JP3695493B2 - In-cylinder injection internal combustion engine control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a direct injection internal combustion engine that can optimally set the fuel injection timing in the compression stroke injection mode in the direct injection internal combustion engine and improve fuel consumption and stabilize combustion.
[0002]
[Related background]
Recently, a so-called in-cylinder injection gasoline engine that directly injects fuel into a combustion chamber in place of a conventional intake pipe injection type internal combustion engine in order to reduce harmful exhaust gas components from the internal combustion engine and improve fuel efficiency. (Internal combustion engine) has been proposed and put into practical use.
Incidentally, in-cylinder injection gasoline engines, for example, by injecting fuel from a fuel injection valve into a cavity provided at the top of a piston, an air-fuel ratio mixture close to the stoichiometric air-fuel ratio is generated around the spark plug at the time of ignition. Yes. As a result, reliable ignition is possible even with a lean air / fuel ratio as a whole, CO and HC emissions can be reduced, and fuel efficiency during idling and low-load running can be greatly improved. Moreover, acceleration / deceleration responsiveness can be improved because there is no fuel transfer delay through the intake pipe when the fuel injection amount is increased or decreased.
[0003]
However, since the fuel is directly injected into the cavity, the air-fuel ratio in the vicinity of the spark plug may become overrich during high load operation where the required fuel injection amount increases, for example, and misfire may occur. In order to solve such a problem, for example, Japanese Patent Application Laid-Open Nos. 5-79370 and 7-102976 disclose a compression stroke injection mode (late injection mode) and an intake stroke injection mode (previous injection mode) according to the load. ) Is proposed.
[0004]
Specifically, during low-load operation, fuel is injected into a cavity made of a deep dish or a concave groove during the compression stroke, so that the air-fuel ratio (weight of air and fuel) is close to the theoretical air-fuel ratio around the spark plug. Ratio) mixture is locally formed [compression stroke injection mode]. On the other hand, during high-load driving, fuel is injected outside the cavity during the intake stroke to form a uniform air-fuel ratio mixture over the entire combustion chamber. The fuel is burned [intake stroke injection mode].
[0005]
[Problems to be solved by the invention]
By the way, in the cylinder 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 injection end timing is such that the fuel injection ends during the intake stroke or the compression stroke. Is determined. 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, in order to reliably vaporize the fuel in the cavity at the time of ignition and avoid incomplete combustion, the above-mentioned injection ends after taking into account the time required for fuel vaporization and the time required for the spray to diffuse. The timing and the injection start timing are determined.
[0006]
However, in the compression stroke injection mode, the fuel vaporization rate and the spray diffusion rate are likely to change under the influence of the ambient temperature, specifically the in-cylinder temperature in the internal combustion engine. It became clear.
That is, in order to collect the spray in a compact manner and carry it near 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. Furthermore, the fuel vaporization rate is more advantageous in terms of securing the temperature for vaporization as it approaches the compression top dead center where the compression pressure increases. For these reasons, the optimum injection timing to be set varies depending on the internal combustion engine temperature.
[0007]
For this reason, for example, when the temperature of the internal combustion engine is low, such as during warm-up operation, it is difficult to locally form an optimal air-fuel ratio mixture around the spark plug due to insufficient fuel vaporization. As a result, poor combustion (misfire) may occur, and harmful exhaust gas components may increase somewhat. Therefore, conventionally, during the warm-up, the compression stroke injection mode, which is susceptible to the influence of combustion due to the change in the optimal injection timing, is prohibited and the intake stroke injection mode is set. However, there is a strong demand from the viewpoint of fuel consumption and the like to set the compression stroke injection mode even during warm-up to reduce harmful exhaust gas components and improve fuel consumption.
[0008]
The present invention has been made in consideration of such circumstances, and its purpose is to effectively prevent misfire 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. An object of the present invention is to provide a control device for a direct injection internal combustion engine that can be suppressed to a low level.
