JP6049497B2 - Diesel engine control device and control method - Google Patents

Description

  The present invention relates to a control device and a control method for a diesel engine, and more particularly to a control device and a control method for controlling late post injection for DPF regeneration.

  The exhaust gas discharged from the diesel engine contains harmful substances that cause air pollution. One of the harmful substances is particulate matter (PM). As a technique for reducing the amount of PM released into the atmosphere from an industrial machine equipped with a diesel engine, a DPF (Diesel Particulate Filter) as disclosed in Patent Document 1 is known.

  PM contained in the exhaust gas generated by the operation of the diesel engine is collected by the DPF, and the collected PM accumulates in the DPF. As a result, clogging of the DPF occurs, exhaust gas flow resistance in the exhaust system increases, and the output of the diesel engine is adversely affected. In order to prevent this, the temperature of the exhaust gas flowing into the DPF is forcibly raised, and PM deposited on the DPF is incinerated and removed. This processing is called DPF forced regeneration processing.

JP 2012-72686 A

  In the forced regeneration process of the DPF, late post injection is performed, and there is a possibility that an oil dilution may occur depending on the operation state of the diesel engine due to the late post injection.

  The present invention eliminates such inconvenience and changes the fuel injection amount in late post injection in accordance with the current operating state of the diesel engine, thereby suppressing the occurrence of oil dilution and An object is to provide a control method.

  In order to achieve the above object, a control apparatus for a diesel engine according to the present invention determines an injection condition for tentatively determining a fuel injection amount and fuel injection pressure in late post injection based on a current operating state of the diesel engine. Means, fuel injection period calculating means for calculating a fuel injection period using the fuel injection amount and the fuel injection pressure, and fuel spray arrival distance calculation for calculating a predicted value of the fuel spray arrival distance using the fuel injection period Means, the predicted value, and a target value that is a value of the fuel spray reach distance assumed when late post-injection is performed at the fuel injection amount during steady operation of the diesel engine, and the comparison result Fuel injection amount correction means for correcting the fuel injection amount in response to the fuel injection period calculation means until the predicted value is equal to or less than the target value. Processing serial fuel spray travel calculating means by said fuel injection quantity correction means is characterized in that repeated.

  In order to achieve the above object, a control device for a diesel engine according to the present invention tentatively sets a fuel injection amount and a fuel injection pressure in late post injection based on a current operating state of the diesel engine as another form. An injection condition determining means for determining; a fuel injection pressure correcting means for correcting the fuel injection pressure in accordance with the fuel injection amount; and a fuel injection period for calculating a fuel injection period using the fuel injection amount and the fuel injection pressure. A calculation means; a fuel spray arrival distance calculation means for calculating a predicted value of the fuel spray arrival distance using the fuel injection period; the predicted value; and a late post injection at the fuel injection amount during steady operation of the diesel engine. Is compared with a target value which is a value of the fuel spray reach distance assumed when the fuel injection is performed, and the fuel injection amount is corrected according to the comparison result The fuel injection pressure correction means, the fuel injection period calculation means, the fuel spray arrival distance calculation means, and the fuel injection amount correction means until the predicted value is equal to or less than the target value. The process is repeated.

  Furthermore, the relationship between the predicted value obtained by the diesel engine control device and the fuel injection amount can be stored as a late post injection amount correction map.

  In order to achieve the above object, a method for controlling a diesel engine according to the present invention determines an injection condition for tentatively determining a fuel injection amount and fuel injection pressure in late post injection based on a current operating state of the diesel engine. A fuel injection period calculation step for calculating a fuel injection period using the fuel injection amount and the fuel injection pressure; and a fuel spray arrival distance calculation for calculating a predicted value of the fuel spray arrival distance using the fuel injection period Comparing the step, the predicted value, and a target value that is a value of the fuel spray arrival distance assumed when late post-injection is performed with the fuel injection amount during steady operation of the diesel engine, and the comparison result A fuel injection amount correction step for correcting the fuel injection amount according to the fuel injection amount, and the fuel injection amount until the predicted value becomes equal to or less than the target value. Period calculating step and said fuel spray travel calculation step and the fuel injection amount correction step, characterized in that the repeated.

