JP6444823B2 - diesel engine - Google Patents

Description

The present invention relates to a diesel engine. Specifically, the present invention relates to a configuration that suppresses slipping of ammonia (NH ₃ , hereinafter referred to as “NH ₃ ”) while preventing generation of white smoke in a diesel engine with a urea SCR (selective reduction catalyst) system.

  Conventionally, a diesel engine having a system for purifying exhaust gas has been known. Patent document 1 discloses the exhaust gas purification method performed in this kind of diesel engine. In the exhaust gas purification method of Patent Document 1, the amount of unburned hydrocarbon (hereinafter referred to as “HC”) accumulated in the oxidation catalyst carrier is estimated, and the estimated amount of accumulation of HC has a predetermined judgment value. When it exceeds, HC removal control is performed, the exhaust gas temperature is raised to activate the oxidation catalyst, and the accumulated HC is oxidized and removed. With such a configuration, it is possible to prevent white smoke from being generated due to excessive accumulation of HC and peeling off.

JP 2004-108320 A

However, when the configuration of Patent Document 1 is applied as it is to a diesel engine with a urea SCR system, the estimated amount of HC accumulation is high regardless of whether the amount of NH ₃ adsorbed on the SCR (selective reduction catalyst) is large or small. When the predetermined determination value is exceeded, HC removal control is uniformly performed, and the exhaust gas temperature is raised. For this reason, NH ₃ adsorbed on the SCR may slip excessively as the temperature rises, and there is room for improvement.

The present invention has been made in view of the above circumstances, and an object thereof is to suppress NH ₃ slip while preventing generation of white smoke in a diesel engine with a urea SCR system.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

According to an aspect of the present invention, a diesel engine having the following configuration is provided. That is, the diesel engine includes a soot filter, a diesel oxidation catalyst, a diesel oxidation catalyst temperature sensor, a selective reduction catalyst, a urea water injector, and a control unit. The soot filter is installed in an exhaust gas flow path from the internal combustion engine to collect particulate matter. The diesel oxidation catalyst is installed upstream of the soot filter to promote the oxidation of fuel in the exhaust gas passage. The diesel oxidation catalyst temperature sensor detects the temperature of the diesel oxidation catalyst. The selective reduction catalyst is installed downstream of the soot filter to reduce nitrogen oxides. The urea water injector is installed between the soot filter and the selective reduction catalyst, and injects urea water into the exhaust gas discharged from the soot filter. The control unit performs temperature increase control of the diesel oxidation catalyst, the soot filter, and the selective reduction catalyst, and performs injection control of urea water from the urea water injector. The control unit performs a first control and a second control. In the first control, the HC is oxidized and removed by raising the temperature of the diesel oxidation catalyst in order to keep the amount of HC accumulated below a predetermined limit amount. In the second control, the urea water injection from the urea water injector is stopped or reduced until the adsorption amount of NH _{3 on} the selective reduction catalyst is reduced to a predetermined reduction target amount. The control unit, based on the emission amount of HC calculated from the past operation state and the temperature of the diesel oxidation catalyst detected by the diesel oxidation catalyst temperature sensor, to at least the current HC to the diesel oxidation catalyst The amount of accumulation is estimated, and the first time required from the current state until the amount of HC accumulation reaches the limit amount is estimated. The control unit is configured to estimate the amount of adsorption of NH ₃ to the selective reduction catalyst based on past operating conditions, when the current state performing the second control, the adsorption amount of NH ₃ is A second time required until the reduction target amount is reduced is estimated. The control unit performs the first control immediately after performing the second control at the timing when the first time and the second time become the same length.

As a result, the limit amount is set to an appropriate value at which white smoke starts to be generated, and the reduction target amount is set to an appropriate value at which the NH ₃ slip hardly occurs even when the temperature of the selective reduction catalyst is increased. By doing so, it is possible to prevent white smoke from being discharged from the diesel oxidation catalyst, and it is possible to prevent NH ₃ from slipping excessively from the selective reduction catalyst. In addition, by setting the limit amount and target reduction amount to appropriate values as described above, the time when the temperature rise is necessary to prevent white smoke is estimated from the amount of HC accumulated, and this time is selected. By performing the control so that the NH ₃ purge of the reduction catalyst is completed, the NH ₃ purge time can be significantly shortened, so that the working efficiency can be improved.

