JP2012057492A - Catalyst warming-up control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst warming-up control device for promoting the warming-up of a three-way catalyst.SOLUTION: When the warming-up of the three-way catalyst is requested, among a plurality of cylinders 11, an optional cylinder is set to be a lean cylinder #1, and a cylinder other than a lean cylinders #2, #3, and #4 is set to be a rich cylinder #1. The catalyst warming-up control device includes a catalyst warming-up control means for controlling the fuel injection amount of each cylinder in such a manner that fuel is combusted at an air-fuel ratio greater than a theoretical air-fuel ratio at the lean cylinders #2, #3, and #4 and an average of the air-fuel ratios of all the cylinders #1 to #4 becomes equal to the theoretical air-fuel ratio. The number of lean cylinders #2, #3, #4 among the plurality of cylinders is set greater than that of rich cylinders #1.

Description

  The present invention relates to a catalyst warm-up control device applied to a three-way catalyst of an internal combustion engine having a plurality of cylinders.

  Generally, a three-way catalyst that purifies harmful components (HC, CO, NOx) in exhaust has an atmosphere of the catalyst in the vicinity of stoichiometric (for example, air-fuel ratio = 14.7 ± 0.1-0.2). Occasionally its purification ability is demonstrated. However, if the catalyst is not activated at a low temperature, such as during a cold start of the internal combustion engine, the purification capability cannot be fully exhibited. Therefore, it is essential to perform catalyst warm-up to raise the catalyst to the activation temperature at an early stage. As a method for warming up the catalyst, in addition to a method for retarding the ignition timing and increasing the exhaust gas temperature, a method for performing perturbation control described below (see Patent Documents 1 and 2) is known. Yes.

  In the perturbation control, for example, in the case of a 4-cylinder internal combustion engine, # 1 and # 4 cylinders are set as rich cylinders, and # 3 and # 2 cylinders are set as lean cylinders. The fuel injection amount in each cylinder is controlled so that the rich cylinder is burned and burned at an air-fuel ratio smaller than the stoichiometric air-fuel ratio. When this perturbation control is carried out, HC and CO from the rich cylinder and O2 from the lean cylinder undergo an oxidation reaction at the gathering portion of the exhaust pipe where exhaust from each cylinder gathers, and the reaction heat causes the catalyst to react. The temperature can be raised.

  However, as described above, since the atmosphere of the three-way catalyst is required to be stoichiometric, when performing perturbation control, the average of the excess air ratio (λL) of the lean cylinder and the excess air ratio (λR) of the rich cylinder It is necessary to control the fuel injection amount so that becomes 1, so that the exhaust gas gathered at the gathering portion of the exhaust pipe becomes near the stoichiometric.

JP 2006-183637 A JP-A-8-61052

  Here, if the λL of the lean cylinder is increased and the λR of the rich cylinder is decreased to increase the air-fuel ratio difference between the cylinders, the amount of reaction heat increases, so that the catalyst warm-up can be promoted. However, if λL becomes excessive, combustion in the lean cylinder exceeds the allowable value and becomes unstable, so there is a limit in increasing the air-fuel ratio difference. Therefore, in the conventional perturbation control, there is a limit in increasing the amount of heat of oxidation reaction, and the present situation is that the catalyst warm-up has not been sufficiently promoted.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a catalyst warm-up control device that promotes warm-up of a three-way catalyst.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  According to the first aspect of the present invention, the exhaust pipe of the internal combustion engine having a plurality of cylinders is disposed downstream of the collecting portion where the exhaust from each cylinder collects, and a specific component in the exhaust is oxidized or reduced. This is applied to a three-way catalyst to be purified, and when a warm-up of the three-way catalyst is required, an arbitrary cylinder among the plurality of cylinders is set as a lean cylinder, and a cylinder different from the lean cylinder is set as a rich cylinder. The lean cylinder is burned at an air / fuel ratio larger than the stoichiometric air / fuel ratio, the rich cylinder is burned at an air / fuel ratio smaller than the stoichiometric air / fuel ratio, and each cylinder has an average air / fuel ratio equal to the stoichiometric air / fuel ratio. And the number of lean cylinders among the plurality of cylinders is set to be larger than the number of rich cylinders.

  First, according to the catalyst warm-up control means according to the present invention, the oxidation reaction between the reducing component (HC, CO) discharged from the rich cylinder and the oxidizing component (O2) discharged from the lean cylinder is a collection of exhaust pipes. Therefore, warming up can be promoted by raising the temperature of the three-way catalyst by the heat of reaction.

