JP3959957B2 - Engine internal EGR amount estimation method, variable valve control method using the internal EGR amount estimation value, cylinder intake air amount calculation method, and ignition timing control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention estimates the internal EGR amount in an engine that can arbitrarily variably control the opening / closing timing of the intake / exhaust valves, and also uses the estimated internal EGR amount to control the variable valve and control the cylinder intake air amount. The present invention relates to a technique for performing calculation and ignition timing control.
[0002]
[Prior art]
In a conventional general engine, the intake air amount is controlled by the opening degree of the throttle valve. Recently, however, an electromagnetically driven intake / exhaust valve is provided, and the intake air amount is controlled mainly by controlling the closing timing of the intake valve. Have been proposed (see JP 10-37727 A).
[0003]
In this type of intake air amount control, when the throttle valve is not provided, the intake valve is closed with respect to the intake pressure that is maintained at a substantially atmospheric pressure, and when the throttle valve is also used, the intake pressure according to the throttle valve opening. By controlling the volume of the cylinder intake air according to the effective intake stroke determined by the timing, it is possible to control to obtain the target air amount (required intake air amount) according to the required torque.
[0004]
[Problems to be solved by the invention]
By the way, when the intake air amount is controlled mainly by the closing timing of the intake valve as described above, a piston in which a new air amount corresponding to the target air amount is included in the cylinder in addition to the residual gas amount (internal EGR amount) in the combustion chamber. It is necessary to control the intake valve to close at the position.
[0005]
In the case of the variable valve, the amount of internal EGR varies greatly depending on whether or not the intake / exhaust valves overlap and the amount of overlap. In particular, in the case of a variable valve with high opening / closing responsiveness such as an electromagnetic drive type, since the exhaust valve and the intake valve overlap in a substantially fully open state during the overlap period, the change in the internal EGR amount is large.
Therefore, if the intake valve closing timing corresponding to the target air amount is fixedly corrected for the internal EGR amount or simply corrected in consideration of only a predetermined operating state, good intake air amount control and therefore It turns out that engine torque control cannot be performed. Even if the target closing timing of the exhaust valve, the target opening timing of the intake valve, etc. are set according to the operating state and the target closing timing of the intake valve is corrected accordingly, Since the internal EGR amount greatly varies depending on factors other than the valve timing, good control cannot be performed.
[0006]
From the above, in order to control with good responsiveness using a variable valve, it is required to accurately grasp the amount of internal EGR that changes greatly in a transient manner.
In addition, the cylinder intake air amount is feedback-controlled with high accuracy, and furthermore, highly accurate air-fuel ratio control is performed. For other purposes, the cylinder intake air amount is estimated with high accuracy, and the ignition timing is set to be efficient. It is required to accurately grasp the amount of internal EGR in order to perform control so as to be optimal.
[0007]
The present invention has been made paying attention to such a conventional problem. In an engine that variably controls the opening and closing timings of intake and exhaust valves, the internal EGR amount is estimated with high responsiveness and high accuracy. The purpose is to enable good control.
[0008]
[Means for Solving the Problems]
  For this reason, the invention of the internal EGR amount estimation method for an engine according to claim 1 is
  In an engine equipped with a variable valve device that can variably control the closing timing of the exhaust valve,
  Based on the closing timing of the exhaust valve, the basic value of the internal EGR amount is calculated, and when the opening period of the exhaust valve and the opening period of the intake valve do not overlap, the basic value is estimated as the internal EGR amount as it is, When overlapping, correct the basic value according to the overlap state and estimate the internal EGR amountIt is characterized by.
[0009]
  According to the invention of claim 1,
  When the basic value of the internal EGR amount with no intake / exhaust valve overlap is calculated based on the closing timing of the exhaust valve, if there is an overlap, there is an increase in the internal EGR amount due to blowback, etc. Therefore, the internal EGR amount is estimated by correcting the basic value according to the overlap state.
  In this way, the internal EGR amount can be estimated with high accuracy by correcting the basic value of the internal EGR amount in a state where there is no overlap between the intake and exhaust valves in accordance with the overlap state.
[0010]
  The invention according to claim 2
  As the closing timing of the exhaust valve used for estimating the internal EGR amount,Target closing timing of exhaust valveIt is characterized by using.
  According to the invention which concerns on Claim 2, it can simplify by using the target value of control compared with the case where the closing timing of an exhaust valve is detected with a sensor.
[0011]
  The invention according to claim 3
  The basic value of the internal EGR amount is calculated based on the engine speed in addition to the closing timing of the exhaust valve.Characterized by
[0013]
In this way, the basic value of the internal EGR amount in the state where there is no overlap between the intake and exhaust valves is largely determined by the closing timing of the exhaust valve, but is slightly changed depending on the engine speed. By taking the engine rotation speed into account, the amount of internal EGR can be estimated with high accuracy by calculating the accuracy with high accuracy and correcting the basic value according to the overlap state.
[0014]
The invention according to claim 4
When the opening period of the exhaust valve and the opening period of the intake valve overlap, the estimated value of the internal EGR amount is calculated by adding the overlap correction amount set according to the overlap state to the basic value. Features.
According to the invention of claim 4,
The basic value is calculated as the internal EGR amount when there is no overlap between the intake and exhaust valves, and the overlap correction amount is set according to the overlap state. The amount of internal EGR can be estimated.
[0015]
The invention according to claim 5
When the opening period of the exhaust valve and the opening period of the intake valve overlap, the basic value is increased as the interval between the exhaust top dead center and the closing timing of the exhaust valve increases.
According to the invention of claim 5,
The basic value of the internal EGR amount is the amount of burned gas remaining in the cylinder without the overlap of the intake and exhaust valves, and the burned gas amount is determined by the cylinder volume determined by the piston position at the closing timing of the exhaust valve. Becomes the minimum at the exhaust top dead center, and increases as the distance from the exhaust top dead center increases and the cylinder volume increases.
[0016]
Therefore, the basic value can be appropriately set by setting the basic value according to the above characteristics.
The invention according to claim 6
When the opening period of the exhaust valve and the opening period of the intake valve overlap, when the closing timing of the exhaust valve is before the exhaust top dead center, the basic value is increased as the engine speed increases. Features.
[0017]
According to the invention of claim 6,
Even at the same piston position, if the closing timing of the exhaust valve is before exhaust top dead center, the exhaust valve closes with the residual gas slightly compressed, and the higher the engine speed, the higher the degree of compression increases due to inertia. The gas amount (internal EGR amount) increases.
