JP2000192846A - Combustion controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stable self-ignition combustion by optimally controlling a pressure and a temperature in a cylinder which are parameters for combustion control under the conditions enabling self-ignition combustion. SOLUTION: This controller predicts a scope of self-ignition formation from a demand torque T, calculates a target intake pressure Pin from the demand torque T under the conditions enabling self-ignition combustion, and controls supercharged pressure (S27). It calculates temperatures in a cylinder P2, T2 at a compression top dead center based on the intake pressure Pin and an intake temperature Tin (S28 to S29) and calculates knocking limit air-fuel ratio AFR and stability limit air-fuel ratio AFL based on these values (S30). It calculates target air-fuel ratio AF based on these values and controls combustion (S31).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine (particularly, 4
Cycle engine).

[0002]

2. Description of the Related Art In order to improve the thermal efficiency of a gasoline engine, there is known a method of reducing the pump loss by making the air-fuel mixture lean and increasing the specific heat ratio of the working gas to improve the theoretical thermal efficiency. . However, in the conventional spark ignition engine, when the air-fuel ratio is made lean, the combustion period becomes longer, and the combustion stability deteriorates. For this reason, there is a limit to lean air-fuel ratio.

As means for solving the above problem, Japanese Patent Laid-Open No.
As shown in US Pat. No. 71279, a means for causing homogeneous charge compression auto-ignition combustion is provided. This is because in a two-cycle engine, an exhaust control valve capable of controlling the opening degree of the exhaust port is provided near the exhaust port, and by controlling the exhaust control valve, the in-cylinder pressure is controlled to cause self-ignition combustion. ing.

In the homogeneous charge compression self-ignition, a combustion reaction occurs from a plurality of positions. Therefore, even when the air-fuel ratio becomes lean, the combustion period is not prolonged as compared with spark ignition, and combustion at a leaner air-fuel ratio is performed. Becomes possible. Further, since the air-fuel ratio is lean, the combustion temperature is reduced, and the NOx can be significantly reduced.

[0005]

However, self-ignition combustion is strongly affected by the air-fuel ratio, and knocking occurs on the rich side and misfires occur on the lean side, so that the operable air-fuel ratio range is limited.

FIG. 2 shows a self-ignition combustion range. As can be seen from the figure, self-ignition combustion is performed mainly on the low load side in a region considered in terms of engine speed and load, and spark ignition combustion is performed in other regions.

FIG. 3 shows the relationship between the stability and the knocking with respect to the air-fuel ratio under specific operating conditions. As can be seen from the figure, when the air-fuel ratio is made lean, the stability deteriorates.
Therefore, when the drivability is considered, the air-fuel ratio that becomes the stability limit becomes the lean limit. Conversely, when the air-fuel ratio is made rich, knocking occurs. Therefore, when the problem of sound vibration is considered, the air-fuel ratio serving as the knocking limit becomes the rich limit. Thus, the air-fuel ratio range between the stability limit and the knocking limit is the auto-ignition establishment range.

Here, as a factor affecting the air-fuel ratio at the knocking limit, there is a cylinder pressure as described in the above-mentioned publication. However, in addition to the in-cylinder pressure, the in-cylinder temperature has a large effect on the air-fuel ratio at the knocking limit.

FIG. 4 shows the effect of cylinder pressure and cylinder temperature on the knocking limit air-fuel ratio. The knocking limit air-fuel ratio becomes leaner as the cylinder pressure is higher and the cylinder temperature is higher. The air-fuel ratio at the lean limit, which is the stability limit, has a similar tendency. Therefore, it is difficult to stably cause self-ignition combustion only by the in-cylinder pressure.

FIG. 5 shows a range in which self-ignition combustion is effected when the intake air temperature affecting the in-cylinder temperature changes. Looking at specific operating conditions, for a certain in-cylinder pressure condition, the air-fuel ratio that determines the fuel injection amount is set in a self-ignition establishment range between the stability limit and the knocking limit. However, when the intake air temperature decreases, the stability limit moves to the rich side, and the stability deteriorates at the set air-fuel ratio. Conversely, when the intake air temperature increases, the air-fuel ratio at the knocking limit moves to the lean side. Therefore, knocking occurs at the set air-fuel ratio.

As described above, in the above publication, the self-ignition combustion is caused by controlling the in-cylinder pressure by controlling the exhaust control valve of the two-stroke engine. And the in-cylinder temperature, the pressure and temperature cannot be controlled independently only by controlling the exhaust control valve.

For this reason, knocking or misfire may occur depending on the operating conditions, and the operability may be significantly deteriorated. In addition, in the control of the air-fuel ratio, since the self-ignition establishment range is not predicted according to the temperature and the pressure at the compression top dead center, the self-ignition combustion cannot be performed under the operating condition in which the thermal efficiency is the best. Fuel economy had deteriorated.

