JP2001227377A - Control device for direct cylinder injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change over combustion modes of a direct cylinder injection type internal combustion engine while holding the NOx reduction effect by the combustion stability and EGR(exhaust gas recalculation). SOLUTION: When issuing a combustion mode changeover requirement from a atratified combustion mode to a homogeneous combustion mode, a target EGR rate is changed over to a target EGR rate of the homogeneous combustion mode, or the combustion mode of the changeover target, and at the same time a target air-fuel ratio is changed over to an intermediate target air-fuel ratio stably combusting either of the stratified combustion and the homogenous combustion. After that, when the estimated cylinder injection air-fuel ratio reaches the air-fuel ratio stably combusting either of the stratified combustion and the homogenous combustion and the estimated EGR rate reaches such a EGR rate as reducing the NOx while holding the stable combustion under of the stratified combustion and the homogenous combustion, the combustion mode is changed over to the homogenous combustion mode. After changing over the combustion mode, the target air-fuel ration is changed over to the target air-fuel ratio of the homogenous combustion mode, or the combustion mode of the changeover target and the fuel injection timing is changed over to intake stroke injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-cylinder injection type in which the combustion mode is switched between a stratified combustion mode (compression stroke injection mode) and a homogeneous combustion mode (intake stroke injection mode) in accordance with the operation state. The present invention relates to a control device for an internal combustion engine.

[0002]

2. Description of the Related Art In recent years, the demand for an in-cylinder injection type engine (direct injection type engine) having features of low fuel consumption, low exhaust emission, and high output has been rapidly increasing. At the time of low load, this in-cylinder injection engine improves fuel efficiency by directly injecting a small amount of fuel into the cylinder in a compression stroke to form a stratified mixture and perform stratified combustion. The engine output is increased by increasing the injection amount and injecting directly into the cylinder during the intake stroke to form a homogeneous mixture and perform homogeneous combustion. In such a direct injection engine, as described in Japanese Patent Application Laid-Open No. 9-195839, when switching from the stratified combustion mode to the homogeneous combustion mode, the throttle valve and the EGR valve (exhaust recirculation control valve) are simultaneously switched. There is something.

[0003]

Generally, the drive response of an EGR valve driven by a step motor is slower than the drive response of a throttle valve driven by a DC motor. Valve and EGR when switching from homogeneous mode to homogeneous combustion mode
If the valves are switched at the same time, the EGR rate rises due to the response delay of the EGR valve, and combustion becomes unstable. In the worst case, misfire may occur.

Therefore, as shown in Japanese Patent Application Laid-Open No. 11-72032, when switching from the stratified combustion mode to the homogeneous combustion mode, E is first set to maintain a stable combustion state.
It has been proposed to fully close the GR valve. But,
In the direct injection engine, the EGR is an indispensable control for reducing the emission of nitrogen oxides (NOx). Therefore, when the EGR valve is fully closed first when switching the combustion mode, the NOx emission is reduced. Increases and exhaust emissions deteriorate.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, an object of the present invention is to switch the combustion mode while maintaining the combustion stability and the NOx reduction effect by EGR when switching the combustion mode. It is an object of the present invention to provide a control device for a direct injection type internal combustion engine that can perform the following.

[0006]

Means for Solving the Problems When switching the combustion mode,
The in-cylinder air-fuel ratio greatly affects the combustion stability, and the exhaust gas recirculation rate (EGR rate) of the exhaust gas recirculation device greatly affects the NOx emission.

Focusing on this point, the control apparatus for a direct injection internal combustion engine according to the first aspect of the present invention estimates the in-cylinder air-fuel ratio by the in-cylinder air-fuel ratio estimating means and the EGR rate by the EGR rate estimating means. The rate or information having a correlation with the rate (hereinafter, referred to as “EGR rate information”) is estimated. The combustion mode switching means may be configured to perform a combustion mode switching request when the in-cylinder air-fuel ratio estimated by the in-cylinder air-fuel ratio estimating means reaches a predetermined air-fuel ratio, and / or by an EGR rate estimating means. When the obtained EGR rate information reaches a predetermined value, the combustion mode is switched. With this configuration, when a combustion mode switching request is issued, the combustion mode can be switched after waiting for the in-cylinder air-fuel ratio to reach a range in which stable combustion can be performed.
The combustion mode can be switched after waiting for the EGR rate to fall within the range where the NOx emission can be reduced, and both the combustion stability at the time of switching the combustion mode and the reduction of the NOx emission can be achieved.

Further, when a request for switching the combustion mode is made, the target air-fuel ratio is switched to a target air-fuel ratio capable of performing stable combustion in either stratified combustion or homogeneous combustion, and the estimated in-cylinder air-fuel ratio is stratified. When a predetermined air-fuel ratio that enables stable combustion in either combustion or homogeneous combustion is reached, and / or an estimated EG
When the R rate information reaches a predetermined value that can reduce NOx emission while ensuring stable combustion in either stratified combustion or homogeneous combustion, the target air-fuel ratio is switched to a target air-fuel ratio according to the switching destination combustion mode. The combustion mode may be switched. In this way, the in-cylinder air-fuel ratio can be controlled to an appropriate range by the target air-fuel ratio when switching the combustion mode, and the NOx emission can be reduced while improving the combustion stability.

