JP4433685B2 - Operation control method for compression self-ignition internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an operation control method for an internal combustion engine, and more particularly to an operation control method suitable for use in a self-ignition internal combustion engine that uses a plurality of types of fuel.
[0002]
[Prior art]
In general, an internal combustion engine (hereinafter referred to as a diesel engine) that uses a high cetane fuel (for example, light oil) as a fuel injects fuel into a combustion chamber filled with high-pressure air to cause self-ignition. In such an engine, the fuel injected into the combustion chamber is burned (self-ignited) before it is sufficiently mixed with air, so that the exhaust characteristics are likely to deteriorate.
[0003]
On the other hand, an internal combustion engine (hereinafter referred to as a gasoline engine) that uses low cetane number fuel (for example, gasoline) as a fuel ignites an air-fuel mixture supplied into the combustion chamber using an ignition plug. In such an engine, the ignition timing can be freely controlled. For example, the fuel injection timing and the ignition timing are precisely controlled so that ignition is performed after a sufficiently homogeneous mixture is formed. can do. For this reason, the control of exhaust characteristics is easy to compare. A gasoline engine is superior to a diesel engine in this respect.
[0004]
However, in a gasoline engine, when the air-fuel mixture is ignited, the flame propagates from the spark plug to the peripheral edge of the combustion chamber. At this time, the unburned air-fuel mixture (terminal gas) present at the peripheral edge of the combustion chamber is compressed by the flame (pressure wave) spreading from the spark plug, and the flame propagating from the spark plug reaches the peripheral edge of the combustion chamber. Auto-ignite before doing. This self-ignition of the terminal gas is called knocking, and causes problems such as generation of abnormal noise and deterioration of engine durability.
[0005]
In order to deal with such problems with gasoline engines, a method of operating an internal combustion engine by injecting gasoline as a main fuel into a combustion chamber and light oil as an auxiliary fuel into an intake passage is known. For example, Patent Document 1 describes a method in which light oil is injected into an intake passage and gasoline is injected into a combustion chamber through a fuel injection valve provided in each of the intake passage and the combustion chamber, and a mixture of these fuels is self-ignited. Has been. According to such a method, an air-fuel mixture mainly composed of gasoline is self-ignited and burned by the action of light oil as a subcomponent. Thus, the occurrence of terminal gas self-ignition (knocking), which is a problem peculiar to gasoline engines, is also eliminated, and the deterioration of exhaust characteristics, which is a problem peculiar to diesel engines, is also eliminated.
[0006]
[Patent Document 1]
JP 2001-355471 A
[Problems to be solved by the invention]
However, in the operation method of the internal combustion engine disclosed in the above-mentioned patent document, it is difficult to control the timing at which the fuel self-ignites with high accuracy. As a result, the operating range in which the combustion state of the engine can be stably maintained has been limited.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to stabilize the combustion state of the engine and exhaust characteristics in an internal combustion engine using a plurality of types of fuels having different ignitability and the like. It is to expand the operating area advantageous for improvement.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention A low cetane number fuel supply means for supplying a low cetane number fuel to form a premixed gas in the combustion chamber of the internal combustion engine, and a high cetane number fuel supply means for injecting a high cetane number fuel into the combustion chamber. In the compression self-ignition internal combustion engine, the operation control corresponding to the predetermined first operation region where the load of the engine is low load or medium load and the predetermined second operation region where the load is higher than the first operation region is performed. In the first operating region, the high cetane number fuel is injected when the timing of the injection supply of the high cetane number fuel is advanced compared to the vicinity of the compression top dead center and the load on the engine increases. The timing of the injection supply of the fuel is advanced, and in the second operation region, the timing of the injection supply of the high cetane number fuel is retarded from a predetermined value. This is the gist.
[0013]
Low A cetane number fuel generally means a fuel having a relatively low ignitability and a property of easily forming a premixed gas prior to ignition. For this reason, the low cetane number fuel can be replaced with a term such as a low ignitable fuel, a high octane number fuel or the like. As a low cetane fuel , Gasoline or gasoline The fuel which has a main component can be illustrated.
[0014]
On the other hand, a high cetane number fuel generally means a fuel that has relatively high ignitability and easily self-ignites under high pressure or high temperature conditions. For this reason, the high cetane number fuel can be replaced with a term such as a highly ignitable fuel, a low octane number fuel, or the like. As high cetane fuel, Light oil or light oil The fuel which has a main component can be illustrated.
[0017]
Since the low cetane number fuel has low ignitability, pre-ignition does not occur even if the fuel is supplied into the combustion chamber relatively early (for example, the intake stroke). For this reason, the premixed gas which has an advantageous property in order to improve exhaust characteristics can be formed easily. However, since low cetane number fuel has low ignitability, it must be burned using a spark plug or the like. The combustion of fuel by the spark plug is likely to cause knocking.
[0018]
On the other hand, high cetane number fuel has high ignitability and can be burned by self-ignition. However, since pre-ignition tends to occur, it is difficult to form a premixed gas.
[0019]
According to the above method, the ignition timing is controlled by the high cetane number fuel having high ignitability, and the output of the engine is obtained using the low cetane number fuel having low ignitability.
[0020]
And first The first driving area In the region, for example, the timing of the injection supply of the high cetane fuel is advanced as the required torque increases. As a result, the ignition timing can be kept substantially constant, and the spray of the high cetane fuel can be sufficiently dispersed (premixed) before ignition.
[0021]
Meanwhile, before 2nd driving area In other words, in areas where pre-ignition is very likely to occur due to high pressure and temperature in the combustion chamber , High To the extent that pre-ignition does not occur when tan fuel is injected at the same time as tan fuel is injected (for example, close to compression top dead center) , High Set the timing of fuel supply of tan fuel to the retard side. Thereby, generation | occurrence | production of premature ignition can be prevented reliably.
[0022]
That is, according to the above method, high cetane fuel is dispersed as much as possible in the premixed gas of low cetane fuel as an advantageous combustion mode for effectively suppressing the generation of smoke and NOx in the exhaust gas. While adopting a combustion mode that leads to post-self-ignition in a wider operating range, it is possible to effectively prevent the occurrence of pre-ignition.
[0023]
Note that the above-described method is preferably used only under conditions where the combustion state of the engine is easily stabilized, that is, under conditions where the engine is warmed up.
[0024]
Further, “the timing of the injection supply of the high cetane fuel is retarded from the predetermined value” is a time when the piston of the engine is generally near the compression top dead center, and the pressure rise in the combustion chamber This means that the injection supply timing of the high cetane fuel is retarded to such an extent that the premature ignition accompanying the temperature rise can be suppressed.
[0025]
When In addition, from the viewpoint of achieving both prevention of misfire and prevention of premature ignition, in the above method, the timing of the injection supply of the high cetane fuel is determined in advance. The first driving area In the region, control is performed in the range of 30 ° to 60 ° before the compression top dead center of the engine. 2nd driving area In the region, it is preferable to control in the range of about 0 ° to 10 ° before the compression top dead center of the engine.
[0026]
Ma Further, when the operating state of the engine shifts between an operating region where the parameter has a relatively small value and an operating region where the parameter has a relatively large value, the injection of the high cetane fuel It is preferable to change the exhaust gas recirculation amount and change the total fuel supply amount in conjunction with the change in the supply timing.
[0027]
By changing the timing of injection supply of the high cetane fuel, it is possible to effectively prevent pre-ignition. However, for example, if the total supply amount of fuel (low octane number fuel and high octane number fuel) is increased with the delay of the timing of injection supply of high cetane number fuel, smoke tends to be generated in the exhaust gas. On the other hand, if the exhaust gas recirculation amount is reduced, the occurrence of smoke can be suppressed. on the other hand, High seta If the total amount of fuel supply is reduced with the advance of the timing of injection supply of high-valent fuel, the concentration of NOx in the exhaust tends to increase. On the other hand, if the exhaust gas recirculation amount is increased, the concentration of NOx in the exhaust gas can be reduced.
[0028]
That is, according to the above method, it is possible to efficiently suppress the generation of smoke and NOx accompanying the change in the timing of the high cetane fuel injection supply.
[0029]
Yo Specifically, the operating state of the engine From the first operating area to the second operating area When shifting to a region, the delay in the timing of the injection supply of the high cetane fuel and the reduction of the exhaust gas recirculation amount are determined as To increase This should be done in advance.
[0030]
Ma The operating status of the engine From the first operating area to the second operating area In the case of transition to the region, after delaying the timing of the high cetane fuel injection supply, the exhaust gas recirculation amount is reduced, and then the total fuel supply amount is reduced. Increase You may make it make it.
