JP4547665B2 - Combustion control method of gas fuel direct injection engine - Google Patents

Description

  The present invention relates to a combustion control method for a gas fuel direct injection engine that supplies gas fuel into a cylinder.

  In recent years, so-called gas fuel engines using compressed natural gas (referred to as CNG) or hydrogen gas as fuel have been developed for energy and environmental measures. In such a gas fuel engine, a so-called port injection engine is known in which gas fuel is injected and supplied to an intake passage. By the way, in such a port injection type engine, the charging efficiency is not sufficient, and sufficient output cannot be obtained and the fuel consumption may be deteriorated.

  Therefore, Patent Document 1 discloses a control device for an internal combustion engine in which gaseous fuel is directly injected into a combustion chamber to compensate for such insufficient filling efficiency. In the control apparatus for an internal combustion engine disclosed in Patent Document 1, in order to prevent the cruising distance from being shortened as a result of the difficulty in injecting and supplying gaseous fuel as the pressure of gaseous fuel decreases, The closing timing of the intake valve is set near the intake bottom dead center so that injection from the injector is performed during the intake stroke.

  Further, in the in-cylinder injection type gas fuel engine of Patent Document 2, the in-cylinder turbulence and the mixture formation change due to the change in the spray speed due to the change in the fuel injection pressure. Techniques for dealing with changes in the optimal ignition timing are disclosed. That is, a technique for controlling the opening of the swirl control valve, the opening of the EGR valve, and the ignition timing according to the pressure of the injected gas fuel is disclosed.

JP 2000-328997 A JP 2002-221037 A

  By the way, in the gas fuel direct injection engine, the jet speed of the gas fuel injected from the injection port of the fuel injection valve is extremely high exceeding the speed of sound, and there is no speed attenuation due to vaporization. Disturbances occur. However, since this turbulence is caused by the jet, the amount of energy is small, and when the jet disappears due to the end of the injection of the gas fuel, the disturbance is fast. Therefore, if this disturbance is effectively utilized, the ignitability and combustion of the air-fuel mixture can be improved, and the engine performance can be improved. However, none of the above-mentioned Patent Documents 1 and 2 considers the effective use of this disturbance.

  In view of such circumstances, an object of the present invention is to provide a combustion control method for a gas fuel direct injection engine that leads to improved ignitability and combustion of an air-fuel mixture and can improve engine performance.

A combustion control method for a gas fuel direct injection engine according to an aspect of the present invention that achieves the above object is as follows. Gas fuel is directly injected into a cavity formed on a piston top surface by at least one direct injection injector, and ignition is performed. A gas fuel direct injection engine that performs a stratified combustion mode that forms a combustible air-fuel mixture near a plug in at least a part of an operation region,
At the time of ignition in the stratified combustion mode, from the end of fuel injection to ignition so that a combustible mixture disturbance due to the injection of the gas fuel exists in the vicinity of the spark plug and the combustible mixture remains in the vicinity of the spark plug. An interval is set.

  Here, it is preferable to change the fuel injection start timing while fixing the interval from the end of the fuel injection to the ignition based on the fuel injection amount determined according to the engine operating condition in the stratified combustion mode.

  In addition to the stratified combustion mode, a homogeneous combustion mode is provided. In the homogeneous combustion mode, the main injection is performed in the first half of the compression stroke or the first half of the intake stroke, and the interval from the end of the fuel injection to the ignition is satisfied. You may make it perform sub-injection.

  Here, it is preferable that the fuel injection amount by the main injection is set to an amount obtained by subtracting the fuel injection amount by the sub injection from the required total fuel injection amount.

  Furthermore, at the time of cold start, it is preferable to perform the main injection in the first half of the compression stroke or the first half of the intake stroke and perform the sub-injection while satisfying the interval from the end of the fuel injection to the ignition.

  The gas fuel direct injection engine may include a port injector at an intake port in addition to the direct injection injector, the main injection may be performed by the port injector, and the sub-injection may be performed by the direct injection injector. .

  Further, the gas fuel direct injection engine may include two direct injection injectors in a cylinder, and the sub injection may be performed by a direct injection injector capable of generating a stronger flammable mixture disorder. .

  Furthermore, the gas fuel direct injection engine may include a gasoline port injector at an intake port in addition to the direct injection injector.