The diesel engine preferably has the following configuration. That is, the diesel engine further includes an ammonia slip suppression catalyst, a selective reduction catalyst temperature sensor, and an ammonia slip suppression catalyst temperature sensor. The ammonia slip suppression catalyst is installed downstream of the selective reduction catalyst and oxidizes NH ₃ that has passed through the selective reduction catalyst. The selective reduction catalyst temperature sensor detects the temperature of the selective reduction catalyst. The ammonia slip suppression catalyst temperature sensor detects the temperature of the ammonia slip suppression catalyst. The control unit oxidizes and removes HC by raising the temperature of the selective reduction catalyst and the ammonia slip suppression catalyst in order to keep the amount of HC accumulated below a predetermined limit amount. I do. The control unit, based on the temperature of the selective reduction catalyst detected by the selective reduction catalyst temperature sensor and the temperature of the ammonia slip suppression catalyst detected by the ammonia slip suppression catalyst temperature sensor, the diesel oxidation catalyst, the selective reduction The amount of HC accumulated in the catalyst and the ammonia slip suppression catalyst is estimated, and the amount of HC accumulated in any of the diesel oxidation catalyst, the selective reduction catalyst, and the ammonia slip suppression catalyst from the current state is estimated. A first time required to reach the limit amount is estimated. The control unit performs the first control and the third control immediately after performing the second control at the timing when the first time and the second time become the same length.

As a result, the limit amount is set to an appropriate value such that white smoke starts to be generated, and the reduction target amount is set to an appropriate value at which the NH ₃ slip hardly occurs even when the temperature of the selective reduction catalyst is increased. Further, it is possible to prevent white smoke from being generated from the selective reduction catalyst and the ammonia slip suppression catalyst (not only from the soot filter) while preventing the NH ₃ slip from the selective reduction catalyst.

  In the diesel engine, the control unit preferably performs the first control by adjusting an opening degree of an exhaust valve provided in the exhaust gas passage.

  Thereby, 1st control can be easily performed by adjusting the opening degree of an exhaust valve suitably, and generation | occurrence | production of white smoke can be prevented thereby.

  In the diesel engine, it is preferable that the control unit performs the first control by performing post injection into a combustion chamber of the internal combustion engine.

  Thus, the first control can be easily performed by performing the post injection in the combustion chamber of the internal combustion engine, thereby preventing the generation of white smoke.

The figure which shows the whole structure of the diesel engine which concerns on one Embodiment of this invention. The block diagram which shows the main electrical structures of a diesel engine. While preventing the occurrence of white smoke, the flow chart showing the processing for suppressing the slip of NH _3. (A) is a figure which shows the time-dependent change of the accumulation amount of HC. (B) is a diagram showing the time course of adsorbed NH ₃ amount to the selective reduction catalyst.

  Next, embodiments of the present invention will be described with reference to the drawings. First, a basic configuration of the engine 1 of the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram showing an overall configuration of an engine 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing the main electrical configuration of the engine 1.

  The engine 1 is a diesel engine and is used by being mounted on an agricultural machine such as a tractor and a construction machine such as a skid steer loader.

  The engine 1 is combusted by supplying fuel to compressed air, and obtains rotational power from the expansion energy generated by the combustion. The engine 1 mainly includes a cylinder block, a cylinder head 2, and an ECU 3 (FIG. 2) as a control unit. A piston, a crankshaft, and the like are disposed inside the cylinder block. A cylinder head 2 is disposed on the upper side of the cylinder block. An injector 4 and the like for injecting fuel into the combustion chamber are attached to the cylinder head 2 (see FIG. 1).

  The ECU 3 shown in FIG. 2 is configured as a computer including an arithmetic unit configured by a CPU and the like, and a storage unit configured by a ROM, a RAM, and the like. The calculation unit sends control commands to various actuators based on information from various sensors and operates various parameters (for example, fuel injection amount, air intake amount, exhaust gas reduction amount). Etc.). The storage unit stores various programs and a plurality of control information set in advance with respect to the control of the engine 1.

  As shown in FIG. 1, the engine 1 includes an intake portion, a supercharger 5, an intake throttle (intake throttle device) 6, and an intake manifold 7 as members of an intake system.

  The suction part sucks air from the outside via an air cleaner (not shown). The air sucked by the suction part is supplied to the compressor wheel 5b side of the supercharger 5.

  The supercharger 5 includes a turbine wheel 5a and a compressor wheel 5b. The turbine wheel 5a is configured to rotate using exhaust gas. The compressor wheel 5b is connected to the same shaft 5c as the turbine wheel 5a, and rotates with the rotation of the turbine wheel 5a. Thus, by rotating the compressor wheel 5b, air can be compressed and forced intake can be performed. The air sucked by the supercharger 5 is supplied to the intake manifold 7 via the intake pipe and the intake throttle 6 and the like.

  The intake manifold 7 divides the supplied gas into a number corresponding to the number of cylinders (four in this embodiment) and supplies it to the combustion chamber. A common rail is disposed below the intake manifold 7. The common rail stores the fuel supplied from the fuel pump at a high pressure and supplies the fuel to the injector 4 arranged in the cylinder head 2.

