JP5937468B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine in which fuel is directly injected into a cylinder, and more particularly to control of post injection performed in an expansion stroke of a cylinder.

  Conventionally, a fuel injection valve for directly injecting fuel into a cylinder like a diesel engine has been provided, and main injection for generating engine torque is performed in the vicinity of the compression top dead center of the cylinder, and in the subsequent expansion stroke, Internal combustion engines that perform injection and post-injection are known. In general, most of the fuel by after-injection burns in the cylinder, while the fuel by post-injection flows out to the exhaust system without being burned, and is used for control for recovering the functions of the exhaust purification device and the like.

  For example, in the fuel injection control device described in Patent Document 1, in order to re-burn the fuel and PM that remain unburned immediately after the main injection, after-injection is performed, and fluctuations in torque resulting from the combustion are reduced. The timing of after injection is advanced or retarded. Also, from the viewpoint of suppressing the generation of smoke, a guard value is set for the advance angle correction amount based on the ignition delay period, while from the viewpoint of suppressing the adhesion of fuel to the cylinder wall surface, the retard angle correction amount is guarded. A value is set.

JP 2010-185332 A

  However, the technology of the above-mentioned conventional example is supposed that the combustion state of the after-injected fuel that is originally combusted in the cylinder is suitable, and the fuel is prevented from adhering to the cylinder wall surface while suppressing the fluctuation of torque and the generation of smoke. However, it does not relate to post-injection control that is not combusted in the cylinder.

  In the case of post-injection that is retarded compared to after injection, there is a demand to advance the injection timing in order to reduce the amount of adhesion to the cylinder wall as much as possible. When combustion is performed in the cylinder, the amount of unburned fuel flowing out to the exhaust system is reduced, and the effect of restoring the function of the exhaust purification device is reduced.

  In view of this point, an object of the present invention is to reduce the amount of fuel adhering to the cylinder wall surface due to post-injection and to suppress the combustion of the fuel in the cylinder. It is to be able to supply unburned fuel.

  In order to achieve the above object, in the present invention, first, the post-injection timing is controlled so as to reach the most advanced timing in the range where the fuel does not ignite, and the amount of fuel adhering to the cylinder wall surface still increases. In some cases, the post-injection timing was further advanced while suppressing fuel ignition by reducing the oxygen concentration in the cylinder.

-Solution-
Specifically, the present invention is directed to a control device for an internal combustion engine that includes a fuel injection valve that injects fuel directly into a cylinder and that performs at least main injection and post injection by the fuel injection valve. And a control means for controlling the timing of the post injection and an oxygen concentration adjusting means for adjusting the oxygen concentration in the cylinder so as to reach the most advanced angle timing within a range in which the fuel by the post injection does not ignite. The control means determines whether or not the amount of fuel adhering to the cylinder wall surface due to the post injection is greater than a predetermined amount, and if it is determined that the wall surface adhesion amount is greater than or equal to the predetermined amount even at the most advanced angle timing, While the oxygen concentration in the cylinder is lowered by the oxygen concentration adjusting means, the post injection timing is further advanced.

  Due to this specific matter, during the operation of the internal combustion engine, at least the main injection for controlling the engine torque and the subsequent post injection are executed by the control means, and the injected fuel is ignited at the timing of the post injection. It is controlled to the most advanced timing in the range where it does not. Therefore, the post-injected fuel is not ignited, and a sufficient amount is supplied to an exhaust system purification device or the like, and the post-injection timing is controlled closer to the advance angle. The adhesion of can also be reduced.

  Further, when the post-injection timing is close to the advance angle, when the amount of fuel adhering to the wall surface increases (for example, when the post-injection amount is large), the fuel is reduced by reducing the oxygen concentration in the cylinder. By making the state difficult to ignite and by further advancing the post injection timing, it is possible to further reduce the fuel wall adhesion. In other words, while preventing the fuel from sticking to the cylinder wall due to post-injection, the fuel can also be prevented from burning in the cylinder, and a sufficient amount of unburned fuel is supplied to the exhaust system purifier, etc. Thus, the function can be effectively restored.

  The control means may change not only the timing of post-injection but also the fuel injection pressure, and if the post-injection is divided into a plurality of times, the number of divisions is changed. May be. That is, if the fuel injection pressure is reduced or the injection is divided and performed, the penetration force of the fuel spray can be reduced and the adhesion to the cylinder wall surface can be reduced.

  Further, the control means estimates the equivalence ratio and temperature state in the post-injected fuel spray, determines whether or not the fuel spray ignites, and retards the post-injection timing if determined to ignite. On the other hand, if it is determined that the ignition is not performed, it may be corrected to the advance side. In this way, it is possible to accurately determine whether or not the fuel by the post-injection is ignited, and to control the most advanced timing in the range where no ignition is performed.

  The equivalence ratio in the fuel spray is determined by taking into account the injection characteristics of the fuel injection valve, the injection conditions such as the fuel injection amount and the injection pressure, and the temperature and pressure in the cylinder at the time of injection. And can be calculated from the spray angle. As for the temperature state in the cylinder, the amount of generated heat is predicted from the injection conditions of fuel injection performed before post-injection (preferably taking into account the spray characteristics of the preceding fuel injection and the history of in-cylinder temperature) The in-cylinder temperature during post injection can be predicted.

