JP2012145042A - Fuel injection control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device for reducing smoke during emission, independently of operating conditions.SOLUTION: The fuel injection control device acquires a target value of a combustion parameter as a ratio of a cylinder oxygen amount to an after-injection amount at an ignition timing for after-injection (S402). The fuel injection control device calculates the ignition timing for the after-injection and a heat generation amount from a heat generation rate (S412, S414), and calculates a value (X_now) of an actual combustion parameter in the current combustion cycle from the cylinder oxygen amount and the after-injection amount calculated from a cylinder oxygen concentration at the ignition timing of the after-injection (S420). When a difference ΔX between a target value (X_target) of the combustion parameter and the actual value (X_now) of the combustion parameter is a predetermined threshold value or greater (S424:No), the fuel injection control device sets an after-injection amount and a main injection amount in the next combustion cycle for zeroing the difference ΔX to reduce smoke (S426, S428).

Description

  The present invention relates to a fuel injection control device applied to a fuel injection system that executes at least main injection and after injection following main injection during one combustion cycle of an internal combustion engine.

  2. Description of the Related Art Conventionally, for the purpose of purifying exhaust gas and improving fuel efficiency, a multi-stage injection type fuel injection system that performs a smaller amount of injection than main injection before and after main injection that generates main torque is known (for example, Patent Documents). 1 and 2).

  In the multi-stage injection type fuel injection system, for example, after the main injection, the after injection is executed in order to burn the smoke that remains as an unburned component because the fuel injected by the main injection does not sufficiently burn.

  In Patent Document 1, in order to prevent the injection characteristic of after-injection, which has a small injection amount with respect to main injection, from being influenced by the in-cylinder pressure, the injection of each injection in multistage injection from a map or mathematical formula based on the engine operating state The pattern is acquired, and the injection command signal for after injection determined from the injection pattern is variably controlled based on the in-cylinder pressure detected by the in-cylinder pressure sensor.

  In Patent Document 2, a plurality of combustion parameters representing the combustion state of the internal combustion engine are calculated based on the in-cylinder pressure and the crank angle detected by the in-cylinder pressure sensor. The target value of the combustion parameter representing the optimal combustion state according to the operating state of the internal combustion engine is set in advance by a mathematical formula or a map or the like, and the actual combustion value is set to the target value of the combustion parameter according to the operating state of the internal combustion engine. The injection command value of each injection in the multistage injection is corrected so that the parameter values match.

JP 2008-196449 A Japanese Patent No. 3798741

  In order to reduce the smoke generated by the main injection, it is necessary to adjust at least one of the main injection amount and the after injection amount based on the combustion state by the main injection.

  In Patent Document 1, the in-cylinder pressure when the after-injection is executed following the main injection is detected and the after-injection injection command signal is variably controlled. However, the in-cylinder pressure does not represent the combustion state related to the generation of smoke. . Therefore, as in Patent Document 1, it is difficult to appropriately adjust at least one of the main injection amount and the after injection amount in order to reduce smoke only by detecting the in-cylinder pressure.

  In Patent Document 2, the change rate of the in-cylinder pressure, the heat generation rate, the amount of heat generation, and the like are calculated as the combustion parameters representing the combustion state from the in-cylinder pressure and the crank angle. Although the change in the pressure and the amount of heat generated is shown, it does not show the combustion state related to the generation of smoke, as in Patent Document 1 described above. Therefore, in Patent Document 2, it is difficult to appropriately adjust at least one of the main injection amount and the after injection amount in order to reduce smoke.

  In a transient operation state, such as during acceleration when the accelerator is depressed, the response of the air flow rate and the EGR (Exhaust Gas Recirculation) amount varies with a delay, so the combustion state in the cylinder varies. Therefore, it is difficult to reduce the smoke by adjusting at least one of the main injection amount and the after injection amount by the combustion parameter calculated based on the in-cylinder pressure or the in-cylinder pressure, particularly in the transient operation state.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel injection control device that reduces smoke in exhaust regardless of the operating state.

  According to the first to tenth aspects of the present invention, the oxygen concentration acquisition means acquires the in-cylinder oxygen concentration at a predetermined time during the combustion period from the start of ignition of fuel injected by after injection to the end of combustion, and the injection amount The adjusting unit adjusts at least one of the main injection amount and the after injection amount based on the in-cylinder oxygen concentration acquired by the oxygen concentration acquiring unit.

  According to this configuration, from the in-cylinder oxygen concentration in the cylinder at a predetermined time during the combustion period from the start of ignition of the fuel injected by the after injection to the end of the combustion, from the combustion by the main injection and the predetermined time by the after injection. You can see how oxygen is consumed by combustion.

  Since the smoke generation state in the cylinder is determined by the injection amount and the oxygen concentration in the cylinder, the smoke generation state can be estimated with high accuracy from the oxygen consumption state representing the combustion state in the cylinder. Therefore, by adjusting at least one of the main injection amount and the after injection amount based on the in-cylinder oxygen concentration at a predetermined time during the combustion period by the after injection, the oxygen in the cylinder is effectively consumed and the inside of the cylinder is The combustion state of can be controlled to an appropriate state. Thereby, the amount of smoke in the exhaust can be reduced.