The present invention has been made in view of such a problem, and predicts a range in which self-ignition is established from a required torque. Under conditions in which self-ignition combustion is possible, in-cylinder pressure and cylinder pressure, which are parameters of combustion control, are set. The internal temperature is controlled optimally, and stable self-ignition combustion is realized.
It is an object to provide a clean internal combustion engine with good fuel efficiency.

[0014]

According to the first aspect of the present invention, as shown in FIG.
Means for calculating a target in-cylinder pressure and a target in-cylinder temperature capable of performing the compression self-ignition combustion for generating the required torque, and means for controlling a combustion parameter so as to obtain the calculated target in-cylinder pressure and target in-cylinder temperature. To form a combustion control device for an internal combustion engine.

In the invention according to claim 2, in the invention according to claim 1, the combustion parameter control means controls at least one of the in-cylinder pressure and the in-cylinder temperature so as to obtain the target in-cylinder pressure and the target in-cylinder temperature. And means for calculating a target air-fuel ratio with respect to the target in-cylinder pressure and the target in-cylinder temperature and controlling the air-fuel ratio to the target air-fuel ratio (see FIG. 1). ).

According to a third aspect of the present invention, in the second aspect of the present invention, a supercharging pressure changing unit is used as the in-cylinder pressure changing unit, and the target in-cylinder pressure is set at a rich level where compression self-ignition combustion is established. It is characterized in that it is set approximately at the middle between the limit pressure and the lean limit pressure.

According to a fourth aspect of the present invention, in the second aspect of the invention, as the means for changing the in-cylinder pressure, a supercharging pressure changing means is used, and the target in-cylinder pressure is controlled so as to achieve lean lean combustion in which compression self-ignition combustion is established. It is characterized in that it is set near the limit pressure.

According to a fifth aspect of the present invention, in the second aspect of the present invention, the in-cylinder temperature changing means uses an intake air temperature changing means, and the target in-cylinder temperature is set to a rich limit at which compression self-ignition combustion is established. It is characterized in that it is set near the temperature.

In the invention according to claim 6, in the invention according to claim 2, as the means for changing the in-cylinder pressure and the in-cylinder temperature, a compression ratio variable means is used, and the target in-cylinder pressure and the target in-cylinder temperature are adjusted. It is set near the lean limit pressure and near the lean limit temperature at which the compression self-ignition combustion is established.

According to a seventh aspect of the present invention, in the second aspect of the invention, the target air-fuel ratio is calculated from a cylinder pressure and a cylinder temperature at a compression top dead center. I do.

In the invention according to claim 8, in the invention according to claims 2 to 6, the calculation of the target air-fuel ratio is calculated from a linear expression of a cylinder pressure and a cylinder temperature at the compression top dead center. It is characterized by.

According to a ninth aspect of the present invention, in the invention of the second to sixth aspects, there is provided means for detecting an octane number of the fuel, and the calculation of the target air-fuel ratio is based on the in-cylinder pressure at the compression top dead center. , And an in-cylinder temperature and an octane number.

[0023]

According to the first aspect of the present invention, the in-cylinder pressure and the in-cylinder temperature are set to a condition for stably achieving the compression self-ignition with respect to the required torque. As a result, self-ignition combustion is established, and fuel efficiency and exhaust gas can be significantly improved.

According to the second aspect of the present invention, for the required torque, first, the in-cylinder pressure and the in-cylinder temperature are set to conditions for stabilizing the compression self-ignition, and then the set in-cylinder pressure is set. An optimum target air-fuel ratio is calculated from the pressure and the in-cylinder temperature to control the air-fuel ratio. For this reason, even under each operating condition in which the compression self-ignition combustion is performed, the compression self-ignition combustion can be stably performed without impairing the operability due to the occurrence of knocking or misfire, and the fuel efficiency and the exhaust gas can be greatly improved.

According to the third aspect of the present invention, the boost pressure changing means is used as the in-cylinder pressure changing means, and the in-cylinder pressure is reduced with respect to the required torque by a rich limit pressure at which autoignition combustion is established. It is set approximately halfway between the lean limit pressure.
For this reason, even when parts variation occurs,
Compression self-ignition combustion can be stably performed without impairing drivability due to occurrence of knocking or misfire, and fuel efficiency and exhaust can be greatly improved.

According to the fourth aspect of the present invention, the supercharging pressure changing means is used as the means for changing the in-cylinder pressure, and the in-cylinder pressure is reduced with respect to the required torque. Is set to For this reason, the operation by the self-ignition combustion becomes possible under the condition of a low supercharging pressure, so that the loss due to the supercharging can be reduced. As a result, compression auto-ignition combustion can be realized under the condition of the best thermal efficiency, and the fuel efficiency and exhaust can be greatly improved.