  Here, in order to increase the amount of reaction heat, while increasing the excess air ratio (λL) of the lean cylinder and decreasing the excess air ratio (λR) of the rich cylinder, the λ at the collecting portion is maintained near 1 When the difference between λL and λR (air-fuel ratio difference) is increased, the amount of reducing component (HC amount and CO amount) discharged from the rich cylinder with respect to the amount of oxidizing component (O2 amount) discharged from the lean cylinder Was found to be in shortage. This is based on the premise that the collecting portion λ is maintained near 1. If the amount of reducing component can be increased without increasing the λL of the lean cylinder, the combustion instability in the lean cylinder due to the increase in λL is suppressed. It means that the heat of reaction can be increased. Therefore, the present inventor has studied the following method for increasing the amount of reducing component as described above.

  That is, it is a well-known fact that both the amount of HC and the amount of CO increase as the excess air ratio λ decreases from 1, but the amount of HC increases in proportion to the amount of decrease in λ. On the other hand, the amount of CO increases rapidly more than the amount proportional to the amount of decrease in λ. In order to support this fact, FIG. 4 shows the test results of measuring the CO concentration in the exhaust gas (corresponding to the CO amount) when the value of λ was decreased from 1. When the λ in the # 1 cylinder is decreased from 1 → 0.98 → 0.95 → 0.85, the CO concentration of the exhaust from the # 1 cylinder becomes 0.34 (see reference numeral P1) → 0.50 ( (See reference P2) → 1.30 (see reference P3) → 4.95 (see reference P4). For example, when P1 and P4 are compared among the test results, when λ in the # 1 cylinder is decreased from 1 to 0.85 (0.85 times), the CO concentration of the exhaust from the # 1 cylinder is 0.34%. It can be seen that it increases from 1 to 4.95% (about 15 times).

  Further, in the test of FIG. 4, in the four-cylinder internal combustion engine, the number of rich cylinders is determined with λL of the lean cylinder fixed at 1.05 on the premise that the average (aggregation part λ) of each cylinder is approximately 1. I am changing it. For example, when the # 1 and # 4 cylinders are set as rich cylinders, and the # 3 and # 2 cylinders are set as lean cylinders as shown in FIG. 4 (R2), the exhaust CO concentration in the collecting portion is 0.71 (see reference numeral P5). ) On the other hand, when only the # 1 cylinder is set as a rich cylinder and the remaining # 3, # 4, and # 2 cylinders are set as lean cylinders as shown in FIG. .33 (see P6).

  In short, this test result shows that the number of lean cylinders is set to be larger than the number of rich cylinders and the number of rich cylinders is reduced while λR per rich cylinder is reduced on the premise that the collective portion λ is maintained near 1. This indicates that the CO amount (reducing component amount) can be increased without increasing the λL of the lean cylinder.

  In view of this test result, in the above invention, the number of lean cylinders is set to be larger than the number of rich cylinders when the catalyst warm-up control means described above promotes the catalyst warm-up with the oxidation reaction heat. The CO amount (reducing component amount) can be increased without increasing λL of the cylinder. Therefore, the amount of reaction heat can be increased while suppressing instability of combustion in the lean cylinder, and further warm-up of the three-way catalyst can be promoted.

  Incidentally, the catalyst warm-up control means according to the invention described above is “to control the fuel injection amount in each cylinder so that the average of the air-fuel ratios of the plurality of cylinders becomes the stoichiometric air-fuel ratio”. (For example, 14.7) It is not limited to what is controlled, but it is controlled to be within a predetermined range (for example, 14.7 ± 0.1 to 0.2) with respect to the theoretical air-fuel ratio. The predetermined range is a range in which the three-way catalyst can exhibit a purifying capacity that exceeds a predetermined level.

  According to a second aspect of the present invention, the internal combustion engine is a direct injection type in which fuel is directly injected into a combustion chamber of the cylinder, and the lean cylinder controls injection timing so that fuel is injected at least in a compression stroke, and the rich engine In the cylinder, the injection timing is controlled so that fuel is injected at least in the intake stroke.

  Here, when the warm-up control by the catalyst warm-up control means according to the invention is performed, the rich cylinder is burned at an air-fuel ratio smaller than the stoichiometric air-fuel ratio. In addition, in the case of a direct injection internal combustion engine that injects fuel in the compression stroke, the amount of PM generated is increased as compared with the case of the port injection type. Therefore, warm-up control by the catalyst warm-up control means is performed in the direct injection internal combustion engine. When implemented, the concern of increasing PM becomes even more pronounced.

  According to the above-mentioned invention in view of this point, since fuel injection is performed in the intake stroke in the rich cylinder, it is possible to suppress an increase in PM that is a concern when the catalyst warm-up control means is applied to a direct injection internal combustion engine.