[0031]
According to such a method, the operating state of the engine From the first operating area to the second operating area When shifting to a region, it is possible to preferentially suppress the occurrence of premature ignition or the occurrence of smoke in the exhaust.
[0032]
Ma The operating status of the engine From the second operating area to the first operating area The total supply of the fuel Reduction The exhaust gas recirculation amount may be increased prior to the advance timing of the high cetane fuel injection supply.
[0033]
Ma The operating status of the engine From the second operating area to the first operating area The total supply of fuel Reduction After that, the exhaust gas recirculation amount may be increased, and then the timing of injection supply of the high cetane fuel may be advanced.
[0034]
According to such a method, the operating state of the engine From the second operating area to the first operating area When shifting to the region, it is possible to preferentially suppress the occurrence of premature ignition or the generation of NOx in the exhaust.
[0035]
Further, the operating state of the engine is the first operating range. Area When the transition is made between the first operation region and the second operation region, it is preferable that the injection supply timing of the high cetane fuel is not set to a value within a predetermined range where pre-ignition occurs.
[0036]
If the timing of the light oil injection supply is sufficiently advanced, the light oil ignites after being dispersed, so pre-ignition does not occur. Further, if the timing of the light oil injection supply is sufficiently retarded (set near the compression top dead center), the ignition delay is almost eliminated, and the injected light oil burns relatively slowly. In other words, premature ignition does not occur in this case. However, if light oil is injected at a specific time between the two, pre-ignition with a loud noise occurs.
[0037]
There is a time when a spray with extremely high ignitability is locally formed before the spray of light oil injected into the combustion chamber is sufficiently dispersed. This is because if the pressure and temperature in the combustion chamber rise to a certain level at this time, premature ignition occurs with the highly ignitable spray as the nucleus.
[0038]
According to the above method, by providing a prohibition range for the timing of supplying and supplying high cetane fuel, it is possible to reliably prevent a locally formed highly ignitable spray from causing premature ignition. Can do.
[0039]
Ma Further, it is preferable to perform a correction to increase the ratio of the supply amount of the high cetane number fuel to the supply amount of the low cetane number fuel as the temperature of the engine is lower.
[0040]
Since the temperature of the engine tends to affect the ignitability of the high cetane fuel, according to the above method, the ignition timing of the high cetane fuel and the combustion state of the fuel supplied to the engine are more precisely defined. Can be controlled.
[0041]
Ma In addition, it is preferable to correct the ratio of the supply amount of the high cetane fuel to the supply amount of the low cetane fuel according to the amount of change in torque or output required for the engine.
[0042]
According to the above method, by changing the ratio of the supply amount of the high cetane fuel to the supply amount of the low cetane fuel, the torque required for the engine or the transient change in output is caused. The shortage or excess of the intake air amount of the engine can be offset. Therefore, the ignition timing of the high cetane fuel and the combustion state of the fuel supplied to the engine can be controlled more precisely.
[0043]
Ma When the torque or output required for the engine increases, the ratio of the supply amount of the high cetane fuel to the supply amount of the low cetane fuel depends on the amount of change. Reduction When the torque or output required for the engine decreases, the ratio of the high cetane number fuel supply amount to the low cetane number fuel supply amount is determined according to the change amount. Increase It is preferable to correct.
[0044]
Ma Further, the supply amount of the low cetane number fuel is based on the supply amount of the high cetane number fuel so that the total calorific value of the fuel supplied to the combustion of the engine becomes a value corresponding to the output required for the engine. It is preferable to adjust.
[0045]
Since the amount of heat generated when a unit amount is burned differs between a high cetane fuel and a low cetane fuel, according to the above method, the amount of low cetane fuel supplied relative to the amount of high cetane fuel supplied is reduced. Even if it is changed, the torque and output of the engine can be precisely controlled.
[0046]
This While the engine is cold started, substantially only the high cetane fuel is injected and supplied to the combustion chamber, and the injection supply timing is set to about 10 ° to 20 ° before the compression top dead center of the engine. It is preferable that the high cetane number fuel and the low cetane number fuel are supplied at the normal temperature start and the injection supply timing of the high cetane number fuel is about 10 ° to 20 ° before the compression top dead center of the engine.
[0047]
According to the above method, at the time of low temperature start, by performing the control to give priority to the improvement of the fuel ignitability, specializing at the time of low temperature start in which the combustion state of the engine and the ignitability of the high cetane number fuel are reduced. Misfire can be effectively prevented.
[0048]
Ma Further, when the engine is started in a warm-up state, the high cetane number fuel and the low cetane number fuel are supplied, and the injection supply timing of the high cetane number fuel is set to 40 ° to 60 ° before the compression top dead center of the engine. It is preferable to set the degree.
[0049]
According to the above method, it is possible to suppress the generation of smoke and NOx in the exhaust gas while sufficiently ensuring the stability of the combustion state of the engine even when the engine is started.
[0050]
Ma In addition, the presence or absence of misfire of the engine is determined, and when it is determined that the engine has misfired, the ratio of the supply amount of the high cetane fuel to the supply amount of the low cetane fuel is increased and corrected. It is preferable that the timing of injection supply of the high cetane number fuel is corrected.
[0051]
According to said method, the misfire of the said engine can be eliminated rapidly.
[0052]
This It is preferable to determine whether or not the engine has been prematurely ignited, and if it is determined that the engine has prematurely ignited, the supply amount of the high cetane fuel is preferably reduced and corrected.
[0053]
According to the above method, even if the pre-ignition of the high cetane fuel supplied to the engine has occurred, it can be quickly resolved.
[0054]
Ma In addition, it is preferable that the supply amount of the high cetane number fuel is not less than the lower limit value capable of autoignition.
[0055]
According to said method, the misfire of the said engine can be prevented reliably.
[0056]
Ma In addition, when correcting the injection supply timing of the high cetane fuel, If the operating state of the engine is in the first operating range, Correction to advance the timing of injection supply of high cetane number fuel, If the operating state of the engine is in the second operating range, It is preferable to make a correction to retard the injection supply timing of the high cetane number fuel.
[0057]
in front The first driving area In the region, pre-ignition occurred due to the timing of the high cetane fuel injection supply being too late. 2nd driving area In the region, pre-ignition occurs because the timing of injection supply of high cetane fuel is too early. According to the above method, even if the operating state of the engine belongs to any region, if pre-ignition occurs, this can be effectively eliminated.
[0058]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an in-vehicle internal combustion engine will be described.
[0059]
[Basic engine structure and functions]
As shown in FIG. 1, the engine 1 is an internal combustion engine that obtains output by repeating four cycles of an intake stroke, a compression stroke, an explosion stroke (expansion stroke), and an exhaust stroke. The engine 1 forms a combustion chamber (cylinder) 2 therein. The explosive force of the fuel generated in the combustion chamber 2 is converted into the rotational force of a crankshaft (not shown) via the piston 3 and the connecting rod 4. Further, the combustion chamber 2 is provided with an intake port 5A that forms the most downstream portion of the intake passage 5 and an exhaust port 6A that forms the most upstream portion of the exhaust passage 6. The boundary between the intake port 5A and the combustion chamber 2 is opened and closed by an intake valve 5B. Further, the boundary between the exhaust port 6A and the combustion chamber 2 is opened and closed by an exhaust valve 6B.
[0060]
The engine 1 includes a first fuel injection valve 10 and a second fuel injection valve 20. The first fuel injection valve 10 exposes the tip (fuel injection port) to the intake port 5A. The first fuel injection valve 10 is an electromagnetically driven on-off valve that supplies low-cetane fuel (gasoline) pressurized by a high-pressure pump (not shown) or the like to the combustion chamber 2 at an appropriate amount and at an appropriate timing. is there. The second fuel injection valve 20 exposes the tip (fuel injection port) to the combustion chamber 2. The second fuel injection valve 20 is an electromagnetically driven on-off valve that supplies high-cetane fuel (light oil) pressurized by a high-pressure pump (not shown) or the like to the combustion chamber 2 at an appropriate amount and at an appropriate timing. is there.
[0061]
The engine 1 outputs an accelerator position sensor (not shown) that outputs a signal corresponding to a depression amount ACC of an accelerator pedal (not shown) by a driver, and a rotational speed (engine speed) NE of a crankshaft (not shown). A rotational speed sensor, a temperature sensor that outputs a signal corresponding to the temperature (cooling water temperature) THW of the cooling water circulating in the engine 1, and the flow rate (intake air amount) GA of the air introduced into the combustion chamber 2 through the intake passage 5 Various sensors such as an air flow meter for outputting a signal corresponding to the above are provided. Signals from various sensors are input to an electronic control unit (ECU) 30.
