JP7754040B2 - Ignition timing control device for internal combustion engine - Google Patents

Description

The present invention relates to an ignition timing control device for an internal combustion engine.

Internal combustion engines that employ a variable valve mechanism are known for the purpose of improving fuel economy by reducing pumping losses in response to the introduction of internal EGR (Exhaust Gas Recirculation). When the variable valve mechanism is activated, the amount of internal EGR may change. Because changes in the amount of internal EGR affect the combustion state in the internal combustion engine, it is known that the ignition timing of the spark plug is corrected depending on the operating status of the variable valve mechanism (see, for example, Patent Document 1).

JP 2010-248983 A

When controlling the ignition timing in an internal combustion engine, a misfire limit ignition timing is set to prevent misfires while the engine is running. In this case, the ignition timing in the internal combustion engine is set so that it does not exceed the misfire limit ignition timing. Possible causes of misfires include the operation of the variable valve characteristics mechanism and an increase in back pressure caused by the wastegate valve installed in conjunction with the turbocharger transitioning to a closed state. On the other hand, misfires become less likely when the actual compression ratio increases due to the operation of the variable valve characteristics mechanism.

Patent Document 1 above proposes correcting the ignition timing itself, but makes no mention of setting the misfire limit ignition timing, nor does it propose correcting the misfire limit ignition timing.

The invention disclosed in this specification aims to appropriately correct the misfire limit ignition timing in an internal combustion engine equipped with a variable valve characteristic mechanism.

The above-mentioned objectives are achieved by an ignition timing control device that is applied to an internal combustion engine equipped with a variable valve characteristics mechanism that changes the opening and closing characteristics of at least the intake valve out of the intake valve and exhaust valve, and that sets a misfire limit ignition timing, which is the limit ignition timing on the retard side at which misfire does not occur in the internal combustion engine. The ignition timing control device for an internal combustion engine includes a misfire limit ignition timing correction amount calculation unit that calculates a correction amount for the misfire limit ignition timing relative to the basic misfire limit ignition timing that is preset as the misfire limit ignition timing in the internal combustion engine, using an amount of change in the actual compression ratio that changes with changes in the opening and closing characteristics of the intake valve, and an intake manifold pressure difference, which is the difference between a base intake manifold pressure in the internal combustion engine when the variable valve characteristics mechanism is in a base state set in the internal combustion engine as a reference state when the opening and closing characteristics of the intake valve and the exhaust valve are changed, and a current intake manifold pressure that is determined based on the current state of the internal combustion engine, including the current state of the variable valve characteristics mechanism.

In the ignition timing control device for an internal combustion engine configured as described above, the internal combustion engine may further include a turbocharger and a wastegate valve, and the misfire limit ignition timing correction amount calculation unit may calculate the intake manifold pressure difference using the current intake manifold pressure determined based on the current state of the internal combustion engine, including the current state of the variable valve characteristics mechanism and the current state of the wastegate valve.

Furthermore, in the ignition timing control device for an internal combustion engine configured as described above, the misfire limit ignition timing correction amount calculation unit can calculate the misfire limit ignition timing correction amount by adding together a first ignition timing correction amount calculated using the change in the actual compression ratio and a second ignition timing correction amount calculated using the intake manifold pressure difference.

Furthermore, in the ignition timing control device for an internal combustion engine configured as described above, the misfire limit ignition timing correction amount calculation unit can be configured to calculate the misfire limit ignition timing correction amount by setting a correction sensitivity for the actual compression ratio change amount and the intake manifold pressure difference that is different from the correction sensitivity set for the actual compression ratio change amount and the intake manifold pressure difference when calculating the correction amount for the MBT ignition timing, which is the ignition timing at which engine torque is highest.

Furthermore, in the ignition timing control device for an internal combustion engine configured as described above, the misfire limit ignition timing correction amount calculation unit may calculate the first ignition timing correction amount based on the amount of change in the actual compression ratio corrected by a correction coefficient calculated based on the engine load and the rotational speed of the internal combustion engine, and may calculate the second ignition timing correction amount based on the intake manifold pressure difference corrected by a correction coefficient calculated based on the engine load and the rotational speed of the internal combustion engine.