  Further, the post-injected fuel wall surface adhesion amount is determined by the control means based on the fuel injection distance by the post injection and the distance from the injection hole to the cylinder wall surface, whether or not the wall surface adhesion amount is greater than a predetermined amount. can do. That is, based on the mass and speed of the fuel ejected from the nozzle hole of the fuel injection valve and the temperature and density in the cylinder, the flight distance of the fuel in a minute unit time is calculated, and this flight distance is calculated from the nozzle hole to the cylinder. The amount of fuel that reaches the cylinder wall surface may be integrated within a time that is greater than or equal to the distance to the wall surface.

  Further, the control means preferably reduces the oxygen concentration so that the equivalent ratio in the spray of the post-injected fuel falls outside the combustible range when the oxygen concentration in the cylinder is reduced by the oxygen concentration adjusting means. . In this way, when the post-injection timing is advanced from the above-mentioned most advanced angle timing, even if the temperature in the cylinder is higher than the ignition temperature of the fuel spray, fuel ignition by post-injection is prevented. Can be almost blocked.

  In order to reduce the oxygen concentration, the amount of burnt gas remaining in the cylinder may be increased, or the burnt gas (exhaust gas) once discharged into the exhaust system may be sucked back. Preferably, the oxygen concentration adjusting means adjusts the oxygen concentration of the intake air into the cylinder by returning a part of the exhaust gas from the exhaust passage of the internal combustion engine to the intake passage and adjusting the amount of the return gas. And it is sufficient.

  In other words, the exhaust gas recirculated from the exhaust passage to the intake passage has a lower temperature than the burned gas remaining in the cylinder and the exhaust gas sucked back from the exhaust system, so that the recirculation is performed to reduce the oxygen concentration in the cylinder. Even if the amount of exhaust gas to be increased is increased, the increase in the in-cylinder temperature accompanying this becomes relatively small, which is advantageous in suppressing ignition of post-injected fuel. The exhaust gas may be cooled during the reflux.

  According to the control apparatus for an internal combustion engine according to the present invention, if the timing of post-injection performed after the main injection is controlled to the most advanced timing in a range where the fuel is not ignited, and it is determined that the fuel wall adhesion amount still increases. The ignition of the fuel was suppressed by lowering the oxygen concentration in the cylinder, and the post injection timing was further advanced. As a result, adhesion of post-injected fuel to the cylinder wall surface is further reduced, and a sufficient amount of unburned fuel is supplied to an exhaust system purifier and the like while sufficiently suppressing oil dilution. Can be effectively recovered.

It is a mimetic diagram showing the whole engine control system composition concerning an embodiment. It is a longitudinal cross-sectional view in a cylinder shown about post injection. It is explanatory drawing which shows typically the injection form of fuel, such as main injection and post injection. It is a graph which shows the comparison of the calculated value of the air-fuel | gaseous temperature in fuel spray, and an experimental value. It is a flowchart figure which shows the first half part of the control routine of post injection. It is a flowchart figure which shows the latter half part of the control routine. It is a graph which shows the change of the fuel-air mixture temperature, the equivalence ratio, the oil dilution rate, and the DPF bed temperature in the fuel spray when the post-injection time changes, in relation to each other. FIG. 8 is a view corresponding to FIG. 7 in a case where the oxygen concentration in the cylinder is reduced by EGR control.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

-Overall configuration of internal combustion engine-
FIG. 1 is a schematic diagram showing an overall configuration of an internal combustion engine 1 and its control system according to an embodiment of the present invention. The internal combustion engine 1 is a cylinder injection type diesel engine having four cylinders 1a, 1a,... As an example, and a cooling water flow path (water jacket) so as to surround the cylinders 1a, 1a,. 1b is formed. A water temperature sensor 21 that outputs a signal corresponding to the coolant temperature is disposed in the coolant channel 1b.

  A piston 2 is arranged in each cylinder 1a as shown in an enlarged view in FIG. 2, and a combustion chamber is defined between the cylinder head 3 and the cylinder head 3 that closes the upper end of the cylinder 1a. In addition, a cavity 2 a that constitutes a part of the combustion chamber is recessed at the top of the piston 2. The piston 2 is connected to the crankshaft 5 via connecting rods 4, 4,... In the vicinity thereof, a crank angle sensor 22 for transmitting a pulse signal every time the crankshaft 5 rotates by a predetermined angle is disposed. Has been.

  Further, as shown only in FIG. 2, for each cylinder 1a, an intake port 3a and an exhaust port 3b are formed in the cylinder head 3, and are opened and closed by an intake valve 3c and an exhaust valve 3d, respectively. Between the intake port 3a and the exhaust port 3b, fuel injection valves 6, 6,... Are arranged from the ceiling portion of the combustion chamber into the cylinder 1a, and a plurality of tip portions (lower end portions in the figure) are arranged. The fuel spray S is formed so as to extend slightly downward from the nozzle hole toward the outer peripheral side in the cylinder 1a.

  As shown in FIG. 1, the fuel injection valve 6 of each cylinder 1a is connected to a common rail 7 that is a fuel pressure accumulating vessel, and a common rail pressure sensor 23 that detects the internal pressure (fuel pressure) is connected to the common rail 7. It is arranged. A booster pump 8 is connected to the common rail 7 via a fuel pipe, and the fuel in the fuel tank 9 is boosted by the booster pump 8 and supplied to the common rail 7.

