JP2011174476A - Combustion controller of spark-ignition multicylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion controller of a spark-ignition multicylinder engine, capable of correcting the variation in the torque generated among cylinders with a high degree of precision. <P>SOLUTION: Ignition timing MBT at which the torque generated in each cylinder is maximized is determined. Further, a mean value of the torque generated in each cylinder at the ignition at the ignition timing MBT or the ignition timing subjected to the correction of delaying the ignition timing MBT is determined as target torque. Then, ignition timing, a fuel injection volume and a cylinder intake air volume are corrected so that the torque generated in each cylinder becomes the target torque. When the torque generated in each cylinder comes to conform with the target torque, a target idling revolution speed is lowered. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a combustion control device that controls a generated torque for each cylinder in a spark ignition type multi-cylinder engine.

  Patent Document 1 discloses a fuel injection control that equalizes the explosive force between cylinders and smoothly reduces the engine speed by adjusting the time of asynchronous injection for each cylinder at the time of restarting fuel injection from a deceleration fuel cut. An apparatus is disclosed.

JP 2002-332894 A

By the way, in a spark ignition type multi-cylinder engine, there may be a deviation in ignition position for each cylinder due to component variations, deterioration, deformation, etc., and depending on the adjustment of the fuel injection amount for each cylinder, the generated torque of each cylinder may be reduced. In some cases, it could not be made uniform.
For example, if a part of the detected portion in the crankshaft position sensor that detects the angular position of the crankshaft is missing or deformed, a crank angle detection error occurs and the ignition timing is erroneously detected.

If an attempt is made to eliminate the difference in generated torque due to such ignition timing deviation by adjusting the fuel injection amount, the air-fuel ratio adjusted to the target air-fuel ratio is forcibly shifted, so that there is a demand for exhaust properties and combustion stability. Therefore, there are cases where the adjustment range of the fuel injection amount is limited and the difference in generated torque cannot be sufficiently reduced.
If there is a difference in the generated torque between the cylinders, generally, the lower the engine speed, the greater the fluctuations in the rotation, giving the driver a sense of incongruity, and the fluctuations in rotation are so great that the idle speed cannot be reduced. There arises a problem that the fuel efficiency is deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a combustion control device for a spark ignition type multi-cylinder engine capable of correcting a variation in generated torque between cylinders with high accuracy.

  Therefore, in the spark ignition multi-cylinder engine combustion control apparatus according to the present invention, the ignition timing for generating the maximum torque is obtained for each cylinder, and the reference ignition timing for each cylinder is determined based on the ignition timing for generating the maximum torque. Is set to each, and control is performed to reduce the difference in torque generated between the cylinders during operation at the reference ignition timing.

According to the above invention, by controlling to the ignition timing (MBT) that generates the maximum torque for each cylinder, the deviation of the actual ignition timing between the cylinders is corrected, and the deviation of the actual ignition timing is corrected, A torque difference between the cylinders caused by variations in the cylinder intake air amount and the fuel injection amount among the cylinders is reduced.
Therefore, correction of the difference in generated torque between the cylinders due to the difference in ignition timing is avoided or suppressed by correcting the cylinder intake air amount and the fuel injection amount of each cylinder, so that the cylinder does not lose combustion stability. Torque difference can be reduced.

The system diagram of the engine in the embodiment of the present invention. The figure which shows arrangement | positioning of the fuel injection valve and throttle valve in the engine of FIG. The flowchart which shows 1st Embodiment of adjustment control of the generated torque for every cylinder which concerns on this invention. The flowchart which shows the fall control of the target idle rotational speed in the said 1st Embodiment. The time chart which shows the timing which discriminate | determines rotation fluctuation | variation in the said 1st Embodiment. The flowchart which shows 2nd Embodiment of adjustment control of the generated torque for every cylinder which concerns on this invention. The diagram which shows the correlation with the engine load and engine rotation speed in the said 2nd Embodiment, and the retardation correction value of MBT. The diagram which shows the correlation with the engine temperature (water temperature) and retardation correction value in the said 2nd Embodiment. The flowchart which shows 3rd Embodiment of adjustment control of the generated torque for every cylinder which concerns on this invention. The flowchart which shows 4th Embodiment of adjustment control of the generated torque for every cylinder which concerns on this invention. The flowchart which shows 5th Embodiment of adjustment control of the generated torque for every cylinder which concerns on this invention.

Embodiments of the present invention will be described below.
FIG.1 and FIG.2 is a system block diagram of the vehicle engine in embodiment.
In the drawing, an engine 101 is a four-cylinder spark ignition engine, and a fuel injection valve 103 is provided in a branch portion 102A of an intake manifold 102 for each cylinder.
The engine 101 is not limited to four cylinders, and the fuel injection valve 103 may be an in-cylinder direct injection engine in which fuel is directly injected into the combustion chamber of each cylinder.

