to the theoretical air-fuel ratio. Therefore, the air-fuel ratio AF (target air-fuel ratio becomes higher as the catalyst temperature TCAT becomes higher. High purification performance can be obtained by reducing (ACMD). Further, by reducing the air-fuel ratio AF, stable combustion can be obtained even if the advance angle of the discharge start timing CAIG and the discharge duration time TSPK are shortened, so that the discharge start timing CAIG is advanced as much as possible and the discharge is continued. By reducing the time TSPK, the engine output can be increased and the energy efficiency can be increased.

  At the start of the second temperature increase promotion control, the opening degree of the tumble flow control valve 4 is set to the first predetermined opening degree TCVTRA1, and the flow intensity is controlled to be relatively high. Control is performed to gradually decrease the strength of the flow from the time when it is reduced to the vicinity of the predetermined air-fuel ratio AFTRA1. By controlling to reduce the air-fuel ratio AF, combustion does not become unstable even if the flow intensity is reduced, so the flow intensity is reduced, heat loss during combustion is reduced, and thermal efficiency is improved. Can do.

  In addition, fuel is injected into the intake passage 2 of the engine 1 by using the fuel injection valve 6 that can inject and atomize the fuel, so that a highly homogenous mixture is formed and the homogeneous lean mixture is spark-ignited. Therefore, it is possible to realize ignition with high efficiency and low NOx emission amount and high efficiency combustion.

  In the present embodiment, the ignition circuit unit 7 and the spark plug 8 correspond to spark ignition means, the partition wall 2a and the tumble flow control valve 4 correspond to flow generation means, and the catalyst temperature sensor 18 constitutes temperature parameter acquisition means. The ECU 5 constitutes first and second temperature increase promotion control means, and the fuel injection valve 6 and the ECU 5 constitute a homogeneous lean mixture forming 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 detected catalyst temperature TCAT is used as the catalyst temperature parameter. However, instead of the catalyst temperature TCAT, the following parameter, that is, an exhaust temperature sensor is arranged on the upstream side of the three-way catalyst 10. The exhaust temperature TEXH detected by the exhaust temperature sensor may be used as the catalyst temperature parameter. In such a modification, the exhaust temperature sensor constitutes a temperature parameter acquisition means. Further, for example, the estimated catalyst temperature TCATE may be calculated according to the operating state of the engine 1 using a catalyst temperature estimation method disclosed in JP 2012-77740 A, and the estimated catalyst temperature TCATE may be used as a catalyst temperature parameter.

  In the above-described embodiment, the control switching timing (time t1) at which the first temperature increase promotion control is shifted to the second temperature increase promotion control is set to the time when the catalyst temperature TCAT reaches the predetermined lower temperature TCATL. For example, the elapsed time from the cold start start time of the engine 1 reaches the time when the catalyst temperature TCAT is estimated to reach the predetermined lower temperature TCATL, or from the cold start start time. When the fuel injection amount integrated value reaches a value estimated that the catalyst temperature TCAT reaches the predetermined lower temperature TCATL, that is, the catalyst temperature TCAT is estimated to reach a temperature at which the second temperature increase promotion control is effective. The time point may be the “control switching time”.

  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. Further, although two coil pairs of the ignition circuit unit 7 are provided corresponding to one ignition plug, three or more coil pairs may be provided.

  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 combustion 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 2a Partition (flow production | generation means)
3 Throttle valve 4 Tumble flow control valve (flow generation means)
5 Electronic control unit (first and second temperature rise promotion control means, homogeneous lean mixture formation means)
6 Fuel injection valve (homogeneous lean mixture formation means)
7 Ignition circuit unit (spark ignition means)
8 Spark plug (spark ignition means)
9 Exhaust passage 10 Three-way catalyst 18 Catalyst temperature sensor (temperature parameter acquisition means)
19 Actuator AFCMD Target air-fuel ratio CAIG Discharge start timing TSPK Discharge duration

Claims (5)

In the combustion control device for an internal combustion engine in which a three-way catalyst containing platinum is provided in the exhaust passage,
Spark ignition means for performing spark ignition of the air-fuel mixture in the combustion chamber of the engine;
Homogeneous lean mixture forming means for forming a homogeneous and lean mixture in the combustion chamber;
First temperature increase promotion control means for executing first temperature increase promotion control for accelerating the temperature increase of the three-way catalyst immediately after starting the engine until the control switching time;
Second temperature increase promotion control means for executing second temperature increase promotion control for promoting temperature increase of the three-way catalyst after the control switching timing;
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 start timing and duration in the ignition plug,
The first temperature increase promotion control means increases the intake air amount of the engine to control the air-fuel ratio of the air-fuel mixture to a first lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio, and to start discharge of the spark plug Is set to a predetermined retarded ignition timing that is retarded from the optimal ignition timing, to execute the first temperature increase promotion control,
The second temperature increase promotion control means controls the air-fuel ratio to a second lean air-fuel ratio that is leaner than the first lean air-fuel ratio, and retards the discharge start timing further than the predetermined retard ignition timing. In addition, a combustion control apparatus for an internal combustion engine, characterized by increasing a discharge duration of the spark plug. Comprising a temperature parameter acquisition means for acquiring a catalyst temperature parameter correlated with the temperature of the three-way catalyst,
The combustion control device for an internal combustion engine according to claim 1, wherein the control switching time is a time when the catalyst temperature parameter reaches a predetermined temperature. The second temperature increase promotion control means, the catalyst temperature parameter reduces the air-fuel ratio higher increases, according to claim 2, characterized in that reducing the discharge duration time with advancing the said discharge start timing Combustion control device for internal combustion engine. A flow generation means for generating a flow of the air-fuel mixture sucked into the combustion chamber;
The second temperature increase promotion control means controls the flow intensity to be relatively high at the start of the second temperature increase promotion control, and from the time when the air-fuel ratio is reduced to the vicinity of the first lean air-fuel ratio. The combustion control device for an internal combustion engine according to any one of claims 1 to 3, wherein the strength of the flow is gradually reduced.   The said homogeneous lean air-fuel | gaseous mixture formation means injects a fuel in the intake passage of the said engine using the fuel injection valve which can atomize and inject fuel. A combustion control device for an internal combustion engine according to claim 1.

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