Combustion control system for engine

Abstract

To provide a combustion control system for an engine enabling proper combustion of air-fuel mixture while promoting early activation of a catalyst.SOLUTION: A combustion control system for an engine performs AWS control when the temperature of a catalyst 61A is lower than a catalyst determination temperature, by retarding the ignition timing and carrying out split injection in which fuel is injected in two or more specified injections including one injection during a compression stroke. During the AWS control, when the actual number of injections is equal to or less than the predetermined number of determination injections that is less than the specified number, the system determines that a split-injection abnormality has occurred. When the temperature of the catalyst 61A is lower than the catalyst determination temperature and the split-injection abnormality has occurred, the system performs failure-mode AWS control by injecting fuel collectively during an intake stroke and setting the ignition timing to a timing that is more advanced than during the AWS control and more retarded than when the temperature of the catalyst 61A is equal to or higher than the catalyst determination temperature.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a combustion control device for an engine. [Background technology]

[0002] Split injection, in which fuel is injected into the combustion chamber in multiple increments, is a known form of fuel injection in engines with spark plugs. Split injection allows the fuel to be dispersed by the first injection, while the fuel mixture around the spark plug is enriched by the second injection, thereby improving combustion stability.

[0003] Furthermore, methods for determining whether split injections are being performed appropriately have also been studied. For example, Patent Document 1 discloses a method for determining whether the number of injections has reached a desired number based on the opening period of the fuel injection valve, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 1,135,2969 Summary of the Invention [Problem to be solved by the invention]

[0005] In an engine with a catalyst installed in the exhaust passage, split injection and retarded ignition timing can suppress the deterioration of combustion stability that occurs with retarded ignition timing, while increasing the exhaust gas temperature and activating the catalyst early. However, with split injection, the fuel injection valve is repeatedly driven in a short period of time, so there is a possibility that some of the split injections will not be performed properly due to deterioration of the fuel injection valve, etc. If split injection is not performed properly, sufficient fuel will not be supplied to the combustion chamber, and good combustion will not be achieved.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to provide an engine combustion control device that can achieve early activation of a catalyst while favorably combusting an air-fuel mixture. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a combustion control device for an engine having an engine body with a combustion chamber, an exhaust passage connected to the engine body, and a catalyst arranged in the exhaust passage for purifying exhaust gas, the combustion control device comprising: a fuel injection valve that injects fuel into the combustion chamber; an ignition plug that ignites a mixture of fuel and air in the combustion chamber; and a control device that controls the fuel injection valve and the ignition plug, wherein when the temperature of the catalyst is lower than a predetermined judgment catalyst temperature, the control device retards the ignition timing of the spark plug compared to when the temperature of the catalyst is equal to or higher than the judgment catalyst temperature, and performs a split injection that injects fuel in two or more specified injections during the period from the intake stroke to the compression stroke, including one injection performed during the compression stroke. and when the AWS control is being performed, if the actual injection number, which is the number of fuel injections performed during the period from the intake stroke to the compression stroke, is equal to or less than a predetermined judgment injection number, which is less than the specified number, it is determined that a split injection abnormality has occurred in which the split injections are not being performed properly, and when the temperature of the catalyst is lower than the judgment catalyst temperature and the split injection abnormality has occurred, the fuel injection valve is made to inject fuel all at once during the intake stroke, and the ignition timing is set to a timing that is more advanced than the timing when the AWS control is being performed and more retarded than when the temperature of the catalyst is equal to or higher than the judgment catalyst temperature, and an AWS control is performed during a failure.

[0008] According to the present invention, by implementing the AWS control and retarding the ignition timing, the exhaust gas temperature can be increased, allowing the catalyst temperature to reach or exceed the critical catalyst temperature early. Furthermore, fuel is injected in two or more specified injections, including one injection during the compression stroke. This split injection allows the fuel to be dispersed over a wide area of ​​the combustion chamber, forming a highly fuel-concentrated mixture around the spark plug and improving combustion stability. This allows the catalyst to be activated early and the mixture to be combusted well.

[0009] Furthermore, when the number of fuel injections is below the threshold injection count and split injections are not performed appropriately, fault-time AWS control is implemented, in which fuel is injected into the combustion chamber all at once rather than split injections. As with AWS control, the ignition timing is set to a more retarded timing than when the catalyst temperature is equal to or higher than the threshold catalyst temperature. This ensures a sufficient amount of fuel is supplied to the combustion chamber while increasing the exhaust gas temperature and, therefore, the catalyst temperature, thereby promoting its activation. However, a fuel injection pattern in which fuel is injected all at once does not achieve the fuel distribution seen in split injections described above, resulting in lower combustion stability compared to split injections. In contrast, fault-time AWS control injects fuel all at once during the intake stroke, forming a uniform mixture throughout the combustion chamber by the time of ignition, and the ignition timing is more advanced than when AWS control is implemented. This ensures combustion stability, enabling early catalyst activation and good combustion of the mixture even when fault-time AWS control is implemented.

