Engine control device

Abstract

To suppress the occurrence of intermittent chain misfire and improve stability of an operation state of an engine, regarding a control device of the engine.SOLUTION: A control device 9 of an engine controls the engine 10 which has a plurality of cylinders 1 which can execute ignition retard control and in which valve overlap of an intake valve 2 and an exhaust valve 3 can be set. The exhaust valve 3 is provided in each of the plurality of cylinders 1. When misfire occurs in a first cylinder to be one of the plurality of cylinders 1 during execution of the ignition retard control and the valve overlap in the plurality of cylinders 1, the control device 9 advances ignition timing of a second cylinder which is a cylinder different from the first cylinder and has an exhaust valve 3 which becomes an open state during opening of the exhaust valve 3 provided in the first cylinder, as compared with a case where misfire does not occur in the first cylinder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device for a multi-cylinder engine in which ignition retard control can be performed and valve overlap of intake valves and exhaust valves can be set. [Background technology]

[0002] Conventionally, in the control of a multi-cylinder engine (internal combustion engine), a technique is known that improves the startability and stability of the engine's operating state by changing the fuel injection timing of a cylinder in which a misfire has occurred. For example, a control is known in which the fuel injection timing is advanced from normal in the next combustion cycle in the cylinder in which a misfire has occurred (see Patent Document 1). Such control can improve the ignitionability of the fuel and suppress the recurrence of misfire in that cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-169999 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of this invention discovered a phenomenon in which misfires occur intermittently and in a chain reaction between different cylinders at intervals of three or more strokes in multi-cylinder engines in which valve overlap between the intake and exhaust valves can be set. This phenomenon is hereinafter referred to as "intermittent chain misfires." It is believed that intermittent chain misfires occur when a temporary drop in exhaust manifold pressure (exhaust manifold pressure) caused by a misfire in one cylinder adversely affects the intake conditions of other cylinders.

[0005] For example, in an engine with a valve overlap setting, the exhaust manifold is under higher pressure than the intake manifold, causing a portion of the exhaust gas to flow back into the intake port during the valve overlap period. This causes the fuel adhering to the intake port to vaporize quickly and then enter the cylinder. On the other hand, if a cylinder misfires, the internal cylinder pressure during the combustion stroke of that cylinder drops, and when the exhaust valve opens, gases (exhaust gases and unburned gases) present inside the exhaust manifold flow back into the cylinder, temporarily reducing the exhaust manifold pressure. This also reduces the temperature of the gases present inside the exhaust manifold.

[0006] If another cylinder enters its valve overlap period before the reduced exhaust manifold pressure recovers, less gas flows back into the intake port of that cylinder, causing the temperature to drop. This reduces the amount of fuel vaporized in the intake port, making misfires more likely. The likelihood of misfires increasing the further the ignition timing is retarded from the optimal ignition timing MBT (Minimum Spark Advance for Best Torque) (i.e., the greater the retard amount of ignition retard control).

[0007] One of the objectives of the present invention, which was devised in light of the above-mentioned problems, is to provide an engine control device that can suppress the occurrence of intermittent misfires and improve the stability of the engine's operating state. However, in addition to this objective, another objective of the present invention is to achieve effects derived from the various configurations shown in the "Mode for Carrying Out the Invention" below, which are not obtainable with conventional technologies. [Means for solving the problem]

[0008] The disclosed engine control device can be realized as the following disclosed aspects (application examples), which solve at least part of the above-mentioned problems. Each of the aspects from aspect 2 onwards is an aspect that can be selected as an additional aspect, and each of the aspects can be omitted. None of the aspects from aspect 2 onwards discloses an aspect or configuration that is essential to the present invention.

[0009] Aspect 1. The disclosed engine control device controls an engine having multiple cylinders in which ignition retard control can be performed and valve overlap of the intake valve and the exhaust valve can be set. The exhaust valve is provided for each of the multiple cylinders. Furthermore, when a first cylinder, which is one of the multiple cylinders, misfires while the ignition retard control and the valve overlap are being performed for the multiple cylinders, the control device advances the ignition timing of a second cylinder, which is a different cylinder from the first cylinder and has an exhaust valve that opens when the exhaust valve of the first cylinder opens, compared to when the first cylinder does not misfire.

[0010] Aspect 2. In the aspect 1 described above, it is preferable that the amount of advance of the ignition timing of the second cylinder is increased as the valve overlap of the second cylinder increases. Aspect 3. In the above aspect 1 or 2, it is preferable that the amount of advance of the ignition timing of the second cylinder is increased as the amount of retard of the ignition timing of the second cylinder is increased. Aspect 4. In any of Aspects 1 to 3 above, it is preferable that the advance amount of the ignition timing of the second cylinder is increased as the temperature of the engine decreases.

