JP2010121534A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine, certainly suppressing the local excessive temperature rise of the turbine housing of a twin entry turbocharger. <P>SOLUTION: This control device for the internal combustion engine includes: the turbocharger provided with a turbine having two inlets; a first exhaust passage allowing exhaust gas in a first cylinder group of the internal combustion engine having a plurality of cylinders to flow into one inlet of the turbine; a second exhaust passage allowing exhaust gas in a second cylinder group to flow into the other inlet of the turbine and having a smaller surface area than that of the first exhaust passage; a determination means determining whether or not the operating condition of the internal combustion engine is in a high-exhaust gas temperature range; and an air-fuel ratio correction means performing correction so that an air-fuel ratio of at least one of the cylinders of the second cylinder group is enriched in comparison with a theoretical air-fuel ratio when it is determined that the operating condition is in the high-exhaust gas temperature range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  A twin-entry turbocharger having two turbine inlets is known (for example, see Patent Document 1 below). This twin entry turbocharger is employed for the purpose of preventing the exhaust pulsations of a multi-cylinder internal combustion engine from interfering with each other and increasing the output. In an internal combustion engine equipped with a twin entry turbocharger, a plurality of cylinders are divided into groups of cylinders whose exhaust strokes are not adjacent to each other, and exhaust gas is guided to the turbine inlet independently for each group. .

JP 2007-32476 A JP 2007-154836 A

  A case of an in-line four-cylinder engine equipped with a twin entry turbocharger will be described as an example. In this engine, the exhaust gases of the first and fourth cylinders are collected and flowed into one inlet of the turbine, and the exhaust gases of the second and third cylinders are collected and flowed into the other inlet of the turbine. In this case, since the second and third cylinders are adjacent to each other, the lengths of their exhaust manifolds are short. Therefore, the exhaust manifolds of the second and third cylinders have a small surface area and a small amount of heat radiation. On the other hand, since the first and fourth cylinders are separated from each other, their exhaust manifolds are long. Therefore, the exhaust manifolds of the first and fourth cylinders have a large surface area and a large amount of heat radiation. For this reason, the temperature of the exhaust gas flowing into the turbine from the second and third cylinders becomes higher than the temperature of the exhaust gas flowing into the turbine from the first and fourth cylinders. For this reason, in the turbine housing, the temperature of the wall where the exhaust gas flowing in from the second and third cylinders hits tends to increase.

  Further, the exhaust manifolds of the 2nd and 3rd cylinders have a shorter radius of curvature than the exhaust manifolds of the 1st and 4th cylinders because of their shorter length. Therefore, in the exhaust manifolds of the 2nd and 3rd cylinders, the bending of the exhaust gas flow becomes large, so that the flow of the exhaust gas tends to be biased to one side wall. For this reason, the exhaust gas from the second and third cylinders tends to drift even after flowing into the turbine housing. As a result, the wall of the portion where the exhaust gas hits is particularly concentrated and heated.

  For this reason, in the turbine housing, the temperature of the wall of the portion where the exhaust gas from the second and third cylinders hits is particularly likely to rise. During high-rotation and high-load operation where the exhaust gas temperature is high, in order to protect the turbine housing, it is necessary to take some care so that the temperature of the wall of that portion does not rise excessively.

  The present invention has been made to solve the above-described problems, and provides a control device for an internal combustion engine that can reliably suppress a local overtemperature of a turbine housing of a twin entry turbocharger. With the goal.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
A turbocharger with a turbine having two inlets;
A first exhaust passage through which exhaust gas of a first cylinder group of an internal combustion engine having a plurality of cylinders flows into one inlet of the turbine;
A second exhaust passage for causing exhaust gas of a second cylinder group of the internal combustion engine to flow into the other inlet of the turbine and having a surface area smaller than that of the first exhaust passage;
Determining means for determining whether or not the operating condition of the internal combustion engine is in a high exhaust temperature region;
Air-fuel ratio correction means for correcting the air-fuel ratio of at least one cylinder of the second cylinder group to be richer than the stoichiometric air-fuel ratio when it is determined that the operating condition is in the high exhaust temperature region. When,
It is characterized by providing.

