JP2014238058A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of suppressing variation of an initial exhaust temperature due to an outside air temperature.SOLUTION: An exhaust emission control device includes an oxidation catalyst 18 and a filter 19 disposed in an exhaust passage 5 of an engine 1, an exhaust throttle valve 6 changing an opening of the exhaust passage 5, and a control device (ECU 50) constituted to control the exhaust throttle valve 6. When regeneration of the filter 18 is requested, the opening of the exhaust passage 5 is gradually reduced in accordance with lowering of an intake temperature. The opening of the exhaust passage 5 is variably controlled even when either an idle operation or a non-idle operation is executed when the regeneration of the filter 19 is requested.

Description

  The present invention relates to an oxidation catalyst and a filter disposed in an exhaust path of an engine, an exhaust throttle valve that changes an opening degree of the exhaust path, and a control device configured to control the exhaust throttle valve; The present invention relates to an exhaust gas purifying apparatus.

  Conventionally, a diesel particulate filter having an oxidation catalyst and a filter is known. Patent Document 1 also discloses an example of an exhaust gas purifying apparatus including such a diesel particulate filter.

  Such an exhaust gas purification device is configured to activate the oxidation catalyst by increasing the temperature of the exhaust gas. When the oxidation catalyst is activated, nitrogen oxides in the exhaust gas are oxidized to generate nitrogen dioxide. Since nitrogen dioxide has a strong oxidizing action, PM (particulate matter) on the filter is oxidized and removed.

  In order to increase the temperature of the oxidation catalyst, there is a method of applying a load to the engine by narrowing the opening of the exhaust passage 5 (exhaust throttle). When a load is applied to the engine while it is controlled to maintain the rotation speed, the main injection amount increases. As a result, the initial exhaust temperature (temperature of exhaust gas generated in the combustion chamber) increases. Since the oxidation catalyst is heated by the exhaust gas, the temperature of the oxidation catalyst also rises. Patent Document 1 also discloses that the catalyst inlet temperature is increased by exhaust throttling in order to regenerate the filter.

  According to Patent Document 1, in the regeneration control, the throttle amount of the exhaust throttle valve is controlled as follows. When the engine operating region is in an idling state, the throttle amount is fixed. When the engine operating region is not in the idling state, the throttle amount is controlled variably. The paragraph 0026 of the same document describes that when the engine is idling, the throttle amount of the exhaust throttle valve is fixed to the minimum exhaust gas amount. In addition, paragraph 0025 of the same document describes that when the initial exhaust temperature in an idling operation or the like is in a very low temperature range, exhaust throttling is performed to increase the initial exhaust temperature. That is, in Patent Document 1, fixing the throttle amount indicates that the opening degree of the exhaust path is set to the minimum opening degree.

Japanese Patent Laying-Open No. 2005-076604

  The initial exhaust temperature is affected by the outside air temperature. In particular, when the engine is started, the outside air temperature greatly affects the initial exhaust temperature. In an environment where the outside air temperature is high as in the summer, the initial exhaust temperature is high, and in an environment where the outside temperature is low as in the winter, the initial exhaust temperature is low.

  In Patent Document 1, the opening degree of the discard path is fixed during idle operation. For this reason, in an extremely low temperature environment, the increase in the initial exhaust temperature may be delayed, and in a high temperature environment, the initial exhaust temperature may increase more than necessary, leading to deterioration in fuel consumption.

  An object of the present invention is to provide an exhaust gas purification device capable of suppressing fluctuations in initial exhaust temperature due to outside air temperature.

  An exhaust gas purifying apparatus according to the present invention is configured to control an oxidation catalyst and a filter disposed in an exhaust path of an engine, an exhaust throttle valve that changes an opening degree of the exhaust path, and the exhaust throttle valve. An exhaust gas purifying device, wherein when the regeneration request for the filter occurs, the opening degree of the exhaust path is reduced as the intake air temperature decreases, and the regeneration of the filter is performed. Regardless of whether the idle operation or the non-idle operation is performed when the request is generated, the opening degree of the exhaust path is variably controlled.

  The exhaust gas purification device includes a fuel injection device that injects fuel in accordance with a fuel injection pattern, and the control device is configured to set the fuel injection pattern, and a regeneration request for the filter is generated. When the engine coolant temperature is equal to or higher than the warm-up water temperature, a temperature increase pattern is set, and the temperature increase pattern is the fuel injection pattern in which the total injection amount in the compression stroke and the expansion stroke is increased. The warm-up water temperature is the cooling water temperature when the engine is considered to be in a warm-up state, and is higher by a predetermined temperature range than the idle water temperature at which the cooling water temperature converges as the idling operation continues. .

  In the exhaust gas purification apparatus, the opening degree of the exhaust path is reduced as the total injection amount decreases.

  In the exhaust gas purifying device, the control device stores a plurality of opening maps having different ranges of the corresponding intake air temperatures, and each of the plurality of opening maps includes a rotation speed of the engine and the total injection. And an opening degree map corresponding to the intake air temperature is selected from the plurality of opening degree maps, and based on the selected opening degree map. Thus, the opening degree of the exhaust path is changed to an opening degree corresponding to the rotational speed and the total injection amount.

  The exhaust gas purification apparatus according to the present invention can suppress fluctuations in the initial exhaust temperature due to the outside air temperature.

It is a figure which shows the structure of the engine which concerns on this embodiment. It is a figure which shows the structure of the cooling water circuit of an engine. It is a figure which shows an example of a fuel-injection pattern. It is a figure which shows the list of control modes. It is a figure which shows a self reproduction | regeneration area | region, a reproducible area | region, and a nonreproducible area | region. It is a figure which shows an example of the time change of deposition amount. It is a flowchart which shows the transition of a control mode. It is a flowchart which shows the processing flow performed based on a reproduction | regeneration request | requirement. It is a figure which shows an example of a 2nd opening degree map.

  A diesel engine 1 equipped with an exhaust gas purifying apparatus according to the present embodiment will be described with reference to the drawings. A diesel engine (hereinafter, engine) 1 is connected to a drive mechanism 100. The drive mechanism 100 is a traveling device and / or a working device driven by the engine 1. The engine 1 and the drive mechanism 100 are mounted on a work vehicle such as a backhoe or a tractor, for example.