[0011] Aspect 5. In any of Aspects 1 to 4 above, when the second cylinder experiences intermittent misfires after the first cylinder experiences misfires, it is preferable to advance the ignition timing of a third cylinder, separate from the second cylinder, that has an exhaust valve that opens when the exhaust valve of the second cylinder opens, and increase the valve overlap of the third cylinder, compared to when the second cylinder does not experience intermittent misfires. [Effects of the Invention]

[0012] The disclosed engine control device makes it difficult for misfires to occur, even when a temporary drop in exhaust manifold pressure due to a misfire in one cylinder adversely affects the intake state of another cylinder, thereby suppressing the occurrence of intermittent chain misfires and improving the stability of the engine's operating state. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a block diagram showing the configuration of an engine to which a control device of the present invention is applied; [Figure 2] FIG. 2 is a diagram showing a combustion cycle of the engine shown in FIG. [Figure 3] These are graphs showing changes in the operating state of the engine over time. (A) is a graph of the in-cylinder pressure (cylinder #1), (B) is a graph of the valve lift (cylinder #1), (C) is a graph of the flow rate through the exhaust valve (cylinder #1), (D) is a graph of the exhaust manifold pressure, (E) is a graph of the valve lift (cylinder #2), and (F) is a graph of the flow rate through the intake valve (cylinder #2). [Figure 4] (A) is a graph showing the relationship between valve overlap and advance angle amount, (B) is a graph showing the relationship between retard amount and advance angle amount, and (C) is a graph showing the relationship between engine coolant temperature (cylinder temperature) and advance angle amount. [Figure 5] 4 is a flowchart illustrating a control procedure performed by the control device. [Figure 6] 4 is a flowchart illustrating a control procedure performed by the control device. [Figure 7] 1 shows the combustion cycle of a multi-cylinder engine, where (A) is an example of a five-cylinder in-line engine, (B) is an example of a six-cylinder in-line engine, and (C) is an example of an eight-cylinder in-line engine. DETAILED DESCRIPTION OF THE INVENTION

[0014] The disclosed control device is applied to an engine shown in the following embodiment. This engine is an internal combustion engine mounted on, for example, a vehicle, a machine tool, a ship, a generator, various test equipment, etc. In the following embodiment, an engine mounted on a vehicle is assumed. The engine according to the present invention is an engine capable of implementing ignition retard control and is a multi-cylinder engine in which the valve overlap (VOL) of the intake valve and the exhaust valve can be set.

[0015] The engine according to the present invention is an engine having multiple cylinders each having at least a spark plug, an intake valve, and an exhaust valve, and is equipped with a means for controlling the timing of ignition by the spark plug. The valve overlap may be preset to a fixed value so that the opening periods of the intake valve and the exhaust valve overlap, or the overlap period may be variable. In the latter case, the valve overlap may be set according to, for example, the engine's operating conditions (engine speed, load, intake air amount, air-fuel ratio, cylinder temperature, engine coolant temperature, oil temperature, etc.). Note that "ignition" in the present invention refers to the generation of a spark that triggers a combustion reaction in a cylinder. The engine according to the present invention includes SI (Spark Ignition) engines and SCCI (Spark Controlled Compression Ignition) engines.

[0016] The ignition retard control in this case refers to control that retards the ignition timing for each cylinder relative to normal operation (when ignition retard control is not being performed). In this embodiment, the ignition timing is retarded relative to the optimal ignition timing MBT. The optimal ignition timing MBT refers to the ignition timing that is expected to maximize engine torque under the current operating conditions. It is determined, for example, based on the amount of air introduced into the cylinder (charging efficiency), the air-fuel ratio (fuel amount), the compression ratio, and other factors. On the other hand, if the ignition timing is always set to the optimal ignition timing MBT, knocking may occur more easily depending on the operating conditions, or combustion stability and exhaust temperature may not increase easily. The ignition retard control is implemented in consideration of these circumstances. In the ignition retard control, the amount of retardation of the ignition timing (the amount of retardation relative to the optimal ignition timing MBT) is controlled based on, for example, the expected knocking intensity, engine combustion stability, exhaust temperature (the activation temperature of the exhaust gas purification catalyst), and required torque. [Example]

[0017] [1. Configuration] FIG. 1 is a block diagram showing an engine 10 to which a control device 9 according to an embodiment of the present invention is applied. The engine 10 is a four-cylinder in-line engine, and each of the four aligned cylinders 1 is provided with an ignition plug 4. An intake port 11 and an exhaust port 12 are connected to each cylinder 1. An intake valve 2 is provided at the boundary between each cylinder 1 and the intake port 11 in an openable and closable manner, and an exhaust valve 3 is provided at the boundary between each cylinder 1 and the exhaust port 12 in an openable and closable manner. In the example shown in FIG. 1, two intake ports 11 and two exhaust ports 12 are connected to each cylinder 1.

