JP2011214447A - Method and device for controlling spark ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of preignition while maintaining emission efficiency as favorably as possible.SOLUTION: When preignition is detected based on a detection value of detection means (33 and 34) in a low rotation and high load region of the engine (specified operation region R), an injection amount of fuel from an injector 18 is increased, and an air-fuel ratio in a cylinder is enriched (S42), and when the preignition is detected after the control, the injection timing of a part of the fuel to be injected from the injector 18 is retarded to the middle period of a compression stroke or later (S44).

Description

  The present invention relates to a spark ignition engine comprising a detecting means for detecting a pre-ignition in which an air-fuel mixture self-ignites before a normal combustion start timing by spark ignition, and an injector for directly injecting fuel into a cylinder. The present invention relates to a method and an apparatus for controlling the device.

  2. Description of the Related Art Conventionally, as shown in Patent Document 1 below, in a direct injection engine with an in-cylinder provided with an injector that directly injects fuel into a cylinder (combustion chamber) and an ignition plug that ignites an air-fuel mixture in the cylinder, The occurrence of abnormal combustion (hereinafter referred to as pre-ignition) in which the air-fuel mixture self-ignites before the normal combustion start timing due to ignition is detected. When pre-ignition is detected, the fuel injection timing from the injector is delayed. The generation of pre-ignition is suppressed by cornification.

  More specifically, in Patent Document 1 below, the normal fuel injection timing is set during the intake stroke, while when the pre-ignition is detected, the injection timing is retarded so that the fuel is injected during the compression stroke. Thus, by shortening the period from the injection timing to ignition (that is, shortening the heat receiving period of the fuel), the occurrence of pre-ignition is suppressed.

JP 2002-339780 A

  However, when the fuel injection timing is retarded to the compression stroke in order to avoid pre-ignition as in the technique disclosed in Patent Document 1, ignition is performed while the fuel is not sufficiently vaporized and atomized. As a result, a relatively large amount of unburned carbon remains, smoke is generated, and the emission property may be deteriorated. For this reason, while preventing the engine damage due to pre-ignition, it is desirable to keep the frequency at which the fuel injection timing as described above is retarded as low as possible and to minimize the deterioration of the emission performance.

  The present invention has been made in view of the above circumstances, and a spark ignition engine control method capable of effectively suppressing the occurrence of pre-ignition while maintaining the emission property as good as possible. And it aims at providing a control device.

  In order to solve the above-described problems, the present invention is directed to detecting means for detecting a pre-ignition in which an air-fuel mixture self-ignites before normal combustion start timing by spark ignition, and directly injecting fuel into a cylinder. A spark ignition type engine having an injector for controlling the fuel from the injector when a pre-ignition is detected based on a detection value of the detection means in a low rotation and high load range of the engine. When the pre-ignition is detected after the control, the injection timing of a part of the fuel to be injected from the injector is compressed in the compression stroke. In this case, the angle is retarded after the middle period.

  Further, the present invention provides a detection means for detecting a pre-ignition in which the air-fuel mixture self-ignites before the normal combustion start timing by spark ignition, an injector that directly injects fuel into the cylinder, and an engine including the injector And a control device for controlling each part of the spark ignition type engine, wherein the control means detects pre-ignition based on the detection value of the detection means in a low engine speed and high load range. In this case, the amount of fuel injected from the injector is increased to enrich the air-fuel ratio in the cylinder, and one of the fuels to be injected from the injector when pre-ignition is detected even after the control is performed. The fuel injection timing of the portion is retarded after the middle stage of the compression stroke (claim 8).

  According to these inventions, when pre-ignition is detected, the control for enriching the air-fuel ratio is performed first, and the control for retarding the fuel injection timing (injecting part of the fuel in the compression stroke) is performed. Since it is postponed, generation | occurrence | production of a preignition can be suppressed effectively, avoiding that a smoke generate | occur | produces and an emission property deteriorates as much as possible.

  That is, regardless of whether the air-fuel ratio is enriched or the fuel injection timing is retarded, the in-cylinder fuel temperature (the fuel temperature near the compression top dead center) is reduced to suppress pre-ignition. However, retarding the fuel injection timing (compression stroke injection) may lead to the generation of smoke due to the remaining unburned carbon, so if you suddenly retard the injection timing, the smoke will frequently There are concerns about the occurrence. On the other hand, in the present invention, when the pre-ignition occurs, the air-fuel ratio is first enriched to lower the fuel temperature in the cylinder, and only when the pre-ignition cannot be avoided, the injection timing is retarded. Therefore, there is an advantage that the generation of smoke as described above can be avoided as much as possible and the emission property can be maintained as good as possible.

  In the control method of the present invention, when pre-ignition is detected even after the air-fuel ratio is enriched, the effective compression ratio of the engine is preferably set prior to the control for retarding the injection timing of the part of the fuel. The control to decrease is executed, and when the pre-ignition is still detected, the injection timing is retarded (Claim 2).

  When the control device of the present invention includes compression ratio adjusting means for variably setting the effective compression ratio of the engine, and pre-ignition is detected even after the air-fuel ratio is enriched, the control is preferably performed. The means controls the compression ratio adjusting means to lower the effective compression ratio of the engine prior to the control for retarding the injection timing of the part of the fuel, and when the pre-ignition is still detected, The retarding of the injection timing is executed (claim 9).

  According to these aspects, after the enrichment of the air-fuel ratio is performed, the control for reducing the effective compression ratio of the engine is executed to reduce the in-cylinder pressure. Since the injection timing is retarded, it is possible to avoid pre-ignition with higher probability without retarding the fuel injection timing. Thereby, the frequency at which the retarding of the fuel injection timing is executed becomes extremely low, and the pre-ignition can be suppressed while avoiding the generation of smoke as much as possible.

  In addition, by reducing the effective compression ratio after the enrichment of the air-fuel ratio first, avoiding a reduction in the engine output due to the reduction in the compression ratio as much as possible, and further suppressing it immediately after the occurrence of pre-ignition. It can be done quickly.

  In the control method and the control device, preferably, in the control for enriching the air-fuel ratio, the air-fuel ratio is enriched by a predetermined amount, and if the pre-ignition is still detected, the air-fuel ratio is further enriched and maximized. When pre-ignition is detected even in a rich state, control for reducing the effective compression ratio of the engine is executed (claims 3 and 10).

  If the air-fuel ratio enrichment is performed stepwise as in this aspect, for example, it is necessary when the degree of pre-ignition is light and the pre-ignition can be avoided by slightly enriching the air-fuel ratio. As described above, the air-fuel ratio is not enriched, and the deterioration in fuel efficiency due to the enrichment of the air-fuel ratio can be minimized. Also, when pre-ignition cannot be avoided even if the air-fuel ratio is maximized, the air-fuel ratio becomes excessively rich by reducing the effective compression ratio and further suppressing the pre-ignition by retarding the fuel injection timing. Even if the pre-ignition is relatively advanced, it is possible to surely avoid it.

  In the control method and the control device, preferably, in the control for reducing the effective compression ratio, the effective compression ratio is reduced by a predetermined amount, and if the pre-ignition is still detected, the effective compression ratio is further reduced and the maximum When pre-ignition is detected even in a state where the fuel consumption is reduced to the limit, control is performed to retard the injection timing of the part of the fuel (claims 4 and 11).

  According to this aspect, there is an advantage that the pre-ignition can be avoided more reliably while preventing the effective compression ratio from being reduced more than necessary and the engine output from being significantly reduced.

  In the above control method and control apparatus, preferably, in the control for retarding the injection timing of the part of the fuel, when the injection timing is retarded to the middle stage of the compression stroke and the pre-ignition is still detected. The retardation is delayed until the later stage of the compression stroke (claims 5 and 12).

  According to this aspect, in the case where the pre-ignition can be sufficiently avoided by delaying the injection timing of a part of the fuel to the middle stage of the compression stroke, the smoke stroke is likely to occur until the latter half of the compression stroke. The injection timing is not delayed, and the deterioration of the emission property can be more effectively prevented.

  In the above control method, preferably, the closing timing of the intake valve during normal time is set to the retard side with respect to the intake bottom dead center, and when closing the effective compression ratio, the closing timing of the intake valve is preferably set. Further, the timing is further changed to the retarded side with respect to the normal closing timing.

  In the above control device, when the compression ratio adjusting means is a variable mechanism that variably sets the closing timing of the intake valve, it is preferable that the closing timing of the intake valve at the normal time is retarded from the intake bottom dead center. The control means controls the variable mechanism during the control to lower the effective compression ratio, thereby further delaying the closing timing of the intake valve from the closing timing at the normal time. (Claim 13).

  According to these aspects, it is possible to efficiently reduce the effective compression ratio when necessary while sufficiently securing the engine output at the normal time by using the intake inertia.

  In the above control method and control device, when the pre-ignition is avoided as a result of delaying the injection timing of the part of the fuel, preferably the control is performed to return the retarded fuel injection timing to the advance side. This is executed prior to returning the rich air-fuel ratio or the reduced effective compression ratio (claims 7 and 14).

  According to this aspect, when the pre-ignition is avoided, the delay in the fuel injection timing is first canceled to eliminate the possibility of the occurrence of smoke, thereby minimizing the time when the emission performance deteriorates. Can be suppressed.

  As described above, according to the control method and the control device for the spark ignition engine of the present invention, it is possible to effectively suppress the occurrence of pre-ignition while maintaining the emission property as good as possible.