In addition, an electronically controlled throttle valve 104 for controlling the cylinder intake air amount of each cylinder independently is interposed on the upstream side of the fuel injection valve 103 in the branch portion of the intake manifold 102.
Each throttle valve 104 is combined with an actuator (not shown) such as a motor, and the throttle valve 104 of each cylinder can be driven to a different opening degree by controlling each actuator independently. It has become.

The fuel injected from the fuel injection valve 103 and the air measured by the throttle valve 104 are sucked into the combustion chamber 106 through the intake valve 105, and the fuel is sparked by the spark plug 107 in the combustion chamber 106. Ignition combustion by ignition.
The combustion chamber 106 is formed by a cylinder 108, a cylinder head 109, and a piston 110.

The exhaust gas is discharged through an exhaust valve 111, an exhaust manifold 112, and an exhaust duct 113, and harmful components (CO2, HC, NOx) in the exhaust gas are harmless to the exhaust duct 113 by a catalytic reaction (CO2). , H2O, NO2) is provided.
Each ignition plug 107 is directly attached with an ignition coil 115 containing a power transistor. By controlling on / off of the power transistor, the timing of starting energization and the timing of interrupting energization of the ignition coil 115 are controlled. The ignition timing of each cylinder can be controlled independently.

The electronic control unit (ECU) 201 controls the opening degree of the throttle valve 104, the fuel injection amount by the fuel injection valve 103, and the ignition timing by the spark plug 107 (the start / break timing of energization of the ignition coil 115).
The ECU 201 includes a microcomputer, sets control targets such as the throttle opening, fuel injection amount, ignition timing, and the like by performing arithmetic processing on signals from various sensors and switches in accordance with a program stored in advance. An operation signal based on the target is output to the throttle valve 104, the fuel injection valve 103, and the ignition coil 115 of each cylinder.

  As the various sensors, an accelerator opening sensor 202 for detecting the depression amount (accelerator opening) ACC of the accelerator pedal 121, an intake duct 122 connected to the upstream side of the intake manifold 102, and an intake of the engine 101 are provided. Based on the air flow sensor 203 for measuring the air flow rate QA, the water temperature sensor 204 for detecting the temperature TW of the cooling water in the cooling jacket of the engine 101, and the oxygen concentration in the exhaust in the exhaust duct 113 upstream of the catalytic converter 114. The air-fuel ratio sensor 205 for detecting the air-fuel ratio AF, the crankshaft position sensor 206 for outputting the unit angle signal POS every time the crankshaft 123 rotates by a unit angle, and the cylinder discrimination signal PHASE in synchronization with the rotation of the intake camshaft 124. Output camshaft position sensor It is provided, such as 207.

The ECU 201 calculates the rotational speed NE of the engine 101 based on a signal from the crankshaft position sensor 206 or the camshaft position sensor 207, and the intake air flow rate QA detected by the engine rotational speed NE and the airflow sensor 203. From this, the basic fuel injection amount (basic injection pulse width) TP is calculated.
Further, the basic fuel injection amount TP is set to an increase correction coefficient KTW corresponding to the coolant temperature TW, an air-fuel ratio feedback correction coefficient α for bringing the actual air-fuel ratio detected by the air-fuel ratio sensor 205 close to the target air-fuel ratio, etc. The final fuel injection amount (injection pulse width) TI is calculated and the injection pulse signal having a pulse width corresponding to the final fuel injection amount TI is synchronized with the intake stroke of each cylinder. Output to each fuel injection valve 103.

Further, the ECU 201 calculates an ignition advance value (ignition timing) ADV based on the basic fuel injection amount TP indicating the engine load and the engine rotational speed NE, and each ignition advance value (ignition timing) ADV is calculated according to the ignition advance value (ignition timing) ADV. Energization of the ignition coil 115 is controlled so that ignition is performed in the cylinder.
The ignition advance value (ignition timing) ADV represents the ignition timing as an advance angle from the compression top dead center.

Further, the ECU 201 calculates a target throttle opening based on the accelerator opening ACC detected by the accelerator opening sensor 202 so that the actual opening of the throttle valve 104 becomes the target throttle opening. The actuator (motor) that drives the throttle valve 104 is controlled.
Further, the ECU 201 has a function of adjusting the generated torque for each cylinder in order to reduce the difference in generated torque between the cylinders.

The flowchart of FIG. 3 shows the flow of adjustment control of the generated torque for each cylinder.
In step S1001, the ignition timing is forcibly corrected in the direction of increasing the generated torque for each cylinder, and in step S1002, the generated torque when ignition is performed at the corrected ignition timing is detected for each cylinder.
The generated torque for each cylinder can be detected based on the angular velocity of the engine 101 (crankshaft 123).