[0062]
The ECU 30 includes a logical operation circuit including a CPU, a RAM, a ROM, and the like, and comprehensively controls various components of the engine 1 based on signals from various sensors. For example, the ECU 30 operates the first fuel injection valve 10 and the second fuel injection valve 20 (fuel injection control) based on the operating state of the engine 1 and supplies an appropriate amount of fuel to the combustion chamber 2 at an appropriate timing. To do.
[0063]
In the description of the present embodiment, the term “fuel” refers to both light oil and gasoline, and the term “fuel injection” refers to the first fuel injection valve 10. gasoline And through the second fuel injection valve 20 Light oil This means any of the above injections.
[0064]
[Overview of fuel injection control]
As described above, the engine 1 has both the function of injecting gasoline into the intake port 5 </ b> A through the first fuel injection valve 10 and the function of injecting light oil into the combustion chamber 2.
[0065]
As a first operation mode of the engine 1, the ECU 30 injects gasoline into the intake port 5A in the intake stroke and injects light oil into the combustion chamber 2 in the compression stroke (hereinafter referred to as a plurality of fuels). Adopt injection mode). In the multiple fuel injection mode, the gasoline injected into the intake port 5A in the intake stroke diffuses substantially uniformly in the combustion chamber 2 and is sufficiently mixed with air (a premixed mixture of air and gasoline is formed). Next, light oil is injected into the combustion chamber 2 when the premixed gas is compressed and becomes high temperature in the compression stroke. Then, the spray of the injected light oil is self-ignited, and starting from this, the entire air-fuel mixture in the combustion chamber 2 is combusted.
[0066]
In addition, as a second operation mode of the engine 1, the ECU 30 performs an operation mode (hereinafter referred to as a single fuel injection mode) in which only the light oil is injected and the engine 1 is burned without performing gasoline injection (supply). adopt. In the single fuel injection mode, light oil is injected into the air that has been compressed in the combustion chamber 2 and heated to a high temperature, and is self-ignited, as in a generally known diesel engine.
[0067]
The multiple fuel injection mode and the single fuel injection mode are selectively used according to the operating state of the engine 1 that changes every moment.
[0068]
FIG. 2 is a schematic diagram showing a map used for selecting the operation mode and determining the basic injection amount of light oil when executing the fuel injection control according to the present embodiment. As shown in FIG. 2, four operating areas A1, A2, A3 and ATR defined by the engine load LD and the engine speed NE are set on the map. The operation region A1 is a so-called low load / low rotation region. When the operating state of the engine 1 is in the region A1, the single fuel injection mode (injection of only light oil) is adopted. The operation area A2 is a so-called medium load / medium rotation area, and the operation area A3 is a high load / high rotation area. The transition area ATR is a boundary area between the operation area A2 and the operation area A3. When the operating state of the engine 1 is in the region A2, A3 or ATR, the multiple fuel injection mode (light oil and gasoline injection) is employed.
[0069]
Further, the injection amount of light oil and the injection amount of gasoline per combustion cycle differ depending on the operation region.
[0070]
[Relationship between light oil injection amount and gasoline injection amount]
For example, when the engine operating state (the rotational speed NE and the load LD) changes along the straight line L in FIG. 2, the light oil injection amount and the gasoline injection amount correspond to the change in the engine load LD, as shown in FIG. ).
[0071]
As shown in FIG. 3A, when the engine load LD is less than the predetermined value LD1 (in the region A1), the single fuel injection mode is adopted (only light oil is injected), and the engine load LD is set to the predetermined value. When the value is equal to or greater than the value LD1 (in the regions A2, ATR, and A3), the multiple fuel injection mode is adopted (light oil and gasoline are injected). Further, the injection amount of the light oil is controlled so as to increase monotonously as the engine load LD increases in the region A1, and is controlled so as to decrease monotonously as the engine load LD increases in the regions A2, ATR, and A3. Is done. On the other hand, in regions A2, ATR, and A3, the gasoline injection amount is controlled to increase monotonously. In addition, as shown in FIG.3 (b), the ratio of the injection quantity of the light oil with respect to the injection quantity of gasoline seems to decrease monotonously with the increase in engine load LD in all the areas where the multiple fuel injection mode is adopted. Controlled.
[0072]
[Light oil injection timing]
In the engine 1, light oil is injected into the combustion chamber 2, and combustion is caused by self-ignition. Further, the ignition delay time until the injected light oil reaches self-ignition varies depending on the operating state of the engine 1. For this reason, the ignition timing of the engine 1 is controlled by changing the light oil injection timing (crank angle corresponding to the injection start timing) according to the operating state of the engine 1.
[0073]
For example, when the engine operating state (the rotational speed NE and the load LD) changes along the straight line L in FIG. 2, the light oil injection timing corresponds to the change in the engine load LD, as shown in FIGS. It changes as shown in b). FIG. 4B is an enlarged view of a part of FIG. 4A in the horizontal axis direction.
[0074]
As shown in FIG. 4A, the light oil injection timing corresponds to a condition in which the engine load LD is substantially “0” when the engine load LD is less than the predetermined value LD2 (in the regions A1 and A2). BTDC 40 ° (timing at which the piston 3 is 40 ° before compression top dead center) is set to the most retarded value, and is controlled so as to advance monotonously as the engine load LD increases.
[0075]
When the engine load LD is equal to or greater than the predetermined value LD3 (in the region A3), the light oil injection timing is about BTDC 10 ° as the most retarded value, and advances monotonously as the engine load LD increases. To be controlled.
[0076]
On the other hand, as shown in FIG. 4B, when the engine load LD is equal to or greater than the predetermined value LD2 and less than LD3 (in the transition region ATR), the light oil injection timing is BTDC 60 °, the most advanced value, BTDC 10 °. Is the most retarded value, and is controlled so as to be retarded monotonously as the engine load LD increases. In particular, the injection timing of the light oil is prevented from being in the predetermined range under the condition that the engine load LD is in the predetermined range (in this embodiment, the injection timing of the light oil is BTDC 30 ° under the condition that the engine load LD is in the vicinity of LDx. Not to be in the range of ~ 40 °). Specifically, in the transition region ATR, when the light oil injection timing is retarded in response to the increase in the engine load LD, the light oil injection timing is not changed from α to β when the engine load LD passes LDx. Change to continuous. Further, when the light oil injection timing is advanced according to the decrease in the engine load LD, the light oil injection timing is discontinuously changed from β to α when the engine load LD passes LDx.
[0077]
[Characteristics of each operation area]
[Area A1]
In the region A1, since the engine 1 is in a low load or low rotation state and the ignitability of the fuel is low, only light oil is used as the fuel. In particular, compared with the timing when the pressure and temperature of the combustion chamber 2 become maximum (near BTDC 0 °), the fuel (light oil) is relatively early (in this embodiment, about 40 ° BTDC is set to the most retarded value). Is injected (see FIG. 3A). As a result, for the light oil injected at an early stage, an opportunity for uniform diffusion in the combustion chamber 2 is provided, and sufficient ignitability is ensured.
[0078]
In addition, although the fuel (light oil) injection amount increases as the engine load LD or the engine speed NE increases, the pressure of the light oil supplied to the second fuel injection valve 20 in this embodiment is constant. For this reason, control is performed to increase the valve opening time of the second fuel injection valve 20 by advancing the injection timing of the light oil as the engine load LD or the engine speed NE increases.
[0079]
[Area A2]
In the region A2, the required fuel injection amount further increases as the engine load LD or the engine speed NE increases. However, since the temperature and pressure of the combustion chamber 2 are higher in the region A2 than in the region A1, pre-ignition is likely to occur. Here, pre-ignition means a phenomenon in which light oil starts to ignite for some reason before the ignition delay time elapses and the mixture in the combustion chamber 2 burns in an unstable manner. In region A2, where ignition is more likely to occur than in region A1, control is performed so that gasoline is injected during the intake stroke in addition to light oil injection during the compression stroke. Then, by decreasing the injection amount of light oil while increasing the engine load LD or the engine speed NE, while increasing the injection amount of gasoline (while reducing the ratio of the injection amount of light oil to the injection amount of gasoline) Then, control is performed to increase the total fuel injection amount (see FIGS. 3A and 3B). In addition, in order to keep the ignition timing of the injected light oil constant, the injection timing of the light oil is advanced at a gradual rate of change compared to the region A1 as the engine load LD or the engine speed NE increases. (Refer to FIG. 4A).