According to the fifth aspect of the present invention, the intake air temperature changing means is used as the means for changing the in-cylinder temperature, and the in-cylinder temperature is set to the substantially rich limit temperature at which the compression self-ignition combustion is established with respect to the required torque. You have set. Therefore, efficient compression self-ignition combustion can be performed without impairing drivability due to occurrence of knocking or misfire, and fuel efficiency and exhaust gas can be significantly improved.

According to the invention of claim 6, the compression ratio variable means is used as the means for changing the in-cylinder pressure and the in-cylinder temperature,
For the required torque, the in-cylinder pressure and the in-cylinder temperature are set to a lean limit pressure and a lean limit temperature at which compression self-ignition combustion is established. Therefore, self-ignition combustion can be performed in a state where the compression ratio is higher, and the thermal efficiency can be improved. As a result, efficient compression self-ignition combustion can be performed, and fuel efficiency and exhaust can be significantly improved.

According to the present invention, the target air-fuel ratio is calculated from the in-cylinder pressure at the compression top dead center and the in-cylinder pressure. Thereby, the air-fuel ratio range in which the compression self-ignition is established can be accurately predicted. As a result, compression self-ignition combustion can be stably performed without impairing drivability due to occurrence of knocking or misfire, and fuel efficiency and exhaust can be significantly improved.

According to the eighth aspect of the invention, the target air-fuel ratio is calculated from the in-cylinder pressure at the compression top dead center and the linear expression of the in-cylinder pressure. Thereby, the air-fuel ratio range in which the compression self-ignition is established can be accurately predicted. As a result, compression self-ignition combustion can be stably performed without impairing drivability due to occurrence of knocking or misfire, and fuel efficiency and exhaust can be significantly improved.

According to the ninth aspect of the present invention, there is provided means for detecting an octane number, and the target air-fuel ratio is calculated from a linear expression of a cylinder pressure at the compression top dead center, a cylinder temperature, and an octane number. . Thereby, even when the fuel property changes, the air-fuel ratio range in which the compression self-ignition is established can be accurately predicted. As a result, compression self-ignition combustion can be stably performed without impairing drivability due to occurrence of knocking or misfire, and fuel efficiency and exhaust can be significantly improved.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 6 is a configuration diagram of the first embodiment of the present invention. The engine 10 in the figure includes an intake valve 11, an exhaust valve 12, and a piston 13. The intake system includes an intake pressure detecting means (intake pressure sensor) 14,
An intake temperature detecting means (intake temperature sensor) 15 is provided. The engine control unit (ECU) 16 calculates the fuel injection amount and the ignition timing in consideration of the signals of the intake pressure and the intake temperature, and sends signals to the fuel injection device 17 and the ignition plug 18 based on the calculation results. Further, a supercharging device 19 is connected to the intake system as a supercharging pressure changing unit that functions as a changing unit of the in-cylinder pressure, and controls an intake pressure (supercharging pressure). The fuel injection device 17 may be installed at a position where fuel can be directly injected into the cylinder.

Under such a configuration, in the present invention, FIG.
Compression self-ignition combustion is performed under specific operating conditions as shown in FIG. Next, the operation will be described.

First, FIG. 7 shows an air-fuel ratio range in which self-ignition combustion is established when the supercharging pressure is changed. Looking at the influence of the air-fuel ratio on the specific supercharging pressure as described above, the stability becomes worse as the air-fuel ratio becomes leaner. As a result, the stability limit becomes the lean limit. On the other hand, when the air-fuel ratio is made rich, knocking occurs. As a result, the knocking limit becomes the rich limit. Therefore, the air-fuel ratio surrounded by the stability limit and the knocking limit is the self-ignition establishment range.

Here, when the supercharging pressure is changed, the stability limit air-fuel ratio and the knocking limit air-fuel ratio also become lean. However, since the tendency of the change in the stability limit air-fuel ratio and the change in the knocking limit air-fuel ratio are different, when the boost pressure is increased, the range in which the self-ignition is established becomes wide.

Next, FIG. 8 shows a torque range in which self-ignition combustion is achieved when the supercharging pressure is changed. As in the case of the air-fuel ratio range, the range between the stability limit (lean limit) and the knocking limit (rich limit) is the auto-ignition establishment range. Here, at the knocking limit, although the air amount increases due to an increase in the supercharging pressure, the generated torque becomes substantially constant because the air-fuel ratio becomes lean. Further, at the stability limit, the generated torque decreases because the effect of the lean air-fuel ratio on the increase in the air amount becomes strong. Accordingly, the range of generated torque becomes wider as the boost pressure increases. Therefore, there are a plurality of supercharging pressures at which self-ignition is established for the required torque.