[0009]
[Means for Solving the Problems]
  In order to achieve the above-described object, the present invention controls a direct injection internal combustion engine capable of selectively switching a plurality of fuel injection modes including a compression stroke injection mode in which fuel is mainly injected in a compression stroke according to an operating state. Involved in the equipment,
  In particular, the fuel injection start timing in the compression stroke injection mode is set as the timing at which the fuel injection ends during the compression stroke according to the amount of injected fuel, assuming that the in-cylinder injection internal combustion engine is warmed up. Means, temperature detecting means for detecting the engine temperature of the direct injection internal combustion engine, and the detected engine temperatureWhen the temperature is lower than the temperature after the warm-up, a correction amount T indicating a retardation that is obtained in advance according to the engine temperature as a value inherent to the direct injection internal combustion engine and a correction coefficient K1 according to the engine speed And the fuel injection start timing T determined by the injection timing setting means in accordance with the correction coefficient K2 corresponding to the engine load. inj The
T inj = T inj + T ・ K1 ・ K2
Correct asAnd a correction means.
[0010]
That is, when the compression stroke injection mode is set, it becomes a reference in the compression stroke injection mode.The fuel injection start timing is based on the premise that the in-cylinder injection internal combustion engine is after warm-up,Depending on the amount of fuel injectedAs the timing when the fuel injection ends during the compression strokeThe temperature of the in-cylinder injection internal combustion engine is detected as, for example, the engine cooling water temperature, and the temperature isFuel injection start timeIs corrected according to the characteristics inherent to the direct injection internal combustion engine, so that the fuel vaporization state and the spray diffusion state at the time of ignition are optimized without regard to the temperature of the direct injection internal combustion engine. In addition, a local and ideal air-fuel ratio mixture is formed to effectively suppress misfires and generation of harmful exhaust gas components.
[0011]
  In particular, when the engine temperature is at least lower than the temperature after warm-up, the fuel injection start timing is determined in advance in the correction means as a fuel vaporization rate specific to the in-cylinder injection internal combustion engine, which is obtained in advance. Depending on the characteristics indicated by the fuel stratificationDelay angle correctionIt is characterized by doing.
[0012]
  Furthermore, as shown in claim 3, the correction means is adapted to the fuel injection timing.Delay angle correction amountA means for defining the maximum value is provided so that excessive retardation correction that deviates from the compression stroke injection mode is prevented.
  In the cylinder injection internal combustion engine, the higher the engine temperature is, the better the fuel vaporization rate is when the fuel injection timing is advanced. When the engine temperature is low, the fuel injection timing is increased regardless of the fuel injection timing. The fuel vaporization rate does not change, the fuel stratification is the same regardless of the engine temperature, and the fuel stratification increases when the fuel injection timing is retarded.Become.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a control apparatus for a direct injection internal combustion engine according to an embodiment of the present invention will be described 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 drawings, 1 is an in-cylinder injection type in-line four-cylinder gasoline engine (hereinafter abbreviated as an engine) according to an embodiment, and an intake device, an EGR device, and the like including a combustion chamber are dedicated to in-cylinder injection. Designed to.
[0014]
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, so that fuel is directly injected into the combustion chamber 5. It has become. A hemispherical cavity 8 is formed on the top surface of the piston 7 slidably held by the cylinder 6 at a position where fuel spray from the fuel injection valve 4 reaches later in the compression stroke. ing. Incidentally, the compression ratio of the engine 1 is set to be higher (about 12 in this embodiment) than that of a general intake pipe injection type. Further, a DOHC four-valve type is adopted as the valve operating mechanism, and an intake side camshaft 11 and an exhaust side camshaft 12 are respectively provided above the cylinder head 2 so as to drive the intake and exhaust valves 9 and 10 respectively. It is held rotatably.
[0015]
On the other hand, an intake port 13 is formed in the cylinder head 2 in a substantially upright direction so as to pass between the cam shafts 11 and 12. The intake air flow that has passed through the intake port 13 generates a reverse tumble flow that will be described later in the combustion chamber 5. Further, the exhaust port 14 is formed in a substantially horizontal direction as in a normal (intake pipe injection type) engine, but a large-diameter EGR port 15 (not shown in FIG. 2) is obliquely below the exhaust port 15. Z) is provided in a branched manner.
