JP2017186931A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine that suppresses an excessive temperature rise of a catalyst during execution of catalyst regeneration control performed by setting a target air-fuel ratio of one cylinder to a rich air-fuel ratio and setting a target air-fuel ratio of the other cylinder to a lean air-fuel ratio.SOLUTION: An exhaust emission control device for an internal combustion engine includes: an estimation section for estimating a temperature of a catalyst on the basis of an acquired operating state of the internal combustion engine and a degree of a difference between a lean air-fuel ratio and a rich air-fuel ratio each set as a target air-fuel ratio during execution of catalyst regeneration control; a determination section for determining whether or not the estimated temperature of the catalyst exceeds a threshold value during execution of the catalyst regeneration control; and a prohibition section for prohibiting the catalyst regeneration control when a determination that the estimated temperature of the catalyst exceeds the threshold value is made during execution of the catalyst regeneration control.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  A method of raising the temperature of the catalyst by so-called dither control in which a target air-fuel ratio of one cylinder among a plurality of cylinders of an internal combustion engine is set to a rich air-fuel ratio and a target air-fuel ratio of another cylinder is set to a lean air-fuel ratio Is known (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 9-088663

  It is conceivable to regenerate the catalyst by raising the temperature to a temperature range higher than the temperature range where the catalyst is activated by such a method.

  Here, the rich air-fuel ratio and the lean air-fuel ratio set as the target air-fuel ratio by the above method are variably set according to the operating state of the internal combustion engine so that the influence on drivability is small. Therefore, during the execution of the control for regenerating the catalyst, the catalyst excessively exceeds the temperature range required for the regeneration of the catalyst depending on the operating state of the internal combustion engine and the set rich air / fuel ratio. There is a possibility of warming.

  Accordingly, the present invention provides a catalyst overheating temperature during execution of catalyst regeneration control in which the target air-fuel ratio in one cylinder is set to a rich air-fuel ratio and the target air-fuel ratio in another cylinder is set to a lean air-fuel ratio. It is an object of the present invention to provide an exhaust purification device for an internal combustion engine that suppresses combustion.

  The object is to obtain a catalyst for purifying exhaust gas discharged from a plurality of cylinders of the internal combustion engine, an acquisition unit for acquiring an operating state of the internal combustion engine, and a target air-fuel ratio in at least one of the plurality of cylinders. Is set to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, and the target air-fuel ratio in the remaining other cylinders among the plurality of cylinders is set to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio, thereby increasing the catalyst. A control unit for performing catalyst regeneration control for regenerating the catalyst by heating, an operating state of the internal combustion engine acquired during execution of the catalyst regeneration control, and the lean air-fuel ratio set as a target air-fuel ratio; Based on the magnitude of the difference from the rich air-fuel ratio, an estimation unit that estimates the temperature of the catalyst, and determines whether or not the estimated temperature of the catalyst exceeds a threshold during the execution of the catalyst regeneration control With the determination unit Achieved by an exhaust gas purification apparatus for an internal combustion engine, comprising: a prohibiting unit that prohibits the catalyst regeneration control when it is determined that the estimated temperature of the catalyst exceeds the threshold value during execution of the catalyst regeneration control it can.

  During the execution of the catalyst regeneration control, the catalyst temperature is accurately estimated based on the operating state of the internal combustion engine and the magnitude of the difference between the lean air-fuel ratio set as the target air-fuel ratio. When the estimated temperature of the catalyst exceeds the threshold value, catalyst regeneration control is prohibited, so that excessive temperature rise of the catalyst is suppressed.

  The prohibition unit may be configured to prohibit the catalyst regeneration control for a predetermined period when it is determined that the estimated temperature of the catalyst exceeds the threshold during the execution of the catalyst regeneration control.

  According to the present invention, the catalyst overheating during the catalyst regeneration control in which the target air-fuel ratio in one cylinder is set to the rich air-fuel ratio and the target air-fuel ratio in the other cylinder is set to the lean air-fuel ratio is performed. An exhaust gas purification apparatus for an internal combustion engine that suppresses temperature can be provided.