  FIG. 1 is a diagram illustrating a configuration of an engine 1 according to the present embodiment. The engine 1 includes an intake path 2, an intake throttle valve 3, a cylinder block 4, an exhaust path 5, an exhaust throttle valve 6, a filter unit 7, an EGR pipe 8, an EGR throttle valve 9, a supercharger 10, a crankshaft 11, and fuel. An injection device 13 is provided.

  The engine 1 has four cylinders, and the cylinder block 4 has four combustion chambers 12. The intake path 2 includes an intake pipe 2 a that is open to the outside, and an intake manifold 2 b that connects the intake pipe 2 a to the four combustion chambers 12. Outside air (intake gas) is introduced into the combustion chamber 12 via the intake path 2. The intake throttle valve 3 is disposed on the intake pipe 2a and changes the opening degree of the intake path 2. The exhaust path 5 includes an exhaust pipe 5a that is open to the outside and an exhaust manifold 5b that connects the four combustion chambers 12 to the exhaust pipe 5a. The exhaust gas is discharged from the combustion chamber 12 into the atmosphere via the exhaust path 5. The exhaust throttle valve 6 is provided on the exhaust pipe 5 a and changes the opening degree of the exhaust path 5. An EGR pipe (EGR path) 8 connects the exhaust path 5 to the intake path 2. Part of the exhaust gas is introduced into the intake path 2 via the EGR pipe 8 and merges with the intake gas. The EGR throttle valve 9 is provided on the EGR pipe 8 and changes the opening degree of the EGR pipe 8. A later-described EGR cooler 24 (FIG. 2) is provided on the EGR pipe 8 on the downstream side of the EGR throttle valve 9. The supercharger 10 includes an exhaust turbine 10a disposed on the exhaust pipe 5a and a compressor 10b disposed on the intake pipe 2a. The fuel injection device 13 employs a common rail system, and supplies fuel to each combustion chamber 12 according to a fuel injection pattern.

  The filter unit 7 is provided on the exhaust path 5. The filter unit 7 is a diesel particulate filter and includes an oxidation catalyst 18 and a filter 19. The oxidation catalyst 18 is disposed upstream of the filter 19 in the exhaust path 5. When the exhaust gas is exhausted along the exhaust path 5, the exhaust gas passes through the filter 19 after passing through the oxidation catalyst 18. PM (particulate matter) contained in the exhaust gas is captured by the filter 19.

  The ECU (control device) 50 is configured to control various devices related to the operation of the engine 1.

  The rotational speed input device 14 is an operating device for designating a target rotational speed. In the present embodiment, the rotational speed input device 14 represents an accelerator lever group that changes the operating state of the engine 1.

  The warning device 15 executes various warnings to the operator. In the present embodiment, the warning device 15 includes a large number of lamp groups that can display a plurality of different warnings.

  The stationary regeneration button 16 is an input device that generates a command (stationary regeneration mode command) for changing the control mode to the stationary regeneration mode by a manual input operation. The stationary reproduction button 16 is a push button, and can specify a command “present” state and a command “none” state. The contents of the control mode will be described later.

  In FIG. 1, the engine 1 includes an environmental temperature sensor 31, an intake air temperature sensor 32, an initial exhaust gas temperature sensor 33, a catalyst inlet temperature sensor 34, a filter inlet temperature sensor 35, and an EGR temperature sensor 36. The environmental temperature sensor 31 detects the temperature (environmental temperature) of the intake gas in the intake passage 2 on the upstream side of the compressor 10b and the outlet 8b. The intake air temperature sensor 32 detects the temperature (intake air temperature) of the intake gas in the intake passage 2 on the downstream side of the compressor 10 b and the outlet 8 b of the EGR pipe 8. The initial exhaust temperature sensor 33 detects the temperature of the exhaust gas (initial exhaust temperature) in the exhaust path 5 on the upstream side of the exhaust throttle valve 6, the exhaust turbine 10 a, and the inlet 8 a of the EGR pipe 8. The catalyst inlet temperature sensor 34 detects the temperature of exhaust gas (catalyst inlet temperature) in the exhaust path 5 on the downstream side of the exhaust throttle valve 6 and the exhaust turbine 10a and on the upstream side of the oxidation catalyst 18. The filter inlet temperature sensor 35 detects the temperature of the exhaust gas (filter inlet temperature) in the exhaust path 5 on the downstream side of the oxidation catalyst 18 and the upstream side of the filter 19. The EGR temperature sensor 36 detects the temperature (EGR temperature) of the exhaust gas in the EGR pipe 8 on the downstream side of the EGR cooler 24 and the EGR throttle valve 9.

  In FIG. 1, the engine 1 includes a differential pressure sensor 40, an atmospheric pressure sensor 41, an intake pressure sensor 42, and an initial exhaust pressure sensor 43. The differential pressure sensor 40 includes a filter inlet pressure sensor 40a and a filter outlet pressure sensor 40b. The filter inlet pressure sensor 40 a detects the pressure in the exhaust path 5 on the downstream side of the oxidation catalyst 18 and the upstream side of the filter 19. The filter outlet pressure sensor 40 b detects the pressure in the exhaust path 5 on the downstream side of the filter 19. The differential pressure sensor 40 detects a differential pressure between both sides of the filter 19 based on detection information from the filter inlet pressure sensor 40a and the filter outlet pressure sensor 40b. The atmospheric pressure sensor 41 detects a pressure (atmospheric pressure) outside the engine 1. The intake pressure sensor 42 detects the pressure (intake pressure) of the intake gas in the intake path 2 on the downstream side of the compressor 10b and the outlet 8b of the EGR pipe 8. The initial exhaust pressure sensor 43 detects the pressure of the exhaust gas in the exhaust path 5 (initial exhaust pressure) on the upstream side of the exhaust throttle valve 6, the exhaust turbine 10 a, and the inlet 8 a of the EGR pipe 8.

  In FIG. 1, the engine 1 includes a rotation speed sensor 51. The rotational speed sensor 51 detects the rotational speed (engine rotational speed) of the crankshaft 11.

  FIG. 2 is a diagram illustrating a configuration of the cooling water circuit 20 of the engine 1. The cooling water circuit 20 includes a water path 21, a water pump 22, a water jacket 23, an EGR cooler 24, and a radiator 25. The water pump 22 causes the cooling water of the engine 1 to flow along the water path 21. The water jacket 23 is formed in the cylinder block 4. Further, the engine 1 includes a water temperature sensor 26. The water temperature sensor 26 detects the temperature (cooling water temperature) of the cooling water flowing through the water path 21 on the downstream side of the water jacket 23 and the upstream side of the radiator 25.

