JP3873500B2 - In-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a direct injection internal combustion engine that directly injects fuel into a combustion chamber using a high-pressure pump driven by the engine.
[0002]
[Prior art]
Currently, in-cylinder injection internal combustion engines that inject fuel directly into the combustion chamber have been put into practical use. In such in-cylinder injection internal combustion engines, the timing of fuel injection can be freely set. When the required output is sometimes obtained, fuel injection is performed during the intake stroke, and fuel efficiency is improved by a lean combustion operation by premixed combustion. Furthermore, in the low-load operation region, fuel injection is performed in the compression stroke, and an air-fuel mixture with sufficient fuel concentration for ignition is partially collected in the vicinity of the spark plug, so that ultra-lean combustion by so-called stratified combustion is performed. The fuel consumption is improved.
[0003]
In order to realize such lean combustion, it is essential to atomize the fuel injected into the combustion chamber. In addition, in order to perform ultra lean combustion by stratified combustion, it is also necessary to inject fuel during a high pressure compression stroke. Therefore, in this type of internal combustion engine, fuel that has been pressurized to a high pressure by a high-pressure pump is supplied to a fuel injection valve, and this high-pressure fuel is injected, thereby enabling reliable fuel injection even during a high-pressure compression stroke. The atomization of fuel is aimed at. As a high-pressure pump used in a direct injection internal combustion engine, for example, as described in Japanese Patent Laid-Open No. 9-42095, fuel is sucked by reciprocation of a single or a plurality of pistons driven by the internal combustion engine.・ There is something to discharge.
[0004]
[Problems to be solved by the invention]
However, in the high-pressure pump as described above, fuel is supplied to the injection valve by reciprocating movement of the piston, etc., so that a cycle corresponding to the engine rotation is provided in the fuel pipe between the high-pressure pump and the injection valve. Fuel pressure pulsation will occur. For this reason, when the injection timing varies widely (for example, from the latter half of the exhaust stroke to the latter half of the compression stroke) as in a cylinder injection type internal combustion engine, the low fuel pressure time becomes the injection period or the high fuel pressure depends on the injection timing. Time is the injection period. For this reason, even in the same drive time, the amount of fuel injected from the injection valve differs depending on the injection timing, causing a problem that the air-fuel ratio shifts.
[0005]
The present invention has been made in view of such problems, and an object of the present invention is to provide an in-cylinder injection internal combustion engine that can suppress the deviation of the air-fuel ratio due to fuel pressure pulsation.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, in the direct injection internal combustion engine of the present invention, high pressure fuel is supplied to an injection valve for directly injecting fuel into a combustion chamber of the internal combustion engine by a fuel pump driven by the engine, The control means controls the operation timing of the injection valve according to the operation state of the engine, and the fuel injection amount control means controls the fuel injection from the injection valve based on the operation state of the engine and the operation timing of the injection valve. Control the amount. In the fuel injection amount control means, when the fuel injection amount is controlled, an injection center timing which is an intermediate crank angle between the injection start timing and the injection end timing is used as the operation timing of the injection valve. Further, the fuel injection amount control means has a map showing the relationship between the fuel injection amount correction coefficient and the injection center time, reads the correction coefficient corresponding to the injection center time from the map, and reads the read correction coefficient. Is multiplied by the basic fuel amount calculated based on the operating state of the engine to correct the fuel amount, and the fuel injection amount from the injection valve is controlled based on the corrected fuel amount.
[0007]
Thereby, increase / decrease in the fuel injection amount due to the fuel pressure pulsation generated in conjunction with the drive of the fuel pump by the engine is suppressed .
Further, it is preferable that the fuel injection amount control means corrects the correction coefficient for correcting the fuel amount based on the throttle position and the water temperature of the engine.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
1 to 7 show a direct injection internal combustion engine as an embodiment of the present invention, and FIG. 1 is a diagram showing a schematic configuration thereof.
As shown in FIG. 1, the in-cylinder injection internal combustion engine is an internal combustion engine that has intake, compression, expansion, and exhaust strokes in one operation cycle, that is, a four-cycle engine, is a spark ignition type, and A cylinder injection type internal combustion engine that directly injects fuel into the combustion chamber is configured.