[0018] An intake port 11 of each cylinder 1 is provided with a fuel injection valve 5 (port injection valve) that injects fuel into the intake port 11. In this embodiment, a control device 9 controls the opening and closing states (valve lift amount, valve timing) of the intake valve 2 and the exhaust valve 3, the ignition timing of the spark plug 4, and the injection state (injection amount, injection timing) from the fuel injection valve 5. Note that the engine 10 may be one that performs in-cylinder injection instead of port injection, or one that uses both port injection and in-cylinder injection.

[0019] An intake manifold 13 is connected upstream of the intake ports 11 of each cylinder 1, and a throttle valve 16 is installed in an intake passage 15 upstream of the intake manifold 13. Intake air that passes through the throttle valve 16 passes through the inside of the intake manifold 13, which is formed into branches, and is introduced into each cylinder 1. An exhaust manifold 14 is connected downstream of the exhaust ports 12 of each cylinder 1, and an exhaust purification catalyst 18 is installed in an exhaust passage 17 downstream of the exhaust manifold 14. Exhaust gas emitted from each cylinder 1 passes through the inside of the exhaust manifold 14 and is introduced into the exhaust purification catalyst 18, where it is purified.

[0020] The control device 9 is a computer (electronic control device, ECU, Electronic Control Unit) for controlling the operating state of the engine 10 in accordance with the running state of the vehicle. The control device 9 has a built-in processor (arithmetic processing device) and memory (storage device). The contents of the control (control program) performed by the control device 9 are stored in the memory, and are executed by being read into the processor as appropriate.

[0021] A knock sensor 6, an engine speed sensor 7, and a temperature sensor 8 are connected to the control device 9. The knock sensor 6 is a sensor that detects knocking vibrations (vibration displacement, deflection, acceleration, etc.) of the engine 10, and is attached to the cylinder block or the like. Information on the knocking vibrations detected here is used to set the retard amount in ignition retard control.

[0022] The engine speed sensor 7 is a sensor that detects the rotational speed (number of rotations per unit time, angular velocity) of the engine 10, and is attached near the crankshaft or flywheel, etc. The information on the rotational speed detected here is used to determine misfires in each cylinder 1, as well as to set the retard amount in ignition retard control.

[0023] The temperature sensor 8 is a sensor that detects the temperature of the engine 10 (cylinder temperature, engine coolant temperature, oil temperature, etc.), and is attached to the cylinder block, cooling system, etc. The temperature information detected here is used, for example, to set the valve overlap, the retard amount in ignition retard control, and the advance amount in chain break control, which will be described later.

[0024] The control device 9 of this embodiment has a function to implement control to prevent intermittent chain misfires. Intermittent chain misfires are misfires that occur intermittently and in a chain reaction between different cylinders 1 at intervals of three or more strokes. Intermittent chain misfires are thought to be caused by a temporary drop in exhaust manifold pressure due to a misfire in one cylinder 1 adversely affecting the intake condition of another cylinder 1, thereby reducing the combustion stability of that cylinder 1.

[0025] The mechanism by which intermittent chain misfires occur will be explained using Figures 2 and 3. Figure 2 is a diagram showing the combustion cycle of each cylinder 1 of the engine 10. #1, #2, #3, and #4 in Figure 2 are cylinder numbers corresponding to #1, #2, #3, and #4 in Figure 1, and are numbered to correspond to the physical arrangement order of each cylinder 1. The ignition order in this embodiment is #1, #3, #4, and #2. The crank angle [° CA] shown in Figure 2 represents the rotation angle of the crankshaft relative to the bottom dead center where the compression stroke of cylinder #1 begins.

[0026] 3A and 3B are graphs showing changes over time in the operating state of the engine 10. Fig. 3A is a graph of the in-cylinder pressure (cylinder #1), Fig. 3B is a graph of the valve lift (cylinder #1), Fig. 3C is a graph of the flow rate through the exhaust valve (cylinder #1), Fig. 3D is a graph of the exhaust manifold pressure, Fig. 3E is a graph of the valve lift (cylinder #2), and Fig. 3F is a graph of the flow rate through the intake valve (cylinder #2).

[0027] As shown in Figure 2, let us consider the case where a misfire occurs for some reason during the combustion stroke of cylinder #1. Each cylinder 1 is set to a specific valve overlap, and the ignition timing is controlled to be more retarded than the optimal ignition timing MBT by ignition retard control. When a misfire occurs in cylinder #1, the in-cylinder pressure during the combustion stroke of cylinder #1 drops significantly compared to when no misfire occurs, as shown in Figure 3(A). As a result, the in-cylinder pressure of cylinder #1 becomes negative (a pressure below atmospheric pressure, or at least lower than the exhaust manifold pressure) just before the exhaust valve 3 opens (in the latter half of the combustion stroke).