  A method for estimating the deposition amount will be described. The accumulation amount indicates the amount of PM accumulated on the filter 19. The ECU 50 can estimate the accumulation amount based on two estimation methods. The two estimation methods are a calculation formula estimation method and a differential pressure type estimation method.

  The calculation formula estimation method is a method for estimating the accumulation amount based on the operating condition of the engine. In the calculation formula estimation method, the PM emission amount and the PM regeneration amount are estimated based on the operating condition of the engine, and the accumulation amount is estimated based on the obtained PM emission amount and PM regeneration amount. The PM discharge amount indicates the amount of PM discharged from the engine 1 per unit time. The PM regeneration amount indicates the amount of PM removed from the filter 19 by regeneration in a unit time. The accumulation amount is obtained by subtracting the PM regeneration amount from the PM discharge amount. Both the PM emission amount and the PM regeneration amount are estimated based on the engine operating conditions. The PM emission amount is basically estimated based on the engine speed and the total injection amount in one cycle. The PM regeneration amount is estimated based on the flow rate of the exhaust gas and the filter inlet temperature detected by the filter inlet temperature sensor 35. The engine operating conditions are the temperature group detected by the temperature sensors 31-36, the pressure group detected by the pressure sensors 41-45, the engine rotational speed detected by the rotational speed sensor 51, and the fuel injection device 13. It is specified based on the total injection amount.

  The differential pressure type estimation method is a method for estimating the deposition amount based on the differential pressure between both sides of the filter 19. As the amount of deposition increases, clogging of the filter 19 increases, and the differential pressure of the filter 19 increases. On the contrary, the differential pressure of the filter 19 decreases as the accumulation amount decreases. That is, the differential pressure type estimation method estimates the deposition amount using the correlation between the differential pressure and the deposition amount. Strictly speaking, the accumulation amount is obtained by adding a correction based on the flow rate of the exhaust gas to the differential pressure obtained by the differential pressure sensor 40. The flow rate of the exhaust gas is estimated based on the operating conditions of the engine.

  The regeneration of the filter 19 will be described with reference to FIGS. In the following, numerical values of various temperatures (° C.) and deposition amounts (g / L) are listed, but these numerical values are merely exemplary numerical values used in the present embodiment. The unit g / L of the deposition amount indicates the weight of PM per unit volume.

  The regeneration of the filter 19 is performed by combustion of PM with oxygen and oxidation of PM with nitrogen dioxide. PM accumulated on the filter 19 is removed by combustion or oxidation. Combustion of PM by oxygen indicates combustion by self-ignition of PM. Self-ignition occurs when the PM temperature exceeds the PM combustion temperature (400 ° C.). Nitrogen dioxide functions as an oxidizing agent for PM. When the temperature of the oxidation catalyst 18 exceeds a predetermined activation temperature (300 ° C.), the oxidation catalyst 18 is activated, and highly active nitrogen dioxide is generated from nitrogen oxides in the exhaust gas. Since the filter 19 is provided on the downstream side of the oxidation catalyst 18, nitrogen dioxide generated around the oxidation catalyst 18 passes through the filter 19. For this reason, PM deposited on the filter 19 is oxidized and removed. Note that when the catalyst inlet temperature is higher than the high temperature (550 ° C.), nitrogen dioxide is not generated, and regeneration is performed only by combustion with oxygen.

  When the catalyst inlet temperature is lower than the activation temperature, oxidation by nitrogen dioxide and combustion by oxygen do not occur. For this reason, the engine 1 uses the change of the exhaust throttle and the fuel injection pattern in order to increase the catalyst inlet temperature.

  FIG. 3 is a diagram illustrating an example of a fuel injection pattern. In FIG. 3, the horizontal axis indicates the injection timing, and the vertical axis indicates the injection amount. The fuel injection pattern indicates the form of fuel injection defined by the injection timing and the injection amount. The fuel injection pattern shown in FIG. 3 includes pre-injection, main injection, after-injection, and post-injection. The injection period of the main injection includes top dead center (TDC). Pre-injection is performed to ensure ignitability. Main injection is performed for main combustion. After-injection is performed to increase the catalyst inlet temperature and post-injection is performed to increase the filter inlet temperature.

  By causing the intake throttle valve 3 to perform intake throttling, the load applied to the engine 1 increases, so the fuel injection amount (main injection amount) increases. As a result, the catalyst inlet temperature rises. Further, by changing the fuel injection pattern to be executed by the fuel injection device 13, the total fuel injection amount can be increased without increasing the torque. Specifically, the main injection retard and / or after injection is used. As a result, the filter inlet temperature rises. In addition, when the fuel injection pattern is set so as to include post injection, the total fuel injection amount further increases. In this case, the fuel supplied by the post injection is combusted by the oxidation catalyst 18, and the filter inlet temperature rises greatly with respect to the catalyst inlet temperature.

  FIG. 4 is a diagram showing a list of control modes. The engine 1 has six possible control modes. The six control modes are a self-regeneration mode, an assist regeneration mode, a reset regeneration mode, a stationary standby mode, a stationary regeneration mode, and a maintenance standby mode. When the engine 1 is activated, any one of the six control modes is selected, and the ECU 50 controls the engine 1 based on the selected control mode. Control conditions, start conditions, and end conditions are set for each of these control modes. The control conditions include a fuel injection pattern configuration, an intake throttle amount, and a target rotational speed configuration. The configuration of the fuel injection pattern indicates the presence / absence of pre-injection, main injection, after-injection, and post-injection, and the injection amount and injection timing of these injections. The configuration of the target rotational speed indicates the presence / absence and the magnitude of the target rotational speed.

  The self-regeneration mode is a control mode in which no special control for regenerating the filter 19 is performed. In the self-regeneration mode, normal operation is executed. As shown in FIG. 3, the fuel injection pattern in the self-regeneration mode includes pre-injection and main injection. If the catalyst inlet temperature becomes higher than the activation temperature during normal operation (self-regeneration mode), the filter 19 is automatically regenerated.

