JP2000345889A - Cylinder injection-type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylinder injection-type internal combustion engine in which acceleration response from a specified operating range in which the engine rotational speed is low and the turbine rotational speed is also low is improved. SOLUTION: In this internal combustion engine, when operating range judging means (S10, S12) judge the operation of a specified operating range (Ne<=Ne0, Pe<Pe0) in which the engine rotational speed and the turbine rotational speed of a supercharging means are low, additional fuel is injected (two-stage combustion) from a fuel injection valve by a turbine speed increasing means (S20) in timing in which re-combustion is possible in a combustion chamber or in an exhaust passage close to the combustion chamber after main injection of fuel to the combustion chamber by the fuel injection valve. Therefore, the additional fuel is re-burnt upstream of the turbine, exhaust gas pressure in the exhaust passage is increased, and the turbine rotational speed is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection internal combustion engine, and more particularly, to a technique related to the acceleration response of a turbocharger in which a turbine is rotated by exhaust energy to supercharge intake air.

[0002]

2. Related Background Art In recent years, an internal combustion engine having a turbocharger (turbocharger) for supercharging intake air by rotating a turbine by exhaust energy has been put to practical use to improve the engine output. I have. Then, for example, in a diesel engine, as a technique for improving responsiveness during acceleration, the energy in exhaust gas, that is, by executing after-fuel injection as a sub-injection during the expansion stroke in addition to main fuel injection, that is, An apparatus configured to increase the pressure of exhaust gas and thereby improve the output of a supercharger is disclosed in Japanese Patent Laid-Open No.
No. 103013.

[0003]

However, the technology disclosed in the above publication executes after-fuel injection at a predetermined vehicle speed or higher and a predetermined engine rotation speed or higher, and mainly aims at improving output in a high rotation speed range. It is a thing. Therefore, according to the technique disclosed in the above publication, the output in the high rotation range can be improved, but the acceleration response is poor and the acceleration feeling is poor when accelerating from the low rotation / low load range or when returning from the deceleration fuel cut range. There is a problem.

The present invention has been made to solve such a problem, and an object of the present invention is to improve the acceleration responsiveness from a specific operating range where the engine speed is low and the turbine speed is low. It is an object of the present invention to provide an in-cylinder injection type internal combustion engine.

[0005]

In order to achieve the above object, according to the present invention, in an in-cylinder injection type internal combustion engine, an engine speed and a turbine speed of a supercharging device are determined by an operating range determining device. Is determined to be an operation in a specific operation range in which the fuel is reduced, the timing at which the turbine can be reburned in the combustion chamber or in the exhaust passage near the combustion chamber after the main injection of fuel into the combustion chamber by the fuel injection valve by the turbine speed increasing means Then, additional fuel is injected from the fuel injection valve, the additional fuel reburns upstream of the turbine, and the exhaust pressure in the exhaust passage increases, thereby increasing the rotation speed of the turbine.

[0006] When the rotation speed of the turbine increases in this way, the supercharging pressure of the intake air increases, the filling efficiency in the combustion chamber improves, the output of the internal combustion engine increases, and the engine rotation speed and the turbine of the supercharging means increase. Even at the time of acceleration from a specific operation range where the rotation speed becomes low, acceleration traveling with good acceleration response and good acceleration feeling is realized. In this case, the in-cylinder injection type internal combustion engine may be a gasoline engine having a throttle valve for adjusting the amount of intake air flowing into the combustion chamber and a spark plug facing the combustion chamber, or a diesel engine having no spark plug. However, in the case of a diesel engine, since the exhaust gas temperature is generally low in a low-speed and low-load region and reburning is unlikely to occur, preferably, the direct injection internal combustion engine is forcibly ignited even in a low-speed and low-load region. It is preferable to use a direct injection type gasoline engine whose exhaust temperature is relatively high.

The in-cylinder injection type gasoline engine not only performs uniform combustion in which fuel is injected in the intake stroke (intake stroke injection), but also ignites fuel in the compression stroke, similarly to a normal intake pipe injection type gasoline engine. This is an internal combustion engine that can also perform stratified combustion in which injection is performed so as to gather only near the stopper (compression stroke injection), and its basic configuration is known. Further, the specific operation region is a low rotation / low load region or a deceleration fuel cut region,
In the case of a low rotation speed / low load range, it is preferable to increase the rotation speed of the turbine by the turbine speed increasing means when detecting the acceleration standby state or the start of acceleration of the internal combustion engine,
In the deceleration fuel cut region, it is preferable that the turbine speed increase means increase the rotation speed of the turbine after a predetermined time has elapsed from the start of the fuel cut.