Therefore, when the exhaust valve closing timing is before exhaust top dead center according to the above trend, the basic value is set to an appropriate value by increasing the basic value as the engine speed increases. be able to.
[0018]
The invention according to claim 7
When the opening period of the exhaust valve and the opening period of the intake valve overlap, when the exhaust valve closing time is after exhaust top dead center, the basic value decreases as the engine speed increases. And
Even at the same piston position, when the exhaust valve closes after exhaust top dead center, the exhaust valve closes with the exhaust once exhausted into the exhaust passage being pulled back into the cylinder. The quantity, that is, the internal EGR quantity decreases. The tendency is further strengthened as the engine speed Ne increases, and the inertia increases.
[0019]
Therefore, when the exhaust valve closing timing is after exhaust top dead center according to the above trend, the basic value is set to an appropriate value by decreasing the basic value as the engine speed increases. Can do.
The invention according to claim 8 is
The estimated value of the internal EGR amount is increased by increasing the overlap correction amount as the overlap amount between the exhaust valve open period and the intake valve open period increases.
[0020]
According to the invention of claim 8,
Basically, as the overlap amount of the intake / exhaust valve increases, the return amount into the exhaust cylinder increases during the overlap and the internal EGR amount increases. Therefore, the overlap correction amount increases in accordance with this tendency. By doing so, the estimated value of the amount of internal EGR can be increased appropriately.
[0021]
The invention according to claim 9 is
When the exhaust valve closing timing is after exhaust top dead center, the overlap correction amount is decreased as the retardation amount from the exhaust top dead center at the closing timing increases, thereby estimating the internal EGR amount. It is characterized by decreasing the value.
According to the invention of claim 9,
During the overlap when the exhaust valve closing timing is after exhaust top dead center, the piston is descending, so the suction negative pressure in the cylinder develops as the closing timing moves away from exhaust top dead center, and the intake port The difference in pressure with respect to the intake negative pressure becomes smaller, making it difficult for the exhaust to be blown back to the intake port, and the difference in the return amount of the exhaust into the cylinder when compared with the non-overlap time is also reduced. That is, the amount of increase in the internal EGR amount due to the overlap decreases as the exhaust valve closing timing moves away from the exhaust top dead center.
[0022]
Therefore, the estimated value of the internal EGR amount can be calculated to an appropriate value by decreasing the overlap correction amount as the retardation amount from the exhaust top dead center at the exhaust valve closing timing increases.
The invention according to claim 10 provides
The estimated value of the internal EGR amount is increased by increasing the overlap correction amount as the absolute value of the intake negative pressure increases.
[0023]
According to the invention of claim 10,
As the absolute value of the intake negative pressure increases, the differential pressure from the exhaust pressure increases, so the amount of exhaust that is returned into the cylinder during the overlap or sucked into the cylinder after returning to the intake port increases. To do.
Therefore, the estimated value of the internal EGR amount can be appropriately increased by increasing the overlap correction amount as the absolute value of the intake negative pressure increases.
[0024]
The invention according to claim 11 is
The overlap correction amount is calculated by correcting the basic correction value determined by the overlap amount using the intake pressure correction amount determined based on the intake pressure and the closing timing of the exhaust valve. And
According to the invention of claim 11,
The basic correction value determined based on the characteristics of the internal EGR amount according to the overlap amount described above is used as the intake pressure correction amount determined based on the characteristics according to the intake pressure described above and the closing timing of the exhaust valve. By using and correcting, the overlap correction amount can be calculated to an appropriate value.
[0025]
The invention according to claim 12
The overlap amount is characterized by using a value obtained by time-converting a crank angle period corresponding to the overlap amount.
According to the invention of claim 12,
The change in the internal EGR amount due to the overlap of the intake / exhaust valves occurs during the overlapped time. Therefore, by using the time converted value of the crank angle period corresponding to the overlap amount, the overlap The basic correction value can be calculated as an appropriate value.
[0026]
  The invention according to claim 13 is
  The basic correction value is constant with respect to the basic correction value set according to the overlap amount, when the closing timing of the exhaust valve is before the exhaust top dead center, without correction by the closing timing of the exhaust valve. When the exhaust valve closing timing is after exhaust top dead center, a reduction correction amount proportional to the retardation amount of the closing timing from the exhaust top dead center is set according to the overlap amount. Subtracted from the basic correction valueIt is characterized by.
[0027]
According to the invention of claim 13,
As described above, the internal EGR amount increases as the overlap amount increases, and when the exhaust valve closes before exhaust top dead center, the blowback to the intake port during the overlap is dominant. Therefore, the amount of increase in the internal EGR amount is substantially constant regardless of the exhaust valve closing timing. On the other hand, when the exhaust valve closing timing is after the exhaust top dead center, the retard amount from the exhaust top dead center increases. As a result, the increase in the internal EGR amount during the overlap decreases.
[0028]
  Therefore, it was set according to the increase in overlap amount.Basic correction valueIs set as the basic correction value when the exhaust valve closing timing is before the exhaust top dead center, and when the exhaust valve closing timing is after the exhaust top dead center,ofA reduction correction amount proportional to the retardation amount from the exhaust top dead center isA value obtained by subtracting correction from the basic correction value set according to the increase in the overlap amount is newly set as the basic correction value.Thus, the basic correction value can be calculated to an appropriate value.
[0029]
The invention according to claim 14 is
An intake pressure correction coefficient is determined as an intake pressure correction amount corresponding to the intake pressure and the exhaust valve closing timing, and the overlap correction amount is calculated by multiplying the basic correction value by the intake pressure correction coefficient. .
According to the invention of claim 14,
By determining the intake pressure correction coefficient based on the change in the internal EGR amount during the overlap according to the intake pressure and the exhaust valve closing timing as described above, the basic correction value is multiplied by the intake pressure correction coefficient. The lap correction amount can be easily calculated to an appropriate value.
[0030]
The invention according to claim 15 is
When the absolute value of the intake negative pressure increases, the intake pressure correction amount is increased.When the exhaust valve closing timing is after exhaust top dead center and the absolute value of the intake negative pressure is higher than a predetermined value, The intake pressure correction amount is increased in accordance with a retard amount from the exhaust top dead center at the closing timing.
[0031]
According to the invention of claim 15,
As described above, the internal EGR amount during the overlap increases as the absolute value of the intake negative pressure increases, so that the intake pressure correction amount increases. On the other hand, the overlap occurs as the exhaust valve closing timing increases from the exhaust top dead center. The difference in the pressure inside the cylinder due to the presence or absence of exhaust tends to decrease, so the increase in the return amount of exhaust tends to decrease. Since the difference is increased and the increased amount is maintained large, the intake pressure correction amount is increased compared to when the absolute value of the intake negative pressure is small.