[0028] As shown in Figure 3(B), the exhaust valve 3 of cylinder #1 begins to open at a crank angle of approximately 360° CA, and the cylinder enters the exhaust stroke. At this time, the internal pressure of cylinder #1 is negative, so exhaust gases present in the exhaust manifold 14 and exhaust port 12 flow back into cylinder #1. As shown by the dashed line in Figure 3(C), the flow rate of gas passing through the exhaust valve 3 of cylinder #1 is negative at the beginning of the exhaust stroke. This causes the exhaust manifold pressure to temporarily become negative, as shown by the dashed line in Figure 3(D).

[0029] At this time, as shown in Figure 3(E), the combustion cycle of the #2 cylinder is transitioning from the exhaust stroke to the intake stroke, and both the intake valve 2 and the exhaust valve 3 are open (valve overlap period). If the exhaust manifold pressure had been maintained at a certain level, the high-temperature exhaust gas present inside the exhaust manifold 14 would have passed through the intake valve 2 and the exhaust valve 3 of the #2 cylinder and flowed backward, promoting the vaporization of the fuel adhering to the intake port 11 of the #2 cylinder. In this case, as shown by the solid line in Figure 3(F), the exhaust gas in the exhaust manifold 14 flows into the intake manifold 13, causing the flow rate of gas passing through the intake valve 2 of the #2 cylinder to swing significantly to a negative value (backflow).

[0030] However, because the exhaust manifold pressure is low at the beginning of the exhaust stroke of cylinder #1, the amount of backflow (blowback) to the intake port 11 of cylinder #2 is reduced. As shown by the dashed line in Figure 3(F), the flow rate of gas passing through intake valve 2 of cylinder #2 only slightly fluctuates toward negative values, or becomes nearly zero. Also, because high-temperature exhaust gas is not generated during the combustion stroke of cylinder #1, even if backflow occurs, the temperature of the gas will be low.

[0031] For these reasons, the fuel adhering to the intake port 11 of the #2 cylinder is less likely to vaporize, reducing the amount of fuel flowing into the #2 cylinder during its intake stroke, causing the #2 cylinder's air-fuel ratio to become leaner than expected. As a result, the #2 cylinder misfires during its combustion stroke (after the crank angle reaches 720° CA in Figure 2). In other words, after the #1 cylinder misfires, only the #2 cylinder misfires after an interval of three strokes, even though the #3 and #4 cylinders do not misfire.

[0032] Furthermore, the intermittent chain misfires continue to occur. That is, the temporary drop in exhaust manifold pressure caused by the misfire in cylinder #2 adversely affects the intake condition of cylinder #4, causing a misfire in cylinder #4 after a three-stroke interval. Furthermore, the temporary drop in exhaust manifold pressure caused by the misfire in cylinder #4 causes a misfire in cylinder #3 after a three-stroke interval. Therefore, the intermittent chain misfires continue cyclically in the reverse order of ignition: #1, #2, #4, #3, #1, #2, #4, #3...

[0033] To suppress the above-described intermittent chain misfires, the control device 9 of this embodiment implements control (chain breaking control) to break the intermittent chain. Chain breaking control is a control that advances the initial ignition timing of another cylinder 1 after a misfire occurs when one cylinder 1 (first cylinder) among the multiple cylinders 1 misfires. Here, the misfiring cylinder 1 is defined as the first cylinder, and the cylinder 1 whose ignition timing is to be advanced is defined as the second cylinder. The second cylinder is defined as a cylinder 1 that satisfies the following conditions: A cylinder 1 that does not satisfy the following conditions is not targeted for advancing the ignition timing. Furthermore, if the valve overlap of all cylinders 1 is zero, intermittent chain misfires due to the above-described mechanism do not occur, and therefore chain breaking control is not implemented. Immediately after the exhaust valve 3 of the first cylinder opens, the second cylinder begins its intake stroke. When the exhaust valve 3 of the first cylinder is open, the exhaust valve 3 of the second cylinder is open. The valve overlap of the second cylinder is set to include the period after the exhaust valve 3 of the first cylinder is opened.

[0034] The chain breaking control is executed at least when the ignition retard control is executed for the second cylinder when the misfire occurs in the first cylinder. The execution conditions for the chain breaking control may include the following conditions. The temperature of the engine 10 is below a predetermined temperature (is in a cold state). Catalyst warm-up control for the exhaust purification catalyst 18 is being carried out. The retard amount of the ignition retard control exceeds the specified amount R0. (The ignition timing is controlled to a certain extent in the retard direction.) The valve overlap exceeds the specified value V0. (This is a condition in which some exhaust gas is expected to blow back into the intake port.)

[0035] In this embodiment, a misfire occurs when the exhaust temperature is increased by ignition retard and valve overlap for catalyst warm-up. The second cylinder may be defined as follows: If the first cylinder had not misfired, the exhaust gas emitted by the first cylinder would have been drawn into the cylinder.