As a result, the rotational speed of the turbine is efficiently increased as required, and the acceleration response is improved.
Further, the injection timing of the additional fuel by the turbine speed-up means is:
It is preferable to set it within a predetermined range after the middle stage of the expansion stroke so as not to affect the output of the internal combustion engine and to surely reburn in the combustion chamber or the exhaust passage near the combustion chamber.

As a result, the additional fuel is reliably reburned upstream of the turbine, the exhaust pressure in the exhaust passage is sufficiently increased, and the acceleration response is improved. In addition, depending on the operating state of the internal combustion engine, the in-cylinder injection type internal combustion engine performs intake combustion in which the air-fuel ratio is set to a rich air-fuel ratio or near a stoichiometric air-fuel ratio by the above-described intake stroke injection mainly at a high load such as during acceleration. It is preferable to be able to switch between a stroke injection mode and a compression stroke injection mode in which stratified combustion is performed at a lean air-fuel ratio mainly by the compression stroke injection at a low load.In this case, during normal acceleration, the intake stroke injection mode is selected. On the other hand, when accelerating from the specific operation region, it is preferable to select the compression stroke injection mode for a predetermined period from the start of acceleration.

As a result, during acceleration from a specific operation range accompanied by an increase in the rotation speed of the turbine, the output increases sharply in uniform combustion in which the air-fuel ratio is close to the rich air-fuel ratio, and an acceleration shock occurs. There is a possibility,
Temporary stratified combustion with a lean air-fuel ratio from the start of acceleration prevents the output from rising sharply, increases the turbine speed and improves acceleration responsiveness, while also accelerating the shock. Is prevented.

Further, when the rotation speed of the turbine is increased by the turbine speed-up means and the acceleration is continued, the main injection is preferably divided into an intake stroke injection and a compression stroke injection. As a result, when the rotation speed of the turbine is increased and the intake air is supercharged as described above, the charging efficiency in the combustion chamber is increased, and the internal pressure of the combustion chamber is increased. Therefore, knocking occurs only with uniform combustion by the intake stroke injection. However, by dividing the main injection into the intake stroke injection and the compression stroke injection in this way, it becomes possible to reduce the fuel concentration in the fuel mixture of uniform combustion and to suppress the self-ignition, and to reduce knocking. The occurrence is prevented.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of a direct injection internal combustion engine according to the present invention mounted on a vehicle, and the configuration of the direct injection internal combustion engine according to the present invention will be described with reference to FIG. explain.

Engine body (hereinafter simply referred to as engine) 1
Performs, for example, fuel injection in the intake stroke (intake stroke injection mode) in which uniform combustion is performed by switching the fuel injection mode (operation mode) or fuel injection in the compression stroke (compression stroke injection mode) in which stratified combustion is performed. It is a possible in-cylinder injection spark ignition in-line four-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). Operation), and especially in the compression stroke injection mode, the super lean air-fuel ratio (for example, a value of 25 to
Operation at the value 50) is possible.

As shown in FIG. 1, an electromagnetic fuel injection valve 6 is attached to a cylinder head 2 of an engine 1 together with an ignition plug (ignition plug) 4 for each cylinder. The fuel can be directly injected into the inside. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6, that is, the fuel injection time.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the intake manifold 10.
1 is provided with a throttle sensor 11a for detecting the throttle opening θth. In addition, intake manifold 1
0 is connected to an intake pipe 12, and an air cleaner 14 is provided at a tip of the intake pipe 12.

An air flow sensor 16 is provided in the intake pipe 12 near the air cleaner 14. Here, a Karman vortex airflow sensor is employed as the airflow sensor 16. The Karman vortex air flow sensor measures the amount of intake air by detecting the vortex frequency by utilizing the proportional relationship between the amount of intake air and the number of vortices of air, that is, the vortex frequency (Kalman frequency (Hz)). It is a known sensor.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder. An exhaust manifold (exhaust passage) communicates with each exhaust port.
One end of each 20 is connected. Further, an exhaust pipe 22 is connected to the exhaust manifold 20, and a muffler (not shown) is connected to the exhaust pipe 22 via an exhaust purification catalyst 30. The exhaust purification catalyst 30 is mainly a three-way catalyst, but may be a combination of another catalyst such as a NOx catalyst.

Reference numeral 26 in the figure denotes a crank angle sensor for detecting a crank angle CA. The crank angle sensor 26 is capable of detecting an engine rotation speed (engine rotation speed) Ne together with the crank angle CA. The in-cylinder injection type gasoline engine 1 is already known, and its basic structure will not be described in detail here.