The second invention is the first invention, wherein
A waste gate that bypasses the turbine and passes exhaust gas;
A wastegate valve for opening and closing the wastegate;
With
The air-fuel ratio correcting means includes means for correcting the richness of the air-fuel ratio of the cylinder to be corrected according to the opening degree of the waste gate valve.

The third invention is the first or second invention, wherein
The air-fuel ratio correction means is configured to make the air-fuel ratio of at least one cylinder of the first cylinder group leaner than the stoichiometric air-fuel ratio when it is determined that the operating condition is in the high exhaust temperature region. It is characterized by including a correction means.

  According to the first invention, in the internal combustion engine including the first cylinder group and the second cylinder group in which the exhaust passage on the upstream side of the turbine of the turbocharger is separated from each other, it is determined that the operating condition is in the high exhaust temperature region. In this case, correction can be made so that the air-fuel ratio of at least one cylinder in the second cylinder group having a small surface area of the exhaust passage upstream of the turbine is richer than the stoichiometric air-fuel ratio. The exhaust gas flowing into the turbine from the second cylinder group has a high temperature because the surface area of the exhaust passage is small and the heat dissipation amount is small. For this reason, the temperature of the turbine housing in the portion where the exhaust gas from the second cylinder group hits easily rises under the operating condition in which the exhaust temperature becomes high. In such a case, according to the first aspect of the invention, the temperature of the exhaust gas emitted from the second cylinder group can be lowered. Therefore, the rise in turbine housing temperature can be reliably suppressed. At this time, since the air-fuel ratio is not made rich for the first cylinder group, fuel can be saved and fuel efficiency can be improved.

  According to the second invention, the rich degree of the cylinder that makes the air-fuel ratio rich can be corrected according to the opening degree of the waste gate valve. When the waste gate valve opens, the amount of exhaust gas flowing into the turbine changes. For this reason, the temperature of a turbine housing changes according to the opening degree of a waste gate valve. According to the second invention, the richness of the air-fuel ratio can be adjusted to a necessary and sufficient value according to the opening degree of the waste gate valve. For this reason, the rise in turbine housing temperature can be suppressed more reliably, and fuel can be further saved.

  According to the third aspect, when it is determined that the operating condition of the internal combustion engine is in the high exhaust temperature region, the air-fuel ratio of at least one cylinder in the first cylinder group is leaner than the stoichiometric air-fuel ratio. Can be corrected as follows. Thereby, fuel can be further saved. In addition, since the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst can be maintained in the vicinity of the stoichiometric air-fuel ratio, it is possible to reliably avoid deterioration of emissions.

Embodiment 1 FIG.
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 1, the system of the present embodiment includes an internal combustion engine 10 that is used as a power source for a vehicle or the like. The internal combustion engine 10 of the present embodiment is an in-line four-cylinder type having four cylinders # 1 to # 4. The explosion order is # 1 → # 3 → # 4 → # 2.

  Each cylinder of the internal combustion engine 10 is provided with an intake valve 12, an exhaust valve 14, and a fuel injector 16. The fuel injector 16 is provided so as to inject fuel into the intake port of each cylinder. The present invention is not limited to such a configuration, and a fuel injector may be provided so as to inject fuel directly into the cylinder of each cylinder.

  An intake passage 20 is connected to the internal combustion engine 10 via an intake manifold 18. A throttle valve 22 for adjusting the amount of intake air is installed in the intake passage 20.

  The internal combustion engine 10 of the present embodiment is provided with a turbocharger 24. The turbocharger 24 includes a turbine 241 that is operated by the energy of the exhaust gas of the internal combustion engine 10 and a compressor 242 that is driven by the turbine 241. Although not shown, the intake passage 20 is connected to the compressor 242. The intake air can be compressed by the compressor 242.

  The turbine 241 has two inlets. That is, the turbocharger 24 is of a twin entry type (twin scroll type). A first exhaust manifold 26 is connected to one inlet of the turbine 241, and a second exhaust manifold 28 is connected to the other inlet. The first exhaust manifold 26 is connected to the # 1 cylinder and the # 4 cylinder. That is, the exhaust gas discharged from the # 1 cylinder and the exhaust gas discharged from the # 4 cylinder merge at the first exhaust manifold 26 and flow into one inlet of the turbine 241.