  In order to achieve the above object, as another mode, the diesel engine control method according to the present invention tentatively sets the fuel injection amount and fuel injection pressure in the late post injection based on the current operating state of the diesel engine. An injection condition determining step for determining, a fuel injection pressure correcting step for correcting the fuel injection pressure according to the fuel injection amount, and a fuel injection period for calculating a fuel injection period using the fuel injection amount and the fuel injection pressure A calculation step; a fuel spray arrival distance calculating step for calculating a predicted value of the fuel spray arrival distance using the fuel injection period; the predicted value; and a late post injection at the fuel injection amount during steady operation of the diesel engine. Is compared with a target value which is a value of the fuel spray reach distance assumed when the fuel injection is performed, and the fuel injection is performed according to the comparison result The fuel injection pressure correction step, the fuel injection period calculation step, the fuel spray arrival distance calculation step, and the fuel injection amount until the predicted value becomes equal to or less than the target value. The correction step is repeated.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus and control method of a diesel engine which suppressed generation | occurrence | production of oil dilution by changing the fuel injection amount in late post injection according to the present driving | running state of a diesel engine are provided. Is done.

It is explanatory drawing which shows the whole structure of a diesel engine and waste gas aftertreatment apparatus. It is sectional drawing of the cylinder of a diesel engine. It is an enlarged view of fuel spray. (A) It is the graph showing the relationship between the operation time of a diesel engine, and load. (B) It is the graph showing the relationship between the operation time of a diesel engine, and a supercharging pressure. It is a block diagram which shows the function structural example of the control apparatus which concerns on 1st Embodiment. It is a flowchart of the process performed by the control apparatus which concerns on 1st Embodiment. It is a graph showing the relationship between the late post injection amount and the spray reach distance. It is sectional drawing of the nozzle of a fuel injection valve. It is a graph showing the relationship between lift amount and time. It is a block diagram which shows the function structural example of the control apparatus which concerns on 2nd Embodiment. It is a flowchart of the process performed by the control apparatus which concerns on 2nd Embodiment.

Hereinafter, a control device and a control method for a diesel engine according to the present invention will be described with reference to embodiments (first embodiment, second embodiment, and other embodiments) shown in the accompanying drawings.
First, an embodiment of a forced regeneration process of a DPF executed in association with the diesel engine control apparatus and method according to the present invention will be described with reference to FIG.

  Although not shown, the diesel engine 1 is provided with a common rail fuel injection device that controls the fuel injection timing, injection amount, and injection pressure to inject fuel into the combustion chamber 25. This common rail type fuel injection device supplies fuel controlled to a predetermined fuel pressure at a predetermined fuel injection timing to the fuel injection valve 27 of each cylinder.

  An exhaust passage 3 is provided in the diesel engine 1, and an exhaust gas aftertreatment device 9 is provided on the downstream side of the exhaust passage 3. The exhaust gas aftertreatment device 9 includes a DOC (Diesel Oxidation Catalyst) 5 and a DPF 7 on the downstream side when viewed from the DOC 5. The exhaust passage 3 is further provided with an exhaust turbocharger 11 upstream from the exhaust gas aftertreatment device 9. The exhaust turbocharger 11 has an exhaust turbine 11a and a compressor 11b driven coaxially thereto. Further, an EGR (Exhaust Gas Recirculation) passage 31 is provided so as to branch from the middle of the exhaust passage 3 or the exhaust manifold 29.

  The combustion gas, that is, the exhaust gas 37 combusted in the combustion chamber 25 of the diesel engine 1 passes through the exhaust valve 39, the exhaust port 41, the exhaust manifold 29, and the exhaust passage 3 provided for each cylinder, and the exhaust turbine 11a. Then, it flows into the exhaust gas aftertreatment device 9. By driving the exhaust turbine 11a, the compressor 11b is also driven to pressurize the intake air. The air discharged from the compressor 11 b passes through the air supply passage 13, is cooled by the intercooler 15, and is subjected to flow rate control by the air supply throttle valve 17. A part of the exhaust gas 37 passes through the EGR passage 31, is cooled by the EGR cooler 33, and then receives a flow rate control by the EGR valve 35. The air supplied via the air supply throttle valve 17 and the air supplied via the EGR valve 35 flow into the combustion chamber 25 from the intake manifold 19 via the intake port 21 and the intake valve 23 provided for each cylinder.