  The injector 4 injects fuel into the combustion chamber at a predetermined timing. The injector 4 is configured to perform main injection near the top dead center (TDC). The injector 4 performs after injection for the purpose of reducing particulate matter (PM), promoting purification of exhaust gas, and raising the temperature immediately after main injection, or at a later timing of after injection. Post injection can be performed for the purpose of increasing the temperature. As shown in FIG. 2, the injector 4 includes an injector solenoid valve 8. The injector electromagnetic valve 8 is opened and closed at a timing according to an instruction from the ECU 3 to inject fuel into the combustion chamber.

  With the above configuration, the fuel injected in the combustion chamber burns to drive the piston, and the crankshaft connected to the piston rotates. Therefore, power can be taken out from the crankshaft.

  An engine speed sensor 9 is attached in the vicinity of the crankshaft. The engine speed detected by the engine speed sensor 9 is output to the ECU 3.

  As shown in FIG. 1, the engine 1 includes an exhaust manifold 10, an exhaust pipe 11, an exhaust valve 12, a DPF device 13, an exhaust pipe 14, and an SCR device 15 as exhaust system members.

  The exhaust manifold 10 collectively supplies exhaust gases generated in a plurality of combustion chambers (four in this embodiment) to the turbine wheel 5a.

  The exhaust pipe 11 is a tubular member and forms a passage for exhaust gas from the engine 1. The exhaust pipe 11 connects the turbine wheel 5 a side of the supercharger 5 and the DPF device 13. An exhaust valve 12 is installed in the middle of the exhaust pipe 11. The exhaust valve 12 is configured as a throttle valve, and its opening degree can be changed in a stepless manner (or in a sufficiently large number of steps). The exhaust valve 12 is electrically connected to the ECU 3 and adjusts the amount of exhaust gas sent to the DPF device 13 in accordance with a command from the ECU 3. Thereby, the temperature of the exhaust gas sent to the DPF device 13 can be adjusted.

  The DPF device 13 is configured by accommodating a diesel oxidation catalyst (DOC) 16 and a soot filter (SF) 17 in a substantially cylindrical hollow case. The soot filter 17 of the present embodiment is configured as a filter with a catalyst coated with an oxidation catalyst, but may be a filter without a catalyst.

  As shown in FIG. 1, the soot filter 17 is disposed in an exhaust passage from the engine 1 that is an internal combustion engine. The soot filter 17 is formed of a heat-resistant porous material such as ceramic or metal nonwoven fabric, and has a large number of fine channels through which exhaust flows. The soot filter 17 has an oxidation catalyst, and the oxidation catalyst is provided integrally with the filter. When exhaust from the engine 1 flows into the soot filter 17, the soot filter 17 collects particulate matter mainly including carbon particles contained in the exhaust, and the collected particulate matter is accumulated in the soot filter 17.

  As shown in FIG. 1, the diesel oxidation catalyst 16 is disposed upstream of the soot filter 17. Thus, the diesel oxidation catalyst 16 is also disposed in the exhaust gas flow path. The diesel oxidation catalyst 16 is made of platinum or the like, and can promote oxidation of unburned fuel, carbon monoxide, nitrogen monoxide and the like contained in the exhaust gas. The action of the diesel oxidation catalyst 16 oxidizes nitrogen monoxide in the exhaust gas to unstable nitrogen dioxide. The oxygen released when the nitrogen dioxide returns to nitric oxide is supplied for the combustion of the particulate matter captured by the downstream soot filter 17.

  The diesel oxidation catalyst 16 is provided with a diesel oxidation catalyst temperature sensor 18 that detects the temperature of the diesel oxidation catalyst 16. The diesel oxidation catalyst temperature sensor 18 outputs the detected temperature of the diesel oxidation catalyst 16 to the ECU 3.

The exhaust gas that has passed through the DPF device 13 is sent to the SCR device 15 via the exhaust pipe 14. A urea water injection nozzle 19 as a urea water injection body is provided in the middle of the exhaust pipe 14. That is, the urea water injection nozzle 19 is installed between the soot filter 17 and the selective reduction catalyst 20 in the exhaust gas passage. From this urea water injection nozzle 19, urea water is injected into the exhaust gas passing through the exhaust pipe 14. At this time, the exhaust gas takes in NH ₃ obtained from urea injected by the urea water injection nozzle 19. The urea water injection nozzle 19 is connected to the ECU 3, and the urea water injection state from the urea water injection nozzle 19 is controlled in accordance with a command from the ECU 3.

  The SCR device 15 is configured by accommodating a selective reduction catalyst (SCR) 20 and an ammonia slip suppression catalyst (ASC) 21 in a substantially cylindrical hollow case.