  In addition, when the ignition delay control is performed simultaneously with the warm-up control by the catalyst warm-up control means to promote the warm-up, if the ignition timing is excessively retarded, the combustion becomes unstable beyond the tolerance. There is a limit to the amount of retardation. In the case of the direct injection type capable of fuel injection in the compression stroke, combustion is more stable than in the case of the port injection type even if the ignition timing is greatly retarded. It is advantageous in promoting. In the above invention in view of this point, since the fuel is injected in the compression stroke in the lean cylinder, the retard amount of the ignition timing can be increased as compared with the case of fuel injection in the intake stroke, and further warm-up can be promoted. it can.

  Incidentally, as described above, combustion is more stable when fuel is injected during the compression stroke than when fuel is injected during the intake stroke. In the rich cylinder according to the present invention, fuel is injected in the intake stroke, so that it can be said that the combustion stability is lower than in the case of injection in the compression stroke. However, since the rich cylinder burns at an air-fuel ratio smaller than the stoichiometric air-fuel ratio, there is no concern that the combustion becomes unstable in the first place. Therefore, sufficient combustion stability can be secured in the rich cylinder according to the invention.

  The invention according to claim 3 is characterized in that in the rich cylinder, the injection timing is controlled so that fuel is injected during the first half of the intake stroke period.

  Here, in a rich cylinder that injects an excessive amount of fuel, stirring the injected fuel and intake air as much as possible to make the air-fuel mixture in the combustion chamber in a homogeneous air-fuel ratio state suppresses the amount of PM generated. Desirable above. In the above-described invention focusing on this point, since fuel is injected during the first half of the intake stroke period in the rich cylinder, stirring of the injected fuel is promoted by the airflow of the intake air flowing into the combustion chamber. Therefore, compared with the case where fuel is injected in the latter half of the intake stroke, it is possible to promote the air-fuel ratio in the combustion chamber to be in a homogeneous state, so that the amount of PM generated can be reduced.

  The “first half of the intake stroke period” is a period in which the retardation amount (BTDC) based on the top dead center of the compression stroke is 270 to 360 deg. In the first half period, it is desirable to set the fuel injection timing in the rich cylinder particularly in the period of 240 to 320 deg (more preferably 260 to 300 deg) in the following points. That is, if the injection timing is retarded too much, there is a concern that the injected fuel adheres to the piston head and promotes the generation of PM. Moreover, if the injection timing is advanced too much, the stirring effect between the injected fuel and the intake air is reduced.

  According to a fourth aspect of the present invention, the number of lean cylinders among the plurality of cylinders is set to one.

  As described above with reference to FIG. 4, when λR in the rich cylinder is decreased, the amount of CO discharged from the rich cylinder increases rapidly. Therefore, the amount of CO can be increased as the number of rich cylinders is reduced and the λR per rich cylinder is reduced. Therefore, according to the above invention in which the number of rich cylinders is one, the amount of CO can be increased by minimizing λR per rich cylinder, so that the reaction heat amount is maximized and the catalyst warm-up performance is improved. it can.

1 is a diagram illustrating a hardware configuration of an internal combustion engine, a three-way catalyst device, a fuel injection system, and the like to which a catalyst warm-up control device according to an embodiment of the present invention is applied. The flowchart which shows the procedure of the catalyst warm-up control (perturbation control) by the said embodiment. The test result which confirmed that CO emission concentration increased by the perturbation control concerning the said embodiment. The test result which confirmed that CO emission concentration increased by the perturbation control concerning the said embodiment. The test result which measured the relationship between the number of rich cylinders, and catalyst temperature in the perturbation control concerning the said embodiment. The test result which confirmed that the catalyst temperature rose by the perturbation control concerning the said embodiment. The test result which measured the oxidation reaction start time (start temperature) of CO, and the oxidation reaction start time (start temperature) of HC. The test result which measured the relationship between the fuel injection timing in a rich cylinder, PM generation amount, and catalyst temperature in the perturbation control concerning the said embodiment. The test result which measured the relationship between the fuel injection timing in a rich cylinder, and PM generation amount in the perturbation control concerning the said embodiment.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a hardware configuration of an internal combustion engine 10, a three-way catalyst device 20, a fuel injection system, and the like to which the catalyst warm-up control device according to the present embodiment is applied.

  The internal combustion engine 10 is mounted on a vehicle and functions as a travel drive source, and is a multi-cylinder engine having a plurality of cylinders 11. FIG. 1 illustrates a four-cylinder engine. The internal combustion engine 10 is a spark ignition internal combustion engine having an ignition device (not shown) and a direct injection engine that directly injects fuel into the combustion chamber 11a. In the example of FIG. 1, a fuel injection valve 13 that injects fuel is attached to a cylinder block 12 of the internal combustion engine 10.