[0009]
As a mode of fuel injection, for example, a late lean injection mode in which fuel is injected during the compression stroke (particularly in the latter half of the compression stroke) in order to realize lean operation by stratified combustion and improve fuel efficiency, and lean by premixed combustion. In order to realize the operation and obtain the output by slow acceleration, the first term lean injection mode in which fuel is injected during the intake stroke (particularly the first half of the intake stroke) and the stoichiometric operation (theoretical air-fuel ratio operation) by premixed combustion are realized. In order to improve the output from the injection mode, a stoichiometric mode in which fuel is injected during the intake stroke is provided, and is selected according to the operating state of the engine.
[0010]
The configuration of the cylinder injection internal combustion engine (hereinafter referred to as the engine) 1 will be described in detail. As shown in FIG. 1, an intake port 6 and an exhaust port 7 are provided in the combustion chamber 3 in the cylinder head 2 of the engine 1. The intake port 6 is controlled to be communicated by driving an intake valve 8, and the exhaust port 7 is controlled to be communicated by driving an exhaust valve 9. The upper part of the cylinder head 2 is provided with an intake side camshaft 10 having an intake side cam 10A and an exhaust side camshaft 11 having an exhaust side cam 11A, and the intake valve 8 is driven by the rotation of the intake side cam 10A. The exhaust valve 9 is driven by the rotation of the exhaust side cam 11A.
[0011]
The cylinder head 2 is provided with a spark plug 4 at the center of the top of the combustion chamber 3 for each cylinder, and an injector (injection valve) 5 is provided in the combustion chamber 3 on the intake port 6 side of the combustion chamber 3. It is arranged to face. The injector 5 used here needs to be selected in consideration of the controllability of the operation timing and the injection amount and the atomization of the fuel. For example, an electromagnetic swirl injector can be applied.
[0012]
The fuel to be injected from the injector 5 is supplied from the fuel tank 13. A high-pressure pump (fuel pump) 12 is provided on a fuel pipe 14 connecting the injector 5 and the fuel tank 13, and the fuel in the fuel tank 13 is given a predetermined pressure (for example, After being pressurized to 5 MPa), it is supplied to the injector 5. The high-pressure pump 12 can be applied to a single plunger pump that sucks and discharges fuel by reciprocating movement of one piston, or a multi-plunger pump that sucks and discharges fuel by reciprocating movement of a plurality of pistons. Then, the case where a single plunger pump is applied is demonstrated.
[0013]
The high pressure pump 12 is provided at the shaft end of the intake side camshaft 10, and the piston in the high pressure pump reciprocates in conjunction with the rotation of the intake side camshaft 10. In the case of a single plunger pump, pulsation is generated in conjunction with the reciprocation of the piston in the pressure (fuel pressure) of the discharged fuel, but here the reciprocation of the piston is in conjunction with the rotation of the intake side camshaft 10, Since the intake side camshaft 10 is interlocked with the crankshaft 18, the pulsation of the fuel pressure is generated in conjunction with the rotation of the crankshaft 18.
[0014]
In particular, since the operation of the piston of the single plunger pump is set so as to be interlocked with the operation of the piston of each cylinder, in a four-cylinder engine, the piston of the single plunger pump is set to 720 ° CA / 4 = 180 ° CA as one cycle. Operate.
For example, FIG. 2 shows the fuel pressure of the fuel discharged from the high-pressure pump 12 in the case of a four-cylinder engine with respect to the crank angle of the crankshaft 18. As shown in FIG. ° Pulsation occurs in CA cycle. Incidentally, in the case of a 6-cylinder engine, fuel pressure pulsation occurs at a 120 ° CA cycle from 720 ° CA / 6 = 120 ° CA.
[0015]
Incidentally, 15 provided on the fuel pipe 14 is a high-pressure regulator, and 16 is a low-pressure regulator. In addition, a fuel supply pump (low pressure pump) 17 is provided in the fuel tank 13. This is because the high pressure pump 12 is not driven sufficiently when the engine 1 is extremely low, such as when the engine is started. Since the fuel supply amount to the injector 5 is insufficient, the fuel is supplied by the fuel supply pump 17 at that time. For this reason, the high-pressure regulator 15 is provided with a fuel bypass valve.