The invention disclosed in this specification can appropriately correct the misfire limit ignition timing in an internal combustion engine equipped with a variable valve characteristic mechanism.

FIG. 1 is a schematic diagram showing the general configuration of an internal combustion engine equipped with an ignition timing control device according to an embodiment of the present invention. FIG. 2 is a block diagram showing a schematic configuration of an electronic control unit that functions as an ignition timing control device in the embodiment. Figure 3(A) is an example of a map for calculating a correction coefficient kdinvvt for the actual compression ratio change amount dinvvt used to calculate the first ignition timing correction amount for the misfire limit ignition timing at a certain engine speed, and Figure 3(B) is an example of a map for calculating a correction coefficient kdPm for the intake manifold pressure difference dPm used to correct the second ignition timing for the misfire limit ignition timing at a certain engine speed. FIG. 4 shows an example of a map for calculating the first ignition timing correction amount for the misfire limit ignition timing based on the actual compression ratio change amount in the ignition timing control device of the embodiment. FIG. 5 shows an example of a map for calculating the second ignition timing correction amount for the misfire limit ignition timing based on the intake pipe pressure difference in the ignition timing control device of the embodiment. FIG. 6 is a time chart showing an example of changes in ignition timing in an internal combustion engine equipped with the ignition timing control device of the embodiment.

Embodiments of the present invention will be described below with reference to the accompanying drawings. However, the dimensions, proportions, etc. of each part in the drawings may not be illustrated to be exactly the same as the actual ones. Also, some details may be omitted in some drawings.

(Embodiment)
[Configuration of an internal combustion engine]
First, a schematic configuration of an internal combustion engine 100 equipped with an ECU (Electronic Control Unit) 40 that functions as an ignition timing control device of the embodiment will be described with reference to Figure 1. The internal combustion engine 100 uses gasoline as fuel, but can use conventionally known gasoline substitute fuels such as ethanol and natural gas instead of gasoline.

The internal combustion engine 100 has multiple cylinders 2 within a cylinder block 1a (only one cylinder 2 is shown in Figure 1). A piston 3 is slidably housed within each cylinder 2, and a combustion chamber 2a is formed between the piston 3 and a cylinder head 1b located above the cylinder block 1a. The piston 3 is connected to a crankshaft 5 via a connecting rod 4. The combustion chamber 2a is equipped with an injector 6 that injects fuel into the cylinder and a spark plug 7. The fuel injected from the injector 6 is mixed with air in the combustion chamber 2a and ignited by the spark plug 7. The ignited mixture burns and explodes, pushing the piston 3 downward. The pushed-down piston 3 transmits the explosive force to the crankshaft 5 via the connecting rod 4, causing it to rotate. The injector 6 may also be installed in an intake pipe 10 near the combustion chamber 2a.

The internal combustion engine 100 has an intake port 8 and an exhaust port 9 facing the combustion chamber 2a. An intake pipe 10 forming an intake passage is connected to the intake port 8, and an exhaust pipe 11 forming an exhaust passage is connected to the exhaust port 9.

The intake pipe 10 is provided with, from upstream to downstream in the intake air flow, an air cleaner 12, an air flow meter 13, a compressor 14a of a turbocharger 14 (supercharger), an intercooler 15, a boost pressure sensor 16, a throttle valve 17, and an intake manifold 18. The throttle valve 17 is provided with a throttle opening sensor 17a. The air flow meter 13 detects the amount of air flowing through the intake pipe 10. The boost pressure sensor 16 detects the boost pressure of the air being sent into the combustion chamber 2a. The boost pressure detected by the boost pressure sensor 16 is used as the current boost pressure to calculate the misfire limit ignition timing correction amount. The calculation of the misfire limit ignition timing correction amount will be described in detail later. The throttle valve 17 adjusts the amount of air being sent into the combustion chamber 2a. The throttle opening sensor 17a detects the opening of the throttle valve 17.

The intake pipe 10 branches off at the intake manifold 18 and connects to the intake ports 8 of each cylinder.