Specifically, the average angular velocity (time required for rotation from the compression top dead center to the expansion bottom dead center) of each cylinder is detected, or the torque detection angle set based on the ignition timing An angular velocity in a region (for example, a crank angle range of about 10 deg including the ignition timing) is calculated.
Instead of calculating the angular velocity of the engine 101, the angular acceleration is calculated, for example, the output of a torque sensor that detects torque from the deflection of the crankshaft is sampled in time with the explosion stroke of each cylinder, or combustion By providing a pressure (in-cylinder pressure) sensor in each cylinder and sampling the combustion pressure (in-cylinder pressure) in the explosion stroke in each cylinder, the generated torque of each cylinder can be detected.

In the next step S1003, it is determined whether or not the maximum value of the generated torque (angular velocity) in each cylinder has been detected, and the forced advance / retard change of the ignition timing is repeated until the maximum torque is detected, An ignition timing MBT (MBT: minimum advance for the best torque) at which the generated torque is maximized is obtained for each cylinder.
Specifically, the ignition timing is changed from the standard ignition timing determined based on the engine load TP and the engine rotational speed NE to the advance angle or the retard angle direction, and the change direction of the ignition timing at which the generated torque increases is changed. The ignition timing is gradually changed in the direction in which the generated torque (angular velocity) increases, and the ignition timing immediately before the generated torque (angular velocity) starts to decrease is the ignition at which the generated torque (angular velocity) becomes maximum in each cylinder. It is time MBT.

The calculation function of steps S1001 to S1003 corresponds to the ignition timing detection means.
When obtaining the ignition timing MBT at which the generated torque is maximum in each cylinder, the ignition timing as a base point is set to an ignition timing that is expected to be retarded from the MBT, and gradually advanced from the ignition timing. To obtain the MBT.

With such a configuration, it is possible to avoid the occurrence of knocking due to excessive advance of the ignition timing.
When the ignition timing MBT at which the generated torque is maximum is obtained for each cylinder as described above, in the next step S1004, the ignition timing MBT is set to the ignition advance value (reference ignition timing) ADV in each cylinder. Then, ignition control is performed with the ignition timing MBT as a target (reference ignition timing setting means).

If there is no difference in the fuel injection amount and the cylinder intake air amount in each cylinder, the ignition timing at which the maximum torque is obtained should be substantially the same in each cylinder. However, the actual ignition with respect to the ignition timing ADV as a control target If the timing is shifted between the cylinders, the ignition timing ADV for obtaining MBT also varies among the cylinders according to the shift.
In other words, the MBT obtained by detecting the generated torque of each cylinder can be regarded as a result of correcting the actual ignition timing deviation between the cylinders, and is generated between the cylinders due to the actual ignition timing deviation. If there is a difference in torque, the difference in generated torque between the cylinders due to the ignition timing deviation is eliminated by setting MBT as the control target of the ignition timing.

  Note that the actual ignition timing shift between the cylinders may be caused when, for example, the crank angle position cannot be correctly detected due to deformation or chipping in the detected portion of the crankshaft position sensor 206, or the camshaft position sensor. This occurs when a reference phase position for ignition timing measurement is detected at 207, such as when a rotational phase difference between the crankshaft and the camshaft occurs due to bending of the timing belt or the like.

In the next step S1005, the average value of the torque (maximum angular velocity) generated when each cylinder is ignited at the ignition timing MBT (reference ignition timing) (sum of generated torque of each cylinder / number of cylinders) Set to a common target torque (target angular velocity).
Instead of setting the average value of the generated torque for each cylinder as the target torque, the generated torque of a predetermined cylinder is set as the target torque, or the minimum, maximum, and median values of the generated torque for each cylinder are set. The target torque can be set as the target torque, or the average value excluding the maximum and minimum values can be set as the target torque.

Here, when there is no difference in the fuel injection amount / cylinder intake air amount (actual amount) between the cylinders, the generated torques for each cylinder when the MBT is ignited are substantially the same, and the generated torques for each cylinder. If there is a variation in the fuel consumption, it can be estimated that there is a difference in the fuel injection amount / cylinder intake air amount (actual amount) between the cylinders.
The difference between the fuel injection amount and the cylinder intake air amount (actual amount) between the cylinders is caused by the deterioration of the fuel injection valve 103 over time, the deposits and deformations of the intake manifold 102, the throttle valve 104, and the intake valve 105, and the like. This also occurs due to the design air distribution characteristics of the intake manifold 102.

