JPH10141115A - Control device for in-cylinder injection internal combustion engine - Google Patents

Abstract

(57) [Problem] To effectively suppress the occurrence of misfires and harmful exhaust gas components in the compression stroke injection mode regardless of the operating state of a direct injection internal combustion engine. SOLUTION: In a cylinder injection internal combustion engine operating by selectively switching a plurality of fuel injection modes, an injection timing setting means for setting a fuel injection timing in a compression stroke injection mode in accordance with an injected fuel amount; Means for correcting the fuel injection timing according to the engine temperature of the internal injection internal combustion engine. In particular, when the temperature of the internal combustion engine is lower than the temperature after warm-up, the fuel injection timing is retarded so that the fuel is injected at the time when the in-cylinder pressure increases, so that the vaporization is performed well. It is characterized by the following.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control of a direct injection internal combustion engine in which the fuel injection timing in a compression stroke injection mode in a direct injection internal combustion engine can be optimized to improve fuel efficiency and stabilize combustion. Related to the device.

[0002]

2. Related Background Art In recent years, in order to reduce harmful exhaust gas components from an internal combustion engine and improve fuel efficiency, fuel is directly injected into a combustion chamber instead of a conventional general intake pipe injection type internal combustion engine. A so-called in-cylinder injection gasoline engine (internal combustion engine) has been proposed and put into practical use. By the way, in a direct injection gasoline engine, for example, by injecting fuel from a fuel injection valve into a cavity provided at the top of the piston, an air-fuel mixture having an air-fuel ratio close to the stoichiometric air-fuel ratio is generated around the ignition plug during ignition. I have. As a result, even if the air-fuel ratio is lean as a whole, reliable ignition can be achieved, the emission amount of CO and HC can be reduced, and the fuel efficiency during idling operation or low-load running can be greatly improved. Moreover, even when the fuel injection amount is increased or decreased, there is no delay in fuel transfer by the intake pipe, so that acceleration / deceleration responsiveness can be improved.

However, on the other hand, since fuel is directly injected into the cavity, the air-fuel ratio in the vicinity of the spark plug becomes over-rich during, for example, a high load operation in which the required fuel injection amount increases, and there is a possibility that a misfire may occur. In order to solve such a problem, for example, Japanese Patent Application Laid-Open Nos.
Japanese Patent Application Laid-Open No. -1029776 proposes switching between a compression stroke injection mode (late injection mode) and an intake stroke injection mode (early injection mode) according to the load.

More specifically, during low-load operation, fuel is injected into the cavity formed by the deep plate and the concave groove during the compression stroke, so that the air-fuel ratio (air and fuel) close to the stoichiometric air-fuel ratio around the spark plug is obtained. (Compressed stroke injection mode). On the other hand, during high load traveling, fuel is injected outside the cavity during the intake stroke to form an air-fuel mixture having a uniform air-fuel ratio over the entire area of the combustion chamber. [Intake stroke injection mode].

[0005]

In a direct injection gasoline engine, after the opening time of the fuel injection valve is set based on the fuel pressure and the required fuel injection amount, the fuel is injected during the intake stroke and the compression stroke. Is determined so that the injection ends. Further, the injection start timing is determined based on the injection end timing and the valve opening time. In particular, in the compression stroke injection mode, the injection is terminated after taking into account the time required for fuel vaporization and the time required for diffusion of the spray in order to reliably vaporize the fuel in the cavity at the time of ignition and avoid incomplete combustion. The timing and the injection start timing are determined.

However, in the compression stroke injection mode, the present inventors have found that the vaporization rate of fuel and the diffusion rate of spray are liable to change under the influence of the ambient temperature, specifically, the cylinder temperature in an internal combustion engine. A study by the authors. That is, in order to collect the spray compactly and carry it to the vicinity of the spark plug, it is preferable to retard the injection timing within a range where the spray reaches the spark plug. In order to sufficiently vaporize the fuel, it is preferable to advance the injection timing. Further, as the fuel vaporization rate approaches the compression top dead center at which the compression pressure increases, it is more advantageous in terms of securing a temperature for vaporization. Due to these causes, the optimum injection timing to be set varies depending on the internal combustion engine temperature.