The exhaust pipe 11 is provided with an exhaust manifold 20, the turbine 14b of the turbocharger 14, and a catalyst 21, arranged in this order from upstream to downstream in the exhaust flow. The turbine 14b is connected to the compressor 14a by a rotating shaft and is rotated by gas discharged from the combustion chamber 2a through the exhaust port 9. Rotation of the turbine 14b rotates the compressor 14a, supercharging the intake air. The catalyst 21 purifies the exhaust. The exhaust pipe 11 is provided with an exhaust bypass passage 60 that bypasses the turbine 14b. The exhaust bypass passage 60 is provided with a wastegate valve (hereinafter referred to as "WGV") 61 that opens and closes the exhaust bypass passage 60. The WGV 61 is driven to open and close by an actuator 62 connected to a vacuum pump 63 that generates negative pressure. The WGV 61 adjusts the supercharging pressure provided by the turbocharger 14. Specifically, when supercharging is required, the WGV 61 closes to close the exhaust bypass passage 60 and guide the exhaust gas to the turbine 14b. When the WGV 61 operates to the closing side, the back pressure in the internal combustion engine 100 increases.

The internal combustion engine 100 is equipped with an intake valve 23 that opens and closes the intake port 8, and an exhaust valve 24 that opens and closes the exhaust port 9. The intake valve 23 and the exhaust valve 24 open and close in accordance with the rotation of an intake camshaft and an exhaust camshaft (not shown) that are drivingly connected to the crankshaft 5. As a result, the intake valve 23 and the exhaust valve 24 are driven to open and close at predetermined timing in synchronization with the rotation of the crankshaft 5 and in response to the reciprocating movement of each piston 3. The internal combustion engine 100 is equipped with an intake VVT mechanism 25a, which is a variable valve mechanism that variably sets the valve timing, i.e., the opening and closing timing of the intake valve 23, and an exhaust VVT mechanism 25b, which is a variable valve mechanism that variably sets the valve timing, i.e., the opening and closing timing of the exhaust valve 24. The intake VVT mechanism 25a and the exhaust VVT mechanism 25b are included in the variable valve characteristics mechanism 25 (see Figure 2). When the intake VVT mechanism 25a changes the opening and closing timing of the intake valve 23, the actual compression ratio changes. The rotation speed of each camshaft is detected by a cam angle sensor 72.

The ECU 40 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a storage device. The ECU 40 controls the internal combustion engine 100 by executing programs stored in the ROM and the storage device. In this embodiment, the ECU 40 functions as a required engine load calculation unit 30 and a required valve characteristic calculation unit 31. The ECU 40 also functions as an engine load acquisition unit 41, an engine speed acquisition unit 42, a WGV control unit 43, and a base valve characteristic setting unit 44. The ECU 40 also functions as a current valve characteristic acquisition unit 45, a current intake manifold pressure acquisition unit 46, a base intake manifold pressure acquisition unit 48, a first difference calculation unit 49, a second difference value calculation unit 50, and an ignition timing correction amount calculation unit 51. The ignition timing correction amount calculation unit 51 includes a misfire limit ignition timing correction amount calculation unit 51a and an MBT (Minimum Spark Advance for Best Torque) ignition timing correction amount calculation unit 51b. The ignition timing correction amount calculation unit 51 includes a knock ignition timing correction amount calculation unit (not shown). MBT is the ignition timing at which engine torque is highest.

The required engine load calculation unit 30 calculates the load that is required to be output to the internal combustion engine 100 based on the detection value of the accelerator pedal opening sensor 71. The required valve characteristics calculation unit 31 calculates and sets the required valve characteristics, i.e., the opening and closing timing required for the intake valve 23 and the exhaust valve 24, based on the required engine load calculated by the required engine load calculation unit 30. The valve characteristics variable mechanism 25 is controlled so that the required valve characteristics calculated by the required valve characteristics calculation unit 31 are realized.

The engine load acquisition unit 41 acquires the engine load KL based on the intake air volume acquired by the air flow meter 13.

The engine speed acquisition unit 42 acquires the rotation speed of the crankshaft 5, i.e., the engine speed NE, based on the detection value of the crank angle sensor 70.