[0016]
Control of the injector 5, that is, control of the operation timing and the fuel injection amount is performed by an ECU (control means) 25. The ECU 25 includes an operation mode selection unit 26, an injection timing control unit 27, and a fuel injection amount control unit 28 as functional elements. The ECU 25 includes a crank angle sensor 19, a water temperature sensor 20, and other sensors such as a TPS (throttle position sensor). The injector 5 is controlled based on the detected information.
[0017]
First, the operation mode selection means 26 selects one mode corresponding to the operation state from the above-described operation modes. The operating state is determined from the engine speed Ne and the average effective pressure Pe, the detection information of the crank angle sensor 19 is used for the engine speed Ne, and the throttle detected by the engine speed Ne and TPS is used for the average effective pressure Pe. What is calculated based on each information of the opening degree θ is used.
[0018]
The injection timing control unit 27 controls the operation timing (injection timing) of the injector 5 according to the operation mode selected by the operation mode selection unit 26. For example, when the selected operation mode is the late lean injection mode, the operation timing of the injector 5 is set to the latter half of the compression stroke, and when the selected operation mode is the lean lean injection mode, it is set to the first half of the intake stroke. It is designed to be set during the intake stroke. However, the injection timing set by the injection timing control means 27 here refers to the injection end timing at which a series of fuel injection ends, and is read from a map stored in advance according to the operation mode.
[0019]
The fuel injection amount control unit 28 controls the injected fuel amount according to the operation mode selected by the operation mode selection unit 26. For example, in the case of the early lean injection mode, a lean target air-fuel ratio is set, and the fuel amount is set from the intake air amount and the target air-fuel ratio. In the case of the late lean injection mode, a leaner target air-fuel ratio is set. The fuel amount is set from the intake air amount and the target air-fuel ratio, and in the stoichiometric mode, the fuel amount is feedback-controlled based on an O ₂ sensor output (not shown) so as to be the stoichiometric air-fuel ratio. Then, the drive time of the injector 5 (injection pulse width input to the injector 5) is converted based on a predetermined average fuel pressure (for example, 5 MPa) according to the set fuel amount.
[0020]
However, as shown in FIG. 2, pulsation occurs in the fuel pressure of the fuel discharged from the high-pressure pump 12, and accordingly, the amount of fuel injected from the injector 5 also increases or decreases. For this reason, when the fuel pressure at the time of injection is substantially equal to the predetermined average fuel pressure, it is possible to obtain a desired air-fuel ratio, but when the difference between the fuel pressure at the time of injection and the predetermined average fuel pressure is large, A deviation occurs in the air-fuel ratio.
[0021]
Therefore, the fuel injection amount control means 28 performs correction in consideration of fuel pressure pulsation as follows.
First, considering the characteristics of the pulsation of the fuel pressure, as described above, the pulsation is generated in a cycle of 180 ° CA in conjunction with the rotation of the crankshaft 18. Therefore, it is possible to estimate the fuel pressure from the output of the crank angle sensor 19.
[0022]
However, when the fuel injection period is represented by a crank angle, the fuel injection period (crank angle) changes depending on the engine speed Ne even when the drive time of the injector 5 is the same. That is, if the engine speed Ne is doubled, the fuel injection period is also doubled, and the fuel amount is increased or decreased by the pulsation of the fuel pressure during that period.
[0023]
For example, FIG. 3 shows a fuel amount ratio (320 ° to the injection end timing with the same injection pulse width) based on a predetermined fuel amount (amount of fuel actually injected) when the injection end timing is set to 320 ° BTDC. The ratio to the fuel amount during BTDC is determined under the conditions of engine speed Ne (1000, 3000, 4000 rpm), volumetric efficiency Ev (40, 60%, throttle valve fully open: hot), and water temperature Tw (hot: temperature). It is measured. The volumetric efficiency Ev indicates the ratio of the volume of fresh air sucked in with respect to the stroke volume of the engine 1, and this is calculated based on the throttle opening θ detected by the TPS.