As shown in FIG. 1, a turbocharger (supercharging means) 40 is provided between the intake pipe 12 and the exhaust pipe 22. The turbocharger 40 is
A turbine 4 in which a compressor wheel 42 provided on the intake pipe 12 side and a turbine wheel 44 provided on the exhaust pipe 22 side are connected by a shaft 46 so as to be synchronously rotatable.
1, which is configured to rotate the turbine 41 at high speed in accordance with the exhaust pressure, compress the intake air in the intake pipe 12, and increase the charging efficiency in the combustion chamber 8.

The in-cylinder injection type engine 1 has an ECU including an input / output device, a storage device (ROM, RAM, etc.), a central processing unit (CPU), a timer counter and the like.
(Electronic control unit) 50 is provided,
The ECU 50 performs comprehensive control of the direct injection internal combustion engine according to the present invention including the engine 1. EC
The input side of U50 is provided with the throttle sensor 11 described above.
a, various sensors such as an air flow sensor 16 and a crank angle sensor 26 are connected, and detection information from these sensors is input.

On the other hand, to the output side of the ECU 50, the above-described ignition plug 4, fuel injection valve 6, etc. are connected via an ignition coil 5. Various sensors are connected to the ignition coil 5, fuel injection valve 6, etc. The optimum values such as the fuel injection amount, the fuel injection timing, the ignition timing, and the like calculated based on the detection information from the class are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

More specifically, the ECU 50 calculates a target average effective pressure Pe corresponding to the engine load based on the throttle opening information θth from the throttle sensor 11a and the engine speed information Ne from the crank angle sensor 26. Usually, a fuel injection mode, that is, an operation mode is set from a fuel injection mode setting map (not shown) according to the target average effective pressure Pe and the engine rotation speed information Ne. For example, when the target average effective pressure Pe and the engine rotation speed Ne are both small, the operation mode is the compression stroke injection mode (compression lean mode), and fuel is injected in the compression stroke, while the target average effective pressure Pe is large. Or the engine speed Ne increases, the operation mode is set to the intake stroke injection mode,
Fuel is injected during the intake stroke. In the intake stroke injection mode, the lean air-fuel ratio (for example, the value 1
8 to value 22), an stoichiometric feedback mode (S-F / B mode) in which the actual air-fuel ratio (actual A / F) is feedback-controlled to be stoichiometric, and an open loop that is a rich air-fuel ratio. Mode (O
/ L mode).

Thus, a target air-fuel ratio (target A / F) as a control target is set from the target average effective pressure Pe and the engine speed Ne, and the appropriate amount of fuel injection and the like are determined by the target A / F. Is determined based on Furthermore, in the in-cylinder injection type gasoline engine 1, various fuel injection patterns are not limited to the above-described operation modes and can be realized depending on the operation state.
That is, a description will be given of fuel injection control in the case where acceleration is performed when the engine 1 is in a low rotation speed / low load state.

First, a first embodiment will be described. Referring to FIG. 2, the fuel injection control according to the first embodiment of the present invention, that is, when the engine 1 is in a low rotation speed and low load state, the rotation speed of the turbocharger 40 is forcibly increased to increase the output of the engine 1. The control routine of the turbine speed-up control for increasing the pressure is shown by a flowchart, and the operation and effect of the present invention will be described below based on the flowchart.

First, in step S10 of FIG. 2, the engine speed Ne is reduced to a predetermined low speed Ne0 (for example, 30).
(Operating range determining means). If the result of the determination is true (Yes) and the engine 1 is rotating at high speed, the process proceeds to step S30, where control flags F1, F2, and F3, which will be described later, are reset to a value of 0. Normal engine control according to the setting map is performed.

On the other hand, if the determination result of step S10 is false (N
If it is determined in o) that the engine 1 is rotating at a low speed, the process proceeds to step S12. In step S12, it is determined whether or not the load required for the engine 1, that is, the target average effective pressure Pe is smaller than a predetermined low load Pe0 (operating range determining means). Judgment result is false (No)
If the load required for the engine 1 is large, the process proceeds to step S14.