It is a figure showing the whole spark ignition engine composition concerning one embodiment of the present invention. It is a block diagram which shows the control system of the said engine. It is a figure which shows the specific driving | operation area | region where pre-ignition may generate | occur | produce. It is a figure which shows distribution (time change) of the heat generation amount which arises at the time of generation | occurrence | production of a pre-ignition, and normal combustion. It is a figure which compares and shows the change of the in-cylinder pressure when a pre-ignition generate | occur | produces, and the change of the in-cylinder pressure when knocking generate | occur | produces. It is a figure which illustrates the waveform inputted from a vibration sensor, when preignition occurs. It is an example of a waveform input from a vibration sensor when knocking occurs. It is a figure which shows how the magnitude | size of the maximum vibration intensity | strength and its detection timing change when ignition timing is retarded at the time of the occurrence of pre-ignition and knocking. It is a flowchart which shows the content of the control action for detecting pre-ignition and knocking. It is a flowchart which shows the content of the control action performed in response to the detection result of FIG. 11 is a subroutine showing specific contents of pre-ignition avoidance control included in the flowchart of FIG. 10. It is a subroutine which shows the specific content of the return control contained in the flowchart of FIG. It is a graph which shows the relationship between the amount of retardation of the closing timing of an intake valve, and an effective compression ratio. It is a graph which shows how the retard amount of the closing timing of an intake valve required in order to reduce an effective compression ratio by 0.5 changes according to the value of the present retard amount. It is a figure which shows the injection timing of a fuel, (a) has shown the injection timing at the time of normal, (b) has shown the injection timing at the time of pre-ignition generation | occurrence | production. It is a time chart which shows the operation example of the said preig avoidance control in a time series. It is a time chart which shows the operation example of the said return control in time series. It is a figure for demonstrating the modification of this invention.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of an engine according to an embodiment of the present invention. The engine shown in this figure is a reciprocating piston type multi-cylinder gasoline engine, and is mounted on a vehicle as a power source for driving driving. An engine body 1 of this engine includes a cylinder block 3 having a plurality of cylinders 2 (only one of which is shown in the drawing) arranged in a direction orthogonal to the paper surface, and a cylinder head 4 provided on the upper surface of the cylinder block 3. And a piston 5 inserted in each cylinder 2 so as to be slidable back and forth. In addition, the fuel supplied to the engine body 1 may be anything that contains gasoline as a main component, and the contents may be all gasoline, or gasoline containing ethanol (ethyl alcohol) or the like. But you can.

  The piston 5 is connected to the crankshaft 7 via a connecting rod 8, and the crankshaft 7 rotates around the central axis in accordance with the reciprocating motion of the piston 5.

  A combustion chamber 6 is formed above the piston 5, an intake port 9 and an exhaust port 10 are opened in the combustion chamber 6, and an intake valve 11 and an exhaust valve 12 that open and close the ports 9 and 10 are connected to the cylinder head 4. Are provided respectively. The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts (not shown) disposed in the cylinder head 4. .

  A VVT 15 is incorporated in the valve operating mechanism 13 for the intake valve 11. The VVT 15 is called a variable valve timing mechanism, and is a variable mechanism for variably setting the operation timing of the intake valve 11.

  Various types of VVT 15 have already been put into practical use and are known. For example, a hydraulic variable mechanism can be used as the VVT 15. Although not shown in the drawings, the hydraulic variable mechanism is configured so that a driven shaft arranged coaxially with the camshaft for the intake valve 11 and a circumferential arrangement between the camshaft and the driven shaft. A plurality of liquid chambers arranged, and by forming a predetermined pressure difference between the liquid chambers, a phase difference is formed between the camshaft and the driven shaft. It has become. The phase difference is variably set within a predetermined angle range, whereby the operation timing of the intake valve 11 is continuously changed.

  Note that a variable mechanism of a type that changes the closing timing of the intake valve 11 by changing the valve lift amount may be provided as the VVT 15. Further, such a lift-type variable mechanism may be used in combination with the above-described phase-type variable mechanism.

  The cylinder head 4 of the engine body 1 is provided with one set of spark plugs 16 and injectors 18 for each cylinder 2.

  The injector 18 is provided so as to face the combustion chamber 6 from the side of the intake side, and injects fuel (gasoline) supplied from a fuel supply pipe (not shown) from the tip. Then, fuel is injected from the injector 18 into the combustion chamber 6 in the intake stroke of the engine, and the injected fuel is mixed with air, so that an air-fuel mixture having a desired air-fuel ratio is generated in the combustion chamber 6. It is like that.

  The spark plug 16 is provided so as to face the combustion chamber 6 from above, and discharges a spark from the tip portion in response to power supply from an ignition circuit (not shown). The spark is discharged from the spark plug 16 at a predetermined timing set near the compression top dead center, and the combustion of the air-fuel mixture is started as a result.

  The cylinder block 3 is provided with an engine rotation speed sensor 30 that detects the rotation speed of the crankshaft 7 as an engine rotation speed (engine rotation speed).

  The cylinder block 3 is provided with a vibration sensor 33 that detects vibration of the cylinder block 3. The value detected by the vibration sensor 33 is used to detect abnormal combustion occurring in the engine.

  Specifically, in the present embodiment, two types of abnormal combustions, knocking and pre-ignition, are detected based on the detection value of the vibration sensor 33. Here, the knocking is a phenomenon in which the unburned portion (end gas) of the air-fuel mixture self-ignites in the process of the flame propagating after the combustion of the air-fuel mixture has started by spark ignition. . On the other hand, the pre-ignition is a phenomenon in which the air-fuel mixture self-ignites before the normal combustion start timing by spark ignition (that is, regardless of spark ignition). When knocking or pre-ignition occurs, a relatively large vibration is generated in the cylinder block 3 due to a sudden fluctuation in combustion pressure. In this embodiment, such vibration of the cylinder block 3 is detected by the vibration sensor. By checking based on the detected value of 33, knocking or pre-ignition is detected.

  In the vicinity of the spark plug 16, an ion current sensor 34 is provided for detecting a flame generated when the air-fuel mixture burns in the combustion chamber 6. The ion current sensor 34 has an electrode to which a bias voltage of about 100 V, for example, is applied, and detects the flame by detecting an ion current generated when a flame is formed around the electrode. It is configured.

  By detecting the flame using the ion current sensor 34, it is possible to detect the occurrence of pre-ignition, similar to the vibration sensor 33. That is, when the air-fuel mixture is forcibly burned by spark ignition, if it is in a normal combustion state, combustion starts after a predetermined delay time from the timing of spark ignition, but when pre-ignition occurs, Since the air-fuel mixture self-ignites early irrespective of spark ignition, combustion starts before the normal combustion start timing (when a predetermined delay time has elapsed from spark ignition) as described above. Therefore, when the flame is detected by the ion current sensor 34 and the detection timing (flame generation timing) is too early compared with the normal combustion start timing, it is determined that pre-ignition has occurred. Thus, in this embodiment, two types of sensors, the ion current sensor 34 and the vibration sensor 33, are provided as sensors (detection means according to the present invention) for detecting pre-ignition, and these two types of sensors are provided. Is used to more reliably detect pre-ignition.

  However, only the pre-ignition can be detected using the ion current sensor 34, and knocking cannot be detected. That is, as described above, knocking is a phenomenon in which, after a flame is generated once triggered by spark ignition, an unburned portion (end gas) of the air-fuel mixture is self-ignited in the process of propagation. Even if it occurs, the flame generation timing does not change as usual, and even if the flame generation timing is examined by the ion current sensor 34, it is not possible to specify whether knocking has occurred or not. For this reason, when detecting knocking, only the detection value of the vibration sensor 33 is used, and the ion current sensor 34 is not used.

  An intake passage 20 and an exhaust passage 21 are connected to the intake port 9 and the exhaust port 10 of the engine body 1, respectively. In other words, intake air (fresh air) from the outside is supplied to the combustion chamber 6 through the intake passage 20, and burned gas (exhaust gas) generated in the combustion chamber 6 is discharged to the outside through the exhaust passage 21. It has become so.

  The intake passage 20 is provided with a throttle valve 22 that adjusts the flow rate of intake air flowing into the engine body 1 and an air flow sensor 31 that detects the flow rate of intake air.

  The throttle valve 22 is an electronically controlled throttle valve, and is electrically opened and closed according to the degree of opening of an accelerator pedal (not shown) that is depressed by the driver. That is, the accelerator pedal is provided with an accelerator opening sensor 32 (FIG. 2), and an electric power (not shown) is shown in accordance with the accelerator pedal opening (accelerator opening) detected by the accelerator opening sensor 32. An actuator of the type is configured to open and close the throttle valve 22.

  The exhaust passage 21 is provided with a catalytic converter 23 for purifying exhaust gas. For example, a three-way catalyst is incorporated in the catalytic converter 23, and harmful components in the exhaust gas passing through the exhaust passage 21 are purified by the action of the three-way catalyst.

(2) Control System FIG. 2 is a block diagram showing an engine control system. The ECU 40 shown in this figure is a control means for comprehensively controlling each part of the engine, and includes a well-known CPU, ROM, RAM, and the like.

  The ECU 40 receives detection signals from various sensors. That is, the ECU 40 is electrically connected to the engine rotation speed sensor 30, the airflow sensor 31, the accelerator opening sensor 32, the vibration sensor 33, and the ion current sensor 34, and values detected by these sensors 30 to 34 are used. Information such as the engine speed Ne, the intake air amount Qa, the accelerator opening degree AC, the vibration intensity (acceleration) Va, and the ion current value Io is sequentially input to the ECU 40.

  The ECU 40 is also electrically connected to the VVT 15, the spark plug 16, the injector 18, and the throttle valve 22, and is configured to output drive control signals to these devices.

  A more specific function of the ECU 40 will be described. The ECU 40 includes, as main functional elements, a storage means 41, an abnormal combustion determination means 42, an ignition control means 43, a fuel control means 44, and a VVT control means 45. have.

  The storage means 41 stores various data and programs necessary for controlling the engine. As an example, the storage means 41 stores the range of the specific operation region R shown in FIG. The specific operation region R is an operation region in which pre-ignition may occur, and is set near the maximum load line WOT (that is, high load) and close to low rotation.

  That is, as described above, the pre-ignition is a phenomenon in which the air-fuel mixture self-ignites before the normal combustion start timing by spark ignition, so that the air in the combustion chamber 6 is heated to a high temperature and pressure, and from the air. Pre-ignition is most likely to occur in a low rotation and high load region where the heat receiving period for the fuel is long. Therefore, as shown in FIG. 3, a region where the engine rotational speed Ne is relatively low and the load Ce is high is set as a specific operation region R in which pre-ignition may occur.