  Reference numeral 45 denotes a control device, which is generally called an ECU (Engine Control Unit). The operation of the diesel engine 1 is electronically controlled by the control device 45. The control device 45 includes an air flow meter 47 for detecting a supply air flow rate flowing into the compressor 11b, a DOC inlet temperature sensor 49 provided at the inlet of the DOC 5, and a DPF inlet temperature sensor 51 provided at the inlet of the DPF 7. A signal from the DPF outlet temperature sensor 53 provided at the outlet of the DPF 7 is input. Further, the rotational speed and load of the diesel engine 1 are detected by a sensor (not shown), and the detection signal is also input to the control device 45. The control device 45 receives these signals and controls the common rail fuel injection device that supplies fuel to the fuel injection valve 27, the air supply throttle valve 17, and the EGR valve 35, thereby controlling the diesel engine 1. Control driving.

  Then, the control device 45 estimates the amount of PM accumulated in the DPF 7 and starts the forced regeneration process of the DPF 7 when the estimated amount exceeds a predetermined value. First, the control device 45 throttles the opening of the air supply throttle valve 17 to reduce the amount of air flowing into the combustion chamber 25. Then, the unburned fuel in the exhaust gas 37 increases. Further, by the further control of the control device 45, immediately after the main injection performed when the piston 2 is located near the top dead center, a smaller amount of fuel is injected than the main injection while the pressure in the cylinder is still high. The This injection is called early post injection. By this early post-injection, the temperature of the exhaust gas 37 increases without affecting the output of the diesel engine 1, and the DOC 5 is activated by the exhaust gas 37 that has reached a high temperature flowing into the DOC 5. As the DOC 5 is activated, the exhaust gas temperature is further increased by the oxidation heat generated when the unburned fuel in the exhaust gas 37 is oxidized.

  Subsequently, the control device 45 determines whether or not the DOC inlet temperature has reached a predetermined temperature. When the determination result is “positive”, the fuel injection valve 27 is controlled to perform the late post injection following the early post injection. This late post injection is performed in a state where the piston 2 has advanced to near the bottom dead center after the early post injection. By late post injection, fuel is discharged from the combustion chamber 25 to the exhaust passage 3 when the exhaust valve 39 is open, and the fuel reacts in the already activated DOC 5 to further increase the exhaust gas temperature by the generated oxidation heat. . Then, the inlet temperature of the DPF 7 rises from 600 ° C. necessary for forced regeneration of the DPF 7 to about 700 ° C. The PM accumulated on the DPF 7 is incinerated and removed by the high-temperature exhaust gas.

  As described above, the main injection is performed when the piston 2 is located at or near the top dead center. In FIG. 2, the piston 2 located at the top dead center is indicated by a virtual line. As shown in the figure, the fuel spray S generated by the main injection mainly collides with a piston cavity 2 a provided in the piston 2. Therefore, the possibility that fuel adheres to the cylinder liner 4 that is the sliding surface of the piston 2 is relatively low. The same can be said for the early post injection performed immediately after the main injection.

  Unlike the main injection as described above, the late post injection is performed when the piston 2 is positioned near the bottom dead center as described above. In FIG. 2, the piston 2 located at the bottom dead center is shown by a solid line. As shown in the drawing, the exposed area of the cylinder liner 4 is larger than that of the main injection and the early post injection, so that the possibility that the fuel spray S adheres to the cylinder liner 4 is increased.

  FIG. 3 shows an enlarged view of the fuel spray S shown in FIG. The nozzle body 271 of the fuel injection valve 27 is provided with an injection hole 272. When fuel is injected from the nozzle hole 272, a flat, substantially triangular fuel spray S is formed. The symbol X is the reach distance of the fuel spray S with reference to the nozzle hole 272.

By the way, the forced regeneration process of the DPF accompanied by the late post injection includes a forced regeneration process during operation performed during operation of the industrial machine equipped with the diesel engine and a forced regeneration process during stop performed while the industrial machine is stopped. is there. In the former forced regeneration process during driving, as shown in FIG. 4A, there is a possibility that the diesel engine suddenly increases when there is a load. A point in time when the load suddenly increases from ML ₁ to ML ₂ is shown as MT ₁ . Although the supercharging pressure is controlled to increase with a sudden increase in the load, the exhaust turbocharger 11 is driven by exhaust gas, so that the increase in the supercharging pressure is delayed from the sudden increase in the load. Specifically, FIG. 4 (B), the the boost pressure MP ₁ preload spike, point MT ₁ is the supercharging pressure rises to the appropriate boost pressure MP ₂ with the load spikes the time MT ₂ of after than. As a result, between the time MT ₁ time MT ₂ is the cylinder pressure in the combustion chamber 25 as compared with the steady operation of the diesel engine is lowered. In FIG. 4B, an ideal supercharging pressure corresponding to a sudden increase in load is indicated by a virtual line.