[0032]
Thereby, since the intake pressure correction amount is set with high accuracy according to the intake pressure, the overlap correction amount can be calculated to an appropriate value.
An invention of a control method for a variable valve according to claim 16 includes:
In an engine provided with a variable valve gear that can variably control the opening and closing timings of an intake valve and an exhaust valve, the internal EGR amount is estimated using the internal EGR amount estimation method according to any one of claims 1 to 15. Estimating the amount, calculating a target air amount based on the operating state of the engine, calculating a target closing timing of the intake valve based on the estimated value of the internal EGR amount and the calculated value of the target air amount, The closing timing of the intake valve is controlled so as to be the calculated target closing timing.
[0033]
According to the invention of claim 16,
Based on the internal EGR amount estimated with high accuracy as described above and the target air amount calculated for each engine operating state, the target closing timing of the intake valve is calculated so that the target closing timing is reached. The closing timing of the intake valve is controlled.
In this way, the intake valve closing timing is corrected while accurately and accurately estimating the internal EGR amount, which varies greatly depending on whether the intake / exhaust valve overlaps or changes in the overlap amount according to the engine operating conditions. Since the control is performed, a fresh air amount corresponding to the target intake air amount can be obtained, and highly accurate torque control can be performed.
[0034]
An invention of a cylinder intake air amount calculation method for an engine according to claim 17
The internal EGR amount is estimated using the internal EGR amount estimation method according to any one of claims 1 to 15, and the amount of air taken into the cylinder using the estimated value of the internal EGR amount Is calculated.
According to the invention of claim 17,
By using the internal EGR amount estimated with high accuracy as described above, the cylinder intake air amount that is the amount obtained by subtracting the internal EGR amount from the total gas amount sucked into the cylinder can be calculated with high accuracy. it can.
[0035]
The invention according to claim 18 provides
Based on the estimated value of the internal EGR amount and the cylinder volume calculated from the intake valve closing timing, the volume air amount in the cylinder is calculated, the mass air amount in the intake manifold is calculated, and the volume in the cylinder is calculated. The mass air amount sucked into the cylinder is calculated based on the air amount, the mass air amount in the intake manifold, and the intake manifold volume.
[0036]
According to the invention of claim 18,
The cylinder volume, that is, the total gas volume sucked into the cylinder is calculated from the closing timing of the intake valve, and the volume air volume sucked into the cylinder is subtracted from the estimated value of the internal EGR amount (volume) from the total gas volume. Is calculated.
Assuming that the pressure and temperature in the intake manifold are equal to the pressure and temperature in the cylinder at the end of the intake stroke, the air density in the intake manifold and the cylinder Therefore, the mass air amount sucked into the cylinder can be calculated using this relationship.
[0037]
The invention according to claim 19 is
The mass air amount in the intake manifold is calculated by performing a balance calculation of the inflow amount and outflow amount of the mass air in the intake manifold.
According to the invention of claim 19,
Calculate the balance between the mass air inflow into the intake manifold detected by an air flow meter and the mass air outflow from the intake manifold, which is sequentially calculated as the mass air inhaled into the cylinder. Thus, the mass air amount in the intake manifold can be calculated successively with high accuracy.
[0038]
An invention of an engine ignition timing control method according to claim 20 comprises:
The internal EGR amount is estimated using the internal EGR amount estimation method according to any one of claims 1 to 15, and the ignition timing is controlled using the estimated value of the internal EGR amount. Features.
According to the invention of claim 20,
By using the internal EGR amount estimated with high accuracy as described above, the combustion state can be grasped with high accuracy and the ignition timing can be appropriately controlled.
[0039]
The invention according to claim 21 is
Based on the estimated value of the internal EGR amount, a residual gas rate that is a mass ratio of the residual gas amount to the total gas amount in the cylinder is calculated, a combustion speed is calculated based on the residual gas rate, and based on the combustion rate Then, the combustion reaction time from the start of ignition to the peak of the combustion pressure is calculated, the MBT (maximum torque generation ignition timing) is calculated based on the combustion reaction time, and the ignition timing is controlled to be the MBT. It is characterized by that.
[0040]
According to the invention of claim 21,
The combustion speed can be estimated with high accuracy by the residual gas rate calculated based on the internal EGR amount, and therefore, the MBT can be accurately calculated even during a transient state, and optimal ignition timing control can be performed, which in turn can improve fuel efficiency.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 1 is a system diagram of a variable valve engine showing an embodiment of the present invention.
The combustion chamber 3 defined by the piston 2 of each cylinder of the engine 1 is provided with an electromagnetically driven intake valve 5 and an exhaust valve 6 so as to surround the spark plug 4. 7 is an intake passage and 8 is an exhaust passage.
[0042]
FIG. 2 shows the basic structure of an electromagnetic drive device (variable valve operating device) for the intake valve 5 and the exhaust valve 6. A plate-like movable element 22 is attached to the valve shaft 21 of the valve body 20, and the movable element 22 is biased to a neutral position by springs 23 and 24. A valve opening electromagnetic coil 25 is disposed below the movable element 22, and a valve closing electromagnetic coil 26 is disposed above the movable element 22.
[0043]
Then, before starting the engine 1, the valve opening electromagnetic coil 25 and the valve closing electromagnetic coil 26 are alternately energized to resonate the movable element 22, and when the amplitude becomes sufficiently large, the electromagnetic coil moves to any one of the electromagnetic coils. The child 22 is held by suction.
Thereafter, when the valve is opened from the closed state, the energization of the upper valve closing electromagnetic coil 26 adsorbing the mover 22 is stopped, and then the mover 22 is moved downward by the urging force of the spring 23. The valve element 20 is lifted and opened by energizing the valve-opening electromagnetic coil 25 and adsorbing the mover 22 from a position sufficiently close to the lower valve-opening electromagnetic coil 25.
[0044]
On the contrary, when closing the valve from opening, after the energization to the lower valve opening electromagnetic coil 25 adsorbing the mover 22 is stopped, the mover 22 is moved upward by the urging force of the spring 24. Then, the valve closing electromagnetic coil 26 is energized from a position sufficiently close to the upper valve closing electromagnetic coil 26 to attract the mover 22, thereby causing the valve body 20 to be seated on the seat portion and closed. .