  The abnormal combustion determination means 42 determines whether or not pre-ignition or knocking has occurred based on the detection values of the vibration sensor 33 and the ion current sensor 34. Specifically, the abnormal combustion determination means 42 specifies the flame generation timing based on the detection value (ion current value Io) of the ion current sensor 34 when the engine operating state is in the specific operation region R, By comparing this with the normal combustion start timing, it is determined whether or not pre-ignition has occurred. Further, the abnormal combustion determination means 42 examines the maximum value of the vibration intensity and the generation timing thereof based on the detection value (vibration intensity Va) of the vibration sensor 33, so that either pre-ignition or knocking has occurred. (Refer to item (3) described later for details).

  The ignition control means 43 outputs a power supply signal to the ignition circuit of the spark plug 16 at a predetermined timing that is predetermined according to the operating state of the engine, whereby the spark plug 16 performs a spark discharge (ignition timing). Etc. are controlled.

  For example, in the specific operation region R set in the low rotation / high load region of the engine, the spark plug 16 is controlled so that spark ignition is performed at a timing slightly delayed from the compression top dead center. However, in the specific operation region R, when a vibration of a predetermined level or more is input from the vibration sensor 33, the ignition control means 43 causes the ignition timing to be slightly delayed from the above timing (compression top dead center). ) To the more retarded angle than. This is to determine whether the vibration of a predetermined level or more input from the vibration sensor 33 is due to pre-ignition or knocking.

  In other words, retarding the ignition timing works in the direction of suppressing knocking but does not particularly affect preignition (the reason will be described in detail later). When this occurs, the ignition control means 43 intentionally retards the ignition timing in order to determine whether the cause is pre-ignition or knocking. Then, the vibration change after the ignition timing is retarded is examined by the abnormal combustion determination means 42, and it is determined whether pre-ignition or knocking has occurred depending on the result. ing.

  The fuel control means 44 controls the injection amount and timing of fuel injected from the injector 18 into the combustion chamber 6. More specifically, the fuel control means 44 performs target fuel injection based on information such as the engine speed Ne input from the engine speed sensor 30 and the intake air amount Qa input from the airflow sensor 31. The amount and the injection timing are calculated, and the valve opening timing and valve opening period of the injector 18 are controlled based on the calculation result.

  In particular, when a pre-ignition is detected in the specific operation region R, the fuel control means 44 performs control to enrich the in-cylinder air-fuel ratio by increasing the fuel injection amount from the injector 18. To do. Such control is performed by injecting a relatively large amount of fuel to reduce the amount of fuel received per unit mass, thereby lowering the temperature of the fuel in the cylinder near the compression top dead center and pre-ignition. This is to suppress the occurrence of the above. Further, if necessary, the fuel control means 44 injects a part of the fuel that should be injected during the intake stroke by delaying it until the latter stage of the compression stroke (that is, the fuel is divided into the intake stroke and the compression stroke). (Inject) control. As a result, the heat receiving period of the fuel is shortened, and the temperature of the fuel in the cylinder near the compression top dead center is lowered, so that it is possible to create an environment in which pre-ignition is difficult to occur.

  The VVT control means 45 variably sets the effective compression ratio of the engine by driving the VVT 15 and changing the closing timing of the intake valve 11. That is, the closing timing of the intake valve 11 is normally set in the vicinity of the retarded side of the intake bottom dead center (timing slightly past the intake bottom dead center), and by setting at such timing, The air once sucked is hardly blown back to the intake port 9, and the substantial compression ratio (effective compression ratio) of the engine is set to a value close to the geometric compression ratio. On the other hand, when the closing timing of the intake valve 11 is set to be significantly later than the intake bottom dead center, the effective compression ratio of the engine is reduced by that amount so that a considerable amount of intake air blows back. Become. The VVT control means 45 variably sets the effective compression ratio of the engine by driving the VVT 15 to increase / decrease the retard amount (retard amount) at the closing timing of the intake valve 11.

  In particular, when a pre-ignition is detected in the specific operation region R, the VVT control means 45 executes a control to retard the effective compression ratio by retarding the closing timing of the intake valve 11 as necessary. As a result, the in-cylinder pressure (pressure in the combustion chamber 6) is mainly reduced, and pre-ignition is suppressed.

  In the above description, the “closing timing of the intake valve 11” refers to the closing time when the valve opening period is defined as a section excluding the ramp portion of the lift curve (the buffer section where the lift amount rises gently). It does not indicate a time when the lift amount of the intake valve 11 becomes completely zero.

(3) Preignition and knock determination method Next, a more specific procedure when the abnormal combustion determination means 42 determines the occurrence of preignition and knocking will be described.

  First, the procedure for detecting pre-ignition using the ion current sensor 34 will be described. FIG. 4 is a diagram showing a distribution (time change) of the amount of heat generated when pre-ignition occurs and during normal combustion. In this figure, IG indicates spark ignition, and the amount of heat generated during normal combustion that is triggered by this spark ignition IG is indicated by a solid waveform J0. Note that, as described above, the timing of the spark ignition IG is set to a timing slightly delayed from the compression top dead center in the specific operation region R where pre-ignition can occur. For this reason, the position of IG in the figure is set on the retard side with respect to the compression top dead center (TDC), and in the example shown in FIG. .

  Assuming that the state where combustion has progressed to such an extent that the flame can be detected by the ion current sensor 34 (substantial combustion start timing) in the waveform J0 at the time of normal combustion caused by the spark ignition IG is t0, It is later than the point of spark ignition IG by a predetermined crank angle. That is, during normal combustion, the combustion gradually spreads around the flame kernel generated by the spark ignition, so that the substantial combustion start timing t0 is delayed to some extent from the spark ignition IG. .

  On the other hand, the distribution of the heat generation amount when pre-ignition occurs is as shown by the dashed-dotted waveforms J1 to J3. Waveform J1 indicates a mild preignition, waveform J2 indicates a moderate preignition, and waveform J3 indicates a severe preignition. If the substantial combustion start timings in each case are t1, t2, and t3, respectively, the crank The angular position is shifted to the advance side from the normal combustion start timing t0. That is, when pre-ignition occurs, the air-fuel mixture self-ignites, so that combustion can no longer be controlled by spark ignition, and combustion starts before the normal combustion start timing t0. In addition, as the combustion starts earlier, the combustion becomes sharper and the combustion period becomes shorter.

  In addition, the pre-ignition has a property of gradually developing from a mild pre-ignition (J1) to a severe pre-ignition (J3) when left untreated. That is, once the pre-ignition occurs, the temperature of the combustion chamber 6 is spurred and an environment that is more likely to self-ignite is created, so that the pre-ignition develops in a chain. In particular, when it develops to a severe pre-ignition (J3), the combustion becomes extremely steep and a considerable noise and vibration are generated in the engine, which leads to damage to the piston and the like.

  For this reason, it is necessary to appropriately detect the occurrence of pre-ignition and take necessary measures (for example, enrichment of the air-fuel ratio) before developing into at least the above-described severe pre-ignition. Therefore, in the present embodiment, as one means for detecting pre-ignition, flame is detected using the ion current sensor 34, and the presence or absence of occurrence of pre-ignition is determined based on the detection timing (flame generation timing). I try to distinguish. Specifically, when the ion current sensor 34 detects a flame at a stage earlier than the normal combustion start timing t0 by a predetermined time or more, this is detected as a pre-ignition. At this time, in order to detect the pre-ignition at the lightest possible stage, it is preferable to determine that the pre-ignition is performed when the flame detection timing by the ion current sensor 34 is advanced to about t1, for example.

  By the way, the occurrence of pre-ignition is detected using not only the ion current sensor 34 but also the vibration sensor 33 as described above. In the present embodiment, the vibration sensor 33 is used not only for pre-ignition but also for detecting knocking. Next, a detection procedure using the vibration sensor 33 will be described.

  FIG. 5 is a diagram showing a change in the in-cylinder pressure when pre-ignition occurs and a change in the in-cylinder pressure when knocking occurs. In FIG. 5, the change in the in-cylinder pressure when the pre-ignition occurs is shown as a waveform Pp, and the change in the in-cylinder pressure when the knocking occurs is shown as a waveform Pn. Further, in the same figure, in order to clearly represent the difference between both waveforms Pp and Pn, as a waveform Pp at the time of pre-ignition occurrence, the in-cylinder when the pre-ignition is considerably developed (when it is severely developed or close to it). The change in pressure is illustrated.

  As is apparent from the waveform Pp, when the pre-ignition is considerably developed, the in-cylinder pressure greatly increases near the compression top dead center, and the increased pressure converges in a relatively short period. . On the other hand, when knocking occurs, as shown by the waveform Pn, the peak portion of the waveform where the in-cylinder pressure suddenly rises is generated at a position that is greatly deviated to the retard side than during pre-ignition. . That is, knocking is a phenomenon in which the remaining unburned gas mixture (end gas) self-ignites when combustion proceeds to some extent, so a sudden rise in pressure due to the self-ignition occurs at the end of the combustion process, The peak of the waveform is shifted to the retard side.

  6 and 7 show what vibration waveform is input from the vibration sensor 33 when pre-ignition or knocking occurs and a change in in-cylinder pressure as shown in FIG. 5 occurs. Yes. The vibration waveform here is obtained by taking the vibration intensity (acceleration) Va input from the vibration sensor 33 on the vertical axis and the crank angle CA on the horizontal axis, and the vibration intensity Va corresponding to the crank angle CA. Shows changes.

  Comparing the waveforms of FIG. 6 and FIG. 7, the vibration waveform when pre-ignition occurs (FIG. 6) is greater than the vibration waveform when knocking occurs (FIG. 7), and the maximum value Vmax of the detected vibration intensity Va. It can be seen that (hereinafter abbreviated as the maximum vibration intensity Vmax) is large and the detection time is early. This is because, in the case of the pre-ignition that is considerably advanced as shown in FIG. 5, the fluctuation range of the portion where the in-cylinder pressure changes most rapidly (that is, the peak portion of the waveform) is larger than that of the knocking, and This is probably due to the fact that it is occurring on the advance side.