  Thus, the high-pressure fuel stored in the common rail 7 is distributed to the fuel injection valve 6 of each cylinder 1a and is injected into the cylinder 1a through the injection hole as described above. The operation control of the fuel injection valve 6 is performed by an ECU (Electronic Control Unit) 30 via an EDU (Electrical Driving Unit) 40. The EDU 40 is configured by a known drive circuit that operates an electromagnetic actuator of the fuel injection valve 6 based on a control signal from the ECU 30.

  An intake system including an intake manifold 10 and a throttle valve 11 is disposed on one side of the internal combustion engine 1 (upper side in FIG. 1), and is connected to the cylinder 1a via the intake port 3a. An exhaust system including an exhaust manifold 12 and an exhaust purification device (not shown) is disposed on the other side (lower side in FIG. 1) of the internal combustion engine 1, and is connected to the cylinder 1a via the exhaust port 3b. Has been.

  In the intake stroke for each cylinder 1a, the intake valve 3c is opened in synchronization with the lowering of the piston 3, and air is drawn into the cylinder 1a from the intake system. This air is compressed by the piston 3 ascending in the compression stroke of the cylinder 1a to become high temperature and high pressure, and fuel is injected from the fuel injection valve 6 from the latter half of the compression stroke to the vicinity of the compression top dead center and further from the expansion stroke. The control related to the fuel injection will be described in detail later.

  Thus, the injected fuel is split and entrains the surrounding air to form a spray S (see FIG. 2), in which minute fuel droplets are mixed with air while evaporating. Then, after a so-called ignition delay period, the air-fuel mixture self-ignites (premixed combustion) to generate a flame, and further burns with surrounding air (diffusion combustion). The piston 2 is pushed down by this combustion pressure, and the crankshaft 5 is rotated via the connecting rod 4.

  The burned gas that has rotated the crankshaft 5 through the piston 2 in this way flows out to the exhaust port 3b when the exhaust valve 3d is opened at the end of the expansion stroke of the cylinder 1a, and in the exhaust stroke, the piston 2 rises. It is discharged from the cylinder 1a. The burned gas (exhaust gas) discharged to the exhaust port 3b in this manner flows through the exhaust manifold 12 and is purified by the exhaust purification device, and then released into the atmosphere.

  Although not shown, the exhaust gas purification device includes a known NSR (NOx Storage Reduction) catalyst and DPF (Diesel Particulate Filter). The DPF is, for example, a ceramic structure including a large number of cells, and collects PM (Particulate Matter) contained in the exhaust gas when the exhaust gas passes through the cell wall. is there.

  In the present embodiment, a pipeline 13 (hereinafter referred to as an EGR passage 13) that connects the intake system and the exhaust system is provided. The EGR passage 13 is branched from the vicinity of the collecting portion of the exhaust manifold 12, takes out a part of the high-pressure exhaust gas, and returns to the vicinity of the collecting portion of the intake manifold 10 (downstream side of the throttle valve 11). An EGR valve 14 that adjusts the flow rate of the exhaust gas that recirculates (hereinafter also referred to as EGR gas) is provided. The EGR passage 13 may be provided with an EGR cooler that cools the EGR gas.

  By recirculating the exhaust gas to the intake system and supplying it into the cylinder 1a, the combustion temperature can be lowered and NOx generation can be suppressed. However, as the amount of EGR gas increases, the oxygen concentration decreases accordingly. As a result, the combustion state may deteriorate. Therefore, the opening degree of the EGR valve 14 is controlled according to the engine operating state, and the EGR gas amount is adjusted. The EGR passage 13 and the EGR valve 14 constitute oxygen concentration adjusting means for adjusting the oxygen concentration in the cylinder 1a.

-Control system-
Output signals from the water temperature sensor 21, the crank angle sensor 22, and the common rail pressure sensor 23 are input to an ECU 30 serving as control means. Further, an accelerator opening sensor 24 that detects the amount of depression of the accelerator pedal by the driver, an air flow meter 25 that detects the intake air amount, an intake pressure sensor 26 that detects intake pressure, and the like are also electrically connected to the ECU 30. Output signals from these sensors 24 to 26 are also input to the ECU 30.

  On the other hand, the ECU 30 is electrically connected to, for example, the fuel injection valve 6, the boost pump 8, the throttle valve 11, the EGR valve 14, and the like (the fuel injection valve 6 is connected via the EDU 40, and is connected to the EGR valve 14. Again, it is connected via the same drive unit 15) and outputs a control signal as required.

For example, the ECU 30 controls the operation of the booster pump 8 to control the pressure of fuel supplied from the fuel tank 9 to the common rail 7 (corresponding to the fuel injection pressure _Pinj ). This pressure is basically higher as the engine load is higher and as the engine speed is higher. That is, the ECU 30 controls the boost pump 8 so that the fuel pressure in the common rail becomes equal to the target rail pressure set based on the operating state of the internal combustion engine 1, that is, the fuel injection pressure becomes the target injection pressure. Meter the fuel discharge.

Further, the ECU 30 controls the operation of the fuel injection valve 6 to control the injection amount, the injection timing, and the like. In this embodiment, as schematically shown in FIG. 3, as an example, after the main injection that mainly contributes to torque generation, sub-injection called after-injection or post-injection is performed, or pilot injection or A secondary injection called pre-injection is performed. That is, the injection amount... Q _main , Q _post ,... And the injection timing ... t _main , t _post ,.