Here, in the self-ignition combustion, as the combustion parameter to be changed with respect to the required torque, it is sufficient to control the in-cylinder pressure, that is, the supercharging pressure. As a result, a necessary air-fuel ratio is calculated for the obtained optimal boost pressure. In addition, as this combustion parameter,
Any combustion parameter that changes the in-cylinder pressure or in-cylinder temperature may be used. As will be described in other embodiments, for example, an intake air temperature and a compression ratio may be used.

The outline of the combustion control method will be described.
In the present embodiment, the combustion parameters, that is, the supercharging pressure and the air-fuel ratio are controlled in the self-ignition establishment range substantially at the center between the knocking limit and the stability limit. As a result, even in the case where a component variation or the like occurs, it is possible to reliably control the combustion parameter within the range in which the self-ignition is established.

First, it is determined whether self-ignition combustion is established for the required torque. Next, when self-ignition combustion is established, a target boost pressure intermediate between the knocking limit and the stability limit is set for the required torque. Next, a knocking limit air-fuel ratio and a stability limit air-fuel ratio are calculated for the target boost pressure.

A method of calculating the knocking limit air-fuel ratio and the stability limit air-fuel ratio will be described. The knocking limit air-fuel ratio has a correlation between the in-cylinder pressure at the compression top dead center and the in-cylinder temperature, and can be represented by, for example, the following linear relationship under specific operating conditions.

Knocking limit air-fuel ratio = a × top dead center cylinder pressure + b × top dead center cylinder temperature + c Equation (1) The knocking limit air-fuel ratio predicted by Equation (1) and the actually measured knocking limit air-fuel ratio are: Good correlation (correlation coefficient:
0.99). Therefore, the knocking limit air-fuel ratio can be accurately predicted. Prediction accuracy can be increased by expressing the relational expression of the knocking limit air-fuel ratio with a more complicated relational expression than the linear expression.

Next, a similar relationship holds for the stability limit air-fuel ratio. That is, the stability limit air-fuel ratio also has a correlation between the in-cylinder pressure at the compression top dead center and the in-cylinder temperature, and can be expressed by, for example, the following linear relationship.

Stability limit air-fuel ratio = a ′ × top dead center cylinder pressure + b ′ × top dead center cylinder temperature + c ′ Equation (2) The stability limit air-fuel ratio predicted by equation (2) and the actually measured stability There is a similarly good correlation with the temperature limit air-fuel ratio just before (correlation coefficient: 0.98). Therefore, the stability limit air-fuel ratio can be accurately predicted. Prediction accuracy can be improved by expressing the relational expression of the stability limit air-fuel ratio with a more complicated relational expression than the linear expression.

In this manner, if the in-cylinder temperature and the in-cylinder pressure at the compression top dead center are known, the knocking limit air-fuel ratio and the stability limit air-fuel ratio can be predicted, and the range in which the compression self-ignition is established can be predicted. Here, if the compression ratio is known from the geometric shape and valve timing of the internal combustion engine, the in-cylinder pressure at the start of compression based on the polytrope change, the in-cylinder pressure at the compression top dead center from the in-cylinder temperature, In-cylinder temperature can be predicted. Therefore, when the in-cylinder pressure and the in-cylinder temperature at the start of compression are respectively predicted from the intake pressure and the intake temperature, the in-cylinder pressure and the in-cylinder temperature at the compression top dead center can be predicted from the intake pressure and the intake temperature.

Using the method described so far, the stability limit air-fuel ratio and the knocking limit air-fuel ratio can be predicted from the intake pressure (supercharging pressure) and the intake air temperature, and the stability limit air-fuel ratio and the knocking limit air-fuel ratio can be estimated. A substantially intermediate air-fuel ratio can be calculated. As a result, at a certain engine speed, the supercharging pressure and the air-fuel ratio can be controlled in the supercharging pressure control line and the air-fuel ratio control line as shown in FIGS. 8 and 7, and a stable self-ignition combustion operation can be realized.

The control flow will be described with reference to the flowchart of FIG. First, at S20, the intake air temperature Tin is detected. Next, in S21, a compression start in-cylinder temperature T1 is calculated from the intake air temperature Tin. For example, it is calculated by the following equation.

T1 = Tin + α α is a constant, for example α = 30, but may be given according to the load. Next, in S22, the required engine speed N and the required torque T are detected. In S23, the intake pressure (supercharging pressure) provided for each of the engine speed N and the compression start cylinder temperature T1.
Reference is made to a map of Pin and torque T (FIG. 8).

At S24, it is determined from the map shown in FIG. 8 whether self-ignition combustion is possible. S2 if self-ignition combustion is not possible
In step 5, control of spark ignition combustion is started. If it is determined that self-ignition combustion is possible, control of self-ignition combustion is started in S26.