  On the other hand, the second exhaust manifold 28 is connected to the # 2 cylinder and the # 3 cylinder. That is, the exhaust gas discharged from the # 2 cylinder and the exhaust gas discharged from the # 3 cylinder merge at the second exhaust manifold 28 and flow into the other inlet of the turbine 241. According to such a twin entry type turbocharger 24, interference of exhaust pulsation between cylinders can be suppressed, and excellent supercharging characteristics can be obtained.

  An exhaust passage 30 is connected to the outlet of the turbine 241. A catalyst 32 for purifying exhaust gas is installed in the middle of the exhaust passage 30. The catalyst 32 is composed of, for example, a three-way catalyst having an oxygen storage function.

  In the vicinity of the turbocharger 24, there is a waste gate 34 that allows a part of the exhaust gas in the first exhaust manifold 26 to flow into the exhaust passage 30 on the downstream side of the turbine 241 without passing through the turbine 241; 2 A waste gate 36 that allows a part of the exhaust gas in the exhaust manifold 28 to flow through the exhaust passage 30 on the downstream side of the turbine 241 without passing through the turbine 241, and a waste that opens and closes both waste gates 34, 36. A gate valve 38 is provided.

  The waste gate valve 38 of the present embodiment is configured to displace the valve body that can rotate between a closed position that seals the outlets of the waste gates 34 and 36 and an open position that opens the outlets. Actuator (not shown). An opening degree sensor 39 that detects an actual opening degree of the waste gate valve 38 (hereinafter referred to as “actual opening degree”) is provided in the vicinity of the waste gate valve 38. The opening degree of the waste gate valve 38 is controlled by an ECU 50 described later.

  In the system of the present embodiment, for example, during a high load operation, the waste gate valve 38 is opened so that a part of the exhaust gas flows through the exhaust passage 30 without passing through the turbine 241. Thereby, it is possible to reliably prevent the exhaust pressure (back pressure) and the supercharging pressure from becoming excessive.

  A pre-catalyst sensor 40 that detects the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is installed downstream of the turbine 241 and the waste gate valve 38 and upstream of the catalyst 32. As the pre-catalyst sensor 40, for example, a so-called wide-range air-fuel ratio sensor that can continuously detect an air-fuel ratio over a relatively wide range can be used.

A post-catalyst sensor 42 that detects the air-fuel ratio of the exhaust gas flowing out from the catalyst 32 is installed on the downstream side of the catalyst 32. As the post-catalyst sensor 42, a so-called O ₂ sensor having a characteristic that the output changes suddenly at the theoretical air-fuel ratio can be used.

  The system of the present embodiment further detects an engine speed sensor 44 that detects the speed of the internal combustion engine 10, an air flow meter 46 that detects the intake air amount of the internal combustion engine 10, and an accelerator pedal position of the driver's seat of the vehicle. An accelerator position sensor 48 and an ECU (Electronic Control Unit) 50 are provided. The ECU 50 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like (all not shown). The ECU 50 is electrically connected to the various sensors and actuators described above. The ECU 50 controls the opening degree of the throttle valve 22, the fuel injection amount from the fuel injector 16, the opening degree of the waste gate valve 38 and the like based on the detection values of various sensors.

  Of the control executed by the ECU 50, air-fuel ratio feedback control will be described. When the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is in the vicinity of the stoichiometric air-fuel ratio, the catalyst 32 can efficiently simultaneously purify the three components of NOx, HC, and CO. Therefore, during normal operation of the internal combustion engine 10, the ECU 50 performs air-fuel ratio feedback control so that the air-fuel ratio of the exhaust gas flowing into the catalyst 32 becomes the stoichiometric air-fuel ratio. According to the air-fuel ratio feedback control, the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is corrected by correcting the fuel injection amount from the fuel injector 16 based on the air-fuel ratio detected by the pre-catalyst sensor 40 and the post-catalyst sensor 42. Can be accurately maintained in the vicinity of the theoretical air-fuel ratio.