In step S1006, control is performed to bring the generated torque of each cylinder closer to the target torque, and the difference in generated torque due to the difference between the fuel injection amount and the cylinder intake air amount (actual amount) between the cylinders is suppressed. The generated torque substantially coincides with the target torque, and the generated torque of all the cylinders is made substantially uniform (torque difference control means).
Specifically, when the generated torque (angular velocity) of a cylinder is larger than the target torque (target angular velocity), the fuel injection amount reduction correction, the intake air amount (throttle opening) reduction correction, ignition in the cylinder concerned At least one of the timing retardation corrections is executed to reduce the generated torque (angular velocity) in the cylinder so as to approach the target torque.

On the other hand, when the generated torque (angular velocity) of a cylinder is smaller than the target torque (target angular velocity), the fuel injection amount increase correction, the intake air amount (throttle opening) increase correction, and the ignition timing advance in the cylinder concerned. At least one of the angle corrections is executed to increase the torque (angular velocity) generated in the cylinder so as to approach the target torque.
When correcting the fuel injection amount, intake air amount (throttle opening), and ignition timing, the fuel injection amount, intake air amount, and ignition timing correction amount for each cylinder are gradually changed based on a preset step width. The correction amount change is stopped when the actual generated torque substantially matches the target torque (when the absolute value of the deviation between the actual generated torque and the target torque becomes less than the allowable value). .

  The correction of the cylinder intake air amount for each cylinder can be realized by correcting the target opening degree of the throttle valve 104 for each cylinder, as well as the open characteristics of the intake valve 105 (the central phase of the valve operating angle, the valve lift amount, the valve operation). When a variable valve mechanism that can vary the angle) for each cylinder is provided, the cylinder intake air amount of each cylinder can be increased or decreased individually by correcting the opening characteristics of the intake valve 105 for each cylinder. is there.

Further, when an exhaust gas recirculation device capable of adjusting the exhaust gas recirculation amount for each cylinder is provided, the amount of fresh air in each cylinder can be changed and the generated torque can be increased or decreased by adjusting the exhaust gas recirculation amount for each cylinder. .
Further, in the correction of the fuel injection amount / cylinder intake air amount, the fuel injection amount / cylinder is changed so that the air-fuel ratio changes within a range between the allowable maximum value (lean limit) and the allowable minimum value (rich limit). It is preferable to limit the correction range of the intake air amount, and the allowable maximum value (lean limit) and allowable minimum value (rich limit) are determined in advance through experiments and simulations based on requirements such as combustion stability, exhaust properties, and exhaust temperature. Adapted based on.

If the generated torque (angular velocity) does not change even after correcting the ignition timing, fuel injection amount, and cylinder intake air amount, the correction in the cylinder is stopped, and the generated torque (angular velocity) is changed according to the correction. The correction of changing cylinders can be continued, or the correction control for bringing the generated torque close to the target torque can be stopped for all the cylinders.
In addition, when a cylinder is generated that does not change the generated torque (angular velocity) according to the correction of ignition timing, fuel injection amount, and cylinder intake air amount, the generated torque in the cylinder is set as the target torque, and The generated torque of other cylinders in which the generated torque (angular velocity) changes can be made closer to the target torque.

In addition, when multiple cylinders are generated that do not change the generated torque (angular velocity) according to the correction, the average value of the generated torque in these cylinders is set as the target torque, or a target torque that can ensure the overall torque balance is set. Can be.
For example, if the generated torque does not change is 3 out of 4 cylinders, the generated torque of 2 of the 3 cylinders is high and the generated torque of the remaining 1 cylinder is low, the order of ignition is also affected. In some cases, by adjusting the target of the cylinder whose generated torque changes according to the correction to the low generated torque, the entire torque balance can be secured and the rotational fluctuation can be suppressed to a small value.

If the generated torque in a cylinder whose generated torque does not change according to the correction is extremely low, setting the target torque according to the cylinder with the low generated torque is prohibited, and the generated torque in other cylinders is prohibited. The target torque can be set based on
Before proceeding to step S1006, the ignition timing of each cylinder is controlled to MBT, and the deviation of the actual ignition timing between the cylinders is corrected, and the difference in the generated torque between the cylinders is reduced accordingly. The correction allowance required for the processing in step S1006 can be reduced, and the difference in generated torque between the cylinders can be sufficiently reduced by correcting the fuel injection amount, the intake air amount, and the ignition timing within a range that does not deteriorate the drivability. .

When the generated torque of each cylinder coincides with the vicinity of the target torque by the processing of step S1006, the process proceeds to step S1007, and a setting for decreasing the target idle rotation speed in the engine 101 is performed (idle rotation reduction means).
The reduction in the target idle rotation speed may be a process of switching the target idle rotation speed to a value lower than a standard value by a certain value (for example, 100 rpm). The speed is decreased by a minute value (for example, 25 to 50 rpm) from the standard value, and the target idle rotation speed immediately before the rotation fluctuation (change amount per unit time) of the engine 101 exceeds the allowable value is finally determined. Can be set to a specific goal.