Further, the opening degree of an exhaust gas recirculation control valve (EGR valve) may be estimated or detected as the EGR rate information. The EGR rate and EG
By associating the opening of the R valve with the opening of the EGR valve, the same combustion mode switching control as in the case of using the EGR rate can be performed.

Further, when there is a request for switching the combustion mode, the drive speed of the faster one of the throttle valve and the exhaust recirculation control valve is reduced until the combustion mode is switched. The control may be performed so as to be slower in accordance with the driving speed of the other. With this configuration, the timing at which the in-cylinder air-fuel ratio reaches the air-fuel ratio at which stable combustion can be performed and the timing at which the EGR rate reaches the predetermined value at which the NOx emission can be reduced can be made to substantially coincide with each other. E
The combustion mode can be switched at a time when the GR rate is the best, and the effects of improving combustion stability and reducing NOx can be enhanced.

[0011]

[Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner (not shown) is provided at the most upstream portion of the intake pipe 12 of the direct injection engine 11 which is a direct injection internal combustion engine, and an air for detecting an intake air amount is provided downstream of the air cleaner. A flow meter 13 is provided. A throttle valve 15 whose opening is adjusted by a motor 14 such as a DC motor is provided downstream of the air flow meter 13. The motor 14 is driven based on an output signal from an engine electronic control circuit (hereinafter referred to as “ECU”) 16 so that
The opening of the throttle valve 15 (throttle opening) is controlled, and the amount of intake air to each cylinder (in-cylinder air amount) is adjusted according to the throttle opening.

A surge tank 17 is provided downstream of the throttle valve 15.
An intake pressure sensor 18 for detecting an intake pressure is attached. An intake manifold 19 for introducing air into each cylinder of the engine 11 is connected to the surge tank 17. A swirl control valve 20 for controlling a swirl flow in the cylinder of the engine 11 is provided in the intake manifold 19 of each cylinder. Is provided.

A fuel injection valve 21 for injecting fuel directly into the cylinder is mounted on an upper part of each cylinder of the engine 11, and the fuel in a fuel tank 22 is pressurized to a high pressure by a fuel pump 23, and the fuel in each cylinder is The fuel is supplied to the injection valve 21 and the fuel pressure (fuel pressure) is detected by the fuel pressure sensor 24. An ignition plug 25 is attached to a cylinder head of the engine 11 for each cylinder, and the mixture in the cylinder is ignited by spark discharge of each ignition plug 25.

An intake valve 26 and an exhaust valve 27 of the engine 11 are driven by camshafts 28 and 29, respectively. A camshaft 28 on the intake side is provided with a hydraulic type that varies opening and closing timings of the intake valve 26 in accordance with an operation state. The variable valve timing mechanism 30 is provided. The hydraulic pressure for driving the variable valve timing mechanism 30 is controlled by the hydraulic control valve 3
1 is controlled. The reciprocating motion of the piston 32 of each cylinder of the engine 11 drives the crankshaft 33 to rotate, and the torque of the crankshaft 33 drives the external load 34 (compressor, alternator, pump for power steering, etc.) and the vehicle drive system. Is done.
A water temperature sensor 35 for detecting a cooling water temperature is attached to a cylinder block of the engine 11.

On the other hand, a catalyst 37 such as a three-way catalyst for purifying exhaust gas is provided in an exhaust pipe 36 of the engine 11, and an air-fuel ratio sensor 38 for detecting an air-fuel ratio of exhaust gas is provided upstream of the catalyst 37. ing. An EGR pipe 39 for recirculating a part of the exhaust gas to the intake side is provided between the upstream side of the air-fuel ratio sensor 38 of the exhaust pipe 36 and the surge tank 17.
An EGR valve 40 (exhaust recirculation control valve) for controlling the exhaust recirculation flow rate (EGR amount) is provided in the EGR pipe 39.

ECU 16 for controlling the operating state of the engine
Is mainly composed of a microcomputer, and executes a torque demand control program stored in a ROM (storage medium) of the microcomputer, whereby a required illustrated torque calculating means 51, a combustion mode switching means 52, a homogeneous combustion mode The functions of the control unit 53, the stratified combustion mode control unit 54, the target air-fuel ratio setting unit 55, the target EGR rate setting unit 56, the in-cylinder air-fuel ratio estimation unit 57, and the EGR rate estimation unit 58 are realized. Hereinafter, each of these functions will be specifically described.