  The assist regeneration mode is a control mode for regenerating the filter 19 without using post injection. In the assist regeneration mode, the fuel injection pattern is set so as to increase the catalyst inlet temperature, and the intake throttle is used. As shown in FIG. 3, the fuel injection pattern in the assist regeneration mode includes pre-injection, main injection, and after-injection. Further, the injection timing of the main injection in the assist regeneration mode is delayed from the injection timing of the main injection in the self regeneration mode. The delay in the injection timing of the main injection and the use of after-injection reduce the proportion of the fuel amount that contributes to torque generation and increase the proportion of the fuel amount that contributes to the temperature increase. Further, the intake air throttle increases the load applied to the engine 1, so the main injection amount is increased. As shown in FIG. 3, the main injection is executed in the compression stroke and the expansion stroke. That is, in the assist regeneration mode, the total injection amount in the compression stroke and the expansion stroke is increased. For this reason, the catalyst inlet temperature rises.

  The assist regeneration mode is intended to reach the catalyst inlet temperature at an assist target temperature (350 ° C.) that is higher than the activation temperature and lower than the combustion temperature. When the catalyst inlet temperature reaches the activation temperature, the filter 19 is gradually regenerated. However, the execution of work is permitted in the assist playback mode, and fluctuations in the rotational speed are assumed. When the rotational speed varies, the main injection amount also varies, and the catalyst inlet temperature also varies. For this reason, when the rotational speed is kept low, the catalyst inlet temperature does not reach the assist target temperature.

  The reset regeneration mode is a control mode for rapidly regenerating the filter 19 using post injection. In the reset regeneration mode, the fuel injection pattern is set so as to increase the filter inlet temperature, and the intake throttle is used. As shown in FIG. 3, the fuel injection pattern in the reset regeneration mode includes pre-injection, main injection, after-injection, and post-injection. That is, the control condition in the reset regeneration mode includes the use of post injection in addition to the control condition in the assist regeneration mode. If post-injection is executed when the catalyst inlet temperature exceeds the activation temperature, the fuel burns in the oxidation catalyst 18. As a result, the exhaust gas is further heated, and the filter inlet temperature further increases.

  The reset regeneration mode is intended to reach the filter inlet temperature to a reset target temperature (600 ° C.) higher than the combustion temperature so that the accumulation amount becomes almost zero. When the filter inlet temperature reaches the reset target temperature (600 ° C.), the filter 19 is regenerated in a relatively short time. However, the execution of work is permitted even in the reset regeneration mode, and fluctuations in the rotational speed are assumed. For this reason, when the rotation speed is kept low, the filter inlet temperature does not reach the reset target temperature.

  In the self regeneration mode, the assist regeneration mode, and the reset regeneration mode, since the rotational speed is not fixed as described above, the catalyst inlet temperature or the filter inlet temperature may not be favorably increased. In such a case, the regeneration of the filter 19 is not performed well. Therefore, a stationary regeneration mode is provided so that the filter 19 is reliably regenerated.

  The stationary regeneration mode is a control mode for rapidly regenerating the filter 19 while maintaining the rotational speed at a predetermined rotational speed and using post injection. In the stationary regeneration mode, the fuel injection pattern is set so as to increase the filter inlet temperature, the intake throttle is used, and the target rotational speed is maintained at a predetermined rotational speed. That is, in the stationary regeneration mode, the rotational speed is fixed in addition to the control executed in the reset regeneration mode. The predetermined rotation speed is 2200 rpm in this embodiment. The control conditions in the stationary regeneration mode are set so that the filter inlet temperature reaches a stationary target temperature (600 ° C.) higher than the combustion temperature (400 ° C.). In the present embodiment, the stationary target temperature is equal to the reset target temperature.

  As the filter inlet temperature increases, the rate at which the amount of deposition decreases increases. However, if the filter inlet temperature becomes too high, the filter 19 may be melted or cracked. For this reason, the stationary target temperature (600 ° C.) is set so that the execution time of the stationary regeneration mode is a predetermined time H5a (30 minutes), which is a short time. Similarly, the height of the reset target temperature is also set so that the execution time of the reset regeneration mode is also a predetermined time H3a (30 minutes), which is a short time.

  The stationary standby mode is a control mode for waiting for execution of the stationary regeneration mode. When the regeneration of the filter 19 is not performed well in the self regeneration mode, the assist regeneration mode, and the reset regeneration mode, it is necessary to execute the stationary regeneration mode as described above. However, in the stationary regeneration mode, the rotation speed is maintained at a predetermined rotation speed. It is not preferable that the stationary regeneration mode is suddenly executed during the work because it causes a sudden change in the rotational speed. For this reason, a stationary standby mode is provided in order to wait for a command from the operator. In the stationary standby mode, the ECU 50 operates the warning device 15 so as to issue a stationary warning. The stationary warning is a warning that prompts the operator to execute the stationary regeneration mode. Specifically, the ECU 50 turns on a warning lamp. Upon receiving the stationary warning, the operator stops the work and moves the work vehicle equipped with the engine 1 from the work place to another place as necessary. Thereafter, the operator inputs a stationary regeneration instruction via the stationary regeneration button 16. When a stationary regeneration instruction is input, the stationary regeneration mode is started.

  EGR (exhaust gas recirculation) can be used in the self-regeneration mode. On the other hand, EGR is not used in the assist regeneration mode, the reset regeneration mode, and the stationary regeneration mode. In these control modes, the total injection amount is increased, and the amount of unburned hydrocarbons generated is also increased. That is, EGR is not used in these control modes in order to prevent unburned hydrocarbons from adhering to the EGR pipe 8.

  FIG. 5 is a diagram showing a self-reproducing area, a reproducible area, and a non-reproducible area. In FIG. 5, the horizontal axis indicates the rotational speed of the engine 1, and the vertical axis indicates the load (torque). FIG. 5 shows an output characteristic curve of the engine 1, and an area within the output characteristic curve is divided into a self-reproducing area, a reproducible area, and a non-reproducible area. The first boundary line L1 indicates the boundary between the self-reproducing area and the reproducible area. The second boundary line L2 indicates the boundary between the reproducible area and the non-reproducible area. The first boundary line L1 shows the rotational speed-torque curve when the catalyst inlet temperature in normal operation is the activation temperature (300 ° C.). That is, the self-regeneration region indicates a region where the catalyst inlet temperature is equal to or higher than the activation temperature. When the rotation speed and torque are within the self-regeneration region, the filter 19 is regenerated without performing special control. That is, the self-reproducing area indicates an area where the filter 19 is necessarily reproduced in the self-reproducing mode. The second boundary line L2 indicates the rotational speed-torque curve when the catalyst inlet temperature in the normal operation is at the regeneration limit temperature. The catalyst inlet temperature rises by executing the reset regeneration mode. However, if the catalyst inlet temperature in normal operation is too low, the catalyst inlet temperature does not reach the activation temperature even if the reset regeneration mode is executed. The regeneration limit temperature indicates the lower limit value of the catalyst inlet temperature at which the activation temperature can be reached. The reproducible region indicates a region where the catalyst inlet temperature is lower than the activation temperature and is equal to or higher than the regeneration limit temperature. If the assist regeneration mode or the reset regeneration mode is executed when the rotation speed and torque are within the reproducible region, the filter 19 can be regenerated. The non-renewable region indicates a region where the catalyst inlet temperature is lower than the regeneration limit temperature. When the rotation speed and the torque are within the non-recoverable region, the filter 19 cannot be regenerated regardless of whether the assist regeneration mode or the reset regeneration mode is executed.