The idle rotation speed control based on the target idle rotation speed is performed by feedback control of the intake air amount of the engine 101 so that the actual idle rotation speed approaches the target idle rotation speed.
Here, if the idling rotational speed is reduced in a state where the difference in generated torque between the cylinders is large, the rotational fluctuation will increase and give the driver a sense of incongruity. Is sufficiently small, stable rotation can be obtained even if the idling speed is reduced, and the driver does not feel uncomfortable, and by reducing the idling speed, the fuel efficiency can be improved. I can plan.

The flowchart in FIG. 4 shows in detail the process of gradually decreasing the target idle speed as the process in step S1007, and the engine 101 is in an idling state (when the execution condition of the idle speed control is satisfied). Executed.
First, in step S8001, the target idle rotation speed NETG is reduced by a preset step width A (for example, 25 to 50 rpm) from the previous value.

The initial value of the target idle rotational speed NETG is set to a high rotational speed that does not cause rotational fluctuations that give the driver a sense of incongruity even if the generated torque varies between cylinders to some extent. In the state where the difference in generated torque between the cylinders is suppressed, there is a margin that can be further reduced within a range in which a large rotational fluctuation is not generated.
Further, the step width A can be changed to a smaller value every time the target idle speed NETG is decreased.

In the next step S8002, the process waits for a time T (see FIG. 5) in which the actual engine speed is predicted to converge to the target idle speed NETG reduced by the step width A.
Since the convergence time becomes longer as the step width A is larger, the waiting time T is set to a longer time as the step width A is larger.

In step S8003, it is determined whether or not the fluctuation (the absolute value of the amount of change per unit time) of engine speed NE is greater than allowable value B.
The allowable value B is set based on the minimum value of the rotational fluctuation amount that gives the driver a sense of incongruity, and is adapted in advance so as not to give the driver a sense of incongruity if the rotational fluctuation is less than the allowable value B. Yes.

  If the fluctuation of the engine rotational speed NE is less than or equal to the allowable value B and the engine rotational speed NE is stable, the process returns to step S8001 to further decrease the target idle rotational speed NETG by the step width A, While it is determined that the fluctuation of the rotational speed NE is equal to or less than the allowable value B, the process of reducing the target idle rotational speed NETG by the step width A is repeated.

  When it is determined that the fluctuation of the engine speed NE exceeds the allowable value B, the process proceeds to step S8004, where the previous value of the target idle speed NETG that has been decreased by the step width A, that is, the engine speed. The lowest rotation speed among the target idle rotation speeds NETG determined that the fluctuation of the speed NE is equal to or less than the allowable value B is set as the final target idle rotation speed NETG.

Note that the difference in the generated torque between the cylinders causes a large rotation fluctuation in a low rotation range, so the processing shown in the flowchart of FIG. It can be performed only when it is in a state.
Further, in the case where the process of reducing the difference in generated torque between the cylinders is performed even when the engine is not idling, in order to suppress the influence on the vehicle due to the torque fluctuation, It is preferable to perform processing (correction control of fuel injection amount, intake air amount, ignition timing) to reduce the difference in generated torque between the two.

Also, the fuel injection amount, the intake air amount, and the correction amount of the ignition timing when the generated torque of each cylinder coincides with the target torque are stored, and the fuel injection amount and the intake air amount corrected with the correction amount up to the previous time are stored. The stored correction amount can be updated when a difference occurs in the generated torque during operation at the ignition timing.
Further, during one trip from the start to the stop of the engine 101, the process of reducing the difference in generated torque between the cylinders is performed only once, and after the difference in generated torque between the cylinders is once reduced, The fuel injection amount, the intake air amount, and the correction amount of the ignition timing at that time can be continuously used as they are.

In addition, the control to reduce the target idle speed by aligning the torque generated between cylinders can ensure the stability of idle operation by canceling the execution when an increase in the idle speed accompanying an air conditioner load is requested. This is preferable.
Further, it is possible to learn the correction amount of the ignition timing, the fuel injection amount, and the cylinder intake air amount for aligning the generated torque of each cylinder for each target idle rotation speed, and to reflect the learning result in the subsequent idle operation. it can.

  Further, when an external load such as an air conditioner changes, if the generated torque does not change even if the ignition timing, fuel injection amount, and cylinder intake air amount are changed, the fuel injection valve 103, the ignition plug 107, the ignition coil 115, the throttle valve When parts related to control of generated torque such as 104 are out of order, or when ignition timing is corrected by other control such as correction of ignition timing for catalyst temperature rise, the generated torque of each cylinder is made uniform. It is preferable not to perform control.