The WGV control unit 43 controls the actuator 62 that operates the WGV 61 based on the detection value of the accelerator pedal opening sensor 71 and the engine speed NE acquired by the engine speed acquisition unit 42.

The base valve characteristic setting unit 44 sets base valve characteristics for the open/closed states of the intake valve 23 and exhaust valve 24 based on the engine load KL acquired by the engine load acquisition unit 41 and the engine speed NE acquired by the engine speed acquisition unit 42.

The current valve characteristics acquisition unit 45 acquires information about the current opening and closing states of the intake valves 23 and exhaust valves 24, whose opening and closing timings are changed by the valve characteristics variable mechanism 25, based on the detection value of the cam angle sensor 72.

The current intake pipe pressure acquisition unit 46 acquires the current intake pipe pressure pmsm using an air model that uses the current boost pressure detected by the boost pressure sensor 16. In other words, the current intake pipe pressure acquisition unit 46 uses the current boost pressure detected by the boost pressure sensor 16 as an argument for acquiring the current intake pipe pressure pmsm. The air model also uses information regarding the current open/closed states of the intake valve 23 and exhaust valve 24 acquired by the current valve characteristic acquisition unit 45. The air model also uses the difference value between the base valve characteristic and the current valve characteristic calculated by the first difference value calculation unit 49, which will be described in detail later. Note that methods for acquiring intake pipe pressure using an air model are conventionally known, and since this embodiment also uses a conventionally used air model, detailed description thereof will be omitted here.

The base intake manifold pressure acquisition unit 48 acquires the base intake manifold pressure pmbs using an air model that uses the current boost pressure detected by the boost pressure sensor 16. The air model also uses information on the base valve characteristics for the open/closed states of the intake valve 23 and the exhaust valve 24, set by the base valve characteristics setting unit 44. The air model also uses the engine load KL acquired by the engine load acquisition unit 41 and the engine speed NE acquired by the engine speed acquisition unit 42. When acquiring the base intake manifold pressure pmbs, the same air model as when acquiring the current intake manifold pressure pmsm is used. Note that when acquiring the base intake manifold pressure pmbs, the base state boost pressure, which is the boost pressure in the internal combustion engine 100 when the valve characteristics variable mechanism 25 is in the base state, may be used instead of the current boost pressure. The base boost pressure can be acquired based on a map that uses the engine speed NE and the engine load KL as parameters, but a detailed description of this will be omitted here.

The first difference value calculation unit 49 obtains the actual compression ratio change amount dinvvt, which changes due to changes in the opening and closing timing of the intake valve 23 set by the intake VVT mechanism 25a. Specifically, the first difference value calculation unit 49 obtains the actual compression ratio change amount based on the opening and closing timing of the intake valve 23 for the base valve characteristics set by the base valve characteristics setting unit 44 and the opening and closing timing of the intake valve 23 for the current valve characteristics acquired by the current valve characteristics acquisition unit 45. For example, if the current opening and closing timing of the intake valve 23 is advanced compared to the opening and closing timing of the intake valve 23 in the base state, the actual compression ratio will be higher. A higher actual compression ratio makes misfire less likely. Therefore, in this embodiment, the actual compression ratio change amount dinvvt based on the opening and closing timing of the intake valve 23 is used to correct the misfire limit ignition timing.

The second difference value calculation unit 50 calculates the intake pipe pressure difference dPm, which is the difference between the current intake pipe pressure pmsm acquired by the current intake pipe pressure acquisition unit 46 and the base intake pipe pressure pmbs acquired by the base intake pipe pressure acquisition unit 48. The intake pipe pressure difference dPm is a value that correlates with the amount of change in residual gas in the cylinder. The amount of change in residual gas in the cylinder affects the misfire limit ignition timing. For example, if the valve overlap determined by the closing timing of the exhaust valve 24 and the opening timing of the intake valve 23 increases, or if the WGV 61 transitions to a closed state and back pressure increases, and the amount of residual gas increases, misfire resistance decreases and misfires become more likely. Therefore, in this embodiment, the intake pipe pressure difference dPm is used to correct the misfire limit ignition timing.