[0080]
[Area A3]
In the region A3, the temperature and pressure of the combustion chamber 2 are further increased compared to the region A2. As a result, as in the control in the region A2, in accordance with the increase in the engine load LD or the engine speed NE, the light oil injection timing is advanced and the ratio of the light oil injection amount to the gasoline injection amount is decreased. In such a case, even if the amount of light oil injected decreases and approaches the minimum required for self-ignition, pre-ignition occurs.
[0081]
Therefore, in the region A3, the light oil injection timing is significantly retarded compared to the region A2, and the piston 3 is in the vicinity of the compression top dead center and the pressure and temperature of the combustion chamber 2 are highest (for example, BTDC 0 ° to 10 °). ) Is injected with light oil (see FIG. 4A). In this case, the injected light oil ignites promptly (although the ignition delay itself is short), but there is no abnormality that causes unstable combustion like pre-ignition. Incidentally, in region A1 and region A2, since the temperature of engine 1 is low and the light oil ignitability is low, if light oil is injected at BTDC 0 ° to 10 °, combustion becomes unstable or misfiring tends to occur. .
[0082]
Regarding the adjustment of the injection amount of light oil and gasoline, in the region A3 as well as the region A2, the ratio of the injection amount of light oil to the injection amount of gasoline is decreased as the engine load LD or the engine speed NE increases. Then, control is performed to increase the total fuel injection amount (see FIGS. 3A and 3B).
[0083]
[Transition region ATR]
In the region A2, since light oil is injected relatively early, the injected light oil is appropriately dispersed (premixed) in the combustion chamber 2, and then the spray of the dispersed light oil is self-ignited as a plurality of nuclei. . As a result, the air-fuel mixture in the combustion chamber 2 burns stably. In the region A3, since light oil is injected at a relatively late time, in other words, under conditions where the pressure and temperature of the combustion chamber 2 are high, the light oil self-ignites instantly while being injected. Even in such a case, the air-fuel mixture in the combustion chamber 2 burns stably.
[0084]
However, in the transition region ATR, when the light oil injection timing is continuously changed between the two, a region in which a self-ignition occurs in a state where the spray of injected light oil diffuses unevenly and a premature ignition occurs ( Hereinafter, it passes through the pre-ignition zone.
[0085]
Therefore, in the present embodiment, in the transition region ATR, the following control is performed in order to prevent the light oil injection timing from entering the pre-ignition generation zone. That is, basically, control is performed so that the light oil injection timing is linearly interpolated between the regions A2 and A3, while the light oil injection timing is changed from α to β when the engine load LD passes the specific value LDx. Or from β to α discontinuously (see FIG. 4B).
[0086]
Regarding the adjustment of the injection amount of light oil and gasoline, also in the region ATR, the ratio of the injection amount of light oil to the injection amount of gasoline decreases as the engine load LD or the engine speed NE increases as in the regions A2 and A3. In this way, control is performed to increase the total fuel injection amount (see FIGS. 3A and 3B).
[0087]
[Outline of control procedure]
A specific procedure for the fuel injection control of the present embodiment described above will be described.
[0088]
FIG. 5 shows an outline of a fuel injection control routine (main routine) that is periodically executed through the ECU 30 during the operation of the engine 1.
[0089]
In this routine, first in step S101, the ECU 30 acquires information such as the accelerator pedal depression amount ACC, the engine speed NE, and the coolant temperature THW.
[0090]
In step S102, the ECU 30 determines whether or not it is within a predetermined period (several seconds to several minutes are set) after the engine 1 is started (when the engine 1 is started). In step S103, the ECU 30 determines whether or not the coolant temperature THW is equal to or lower than a predetermined value (for example, 70 ° C.) (before completion of warm-up).
[0091]
If the determinations in steps S102 and S103 are negative, the ECU 30 follows a control procedure (S104 to S108) specialized for the state after the engine 1 is started and after the engine is warmed up. On the other hand, when determination of at least one of steps S102 and 103 is affirmative, the control procedure (S200) specialized for the state at the time of starting of engine 1 or before completion of warm-up is followed.
[0092]
In step S104, the ECU 30 refers to the map (FIG. 2), and as the numerical values corresponding to the region (coordinates on the map) to which the operating state of the engine 1 belongs, the basic injection amount QDB and basic injection timing CADB of light oil, and gasoline A basic fuel injection amount QGB and a basic injection timing CADB are determined.
[0093]
In step S105, a feed forward correction value (hereinafter referred to as FF correction value) for correcting the basic injection amount QDB of light oil is determined with reference to a map prepared in advance. In the present embodiment, a temperature correspondence correction value kQD1 corresponding to the temperature of the engine 1 and a transient correspondence correction value kQD2 corresponding to a transient change in the operating state of the engine 1 are employed as the FF correction value.
[0094]
In step S106, the ECU 30 determines a feedback correction value (hereinafter referred to as an FB correction value) for correcting the basic injection amount QDB of light oil and the basic injection timing CADB. In the present embodiment, the misfire correspondence correction values kQD3 and kCAD3 corresponding to the misfire of the engine 1 and the premature ignition correspondence correction values kQD4 and kCAD4 corresponding to the premature ignition of light oil are adopted as the FB correction values. The correction values kQD3 and kQD4 are used to correct the basic fuel injection amount QDB, and the correction values kCAD3 and kCAD4 are used to correct the basic fuel injection timing CADB.
[0095]
In step S107, the ECU 30 multiplies the basic injection amount QDB and basic injection timing CADB of the light oil determined in step S104 by the FF correction values (kQD1, kQD2) and the FB correction values (kQD3, kCAD3, kQD4, kCAD4). The injection amount QD and the injection timing CAD are determined. Also, the gasoline injection amount QG and the injection timing CAG are determined. That is, in step S107, final adjustment is performed on the injection amount and injection timing of light oil and gasoline.
[0096]
In step S108, the ECU 30 sets the first fuel injection valve 10 and the second fuel injection valve 10 so that the light oil injection amount QD and the injection timing CAD, and the gasoline injection amount QG and the injection timing CAG become values determined in this routine. The fuel injection valve 20 is operated.
[0097]
After the processing of step S108 or step 200, the ECU 30 once exits this routine.
[0098]
Next, in the main routine, step S105 for calculating the FF correction value, step S106 for calculating the FB correction value, step S107 for performing final adjustment of the injection amount and injection timing of the light oil and gasoline, The contents of step S108 for operating the first fuel injection valve 10 and the second fuel injection valve 20, etc., and step S200 for performing specialized processing at the start of the engine 1 or before completion of warm-up are described. This will be described in detail.
[0099]
[S105 (calculation of FF correction value)]
For example, when the temperature of the engine 1 decreases, the ignitability of light oil injected into the combustion chamber 2 decreases. On the other hand, when the injection amount of light oil relative to the injection amount of gasoline is increased, the ignitability of the fuel supplied to the combustion chamber 2 is substantially increased. Therefore, in step S105, the temperature-corresponding correction value kQD1 is determined so that the injection amount of light oil increases as the temperature of the engine 1 decreases. Further, the temperature-corresponding correction value kQD1 is determined so that the light oil injection amount decreases as the temperature of the engine 1 increases.
[0100]
Further, for example, when the torque required for the engine 1 is increased when the driver depresses the accelerator pedal strongly, the fuel injection amount (total injection amount of light oil and gasoline) increases, and the engine is increased along with the increase in the fuel injection amount. The rotational speed NE and the intake air amount GA also increase. At this time, it is necessary to increase the intake air amount as the fuel injection amount increases. However, while the fuel injection amount responds quickly to the accelerator pedal depression, the intake air amount changes relatively slowly. As a result, the amount of intake air is insufficient, premature ignition occurs, and smoke is generated in the exhaust.
[0101]
Therefore, in step S105, when the torque required for the engine 1 increases transiently, the transient response correction value kQD2 is determined so that the injection amount of light oil decreases by taking into account the shortage of the intake air amount. . When the torque required for the engine 1 decreases transiently, the transient response correction value kQD2 is determined so that the injection amount of light oil increases by taking into account the excess intake air amount.