  Next, control of the waste gate valve 38 will be described. In the present embodiment, the opening degree of the waste gate valve 38 is controlled by the ECU 50 according to the operating conditions of the internal combustion engine 10. That is, the ECU 50 defines the relationship between the operating conditions (for example, the engine speed and the engine load) of the internal combustion engine 10 and the target opening of the waste gate valve 38 (hereinafter simply referred to as “target opening”). A waste gate valve opening degree map is stored in advance. Then, the ECU 50 controls the waste gate valve 38 such that the actual opening of the waste gate valve 38 matches the target opening calculated based on the waste gate valve opening map.

  As shown in FIG. 1, the turbine 241 is disposed on the side of the main body of the internal combustion engine 10 and at a position close to the # 2 cylinder and the # 3 cylinder. The # 2 cylinder and the # 3 cylinder are adjacent to each other and close to the turbine 241. For this reason, the length of the second exhaust manifold 28 is relatively short. Therefore, the second exhaust manifold 28 has a relatively small surface area and a relatively small amount of heat dissipation.

  On the other hand, the # 1 cylinder and the # 4 cylinder are apart from each other and are also far from the turbine 241. For this reason, the length of the first exhaust manifold 26 is longer than that of the second exhaust manifold 28. Therefore, the first exhaust manifold 26 has a larger surface area and a larger amount of heat radiation than the second exhaust manifold 28.

  Due to the difference in the heat dissipation amount as described above, the temperature of the exhaust gas flowing into the turbine 241 from the # 2 cylinder and the # 3 cylinder is higher than the temperature of the exhaust gas flowing into the turbine 241 from the # 1 cylinder and the # 4 cylinder. Also gets higher. For this reason, in the housing of the turbine 241 (hereinafter referred to as “turbine housing”), the temperature of the wall of the portion where the exhaust gas flowing in from the # 2 cylinder and the # 3 cylinder (second exhaust manifold 28) hits easily increases.

  Further, the second exhaust manifold 28 has a shorter radius of curvature than the first exhaust manifold 26 because of its shorter length. For this reason, in the 1st exhaust manifold 26, since the curve of exhaust gas flow becomes large, the flow of exhaust gas tends to be biased to the wall on one side. For this reason, the exhaust gas from the # 2 cylinder and the # 3 cylinder (second exhaust manifold 28) tends to drift even after flowing into the turbine housing. As a result, the wall of the portion that is exposed to the exhaust gas is heated particularly concentratedly.

  For this reason, in the turbine housing, the temperature of the wall where the exhaust gas from the # 2 and # 3 cylinders hits is particularly likely to rise. If the temperature of this portion rises excessively during high-rotation and high-load operation where the exhaust gas temperature becomes high, the turbine housing may be damaged.

  Therefore, in this embodiment, when the temperature of the wall of the turbine housing in the portion where the exhaust gas from the # 2 cylinder and the # 3 cylinder hits may increase excessively, the air-fuel ratio of the # 2 cylinder and the # 3 cylinder Was corrected to be richer than the stoichiometric air-fuel ratio. If the air-fuel ratio of the # 2 and # 3 cylinders is made richer than the stoichiometric air-fuel ratio, the exhaust gas temperatures of the # 2 and # 3 cylinders can be lowered by the heat of vaporization of the injected fuel. For this reason, it is possible to suppress an increase in the temperature of the wall of the turbine housing where the exhaust gas from the # 2 cylinder and the # 3 cylinder hits (hereinafter simply referred to as “turbine housing temperature”). It can be surely protected.

  In addition, fuel can be saved by making the air-fuel ratio of only the # 2 and # 3 cylinders richer than the stoichiometric air-fuel ratio, rather than making the air-fuel ratio of all cylinders uniformly richer than the stoichiometric air-fuel ratio. , Fuel economy can be improved.

  Further, in this embodiment, when the air-fuel ratio of the # 2 cylinder and # 3 cylinder is made richer than the stoichiometric air-fuel ratio, the air-fuel ratio of the # 1 cylinder and # 4 cylinder is corrected to be leaner than the stoichiometric air-fuel ratio at the same time. It was decided to. Thereby, fuel can be further saved and fuel consumption can be further improved. Further, the rich air-fuel ratio exhaust gas discharged from the # 2 cylinder and the # 3 cylinder and the lean air-fuel ratio exhaust gas discharged from the # 1 cylinder and the # 4 cylinder are mixed to flow into the catalyst 32. The air-fuel ratio of the exhaust gas can be maintained near the stoichiometric air-fuel ratio. Thereby, the reduction of the purification rate in the catalyst 32 can be avoided, and the deterioration of the emission can be prevented.