The misfire limit ignition timing correction amount calculation unit 51a included in the ignition timing correction amount calculation unit 51 calculates the correction amount for the misfire limit ignition timing. The correction amount for the misfire limit ignition timing is calculated based on the actual compression ratio change amount dinvvt obtained by the first difference value calculation unit 49 and the intake pipe pressure difference dPm obtained by the second difference value calculation unit 50.

The MBT ignition timing correction amount calculation unit 51b included in the ignition timing correction amount calculation unit 51 calculates the correction amount for the MBT ignition timing. The correction amount for the MBT ignition timing can also be calculated based on the actual compression ratio change amount dinvvt acquired by the first difference value calculation unit 49 and the intake manifold pressure difference dPm acquired by the second difference value calculation unit 50. However, when comparing the misfire limit ignition timing and the MBT ignition timing, the correction sensitivity to the actual compression ratio change amount dinvvt and the intake manifold pressure difference dPm is different. Therefore, the correction amount for the misfire limit ignition timing and the MBT ignition timing are different values. Similarly, a correction is also made for the knock ignition timing, but because the correction sensitivity to the actual compression ratio change amount dinvvt and the intake manifold pressure difference dPm for the knock ignition timing is different from that for the misfire limit ignition timing, the correction amounts for these are also different values.

The ECU 40 functions as an ignition timing control device through the cooperation of these components. The WGV control unit 43 does not directly function as part of the ignition timing control device, but controls the open/close state of the WGV 61 as part of engine control. When the open/close state of the WGV 61 changes, the boost pressure and back pressure change, and ultimately the misfire resistance changes. The ignition control device of this embodiment uses the intake manifold pressure difference dPm to reflect the influence of the open/close state of the WGV 61 in the misfire limit ignition timing correction amount. In this way, the ignition timing control device of this embodiment is preferably applied to an internal combustion engine 100 equipped with a turbocharger 14 and a WGV 61, but can also be applied to an internal combustion engine 100 that does not have a turbocharger 14 and a WGV 61. The internal combustion engine 100 of this embodiment is equipped with a catalyst 21, but if it is equipped with a GPF (Gasoline Particulate Filter), for example, the back pressure may change, and the ignition timing control device of this embodiment can therefore be effective. Furthermore, for example, in an internal combustion engine 100 connected to a muffler incorporating a variable valve, the ignition timing control device of this embodiment can be suitably used, since the back pressure changes depending on the opening and closing of the variable valve.

[Determination of Misfire Limit Ignition Timing Correction Amount]
Next, the process of determining the misfire limit ignition timing correction amount performed by the ignition timing control device of this embodiment will be described. The ECU 40 corrects the misfire limit ignition timing using the misfire limit ignition timing correction amount calculated by the misfire limit ignition timing correction amount calculation unit 51a. The ECU 40 performs the process of determining the misfire limit ignition timing correction amount at a predetermined interval so that the operating state of the internal combustion engine 100 is reflected in the misfire limit ignition timing correction. The misfire limit ignition timing correction amount is expressed by the following equation (1):
Misfire limit ignition timing correction amount = First ignition timing correction amount + Second ignition timing correction amount (Equation 1)
The first ignition timing correction amount is a correction amount calculated based on the actual compression ratio change amount dinvvt, and the second ignition timing correction amount is a correction amount calculated based on the intake pipe pressure difference dPm.

The ECU 40 corrects the basic misfire limit ignition timing using the misfire limit ignition timing correction amount. Here, the basic misfire limit ignition timing is the ignition timing that can be retarded the most without causing misfire when the internal combustion engine 100 is in its base state. Therefore, if the ignition timing is retarded beyond the basic misfire limit ignition timing when the internal combustion engine 100 is in its base state, misfire will occur. The basic misfire limit ignition timing is preset according to the model of the internal combustion engine 100.