[0036] When the #1 cylinder shown in FIG. 2 misfires, the first cylinder is #1 and the second cylinder is #2. Therefore, immediately after the #1 cylinder misfires, the ignition timing of the #3 and #4 cylinders is not advanced, but only the ignition timing of the #2 cylinder is advanced. Furthermore, when the #2 cylinder misfires, the #2 cylinder becomes the first cylinder and the #4 cylinder becomes the second cylinder. Therefore, immediately after the #2 cylinder misfires, the ignition timing of the #1 and #3 cylinders is not advanced, but only the ignition timing of the #4 cylinder is advanced. This type of ignition timing advance control in the chain break control need only be performed once, at the first ignition of the second cylinder after the first cylinder misfires, but may also be performed continuously during subsequent ignitions of the second cylinder.

[0037] The amount of advance of the ignition timing in the chain break control is preferably set within a range equal to or less than the retard amount in the ignition retard control currently being performed. In other words, the ignition timing is preferably adjusted within a range on the retard side of the optimal ignition timing MBT. The amount of advance may be set according to the valve overlap, the amount of retard, or the temperature of the engine 10. Alternatively, the amount of advance may be set by a combination of these (for example, according to the valve overlap and the amount of retard).

[0038] For example, the advance amount may be set using the relationships shown in Figures 4(A) to 4(C). Figure 4(A) is a graph showing the relationship between valve overlap and advance amount. As shown in Figure 4(A), the advance amount of the ignition timing of the second cylinder may be increased as the valve overlap of the second cylinder increases. The predetermined value V0 in Figure 4(A) corresponds to the minimum value of valve overlap for advancing the ignition timing, and is set to a value greater than or equal to 0.

[0039] FIG. 4B is a graph showing the relationship between the retard amount and the advance amount. As shown in FIG. 4B, the greater the retard amount of the ignition timing of the second cylinder, the greater the advance amount of the ignition timing of the second cylinder. The predetermined amount R0 in FIG. 4B corresponds to the minimum retard amount for advancing the ignition timing and is set to a value greater than or equal to 0. The dashed line in FIG. 4B plots the advance amount at which the ignition timing after advance reaches the optimal ignition timing MBT (the line at which the advance amount and the retard amount are the same value).

[0040] 4(C) is a graph showing the relationship between engine coolant temperature (cylinder temperature) and the advance amount. As shown in FIG. 4(C), the advance amount of the ignition timing of the second cylinder may be increased as the temperature of engine 10 (engine coolant temperature or cylinder temperature) decreases. Note that the temperature of engine 10 referred to here may be the temperature detected by temperature sensor 8, or may be a temperature calculated based on the temperature detected by temperature sensor 8.

[0041] The chain break control described above may include a control for increasing the valve overlap. For example, when the #1 cylinder shown in FIG. 2 misfires, the valve overlap of the #2 cylinder may be temporarily increased and the ignition timing of the #2 cylinder may be advanced. Furthermore, a control for increasing the valve overlap may be added when an intermittent chain misfire occurs. For example, when the #1 cylinder shown in FIG. 2 misfires, the ignition timing of the #2 cylinder may be advanced, but if a misfire occurs in the #2 cylinder, the valve overlap of the #4 cylinder (the third cylinder whose exhaust valve 3 opens when the exhaust valve 3 of the second cylinder opens) may be temporarily increased and the ignition timing of the #4 cylinder may be advanced. The increase in the valve overlap of the third cylinder after the intermittent chain misfire of the second cylinder may be performed not only on the third cylinder but also on all cylinders.

[0042] In the chain break control described above, a control for increasing the fuel injection amount may be added. For example, when the #1 cylinder shown in FIG. 2 misfires, the fuel injection amount of the #2 cylinder may be temporarily increased and the ignition timing of the #2 cylinder may be advanced. Furthermore, a control for increasing the fuel injection amount may be added on the condition that an intermittent chain misfire occurs. For example, when the #1 cylinder shown in FIG. 2 misfires, the ignition timing of the #2 cylinder may be advanced, but if a misfire occurs in the #2 cylinder, the fuel injection amount of the subsequent #4 cylinder may be temporarily increased and the ignition timing of the #4 cylinder may be advanced.

[0043] [2. Flowchart] 5 is a flowchart illustrating the procedure for the chain break control. The chain break control shown in this flowchart is repeatedly executed at a predetermined interval when ignition retard control and valve overlap are being performed while the engine 10 is operating. In this embodiment, the control is executed when the catalyst is warming up. Here, it is assumed that all four cylinders 1 have the same valve overlap and the retard amount by the ignition retard control is also the same.