For this reason, when the temperature of the internal combustion engine is low, for example, during a warm-up operation, the air-fuel mixture having the optimum air-fuel ratio is locally formed around the spark plug due to insufficient fuel vaporization. It was difficult to form, and poor combustion (misfire) occurred, and harmful exhaust gas components increased in some cases. For this reason, in the related art, during the warm-up period, the compression stroke injection mode, which is likely to affect the combustion due to the change of the optimal injection timing, is prohibited, and the intake stroke injection mode is set.
However, from the viewpoint of fuel efficiency and the like, there is a strong demand to set the compression stroke injection mode even during warm-up to reduce harmful exhaust gas components and improve fuel efficiency.

The present invention has been made in view of such circumstances, and has as its object to generate misfires and generation of harmful exhaust gas components in the compression stroke injection mode regardless of the operating state of the direct injection internal combustion engine. It is an object of the present invention to provide a control device for a direct injection internal combustion engine, which can effectively suppress the occurrence of pressure.

[0009]

In order to achieve the above object, the present invention selectively switches a plurality of fuel injection modes including a compression stroke injection mode for injecting fuel mainly in a compression stroke in accordance with an operation state. More specifically, the present invention relates to a control device for a direct injection internal combustion engine, particularly an injection timing setting means for setting a fuel injection timing in a compression stroke injection mode according to an amount of injected fuel, and detecting an engine temperature of the direct injection internal combustion engine It is characterized by comprising temperature detecting means and correcting means for correcting the fuel injection timing determined by the injection timing setting means according to the detected engine temperature.

That is, when the compression stroke injection mode is set, the reference fuel injection timing in the compression stroke injection mode is set according to the amount of injected fuel, and the temperature of the direct injection internal combustion engine is set to, for example, engine cooling water. By detecting the temperature as a temperature and correcting the fuel injection timing in accordance with the characteristic characteristic of the direct injection internal combustion engine in accordance with the temperature, the fuel injection timing at the time of ignition is independent of the temperature of the direct injection internal combustion engine. Optimization of the vaporization state and the diffusion state of the spray to form a local and ideal air-fuel mixture around the spark plug to effectively suppress misfires and the generation of harmful exhaust gas components. It is a feature.

In particular, as set forth in claim 2, the injection timing setting means calculates a fuel injection timing in a steady operation state of the in-cylinder injection internal combustion engine after warm-up, and based on this fuel injection timing, The correction means is characterized in that when at least the engine temperature is lower than the post-warm-up temperature, the fuel injection timing is advanced or retarded in accordance with the characteristic characteristic of the direct injection internal combustion engine.

Further, the correction means is provided with means for defining the maximum value of the advance or retard correction amount with respect to the fuel injection timing, whereby an excessive delay such as to deviate from the compression stroke injection mode is provided. The feature is that angle correction is prevented.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A control device for a direct injection internal combustion engine according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall system configuration diagram of a direct injection internal combustion engine, and FIG. 2 is a longitudinal sectional view of a main part of the direct injection internal combustion engine (gasoline engine). In these figures, reference numeral 1 denotes an in-cylinder in-line type four-cylinder gasoline engine (hereinafter simply referred to as an engine) for an automobile according to the embodiment, in which a combustion chamber, an intake device, an EGR device, etc. Designed for

That is, in this embodiment, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 4 together with a spark plug 3 for each cylinder.
The fuel is directly injected into the inside. A hemispherical cavity 8 is formed on the top surface of the piston 7 slidably held by the cylinder 6 at a position where the fuel spray from the fuel injection valve 4 reaches in the latter stage of the compression stroke. ing. Incidentally, the compression ratio of the engine 1 is set higher (about 12 in this embodiment) than that of a general intake pipe injection type. In addition, DO as the valve mechanism
The HC4 valve type is adopted, and the cylinder head 2
In order to drive the intake and exhaust valves 9 and 10 respectively,
An intake side camshaft 11 and an exhaust side camshaft 12 are each held rotatably.

On the other hand, an intake port 13 is formed in the cylinder head 2 in a substantially upright direction so as to pass through between the camshafts 11 and 12. This intake port 13
The intake air flow that has passed through generates a reverse tumble flow described later in the combustion chamber 5. Although the exhaust port 14 is formed in a substantially horizontal direction similarly to a normal (intake pipe injection type) engine, a large-diameter EGR port 15 (shown in FIG. ) Is provided in a branched manner.

In the figure, reference numeral 16 denotes a water temperature sensor for detecting an engine cooling water temperature Tw. Reference numeral 17 denotes a vane type crank which outputs a crank angle signal SGT at a predetermined crank position of each cylinder (for example, BTDC 5 ° and BTDC 75 °). Angle sensor,
Reference numeral 19 denotes an ignition coil that outputs a high voltage to the ignition plug 3. A cylinder discrimination sensor (not shown) that outputs a cylinder discrimination signal SGC is attached to a camshaft that rotates at half the number of revolutions of the crankshaft, and discriminates which cylinder the crank angle signal SGT belongs to. It has become.