FIG. 1 is a schematic configuration diagram of an exhaust emission control device. FIG. 2 is a flowchart illustrating an example of the regeneration prohibition control executed by the ECU. 3A and 3B are examples of a catalyst temperature map. FIG. 4 is a time chart showing an example of the reproduction prohibition control. FIG. 5 is a flowchart showing a modification of the regeneration prohibition control executed by the ECU. FIG. 6 is a time chart showing a modification of the regeneration prohibiting control.

  FIG. 1 is a schematic configuration diagram of an exhaust purification device 1 (an exhaust purification device for an internal combustion engine). As shown in FIG. 1, the exhaust gas purification apparatus 1 includes a three-way catalyst 31 that purifies the exhaust gas of the internal combustion engine 20. The internal combustion engine 20 burns the air-fuel mixture in the combustion chamber 23 in the cylinder block 21 and reciprocates the piston 24. The internal combustion engine 20 is an in-line four-cylinder gasoline engine, but is not limited to this as long as it has a plurality of cylinders, and may be a diesel engine, for example.

  The cylinder head of the internal combustion engine 20 is provided with an intake valve Vi for opening and closing an intake port and an exhaust valve Ve for opening and closing an exhaust port for each cylinder. A spark plug 27 for igniting the air-fuel mixture in the combustion chamber 23 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to the surge tank 18 via a branch pipe for each cylinder. An intake pipe 10 is connected to the upstream side of the surge tank 18, and an air cleaner 19 is provided at the upstream end of the intake pipe 10. The intake pipe 10 is provided with an air flow meter 15 for detecting the intake air amount and an electronically controlled throttle valve 13 in order from the upstream side.

  An injector 12 for injecting fuel into the intake port is installed at the intake port of each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 23 when the intake valve Vi is opened, compressed by the piston 24, and ignited and burned by the spark plug 27. It is done.

On the other hand, the exhaust port of each cylinder is connected to the exhaust pipe 30 via a branch pipe for each cylinder. A three-way catalyst 31 is provided in the exhaust pipe 30. The three-way catalyst 31 has an oxygen storage capacity and purifies NOx, HC and CO. The three-way catalyst 31 is, for example, a catalyst carrier such as alumina (Al ₂ O ₃ ) on a base material such as cordierite, particularly a honeycomb base material, and platinum (Pt), palladium supported on the catalyst carrier. One or a plurality of catalyst layers containing a catalyst metal such as (Pd) and rhodium (Rh) are formed. The three-way catalyst 31 is an example of a catalyst that purifies exhaust gas discharged from a plurality of cylinders of the internal combustion engine 20, and may be an oxidation catalyst or a gasoline particulate filter coated with an oxidation catalyst.

  An air-fuel ratio sensor 33 for detecting the air-fuel ratio of the exhaust gas is installed on the upstream side of the three-way catalyst 31. The air-fuel ratio sensor 33 is a so-called wide-area air-fuel ratio sensor, which can continuously detect an air-fuel ratio over a relatively wide range and outputs a signal having a value proportional to the air-fuel ratio.

  The exhaust purification device 1 includes an ECU (Electronic Control Unit) 50. The ECU 50 includes a central processing unit (CPU), a random access memory (RAM), a read only memory (ROM), and a storage device. The ECU 50 performs various controls by executing a program stored in the ROM or the storage device. Further, the ECU 50 executes regeneration prohibition control described later. The reproduction prohibition control is realized by an acquisition unit, a control unit, an estimation unit, and a prohibition unit of the ECU 50 that are functionally realized by a CPU, a ROM, and a RAM. Details will be described later.