  In the stationary regeneration mode, the rotational speed is maintained at a predetermined rotational speed R0. In FIG. 5, when the rotation speed is equal to or higher than the predetermined rotation speed R0, there is no non-reproducible area. For this reason, in the stationary regeneration mode, the catalyst inlet temperature always reaches the activation temperature, and the filter 19 is necessarily regenerated. The predetermined rotational speed R0 is specified based on an experimentally obtained output characteristic curve as shown in FIG.

  With reference to FIG. 6, an example of the temporal change of the deposition amount according to the change of the control mode will be described. FIG. 6 is a diagram illustrating an example of a temporal change in the deposition amount. In FIG. 6, the horizontal axis represents the continuous operation time (hr) of the engine 1, and the vertical axis represents the accumulation amount (g / L). Note that the time difference due to the control delay is ignored for convenience of explanation.

  From time T0 to time T1, the self-regeneration mode (normal operation) is executed, and the amount of deposition is increasing. At time T1, the accumulation amount reaches the assist threshold value A2 (8 g / L), and the control mode is changed from the self regeneration mode to the assist regeneration mode. One of the conditions for starting the assist regeneration mode is that the deposition amount is equal to or greater than the assist threshold value A2. From time T1 to time T2, the accumulation amount is decreased by the control of the assist regeneration mode. At time T2, the deposition amount reaches the allowable threshold value A1 (6 g / L), and the control mode is changed from the assist regeneration mode to the self regeneration mode. One of the conditions for starting the self-regeneration mode is that the deposition amount is smaller than the allowable threshold value A1. The self-regeneration mode is executed from time T2 to time T3, and the deposition amount increases. Further, the assist regeneration mode is executed from the time T3 to the time T4, and the deposition amount decreases. In this way, basically, the self-regeneration mode and the assist regeneration mode are repeatedly executed alternately. As a result, an increase in the deposition amount is suppressed.

  Time T5 indicates a time later than time T4. The self-regeneration mode is executed from time T5 to time T6, and the deposition amount increases. At time T6, the continuous operation time has reached the allowable continuous time Hd (100 hours), and the control mode is changed from the self-regeneration mode to the reset regeneration mode. The continuous operation time exceeding the allowable continuous time Hd is one of the conditions for starting the reset regeneration mode. The reset regeneration mode is executed from time T6 to time T7, and the amount of deposition is greatly reduced to almost zero. When the reset regeneration mode ends, the continuous operation time is reset to 0 hour. Time T0 and time T6 indicate times when the continuous operation time is 0 hour.

  Time T8 indicates a time later than time T7. From time T8 to time T9, the control mode is maintained in the self-regeneration mode, and the deposition amount increases. At time T9, the accumulation amount reaches the assist threshold value A2 (8 g / L), and the control mode is changed from the self regeneration mode to the assist regeneration mode. From time T9 to time T10, the control mode is maintained in the assist playback mode. However, although the assist regeneration mode is being executed, the deposition amount is increasing. As described above, such a situation occurs when the rotational speed is low, for example. For this reason, at time T10, the accumulation amount reaches the stationary threshold A3 (10 g / L), and the control mode is changed from the assist regeneration mode to the stationary standby mode. In the stationary standby mode, a stationary warning is issued. In response to the stationary warning, the operator decides, for example, to stop the operation in order to execute the stationary regeneration mode. At time T11, a stationary regeneration mode command is manually input, and the control mode is changed from the stationary standby mode to the stationary regeneration mode. The stationary regeneration mode is executed from the time T11 to the time T12, the accumulation amount is greatly reduced, and is smaller than the allowable threshold value A1 (6 g / L).

  Next, the maintenance standby mode will be described. If the control mode is changed to the stationary regeneration mode, the filter 19 is normally reliably regenerated. However, the change to the stationary regeneration mode is performed manually. For this reason, if the driving of the engine 1 is continued without the stationary regeneration mode being executed, the accumulation amount becomes excessive. If the reset regeneration mode or the stationary regeneration mode is executed when the accumulation amount is excessive, the PM on the filter 19 may burn in a chain. Hereinafter, this chain combustion is called rapid regeneration. Since high heat is generated with rapid regeneration, the high heat may cause the filter 19 to melt or break. Therefore, a maintenance standby mode is provided as a control mode for prohibiting regeneration of the filter 19 when excessive deposition occurs.

  When the accumulation amount exceeds the maintenance threshold value, the control mode is changed to the maintenance standby mode. The maintenance threshold A4 (12 g / L) is larger than the assist threshold A2 (8 g / L) and the stationary threshold A3 (10 g / L). Similar to the stationary standby mode, a maintenance standby mode is provided to wait for a command from the operator. In the maintenance standby mode, the ECU 50 operates the warning device 15 so as to issue a maintenance warning. The maintenance warning is a warning that prompts the operator to perform maintenance of the engine 1. Specifically, the ECU 50 turns on a warning lamp. When receiving the maintenance warning, the operator moves the work vehicle equipped with the engine 1 from the work place to another place as necessary, and stops the driving of the engine 1.

  FIG. 7 is a flowchart showing the transition of the control mode. In FIG. 7, the ECU 50 selects any one of a self-regeneration mode M1, an assist regeneration mode M2, a reset regeneration mode M3, a stationary standby mode M4, a stationary regeneration mode M5, and a maintenance standby mode M6 as a control mode. Each control mode starts when a predetermined start condition is satisfied, ends when a predetermined end condition is satisfied, and shifts to another control mode. Basically, a transition of the control mode occurs as the deposition amount increases or decreases.