[0102]
Specifically, for example, referring to a map (not shown) based on the relationship between the actual measured value GA of the intake air amount calculated based on the output signal of the air flow meter, the accelerator depression amount ACC, and the engine speed NE. The calculated intake air amount is grasped with an estimated value (target value) GATRG, and a ratio GA / GATRG between the two is calculated. And the ratio GA / GATRG is less than “1.0” small In this case, the transient response correction value kQD2 is determined in consideration of the shortage of the intake air amount. When the ratio GA / GATRG is larger than “1.0”, the transient response correction value kQD2 is determined in consideration of the excessive intake air amount.
[0103]
[S106 (Calculation of FB correction value)]
Step S106 includes a process for determining misfire correspondence correction values kQD3 and kCAD3 and a process for determining pre-ignition correspondence correction values kQD4 and kCAD4.
[0104]
The misfire corresponding correction value kQD3 is a parameter for correcting the basic injection amount kQD of light oil, and the misfire corresponding correction value kCAD3 is a parameter for correcting the basic injection timing CAD of light oil. The correction values kQD3 and kCAD3 play a role of quickly eliminating a misfire when this occurs. The pre-ignition correspondence correction value kQD4 is a parameter for correcting the basic injection amount QDB of light oil, and the pre-ignition correspondence correction value kCAD4 is a parameter for correcting the basic injection timing CAD of light oil. The correction values kQD4 and kCAD4 play a role of quickly eliminating the light oil injected into the combustion chamber 2 when premature ignition occurs.
[0105]
First, FIG. 6 shows a process (subroutine S106 (1)) for determining misfire correspondence correction values kQD3 and kCAD3.
[0106]
When the process proceeds to the subroutine S106 (1), the ECU 30 first determines whether or not there is a misfire (S106A). The presence or absence of misfiring may be determined based on, for example, the magnitude of fluctuation per unit time of the engine speed NE. Alternatively, the pressure in the combustion chamber 2 may be monitored using a pressure sensor or the like, and the determination may be made based on the magnitude of the fluctuation range per unit time of the pressure.
[0107]
When a misfire occurs (when the determination in S106A is affirmative), the ECU 30 calculates a misfire corresponding correction value kQD3 that increases the ratio of the light oil injection amount to the gasoline injection amount by a predetermined amount, and determines the light oil injection timing. After calculating the misfire correspondence correction value kCAD3 to be retarded by a fixed amount (S106B), the subroutine S106 (1) is exited.
[0108]
On the other hand, if no misfire has occurred (if the determination in S106A is negative), the ECU 30 exits the subroutine S106 (1) without performing any processing. In this case, the misfire handling correction values kQD3 and kCAD3 employed in the previous routine are employed again in the current routine.
[0109]
By adopting such a control structure, if misfire occurs during operation of the engine 1, the proportion of the light oil injection amount increases by a predetermined amount as long as the misfire continues, and the light oil injection timing increases by a predetermined amount. Be retarded.
[0110]
After exiting the subroutine S106 (1), the ECU 30 proceeds to the subroutine S106 (2) shown in FIG.
[0111]
In the subroutine S106 (2), the ECU 30 first determines whether or not pre-ignition has occurred (S106C). If it is determined that pre-ignition has occurred, it is determined whether or not the light oil injection amount QD determined in step S107 of the main routine exceeds a lower limit (minimum amount necessary for light oil to self-ignite). (106D).
[0112]
If the determination in step S106D is affirmative, the ECU 30 proceeds to step S106E, calculates the pre-ignition correspondence correction value kQD4 that decreases the ratio of the light oil injection amount to the gasoline injection amount by a predetermined amount, and then executes the subroutine S106 ( Exit 2). In this case, the value adopted in the previous routine is again adopted as the latest value as the pre-ignition ignition correction value kCAD4.
[0113]
On the other hand, if the determination in step S106D is negative, the ECU 30 proceeds to step S106F and determines whether or not the operating state of the engine 1 belongs to the region A3 (see FIG. 2).
[0114]
When the operating state of the engine 1 belongs to the region A3 side with respect to the predetermined boundary line BL existing in the region ATR (when belonging to the high load / high rotation region), the ECU 30 retards the injection timing of the light oil by a predetermined amount. After calculating the pre-ignition correspondence correction value kCAD4 (S106G), the subroutine S106 (2) is exited. In this case, the value adopted in the previous routine is again adopted as the latest value as the pre-ignition ignition correction value kQD4. On the other hand, when the operating state of the engine 1 belongs to the regions A1 and A2 from the boundary BL (when it belongs to the low / medium load / low / medium rotation region), the ECU 30 advances the ignition timing by a predetermined amount to advance the light oil injection timing. After calculating the corresponding correction value kCAD4 (S106H), the subroutine 106 (2) is exited. Also in this case, the value adopted in the previous routine is again adopted as the latest value as the pre-ignition correspondence correction value kQD4.
[0115]
When it is determined in step S106 that premature ignition has not occurred, the ECU 30 exits the subroutine 106 (2) without performing any arithmetic processing. In this case, the pre-ignition ignition correction values kQD4 and kCAD4 employed in the previous routine are again employed as the latest values.
[0116]
In the subroutine 106 (2), when pre-ignition occurs, first, a process of gradually decreasing the ratio of the light oil injection amount to the gasoline injection amount is performed. This is because pre-ignition is less likely to occur as the ratio of the light oil injection amount decreases. However, if the injection amount of light oil decreases, the ignitability of light oil decreases and eventually misfire occurs. For this reason, when it is determined that the light oil injection amount is equal to or less than the predetermined lower limit value, the pre-ignition is suppressed by changing the light oil injection timing without reducing the light oil injection amount. As shown in FIG. 8A, during the execution of the fuel injection control according to the present embodiment, the light oil injection timing is advanced (region) in the pre-ignition generation zone over the entire operation region of the engine 1. It is set to a part of ATR and areas A1 and A2) or on the retarded side (part of area ATR and area A3). In many cases, the pre-ignition generation zone is expanded for some reason, and the inventors have confirmed that pre-ignition occurs when the light oil injection timing enters the pre-ignition generation zone. Yes.
[0117]
Therefore, in the present embodiment, when pre-ignition occurs (continues) under conditions where the amount of light oil injection cannot be reduced, the light oil injection timing is separated from the pre-ignition occurrence zone. Feedback control is performed (indicated by an arrow in FIG. 8A). As described above with reference to FIG. 4B, the engine load specific value LDx for discontinuously changing the light oil injection timing exists in the transition region ATR. The boundary line BL for determining whether to advance or retard the light oil injection timing is the specific value LDx and the engine speed NE that changes the light oil injection timing discontinuously within the transition region ATR. (NEx, LDx) (FIGS. 8A and 8B).
[0118]
[S107 (adjustment of gasoline injection amount, etc.)]
In step S107, after adjusting the injection amount of gasoline (correcting the basic injection amount QGB), etc., the injection amount QD and injection timing CAD of light oil, and the injection amount QG and injection timing CAG of gasoline are determined.
[0119]
The engine 1 generates thermal energy commensurate with the required torque by burning two types of fuel. For this reason, when changing (correcting) the light oil injection amount (volume) in order to suppress premature ignition and smoke, it is necessary to adjust the gasoline injection amount (volume) in conjunction with this correction. That is, when increasing the injection amount of light oil, it is necessary to decrease the injection amount of gasoline, and when decreasing the injection amount of light oil, it is necessary to increase gasoline. At this time, since the calorific value per unit amount is different between light oil and gasoline, the amount of decrease (increase) in the injection amount of light oil is simply added (multiplied) to the amount of increase (decrease) in the injection amount of gasoline. Then, the sum total of the thermal energy generated by the combustion of light oil and gasoline will change. Therefore, in the present embodiment, the gasoline injection amount QG is calculated in consideration of the difference between the heat generation amount due to light oil combustion and the heat generation amount due to gasoline combustion.
[0120]
The gasoline injection amount QG is calculated, for example, according to the following procedure.
[0121]
First, a correction value kQD multiplied by the basic injection amount QDB to determine the light oil injection amount QD of light oil is calculated as a function of each correction value kQD1, kQD2, kQD3, kQD4 (formula (1)).
[0122]
kQD = f (kQD1, kQD2, kQD3, kQD4)
... (1)
Next, the basic injection amount QDB is multiplied by the correction value kQD to calculate the light oil injection amount QD (Equation (2)).
[0123]
QD = kQD × QDB
... (2)
Next, a calorific value ΔH that increases by correcting the basic injection amount QDB of light oil is calculated (formula (3)).
[0124]
ΔH = (kQD-1) × QDB × ρD × HD
... (3)
However,
ρD: Specific gravity of light oil
HDB: calorific value due to combustion of light oil of unit volume (for example, 1 mm ^ 3)
Next, the gasoline amount (volume) corresponding to the heat generation amount ΔH is calculated as a correction value ΔQG to be subtracted from the gasoline basic injection amount QGB (formula (4)).