  The ECU 50 is electrically connected to the spark plug 27, the throttle valve 13, the injector 12, and the like. In addition to the above-described air flow meter 15, air-fuel ratio sensor 33, crank angle sensor 25 that detects the crank angle of the internal combustion engine 20, the accelerator opening sensor 11 that detects the accelerator opening and various other sensors are shown in the ECU 50. It is electrically connected via an A / D converter or the like that is not performed. The ECU 50 controls the ignition plug 27, the throttle valve 13, the injector 12 and the like so as to obtain a desired output based on the detection values of various sensors, etc., and performs ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc.

  Next, setting of the target air-fuel ratio by the ECU 50 will be described. In a normal state where catalyst regeneration control, which will be described later, is not executed, the target air-fuel ratio is set based on a normal air-fuel ratio map corresponding to the engine speed and engine load of the internal combustion engine 20. The normal air-fuel ratio map is acquired in advance by experiments and stored in the ROM of the ECU 50.

  For example, the target air-fuel ratio is set to the stoichiometric air-fuel ratio in the low rotation / low load region, and is set to a richer side than the stoichiometric air / fuel ratio in the high rotation / high load region. When the target air-fuel ratio is set, the fuel injection amount to each cylinder is feedback-controlled so that the air-fuel ratio detected by the air-fuel ratio sensor 33 matches the target air-fuel ratio. Instead of the normal air-fuel ratio map, the target air-fuel ratio corresponding to the engine speed and the engine load may be calculated by a calculation formula.

Further, the ECU 50 raises the temperature of the three-way catalyst 31 to a predetermined temperature range, thereby releasing the sulfur compound (SO _X ) deposited on the three-way catalyst 31 and regenerating the purification ability of the three-way catalyst 31. Perform playback control. In the catalyst regeneration control, the target air-fuel ratio in one of a plurality of cylinders is set to a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio, and the target air-fuel ratios in the remaining three cylinders are set to be lower than the stoichiometric air-fuel ratio. A so-called dither control, which is set to a large lean air-fuel ratio, is executed. Further, the average of the target air-fuel ratios of all the cylinders is set to be the stoichiometric air-fuel ratio.

  Similarly, the target air-fuel ratio in the catalyst regeneration control is set based on the regeneration air-fuel ratio map corresponding to the engine speed and the engine load. The regeneration air-fuel ratio map is acquired in advance by experiments and stored in the ROM of the ECU 50. For example, the rich air-fuel ratio is set between 9 and 12, and the lean air-fuel ratio is set between 15 and 16. Further, as the engine speed and the engine load are larger, the rich air-fuel ratio is smaller and the lean air-fuel ratio is set larger.

  The rich air-fuel ratio and the lean air-fuel ratio set as the target air-fuel ratio by the regeneration air-fuel ratio map are variably set according to the engine speed of the internal combustion engine 20 and the engine load within a range where the influence on drivability is small. Instead of the regeneration air-fuel ratio map, the target air-fuel ratio in the catalyst regeneration control corresponding to the engine speed and the engine load may be calculated by a calculation formula. Note that the catalyst regeneration control is not executed during idle operation or when the accelerator opening is zero.

When the catalyst regeneration control is executed as described above, the surplus fuel discharged from the cylinder whose target air-fuel ratio is set to the rich air-fuel ratio adheres to the three-way catalyst 31, and is generated by the exhaust discharged from the lean air-fuel ratio. Burns in a lean atmosphere. As a result, the temperature of the three-way catalyst 31 is raised and SO _X is released.

  However, during the catalyst regeneration control in which the three-way catalyst 31 is maintained at a high temperature, the three-way catalyst 31 is regenerated depending on the operating state of the internal combustion engine 20 and the rich air / fuel ratio set as the target air / fuel ratio. There is a possibility of overheating beyond the necessary temperature range. Therefore, the ECU 50 executes regeneration prohibition control that prohibits catalyst regeneration control during execution of catalyst regeneration control.

  FIG. 2 is a flowchart showing an example of the regeneration prohibiting control executed by the ECU 50. The control in FIG. 2 is repeatedly executed at a predetermined cycle. The ECU 50 determines whether or not the catalyst regeneration control is being executed (step S1). If the determination is negative, the control is terminated.