[0010] In the above configuration, the AWS control and the AWS control during a failure are preferably performed while the engine body is idling (claim 2).

[0011] As described above, by implementing AWS control and fault AWS control, catalyst activation can be promoted while ensuring combustion stability. Therefore, this configuration makes it possible to promote catalyst activation by utilizing the timing of idle operation while ensuring combustion stability during idle operation and, ultimately, good engine behavior.

[0012] In the above configuration, preferably, the engine body has a plurality of cylinders, and the control device determines for each cylinder whether a condition that the actual injection number is equal to or less than the judgment injection number over a plurality of combustion cycles is met, and if the condition is met for any cylinder, it determines that the split injection abnormality has occurred and performs the AWS control during failure for all cylinders (claim 3).

[0013] With this configuration, it is determined that a split injection abnormality has occurred when the condition that the number of actual injections is equal to or less than the reference injection number occurs not just once but multiple times is met, thereby preventing erroneous determination of a split injection abnormality. Furthermore, the fulfillment of the above condition is determined for each cylinder, allowing abnormalities to be detected for each cylinder. Furthermore, when the above condition is met for any cylinder, it is determined that a split injection abnormality has occurred, and failure AWS control is implemented for all cylinders. Therefore, the combustion pattern of all cylinders is made the same, thereby suppressing combustion variations between cylinders.

[0014] In the above configuration, preferably, when the failure-time AWS control is performed, the control device advances the start timing of the fuel injection when the temperature of the cooling water that cools the engine body is low more than when the temperature is high (claim 4).

[0015] With this configuration, when the cooling water temperature is low and combustion is likely to become unstable, the period during which fuel and air mix before the ignition timing is extended, thereby promoting the mixing of fuel and air before the ignition timing and ensuring combustion stability.

[0016] In the above configuration, preferably, when the AWS control during failure is performed, the control device advances the ignition timing when the temperature of the cooling water that cools the engine body is low more than when the temperature is high (claim 5).

[0017] With this configuration, when the coolant temperature is low and combustion is likely to become unstable, the ignition timing is advanced, preventing a deterioration in combustion stability.Also, when the coolant temperature is high and combustion stability is likely to be ensured, the ignition timing is retarded, raising the temperatures of the exhaust gas and the catalyst and further promoting catalyst activation. [Effects of the Invention]

[0018] As described above, the engine combustion control device of the present invention makes it possible to quickly activate the catalyst and to combust the air-fuel mixture well. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram showing a configuration of an engine according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a control block of the engine. [Figure 3] 4 is a flowchart showing the control contents executed by the control device. [Figure 4] FIG. 10 is a diagram showing the fuel injection timing, ignition timing, and combustion waveform when normal AWS control is performed. [Figure 5] FIG. 10 is a diagram showing the fuel injection timing, ignition timing, and combustion waveform when AWS control during a failure is performed. [Figure 6] 10 is a graph showing the relationship between engine water temperature and fuel injection start timing when AWS control during a failure is being performed. [Figure 7] 10 is a graph showing the relationship between engine water temperature and ignition timing when AWS control during a failure is being performed. [Figure 8] 10 is a flowchart showing a procedure for determining an abnormality in split injection. [Figure 9] FIG. 5 is a diagram corresponding to FIG. 4 and illustrating the number of times of injection skip. [Figure 10] 10 is a graph showing another example of the relationship between engine water temperature and ignition timing when AWS control during a failure is performed. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Overall engine configuration) FIG. 1 is a schematic system diagram showing a preferred embodiment of an engine E to which a combustion control device 100 according to an embodiment of the present invention is applied. The engine E includes an engine body 1 that is driven by a supply of fuel, and an intake passage 50 and an exhaust passage 60 connected to the engine body 1. The intake passage 50 is a passage through which intake air introduced into the engine body 1 flows. The exhaust passage 60 is a passage through which exhaust gas discharged from the engine body 1 flows. The engine E is installed in a vehicle such as an automobile as a power source for driving the vehicle.

[0021] The engine body 1 is a multi-cylinder engine having a plurality of cylinders 2a (only one of which is shown in FIG. 1). In this embodiment, the engine body 1 is a four-cylinder in-line engine, with the four cylinders 2a aligned in a direction perpendicular to the plane of the paper in FIG. 1. The engine body 1 includes a cylinder block 2 having the plurality of cylinders 2a formed therein, a cylinder head 3 attached to the upper surface of the cylinder block 2 so as to close the upper end openings of each cylinder 2a, and a plurality of pistons 4 housed in each cylinder 2a so as to be able to slide back and forth.