The required indicated torque calculating means 51 calculates the required indicated torque based on the output of an accelerator sensor 41 for detecting the opening of the accelerator pedal (accelerator opening).
Here, the required indicated torque is a required value (a target value) of the indicated torque, and the indicated torque is a torque generated by combustion of the engine 11, that is, an internal loss torque or an external load torque (load of an auxiliary device). ). Therefore, the torque obtained by subtracting the internal loss torque and the external load torque from the indicated torque becomes the shaft torque (net torque) extracted from the crankshaft 33, and the vehicle drive system is driven by the shaft torque.

As shown in FIG. 3, the required indicated torque calculating means 51 calculates a required shaft torque based on the output of the accelerator sensor 41 (accelerator opening), the engine speed Ne, the vehicle speed, and the like. Is added to various loss torques described later, and a torque increase / decrease by idle speed control (ISC control) is corrected from the torque to obtain a required indicated torque. Here, the internal loss torque to be added to the required shaft torque is a mechanical friction loss and a pumping loss.
e and the cooling water temperature THW are calculated by a map or a mathematical formula, and the pumping loss is calculated based on the engine speed Ne.
It is calculated by a map or a mathematical expression based on and the intake pressure Pm. The external load torque to be added to the required shaft torque is a load torque of accessories (an air conditioner compressor, an alternator, a power steering pump, etc.) driven by the power of the engine 11, and includes an air conditioner signal and an alternator field current. It is set according to the like.

Further, the required indicated torque calculating means 51 obtains the required indicated torque by correcting the required shaft torque obtained by adding the internal loss torque and the external load torque by a torque increase / decrease by idle speed control (ISC control). . Correction torque by ISC control (torque increase / decrease)
Is calculated by a map or a mathematical expression based on the target idle rotation speed Netarget and the current engine rotation speed Ne.

On the other hand, the target air-fuel ratio setting means 55 sets a target air-fuel ratio (target A / F) using a map or the like based on the required indicated torque calculated by the required indicated torque calculating means 51 and the engine rotation speed Ne. The target air-fuel ratio is determined by the homogeneous combustion mode control means 53 and the stratified combustion mode control means 54.
Used in both. Further, the target EGR rate setting means 56 sets the target EGR rate by a map or the like according to the operating state (for example, the target air-fuel ratio, the engine speed Ne, etc.) so as to increase the NOx reduction effect by the EGR.

The combustion mode switching means 52 determines the required combustion mode from a map or the like according to the required indicated torque and the engine speed Ne. If the required combustion mode is different from the current combustion mode, the combustion mode switching request is made. Judge that there is. In this case, as described later, the estimated in-cylinder air-fuel ratio calculated by the in-cylinder air-fuel ratio estimating means 57 reaches a predetermined range in which stable combustion can be performed in either stratified combustion or homogeneous combustion, and
When the estimated EGR rate calculated by the EGR rate estimating means 58 described later reaches a predetermined range in which NOx can be reduced in both stratified combustion and homogeneous combustion, the combustion mode control means 53, 54.
To switch the combustion mode.

For example, in a low rotation region and a low torque region,
The stratified combustion mode control means 54 is selected and operated in the stratified combustion mode. During the stratified combustion mode operation, a small amount of fuel is directly injected into the cylinder in the compression stroke to form a stratified mixture and perform stratified combustion, thereby improving fuel efficiency. In the middle / high rotation range and the middle / high torque range, the homogeneous combustion mode control means 53 is selected, and the engine is operated in the homogeneous combustion mode. During the homogeneous combustion mode operation, the engine output and the shaft torque are increased by increasing the fuel injection amount and injecting directly into the cylinder during the intake stroke to form a homogeneous mixture and perform homogeneous combustion.

On the other hand, the in-cylinder air-fuel ratio estimating means 57 calculates the estimated in-cylinder air-fuel ratio by the following equation when there is a combustion mode switching request. Estimated in-cylinder air-fuel ratio = estimated in-cylinder air amount / target fuel amount

Actually, the in-cylinder air-fuel ratio = in-cylinder air amount / fuel amount, but since the in-cylinder air amount and the fuel amount cannot be measured,
It needs to be estimated. A method of estimating the in-cylinder air amount includes a cylinder air amount estimation model (an intake air system) that uses a throttle passing air amount (detected value of the air flow meter 13), an engine rotation speed Ne, an intake pressure Pm, an EGR amount, and the like as input information. model)
Is used to estimate the in-cylinder air amount. In addition, in the in-cylinder injection engine 11 that injects fuel directly into the cylinder, the fuel amount may be assumed to be equal to the target fuel amount because there is no fuel (wet) attached to the intake port inner wall. Accordingly, the in-cylinder air-fuel ratio estimating means 56 calculates the estimated in-cylinder air-fuel ratio by calculating the estimated in-cylinder air-fuel ratio = estimated in-cylinder air amount / target fuel amount. At this time, the target fuel amount is calculated by a map or the like based on the required indicated torque and the engine rotation speed Ne.