As shown in FIG. 2, an air flow sensor 32, an air cleaner 22, a throttle body 23, and a first air bypass valve of a step motor type are connected to an intake port 13 via an intake manifold 21 having a surge tank 20. An intake pipe 25 having (# 1ABV) 24 is connected. Further, the intake pipe 25 is provided around the intake manifold 21 so as to bypass the throttle body 23.
A large-diameter air bypass pipe 26 for introducing the intake air is provided along with a large second air bypass valve (# 2ABV) 27 of a linear solenoid type. The air bypass pipe 26 has a flow passage area similar to that of the intake pipe 25. When the second air bypass valve (# 2ABV) 27 is fully opened, the engine 1
Of the intake air required in the low to medium speed range.

The throttle body 23 has a butterfly type throttle valve 28 for opening and closing its flow path, a throttle sensor 29 for detecting the opening θTH of the throttle valve 28, and detecting a fully closed state of the throttle valve 28. An idle switch 30 is provided. Note that the opening degree θTH is actually obtained from the throttle sensor 29.
Is output, and the throttle opening .theta.TH is recognized based on the throttle voltage VTH. The airflow sensor 32 detects the intake air amount Qa, and for example, a Karman vortex airflow sensor is used. For the intake air amount Qa, a boost pressure sensor is attached to the surge tank 20,
It may be determined from the suction pipe pressure detected by the boost pressure sensor.

Further, an exhaust pipe 43 having a three-way catalyst 42 and a muffler (not shown) is connected to the exhaust port 14 via an exhaust manifold 41 to which an O ₂ sensor 40 is attached.
Is connected. The EGR port 15 is connected to the upstream of the intake manifold 21 via a large-diameter EGR pipe 44, and a step motor type EGR valve 45 is provided in a pipe line thereof.

The fuel stored in a fuel tank 50 installed at the rear of the vehicle body (not shown) is sucked up by an electric low-pressure fuel pump 51 and supplied to the engine 1 via a low-pressure feed pipe 52. The pressure (fuel pressure) of the supplied fuel in the low-pressure feed pipe 52 is set to a relatively low pressure (low fuel pressure) by a first fuel pressure regulator 54 interposed in the return pipe 53.
The fuel supplied to the engine 1 is supplied from the high-pressure fuel pump 55 attached to the cylinder head 2 to each of the fuel injection valves 4 via the high-pressure feed pipe 56 and furthermore the delivery pipe 57.

The fuel pressure in the delivery pipe 57 is regulated to a relatively high pressure (high fuel pressure) by a second fuel pressure regulator 59 interposed in the return pipe 58.
The electromagnetic fuel pressure switching valve 60 attached to the second fuel pressure regulator 59 plays a role of reducing the fuel pressure in the delivery pipe 57 to a low fuel pressure by relieving the fuel in the ON state. The fuel that has been lubricated or cooled by the high-pressure fuel pump 55 is returned to the fuel tank 50 via the return pipe 61.

An engine control unit (ECU) 70 for overall control of the engine 1 includes an input / output device (not shown), a storage device (ROM, RAM, etc.) storing control programs and control maps, and a central processing unit. (CP
U), a timer counter and the like. And E
The CU 70 inputs the detection information from the various sensors described above, determines the fuel injection mode, the fuel injection amount, the ignition timing, the amount of EGR gas introduced, and the like.
And the ignition coil 19, the EGR valve 45, and the like. In addition, a large number of switches and other sensors (not shown) are connected to the ECU 70, and various warning lights, devices, and the like are connected to the ECU 70.

Next, the basic flow of engine control in the in-cylinder injection internal combustion engine (engine) configured as described above will be briefly described. When the ignition key is turned on when the engine is cold, the ECU 70 turns on the low-pressure fuel pump 51 and the fuel pressure switching valve 60 to supply low fuel pressure fuel to the fuel injection valve 4. When the ignition key is operated in this state, the engine 1 is cranked by a cell motor (not shown), and at the same time, the fuel injection control is started under the control of the ECU 70. However, at this time, since the fuel vaporization rate is low and the fuel pressure is low, E
The CU 70 injects fuel so as to have a relatively rich air-fuel ratio. Also, at the time of this start, the second air bypass valve 27 is closed by the ECU 70, so that the combustion chamber 5
Is supplied from the gap of the throttle valve 28 or the first air bypass valve 24. The first and second air bypass valves 24 and 27 are centrally managed by the ECU 70, and their opening amounts are determined in accordance with the required amount of intake air (bypass air) bypassing the throttle valve 28, respectively. Is done.