<Calculation of actual compression ratio change amount dinvvt>
The actual compression ratio change amount dinvvt is calculated by the first difference value calculation unit 49 as described above. The first difference value calculation unit 49 has information about the opening and closing timings of the intake valve 23 set by the base valve characteristic setting unit 44 and information about the actual compression ratio related to this information. The first difference value calculation unit 49 also acquires information about the current opening and closing timings of the intake valve 23 acquired by the current valve characteristic acquisition unit 45, and acquires information about the current actual compression ratio based on this information. The first difference value calculation unit 49 is provided with a map (not shown) prepared in advance for obtaining information about the actual compression ratio from the information about the opening and closing timings of the intake valve 23, and acquires information about the actual compression ratio based on this map. The actual compression ratio change amount dinvvt is thus acquired as the difference between the current actual compression ratio and the actual compression ratio in the base state.

<Calculation of difference value dPm>
As described above, the difference value dPm is obtained by the second difference value calculation unit 50. The second difference value calculation unit 50 calculates the difference value dPm by subtracting the base intake pipe pressure pmbs from the current intake pipe pressure pmsm.

As described above, the current intake pipe pressure pmsm is acquired by the current intake pipe pressure acquisition unit 46. The current boost pressure used when the current intake pipe pressure pmsm is acquired by the air model is the detected value of the boost pressure sensor 16.

As described above, the base intake pipe pressure pmbs is acquired by the base intake pipe pressure acquisition unit 48. In this embodiment, when the base intake pipe pressure pmbs is acquired using the air model, the detection value of the supercharging pressure sensor 16 is used, just as when the current intake pipe pressure pmsm is acquired.

<Calculation of correction coefficient kdPm and correction coefficient kdinvvt>
The correction coefficients kdPm and kdinvvt are calculated in an ignition timing correction amount calculation section 51 .

The correction coefficient kdinvvt is obtained using the map shown in Figure 3(A). Figure 3(A) is an example of a map for obtaining the correction coefficient kdinvvt. However, Figure 3(A) shows only a portion of the map. In other words, the map shown in Figure 3(A) obtains the correction coefficient kdinvvt according to the engine load KL at a certain engine speed NE. Therefore, if the engine speed NE is different, another portion of the map is referenced. By using the correction coefficient kdinvvt, which uses the engine speed NE and the engine load KL as parameters, it is possible to calculate a misfire limit ignition timing correction amount that more accurately reflects the operating state of the internal combustion engine 100.

The correction coefficient kdPm is obtained using the map shown in Figure 3(B). Figure 3(B) is an example of a map for obtaining the correction coefficient kdPm. However, Figure 3(B) shows only a portion of the map. In other words, the map shown in Figure 3(B) obtains the correction coefficient kdPm according to the engine load KL at a certain engine speed NE. Therefore, if the engine speed NE is different, another portion of the map is referenced. By using the correction coefficient kdPm, which uses the engine speed NE and the engine load KL as parameters, it is possible to calculate a misfire limit ignition timing correction amount that more accurately reflects the operating state of the internal combustion engine 100.

<Calculation of First Ignition Timing Correction Amount>
The misfire limit ignition timing correction amount calculation unit 51a calculates the first ignition timing correction amount based on the map shown in FIG. 4. FIG. 4 is an example of a map for calculating the first ignition timing correction amount, with the horizontal axis representing the actual compression ratio change amount dinvvt and the vertical axis representing the first ignition timing correction amount. The actual compression ratio change amount dinvvt shown on the horizontal axis is corrected by the correction coefficient kdinvvt obtained from the map shown in FIG. 3A. Note that FIG. 4 shows only a portion of the map. That is, the map shown in FIG. 4 is designed to obtain the second ignition timing correction amount at a certain engine speed NE. Therefore, if the engine speed NE is different, another portion of the map is referenced. Therefore, although the map shown in FIG. 4 shows the first ignition timing correction amount as a correction amount toward the retard side, this does not necessarily mean that the first ignition timing correction amount is corrected toward the retard side. In some cases, the first ignition timing correction amount may be corrected toward the advance side. The map is created through actual engine testing or simulation.

Figure 4 shows the cases when the valve overlap is large and small. As such, the value of the first ignition timing correction amount varies depending on the valve overlap.