  The operation of the fuel injection valve 13 is controlled by an injection command signal output from an electronic control unit (ECU 30). Specifically, by controlling the valve opening time of the fuel injection valve 13 provided in each cylinder 11, the injection amount injected by one valve opening is controlled for each cylinder. Moreover, the injection start timing is controlled for each cylinder by controlling the valve opening timing of the fuel injection valve 13. The fuel injection valve 13 is disposed such that an injection hole (not shown) for injecting fuel is exposed to the combustion chamber 11a. Although not shown, the fuel in the fuel tank is pumped to a pressure accumulating vessel (delivery pipe) by a high pressure pump, and the high pressure fuel accumulated in the pressure accumulating vessel is distributed and supplied to the fuel injection valve 13 of each cylinder. It is configured to be.

  Further, the ECU 30 switches between stratified combustion and homogeneous combustion based on the engine rotation speed and the engine load (for example, intake air amount). For example, in an area with a low rotational speed and a low load, such as during idling or urban driving, switching to stratified combustion with a lean air-fuel ratio (for example, 17 to 50) is performed to improve fuel efficiency. On the other hand, in high-speed and high-load regions, such as during high-speed travel, acceleration travel, and uphill travel, the engine output is improved by switching to homogeneous combustion with an air-fuel ratio (for example, 12 to 15) near the stoichiometric range.

  In stratified combustion, fuel is injected in the latter half of the compression stroke in which a piston (not shown) in the cylinder 11 rises. Then, the air-fuel mixture containing the injected fuel is collected as a rich air-fuel mixture in the vicinity of the spark plug along the shape of the piston top surface. On the other hand, in homogeneous combustion, fuel is injected in the intake stroke in which the piston descends. Then, the sprayed fuel is stirred in the combustion chamber 11a during the intake stroke and the compression stroke after the injection, and becomes a homogeneous air-fuel mixture. At the time of stratified combustion, the amount of generation of PM (Particulate Matter) is reduced by dividing the fuel into two injections of injection in the intake stroke and injection in the compression stroke in one combustion cycle. You may do it.

  An intake manifold (intake pipe) (not shown) is connected to the intake port of each cylinder 11, and a throttle valve (not shown) is provided at the upstream side portion of the collecting portion. The intake air amount is controlled by the ECU 30 controlling the operation (throttle opening) of the throttle valve. The ECU 30 controls the amount of intake air so that the output torque of the internal combustion engine 10 becomes the required load by controlling the throttle opening based on the required load (for example, accelerator operation amount) of the internal combustion engine 10 and the engine speed.

  An exhaust manifold 14 (exhaust pipe) is connected to the exhaust port of each cylinder 11, and a three-way catalyst device 20 is connected to an exhaust pipe 15 connected to the downstream end of the exhaust manifold 14. Exhaust gas discharged from each cylinder 11 is mixed in a collection portion 14 a where exhaust gas from each cylinder gathers in the exhaust manifold 14, and the mixed exhaust gas flows into the three-way catalyst device 20 through the exhaust pipe 15. Then, the hydrocarbon HC, carbon monoxide CO, and nitrogen oxide NOx, which are harmful components (specific components) in the exhaust gas, are purified by the three-way catalyst device 20.

  The three-way catalyst device 20 is configured by holding a catalyst such as platinum (three-way catalyst) on a honeycomb structure carrier 22 accommodated in a casing 21. HC and CO in the exhaust are oxidized on the catalyst and converted into harmless carbon dioxide CO2 and steam H2O. Further, NOx in the exhaust gas is reduced on the catalyst and converted into harmless nitrogen N2 and oxygen O2. However, if the air-fuel ratio (ratio between the intake air amount and the fuel injection amount) is too low and the mixed exhaust is in a rich state, HC and CO cannot be oxidized due to insufficient oxygen, and if it is in a lean state, NOx is reduced. become unable. Therefore, the three-way catalyst device 20 has a sufficient purification capacity on condition that the atmosphere of the catalyst is in the vicinity of stoichiometric (theoretical air-fuel ratio) (for example, air-fuel ratio = 14.7 ± 0.1-0.2). To be demonstrated.