[0045]
In this embodiment, an electromagnetically driven type is used as the variable valve operating device, but a hydraulically driven type can also be used.
Returning to FIG. 1, the intake passage 7 is provided with an air flow meter 9 for detecting the intake air amount and a throttle valve 10 for electronically controlling the opening upstream of the manifold portion. An electromagnetic fuel injection valve 11 is provided.
[0046]
Here, the operation of the intake valve 5, the exhaust valve 6, the throttle valve 10, the fuel injection valve 11 and the spark plug 4 is controlled by a control unit 12, which receives a crank angle signal in synchronism with engine rotation. Are output from the crank angle sensor 13 that can detect the engine speed and the accelerator pedal sensor 14 that detects the accelerator opening (the amount of depression of the accelerator pedal).
[0047]
The intake air amount is controlled mainly by controlling the closing timing of the intake valve 5 so that the target torque is obtained based on the engine operating conditions such as the accelerator opening and the engine speed. Further, in order to reduce exhaust emissions, particularly NOx emissions, the closing timing of the exhaust valve 6 and the opening timing of the intake valve 5 (and the exhaust valve 6 are further controlled so as to be controlled to an appropriate internal EGR amount according to the operating conditions. However, since the internal EGR amount varies depending on factors other than these valve timings, the internal EGR amount is estimated for each operating state, and the estimated internal EGR amount is set to the estimated internal EGR amount. Accordingly, the closing timing of the intake valve 5 is corrected and controlled.
[0048]
An intake air amount is detected based on the values detected by the various sensors, and the fuel injection amount from the fuel injection valve 9 is controlled based on the intake air amount. Hereinafter, as a first embodiment based on the estimation of the internal EGR amount according to the present invention, an embodiment of intake valve closing timing control will be described with reference to the drawings.
FIG. 3 is a flowchart of the main routine.
[0049]
In step 1, the accelerator opening detected by the accelerator pedal sensor 14 and the engine speed detected by the crank angle sensor 13 are read, and based on these operating state parameters, the target air amount FQH0EM corresponding to the required torque is calculated. calculate.
In step 2, a basic value EVEGR0 in a state where there is no overlap between the intake and exhaust valves of the internal EGR amount is calculated. The calculation is performed according to the subroutine of FIG. That is, the engine speed Ne and the exhaust valve target closing timing (EVC) are read in steps 21 and 22, and a map table created based on the characteristic data as shown in FIG. Then, the basic value EVEGR0 of the internal EGR amount is calculated as the EGR rate with respect to the target air amount FQH0EM. The basic value EVEGR0 is the amount of burned gas remaining in the cylinder without any overlap between the intake and exhaust valves. Therefore, the smaller the cylinder volume determined by the piston position at the exhaust valve closing timing EVC, the smaller the figure. As shown in FIG. 7, the exhaust top dead center is minimized, but when the EVC is in front of the exhaust top dead center even in the same piston position (hereinafter referred to as BTDC as appropriate), the exhaust valve is closed with the remaining gas slightly compressed. On the other hand, when the EVC is after the exhaust top dead center (hereinafter referred to as ATDC as appropriate), the exhaust valve 6 closes in a state where the exhaust once exhausted into the exhaust passage is pulled back into the cylinder. The residual gas amount, that is, the internal EGR amount decreases. Moreover, since the tendency is due to inertia, it also changes depending on the engine rotational speed Ne. As the engine rotational speed Ne increases, the inertia increases and the influence on the internal EGR amount increases. In particular, when the exhaust valve closing timing EVC is at ATDC, the flow of exhaust gas is converted and the influence of inertia is large. Therefore, the amount of decrease in the internal EGR amount due to the increase in the engine speed Ne increases. Further, at a position away from the exhaust top dead center, the piston speed is high, so that the amount of change in the internal EGR amount due to the change in the engine rotational speed Ne increases.
[0050]
Returning to FIG. 3, in step 3, it is determined whether or not the target closing timing EVC of the exhaust valve 6 and the target opening timing IVO of the intake valve 5 overlap.
When it is determined that there is no overlap, the routine proceeds to step 4 where the correction amount OLEGR1 of the internal EGR amount due to the overlap is set to zero. Thereby, the internal EGR amount is determined to be the basic value EVEGR0.
[0051]
If it is determined in step 3 that the intake / exhaust valves overlap, the process proceeds to step 5 to calculate the basic correction value OLEGR0 at the time of the overlap.
The calculation is performed according to the subroutine of FIG.
That is, the engine rotational speed Ne, the target closing timing EVC of the exhaust valve 6 and the target opening timing IVO of the intake valve 5 are sequentially read in steps 31, 32, and 33 in FIG. 5, and based on these input values in step 34, The overlap amount (crank angle period) is converted into the overlap time OLTIME by the following equation.
[0052]
OLTIME = (EVC-IVO) / Ne
Next, in step 35, based on the overlap time OLTIME, a value OLEGC0 set in advance corresponding to the overlap time OLTIME is retrieved from the map table. Here, since the amount of internal EGR increases as the overlap time OLTIME increases, the value OLEGCO is set to increase in accordance with the increase of the overlap time OLTIME.
[0053]
In step 36, it is determined whether the target closing timing EVC of the exhaust valve 6 is in BTDC or ATDC.
If it is determined in step 36 that EVC is in BTDC, the routine proceeds to step 37, where the value OLEGC0 searched in step 35 is set as the basic correction value OLEGR0 at the time of overlap.
[0054]
Further, when it is determined in step 36 that EVC is in ATDC, the routine proceeds to step 38, where the value obtained by correcting the search value OLEGC0 according to the target closing timing EVC as follows is Set as the basic correction value OLEGR0.
OLEGR0 = OLEGC0−EVC (retard amount after top dead center) × constant
That is, the amount of change (increase) when the intake / exhaust valves overlap with respect to the basic value of the internal EGR amount, even if the overlap amount (time) is the same, the influence of blowback differs depending on the closing timing EVC of the exhaust valve, etc. It depends on. FIG. 8 shows changes in the amount of increase in the internal EGR amount due to the EVC for a plurality of overlap amounts (time) under the conditions of the engine speed Ne and the constant intake pressure. As shown in the figure, when it is determined that the EVC is in BTDC, the increase in the internal EGR amount due to the overlap is maintained substantially constant regardless of the EVC. This is because when the EVC is at BTDC, the burned gas in the cylinder during the overlap is more dominant in the return to the intake port side on the low pressure side than the scavenging to the exhaust port. This is because the burned gas that has been blown back is sucked again in the subsequent intake stroke, so that the EGR rate becomes substantially constant. Therefore, unlike the step 37, correction by EVC (advance amount before top dead center) is not performed.