Thus cylinder pressure than during steady operation is likely to late post injection is performed during the time MT ₂ from the time MT ₁ are reduced. Then, the reach distance X of the fuel spray S increases compared to that during steady operation. This is because the momentum of the fuel spray is less likely to be transmitted to the air in the cylinder as compared to the steady operation. As a result, it is assumed that the possibility of fuel adhesion to the cylinder liner 4 is further increased.

  The fuel adhering to the cylinder liner 4 falls along the wall surface of the cylinder liner 4 toward the bottom dead center. The fuel is mixed with the lubricating oil and dilution of the lubricating oil, that is, oil dilution occurs. As a result, it is assumed that the lubricating oil deteriorates and adversely affects the performance of the diesel engine.

  As described above, when late post-injection is performed with the same injection amount as during steady operation when the in-cylinder pressure is lower than during steady operation, the possibility of oil dilution is greater than during steady operation. It is assumed that it will be high.

The present inventors diligently investigated the inconvenience assumed as described above.
A diesel engine control apparatus and control method according to the present invention will be described in an exemplary and detailed manner with respect to the following first embodiment, second embodiment, and other embodiments.

[First Embodiment]
FIG. 5 shows a functional configuration example of the control device 45 in the first embodiment. The control device 45 includes an injection condition determination unit 452, a fuel injection period calculation unit 454, a fuel spray reach distance calculation unit 455, and a fuel injection amount correction unit 456. The injection condition determining means 452 provisionally determines the fuel injection pressure and the injection amount in the late post injection. Based on the fuel injection pressure and the injection amount determined in this way, the fuel injection period calculation means 454 calculates the fuel injection period. The fuel spray reach distance calculation unit 455 calculates the fuel spray reach distance based on the calculated fuel injection period. The fuel injection amount correcting means 456 is a means for correcting the fuel injection amount in accordance with the calculated fuel spray arrival distance. Each of the above means can communicate with each other. Details of the function of each means will be described later.

  The control device 45 includes a processor and a memory as a hardware configuration. Since the hardware configuration itself of the control device 45 is the same as that of a general ECU, illustration is omitted.

Processing performed after the control device 45 shown in FIG. 5 determines that the forced regeneration processing of the DPF 7 is necessary will be described with reference to FIGS. 6 and 7. FIG. 6 shows a flow of processing by the control device 45 for execution of late post injection. FIG. 7 shows the relationship between the late post injection amount M _fuel and the fuel spray reach distance X in accordance with the in-cylinder pressure, which is one index that represents the operating state of the diesel engine. In the figure, plots 710, 720, and 730 are shown. First, a plot 710 shows the relationship between the late post injection amount M _fuel and the fuel spray arrival distance X at the in-cylinder pressure during steady operation. The in-cylinder pressure during steady operation at a certain rotation speed and load of the diesel engine 1 can be calculated in advance, and the plot 710 is also calculated in advance using the in-cylinder pressure and stored in the memory. On the other hand, the plot 720 is for an operating state in which the in-cylinder pressure is reduced by 10% compared to that during steady operation, and the plot 730 is for the operating state in which the in-cylinder pressure is reduced by 20% compared to during steady operation. The plots 720 and 730 are calculated by the process described below with reference to FIG.

First, in step S101, the injection condition determining means 452 determines the current operating state of the diesel engine as the supply air temperature T _inmani (unit: K) and the supply air pressure (or supercharging pressure) P _inmani (unit: Pa). Each measured value is received from a sensor not shown.

In step S102, the injection condition determining means 452 receives the values of the rotational speed and the load from sensors not shown as the current operating state of the diesel engine. Subsequently, the injection condition determination unit 452 determines the fuel injection pressure P _inj (unit: Pa) and the late post injection amount M _fuel (unit: mg) based on the rotation speed and the load. This determination includes a fuel injection pressure map that defines the relationship between the rotational speed and load and the fuel injection pressure P _inj, and a late post injection amount map that defines the relationship between the rotational speed and load and the late post injection amount M _fuel. This is done by referring to the injection condition determining means 452. These fuel injection pressure map and late post injection amount map are stored in advance in a memory in the control means 45. The determination in step S102 is provisional only.