In step S14, the control flag F1
Is 1 or not. As described above, since the flag F1 is normally reset to the value 0, in this case, the flag F1 can be regarded as the value 0, and the determination result is false (No). Further, the next step S15
Then, it is determined whether or not the control flag F3 has a value of 1. As described above, similarly to the flag F1, the flag F3 is normally reset to the value 0. In this case, the flag F3 can be regarded as the value 0, and therefore, the determination result is false (No). And also the above step S3
After 0, normal engine control is performed in step S32. That is, in the operating region (specific operating region) where the engine 1 is rotating at a high speed or the load required for the engine 1 is large, the engine control according to the fuel injection mode setting map is performed as usual. Is done.

If the determination result of step S12 is true (Ye
s), that is, when it is determined that the target average effective pressure Pe is smaller than the predetermined low load Pe0, the process proceeds to step S16. In step S16, the throttle sensor 11
a based on the throttle opening information θth detected by
It is determined whether or not the throttle opening change speed Δθth is larger than a predetermined value X1. That is, it is determined whether or not the driver intends to greatly accelerate from the low rotation / low load state.

If the determination result of step S16 is false (No) and the throttle opening change rate Δθth is equal to or less than the predetermined value X1, it can be determined that the driver does not intend to accelerate significantly. Proceed to step S18. In step S18, it is determined again whether or not the control flag F1 has the value 1, but as described above, the flag F1
Since 1 is normally 0, the determination result is false (No). In this case, normal engine control is also performed in step S32 after step S30.

On the other hand, if the result of the determination in step S16 is true (Y
If the throttle opening change speed Δθth is larger than the predetermined value X1 in es), it can be determined that the driver has a will to accelerate significantly, and in this case, the process proceeds to step S20. In step S20, two-stage combustion control is performed (turbine speed-up means). The two-stage combustion control means that after the fuel is injected (main injection) from the fuel injection valve 6 in the intake stroke or the compression stroke and the main combustion is performed, the additional fuel is divided into two stages from the fuel injection valve 6 in the expansion stroke. The auxiliary fuel is injected (sub-injection), and the additional fuel is burned in the combustion chamber 8 or the exhaust manifold (intake passage) 20 by the residual heat of the main combustion, and the combustion is divided into two stages. It is something.

In practice, the two-stage combustion control is performed by another control routine shown by a flowchart in FIG. Hereinafter, the procedure of the two-stage combustion according to the present invention will be described. In step S40, it is determined whether or not the control flag F2 has a value of 1. In this case, as described above, usually the flag F
Since 2 is reset to a value of 0, the determination result of step S40 is false (No), and in this case, the process proceeds to step S42.

In step S42, in response to the start of the two-stage combustion control, that is, the start of acceleration, the timer TM is set to start counting time. Then, in the next step S44, the value 1 is set to the flag F2, and the fact that the two-stage combustion control is being executed is stored. In the next step S46, it is determined whether or not the time measured by the timer TM has exceeded a predetermined time t1. Immediately after the start of the timer TM, the timer TM has not yet reached the predetermined time t1, so in this case, the determination result is false (No), and the process proceeds to step S50 through step S48.
Execute

That is, for a predetermined time t1 after the start of the two-stage combustion control, main injection is performed in the compression stroke to generate main combustion (step S48), and sub-injection is performed in the expansion stroke. As described above, when the two-stage combustion is performed at the start of the acceleration from the low rotation speed / low load state and the additional fuel is burned after the main combustion, the exhaust pressure in the exhaust manifold 20 sharply increases due to the expansion due to the combustion. Then, receiving the exhaust pressure, the turbine wheel 44 of the turbocharger 40,
As a result, the compressor wheel 42 rotates at a high speed. Therefore, in general, the exhaust gas flow rate is low in the low rotation speed and low load state, and the rotation speed of the turbocharger 40 is low and the intake air is not supercharged sufficiently. By doing so, even when accelerating from a low rotation / low load state, the turbocharger 40
Can be made to function immediately to increase the charging efficiency, and the acceleration performance from low rotation and low load conditions can be improved.

Referring to FIG. 4, the engine rotation speed Ne is shown.
Is lower than a predetermined low rotation speed Ne0 (for example, 200
0 rpm), the experimental results showing the relationship between the target average effective pressure Pe, the turbine rotation speed Rt (a), and the exhaust gas temperature Tex (b) in the exhaust manifold 20 are shown. ) Shows the result when only the intake stroke injection is performed without performing the two-stage combustion and only the main combustion based on the conventional uniform combustion is performed, and the mark (solid line) indicates the case of the present invention, that is, as described above. The results in the case of performing two-stage combustion are shown.
When the stage combustion is performed, the exhaust gas temperature Tex in the exhaust manifold 20 becomes extremely high, and therefore, the exhaust pressure becomes high. As a result, the turbine rotation speed Rt becomes high.