  If the determination in step S1 is affirmative, the ECU 50 acquires the engine speed and engine load of the internal combustion engine 20 (step S3). Specifically, the engine speed is acquired based on the output value from the crank angle sensor 25, and the engine load is acquired based on the output value from the accelerator opening sensor 11. The process of step S3 is an example of a process executed by an acquisition unit that acquires the operating state of the internal combustion engine 20.

  Next, the ECU 50 obtains the difference between the lean air-fuel ratio set as the target air-fuel ratio in the catalyst regeneration control and the rich air-fuel ratio as the air-fuel ratio difference (step S5). Specifically, a value obtained by subtracting the rich air-fuel ratio from the lean air-fuel ratio is acquired as the air-fuel ratio difference. An absolute value obtained by subtracting the lean air-fuel ratio from the rich air-fuel ratio may be acquired as the air-fuel ratio difference.

  Next, the ECU 50 estimates the temperature of the three-way catalyst 31 (step S7). Specifically, the temperature of the three-way catalyst 31 is estimated based on the acquired engine speed, engine load, and catalyst temperature map corresponding to the air-fuel ratio difference. The catalyst temperature map is acquired in advance by experiments and stored in the ROM of the ECU 50. The process of step S7 is based on the obtained operating state of the internal combustion engine 20 and the magnitude of the difference between the lean air-fuel ratio set as the target air-fuel ratio and the rich air-fuel ratio during the catalyst regeneration control. It is an example of the process which the estimation part which estimates the temperature of the original catalyst 31 performs.

  3A and 3B are examples of a catalyst temperature map. The horizontal axis represents the engine speed, and the vertical axis represents the engine load, indicating a plurality of isothermal lines. FIG. 3A shows a catalyst temperature map when the air-fuel ratio difference is relatively large, and FIG. 3B shows a catalyst temperature map when the air-fuel ratio difference is relatively small. Here, the temperatures T1 to T6 are higher in the order of the temperature T1 to the temperature T6.

  As shown in FIGS. 3A and 3B, under the same engine speed and engine load, the temperature of the three-way catalyst 31 is estimated to be higher as the air-fuel ratio difference is larger. Based on such a catalyst temperature map, the temperature of the three-way catalyst 31 during execution of the catalyst regeneration control can be accurately estimated. Instead of such a catalyst temperature map, the temperature of the three-way catalyst 31 may be estimated based on the engine speed, the engine load, and the air-fuel ratio difference using a calculation formula.

  Next, the ECU 50 determines whether or not the estimated temperature of the three-way catalyst 31 exceeds the threshold value (step S9). If the determination is negative, the control is terminated. The threshold value is a value for determining whether or not the three-way catalyst 31 has overheated, and is set to a value slightly lower than the heat-resistant upper limit temperature of the three-way catalyst 31, for example, 900 degrees. It is not limited to. The process of step S9 is an example of a process executed by a determination unit that determines whether or not the estimated temperature of the three-way catalyst 31 exceeds a threshold value during the execution of the catalyst regeneration control.

  If the determination in step S9 is affirmative, the ECU 50 prohibits catalyst regeneration control (step S11). During the period in which the catalyst regeneration control is prohibited, the target air-fuel ratio in all the cylinders is set to be the same. Specifically, the target air-fuel ratio is set based on the normal air-fuel ratio map used in normal operation based on the engine speed and engine load acquired in step S3. Thereby, the excessive temperature rise of the three-way catalyst 31 is suppressed. Note that, during the period when the catalyst regeneration control is prohibited, the target air-fuel ratio in all the cylinders may be set to the stoichiometric air-fuel ratio. The process of step S9 is an example of a process executed by a prohibiting unit that prohibits the catalyst regeneration control when it is determined that the estimated temperature of the three-way catalyst 31 exceeds the threshold during the catalyst regeneration control. .