[0022] A combustion chamber 5 is defined above the piston 4 of each cylinder 2a. Fuel is supplied to the combustion chamber 5 by injection from an injector 10, which will be described later. The mixture of the supplied fuel and air is combusted in the combustion chamber 5, and the expansion force caused by the combustion causes the piston 4 to reciprocate up and down.

[0023] A crankshaft 13, which is the output shaft of the engine body 1, is provided at the bottom of the cylinder block 2 (below the pistons 4). The crankshaft 13 is connected to the pistons 4 of each cylinder 2a via connecting rods, and rotates around its central axis in response to the reciprocating motion (up and down movement) of the pistons 4.

[0024] A crank angle sensor SN1 and an engine water temperature sensor SN2 are attached to the cylinder block 2. The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 13, and the engine speed, which is the rotation speed of the crankshaft 13. The engine water temperature sensor SN2 detects the temperature of the coolant that flows through the cylinder block 2 and the cylinder head 3 to cool the engine body 1, i.e., the engine water temperature. Specifically, the cylinder block 2 and the cylinder head 3 each have a water jacket formed inside through which the coolant flows, and the engine water temperature sensor SN2 detects the temperature of the coolant flowing through this water jacket.

[0025] An intake port 6 and an exhaust port 7 that communicate with the combustion chamber 5 are formed in the cylinder head 3 for each cylinder 2a. The cylinder head 3 is equipped with an intake valve 8 that opens and closes the opening of the intake port 6 on the combustion chamber 5 side, and an exhaust valve 9 that opens and closes the opening of the exhaust port 7 on the combustion chamber 5 side, for each cylinder 2a.

[0026] The cylinder head 3 is equipped with an injector 10 and a spark plug 11, one for each cylinder 2a. One injector 10 and one spark plug 11 are provided for each cylinder 2a. The injector 10 is a fuel injection valve that injects fuel into the combustion chamber 5. In this embodiment, the injector 10 is a side-injection fuel injection valve, and its tip faces the combustion chamber 5 from the inner circumferential surface of the combustion chamber 5. The spark plug 11 is an ignition device that ignites the fuel-air mixture formed in the combustion chamber 5. In this embodiment, the spark plug 11 is disposed so that its tip, including the spark plug, faces the inside of the combustion chamber 5 from the center of the ceiling surface of the combustion chamber 5.

[0027] The intake passage 50 is connected to the cylinder head 3 so as to communicate with the intake ports 6 of each cylinder 2a. The engine E of this embodiment is a supercharged engine, and a compressor 72 is provided in the intake passage 50 as a component of the supercharger. An air cleaner 51 is provided in the intake passage 50 upstream of the compressor 72 (in the flow direction of intake air). A throttle valve 52, an intercooler 53, and a surge tank 54 are arranged in this order from upstream to downstream of the compressor 72 in the intake passage 50.

[0028] The air cleaner 51 is a filter that removes foreign matter from the intake air. The throttle valve 52 is a valve that opens and closes the intake passage 50. The amount of intake air flowing through the intake passage 50, and therefore the amount of air introduced into the engine body 1, is changed depending on the opening of the throttle valve 52. The compressor 72 is driven by a turbine 71 (described later) to supercharge the intake air, that is, to increase the temperature and pressure of the intake air. The intercooler 53 cools the intake air supercharged by the turbocharger 70. The surge tank 54 is a tank that provides a space for evenly distributing the intake air to each cylinder 2a.

[0029] An air flow sensor SN3 is disposed in the intake passage 50. The air flow sensor SN3 is disposed in a portion of the intake passage 50 between the air cleaner 51 and the compressor 72, and detects the intake air amount, which is the flow rate of the intake air passing through this portion.

[0030] The exhaust passage 60 is connected to the cylinder head 3 so as to communicate with the exhaust ports 7 of each cylinder 2a. A turbine 71 and a catalytic converter 61 are provided in the exhaust passage 60, in this order from upstream to downstream. The turbine 71 is a component of a turbocharger and is driven by exhaust gas. The catalytic converter 61 is a device that purifies exhaust gas. The catalytic converter 61 incorporates a catalyst 61A, and purifies the exhaust gas through the function of the catalyst 61A. For example, a three-way catalyst is used as the catalyst 61A. The exhaust passage 60 is also provided with a bypass passage 62 that bypasses the turbine 71 and a wastegate valve 63 that opens and closes the bypass passage 62.

[0031] An exhaust gas temperature sensor SN4 is arranged in the exhaust passage 60. The exhaust gas temperature sensor SN4 is arranged in a portion of the exhaust passage 60 between the turbine 71 and the catalytic converter 61, and detects the exhaust gas temperature, which is the temperature of the exhaust gas passing through that portion.

[0032] (Control system) FIG. 2 is a functional block diagram showing the control system of the engine E. The ECU 80 shown in this diagram is a device for overall control of the engine. The ECU 80 is composed of a microcomputer including a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input / output buses. The ECU 80 corresponds to the "control device" in this disclosure.