[0055]
On the other hand, if it is determined that the EVC is in the ATDC, the piston is lowered during the overlap, so the amount of blowback to the intake port side decreases, and the more the EVC moves away from the top dead center, Since the negative suction pressure develops and the differential pressure from the negative intake pressure in the intake port becomes small, it is difficult to blow back. Also, when compared with non-overlapping, the intake valve opens and the intake negative pressure is transmitted into the cylinder, and the return amount of exhaust from the exhaust port to the cylinder increases (scavenging efficiency decreases). ), The internal EGR amount increases accordingly, but this increased amount is large when the overlap period is near top dead center, but is considered to decrease as the overlap period moves away from top dead center. That is, when the overlap period is close to the top dead center, the cylinder is more affected by the intake negative pressure than when the intake valve is not opened, so that the internal EGR amount is increased by the return of exhaust. The minutes are big. On the other hand, when the overlap period is away from the top dead center, the intake negative pressure in the cylinder that increases due to piston lowering in the non-overlap condition in which the intake valve does not open during this period, and the intake port due to the overlap Since the difference from the intake negative pressure transmitted from the cylinder to the cylinder becomes small, the difference in the exhaust return amount becomes small between the overlap time and the non-overlap time. That is, the increase in the internal EGR amount due to the return of exhaust gas due to the overlap decreases as the overlap period (or EVC) moves away from the top dead center.
[0056]
For the above reasons, as shown in FIG. 8, when the EVC is in the ATDC, the increase in the internal EGR amount due to the overlap decreases as the EVC moves away from the top dead center.
Therefore, as in step 38, a reduction correction proportional to EVC (retard amount after top dead center) is performed.
[0057]
Returning to FIG. 3, in step 6, a correction coefficient OLEGCB for correcting the basic correction value OLEGR0 calculated at the time of overlap according to the intake pressure (boost pressure) is calculated.
That is, the basic correction value OLEGR0 is calculated as an increase in the internal EGR amount at the time of overlap under the condition of constant intake pressure (−50 mmHg). However, even if the overlap amount (time) and EVC are the same, the basic correction value OLEGR0 When the atmospheric pressure changes, the amount of blow-back at the time of overlap changes accordingly, so it is necessary to perform correction according to the intake pressure. In other words, when the intake pressure is controlled at a substantially constant atmospheric pressure without a throttle valve, correction is not necessary, but vacuum pressure for braking, evaporative fuel, and suction negative pressure for blow-by gas to the intake system are required. In the case of performing the intake air amount control by the closing timing of the intake valve 5 after the throttle valve 10 is appropriately throttled and controlled to a predetermined intake pressure, the intake valve 5 is controlled according to the intake pressure. Correction is necessary.
[0058]
Calculation of the correction coefficient OLEGCB corresponding to the intake pressure is performed according to the subroutine of FIG. That is, in step 41, the target intake pressure calculated in the intake pressure control by the throttle valve opening control is read, in step 42, the target closing timing EVC of the exhaust valve 6 is read, and in step 43, based on these, FIG. A map table created on the basis of the characteristic data as shown in FIG. 6 is searched for a correction coefficient OLEGCB corresponding to the intake pressure. FIG. 9 shows the magnification of the increase in the internal EGR amount when the intake pressure = −100 mmHg and −300 mmHg with respect to the increase in the internal EGR amount when the intake pressure (negative pressure) = − 50 mmHg. Four types of data with a lap amount [crank angle] of 20 ° and 40 °). As shown in the figure, when the intake pressure = −100 mmHg, the EVC (center of the overlap period) is constant regardless of a change in EVC, whereas when the intake pressure = −300 mmHg, the EVC is When it is in BTDC, it is approximately constant at about 3 to 4 times, but when it is in ATDC, the magnification increases proportionally as the distance from the top dead center increases. This is because when the intake air pressure is constant (−50 mmHg) and the EVC is in the ATDC, the difference in pressure in the cylinder due to the presence or absence of overlap becomes smaller as the distance from the top dead center increases as described above. The increase in the amount tends to decrease, but if the intake negative pressure increases to about -300mmHg, the difference in the pressure in the cylinder due to the presence or absence of overlap also increases, so the increase is maintained large, -50mmHg This is because the magnification is considered to increase with time.
[0059]
Returning to FIG. 3, in step 7, the basic correction value OLEGR0 calculated in step 5 is multiplied by a correction coefficient OLEGCB corresponding to the intake pressure calculated in step 6, thereby correcting the internal EGR amount at the time of final overlap. The amount OLEGR1 is calculated.
In step 8, the basic value EVEGR0 of the internal EGR amount calculated in step 2 is added to the overlap correction amount OLEGR1 calculated as described above to perform an increase correction, thereby obtaining a final internal value. The EGR amount EGRREM is estimated and calculated (see the following formula).
[0060]
EGRREM = EVEGR0 + OLEGR
As described above, the amount of internal EGR can be estimated with high accuracy by using the estimation method according to the present invention.
Next, at step 9, the target air amount correction value HQHOFM is calculated by correcting the target air amount FQH0EM calculated at step 1 based on the internal EGR amount (see the following equation). Note that this correction does not change the target air amount itself, but is a correction for convenience according to the change in the intake valve closing timing for obtaining the target air amount (new air amount) depending on the internal EGR amount. That is, the total gas amount in the cylinder obtained by adding the internal EGR amount to the target air amount is calculated as the target air amount.
[0061]
HQHOFM = FQH0EM × (1 + EGRREM)
In step 10, the target closing timing IVC of the intake valve 5 is calculated based on the target air amount correction value HQHOFM.
As a result, a control signal corresponding to the target closing timing IVC is output to the electromagnetic drive device, and the intake valve 5 is controlled to close at the target closing timing IVC.
[0062]
In this way, the intake valve closing timing is corrected while accurately and accurately estimating the internal EGR amount, which varies greatly depending on whether the intake / exhaust valve overlaps or changes in the overlap amount according to the engine operating conditions. Since the control is performed, a fresh air amount corresponding to the target intake air amount can be obtained, and highly accurate torque control can be performed.