In the homogeneous combustion mode controlled by the air priority method, the difference between the target air-fuel ratio and the in-cylinder air-fuel ratio is smaller than in the stratified combustion mode controlled by the fuel priority method.
The estimated in-cylinder air-fuel ratio in the homogeneous combustion mode may be assumed to be equal to the target air-fuel ratio (estimated in-cylinder air-fuel ratio = target air-fuel ratio).

The EGR rate estimating means 58 calculates the EGR flow rate by a map or an equation from the opening degree of the EGR valve 40 and the intake pressure Pm when there is a request for switching the combustion mode. The estimated EGR rate is calculated from the air amount and the following equation. Estimated EGR rate = EGR flow rate / (EGR flow rate + estimated in-cylinder air amount) × 100 [%] The opening of the EGR valve 40 is detected by an opening sensor (not shown) built in the EGR valve 40. You.

Next, each function of the homogeneous combustion mode control means 53 will be described with reference to FIG. The homogeneous combustion mode control means 53 performs an air amount priority type torque demand control for converting the required indicated torque into a target air amount and setting the throttle opening. At this time, in consideration of the fact that the indicated torque fluctuates depending on the ignition timing and the air-fuel ratio in the cylinder, the required indicated torque is set to the ignition timing efficiency (SA efficiency) and the air-fuel ratio efficiency (A
/ F efficiency) according to the following equation.

Required indicated torque after correction = Requested indicated torque / (ignition timing efficiency × air-fuel ratio efficiency) Here, the ignition timing efficiency is set by a map or the like according to the ignition retard amount, and the ignition retard amount is set to 0. Since the indicated torque becomes maximum at the time of, the ignition timing efficiency is set to 1 when the ignition retard amount is zero. The air-fuel ratio efficiency is set by a map or the like according to the target air-fuel ratio described above.

Then, a target air amount is calculated by a map or the like based on the corrected required torque indicated and the engine speed Ne, and the target air amount, the engine speed Ne, the target EGR rate, and the internal EGR rate (variable valve timing) are calculated. Mechanism 3
A command value of the throttle opening is calculated using an air system inverse model based on (advancing amount of 0) and the like. Here, the air system inverse model is a model obtained by reversing the input / output relationship of the air system model simulating the flow of air from the throttle valve 15 to the intake port. A control signal corresponding to the throttle opening command value calculated by the air system inverse model is output to the motor 14 of the electronic throttle system, and the throttle valve 15 is driven to control the throttle opening.

The homogeneous combustion mode control means 53 calculates a target fuel amount by dividing the estimated in-cylinder air amount (or actual air amount) by the target air-fuel ratio, and various correction coefficients (water temperature) are added to the target fuel amount. Correction coefficient, feedback correction coefficient, learning correction coefficient, etc.) to obtain a final fuel injection amount, and an injection pulse having a pulse width corresponding to the fuel injection amount is supplied to the fuel injection valve 21 in the intake stroke of each cylinder. Output and execute fuel injection. As a result, during the homogeneous combustion mode operation, the fuel is directly injected into the cylinder during the intake stroke to form a homogeneous mixture and perform homogeneous combustion.

Further, the homogeneous combustion mode control means 53 calculates the opening command value of the EGR valve 40 from the target EGR rate set by the target EGR rate setting means 56, and drives the EGR valve 40 accordingly to drive the EGR valve. The rate is controlled to the target EGR rate. The homogeneous combustion mode control means 53 calculates the ignition timing of each cylinder using a map or the like according to the operating state, and applies a high voltage to the ignition plug 25 at the ignition timing to generate spark discharge. From the ignition timing, the above-described ignition timing efficiency is calculated.

The homogeneous combustion mode control means 53 uses the in-cylinder air amount estimation model to output the air flow meter 13 (the amount of air passing through the throttle) and the engine speed N.
e, The estimated in-cylinder air amount is calculated from the output of the intake pressure sensor 18 (intake pressure Pm), and the estimated in-cylinder air-fuel ratio is calculated from the estimated in-cylinder air amount and the target fuel amount.

Next, each function of the stratified combustion mode control means 54 will be described with reference to FIG. The stratified combustion mode control means 54 converts the required indicated torque into a target fuel amount, multiplies the target fuel amount by the target air-fuel ratio to obtain a target air amount, and sets a throttle opening degree of a fuel amount priority type torque. Performs demand control. At this time, the required indicated torque is corrected by dividing the required indicated torque by the air-fuel ratio efficiency in consideration of the fact that the indicated torque varies depending on the air-fuel ratio in the cylinder. Required required torque after correction = Required required torque / Air-fuel ratio efficiency Here, the method of calculating the air-fuel ratio efficiency is the same as in the case of the homogeneous combustion mode control means 53, in which the air-fuel ratio efficiency is calculated using a map or the like according to the target air-fuel ratio. Just do it.