The selective reduction catalyst 20 has a configuration in which an SCR catalyst is supported on a honeycomb structure. As shown in FIG. 1, the selective reduction catalyst 20 is installed downstream of the soot filter 17. The selective reduction catalyst 20 uses NH ₃ as a reducing agent and selectively reduces NOx in the exhaust gas in an atmosphere in which NH ₃ exists. Specifically, when NH ₃ is taken into the exhaust gas from the urea injected by the urea water injection nozzle 19, the NO 3 in the exhaust is selectively reduced by the NH ₃ according to the following three reaction formulas. .
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O
2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O

Further, the selective reduction catalyst 20 has a function of reducing NOx in the exhaust gas with NH _3, also it has only a function of adsorbing (storing) a predetermined amount of NH _3. In the following description, it may be referred adsorbed NH ₃ amount the amount of NH ₃ adsorbed in the selective reduction catalyst 20. The NH ₃ adsorbed on the selective reduction catalyst 20 is consumed as appropriate together with the NH ₃ supplied from the urea water injection nozzle 19 in order to reduce NOx in the exhaust gas.

However, the amount by which the selective reduction catalyst 20 can adsorb NH ₃ also has an upper limit (hereinafter, this limit may be referred to as the maximum NH ₃ adsorption amount). The maximum NH ₃ adsorption amount varies depending on the temperature of the selective reduction catalyst 20, for example. When adsorbed NH ₃ amount of the selective reduction catalyst 20 exceeds the maximum NH ₃ adsorption, so that the NH ₃ that are no longer completely adsorbed is discharged to the downstream (slip NH _3).

As shown in FIG. 1, the ammonia slip suppression catalyst 21 is installed downstream of the selective reduction catalyst 20. The ammonia slip suppression catalyst 21 oxidizes NH ₃ that has been desorbed from the selective reduction catalyst 20 or not adsorbed by the selective reduction catalyst 20 and has passed through the selective reduction catalyst 20, and NH ₃ is released to the outside. Is to prevent. The ammonia slip suppression catalyst 21 is an oxidation catalyst such as platinum that oxidizes NH _3, and oxidizes ammonia according to the following two reaction formulas to change it to nitrogen, nitrogen monoxide, water, or the like.
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O

  After passing through the ammonia slip suppression catalyst 21, the exhaust gas is discharged to the outside through a predetermined exhaust pipe. By providing the urea water injection nozzle 19 and the SCR device 15 as described above, NOx contained in the exhaust gas can be removed.

  The selective reduction catalyst 20 is provided with a selective reduction catalyst temperature sensor 22 that detects the temperature of the selective reduction catalyst 20. The selective reduction catalyst temperature sensor 22 outputs the detected temperature of the selective reduction catalyst 20 to the ECU 3.

  Similarly, the ammonia slip suppression catalyst 21 is provided with an ammonia slip suppression catalyst temperature sensor 23 that detects the temperature of the ammonia slip suppression catalyst 21. The ammonia slip suppression catalyst temperature sensor 23 outputs the detected temperature of the ammonia slip suppression catalyst 21 to the ECU 3.

Next, the control for suppressing the slip of NH ₃ from the selective reduction catalyst 20 while preventing the generation of white smoke from the diesel oxidation catalyst 16 and the like will be described in detail with reference to FIGS. . FIG. 3 is a flowchart showing a process for suppressing NH ₃ slip while preventing generation of white smoke. FIG. 4A is a diagram showing the change over time in the amount of HC accumulated. 4 (b) is a diagram showing the adsorbed NH ₃ amount of transition to the selective reduction catalyst 20 from the start of the purging process of the NH _3.

  The ECU 3 according to this embodiment controls the injection of urea water from the urea water injection nozzle 19 and controls the temperature of the diesel oxidation catalyst 16, the soot filter 17, the selective reduction catalyst 20, and the ammonia slip suppression catalyst 21. Do.

  As pointed out in Patent Document 1, if HC accumulates excessively in the diesel oxidation catalyst 16, the soot filter 17, the selective reduction catalyst 20, the ammonia slip suppression catalyst 21, etc., the unburned HC is peeled off little by little to the outside. May be emitted, which may cause white smoke. The generation of such white smoke makes it look bad and can also cause odors. Therefore, it is desirable to control the generation of white smoke if possible. Therefore, in the engine 1 of the present embodiment, the diesel oxidation catalyst 16, the soot filter 17, the selective reduction catalyst 20, and the ammonia slip suppression so that the amount of HC accumulated does not reach such an amount that white smoke starts to be generated. The catalyst 21 is appropriately heated to oxidize and remove HC.

  Specifically, the ECU 3 performs control to increase the temperature of the diesel oxidation catalyst 16 at a necessary timing in order to maintain a state where the amount of HC accumulated is smaller than a predetermined limit amount. Here, for example, as shown in FIG. 4A, the above limit amount is set to an amount such that white smoke starts to be generated when a larger amount is accumulated.