[0125]
ΔQG = ΔH / (ρG × HGB)
... (4)
However,
ρG: Specific gravity of gasoline
HGB: calorific value due to combustion of gasoline of unit volume (for example, 1mm ^ 3)
Next, the gasoline injection amount QG is calculated by subtracting the correction value ΔQG from the gasoline basic injection amount QGB (formula (5)).
[0126]
QG = QGB-ΔQG
... (5)
[S108 (execution of fuel injection)]
In step (subroutine) S108, the first fuel injection valve is set so that the injection amount QD and injection timing CAD of light oil and the injection amount QG and injection timing CAG of gasoline converge to the values determined in this routine. 10 and the second fuel injection valve 20 are operated. At this time, the ECU 30 synchronizes with the execution of another routine that controls the operating state of the engine 1, and (1) a process for changing the injection amount of the light oil, (2) a process for changing the injection timing of the light oil, And (3) Priorities are set for processing performed through other routines. Incidentally, in the present embodiment, processing for changing the exhaust gas circulation (EGR) rate of the engine 1 corresponds to processing performed through another routine.
[0127]
FIG. 9 shows details (subroutine) of the process in step S108 in the fuel injection control routine (FIG. 5). When the process proceeds to subroutine S108, ECU 30 determines in step S108A whether the operating state of engine 1 belongs to transition region ATR. If the determination is affirmative, whether the operating state of the engine 1 has shifted from the area A2 to the area A3 (S108B), has shifted from the area A3 to the area A2, or is arbitrary in the area ATR. Is determined (S108C).
[0128]
When the operating state of the engine 1 does not belong to the transition region ATR, or when it remains at an arbitrary position in the transition region ATR, the ECU 30 calculates the light oil injection amount QD and the injection timing CAD calculated this time, and the gasoline injection amount QG. Then, the fuel injection is executed by immediately adopting the injection timing CAG (S108D).
[0129]
On the other hand, when the operating state of the engine 1 belongs to the transition region ATR and is shifted from the region A2 to the region A3, the ECU 30 determines that (A) the delay of the light oil injection timing and (B) the EGR rate Decrease And (C) the reduction in the ratio of the light oil injection amount is performed in accordance with the priority order of (A) → (B) → (C), the first fuel injection valve 10, the second fuel injection valve 20, The other components of the engine 1 are controlled (S108E). Further, the first fuel injection valve 10, the second fuel injection valve 20, and other components of the engine 1 may be controlled so as to be performed according to the priority order of (B) → (A) → (C).
[0130]
On the other hand, when the operating state of the engine 1 belongs to the transition region ATR and is shifted from the region A3 to the region A2, the ECU 30 increases the ratio of the injection amount of (D) light oil, and (E) Of the injection timing and (F) EGR rate Increase Are controlled in accordance with the priority order of (D) → (E) → (F), the first fuel injection valve 10, the second fuel injection valve 20, and other components of the engine 1 are controlled (S108F). . Moreover, you may control the component of the 1st fuel injection valve 10, the 2nd fuel injection valve 20, and other engines 1 so that it may be performed according to the priority of (D)->(F)-> (E).
[0131]
As a means for changing the EGR rate, for example, a well-known EGR system (not shown) provided with an EGR passage communicating between the intake passage and the exhaust passage of the engine 1 and a control valve for changing the passage area of the passage. Can be used. In addition, this also uses a known variable valve system (variable valve timing system or variable valve lift amount system) that varies the operating characteristics of the intake valve 5B and the exhaust valve 6B, and substantially reduces the EGR rate (internal EGR amount). ) Can also be changed.
[0132]
After any one of steps S108D, S108E, and S108F, the ECU 30 returns to the main routine (FIG. 5).
[0133]
[S200 (control at start-up or before completion of warm-up)]
Before the engine 1 is started and a predetermined period elapses or when the engine 1 is not sufficiently warmed up, the ECU 30 performs the following process in step S200 instead of the series of processes in steps S104 to S107 (FIG. 5). I do.
[0134]
FIG. 10 shows the details (subroutine) of the process in step S200 in the fuel injection control routine (FIG. 5).
[0135]
When the processing is shifted to the subroutine S200, the ECU 30 first sets the cooling water temperature THW of the engine 1 to the preset three categories (1) “THW ≦ 0 ° C.” and (2) “0 ° C. <” through step S200A and step S200B. THW ≦ 40 ° C. ”(3) It is determined which one of“ 40 ° C. <THW ”belongs to. Then, the ECU 30 refers to a map (not shown) set in advance so as to correspond to each section, and performs fuel injection control specialized for each temperature condition.
[0136]
First, when the coolant temperature THW belongs to the category (1) “THW ≦ 0 ° C.”, the ECU 30 performs control to inject only light oil without injecting gasoline. At this time, it is preferable to control the injection timing between 10 to 20 ° BTDC and increase the injection amount of light oil while advancing the injection timing, for example, as the engine load LD or the engine speed NE increases (S200C). ).
[0137]
Further, when the coolant temperature THW belongs to the category (2) “0 ° C. <THW ≦ 40 ° C.”, the ECU 30 performs control to inject light oil and gasoline. At this time, it is preferable to control the light oil injection timing between 10 to 20 ° BTDC and advance the injection timing to increase the total fuel injection amount, for example, as the engine load LD or the engine speed NE increases. . For example, it is preferable to increase the ratio of the light oil injection amount to the gasoline injection amount as the engine load LD or the engine speed NE increases (S200D).
[0138]
When the coolant temperature THW belongs to the category (3) “40 ° C. <THW”, the ECU 30 performs control to inject light oil and gasoline. At this time, the injection timing of the light oil is controlled between 40 to 60 ° BTDC, and for example, the injection timing is advanced and the total fuel injection amount is increased as the engine load LD or the engine speed NE increases. preferable. For example, it is preferable to increase the ratio of the light oil injection amount to the gasoline injection amount as the engine load LD or the engine speed NE increases (S200E).
[0139]
[Effects Based on Embodiment]
As described above, according to the operation control method for the engine 1 according to the present embodiment or the apparatus that employs such an operation control method, the following operational effects can be achieved.
[0140]
(A) Of the operating regions A1, A2, ATR, and A3 that are partitioned based on the load LD and the rotational speed NE of the engine 1, in the region A1 where the parameters LD and NE are relatively small values, the ignitability is high. In regions A2, ATR, and A3 where only light oil is used for combustion and parameters LD and NE are relatively large, both light oil with high ignitability and gasoline with low ignitability and easy to form premixed gas are combusted. In addition, as the parameters LD and NE increase (in other words, the required torque increases), the ratio of the light oil supply amount to the gasoline supply amount is decreased.
[0141]
Thereby, in area | region A1, the concern of misfire becomes small by using light oil with high ignitability. Further, since there is little concern about premature ignition in the region A1, it is possible to inject light oil relatively early (for example, on the advance side with respect to 40 ° BTDC) and to mix more uniformly prior to combustion. Thereby, exhaust characteristics can be improved.
[0142]
On the other hand, in the regions A2, ATR, A3 where the parameters LD, NE are relatively large values, both light oil and gasoline are used for combustion, and the larger the parameters LD, NE, the light oil injection amount relative to the gasoline injection amount. Percentage of Decrease Adopting a combustion mode that has excellent fuel efficiency and exhaust characteristics, that is, a method of injecting light oil into a gasoline premixed gas and self-igniting while achieving both prevention of misfire and prevention of premature ignition .
[0143]
(B) Moreover, the following control is performed regarding the injection timing QD of the light oil that determines the ignition timing of the entire fuel. That is, among the operation regions A1, A2, ATR, and A3 divided based on the load LD and the rotational speed NE of the engine 1, in the regions A1, A2, where the parameters LD and NE are relatively small, the parameter LD , NE is advanced, the injection timing CAD is advanced, and the dispersion of light oil spray is promoted before the piston 3 approaches the compression top dead center (before the temperature and pressure of the combustion chamber 2 rises), thereby premature ignition. To prevent.
[0144]
On the other hand, when the operating state of the engine 1 shifts to the region A3 (when the pressure or temperature of the combustion chamber 2 further increases), no matter how much the injection timing CAD is advanced, pre-ignition occurs. For this reason, although it is inferior in fuel consumption characteristics and exhaust characteristics, the light oil injection timing CAD is delayed to near the compression top dead center in order to give priority to prevention of premature ignition.