  For example, if the after-injection amount is larger than the injection amount for properly burning the fuel and reducing the smoke, the in-cylinder oxygen concentration is increased with respect to the tsuin oxygen concentration at a predetermined time during the combustion period of after-injection. At the same time, it is conceivable to decrease the after-injection amount or increase the in-cylinder oxygen concentration when starting the after-injection by decreasing the main injection amount. Alternatively, both the main injection amount and the after injection amount may be appropriately increased or decreased.

  As described above, since at least one of the main injection amount and the after injection amount is adjusted based on the in-cylinder oxygen concentration at a predetermined timing during the combustion period by the after injection, for example, when the accelerator pedal is depressed to accelerate the vehicle. Even in a case where the in-cylinder oxygen concentration varies in a transient operation state, at least one of the main injection amount and the after-injection amount is adjusted based on the in-cylinder oxygen concentration so that the combustion state in the cylinder is appropriately adjusted. Can be controlled to the state.

  According to the second aspect of the present invention, the injection amount adjusting means does not change the total injection amount during one combustion cycle set based on the operating state of the internal combustion engine, but changes the main injection based on the in-cylinder oxygen concentration. Adjust the amount and after-injection amount.

  Thus, since the main injection amount and the after injection amount are adjusted without changing the total injection amount in one combustion cycle, fluctuations in the output torque of the internal combustion engine can be prevented while reducing the smoke amount in the exhaust gas.

  According to the third aspect of the present invention, the oxygen concentration acquisition means includes the intake oxygen concentration in the intake air flowing into the cylinder, the exhaust oxygen concentration in the exhaust discharged from the cylinder, and the heat generation amount in the cylinder. Based on the above, the in-cylinder oxygen concentration is calculated.

  The heat generation amount corresponds to the oxygen concentration in the cylinder, and the oxygen concentration in the cylinder decreases as the heat generation amount increases. Therefore, in one combustion cycle, the after-injection is based on the intake oxygen concentration indicating the oxygen concentration in the cylinder at the start of combustion, the exhaust oxygen concentration indicating the oxygen concentration in the cylinder at the end of combustion, and the heat generation amount. The in-cylinder oxygen concentration at a predetermined time during the combustion period can be calculated.

  According to the invention of claim 4, the heat generation amount calculation means calculates the heat generation rate in the cylinder from the in-cylinder pressure detected by the in-cylinder pressure sensor, the crank angle, and the in-cylinder volume, and calculates the calculated heat The in-cylinder oxygen concentration acquisition unit acquires the heat generation amount for calculating the in-cylinder oxygen concentration from the heat generation amount calculation unit.

  Since the heat generation rate is calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor and the calculated heat generation rate is integrated to calculate the heat generation amount, the heat generation amount can be calculated with high accuracy. Thereby, the in-cylinder oxygen concentration can be calculated with high accuracy based on the heat generation amount.

  According to the invention described in claim 5, the heat generation amount estimation means estimates the heat generation amount based on a physical quantity related to the combustion state in the cylinder, and the in-cylinder oxygen concentration acquisition means calculates the in-cylinder oxygen concentration. The amount of heat generation to be obtained is acquired from the heat generation amount estimation means.

  According to this configuration, since the heat generation amount is calculated based on the physical quantity related to the combustion state in the cylinder, the heat generation amount for calculating the in-cylinder oxygen concentration can be acquired without using the in-cylinder pressure sensor. . Therefore, the manufacturing cost of the fuel injection system can be reduced.

According to the sixth aspect of the present invention, the heat generation amount estimation means estimates the heat generation amount based on a physical quantity including the engine speed.
Since the engine speed or the fluctuation of the engine speed is closely related to the heat generation amount in the cylinder, the engine speed is included in the physical quantity for estimating the heat generation amount without using the in-cylinder pressure sensor. The amount of heat generation can be estimated with high accuracy.

  According to the invention of claim 7, the combustion state calculating means calculates a ratio between the in-cylinder oxygen amount calculated from the in-cylinder oxygen concentration and the after injection amount as a parameter representing the combustion state in the cylinder, and the injection amount The adjusting unit adjusts at least the after injection amount of the main injection amount and the after injection amount so that the ratio value calculated by the combustion state calculating unit becomes a target value of the ratio between the in-cylinder oxygen amount and the after injection amount. .

  In this way, based on the ratio between the dimensionless in-cylinder oxygen amount and the after-injection amount, the combustion of the fuel by the after-injection is no matter what the in-cylinder oxygen amount calculated from the in-cylinder oxygen concentration is. The after-injection amount can be easily adjusted to be optimal.

According to the invention described in claim 8, the injection amount adjusting means presets a target value of the ratio between the in-cylinder oxygen amount and the after injection amount.
According to this configuration, since it is not necessary to calculate the target value of the ratio between the in-cylinder oxygen amount and the after-injection amount during operation of the internal combustion engine, it is based on the difference between the target value of the ratio and the calculated ratio value. Thus, the response when adjusting at least one of the main injection amount and the after injection amount is improved.