When the engine 1 starts idling after the start is completed, the high-pressure fuel pump 55 starts a rated discharge operation. In response to this, the ECU 70 turns off the fuel pressure switching valve 60 to apply a high pressure to the fuel injection valve 4. Supply fuel. Until the engine coolant temperature Tw rises to a predetermined value, the ECU
Numeral 70 injects fuel in the same manner as at the time of starting to secure a rich air-fuel ratio, and also closes the second air bypass valve 27 continuously. Incidentally, the control of the idle speed according to the increase or decrease of the load of the auxiliary function items such as the air conditioner is performed by controlling the first air bypass valve 2 in the same manner as the intake pipe injection type.
4 is performed. After a predetermined cycle, O ₂
When the sensor 40 is activated, the ECU 70 starts the air-fuel ratio feedback control according to the output voltage of the O ₂ sensor 40, and purifies the harmful exhaust gas component by the three-way catalyst 42. As described above, when the engine is cold, substantially the same fuel injection control as in the case of the intake pipe injection engine is performed.

On the other hand, when the warm-up of the engine 1 ends, E
CU 70 is the intake air amount Qa or the throttle opening θTH
Based on the target average effective pressure Pe obtained from the above and the engine rotation speed Ne, for example, the current fuel injection control area is searched from the fuel injection control map shown in FIG. Then, the fuel injection mode, the fuel injection amount and the fuel injection timing are determined, and the fuel injection valve 4 is driven. Further, in connection with this, the first and second air bypass valves 24 and 27 and the EGR
Open / close control of the valve 45 is also performed. It should be understood that the fuel injection amount is proportional to the valve opening time width of the fuel injection valve 4.

In the low load range such as during idling or low speed running, the ECU 70 selects the compression stroke injection mode because it is in the compression lean range as shown in the map of FIG. Then, the second air bypass valve 27 is opened to obtain a lean average air-fuel ratio (for example, about 30 to 40).
Inject fuel so that Then, since the vaporization rate of the fuel at this time is rising, the intake air flowing from the intake port 13 forms a reverse tumble flow, and the fuel spray is stored in the cavity 8 of the piston 7. As a result, at the time of ignition, an air-fuel mixture in the vicinity of the stoichiometric air-fuel ratio is formed in a layer around the spark plug 3, and ignition can be performed even with a lean air-fuel ratio as a whole. The control of the idle speed according to the increase or decrease of the load of the auxiliary function items in this state is performed, for example, by increasing or decreasing the fuel injection amount. In this control region, the ECU 70
Opens the EGR valve 45 and introduces a large amount (for example, 30% or more) of EGR gas into the combustion chamber 5 to reduce NO.
x is greatly reduced.

On the other hand, in a medium load region such as when the vehicle is traveling at a constant speed, FIG.
The ECU 70 selects the intake stroke injection mode and injects fuel so as to attain a predetermined air-fuel ratio. That is, in the intake lean region of the intake stroke injection mode, the opening amounts of the first and second air bypass valves 24 and 27 and the fuel amount are adjusted so as to obtain a relatively lean air-fuel ratio (for example, about 20 to 23). Control the injection quantity. In the stoichiometric feedback range, the second air bypass valve 27 and E
Open / close control of the GR valve 45 is performed, and air-fuel ratio feedback control is performed according to the output voltage of the O ₂ sensor 40.

In this case, it is possible to ignite even at a lean air-fuel ratio due to the effect of the turbulence caused by the reverse tumble flow formed by the intake air flowing from the intake port 13. In the stoichiometric feedback region, the harmful exhaust gas components are purified by the three-way catalyst 42, the EGR valve 45 is controlled, and an appropriate amount of EGR gas is introduced into the combustion chamber 5, whereby NOx generated as harmful exhaust gas is emitted. Etc. are reduced.

When the vehicle is in a high load region such as during rapid acceleration or high speed driving, the open loop control region shown in FIG. 3 is established. It closes and injects fuel so as to have a relatively rich air-fuel ratio according to the throttle opening θTH and the engine speed Ne. Note that the ECU 70 stops the fuel injection during the coasting operation during the middle-to-high-speed running because the fuel cut-off region is as shown in FIG. This fuel cut is immediately stopped when the engine rotation speed Ne falls below the return rotation speed or when the accelerator pedal is depressed.