  Thus, it can be seen that when the pre-ignition is considerably advanced, a relatively clear feature is found in the detected maximum vibration intensity Vmax and its detection timing. However, when the pre-ignition is not sufficiently developed (for example, when a mild pre-ignition such as the waveform J1 shown in FIG. 4 occurs), the maximum vibration intensity Vmax and the detection timing thereof are large compared to the case of knocking. There is a possibility that pre-ignition and knocking cannot be clearly distinguished and detected simply by comparing the waveforms of the vibration intensity Va.

  Therefore, in the present embodiment, when the vibration sensor 33 detects the maximum vibration intensity Vmax that is equal to or greater than a predetermined threshold value and the occurrence of pre-ignition or knocking is suspected, the ignition timing is intentionally determined in order to discriminate both. Is retarded, and based on the subsequent change in the maximum vibration intensity Vmax, it is determined whether it is pre-ignition or knocking.

  That is, in the specific operation region R near the low rotation and high load where pre-ignition can occur, the ignition timing is set at a timing slightly delayed from the compression top dead center (for example, about 5 ° ATDC) in normal times. When the vibration sensor 33 detects the maximum vibration intensity Vmax equal to or greater than a predetermined threshold, the ignition timing is retarded by a predetermined amount with respect to the timing, and spark ignition is performed at a timing further delayed from the compression top dead center. To be done. Then, the abnormal combustion determination means 42 examines how the maximum vibration intensity Vmax changes in response to such a retarded ignition timing, and whether pre-ignition or knocking has occurred. Determined.

  For example, when knocking has occurred, the ignition timing is retarded as described above, so that the compression top dead center is further retarded (that is, the in-cylinder temperature and pressure are further reduced). Since the combustion is started, the self-ignition of the unburned mixture (end gas) becomes difficult to occur in the subsequent combustion process. Therefore, if the ignition timing is retarded when knocking occurs, the degree of knocking is reduced and the generation timing is delayed. Then, according to this, the phenomenon that the magnitude of the maximum vibration intensity Vmax detected by the vibration sensor 33 decreases and the detection timing is delayed is observed.

  The “x” mark in FIG. 8 indicates how the maximum vibration intensity Vmax detected by the vibration sensor 33 changes by gradually retarding the ignition timing when knocking occurs. According to this figure, as the ignition timing is retarded, the plot of the maximum vibration intensity Vmax (“×” mark) gradually moves in the lower right direction. That is, as the ignition timing is retarded, the maximum vibration intensity Vmax gradually decreases, and the crank angle at the time when this Vmax is detected gradually shifts to the retard side. Note that the value X on the vertical axis in FIG. 8 is a threshold value for determining whether or not to retard the ignition timing. When the maximum vibration intensity Vmax equal to or greater than the threshold value X is detected, the ignition timing delay is determined. Keratinization is performed.

  As described above, it is possible to suppress knocking by retarding the ignition timing, but when pre-ignition occurs, the air-fuel mixture self-ignites regardless of the ignition timing. Even if the ignition timing is retarded, self-ignition still occurs and pre-ignition is not suppressed. Rather, as described with reference to FIG. 4, once the pre-ignition occurs, the pre-ignition gradually develops as time elapses, leading to premature combustion start timing and steep combustion. In FIG. 8, the “Δ” mark indicating the maximum vibration intensity Vmax at the time of the pre-ignition is gradually moving in the upper left direction. That is, when pre-ignition occurs, the magnitude of the maximum vibration intensity Vmax gradually increases with the lapse of time and the detection timing is advanced regardless of the retard of the ignition timing.

  From the above, when pre-ignition occurs, even if the ignition timing is retarded, the maximum vibration intensity Vmax is increased and the detection timing is advanced. When knocking occurs, the ignition timing It can be seen that a decrease in the maximum vibration intensity Vmax and a delay in the detection timing are observed as the angle is retarded. Therefore, in the present embodiment, it is determined whether pre-ignition or knocking has occurred based on the change in the maximum vibration intensity Vmax (the change in the magnitude and the detection timing) accompanying the retarded ignition timing. I am doing so. Accordingly, it is possible to accurately determine whether the pre-ignition or knocking is performed while using the vibration sensor 33.

(4) Control Operation Next, the control operation by the ECU 40 having the above functions will be described based on the flowcharts of FIGS. Here, the description will focus on the detection of pre-ignition and knocking, and the avoidance operation when these are detected.

  When the process shown in the flowchart of FIG. 9 starts, first, control for reading various sensor values is executed (step S1). Specifically, from the engine rotation speed sensor 30, the air flow sensor 31, the accelerator opening sensor 32, the vibration sensor 33, and the ion current sensor 34, the engine rotation speed Ne, the intake air amount Qa, the accelerator opening AC, The vibration intensity Va and the ionic current value Io are read out and input to the ECU 40.

  Next, based on the information read in step S1, control is performed to determine whether or not the current engine operating state is within the specific operating region R shown in FIG. 3 (step S2). Specifically, both the engine rotational speed Ne read in step S1 and the engine load Ce calculated from the intake air amount Qa (or the accelerator opening degree AC) are within the range of the specific operation region R in FIG. It is determined whether it is included.

  If it is determined NO in step S2 and it is confirmed that the vehicle is out of the specific operation region R, pre-ignition cannot occur. Therefore, the processing after step S3 described later (determination of abnormal combustion and its avoidance control) ) Is not required, and normal operation is maintained (step S32 in FIG. 10). That is, the fuel injection amount and injection timing, the operation timing of the intake valve 11, and the like are controlled along normal target values that are predetermined according to the operating state.

  On the other hand, if it is determined YES in step S2 and it is confirmed that the vehicle is in the specific operation region R, the flame generation timing is earlier than usual based on the ion current value Io read in step S1. Control for determining whether or not pre-ignition has occurred is executed (step S3). Specifically, the occurrence timing of the flame specified based on the ion current value Io is a predetermined time from the normal combustion start timing (a timing slightly delayed from the spark ignition; for example, time t0 in FIG. 4) stored in advance. If it is earlier, it is determined that the pre-ignition has occurred.

  If it is determined YES in step S3 and occurrence of pre-ignition is confirmed, it is confirmed that the pre-ignition has occurred in the abnormal combustion flag Fabnrm (whose default value is 0) for recording the combustion state. Control for inputting “1” is executed (step S4).

  On the other hand, if NO is determined in step S3, that is, if the pre-ignition detection based on the ionic current value Io is not performed, the information on the vibration intensity Va read from the vibration sensor 33 in step S1 is displayed. Based on this, the maximum value (maximum vibration intensity) Vmax is acquired, and the control for storing this as Vmax1 is executed (step S5). Then, it is determined whether or not the stored maximum vibration intensity Vmax1 is equal to or greater than a predetermined threshold value X (see FIG. 8) (step S6).

  When it is determined YES in step S6 and it is confirmed that the maximum vibration intensity Vmax1 ≧ threshold value X, control for retarding the ignition timing by the spark plug 16 by a predetermined amount (retard) is executed (step S7). ). As described above, the normal ignition timing in the specific operation region R is set to a timing slightly delayed from the compression top dead center (for example, about ATDC 5 °). The retard amount from the dead center to the ignition timing is further increased.

  When the ignition timing is retarded as described above, the maximum vibration intensity Vmax is acquired from the information input from the vibration sensor 33 in the state after the retardation, and the value is stored as Vmax2. It is executed (steps S8 and S9). Then, it is determined whether or not the stored maximum vibration intensity Vmax2 is larger than the maximum vibration intensity Vmax1 stored in the previous step S5 (that is, the maximum vibration intensity stored before retarding the ignition timing). (Step S10). Hereinafter, the maximum vibration intensity Vmax2 stored after retarding the ignition timing is referred to as “maximum vibration intensity Vmax2 after ignition retard”, and the maximum vibration intensity Vmax1 stored before retarding the ignition timing. This is referred to as “maximum vibration intensity Vmax1 before ignition retard”.

  If YES is determined in step S10, that is, if it is confirmed that (maximum vibration intensity Vmax2 after ignition retard)> (maximum vibration intensity Vmax1 before ignition retard), the ignition timing is retarded. Since the maximum vibration intensity Vmax is increased even if it is set, “1” indicating that pre-ignition has occurred is input to the abnormal combustion flag Fabnrm (step S4). That is, as shown by the “Δ” mark in FIG. 8, when pre-ignition occurs, pre-ignition is not suppressed even if the ignition timing is retarded, and the maximum vibration intensity Vmax increases. When Vmax2> Vmax1 as described above, it can be determined that pre-ignition has occurred, and as a result, the abnormal combustion flag Fabnrm = 1 is set.

  On the other hand, when it is determined NO in step S10, that is, when it is confirmed that (maximum vibration intensity Vmax2 after ignition retard) ≦ (maximum vibration intensity Vmax1 before ignition retard), the above is further performed. Control is performed to determine whether or not the detection timing of the maximum vibration intensity Vmax2 after ignition retard is earlier than the detection timing of the maximum vibration intensity Vmax1 before ignition retard (step S11).

  If it is determined YES in step S11 and it is confirmed that the detection time of Vmax2 is earlier than the detection time of Vmax1, the detection time of the maximum vibration intensity Vmax is advanced even if the ignition timing is retarded. Therefore, as in the case of YES in step S10, “1” indicating that pre-ignition has occurred is input to the abnormal combustion flag Fabnrm (step S4). That is, as indicated by the “Δ” mark in FIG. 8, it can be determined that pre-ignition has occurred when the detection timing of the maximum vibration intensity Vmax is advanced irrespective of the retarded ignition timing. The abnormal combustion flag Fabnrm = 1.

  As shown in steps S10 and S11, in the present embodiment, after retarding the ignition timing, it is first determined whether or not the maximum vibration intensity Vmax has increased (S10). Even if it is determined that it has not increased, it is determined whether or not the detection time of Vmax is further advanced (S11). And when it determines with YES in either of these steps S10 and S11, it determines with the pre-ignition having generate | occur | produced. That is, as shown by the “Δ” mark in FIG. 8, when pre-ignition has occurred, there should be a phenomenon that the maximum vibration intensity Vmax is increased and the detection timing is advanced. However, in some cases, there is a possibility that only one of these phenomena may be observed. Therefore, if one of the two determinations of steps S10 and S11 is YES, it is determined as pre-ignition.