  Next, the reproduction prohibition control will be described using a time chart. FIG. 4 is a time chart showing an example of the reproduction prohibition control. FIG. 4 shows the vehicle speed, the idle determination flag, the engine speed, the engine load, the estimated temperature of the three-way catalyst 31, the catalyst regeneration execution flag, the target air-fuel ratio in the cylinder in which the target air-fuel ratio is set to the lean air-fuel ratio, the target A waveform showing a target air-fuel ratio in a cylinder in which the air-fuel ratio is set to a rich air-fuel ratio is shown. In FIG. 4, for easy understanding, the estimated temperature of the three-way catalyst 31 is shown even during a period when the catalyst regeneration control is not executed.

  If there is a catalyst regeneration request at time t2 from the state where the catalyst regeneration execution flag is off at time t1, the catalyst regeneration execution flag is turned on. Thus, the ECU 50 sets the target air-fuel ratio of one cylinder to a rich air-fuel ratio, sets the target air-fuel ratio of the other cylinders to a lean air-fuel ratio, and executes catalyst regeneration control.

  When the idle determination flag is turned on at time t3, the catalyst regeneration execution flag is turned off and the catalyst regeneration control is stopped, assuming that the engine 10 is in an idle operation state, even when there is a catalyst regeneration request. When the idle determination flag is turned off at time t4, it is assumed that the engine 10 has exited the idle operation state, the catalyst regeneration execution flag is turned on, and the catalyst regeneration control is performed again. When the idle determination flag is turned on again at time t5, the catalyst regeneration execution flag is turned off and the catalyst regeneration control is stopped.

  When the idle determination flag is turned off at time t6, the catalyst regeneration execution flag is turned on and the catalyst regeneration control is executed again. After time t6, when the air-fuel ratio difference between the lean air-fuel ratio and the rich air-fuel ratio increases and the estimated temperature of the three-way catalyst 31 exceeds the threshold value at time t7, the catalyst regeneration execution flag is turned off for a predetermined period, and the catalyst Playback control is prohibited. Thereafter, the idle determination flag is turned on at time t8, and the estimated temperature of the three-way catalyst 31 further decreases.

  As described above, when the catalyst regeneration control is prohibited during the execution of the catalyst regeneration control, the temperature of the three-way catalyst 31 is lowered and the excessive temperature rise is suppressed. Thereby, the possibility that the three-way catalyst 31 is deteriorated by heat can be suppressed. If the catalyst regeneration control is prohibited, the catalyst regeneration control prohibition state is maintained during the current trip until the ignition key is turned off. Therefore, when a predetermined condition is satisfied during the next trip, catalyst regeneration control is executed, and the sulfur compound deposited on the three-way catalyst 31 can be removed.

  Here, instead of estimating the temperature of the three-way catalyst 31 as in the above method, the temperature sensor is directly measured, or temperature sensors are arranged on the upstream side and the downstream side of the three-way catalyst 31 and detected. It is also conceivable to estimate the temperature of the three-way catalyst 31 based on the temperature difference. However, in this case, the number of parts may increase. In the present embodiment, since the temperature of the three-way catalyst 31 can be estimated without providing such a temperature sensor, an increase in the number of parts is suppressed.

  Next, a modified example of the reproduction prohibition control will be described. FIG. 5 is a flowchart showing a modified example of the regeneration prohibition control executed by the ECU 50. FIG. 6 is a time chart showing a modification of the regeneration prohibiting control. Note that the processing in steps S1, S3, S5, S7, and S9 is the same as the reproduction prohibition control in FIG. Further, since the operating state such as the engine speed from the time t1 to the time t7 is the same, the description is omitted.