Then, a target fuel amount is calculated by a map or the like based on the corrected required torque indicated and the engine speed Ne, and various correction coefficients (water temperature correction coefficient, feedback correction coefficient, learning correction A final fuel injection amount is obtained by multiplying by a coefficient or the like, and an injection pulse having a pulse width corresponding to the fuel injection amount is output to the fuel injection valve 21 in the compression stroke of each cylinder to execute fuel injection. Thus, during the stratified charge combustion mode operation, the fuel is directly injected into the cylinder during the compression stroke to form a stratified mixture and perform stratified charge combustion.

Further, the stratified combustion mode control means 54 calculates the ignition timing according to the target fuel amount and the engine speed Ne by using a map or the like, and applies a high voltage to the ignition plug 25 at the ignition timing to generate the spark discharge. generate.

The stratified combustion mode control means 54 calculates a target air amount by multiplying the target fuel amount by the target air-fuel ratio.
The target air amount, the engine speed Ne, and the target EGR
A throttle opening command value is calculated using an air system inverse model based on the rate, the internal EGR rate (the advance amount of the variable valve timing mechanism 30), and the like, and a control signal corresponding to the throttle opening command value is calculated. Motor 14 for electronic throttle system
And the throttle valve 15 is driven to control the throttle opening. Further, an opening command value of the EGR valve 40 is calculated from the target EGR rate, and the EGR valve 40 is driven accordingly to control the EGR rate to the target EGR rate.

Next, a control method for switching the combustion mode from the stratified combustion mode to the homogeneous combustion mode will be described with reference to FIG. When a request for switching the combustion mode from the stratified combustion mode to the homogeneous combustion mode is issued, the target E
At the same time as switching the GR rate to the target EGR rate in the homogeneous combustion mode, which is the switching destination combustion mode, the target air-fuel ratio is switched to the target air-fuel ratio for switching the combustion mode that enables stable combustion in either stratified charge combustion or homogeneous charge combustion.

When a combustion mode switching request occurs, the target EGR
The switching of the rate switches the opening command value of the EGR valve 40 in a step-like manner. However, since the driving speed of the EGR valve 40 driven by a stepping motor or the like is slow, the actual opening of the EGR valve 40 is changed to the opening command value. Of the EGR rate (actual EGR rate)
Changes with a response delay from a change in the target EGR rate.
Further, the target air amount is switched stepwise by switching the target air-fuel ratio for switching the combustion mode. However, in order to match the actual change in the in-cylinder air-fuel ratio with the change in the actual EGR rate having a slow response, the throttle is opened. The change in the degree command value is delayed according to the change in the actual opening of the EGR valve 40 having a slow response, and the estimated in-cylinder air-fuel ratio (actual in-cylinder air-fuel ratio) is responded from the change in the target air-fuel ratio for switching the combustion mode. Change with a delay.

Thereafter, the estimated in-cylinder air-fuel ratio reaches an air-fuel ratio (switching execution air-fuel ratio) at which stable combustion can be performed in both stratified combustion and homogeneous combustion, and the estimated EGR rate is stable combustion in both stratified combustion and homogeneous combustion. When the switching execution EGR rate at which NOx can be reduced is reached while maintaining the combustion mode, the combustion mode is switched to the homogeneous combustion mode. After the switching of the combustion mode, the target air-fuel ratio is switched to the target air-fuel ratio of the homogeneous combustion mode which is the switching destination combustion mode, and the fuel injection timing is switched to the intake stroke injection.

Next, a control method for switching the combustion mode from the homogeneous combustion mode to the stratified combustion mode will be described with reference to FIG. When a request for switching the combustion mode from the homogeneous combustion mode to the stratified combustion mode is issued, the target E
At the same time as switching the GR rate to the target EGR rate in the stratified combustion mode, which is the switching destination combustion mode, the target air-fuel ratio is switched to a target air-fuel ratio for switching the combustion mode in which stable combustion can be performed in either homogeneous combustion or stratified combustion.

When a combustion mode switching request occurs, the target EGR
By switching the rate, the opening command value of the EGR valve 40 is switched in a step-like manner. However, the actual opening of the EGR valve 40 having a slow response changes with a response delay from the change in the opening command value, and due to the effect, The estimated EGR rate (actual EGR rate) changes with a response delay from a change in the target EGR rate. Further, the target air amount is switched stepwise by switching the target air-fuel ratio for switching the combustion mode. However, in order to match the actual change in the in-cylinder air-fuel ratio with the change in the actual EGR rate having a slow response, the throttle is opened. Change of the command value
The estimated in-cylinder air-fuel ratio (actual in-cylinder air-fuel ratio) is changed with a response delay from the change in the target air-fuel ratio for switching the combustion mode, by delaying in accordance with the change in the actual opening of the GR valve 40.