According to the ninth aspect of the invention, the oxygen concentration acquisition means acquires the in-cylinder oxygen concentration at the ignition timing of after injection.
According to this configuration, since the in-cylinder oxygen concentration at the ignition timing that is not affected by the combustion due to after injection is acquired, it is possible to determine with high accuracy whether or not the in-cylinder oxygen amount is insufficient with respect to the after injection amount. As a result, at least one of the main injection amount and the after injection amount can be adjusted with high accuracy based on the in-cylinder oxygen concentration.

  According to the tenth aspect of the invention, the oxygen concentration acquisition means sets the ignition timing of the after injection when the heat generation rate by the combustion of the main injection decreases and the heat generation rate starts to increase by the combustion of the after injection. .

  According to this configuration, since the ignition timing can be calculated with high accuracy from the change in the heat generation rate, at least one of the main injection amount and the after injection amount is increased based on the in-cylinder oxygen concentration at the ignition timing. The accuracy can be adjusted.

  The functions of the plurality of means provided in the present invention are realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof. The functions of the plurality of means are not limited to those realized by hardware resources that are physically independent of each other.

The block diagram which shows the fuel-injection system of this embodiment. It is a schematic diagram which shows the in-cylinder combustion state according to the main injection amount and the after injection amount, (A) is a state where there is too much after injection amount, (B) is a state where there is too little after injection amount, (C) is after sales. The injection amount is in an appropriate state. The characteristic view which shows the relationship between a combustion parameter, smoke concentration, and a smoke deterioration rate. The characteristic view which shows the relationship between a crank angle, a heat release rate, a heat release amount, and in-cylinder oxygen concentration. The flowchart which shows the adjustment process of the main injection quantity and the after injection quantity.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a pressure accumulation type four-cylinder diesel internal combustion engine (hereinafter also referred to as “engine”).

  In the engine 10, a piston 16 is accommodated in a cylinder (cylinder) 14 formed in the cylinder block 12, and the movement of the piston 16 reciprocating in the cylinder 14 is caused by a crankshaft (not shown) of the engine 10 via a connecting rod 18. To be transmitted as a rotational motion.

  A cylinder head 22 that forms a combustion chamber 20 in the upper part of the piston 16 is fixed to the upper end surface of the cylinder block 12. The cylinder head 22 is formed with an intake port 24 and an exhaust port 26 that open to the combustion chamber 20.

The intake port 24 and the exhaust port 26 are opened and closed by an intake valve 28 and an exhaust valve 30 driven by cams (not shown), respectively.
An intake pipe 32 for sucking outside air is connected to the intake port 24, and an exhaust pipe 34 for discharging exhaust gas from the cylinder 14 is connected to the exhaust port 26. Are connected by an EGR pipe 36. When the EGR valve 38 installed in the EGR pipe 36 is opened, the EGR amount of the exhaust gas recirculated from the exhaust pipe 34 to the intake pipe 32 is controlled.

  During the intake stroke in which the intake valve 28 opens the intake port 24, if the piston 16 descends in the cylinder 14 and negative pressure in the cylinder is generated, the outside air sucked from the intake pipe 32 is recirculated through the EGR pipe 36. EGR gas flows through the intake port 24 into the cylinder.

Further, when the exhaust valve 30 opens the exhaust port 26, the exhaust pushed out of the cylinder by the rise of the piston 16 is discharged to the exhaust pipe 34 through the exhaust port 26.
The fuel injection system 2 includes a common rail 40 that accumulates high-pressure fuel, a fuel supply pump (not shown) that pumps high-pressure fuel to the common rail 40, and high-pressure fuel accumulated in the common rail 40 in each cylinder of the engine 10. A plurality of fuel injection valves 42 each for injecting, and an electronic control unit (ECU) 50 are provided.

  The common rail 40 accumulates the high-pressure fuel supplied from the fuel supply pump up to the target rail pressure, and the accumulated high-pressure fuel is supplied to the fuel injection valve 42 via the fuel pipe 100. The target rail pressure of the common rail 40 is set by the ECU 50. Specifically, the operating state of the engine 10 is detected from the accelerator opening and the rotational speed, and a target rail pressure suitable for the operating state is set.

  The fuel injection valve 42 has a solenoid valve that is electronically controlled by the ECU 50 and a nozzle that injects fuel by opening the solenoid valve, and the tip of the nozzle protrudes into each cylinder. Attached to the head 22.

  The ECU 50 is mainly configured by a microcomputer having a CPU 52, a RAM 54, a ROM 56, a flash memory (not shown), an input / output interface, and the like. The ECU 50 includes a crank angle sensor 60, an accelerator opening sensor 62, a fuel pressure sensor 64, an in-cylinder pressure sensor 66, an intake pressure sensor 68, an intake air temperature sensor 70, an air amount sensor 72, oxygen concentration sensors 74 and 76, a water temperature sensor 78, and the like. The output signals to be output are input, and the operating state of the engine 10 is detected based on these output signals.