[0145]
Thus, by setting the area A1 giving priority to the prevention of misfire and the area A3 giving priority to the prevention of premature ignition, an area having excellent fuel efficiency characteristics and exhaust characteristics (light oil in the premixed gas formed by gasoline). It is easy to expand the area A2 in which the operation mode in which the fuel is injected and self-ignited is adopted. As a result, the design freedom of the engine 1 is increased. For example, it is easy to set the compression ratio lower than that of a normal diesel engine while using light oil as a fuel for self-ignition, and the engine is downsized and has high output. Can be
[0146]
In the present embodiment, the operation region divided based on the load LD and the rotational speed NE of the engine 1 is set. Instead of this, for example, an operation region that is partitioned based on parameters such as torque, output, total fuel injection amount, or heat generation amount of the engine 1 may be set.
[0147]
(C) In the transition region ATR between the region A2 and the region A3, the light oil injection timing CAD is changed discontinuously under specific conditions. As a result, the control method is changed from the control that prevents the pre-ignition ignition by sufficiently advancing the light oil injection timing CAD to the control that prevents the pre-ignition by sufficiently retarding the light oil injection timing CAD. Premature ignition that occurs when switching can be reliably prevented.
[0148]
For example, during the transition from the region A2 to the region A3 (when the required torque increases), the control of increasing the total fuel supply amount and decreasing the EGR rate is performed, thereby suppressing the occurrence of smoke in the exhaust gas. . In particular, in the present embodiment, the operation of reducing the EGR rate is performed prior to (in priority to) the increase in the total supply amount of fuel, so that the generation of smoke in the exhaust gas is more effectively suppressed. Further, in the present embodiment, at the time of transition from the region A2 to the region A3, control is performed so that the retard operation of the light oil injection timing CAD is performed (prioritized) prior to the increase in the total fuel supply amount. Do. Thereby, premature ignition is prevented preferentially.
[0149]
Further, at the time of transition from the region 3 to the region 2 (when the required torque is decreased), the increase in the NOx concentration in the exhaust gas is suppressed by performing the control to decrease the total supply amount of fuel and increase the EGR rate. The In particular, in the present embodiment, the increase in the NOx concentration in the exhaust gas is more effectively suppressed by performing (prioritizing) the reduction in the total fuel supply amount prior to the operation for increasing the EGR rate. Further, in the present embodiment, at the time of transition from the region A3 to the region A2, the total fuel supply amount is controlled to be performed (prioritized) prior to the advance operation of the light oil injection timing CAD. I do. Thereby, premature ignition is prevented preferentially.
[0150]
(D) Further, the lower the coolant temperature THW, the higher the ratio of the light oil injection amount QD to the gasoline injection amount QG is corrected. Thereby, in order to suppress misfire and premature ignition, more reliable control can be performed. The same control can be performed using not only the coolant temperature THW but also other parameters representative of the temperature of the engine 1 (for example, the temperature in the exhaust passage 6).
[0151]
(E) Further, the ratio of the injection amount QD of light oil to the injection amount QG of gasoline is corrected according to the ratio GA / GATRG between the actually measured value GA of the intake air amount and the estimated value (target value) GATRG. As a result, the response delay of the intake air amount with respect to a transient change in the torque or output of the engine 1 (the shortage or excess of the air supplied to the combustion chamber 2) can be offset. Therefore, the ignition timing of the light oil and the combustion state of the fuel can be controlled more precisely. Note that the injection of gasoline is not limited to the ratio GA / GATRG between the actually measured value GA of the intake air amount and the estimated value (target value) GATRG, but based on other parameters that reflect the required torque of the engine 1 or the amount of change in output. You may correct | amend the ratio of the injection quantity QD of the light oil with respect to quantity QG.
[0152]
(F) Further, after calculating the correction value kQD of the basic injection amount QDB of light oil, even if the injection amount of the light oil is changed by the correction value kQD, the fuel (gasoline and light oil used for combustion of the engine 1) ) Is adjusted so that the total amount of generated heat becomes a value corresponding to the output (torque) required for the engine 1 (the correction value ΔQG is adopted). Thus, the torque and output of the engine 1 can be precisely controlled while correcting the light oil injection amount QD to suppress misfire and premature ignition.
[0153]
(G) At the time of low temperature start of the engine, substantially only the high cetane number fuel is injected and supplied to the combustion chamber, and the injection supply timing is set to about 10 ° to 20 ° before the compression top dead center of the engine. When the engine is started at room temperature, the high cetane number fuel and the low cetane number fuel are supplied, and the injection supply timing of the high cetane number fuel is about 10 ° to 20 ° before the compression top dead center of the engine. preferable.
[0154]
(H) In addition to the conditions for completing the warm-up of the engine 1, specialize in the conditions before the completion of the warm-up in which the combustion state and light oil ignitability are reduced, giving priority to improving the ignitability of the fuel Control. Thereby, misfire at the time of cold start etc. can be prevented effectively.
[0155]
(I) Moreover, the presence or absence of misfire of the engine 1 is monitored, and when this is detected, misfire is quickly eliminated by performing feedback control.
[0156]
(J) Further, the presence or absence of pre-ignition of the engine 1 is monitored, and when this is detected, the pre-ignition ignition is completed and canceled by performing feedback control. More specifically, as long as premature ignition continues, the light oil injection amount is reduced, and the light oil injection timing is corrected so as to depart from the premature ignition occurrence zone.
[0157]
At this time, since the injection amount of the light oil serving as the ignition source is not made less than a preset lower limit value, misfire can be reliably prevented.
[0158]
In addition, when correcting the timing of light oil injection supply performed as part of feedback control for eliminating premature ignition, a correction value kCAD4 having different properties is adopted depending on the region to which the operating state of the engine 1 belongs. That is, when the operation state of the engine 1 belongs to the region A3 side with respect to the predetermined boundary line BL existing in the region ATR, the control is performed to retard the injection timing of the light oil, and the operation state of the engine 1 is the boundary BL. If it belongs to the region A1 or A2 side, control for advancing the injection timing of the light oil is performed. Thereby, the injection timing of light oil can swiftly leave the early ignition occurrence zone (see FIG. 8).
[0159]
In the present embodiment, the control of each parameter QD, QG, CAD, and CAG has been described mainly for the case where the load LD and the rotational speed NE of the engine 1 are increased. On the other hand, when the load LD and the rotational speed NE of the engine 1 become small, the ECU 30 executes control in which the numerical values of the parameters QD, QG, CAD, and CAG change in the reverse direction.
[0160]
(Modification of hardware configuration)
FIG. 11 shows a modification of the hardware configuration to which the control structure according to the above embodiment can be applied. That is, a fuel injection valve 10 ′ that directly injects gasoline into the combustion chamber 2 is employed instead of the first fuel injection valve 10 (FIG. 1) that supplies gasoline to the intake port 5A as in the engine 1 ′ shown in FIG. May be. The configuration of FIG. 11 is disadvantageous than the configuration of FIG. 1 from the viewpoint that it is necessary to ensure the pressure resistance at the mounting portion of the fuel injection valve, but the gasoline injection timing is controlled with a higher degree of freedom. 1 is more advantageous than the configuration of FIG.
[0161]
Hereinafter, technical ideas other than the invention according to the claims ascertained from the above embodiments will be described together with the effects thereof.
[0162]
Low cetane number fuel supply means for supplying low cetane number fuel to form a premixed gas in the combustion chamber of the internal combustion engine, and high cetane number fuel supply means for injecting high cetane number fuel into the combustion chamber In an internal combustion engine, the parameter has the smallest value among the three operating regions specified based on any parameter among the output, torque, load, total fuel supply amount, heat generation amount, and rotation speed of the engine. A method of performing operation control corresponding to a region, a region where the parameter has the largest value, and a region where the parameter has an intermediate value, and in the region where the parameter has the smallest value, Only low-value fuel is injected and supplied, and in the region where the parameter is an intermediate value and the region where the parameter is the largest value, low-cetane fuel and high-cetane fuel are supplied. And as the parameter increases, the ratio of the supply amount of the high cetane fuel to the supply amount of the low cetane fuel decreases, and as the parameter increases, the injection supply timing of the high cetane fuel is advanced. A method for controlling the operation of an internal combustion engine, characterized in that in a region where the parameter has the largest value, the timing of injection supply of the high cetane number fuel is retarded from a predetermined value.
[0163]
According to such a method, the engine combustion based on the self-ignition of the premixed fuel can be performed in a wide operation region, and the exhaust characteristics can be improved.