  Therefore, the fuel injection amount by the fuel injection valve 13 is controlled by the ECU 30 so that the air-fuel ratio is in the vicinity of the stoichiometric. In addition, an air-fuel ratio sensor 33 (or an oxygen concentration sensor that detects the oxygen concentration in the mixed exhaust gas) for detecting the air-fuel ratio of the mixed exhaust gas is provided in the exhaust pipe 15 or the like, and a detected value (actual air fuel ratio) of the air-fuel ratio sensor 33 is provided. By controlling the fuel injection amount by the fuel injection valve 13 based on this, the ECU 30 performs feedback control (air-fuel ratio feedback control) of the fuel injection amount so that the actual air-fuel ratio becomes stoichiometric.

  Further, the three-way catalyst device 20 does not exhibit the purification ability by the oxidation-reduction reaction described above unless the temperature of the catalyst is equal to or higher than the activation temperature (for example, 350 ° C.). Therefore, when the catalyst temperature is lower than the activation temperature, such as when the internal combustion engine 10 is cold-started, it is required to perform the catalyst warm-up operation so that the temperature is quickly raised to the activation temperature.

  In the present embodiment, as the catalyst warm-up operation, the ECU 30 performs ignition retard control and perturbation control (corresponding to catalyst warm-up control by the catalyst warm-up control means) described below.

  First, ignition retardation control for the ignition device will be described. It is desirable that the ignition timing (basic ignition timing) in the normal operation after the catalyst warm-up is advanced to such an extent that knocking does not occur, in order to obtain a highly efficient engine output. On the other hand, when the catalyst warm-up is requested, the combustion temperature is raised by correcting the basic ignition timing to be retarded, and the exhaust temperature is raised. Thereby, catalyst temperature can be raised to activation temperature at an early stage, and catalyst warm-up can be completed early.

  Next, perturbation control for the fuel injection valve 13 will be described. In this control, an arbitrary cylinder among the plurality of cylinders 11 is set as a lean cylinder 11L that burns in an air-fuel ratio lean state. Further, the remaining cylinder other than the lean cylinder is set as the rich cylinder 11R that burns in the air-fuel ratio rich state. Then, the number of lean cylinders is set to be larger than the number of rich cylinders. Specifically, as shown in FIG. 2, when there is a catalyst warm-up request (S10: YES), the process proceeds to step S20 (catalyst warm-up control means), and perturbation control, which will be described in detail below, is performed. When there is no warm-up request (S10: NO), the process proceeds to step S30, and the above-described air-fuel ratio feedback control is performed.

  In step S10, when the catalyst temperature or the temperature highly correlated with the catalyst temperature is less than the predetermined temperature, it may be determined that the catalyst warm-up operation is performed by determining that there is a catalyst warm-up request. For example, it may be determined whether the engine coolant temperature detected by the coolant temperature sensor, the exhaust temperature detected by the exhaust temperature sensor, the catalyst temperature detected by the catalyst temperature sensor, or the like is less than a predetermined temperature. Alternatively, the catalyst warm-up operation may be terminated by determining that there is no catalyst warm-up request when a predetermined time has elapsed since the start of the catalyst warm-up operation.

  The perturbation control performed in step S20 will be described in more detail. In the example of FIG. 1, which is a four-cylinder engine, the # 1 cylinder, # 3 cylinder, # 4 cylinder, and # 2 cylinder are ignited in this order, and the combustion stroke is sequentially performed. The # 1 cylinder is set as the rich cylinder 11R, and the remaining # 3, # 4, and # 2 cylinders are set as the lean cylinder 11L. That is, after rich combustion is performed in the # 1 cylinder, lean combustion is sequentially performed in the # 3, # 4, and # 2 cylinders. As indicated by the white arrows in FIG. 1, the exhaust gas discharged from each cylinder sequentially flows into the three-way catalyst device 20 while being mixed in the collecting portion 14a.

  The fuel injection amount in each cylinder when the perturbation control is performed is the average of the air-fuel ratios of all the cylinders 11 (that is, the air-fuel ratio in the collecting portion 14a) while performing the rich combustion and the lean combustion described above. Controlled to be stoic. For example, the fuel injection amount in the # 1 cylinder is controlled so that the excess air ratio λR in the # 1 cylinder that is the rich cylinder 11R is 0.85, and the # 3, # 4, and # 2 cylinders that are the lean cylinder 11L The fuel injection amounts in the # 3, # 4, and # 2 cylinders are controlled so that the excess air ratio λL at 1.0 is 1.05. According to this, the air-fuel ratio in the collecting portion 14a can be set to 1.00 while performing rich combustion and lean combustion.

  When this perturbation control is performed, the amount of HC and CO discharged from the rich cylinder 11R increases. As a result, in the collecting portion 14a, HC and CO from the rich cylinder and O2 from the lean cylinder undergo an oxidation reaction, and the catalyst temperature can be raised by the reaction heat. Thereby, catalyst warm-up can be promoted.