[0016]
In the figure, 16 is a water temperature sensor for detecting the engine cooling water temperature Tw, and 17 is a vane type crank angle sensor for outputting a crank angle signal SGT at a predetermined crank position (for example, BTDC 5 ° and BTDC 75 °) of each cylinder. Reference numeral 19 denotes an ignition coil that outputs a high voltage to the spark plug 3. Also, a cylinder discriminating sensor (not shown) that outputs a cylinder discriminating signal SGC is attached to the camshaft that rotates at half the number of revolutions of the crankshaft, and it is discriminated which cylinder the crank angle signal SGT belongs to. It is like that.
[0017]
As shown in FIG. 2, the intake port 13 is connected to an air flow sensor 32, an air cleaner 22, a throttle body 23, and a step motor type first air bypass valve (# 1ABV) via an intake manifold 21 having a surge tank 20. ) 24 is connected to the intake pipe 25. Further, the intake pipe 25 is provided with a large-diameter air bypass pipe 26 that bypasses the throttle body 23 and introduces intake air into the intake manifold 21. Two air bypass valves (# 2ABV) 27 are provided. 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 intake amount required in the low and medium speed range of the engine 1 is taken. It plays the role of distributing Qi as appropriate.
[0018]
The throttle body 23 includes a butterfly throttle valve 28 that opens and closes the flow path, a throttle sensor 29 that detects the opening θTH of the throttle valve 28, and an idle switch that detects the fully closed state of the throttle valve 28. 30 is provided. Actually, the throttle sensor 29 outputs a throttle voltage VTH corresponding to the opening degree θTH, and the throttle opening degree θTH is recognized based on the throttle voltage VTH. The air flow sensor 32 detects the intake air amount Qa. For example, a Karman vortex air flow sensor is used. The intake air amount Qa may be obtained from a suction pressure detected by the boost pressure sensor by attaching a boost pressure sensor to the surge tank 20.
[0019]
Further, the exhaust port 14 has O₂An exhaust pipe 43 including a three-way catalyst 42 and a muffler (not shown) is connected through an exhaust manifold 41 to which the sensor 40 is attached. The EGR port 15 is connected to the upstream side of the intake manifold 21 via a large-diameter EGR pipe 44, and a step motor type EGR valve 45 is provided in the pipeline.
[0020]
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 fed 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 the first fuel pressure regulator 54 interposed in the conduit of the return pipe 53. The fuel fed to the engine 1 side is fed from the high-pressure fuel pump 55 attached to the cylinder head 2 to the fuel injection valves 4 via the high-pressure feed pipe 56 and the delivery pipe 57.
[0021]
The fuel pressure in the delivery pipe 57 is adjusted to a relatively high pressure (high fuel pressure) by the second fuel pressure regulator 59 interposed in the pipe line of the return pipe 58. The electromagnetic fuel pressure switching valve 60 attached to the second fuel pressure regulator 59 plays a role of relieving the fuel in the on state and reducing the fuel pressure in the delivery pipe 57 to a low fuel pressure. Further, 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.
[0022]
An engine control unit (ECU) 70 that controls the overall control of the engine 1 includes an input / output device (not shown), a storage device (ROM, RAM, etc.) that stores a control program and a control map, and a central processing unit (CPU). , Timer counter and the like. The ECU 70 inputs detection information from the various sensors described above, determines the fuel injection mode, the fuel injection amount, the ignition timing, the EGR gas introduction amount, and the like, and the fuel injection valve 4 and the ignition coil 19. , EGR valve 45 and the like are driven and controlled. The ECU 70 is connected to a number of switches (not shown) and other sensors, and various warning lights, devices, and the like.
[0023]
Next, a basic engine control flow in the 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 and supplies the fuel injection valve 4 with low fuel pressure. When the ignition key is started in this state, the engine 1 is cranked by a cell motor (not shown), and at the same time, 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 also low, the ECU 70 injects the fuel so that the air-fuel ratio becomes relatively rich. In addition, since the second air bypass valve 27 is closed by the ECU 70 at the time of starting, the intake air to the combustion chamber 5 is supplied from the clearance 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 the valve opening amounts are determined according to the necessary introduction amount of intake air (bypass air) that bypasses the throttle valve 28, respectively. Is done.
