JP4406255B2 - Method for maintaining catalyst temperature of internal combustion engine - Google Patents

Description

  The present invention relates to a method for maintaining a catalyst temperature of an internal combustion engine.

  By providing a particulate filter (hereinafter referred to as a filter) in the exhaust passage of the internal combustion engine, particulate matter (hereinafter referred to as PM) in the exhaust can be collected by the filter. The collected PM can be oxidized and removed by increasing the temperature of the filter. Removing the PM collected by the filter in this way is called filter regeneration.

An oxidation catalyst is provided upstream of the filter. When the temperature of the filter is low, the temperature of the filter is raised by the sub-injection after the main injection. When the temperature of the filter is high, the circulation of EGR is stopped, and the main injection timing is further increased. Is known to reduce the temperature of the filter by increasing the advance angle and supercharging, and maintaining the temperature from 200 ° C. to 450 ° C., which is a continuous oxidation region with NO ₂ (see, for example, Patent Document 1).
JP 2002-89327 A JP 2000-213332 A JP 2001-164928 A

  By the way, if the internal combustion engine shifts to a low load operation during the regeneration of the filter, even if the control for maintaining the temperature of the filter as described above is performed, the temperature of the filter is reduced because the temperature of the exhaust gas is low. It may gradually decrease from the upstream side. This makes it difficult to continue the regeneration of the filter.

  The present invention has been made in view of the above-described problems, and in the catalyst temperature maintaining method of an internal combustion engine, the temperature of the filter is maintained or increased even when the filter is in a low load operation state during regeneration. It aims at providing the technology which can be made to do.

In order to achieve the above object, the method for maintaining the catalyst temperature of the internal combustion engine according to the present invention employs the following means. That is,
A method for raising or maintaining the temperature of a particulate filter provided in an exhaust passage of an internal combustion engine and carrying a catalyst,
A first temperature raising step capable of raising the temperature of the particulate filter to at least a carbon monoxide oxidation activation temperature by reducing the amount of intake air taken into the internal combustion engine;
At least a second temperature raising step that can raise the temperature of the particulate filter to the hydrocarbon oxidation activation temperature by fuel injection into the cylinder during the intake stroke;
A third temperature raising step capable of increasing the temperature of the particulate filter to at least the particulate matter oxidation activation temperature by at least sub-injection performed after main injection into the cylinder;
Will be implemented at the same time.

  The greatest feature of the present invention is that the temperature of the filter is maintained or increased by simultaneously increasing the exhaust temperature, increasing the carbon monoxide concentration, increasing the hydrocarbon concentration, and reducing the exhaust flow rate.

  Here, the carbon monoxide oxidation activation temperature (hereinafter referred to as CO oxidation activation temperature) is the temperature of a filter or exhaust that can oxidize carbon monoxide (CO) in exhaust gas at a specified rate or more. Similarly, the hydrocarbon oxidation activation temperature (hereinafter referred to as HC oxidation activation temperature) is the temperature of a filter that can oxidize hydrocarbons (HC) in exhaust gas at a specified rate or more, and the particulate matter oxidation activity. The temperature (hereinafter referred to as PM oxidation activation temperature) is the temperature of the filter at which the particulate matter collected by the filter is oxidized by a specified rate or more.

  According to such a method for maintaining the catalyst temperature of the internal combustion engine, the temperature of the exhaust gas can be raised to the CO oxidation activation temperature by the first temperature raising step. Further, a large amount of CO is contained in the exhaust gas by the second temperature raising step that is executed at the same time. This CO is an exhaust gas that has been raised to the CO oxidation activation temperature by the first temperature raising step. Oxidized to generate heat. Furthermore, a large amount of HC is contained in the exhaust gas by the third temperature raising step executed at the same time, but this HC is oxidized by the heat generated in the second temperature raising step. And since the flow rate of the exhaust gas is reduced by the first temperature raising step, the heat generated in the filter is not lost to the exhaust gas and the temperature of the filter does not decrease. Thus, even if the operating state of the internal combustion engine shifts to a low load operating state during the regeneration of the filter, it is possible to oxidize HC in the exhaust gas and maintain the filter temperature at the PM oxidation activation temperature. It becomes. Thereby, it is possible to continuously perform the regeneration of the filter.