  According to the combustion control method for a gas fuel direct injection engine according to one aspect of the present invention, the gas fuel is directly injected into the cavity formed on the top surface of the piston by at least one direct injection injector, in the vicinity of the spark plug. In a gas fuel direct injection engine that performs a stratified charge combustion mode that forms a combustible mixture in at least a part of an operating region, at the time of ignition in the stratified charge combustion mode, a disturbance of the combustible mixture due to the injection of the gas fuel is an ignition plug Since the interval from the end of fuel injection to ignition is set so that the combustible mixture remains in the vicinity of the spark plug, ignition is performed reliably and the ignited flame propagates rapidly. As a result, combustion can be improved and engine performance can be improved.

  Further, in addition to the stratified combustion mode, a homogeneous combustion mode is provided. In the homogeneous combustion mode, the main injection is performed in the first half of the compression stroke or the first half of the intake stroke, and the interval from the end of the fuel injection to the ignition is satisfied. According to the mode in which the sub-injection is performed, the ignition is reliably performed even in the homogeneous combustion mode and the ignited flame is rapidly propagated, so that the combustion can be improved and the engine performance can be improved.

  Further, at the time of low temperature start, the main injection is performed in the first half of the compression stroke or the first half of the intake stroke, and the sub-injection is performed while satisfying the predetermined value of the interval from the end of the fuel injection to the ignition. Since it can be improved and the injection amount is small, fuel consumption can be improved. Furthermore, since the ignition timing can be set to the retard side, it is advantageous for early warm-up of the catalyst and emission can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  First, an outline of a gas fuel direct injection engine 100 to which the present invention is applied will be described with reference to FIG. 101 is an engine body, 102 is a cylinder block, 103 is a cylinder head, 104 is a piston, 105 is a combustion chamber, 106 is an intake port, 107 is an exhaust port, 108I is an intake valve, 108E is an exhaust valve, 109 is in the combustion chamber 105 Each of the spark plugs arranged at the top of the is shown.

  The intake port 106 is connected to a surge tank 111 via an intake manifold 110, and the surge tank 111 is connected to an air cleaner 113 via an intake duct 112. A throttle valve 115 driven by a step motor 114 is disposed in the intake duct 112. On the other hand, the exhaust port 107 is connected to the NOx occlusion catalytic converter 118 via an exhaust manifold 116 and an exhaust pipe 117. Reference numeral 119 denotes a water temperature sensor for detecting the engine cooling water temperature.

  The engine 100 of FIG. 1 includes a gas fuel supply system that uses CNG as gas fuel. This gas fuel supply system is a direct injection of gas fuel that is disposed in a cylinder combustion chamber 105 so as to be able to inject via an injection port. A CNG direct injection injector 120 as an injector is provided, and the CNG direct injection injector 120 is connected to a CNG cylinder 124 as a gas fuel container mounted on a vehicle via a CNG supply line 122. Note that a fuel cutoff valve and a high-pressure regulator 126 (not shown) are arranged in the CNG supply line 122.

  The CNG filled in the CNG cylinder 124 at a filling pressure PF (for example, 20 MPa) is reduced to a constant high control pressure PH (for example, 5 MPa) by the high pressure regulator 126. It is injected in the compression stroke from the CNG direct injection injector 120 with the adjustment pressure PH. The high adjustment pressure PH is a pressure at which in-cylinder injection can always be performed in the compression stroke regardless of the operating state, and from this point, it may be referred to as normal injection pressure in the following description. The CNG direct injection injector 120 is controlled based on an output signal from the electronic control unit 300.

  Further, as shown in an enlarged view in FIG. 2, the above-described spark plug 109 is disposed in the upper center of the combustion chamber 105 between the intake port 106 and the exhaust port 107. A CNG direct injection injector 120 as a direct injection of gas fuel is disposed on the intake port 106 side with its injection port inclined at a predetermined angle with respect to the cylinder center line. Furthermore, a piston cavity 104 </ b> C adapted to the injection direction from the CNG direct injection injector 120 is formed in the upper part of the piston 104 so as to be offset toward the intake port 106. The piston cavity 104C is formed in the shape of a boat bottom that is offset to the intake port 106 side so that the spray flow from the CNG direct injection injector 120 may circulate and cause turbulence near the gap of the spark plug 109. Further, the spray angle and the spray shape of the CNG direct injection injector 120 with respect to the piston cavity 104C are set such that CNG fuel can be stratifiedly combusted in the piston cavity 104C.