Thereafter, the estimated in-cylinder air-fuel ratio reaches an air-fuel ratio (switching execution air-fuel ratio) at which stable combustion can be performed in both stratified combustion and homogeneous combustion, and the estimated EGR rate is stable combustion in both stratified combustion and homogeneous combustion. The combustion mode is switched to the stratified combustion mode when the switching execution EGR rate at which NOx can be reduced is reached while maintaining the EGR rate. After the switching of the combustion mode, the target air-fuel ratio is switched to the target air-fuel ratio of the stratified combustion mode, which is the switching destination combustion mode, and the fuel injection timing is switched to the compression stroke injection.

The above-described torque demand control of the in-cylinder injection engine 11 is executed by the ECU 16 in a procedure as shown in FIG. First, in step 101, the required shaft torque is calculated based on the output of the accelerator sensor 41 (accelerator opening), the engine speed Ne, the vehicle speed, and the like.
The required torque is obtained by adding the internal loss torque and the external load torque to the required shaft torque, and further correcting the torque consumed in the ISC control from the torque. After this,
Proceeding to step 102, one of the homogeneous combustion mode and the stratified combustion mode is selected as the required combustion mode from a map or the like according to the required indicated torque and the engine rotation speed Ne. It is determined whether or not there is a combustion mode switching request based on whether or not the combustion mode is different. If there is no combustion mode switching request, the current combustion mode is continued as it is (steps 108 to 108).
110).

If it is determined in step 103 that there is a request for switching the combustion mode, the process proceeds to step 104, in which the target air-fuel ratio is set to the target air-fuel ratio for switching the combustion mode that enables stable combustion in either stratified charge combustion or homogeneous charge combustion. At the same time, the target EGR rate is set to a target EGR rate corresponding to the combustion mode of the switching destination. Thereafter, in step 105, the estimated in-cylinder air-fuel ratio and the estimated EGR rate are calculated by the above-described method.

In the next step 106, it is determined whether or not the estimated in-cylinder air-fuel ratio has reached a predetermined range (A <estimated in-cylinder air-fuel ratio <B) that allows stable combustion in either stratified charge combustion or homogeneous charge combustion. At the same time, it is determined whether or not the estimated EGR rate has reached a predetermined range in which NOx can be reduced (C <estimated EGR rate <D) while maintaining stable combustion in either stratified charge combustion or homogeneous charge combustion. As a result, if one of the estimated in-cylinder air-fuel ratio and the estimated EGR rate has not reached the predetermined range, it is determined that the combustion mode switching timing has not been reached, and step 1
Returning to step 05, the process of calculating the estimated in-cylinder air-fuel ratio and the estimated EGR rate again and determining whether or not they have reached a predetermined range is repeated.

Thereafter, when both the estimated in-cylinder air-fuel ratio and the estimated EGR rate reach within a predetermined range, it is determined that the combustion mode switching timing has been reached, and the routine proceeds to step 107, where the required combustion mode is the homogeneous combustion mode. It is determined whether or not the required combustion mode is present.
The program proceeds to step 9 where the combustion mode is switched to the homogeneous combustion mode.
The process proceeds to 0, and the combustion mode is switched to the stratified combustion mode.

During operation in the homogeneous combustion mode, a target air amount is calculated by a map or the like based on the required indicated torque and the engine speed Ne, and an air system inverse model is calculated based on the target air amount and the engine speed Ne. Is used to calculate a throttle opening command value. Thereafter, a control signal corresponding to the command value of the throttle opening is output to the motor 14 of the electronic throttle system, and the throttle valve 15 is driven to control the throttle opening.

During the operation in the homogeneous combustion mode, the fuel injection amount is calculated as follows. First, an estimated in-cylinder air amount is calculated from a throttle passing air amount, an intake pressure Pm, and an engine rotation speed Ne using an in-cylinder air amount estimation model. Thereafter, the estimated in-cylinder air amount is divided by the target air-fuel ratio to calculate a target fuel amount, and the target fuel amount is multiplied by various correction coefficients (water temperature correction coefficient, feedback correction coefficient, learning correction coefficient, etc.). To obtain the final fuel injection amount. After that, an injection pulse having a pulse width corresponding to this fuel injection amount is
During the intake stroke of each cylinder, the output is output to the fuel injection valve 21 to execute the fuel injection. As a result, during operation in the homogeneous combustion mode,
In the intake stroke, fuel is injected directly into the cylinder to form a homogeneous mixture and burn homogeneously.

On the other hand, during operation in the stratified charge combustion mode, a target fuel amount is calculated by a map or the like based on the required indicated torque and the engine speed Ne, and various correction coefficients (water temperature correction coefficient, feedback (A correction coefficient, a learning correction coefficient, etc.) to obtain a final fuel injection amount, and outputs an injection pulse having a pulse width corresponding to the fuel injection amount to the fuel injection valve 21 in the compression stroke of each cylinder. Perform injection. Thus, during the stratified charge combustion mode operation, the fuel is directly injected into the cylinder during the compression stroke to form a stratified mixture and perform stratified charge combustion.