The ECU 50 executes various engine control processes by executing a control program stored in a storage device such as the ROM 56 or a flash memory.
The crank angle sensor 60 is disposed around the pulsar 44 that rotates in synchronization with the crankshaft of the engine 10 and corresponds to the number of teeth provided on the outer peripheral portion of the pulsar 44 while the pulsar 44 rotates once. A plurality of pulse signals (rotation angle signals) are output. The ECU 50 detects the rotational speed NE and the rotational angle position (crank angle θ) of the engine 10 based on the rotational angle signal output from the crank angle sensor 60.

The accelerator opening sensor 62 outputs a signal corresponding to the accelerator opening representing the operation amount (depression amount) of an accelerator pedal (not shown) operated by the driver.
The fuel pressure sensor 64 is attached to the common rail 40 and outputs a signal corresponding to the fuel pressure (rail pressure) accumulated in the common rail 40. The in-cylinder pressure sensor 66 is attached to the cylinder head 22 of at least one cylinder of the engine 10 and outputs a signal corresponding to the in-cylinder pressure. The output signal of the in-cylinder pressure sensor 66 is subjected to noise removal by a low-pass filter (LPF) 80 and input to the ECU 50.

  The intake pressure sensor 68 is attached to the intake pipe 32 and outputs a signal corresponding to the intake pressure Pm in the intake pipe 32. The intake air temperature sensor 70 is attached to the intake pipe 32 and outputs a signal corresponding to the temperature (intake air temperature) Ta of intake air passing through the intake pipe 32. The air amount sensor 72 is attached to the intake pipe 32 and outputs a signal corresponding to the flow rate (air amount) Ga of air passing through the intake pipe 32.

  As the oxygen concentration sensors 74 and 76, for example, A / F sensors for detecting an air-fuel ratio are used. The oxygen concentration sensor 74 is installed downstream of the location where the EGR pipe 36 is connected to the intake pipe 32, and the oxygen concentration in the intake air flowing into the cylinder 14 through the intake pipe 32 and the EGR pipe 36. Output a signal according to. The oxygen concentration sensor 76 is installed in the exhaust pipe 34 and outputs a signal corresponding to the oxygen concentration in the exhaust discharged from the cylinder 14 to the exhaust pipe 34.

The water temperature sensor 78 is attached to the cylinder block 12 and outputs a signal corresponding to the temperature (water temperature) of the cooling water in the cylinder block 12.
The ECU 50 performs injection pressure control, fuel injection control, and the like as operation control of the engine 10. The injection pressure control controls the fuel pressure accumulated in the common rail 40. The discharge amount (pump discharge amount) of the fuel supply pump is adjusted so that the actual rail pressure detected by the fuel pressure sensor 64 matches the target rail pressure. Feedback control.

  The fuel injection control controls the injection amount and injection timing from the fuel injection valve 42, calculates the optimal injection amount and injection timing according to the operating state of the engine 10, and according to the calculation result, the fuel injection valve 42. To control the fuel injection. In the fuel injection control, multi-stage injection such as pilot injection, pre-injection, after-injection, and post-injection may be performed before and after the main injection based on the operating state of the engine 10.

  The pilot injection is performed in order to preliminarily mix air and a small amount of fuel before ignition by main injection that generates main torque. The pre-injection suppresses rapid combustion in the main injection by injecting a small amount of fuel before the main injection and burning the fuel in the cylinder before the main injection. Thereby, combustion noise and vibration are reduced.

  After-injection purifies exhaust by injecting a small amount of fuel after main injection and burning smoke, which is an unburned component generated in the cylinder by main injection. The post-injection is performed to inject a minute amount of fuel and burn particulates collected by a DPF (Diesel Particulate Filter) (not shown).

  Of the pilot injection, pre-injection, main injection, after-injection, and post-injection, the engine 10 generates output torque in the pilot injection, pre-injection, main injection, and after-injection.

(Combustion state)
Next, the combustion state in the cylinder due to changes in the main injection amount and the after injection amount will be described. FIG. 2 shows a cylinder when the main injection amount and the after injection amount are changed under the condition that the total injection amount of the main injection amount and the after injection amount in one combustion cycle is constant so that the output torque of the engine 10 does not change. The combustion state in the inside is shown. In FIG. 2, reference numeral 200 indicates an injection region by main injection, and reference numeral 210 indicates an injection region by after injection.

  In main injection, since main torque is generated, the injection amount in the multi-stage injection is larger than that in the other stages. For this reason, even if the main injection amount increases or decreases, the spray reaches the outer peripheral portion in the cylinder far from the fuel injection valve 42, so that the combustion by the main injection continues in the combustion region 200 in the outer peripheral portion in the cylinder. Then, since oxygen is continuously consumed at the outer peripheral portion in the cylinder, the oxygen concentration at the outer peripheral portion in the cylinder is lowered. On the other hand, since combustion due to main injection does not occur in the center of the cylinder, it is considered that oxygen necessary for combustion is hardly consumed.