  As shown in FIG. 3, the pilot injection is performed at a timing that is greatly advanced from the main injection, and the in-cylinder temperature is raised by the combustion of the lean premixed gas formed in the cylinder 1a (low temperature combustion). In addition, the pre-injection adjusts the ignition delay of the main-injected fuel by injecting and burning a small amount of fuel immediately before the main injection, and prevents the initial combustion from becoming excessively intense.

  On the other hand, the main injection is an injection operation for torque control, and is performed near the compression top dead center (TDC). The fuel injection amount in the main injection is basically determined so as to obtain the required torque according to the operating state such as the engine speed, the accelerator operation amount (accelerator opening), the coolant temperature, the intake air temperature, and the like. . For example, the higher the engine speed and the greater the accelerator opening, the higher the required torque value of the internal combustion engine 1, and accordingly, the fuel injection amount of the main injection is set to be larger accordingly.

  Further, after-injection and post-injection are performed when the functions of the purification device such as the NSR and DPF of the exhaust system are restored. After-injection is an injection operation for raising the exhaust gas temperature, and most of the fuel injected into the cylinder 1a burns, but the heat generated at that time is converted into the torque of the internal combustion engine 1. It is performed at a timing that raises the temperature of the exhaust gas.

  On the other hand, the post injection is performed at a timing at which the fuel does not burn in the cylinder 1a. For example, post-injection is performed at the time of DPF regeneration in which the amount of PM trapped in the DPF exceeds a predetermined value and is burned and removed. The post-injected fuel flows into the exhaust port 3d in an unburned state, reaches the NSR, and oxidizes components such as HC and CO, thereby effectively raising the temperatures of the NSR and DPF.

  As a result, when the temperature of the DPF rises to a predetermined temperature (for example, 600 ° or more), the accumulated PM starts burning, and the temperature of the DPF further rises due to heat generated by this combustion. By maintaining such a state for a predetermined time (for example, about 10 minutes), the deposited PM is almost completely removed, and the PM collection ability of the DPF is restored.

-Control of post injection-
As described above, the post-injection performed for DPF regeneration or the like is performed when the piston 2 is lowered in the expansion stroke of the cylinder 1a as shown in FIG. The fuel spray S extending toward the outer peripheral side of the cylinder 1a may reach the cylinder wall surface. Since this fuel adheres to the cylinder wall surface and a part thereof dilutes the engine oil and changes its properties, it must be avoided that the dilution ratio of the oil by the fuel becomes higher than a predetermined value.

  In this regard, in the expansion stroke of the cylinder 1a, the temperature and pressure in the cylinder decrease as the piston moves down, so that the flight distance of the fuel increases as the post injection timing is retarded, and the amount of adhesion to the cylinder wall surface increases. There is a tendency to increase. Therefore, in order to avoid the adverse effects of oil dilution while ensuring a sufficient post injection amount, it is desirable to advance the post injection timing as much as possible.

  However, as the post-injection timing is advanced, the temperature and pressure in the cylinder 1a at the time of injection increase, and the amount of oxygen remaining in the cylinder 1a increases, so that part of the fuel ignites. The possibility of burning increases. When a part of the fuel burns in the cylinder 1a in this way, the amount of unburned fuel flowing out to the exhaust system is reduced by that amount, and for example, the above-mentioned DPF regeneration effect is reduced. As a result, if the time for performing the DPF regeneration becomes longer, there is a possibility that the fuel consumption is deteriorated.

  Considering this point, in the present embodiment, first, the post-injection timing is advanced to the maximum in a range in which the fuel does not ignite, thereby suppressing the fuel wall surface adhesion. Even in this state, when the amount of fuel adhering to the cylinder wall surface increases and there is a possibility of causing the adverse effect of oil dilution, the oxygen concentration in the cylinder 1a is lowered by increasing the EGR gas amount. In this way, the timing of post-injection is further advanced while suppressing ignition.

  As a configuration for controlling such post injection, the ECU 30 includes a memory 31, an in-cylinder state calculating unit 32, a spray characteristic calculating unit 33, a pre-post-injection state calculating unit 34, an ignition as schematically shown in FIG. A determination unit 35, an injection condition correction unit 36, an oil dilution rate determination unit 37, a target oxygen concentration calculation unit 38, and an EGR opening degree correction unit 39 are provided.

  Note that the functions of these means are realized by the CPU executing a predetermined control routine stored in the ROM of the ECU 30 or the like. In other words, each means is provided in the ECU 30 in the form of software, and the functions of these means are combined organically, and there is an effect specific to the control device for the internal combustion engine according to the present embodiment. is there.

  Hereinafter, the function of each means will be described in detail. First, the in-cylinder state calculation means 32 includes a pulse signal from the crank angle sensor 22, a cooling water temperature detection signal from the water temperature sensor 21, an accelerator opening signal from the accelerator opening sensor 24, and an air flow meter 25. A signal relating to the operating state of the internal combustion engine 1 such as an intake air amount detection signal is read, and the state (cylinder temperature, cylinder density, cylinder pressure, intake air amount, etc.) in the cylinder 1a is calculated.