  In the present embodiment, the temperature increase of the diesel oxidation catalyst 16 is specifically realized by increasing the temperature of the exhaust gas by, for example, control for adjusting the opening degree of the exhaust valve 12 to be small. Alternatively, the temperature of the diesel oxidation catalyst 16 may be increased by increasing the temperature of the exhaust gas by controlling the post-injection in the combustion chamber of the main body of the engine 1 by transmitting a signal to the injector solenoid valve 8.

  In the following description, the control for raising the temperature of the diesel oxidation catalyst 16 to remove the accumulated HC may be referred to as “first control”. Similarly, control for raising the temperature of the selective reduction catalyst 20 and the ammonia slip suppression catalyst 21 in order to keep the amount of HC accumulated below a predetermined limit amount may be referred to as “third control”.

By the way, the maximum NH ₃ adsorption amount of the selective reduction catalyst 20 tends to decrease as the temperature of the selective reduction catalyst 20 increases. Considering this, in order to prevent excessive NH ₃ slip, selective reduction is performed in advance before raising the temperature of various catalysts in the first control and the third control described above (while the temperature of the catalyst is low). It is desirable to purge NH ₃ of the catalyst 20 to reduce the NH ₃ adsorption amount.

Therefore, the ECU 3 according to the present embodiment performs control to purge NH ₃ until the NH ₃ adsorption amount to the selective reduction catalyst 20 becomes smaller than a predetermined reduction target amount (see FIG. 4B) as necessary. Do. Here, the reduction target amount is set to an appropriate amount that prevents the NH ₃ slip from occurring even when the selective reduction catalyst 20 is heated to a predetermined temperature, for example. Specifically, the NH ₃ purge is realized by, for example, a control that transmits a signal to the urea water injection nozzle 19 to stop the urea injection or reduce the injection amount. Alternatively, the purge of the NH ₃ is to increase the emissions of the NO _x from the engine 1, by promoting the consumption of NH ₃ on the SCR catalyst by increasing the amount of reaction with NH ₃ being adsorbed Is also realized. In the following description, the control for purging NH ₃ adsorbed on the selective reduction catalyst 20 in this way may be referred to as “second control”.

The ECU 3 of the present embodiment performs the first control, the second control, and the third control described above at an appropriate time, thereby preventing white smoke from being generated from the diesel oxidation catalyst 16 and the like, and the NH from the selective reduction catalyst 20. Slip suppression of ₃ is realized at the same time. Below, the control which this ECU3 performs is demonstrated in detail with reference to the flowchart of FIG.

  First, the ECU 3 determines whether or not the engine 1 is in operation (step S101). Specifically, when the engine speed detected from the engine speed sensor 9 is equal to or higher than a predetermined speed, it is determined that the engine 1 is in operation. On the other hand, when the engine speed is less than the predetermined speed, it is determined that the engine 1 is not in operation. If the engine 1 is not in operation, the determination in step S101 is repeated (that is, waits until the engine 1 is in operation).

  When the engine 1 is in operation, the ECU 3 estimates the HC emission amount from the past operation state (fuel injection amount, etc.) of the engine 1 by, for example, calculation using a known model, and the obtained HC Based on the discharged amount of HC, the amount of HC accumulated in various catalysts is estimated (step S102). Specifically, the ECU 3 determines the current amount of HC accumulated in the diesel oxidation catalyst 16 based on the calculated HC emission amount and the temperature of the diesel oxidation catalyst 16 detected by the diesel oxidation catalyst temperature sensor 18. Is estimated. Further, based on the calculated HC emission amount and the temperature of the selective reduction catalyst 20 detected by the selective reduction catalyst temperature sensor 22, the current HC accumulation amount in the selective reduction catalyst 20 is estimated. Further, based on the calculated HC discharge amount and the temperature of the ammonia slip suppression catalyst 21 detected by the ammonia slip suppression catalyst temperature sensor 23, the current HC accumulation amount in the ammonia slip suppression catalyst 21 is estimated. .

  Then, the ECU 3 performs the first time from the current state until the accumulated amount of HC in any of the diesel oxidation catalyst 16, the selective reduction catalyst 20, or the ammonia slip suppression catalyst 21 reaches a predetermined limit amount. Is estimated (step S103).

  However, when estimating the accumulation amount of HC in various catalysts and estimating when the accumulation amount reaches a predetermined limit amount, not only the past operating state of the engine 1 but also the engine 1 It is also possible to take into account information on the soil and topography around the agricultural and construction machinery on which is mounted. In addition, information on soil and topography can be obtained by referring to a map database based on positioning information of agricultural machines and construction machines acquired by GPS, which is a kind of GNSS (Global Navigation Satellite System), for example. .

  A specific example of estimating the amount of accumulated HC will be described with reference to FIG. 4A showing the case of the diesel oxidation catalyst 16. The current HC accumulation amount in FIG. 4 (a) is considerably smaller than the amount of white smoke that starts to be generated (the above limit amount), but is a curve estimated from the transition of the past accumulation amount ( According to the estimated curve), the amount of accumulated HC is expected to reach the above limit amount when the first time has elapsed from the present time.