  As the air-fuel ratio becomes richer, the amount of heat taken away by fuel vaporization increases, so the temperature of the exhaust gas decreases. For this reason, as the air-fuel ratio of the # 2 cylinder and the # 3 cylinder becomes richer, the temperature of the exhaust gas flowing into the turbine 241 from the # 2 cylinder and the # 3 cylinder further decreases, and the turbine housing temperature also decreases. However, as the air-fuel ratios of the # 2 cylinder and # 3 cylinder become richer, the fuel consumption deteriorates. For this reason, from the viewpoint of improving fuel efficiency, there is a desire to reduce the richness of the air-fuel ratio of the # 2 cylinder and # 3 cylinder as much as possible as long as the turbine housing temperature can be suppressed to an allowable temperature or less.

  Therefore, in the present embodiment, a map for calculating the rich degree of the # 2 cylinder and the # 3 cylinder necessary for setting the turbine housing temperature to the allowable temperature or less according to the engine speed and the engine load (hereinafter, “ (Referred to as “rich degree map”) is stored in the ECU 50 in advance, and the appropriate rich degree of the # 2 cylinder and the # 3 cylinder is calculated based on the rich degree map.

  On the other hand, the degree of richness of the # 2 cylinder and # 3 cylinder, which is necessary for setting the turbine housing temperature below the allowable temperature, also varies depending on the opening degree of the waste gate valve 38. The reason will be described below.

  When the waste gate valve 38 is open, a part of the exhaust gas discharged from the # 2 cylinder and the # 3 cylinder does not flow into the turbine 241 but passes through the waste gate 36 and is exhausted downstream of the turbine 241. It flows to the passage 30. Accordingly, the amount of exhaust gas flowing into the turbine 241 from the # 2 cylinder and the # 3 cylinder is reduced by the amount of exhaust gas passing through the waste gate 36 as compared to when the waste gate valve 38 is closed. For this reason, when the waste gate valve 38 is open, the amount of increase in the turbine housing temperature is smaller than when the waste gate valve 38 is closed.

  Further, as the opening degree of the waste gate valve 38 increases, the amount of exhaust gas passing through the waste gate 36 also increases. For this reason, when other conditions are the same, the amount of increase in the turbine housing temperature decreases as the opening degree of the waste gate valve 38 increases. Therefore, the degree of richness of the # 2 cylinder and # 3 cylinder necessary for setting the turbine housing temperature below the allowable temperature is smaller as the opening degree of the waste gate valve 38 is larger.

  In the present embodiment, the rich degree map is created in consideration of the effect of the opening degree of the waste gate valve 38 as described above on the turbine housing temperature. When the internal combustion engine 10 is in a steady operation state, it is considered that the actual opening of the waste gate valve 38 is usually coincident with a target opening determined from the engine speed and the engine load. For this reason, when the rich degree map is created, an optimal rich degree under a state where the actual opening degree of the waste gate valve 38 coincides with the target opening degree may be calculated.

  However, the actual opening of the waste gate valve 38 does not always coincide with the target opening. For example, when a situation occurs in which the necessary air amount cannot be ensured with the waste gate valve 38 controlled to the target opening, the actual opening of the waste gate valve 38 is corrected to be closer to the target opening. In some cases, the control for securing the required air amount is executed by increasing the supercharging pressure. In addition, when the internal combustion engine 10 is in a transient operation state, the actual opening of the waste gate valve 38 cannot follow the target opening, and there may be a deviation between the two. Therefore, in the present embodiment, when the actual opening degree of the waste gate valve 38 does not coincide with the target opening degree, the rich degree calculated based on the rich degree map is corrected.

[Specific Processing in Embodiment 1]
FIG. 2 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. According to the routine shown in FIG. 2, first, based on the current engine speed and engine load, the lean degree of the # 1 cylinder and # 4 cylinder is calculated based on the map shown in FIG. 3 (step 100). .