[0044] In step A1, it is determined whether or not the engine 10 is in a cold state based on the temperature detected by the temperature sensor 8. If the condition in step A1 is not established, it is determined that the conditions for implementing chain breaking control are not met (a state in which misfires are unlikely to occur, and chain breaking control is unnecessary), and this flow ends. On the other hand, if the condition in step A1 is established, the flow proceeds to step A2. In step A2, it is determined whether or not the valve overlap exceeds a predetermined value V0. If step A2 is not established, it is determined that the conditions for implementing chain breaking control are not met (a state in which exhaust gas in the exhaust manifold 14 is unlikely to flow back into the intake manifold 13, and intermittent chain misfires are unlikely to occur, and chain breaking control is unnecessary), and this flow ends. On the other hand, if the condition in step A2 is established, the flow proceeds to step A3.

[0045] In step A3, it is determined whether the retard amount in the ignition retard control exceeds a predetermined amount R0. If the condition in step A3 is not established, it is determined that the conditions for implementing the chain breaking control are not met (a state in which misfire is unlikely to occur, and chain breaking control is unnecessary), and this flow ends. On the other hand, if the condition in step A3 is established, the flow proceeds to step A4. From step A4 onwards, a misfire is determined, and the cylinder 1 to be subjected to the chain breaking control is identified based on the cylinder number of the misfiring cylinder 1, and then the chain breaking control is implemented.

[0046] First, in step A4, it is determined whether or not the #1 cylinder has misfired based on the rotational speed of the engine 10 detected by the engine speed sensor 7. If this condition is met, the process proceeds to step A5, where chain breaking control is performed to correct the ignition timing of the #2 cylinder in the advance direction, and the flow ends. Note that if the chain breaking control is performed only on the first ignition timing of the second cylinder, the advance correction of the ignition timing of the #2 cylinder is restored after the completion of ignition of the #2 cylinder after step A5. The same applies to the following steps A7, A9, and A11. If the condition of step A4 is not met, the process proceeds to step A6. In step A6, it is determined whether or not the #2 cylinder has misfired based on the rotational speed of the engine 10. If this condition is met, the process proceeds to step A7, where chain breaking control is performed to correct the ignition timing of the #4 cylinder in the advance direction, and the flow ends. If the condition of step A6 is not met, the process proceeds to step A8.

[0047] In step A8, it is determined whether or not the #4 cylinder has misfired based on the rotational speed of the engine 10. If this condition is met, the process proceeds to step A9, where chain breaking control is implemented to correct the ignition timing of the #3 cylinder in the advance direction, and the process ends. If the condition of step A8 is not met, the process proceeds to step A10. In step A10, it is determined whether or not the #3 cylinder has misfired based on the rotational speed of the engine 10. If this condition is met, the process proceeds to step A11, where chain breaking control is implemented to correct the ignition timing of the #1 cylinder in the advance direction, and the process ends. If the condition of step A10 is not met, it is determined that a misfire has not occurred and the conditions for implementing chain breaking control are not met, and the process ends.

[0048] FIG. 6 is a flowchart illustrating the control procedure performed after any of steps A5, A7, A9, and A11 in FIG. 5 is executed. This flowchart specifies measures to be taken if intermittent consecutive misfires cannot be prevented. In step B1, it is determined whether intermittent consecutive misfires have occurred. For example, if a misfire occurs in cylinder #2 despite the ignition timing of cylinder #2 being advanced in step A5 in FIG. 5, the condition in step B1 is met. Alternatively, if a misfire occurs in cylinder #4 despite the ignition timing of cylinder #4 being advanced in step A7 in FIG. 5, the condition in step B1 is met. If the condition in step B1 is not met, this flow ends. On the other hand, if the condition in step B1 is met, the flow proceeds to step B2.

[0049] In step B2, it is determined whether the second misfire occurred in cylinder #1. If this condition is met, the process proceeds to step B3, where chain breaking control is implemented to increase the valve overlap of cylinder #2 and advance the ignition timing of cylinder #2, and then this flow ends. If the condition in step B2 is not met, the process proceeds to step B4. In step B4, it is determined whether the second misfire occurred in cylinder #2. If this condition is met, the process proceeds to step B5, where chain breaking control is implemented to increase the valve overlap of cylinder #4 and advance the ignition timing of cylinder #4, and then this flow ends. If the condition in step B4 is not met, the process proceeds to step B6.

[0050] In step B6, it is determined whether the second misfire occurred in cylinder #4. If this condition is met, the flow proceeds to step B7, where chain breaking control is implemented to increase the valve overlap of cylinder #3 and advance the ignition timing of cylinder #3, and then this flow ends. If the condition in step B6 is not met (i.e., if the second misfire occurred in cylinder #3), the flow proceeds to step B8. In step B8, chain breaking control is implemented to increase the valve overlap of cylinder #1 and advance the ignition timing of cylinder #1, and then this flow ends.