Next, as described above, the second embodiment of detecting the cylinder intake air amount with high accuracy based on the internal EGR amount calculated by the estimation method according to the present invention shown up to step 8 in FIG. A form is demonstrated. Since the system configuration is the same as that shown in FIG. 1 and the description thereof is omitted, the fuel injection amount by the fuel injection valve 11 is basically the intake air amount (mass flow rate) measured by the air flow meter 9. ) The cylinder intake air amount (cylinder part air mass) Cc calculated as described later based on Qa is controlled so as to have a desired air-fuel ratio.
[0063]
Hereinafter, regarding the calculation of the cylinder intake air amount (cylinder part air mass) Cc according to the second embodiment for the control of the fuel injection amount and the like, the entire block diagram of FIG. 10 and the routines of FIGS. This will be described in detail with reference to a flowchart and the like.
Here, as shown in FIG. 1, the amount of intake air (mass flow rate) measured by the air flow meter 14 is Qa (kg / h), but is multiplied by 1/3600 and handled as (g / msec). .
[0064]
In addition, the pressure of the intake manifold section is Pm (Pa) and the volume is Vm (m^Three Constant), the air mass is Cm (g), and the temperature is Tm (K).
Also, the cylinder part pressure is Pc (Pa) and the volume is Vc (m^Three), The mass of air is Cc (g), and the temperature is Tc (K). Further, the ratio of fresh air in the cylinder is η (%).
[0065]
Further, it is assumed that Pm = Pc and Tm = Tc (pressure and temperature do not change) between the intake manifold portion and the cylinder portion.
FIG. 11 is a flowchart of the intake manifold section inflow air amount calculation routine, which is executed every predetermined time Δt (for example, 1 msec).
In step 51, the intake air amount Qa (mass flow rate; g / msec) is measured from the output of the air flow meter 14.
[0066]
In step 52, the amount of air Ca (air mass; g) = Qa · Δt flowing into the manifold portion at every predetermined time Δt is calculated by integral calculation of the intake air amount Qa.
FIG. 12 is a flowchart of a cylinder part air volume calculation routine, which is executed every predetermined time Δt.
In step 61, the closing timing IVC of the intake valve 5, the opening timing IVO of the intake valve 5, and the closing timing EVC of the exhaust valve 6 are detected. These may be detected directly by providing a lift sensor for the intake valve 5 and the exhaust valve 6, but, as in the first embodiment, a command value (target value) for control in the control unit 12 It can be simplified by using.
[0067]
In step 62, the cylinder volume at that time is calculated from the closing timing IVC of the intake valve 5, and the target Vc (m^Three).
In step 63, based on the opening timing IVO of the intake valve 5, the closing timing EVC of the exhaust valve 6, and the engine speed Ne, the internal EGR amount X (v) (the above-described internal EGR amount is determined by the method described in the first embodiment). EGR amount EGRREM is equivalent).
[0068]
In step 64, based on the target Vc (cylinder volume) and the residual gas amount which is the internal EGR amount X (v), the cylinder fresh air ratio η (%) is calculated by the following equation.
η = (cylinder volume Vc−remaining gas amount) / cylinder volume Vc
That is, the overlap amount is determined by the opening timing IVO of the intake valve 5 and the closing timing EVC of the exhaust valve 6, and the remaining gas amount (internal EGR amount) increases as the overlap amount increases. The cylinder fresh air ratio η is obtained by the above formula based on the quantity. In the variable valve engine, the internal EGR can be freely controlled by controlling the overlap amount. Therefore, in general, an EGR device (external EGR) is not provided. However, when provided, the internal EGR amount is used as the residual gas amount. The cylinder fresh air ratio η is obtained using a value obtained by adding the external EGR amount to.
[0069]
In step 65, the target Vc (suction volume) is multiplied by the cylinder fresh air ratio η to obtain an actual Vc (m equivalent to the target air amount).^Three) = Vc · η is calculated. This actual Vc (m^Three) Corresponds to the cylinder intake air amount (volume amount). When the external EGR amount = 0, the actual Vc can be obtained by subtracting the internal EGR amount from the suction volume Vc.
In step 66, the actual Vc (m^Three) Multiplied by the engine rotation speed Ne (rpm), the Vc change rate (volume flow rate; m^Three/ Msec).
[0070]
Vc change speed = actual Vc, Ne, K
Here, K is a constant for aligning units, and K = (1/30) × (1/1000). 1/30 is for converting Ne (rpm) to Ne (180 deg / sec), and 1/1000 is Vc (m^Three/ Sec) to Vc (m^Three/ Msec).
[0071]
Further, when performing control to stop the operation of some cylinders, the following equation is used.
Vc change speed = actual Vc · Ne · K · n / N
n / N is an operation rate when the operation of some cylinders is stopped, N is the number of cylinders, and n is the number of operating cylinders. Therefore, for example, when the operation of one cylinder is stopped in a four-cylinder engine, n / N = 3/4. When stopping the operation of a specific cylinder, the fuel cut is performed after the intake valve and the exhaust valve of the cylinder are held in a fully closed state.
[0072]
In step 67, Vc change rate (volume flow rate; m^Three/ Msec), the cylinder part air volume Vc (m) which is the amount of air sucked into the cylinder per unit time (1 msec)^Three) = Vc change rate · Δt is calculated.
FIG. 13 is a flowchart of a continuous calculation (manifold portion intake balance calculation and cylinder portion air mass calculation) routine, which is repeatedly executed every predetermined time Δt.
[0073]
In step 71, the manifold portion intake balance calculation (manifold portion air mass Cm balance calculation), the manifold value obtained by the routine shown in FIG. 10 is set to the previous value Cm (n-1) of the manifold portion air mass as shown in the following equation. The air mass Ca flowing into the part Ca (= Qa · Δt) is added, and the cylinder part air mass Cc (n) that is the amount of cylinder intake air flowing out from the manifold part to the cylinder part is subtracted to obtain the manifold part air mass. Cm (n) (g) is calculated.
[0074]
Cm (n) = Cm (n-1) + Ca-Cc (n)
Cc (n) used here is Cc calculated by the next step 72 in the previous routine.
In step 72, in order to calculate the cylinder intake air amount (cylinder part air mass Cc), the cylinder part air mass Cm is multiplied by the cylinder part air volume Vc obtained by the routine of FIG. Then, the cylinder part air mass Cc (g) is obtained by dividing by the manifold part volume Vm (constant value).
[0075]
Cc = Vc · Cm / Vm (1)
This equation (1) is obtained as follows.
From the gas state equation P · V = C · R · T, C = P · V / (R · T).
Cc = Pc · Vc / (R · Tc) (2)
It becomes.