  The diesel oxidation catalyst 16, the selective reduction catalyst 20, and the ammonia slip suppression catalyst 21 have different limit amounts, and therefore the estimated first times are almost different from each other. In this case, in step S103, the shortest time is adopted as the first time.

Subsequently, the ECU 3 uses a known model, for example, for the current NH ₃ adsorption amount to the selective reduction catalyst 20 based on the past operation state of the engine 1 (injection amount of urea water, fuel injection amount, etc.). Estimated by calculation (step S104). Then, when the purge of NH ₃ is temporarily started from the present time, the ECU 3 estimates a second time required until the NH ₃ adsorption amount is reduced to a predetermined reduction target amount (step S105).

However, when estimating the NH ₃ adsorption amount to the selective reduction catalyst 20 and estimating when the NH ₃ adsorption amount is reduced to a predetermined reduction target amount, only the past operating state of the engine 1 is used. In the same manner as described above, it is also possible to take into account information on the soil and topography around the aircraft.

A specific example of estimating the second time relating to the purge of NH ₃ will be described with reference to FIG. Although the current NH ₃ adsorption amount in FIG. 4B is considerably large, assuming that the purge of NH ₃ is started from the present time, the NH ₃ adsorption amount is predetermined when the second time has elapsed from the present time. It is expected to reduce to the reduction target amount.

  Subsequently, the ECU 3 determines whether or not the first time and the second time are substantially the same length (step S106). In the specific example shown in FIG. 4, the first time is shorter than the second time (the first time and the second time are not equal to each other). Accordingly, the process returns to step S101.

Since the amount of accumulated HC increases as the engine 1 is operated, the first time and the second time are eventually equalized. If it is determined in step S106 that the first time and the second time are substantially equal, the second control (that is, the purge of NH ₃ adsorbed on the selective reduction catalyst 20) is started (step S106). Step S107).

Purge NH ₃ until NH ₃ adsorption amount to the selective reduction catalyst 20 becomes less than the predetermined reduction target amount, i.e., usually continued until the elapse of the second time (step S108). As a result, the NH ₃ adsorption amount becomes such an amount that the NH ₃ slip hardly occurs even if the temperature of the selective reduction catalyst 20 is raised thereafter. Although the amount of HC accumulation increases during the purge, when the purge is completed after the second time (= first time) has elapsed, the amount of HC accumulation is limited to the above limit amount. Therefore, no white smoke is produced.

When the NH ₃ purge is completed and the amount of NH ₃ adsorbed on the selective reduction catalyst 20 is reduced to an appropriate amount that prevents the NH ₃ from slipping even if the temperature of the selective reduction catalyst 20 is increased, the ECU 3 Immediately start the first control and the third control (step S109). That is, the diesel oxidation catalyst 16, the selective reduction catalyst 20, and the ammonia slip suppression catalyst 21 are heated to oxidize and remove the accumulated HC. The temperature increase for removing HC is continued until the accumulated amount of HC is sufficiently reduced (step S110). Although the maximum NH ₃ adsorption amount of the selective reduction catalyst 20 decreases as the temperature of the selective reduction catalyst 20 rises, since NH ₃ is sufficiently purged in advance by the second control, excessive slip of NH ₃ Will not occur. Thereafter, the process returns to step S101, and the above process is repeated.

With the control as described above, the engine 1 of the present embodiment predicts a time (from the amount of HC accumulation) that requires a temperature increase to prevent white smoke, and the purge of NH ₃ is completed by this time. Like to do. Therefore, the purge time of NH ₃ can be minimized, and the working efficiency can be improved. Further, useless consumption of NH ₃ can be suppressed. Furthermore, HC poisoning of the selective reduction catalyst 20 and the ammonia slip suppression catalyst 21 can be suppressed, and the purification rate of the catalyst can be improved.