  In FIG. 7, the conditions indicated by the solid and dashed arrows include the deposition amount determination conditions. As described above, the accumulation amount is estimated based on the calculation formula estimation method and the differential pressure type estimation method. Since the accuracy of estimation by the differential pressure type estimation method decreases as the deposition amount increases, the differential pressure type estimation method is not used when the deposition amount is relatively large. On the other hand, when the accumulation amount is relatively small, both the calculation formula estimation method and the differential pressure type estimation method are used. A solid line arrow indicates a case where both the calculation formula estimation method and the differential pressure type estimation method are used. A broken arrow indicates a case where only the calculation formula estimation method is used. Further, the conditions indicated by the two-dot chain line arrows indicate determination conditions other than the deposition amount.

  When the engine 1 is started, first, the self-regeneration mode M1 is selected as the control mode.

  When the condition C1 is satisfied in the self regeneration mode M1, the control mode is changed from the self regeneration mode M1 to the assist regeneration mode M2. Condition C1 is “deposition amount ≧ assist threshold value A2 (8 g / L)”. When the condition C2 or the condition C3 is satisfied in the assist regeneration mode M2, the control mode is changed from the assist regeneration mode M2 to the self regeneration mode M1. Condition C2 is “execution time of assist regeneration mode M2 ≧ predetermined time H2a (30 minutes)”. The condition C3 is “deposition amount <allowable threshold A1 (6 g / L)”.

  When the condition C4 is satisfied in the self regeneration mode M1, the control mode is changed from the self regeneration mode M1 to the reset regeneration mode M3. Condition C4 is “continuous operation time ≧ allowable continuous time Hd (100 hours)”. When the condition C5 or the condition C6 is satisfied in the assist regeneration mode M2, the control mode is changed from the assist regeneration mode M2 to the reset regeneration mode M3. Condition C5 is “continuous operation time ≧ allowable continuous time Hd (100 hours)”. Condition C6 is “deposition amount ≧ assist threshold A2 (8 g / L) and execution time of assist regeneration mode M2 ≧ predetermined time H2c (10 minutes)”. When the condition C7 or the condition C8 is satisfied in the reset regeneration mode M3, the control mode is changed from the reset regeneration mode M3 to the self regeneration mode M1. Condition C7 is “effective time of reset regeneration mode ≧ predetermined time H3b (25 minutes)”. The valid time of the reset regeneration mode M3 indicates a time during which the filter inlet temperature is maintained at the reset target temperature (600 ° C.) or higher during the execution of the reset regeneration mode M3. The ECU 50 measures the valid time based on the detection information of the filter inlet temperature sensor 35. Condition C8 is “reset regeneration mode execution time ≧ predetermined time H3a (30 minutes)”.

  When the condition C9 is satisfied in the assist regeneration mode M2, the control mode is changed from the assist regeneration mode M2 to the stationary standby mode M4. Condition C9 is “deposition amount ≧ stationary threshold A3 (10 g / L)”. When the condition C10 or the condition C11 is satisfied in the reset regeneration mode M3, the control mode is changed from the reset regeneration mode M3 to the stationary standby mode M4. The condition C10 is “deposition amount ≧ stationary threshold A3 (10 g / L)”. The condition C11 is “deposition amount ≧ assist threshold A2 (8 g / L) and execution time of the reset regeneration mode ≧ predetermined time H3c (10 minutes)”.

  When the condition C12 is satisfied in the stationary standby mode M4, the control mode is changed from the stationary standby mode M4 to the stationary regeneration mode M5. Condition C12 is “stationary regeneration mode command: yes”, which indicates that the operator inputs a stationary regeneration instruction via the stationary regeneration button 16.

  When the condition C13 or the condition C14 is satisfied in the stationary regeneration mode M5, the control mode is changed from the stationary regeneration mode M5 to the self regeneration mode M1. Condition C13 is “effective time of stationary regeneration mode M5 ≧ predetermined time H5b (25 minutes)”. The effective time of the stationary regeneration mode M5 indicates a time during which the filter inlet temperature is maintained at the stationary target temperature (600 ° C.) or higher in the stationary regeneration mode M5. The condition C14 is “stationary regeneration mode M5 execution time ≧ predetermined time H5a (30 minutes)”. In the stationary regeneration mode M5, since the rotation speed is maintained at a predetermined rotation speed (2200 rpm), the condition C13 is satisfied except when the outside air temperature is particularly low.

  When the condition C15 or the condition C16 is satisfied in the stationary standby mode M4, the control mode is changed from the stationary standby mode M4 to the maintenance standby mode M6. Condition C15 is “stationary standby mode M4 execution time ≧ predetermined time H4a (10 hours)”. Condition C16 is “deposition amount ≧ recovery threshold A4 (12 g / L)”. When the condition C17 is satisfied in the stationary regeneration mode M5, the control mode is changed from the stationary regeneration mode M5 to the maintenance standby mode M6. Condition C17 is “deposition amount ≧ assist threshold A2 (8 g / L) and execution time of stationary regeneration mode ≧ predetermined time H5a (30 minutes)”.

  FIG. 8 is a flowchart showing a processing flow executed based on the reproduction request. Each process (step) included in the flowchart of FIG. 8 is a process executed by the ECU 50. Step S1 indicates the start of the engine 1. Step S2 is executed after step S1. In step S2, it is determined whether or not a reproduction request has occurred. The playback request is generated when the above-described start conditions for each playback mode are satisfied, and disappears when the end conditions for each playback mode are satisfied. The regeneration request requests the ECU 50 to execute the regeneration mode in which the start condition is satisfied. For example, when the start condition of the assist playback mode is satisfied, a playback request for requesting execution of the assist playback mode is generated. Similarly, there is a reproduction request for executing the reset reproduction mode and a reproduction request for executing the stationary reproduction mode. If a reproduction request has occurred, step S3 is executed, and if no reproduction request has occurred, step S4 is executed.