[0076]
Here, assuming that Pc = Pm and Tc = Tm,
Cc = Pm · Vc / (R · Tm) (3)
It becomes.
On the other hand, from the gas state equation P · V = C · R · T, P / (R · T) = C / V.
Pm / (R · Tm) = Cm / Vm (4)
It becomes.
[0077]
If this equation (4) is substituted into equation (3),
Cc = Vc · [Pm / (R · Tm)] = Vc · [Cm / Vm]
Thus, the above equation (1) is obtained.
As described above, by repeatedly executing steps 71 and 72, that is, by continuously calculating as shown in FIG. 10, the cylinder portion air mass Cc (g) which is the cylinder intake air amount is obtained and output. Can do. The processing order of steps 71 and 72 may be reversed.
[0078]
FIG. 14 is a flowchart of the post-processing routine.
In step 81, the cylinder part air mass Cc (g) is weighted and averaged to calculate Cck (g) as in the following equation.
Cck = Cck × (1-M) + Cc × M
M is a weighted average constant, and 0 <M <1.
[0079]
In step 82, in order to make the cylinder part air mass Cck (g) after the weighted average process correspond to the cycle period, the engine speed Ne (rpm) is used.
Cck (g / cycle) = Cck / (120 / Ne)
Thus, the cylinder part air mass (g / cycle) is converted every cycle (2 rotations = 720 deg).
[0080]
If the weighted average processing is performed only when the pulsation of intake air is large, such as when the throttle valve is largely open (fully open), it is possible to achieve both control accuracy and control responsiveness.
FIG. 15 is a flowchart of the post-processing routine in this case. In step 85, a change amount ΔCc of the cylinder portion air mass Cc (g) is calculated. Subsequently, at step 86, it is determined whether or not the amount of change ΔCc is within a predetermined range (greater than a predetermined value A and smaller than a predetermined value B). If it is within the predetermined range, it is not necessary to perform a weighted average process, so after setting Cck (g) = Cc (g) in step 87, in step 82, one cycle (two rotations = 720 °) as in step 82 of FIG. ) Is converted into cylinder part air mass Cck (g / cycle). If the change amount ΔCc is outside the predetermined range, the cylinder part air mass Cc (g) is weighted and averaged in step 81 as in step 81 of FIG. 14 to calculate Cck (g), and the process proceeds to step 82.
[0081]
By calculating the cylinder intake air amount (cylinder part air mass Cc, Cck) as described above, that is, while calculating the balance of the manifold part air mass Cm, the cylinder intake based on the manifold part air mass Cm and the cylinder volume Vc. When calculating the air amount (cylinder part air mass) Cc, the cylinder intake air amount can be accurately obtained by using the estimated value of the internal EGR amount.
[0082]
Therefore, the calculation accuracy of the cylinder intake air amount in the variable valve engine can be greatly improved, and in the fuel injection amount control, the air-fuel ratio control accuracy is improved, thereby greatly improving the exhaust performance and the operating performance. To do.
Moreover, since it can implement without providing a pressure sensor and a temperature sensor at all, it does not cause a cost increase.
[0083]
Next, a description will be given of a third embodiment in which the optimal ignition timing control is performed by estimating and calculating the internal EGR amount.
FIG. 16 shows a control block diagram of the third embodiment.
The internal EGR amount calculation unit estimates and calculates the internal EGR amount (volume amount) X (v) based on the exhaust valve closing timing EVC, the intake valve opening timing IVO, and the engine rotational speed Ne as described above.
[0084]
In the residual gas rate calculation unit, when external EGR is performed on the internal EGR amount, the external EGR amount is added to obtain the residual gas amount (volume) using the density ρ of EGR gas, and the residual gas amount (mass) X (g ), And a residual gas ratio ζ is calculated by dividing the residual gas amount (mass) X (g) by the total in-cylinder gas amount (mass) Vc (g). Here, the total gas amount (mass) in the cylinder is obtained by adding the cylinder portion air mass Cc (g) calculated as shown in the second embodiment to the residual gas amount (mass) X (g). Is calculated.
[0085]
The combustion speed calculation unit calculates the combustion speed Bv based on the residual gas ratio ζ. Here, the higher the residual gas ratio ζ, the smaller the combustion speed Bv is calculated.
The combustion reaction time calculation unit calculates a combustion reaction time Bt from the ignition timing until the combustion pressure reaches a peak based on the combustion speed Bv.
The MBT calculation unit calculates MBT (maximum torque generation ignition timing) based on the combustion reaction time Bt. Specifically, after converting the combustion reaction time Bt into a crank angle period based on the engine rotational speed Ne, the combustion pressure peaks at a predetermined crank angle position slightly behind the compression top dead center. The crank angle position on the advance side from the predetermined crank angle position during the crank angle period corresponding to the combustion reaction time Bt is calculated as MBT.
[0086]
In this way, it is possible to estimate the combustion speed with high accuracy based on the internal EGR amount, accurately calculate the MBT even in a transient state, and to perform optimal ignition timing control, thereby improving fuel efficiency.
[Brief description of the drawings]
FIG. 1 is a system diagram of an engine provided with a variable valve control device common to each embodiment of the present invention.
FIG. 2 is a basic structural view of an electromagnetic drive device for intake and exhaust valves.
FIG. 3 is a flowchart of a target closing timing setting routine for an intake valve in the first embodiment.
FIG. 4 is a flowchart of a subroutine that similarly calculates a basic value of an internal EGR amount.
FIG. 5 is a flowchart of a subroutine for calculating a basic correction value by overlapping internal EGR amounts.
FIG. 6 is a flowchart of a subroutine for calculating a correction coefficient based on the intake pressure of the basic correction value.
FIG. 7 is a view showing a characteristic of a basic value of the internal EGR amount.
FIG. 8 is a diagram illustrating characteristics of basic correction values due to the overlap.
FIG. 9 is a diagram illustrating the influence of the basic correction value due to intake pressure.
FIG. 10 is a control block diagram according to the second embodiment.
FIG. 11 is a flowchart of the same manifold portion inflow air amount calculation routine;
FIG. 12 is a flowchart of the same cylinder volume calculation routine.
FIG. 13 is a flowchart of the same routine (manifold intake balance calculation and cylinder intake air amount calculation) routine.
FIG. 14 is also a flowchart of a post-processing routine
FIG. 15 is a flowchart of another example of the post-processing routine.
FIG. 16 is a control block diagram of the third embodiment.