  As described above, when the amount of after-injection is too large in a state where oxygen is almost consumed by the combustion by the main injection in the outer peripheral portion in the cylinder, as shown in FIG. Since the spray reaches the outer peripheral portion in the cylinder, the fuel by the after-injection burns in the combustion region 210 where the oxygen concentration is low. As a result, the combustion region 210 by the after injection becomes incomplete combustion, and smoke is generated.

  Therefore, as shown in FIG. 2B, in order to generate combustion by after injection in the center of the cylinder where combustion by main injection has not occurred, the after injection amount is decreased and the main injection amount is increased. It is possible to do.

  However, if the main injection amount is too large, oxygen is insufficient in the combustion region 200 of the main injection during combustion by the main injection, and smoke is generated. On the other hand, by reducing the amount of after-injection, combustion by after-injection is performed in the combustion region 210 where there is sufficient oxygen in the center of the cylinder. However, since the combustion region 210 is narrow, the combustion region is caused by combustion of the main injection. The effect of burning the smoke generated at 200 by the combustion of after-injection is low.

  Therefore, as shown in FIG. 2C, the combustion region near the center in the cylinder in which the oxygen after the main injection does not run short and the oxygen after the main injection remains sufficiently during the combustion by the main injection, as shown in FIG. It is necessary to adjust the main injection amount and the after injection amount so that the combustion by the after injection occurs at 210 and the smoke generated by the combustion of the main injection can be burned by the after injection combustion.

(Injection amount adjustment)
In order to adjust the optimum main injection amount and after injection amount to reduce smoke, the inventor of the present application calculates the in-cylinder oxygen amount calculated from the in-cylinder oxygen concentration at the ignition timing by the after injection, the after injection amount, We focused on the ratio. FIG. 3 (A) shows the combustion ratio representing the combustion state in the cylinder as shown in the following equation (1) by comparing the ratio between the in-cylinder oxygen amount [g] and the after-injection amount [g] at the ignition timing by after injection. The relationship between the combustion parameter and the smoke concentration [FSN (Filter Smoke Number)] in the three types of operation modes when the parameters are used is shown as characteristic curves 300, 302, and 304 for each of the three types of modes.

Combustion parameter = cylinder oxygen amount [g] / after injection amount [g] (1)
The three types of operation modes represent, for example, three types of operation modes of a low load region, a medium load region, and a high load region that are defined from the relationship between the engine speed and the injection amount.

From FIG. 3A, it can be seen that there is a combustion parameter value (parameter value A in the figure) at which the smoke concentration [FSN] is lowest in each of the three types of modes.
Here, in the characteristic curves 300, 302, and 304 of each mode, the smoke amount is calculated based on the product of the exhaust amount and the smoke concentration in each mode, and the minimum value of the smoke amount is a standard with a smoke deterioration rate of 0%. FIG. 3B shows a result obtained by calculating and normalizing the smoke deterioration rate [%] with respect to the reference value when the combustion parameter changes with the characteristic curves 300, 302, and 304, respectively.

  From FIG. 3B, the relationship between the combustion parameter and the smoke deterioration rate [%] becomes a common characteristic curve 310 in the three types of operation modes, and the same combustion parameter value ((A), ( It can be seen that the smoke deterioration rate [%] is the lowest in the parameter value A) shown in B).

  In FIG. 3B, in the range where the combustion parameter is larger than the value at which the smoke deterioration rate [%] is the lowest, the after injection amount is too small relative to the in-cylinder oxygen amount. If the after-injection amount is too small, the combustion region 210 by the after injection is narrow, so that the effect of burning the smoke generated in the combustion region 200 by the combustion of the main injection by the combustion of the after-injection becomes low, and the smoke increases.

  Under the condition that the total injection amount of the main injection amount and the after injection amount in one combustion cycle is constant, the after injection amount being too small means that the main injection amount is too large and oxygen is insufficient in the combustion region 200 by the main injection. This indicates that smoke is generated.

  On the other hand, in FIG. 3B, in the range where the combustion parameter is smaller than the value at which the smoke deterioration rate [%] is the lowest, it indicates that the after injection amount is too much with respect to the in-cylinder oxygen amount. If the amount of after injection is too large, combustion by after injection is performed in the combustion region 200 where oxygen is insufficient due to combustion by main injection, and smoke is generated in the combustion region 210 by after injection.

  Therefore, when the value of the combustion parameter calculated in the current combustion cycle deviates from the target value of the combustion parameter when the smoke deterioration rate [%] is the lowest, the in-cylinder oxygen amount is calculated from the in-cylinder oxygen concentration. Thus, it is possible to calculate the optimum after injection amount that minimizes the amount of smoke generated in the next combustion cycle. The main injection amount can be calculated based on the calculated after injection amount from the condition that the total injection amount of the main injection amount and the after injection amount set based on the engine operating state is not changed.

(In-cylinder oxygen concentration)
Next, the in-cylinder oxygen concentration will be described. Based on the in-cylinder pressure detected by the in-cylinder pressure sensor 66, the ECU 50 calculates the heat generation rate (dQ / dθ) in one combustion cycle by the following equation (2). In equation (2), Q is the amount of heat generated, V is the cylinder volume, P is the cylinder pressure detected by the cylinder pressure sensor 66, θ is the crank angle detected by the crank angle sensor 60, and κ is the specific heat ratio. Respectively. FIG. 4A shows a characteristic curve 320 of the heat generation rate (dQ / dθ) in one combustion cycle.