[0033] The ECU 80 is electrically connected to the crank angle sensor SN1, engine water temperature sensor SN2, air flow sensor SN3, and exhaust temperature sensor SN4. The vehicle is equipped with an accelerator sensor SN5 that detects the accelerator pedal position, which is the position of the accelerator pedal provided on the vehicle. The ECU 80 is also electrically connected to the accelerator sensor SN5. Each injector 10 has a built-in drive current sensor SN6 that detects its drive current. The ECU 80 is also electrically connected to the drive current sensor SN6 of each injector 10.

[0034] The ECU 80 sequentially receives information detected by the sensors SN1 to SN6, ie, information on the crank angle, engine speed, engine water temperature, intake air amount, exhaust temperature, accelerator opening, and drive current of the injector 10.

[0035] The ECU 80 controls each part of the engine E while executing various determinations and calculations based on input information from the above-mentioned sensors SN1 to SN6. The ECU 80 is electrically connected to the injector 10, the spark plug 11, the throttle valve 52, and the wastegate valve 63, and outputs control signals to these devices based on the results of the above-mentioned calculations.

[0036] (AWS: Accelerated Warm-up System) The control for quickly activating the catalyst 61A, which is a feature of the present invention, will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the contents of the control performed by the ECU 80. Steps S1 to S9 shown in Fig. 3 are repeatedly performed at predetermined intervals while the engine body 1 is running.

[0037] First, the ECU 80 reads various information detected by the sensors SN1 to SN6 etc. (Step S1) In Step S1, the ECU 80 reads at least the engine speed, intake air amount, engine water temperature, exhaust temperature, and accelerator opening.

[0038] Next, the ECU 80 estimates the catalyst temperature, which is the temperature of the catalyst 61A (step S2). The ECU 80 estimates the catalyst temperature based on the exhaust gas flow rate estimated from the intake air volume read in step S1 and the exhaust gas temperature read in step S1. For example, the ECU 80 estimates the catalyst temperature so that the higher the exhaust gas temperature, the higher the catalyst temperature.

[0039] Next, the ECU 80 determines whether the engine body 1 is idling (step S3). The ECU 80 determines that the engine body 1 is idling when the engine speed read in step S1 is equal to or lower than a preset idling speed. The idling speed is preset and stored in the ECU 80.

[0040] If the determination in step S3 is NO and the engine body 1 is not idling, the ECU 80 does not perform AWS control or failure AWS control, which will be described later, but performs normal control (step S8). In normal control, the ECU 80 sets a target engine torque, which is a target value of the engine torque, mainly based on the accelerator opening, and controls the injector 10, the throttle valve 52, and the wastegate valve 63 so that the target engine torque is realized. Also, in normal control, the ECU 80 sets the ignition timing to a timing near MBT (Minimum Advance for Best Torque), and controls the spark plug 11 so that ignition occurs at this timing. After performing step S8, the ECU 80 returns to step S1.

[0041] On the other hand, if the determination in step S3 is YES and the engine body 1 is idling, the ECU 80 determines whether or not the AWS execution condition is met (step S4). The AWS execution condition is that the catalyst temperature is equal to or lower than a predetermined determination catalyst temperature and the engine water temperature is equal to or lower than a predetermined determination water temperature. The determination catalyst temperature and the determination water temperature are set in advance and stored in the ECU 80. For example, the determination catalyst temperature is set to about 400°C, and the determination water temperature is set to about 45°C. The ECU 80 makes the determination in step S4 based on the engine water temperature read in step S1 and the catalyst temperature estimated in step S2.

[0042] If the determination in step S4 is NO, that is, if the catalyst temperature is higher than the determination catalyst temperature or the engine water temperature is higher than the determination water temperature and therefore the AWS execution condition is not satisfied, the ECU 80 does not perform AWS control or failure AWS control, but performs normal idle control (step S9). In normal idle control, the ECU 80 controls the injector 10, the throttle valve 52, and the wastegate valve 63 so that the engine speed is maintained near an idle speed set to a value higher than the idle determination speed. In normal idle control, as in normal control, the ECU 80 sets the ignition timing to a time near the MBT and controls the spark plug 11 so that ignition occurs at this time. After performing step S9, the ECU 80 returns to step S1.

[0043] On the other hand, if the determination in step S4 is YES, that is, if the catalyst temperature is equal to or lower than the determination catalyst temperature and the engine water temperature is equal to or lower than the determination water temperature, and therefore the AWS execution condition is met, the ECU 80 determines whether an abnormality has occurred in the split injection (step S5). The details of the abnormality determination in the split injection will be described later.