  Various methods are known for calculating the in-cylinder temperature and pressure. As an example, the in-cylinder density may be calculated by taking into account the amount of intake air and air pressure, the amount of fuel injection, the amount of EGR gas, and the cooling water temperature. Further, a map in which the relationship between the output signal of each sensor and the in-cylinder density is defined in advance by experiments and simulations may be stored in the ROM of the ECU 30, and the in-cylinder density may be obtained from this map.

  The spray characteristic calculation means 33 includes not only main injection and post injection but also pilot injection and the like. The initial value of the injection condition for each injection operation (or the initial value of each injection operation when the main injection is divided) From the state in the cylinder 1a calculated by the in-cylinder state calculation means 32, spray characteristics such as spray penetration force, spray angle, injection period, evaporation amount, equivalent ratio (average equivalent ratio in the spray), etc. calculate. The injection conditions include the fuel pressure (corresponding to the fuel injection pressure) detected by the common rail pressure sensor 23, the fuel injection amount, the injection timing, the number of injections, and the like. The fuel injection amount is recognized based on a control signal output from the ECU 30 to the EDU 40.

  The penetration force and the spray angle increase as the fuel injection pressure increases. The injection period is obtained from the fuel injection amount and the fuel injection pressure, and is calculated as a period during which a target fuel injection amount is obtained. The amount of evaporation and the equivalent ratio are determined from the penetration force and the spray angle. As a method for calculating the spray angle, a well-known arithmetic expression (for example, “Huan's formula”) may be used. Further, the relationship between the fuel injection amount or the injection pressure and the spray angle may be mapped in advance through experiments or simulations and stored in the ROM of the ECU 30, and the spray angle may be obtained from this map. The same applies to the penetration force, the evaporation amount, and the equivalence ratio.

The post-injection state calculation means 34 is a state in the cylinder 1a at the time of post-injection, specifically, the temperature T _post in the cylinder 1a immediately before post-injection (this is the in-cylinder temperature, hereinafter referred to as the pre-injection temperature). ), Oxygen concentration, and the like. The post-injection temperature T _post is based on the state in the cylinder 1a calculated by the in-cylinder state calculation means 32, and is based on the spray characteristics of the main injection, the pre-injection, and the pilot injection before the post-injection. Can be calculated. At this time, it is preferable to consider the history of the in-cylinder temperature.

For example, if the relationship between the combustion amount of each injection prior to post-injection and the temperature T _post- post-injection before post-injection is examined by experiments or simulations in advance, the result is mapped and stored in the ROM of the ECU 30. The post-injection temperature T _post can be obtained from the map. The combustion amount of each injection may be mapped by examining the relationship between the average equivalence ratio in the spray and the in-cylinder temperature. Similarly, the oxygen concentration may be calculated by obtaining the amount of oxygen consumed by each of the injections before the post injection based on the state in the cylinder 1a calculated by the in-cylinder state calculating means 32.

The ignition determination means 35 is based on the fuel spray equivalence ratio (average equivalence ratio in the spray) and the mixture temperature in the fuel spray or the pre-post-injection temperature T _post. Judge whether or not to ignite. The equivalence ratio is calculated based on the pre-post-injection temperature T _post , the oxygen concentration, and the post-injection injection condition (initial value) calculated by the pre-post-injection state calculating unit 34 as described above. Can be calculated.

Further, the mixture temperature in the fuel spray can be calculated from the pre-injection temperature T _post (in-cylinder temperature) by, for example, the following equation (1). If the determination is made based on the mixture temperature T _x , it is possible to determine the presence or absence of ignition more accurately than the determination based on the pre-injection temperature T _post .

In the equation (1), M _fuel is the amount of fuel evaporation in fuel spray, C _fl is the specific heat of the liquid fuel, T _sat is the fuel saturation temperature, and T ₁₀ is the initial temperature of the liquid fuel. H _f is the latent heat of vaporization of the fuel. Further, M _a is the amount of atmospheric gas in the fuel spray, C _fa is the specific heat of the atmospheric gas, T _ent is the atmospheric temperature (ie, temperature T _post before post injection), and C _fv is the fuel vapor. Specific heat.

FIG. 4 shows a comparison between the result of calculating the mixture temperature T _x in the fuel spray by the equation (1) and the result obtained by examining this. The solid line graph is a calculated value when the post-injection temperature T _post is 950K, and the broken line graph is also a calculated value when the temperature is 1200K. In either case, the temperature decreases as the fuel evaporates immediately after injection, and thereafter the temperature increases due to heat received from the surroundings. Further, it can be seen that both the solid line and the broken line are well correlated with the experimental values (indicated by squares or triangles), and the mixture temperature T _x can be calculated by the equation (1).

  Based on the result of the determination by the ignition determination means 35, the injection condition correction means 36 corrects the post injection timing to the advance angle or retard angle side. That is, if it is determined not to ignite, the post injection timing is advanced, whereas if it is determined to ignite, the post injection timing is retarded. As a result, the post injection timing can be controlled to the most advanced timing within a range in which the fuel does not ignite.

At this time, the advance or retard correction amount may be a predetermined constant value, but it depends on the deviation (temperature deviation) between the fuel ignition temperature and the mixture temperature T _x or the pre-injection temperature T _post. Thus, the correction amount may be set to increase as the deviation increases. That is, a table is created by examining a suitable relationship between the temperature deviation and the post-injection timing correction amount in advance through experiments, simulations, etc., stored in the ROM of the ECU 30, and the correction amount is read from this table. do it.