[0024]
When the start is completed and the engine 1 starts idling, the high pressure fuel pump 55 starts the rated discharge operation. In response to this, the ECU 70 turns off the fuel pressure switching valve 60 and supplies high pressure fuel to the fuel injection valve 4. To do. Then, until the engine coolant temperature Tw rises to a predetermined value, the ECU 70 injects fuel in the same way as at the time of starting to ensure a rich air-fuel ratio, and the second air bypass valve 27 is also closed continuously. Incidentally, the control of the idle speed according to the increase / decrease of the load of the auxiliary function products such as the air conditioner is performed by the first air bypass valve 24 as in the intake pipe injection type. Furthermore, when a predetermined cycle elapses,₂When the sensor 40 is activated, the ECU 70₂Air-fuel ratio feedback control is started according to the output voltage of the sensor 40, and harmful exhaust gas components are purified by the three-way catalyst 42. As described above, when the engine is cold, substantially the same fuel injection control as that of the intake pipe injection type engine is performed.
[0025]
On the other hand, when the warm-up of the engine 1 is completed, the ECU 70, for example, a fuel injection control map shown in FIG. 3 based on the target average effective pressure Pe obtained from the intake air amount Qa or the throttle opening θTH and the engine rotational speed Ne. The current fuel injection control region is retrieved from Then, the fuel injection mode, the fuel injection amount and the fuel injection timing are respectively determined and the fuel injection valve 4 is driven. Further, in connection with this, opening / closing control of the first and second air bypass valves 24 and 27 and the EGR valve 45 is also performed. Naturally, the fuel injection amount is proportional to the valve opening time width of the fuel injection valve 4.
[0026]
Incidentally, in a low load range such as during idling or low speed running, the ECU 70 selects the compression stroke injection mode because it is a compression lean range as shown in the map of FIG. Then, the second air bypass valve 27 is opened, and fuel is injected so that a lean average air-fuel ratio (for example, about 30 to 40) is obtained. Then, since the fuel vaporization rate at this time is increasing, the intake air flow that flows in 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, an air-fuel mixture in the vicinity of the theoretical air-fuel ratio is formed in a layer around the spark plug 3 at the time of ignition, and ignition is possible even with a lean air-fuel ratio as a whole. In this state, control of the idle speed according to increase / decrease in load of the auxiliary function products is performed by increasing / decreasing the fuel injection amount, for example. 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 significantly reduce NOx.
[0027]
On the other hand, in the medium load region such as when driving at a constant speed, the ECU 70 selects the intake stroke injection mode because it becomes the intake lean region or stoichiometric feedback region in FIG. 3 according to the load state and the engine speed Ne. Then, fuel is injected so that a predetermined air-fuel ratio is obtained. 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 are set so that the air / fuel ratio becomes relatively lean (for example, about 20 to 23). Control the injection amount. In the stoichiometric feedback region, the second air bypass valve 27 and the EGR valve 45 are controlled to open and close.₂Air-fuel ratio feedback control is performed according to the output voltage of the sensor 40.
[0028]
In this case, ignition is possible even at a lean air-fuel ratio due to the effect of turbulence caused by the reverse tumble flow formed by the intake air flow that flows from the intake port 13. Further, in the stoichiometric feedback region, the harmful exhaust gas component is purified by the three-way catalyst 42 and the EGR valve 45 is controlled to introduce the appropriate amount of EGR gas into the combustion chamber 5 to generate NOx generated as harmful exhaust gas. Etc. can be reduced.
[0029]
In the high load range such as during sudden acceleration or high speed running, the open loop control range shown in FIG. 3 is established, so the ECU 70 selects the first injection mode and closes the second air bypass valve 27, Fuel is injected so that the air-fuel ratio becomes relatively rich according to the throttle opening θTH, the engine speed Ne, and the like. Note that the ECU 70 stops fuel injection because the fuel cut region shown in FIG. This fuel cut is immediately stopped when the engine rotational speed Ne falls below the return rotational speed or when the accelerator pedal is depressed.