[0044] If the determination in step S5 is NO, and it has not been determined that the split injection is abnormal, the ECU 80 performs AWS control (step S6). Figure 4 is a diagram schematically showing the fuel injection, ignition timing, and combustion waveform (dQ) when AWS control is performed in this embodiment.

[0045] In AWS control, split injection is performed. Specifically, the ECU 80 controls the injector 10 so that fuel is injected into the combustion chamber 5 in multiple injections, that is, in the commanded number of injections set to a value equal to or greater than two, during the period from the intake stroke to the compression stroke, i.e., the period from the exhaust top dead center to the compression top dead center. The ECU 80 also controls the injector 10 so that at least a part of the multiple fuel injections is performed during the compression stroke. This commanded number of injections corresponds to the "specified number" in this disclosure.

[0046] As shown in FIG. 4 , in this embodiment, the commanded number of injections is three, and fuel is injected into the combustion chamber 5 in three separate injections during AWS control. The injection start and end timings of the first injection Q1, which is performed first, are both set during the intake stroke. The injection start and end timings of the second injection Q2, which is performed next, are set during the intake stroke and the compression stroke, respectively. The injection start and end timings of the third injection Q3, which is performed last, are both set during the compression stroke. As such, in this embodiment, a portion of the second injection Q2 and the third injection Q3 are performed during the compression stroke. Note that in this embodiment, the injector 10 is controlled so that the amounts of fuel injected into the combustion chamber 5 by the first injection Q1, the second injection Q2, and the third injection Q3 are the same.

[0047] When AWS control is performed, the ECU 80 sets the ignition timing to normal AWS ignition timing Tsp2, which is the ignition timing for AWS control, and controls the spark plug 11 so that ignition occurs at this normal AWS ignition timing Tsp2. The normal AWS ignition timing Tsp2 is retarded from the compression top dead center (TDC). Furthermore, the normal AWS ignition timing Tsp2 is retarded from the ignition timing during normal idle control and normal control. During AWS control, the air-fuel mixture is ignited (SP2) at a timing that is retarded from the ignition timing (SP1) during normal idle control and normal control. Specifically, the normal AWS ignition timing Tsp2 is retarded from the most retarded timing (Tsp1) of the ignition timings set during normal idle control and normal control. In this embodiment, the normal AWS ignition timing Tsp2 is changed according to the charging efficiency within a range that is retarded from the compression top dead center and retarded from the ignition timing during normal idle control and normal control. Hereinafter, the ignition timing during normal idle control and normal control will be referred to as normal ignition timing, where appropriate.

[0048] The normal AWS control is performed for all cylinders 2a. That is, when the normal AWS control is performed, split injection is performed for all cylinders 2a, and the ignition timing is set to the normal AWS ignition timing Tsp2 for all cylinders 2a. After performing step S6, the ECU 80 returns to step S1.

[0049] Returning to step S5, if the determination in step S5 is YES, that is, if it is determined that the split injection is abnormal, the ECU 80 performs AWS control during a failure (step S7). Figure 5 is a diagram that schematically shows the fuel injection timing, ignition timing, and combustion waveform (dQ) when AWS control during a failure is performed in this embodiment.

[0050] During failure-time AWS control, a batch injection Q11 is performed. Specifically, during failure-time AWS control, the ECU 80 controls the injector 10 so that all fuel injected into the combustion chamber 5 in one combustion cycle is injected all at once during the intake stroke. The total amount of fuel injected into the combustion chamber 5 in one combustion cycle is approximately the same during failure-time AWS control and normal AWS control. The dashed lines Q1 to Q3 in FIG. 5 indicate the fuel injection during normal AWS control. As can be seen from a comparison between the dashed line and the solid line, the start timing TQ11 of the fuel injection Q11 during failure-time AWS control is set to a timing that is more advanced than the start timing of the first fuel injection (first injection Q1) during AWS control. Hereinafter, the start timing TQ11 of the fuel injection Q11 during failure-time AWS control will be referred to as the fuel injection start timing TQ11 during failure-time AWS control where appropriate.

[0051] When fault-in-case AWS control is being performed, the ECU 80 sets the ignition timing to fault-in-case AWS ignition timing Tsp3, which is the ignition timing for fault-in-case AWS control, and controls the spark plug 11 so that ignition occurs at this fault-in-case AWS ignition timing Tsp3. Like the normal AWS ignition timing Tsp2, the fault-in-case AWS ignition timing Tsp3 is retarded from the compression top dead center (TDC) and retarded from the normal ignition timing Tsp1. However, the fault-in-case AWS ignition timing Tsp3 is set to be more advanced than the normal AWS ignition timing Tsp2. In other words, when fault-in-case AWS control is being performed, the air-fuel mixture is ignited (SP3) at a timing that is more retarded than the compression top dead center, more retarded than the ignition (SP1) during normal idle control and normal control, and more advanced than the ignition (SP2) during AWS control.