Further, during operation in the stratified combustion mode, the target air amount is obtained by multiplying the target air-fuel ratio and the target fuel amount, and an air system inverse model is used based on the target air amount and the engine speed Ne. To calculate the throttle opening command value.
Then, a control signal corresponding to the command value of the throttle opening is output to the motor 14 of the electronic throttle system, and the throttle valve 15 is driven to control the throttle opening.

In step 106, the combustion mode is switched when the estimated in-cylinder air-fuel ratio and the estimated EGR rate reach respective predetermined ranges. The combustion mode may be switched when reaching (for example, the median of a predetermined range). Further, the predetermined range (A to B, C to D) or the predetermined value (median value) used for the determination of the switching of the combustion mode may be changed according to the combustion mode of the switching destination.

According to the combustion mode switching method for the direct injection type engine 11 of the embodiment (1) described above, when a request for switching the combustion mode is made, the in-cylinder air-fuel ratio falls within a predetermined range in which stable combustion is possible. When the combustion mode is switched, combustion is performed while maintaining combustion stability and the NOx reduction effect of EGR when switching the combustion mode. The mode can be switched, so that torque fluctuation and misfire due to combustion deterioration at the time of combustion mode switching can be prevented, and an increase in NOx emission at the time of combustion mode switching can be prevented.

Further, in the present embodiment (1), the drive response of the EGR valve 40 driven by the step motor is
Considering that the response is slower than the drive response of the throttle valve 15 driven by the DC motor, when the combustion mode switching request is issued, the change in the throttle opening command value is slower than the response E.
Since the delay is made in accordance with the change in the actual opening of the GR valve 40, the timing when the in-cylinder air-fuel ratio reaches the air-fuel ratio at which stable combustion can be performed and the timing when the EGR rate reaches the predetermined range where the NOx can be reduced are substantially the same. And the in-cylinder air-fuel ratio and E
The combustion mode can be switched at a time when the GR rate is the best, and the effects of improving combustion stability and reducing NOx can be enhanced.

[Embodiment (2)] In the embodiment (1), in order to reduce the amount of NOx emission at the time of switching the combustion mode, when determining the combustion mode switching timing, EGR is performed.
The combustion mode switching execution condition is that the estimated EGR rate reaches a predetermined range in which NOx can be reduced in both stratified combustion and homogeneous combustion.
In the embodiment (2) of the present invention, the EGR rate and the opening of the EGR valve 40 (hereinafter abbreviated as “EGRV opening”) are associated in advance, and are used as control parameters when switching the combustion mode. , EGR rate instead of EGRV
Use the opening. This EGRV opening is determined by the EGR valve 40
Is detected by an opening degree sensor (not shown) built in the.

In the present embodiment (2), when the combustion mode is switched from the stratified combustion mode to the homogeneous combustion mode, as shown in FIG. At the same time as switching the EGRV opening to the target EGRV opening of the homogeneous combustion mode, which is the switching destination combustion mode, the target air-fuel ratio is switched to the target air-fuel ratio for switching the combustion mode that enables stable combustion in either stratified combustion or homogeneous combustion. . At this time, the target EGRV opening is the target EGR
Calculated from the rate.

Thereafter, the estimated in-cylinder air-fuel ratio reaches an air-fuel ratio (switching execution air-fuel ratio) at which stable combustion can be performed in either stratified combustion or homogeneous combustion, and the EGRV opening is reduced in NOx in either stratified combustion or homogeneous combustion. When the possible switch execution EGRV opening degree is reached, the combustion mode is switched to the homogeneous combustion mode.

On the other hand, when switching the combustion mode from the homogeneous combustion mode to the stratified combustion mode, as shown in FIG.
At the time when the combustion mode switching request to the stratified combustion mode is issued, the target EGRV opening is switched to the target EGRV opening of the stratified combustion mode which is the switching destination combustion mode, and at the same time,
The target air-fuel ratio is switched to a target air-fuel ratio for switching the combustion mode in which stable combustion can be performed in either stratified charge combustion or homogeneous charge combustion.

Thereafter, the estimated in-cylinder air-fuel ratio reaches an air-fuel ratio (switching execution air-fuel ratio) at which stable combustion can be performed in both stratified combustion and homogeneous combustion, and the EGRV opening is stable in both stratified combustion and homogeneous combustion. The combustion mode is switched to the stratified combustion mode when the switching execution EGRV opening degree at which NOx can be reduced is reached while maintaining.

As in the embodiment (2) described above, EG is used as a control parameter when switching the combustion mode.
Even when the EGRV opening is used instead of the R rate, the same effect as in the first embodiment can be obtained.

Note that the combustion mode switching execution conditions used in each of the above embodiments (1) and (2) are such that the estimated in-cylinder air-fuel ratio reaches an air-fuel ratio that enables stable combustion in either stratified combustion or homogeneous combustion. The estimated EGR rate (or EGRV opening) reaches a switching execution EGR rate (or switching execution EGRV opening) that can reduce NOx in either stratified charge combustion or homogeneous combustion, and when these two conditions are both satisfied The combustion mode (fuel injection timing) was changed.
The combustion mode (fuel injection timing) may be switched when either one of the two conditions is satisfied.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire in-cylinder injection type engine control system showing an embodiment (1).