[0030]
Basically, as described above, in a direct injection internal combustion engine in which a plurality of fuel injection modes are selectively switched according to the operating state, fuel injection in the compression stroke injection mode according to an embodiment of the present invention is performed. The correction of the fuel injection timing based on the setting of the timing and the internal combustion engine temperature detected from the engine coolant temperature Tw and the like is performed as follows.
[0031]
FIG. 4 shows an example of the control procedure, which starts from detecting the operating state of the internal combustion engine [Step S1]. This operation state is detected by determining a specific cylinder for crank rotation based on the crank angle signal SGT and cylinder discrimination signal SGC corresponding to each cylinder described above, detecting the engine speed Ne, and opening the throttle valve 28. This is performed by detecting the degree θTH and its fully closed state, and further detecting the intake air amount Qa. 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.
[0032]
Thereafter, it is determined which fuel injection mode is set or which fuel injection mode should be selected [step S2]. If the compression stroke injection mode is set, the compression stroke shown below is performed. Controls fuel injection. In addition, when the above-described intake stroke injection mode or the air-fuel ratio feedback control mode in the stoichiometric region is selected and set, control according to each of these modes is executed, but here it is not directly related to the gist of the present invention. Therefore, the description is omitted.
[0033]
When the compression stroke injection mode is set, the reference fuel injection timing and ignition timing are first 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 ratio (weight ratio of air and fuel) close to is locally formed, and the timing is set.
[0034]
That is, on the premise that the engine is in a steady operation state, the opening time of the fuel injection valve required to inject the fuel amount into the cylinder is obtained from the fuel pressure and the required fuel injection amount, and the fuel is discharged during the compression stroke. The injection end timing is determined so that the injection ends. 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, taking into account the time required for vaporizing the fuel in the cylinder and the time required for the diffusion of 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 the timing at which the air-fuel mixture in the vicinity of the stoichiometric air-fuel ratio is locally formed in a layered manner around the spark plug.
[0035]
As described above, if the fuel injection timing Tinj and the ignition timing Tig in the compression stroke injection mode assuming that the engine is in a steady operation state are set as the reference timing, then the actual engine temperature is detected next. Performed [step S4]. Specifically, the engine temperature is detected by detecting the aforementioned engine coolant temperature Tw. Then, 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 change in the state of the air-fuel mixture around the spark plug caused by the fuel vaporization rate and diffusivity that change depending on the atmosphere Correction calculation for Tig is performed [step S5].
[0036]
For example, as shown in FIGS. 5A, 5B, and 5C, the correction calculation is performed in advance with the fuel injection timing Tinj set for the engine coolant temperature Tw, which is obtained in advance as a characteristic unique to the engine. Based on the advance / retard angle correction amount T of the ignition timing Tig, the correction coefficient K1 set according to the engine speed Ne, and the correction coefficient K2 set according to the engine load,
Tinj = Tinj + T ・ K1 ・ K2
Tig = Tig + T ・ K1 ・ K2
This is done by performing a correction calculation. In this example, the correction process for the fuel injection timing Tinj and the correction process for the ignition timing Tig are corrected using the same correction amount. However, the correction amounts for these are set separately while being correlated with each other. Of course, it is also possible.
[0037]
That is, when considering the fuel vaporization rate and the fuel stratification in the cylinder according to the fuel injection timing, the characteristics differ slightly depending on the engine type, and in a certain type of engine, as shown in FIGS. 6 (a) and 6 (b). In other types of engines, the characteristics shown in FIGS. 7A and 7B are obtained. 6A and 7A show the fuel vaporization rate according 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. Shows that. FIG. 6B and FIG. 7B 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. (The degree of stratification is large) or evenly diffused throughout the combustion chamber (the degree of stratification is small).