  Returning to FIG. 1 again, the electronic control unit (hereinafter referred to as ECU) 300 is a digital computer, and as is well known, a ROM (read only memory) 320 and a RAM (random) connected to each other via a bidirectional bus. An access memory) 330, a CPU (microprocessor) 340, a B-RAM (backup RAM) 350 connected to a constant power supply, an input port 360, an output port 370, and the like.

  A pressure sensor 140 that generates an output voltage proportional to the absolute pressure in the surge tank 111 is attached to the surge tank 111 connected to the intake manifold 110. In the CNG supply line 122 at the outlet of the CNG cylinder 124, a CNG residual pressure sensor 141 that generates an output voltage proportional to the amount of CNG remaining in the CNG cylinder 124, that is, the residual pressure, is disposed. The output voltages of these sensors 140 and 141 are respectively input to the input ports of the ECU 300 via corresponding AD converters. Further, the input port includes a rotation speed sensor 143 that generates an output pulse representing the engine rotation speed N, a throttle opening sensor 144 that detects the rotation angle of the throttle valve 115, and an accelerator opening that detects the amount of depression of the accelerator pedal. A sensor 145 and the like are connected. On the other hand, the output ports of the ECU 300 are connected to the spark plug 109, the step motor 114, the CNG direct injection injector 120, and the like via corresponding drive circuits.

  In the present embodiment, in order to effectively use the turbulence caused by the jet flow in the stratified combustion mode, the interval Iv from the end of the injection to the ignition is set as described below, and the data mapped in the ROM 320 described above Stored.

  First, the intensity of turbulence (m / s) around the spark plug is obtained by experiment or simulation. 3A, 3B, and 3C are graphs in which the horizontal axis indicates the crank angle (deg) after completion of injection, and the vertical axis indicates the strength of disturbance (m / s) around the spark plug. Yes, FIG. 3 (A) is when the engine is at a low speed (1200 rpm) and low load range, FIG. 3 (B) is when the engine speed is increased (UP) from the low speed and low load range, and FIG. 3 (C). Are respectively shown when the load is increased (UP) from the low speed and low load range. From the graphs of FIGS. 3 (A), (B), and (C) from these experiments or simulations, the tendency of turbulence around the spark plug (increase after the end of injection, timing of damping) depends on the fluctuation of the engine load. Although there is almost no change, it can be seen that the effect of fluctuations in the rotational speed is large.

  In the low speed and low load region of the engine shown in FIG. 3 (A), the peak of turbulence intensity occurs near the crank angle of 10 ° after the end of injection. Therefore, it can be said that the ignition is surely performed if the ignition is performed at the peak point of the turbulence intensity. However, it is not limited to the peak point of the turbulence intensity, and if the turbulence intensity is equal to or greater than a predetermined threshold value (shown by a broken line), ignition can be performed reliably and combustion can be improved. An interval Iv from ignition to ignition is set. That is, in the low speed and low load region of the engine, for example, the interval Iv from the end of injection to ignition can be set to a crank angle of 8 to 20 °. The value of the interval Iv within the crank angle can be set to an optimum value in consideration of the emission, the air-fuel mixture concentration, the engine performance, and the like.

  On the other hand, as shown in FIG. 3 (B), when the rotational speed is increased, the peak of the turbulence intensity becomes smaller than that in the low speed and low load range, and the turbulence intensity occurs near the crank angle of 5 ° after the end of injection. The crank angle range in which is greater than or equal to a predetermined threshold is shortened. Therefore, in this case, for example, the interval Iv from the end of injection to ignition can be set to a crank angle of 4 to 7 °. Since the piston speed increases when the rotational speed increases, the interval Iv represented by the crank angle hardly changes when converted to time.

  Further, as shown in FIG. 3C, when the load is increased, the peak of the turbulence intensity becomes small and occurs near the crank angle of 15 ° after the end of injection, and the turbulence intensity is greater than or equal to a predetermined threshold value. Although the range of the crank angle is longer than that in the case of FIG. Therefore, in this case, for example, the interval Iv from the end of injection to ignition can be set to a crank angle of 13 to 22 °. Thus, the optimum interval Iv from the end of injection to ignition within the operating range in which the rotational speed and load are varied is set and stored as data mapped in the ROM 320 as described above.