FIG. 2 is a block diagram illustrating an outline of torque demand control of a direct injection type engine according to the embodiment (1).

FIG. 3 is a block diagram for explaining the function of a required indicated torque calculating means;

FIG. 4A is a block diagram illustrating a function of a homogeneous combustion mode control unit, and FIG. 4B is a block diagram illustrating a function of a stratified combustion mode control unit;

FIG. 5 is a time chart for explaining a control method when switching from the stratified combustion mode to the homogeneous combustion mode in the embodiment (1).

FIG. 6 is a time chart for explaining a control method when switching from the homogeneous combustion mode to the stratified combustion mode in the embodiment (1).

FIG. 7 is a flowchart for explaining the outline of torque demand control of the direct injection engine of the embodiment (1).

FIG. 8 is a time chart for explaining a control method when switching from the stratified combustion mode to the homogeneous combustion mode in the embodiment (2).

FIG. 9 is a time chart for explaining a control method when switching from the homogeneous combustion mode to the stratified combustion mode in the embodiment (2).

[Explanation of symbols]

11. In-cylinder injection engine (in-cylinder injection internal combustion engine), 1
2: intake pipe, 13: air flow meter, 15: throttle valve, 16: ECU (cylinder air-fuel ratio estimating means, EGR
Rate estimation means, combustion mode switching means), 18 intake pressure sensor, 21 fuel injection valve, 25 spark plug, 33 crankshaft, 34 external load, 36 exhaust pipe, 40 EGR
Valve (exhaust recirculation control valve), 41 ... accelerator sensor, 5
DESCRIPTION OF SYMBOLS 1 ... Required torque calculation means, 52 ... Combustion mode switching means, 53 ... Homogeneous combustion mode control means, 54 ... Stratified combustion mode control means, 55 ... Target air-fuel ratio setting means, 56 ... Target EGR rate setting means, 57 ... Tube Internal air-fuel ratio estimating means, 58 ...
EGR rate estimation means.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G062 AA07 BA05 BA06 BA08 BA09 CA07 CA08 EA10 FA04 FA06 GA01 GA02 GA04 GA06 GA25 GA26 3G084 AA04 BA05 BA09 BA13 BA15 BA20 BA23 CA03 CA04 CA09 DA10 DA25 EA11 EB08 EB12 EC02 EC04 FA05 FA07 FA07 FA10 FA11 FA21 FA32.

Claims (4)

[Claims] 1. A stratified combustion mode in which fuel is injected into a cylinder during a compression stroke to perform stratified combustion, and a homogeneous combustion mode in which fuel is injected into a cylinder during an intake stroke to perform homogeneous combustion is switched according to an operation state. In the cylinder injection type internal combustion engine control device, the in-cylinder air-fuel ratio estimating means for estimating the in-cylinder air-fuel ratio, and the exhaust gas recirculation rate by the exhaust gas recirculation device or information correlated therewith (hereinafter, “EGR rate information”) EG that estimates
R ratio estimating means, and when the in-cylinder air-fuel ratio estimated by the in-cylinder air-fuel ratio estimating means reaches a predetermined air-fuel ratio when a combustion mode switching request is issued, and / or by the EGR rate estimating means. A control device for a direct injection internal combustion engine, comprising: combustion mode switching means for switching a combustion mode when the EGR rate information reaches a predetermined value. 2. The combustion mode switching means switches a target air-fuel ratio to a target air-fuel ratio capable of performing stable combustion in either stratified combustion or homogeneous combustion when a combustion mode switching request is issued,
When the in-cylinder air-fuel ratio estimated by the in-cylinder air-fuel ratio estimating means has reached a predetermined air-fuel ratio that allows stable combustion in either stratified combustion or homogeneous combustion, and / or the EGR rate estimated by the EGR rate estimating means When the information reaches a predetermined value that can reduce the amount of nitrogen oxide emission while ensuring stable combustion in both stratified combustion and homogeneous combustion, the target air-fuel ratio is switched to a target air-fuel ratio according to the switching destination combustion mode. The control apparatus for a direct injection internal combustion engine according to claim 1, wherein the combustion mode is switched. 3. The control of a direct injection internal combustion engine according to claim 1, wherein said EGR rate estimating means estimates or detects an opening of an exhaust recirculation control valve as said EGR rate information. apparatus. 4. The combustion mode switching means, when there is a combustion mode switching request, until the combustion mode is switched.
4. The control method according to claim 1, wherein the drive speed of the throttle valve and the exhaust gas recirculation control valve having a higher response is controlled to be lower in accordance with the drive speed of the lower response. A control device for an in-cylinder injection internal combustion engine according to the above.