[0038]
Therefore, 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. Indicated. That is, it is shown that the fuel is easily vaporized because the temperature of the air sucked into the combustion chamber is high, and that the vaporization rate is further improved when the fuel injection timing is advanced so as to secure a large 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 deteriorate so much. Indicated. That is, it is considered that the fuel that is difficult to vaporize because the temperature of the air sucked into the combustion chamber is low, and the factor that promotes the vaporization of the fuel is rather due to a temperature increase due to compression of the air sucked into the combustion chamber. Therefore, at such a low temperature, even if the fuel injection timing is delayed, it can be said that the fuel vaporization rate does not have much influence.
[0039]
On the other hand, the fuel stratification is substantially the same regardless of the engine temperature, and when the fuel injection timing is retarded, the fuel stratification tends to increase. In the compression stroke injection mode, the combustion condition is not established below a predetermined stratification level. Therefore, it is necessary to set the fuel injection timing so as to be at a predetermined stratification level or higher. However, since the stratification according to the fuel injection timing changes with engine manufacturing errors and changes over time, in practice, when obtaining a predetermined stratification, allow some margin. It is necessary to set the fuel injection timing.
[0040]
In consideration of the above, in an engine having the characteristics shown in FIGS. 6A and 6B, the optimum fuel injection timing at a high temperature is such that a certain degree of fuel vaporization rate is ensured and the stratification degree is It is desirable to set in a range that does not decrease so much. However, since the optimum fuel injection timing varies depending on the engine type and the like, it may of course be set to the advance side or the retard side with respect to the timing illustrated 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, the vaporization rate is significantly lower than that at the high temperature, so that combustion may become unstable. 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 delay of the fuel injection timing at low temperatures. It is possible to stabilize the combustion only.
[0041]
On the other hand, in the 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 (advanced). It shows that the evaporation rate is improved. However, when the engine temperature is low, the vaporization rate is slightly improved by advancing the fuel injection timing, although not as much as when 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 taken into the combustion chamber is slightly higher than that of the engine described above. Specifically, compared to the engine having the characteristics shown in FIGS. 6A and 6B, for example, the in-cylinder flow of fuel is relatively small, and the fuel is relatively adiabatic at low temperatures. Since it is vaporized by the in-cylinder air, it is considered that the vaporization rate can be increased by extending the vaporization time according to the advance angle of the fuel injection timing.
[0042]
In addition, the stratification in this engine is substantially the same regardless of the engine temperature, and it is shown that there is almost no change in the stratification even if the fuel injection timing is retarded to some extent. Such a tendency is particularly remarkable in an engine in which the in-cylinder flow of fuel is relatively small. Therefore, in the engine having the characteristics shown in FIGS. 7 (a) and 7 (b), as in the case of the engine described above, the optimum fuel injection timing at a high temperature ensures a certain degree of fuel vaporization rate and is stratified. It can be said that it is desirable to set a range in which the degree does not decrease so much. On the other hand, when the engine temperature is low, if the fuel vaporization rate is improved by advancing the fuel injection timing, there is almost no deterioration of the stratification due to the advance of the fuel injection timing. It becomes possible to stabilize combustion.
[0043]
The above-described correction of the fuel injection timing is made on the basis of such a viewpoint, and the correction as shown in FIGS. 5A, 5B, and 5C, which is obtained in advance according to the type of the engine. It is executed based on the function.
The advance / retard angle correction amount T with respect to the engine coolant temperature Tw, which is this correction function, will be described briefly. In the case of this engine, the advance / retard angle correction amount T is exemplified in FIG. Thus, when the engine cooling water temperature Tw is lower than the above-mentioned water temperature after warming up with reference to the water temperature after warming up in which the engine 1 operates stably, combustion is stabilized by retarding the fuel injection timing Tinj (retarding). It can be shown that Conversely, when the engine cooling water temperature Tw becomes higher than the water temperature after warming up to some extent, it is shown that the advance of the fuel injection timing Tinj can stabilize the combustion. It is. The advance / retard angle correction amount T with respect to the fuel injection timing Tinj is basically determined on the basis of the engine-specific characteristics as shown in FIG. 5 (a) in accordance with the engine temperature (engine coolant temperature Tw). The The advance / retard angle correction amount T is set after a maximum value is defined under a predetermined condition for realizing the compression stroke injection (clip control).