  FIG. 3 is a diagram showing a map stored in advance in the ECU 50 in order to calculate the lean degree and the rich degree. In the present embodiment, both the lean degree of the # 1 and # 4 cylinders and the rich degree of the # 2 and # 3 cylinders are calculated as the same value according to the common map shown in FIG. That is, the map shown in FIG. 3 corresponds to the rich degree map described above.

  According to the map shown in FIG. 3, the lean degree and the rich degree are calculated as values larger than 1 in the high rotation high load region, that is, the region where the exhaust gas temperature is high. On the other hand, the lean degree and the rich degree are calculated as 1 in a region other than the high rotation high load region (a region where the exhaust temperature is not high).

  The fuel injection amounts from the fuel injectors 16 of the # 1 cylinder and # 4 cylinder are controlled to be a value obtained by dividing the basic injection amount by the lean degree. The basic injection amount is a value calculated based on the engine speed and the intake air amount detected by the air flow meter 46 so that the air-fuel ratio matches the stoichiometric air-fuel ratio. When the lean degree is 1, the fuel injection amounts from the fuel injectors 16 of the # 1 cylinder and the # 4 cylinder are equal to the basic injection amount. Therefore, in this case, the air-fuel ratio of the # 1 cylinder and # 4 cylinder is the stoichiometric air-fuel ratio. On the other hand, when the lean degree is larger than 1, the fuel injection amounts from the fuel injectors 16 of the # 1 cylinder and # 4 cylinder are smaller than the basic injection amount. Therefore, in this case, the air-fuel ratios of the # 1 cylinder and # 4 cylinder are leaner than the stoichiometric air-fuel ratio.

  On the other hand, the fuel injection amounts from the fuel injectors 16 of the # 2 cylinder and the # 3 cylinder are controlled to be a value obtained by multiplying the basic injection amount by the rich degree. When the rich degree is 1, the fuel injection amounts from the fuel injectors 16 of the # 2 cylinder and the # 3 cylinder are equal to the basic injection amount. Therefore, in this case, the air-fuel ratio of the # 2 cylinder and # 3 cylinder is the stoichiometric air-fuel ratio. On the other hand, when the rich degree is larger than 1, the fuel injection amounts from the fuel injectors 16 of the # 2 cylinder and the # 3 cylinder are larger than the basic injection amount. Therefore, in this case, the air-fuel ratios of the # 2 cylinder and # 3 cylinder are richer than the stoichiometric air-fuel ratio.

  Since the exhaust gas temperature is not high in a region other than the high rotation high load region, there is no possibility that the turbine housing temperature exceeds the allowable temperature. Therefore, it is not necessary to enrich the air-fuel ratio of the # 2 cylinder and the # 3 cylinder. Therefore, in the region other than the high rotation / high load region, as described above, the lean degree and the rich degree are calculated as 1 by the map shown in FIG. As a result, the air-fuel ratios of all cylinders # 1 to # 4 are controlled to the stoichiometric air-fuel ratio.

  On the other hand, in the high rotation and high load region, the lean degree and the rich degree are calculated as values larger than one. In this case, as shown in the map shown in FIG. 3, the lean degree and the rich degree are calculated to be larger as the rotation speed is higher and the load is higher. The exhaust temperature becomes higher as the speed becomes higher, and becomes higher as the load becomes higher. The trend of turbine housing temperature is similar to this. That is, according to this embodiment, the air-fuel ratio of the # 2 cylinder and the # 3 cylinder is controlled to be richer as the turbine housing temperature becomes higher. For this reason, the rise in the temperature of the exhaust gas from the # 2 cylinder and the # 3 cylinder can be sufficiently suppressed. That is, the richness of the # 2 cylinder and the # 3 cylinder can be set to a necessary and sufficient value according to the ease with which the turbine housing temperature rises. Therefore, the deterioration of fuel consumption can be minimized while reliably preventing the turbine housing temperature from exceeding the allowable temperature.