  Here, an example of the control according to the first embodiment of the combustion control method for the gas fuel direct injection engine according to the present invention will be described with reference to the flowchart of FIG. In the first embodiment, first, in step S401, the load signal from the pressure sensor 140 and the rotation speed signal from the rotation speed sensor 143 are read as parameters representing the operating state of the engine. Then, based on this load signal and rotation speed signal, it is determined in the next step S402 whether or not it is a stratified combustion mode region to be described later. When it is the stratified combustion mode region, the process proceeds to step S403, and a predetermined fuel injection amount based on the load signal and the rotation speed signal is read from the map and set. This is set as the valve opening time of the CNG direct injection injector 120 under the aforementioned normal injection pressure. Also in the next step S404, a predetermined ignition timing based on the load signal and the rotation speed signal is read from the map and set.

  Then, in the next step S405, the interval Iv from the end of injection to ignition is read from the same stored map, and this interval Iv and predetermined fuel injection are set for the predetermined ignition timing set above. The fuel injection start time is set according to the amount. Thereafter, at this injection timing, the start of fuel injection from the CNG direct injection injector 120 toward the piston cavity 104C of the piston 104 that is in the process of rising, and the ignition of the spark plug 109 in the interval Iv after the end of the injection are executed. . Thus, the turbulence of the combustible air-fuel mixture caused by the spray flow from the CNG direct injection injector 120 toward the piston cavity 104 </ b> C exists in the vicinity of the gap of the spark plug 109, and the combustible in the vicinity of the spark plug 109. Since the ignition is performed at the interval Iv where the air-fuel mixture stays, the ignition is surely performed and the ignited flame propagates rapidly. As a result, combustion can be improved and engine performance can be improved.

  Next, an example of the control according to the second embodiment of the combustion control method for a gas fuel direct injection engine according to the present invention will be described with reference to the flowcharts of FIGS. The second embodiment is applied to an engine in which fuel injection modes are different between the stratified combustion mode and the homogeneous combustion mode. That is, in the second embodiment, as shown in FIG. 6, the engine operating region is divided into a low-speed and low-load stratified combustion mode region “1” and the other homogeneous combustion mode region “2”. The combustion mode area “2” is further divided into a high load area “2-1” and a medium load / high speed low load area “2-2”.

  Therefore, in the second embodiment, as in the first embodiment, first, in step S 401, the load signal from the pressure sensor 140 and the rotation speed signal from the rotation speed sensor 143 are used as parameters representing the operating state of the engine. Is read, and based on the load signal and the rotational speed signal, it is determined in the next step S402 whether or not the stratified combustion mode region is "1". In the stratified combustion mode region, the process proceeds to step S403 and the subsequent steps, and the ignition of the spark plug 109 is performed at the interval Iv after the end of the injection from the CNG direct injection injector 120 as described above.

  On the other hand, if it is determined in step S402 that it is not the stratified combustion mode region “1”, that is, the homogeneous combustion mode region “2”, the process proceeds to step S501 in the flowchart of FIG. In step S501, a predetermined fuel injection amount based on the load signal and the rotation speed signal is read from the map, and the fuel injection amount is set to be divided into a main fuel injection amount and a sub fuel injection amount. In other words, the fuel injection amount by the main injection is set to an amount obtained by subtracting the fuel injection amount by the sub injection from the required total fuel injection amount. Here, the amount of secondary fuel injection is not limited, but is intended to cause turbulence around the spark plug 109. If the amount is too large, the air-fuel mixture may be stratified. The minimum injection amount of the injector 120 is preferable. In the next step S502, a predetermined ignition timing is read from the map and set based on the load signal and the rotation speed signal.

  Furthermore, it progresses to step S503 and it is determined whether it is the high load area | region "2-1" in the homogeneous combustion mode area | region "2". When the high load region is “2-1”, that is, “Yes”, the process proceeds to step S504, and the injection start timing of the main fuel injection amount is set to 180 ° before top dead center (BTDC), which is the start timing of the compression stroke. At the same time, the interval Iv from the end of the sub-injection to the ignition is read from the map stored in the ROM 320, and the sub-fuel injection is performed according to the interval Iv and the sub-fuel injection amount with respect to the predetermined ignition timing set above. The start time is set. Then, the process proceeds to step S506, and main injection from the CNG direct injection injector 120 toward the piston cavity 104C of the piston 104 in the upward process is started before top dead center (BTDC) 180 °.