For comparison, Figure 4 also shows the correction amount for the MBT ignition timing. The actual compression ratio change amount dinvvt is used to calculate the first ignition timing correction amount for calculating the misfire limit ignition timing correction amount. The actual compression ratio change amount dinvvt is also used when calculating the correction amount for the MBT ignition timing, but the correction sensitivity of the actual compression ratio change amount dinvvt to the MBT ignition timing is different from the correction sensitivity to the misfire limit ignition timing. Therefore, the correction amount based on the actual compression ratio change amount dinvvt for the MBT ignition timing is different from the correction amount based on the actual compression ratio change amount dinvvt for the misfire limit ignition timing.

Note that in the map shown in Figure 4, the correction amount for the misfire limit ignition timing is more advanced than the correction amount for the MBT ignition timing, but this map is an example and does not necessarily result in such a magnitude relationship.

<Calculation of Second Ignition Timing Correction Amount>
The misfire limit ignition timing correction amount calculation unit 51a calculates the second ignition timing correction amount based on the map shown in FIG. 5. FIG. 5 is an example of a map for calculating the second ignition timing correction amount, with the horizontal axis representing the intake manifold pressure difference dPm and the vertical axis representing the second ignition timing correction amount. The intake manifold pressure difference dPm shown on the horizontal axis is corrected by the correction coefficient kdPm obtained from the map shown in FIG. 3B. Note that FIG. 5 shows only a portion of the map. That is, the map shown in FIG. 5 is used to obtain the second ignition timing correction amount at a certain engine speed NE. Therefore, if the engine speed NE is different, another portion of the map is referenced. Therefore, although the map shown in FIG. 5 shows the second ignition timing correction amount as a correction amount toward the advance side, it is not necessarily corrected toward the advance side. In some cases, the second ignition timing correction amount may be corrected toward the retard side. The map is created through actual engine testing or simulation.

Figure 5 shows the cases when the valve overlap is large and small. As such, the value of the second ignition timing correction amount varies depending on the valve overlap.

For comparison, Figure 5 also shows the correction amount for the MBT ignition timing. The intake manifold pressure difference dPm is used to calculate the second ignition timing correction amount for calculating the misfire limit ignition timing correction amount. The intake manifold pressure difference dPm is also used when calculating the correction amount for the MBT ignition timing, but the correction sensitivity of the intake manifold pressure difference dPm for the MBT ignition timing is different from the correction sensitivity for the misfire limit ignition timing. Therefore, the correction amount based on the intake manifold pressure difference dPm for the MBT ignition timing is different from the correction amount based on the intake manifold pressure difference dPm for the misfire limit ignition timing.

Note that in the map shown in Figure 5, the correction amount for the misfire limit ignition timing is more advanced than the correction amount for the MBT ignition timing, but this map is an example and does not necessarily result in such a magnitude relationship.

<Combined processing>
The ECU 40 sums the first ignition timing correction amount and the second ignition timing correction amount calculated by the misfire limit ignition timing correction amount calculation unit 51a. Then, the ECU 40 corrects the basic misfire limit ignition timing by the summed correction amount. In this way, the misfire limit ignition timing is set in accordance with the in-cylinder environment caused by the back pressure.

[Ignition timing control]
Next, an example of ignition timing control will be described with reference to the time chart shown in FIG.

Referring to Figure 6, the controlled ignition timing combines three ignition timings: knock ignition timing, MBT ignition timing, and misfire limit ignition timing, to obtain the required torque while improving drivability.

From time T1 to time T4, the accelerator opening increases, and the load factor increases accordingly. Engine torque also increases from time T1 to time T5, during which time the engine is in the acceleration zone. At this time, the ECU 40 retards the ignition timing from time T1 to improve drivability. However, the misfire limit ignition timing is reached at time T2. Therefore, the controlled ignition period from time T2 to time T3 is set to the misfire limit ignition timing. The misfire limit ignition timing at this time is set to the corrected misfire limit ignition timing.

At time T6, the accelerator is fully closed, and fuel cut (CT) is executed at time T7. The engine is in a deceleration period from time T6 to time T7, and the ECU 40 retards the ignition timing from time T6 to improve drivability. As a result, the controlled ignition timing briefly reaches the misfire limit ignition timing at time T7, but is not retarded beyond this. The misfire limit ignition timing at this time is also set to the corrected misfire limit ignition timing. Thereafter, the controlled ignition timing returns to the MBT ignition timing.