[Explanation of symbols]
1 engine
4 Spark plugs
5 Electromagnetically driven intake valve
6 Electromagnetically driven exhaust valve
7 Intake passage
8 Exhaust passage
9 Air flow meter
10 Electric throttle valve
11 Fuel injection valve
12 Control unit
13 Crank angle sensor
14 Accelerator pedal sensor

Claims (21)

In an engine equipped with a variable valve device that can variably control the closing timing of the exhaust valve,
Based on the closing timing of the exhaust valve, the basic value of the internal EGR amount is calculated, and when the opening period of the exhaust valve and the opening period of the intake valve do not overlap, the basic value is estimated as the internal EGR amount as it is, When overlapping, an internal EGR amount estimation method for an engine is characterized in that the internal EGR amount is estimated by correcting the basic value according to the overlap state . 2. The engine internal EGR amount estimation method according to claim 1, wherein a target closing timing of the exhaust valve is used as a closing timing for the exhaust valve used for estimating the internal EGR amount. The engine internal EGR amount estimation method according to claim 1 or 2, wherein the basic value of the internal EGR amount is calculated based on an engine rotation speed in addition to a closing timing of the exhaust valve. When the opening period of the exhaust valve and the opening period of the intake valve overlap, the estimated value of the internal EGR amount is calculated by adding the overlap correction amount set according to the overlap state to the basic value. The engine internal EGR amount estimation method according to any one of claims 1 to 3, wherein the engine internal EGR amount is estimated. Claim the open period of the exhaust valves and the open period of the intake valve when the overlap is according to the interval between the closing timing of the exhaust top dead center and the exhaust valve is increased, characterized by increasing the basic value The engine internal EGR amount estimation method according to any one of claims 1 to 4 . When the opening period of the exhaust valve and the opening period of the intake valve overlap, when the closing timing of the exhaust valve is before the exhaust top dead center, the basic value is increased as the engine speed increases. internal EGR quantity estimating method for an engine according to any one of claims 1 to 5, characterized. When the opening period of the exhaust valve and the opening period of the intake valve overlap, when the exhaust valve closing time is after exhaust top dead center, the basic value decreases as the engine speed increases. internal EGR quantity estimating method for an engine according to any one of claims 1 to 6,. The estimated value of the internal EGR amount is increased by increasing the overlap correction amount as the overlap amount between the exhaust valve open period and the intake valve open period increases. Item 8. The internal EGR amount estimation method for an engine according to any one of Items 7 to 8. When the exhaust valve closing timing is after exhaust top dead center, the overlap correction amount is decreased as the retardation amount from the exhaust top dead center at the closing timing increases, thereby estimating the internal EGR amount. The internal EGR amount estimation method for an engine according to any one of claims 4 to 8, wherein the value is decreased. 10. The internal value of the engine according to claim 8, wherein the estimated value of the internal EGR amount is increased by increasing the overlap correction amount as the absolute value of the intake negative pressure increases. EGR amount estimation method. The overlap correction amount is calculated by correcting the basic correction value determined by the overlap amount using the intake pressure correction amount determined based on the intake pressure and the closing timing of the exhaust valve. The engine internal EGR amount estimation method according to any one of claims 8 to 10. The engine internal EGR amount estimation method according to any one of claims 4 to 11, wherein the overlap amount uses a value obtained by time-converting a crank angle period corresponding to the overlap amount. The basic correction value is constant with respect to the basic correction value set according to the overlap amount, when the closing timing of the exhaust valve is before the exhaust top dead center, without correction by the closing timing of the exhaust valve. When the exhaust valve closing timing is after exhaust top dead center, a reduction correction amount proportional to the retardation amount of the closing timing from the exhaust top dead center is set according to the overlap amount. 13. The internal EGR amount estimation method for an engine according to claim 11 or 12, wherein the value is a value obtained by subtracting and correcting from the basic correction value . An intake pressure correction coefficient is determined as an intake pressure correction amount corresponding to the intake pressure, the exhaust valve closing timing, and the overlap amount, and the overlap correction amount is calculated by multiplying the basic correction value by the intake pressure correction coefficient. The internal EGR amount estimation method for an engine according to any one of claims 11 to 13, characterized in that: When the absolute value of the intake negative pressure increases, the intake pressure correction amount is increased.When the exhaust valve closing timing is after exhaust top dead center and the absolute value of the intake negative pressure is higher than a predetermined value, The engine internal EGR amount estimation according to any one of claims 11 to 14, wherein the intake pressure correction amount is increased in accordance with a retard amount from the exhaust top dead center at a closing timing. Method. In an engine provided with a variable valve gear that can variably control the opening and closing timings of an intake valve and an exhaust valve, the internal EGR amount is estimated using the internal EGR amount estimation method according to any one of claims 1 to 15. Estimating the amount, calculating a target air amount based on the operating state of the engine, calculating a target closing timing of the intake valve based on the estimated value of the internal EGR amount and the calculated value of the target air amount, A control method for a variable valve, characterized in that the closing timing of the intake valve is controlled so as to be the calculated target closing timing. The internal EGR amount is estimated using the internal EGR amount estimation method according to any one of claims 1 to 15, and the amount of air taken into the cylinder using the estimated value of the internal EGR amount A cylinder intake air amount calculation method for an engine, characterized in that Based on the estimated value of the internal EGR amount and the cylinder volume calculated from the intake valve closing timing, the volume air amount in the cylinder is calculated, the mass air amount in the intake manifold is calculated, and the volume in the cylinder is calculated. 18. The engine cylinder intake air amount calculation method according to claim 17, wherein the mass air amount sucked into the cylinder is calculated based on the air amount, the mass air amount in the intake manifold, and the intake manifold volume. 19. The engine cylinder intake air amount calculation according to claim 18, wherein the mass air amount in the intake manifold is calculated by calculating a balance between an inflow amount and an outflow amount of mass air into the intake manifold. Method. The internal EGR amount is estimated using the internal EGR amount estimation method according to any one of claims 1 to 15, and the ignition timing is controlled using the estimated value of the internal EGR amount. An engine ignition timing control method characterized by the above. Based on the estimated value of the internal EGR amount, a residual gas rate that is a mass ratio of the residual gas amount to the total gas amount in the cylinder is calculated, a combustion speed is calculated based on the residual gas rate, and based on the combustion rate Then, the combustion reaction time from the start of ignition to the peak of the combustion pressure is calculated, the MBT (maximum torque generation ignition timing) is calculated based on the combustion reaction time, and the ignition timing is controlled to be the MBT. 21. The ignition timing control method for an engine according to claim 20, wherein:

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