  Next, sub injection is performed at the sub fuel injection start timing set as described above, and ignition of the spark plug 109 is performed at an interval Iv after the end of the injection. Thus, turbulence of the combustible air-fuel mixture caused by the spray flow caused by the sub-injection from the CNG direct injection injector 120 toward the piston cavity 104C is present in the vicinity of the gap of the spark plug 109, and the spark plug 109 Since the ignition is performed at the interval Iv where the combustible air-fuel mixture stays in the vicinity, the ignition is surely performed and the ignition flame is rapidly propagated to improve the combustion.

  On the other hand, if the determination in step S503 is not the high load region “2-1” in the homogeneous combustion mode region “2”, that is, “No” in the medium load and high speed low load region “2-2”, step S505 is performed. In order to improve the mixing with the intake air, the injection start timing of the main fuel injection amount is set to 360 ° before top dead center (BTDC), which is the start timing of the intake stroke, and from the end of the sub injection to the ignition The interval Iv is read from the map stored in the ROM 320. Then, with respect to the predetermined ignition timing set in step S502 described above, the auxiliary fuel injection start timing is set based on the interval Iv and the auxiliary fuel injection amount. Then, the process proceeds to step S506, and main injection from the CNG direct injection injector 120 toward the piston cavity 104C in the descending process is started at 360 ° before top dead center (BTDC). Sub-injection is performed at the sub-fuel injection start timing set as described above in the latter half of the compression stroke, and ignition of the spark plug 109 is performed at interval Iv after the end of the injection. Thus, even in this region “2-2”, the turbulence of the combustible mixture caused by the spray flow caused by the sub-injection from the CNG direct injection injector 120 toward the piston cavity 104C in the ascending process is ignited. Since the ignition is performed at an interval Iv that exists in the vicinity of the gap 109 and the combustible mixture stays in the vicinity of the spark plug 109, the ignition is surely performed and the propagation of the ignited flame is promptly performed to improve the combustion. The

  Here, the time chart of FIG. 7 shows the relationship between the fuel injection amount (including the main fuel injection amount and the sub fuel injection amount), the timing thereof, and the ignition timing in the first and second embodiments of the present invention described above. . In FIG. 7, the middle thick line in the homogeneous combustion mode region “2” indicates the main injection, and the very thick line indicates the start and end of the sub injection, respectively. In addition, the thick line in the stratified combustion mode region “1” indicates the start and end of fuel injection. Note that an asterisk represents ignition, and Iv represents an interval from the end of injection to ignition.

  Next, an example of the control according to the third embodiment of the combustion control method for a gas fuel direct injection engine according to the present invention will be described with reference to the flowchart of FIG. In the third embodiment, the present invention is applied at the time of low temperature start, and control is started when the ignition switch (IG) is turned on and the starter (STA) is turned on. Therefore, in step S801, it is determined whether or not the engine coolant temperature detected by the water temperature sensor 119 is equal to or lower than a predetermined value (for example, 0 ° C.). If it is equal to or less than the predetermined value, that is, "Yes", the process proceeds to step S802, and the ignition timing is set for two-stage injection. That is, the ignition timing is set to the retarded side delayed from the top dead center. In the next step S803, the interval Iv from the end of the sub-injection to the ignition set on the retard side is read from the map stored in the ROM 320, and the ignition timing set in step S802 described above is read. The sub fuel injection start timing is set by the interval Iv and the sub fuel injection amount. Furthermore, in step S804, the injection start timing of the main fuel injection amount is set to 360 ° before top dead center (BTDC), which is the start timing of the intake stroke in order to improve mixing with intake air. The sum of the main fuel injection amount and the above-mentioned sub fuel injection amount is obtained in advance by experiments or the like according to the cooling water temperature of the engine and stored in the map. The

  Then, the process proceeds to step S805, in which the CNG direct injection injector 120 is at 360 ° before top dead center (BTDC) in the same injection mode as in the case of the medium load and high speed low load region “2-2” in the time chart of FIG. Main injection toward the piston cavity 104C of the piston 104 in the descending process is started, sub injection is performed at the sub fuel injection start timing set in the latter half of the compression stroke, and an ignition plug is inserted at an interval Iv after the end of the injection 109 is ignited and started. Thus, at the time of this low-temperature start, the two-stage injection of the main injection and the sub-injection improves the mixing at the low temperature, and the ignition is generated by utilizing the turbulence generated near the gap of the spark plug 109. Surely done.