Heat generation rate (dQ / dθ)
= (V · dP / dθ + κ · P · dV / dθ) / (κ-1) (2)
Then, the ECU 50 integrates and totals the heat generation rates up to a predetermined crank angle at which fuel injection is executed and combustion is completed in one combustion cycle, and up to each crank angle in one combustion cycle. The ratio of the integrated value of the heat generation amount is calculated. The characteristic curve 330 of the heat generation amount shown in FIG. 4B shows the ratio of the integrated value of the heat generation amount up to each crank angle with respect to the total heat generation amount.

  In the heat generation rate characteristic curve 320, peaks 322, 324, and 326 indicate the heat generation rate peaks due to pilot injection, main injection, and after injection, respectively. Therefore, it can be determined that the ignition timing of the after injection is when the heat generation rate by the main injection decreases after the peak 324 and the heat generation rate starts to increase by the after injection.

  Further, the heat generation amount corresponds to the oxygen concentration in the cylinder, and the in-cylinder oxygen concentration decreases as the heat generation amount increases. Therefore, based on the change in the amount of heat generated, as shown in FIG. 4C, the in-cylinder in one combustion cycle is determined from the in-cylinder oxygen concentration at the start of combustion in one combustion cycle and the in-cylinder oxygen concentration after completion of combustion. A characteristic curve 340 of oxygen concentration can be obtained. The in-cylinder oxygen concentration at the start of combustion in one combustion cycle is detected by an oxygen concentration sensor 74 installed on the intake side, and the in-cylinder oxygen concentration after completion of combustion is detected by an oxygen concentration sensor 76 installed on the exhaust side.

  The in-cylinder oxygen concentration at the ignition timing of the after injection is calculated from the characteristic curve 340 of the in-cylinder oxygen concentration, and the in-cylinder oxygen at the ignition timing of the after injection is calculated from the calculated in-cylinder oxygen concentration and the intake air amount flowing into the cylinder. The amount can be calculated.

  Then, the after injection amount that minimizes the smoke generation amount is calculated from the in-cylinder oxygen amount at the ignition timing of the after injection and the target value of the combustion parameter that minimizes the smoke generation amount, and the calculated after injection amount From this, the main injection amount is calculated.

(Injection amount adjustment processing)
Next, the main injection amount and after-injection amount adjustment processing for reducing smoke will be described based on the flowchart of FIG.

  First, the ECU 50 acquires an engine speed and an injection amount representing an engine operating state (S400), and acquires a target value of a combustion parameter set in advance to reduce smoke in accordance with the engine operating state. (S402).

  Next, the ECU 50 acquires the intake oxygen concentration of the intake air flowing into the cylinder where the air and the EGR gas are merged from the oxygen concentration sensor 74 installed on the intake side (S404), and after injection from the injection amount acquired in S400 The amount is acquired (S406), and the in-cylinder pressure is acquired from the in-cylinder pressure sensor 66 (S408).

  The ECU 50 calculates the heat generation rate in the cylinder from the acquired in-cylinder pressure and the crank angle based on the equation (2) (S410), the heat generation rate due to the combustion of the main injection is reduced, and the heat generation rate is increased by the combustion of the after injection. The time when the occurrence rate starts to rise is calculated as the ignition timing of after injection (S412).

  Next, the ECU 50 integrates the heat generation rate to calculate the heat generation amount (S414), and acquires the exhaust oxygen concentration from the oxygen concentration sensor 76 installed on the exhaust side (S416). The ECU 50 calculates the in-cylinder oxygen concentration at the ignition timing of the after injection from the intake oxygen concentration acquired in S404, the heat generation amount characteristic calculated in S414, and the exhaust oxygen concentration acquired in S416 (S418).

  The ECU 50 calculates the intake air amount that flows into the cylinder from the air flow rate detected by the air amount sensor 72 and the EGR amount calculated from the opening degree of the EGR valve 38, and the intake air amount and the in-cylinder oxygen concentration calculated in S418. From the above, the in-cylinder oxygen amount at the ignition timing of after injection is calculated. Then, the ECU 50 calculates the ratio between the in-cylinder oxygen amount and the after injection amount acquired in S406 as the actual combustion parameter value (X_now) in the current one combustion cycle (S420).

  The ECU 50 calculates a difference ΔX = (X_target−X_now) between the target value (X_target) of the combustion parameter acquired in S402 and the calculated value (X_now) of the combustion parameter obtained in S420 (S422), and the difference ΔX is predetermined. It is determined whether it is smaller than the threshold value (S424). When the difference ΔX is smaller than the predetermined threshold (S424: Yes), the ECU 50 determines that the proper after injection amount and the main injection amount are set, and ends this process.

  When the difference ΔX is equal to or greater than the predetermined threshold (S424: No), the ECU 50 determines that the current after injection amount and the main injection amount are inappropriate and the smoke cannot be sufficiently reduced.