  In step S3, the operation mode of the engine 1 shifts to the regeneration operation mode, and in step S4, the operation mode of the engine 1 shifts to the normal operation mode. The operation mode is one of a normal operation mode and a regeneration operation mode. The normal operation mode is an operation mode in which no regeneration request is generated, and the regeneration operation mode is an operation mode in which a regeneration request is generated. When the operation mode is the normal operation mode, the control mode is maintained in any one of the self-regeneration mode, the stationary standby mode, and the maintenance standby mode. On the other hand, when the operation mode is the regeneration operation mode, the control mode is maintained in any one of the self regeneration mode, the assist regeneration mode, the reset regeneration mode, and the stationary regeneration mode. For this reason, the self-regeneration mode can occur in both the normal operation mode and the regeneration operation mode.

  In step S3, the operation mode shifts from the normal operation mode to the regeneration operation mode. In step S3, the control mode is maintained in the self-regeneration mode.

  When the operation mode shifts to the regeneration operation mode in step S3, the intake air temperature is determined (steps S5 and S6), and the variable control of the exhaust throttle valve 6 is executed based on the intake air temperature determination (step S7-). S9). These will be described in order. First, step S5 is executed after step S3. In step S5, it is determined whether or not the intake air temperature is lower than a low temperature threshold (−20 ° C.). If the intake air temperature is lower than −20 ° C., step S7 is executed. If the intake air temperature is equal to or higher than −20 ° C., step S6 is executed. In step S6, it is determined whether or not the intake air temperature is lower than a high temperature threshold (25 ° C.). If the intake air temperature is lower than 25 ° C., step S8 is executed. If the intake air temperature is equal to or higher than 25 ° C., step S9 is executed.

  Step S7 is executed when the intake air temperature is within the first temperature range. The first temperature range refers to a temperature range lower than the low temperature threshold (−20 ° C.). Step S8 is executed when the intake air temperature is within the second temperature range. The second temperature range refers to a temperature range from a low temperature threshold (−20 ° C.) to a high temperature threshold (25 ° C.). Step S9 is executed when the intake air temperature is within the third temperature range. The third temperature range refers to a temperature range equal to or higher than the high temperature threshold (25 ° C.).

  In steps S7 to S9, variable control of the opening degree of the exhaust path based on the opening degree map is started. In each of steps S7 to S9, control based on a different opening degree map is started. In step S7, the exhaust throttle valve 6 is variably controlled based on the first opening degree map. In step S8, the exhaust throttle valve 6 is variably controlled based on the second opening degree map. In step S9, the exhaust throttle valve 6 is variably controlled based on the third opening degree map. The ECU 50 stores first, second, and third opening degree maps.

  FIG. 9 is a diagram illustrating an example of the second opening degree map. In FIG. 9, the horizontal axis indicates the rotational speed of the engine 1 and the vertical axis indicates the total injection amount in one cycle. The curve drawn in FIG. 9 is an equal opening degree line, that is, a set of two-dimensional coordinates having the rotational speed and the total injection amount corresponding to the same opening degree as elements. The opening map shows the correspondence between the rotational speed of the engine 1, the total injection amount, and the opening. The second opening degree map is set so that the opening degree becomes smaller as the total injection amount decreases. When the opening degree of the exhaust path 5 is reduced, the load applied to the engine 1 is increased, and when the rotational speed is controlled to be constant, the total injection amount is increased. That is, the second opening degree map is set so as to increase the total injection amount in accordance with the decrease in the total injection amount.

  The first and third opening degree maps are also created in the same manner as the second opening degree map. The first, second, and third opening degree maps are all set so as to increase the total injection amount in accordance with the decrease in the total injection amount.

  Further, the first, second, and third opening degree maps are set so that the opening degree of the exhaust path 5 becomes smaller as the intake air temperature becomes lower. At the same rotational speed and the same injection amount, the opening degree of the first opening degree map is smaller than the opening degree of the second opening degree map, and the opening degree of the third opening degree map is larger than the opening degree of the second opening degree map. . When the intake air temperature decreases, the initial exhaust temperature also decreases. However, if the opening degree is reduced accordingly, a load is applied to the engine 1 and the fuel injection amount increases. As a result, the initial exhaust temperature rises. A decrease in the initial exhaust temperature due to the outside air temperature is prevented by controlling the opening.

  Refer to FIG. 8 again. In steps S5-S6, the ECU 50 selects an opening map corresponding to the intake air temperature from the first, second, and third opening maps. In steps S7 to S9, the ECU 50 determines, based on the selected opening map, that the opening of the exhaust path 5 corresponds to the rotational speed obtained by the rotational speed sensor 51 and the total injection amount set by itself. The exhaust throttle valve 6 is controlled.

  When one of steps S7 to S9 is completed, step S10 is executed. In step S10, it is determined whether or not the cooling water temperature is equal to or higher than the warm-up water temperature (60 ° C.). The warm-up water temperature is a coolant temperature when the engine 1 is considered to be in a warm-up state, and is 60 ° C. in the present embodiment. When the cooling water temperature is lower than 60 ° C, step S3 is executed again, and when the cooling water temperature is 60 ° C or higher, step S11 is executed.

  Steps S5-S10 are repeatedly executed until the cooling water temperature exceeds 60 ° C. While steps S5-S10 are repeatedly executed without executing step S11, the control mode is maintained in the self-regeneration mode. While the cooling water temperature is lower than 60 ° C., only the variable control of the exhaust throttle valve 6 is executed, and the fuel injection control and the control of the intake throttle valve 3 are not performed. This is because, for example, a regeneration request is generated when the engine 1 is in a cold state, such as immediately after startup, and the self-regeneration mode is being executed while waiting for execution of the regeneration mode corresponding to the regeneration request. pointing.

  In step S11, since the coolant temperature exceeds 60 ° C., the ECU 50 starts the fuel injection control and the control of the intake throttle valve 3. Here, the variable control of the exhaust throttle valve 6 has already been started. For this reason, the reproduction mode corresponding to the reproduction request is started in step S11. In the fuel injection control, a fuel injection pattern corresponding to the regeneration mode is set. In the control of the intake throttle valve 3, the opening of the intake path 2 is made smaller than the opening in normal operation. In the variable control of the exhaust throttle valve 6, the opening degree of the exhaust path 5 is variably controlled as described above.

  Step S12 is performed after step S11. In step S11, it is determined whether or not the playback mode corresponding to the playback request has ended. If the playback mode has ended, step S4 is executed, and if the playback mode has not ended, step S5 is executed. Until the regeneration mode ends, steps S5, S7, S10-S12 are repeatedly executed, and the operation mode is maintained in the regeneration operation mode.