  On the other hand, when the cooling water temperature of the engine exceeds the predetermined value in the determination in step S801, the process proceeds to step S806, and the start in the normal mode is performed. The normal mode is started by injecting an appropriate amount of fuel according to the engine coolant temperature once during the intake stroke.

  In addition, after step S805 and S806, it progresses to step S807, respectively, and it is determined whether the start is complete | finished. This determination can be made based on whether or not the engine speed has exceeded a predetermined complete explosion speed, and the above routine is repeated until the start is successful, and when the start is completed, the routine proceeds to combustion control during normal operation. .

  Even in this low temperature start-up control, a strong turbulence of a relatively rich combustible mixture caused by the spray flow due to the sub-injection exists in the vicinity of the gap of the spark plug 109, and the combustible mixture in the vicinity of the spark plug 109. Since the ignition is performed at the interval Iv where the ignition is stopped, the ignition is surely performed and the propagation of the ignited flame is promptly performed to improve the combustion. Further, since the injection amount is small, fuel consumption can be improved. Furthermore, since the ignition timing can be set to the retard side, it is advantageous for early warm-up of the catalyst 118 and emission can be reduced.

  Next, a fourth embodiment of the present invention will be described with reference to FIGS. 9 (A) and 9 (B). In the fourth embodiment, the present invention is applied to a so-called single-injector engine having one CNG direct injection injector 120 in the above-described embodiment, whereas a so-called double-injector engine having two injectors is used. The present invention is applied. The double injector engine 200 shown in FIG. 9A includes a CNG port injector 130 in addition to the CNG direct injection injector 120, and the double injector engine 250 shown in FIG. 9B includes a second CNG direct injection injector 120 in addition to the CNG direct injection injector 120. 2 CNG direct injection injectors 120-2.

  In the double-injector engine 200 shown in FIG. 9A, in the stratified combustion mode region “1”, as described in the first and second embodiments of the present invention described above, only from the CNG direct injection injector 120. Injection is performed at a timing related to the ignition timing shown in the time chart of FIG. In the middle load and high speed low load region “2-2” in the homogeneous combustion mode region “2”, the main injection shown in FIG. 7 is performed by the CNG port injector 130 and the sub-injection is performed by the CNG direct injection injector 120. Done. The main fuel injection amount is an amount obtained by subtracting the sub fuel injection amount from the total fuel amount required in the operating state. When the operation is performed while injecting fuel from both the CNG direct injection injector 120 and the CNG port injector 130, the injection amount and timing from the CNG port injector 130 are not changed, and the injection timing from the CNG direct injection injector 120 is maintained. May be shifted to a time when the above-mentioned interval Iv is satisfied and disturbance may occur.

  In the double injector engine 250 shown in FIG. 9B, in the stratified combustion mode region “1”, as described in the first and second embodiments of the present invention, the CNG direct injection injector 120 or Injection from the second CNG direct injection injector 120-2 is performed at a timing related to the ignition timing shown in the time chart of FIG. In the middle load and high speed low load region “2-2” of the homogeneous combustion mode region “2”, the main injection shown in FIG. 7 is performed by the second CNG direct injection injector 120-2, and the sub injection is performed. This is done by the CNG direct injection injector 120, which can cause stronger turbulence. As described above, the main fuel injection amount is an amount obtained by subtracting the sub fuel injection amount from the total fuel amount required in the operating state.

  Next, a fifth embodiment of the present invention will be described with reference to FIGS. 9A and 9B. In the fifth embodiment, the present invention is applied to a so-called CNG double injector engine in which the aforementioned fourth embodiment includes two CNG injectors, whereas at least one CNG direct injection injector and other liquids are used. For example, the present invention is applied to a so-called bi-fuel engine including a gasoline injector. In the following description of the bi-fuel engine, the configuration of the engine body is the same as that of the above-described CNG double injector engine except for the injector, and is therefore enclosed in parentheses in FIGS. 9 (A) and 9 (B). Reference numerals are used. 9A is provided with a gasoline port injector 140 in addition to the CNG direct injection injector 120. In the bifuel engine 500 shown in FIG. 9B, the CNG direct injection injector 120 is provided. In addition, a gasoline direct injection injector 150 is provided.