  In the present invention, even if the particulate matter trapped in the particulate filter is oxidized and the temperature of the particulate filter rises, the particulate does not rise to a temperature at which the particulate filter is overheated. The temperature rising start temperature of the filter is obtained, and when the temperature is equal to or lower than this temperature, the first temperature raising step, the second temperature raising step, and the third temperature raising step can be performed.

  Here, when the first temperature raising step, the second temperature raising step, and the third temperature raising step are performed at the same time in a state where much particulate matter remains in the filter, the particulate matter is There is a possibility that the filter is overheated due to the simultaneous oxidation and heat generated at this time. At this time, as the amount of particulate matter collected increases, the temperature rise of the filter increases. Therefore, even if the collected particulate matter is oxidized, the initial value of the filter temperature at which the filter does not overheat, that is, the filter temperature that is a condition for starting the first to third temperature raising steps. If the current filter temperature is higher than this temperature, the first to third temperature raising steps are not performed. Then, after the temperature of the filter is lowered to a temperature at which the filter is not overheated, the first to third temperature raising steps are performed to maintain the temperature of the filter. In this way, filter regeneration can be continued while suppressing overheating of the filter.

  In the present invention, even if the flow rate of the exhaust gas passing through the particulate filter is such that particulate matter trapped in the particulate filter is oxidized and the temperature of the particulate filter rises, the particulate filter is overheated. The first temperature raising step, the second temperature raising step, and the third temperature raising step can be performed when the exhaust gas flow rate is higher than the exhaust gas flow rate so as not to rise to the temperature to be performed.

Here, if the first temperature raising step, the second temperature raising step, and the third temperature raising step are performed at the same time in a state where a large amount of particulate matter remains in the filter, the flow rate of the exhaust gas is small. In this state, the particulate matter is oxidized all at once, and the heat generated at this time may cause the filter to overheat. At this time, the temperature rise of the filter increases as the residual amount of the particulate matter increases or the flow rate of the exhaust gas decreases. Therefore, even if the particulate matter currently collected in the filter is oxidized, the first to third temperature raising steps should be performed at the same time only when the exhaust gas flow rate is such that the filter does not overheat. Is important. That is, when the current flow rate is lower than the exhaust gas flow rate so that the filter does not overheat, the first to third temperature raising steps are not performed. Then, after the oxidation of the particulate matter proceeds and the flow rate of the exhaust gas is reduced to the current exhaust gas flow rate so that the filter does not overheat, the first to third temperature raising steps are performed. In this way, filter regeneration can be continued while suppressing overheating of the filter.

  In the present invention, the first temperature raising step, the second temperature raising step, such that the temperature of the particulate filter is between the hydrocarbon oxidation activation temperature and the particulate matter oxidation activation temperature, And a 3rd temperature rising process can be implemented intermittently.

  Here, if the first to third temperature raising steps are performed at the same time, the HC concentration may be increased with a small flow rate of the exhaust, and HC may adhere to the exhaust passage and the filter. And this HC may generate white smoke. In that respect, the first to third temperature raising steps are intermittently performed, that is, the execution is stopped by providing a period for executing the first to third temperature raising steps and a period for stopping the execution. During this period, HC adhering to the exhaust passage and the filter can be gradually evaporated, and the generation of white smoke can be suppressed.

  In the present invention, while the temperature rise of the particulate filter by the first temperature raising step, the second temperature raising step, and the third temperature raising step is stopped, it passes through the particulate filter. The flow rate of exhaust can be reduced.

  As described above, if the first to third temperature raising steps are intermittently executed, the exhaust gas having a low temperature flows into the filter during the period in which the execution is stopped, and the temperature of the filter is lowered. In that regard, by reducing the flow rate of the exhaust gas that passes through the filter, the amount of heat taken away by the exhaust gas having a low temperature can be reduced, and a decrease in the temperature of the filter can be suppressed.

  In the present invention, when the internal combustion engine shifts to a low load operation state or an idle operation state while oxidizing and removing the particulate matter collected by the particulate filter, the first temperature raising step, Two temperature raising steps and a third temperature raising step can be performed.

  Here, when the particulate matter is oxidized and removed, the particulate filter is brought into a high temperature state, but if the internal combustion engine shifts to a low load operation state or an idle operation state during the oxidation removal, the exhaust gas is exhausted. Since the temperature of the particulate filter decreases, the temperature of the particulate filter also decreases. In that respect, if the first temperature raising step, the second temperature raising step, and the third temperature raising step are carried out at the same time, the temperature of the particulate filter can be maintained, and the particulate matter can be promptly obtained. Can be removed. Here, the low load operation state may be an operation state in which the temperature of the particulate filter may decrease to a temperature at which the particulate matter cannot be oxidized.