[0052] In this embodiment, the fuel injection start timing TQ11 when fault-in-case AWS control is being performed is set to a more advanced timing when the engine water temperature is low than when it is high. Fig. 6 is a graph showing the relationship between the fuel injection start timing TQ11 when fault-in-case AWS control is being performed and the engine water temperature in this embodiment. As shown in Fig. 6, in this embodiment, the lower the engine water temperature, the more advanced the fuel injection start timing TQ11 when fault-in-case AWS control is being performed.

[0053] In this embodiment, the fault-time AWS ignition timing Tsp3 is changed according to the charging efficiency within a range that is more retarded than the compression top dead center, more retarded than the normal ignition timing Tsp1, and more advanced than the normal AWS ignition timing Tsp2. Furthermore, the fault-time AWS ignition timing Tsp3 is set to a more advanced timing when the engine water temperature is low than when it is high. FIG. 7 is a graph showing the relationship between the fault-time AWS ignition timing Tsp3 and engine water temperature in this embodiment. As shown in FIG. 7, in this embodiment, the lower the engine water temperature, the more advanced the fault-time AWS ignition timing Tsp3. Specifically, under the same charging efficiency, the lower the engine water temperature, the more advanced the fault-time AWS ignition timing Tsp3 is.

[0054] The above-described AWS control during failure is performed for all cylinders 2a. That is, when AWS control during failure is performed, simultaneous injection Q11 is performed for all cylinders 2a, and the ignition timing for all cylinders 2a is set to the AWS ignition timing Tsp3 during failure. After performing step S6, the ECU 80 returns to step S1.

[0055] Next, the split injection abnormality determination (step S5) will be described in detail. FIG. 8 is a flowchart showing the contents of the split injection abnormality determination performed by the ECU 80. Steps S21 to S26 shown in FIG. 8 are performed individually for each cylinder 2a, and are repeatedly performed for each combustion cycle of each cylinder 2a. Steps S21 to S25 shown in FIG. 8 are performed when it is determined that the split injection is not abnormal. In other words, once it is determined that the split injection is abnormal, this determination is not performed.

[0056] First, the ECU 80 determines whether or not the AWS control is being performed (step S21). If the determination is NO, ie, the AWS control is not being performed, the process ends and returns to step S21.

[0057] On the other hand, if the determination in step S21 is YES and AWS control is being performed, the ECU 80 reads the drive current of the injector 10 detected by the drive current sensor SN6 (step S22). Next, the ECU 80 identifies the number of missed injections (step S23). The number of missed injections is the number of fuel injections that were not actually performed among the commanded number of injections that the ECU 80 commanded the injector 10 to perform during one combustion cycle. In this embodiment, as described above, the commanded number of injections is three, and the injector 10 is controlled to perform three fuel injections Q1 to Q3. In contrast, as shown in FIG. 9, if the second injection Q2 was not actually performed, the number of missed injections is set to 1. Furthermore, if the first injection Q1 and the second injection Q2 were not performed, the number of missed injections is set to 2.

[0058] The number of missed injections is determined based on the drive current of the injector 10 read in step S22. Specifically, when the injector 10 is driven and fuel injection is actually performed, the drive current increases beyond a predetermined value. As a result, the ECU 80 determines the number of times the drive current of the injector 10 increases beyond the predetermined value during one combustion cycle as the number of actual injections, which is the number of times fuel injections were actually performed. The ECU 80 then determines the difference between the number of actual injections and the number of command injections as the number of missed injections.

[0059] Next, the ECU 80 determines whether the identified number of injection skips is equal to or greater than a predetermined number of determination injections (step S24). The number of determination injections is preset to a value equal to or greater than 1 that is smaller than the command number of injections and is stored in the ECU 80. In this embodiment, the number of determination injections is set to 1.

[0060] If the determination in step S24 is NO, that is, the number of injection skips is less than the number of injections for determination, the ECU 80 ends the process (returns to step S21).

[0061] On the other hand, if the determination in step S24 is YES and the number of injection skips is equal to or greater than the determination injection number, the ECU 80 determines whether or not the number of combustion cycles in which the number of injection skips is equal to or greater than the determination injection number has continued for the determination cycle number or more (step S25). That is, the ECU 80 determines whether or not the number of injection skips is equal to or greater than the determination injection number during the period from the combustion cycle that is the determination number of cycles before to the current combustion cycle. The determination cycle number is set in advance and stored in the ECU 80. In this embodiment, the determination cycle number is set to 2, and it is determined whether or not the number of combustion cycles in which the number of injection skips is equal to or greater than the determination injection number has continued for two consecutive cycles.

[0062] If the determination in step S25 is NO and there are no consecutive combustion cycles in which the number of injection misses is equal to or greater than the determination number of injections, or the number of consecutive combustion cycles has not reached the determination number of cycles, ECU 80 ends the processing (returns to step S21).