  In the bi-fuel engine 400 shown in FIG. 9A, in the stratified combustion mode region “1”, as explained in the first and second embodiments of the present invention described above, only from the CNG direct injection injector 120 Injection is performed at a timing related to the ignition timing shown in the time chart of FIG. In the medium load and high speed low load region “2-2” in the homogeneous combustion mode region “2”, the main injection shown in FIG. 7 is performed by the gasoline port injector 140 and the sub-injection is performed by the CNG direct injection injector 120. Done. The main fuel injection amount, which is gasoline, is an amount obtained by subtracting the sub fuel injection amount of CNG in terms of equivalent heat generation from the total fuel amount required in the operating state. Further, when the operation is performed while injecting fuel from both the CNG direct injection injector 120 and the gasoline port injector 140, the injection amount and timing from the gasoline port injector 140 are not changed and the injection timing from the CNG direct injection injector 120 is maintained. As in the previous embodiment, it may be shifted to a time when disturbance can occur.

  In the bi-fuel engine 500 shown in FIG. 9B, in the stratified combustion mode region “1”, as described in the first and second embodiments of the present invention, the CNG direct injection injector 120 Injection is performed at a timing related to the ignition timing shown in the time chart of FIG. In the middle load and high speed low load region “2-2” in the homogeneous combustion mode region “2”, the main injection shown in FIG. 7 is performed by the gasoline direct injection injector 150, and the sub-injection causes strong turbulence. The CNG direct injection injector 120 is obtained. As described above, the main fuel injection amount is an amount obtained by subtracting the sub fuel injection amount by the equivalent calorific value conversion from the total fuel amount required in the operating state.

  By the way, in the control according to the present invention in the bi-fuel engines 400 and 500 described above, the control is performed in a state where the CNG fuel amount remains sufficiently exceeding a predetermined value, and when the CNG fuel amount falls below the predetermined value. Considering the cruising distance to the nearest refueling station, etc., normal control without turbulence according to the present invention using gasoline fuel is performed.

  Next, a sixth embodiment of the present invention will be described. The sixth embodiment is intended to avoid inconvenience caused by utilizing the turbulence caused by the jet flow from the direct injection injector described in the previous embodiment. That is, as described above, the use of the turbulence caused by the jet improves the combustion. However, the turbulence also increases the in-cylinder flow of the jet and the flame, so that heat is applied to the cylinder block 102 and the cylinder head 103. The cooling loss that escapes is large, and as a result, there is a limit to the improvement of thermal efficiency. Therefore, in the sixth embodiment of the present invention, the thermal efficiency is further improved by reducing the cooling loss.

  An example of a control routine for that purpose will be described with reference to the flowchart of FIG. This control routine is periodically executed by the ECU 300 at time interruptions every predetermined time (for example, 10 ms). Therefore, when this control routine is started, it is determined in step S1001 whether or not the combustion region utilizes the turbulence caused by the jet as described in the first and second embodiments based on the parameter representing the engine operating state. . If "Yes", the process proceeds to step S1002, and it is determined whether or not the region is a region where the thermal efficiency further decreases. The region in which the thermal efficiency decreases is obtained in advance by experiments and stored in a map. For example, a relatively low load region and a homogeneous combustion mode region in the stratified combustion mode region “1” in the graph shown in FIG. The low load area and the relatively low load area in the high load area “2-1” of “2” can be given. Therefore, if “Yes” in step S1002, the process proceeds to step S1003, and cooling capacity reduction control is performed by reducing or stopping the rotation of a water pump that can be controlled such as an electric type (not shown). And it progresses to step S1004, based on the detection from the water temperature sensor 119, it is determined whether a cooling water temperature is more than an upper limit, and when this upper limit is not exceeded, this routine is complete | finished.

  On the other hand, if both the determinations in step S1001 and step S1002 are “No”, the process proceeds to step S1007, where the normal combustion control is performed, and this routine is terminated. In step S1004, when the cooling water temperature is equal to or higher than the upper limit, the process proceeds to step S1005 to control the water pump to be driven at normal use rotation, which is determined in the next step S1006. Continue until it does not exceed. When the cooling water temperature does not exceed the upper limit, this routine is terminated.