The flowchart of FIG. 6 shows a second embodiment of the adjustment control of the generated torque for each cylinder.
In the first embodiment, the ignition timing of each cylinder is controlled to MBT, and the difference in torque generated between the cylinders in the MBT is reduced. However, in the second embodiment, the ignition timing that is retarded from the MBT is corrected. This is characterized in that the difference in torque generated between the cylinders is reduced.
In the flowchart of FIG. 6, each step other than step S2004 performs the same processing as each step other than step S1004 of the flowchart of FIG.

When the ignition timing of each cylinder is adjusted to MBT in steps S2001 to S2003, in step S2004, the ignition timing (reference) that is retarded from MBT, obtained by subtracting the retardation correction value from MBT for each cylinder. Ignition is performed at (ignition timing) (reference ignition timing setting means).
The retard correction value may be a fixed value, or can be variably set according to engine operating conditions such as engine load, engine speed, and engine temperature (cooling water temperature).

  Specifically, as shown in FIG. 7, the operating region of the engine 101 is divided into a low rotation / low load region, a medium rotation / medium load region, a high rotation / high load region based on the engine speed and the engine load. Dividing into three areas, the retard angle correction value is set to be the largest to ensure the rotational stability of the engine 101 in the low rotation and low load areas, and the occurrence of knocking is avoided in the high rotation and high load areas. The retard angle correction value is set to a large value next to the low rotation / low load region, and further, the engine rotation is relatively stable in the medium rotation / medium load region, and knocking is unlikely to occur. From the above, the retard correction value is set to the smallest value, and the ignition timing closest to MBT is set.

Further, with respect to the condition of the engine temperature (cooling water temperature TW), as shown in FIG. 8, the retard correction value is set to a larger value as the engine temperature (water temperature) is lower.
This is because if the exhaust gas temperature is raised by delaying the ignition timing when the engine is cold, the catalytic converter 114 can be activated (heated up) early, and the engine temperature (cooling water temperature) is low. In other words, when the temperature of the catalytic converter 114 is low.

  Note that the variable setting of the retardation correction value according to the engine operating conditions can be performed based on one or more of engine load, engine speed, and engine temperature (cooling water temperature). As described above, the engine temperature (cooling water temperature) correlates with the elapsed time after the engine is started, so that the retardation correction value can be set according to the elapsed time after the engine is started.

In step S2005, the generated torque in each cylinder when the MBT is burned at the ignition timing (reference ignition timing) corrected for retarding is obtained, and the average value of the generated torque in each cylinder is obtained as the target torque (target angular velocity). ).
In step S2006 and step S2007, in order to bring the generated torque of each cylinder close to the target torque, the ignition timing, fuel injection amount, and cylinder intake air amount of each cylinder are individually corrected and set, and the generated torque of each cylinder is set to the target torque. After substantially aligning with the above, processing for reducing the target idle rotation speed is performed.

As described above, since the target torque is set from the torque generated in each cylinder when combustion is performed at the ignition timing with the MBT retarded, the ignition timing advance direction for aligning the generated torque of each cylinder with the target torque It is possible to secure a correction fee.
Therefore, it is possible to substantially match the generated torque for each cylinder while avoiding the deterioration of engine rotation stability and knocking, and to substantially match the generated torque for each cylinder while activating the catalyst early. It becomes possible to make it.

The flowchart of FIG. 9 shows a third embodiment of the adjustment control of the generated torque for each cylinder.
In the third embodiment, the amount of change in torque generated for each combustion in the same cylinder in the steady operation state where the ignition timing of each cylinder is set to MBT, or the cylinder in the state where the ignition timing of each cylinder is set to MBT It is characterized in that normality / abnormality of the engine 101 is determined based on whether or not the difference in generated torque exceeds an allowable value.

In the flowchart of FIG. 9, in steps S3001 to S3004, the ignition timing of each cylinder is adjusted to MBT in the same manner as in steps S1001 to S1004 of the flowchart of FIG.
In step S3005, it is determined whether or not the absolute value of the change amount of the torque generated for each combustion in the same cylinder in the steady operation state with the ignition timing MBT exceeds the allowable change amount.

If even one cylinder has a cylinder in which the change in generated torque for each combustion exceeds an allowable level, the process advances to step S3007 to determine whether the engine 101 is abnormal.
If the absolute value of the change amount of the generated torque for each combustion in the same cylinder is less than the allowable value and the generated torque in each cylinder is stable, the process proceeds to step S3006 and the generated torque between the cylinders. It is determined whether or not the absolute value of the difference exceeds the allowable deviation.

The difference in generated torque among the cylinders can be obtained as an absolute value of the difference between the highest generated torque and the lowest generated torque in each cylinder, and the difference in generated torque of each cylinder with respect to the average value of generated torque. Can be obtained as an absolute value of.
If it is determined in step S3006 that the absolute value of the generated torque difference between the cylinders exceeds the allowable deviation, the process proceeds to step S3007 to determine whether the engine 101 is abnormal.