  Next, the control operation when NO is determined in step S11 will be described. In this case, as the ignition timing is retarded, the maximum vibration intensity Vmax is reduced and the detection timing is delayed, so that knocking occurs in the abnormal combustion flag Fabnrm in the next step S12. Control to input “2” representing this is executed. That is, as shown by the “x” mark in FIG. 8, when the ignition timing is retarded when knocking occurs, the maximum vibration intensity Vmax decreases and the detection timing is retarded. When such a phenomenon is observed, it can be determined that knocking has occurred, and as a result, the abnormal combustion flag Fabnrm = 2 is set.

  Further, when it is determined NO in step S6, that is, when it is confirmed that the maximum vibration intensity Vmax1 before ignition retard is smaller than the threshold value X, neither pre-ignition nor knocking has occurred. Therefore, the control for inputting “0” indicating that the combustion state is normal is executed to the abnormal combustion flag Fabnrm (step S13).

  As described above, in the flowchart of FIG. 9, whether or not pre-ignition or knocking has occurred based on the detection values of the ion current sensor 34 and the vibration sensor 33 when the engine operating state is in the specific operation region R. In accordance with the result, any value of “0”, “1”, and “2” is input to the abnormal combustion flag Fabnrm.

  The processing following the flowchart of FIG. 9 is shown in FIG. When the process shown in the figure starts, it is first determined whether or not the abnormal combustion flag Fabnrm = 1 (step S20), where YES (Fabnrm = 1) is determined and pre-ignition has occurred. Is confirmed, pre-ignition avoidance control is executed as control for avoiding this (step S21).

  Next, the specific contents of the pre-ignition avoidance control in step S21 will be described with reference to FIG. When the pre-ignition avoidance control is started, first, control for determining whether or not the currently set in-cylinder air-fuel ratio (A / F) is smaller than 11 is executed (step S40). The determination threshold value (A / F = 11) here is a limit value that is allowed when the air-fuel ratio is enriched in step S42 described later. If the air-fuel ratio is enriched to a value smaller than A / F = 11, smoke may be generated, and the fuel consumption is disadvantageous. Therefore, the limit value for enrichment is A / F. = 11 is set.

  In the specific operation region R, initially, the air-fuel ratio in the cylinder is set to the stoichiometric air-fuel ratio (= 14.7) or a value slightly richer than this, and leaner than the limit value (= 11). The air / fuel ratio is set. Therefore, the first determination in step S40 is naturally YES, and the process proceeds to the next step S42 to execute control for enriching the air-fuel ratio. Specifically, the fuel injection amount from the injector 18 is increased, so that the air-fuel ratio in the cylinder is made richer by a predetermined amount than the currently set air-fuel ratio.

  The enrichment of the air-fuel ratio is performed step by step in a plurality of times. For example, if the current air-fuel ratio is A / F = 14.7 (theoretical air-fuel ratio), the air-fuel ratio is enriched to A / F = 12.5, which is smaller than this, and pre-ignition cannot be avoided. Further, the air / fuel ratio is further enriched to A / F = 11 (limit value). Conversely, if pre-ignition is avoided at the time of A / F = 12.5, enrichment is stopped at that time.

  If the pre-ignition continues after the air-fuel ratio is enriched to the limit value A / F = 11 in step S42, it is determined NO in step S40, so in the next step S41. Whether the currently set closing timing (IVC) of the intake valve 11 is earlier than Tx, which is the closing timing (latest timing) when IVC is retarded to the maximum in step S43 described later. Control to determine is executed. The latest timing Tx, which is the determination threshold here, is a timing at which the effective compression ratio of the engine decreases to some extent with respect to the geometric compression ratio and the intake air blows back, for example, after passing through the intake bottom dead center. (ABDC) It is set to about 110 ° CA. If the closing timing of the intake valve 11 is further retarded than the latest timing Tx, the effective compression ratio of the engine is extremely reduced and the output becomes insufficient. Late time Tx is set.

  In the specific operation region R, initially, the closing timing of the intake valve 11 is set to, for example, about 35 ± 5 ° CA after passing through the intake bottom dead center (ABDC) as a timing at which the intake air blow-back hardly occurs. Yes. For this reason, the first determination in step S41 is naturally NO, the process proceeds to the next step S43, and control for retarding the closing timing of the intake valve 11 is executed. Specifically, by driving the VVT 15 in a direction in which the operation timing of the intake valve 11 is delayed, the closing timing of the intake valve 11 is retarded by a predetermined amount from the current set value, and the effective compression ratio of the engine is lowered. .

  The delay of the closing timing of the intake valve 11 is performed in stages in a plurality of steps, similar to the enrichment of the air-fuel ratio in step S42. In other words, the closing timing of the intake valve 11 is first retarded by a predetermined amount, and if pre-ignition is avoided in that state, further retarding is prohibited, while if the pre-ignition cannot be avoided, the retard amount is further increased. Increase.

  Further, in the present embodiment, when the closing timing of the intake valve 11 is retarded stepwise as described above, each time the retarding angle is set so that the effective compression ratio decreases at regular intervals as the retardation is retarded. Set the amount. Therefore, the amount of retardation of each time is increased as the closing timing before the retardation is closer to the intake bottom dead center, and is gradually decreased as the retardation is advanced.

  The reason for controlling the retardation amount as described above will be described with reference to FIG. FIG. 13 is a graph showing the relationship between the retard amount of the closing timing (IVC) of the intake valve 11 and the effective compression ratio in an engine with a geometric compression ratio of 14. According to this graph, as the closing timing of the intake valve 11 is further away from the intake bottom dead center (BDC) (the right side of the horizontal axis), the inclination of the graph increases and the rate of decrease in the effective compression ratio gradually increases. I understand. For this reason, if the effective compression ratio is always reduced by a certain amount, the more the current closing timing of the intake valve 11 is retarded with respect to the intake bottom dead center, the smaller the retard amount is. Conversely, the closer the intake valve 11 closes to the intake bottom dead center, the greater the retard amount.

  FIG. 14 shows how the retard amount (vertical axis) of the closing timing of the intake valve 11 necessary for reducing the effective compression ratio by 0.5 depends on the current retard amount (horizontal axis). It is the graph which showed whether it changes to in the range whose retardation amount is 30 degrees CA or more. According to this graph, for example, if the current retardation amount is 30 ° CA, the effective compression ratio cannot be reduced by 0.5 unless the retardation is further delayed by about 10 ° CA. If the current retard amount is 40 ° CA, the effective compression ratio can be reduced by 0.5 by simply retarding the angle by about 8 ° CA. Thus, the retard amount of the closing timing of the intake valve 11 necessary for reducing the effective compression ratio by a certain amount decreases as the current retard amount increases.

  Therefore, when the closing timing of the intake valve 11 is retarded with respect to the intake bottom dead center in step S43, the amount of retardation is gradually decreased as the closing timing before the retard is further away from the intake bottom dead center. The effective compression ratio is decreased stepwise by a predetermined interval by delaying the closing timing of the intake valve 11 in a plurality of times within the range up to the latest timing Tx.

  If the pre-ignition continues after the closing timing of the intake valve 11 is delayed to the latest timing Tx in step S43, it is determined NO in step S41, so that the next step S44 is performed. Thus, control for dividing the fuel injection timing and injecting a part thereof in the compression stroke is executed. That is, as shown in FIG. 15, where all the fuel should be injected during the intake stroke (F in FIG. 15A), the injection timing of some of the fuel is delayed until the later stage of the compression stroke. By being angled, the fuel is injected into the intake stroke and the compression stroke (F1 and F2 in FIG. 5B).

  As described above, in the pre-ignition avoidance control, the air-fuel ratio is enriched (step S42), the closing timing of the intake valve 11 is retarded (step S43), and the fuel injection timing is retarded (step S44). Are preferentially executed in this order.

  When the control of any of the above steps S42, S43, and S44 is started, then the pre-ignition avoidance control is being executed in the control execution flag FF (its default value is 0) for recording the execution state of the control. “1” representing the presence is input (step S45), and the process returns to the main flow of FIG.

  FIG. 16 shows the air-fuel ratio (A / F) and the intake valve 11 closed when it is assumed that the pre-ignition cannot be avoided unless all the control steps S42, S43, and S44 are executed in the pre-ignition avoidance control. It is a time chart which shows how time (IVC) and a fuel-injection time each change with time passage. As can be understood from this figure, in the pre-ignition avoidance control, first, the control for enriching the air-fuel ratio step by step is preferentially executed, and after being enriched to the maximum (up to A / F = 11). However, if the pre-ignition cannot be avoided, the closing timing (IVC) of the intake valve 11 is retarded stepwise, and if the pre-ignition is still unavoidable even after being retarded to the maximum, the fuel injection timing is delayed. Keratinization (compression stroke injection of part of the fuel) is performed.

  Returning to FIG. 10 again, the control operation in the case where the determination in step S20 is NO will be described. As a result of the pre-ignition avoidance control (S21) described above, when the pre-ignition is sufficiently suppressed, or when pre-ignition has not occurred from the beginning, the abnormal combustion flag Fabnrm ≠ 1, and the above-described step S20 is performed. The determination is NO. Then, in the next step S23, it is determined whether or not the abnormal combustion flag Fabnrm = 2, that is, whether or not knocking has occurred.

  When it is determined as YES in step S23 and it is confirmed that knocking has occurred, control for retarding the ignition timing (retard) is executed until the knocking is sufficiently suppressed (step S24). In order to record that the control is being executed, the control for inputting “2” to the control execution flag FF is executed (step S25).

  If knocking is sufficiently suppressed by retarding the ignition timing, or if knocking has not occurred from the beginning, the determination in step S23 is NO. That is, since both NO in steps S20 and S23, the abnormal combustion flag Fabnrm = 0, neither pre-ignition nor knocking occurs, and the combustion state is normal. Then, in the next step S26, it is determined whether or not the control execution flag FF is “1”, that is, whether or not the pre-ignition avoidance control (S21) is being executed.