  Returning to the routine shown in FIG. 2, when the lean degree is calculated in step 100, it is next determined whether or not the calculated lean degree is 1 (step 102). As described above, the lean degree is 1 when the turbine housing temperature does not exceed the allowable temperature and the air-fuel ratios of all cylinders # 1 to # 4 are controlled to the stoichiometric air-fuel ratio. In this case, it is not necessary to execute the following processing of this routine. Therefore, when it is determined in step 102 that the lean degree is 1, the process of this routine is terminated here.

  On the other hand, if it is determined in step 102 that the lean degree is not 1, then the rich degree of the # 2 cylinder and the # 3 cylinder is calculated based on the map shown in FIG. 3 (step 104). . In the present embodiment, as described above, the rich degree is the same value as the lean degree. For this reason, the process of step 104 may be omitted.

  In this embodiment, as the richness of the # 2 and # 3 cylinders increases, the leanness of the # 1 and # 4 cylinders also increases. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 32 (that is, the mixture of exhaust gases of all cylinders) is made close to the stoichiometric air-fuel ratio regardless of the richness of the # 2 and # 3 cylinders. It can be maintained with high accuracy. Thereby, the reduction of the purification rate in the catalyst 32 can be avoided, and the deterioration of the emission can be prevented.

  Subsequent to the process of step 104, the deviation between the actual opening of the waste gate valve 38 detected by the opening sensor 39 and the target opening calculated based on the waste gate valve opening map is a predetermined value. It is determined whether or not the following is true (step 106).

  If an affirmative determination is made in step 106, it can be determined that the actual opening of the waste gate valve 38 substantially matches the target opening. In this case, if the fuel injection amounts of the # 2 cylinder and # 3 cylinder are corrected using the rich degree calculated based on the map shown in FIG. 3 as it is, the richness of the air-fuel ratio of the # 2 cylinder and # 3 cylinder is corrected. The degree can be controlled to an optimum value (that is, a value necessary and sufficient to keep the turbine housing temperature below the allowable temperature). In such a case, it is not necessary to execute the following processing of this routine. Therefore, if an affirmative determination is made in step 106, the processing of this routine is terminated here.

  On the other hand, if a negative determination is made in step 106, it can be determined that a deviation has occurred between the actual opening of the waste gate valve 38 and the target opening. In this case, the following processing is executed to correct the richness and leanness calculated based on the map shown in FIG. 3 to more appropriate values.

  First, the turbine housing temperature deviation resulting from the deviation between the actual opening of the waste gate valve 38 and the target opening is calculated as follows (step 108). FIG. 4 is a diagram showing a map stored in advance in the ECU 50 in order to calculate the estimated value of the turbine housing temperature. The map shown in FIG. 4 is for calculating an estimated value of the turbine housing temperature based on the intake air amount and the opening degree of the waste gate valve 38. As the intake air amount increases, the exhaust gas amount also increases. For this reason, as the intake air amount increases, the turbine housing temperature increases. Further, as described above, the turbine housing temperature decreases as the opening degree of the waste gate valve 38 increases. Corresponding to these, in the map shown in FIG. 4, the larger the intake air amount, the higher the estimated value of the turbine housing temperature, and the larger the opening degree of the waste gate valve 38, the greater the turbine. The estimated housing temperature is calculated to a low value.

In the above step 108, the turbine housing temperature deviation is estimated as the turbine housing temperature estimated value when the waste gate valve 38 has the current actual opening, and the turbine housing temperature estimation when the waste gate valve 38 has the current target opening. Calculated as the difference from the value. For example, in FIG. 4, if the current actual opening of the waste gate valve 38 is point A and the target opening is point B, the estimated turbine housing temperature TA at point _A and the point _A difference (T _A −T _B ) from the estimated turbine housing temperature TB in _B is calculated as a turbine housing temperature deviation. In this example, since the actual opening of the waste gate valve 38 is smaller than the target opening, T _A > T _B. Accordingly, the turbine housing temperature deviation (T _A -T _B) is a positive value. When the turbine housing temperature deviation is a positive value, it can be determined that the current turbine housing temperature is higher than the intended turbine housing temperature. Conversely, when the turbine housing temperature deviation is a negative value, it can be determined that the current turbine housing temperature is lower than the intended turbine housing temperature.