As described above, the engine 1 of the present embodiment includes the soot filter 17, the diesel oxidation catalyst 16, the diesel oxidation catalyst temperature sensor 18, the selective reduction catalyst 20, the urea water injection nozzle 19, the ECU 3, Is provided. The soot filter 17 is installed in the exhaust gas flow path from the engine 1 body and collects particulate matter. The diesel oxidation catalyst 16 is installed upstream of the soot filter 17 and promotes oxidation of fuel in the exhaust gas passage. The diesel oxidation catalyst temperature sensor 18 detects the temperature of the diesel oxidation catalyst 16. The selective reduction catalyst 20 is installed downstream of the soot filter 17 to reduce nitrogen oxides. The urea water injection nozzle 19 is installed between the soot filter 17 and the selective reduction catalyst 20 and injects urea water into the exhaust gas discharged from the soot filter 17. The ECU 3 performs temperature increase control of the diesel oxidation catalyst 16, the soot filter 17, and the selective reduction catalyst 20, and performs urea water injection control from the urea water injection nozzle 19. The ECU 3 performs a first control and a second control. In the first control, the HC is oxidized and removed by raising the temperature of the diesel oxidation catalyst 16 in order to keep the amount of HC accumulated below a predetermined limit amount. In the second control, the urea water injection from the urea water injection nozzle 19 is stopped or reduced until the adsorption amount of NH ₃ on the selective reduction catalyst 20 is reduced to a predetermined reduction target amount. The ECU 3 accumulates at least the current HC in the diesel oxidation catalyst 16 based on the HC emission amount calculated from the past operation state and the temperature of the diesel oxidation catalyst 16 detected by the diesel oxidation catalyst temperature sensor 18. In addition to estimating the amount, a first time required from the current state until the accumulated amount of HC reaches the predetermined limit amount is estimated. Further, the ECU 3 estimates the adsorption amount of NH ₃ to the selective reduction catalyst 20 based on the past operation state, and when the second control is performed from the current state, the adsorption amount of NH ₃ is reduced to the reduction target. Estimate the second time it takes to be reduced to a quantity. Then, the ECU 3 performs the first control immediately after performing the second control at the timing when the first time and the second time become the same length.

Thereby, the limit amount is set to an appropriate value at which white smoke starts to be generated, and the reduction target amount is set to an appropriate value that prevents NH ₃ from slipping even when the selective reduction catalyst 20 is heated. By setting, it is possible to prevent white smoke from being discharged from the diesel oxidation catalyst 16 and to prevent NH ₃ from slipping excessively from the selective reduction catalyst 20. In addition, by setting the limit amount and target reduction amount to appropriate values as described above, the time when the temperature rise is necessary to prevent white smoke is estimated from the amount of HC accumulated, and this time is selected. By performing the control so that the NH ₃ purge of the reduction catalyst 20 is completed, the NH ₃ purge time can be greatly shortened, so that the working efficiency can be improved.

The engine 1 of the present embodiment further includes an ammonia slip suppression catalyst 21, a selective reduction catalyst temperature sensor 22, and an ammonia slip suppression catalyst temperature sensor 23. The ammonia slip suppression catalyst 21 is installed downstream of the selective reduction catalyst 20 and oxidizes NH ₃ that has passed through the selective reduction catalyst 20. The selective reduction catalyst temperature sensor 22 detects the temperature of the selective reduction catalyst 20. The ammonia slip suppression catalyst temperature sensor 23 detects the temperature of the ammonia slip suppression catalyst 21. The ECU 3 performs third control to oxidize and remove HC by raising the temperature of the selective reduction catalyst 20 and the ammonia slip suppression catalyst 21 in order to keep the accumulated amount of HC below a predetermined limit amount. . The ECU 3 determines the diesel oxidation catalyst 16, the selective reduction catalyst 20, the temperature of the selective reduction catalyst 20 detected by the selective reduction catalyst temperature sensor 22, and the temperature of the ammonia slip suppression catalyst 21 detected by the ammonia slip suppression catalyst temperature sensor 23. Then, the amount of HC accumulated in the ammonia slip suppression catalyst 21 is estimated, and the amount of HC accumulated in any of the diesel oxidation catalyst 16, the selective reduction catalyst 20, and the ammonia slip suppression catalyst 21 from the current state is estimated. The first time required to reach the limit amount is estimated. Then, the ECU 3 performs the first control and the third control immediately after performing the second control at the timing when the first time and the second time become the same length.

As a result, the limit amount is set to an appropriate value such that white smoke starts to be generated, and the reduction target amount is set to an appropriate value at which the NH ₃ slip hardly occurs even when the temperature of the selective reduction catalyst is increased. Further, it is possible to prevent the generation of white smoke from the selective reduction catalyst 20 and the ammonia slip suppression catalyst 21 (not only from the DPF device 13) while preventing the NH ₃ slip from the selective reduction catalyst 20.

  In the engine 1 of the present embodiment, the ECU 3 performs the first control by adjusting the opening degree of the exhaust valve 12 provided in the exhaust gas passage.

  Thereby, 1st control can be easily performed by adjusting the opening degree of the exhaust valve 12 suitably, and generation | occurrence | production of white smoke can be prevented thereby.

  In the engine 1 of the present embodiment, the ECU 3 performs the first control by performing post injection into the combustion chamber of the engine 1 body.

  Thus, the first control can be easily performed by performing the post injection in the combustion chamber of the main body of the engine 1, thereby preventing the generation of white smoke.

  The preferred embodiment of the present invention has been described above, but the above configuration can be modified as follows, for example.