If it is determined in step S3007 that the engine 101 is abnormal, for example, a display device / warning device (such as a warning lamp or buzzer) provided near the driver's seat of the vehicle may cause the engine abnormality to occur to the driver. Warning.
The permissible change amount and permissible deviation are values set corresponding to the permissible limit of torque fluctuation (rotational fluctuation) felt by the driver, and are set in advance based on experiments, simulations, and the like.

On the other hand, if it is determined in step S3006 that the absolute value of the generated torque difference between the cylinders is equal to or smaller than the allowable deviation, the process proceeds to step S3008, and normality of the engine 101 is determined.
When the ignition timing is set to MBT and the generated torque of the same cylinder fluctuates greatly or the difference in generated torque between the cylinders is large, each cylinder of the fuel injection amount and the cylinder intake air amount Alternatively, since it is estimated that the variation among the cylinders exceeds the allowable level, the abnormality of the engine 101 is determined, and the continuous operation in the abnormal state is avoided.

On the other hand, if it is determined in step S3008 that the engine 101 is normal, the generated torque in the same cylinder is stable and the difference in generated torque between the cylinders is small. It is assumed that the generated torque in each cylinder can be made substantially equal by correcting the amount and the cylinder intake air amount.
Therefore, if it is determined in step S3008 that the engine 101 is normal, the process proceeds to steps S3009 to S3011, where the average torque generated in MBT is set as the target torque, and the generated torque of each cylinder is set as the target torque. In order to make it closer, the ignition timing, the fuel injection amount, and the cylinder intake air amount of each cylinder are corrected and set, and after the generated torque in each cylinder converges near the target torque, the target idle rotation speed is reduced.

  If it is determined in step S3007 that the engine 101 is abnormal, the generated torque of the same cylinder largely fluctuates, or the generated torque difference between the cylinders is large. In order to be unable to stably converge to the vicinity of the torque or to approach the target torque, it is necessary to largely correct the ignition timing, the fuel injection amount, and the cylinder intake air amount.

Therefore, when it is determined in step S3007 that the engine 101 is abnormal, control for causing the generated torque of each cylinder to approach the target and control for reducing the target idle rotation speed are not performed, and excessive correction or repeated correction that does not converge is performed. Therefore, the operability of the engine is not deteriorated.
Note that, as in the second embodiment, MBT is retarded to set a reference ignition timing, and abnormality of the engine 101 is diagnosed from variations in torque generated at the retarded reference ignition timing. Can do.

In addition, when the control is performed to bring the generated torque of each cylinder close to the target torque, it is not possible to make it sufficiently close to the target torque, or when the difference in the generated torque between the cylinders does not become sufficiently small, A fourth embodiment having such a configuration will be described with reference to the flowchart of FIG.
In the flowchart of FIG. 10, in steps S4001 to S4006, similarly to steps S1001 to S1006 in the flowchart of FIG. 3, the ignition timing of each cylinder is controlled to MBT, and the target torque is calculated from the generated torque of each cylinder in MBT. The ignition timing, the fuel injection amount, and the cylinder intake air amount are corrected and set for each cylinder so as to set the generated torque of each cylinder to the target torque.

In step S4007, as a result of performing correction control to align the generated torque of each cylinder with the target torque, the generated torque of each cylinder approaches the target torque, and the absolute value of the difference in generated torque between the cylinders is less than the allowable difference. It is determined whether or not.
Note that the verification of the correction result of the generated torque in the step S4007 is performed by, for example, converging the correction control when the difference between the current value and the previous value of the deviation between the target torque and the actual generated torque hardly changes. At the time when the determination is made and the convergence control is determined for the correction control of all the cylinders, it is determined whether or not the generated torque of each cylinder is within a predetermined range including the target torque.

If the generated torque of each cylinder is within a predetermined range including the target torque and the generated torque of each cylinder is in the vicinity of the target torque, the process proceeds to step S4008, where it is determined that the engine 101 is normal, In the next step S4009, processing for reducing the target idle rotation speed is executed.
On the other hand, when there is at least one cylinder in which the generated torque cannot be sufficiently close to the target torque and the absolute value of the difference in generated torque between the cylinders exceeds the allowable difference, for example, the fuel injection valve 103 It is presumed that the variable range of the generated torque is limited in some cylinders due to clogging of the intake valve, dirt on the intake valve 105, etc., and the process proceeds to step S4010 to determine whether the engine 101 is abnormal.

If it is determined that the engine 101 is abnormal, the difference in torque generated between the cylinders is not sufficiently small. Therefore, the process proceeds to bypass the process of reducing the target idle speed in step S4009, and the target idle speed is increased. Let it remain.
Therefore, it is possible to prevent the target idle rotation speed from being lowered in a state where the generated torque difference between the cylinders is large, and to prevent the occurrence of large rotation fluctuations.