  If it is assumed that the current combustion state becomes normal as a result of the execution of the pre-ignition avoidance control, the flag FF = 1, so that YES is determined in the step S26. Then, in the next step S27, return control for canceling the pre-ignition avoidance control and returning to normal operation is executed.

  FIG. 12 shows the specific contents of the return control in step S27. When the return control is started, it is first determined whether or not the control (step S44 in FIG. 11) for delaying the injection timing of a part of the fuel to the latter stage of the compression stroke is being executed (step S50). When it is determined as YES and it is confirmed that the retarding of the fuel injection timing (compression stroke injection) is being performed, the fuel injection timing of the part of the fuel is changed to the intake stroke that is the normal injection timing. The returning control is executed (step S53).

  When the pre-ignition did not occur after the fuel injection timing was returned to the normal timing (during the intake stroke) as described above, or when the fuel injection timing was not retarded from the beginning The determination in step S50 is NO. Then, the process proceeds to step S51, and control for determining whether or not the closing timing of the intake valve 11 is set to the retard side with respect to the original setting timing is executed.

  If the closing timing of the intake valve 11 is retarded in step S43 of FIG. 11, the determination in step S51 is YES. Then, the process proceeds to step S54, and control is performed to increase the effective compression ratio by returning the closing timing of the intake valve 11 to the advance angle (advance) side.

  The advancement of the closing timing of the intake valve 11 is performed stepwise in a plurality of times, as in step S43 of FIG. Corresponding to the graph of FIG. 14, the advance amount of each time at this time is smaller as the closing timing before the advance is further from the intake bottom dead center, and is increased as the intake bottom dead center is approached. Such stepwise advancement is effective by continuing the closing timing of the intake valve 11 until it reaches a normal timing (a timing at which the intake air hardly blows back; for example, about ABDC 35 ± 5 °). The compression ratio is gradually increased at regular intervals and returned to a value close to the geometric compression ratio.

  When pre-ignition has not occurred even after the closing timing of the intake valve 11 has been returned to the normal timing as described above, or when the closing timing of the intake valve 11 has not been delayed from the beginning, The determination in step S51 is NO. Then, the process proceeds to step S52, and control is performed to determine whether or not the in-cylinder air-fuel ratio is richer than the normal value (theoretical air-fuel ratio or its vicinity). Then, when it is determined as YES and it is confirmed that the air-fuel ratio is enriched, control is performed to return the air-fuel ratio to the lean side (side approaching the normal value) (step S55).

  The leaning of the air-fuel ratio is performed in stages in a plurality of steps, as in step S42 in FIG. For example, the in-cylinder air-fuel ratio is made lean in stages as A / F = 11 → 12.5 → 14.7 and returned to the normal value.

  When the control in step S55 is completed and the air-fuel ratio is returned to the normal value, the determination in step S52 is NO. Then, “0” is input to the control execution flag FF (step S56), and the process returns to the main flow of FIG.

  FIG. 17 is a time chart showing temporal changes in the air-fuel ratio, fuel injection timing, and the like when the return control as described above is performed. Here, when the pre-ignition avoidance control as shown in FIG. 16 is performed, that is, in order to avoid pre-ignition, the air-fuel ratio is enriched, the closing timing of the intake valve 11 is retarded, In addition, it is shown how each state quantity is changed by the subsequent return control when it is necessary to perform all of the retarded fuel injection timing (compression stroke injection of a part of the fuel).

  As shown in FIG. 17, when returning from the pre-ignition avoidance control, first, the retarding of the fuel injection timing is canceled and the injection timing is returned to the normal timing (during the intake stroke), and then the pre-ignition does not occur. In the case where the intake valve 11 is closed in a stepwise manner toward the normal timing (IVC), when the pre-ignition does not occur, the air-fuel ratio is set to the normal value. The lean control is executed.

  Returning to FIG. 10 again, the control operation in the case where the determination in step S26 is NO will be described. As a result of the return control described above, the pre-ignition avoidance control (S21) is completely cancelled, and the air-fuel ratio, the closing timing of the intake valve 11 and the fuel injection timing are all returned to normal values, or the pre-ignition avoidance control is performed from the beginning. If not, the control execution flag FF ≠ 1 and the determination in step S26 is NO. Then, in the next step S29, it is determined whether or not the control execution flag FF = 2, that is, whether or not the control for retarding the ignition timing is executed to avoid knocking.

  If it is determined YES in step S29 and it is confirmed that the ignition timing is retarded, the ignition timing after the retard is advanced to normal ignition timing (for example, ATDC 5 ° in the specific operation region R). (Step S30), and control for inputting “0” to the control execution flag FF is executed (step S31).

  If knocking does not occur after the ignition timing is returned to the normal timing as described above, or if the ignition timing has not been retarded from the beginning, it is determined NO in step S29. Thus, normal operation is continued (step S32).

(5) Effects In the spark ignition type engine of the present embodiment, pre-ignition is performed based on the detection values of the ion current sensor 34 and the vibration sensor 33 in the specific operation region R set in the low rotation / high load region of the engine. If it is determined whether or not pre-ignition has occurred (YES in any of S3, S10, and S11), pre-ignition is performed as control for avoiding this. Avoidance control (S21) is executed. Then, in the pre-ignition avoidance control, first, a control (S42) for increasing the fuel injection amount from the injector 18 to enrich the air-fuel ratio in the cylinder is executed, and after the control, the pre-ignition is detected. In addition, the control (S43) is executed to retard the closing timing of the intake valve 11 to lower the effective compression ratio of the engine (S43). Even when pre-ignition is detected, the injection timing of a part of the fuel is reduced to the compression stroke. Control (S44) for delaying to the later stage is executed. According to such a configuration, there is an advantage that the occurrence of pre-ignition can be effectively suppressed while maintaining the emission property as good as possible.

  That is, in the above-described embodiment, in the pre-ignition avoidance control for avoiding the pre-ignition, the control for enriching the air-fuel ratio is first performed, and the fuel injection timing is retarded (a part of the fuel is injected in the compression stroke). ) Since control is most delayed, it is possible to effectively suppress the occurrence of pre-ignition while avoiding as much as possible the occurrence of smoke and deterioration of emissions.

  In a spark ignition type engine, whether the air-fuel ratio is enriched or the fuel injection timing is retarded, the temperature of the fuel in the cylinder (the temperature of the fuel near the compression top dead center) is lowered to pre- Ignition can be suppressed, but retarding the fuel injection timing (compression stroke injection) may lead to the generation of smoke due to the remaining unburned carbon, so suddenly retard the injection timing. There is a concern that smoke will frequently occur. In contrast, in the above-described embodiment, when the pre-ignition occurs, the air-fuel ratio is first enriched to reduce the fuel temperature in the cylinder, and only when the pre-ignition cannot be avoided, the injection timing is retarded. Therefore, there is an advantage that the generation of smoke as described above can be avoided as much as possible and the emission performance can be maintained as good as possible.

  Further, as a control having a lower priority than the enrichment of the air-fuel ratio (S42) and a higher priority than the retarding of the fuel injection timing (S44), the closing timing of the intake valve 11 is retarded to lower the effective compression ratio. Since the control (S43) is executed, there is an advantage that the frequency at which the fuel injection timing is retarded can be reduced to prevent the deterioration of the emission property due to the occurrence of smoke more effectively.

  That is, following the enrichment of the air-fuel ratio, control is performed to reduce the effective compression ratio of the engine, and after reducing the in-cylinder pressure, the fuel injection timing is retarded only when pre-ignition cannot be avoided. Therefore, it is possible to avoid the pre-ignition with higher probability without delaying the fuel injection timing. Thereby, the frequency at which the retarding of the fuel injection timing is executed becomes extremely low, and the pre-ignition can be suppressed while avoiding the generation of smoke as much as possible.

  In the above configuration, when the control is shifted to the pre-ignition avoidance control, first, the control for enriching the air-fuel ratio is executed. If the pre-ignition cannot be avoided even after that, the closing timing of the intake valve 11 is retarded to increase the effective compression ratio. However, these two controls (the enrichment of the air-fuel ratio and the reduction of the effective compression ratio) do not affect the emission performance (smoke generation). Considering only the above, it is considered that the reduction of the effective compression ratio may be prioritized over the enrichment of the air-fuel ratio. However, the control for reducing the effective compression ratio not only causes a reduction in engine output, but also has a problem of poor control response. That is, particularly when the VVT 15 is a hydraulic variable mechanism, a relatively long response delay occurs when the operation timing of the intake valve 11 is changed by driving the VVT 15, so that the closing timing of the intake valve 11 is delayed. It can be said that the control for decreasing the effective compression ratio by inclining is inferior in control responsiveness compared to the control for increasing the injection amount from the injector 18 to enrich the air-fuel ratio.

  Therefore, in the above embodiment, at the time of the pre-ignition avoidance control, the air-fuel ratio is enriched first and the effective compression ratio is lowered later. In this way, by reducing the effective compression ratio later, it is possible to avoid as much as possible a decrease in engine output caused by a decrease in the compression ratio, and by performing enrichment of the air-fuel ratio with excellent responsiveness with the highest priority. There is an advantage that the suppression can be achieved more quickly immediately after the occurrence of the pre-ignition.

  In the above-described embodiment, when pre-ignition control is performed, the air-fuel ratio is enriched stepwise, and pre-ignition is detected even in a fully enriched state (up to the limit value A / F = 11). The control for reducing the effective compression ratio is executed (see FIG. 16). In this way, if the enrichment of the air-fuel ratio is performed stepwise, for example, if the degree of pre-ignition is light and the pre-ignition can be avoided by simply enriching the air-fuel ratio slightly, it is more than necessary. The air-fuel ratio is not enriched, and the deterioration in fuel efficiency due to the enrichment of the air-fuel ratio can be minimized. Also, when pre-ignition cannot be avoided even if the air-fuel ratio is maximized, the air-fuel ratio becomes excessively rich by reducing the effective compression ratio and further suppressing the pre-ignition by retarding the fuel injection timing. Even if the pre-ignition is relatively advanced, it is possible to surely avoid it.