  In the above embodiment, the amount of HC accumulated in the diesel oxidation catalyst 16, the amount of HC accumulated in the selective reduction catalyst 20, and the amount of HC accumulated in the ammonia slip suppression catalyst 21 are individually estimated, The first time required for any of the accumulated amount to reach the limit amount was estimated, and that time was used for the subsequent control. However, instead of this, the total amount of HC accumulated in the diesel oxidation catalyst 16, the selective reduction catalyst 20, and the ammonia slip suppression catalyst 21 is estimated, and the total amount of accumulation in various catalysts is the above limit. The time taken to reach the quantity may be estimated as the “first time”.

In the control process shown in the above embodiment, the amount of HC accumulated in the various catalysts and the first time are estimated first, and then the NH ₃ adsorption amount to the selective reduction catalyst and the second time are estimated. However, the order of processing is not limited to this. That is, the NH ₃ adsorption amount to the selective reduction catalyst and the second time may be estimated first, and then the amount of HC accumulated in various catalysts and the first time may be estimated.

  The limit amount and the reduction target amount may be determined in consideration of circumstances, for example, taking into account a certain margin.

1 engine (diesel engine)
3 ECU (control unit)
16 Diesel oxidation catalyst 17 Soot filter 18 Diesel oxidation catalyst temperature sensor 19 Urea water injection nozzle (urea water injection body)
20 Selective reduction catalyst (SCR)
21 Ammonia slip suppression catalyst 22 Selective reduction catalyst temperature sensor 23 Ammonia slip suppression catalyst temperature sensor

Claims (4)

A soot filter installed in an exhaust gas flow path from the internal combustion engine to collect particulate matter;
A diesel oxidation catalyst installed upstream of the soot filter to promote oxidation of fuel in the exhaust gas flow path;
A diesel oxidation catalyst temperature sensor for detecting the temperature of the diesel oxidation catalyst;
A selective reduction catalyst installed downstream from the soot filter to reduce nitrogen oxides;
A urea water injector that is installed between the soot filter and the selective reduction catalyst and injects urea water into the exhaust gas discharged from the soot filter;
A control unit that performs temperature rise control of the diesel oxidation catalyst, the soot filter, and the selective reduction catalyst, and performs injection control of urea water from the urea water injector,
In a diesel engine comprising
The controller is
A first control for oxidizing and removing HC by raising the temperature of the diesel oxidation catalyst in order to keep the amount of HC accumulated below a predetermined limit amount;
A second control for stopping or reducing the injection of urea water from the urea water injector until the adsorption amount of NH ₃ on the selective reduction catalyst is reduced to a predetermined reduction target amount;
And
The controller is
Based on the HC emission amount calculated from the past operating state and the temperature of the diesel oxidation catalyst detected by the diesel oxidation catalyst temperature sensor, the amount of current HC accumulated in at least the diesel oxidation catalyst is estimated. And estimating a first time required from the current state until the accumulated amount of HC reaches the limit amount,
When the adsorption amount of NH ₃ to the selective reduction catalyst is estimated based on the past operation state, and the second control is performed from the current state, the adsorption amount of NH ₃ is reduced to the reduction target amount. Estimate the second time it takes to
The diesel engine according to claim 1, wherein the control unit performs the first control immediately after performing the second control at a timing when the first time and the second time become the same length. The diesel engine according to claim 1,
An ammonia slip suppression catalyst that is installed downstream of the selective reduction catalyst and oxidizes NH ₃ that has passed through the selective reduction catalyst;
A selective reduction catalyst temperature sensor for detecting the temperature of the selective reduction catalyst;
An ammonia slip suppression catalyst temperature sensor for detecting the temperature of the ammonia slip suppression catalyst;
Further comprising
The control unit oxidizes and removes HC by raising the temperature of the selective reduction catalyst and the ammonia slip suppression catalyst in order to keep the amount of HC accumulated below a predetermined limit amount. And
The control unit, based on the temperature of the selective reduction catalyst detected by the selective reduction catalyst temperature sensor and the temperature of the ammonia slip suppression catalyst detected by the ammonia slip suppression catalyst temperature sensor, the diesel oxidation catalyst, the selective reduction The amount of HC accumulated in the catalyst and the ammonia slip suppression catalyst is estimated, and the amount of HC accumulated in any of the diesel oxidation catalyst, the selective reduction catalyst, and the ammonia slip suppression catalyst from the current state is estimated. Estimating the first time it takes to reach the limit amount,
The control unit performs the first control and the third control immediately after performing the second control at a timing when the first time and the second time become the same length. diesel engine. The diesel engine according to claim 1 or 2,
The diesel engine according to claim 1, wherein the control unit performs the first control by adjusting an opening degree of an exhaust valve provided in the exhaust gas passage. The diesel engine according to any one of claims 1 to 3,
The diesel engine according to claim 1, wherein the control unit performs the first control by performing post injection into a combustion chamber of an engine body.

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