  In step S4, the operation mode shifts to the normal operation mode. In the normal operation mode, the control mode is basically changed to the self-regeneration mode. Note that the control mode may be changed to the stationary standby mode or the maintenance standby mode instead of the self-regeneration mode depending on the amount of accumulation or the execution time of the regeneration mode. Step S2 is executed again after step S4. Unless the regeneration request is generated, steps S2 and S4 are repeatedly executed, and the operation mode is maintained in the normal operation mode.

  In the processing flow shown in FIG. 8, the opening degree of the exhaust path 5 is always variably controlled. That is, the opening degree of the exhaust path 5 is variably controlled regardless of whether the idle operation or the non-idle operation is performed when the regeneration request for the filter 19 is generated. The non-idle operation indicates an operation that is not an idle operation.

  The exhaust gas purification apparatus according to this embodiment has the following effects due to the following configuration.

(1) The exhaust gas purification apparatus according to this embodiment includes an oxidation catalyst 18 and a filter 19 disposed in the exhaust path 5 of the engine 1, an exhaust throttle valve 6 that changes the opening degree of the exhaust path 5, And a control device (ECU 50) configured to control the exhaust throttle valve 6. When the regeneration request for the filter 19 is generated, the opening degree of the exhaust path 5 is reduced as the intake air temperature decreases. Regardless of whether the idle operation or the non-idle operation is performed when the regeneration request for the filter 19 is generated, the opening degree of the exhaust path 5 is variably controlled.

  Since the opening degree of the exhaust path 5 decreases as the intake air temperature decreases, an increase in the initial exhaust temperature is suppressed in an environment where the outside air temperature is high, and an increase in the initial exhaust temperature is promoted in an environment where the outside air temperature is low. For this reason, the exhaust gas purification apparatus according to the present embodiment can suppress fluctuations in the initial exhaust temperature due to the outside air temperature.

(2) The exhaust gas purification apparatus according to this embodiment includes a fuel injection device that injects fuel according to a fuel injection pattern. The control device (ECU 50) is configured to set the fuel injection pattern. When a regeneration request for the filter 19 is generated and the coolant temperature of the engine 1 is equal to or higher than the warm-up water temperature, a temperature increase pattern is set. The temperature increase pattern is the fuel injection pattern in which the total injection amount in the compression stroke and the expansion stroke is increased. The warm-up water temperature is the cooling water temperature when the engine 1 is considered to be in a warm-up state, and is higher by a predetermined temperature range than the idle water temperature at which the cooling water temperature converges as the idling operation continues. .

  When the engine 1 is in a warm state, the total fuel injection amount is increased from the total fuel injection amount in normal operation in order to regenerate the filter 19. That is, fuel injection for regenerating the filter 19 is suppressed in a cold state in which incomplete combustion is likely to occur. For this reason, the exhaust gas purification apparatus according to the present embodiment can regenerate the filter 19 while preventing the release of unburned hydrocarbons.

(3) The opening degree of the exhaust path 5 is reduced as the total injection amount decreases.

  A load is applied to the engine 1 so as to increase the total injection amount by reducing the opening when the initial exhaust gas temperature decreases, where the total injection amount decreases. For this reason, the exhaust gas purification apparatus according to the present embodiment can increase the rising speed of the initial exhaust gas temperature.

(4) The control device (ECU 50) stores a plurality of opening degree maps (first, second, and third opening degree maps) having different corresponding intake air temperature ranges. Each of the plurality of opening maps shows a correspondence relationship between the rotational speed of the engine, the total injection amount, and the opening of the exhaust path 5. The opening map corresponding to the intake air temperature is selected from the plurality of opening maps, and based on the selected opening map, the opening of the exhaust path 5 is calculated based on the rotation speed and the total speed. The opening is changed to correspond to the injection amount.

  Based on the opening map, the opening of the exhaust path 5 is reduced as the intake air temperature decreases. For this reason, the exhaust gas purifying apparatus according to the present embodiment can realize the control corresponding to the intake air temperature without increasing the load required for the control.

  The engine 1 according to the present embodiment can employ the following modifications.

  In the engine 1, the supercharger 10 and the EGR device (EGR pipe 8, EGR throttle valve 9, EGR cooler 24) are not essential components. The engine 1 may not include the supercharger 10 and / or the EGR device. When the engine 1 does not include the supercharger 10 and / or the EGR device, the intake air temperature is approximately equal to the environmental temperature, and the initial exhaust temperature is approximately equal to the catalyst inlet temperature.

DESCRIPTION OF SYMBOLS 1 Engine 5 Exhaust path 6 Exhaust throttle valve 13 Fuel injection apparatus 18 Oxidation catalyst 19 Filter 50 ECU (control apparatus)

Claims (4)

An oxidation catalyst and a filter disposed in the exhaust path of the engine;
An exhaust throttle valve for changing the opening of the exhaust path;
A control device configured to control the exhaust throttle valve, and an exhaust gas purification device comprising:
When the regeneration request for the filter occurs, the opening degree of the exhaust path is reduced as the intake air temperature decreases,
An exhaust gas purification device in which the opening degree of the exhaust path is variably controlled regardless of whether idle operation or non-idle operation is performed when a regeneration request for the filter is generated. A fuel injection device for injecting fuel according to a fuel injection pattern;
The control device is configured to set the fuel injection pattern,
When the regeneration request for the filter is generated and the cooling water temperature of the engine is equal to or higher than the warm-up water temperature, a temperature rising pattern is set,
The temperature increase pattern is the fuel injection pattern in which the total injection amount in the compression stroke and the expansion stroke is increased,
The warm-up water temperature is the cooling water temperature when the engine is considered to be in a warm-up state, and is higher by a predetermined temperature range than the idle water temperature at which the cooling water temperature converges by continuing idle operation. The exhaust gas purification apparatus according to claim 1.   The exhaust gas purification device according to claim 2, wherein the opening degree of the exhaust path is reduced as the total injection amount decreases. The control device stores a plurality of opening maps corresponding to different ranges of the intake air temperature, and each of the plurality of opening maps includes a rotation speed of the engine, a total injection amount, and an exhaust path. The correspondence of the opening is shown,
The opening map corresponding to the intake air temperature is selected from the plurality of opening maps, and based on the selected opening map, the opening of the exhaust path is determined by the rotational speed and the total injection. The exhaust gas purification device according to claim 2 or 3, wherein the exhaust gas purification device is changed to an opening corresponding to the amount.

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