Further, it is a method for increasing or maintaining the temperature of a particulate filter provided in an exhaust passage of an internal combustion engine and carrying a catalyst,
At least first temperature raising means for reducing the amount of intake air taken into the internal combustion engine;
At least, the CO concentration in the exhaust is set to 5000 p. p. m. The second temperature raising means as described above;
At least, the HC concentration in the exhaust is set to 10,000 p. p. m. A third temperature raising means as described above;
May be implemented at the same time.

  Thereby, a suitable state for maintaining or raising the filter temperature can be obtained. Note that the intake amount may be the amount of exhaust.

  In the catalyst temperature maintaining method for an internal combustion engine according to the present invention, the temperature of the particulate filter can be maintained even when a low load operation is performed during regeneration of the particulate filter.

  Hereinafter, specific embodiments of a method for maintaining a catalyst temperature of an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which the catalyst temperature maintaining method for an internal combustion engine according to the present embodiment is applied and its intake / exhaust system.

  The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  The internal combustion engine 1 is provided with a fuel injection valve 3 that injects light oil into the cylinder 2.

  An intake passage 4 is connected to the internal combustion engine 1. The intake passage 4 is provided with an intake throttle valve 5 for adjusting the flow rate of intake air flowing through the intake passage 4.

  An exhaust passage 6 communicating with the combustion chamber is connected to the internal combustion engine 1. The exhaust passage 6 communicates with the atmosphere downstream.

  In the middle of the exhaust passage 6, a particulate filter 7 (hereinafter referred to as a filter 7) carrying an oxidation catalyst is provided. The exhaust passage 6 downstream of the filter 7 is provided with an exhaust temperature sensor 8 that detects the temperature of the exhaust gas flowing through the exhaust passage 6.

  The internal combustion engine 1 configured as described above is provided with an ECU 9 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 9 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  Various sensors and the like are connected to the ECU 9 via electric wiring, and output signals from the sensors and the like are input.

  On the other hand, the fuel injection valve 3 and the intake throttle valve 5 are connected to the ECU 9 via electric wiring, and can be controlled by the ECU 9.

  Here, the regeneration of the filter 7 is performed by increasing the temperature of the filter 7 to, for example, 600 ° C. through a plurality of temperature raising steps.

  For example, when the internal combustion engine 1 is started or during low-load operation and the temperature of the exhaust gas or the filter 7 is low, these temperatures are raised to the CO oxidation activation temperature (for example, 200 ° C.). As this method, a method of reducing the amount of intake by the intake throttle valve 5 is known. That is, by reducing the amount of intake air by the intake throttle valve 5, the temperature of the exhaust gas can be raised, and the exhaust gas whose temperature has risen can be circulated to the filter 7 to raise the temperature of the filter 7. At this time, the injection timing of the fuel injected from the fuel injection valve 3 may be delayed than usual. If the fuel injection timing is delayed from the normal time, the amount of energy consumed for the movement of the piston is reduced as compared with the case where fuel injection is performed at the normal time, and therefore the temperature of the exhaust gas is increased. Hereinafter, the method of raising the temperature of the exhaust gas or the temperature of the filter 7 to the CO oxidation activation temperature is referred to as a first temperature raising step.

Further, the CO concentration in the exhaust gas is increased so that the temperature of the filter 7 rises to the HC oxidation activation temperature (for example, 300 ° C.). The CO concentration at this time is preferably set to 5000 p.pm or more, for example. As this method, a method of injecting fuel in the vicinity of exhaust top dead center (hereinafter referred to as a second temperature raising step) is known. The CO generated in the second temperature raising step is oxidized by the oxidation catalyst that has reached the CO oxidation activation temperature, and the temperature of the filter 7 rises to the HC oxidation activation temperature by the reaction heat at this time. In addition, it is possible to stabilize the combustion state by injecting fuel near the exhaust top dead center.