For a while from time T5 when the accelerator opening is in a steady state, the controlled ignition timing is set to the knock ignition timing. This is because maintaining the MBT ignition timing could cause knock, so the knock ignition timing is set to the controlled ignition timing in order to avoid knock. Note that the occurrence of knock can be expressed, for example, by an equation represented by the Livengood-Wu integral as shown in the following equation (2), and is considered to be a different concept from the MBT ignition timing.
...(Formula 2)
The time ti indicates the time when knock occurs, A, n, and B are constants that depend on the fuel, p is pressure, and T is temperature.

Such knock ignition timing is also corrected based on the intake manifold pressure difference dPm and the actual compression ratio change amount dinvvt, but the correction sensitivity for knock ignition timing is different from the correction sensitivity for misfire limit ignition timing, and the correction amounts are different values.

The ignition timing control device of this embodiment can appropriately correct the misfire limit ignition timing in an internal combustion engine equipped with a variable valve characteristics mechanism.

The above embodiments are merely examples for implementing the present invention, and the present invention is not limited to these. Various modifications of these embodiments are within the scope of the present invention, and it is clear from the above description that various other embodiments are possible within the scope of the present invention.

14 Turbocharger 16 Supercharging pressure sensor 23 Intake valve 24 Exhaust valve 25 Valve characteristic variable mechanism 25a Intake VVT mechanism 25b Exhaust VVT mechanism 40 ECU
44 Base valve characteristic setting unit 45 Current valve characteristic acquisition unit 46 Current intake pipe pressure acquisition unit 48 Base intake pipe pressure acquisition unit 49 First difference value calculation unit 50 Second difference value calculation unit 51 Ignition timing correction amount calculation unit 51a Misfire limit ignition timing correction amount calculation unit 61 Wastegate valve (WGV) 100 Internal combustion engine

Claims (4)

1. An ignition timing control device that is applied to an internal combustion engine having a variable valve characteristic mechanism that changes the opening and closing characteristics of at least an intake valve out of an intake valve and an exhaust valve, and that sets a misfire limit ignition timing that is a limit ignition timing on the retard side at which no misfire occurs in the internal combustion engine,
a misfire limit ignition timing correction amount calculation unit that calculates a correction amount of a misfire limit ignition timing relative to a basic misfire limit ignition timing that is preset as the misfire limit ignition timing in the internal combustion engine, using an amount of change in an actual compression ratio that changes with a change in the opening/closing characteristic of the intake valve, and an intake pipe pressure difference that is a difference value between a base intake pipe pressure in the internal combustion engine when the valve characteristics variable mechanism is in a base state that is set in the internal combustion engine as a reference state when the opening/closing characteristics of the intake valve and the exhaust valve are changed, and a current intake pipe pressure that is determined depending on the current state of the internal combustion engine including the current state of the valve characteristics variable mechanism.
Ignition timing control device for internal combustion engines. The internal combustion engine further includes a supercharger and a wastegate valve.
the misfire limit ignition timing correction amount calculation unit calculates the intake pipe pressure difference using the current intake pipe pressure determined according to a current state of the internal combustion engine including a current state of the valve characteristics variable mechanism and a current state of the wastegate valve.
2. The ignition timing control device for an internal combustion engine according to claim 1. the misfire limit ignition timing correction amount calculation unit calculates the correction amount of the misfire limit ignition timing by adding together a first ignition timing correction amount calculated using the change in the actual compression ratio and a second ignition timing correction amount calculated using the intake manifold pressure difference.
2. The ignition timing control device for an internal combustion engine according to claim 1. the misfire limit ignition timing correction amount calculation unit calculates the first ignition timing correction amount based on an amount of change in the actual compression ratio corrected by a correction coefficient calculated based on an engine load and a rotation speed of the internal combustion engine, and calculates the second ignition timing correction amount based on the intake manifold pressure difference corrected by a correction coefficient calculated based on the engine load and the rotation speed of the internal combustion engine.
4. An ignition timing control device for an internal combustion engine according to claim 3 .