In FIG. 4, the results of a case in which only the compression stroke injection is performed and only the main combustion by the stratified combustion are performed are shown for reference. According to this,
It can be seen that even when only the compression stroke injection is performed without performing the two-stage combustion, there is an effect of increasing the turbine rotational speed Rt as compared with the case where only the intake stroke injection is performed.
This is because when performing the compression stroke injection, it is necessary to set the air-fuel ratio to a lean air-fuel ratio as described above due to structural reasons. As a result, the intake air amount increases and the exhaust gas generation amount increases, It is thought that the exhaust flow rate increases. However, if the two-stage combustion is performed, the turbocharger 40 can function much more effectively than the compression stroke injection alone.

By the way, the main injection may be performed in the intake stroke. However, if the compression stroke injection mode is selected and performed in the compression stroke as described above, while maintaining the total air-fuel ratio substantially constant, As described above, the effect of the two-stage combustion can be enhanced by reducing the fuel of the main combustion and increasing the amount of the additional fuel by the sub-injection under the super lean air-fuel ratio, and the combustion of the main combustion directly affecting the output torque. Therefore, there is an advantage that a rapid increase in output torque during acceleration, that is, occurrence of an acceleration shock can be prevented.

Then, the determination result of step S46 is true (Yes), that is, the time measured by the timer TM is equal to the predetermined time t1.
If it is determined that the pressure has exceeded the threshold, the main injection is performed in the intake stroke to cause main combustion (step S52).
That is, when the predetermined time t1 has elapsed, the acceleration shock is considered to be no longer a concern,
It is preferable to increase the main injection during acceleration and make the air-fuel ratio closer to the rich air-fuel ratio to make the main combustion that contributes to the output torque stronger, so in such a case, the main injection is performed in the intake stroke. The effect of the two-stage combustion is continuously enjoyed while increasing the output torque. In this sense, the predetermined time t1 is set to a time that can sufficiently suppress the acceleration shock.

It is preferable that the injection timing of the sub-injection in the above-described expansion stroke be within a predetermined range in the middle stage of the expansion stroke. With this configuration, the additional fuel due to the sub-injection to the expansion stroke is prevented from contributing to the output torque as much as possible, and
It is possible to reliably burn the additional fuel with the residual heat of the main combustion. Further, when performing two-stage combustion, it is preferable to retard the ignition timing. As a result, the main combustion occurs at a relatively late stage of the compression stroke. Therefore, the residual heat of the main combustion is sufficiently maintained until the timing of the sub-injection in the expansion stroke, and the additional fuel is satisfactorily burned. The effect of raising the exhaust gas temperature Tex is further enhanced.

After the two-stage combustion is performed in step S20 of FIG. 2, the control flag F is then set in step S22.
1 is set to a value of 1 to store that the two-stage combustion is being performed. Then, the routine is repeatedly executed. In this case, as long as the control flag F1 is set to the value 1, the determination result of step S16 is false (No), and even if the throttle opening change speed Δθth is equal to or less than the predetermined value X1, the determination result of step S18 is The result is true (Yes), and the two-stage combustion is continuously performed.

By the way, when the acceleration operation is performed, the target average effective pressure Pe usually increases, and eventually exceeds the predetermined low load Pe0. When the target average effective pressure Pe exceeds the predetermined low load Pe0, the determination result of step S12 is again false (No), and then step S14 is executed. In step S14, it is determined whether or not the flag F1 has the value 1 as described above. However, this time, since the flag F1 was set to the value 1 in step S22, the determination result is true (Y
es), and then proceeds to step S24.

In step S24, the target average effective pressure Pe
Rises and is no longer in the low load range, the two-stage combustion is stopped (terminated), and both the control flags F1 and F2 relating to the two-stage combustion set to the value 1 as described above are reset to the value 0. I do. In the next step S26, it is determined whether or not the turbine rotation speed Rt is higher than a predetermined value Rt1. The turbine rotation speed Rt can be estimated from, for example, Kalman frequency information detected by the air flow sensor 16. That is, with reference to FIG. 5, the relationship between the turbine speed Rt and the Kalman frequency with respect to the engine speed Ne and the target average effective pressure Pe is shown. In such a region where the engine speed Ne is low,
Kalman frequency (dashed line) and turbine rotation speed Rt
(Solid line) overlaps relatively well, so that the turbine rotation speed Rt can be easily estimated based on the Kalman frequency information from the air flow sensor 16.