Basically, as described above, in a direct injection internal combustion engine in which a plurality of fuel injection modes are selectively switched and set in accordance with an operating state, a compression stroke injection mode according to an embodiment of the present invention is used. The fuel injection timing setting and the correction of the fuel injection timing based on the internal combustion engine temperature detected from the engine coolant temperature Tw and the like are performed as follows.

FIG. 4 shows an example of the control procedure.
The process is started by detecting the operating state of the internal combustion engine [Step S1]. The detection of the operation state is performed by the above-described crank angle signal SGT and cylinder discrimination signal SGC corresponding to each cylinder.
, The specific cylinder with respect to the rotation of the crank is determined, the engine speed Ne is detected, the opening degree θTH of the throttle valve 28 and its fully closed state are detected, and the intake air amount Qa is further detected. Done. The load state of the internal combustion engine is determined according to the detection result of the operating state, and the plurality of fuel injection modes described above are selectively set.

Thereafter, it is determined which fuel injection mode is set or which fuel injection mode is to be selected [Step S2]. If the compression stroke injection mode is set, the following is performed. The compression stroke fuel injection shown is controlled. When the intake stroke injection mode and the air-fuel ratio feedback control mode in the stoichiometric range are selected and set, the control according to each of these modes is executed, but here, there is no direct relation to the gist of the present invention. Therefore, the description is omitted.

Now, when the compression stroke injection mode is set,
First, a reference fuel injection timing and ignition timing are calculated [step S3]. The calculation of the fuel injection timing and the ignition timing is based on the assumption that the engine is in a steady operation state after the warm-up operation, and the stoichiometric air-fuel ratio around the spark plug and in the cavity according to the fuel injection amount injected into the cylinder. Is calculated as a timing at which an air-fuel mixture (air / fuel weight ratio) close to the above is locally formed, and the timing is set.

That is, assuming that the engine is in a steady operation state, the opening time of the fuel injection valve required for injecting the fuel amount into the cylinder is obtained from the fuel pressure and the required fuel injection amount, and the compression stroke is determined. The injection ending timing is determined so that the fuel injection ends during the injection. Thereafter, the fuel injection start timing is determined based on the determined injection end timing and the valve opening time, and the ignition timing is determined based on the injection end timing. In particular, in this compression stroke injection mode, considering the time required for vaporizing fuel in the cylinder and the time required for dispersing the spray, the fuel in the cavity at the time of ignition is surely vaporized and the spray is diffused widely. The fuel injection timing and the ignition timing are determined as timings at which the fuel-air mixture gathers around the spark plug and locally forms a mixture near the stoichiometric air-fuel ratio in a stratified manner.

As described above, if the fuel injection timing Tinj and the ignition timing Tig in the compression stroke injection mode on the assumption that the engine is in a steady operation state are set as reference timings, then the actual engine temperature Is detected [Step S4]. Specifically, the detection of the engine temperature is performed by detecting the above-described engine cooling water temperature Tw. According to the detected engine temperature (engine cooling water temperature Tw), the fuel injection timing Tinj and the ignition timing are corrected in order to correct the state change of the air-fuel mixture around the spark plug caused by the vaporization rate and diffusion degree of the fuel, which change depending on the atmosphere. A correction operation is performed on Tig [Step S
5].

This correction calculation is performed, for example, by referring to FIGS.
As shown in (c), the fuel injection timing Tinj and the ignition timing Tig advance / lag correction amount T set with respect to the engine cooling water temperature Tw, which are obtained in advance as characteristics specific to the engine, Based on the correction coefficient K1 set in accordance with the number Ne and the correction coefficient K2 set in accordance with the engine load, a correction operation of Tinj = Tinj + T ・ K12K2 Tig = Tig + T ・ K1 ・ K2 is performed. It is done by applying. In this example, the correction process for the fuel injection timing Tinj and the ignition timing Ti
Although the correction process for g is corrected using the same correction amount, it is of course possible to set the correction amounts for these separately while associating them with each other.

That is, when considering the fuel vaporization rate and the fuel stratification in the cylinder according to the fuel injection timing, the characteristics are slightly different depending on the engine type. In a certain type of engine, FIGS. The characteristics shown in Fig. 7 (b), and in other types of engines, Figs. 7 (a) and 7 (b)
The characteristics are as shown in FIG. 6 (a) and 7 (a)
Indicates the fuel vaporization rate corresponding to the fuel injection timing, that is, how much the fuel injected into the cylinder at a certain injection timing is vaporized before being ignited by the spark plug. 6 (b) and 7 (b) show the fuel stratification according to the fuel injection timing, that is, the fuel injected into the cylinder at a certain injection timing is formed as a reduced spray in a part of the combustion chamber. Indicates whether the layer has a large degree of stratification or whether it is uniformly diffused throughout the combustion chamber (a small degree of stratification).