That is, in S27, the required torque T is calculated as shown in FIG.
The target intake pressure (supercharging pressure) Pin is calculated with reference to the map of the intake pressure (supercharging pressure) Pin and the torque T, and is controlled. In the present embodiment, an intake pressure Pin approximately intermediate between the knocking limit and the stability limit is selected.

The target intake pressure (supercharging pressure) calculated here
Pin corresponds to the target in-cylinder pressure, and thus this portion corresponds to a target in-cylinder pressure calculating means. Further, the current value of the target in-cylinder temperature is used as it is.

Next, in S28, the compression start cylinder pressure P1 is calculated from the intake pressure Pin. P1 is calculated by the following equation, for example. P1 = Pin × β β is a constant, for example, β = 0.9.

Next, in S29, a compression top dead center cylinder pressure P2 and a compression top dead center cylinder temperature T2 are calculated from the compression start cylinder pressure P1 and the compression start cylinder temperature T1. P2 and T2 are calculated by the following formula, for example.

P2 = P1 × ε ⁿ T2 = T1 × ε ^(n-1) ε is a compression ratio. n is a polytropic exponent, for example, n
= 1.33, but may be given according to the required torque.

Next, at S30, the knocking limit air-fuel ratio (rich limit air-fuel ratio) AFR and the stability limit air-fuel ratio (lean limit air-fuel ratio) AFL are calculated from the compression top dead center cylinder pressure P2 and the compression top dead center cylinder temperature T2. calculate. Here, the calculation of the AFR and the AFL uses the equations (1) and (2).

Finally, at step S31, the target air-fuel ratio AF is calculated.
Control. In the present embodiment, AF is set to a substantially intermediate value between the knocking limit air-fuel ratio AFR and the stability limit air-fuel ratio AFL, and is calculated by the following formula, for example.

AF = (AFR + AFL) / 2 This portion corresponds to target air-fuel ratio calculation control means. By performing such combustion control, self-ignition combustion can be realized under stable conditions with respect to the required engine speed and the required torque.

Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is the same as that of the first embodiment (FIG. 6). In the present embodiment, the target intake pressure (supercharging pressure) Pin for the required torque T is set to a stability limit (lean limit).
Calculate from the vicinity.

FIG. 10 shows the relationship between the supercharging pressure and the supercharging work. The supercharging work increases as the supercharging pressure increases. Therefore, it is more efficient to perform the self-ignition combustion under the condition of the supercharging pressure as low as possible. Therefore, component variations can be reduced,
If the prediction accuracy of the self-ignition region can be improved, it is better to control the combustion parameters near the stability limit (lean limit). Therefore, in the present embodiment, the boost pressure is controlled near the stability limit as shown in FIG.

The flow of the control is the same as in the first embodiment (FIG. 9), and will be described with reference to FIG. In FIG. 9, S27 and S31 are different. In S27, the target intake pressure (supercharging pressure) Pin is referred to from the required torque T with reference to a map.
Is calculated and controlled. In the present embodiment, the required torque T
The target intake pressure (supercharging pressure) Pin calculated from the supercharging pressure line (Pin) near the stability limit (lean limit) in FIG.
And

In S31, the target air-fuel ratio AF is calculated and controlled. In the present embodiment, the target air-fuel ratio AF is obtained by the following equation so as to be an air-fuel ratio near the stability limit (lean limit).

AF = AFL × γ γ is a constant, for example, γ = 0.9. As described above, by controlling the combustion parameters, the efficiency of the self-ignition combustion can be improved, and the fuel efficiency can be improved.

Next, a third embodiment of the present invention will be described. FIG. 12 shows the configuration of the third embodiment. In the present embodiment, the intake air temperature is used as a parameter of the combustion control. For this reason, the supercharging device 19 of the first embodiment is provided in the intake system.
Instead, an intake air temperature control device 20 such as a heater is connected as an intake air temperature changing device serving as a changing device for the in-cylinder temperature. As shown in FIG. 13, an EGR control device 21 that controls the amount of EGR gas from the exhaust system to the intake system may be used as the intake air temperature changing means. Further, the temperature may be raised by increasing the internal EGR by changing the valve timing.

FIG. 14 shows an air-fuel ratio range in which self-ignition combustion is established with respect to the intake air temperature. As in the case of the supercharging pressure (FIG. 7), when the intake air temperature increases, both the stability limit air-fuel ratio and the knocking limit air-fuel ratio become lean. However, since the inclination is different, the higher the intake air temperature, the wider the air-fuel ratio range in which the self-ignition combustion is established.