  The oil dilution rate determination means 37 is a spray characteristic at the post-injection time corrected mainly as described above (spray penetration force, spray angle, injection period, evaporation amount, equivalence ratio calculated by the spray characteristic calculation means 33). Etc.), the amount of fuel adhering to the wall surface of the cylinder 1a is calculated, and it is determined whether or not this amount exceeds a predetermined threshold value. This threshold value is set based on the results of experiments and simulations to such a value that the oil dilution rate due to the fuel adhering to the wall surface becomes higher than a predetermined value and causes an adverse effect due to dilution of engine oil.

  There are various known ways of calculating the amount of fuel adhering to the cylinder wall surface. For example, as disclosed in Japanese Patent Application Laid-Open No. 2011-241774, the fuel ejected from the nozzle hole of the fuel injection valve 6 The flight distance of the fuel droplets in a minute unit time is calculated based on the speed of the cylinder 1a and the temperature and density in the cylinder 1a, and this flight distance is the distance in the fuel flight direction from the nozzle hole to the cylinder wall surface (see FIG. The amount of fuel that reaches the cylinder wall surface in the form of droplets may be integrated within a time period equal to or greater than (see D of 2).

  Here, if the fuel injection valve is the same, the speed of the fuel from the injection hole is highly dependent on the injection pressure and the injection amount, and the temperature and density in the cylinder 1 a calculated by the in-cylinder state calculation means 32. Is strongly correlated with the operating state of the internal combustion engine 1. Therefore, if the relationship between the operating state of the internal combustion engine 1, the post-injection amount and the fuel pressure, and the amount of fuel adhering to the wall surface is examined in advance by experiments, simulations, etc., this result is mapped and stored in the ROM of the ECU 30. From this, the amount of fuel wall surface adhesion can be determined.

  When the amount of fuel adhering to the cylinder wall surface calculated as described above is larger than the threshold value and the oil dilution rate determination unit 37 determines that the oil dilution rate is higher than a predetermined value, the injection condition correction unit 36 However, the post injection timing is further corrected to the advance side. That is, the injection condition correction means 36 controls the post injection timing to the most advanced angle timing within the range where the fuel is not ignited, and when the oil dilution rate becomes higher than a predetermined value at the most advanced angle timing, It is to advance.

  In this case, the post injection timing is advanced so that the amount of fuel adhering to the cylinder wall surface becomes substantially a threshold value. That is, for example, a post-injection timing at which the fuel wall surface adhesion amount calculated by the oil dilution rate determination means 37 based on the map becomes the threshold value is obtained and advanced to this target injection timing. That's fine.

  As described above, the target oxygen concentration calculating means 38 is the in-cylinder temperature at the post-injection timing corrected from the most advanced timing to the advanced angle side (calculated by the in-cylinder state calculating means 32, and more than the ignition temperature of the air-fuel mixture). The target oxygen concentration is calculated so that the average equivalence ratio in the spray is higher than the combustible range of the fuel (that is, the fuel is rich). Note that the relationship between the in-cylinder temperature and the upper limit of the combustible range of the equivalence ratio may be preliminarily examined through experiments, simulations, or the like to create a table and store it in the ROM of the ECU 30.

  Then, the EGR opening degree correcting means 39 corrects the opening degree of the EGR valve 14 so that the oxygen concentration calculated as described above is obtained. That is, the deviation between the target oxygen concentration and the oxygen concentration in the cylinder 1a at the post-injection timing corrected from the most advanced angle timing to the advanced angle side as described above and the pre-post-injection state calculation means 34. Accordingly, the target value of the opening degree of the EGR valve 14 is corrected to the open side. This correction amount may also be stored in the ROM of the ECU 30 by examining a suitable relationship between the oxygen concentration deviation and the correction amount of the opening degree of the EGR valve 14 in advance by experiments or simulations.

-Post injection control routine-
Hereinafter, a specific procedure of post injection control performed by the ECU 30 will be described with reference to the flowcharts of FIGS. 5 and 6. Note that the processing shown in these flowcharts is executed at predetermined time intervals when the internal combustion engine 1 is in an operation state in which post-injection is executed, for example, DPF regeneration.

  First, the current operating state of the internal combustion engine 1 is read in step ST1 of the flow of FIG. For example, reading of the coolant temperature by the water temperature sensor 21, reading of the engine speed calculated based on the detection value of the crank angle sensor 22, reading of the internal pressure (fuel pressure) of the common rail 7 by the common rail pressure sensor 23, accelerator opening sensor Reading of the accelerator opening detected by 24, reading of the intake air amount by the air flow meter 25, reading of the intake pressure by the intake pressure sensor 26, and the like are performed.

  Subsequently, in step ST2, the state quantity in the cylinder 1a is calculated, that is, the in-cylinder temperature, the in-cylinder density, the in-cylinder pressure, the intake air amount, etc. are calculated by the in-cylinder state calculation means 32, and in the next step ST3 Among the pilot injection, pre-injection, main injection, after-injection, and post-injection, the initial value (injection initial value) of the injection condition is read for the injection operation to be executed in the current operating state.