[0024]
In this case, as shown in FIG. 3, the characteristics of the fuel amount ratio with respect to the injection end timing greatly change depending on the engine speed Ne, the volumetric efficiency Ev, and the water temperature Tw, and do not show a constant tendency. For this reason, it is not sufficient to correct only the pulse width of the injector 5 from the fuel pressure at the injection end timing. In this case, further correction is required according to the engine speed Ne, the volumetric efficiency Ev, and the water temperature Tw.
[0025]
On the other hand, FIG. 4 is an arrangement of the characteristic chart of the fuel amount ratio with respect to the injection end timing shown in FIG. 3 on the basis of the injection center timing. The injection center time is obtained by calculating back the injection start time from the injection end time, the injection pulse width, and the engine speed Ne, and taking an intermediate crank angle between the injection start time and the injection end time. In this case, as shown in FIG. 4, the characteristic of the fuel amount ratio with respect to the injection center timing shows a substantially constant tendency regardless of the engine speed Ne, the volumetric efficiency Ev, and the water temperature Tw. Therefore, for example, as shown in FIG. 5, the characteristic of the fuel amount ratio with respect to the injection center timing can be approximated by a single curve.
[0026]
Therefore, the fuel injection amount control means 28 shows the relationship between the injection center timing and the correction coefficient (coefficient corresponding to the reciprocal of the fuel amount ratio ) based on the characteristics shown in FIG. 5 with reference to the injection center timing. A map is provided, and a correction coefficient corresponding to the injection center timing is read from the map, and the fuel quantity (injection pulse) is calculated by multiplying the read correction coefficient by the basic fuel quantity (basic injection pulse width) calculated based on the operating state. (Width) is corrected. However, as shown in FIG. 4, the amplitude of the fuel amount ratio varies depending on the volume efficiency Ev and the water temperature Tw. Therefore, the variation in the amplitude is corrected based on the output of the TPS and the output of the water temperature sensor 20. Shall.
[0027]
Since the direct injection internal combustion engine as one embodiment of the present invention is configured as described above, fuel injection control is performed, for example, according to the flow shown in FIG. Hereinafter, the fuel amount correction method shown in FIGS. 7A to 7D will be described together with an explanatory diagram for explaining the method.
As shown in FIG. 6, first, an operation mode is selected by the operation mode selection means 26 based on the engine rotation Ne and the average effective pressure Pe (step S100). Then, the injection timing control means 27 reads out the injection timing (injection end timing X ° CA) corresponding to the selected operation mode from the map [FIG. 7 (a), step S110] and the fuel injection amount control means 28. A basic fuel amount (basic injection pulse width) corresponding to the operating state is calculated (step S120).
[0028]
When the injection end timing X ° CA and the basic fuel amount are calculated, the injection start timing Y ° CA is calculated in consideration of the engine speed Ne [FIG. 7 (b)]. Then, the injection center timing Z ° CA [= (X + Y) ° CA / 2] is calculated from the injection start timing Y ° CA and the injection end timing X ° CA, and a correction coefficient corresponding to the injection center timing Z ° CA is mapped. It reads out from (a map in which a correction coefficient for the injection center timing is determined) [FIG. 7 (c), step S130].
[0029]
By recalculating the fuel amount (injection pulse width) by multiplying the read correction coefficient by the basic fuel amount, and setting the most calculated fuel amount (injection pulse width) with reference to the injection start timing Y ° CA The injection end timing X ° CA is corrected, and the corrected injection end timing XX ° CA is set [FIG. 7 (d), step S140]. Then, fuel injection from the injector 5 is started from the calculated injection start timing Y ° CA, and the fuel injection is ended at the corrected injection end timing XX ° CA (step S150).
[0030]
As described above, according to the cylinder injection internal combustion engine, the fuel pressure of the fuel discharged from the high pressure pump 12 is estimated from the crank angle, and the injection pulse width of the injector 5 is corrected in consideration of the fuel pressure. Therefore, the fuel injection amount can be prevented from increasing or decreasing depending on the injection timing due to the pulsation of the fuel pressure, and there is an advantage that highly accurate air-fuel ratio control can be realized. As a result, it is possible to suppress smoke at low water temperatures that occurs when the air-fuel ratio becomes too dense and knocking at high temperatures that occurs when the air-fuel ratio becomes too thin.