  Further, the HC concentration in the exhaust is increased so that the temperature of the filter 7 rises to the PM oxidation activation temperature (for example, 600 ° C.). The HC concentration at this time is preferably, for example, 10,000 to 12000 p.p.m. As this method, during the expansion stroke or the exhaust stroke after the main injection from the fuel injection valve 3, a method of performing sub-injection in which fuel is injected again from the fuel injection valve 3 (hereinafter referred to as a third temperature raising step). )It has been known. According to the third temperature raising step, a large amount of unburned fuel HC is discharged from the cylinder 2. The HC is oxidized by the oxidation catalyst that has reached the HC oxidation activation temperature, and the temperature of the filter 7 rises to the PM oxidation activation temperature due to the reaction heat at this time.

  In this way, the temperature of the filter 7 is raised to the PM oxidation activation temperature, and PM deposited on the filter 7 can be oxidized and removed.

  By the way, when the temperature of the filter 7 is set to 600 ° C., for example, and the operating state of the internal combustion engine 1 shifts to a low load state such as an idle state while the filter 7 is being regenerated, the temperature of the exhaust gas is lower than 200 ° C. If this state continues, the temperature of the filter 7 will decrease. This can occur even if the sub-injection is performed in order to maintain the temperature of the filter 7. That is, even if the HC concentration in the exhaust gas is increased by the sub-injection, the exhaust gas temperature is low due to the low load. Therefore, the upstream side of the filter 7 is affected by the lower exhaust gas temperature than the temperature increase caused by the HC reaction heat. The temperature of the filter 7 will fall. When the temperature on the upstream side of the filter 7 decreases, the reaction rate of HC decreases on the upstream side. As a result, the temperature on the downstream side gradually decreases, the reaction rate of HC also decreases on the downstream side, and finally the temperature of the entire filter 7 becomes equal to or lower than the HC oxidation activation temperature. Thus, when the temperature is lower than the HC oxidation activation temperature, the temperature of the filter 7 cannot be increased or maintained even if the sub-injection is performed. Thereby, temperature will fall further.

  Therefore, in order to regenerate the filter 7, the process of raising the temperature of the filter 7 to the HC oxidation activation temperature once again and further to the PM oxidation activation temperature must be performed, and the regeneration of the filter 7 is completed. It takes time to complete. In addition, when the temperature of the filter 7 is increased, if the operation state of the internal combustion engine in which the regeneration of the filter 7 cannot be performed is entered, the opportunity to regenerate the filter 7 is lost.

  In this regard, in the present embodiment, when the operating state of the internal combustion engine 1 shifts to a low-load operating state such as an idle operation during the regeneration of the filter 7, the first temperature raising step, the second temperature rising step, and the like. All of the heating step and the third heating step are performed at the same time. That is, conventionally, only the third temperature raising step is performed even when the operating state of the internal combustion engine 1 becomes a low load state during the regeneration of the filter 7. As a result, the temperature of the filter 7 has decreased from the upstream side of the filter 7. On the other hand, in this embodiment, even if the temperature of the filter 7 is 600 ° C., all of the first temperature raising step, the second temperature raising step, and the third temperature raising step are performed simultaneously. To implement. That is, the exhaust gas flow rate is reduced as much as possible while the exhaust gas temperature is set to 200 ° C. or higher, the CO concentration in the exhaust gas is set to 5000 p.p.m., and the HC concentration in the exhaust gas is set to 10,000 to 12000 p.m.

Here, by controlling the intake throttle valve 5 to the closed side, the flow rate of the exhaust gas can be reduced as much as possible, so that the heat generated in the filter 7 in the second and third temperature raising steps is reduced. It is possible to suppress the temperature of the filter 7 from being lowered due to exhaust.

  Further, according to the present embodiment, even in the low load operation state, the temperature of the exhaust is raised to the CO oxidation activation temperature, so that CO can be oxidized upstream of the filter 7. At this time, since the CO concentration in the exhaust gas is increased by the second temperature raising step, the temperature on the upstream side of the filter 7 is raised to at least the HC oxidation activation temperature. Further, since the HC concentration in the exhaust gas is increased by the third temperature raising step, HC is oxidized upstream of the filter 7 and raised to the PM oxidation activation temperature. That is, when exhaust gas having a high temperature flows into the filter 7 and oxidation of CO and HC is performed at the same time, and the temperature of the filter 7 becomes the PM oxidation activation temperature during the regeneration of the filter 7, the filter 7 It can suppress that temperature of this falls.