As an example of step S102, it is assumed that the late post-injection amount M _fuel is determined to be 8 mg. In this case, the spray travel distance X is in-cylinder pressure at the time of steady operation, it is 70mm as shown in point CP ₁ on the plot 710 of FIG. The spray reach distance X at the in-cylinder pressure during the steady operation is expressed as a target value X _target of the spray reach distance. As described above, the target value X _target is calculated in advance and stored in the memory.

In step S103, the fuel injection period calculation means 454 performs the late post injection based on the supply air temperature T _inmani and the supply air pressure P _inmani acquired in step S101 and the rotation speed and load acquired in step S102. In-cylinder temperature _Tlatepost (unit: K) and in-cylinder pressure _Platepost (unit: Pa) are determined. This determination is based on the relationship between the four values of the supply air temperature T _inmani , the supply air pressure P _inmani , the diesel engine speed, and the diesel engine load, and the in-cylinder temperature T _latepost and the pressure P _latepost during late post injection. The fuel injection period calculation means 454 refers to the in-cylinder state map that defines the above. The in-cylinder state map is stored in advance in the memory.

In step S104, the fuel injection period calculation means 454 calculates the fuel injection period t (unit: second). For this purpose, first, a differential pressure ΔP between the fuel injection pressure P _inj and the in-cylinder pressure P _comp is calculated as follows. However, at the time of late post injection, since the piston 2 is located near the bottom dead center, the in-cylinder pressure P _comp is relatively small, so the influence of the in-cylinder pressure P _comp can be ignored.

Subsequently, the fuel injection period calculation means 454 calculates the fuel injection speed V _inj (unit: m / s) using the constant fuel density ρ _f (unit: kg / m ³ ). Incidentally, it is possible to use a value of 826kg / ^{m 3} as an approximation of the fuel density [rho _f.

Further, the fuel injection period calculation unit 454 calculates the nozzle hole area A _noz (unit: m ² ) using the nozzle hole diameter d _noz (unit: m) for the nozzle hole 272 provided in the fuel injection valve 27.

Then, the fuel injection period calculation means 454 calculates the fuel injection period t (unit: second) according to the following equation. However, n _nozzle is the number of injection holes 272 provided in the fuel injection valve 27.

In step S105, the fuel spray reach distance calculation means 455 calculates the predicted value X _calc (unit: mm) of the spray post reach X of the late post injection. For this purpose, first, the fuel spray reach distance calculation means 455 calculates the in-cylinder air density ρ _a (unit: kg / m ³ ) using the gas constant R as follows.

Subsequently, the fuel spray reach distance calculation means 455 uses the fuel injection period t calculated in step S104, and predicts the spray reach distance X of late post-injection X _calc according to the spray reach distance prediction formula, so-called Guang'an formula. Is calculated.

However, t _b is a point in time after the start of fuel injection is expressed as follows.

As shown in equation (6), in the case of 0 _<t ≦ t _b, the predicted value _{X calc} the fuel spray travel is proportional to the fuel injection period t. Further, as shown in Expression (7), when t _b <t, the predicted value X _calc of the spray reach distance is proportional to the 1/2 power of the fuel injection period t.

As an example of this step S105, as shown in point CP ₂ on the plot 730 of FIG. 7, and the predicted value _{X calc} the spray travel is calculated as 76 mm.

Step S106 The controller 45, the predicted value _{X calc} the fuel spray travel calculated in step S105 to determine whether it is less than the target value _{X target} of fuel spray travel described above. As described above, an example of the target value X _target of the spray reach distance is 70 mm. In this case, since the predicted value X _calc = 76 mm of the spray reach distance exceeds the target value X _target = 70 mm of the spray reach distance, the determination result is “No”, and the process proceeds to step S107.

In step S107, the fuel injection amount correction means 456 corrects the value of the late post injection amount M _fuel . Specifically, the value of the late post injection amount M _fuel is reduced by a predetermined amount. This predetermined amount is, for example, 0.1 mg. In the above example, as a result of this step, the late post injection amount M _fuel = 8−0.1 = 7.9. Thereafter, steps S104 and S105 are performed.

Then, step S106 is performed again. If the determination result in step S106 is “No”, steps S107, S104, and S105 are repeated. As a result, the value of the late post-injection amount M _fuel further decreases.

Then, the late post-injection amount M _fuel is corrected to a value of 6.8 mg in a plurality of steps S107. This value is only an example. Subsequently, as a result of performing Steps S104 and S105, the predicted value _Xcalc of the fuel spray reach distance is calculated as 70 mm although it is an example. This corresponds to a point CP ₃ on the plot 730 of FIG. In other words, the predicted value _{X calc} is to become equal to the target value _{X target} of spray travel, the judgment result of the subsequent step S106 is processed by the "positive" and the control device 45 is terminated. Thereafter, although not shown, late post injection is performed at a late post injection amount M _fuel = 6.8 mg determined by the above processing.