[0051] [3.Effects] (1) The control device 9 of this embodiment controls an engine 10 having a plurality of cylinders 1 in which ignition retard control can be performed and valve overlap can be set for an intake valve 2 and an exhaust valve 3. An exhaust valve 3 is provided for each of the plurality of cylinders 1. If a first cylinder, which is one of the plurality of cylinders 1, misfires while ignition retard control and valve overlap are being performed on the plurality of cylinders 1, the control device 9 advances the ignition timing of a second cylinder, which is a cylinder other than the first cylinder, and which has an exhaust valve 3 that is in an open state when the exhaust valve 3 of the first cylinder opens, compared to when the first cylinder does not misfire.

[0052] This configuration makes it difficult for misfires to occur in the second cylinder, even when a misfire in the first cylinder temporarily reduces exhaust manifold pressure, making it difficult for exhaust gas to flow into the second cylinder. This reduces intermittent misfires and improves the stability of the engine 10's operating state. Ignition timing control has higher responsiveness than intake air volume control, so it can more effectively reduce intermittent misfires. Ignition timing control also reduces the probability of misfires occurring without increasing the fuel injection amount, making it possible to reduce intermittent misfires without deteriorating the fuel economy of the engine 10.

[0053] Furthermore, the chain break control does not change the ignition timing of any of the multiple cylinders 1 that do not correspond to the second cylinder. In other words, if the #1 cylinder shown in FIG. 2 misfires, the ignition timing of the #3 and #4 cylinders remains retarded by the ignition retard control, while only the ignition timing of the #2 cylinder advances. This prevents sudden changes in engine torque and exhaust temperature while suppressing the occurrence of intermittent chain misfires. Furthermore, for example, if the #1 cylinder misfires during catalyst warm-up control, the ignition timing of the #3 and #4 cylinders can remain retarded, allowing the exhaust purification catalyst 18 to heat up quickly while avoiding intermittent chain misfires in the #2 cylinder.

[0054] (2) Valve overlap is a parameter that affects the likelihood of misfires, and the greater the valve overlap, the greater the likelihood of misfires. Meanwhile, as shown in FIG. 4A, the control device 9 described above can increase the amount of advance of the ignition timing of the second cylinder as the valve overlap of the second cylinder increases. This configuration can more effectively suppress intermittent misfires and further improve the stability of the operating state of the engine 10.

[0055] (3) The amount of retardation of the ignition timing is a parameter that affects the likelihood of misfire, and the greater the retard amount, the greater the likelihood of misfire. Meanwhile, as shown in FIG. 4B, the control device 9 can increase the amount of advancement of the ignition timing of the second cylinder as the amount of retardation of the ignition timing of the second cylinder increases. This configuration can more effectively suppress intermittent chain misfires and further improve the stability of the operating state of the engine 10.

[0056] (4) The temperature of the engine 10 (cylinder temperature, engine coolant temperature, oil temperature, etc.) is a parameter that affects the likelihood of misfire, and the lower the temperature, the higher the likelihood of misfire. On the other hand, as shown in FIG. 4(C), the above-described control device 9 can increase the amount of advance of the ignition timing of the second cylinder as the temperature of the engine 10 decreases. This configuration can more effectively suppress the occurrence of intermittent chain misfires and further improve the stability of the operating state of the engine 10.

[0057] (5) The chain breaking control described above adds a control for increasing valve overlap when intermittent misfires occur. When an intermittent misfire occurs in the second cylinder after a misfire in the first cylinder, the control device 9 advances the ignition timing of a third cylinder, which has an exhaust valve 3 that opens when the exhaust valve 3 of the second cylinder opens, and increases the valve overlap of the third cylinder, compared to when the intermittent misfire does not occur in the second cylinder. This configuration more effectively prevents further intermittent misfires and further improves the stability of the operating state of the engine 10.

[0058] [4. Other] The above-described embodiment is merely illustrative, and is not intended to exclude various modifications and applications of techniques not explicitly stated in the present embodiment. Each configuration of the present embodiment can be modified in various ways without departing from the spirit of the present embodiment. Furthermore, each configuration of the present embodiment can be selected or combined as needed.

[0059] In the above embodiment, the engine 10 is illustrated as one in which fuel is injected into the intake port 11. However, the chain breaking control may also be implemented for an engine 10 in which fuel is injected into the cylinder 1. In this case, since there is no fuel adhering to the intake port 11, the vaporization state of the adhering fuel is not an issue. However, since the temperature of the gas flowing back to the second cylinder immediately after a misfire in the first cylinder drops, the combustion state in the second cylinder may become unstable, potentially resulting in a misfire. On the other hand, implementing the chain breaking control makes it easier to stabilize the combustion state in the cylinder. Therefore, the occurrence of intermittent chain misfires can be suppressed, and the stability of the operating state of the engine 10 can be improved.