FIG. 15 shows a torque range in which self-ignition combustion with respect to the intake air temperature is established. Since the amount of air decreases as the intake air temperature increases, the generated torque decreases. When the intake air temperature is controlled, the intake air temperature for the required torque is set to a value near the knocking limit. By performing such control, the combustion temperature becomes higher than the required torque, so that efficient self-ignition combustion can be realized.

The control flow is the same as in the first embodiment (FIG. 9). The difference is that the combustion control parameter changes from the boost pressure to the intake air temperature. FIG. 16 shows the control flow.
First, at S40, the intake pressure Pin is detected. Next, at S41, a compression start in-cylinder pressure P1 is calculated from the intake pressure Pin.

Next, at S42, the required engine speed N and the required torque T are detected. In S43, a map (FIG. 15) of the intake air temperature Tin and the torque T provided for each of the engine rotational speed N and the compression start in-cylinder pressure P1 is referred to.

In S44, it is determined from the map of FIG. 15 whether self-ignition combustion is possible. S if self-ignition combustion is not possible
At 45, control of spark ignition combustion is started. If it is determined that self-ignition combustion is possible, control of self-ignition combustion is started in S46.

That is, in S47, the required torque T is
The target intake temperature Tin is calculated with reference to the map of the intake temperature Tin and the torque T of No. 5 and controlled. In the present embodiment, the intake air temperature Tin near the knocking limit (rich limit) is selected.

The target intake air temperature Tin calculated here corresponds to the target in-cylinder temperature. Therefore, this portion corresponds to a target in-cylinder temperature calculating means. As for the target in-cylinder pressure, the current value is used as it is.

Next, at S48, a compression start in-cylinder temperature T1 is calculated from the intake air temperature Tin. Next, in S49, the compression top dead center cylinder pressure P is calculated from the compression start cylinder pressure P1 and the compression start cylinder temperature T1.
2. Calculate the compression top dead center in-cylinder temperature T2.

Next, at S50, the knocking limit air-fuel ratio (rich limit air-fuel ratio) AFR and the stability limit air-fuel ratio (lean limit air-fuel ratio) AFL are calculated from the compression top dead center cylinder pressure P2 and the compression top dead center cylinder temperature T2. calculate.

Finally, in S51, a target air-fuel ratio AF is calculated.
Control. In this embodiment, AF is an air-fuel ratio near the knocking limit air-fuel ratio (rich limit air-fuel ratio) AFR, and is calculated by the following equation, for example. This part corresponds to target air-fuel ratio calculation control means.

AF = AFR × τ τ is a constant, for example, τ = 1.1. By performing such combustion control, self-ignition combustion can be realized under stable conditions with respect to the required engine speed and the required torque.

Next, a fourth embodiment of the present invention will be described. FIG. 17 shows the configuration of the fourth embodiment. In the present embodiment, a compression ratio is used as a parameter for combustion control. For this reason, the intake / exhaust valves 11 and 12 have a variable valve timing mechanism 22 such as an electromagnetic drive device as a compression ratio variable means for changing the in-cylinder pressure and the in-cylinder temperature. Incidentally, as the compression ratio variable means, a variable compression ratio mechanism may be attached to a piston, a connecting rod, or the like.

The stability limit air-fuel ratio when the compression ratio is changed,
FIG. 18 shows the tendency of the knocking limit air-fuel ratio. As the compression ratio increases, both the stability limit air-fuel ratio and the knocking limit air-fuel ratio become leaner. In the present embodiment, the compression ratio for the required torque is calculated from around the stability limit (lean limit). The efficiency of self-ignition combustion increases as the compression ratio increases. Therefore, it is more efficient to perform the self-ignition combustion under the condition of the compression ratio as high as possible. Therefore, as shown in FIG. 19, it is better to control the combustion parameters near the lean limit where the compression ratio becomes higher than the required torque.

The control flow is the same as in the first embodiment (FIG. 9). The difference is that the combustion control parameter is changed from the boost pressure to the compression ratio. FIG. 20 shows the control flow.
First, at S60, the intake pressure Pin and the intake air temperature Tin are detected.
Next, in S61, a compression start in-cylinder pressure P1 and a compression start in-cylinder temperature T1 are calculated from the intake pressure Pin and the intake temperature Tin.

Next, at S62, the required engine speed N and the required torque T are detected. In S63, a map (FIG. 19) of the compression ratio ε and the torque T provided for each of the engine speed N, the compression start cylinder pressure P1, and the compression start cylinder temperature T2 is referred to.

At S64, it is determined from the map of FIG. 19 whether auto-ignition combustion is possible. S if self-ignition combustion is not possible
At 65, the control of spark ignition combustion is started. If it is determined that self-ignition combustion is possible, control of self-ignition combustion is started in S66.