As described above, in this embodiment, the late post so that the predicted value X _calc of the spray reach distance in the current operation state of the diesel engine is equal to or less than the target value X _target of the spray reach distance in the in-cylinder pressure during steady operation. The injection amount M _fuel is corrected. That is, even if the in-cylinder pressure is reduced as compared with that during steady operation due to a sudden increase in engine load, the spray reach distance is controlled to be the same as or less than that during steady operation. As a result, even if the in-cylinder pressure is lower than that during steady operation, the possibility that fuel may adhere to the cylinder liner and cause oil dilution can be suppressed to the same extent as during steady operation.

  The details and effects of the first embodiment have been described so far, but there is room for further improvement. In order to explain it, reference is first made to FIGS. First, FIG. 8 is a detailed sectional view of the nozzle at the tip of the fuel injection valve 27. As already described, the nozzle body 271 is provided with the nozzle hole 272. A needle valve 273 is disposed inside the nozzle body 271. Reference symbol L is a lift amount of the needle valve 273 from the nozzle body 271. The needle valve 273 is normally loaded from above in the drawing so that the lift amount L becomes zero. When fuel is injected, the needle valve 273 is lifted upward in the drawing, that is, lifted under the control of the control device 45. Thus, the lift amount L becomes a positive value, and the fuel supplied from the common rail fuel injection device flows between the inner wall of the nozzle body 271 and the needle valve 273 and is injected into the combustion chamber 25 through the injection hole 272. The

FIG. 9 is a graph showing an example of the change over time of the lift amount in the main injection. Lift of the needle valve 273 at the injection start time point LT ₁ begins, injection starts. Thereafter, the lift amount L with time is increased and the lift amount L reaches the maximum value _{L max} at time LT _2. Thereafter, the lift amount L with time decreases, the lift amount L becomes zero at the injection end LT _3, the injection is completed. Period from the injection start time LT ₁ to the injection termination time LT ₃ tau corresponds to the fuel injection period of the main injection.

On the other hand, the fuel injection amount M _fuel of late post injection is usually smaller than the fuel injection amount of main injection. Therefore, the fuel injection period t in the late post-injection is shorter than the fuel injection period τ in the main injection. Speaking more but terminates the fuel injection period t of late post-injection prior to the time LT ₂ to the lift amount L reaches the maximum value L _max. As can be seen from FIG. 8, as the lift amount L is smaller than the maximum value L _max , the fuel injection pressure loss is more likely to occur. Therefore, the late post injection is more susceptible to the pressure loss than the main injection. . As a result, the fuel outlet pressure near the nozzle hole 272, reduced by about equivalent than the fuel injection pressure P _inj determined in the step S102, the actual fuel spray reach distance X is smaller than the predicted value X _calc.

That is, in the first embodiment, since the problem of significant pressure loss is not considered in late post injection, the prediction accuracy of the predicted value _Xcalc is relatively poor. Since step S107 is repeatedly performed more than necessary, the late post-injection amount M _fuel is also decreased more than necessary, and there is a possibility that a corresponding time is required for the forced regeneration process of the DPF 7.

Therefore, in the second embodiment to be described later, processing for correcting the value of the fuel injection pressure P _inj is also performed in consideration of the pressure loss. Thereby, the prediction accuracy of the predicted value X _calc is improved as compared with the first embodiment, and the value of the late post injection amount M _fuel is prevented from becoming too small.

[Second Embodiment]
FIG. 10 shows a functional configuration example of the control device 45 in the second embodiment. The control device 45 includes a fuel injection pressure correction means 458 in addition to the injection condition determination means 452, the fuel injection period calculation means 454, the fuel spray reach distance calculation means 455, and the fuel injection amount correction means 456 that have already been described. Yes. The fuel injection pressure correcting means 458 corrects the fuel injection pressure determined by the injection condition determining means 452. Details will be described later.

  FIG. 11 shows the flow of processing performed by the control device 45 shown in FIG. The same processes as those in FIG. 6 are denoted by the same reference numerals. First, similarly to the first embodiment, steps S101 to S103 are performed.