  Then, based on the read initial value of the injection condition and the state in the cylinder 1a calculated in step ST2, the fuel spray penetration force and the spray angle for each of the injection operations performed before the post injection are performed. The injection period, the evaporation amount, the equivalence ratio, etc. are calculated (step ST4). That is, the fuel spray characteristics of each injection performed before the post injection are calculated by the spray characteristic calculation means 33 described above.

Subsequently, in step ST5, the pre-post-injection state calculation means 34 sets the pre-post-injection temperature T _post (or the mixture temperature T _x in the fuel spray by the post injection) and the oxygen concentration, that is, the initial values. The temperature and oxygen concentration in the cylinder 1a at the post-injection time is calculated. Based on this, in steps ST6 to ST8, the ignition determination unit 35 performs an ignition determination.

First, in step ST6, an average equivalence ratio in the fuel spray by post injection is calculated, and it is determined in step ST7 whether this equivalence ratio is within the combustible range. If this determination is negative (NO), the process proceeds to step ST10 described later. If affirmative (YES), the process proceeds to step ST8, and this time the pre-injection temperature T _post (or the mixture temperature T _x ) is It is determined whether or not the ignition temperature is exceeded.

  If this determination is affirmative (YES), the process proceeds to step ST9, and the post-injection timing read in step ST3 is corrected to the retard side. If the determination is negative (NO), the process proceeds to step ST10. Correct the injection timing to the advance side. That is, in steps ST9 and ST10, the injection condition correction means 36 corrects the post-injection timing to the most advanced timing in the range where fuel does not ignite.

The control procedure up to this point will be described with reference to FIG. 7. As shown in the uppermost stage, the mixture temperature T _x in the fuel spray decreases as the post-injection timing is retarded. The equivalence ratio (average equivalence ratio) becomes higher (fuel rich) with the delay of the injection timing, but is generally within the combustible range. Therefore, as described above, the post-injection timing is advanced or retarded in accordance with the fuel spray ignition determination, and the fuel mixture does not ignite at the time L shown in the drawing when the mixture temperature T _x is below the ignition temperature. It controls to the most advanced angle timing L in the range.

  Here, as shown in the lower part of the figure, the oil dilution rate becomes lower as the post injection timing is on the advance side (left side in the figure). This is because the amount of fuel adhering to the cylinder wall surface is smaller as the injection timing is advanced. At the most advanced angle L, the oil dilution rate is lower than the allowable value. In this example, the amount of post-injected fuel adhering to the cylinder wall surface is less than the threshold value, and no problem occurs. I understand.

Further, as described above, at the most advanced angle L, the mixture temperature T _x is lower than the ignition temperature, so that most of the post-injected fuel flows into the exhaust system without being ignited, and is sufficient for the NSR and DPF. A quantity of unburned fuel is supplied. In the example of the figure, even when the post injection timing is at the most advanced angle L, the DPF floor temperature (shown at the bottom of FIG. 7) exceeds the target value, and the temperature is sufficiently increased during the DPF regeneration, The accumulated PM can be effectively removed by combustion.

Note that if the post injection timing is further advanced than the most advanced timing L, the oil dilution rate further decreases, but the mixture temperature T _x becomes equal to or higher than the fuel ignition temperature, and a part of the mixture is ignited and burned. Resulting in. Since the amount of unburned fuel flowing out to the exhaust system is reduced by the amount of combustion in this way, the DPF floor temperature is lower than the target value (not enough for the target temperature).

  Next, a procedure for further correcting the post-injection timing according to the amount of adhesion to the cylinder wall as described above will be described with reference to FIGS. First, in step ST11 of FIG. 6, the oil dilution rate determination means 37 determines whether or not the amount of post-injected fuel adhering to the cylinder wall surface is greater than a threshold value (whether the wall surface adhering amount is large). Then, as described above with reference to FIG. 7, if the oil dilution rate is lower than the allowable value at the most advanced timing L, the wall surface adhesion amount is less than the threshold value, so a negative determination is made (NO), and the return To do.

  On the other hand, for example, when the post injection amount is large and the oil dilution rate becomes higher than the allowable value even at the most advanced timing L as shown in FIG. Therefore, the determination is affirmative (YES), and the process proceeds to step ST12. Then, the post-injection timing is further corrected to the advance side A by the injection condition correction means 36 (indicated by a white arrow at the top of FIG. 8). As a result, the amount of fuel adhering to the wall surface decreases, and the oil dilution rate becomes lower than the allowable value.

On the other hand, at the corrected injection timing A, the mixture temperature T _x exceeds the ignition temperature of the fuel, and a part thereof may ignite and burn. At time A, the oxygen concentration is calculated such that the equivalent ratio is higher than the combustible range of the fuel (step ST13), and the opening of the EGR valve 14 is corrected to the open side so as to be this oxygen concentration (step ST14).

  As a result, the EGR gas is increased as shown by the black arrow in the lower part of FIG. 8, and the oxygen concentration in the cylinder 1 a is reduced, so that the equivalent ratio of fuel spray by post injection (average equivalent ratio in the spray) is increased. Out of the flammable range (from white square to black triangle), fuel ignition is effectively suppressed. In other words, even if the temperature of the post-injected fuel spray exceeds the ignition temperature, the ignition is almost prevented and a sufficient amount of unburned fuel is supplied to the NSR and DPF of the exhaust system to effectively reduce the temperature. Can be raised.