  Thus, when the low-load operation state is shifted during regeneration of the filter 7, if only the third temperature raising step is performed, the temperature of the filter 7 gradually decreases from the upstream side of the filter 7. By performing all the first to third temperature raising steps at the same time, the temperature on the upstream side of the filter 7 can be maintained at the PM oxidation activation temperature.

  As described above, according to this embodiment, it is possible to suppress the temperature drop of the filter 7 and continuously perform the regeneration of the filter 7.

  In the first temperature raising step, the exhaust passage 2 may be provided with an exhaust throttle valve for adjusting the exhaust flow rate, and the exhaust throttle valve may be controlled to the closed side to reduce the exhaust flow rate. Further, the temperature of the exhaust gas may be raised by burning the sub-injected fuel close to the main injection when the sub-injection is performed.

  The second temperature raising step only needs to increase the concentration of CO in the exhaust gas. For example, CO 2 in the exhaust gas can be reduced by reducing the intake air by the intake throttle valve 5 employed in the first temperature raising step. Since the concentration increases, the reduction of intake air by the intake throttle valve 5 may be included in the second temperature raising step.

  Further, the third temperature raising step only needs to increase the HC concentration in the exhaust. For example, the HC concentration is increased by fuel injection near the exhaust top dead center employed in the second temperature raising step. Therefore, this may be included in the third temperature raising step. Furthermore, fuel addition in the exhaust may be employed.

  Further, the oxidation catalyst may not be carried on the filter, and the oxidation catalyst may be provided upstream of the filter.

  In this embodiment, the temperature of the filter 7 is controlled in consideration of the PM accumulation amount so that the filter 7 does not overheat. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

  Here, when a large amount of PM is accumulated on the filter 7, if the first to third temperature raising steps are performed, the flow rate of the exhaust gas is reduced. May overheat.

Therefore, in this embodiment, (1) when the amount of accumulated PM is calculated and the first to third temperature raising steps are started so that the filter 7 does not overheat even if the PM is oxidized. The temperature of the filter 7 (hereinafter referred to as “OT avoidable temperature”) is calculated. (2) After the transition to the low load operation, the temperature rise control of the filter 7 is not performed until the temperature at which OT avoidance is possible. (3) After the temperature of the filter 7 has decreased to the OT avoidable temperature, the temperature increase control according to the first embodiment, that is, the first temperature increase step, the second temperature increase step, and the third temperature increase step are the same. Implement at the time. At this time, the amount of the sub-injection or the fuel injection amount in the vicinity of the exhaust top dead center is adjusted, and the temperature of the filter 7 is maintained at the OT avoidable temperature. Adjustment of these fuel injection amounts is performed by feedback control so that the exhaust temperature detected by the exhaust temperature sensor 8 becomes the temperature at which OT avoidance is possible.

  Next, the flow of catalyst temperature maintenance control according to this embodiment will be described.

  FIG. 2 is a flowchart showing a flow of catalyst temperature maintenance control according to this embodiment. This flow is executed every predetermined time.

  In step S101, the amount of PM deposited on the filter 7 is calculated.

  As for the amount of PM accumulated in the filter 7, for example, a differential pressure sensor for detecting the differential pressure before and after the filter 7 is attached to the exhaust passage 6, and the PM amount corresponding to the detection value of the differential pressure sensor is previously tested It can be obtained by obtaining in advance. Further, the PM collection amount corresponding to the operation state (exhaust temperature, fuel injection amount, engine speed) of the internal combustion engine 1 is obtained in advance by experiments and mapped, and the PM collection amount obtained from this map is integrated. Thus, the amount of accumulated PM can also be obtained. Furthermore, the PM accumulation amount may be estimated according to the vehicle travel distance or travel time.

  In step S102, it is determined whether or not PM is accumulated to the extent that the filter 7 needs to be regenerated.

This is determined based on whether or not the PM deposition amount (PM) calculated in step S101 is larger than the deposition amount (PM _MAX ) for which the filter 7 needs to be regenerated.

  If an affirmative determination is made in step S102, the process proceeds to step S103, whereas if a negative determination is made, the process returns to step S101.

  In step S103, the temperature rise control of the filter 7 is performed.

  Here, since the temperature of the filter 7 may be lower than the CO oxidation activation temperature, the HC oxidation activation temperature, or the PM oxidation activation temperature, the first temperature increase step, the second temperature increase step, and the third temperature increase No control is performed to perform the process at the same time. Therefore, the temperature of the filter 7 is raised to the PM oxidation activation temperature by sequentially performing the first to third temperature raising steps.