In the engine having the characteristics shown in FIGS. 6A and 6B, the higher the engine temperature is, the more the fuel injection timing is advanced, the higher the vaporization rate is. Is shown. That is, it is shown that the fuel is easily vaporized due to the high temperature of the air taken into the combustion chamber, and that the vaporization rate is further improved when the fuel injection timing is advanced so as to secure a long vaporization time. Further, when the engine temperature is low, the fuel vaporization rate hardly changes regardless of the fuel injection timing, and even if the fuel injection timing is retarded (retarded), the fuel vaporization rate does not significantly deteriorate. Is shown. In other words, the fuel is hardly vaporized because the temperature of the air taken into the combustion chamber is low, and it is considered that the factor that promotes the vaporization of the fuel is rather a temperature rise due to the compression of the air taken into the combustion chamber. Therefore, at such a low temperature, it can be said that retarding the fuel injection timing does not significantly affect the fuel vaporization rate.

On the other hand, the stratification of the fuel is substantially the same irrespective of the engine temperature, and the fuel stratification tends to increase when the fuel injection timing is retarded. In the compression stroke injection mode, the combustion condition is not satisfied below a predetermined stratification, so it is necessary to set the fuel injection timing so as to attain the predetermined stratification or more. However, the stratification according to the fuel injection timing changes with engine manufacturing errors and their aging, so in practice, when trying to obtain a predetermined stratification, some allowance is required. It is necessary to set the fuel injection timing.

In consideration of the above, FIG.
In the engine having the characteristic shown in FIG. 3B, it is desirable that the optimum fuel injection timing at the time of high temperature be set in a range where the fuel vaporization rate is secured to some extent and the stratification does not significantly decrease. However, since the optimum fuel injection timing varies depending on the engine type or the like, there may of course be a case where the timing is set to be more advanced or retarded than the timings shown in FIGS. 6 (a) and 6 (b). However, when the fuel is injected at the optimum fuel injection timing described above at a low temperature, there is a possibility that the combustion becomes unstable because the vaporization rate is greatly reduced as compared with the high temperature. Therefore, in this case, if the fuel stratification is improved by retarding the fuel injection timing, there is almost no deterioration in the vaporization rate due to the retardation of the fuel injection timing at low temperatures. Only the combustion can be stabilized.

On the other hand, in the case of an engine having the characteristics shown in FIGS. 7A and 7B, if the engine temperature is high as in the previous engine, the fuel injection timing is advanced.
It is shown that the vaporization rate is improved by doing so. However, when the engine temperature is low, by advancing the fuel injection timing, the vaporization rate is slightly improved, though not so much as when the engine temperature is high. That is, it can be said that the effect of improving the vaporization rate due to the temperature rise due to the compression of the air sucked into the combustion chamber is slightly higher than that of the engine described above. Specifically, FIGS. 6 (a) and 6 (b)
For example, compared to an engine having the characteristics shown in Fig. 1, the fuel in-cylinder flow is relatively small, and the fuel is vaporized by the relatively insulated in-cylinder air even at low temperatures. By increasing the vaporization time by advance,
It is believed that the vaporization rate can be increased.

It is also shown that the stratification in this engine is substantially the same irrespective of the engine temperature, and that the stratification hardly changes even if the fuel injection timing is retarded to some extent. In particular, such a tendency is remarkable in an engine in which the in-cylinder flow of fuel is relatively small. Therefore, FIG.
In the engine having the characteristics shown in (a) and (b), similarly to the engine described above, the optimum fuel injection timing at a high temperature is such that the fuel vaporization rate is secured to some extent and the stratification is significantly reduced. It can be said that it is desirable to set it in a range that does not. On the other hand, when the engine temperature is low, if the fuel injection timing is advanced to improve the fuel vaporization rate even a little, there is almost no deterioration in stratification due to the advanced fuel injection timing.
To that extent, it is possible to stabilize combustion.