  Therefore, according to the control apparatus for an internal combustion engine according to the present embodiment, first, the equivalence ratio and the temperature state of the post-injected fuel spray are estimated, and it is determined whether or not the fuel spray is ignited. By controlling to the most advanced angle L, it is possible to effectively control the regeneration of the DPF, for example, by supplying sufficient unburned fuel to the exhaust system while reducing the adhesion of post-injected fuel to the cylinder wall surface.

  Furthermore, if the wall surface adhesion amount of the post-injected fuel increases, the oxygen concentration in the cylinder 1a is reduced by increasing the EGR gas amount, and the injection timing is further reduced while suppressing the ignition of the post-injected fuel. By advancing the angle, it is possible to further reduce the amount of fuel adhering to the cylinder wall surface and avoid the adverse effects caused by oil dilution.

  Thus, when the oxygen concentration in the cylinder is reduced, in this embodiment, by reducing the oxygen concentration in the cylinder 1a so that the equivalence ratio in the spray of the post-injected fuel is outside the combustible range, Even if the temperature state of the cylinder 1a or the fuel spray is equal to or higher than the ignition temperature, the ignition and combustion can be substantially prevented.

  In the present embodiment, in order to reduce the oxygen concentration in the cylinder 1a, the amount of EGR gas flowing through the EGR passage 13 is increased, and the cylinder 1a is driven by external EGR gas having a temperature lower than that of so-called internal EGR gas. The oxygen concentration can be adjusted without increasing the temperature inside. Therefore, it becomes advantageous in suppressing the ignition of the post-injected fuel.

-Other embodiments-
The embodiment described above has been described for the case where the present invention is applied to a common rail in-cylinder direct injection type diesel engine. The present invention can also be applied to various internal combustion engines that use fuels other than diesel oil.

  In the above-described embodiment, the injection timing is advanced in order to reduce the adhesion of post-injected fuel to the cylinder wall surface. In addition to this, the fuel injection pressure is reduced, or post-injection is performed. May be divided into a plurality of times and the number of divisions may be increased.

  Further, in the above embodiment, when the post injection timing is further advanced from the most advanced angle L, the so-called external EGR gas amount is increased to decrease the oxygen concentration in the cylinder 1a. Instead of or in addition to this, the so-called internal EGR gas amount may be adjusted, or the opening degree of the throttle valve 11 may be changed.

  INDUSTRIAL APPLICABILITY The present invention can effectively recover the functions of an exhaust system purification device and the like while preventing adverse effects caused by oil dilution in a direct injection internal combustion engine that performs post injection after main injection. In particular, it is highly effective when applied to diesel engines installed in automobiles.

1 Internal combustion engine 1a Cylinder 6 Fuel injection valve 10 Intake manifold (intake passage)
12 Exhaust manifold (exhaust passage)
13 EGR passage (oxygen concentration adjusting means)
14 EGR valve (oxygen concentration adjusting means)
30 ECU (control means)
32 In-cylinder state calculation means 33 Spray characteristic calculation means 34 Pre-post-injection state calculation means 35 Ignition determination means 36 Injection condition correction means 37 Oil dilution rate determination means 38 Target oxygen concentration calculation means,
39 EGR opening correction means S Fuel spray by post injection

Claims (5)

A control device for an internal combustion engine comprising a fuel injection valve for directly injecting fuel into a cylinder, and performing at least main injection and post injection by the fuel injection valve,
Control means for controlling the timing of the post-injection so as to be the most advanced timing in a range where the fuel by the post-injection does not ignite,
Oxygen concentration adjusting means for adjusting the oxygen concentration in the cylinder,
The control means determines whether or not the amount of fuel adhering to the cylinder wall surface due to the post-injection is greater than a predetermined amount, and if it is determined that the wall surface adhesion amount is greater than a predetermined amount even at the most advanced timing, A control apparatus for an internal combustion engine, characterized in that the oxygen concentration in the cylinder is reduced by the concentration adjusting means and the post injection timing is further advanced. The control apparatus for an internal combustion engine according to claim 1,
The control means estimates the equivalence ratio and the temperature state in the fuel spray by the post injection, determines whether or not the fuel spray is ignited, and if it is determined to ignite, the post injection timing is retarded On the other hand, the control device for the internal combustion engine is configured to correct to the advance side if it is determined that the ignition is not performed. The control apparatus for an internal combustion engine according to claim 1 or 2,
The control device of the internal combustion engine, wherein the control means is configured to determine whether or not a wall surface adhesion amount is greater than a predetermined amount based on a fuel flight distance by the post injection and a distance from the injection hole to the cylinder wall surface. The control device for an internal combustion engine according to any one of claims 1 to 3,
When the oxygen concentration in the cylinder is reduced by the oxygen concentration adjusting means, the control means is configured to reduce the oxygen concentration so that the equivalent ratio in the fuel spray by the post injection is out of the combustible range. Control device for internal combustion engine. The control apparatus for an internal combustion engine according to claim 4,
The oxygen concentration adjusting means is configured to recirculate a part of the exhaust gas from the exhaust passage of the internal combustion engine to the intake passage, and to adjust the oxygen concentration of the intake air into the cylinder by adjusting the amount of the recirculated gas. A control device for an internal combustion engine.

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