[0063] On the other hand, if the determination in step S25 is YES and the number of consecutive combustion cycles has reached the determination cycle number, the ECU 80 determines that a split injection abnormality has occurred, in which split injection is not performed normally, and ends the process.

[0064] As described above, steps S21 to S25 are performed individually for each cylinder 2a, and if the determination in step S24 is YES for any of the cylinders 2a, the ECU 80 determines that a split injection abnormality has occurred.

[0065] (effect, etc.) In the above embodiment, when the catalyst temperature is lower than the catalyst determination temperature, AWS control is performed, and the ignition timing is set to the normal AWS ignition timing Tsp2, which is more retarded than the normal ignition timing Tsp1. This allows the air-fuel mixture to be burned at a later timing, thereby increasing the temperature of the exhaust gas discharged from the combustion chamber 5 to the exhaust passage 60 and, consequently, the temperature of the catalyst 61A. However, retarding the ignition timing degrades combustion stability. In contrast, AWS control injects fuel into the combustion chamber 5 in multiple increments, and fuel injection occurs during the compression stroke. This allows the air-fuel mixture in the combustion chamber 5 to be stratified. Specifically, this allows the fuel to be dispersed over a wide area in the combustion chamber 5, forming a highly fuel-concentrated air-fuel mixture around the spark plug 11. This allows the initial flame to be generated and grown more reliably, improving combustion stability. Therefore, according to the above embodiment, AWS control promotes activation of the catalyst 61A while ensuring combustion stability, i.e., while favorably combusting the air-fuel mixture.

[0066] In the above embodiment, when AWS control is being performed, if the actual injection count is smaller than the critical injection count, i.e., if there is a high possibility that split injection is not being performed appropriately, it is determined that a split injection abnormality has occurred. Then, when the catalyst temperature is lower than the catalyst critical temperature and a split injection abnormality has occurred, failure AWS control is performed, and fuel is injected into the combustion chamber 5 all at once. Therefore, compared to when split injection is performed, an appropriate amount of fuel can be more reliably supplied to the combustion chamber 5. Also, when failure AWS control is being performed, as with AWS control, the ignition timing is set to a timing that is more retarded than when the catalyst temperature is equal to or higher than the critical catalyst temperature. Therefore, the temperature of the catalyst 61A can be increased.

[0067] However, with a lump-sum fuel injection method, the concentration of the mixture around the spark plug at the ignition timing is lower than with split injection, increasing the possibility that the initial flame will not be properly generated and grow. In other words, a lump-sum fuel injection method results in lower combustion stability than split injection. In contrast, with fault-state AWS control, the ignition timing is advanced compared to when AWS control is implemented. This allows the initial flame to be properly generated and grow. Furthermore, with fault-state AWS control, fuel is injected all at once during the intake stroke, forming a uniform mixture throughout the combustion chamber 5 by the time of ignition, achieving good flame propagation. Therefore, even when fault-state AWS control is implemented, early catalyst activation can be achieved while maintaining combustion stability.

[0068] In the above embodiment, normal AWS control or fault AWS control is performed during idle operation, which ensures combustion stability and engine behavior during idle operation, while promoting activation of the catalyst 61A by utilizing the timing of idle operation.

[0069] In addition, in the above embodiment, it is determined that a split injection abnormality has occurred when a combustion cycle in which the actual injection number is equal to or less than the reference injection number occurs multiple times in the same cylinder 2a. Therefore, it is possible to avoid immediately erroneously determining that a split injection abnormality has occurred when it is determined that the actual injection number is equal to or less than the reference injection number due to accidental noise, etc. In this way, according to the above embodiment, it is possible to more appropriately determine whether a split injection abnormality has occurred.

[0070] In the above embodiment, when failure AWS control is performed, the control is performed on all cylinders 2a. That is, the ignition timing of all cylinders 2a is set to the failure AWS ignition timing Tsp3, and fuel is injected simultaneously during the intake stroke into all cylinders 2a. This prevents combustion variations due to differences in combustion patterns between the cylinders 2a.

[0071] In the above embodiment, the fuel injection start timing TQ11 during failure-time AWS control is set to be more advanced when the engine water temperature is low than when it is high. In other words, when failure-time AWS control is being performed and the engine water temperature is low, making combustion unstable, the period during which fuel and air mix before the ignition timing is extended. This promotes mixing of fuel and air before the ignition timing, ensuring combustion stability.

[0072] In the above embodiment, the failure AWS ignition timing Tsp3 is more advanced when the engine water temperature is low than when it is high. That is, when the engine water temperature is low and combustion is likely to become unstable, the ignition timing is advanced. This ensures combustion stability. When the engine water temperature is high and combustion stability is likely to be ensured, the ignition timing is retarded, which increases the temperatures of the exhaust gas and the catalyst 61A and promotes activation of the catalyst 61A.