  Therefore, the ECU 50 sets the after injection amount in the next combustion cycle so that the difference ΔX becomes 0 based on the in-cylinder oxygen amount at the ignition timing of the current after injection and the target value (X_target) of the combustion parameter. (S426) The main injection amount in the next combustion cycle is set from the set after injection amount so that the total injection amount in one combustion cycle determined from the engine operating state is constant (S428).

  Note that if the main injection amount in the current combustion cycle changes in the next combustion cycle, the in-cylinder oxygen concentration at the ignition timing of after injection also changes. Therefore, in the calculated after injection amount, the amount of smoke generated in the next combustion cycle May not be sufficiently reduced. However, the optimum main injection that reduces smoke by continuing to adjust the main injection amount and the after injection amount based on the combustion parameter that is the ratio of the in-cylinder oxygen amount and the after injection amount at the ignition timing of the after injection. The amount and after-injection amount can be set.

  In the above-described embodiment, focusing on the in-cylinder oxygen concentration at the ignition timing of the after injection, the in-cylinder oxygen at the ignition timing of the after injection is used as a combustion parameter representing the smoke generation state in the cylinder, that is, the combustion state in the cylinder. The ratio between the quantity and the after injection quantity was set. Based on the combustion parameters, the main injection amount and the after injection amount were adjusted so as to reduce smoke as much as possible. Thereby, oxygen in a cylinder can be consumed efficiently by main injection and after injection, and smoke can be reduced as much as possible.

Further, since the heat generation rate is calculated from the in-cylinder pressure detected by the in-cylinder pressure sensor 66, the heat generation rate can be calculated with high accuracy by integrating the calculated heat generation rates.
In addition, since the main injection amount and the after injection amount are adjusted based on the in-cylinder oxygen concentration, the in-cylinder oxygen concentration can be reduced even when the in-cylinder oxygen concentration varies in a transient operation state, for example, when the accelerator pedal is depressed to accelerate. Based on the oxygen concentration, the main injection amount and the after injection amount can be adjusted to control the combustion state in the cylinder to an appropriate state. Thereby, smoke can be reduced regardless of a steady operation state or a transient operation state.

  Further, the after injection amount and the main injection amount for reducing the smoke are adjusted based on the target value of the ratio between the in-cylinder oxygen amount and the after-injection amount at the ignition timing of the after injection and the in-cylinder oxygen amount. In order to adjust the after-injection amount and the main injection amount to reduce the amount, it is not necessary to store a large amount of maps in conformity with the engine operating state, so that the storage capacity for storing the maps can be reduced.

  In the above embodiment, the fuel injection system 2 corresponds to the fuel injection system of the present invention, and the ECU 50 corresponds to the fuel injection control device of the present invention. The ECU 50 functions as an oxygen concentration acquisition unit, an injection amount adjustment unit, a heat generation amount calculation unit, and a combustion state calculation unit.

  5 corresponds to the function executed by the heat generation amount calculating means, S418 corresponds to the function executed by the oxygen concentration obtaining means, and S420 corresponds to the function executed by the combustion state calculating means. S426 and S428 correspond to the function executed by the injection amount adjusting means.

  Rather than calculating the amount of heat generation based on the in-cylinder pressure detected by the in-cylinder pressure sensor 66 in S414, the engine rotation speed, the fluctuation amount of the engine rotation speed, the injection timing, the injection, as the physical quantity related to the combustion state in the cylinder The amount of heat generation may be estimated from a physical model based on physical quantities related to the combustion state in the cylinder, such as the quantity, common rail pressure, intake oxygen concentration, intake air quantity, intake air temperature, and the like. In this case, S408 is unnecessary. Then, in S410, the heat generation rate is estimated based on the physical quantity related to the combustion state in the cylinder, the after-ignition ignition timing is calculated in S412 from the heat generation rate estimated in S410, and the heat generation rate estimated in S410 is calculated. The amount of heat generation is estimated in S414. In this case, S410 and S414 correspond to the function executed by the heat generation amount estimation means, and the ECU 50 functions as the heat generation amount estimation means. In order to estimate the heat generation amount with high accuracy based on the physical quantity related to the combustion state, it is necessary to estimate the heat generation rate and the heat generation amount based on the physical quantity including the engine speed closely related to the combustion state. desirable.

[Other Embodiments]
In the above-described embodiment, when performing the multi-stage injection, the total injection amount related to the output torque of the engine 2 calculated from the engine operating state is not changed, and the smoke is reduced as much as possible in the ignition timing of the after injection. The after injection amount and the main injection amount were adjusted based on the in-cylinder oxygen concentration.

  On the other hand, the timing for acquiring the in-cylinder oxygen concentration, which is a reference for adjusting the after injection amount and the main injection amount, is not limited to the ignition timing when the after injection starts ignition, and the in-cylinder oxygen concentration is specified. If possible, any predetermined time in the combustion period from the start of ignition of after injection to the end of combustion by after injection may be used. For example, it may be when the heat generation rate due to after injection peaks.