  Here, in order to increase the amount of reaction heat, the λL of the lean cylinder 11L is increased and the λR of the rich cylinder 11R is decreased to maintain the collective portion λ in the vicinity of 1, while the difference between λL and λR (air-fuel ratio difference). Is increased, the amount of heat of reaction increases, so that catalyst warm-up can be further promoted. However, if λL becomes excessive, combustion in the lean cylinder 11L exceeds the allowable value and becomes unstable, so there is a limit in increasing the air-fuel ratio difference. In this embodiment, the number of lean cylinders 11L is set to be larger than the number of rich cylinders 11R as described above, thereby avoiding instability of combustion and increasing the amount of reaction heat for the reason described below. A balance can be realized.

  FIG. 3 shows a test result obtained by measuring the CO concentration in the exhaust gas discharged from the cylinder when the excess air ratio λ in any one cylinder is changed. This shows that the CO concentration increases as λ is decreased from 1 to promote enrichment. The amount of increase in the CO concentration is not less than an amount proportional to the amount of decrease in λ, and the gradient of the increase is larger than the linear line. Therefore, compared with the case where the number of rich cylinders 11R is set to two, the amount of CO in the collecting portion 14a can be increased by setting the number of rich cylinders 11R to one and greatly reducing one λR.

  The results of the following tests conducted to confirm this finding are shown in FIG. In this test, the CO concentration in each cylinder and the CO concentration in the collecting portion when the combination of the excess air ratio λ in all cylinders is changed are measured. (R0) in FIG. 4 is the case where all the excess air ratios λ are set to 1 without performing the perturbation control, and there is no air-fuel ratio difference between the cylinders. In this case, the CO concentration in the exhaust discharged from each cylinder was 0.34.

  (R3) in FIG. 4 is a case where the three cylinders # 1, # 2, and # 3 are set as the rich cylinder 11R, and λL = 0.98 with respect to λL = 1.05, and the collective portion λ Is set to 1. Incidentally, if λL is larger than 1.05, the combustion in the lean cylinder 11L exceeds the allowable value and becomes unstable. That is, λL = 1.05 is the maximum value of the allowable range of combustion stabilization. The CO concentration in this case was 0.50 for the rich cylinder 11R and 0.12 for the lean cylinder 11L, and the total CO concentration (CO concentration in the collecting portion 14a) was 0.45.

  (R2) in FIG. 4 is a case where the two cylinders # 1 and # 2 are set as the rich cylinder 11R, and λL = 1.05 (maximum value of the allowable range of combustion stabilization), λR = The aggregate portion λ is set to 1 by 0.95. The CO concentration in this case is 1.30 for the rich cylinder 11R and 0.12 for the lean cylinder 11L, and the total CO concentration is 0.71.

  (R3) in FIG. 4 is a case where one of the # 1 cylinders is set to the rich cylinder 11R, and λR = 0.85 with respect to λL = 1.05 (the maximum value of the allowable range of combustion stabilization). Thus, the set part λ is set to 1. The CO concentration in this case is 4.98 for the rich cylinder 11R and 0.12 for the lean cylinder 11L, and the total CO concentration is 1.33.

  As described above, according to the test results of FIG. 4, it can be confirmed that the CO concentration in the rich cylinder 11R can be increased rapidly and the total CO concentration can be increased as the number of the rich cylinders 11R is decreased. FIG. 5 summarizes the test results of FIG. 4. The aggregated portion λ, aggregated portion CO concentration (total CO concentration), and pattern corresponding to each of the tests (R0) to (R3) in FIG. The catalyst center temperature at the time when the basation control is performed for a predetermined time is shown. This shows that when only one cylinder is made rich (R3), the total CO concentration can be maximized and the catalyst center temperature can be maximized.

  FIG. 6 shows test results obtained by measuring changes in the exhaust gas temperature and the catalyst center temperature flowing into the three-way catalyst device 20 after starting the internal combustion engine 10. The broken line in the figure indicates the test result when the internal combustion engine 10 is operated in the state where there is no air-fuel ratio difference between the cylinders as shown in FIG. 4 (R0), and the solid line in the figure indicates (R1 in FIG. 4). The test results when the perturbation control in which the air-fuel ratio difference between the cylinders is generated as shown in FIG. According to this test result, it can be seen that by performing perturbation control, it is possible to increase the rate of increase of the catalyst center temperature by increasing the rate of increase of the exhaust gas temperature.