The above-described correction of the fuel injection timing is based on such a viewpoint, and FIG. 5A, FIG. 5B, and FIG. This is executed based on the correction function as shown. This correction function is
The advance / retard correction amount T with respect to the engine coolant temperature Tw will be briefly described. In the case of this engine, the advance / retard correction amount T is such that the engine 1 is stable as exemplified in FIG. If the engine coolant temperature Tw is lower than the post-warm water temperature based on the operating post-warm water temperature,
It is shown that combustion can be stabilized by retarding the fuel injection timing Tinj. On the other hand, when the engine cooling water temperature Tw becomes higher than the above-mentioned water temperature by a certain degree after the warm-up, it is shown that the advance of the fuel injection timing Tinj can stabilize the combustion. It is. Advancing / retarding correction amount T for fuel injection timing Tinj
Is basically determined according to the engine temperature (engine cooling water temperature Tw) based on characteristics inherent to the engine as shown in FIG. The advance / retardation correction amount T is set after its maximum value is defined under predetermined conditions for realizing the compression stroke injection (clip control).

On the other hand, the correction coefficient K1 relating to the engine speed Ne and the correction coefficient K2 relating to the engine load are used to correct the advance / retard correction amount T according to the operating state of the engine. These correction coefficients K1,
K2 is also obtained in advance as a characteristic unique to the engine. In particular, the correction coefficient K1 is set so as to increase the advance / retard correction amount T when the engine speed Ne becomes equal to or higher than a certain speed. The correction coefficient K2 is set so as to decrease the advance / retard angle correction amount T when the engine load becomes larger than a certain level.

In the correction calculation shown in step S5, first, the fuel injection timing Tinj optimized in the compression stroke injection mode in the stable operation state of the engine should be further optimized according to the characteristics shown in FIG. 5 (a). The correction amount T is obtained based on the engine cooling water temperature Tw. This correction amount is obtained as an advance / retard time T based on the crank angle, for example, CA5 °, CA10 °, or the like. Then, the correction coefficients K1 and K2 are obtained from the characteristics shown in FIGS. 5A and 5B in order to correct the advance / retard time T according to the condition of the engine speed and the engine load as described above. By multiplying this by the advance / retard time T,
A correction amount for the fuel injection timing Tinj is determined.

At this time, the ignition timing Tig is set so that the mixture injected into the cylinder is ignited before the mass is diffused. Specifically, in order to secure sufficient time for the fuel injected at the timing of the advance / retard correction as described above to evaporate sufficiently in the cylinder, and to reliably ignite and realize stable combustion.
Regarding the ignition timing Tig, the engine cooling water temperature Tw described above is also used.
The advance / retard control is performed according to.

When the fuel injection timing is retarded as described above, the injected fuel tends to collide with the cavity 8 on the top surface of the piston 7, but the injection timing is reduced as described above. Due to the high state, the fuel vaporizes immediately to form an air-fuel mixture. Therefore, there is no problem such that the injected fuel adheres to the cavity 8 or the like and combustion deteriorates.

As described above, the fuel injection timing Tinj and the ignition timing Tig are advanced according to the engine cooling water temperature Tw.
If the timing is determined after the retard correction, the fuel injection control and the ignition control in the compression stroke injection mode are executed under the set timing [Step S
6]. Until the fuel injection mode is changed, the engine 1 is operated in the compression stroke injection mode while changing the correction amount in accordance with the change in the engine coolant temperature Tw.

As described above, the fuel injection timing Tinj and the ignition timing Tig in the compression stroke injection mode are corrected according to the internal combustion engine temperature (engine cooling water temperature Tw).
According to the present apparatus that performs control so as to ignite the air-fuel mixture after stably forming an air-fuel ratio-optimized mixture, for example, when the engine is warmed up immediately after the engine is started and the engine temperature is low. Even in this case, it is possible to reliably burn the fuel injected into the cylinder.

FIGS. 8A and 8B show that the temperature of the internal combustion engine is low (35 ° C.).
° C), the fuel injection timing calculated assuming that the internal combustion engine is in a steady operation state after a warm-up operation, as shown in an experimental example of misfire frequency and NOx emission amount in the compression stroke injection mode when Compared with the case where the control is performed under the ignition timing, the frequency of misfire can be suppressed by retard correction of the fuel injection timing and the ignition timing (for example, 5 ° retard, 8 ° retard), and NOx emission can be suppressed. The amount can be reduced. In particular, the above-described fuel injection timing T
By adding the correction control of the EGR amount in addition to the correction control of the inj and the ignition timing Tig, for example, it is possible to obtain the effect that the misfire frequency can be further reduced. In other words, even in a low-temperature period during which the warm-up operation is performed, an effective operation in the compression stroke injection mode can be realized by retarding (retarding) the fuel injection timing and the ignition timing.
It is possible to improve fuel efficiency.