  As shown in FIG. 5, if the determination in step S9 is affirmative, the ECU 50 prohibits catalyst regeneration control for a predetermined period (step S11a). The predetermined period is a period suitable for suppressing the excessive temperature rise of the three-way catalyst 31, and is acquired in advance by an experiment and stored in the ROM of the ECU 50. The predetermined period is, for example, about 500 to 1500 milliseconds, but is not limited thereto. After the prohibition period of the catalyst regeneration control has elapsed, the catalyst regeneration control is executed again as long as there is a catalyst regeneration request.

  Further, as shown in FIG. 6, at a time t7 ′ when a predetermined period has elapsed from the time t7 when the catalyst regeneration control is prohibited, the prohibition of the catalyst regeneration control is released, the catalyst regeneration execution flag is turned on, and the catalyst regeneration control is performed. Will be executed again. When the idle determination flag is turned on at time t8 thereafter, the catalyst regeneration execution flag is turned off and the catalyst regeneration control is stopped.

  By prohibiting the catalyst regeneration control for a predetermined period in this manner, the excessive temperature rise of the three-way catalyst 31 is suppressed, and when the prohibition of the catalyst regeneration control is canceled after the lapse of the predetermined period, the temperature of the three-way catalyst 31 is raised again. The sulfur compound deposited on the three-way catalyst 31 can be removed as early as possible.

  Note that the predetermined period during which the catalyst regeneration control is prohibited is not limited to the above case. For example, the predetermined period during which the catalyst regeneration control is prohibited may be a period from when the catalyst regeneration control is prohibited until the idle operation flag is turned on. As described above, the catalyst regeneration execution flag is turned off when the idle operation flag is on. For this reason, when the idle operation state is entered after the catalyst regeneration control is prohibited, the catalyst regeneration control can actually be executed only after returning from the idle operation. The predetermined period during which the catalyst regeneration control is prohibited may be a period from when the catalyst regeneration control is prohibited until the accelerator opening becomes zero. Also in this case, since the catalyst regeneration control is not executed when the accelerator opening is zero, the catalyst regeneration control can actually be executed only after the accelerator opening is other than zero.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

  Although the inline four-cylinder engine has been described as an example of the internal combustion engine in the above embodiment, a V-type multi-cylinder engine having a catalyst for each bank may be used. In this case, in the catalyst regeneration control, the target air-fuel ratio of one cylinder in each bank is set to a rich air-fuel ratio, the target air-fuel ratio of the remaining cylinders is set to a lean air-fuel ratio, and the catalyst regeneration control is performed for each bank. Execute.

1 Exhaust gas purification device (exhaust gas purification device for internal combustion engine)
20 Internal combustion engine 31 Three-way catalyst (catalyst)
50 ECU (acquisition part, control part, estimation part, determination part, prohibition part)

Claims (2)

A catalyst for purifying exhaust discharged from a plurality of cylinders of the internal combustion engine;
An acquisition unit for acquiring an operating state of the internal combustion engine;
The target air-fuel ratio in at least one cylinder among the plurality of cylinders is set to a rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and the target air-fuel ratio in the remaining other cylinders among the plurality of cylinders is set to be higher than the stoichiometric air-fuel ratio. A control unit for performing catalyst regeneration control for raising the temperature of the catalyst to regenerate the catalyst by setting the lean air-fuel ratio to a larger value,
Based on the obtained operating state of the internal combustion engine during execution of the catalyst regeneration control and the magnitude of the difference between the lean air-fuel ratio set as a target air-fuel ratio and the rich air-fuel ratio, An estimation unit for estimating
A determination unit that determines whether the estimated temperature of the catalyst exceeds a threshold value during execution of the catalyst regeneration control;
An exhaust gas purification apparatus for an internal combustion engine, comprising: a prohibition unit that prohibits the catalyst regeneration control when it is determined that the estimated temperature of the catalyst exceeds the threshold during execution of the catalyst regeneration control.   2. The internal combustion engine according to claim 1, wherein the prohibiting unit prohibits the catalyst regeneration control for a predetermined period when it is determined that the estimated temperature of the catalyst exceeds the threshold during execution of the catalyst regeneration control. Exhaust purification device.

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