  3 to 6 described above have described the effect of increasing the amount of heat of oxidation reaction by increasing the amount of CO, but the amount of heat of oxidation reaction can also be increased by increasing the amount of HC. However, when λ in one cylinder is decreased, the CO amount increases more rapidly than the λ decrease amount as shown in FIG. 3, whereas the HC increase amount becomes the CO increase amount. There are few compared. Further, when the catalyst temperature is increased toward the activation temperature, the temperature at which HC starts the oxidation reaction is higher than the temperature at which CO starts the oxidation reaction.

  The results of the following test conducted to confirm this finding are shown in FIG. In this test, the CO purification rate and the HC purification rate after the start of the engine and the start of perturbation control are measured. The solid line in FIG. 7 shows the change in the CO purification rate with respect to the elapsed time after engine start, and the broken line in FIG. 7 shows the change in the HC purification rate. This test result indicates that the HC purification rate starts increasing at about 4 seconds after the start of the warm-up operation, whereas the CO purification rate starts increasing at about 3 seconds. That is, the oxidation reaction of CO on the catalyst starts even at a lower temperature than HC. In this respect, the perturbation control that increases the amount of heat of reaction by increasing the amount of CO instead of HC is advantageous in promoting catalyst warm-up.

  Furthermore, when performing the perturbation control in step S20 of FIG. 2, the fuel injection timing is controlled as follows. That is, in the lean cylinder 11L, the injection timing is controlled so that fuel is injected in the compression stroke, and the above-described stratified combustion state is obtained. On the other hand, in the rich cylinder 11R, the injection timing is controlled so that fuel is injected in the intake stroke, and the above-described homogeneous combustion state is obtained.

  Note that in the rich cylinder 11R, split injection in which fuel is injected a plurality of times during one combustion cycle may be performed, and the target injection amount may be divided into a plurality of times for injection. For example, split injection may be performed in which the injection is performed in two times so that the injection is performed once in the compression stroke and the intake stroke, or only one injection may be performed in the intake stroke.

  In this way, in the rich cylinder 11R, fuel is injected during the intake stroke for homogeneous combustion, so that the amount of PM generated can be reduced compared to the case of stratified combustion. The test result for confirming the PM reduction effect is shown in FIG. 8 (a), and the test result for confirming the effect of increasing the catalyst temperature is shown in FIG. 8 (b).

  In the test of FIG. 8, the test result when there is no air-fuel ratio difference between the cylinders without performing the perturbation control in the same manner as (R0) in FIG. 4, and the same as (R1) in FIG. Thus, the test result when only the # 1 cylinder is the rich cylinder 11R and the air-fuel ratio difference between the cylinders is generated will be shown. Further, when the air-fuel ratio difference is generated, the fuel injection of the rich cylinder 11R is performed once in the intake stroke, and the fuel injection of the rich cylinder 11R is divided and injected once in the intake stroke and the compression stroke. The test results are shown. The horizontal axis in FIG. 8 represents the injection timing, and represents the retard amount (BTDC) based on the top dead center of the compression stroke. In the case of split injection with an air-fuel ratio difference between cylinders, the injection timing for the first split injection (intake injection) is shown.

  According to the test result of FIG. 8A, when there is an air-fuel ratio difference between cylinders, if the intake stroke is injected once in the rich cylinder 11R, compared to the case where the rich injection is performed in the rich cylinder 11R. Thus, it can be seen that the amount of PM generated can be reduced. It can also be seen that the PM generation amount in the rich cylinder 11R when the intake stroke is injected once can be made equal to the PM generation amount when no inter-cylinder air-fuel ratio difference is caused.

  Further, according to the test results of FIG. 8B, if the perturbation control is performed to generate the inter-cylinder air-fuel ratio difference in both the single injection and the split injection in the intake stroke, the injection timing It can be seen that the catalyst temperature can be increased regardless of the retardation amount of the catalyst as compared with the case where the perturbation control is not performed.

  Furthermore, when the fuel is injected in the intake stroke as described above in the rich cylinder 11R related to the perturbation control, the injection timing is preferably set to the first half of the intake stroke. Specifically, it is desirable that the retardation amount (BTDC) with reference to the top dead center of the compression stroke be 240 to 320 deg (more preferably 260 to 300 deg).

  If fuel is injected in the first half of the intake stroke in this way, the agitation between the injected fuel and the intake air is promoted compared to the case where the fuel is injected in the second half of the intake stroke, so that homogeneous combustion can be promoted and, in turn, the amount of PM generated can be suppressed. The test result which confirmed the PM reduction effect is shown in FIG.