That is, at S67, the required torque T is
The target compression ratio ε is calculated with reference to the map of the compression ratio ε and the torque T of No. 9 and controlled. In the present embodiment, a compression ratio ε near the stability limit (lean limit) is selected.

The compression ratio ε calculated here corresponds to the target in-cylinder pressure and the target in-cylinder temperature. Therefore, this portion corresponds to a means for calculating the target in-cylinder pressure and the target in-cylinder temperature.

Next, in S68, the compression top dead center cylinder pressure P2 and the compression top dead center cylinder temperature T2 are calculated from the compression start cylinder pressure P1, the compression start cylinder temperature T1 and the compression ratio ε. Next, S6
9, the compression top dead center cylinder pressure P2 and the compression top dead center cylinder temperature T2
Knocking limit air-fuel ratio AFR, stability limit air-fuel ratio A
Calculate FL.

Finally, in S70, the target air-fuel ratio AF is calculated.
Control. In this embodiment, AF is an air-fuel ratio near the stability limit air-fuel ratio (lean limit air-fuel ratio) AFL, and is calculated by the following equation, for example. This part corresponds to target air-fuel ratio calculation control means.

AF = AFL × δ δ is a constant, for example, δ = 0.9. By performing such combustion control, self-ignition combustion can be realized under stable conditions with respect to the required engine speed and the required torque.

Next, a fifth embodiment of the present invention will be described. FIG. 21 shows the configuration of the fifth embodiment. In the present embodiment, an octane number detecting means (fuel property sensor) 23 is added to the configuration of the first embodiment (FIG. 6). As a result, the in-cylinder pressure and the in-cylinder temperature can be controlled in consideration of the octane number of the fuel, so that stable self-ignition combustion can be realized even when the fuel properties change.

FIG. 22 shows an air-fuel ratio range in which self-ignition combustion with respect to the supercharging pressure is established when the octane number changes.
As can be seen, as the octane number increases, the air-fuel ratio range in which self-ignition combustion is established becomes rich.

FIG. 23 shows a torque range in which the self-ignition combustion with respect to the supercharging pressure is established when the octane number changes.
As can be seen from the figure, as the octane number increases, the torque range in which self-ignition combustion is established shifts to the higher load side. Since the range in which self-ignition is established changes depending on the octane number, control of the combustion parameters is performed in consideration of the octane number.

The control flow is almost the same as in the first embodiment (FIG. 9). In FIG. 9, S20, S23, S27, and S30 are different. FIG. 24 shows the control flow. In S20, the intake air temperature Tin and the octane number O are detected.

In S23, a map of intake pressure (supercharging pressure) Pin and torque T provided for each engine speed N, compression start cylinder temperature T1, and octane number O (FIG. 23) is referred to. In S27, a target intake pressure (supercharging pressure) Pin is calculated from the required torque T with reference to a map of the intake pressure (supercharging pressure) Pin and the torque T in FIG. Therefore, the selection of the supercharging pressure Pin is also performed for each octane number.

In step S30, the knocking limit air-fuel ratio (rich limit air-fuel ratio) AFR and the stability limit air-fuel ratio (lean limit air-fuel ratio) AFL are obtained from the compression top dead center cylinder pressure P2, the compression top dead center cylinder temperature T2, and the octane number O. Is calculated. Where AF
For calculation of R and AFL, the following equations (3) and (4) taking into account the octane number are used for equations (1) and (2).

AFR = a × P2 + b × T2 + c × octane number + d Equation (3) AFL = a ′ × P2 + b ′ × T2 + c ′ × octane number + d Equation (4) By controlling the combustion parameters as described above,
Even when the fuel property changes, the self-ignition combustion can be stably performed.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a configuration of the present invention.

FIG. 2 is a diagram illustrating a combustion mode with respect to an operation region.

FIG. 3 is an explanatory diagram of a self-ignition combustion establishment range.

FIG. 4 is a characteristic diagram of a knocking limit air-fuel ratio.

FIG. 5 is a diagram illustrating a problem of a conventional example.

FIG. 6 is a configuration diagram of the first embodiment.

FIG. 7 is a diagram for explaining an air-fuel ratio range in which self-ignition with respect to a boost pressure is established;

FIG. 8 is a diagram for explaining a torque range in which self-ignition with respect to a supercharging pressure is established;

FIG. 9 is a control flowchart of the first embodiment.

FIG. 10 is a diagram illustrating the relationship between supercharging pressure and supercharging work.

FIG. 11 is a diagram illustrating a supercharging pressure control method according to a second embodiment.

FIG. 12 is a configuration diagram of a third embodiment.

FIG. 13 is a configuration diagram of a modified example of the third embodiment.