  Further, in order to reduce smoke, both the after injection amount and the main injection amount may be adjusted based on the in-cylinder oxygen concentration instead of adjusting both the after injection amount and the main injection amount.

  For example, when the in-cylinder oxygen concentration at the ignition timing of after injection is lower than a predetermined concentration, it may be determined that the main injection amount is too large and smoke increases, and only the main injection amount may be decreased. Further, the main injection amount is not adjusted, and the after injection amount may be increased when the in-cylinder oxygen concentration at the ignition timing of the after injection is high, and the after injection amount may be decreased when the in-cylinder oxygen concentration is low. . When adjusting only one of the main injection amount and the after injection amount, it is desirable to adjust the after injection amount so as not to fluctuate the output torque of the engine as much as possible.

Moreover, in the said embodiment, although the target value of the combustion parameter was set according to the engine operating state, you may set the target value of the same value irrespective of the engine operating state.
Further, instead of setting the target value of the combustion parameter in advance, the value of the combustion parameter that minimizes the amount of smoke generated may be learned during engine operation.

  Further, instead of detecting the intake oxygen concentration and the exhaust oxygen concentration from the oxygen concentration sensors 74 and 76, respectively, the intake oxygen concentration is calculated from the physical model based on the air flow rate, the intake air temperature, the intake pressure, the engine speed, the injection amount, and the like. The exhaust oxygen concentration may be estimated.

  In the above embodiment, the oxygen concentration acquisition unit, the injection amount adjustment unit, the heat generation amount calculation unit, the heat generation amount estimation unit, and the combustion state calculation unit are realized by the ECU 50 whose functions are specified by the control program. On the other hand, at least some of the functions of the plurality of means may be realized by hardware whose functions are specified by the circuit configuration itself.

  As described above, the present invention is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

2: fuel injection system, 10: diesel engine (internal combustion engine), 42: fuel injection valve, 50: ECU (fuel injection control device, oxygen concentration acquisition means, injection amount adjustment means, heat generation amount calculation means, heat generation amount estimation Means, combustion state calculating means), 66: in-cylinder pressure sensor

Claims (10)

In a fuel injection control device applied to a fuel injection system that executes at least main injection and after injection following the main injection during one combustion cycle of an internal combustion engine,
Oxygen concentration acquisition means for acquiring an in-cylinder oxygen concentration at a predetermined time during a combustion period from the start of ignition of the fuel injected by the after injection to the end of combustion;
An injection amount adjusting unit that adjusts at least one of a main injection amount and an after injection amount based on the in-cylinder oxygen concentration acquired by the oxygen concentration acquiring unit;
A fuel injection control device comprising:   The injection amount adjusting means sets the main injection amount and the after injection amount based on the in-cylinder oxygen concentration without changing the total injection amount in one combustion cycle set based on the operating state of the internal combustion engine. The fuel injection control device according to claim 1, wherein the fuel injection control device is adjusted.   The oxygen concentration acquisition means calculates the in-cylinder oxygen concentration based on the intake oxygen concentration in the intake air flowing into the cylinder, the exhaust oxygen concentration in the exhaust exhausted from the cylinder, and the heat generation amount in the cylinder. The fuel injection control device according to claim 1, wherein the fuel injection control device calculates the fuel injection control device. Calculates the heat generation amount by calculating the heat generation rate in the cylinder from the in-cylinder pressure detected by the in-cylinder pressure sensor, the crank angle, and the in-cylinder volume, and calculating the heat generation amount by integrating the calculated heat generation rate. With means,
The oxygen concentration acquisition means acquires the heat generation amount for calculating the in-cylinder oxygen concentration from the heat generation amount calculation means.
The fuel injection control device according to claim 3. A heat generation amount estimating means for estimating the heat generation amount based on a physical quantity related to a combustion state in a cylinder;
The oxygen concentration acquisition means acquires the heat generation amount for calculating the in-cylinder oxygen concentration from the heat generation amount estimation means;
The fuel injection control device according to claim 3.   The fuel injection control device according to claim 5, wherein the heat generation amount estimation means estimates the heat generation amount based on the physical quantity including an engine speed. Combustion state calculation means for calculating a ratio between the in-cylinder oxygen amount calculated from the in-cylinder oxygen concentration and the after-injection amount as a parameter representing the combustion state in the cylinder;
The injection amount adjusting means adjusts at least the after injection amount of the main injection amount and the after injection amount so that the ratio value calculated by the combustion state calculating means becomes a target value of the ratio. The fuel injection control device according to claim 1, wherein the fuel injection control device is a fuel injection control device.   The fuel injection control device according to claim 7, wherein the injection amount adjusting means presets a target value of the ratio.   The fuel injection control apparatus according to any one of claims 1 to 8, wherein the oxygen concentration acquisition unit acquires the in-cylinder oxygen concentration at an ignition timing of after injection.   10. The after-ignition ignition timing is set when the oxygen concentration acquisition means starts the increase in the heat generation rate due to combustion in the main injection and the increase in the heat generation rate due to combustion in the after injection. The fuel injection control device described.

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