In step S104, it is determined whether or not the PM accumulation amount (PM) of the filter 7 is larger than the PM accumulation amount (PM _MIN ) that can be regarded as the regeneration of the filter 7 being completed.

  The PM deposition amount (PM) of the filter 7 can be obtained, for example, by obtaining the PM removal amount from the period during which the filter 7 is regenerated and subtracting this removal amount from the PM deposition amount calculated in step S101. it can.

  If an affirmative determination is made in step S104, the process proceeds to step S105. On the other hand, if a negative determination is made, this routine is terminated.

  In step S105, it is determined whether or not the operating state of the internal combustion engine 1 is an idle state. For example, when the number of revolutions of the internal combustion engine 1 is not more than a specified value and the driver does not step on the accelerator at all, it is determined that the engine is in the idle state.

  If an affirmative determination is made in step S105, the process proceeds to step S106, whereas if a negative determination is made, the process returns to step S104.

  In step S106, an OT avoidable temperature Tot is calculated. Here, the temperature at which the filter 7 does not overheat even when the intake throttle valve 5 is throttled is calculated from the amount of PM deposited on the filter 7. Here, the relationship between the PM accumulation amount and the OT avoidable temperature may be obtained in advance through experiments or the like and mapped. Further, the PM accumulation amount may be obtained, for example, by detecting the pressure difference between the upstream and downstream of the filter 7 and based on the pressure difference, or from the time when the filter 7 is regenerated. good.

  In step S107, the temperature Tf of the filter 7 is obtained from the temperature detected by the exhaust temperature sensor 8.

  In step S108, it is determined whether or not the filter temperature Tf is lower than the OT avoidable temperature Tot.

  If an affirmative determination is made in step S108, the process proceeds to step S109. On the other hand, if a negative determination is made, the process proceeds to step S110.

  In step S109, the temperature rise control of the filter 7 is performed.

  Here, all of the first temperature raising step, the second temperature raising step, and the third temperature raising step are performed at the same time. At this time, the temperature of the filter 7 is set to the HC oxidation activation temperature or higher by the temperature increase control in step S103. Therefore, CO and HC can be oxidized even if all of the first to third temperature raising steps are performed simultaneously.

  In step S110, the temperature rise control is stopped, and then the process returns to step S106.

  In this way, the temperature rise control is performed only when the temperature of the filter 7 is lower than the OT avoidable temperature, thereby maintaining the temperature of the filter 7 at the OT avoidable temperature and suppressing the overheating of the filter 7. Can do.

  In this embodiment, the OT avoidable temperature may be constant at a temperature of about 500 ° C., for example.

  In this embodiment, the temperature of the filter 7 is controlled in consideration of the PM accumulation amount so that the filter 7 does not overheat. Since other configurations are the same as those in the first embodiment, description thereof is omitted. In the second embodiment, the temperature of the filter 7 is controlled based on the OT avoidable temperature. However, in this embodiment, the first to third temperature raising steps are performed at the same time to reduce the flow rate of the exhaust gas. Even if it does, only when there is no possibility that the filter 7 is overheated, the first to third temperature raising steps are performed at the same time.

  Here, when a large amount of PM is accumulated on the filter 7, if the temperature of the filter 7 is increased in the first temperature increasing process of the first embodiment, the exhaust flow rate is decreased and the filter 7 may be overheated. is there.

Therefore, in this embodiment, (1) the amount of accumulated PM is calculated, and an exhaust flow rate (hereinafter referred to as an OT avoidable exhaust flow rate) is calculated so that the filter 7 does not overheat even if the PM is oxidized. . When the actual exhaust gas flow rate is equal to or higher than the OT avoidable exhaust gas flow rate, the filter 7 is not overheated even if the first to third temperature raising steps are performed at the same time. (2) After the shift to the low load operation, if the exhaust flow rate capable of OT avoidance is larger than the flow rate of the exhaust gas passing through the filter 7, the temperature rise control of the filter 7 is not performed. (3) After the OT avoidable exhaust flow rate has decreased to the flow rate of the exhaust gas passing through the filter 7, the temperature increase control according to the first embodiment, that is, the first temperature increase step, the second temperature increase step, and the third Control to perform the temperature raising process at the same time.