[0031]
Further, in the cylinder injection internal combustion engine, correction by the fuel pressure is performed with reference to the injection center timing, so that the influence of the engine speed Ne is removed from the relationship of the fuel amount ratio with respect to the fuel injection engine. For example, it is possible to control by a single map in all the engine speed Ne ranges, and there is an advantage that the cost for creating the map and the cost of the RAM for storing the map can be reduced.
[0032]
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, three modes of the late injection mode, the early injection mode, and the stoichiometric mode are listed as the operation mode. However, this is merely an example, and control is performed by dividing into more detailed modes. Of course it is possible.
[0033]
Moreover, although the case where the single plunger pump was applied as the high pressure pump 12 was demonstrated, it is also possible to apply a multi plunger pump. In the case of the multi-plunger pump, the pulsation of the fuel pressure is small compared to the single plunger pump, but even in this case, there is an advantage that more accurate air-fuel ratio control can be realized by applying the present invention.
[0034]
In the above-described embodiment, correction is performed over the entire area of fuel injection. However, when the fuel amount is increased from the basic fuel amount, the fuel is injected without correction and the fuel is insufficient. You may make it correct | amend only to. This also makes it possible to suppress misfire due to fuel shortage and knocking at high temperatures.
[0035]
【The invention's effect】
As described above in detail, according to the direct injection internal combustion engine of the present invention, the fuel injection amount from the injection valve is set based on the operating state of the internal combustion engine and the operation timing of the injection valve. The fuel pressure pulsation generated when the fuel pump is driven by the engine can suppress the increase or decrease in the fuel injection amount depending on the operation timing of the injection valve, and the advantage that highly accurate air-fuel ratio control can be realized. is there.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a direct injection internal combustion engine as an embodiment of the present invention.
FIG. 2 is a view showing pulsation of fuel pressure applied to a direct injection internal combustion engine as one embodiment of the present invention.
FIG. 3 is a diagram showing the influence of fuel pressure pulsation when the injection end timing of the direct injection internal combustion engine according to the embodiment of the present invention is used as a reference.
FIG. 4 is a diagram showing the influence of fuel pressure pulsation when the injection center timing applied to the direct injection internal combustion engine as one embodiment of the present invention is used as a reference.
FIG. 5 is a diagram showing an example of a correction coefficient map for the injection center timing in the direct injection internal combustion engine according to the embodiment of the present invention.
FIG. 6 is a flowchart showing the flow of fuel injection control for a direct injection internal combustion engine according to an embodiment of the present invention.
FIG. 7 is a view for explaining a fuel amount correction method for a direct injection internal combustion engine according to an embodiment of the present invention.
[Explanation of symbols]
1 engine (internal combustion engine)
2 Cylinder head 3 Combustion chamber 4 Spark plug 5 Injector (injection valve)
12 High-pressure pump (fuel pump)
13 Fuel tank 14 Fuel pipe 20 Water temperature sensor 25 ECU
27 Injection timing control means 28 Fuel injection amount control means

Claims (2)

An injection valve for directly injecting fuel into the combustion chamber of the internal combustion engine;
A fuel pump driven by the engine to supply high pressure fuel to the injection valve;
Injection timing control means for controlling the operation timing of the injection valve in accordance with the operating state of the engine;
Fuel injection amount control means for controlling the fuel injection amount from the injection valve based on the operating state of the engine and the operation timing of the injection valve;
In the fuel injection amount control means,
When controlling the fuel injection amount, as the operation timing of the injection valve, an injection center timing that is an intermediate crank angle between the injection start timing and the injection end timing is used .
A map showing the relationship between the fuel injection amount correction coefficient and the injection center time is prepared, the correction coefficient corresponding to the injection center time is read from the map, and the read correction coefficient is calculated based on the operating state of the engine A direct injection internal combustion engine, wherein a fuel amount is corrected by multiplying a basic fuel amount, and a fuel injection amount from the injection valve is controlled based on the corrected fuel amount . Fuel injection amount control means, the correction coefficient for correcting the amount of fuel, characterized by using on corrected based on the throttle position and coolant temperature of the engine, cylinder injection type internal combustion engine according to claim 1.

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