[0073] (Variation) In the above embodiment, the case where fuel is injected into the combustion chamber 5 in three separate injections during normal AWS control has been described, but the number of injections of fuel is not limited to three.

[0074] In the above embodiment, a case has been described in which it is determined that a split injection abnormality has occurred when the number of combustion cycles in which the number of injection skips is equal to or greater than the determination injection number continues for a number of cycles or more. However, instead of this, it may be determined that a split injection abnormality has occurred when the number of combustion cycles in which the number of injection skips is equal to or greater than the determination injection number is equal to or greater than the determination cycle number. In other words, the total number of combustion cycles in which the number of injection skips is equal to or greater than the determination injection number may be used for the above determination, rather than the number of consecutive combustion cycles in which the number of injection skips is equal to or greater than the determination injection number. Furthermore, it may be determined that a split injection abnormality has occurred when the number of injection skips becomes equal to or greater than the determination injection number, regardless of the number of combustion cycles.

[0075] In the above embodiment, the fuel injection start timing TQ11 during failure-time AWS control is set to a more advanced timing as the engine water temperature decreases. However, instead, this fuel injection start timing may be set as shown in FIG. 10 . Specifically, the fuel injection start timing may be set to the same timing regardless of the engine water temperature within a predetermined range, and the lower the engine water temperature, the more advanced the fuel injection start timing becomes. Alternatively, the fuel injection start timing may be set to the same timing regardless of the engine water temperature. Similarly, the failure-time AWS ignition timing Tsp3 may be set to the same timing regardless of the engine water temperature within a predetermined range, and the lower the engine water temperature, the more advanced the failure-time AWS ignition timing Tsp3 becomes. Alternatively, the failure-time AWS ignition timing Tsp3 may be set to the same timing regardless of the engine water temperature.

[0076] The specific values ​​of the above-mentioned determination catalyst temperature, determination water temperature, determination number of injections, and determination number of cycles are not limited to those mentioned above.

[0077] In the above embodiment, the case where it is determined whether the number of injection skips is equal to or greater than the determination number of injections using the detection value of the drive current sensor SN6 built into the injector 10 has been described. However, the specific procedure for this determination is not limited to the above.

[0078] Furthermore, the specific structure of the engine body 1, such as the number of cylinders, is not limited to that described above. [Explanation of symbols]

[0079] 1 Engine body 2a cylinder 5 Combustion chamber 10 Injector (fuel injection valve) 11 Spark plug 61A Catalyst 80 ECU (control unit)

Claims

1. A combustion control device for an engine including an engine body having a combustion chamber, an exhaust passage connected to the engine body, and a catalyst disposed in the exhaust passage for purifying exhaust gas, a fuel injection valve that injects fuel into the combustion chamber; a spark plug that ignites a mixture of fuel and air in the combustion chamber; a control device for controlling the fuel injection valve and the spark plug; The control device AWS control is implemented to retard the ignition timing of the spark plug when the temperature of the catalyst is lower than a predetermined judgment catalyst temperature, compared to when the temperature of the catalyst is equal to or higher than the judgment catalyst temperature, and to cause the fuel injection valve to perform split injection, injecting fuel in two or more specified injections during the period from the intake stroke to the compression stroke, including one injection during the compression stroke; When the AWS control is being performed, if the actual injection number, which is the number of fuel injections performed during the period from the intake stroke to the compression stroke, is equal to or less than a predetermined judgment injection number, which is smaller than the specified number, it is determined that a split injection abnormality has occurred, in which the split injection is not performed appropriately, When the temperature of the catalyst is lower than the judged catalyst temperature and the split injection abnormality has occurred, the fuel injection valve injects fuel all at once during the intake stroke, and the ignition timing is advanced relative to the timing when the AWS control is performed and retarded relative to the timing when the temperature of the catalyst is equal to or higher than the judged catalyst temperature.

2. 2. The engine combustion control device according to claim 1, 10. An engine combustion control device, comprising: a combustion control unit for controlling a combustion state of an engine, the combustion state of an engine being controlled by the engine;

3. 3. The engine combustion control device according to claim 1, The engine body has a plurality of cylinders, The control device determines for each cylinder whether the condition that the actual injection number is equal to or less than the judgment injection number over a plurality of combustion cycles is met, and if the condition is met for any cylinder, determines that the split injection abnormality has occurred and performs the AWS control in the event of a failure for all cylinders.

4. 2. The engine combustion control device according to claim 1, When the AWS control during failure is performed, the control device advances the start timing of the fuel injection when the temperature of the cooling water that cools the engine body is low more than when the temperature is high.

5. 2. The engine combustion control device according to claim 1, When the AWS control during failure is performed, the control device advances the ignition timing when the temperature of the cooling water that cools the engine body is low more than when the temperature is high.

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