More specifically, the turbine rotational speed Rt is obtained by calculation based on the turbine rotational speed Rt estimation routine shown in the flowchart of FIG. Step S6
At 0, first, the intake air amount Q is calculated from the following equation (1) based on the Kalman frequency F. Q (n) = Kp · F (n) (1) where F (n) is the Kalman frequency in the nth cycle, Kp is the pulse constant, and Q (n) is the amount of intake air per time.

In step S62, the calculated intake air amount Q (n)
Is filtered based on the following equation (2). Note that this filtering process is general. Qf (n) = Kf · Qf (n−1) + (1−Kf) · Q (n) (2) where Kf is a smoothing coefficient corresponding to a turbine response delay. Then, in step S64, the turbine rotation speed Rt is finally estimated based on the following equation (3).

Rt (n) = Kt · Qf (n) (3) where Kt is a conversion coefficient for converting the intake air amount into the turbine rotation speed. If the determination result of step S26 is false (No), the turbine rotational speed Rt is set to the predetermined value Rt.
In the case of 1 or less, that is, even after performing the two-stage combustion, for example, the target average effective pressure Pe rises too rapidly and the two-stage combustion is not sufficiently performed, and the turbine rotation speed Rt
In the case where does not reach the predetermined value Rt1, for example, the process proceeds to step S32, and normal engine control is performed.

On the other hand, if the decision result in the step S26 is true (Y
If the turbine rotation speed Rt exceeds the predetermined value Rt1 in es), there is a possibility that the charging efficiency is high and the internal pressure of the combustion chamber 8 is very high. Is performed, knocking may occur. In the next step S28, two-stage mixing control is performed.

In the two-stage mixing, an amount of fuel that cannot self-ignite is injected during the intake stroke prior to the compression stroke injection, which is the main injection, and the total air-fuel ratio is a rich air-fuel ratio, but the total air-fuel ratio is limited by the intake stroke injection. This is control for suppressing the occurrence of knocking by lowering the fuel concentration of the air-fuel mixture. Thereby, the target average effective pressure P
Even if the turbine rotation speed Rt is increased by performing the two-stage combustion after e has increased and the two-stage combustion has been completed, the occurrence of knocking can be suitably suppressed by performing the two-stage mixing. it can.

After the two-stage mixing is performed, the next step S2
In step 9, the control flag F3 is set to a value of 1 to store that two-stage mixing is being performed. Then, the routine is repeatedly executed. In this case, as long as the control flag F3 is set to the value 1, steps S10 to S14
, The determination result in step S15 becomes true (Yes), and the two-stage mixing is continuously performed unless the control flag F3 is reset in step S30.

In the first embodiment, the throttle opening change rate Δθth is set to the predetermined value X1 under low rotation and low load conditions.
Although the two-stage combustion is performed after detecting that it has become larger than the above, preferably, the acceleration transition state before the start of acceleration is detected, and the two-stage combustion is performed in advance when the acceleration transition state is detected. It is good to carry out. In this case, a signal based on an operation estimated to be executed before the driver accelerates, for example, a brake signal, a shift position signal of the transmission, or the like is raised as the acceleration shift state detecting means. In particular,
For example, after the vehicle is decelerated by braking, two-stage combustion may be started when the engine rotation speed Ne becomes equal to or lower than the predetermined low rotation speed Ne0 and the brake signal changes from on to off, or When the vehicle is accelerated from a low rotational speed Ne0 or lower, the shift position of the transmission is normally switched to a lower gear (first gear, second gear, etc.), so that the shift position signal is switched to a signal corresponding to the lower gear. May start two-stage combustion.

In addition, even when the acceleration transition state before the start of acceleration is detected, the two-stage combustion can be always performed in the low rotation speed and low load state. In the first embodiment, two-stage combustion is performed when the engine rotation speed Ne is equal to or lower than the predetermined low rotation speed Ne0 and the target average effective pressure Pe is smaller than the predetermined low load Pe0. However, in the in-cylinder injection type gasoline engine 1 configured to perform fuel cut (temporary suspension of fuel injection) at the time of deceleration, it is also possible to perform turbine speed-up control by using fuel cut information. It is.

Hereinafter, the second embodiment, that is, turbine speed-up control using fuel cut information will be described.
Referring to FIG. 7, a control routine of the turbine speed-up control using the fuel cut information is shown in a flowchart. Hereinafter, the operation and effect of the second embodiment of the present invention will be described based on the flowchart.