FIG. 14 is a view for explaining an air-fuel ratio range in which self-ignition with respect to intake air temperature is established;

FIG. 15 is a diagram for explaining a torque range in which self-ignition is established with respect to intake air temperature;

FIG. 16 is a control flowchart of the third embodiment.

FIG. 17 is a configuration diagram of a fourth embodiment.

FIG. 18 is a diagram illustrating an air-fuel ratio range in which self-ignition is established with respect to a compression ratio.

FIG. 19 is a diagram illustrating a torque range in which self-ignition is established with respect to a compression ratio.

FIG. 20 is a control flowchart of the fourth embodiment.

FIG. 21 is a configuration diagram of a fifth embodiment.

FIG. 22 is a diagram for explaining an air-fuel ratio range in which self-ignition with respect to a supercharging pressure due to a difference in octane value is established;

FIG. 23 is a diagram for explaining a torque range in which self-ignition is established with respect to a supercharging pressure due to a difference in octane number.

FIG. 24 is a control flowchart of the fifth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Engine 11 Intake valve 12 Exhaust valve 13 Piston 14 Intake pressure detection means 15 Intake temperature detection means 16 ECU 17 Fuel injection device 18 Spark plug 19 Supercharger 20 Intake temperature control device 21 EGR control device 22 Variable valve timing mechanism 23 Octane number detection means

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 43/00 301 F02D 43/00 301E 301S F02M 25/07 570 F02M 25/07 570Z (72) Inventor Akihiro Iiyama Kanagawa Prefecture Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama-shi (72) Inventor Tsuyoshi Taniyama 2nd Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. F-term (reference) 3G023 AA01 AA02 AA06 AB06 AC02 AC04 AG02 AG03 AG05 3G062 AA05 AA06 AA10 BA02 BA09 CA07 CA08 GA02 GA06 GA12 GA14 3G084 AA00 AA04 BA07 BA09 BA20 BA22 CA03 CA04 DA02 DA38 FA02 FA11 FA16 FA21 FA22 FA33 3G092 AA01 AA06 AA09 AA11 AA12 AA17 AA18 AB02 BA04 GA03 FA05 GA05 FA05 FA05 HA16Z HB07Z HC01X HC01Z HC03X HC03Z HE01Z HE06Z 3G301 HA00 HA01 HA04 HA11 HA13 HA15 HA19 JA02 JA22 JA23 KA08 KA09 LA00 MA01 NE13 NE15 PA07Z PA10Z PB02Z PC01Z PC05Z PE01Z PE06Z

Claims (9)

[Claims] 1. A means for calculating a target in-cylinder pressure and a target in-cylinder temperature capable of performing a compression self-ignition combustion that generates the required torque, a calculated target in-cylinder pressure and a target in-cylinder temperature. Means for controlling a combustion parameter so as to obtain a combustion control apparatus. 2. The combustion parameter control means includes means for changing at least one of an in-cylinder pressure and an in-cylinder temperature so as to obtain a target in-cylinder pressure and a target in-cylinder temperature. 2. A combustion control apparatus for an internal combustion engine according to claim 1, further comprising means for calculating a target air-fuel ratio for the target air-fuel ratio and controlling the air-fuel ratio to the target air-fuel ratio. 3. A means for changing the in-cylinder pressure, wherein a supercharging pressure changing means is used, and the target in-cylinder pressure is set at a substantially intermediate value between a rich limit pressure and a lean limit pressure at which compression self-ignition combustion is established. 3. The combustion control apparatus for an internal combustion engine according to claim 2, wherein: 4. A method according to claim 2, wherein the means for changing the in-cylinder pressure is a boost pressure changing means, and the target in-cylinder pressure is set near a lean limit pressure at which compression self-ignition combustion is established. A combustion control device for an internal combustion engine according to the above. 5. An in-cylinder temperature changing means using an intake air temperature changing means, and setting the target in-cylinder temperature near a rich limit temperature at which compression self-ignition combustion is established. Combustion control device for an internal combustion engine. 6. A method for changing the in-cylinder pressure and the in-cylinder temperature, wherein a compression ratio variable means is used. 3. The combustion control device for an internal combustion engine according to claim 2, wherein the temperature is set near the temperature. 7. The internal combustion engine according to claim 2, wherein the target air-fuel ratio is calculated from a cylinder pressure and a cylinder temperature at a compression top dead center. Combustion control device. 8. The method according to claim 2, wherein the target air-fuel ratio is calculated from a linear expression of a cylinder pressure and a cylinder temperature at a compression top dead center. Combustion control device for an internal combustion engine. 9. Means for detecting an octane number of the fuel,
The internal combustion engine according to any one of claims 2 to 6, wherein the target air-fuel ratio is calculated from a linear expression of a cylinder pressure at a compression top dead center, a cylinder temperature, and an octane number. Combustion control device.