[0164]
In particular, the injection timing of the high cetane fuel is controlled in a range of about 30 ° to 50 ° before the compression top dead center of the engine in the region where the parameter is the smallest value, and the parameter is set to an intermediate value. Is controlled in the range of about 50 ° to 60 ° before the compression top dead center of the engine, and in the region where the parameter is the largest value, it is about 0 ° to 10 ° before the compression top dead center of the engine. By controlling in the range, the reliability of the control is further enhanced.
[0165]
【The invention's effect】
As described above, according to the present invention, engine combustion based on self-ignition of premixed fuel can be performed in a wide operating range, and exhaust characteristics can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of an engine according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing characteristics of a map used for selecting an operation mode when executing fuel injection control according to the embodiment;
FIG. 3 is a schematic diagram showing a relationship between an injection amount of light oil and gasoline and an engine load when executing fuel injection control according to the embodiment;
FIG. 4 is a graph showing a change in light oil injection timing corresponding to a change in engine load when executing fuel injection control according to the embodiment;
FIG. 5 is a flowchart showing a fuel injection control routine employed in the same embodiment.
FIG. 6 is a flowchart showing a part (subroutine) of a fuel injection control routine employed in the embodiment.
FIG. 7 is a flowchart showing a part (subroutine) of a fuel injection control routine employed in the embodiment.
FIG. 8 is a schematic diagram showing the relationship between the light oil injection timing and the pre-ignition occurrence zone adopted in the same embodiment;
FIG. 9 is a flowchart showing a part (subroutine) of a fuel injection control routine employed in the embodiment.
FIG. 10 is a flowchart showing a part (subroutine) of a fuel injection control routine employed in the embodiment.
FIG. 11 is a schematic diagram showing another example of the configuration of the engine according to the embodiment;
[Explanation of symbols]
1 engine (internal combustion engine)
2 Combustion chamber
3 Piston
4 Connecting rod
5 Intake passage
5A Intake port
5B Intake valve
6 Exhaust passage
6A Exhaust port
6B Exhaust valve
30 Electronic control unit (ECU)

Claims (18)

Low cetane number fuel supply means for supplying low cetane number fuel to form a premixed gas in the combustion chamber of the internal combustion engine, and high cetane number fuel supply means for injecting high cetane number fuel into the combustion chamber In a compression self-ignition internal combustion engine, except for a state before starting the engine and before warming-up is completed, a predetermined first operating region where the load is low or medium load and a predetermined higher load than the first operating region A method of performing operation control corresponding to the second operation region,
In the first operating region,
The timing of the injection supply of the high cetane number fuel is advanced compared to the vicinity of the compression top dead center and the timing of the injection supply of the high cetane number fuel is advanced as the load of the engine increases.
Further, only the high cetane number fuel is injected and supplied to the combustion chamber in the low load region in the first operation region, and the low cetane number fuel and the high cetane number fuel are supplied to the combustion chamber in the medium load region in the first operation region. The ratio of the supply amount of the high cetane number fuel to the supply amount of the low cetane number fuel decreases as the load increases with the supply,
In the second operation region,
The timing of injection supply of the high cetane number fuel is retarded until a time near the compression top dead center,
In addition, the low cetane number fuel and the high cetane number fuel are supplied to the combustion chamber, and the ratio of the high cetane number fuel supply amount to the low cetane number fuel supply amount is decreased as the load increases. An operation control method for a compression self-ignition internal combustion engine. The timing of the injection supply of the high cetane number fuel,
In the first operating region, control is performed in a range of 30 ° to 60 ° before compression top dead center of the engine,
2. The operation control method for a compression self-ignition internal combustion engine according to claim 1, wherein in the second operation region, control is performed in a range of 0 ° to 10 ° before compression top dead center of the engine. When the operating state of the engine transitions between the first operating region and the second operating region,
The compression self-ignition internal combustion engine according to claim 1 or 2, wherein a change in the exhaust gas recirculation amount and a change in the total supply amount of fuel are performed together with a change in the timing of the injection supply of the high cetane fuel. Operation control method. When the operating state of the engine shifts from the first operating region to the second operating region,
4. The compression self-ignition internal combustion engine according to claim 3, wherein the delay of the injection supply timing of the high cetane number fuel and the reduction of the exhaust gas recirculation amount are performed prior to the increase of the total fuel supply amount. Operation control method. When the operating state of the engine shifts from the first operating region to the second operating region,
5. The operation control of a compression self-ignition internal combustion engine according to claim 4, wherein after the timing of injection supply of the high cetane fuel is retarded, the exhaust gas recirculation amount is reduced and then the total fuel supply amount is increased. Method. When the operating state of the engine shifts from the second operating region to the first operating region,
The reduction in the total supply amount of the fuel and the increase in the exhaust gas recirculation amount are performed prior to the advance of the injection supply timing of the high cetane number fuel. An operation control method for a compression self-ignition internal combustion engine. When the operating state of the engine shifts from the second operating region to the first operating region,
7. The operation control of a compression self-ignition internal combustion engine according to claim 6, wherein after the total supply amount of fuel is reduced, the exhaust gas recirculation amount is increased, and thereafter the timing of injection supply of the high cetane fuel is advanced. Method. When the operating state of the engine transitions between the first operating region and the second operating region,
The operation control method for a compression self-ignition internal combustion engine according to any one of claims 1 to 7, wherein the timing of injection supply of the high cetane fuel is not set to a value within a predetermined range in which pre-ignition occurs.   The compression according to any one of claims 1 to 8, wherein a correction is performed to increase a ratio of the supply amount of the high cetane number fuel to the supply amount of the low cetane number fuel as the temperature of the engine is lower. Operation control method for self-ignition internal combustion engine.   The ratio of the supply amount of the high cetane number fuel to the supply amount of the low cetane number fuel is corrected according to the amount of change in torque or output required for the engine. An operation control method for a compression self-ignition internal combustion engine according to claim 1. When the torque or output required for the engine increases, the ratio of the supply amount of the high cetane number fuel to the supply amount of the low cetane number fuel is reduced and corrected according to the amount of change,
When the torque or output required for the engine decreases, the ratio of the supply amount of the high cetane fuel to the supply amount of the low cetane fuel is increased and corrected according to the change amount. The operation control method for a compression self-ignition internal combustion engine according to claim 10.   The supply amount of the low cetane fuel is adjusted based on the supply amount of the high cetane fuel so that the total calorific value of the fuel used for combustion of the engine becomes a value corresponding to the output required for the engine. An operation control method for a compression self-ignition internal combustion engine according to any one of claims 9 to 11. While the engine is cold started, substantially only the high cetane fuel is injected and supplied to the combustion chamber, and the injection supply timing is set to 10 ° to 20 ° before the compression top dead center of the engine,
The high cetane number fuel and the low cetane number fuel are supplied at the normal temperature start of the engine, and the injection supply timing of the high cetane number fuel is set to 10 ° to 20 ° before the compression top dead center of the engine. An operation control method for a compression self-ignition internal combustion engine according to any one of claims 1 to 12.   When the engine is warmed up, the high cetane number fuel and the low cetane number fuel are supplied, and the injection supply timing of the high cetane number fuel is 40 ° to 60 ° before the compression top dead center of the engine. The operation control method for a compression self-ignition internal combustion engine according to claim 13.   When it is determined whether or not the engine has misfired, and when it is determined that the engine has misfired, the ratio of the high cetane number fuel supply amount to the low cetane number fuel supply amount is increased and corrected. 15. The operation control method for a compression self-ignition internal combustion engine according to any one of claims 1 to 14, wherein the timing of injection supply of the valence fuel is retarded.   16. The engine according to any one of claims 1 to 15, wherein the presence or absence of pre-ignition of the engine is determined, and the supply amount of the high cetane fuel is reduced and corrected when it is determined that the engine has pre-ignited. An operation control method for a compression self-ignition internal combustion engine according to claim 1.   The operation control method for a compression self-ignition internal combustion engine according to claim 16, wherein the supply amount of the high cetane number fuel is not less than a lower limit value capable of self-ignition.   When it is determined that the engine has ignited prematurely, when correcting the injection timing of the high cetane fuel to be performed to eliminate premature ignition, when the operating state of the engine is in the first operating region Corrects to advance the timing of injection supply of the high cetane fuel, and retards the timing of injection supply of the high cetane fuel when the operating state of the engine is in the second operating region The operation control method for a compression self-ignition internal combustion engine according to claim 16 or 17, characterized in that:

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