  That is, even if the temperature of the filter 7 rises due to oxidation of PM, overheating of the filter 7 can be suppressed if the flow rate of the exhaust gas is large. Further, the degree of temperature rise of the filter 7 varies depending on the amount of PM deposited on the filter 7. If the regeneration of the filter 7 progresses and the amount of PM deposited on the filter 7 decreases, the exhaust flow rate that can avoid OT decreases. When the OT avoidable exhaust flow rate decreases to a current exhaust flow rate or less, an amount of exhaust gas that can suppress overheating of the filter 7 passes through the filter 7. Only when such an amount of exhaust gas passes through the filter 7, overheating of the filter 7 can be suppressed by performing the first to third temperature raising steps at the same time.

  Here, the flow rate of the exhaust gas passing through the filter 7 can be obtained by an air flow meter or the like that measures the flow rate of the intake air. Alternatively, a map obtained by previously obtaining the relationship between the rotational speed of the internal combustion engine 1, the load, and the flow rate of the exhaust gas may be used.

  Next, the flow of catalyst passing exhaust gas flow control according to this embodiment will be described.

  FIG. 3 is a flowchart showing the flow of the catalyst passage exhaust gas flow rate control according to this embodiment. This flow is executed every predetermined time. In addition, the same number is attached | subjected about the step in which the same process as the flow shown in FIG. 2 is performed, and description is abbreviate | omitted.

  In step S206, an OT avoidable exhaust flow rate Qot is calculated. Here, the amount of PM remaining in the filter 7 is obtained from the elapsed time from the start of regeneration of the filter 7, and the exhaust gas flow rate is calculated so that the filter 7 does not overheat even if the PM is oxidized. The relationship between the amount of PM remaining in the filter 7 and the OT avoidable exhaust flow rate Qot may be obtained and mapped in advance. Further, the amount of PM remaining in the filter 7 may be obtained in the same manner as in step S104.

  In step S207, the flow rate Qa of the exhaust gas passing through the filter 7 is obtained. This can be obtained from an air flow meter or the like as described above.

  In step S208, it is determined whether or not the OT avoidable exhaust flow rate Qot is equal to or lower than the flow rate Qa of the exhaust gas passing through the filter 7.

  If an affirmative determination is made in step S208, the process proceeds to step S109. On the other hand, if a negative determination is made, the process proceeds to step S110.

  In this way, the first to third temperature raising steps are performed at the same time only when the OT avoidable exhaust flow rate is equal to or lower than the exhaust flow rate passing through the filter 7, while suppressing overheating of the filter 7. A temperature of 7 can be maintained.

  In this embodiment, generation of white smoke due to HC adhering to the filter 7 during regeneration of the filter 7 is suppressed. Since other configurations are the same as those in the first embodiment, description thereof is omitted.

Here, when the temperature increase control described in the first embodiment, that is, the temperature increase control in which the first, second, and third temperature increase steps are performed simultaneously at the time of low load such as idle operation, the filter 7 In this case, the HC supply amount locally exceeds the HC oxidizable amount, and the HC supply amount becomes excessive. As a result, HC may adhere to the portion where the HC supply is excessive. Further, HC can also adhere to the wall surface of the exhaust passage 2. When the amount of HC attached increases, when acceleration is performed after the idle operation, the attached HC may be desorbed all at once and white smoke may be generated. This can occur particularly in places where the temperature is low, such as the upstream side of the filter 7 or the outer periphery.

  In this respect, in this embodiment, the temperature raising control for performing the first, second, and third temperature raising steps at the same time is performed intermittently.

  FIG. 4 is a time chart showing the time transition of the bed temperature of the filter 7 when the temperature raising control according to this embodiment is performed.

  In this embodiment, the temperature increase control may be performed, for example, for 1 minute, and then the temperature increase control may be performed based on a preset time such as, for example, stopping for 2 minutes. Further, the temperature increase control may be stopped when the temperature of the filter 7 becomes 600 ° C., for example, and the temperature increase control may be performed when the temperature becomes 400 ° C. or lower. .

  Thus, by providing the period for stopping the temperature rise control, the HC concentration in the exhaust gas is reduced, and the HC adhering to the filter 7 or the like during the temperature rise control gradually evaporates during this stop period, Furthermore, since it is oxidized, generation | occurrence | production of white smoke can be suppressed.