Note that the present invention is not limited to the above embodiment. For example, the advance / retard correction amount for the fuel injection timing and the ignition timing may be determined according to the specifications of the internal combustion engine and the properties of the fuel. The maximum value of the advance / retardation correction amount may be set within a timing range that does not deviate from the conditions of the compression stroke injection mode, and the correction coefficients K1 and K2 based on the rotational speed and the load are also determined by the operation of the internal combustion engine. It may be determined according to characteristics and the like. The correction amount T and the correction coefficients K1 and K2 for the engine cooling water temperature may be mapped on a table in advance and obtained from the map data. In addition, the present invention can be implemented with various modifications within the scope of the gist.

[0052]

As described above, according to the present invention, a plurality of fuel injection modes including a compression stroke injection mode for injecting fuel mainly in a compression stroke can be selectively switched in accordance with an operation state. In the injection internal combustion engine, the fuel injection timing in the compression stroke injection mode when the internal combustion engine is in a stable operation state is set according to the injected fuel amount,
A means for correcting the fuel injection timing according to the engine temperature of the in-cylinder injection internal combustion engine is provided, so that regardless of the temperature of the in-cylinder injection internal combustion engine, the fuel vaporization state and spray diffusion state at the time of ignition To optimize combustion and stabilize combustion.
It can be assured. In addition, fuel efficiency can be improved while effectively suppressing misfires and the generation of harmful exhaust gas components. In particular, there is a great practical effect that the operation in the compression stroke injection mode is enabled during the warm-up operation when the temperature of the internal combustion engine is low.

Further, when the engine temperature is lower than the temperature after warm-up, the fuel injection timing is advanced / retarded according to the characteristic of the engine, so that it is simplified and effectively stabilized. Combustion (operation) can be realized. Furthermore, since means for defining the maximum value of the advance / retard correction amount is provided as set forth in claim 3, it is possible to effectively prevent excessive advance / retard correction that deviates from the compression stroke injection mode. Therefore, the effect of realizing stable operation in the compression stroke injection mode can be achieved.

[Brief description of the drawings]

FIG. 1 is an overall system configuration diagram of a direct injection internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a main part of the direct injection gasoline engine according to the embodiment of the present invention.

FIG. 3 is a diagram showing an example of an operation range of fuel injection control in a direct injection gasoline engine.

FIG. 4 is a diagram showing an example of a control procedure of a fuel injection timing and an ignition timing in a compression stroke injection mode according to the embodiment.

FIG. 5 is a diagram showing an example of correction data used in the control processing shown in FIG.

FIG. 6 is a diagram showing the relationship between fuel vaporization rate and fuel stratification with respect to fuel injection timing in a certain type of engine.

FIG. 7 is a diagram showing a relationship between a fuel vaporization rate and a fuel stratification degree with respect to a fuel injection timing in another type of engine.

FIG. 8 is a characteristic diagram showing misfire frequency and NOx emission showing the effect of retard control of fuel injection timing and ignition timing at low temperatures.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder head 3 Spark plug 4 Fuel injection valve 5 Combustion chamber 6 Cylinder 7 Piston 8 Cavity 13 Intake port 70 ECU

Claims (3)

[Claims] An in-cylinder injection internal combustion engine capable of selectively switching a plurality of fuel injection modes including a compression stroke injection mode for injecting fuel mainly in a compression stroke in accordance with an operation state, wherein the compression stroke injection mode Injection timing setting means for setting the reference fuel injection timing in accordance with the injected fuel amount,
Temperature detection means for detecting an engine temperature of the in-cylinder injection internal combustion engine; and correction means for correcting the fuel injection timing obtained by the injection timing setting means in accordance with the detected engine temperature. Control device for a direct injection internal combustion engine. 2. The injection timing setting means calculates a fuel injection timing in a steady operation state after the warm-up of the in-cylinder injection internal combustion engine, and the correction means includes at least an engine temperature after the warm-up. 2. The control apparatus for a direct injection internal combustion engine according to claim 1, wherein when the temperature is lower than the temperature, the fuel injection timing is advanced or retarded in accordance with characteristics unique to the direct injection internal combustion engine. . 3. The cylinder injection internal combustion engine according to claim 1, wherein said correction means includes means for defining a maximum value of a correction amount of an advance angle or a retard angle with respect to a fuel injection timing. Control device.