  Similarly, in the above-described embodiment, the control for reducing the effective compression ratio by retarding the closing timing of the intake valve 11 is performed in stages to maximize the effective compression ratio (to the compression ratio corresponding to the latest timing Tx). ) When the pre-ignition is detected even in the lowered state, the control for delaying the fuel injection timing is executed. According to such a configuration, there is an advantage that the pre-ignition can be avoided more reliably while preventing the effective compression ratio from being reduced more than necessary and the engine output from being significantly reduced.

  In particular, in the above embodiment, when the closing timing of the intake valve 11 is retarded stepwise, as shown in FIG. 14, the closer the current closing timing is to the intake bottom dead center, the more the amount of retardation from there. Therefore, each time the closing timing of the intake valve 11 is retarded once, the effective compression ratio can be decreased at regular intervals. For this reason, it is possible to properly avoid situations where the engine output suddenly drops due to a single retarded angle, or the compression ratio decreases only slightly and the effect on the pre-ignition is hardly obtained, and pre-ignition occurs. There is an advantage that can be suppressed more effectively.

  Further, in the above-described embodiment, the closing timing of the intake valve 11 at the normal time (when pre-ignition has not occurred) is set to a timing that is retarded from the intake bottom dead center and the respiration of the intake hardly occurs (specifying On the other hand, when the effective compression ratio is lowered by the pre-ignition avoidance control, the VVT 15 is driven to further set the closing timing of the intake valve 11 with respect to the intake bottom dead center. Since the retarding angle is set, there is an advantage that the effective compression ratio can be efficiently reduced when necessary while sufficiently securing the engine output at the normal time.

  For example, if the effective compression ratio is simply decreased, the effective compression ratio can be decreased by advancing the closing timing of the intake valve 11 to the advance side of the intake bottom dead center. However, if the closing timing of the intake valve 11 in the normal time is retarded from the intake bottom dead center, the closing timing is changed from there to the advance side of the intake bottom dead center to reduce the effective compression ratio. Then, it is necessary to change the operation timing of the intake valve 11 significantly, and there is a problem that the control amount of the VVT 15 increases and the control responsiveness deteriorates. In order to avoid this, it is conceivable to set the closing timing of the intake valve 11 at the normal time to a timing substantially coincident with the intake bottom dead center, or to an advance side than this, The intake inertia cannot be fully utilized, resulting in a decrease in engine output.

  From this point, as in the above-described embodiment, when the closing timing of the intake valve 11 in the normal state is set to the retard side with respect to the intake bottom dead center and the effective compression ratio is reduced, the intake valve It is advantageous to delay the closing timing of 11 with respect to the normal time in that the effective compression ratio can be efficiently reduced when necessary while sufficiently securing the normal engine output.

  Further, in the above embodiment, when returning from the pre-ignition avoidance control to the normal operation, the control for canceling the retarding of the fuel injection timing (partial compression stroke injection of the fuel) is executed with the highest priority, and the latter half of the compression stroke is performed. Since the injection timing of the part of the fuel that has been delayed until is returned to the intake stroke, the emission performance can be recovered as soon as possible after the control to avoid pre-ignition. is there.

  For example, in the pre-ignition avoidance control, when it is necessary to enrich the air-fuel ratio, lower the effective compression ratio (retard the closing timing of the intake valve 11), and retard the fuel injection timing. When returning to normal operation from this state, as shown in FIG. 17, first, the retarding of the fuel injection timing is canceled and the injection timing is returned to the intake stroke, and after that, pre-ignition is not detected. The effective timing is increased by returning the closing timing of the intake valve 11 to the advance side, and the air-fuel ratio is returned to the lean side when no pre-ignition is detected. According to such a configuration, when pre-ignition is avoided, the delay in the fuel injection timing is first canceled to eliminate the possibility of the occurrence of smoke, thereby reducing the time when the emission performance deteriorates. Can be minimized.

  If pre-ignition is not detected after that, the next priority control is to advance the closing timing of the intake valve 11 and increase the effective compression ratio, thereby increasing the engine output due to the decrease in the compression ratio. The decline can be resolved early. If no pre-ignition is detected, the air-fuel ratio is finally returned to the lean side, so that it is possible to properly return to the normal operation while ensuring that no pre-ignition occurs.

  In the above embodiment, flame is detected by the ion current sensor 34, and the presence / absence of pre-ignition is determined based on the detection timing (flame generation timing), while the pre-ignition is detected by detection using the ion current sensor 34. Even if the above is not confirmed, since the pre-ignition is further detected using the vibration sensor 33, there is an advantage that the pre-ignition can be detected with higher accuracy.

  Specifically, in the above embodiment, when detecting the pre-ignition using the vibration sensor 33, first, it is determined whether or not the maximum vibration intensity Vmax1 acquired from the vibration sensor 33 is equal to or greater than the threshold value X. (S6) If it is equal to or greater than the threshold value X, the ignition timing by the spark plug 16 is further changed from a normal ignition timing corresponding to a slightly retarded side of the compression top dead center (for example, about ATDC 5 °) to a more retarded side. To do. The maximum vibration intensity (maximum vibration intensity after ignition retard) Vmax2 acquired after the ignition timing is retarded is greater than the maximum vibration intensity (maximum vibration intensity before ignition retard) Vmax1 before the retarding. It is determined whether it is larger (S10). If Vmax2 is larger than Vmax1, it is determined that pre-ignition has occurred. By taking such a procedure, even a relatively early stage pre-ignition (for example, a light pre-ignition such as the waveform J1 in FIG. 4 or a similar one) is knocked out. There is an advantage that it can be detected reliably while distinguishing.

  For example, simply comparing the maximum vibration intensity Vmax with the reference value makes it difficult to determine whether the pre-ignition is knocking or knocking, particularly when the pre-ignition is at a relatively early stage. is there. With respect to such a problem, in the above configuration, when the maximum vibration intensity Vmax equal to or greater than the predetermined threshold is confirmed, the ignition timing is intentionally retarded, and an increase in the maximum vibration intensity Vmax is confirmed before and after that. In this case, since it is determined that pre-ignition has occurred, retarding the ignition timing is effective only for suppressing knocking (not effective for suppressing pre-ignition). It is possible to accurately determine whether the pre-ignition or knocking.

  Therefore, according to the above configuration, while using the vibration sensor 33, it is possible to reliably detect pre-ignition, which is a phenomenon in which the air-fuel mixture self-ignites prematurely, while distinguishing it from knocking. Even if a failure such as disconnection occurs or the detection accuracy is not sufficient, the occurrence of pre-ignition is not overlooked. Then, when pre-ignition is detected, pre-ignition is continued by taking necessary measures for avoiding the pre-ignition (that is, controlling the above-described enrichment of the air-fuel ratio, reduction of the effective compression ratio, etc.). It is possible to reliably prevent engine trouble (for example, damage to the piston 5 and the like) resulting from the above.

  Further, in the above embodiment, even when the maximum vibration intensity Vmax2 after ignition retard is equal to or less than the maximum vibration intensity Vmax1 before ignition retard, the detection time of Vmax2 can be earlier than the detection time of Vmax1. For example, it was determined that pre-ignition occurred. That is, once the pre-ignition occurs, the maximum vibration intensity Vmax should increase and the detection timing should be accelerated regardless of the retarded ignition timing. Since only one of the phenomena may be observed, it is determined that pre-ignition has occurred if either an increase in the maximum vibration intensity Vmax or an early detection timing is confirmed. Thereby, the detection accuracy of the pre-ignition can be further increased.

(6) Modifications etc. In the above embodiment, when the air-fuel ratio is enriched in the pre-ignition avoidance control, for example, A / F = 14.7 → 12.5 → 11. However, the air-fuel ratio may be enriched in multiple stages by dividing the number of times. Conversely, if the number of times of enrichment is set to one and then pre-ignition is not avoided, the control may immediately shift to the control for reducing the effective compression ratio by retarding the closing timing of the intake valve 11.

  Further, in the above-described embodiment, when the effective closing ratio is lowered by retarding the closing timing of the intake valve 11 in the pre-ignition avoidance control, the closing timing of the intake valve 11 is retarded in stages in a plurality of times. However, the number of times of retarding can be appropriately set according to the characteristics of the engine.

  Further, when it is not desired to reduce the output as much as possible due to engine characteristics, the closing timing of the intake valve 11 may be retarded only once. However, even in this case, as the closing timing of the intake valve 11 before the retard is retarded with respect to the intake bottom dead center, the retard amount should be made smaller. That is, in the specific operation region R where pre-ignition can occur, the normal closing timing of the intake valve 11 has a certain width, for example, about 35 ± 5 ° after passage of the intake bottom dead center (ABDC). If the closing timing of the intake valve 11 before starting the retarding is, for example, ABDC 40 °, the retardation amount is set smaller than when the ABCD is 30 °. Thereby, regardless of the closing timing of the intake valve 11 at the normal time, the reduction range of the effective compression ratio can always be made constant.

  In the above embodiment, for example, as shown in FIG. 15A, the normal fuel injection timing in which no pre-ignition has occurred is set to only one time during the intake stroke (that is, during the intake stroke). However, the fuel injection timing at the normal time may be during the intake stroke, and the fuel may be divided into a plurality of times during the intake stroke.

  In the above-described embodiment, when pre-ignition is detected, the air-fuel ratio is enriched and the effective compression ratio is decreased in order, and when the pre-ignition cannot be avoided, the injection of a part of the fuel to be injected is performed. Although the timing is retarded at a stretch until the latter stage of the compression stroke (FIG. 15B), for example, as shown in FIG. 18, the second injection F2 that is retarded until the compression stroke (hereinafter referred to as a post-stage injection). ) May be retarded in stages from the middle to the later stage of the compression stroke. That is, first, the timing of the post-injection F2 is retarded to the middle stage of the compression stroke (FIG. 18B), and if the pre-ignition cannot be avoided even in this state, the timing of the post-injection F2 is further retarded, The latter stage of the compression stroke (FIG. 18C) is set. In this way, when the post-injection F2 is delayed to the middle stage of the compression stroke, pre-ignition can be sufficiently avoided, and the injection timing is suddenly delayed until the later stage of the compression stroke where the possibility of smoke is high. There is no cornering, and it is possible to more effectively prevent the emission property from deteriorating.