  In the present embodiment, as in the fourth embodiment, a temperature increase control stop period is provided, and the exhaust gas flow rate is reduced in order to prevent the temperature of the filter 7 from decreasing during the stop period. The reduction of the flow rate of the exhaust gas is performed by, for example, exhaust gas recirculation (hereinafter referred to as EGR), an intake throttle, an exhaust throttle, or the like. Since other configurations are the same as those in the first embodiment, description thereof is omitted. Here, in order to perform EGR, the internal combustion engine 1 is provided with an EGR device, and in the case of exhaust throttling, an exhaust throttle valve for adjusting the flow rate of the exhaust is provided in the exhaust passage 2.

  Here, when EGR, intake throttle, exhaust throttle, etc. are performed, the flow rate of exhaust gas decreases. That is, since EGR recirculates the exhaust gas to the intake passage, the flow rate of the exhaust gas is reduced accordingly. The intake throttle is to reduce the intake flow rate by the intake throttle valve 5, and the exhaust flow rate decreases as the intake flow rate decreases. Further, the exhaust flow rate is reduced by the exhaust throttle. Thus, by reducing the flow rate of the exhaust gas, the temperature of the filter 7 is decreased by suppressing the exhaust gas having a low temperature discharged during the temperature increase control stop, that is, during normal idling, from passing a lot through the filter 7. This can be suppressed. Therefore, in addition to EGR, intake throttle, exhaust throttle, etc., any apparatus that can reduce the flow rate of the exhaust gas passing through the filter 7 can be applied in this embodiment.

  FIG. 5 is a time chart showing the time transition of the bed temperature of the filter 7 when the temperature raising control according to this embodiment is performed. The solid line indicates the case where the control for reducing the exhaust flow rate according to the present embodiment is performed, and the broken line indicates the case where the control for reducing the exhaust flow rate according to the present embodiment is not performed, that is, the case according to the fourth embodiment. .

  As described above, the temperature decrease of the filter 7 can be suppressed, and the period during which the temperature raising control is stopped can be lengthened, so that the fuel required for raising the temperature of the filter 7 can be reduced and the fuel consumption can be improved. Can do.

  In a multi-cylinder engine, a cylinder that does not supply fuel for combustion may be provided, and a reduced-cylinder operation that operates the internal combustion engine may be performed to reduce the exhaust gas flow rate.

It is a figure which shows schematic structure of the internal combustion engine which applies the catalyst temperature maintenance method of the internal combustion engine which concerns on an Example, and its intake / exhaust system. It is the flowchart figure which showed the flow of the catalyst temperature maintenance control by Example 2. FIG. 9 is a flowchart showing a flow of catalyst passage exhaust gas flow control according to a third embodiment. FIG. 10 is a time chart showing the time transition of the bed temperature of the filter when the temperature raising control according to Example 4 is performed. FIG. 10 is a time chart showing the time transition of the bed temperature of the filter when the temperature raising control according to Example 5 is performed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Intake passage 5 Intake throttle valve 6 Exhaust passage 7 Particulate filter 8 Exhaust temperature sensor 9 ECU

Claims (2)

A method for raising or maintaining the temperature of a particulate filter provided in an exhaust passage of an internal combustion engine and carrying a catalyst,
A first temperature raising step capable of raising the temperature of the particulate filter to at least a carbon monoxide oxidation activation temperature by reducing the amount of intake air taken into the internal combustion engine;
At least a second temperature raising step that can raise the temperature of the particulate filter to the hydrocarbon oxidation activation temperature by fuel injection into the cylinder during the intake stroke;
A third temperature raising step capable of increasing the temperature of the particulate filter to at least the particulate matter oxidation activation temperature by at least sub-injection performed after main injection into the cylinder;
At the same time ,
Furthermore, the first temperature raising step, the second temperature raising step, and the third temperature so that the temperature of the particulate filter is between the hydrocarbon oxidation activation temperature and the particulate matter oxidation activation temperature. A method for maintaining the catalyst temperature of an internal combustion engine, wherein the temperature raising step is intermittently performed . While the temperature increase of the particulate filter by the first temperature raising step, the second temperature raising step, and the third temperature raising step is stopped, the flow rate of the exhaust gas passing through the particulate filter is reduced. The method for maintaining a catalyst temperature of an internal combustion engine according to claim 1 , wherein:

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