Then, it progresses to step S201. In this step, the fuel injection pressure correction means 458 corrects the fuel injection pressure P _inj determined in step S102. Specifically, the value of the fuel injection pressure P _inj is decreased. By this correction, the value of the fuel injection pressure P _inj can be brought close to the value of the actual fuel outlet pressure in consideration of a significant pressure loss in the late post injection.

The correction amount, that is, the decrease amount of the value of the fuel injection pressure P _inj in this step depends on the characteristics of the fuel injection valve 27 such as the lift speed of the needle valve 273. Therefore, a unit test of the fuel injection valve 27 is performed to obtain a relationship between the late post injection amount M _fuel and the correction amount of the fuel injection pressure P _inj , and the relationship is stored in advance in the memory in the control device 45 as a fuel injection pressure correction map. Save to. In this step, the fuel injection pressure correction means 458 corrects the fuel injection pressure P _inj after referring to the fuel injection pressure correction map.

Subsequent to step S201, steps S104 to S106 already described are performed. If the determination result in step S106 is “No”, the process proceeds to step S107, and the late post injection amount M _fuel is corrected. Then, Step S201 is performed again, and the fuel injection pressure P _inj is also corrected according to the late post injection amount M _fuel corrected in Step S107. Finally, the determination result in step S106 becomes “positive”, and the process ends.

As effects of this embodiment, in addition to the same effects as those of the first embodiment, the following effects can be obtained. For that purpose, reference is first made to equation (4) for the fuel injection period t. Expression (4) includes the fuel injection speed V _inj . From the equations (1) and (2), V _inj is proportional to P _{inj to} the 1/2 power. Therefore, t is proportional to P _{inj to} the power of (−1/2).

In addition, ΔP = P _inj and t are included in the expressions (6) and (7) related to the predicted value X _calc of the fuel spray reach distance. In view of the above relationship that t is proportional to (-1/2) power of _{P inj,} t is increased if _{P inj} decreases. With such an increase in t, X _calc does not change from Equation (6) when t ≦ t _b , but X _calc decreases from Equation (7) when t> t _b . That is, when P _inj is decreased, X _calc does not change or decreases.

That is, in the present embodiment, the fuel injection pressure P _inj is corrected to a smaller value than before in step S201, so that the determination result regarding the predicted value _Xcalc becomes “positive” in step S106. The number of execution times of the loop processing is reduced as compared with the first embodiment. At the same time, the number of corrections of the late post injection amount M _fuel in step S107 is reduced, and the reduction amount of the late post injection amount can be suppressed. As a result, the forced regeneration time of the DPF is suppressed. As in the first embodiment, even if the in-cylinder pressure is lower than that in steady operation, the possibility that fuel may adhere to the cylinder liner and cause oil dilution is suppressed to the same extent as in steady operation. Needless to say, you can.

[Other forms]
According to the plots 720 and 730 obtained by the processing shown in FIG. 6 in the first embodiment, that is, the late post-injection amount M _fuel and the predicted value X _calc according to the amount of decrease in the in-cylinder pressure based on the steady operation. Can be stored in the memory as a late post injection amount correction map. Then, when performing the processing of FIG. 6 in the next late post injection for DPF forced regeneration, the late post injection amount M _fuel is reduced from 8 mg by a predetermined amount in step S107, and this is repeated a plurality of times. Rather than finding the value of 8 mg, the fuel injection amount correction means 456 refers to the late post injection amount correction map in step S107, and the value of 6.8 mg can be found in one execution of step S107. . This eliminates the need to repeatedly execute steps S104 to S107. In particular, it is advantageous to be able to reduce the number of executions of steps S104 and S105 that include a power calculation with a relatively high calculation cost.

Similarly, the late post-injection amount M _fuel and the predicted value X _calc according to the amount of decrease in the in-cylinder pressure based on the steady operation obtained by the processing shown in FIG. 11 in the second embodiment. The relationship can also be stored in the memory as a late post injection amount correction map.

  The functional configuration of the control device 45 described above is not limited to the above-described mode. For example, each unit can be integrated and mounted, or conversely, can be further distributed and mounted.

  Although specific embodiments of the present invention have been described, the present invention is not limited to such embodiments, and various modifications based on the technical idea of the present invention are included in the concept of the present invention.