[0060] Although the above embodiment illustrates a four-cylinder in-line engine 10, the number of cylinders 1 is not limited to this. Furthermore, the cylinder 1 and the number of cylinders that are the targets of the chain break control can vary depending on the total number of cylinders in the engine 10. Figure 7 shows the combustion cycle of a multi-cylinder engine, with Figure 7(A) being an example of a five-cylinder in-line engine, Figure 7(B) being an example of a six-cylinder in-line engine, and Figure 7(C) being an example of an eight-cylinder in-line engine. The cylinder numbers in Figure 7 indicate the ignition order.

[0061] In the five-cylinder in-line engine shown in Figure 7(A), the start of the exhaust stroke of cylinder #1X (crank angle around 360° CA) overlaps with the exhaust stroke of cylinder #5X, and immediately after that, cylinder #5X enters a valve overlap state. In other words, a temporary drop in exhaust manifold pressure due to a misfire in cylinder #1X adversely affects the intake state of cylinder #5X. As a result, after a misfire in cylinder #1X, cylinders #2X to #4X may not misfire, and only cylinder #5X may misfire after an interval of four strokes. Therefore, when cylinder #1X misfires, chain reaction breaking control should be implemented for cylinder #5X.

[0062] In the six-cylinder in-line engine shown in Figure 7(B), the start of the exhaust stroke of cylinder #1Y (crank angle around 360° CA) overlaps with the exhaust stroke of cylinder #6Y, and immediately thereafter, cylinder #6Y enters a valve overlap state. In other words, a temporary drop in exhaust manifold pressure due to a misfire in cylinder #1Y adversely affects the intake state of cylinder #6Y. As a result, after a misfire in cylinder #1Y, cylinders #2Y through #5Y may not misfire, and only cylinder #6Y may misfire after an interval of five strokes. Therefore, when cylinder #1Y misfires, chain reaction breaking control should be implemented for cylinder #6Y.

[0063] In the eight-cylinder in-line engine shown in FIG. 7C, the start of the exhaust stroke of cylinder #1Z (crank angle approximately 360° CA) overlaps with the exhaust strokes of cylinders #7Z and #8Z, and immediately thereafter, cylinders #7Z and #8Z sequentially enter a valve overlap state. In other words, a temporary drop in exhaust manifold pressure due to a misfire in cylinder #1Z adversely affects the intake conditions of cylinders #7Z and #8Z. As a result, after a misfire in cylinder #1Z, cylinders #2Z through #6Z may not misfire, but cylinders #7Z and #8Z may misfire after an interval of six or seven strokes. Therefore, when cylinder #1Z misfires, chain break control should be implemented for at least either cylinder #7Z or cylinder #8Z (preferably both cylinders). [Industrial Applicability]

[0064] This invention can be used in the manufacturing industry of engine control devices, the manufacturing industry of vehicles equipped with engines and their control devices, and the manufacturing industry of drive systems including engines and their control devices (machine tool drive devices, ship drive devices, generator drive devices, etc.). [Explanation of symbols]

[0065] 1 cylinder 2 intake valves 3 Exhaust valve 4 spark plugs 5 fuel injection valve 6 Knock sensor 7 Engine RPM Sensor 8 Temperature Sensor 9 Control Device 10 Engine 11 Intake port 12 Exhaust port 13 Intake manifold 14 Exhaust manifold 15 Intake passage 16 Throttle valve 17 Exhaust passage 18 Exhaust purification catalyst R0 predetermined amount V0 predetermined value

Claims

1. A control device for controlling an engine having a plurality of cylinders in which ignition retard control can be performed and valve overlap of intake valves and exhaust valves can be set, The exhaust valve is provided in each of the plurality of cylinders, When a first cylinder that is one of the plurality of cylinders misfires while the ignition retard control and the valve overlap are being performed in the plurality of cylinders, the ignition timing of a second cylinder that is a cylinder other than the first cylinder and has an exhaust valve that is in an open state when the exhaust valve of the first cylinder is opened is advanced compared to when the first cylinder does not misfire. An engine control device characterized by:

2. The greater the valve overlap of the second cylinder, the more the advance amount of the ignition timing of the second cylinder is increased.

2. The engine control device according to claim 1.

3. The greater the retard amount of the ignition timing of the second cylinder, the greater the advance amount of the ignition timing of the second cylinder.

2. The engine control device according to claim 1.

4. The lower the temperature of the engine, the more the advance amount of the ignition timing of the second cylinder is increased.

2. The engine control device according to claim 1.

5. When the second cylinder experiences intermittent misfires after the first cylinder experiences misfires, the ignition timing of a third cylinder, which is different from the second cylinder and has an exhaust valve that is opened when the exhaust valve of the second cylinder is opened, is advanced, and the valve overlap of the third cylinder is increased, compared to when the second cylinder does not experience intermittent misfires.

2. The engine control device according to claim 1.

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