  The present invention has been described with respect to an engine using CNG as a gas fuel engine in which gas fuel is injected and supplied by at least one direct injection injector. Examples of the gas fuel include CNG and hydrogen gas exemplified above. Not limited to this, propane gas, dimethyl ether gas, or the like can be used. In short, the present invention can be applied to all types of engines that inject and supply gas in a cylinder.

It is a schematic structure figure showing a gas fuel engine provided with at least one direct-injection injector to which the present invention is applied. It is a principal part expanded sectional view of FIG. It is a graph which shows the turbulence intensity which arises around a spark plug, (A) at the time of low speed and low load, (B) when the rotation speed was increased in that state, (C) also increased the load. Is the time. It is a flowchart which shows an example of the control procedure in the 1st Embodiment of this invention. It is a flowchart which shows an example of the control procedure in the 2nd Embodiment of this invention. It is a graph which shows the operation area | region of the engine divided | segmented into the stratified combustion mode area | region and the homogeneous combustion mode area | region in the 1st and 2nd embodiment of this invention. 6 is a time chart showing a relationship between a fuel injection amount (including a main fuel injection amount and a sub fuel injection amount), a timing thereof, and an ignition timing in the first and second embodiments of the present invention. It is a flowchart which shows an example of the control procedure in the 3rd Embodiment of this invention. (A) And (B) is a sectional side view which respectively shows the principal part of the double injector engine and bi-fuel engine in the 4th and 5th embodiment of this invention. It is a flowchart which shows an example of the control procedure in the 6th Embodiment of this invention.

Explanation of symbols

100 Gas Fuel Direct Injection Engine 103 Cylinder Head 104 Piston 104C Cavity 105 Combustion Chamber 109 Spark Plug 120 CNG Direct Injection Injector 120-2 Second CNG Direct Injection Injector 130 CNG Port Injector 140 Gasoline Port Injector 150 Gasoline Direct Injection Injector 200, 250 Double injector engine 300 Electronic control unit 400,500 Bi-fuel engine

Claims (8)

Gas in which gas fuel is directly injected into a cavity formed on the piston top surface by at least one direct injection injector, and a stratified combustion mode in which a combustible mixture is formed in the vicinity of the spark plug is performed in at least a part of the operation region. A direct fuel injection engine,
An interval from the end of fuel injection to ignition is set so that the intensity of turbulence of the combustible air-fuel mixture near the spark plug due to the injection of gas fuel reaches a peak at the time of ignition in the stratified combustion mode. A combustion control method for a gas fuel direct injection engine.   The fuel injection start timing is changed based on a fuel injection amount determined according to an engine operating condition in the stratified combustion mode while fixing an interval from the end of the fuel injection to ignition. A combustion control method for a gas fuel direct injection engine according to claim 1.   In addition to the stratified combustion mode, a homogeneous combustion mode is provided. In the homogeneous combustion mode, the main injection is performed in the first half of the compression stroke or the first half of the intake stroke, and the sub-injection is performed while satisfying the interval from the end of the fuel injection to the ignition. The combustion control method for a gas fuel direct injection engine according to claim 1, wherein:   4. The combustion control of a gas fuel direct injection engine according to claim 3, wherein the fuel injection amount by the main injection is set to an amount obtained by subtracting the fuel injection amount by the sub injection from the required total fuel injection amount. Method.   2. The gas fuel direct injection according to claim 1, wherein at the time of low temperature start, the main injection is performed in the first half of the compression stroke or the first half of the intake stroke, and the sub-injection is performed while satisfying an interval from the end of the fuel injection to the ignition. Engine combustion control method. The gas fuel direct injection engine includes a port injector at an intake port in addition to the direct injection injector,
The combustion control method for a gas fuel direct injection engine according to claim 3, wherein the main injection is performed by the port injector and the sub-injection is performed by the direct injection injector. The gas fuel direct injection engine includes two direct injection injectors in a cylinder,
The combustion control method for a gas fuel direct injection engine according to claim 3, wherein the sub-injection is performed by a direct injection injector capable of generating a stronger disturbance of the combustible air-fuel mixture.   6. The combustion control method for a gas fuel direct injection engine according to claim 1, wherein the gas fuel direct injection engine includes a gasoline port injector at an intake port in addition to the direct injection injector. .

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