  On the other hand, depending on the engine characteristics and the like, it may be assumed that there is still a situation where pre-ignition cannot be avoided even if the post-injection F2 is delayed until the later stage of the compression stroke. Therefore, in such a case, for example, at the same time or after the control for retarding the post-injection F2 to the latter stage of the compression stroke, the air-fuel ratio is set to a richer side than the limit value A / F = 11 (for example, (A / F = up to about 10) may be changed. As a result, the possibility that smoke is temporarily generated is further increased, but this can be reliably avoided even when the pre-ignition is considerably developed.

  Further, in the above embodiment, the control is performed in which the fuel injection is divided and a part (the latter injection F2) is retarded until the compression stroke is performed, and the compression stroke is avoided when the pre-ignition is avoided as a result of the control. The injection timing of the part of the fuel retarded to the inside is immediately returned to the normal timing (during the intake stroke), but the injection timing after the pre-ignition has been avoided is at least the advance side (intake It may be returned to the side closer to the stroke) and may be advanced step by step until the normal time.

  Further, in the above embodiment, the ion current sensor 34 is provided separately from the spark plug 16, and by detecting the flame generation timing by the ion current sensor 34, it is determined whether pre-ignition has occurred. However, if a bias voltage for ion current detection is applied to the center electrode (plug electrode) of the spark plug 16, the spark plug 16 can also be used as the ion current sensor. In this way, the structure can be simplified and the cost of the ion current sensor 34 can be reduced.

  However, if the spark plug 16 is also used as the ion current sensor 34 as described above, the moment when a spark is discharged from the spark plug 16 (that is, the moment when a high voltage for discharge is applied to the plug electrode) is biased to the plug electrode. Since the voltage cannot be applied and the ion current cannot be detected, the detection accuracy of the pre-ignition by the ion current sensor 34 alone is lowered. However, according to the configuration of the above-described embodiment in which the pre-ignition can be detected using the vibration sensor 33, the above-described decrease in detection accuracy can be covered by the vibration sensor 33. Therefore, the detection accuracy of the pre-ignition The structure can be simplified and the parts cost can be reduced without reducing the cost.

  In the above embodiment, the occurrence of pre-ignition is detected by using both the ion current sensor 34 and the vibration sensor 33. However, the detection of the pre-ignition by the ion current sensor 34 may be omitted. In this way, it is possible to further simplify the structure and control and further reduce the component cost while detecting the occurrence of pre-ignition with the vibration sensor 33 alone.

  In the above-described embodiment, the vibration of the engine body 1 is detected by the vibration sensor 33, and the magnitude of the maximum vibration intensity Vmax specified from the detected value and the detection timing are determined as the ignition timing is retarded. It is determined whether pre-ignition or knocking is occurring based on whether the engine pressure changes. However, a similar detection method is used when an in-cylinder pressure sensor that detects the in-cylinder pressure of the engine is used. Is also applicable.

  Specifically, detection of pre-ignition and knocking using the in-cylinder pressure sensor is performed as follows. First, when the engine operating state is in the specific operation region R, the maximum value of the in-cylinder pressure is specified from the in-cylinder pressure waveform input from the in-cylinder pressure sensor (see, for example, FIG. 5), and this is a predetermined threshold value. It is determined whether it is above. If it is equal to or greater than the threshold, the ignition timing is retarded, and then the maximum value of the in-cylinder pressure is acquired again. The maximum in-cylinder pressure obtained after retarding the ignition timing is the maximum in-cylinder pressure after ignition retard, and the maximum in-cylinder pressure obtained before the ignition timing is retarded. It is determined whether the maximum in-cylinder pressure after ignition retard is greater than the maximum in-cylinder pressure before ignition retard. If it is greater, it is determined that pre-ignition has occurred.

  Further, as in the above embodiment, even when the maximum in-cylinder pressure after ignition retard is equal to or less than the maximum in-cylinder pressure before ignition retard, the detection timing of the maximum in-cylinder pressure after ignition retard is the maximum in-cylinder pressure before ignition retard. If it is earlier than the detection time, it may be determined that pre-ignition has occurred. On the other hand, if the detection timing after the ignition retard is not earlier than before the ignition retard, it is determined that the knocking is occurring.

11 Intake valve 15 VVT (variable mechanism)
18 Injector 33 Vibration sensor (detection means)
34 Ion current sensor (detection means)
40 ECU (control means)

Claims (14)

Method for controlling a spark ignition engine having a detecting means for detecting pre-ignition in which an air-fuel mixture self-ignites before the normal combustion start timing by spark ignition and an injector for directly injecting fuel into a cylinder Because
When pre-ignition is detected based on the detection value of the detection means in a low engine speed and high load range, the fuel injection amount from the injector is increased to enrich the in-cylinder air-fuel ratio, and control thereof Control of a spark ignition engine characterized by retarding the injection timing of a part of the fuel to be injected from the injector after the middle of the compression stroke when pre-ignition is detected after Method. In the control method of the spark ignition type engine according to claim 1,
If pre-ignition is detected even after the air-fuel ratio is enriched, control for reducing the effective compression ratio of the engine is executed prior to the control for retarding the injection timing of the part of the fuel. A control method for a spark ignition type engine, characterized in that when the pre-ignition is detected, the retarding of the injection timing is executed. In the control method of the spark ignition type engine according to claim 2,
In the control for enriching the air-fuel ratio, if the air-fuel ratio is enriched by a predetermined amount and still the pre-ignition is detected, the air-fuel ratio is further enriched, and the pre-ignition is detected even when the air-fuel ratio is maximized. And a control method for reducing the effective compression ratio of the engine. In the control method of the spark ignition type engine according to claim 2 or 3,
In the control for reducing the effective compression ratio, the effective compression ratio is decreased by a predetermined amount, and if the pre-ignition is still detected, the effective compression ratio is further decreased and the pre-ignition is performed even when the effective compression ratio is reduced to the maximum. A control method for a spark ignition engine, characterized in that when it is detected, control is performed to retard the injection timing of the part of the fuel. In the control method of the spark ignition type engine according to any one of claims 2 to 4,
In the control for retarding the injection timing of some of the fuels, the injection timing is retarded to the middle of the compression stroke, and if pre-ignition is still detected, it is retarded to the latter half of the compression stroke. A control method for a spark ignition engine characterized by the above. In the control method of the spark ignition type engine according to any one of claims 2 to 5,
In normal control, the closing timing of the intake valve is set to be retarded from the intake bottom dead center, and in the control for reducing the effective compression ratio, the closing timing of the intake valve is set to be higher than the normal closing timing. Further, the control method for the spark ignition type engine is characterized by further changing to the retard side. In the control method of the spark ignition type engine according to any one of claims 2 to 6,
When the pre-ignition is avoided as a result of retarding the injection timing of the part of the fuel, control for returning the retarded fuel injection timing to the advance side is performed by the air-fuel ratio after the enrichment or A control method for a spark ignition type engine, which is executed prior to returning the effective compression ratio after the reduction. Control means for detecting a pre-ignition in which the air-fuel mixture self-ignites before the normal combustion start timing by spark ignition, an injector for directly injecting fuel into the cylinder, and a control for controlling each part of the engine including the injector A spark ignition engine control device comprising:
The control means includes
When pre-ignition is detected based on the detection value of the detection means in a low engine speed and high load range, the fuel injection amount from the injector is increased to enrich the in-cylinder air-fuel ratio, and control thereof Control of a spark ignition engine characterized by retarding the injection timing of a part of the fuel to be injected from the injector after the middle of the compression stroke when pre-ignition is detected after apparatus. The control device for a spark ignition engine according to claim 8,
A compression ratio adjusting means for variably setting the effective compression ratio of the engine;
If pre-ignition is detected even after the air-fuel ratio is enriched, the control means controls the compression ratio adjusting means to control the engine before the control for delaying the injection timing of the part of the fuel. A control device for a spark ignition type engine, characterized in that when the effective compression ratio is lowered and pre-ignition is still detected, the injection timing is retarded. The control device for a spark ignition engine according to claim 9,
In the control for enriching the air-fuel ratio, the control means enriches the air-fuel ratio by a predetermined amount, and if still pre-ignition is detected, the air-fuel ratio is further enriched, and even in a state where the air-fuel ratio is maximized, A control device for a spark ignition engine, characterized in that, when an ignition is detected, control for reducing the effective compression ratio of the engine is executed. The control device for a spark ignition engine according to claim 9 or 10,
In the control for reducing the effective compression ratio, the control means reduces the effective compression ratio by a predetermined amount, and if a pre-ignition is still detected, the effective compression ratio is further reduced to a maximum level. However, when the pre-ignition is detected, the control device for the spark ignition engine is configured to execute the control to retard the injection timing of the part of the fuel. The control device for a spark ignition engine according to any one of claims 9 to 11,
The control means delays the injection timing to the middle stage of the compression stroke in the control for retarding the injection timing of the part of the fuel, and if the pre-ignition is still detected, until the latter stage of the compression stroke. A control device for a spark ignition engine characterized by retarding. The control device for a spark ignition engine according to any one of claims 9 to 12,
The compression ratio adjusting means is a variable mechanism that variably sets the closing timing of the intake valve,
The normal closing timing of the intake valve is set to the retard side from the intake bottom dead center,
The control means changes the intake valve closing timing further to the retard side than the normal closing timing by controlling the variable mechanism during the control to reduce the effective compression ratio. A control device for a spark ignition type engine. The control device for a spark ignition engine according to any one of claims 9 to 13,
When pre-ignition is avoided as a result of retarding the injection timing of the part of the fuel, the control means performs control for returning the retarded fuel injection timing to the advance side. A control apparatus for a spark ignition type engine, which is executed prior to returning an air-fuel ratio or a reduced effective compression ratio.

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