First, in step S70, it is determined whether or not the engine speed Ne is higher than a predetermined low speed Ne0 (for example, 3000 rpm) as in the case of the first embodiment. Engine 1 if the determination result is true (Yes)
If the engine is rotating at high speed, the routine proceeds to step S90, where the control flag F2 for the two-stage combustion is reset to a value of 0, and in step S92, normal engine control according to the fuel injection mode setting map is performed. Do.

On the other hand, if the determination result of step S70 is false (N
If it is determined in o) that the engine 1 is rotating at a low speed, the process proceeds to step S72. In step S72, it is determined whether the vehicle is in a deceleration state and a fuel cut is being performed. If the determination is false (No), and it is determined that the fuel cut has not been performed, the process proceeds to step S74.

In step S74, it is determined whether or not the state has been returned from the fuel cut (temporary release of the suspension of the fuel injection). Immediately after the start of the control routine, the vehicle is not in a state of returning from the fuel cut. In this case, the determination result of step S74 is false (No), and the normal engine control is performed in step S92 after step S90. I do.

On the other hand, if the decision result in the step S72 is true (Y
If it is determined in es) that the fuel cut has been performed, the process proceeds to step S76, and it is determined whether or not a predetermined time ta has elapsed after the start of the fuel cut. The predetermined time ta is, for example, a time until the combustion stops due to the execution of the fuel cut, the exhaust pressure in the exhaust pipe 20 gradually decreases, and the turbine rotational speed Rt reaches the minimum level.
When it is determined that the determination result is false (No) and the predetermined time ta has not yet elapsed, the routine is repeatedly executed as it is.

On the other hand, if the decision result in the step S76 is true (Y
If it is determined in es) that the predetermined time ta has elapsed, the process proceeds to step S78, where two-stage combustion control is performed. The two-stage combustion control is as described in the first embodiment, and the description is omitted here. However, when a predetermined time ta has elapsed after the fuel cut was started, that is, the turbine rotation speed By starting two-stage combustion in advance of the actual acceleration at the time when Rt becomes the minimum, the turbocharger 40 can be efficiently rotated at a high speed as needed during acceleration from the fuel cut state to increase the charging efficiency. Therefore, the acceleration performance from the fuel cut state can be reliably improved.

In the first embodiment, the two-stage combustion control is started at the same time as the start of the acceleration. Therefore, as shown in FIG. The main injection of the main combustion is switched from the compression stroke to the intake stroke when the time measured by the timer TM exceeds the predetermined time t1, but in the second embodiment, two main injections are performed before the start of acceleration. Since the combustion control is started, the timer TM measures the time from the start of acceleration based on acceleration information from the throttle sensor 11a.

When the vehicle shifts from the deceleration state to the acceleration state and returns from the fuel cut, the determination result of step S72 is false (No) through step S70, and the determination result of step S74 is true (Yes). In this case, the process proceeds to step S80. In step S80, it is determined whether or not a predetermined time tb has elapsed after returning from the fuel cut. That is, it is determined whether or not the vehicle is in an initial acceleration state after the start of acceleration by returning from the fuel cut. If the determination result is false (No) and the predetermined time tb has not yet elapsed after the return from the fuel cut, and the vehicle is in the initial acceleration state, the two-stage combustion is continuously performed in step S78.

On the other hand, if the decision result in the step S80 is true (Y
If it is determined in es) that the predetermined time tb has elapsed after the return from the fuel cut, that is, if it is determined that the vehicle has exited the initial acceleration state and is sufficiently accelerated, then the process proceeds to step S82. To stop (end) the two-stage combustion,
The control flag F2 relating to the two-stage combustion set to the value 1 is reset to the value 0.

In the next step S84, as in the case of the first embodiment, the turbine rotational speed Rt is reduced to a predetermined value Rt1.
It is determined whether or not it is higher than the predetermined value. If the determination result is true (Yes) and it is determined that the turbine rotation speed Rt is higher than the predetermined value Rt1, the two-stage mixing control is performed in step S86. The method of estimating the turbine rotation speed Rt and the two-stage mixing control are as described above, and the description is omitted here. In the case where the two-stage combustion is completed, knocking is preferably generated even when the turbine rotational speed Rt is large, the charging efficiency is high, and the internal pressure of the combustion chamber 8 is extremely high due to the two-stage combustion. Can be suppressed.