1 Diesel engine 2 Piston 2a Piston cavity 3 Exhaust passage 4 Cylinder liner 5 DOC
7 DPF
9 Exhaust gas aftertreatment device 11 Exhaust turbocharger 11a Exhaust turbine 11b Compressor 13 Supply passage 15 Intercooler 17 Supply throttle valve 19 Intake manifold 21 Intake port 23 Intake valve 25 Combustion chamber 27 Fuel injection valve 29 Exhaust manifold 31 EGR passage 33 EGR cooler 35 EGR valve 37 exhaust gas 39 exhaust valve 41 exhaust port 45 control device 47 air flow meter 49 DOC inlet temperature sensor 51 DPF inlet temperature sensor 53 DPF outlet temperature sensor 271 nozzle body 272 injection hole 273 needle valve 452 injection condition determining means 454 Fuel injection period calculation means 455 Fuel spray arrival distance calculation means 456 Fuel injection amount correction means 458 Fuel injection pressure correction means S Fuel spray X Fuel spray arrival distance L Lift amount

Claims (5)

Injection condition determining means for tentatively determining the fuel injection amount and fuel injection pressure in late post injection based on the current operating state of the diesel engine;
Fuel injection period calculating means for calculating a fuel injection period using the fuel injection amount and the fuel injection pressure;
Fuel spray arrival distance calculating means for calculating a predicted value of the fuel spray arrival distance using the fuel injection period;
The predicted value is compared with a target value that is a value of a fuel spray arrival distance assumed when late post-injection is performed at the fuel injection amount during steady operation of the diesel engine, and according to the comparison result Fuel injection amount correction means for correcting the fuel injection amount, and until the predicted value becomes equal to or less than the target value, the fuel injection period calculation means, the fuel spray reach distance calculation means, and the fuel injection amount correction means, The control apparatus of the diesel engine characterized by repeating the process by. Injection condition determining means for tentatively determining the fuel injection amount and fuel injection pressure in late post injection based on the current operating state of the diesel engine;
Fuel injection pressure correcting means for correcting the fuel injection pressure according to the fuel injection amount;
Fuel injection period calculating means for calculating a fuel injection period using the fuel injection amount and the fuel injection pressure;
Fuel spray arrival distance calculating means for calculating a predicted value of the fuel spray arrival distance using the fuel injection period;
The predicted value is compared with a target value that is a value of a fuel spray arrival distance assumed when late post-injection is performed at the fuel injection amount during steady operation of the diesel engine, and according to the comparison result Fuel injection amount correction means for correcting the fuel injection amount, and until the predicted value becomes equal to or less than the target value, the fuel injection pressure correction means, the fuel injection period calculation means, and the fuel spray reach distance calculation means, The diesel engine control device, characterized in that the processing by the fuel injection amount correcting means is repeated.   A late post injection amount correction map representing a relationship between the predicted value and the fuel injection amount obtained by the control device according to claim 1. An injection condition determination step for tentatively determining the fuel injection amount and fuel injection pressure in the late post injection based on the current operating state of the diesel engine;
A fuel injection period calculating step of calculating a fuel injection period using the fuel injection amount and the fuel injection pressure;
A fuel spray arrival distance calculating step of calculating a predicted value of the fuel spray arrival distance using the fuel injection period;
The predicted value is compared with a target value that is a value of a fuel spray arrival distance assumed when late post-injection is performed at the fuel injection amount during steady operation of the diesel engine, and according to the comparison result A fuel injection amount correcting step for correcting the fuel injection amount, and until the predicted value is equal to or less than the target value, the fuel injection period calculating step, the fuel spray arrival distance calculating step, and the fuel injection amount correcting step. Is repeated, the control method of the diesel engine characterized by the above-mentioned. An injection condition determination step for tentatively determining the fuel injection amount and fuel injection pressure in the late post injection based on the current operating state of the diesel engine;
A fuel injection pressure correction step of correcting the fuel injection pressure according to the fuel injection amount;
A fuel injection period calculating step of calculating a fuel injection period using the fuel injection amount and the fuel injection pressure;
A fuel spray arrival distance calculating step of calculating a predicted value of the fuel spray arrival distance using the fuel injection period;
The predicted value is compared with a target value that is a value of a fuel spray arrival distance assumed when late post-injection is performed at the fuel injection amount during steady operation of the diesel engine, and according to the comparison result A fuel injection amount correcting step for correcting the fuel injection amount, and until the predicted value becomes equal to or less than the target value, the fuel injection pressure correcting step, the fuel injection period calculating step, and the fuel spray reaching distance calculating step, The method for controlling a diesel engine, wherein the fuel injection amount correction step is repeated.

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