[0044]
On the other hand, the correction coefficient K1 related to the engine speed Ne and the correction coefficient K2 related to the engine load are used to correct the advance / retard angle correction amount T according to the operating state of the engine. These correction coefficients K1 and K2 are also obtained in advance as characteristics unique to the engine. In particular, the correction coefficient K1 is set so as to increase the advance / retard angle correction amount T when the engine speed Ne exceeds 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.
[0045]
In the correction calculation shown in step S5 described above, first, the fuel injection timing Tinj optimized in the compression stroke injection mode in the stable operation state of the engine according to the characteristics shown in FIG. Is obtained based on the engine coolant temperature Tw. This correction amount is obtained as an advance / retard time T based on the crank angle, for example, CA 5 °, CA 10 °, etc. Then, the correction coefficients K1 and K2 are obtained from the characteristics shown in FIGS. 5 (a) and 5 (b) in order to correct the advance / retard time T according to 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.
[0046]
At this time, the ignition timing Tig is set so that the air-fuel mixture mass injected into the cylinder is ignited before it diffuses. Specifically, as described above, the ignition timing Tig is used in order to ensure that the fuel injected at the timing of the advance / retard correction is sufficiently vaporized in the cylinder and to ignite surely and realize stable combustion. Also, the advance / retard control is performed according to the engine coolant temperature Tw described above.
[0047]
When the fuel injection timing is corrected as described above, the injected fuel easily collides with the cavity 8 on the top surface of the piston 7, but the injection timing is in a state where the in-cylinder pressure is high as described above. As a result, the fuel immediately vaporizes to form an air-fuel mixture. Therefore, there is no problem that the injected fuel adheres to the cavity 8 or the like and the combustion deteriorates.
[0048]
If the timing is determined by correcting the advance / retard angle of the fuel injection timing Tinj and the ignition timing Tig according to the engine coolant temperature Tw as described above, the compression stroke injection mode is set under the set timing. The fuel injection control and the ignition control are executed at [Step S6]. 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.
[0049]
Thus, as described above, the fuel injection timing Tinj and the ignition timing Tig in the compression stroke injection mode are corrected in accordance with the internal combustion engine temperature (engine cooling water temperature Tw), so that the air-fuel mixture with the air-fuel ratio optimized is stably formed. According to this apparatus that performs control so as to ignite, for example, even when the engine is warmed up immediately after the engine is started and the engine temperature is low, the fuel injected into the cylinder can be reliably burned. It becomes.
[0050]
As shown in FIGS. 8 (a) and 8 (b), an experimental example of misfire frequency and NOx emission in the compression stroke injection mode when the internal combustion engine is at a low temperature (35 ° C.), the steady state after the internal combustion engine is warmed up. The fuel injection timing and the ignition timing are retarded (for example, 5 ° retard, 8 ° retard) as compared with the case where the control is performed under the fuel injection timing and the ignition timing that are calculated assuming the operating state. By doing so, the frequency of misfires can be suppressed, and the amount of NOx emissions can also be suppressed. In particular, by adding correction control for the EGR amount in addition to the above-described correction control for the fuel injection timing Tinj and the ignition timing Tig, for example, it is possible to achieve an effect that the misfire frequency can be further reduced. In other words, even when the engine is warming up, the fuel injection timing and the ignition timing can be retarded (retarded) so that the operation in the effective compression stroke injection mode can be realized, thereby improving the fuel consumption. It becomes possible.
[0051]
In addition, this invention is not limited to embodiment mentioned above. For example, the advance / retard angle 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 / retard angle correction amount may be set within a timing range that does not deviate from the compression stroke injection mode conditions. What is necessary is just to determine according to a characteristic etc. Further, regarding the engine coolant temperature, the correction amount T and the correction coefficients K1 and K2 may be previously mapped on a table and obtained from the map data. In addition, the present invention can be implemented with various modifications within the scope of the gist.