On the other hand, if the control routine is repeatedly executed and the result of the determination in step S84 is false (No) and it is determined that the turbine rotational speed Rt is equal to or less than the predetermined value Rt1,
There is no need for two-stage mixing, and normal engine control is performed in step S92 after step S90. In each of the above-described embodiments, during turbine speed-up control, step S10
In the determination in step S12, the two-stage combustion control is performed when the engine rotation speed Ne is low and the target average effective pressure Pe is low, or when the engine rotation speed Ne is low and the deceleration fuel cut is performed, the turbine rotation speed Rt is considered to be low. However, if possible, the turbine rotational speed Rt may be directly detected, and the two-stage combustion may be performed when the turbine rotational speed Rt is smaller than a predetermined value Rt0. In this case, as described above, the turbine rotation speed Rt may be estimated based on the Kalman frequency information detected by the air flow sensor 16.

In each of the above embodiments, the engine 1 is a direct injection type gasoline engine. However, the same effect can be obtained even if the engine 1 is a direct injection type internal combustion engine similar to a gasoline engine. Can be However, since the exhaust temperature of a diesel engine tends to be low overall, a gasoline engine having a high exhaust temperature is better as the engine 1 even in a low rotation speed and low load range.

[0062]

As described above in detail, according to the in-cylinder injection type internal combustion engine of the first aspect of the present invention, the additional fuel is surely reburned upstream of the turbine to increase the exhaust pressure in the exhaust passage. The rotation speed of the turbine can be increased. This makes it possible to increase the supercharging pressure of the intake air, improve the charging efficiency in the combustion chamber, increase the output of the internal combustion engine, and reduce the engine speed and the specific speed at which the turbine speed of the supercharging means decreases. Even when accelerating from a range, an acceleration feeling with good acceleration response can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a direct injection internal combustion engine according to the present invention.

FIG. 2 is a flowchart illustrating a control routine of turbine speed-up control at a low rotation speed and a low load according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating a control routine for two-stage combustion.

FIG. 4 shows that the engine rotation speed Ne is a predetermined low rotation speed Ne0.
FIG. 7 is a diagram showing a relationship between a target average effective pressure Pe, a turbine rotation speed Rt (a), and an exhaust gas temperature Tex (b) when the value is lower than the above value (for example, 2000 rpm).

FIG. 5 is a diagram showing a relationship between a turbine rotation speed Rt and a Kalman frequency with respect to an engine rotation speed Ne and a target average effective pressure Pe.

FIG. 6 is a flowchart illustrating a routine for estimating a turbine rotation speed Rt.

FIG. 7 is a flowchart showing a control routine of turbine speed-up control at the time of fuel cut according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 engine (in-cylinder injection type internal combustion engine) 4 spark plug (ignition plug) 6 fuel injection valve 11a throttle sensor 12 intake pipe 16 air flow sensor 20 exhaust manifold (exhaust passage) 22 exhaust pipe 26 crank angle sensor 40 turbocharger Means) 41 Turbine 50 Electronic control unit (ECU)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 23/02 F02D 41/02 325A 41/02 325 325D 41/34 E 41/34 H 43/00 301H 43 / 00 301 301J 301R F02B 37/12 301S (72) Inventor Joji Matsubara 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Tadakuni Takeda 5-33 Shiba, Minato-ku, Tokyo No. 8 F-term in Mitsubishi Motors Corporation (Reference) 3G005 EA04 EA16 FA04 GB24 GD02 GD13 GD17 GE01 GE09 HA02 HA05 JA06 JA39 JA45 JA51 JB20 3G084 AA00 AA04 BA08 BA13 BA15 CA03 CA04 CA09 DA01 DA05 DA11 DA38 FA07 FA10 FA33 AFA3A38 A013 AA09 AA18 BA05 BA06 BA07 BA09 BB02 BB06 BB10 BB13 DB03 EA08 EA17 EC01 FA01 FA05 FA16 GA05 GA12 GA14 GA17 HA01Z HA07Z HA17X HE01Z H E03Z HF12Z HF26Z 3G301 HA01 HA04 HA11 HA16 JA01 JA03 JA22 KA08 KA12 KA24 LB04 MA11 MA18 MA26 PA05Z PA11Z PE01Z PE03Z

Claims (1)

[Claims] 1. A supercharging means for driving a turbine by exhaust energy to supercharge intake air, a fuel injection valve for injecting fuel directly into a combustion chamber, and a specific operation for reducing an engine speed and a speed of the turbine. Operating range determining means for determining whether or not the operation is in the range, and when the operating range determining means determines that the operation is in the specific operating range, after the main injection of fuel into the combustion chamber by the fuel injection valve. And a turbine speed increasing means for injecting additional fuel by the fuel injection valve at a time when the fuel can be reburned in the combustion chamber or in an exhaust passage near the combustion chamber. .