In step S4004 of the fourth embodiment, the ignition timing obtained by correcting the MBT delay can be set as in the second embodiment.
The flowchart of FIG. 11 shows a fifth embodiment of the adjustment control of the generated torque for each cylinder.
In the fifth embodiment, when the generated torque of each cylinder is adjusted to one target torque and then the target idle rotation speed is lowered, the MBT is controlled again in the idle operation state at the reduced target idle rotation speed. Then, the process of aligning the generated torque of each cylinder with the target torque set from the generated torque at MBT (or ignition timing with MBT retarded) is performed.

  In the flowchart of FIG. 11, in steps S5001 to S5007, similarly to steps S1001 to S1007 in the flowchart of FIG. 3, the ignition timing of each cylinder is individually adjusted to MBT, and MBT (or MBT is retarded) The target torque is set from the generated torque at the timing (time), correction is performed to align the generated torque of each cylinder with the target torque, and processing for reducing the target idle rotation speed after correction is performed.

  Then, when the process of reducing the target idle rotation speed is performed in step S5007, in step S5008, the ignition timing of each cylinder is adjusted to MBT in the idle operation state at the reduced target idle rotation speed, and MBT (or MBT The target torque is set from the generated torque at the ignition timing with the retardation corrected), and the correction for aligning the generated torque of each cylinder with the target torque is performed again.

As described above, the target idle rotation speed is reduced based on the arrangement of the generated torques of the respective cylinders, and the generated torque between the cylinders is made uniform again in the idle operation state at the reduced rotation speed. If it correct | amends to, it can prevent more reliably that the rotation fluctuation | variation exceeding an allowable level generate | occur | produces in idle driving | running | working with the reduced engine speed.
In the second correction control after decreasing the target idle rotation speed, it is preferable to limit the advance / retard angle change range of the ignition timing when adjusting to MBT to be narrower than the first.

In addition, it is possible to repeat the adjustment of the generated torque between the cylinders and the change of the target idle rotation speed. In this case, the decrease width of the target idle rotation speed can be changed more narrowly as the number of repetitions increases. preferable.
In each of the above embodiments, the generated torque of each cylinder is made constant. However, in a V-type or horizontally opposed engine having a plurality of banks, the bank is adjusted to MBT, and the difference in generated torque of each bank at that time is adjusted. The ignition timing, the fuel injection amount, and the intake air amount can be corrected on a bank basis so as to reduce the value.

  Furthermore, the characteristic processes shown in the first to fifth embodiments can be appropriately combined.

  DESCRIPTION OF SYMBOLS 101 ... Engine, 103 ... Fuel injection valve, 104 ... Throttle valve, 107 ... Spark plug, 115 ... Ignition coil, 201 ... Electronic control unit (ECU), 203 ... Air flow sensor, 204 ... Water temperature sensor, 206 ... Crankshaft position sensor 207: Camshaft position sensor

Claims (6)

Ignition timing detection means for determining the ignition timing for generating the maximum torque for each cylinder;
Reference ignition timing setting means for setting a reference ignition timing for each cylinder based on the ignition timing for generating the maximum torque;
Torque difference control means for performing control to reduce the difference in torque generated between the cylinders in operation at the reference ignition timing;
A combustion control device for a spark ignition type multi-cylinder engine, comprising:   The combustion control device for a spark ignition type multi-cylinder engine according to claim 1, wherein the reference ignition timing setting means sets the ignition timing at which the maximum torque is generated as the reference ignition timing.   2. The reference ignition timing of each cylinder according to claim 1, wherein the reference ignition timing setting means sets the reference ignition timing of each cylinder by retarding the ignition timing of each cylinder generating the maximum torque with a retard correction value. A combustion control device for a spark ignition type multi-cylinder engine.   4. The spark ignition type multi-purpose engine according to claim 3, wherein the reference ignition timing setting means variably sets the retardation correction value based on at least one of engine load, engine speed, and engine temperature. Cylinder engine combustion control device.   The torque difference control means sets a target torque common to each cylinder based on the generated torque for each cylinder when ignition is performed based on the reference ignition timing, and the generated torque in each cylinder is set to the target torque. 5. The spark ignition type multi-cylinder according to claim 1, wherein at least one of an ignition timing, a fuel injection amount, and a cylinder intake air amount is corrected for each cylinder so as to approach the torque. Engine combustion control device.   6. An idle rotation reducing means for reducing a target idle rotation speed of the engine after the torque difference control means performs a control for reducing a difference in generated torque between cylinders. The combustion control device for a spark ignition type multi-cylinder engine according to any one of the above.

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