  In the test of FIG. 9, the amount of PM generated when the air-fuel ratio is changed in any one cylinder is measured in the case of injection in the first half of the intake stroke and in the case of injection in the second half. According to the test results of FIG. 9, it can be seen that the amount of PM generated can be reduced in the first half injection compared to the second half injection. In particular, when the rich cylinder 11R related to perturbation control is burned with rich air-fuel ratio, it can be seen that the effect of PM reduction by the first half injection appears greatly.

  As described above, according to the present embodiment, since the perturbation control is performed with the number of the rich cylinders 11R being one, the CO amount is maintained while maintaining the collective portion λ at 1 without increasing the λL of the lean cylinder 11L. Can be increased (see FIG. 4 (R1)). Therefore, the amount of reaction heat can be increased while suppressing the instability of combustion in the lean cylinder 11L due to the increase in λL, and catalyst warm-up can be promoted (see FIG. 5).

  In addition, since the fuel injection timing in the rich cylinder is set to the intake stroke and homogeneous combustion is performed, the amount of PM generated can be reduced as compared with the case of stratified combustion. In addition, since the fuel is injected in the first half of the intake stroke, the amount of PM generated can be further reduced as compared with the case where the fuel is injected in the second half (see FIG. 9).

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be modified as follows. Moreover, you may make it combine the characteristic structure of each embodiment arbitrarily, respectively.

  In the above embodiment, the catalyst warm-up control device according to the present invention is applied to a direct injection engine, but may be applied to a port injection engine that injects fuel into an intake pipe.

  In the perturbation control according to the above embodiment, the fuel injection timing in the rich cylinder 11R is set to the first half (BTDC 240 to 320 deg) of the intake stroke, but may be set to the second half (BTDC 180 to 240 deg). Moreover, you may set to BTDC320-360deg. However, if the fuel is injected on the retard side of the BTDC 320, there is a concern that the injected fuel adheres to the piston head and promotes the generation of PM. Further, when the fuel is injected on the advance side from the BTDC 240, the stirring effect between the injected fuel and the intake air is reduced. Therefore, it is desirable to inject fuel in the range of BTDC 240 to 320 deg in the rich cylinder 11R related to perturbation control.

  In the perturbation control according to the above embodiment, the fuel injection timing in the rich cylinder 11R is set to one intake stroke, but it may be divided and injected into one intake stroke and one compression stroke. It is sufficient to inject at least once in the intake stroke.

  In the above embodiment, a 4-cylinder engine is targeted, but the application target of the present invention is not limited to this, and for example, a 6-cylinder engine or an 8-cylinder engine may be targeted. Further, since the number of rich cylinders 11R related to perturbation control may be made smaller than the number of lean cylinders 11L, for example, in the case of a 6-cylinder engine, in addition to setting the number of rich cylinders 11R to one, 2 It may be set to one. Similarly, in the case of an 8-cylinder engine, the number of rich cylinders 11R may be set to 1 to 3.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder, 14a ... Collecting part of exhaust pipe, 20 ... Three-way catalyst device, 30 ... ECU (catalyst warm-up control device), S20 ... Catalyst warm-up control means, # 1 ... Rich cylinder, # 2, # 3, # 4 ... Lean cylinder.

Claims (4)

Among exhaust pipes of an internal combustion engine having a plurality of cylinders, the exhaust pipe is disposed downstream of a collecting portion where exhaust from each cylinder collects, and is applied to a three-way catalyst that purifies by oxidizing or reducing specific components in the exhaust. ,
When warming up of the three-way catalyst is required, an arbitrary cylinder among the plurality of cylinders is set as a lean cylinder, and a cylinder different from the lean cylinder is set as a rich cylinder. A catalyst that burns at a large air-fuel ratio, burns at an air-fuel ratio smaller than the stoichiometric air-fuel ratio in the rich cylinder, and controls the fuel injection amount in each cylinder so that the average air-fuel ratio of the plurality of cylinders becomes the stoichiometric air-fuel ratio Equipped with warm-up control means,
The catalyst warm-up control apparatus, wherein the number of lean cylinders among the plurality of cylinders is set to be larger than the number of rich cylinders. The internal combustion engine is a direct injection type that directly injects fuel into the combustion chamber of the cylinder,
In the lean cylinder, the injection timing is controlled so that fuel is injected at least in the compression stroke,
2. The catalyst warm-up control device according to claim 1, wherein an injection timing is controlled so that fuel is injected at least in an intake stroke in the rich cylinder.   The catalyst warm-up control apparatus according to claim 2, wherein the rich cylinder controls the injection timing so that fuel is injected during the first half of the intake stroke period.   The catalyst warm-up control device according to any one of claims 1 to 3, wherein the number of lean cylinders among the plurality of cylinders is set to one.

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