[0052]
【The invention's effect】
  As described above, according to the present invention, in the in-cylinder injection internal combustion engine capable of selectively switching a plurality of fuel injection modes including the compression stroke injection mode in which fuel is mainly injected in the compression stroke according to the operation state, The reference fuel injection start timing in the compression stroke injection mode is set as a timing at which the fuel injection ends during the compression stroke according to the amount of injected fuel, assuming that the in-cylinder injection internal combustion engine is warmed up. The fuel injection start timing is determined according to the engine temperature of the direct injection internal combustion engine.Delay angle correctionTherefore, the fuel vaporization state and the spray diffusion state at the time of ignition can be optimized and the combustion can be stabilized and ensured without regard to the temperature of the direct injection internal combustion engine. Further, it is possible to improve fuel efficiency while effectively suppressing misfire and generation of harmful exhaust gas components. In particular, there is a great practical effect that the operation in the compression stroke injection mode at the time of the warm-up operation at a low internal combustion engine temperature is possible.
[0053]
Further, as shown in claim 2, when the engine temperature is lower than the temperature after warm-up, the fuel injection timing is corrected in advance / retarded according to the characteristic of the engine, so that stable combustion (simple and effective) ( Driving). Furthermore, as shown in claim 3, since the means for defining the maximum value of the advance / retard angle correction amount is provided, excessive advance / retard angle correction that deviates from the compression stroke injection mode is effectively prevented. Thus, there is an effect that it is possible to realize the operation in the stable compression stroke injection mode.
[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 a direct injection gasoline engine according to an embodiment of the present invention.
FIG. 3 is a diagram showing an example of an operating range of fuel injection control in a direct injection gasoline engine.
FIG. 4 is a diagram showing an example of a control procedure of fuel injection timing and ignition timing in a compression stroke injection mode according to the embodiment.
FIG. 5 is a view showing an example of correction data used in the control process shown in FIG. 4;
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 graph showing the relationship between fuel vaporization rate and fuel stratification with respect to fuel injection timing in another type of engine.
FIG. 8 is a characteristic diagram of misfire frequency and NOx emission showing the effect of retarding control of fuel injection timing and ignition timing at low temperatures.
[Explanation of symbols]
1 engine
2 Cylinder head
3 Spark plug
4 Fuel injection valve
5 Combustion chamber
6 cylinders
7 Piston
8 cavities
13 Intake port
70 ECU

Claims (4)

A direct injection internal combustion engine capable of selectively switching a plurality of fuel injection modes including a compression stroke injection mode in which fuel is mainly injected in a compression stroke according to an operating state,
The fuel injection start timing used as a reference in the compression stroke injection mode is regarded as the timing at which the fuel injection ends during the compression stroke according to the amount of fuel injected, assuming that the in-cylinder injection internal combustion engine is warmed up. An injection timing setting means for setting, a temperature detection means for detecting the engine temperature of the direct injection internal combustion engine, and when the detected engine temperature is lower than the temperature after the warm-up, the direct injection internal combustion engine is set in advance. It is obtained by the injection timing setting means in accordance with a correction amount T indicating a retard angle obtained as a unique value according to the engine temperature, a correction coefficient K1 according to the engine speed, and a correction coefficient K2 according to the engine load. the fuel injection start timing T inj, which is
T inj = T inj + T ・ K1 ・ K2
A control device for a direct injection internal combustion engine, comprising: a correcting means for correcting as follows .   When the engine temperature is lower than the temperature after warm-up, the correction means is configured to perform the fuel injection according to a characteristic indicated by a fuel vaporization rate and a fuel stratification specific to the in-cylinder injection internal combustion engine that are obtained in advance. 2. The control apparatus for a direct injection internal combustion engine according to claim 1, wherein the start timing is corrected for delay.   2. The control apparatus for a direct injection internal combustion engine according to claim 1, wherein the correction means includes means for defining a maximum value of a correction amount of retardation with respect to a fuel injection start timing.   In the in-cylinder injection internal combustion engine, the higher the engine temperature, the better the fuel vaporization rate when the fuel injection timing is advanced, and the fuel vaporization regardless of the fuel injection timing when the engine temperature is low. The fuel stratification is the same regardless of the engine temperature, and the fuel stratification increases when the fuel injection timing is retarded. The control apparatus of the cylinder injection internal combustion engine of 1-3.

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