  Subsequent to the process of step 108, a correction value for correcting the rich degree and the lean degree is calculated (step 110). FIG. 5 is a diagram showing a map stored in advance in the ECU 50 in order to calculate the correction value. According to the map shown in FIG. 5, the correction value for correcting the rich degree and the lean degree is calculated as a value proportional to the turbine housing temperature deviation calculated in step 110.

  Next, a process of correcting the lean degree of the # 1 cylinder and the # 4 cylinder is executed using the correction value calculated in step 108 (step 112). Specifically, a value obtained by adding the correction value calculated in step 108 to the lean degree calculated in step 100 is calculated as the corrected lean degree.

  Subsequently, a process for correcting the rich degree of the # 2 cylinder and the # 3 cylinder is executed (step 114). Specifically, a value obtained by adding the correction value calculated in step 108 to the rich degree calculated in step 104 is calculated as the corrected rich degree.

  According to the processing of the routine shown in FIG. 2 described above, when the turbine housing temperature deviation is a positive value, the correction value in step 108 is also a positive value. It is corrected in the increasing direction. As described above, when the turbine housing temperature deviation is a positive value, it can be determined that the current turbine housing temperature is higher than the intended turbine housing temperature. In such a case, according to the routine processing of FIG. 2, the temperature of exhaust gas from the # 2 cylinder and the # 3 cylinder is further increased by correcting the rich degree of the # 2 cylinder and the # 3 cylinder in the increasing direction. Can be reduced. For this reason, it can prevent more reliably that turbine housing temperature exceeds permissible temperature.

  Conversely, when the turbine housing temperature deviation is a negative value, the correction value in step 108 is also a negative value, so the richness of the # 2 and # 3 cylinders is corrected in the decreasing direction. As described above, when the turbine housing temperature deviation is a negative value, it can be determined that the current turbine housing temperature is lower than the intended turbine housing temperature. In such a case, even if the richness of the # 2 cylinder and # 3 cylinder is reduced, it can be determined that there is no possibility that the turbine housing temperature exceeds the allowable temperature. In such a case, according to the routine processing of FIG. 2, by correcting the rich degree of the # 2 cylinder and the # 3 cylinder in the decreasing direction, the fuel can be further saved and the fuel consumption can be further improved.

  In the first embodiment described above, in the region where the exhaust temperature is high, the air-fuel ratios of both the # 2 cylinder and the # 3 cylinder are made rich, and the air-fuel ratios of both the # 1 cylinder and the # 4 cylinder are made lean. However, in the present invention, the air-fuel ratio of either the # 2 cylinder or the # 3 cylinder may be made rich, and the air-fuel ratio of either the # 1 cylinder or the # 4 cylinder may be made lean. Even in this case, the same effect can be obtained.

  Further, in the first embodiment described above, the # 1 cylinder and the # 4 cylinder are the “first cylinder group” in the first invention, and the first exhaust manifold 26 is the “first cylinder” in the first invention. In the “exhaust passage”, the # 2 cylinder and the # 3 cylinder are in the “second cylinder group” in the first invention, and the second exhaust manifold 28 is in the “second exhaust passage” in the first invention. It corresponds. Further, the ECU 50 calculates the rich degree and the lean degree as values larger than 1 based on the map shown in FIG. 3 in the high exhaust gas temperature region, so that the “determination means” in the first aspect of the invention becomes the routine shown in FIG. The “air-fuel ratio correction means” in the first to third aspects of the present invention is realized by correcting the fuel injection amount of each cylinder based on the rich degree and the lean degree calculated based on each of them.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a map for calculating a lean degree and a rich degree. It is a map for calculating the estimated value of turbine housing temperature. It is a map for calculating a correction value for correcting the rich degree and the lean degree.

Explanation of symbols

Reference Signs List 10 internal combustion engine 12 intake valve 14 exhaust valve 16 fuel injector 18 intake manifold 20 intake passage 22 throttle valve 24 turbocharger 241 turbine 242 compressor 26 first exhaust manifold 28 second exhaust manifold 30 exhaust passage 32 catalyst 34, 36 waste gate 38 waste Gate valve 39 Opening sensor 40 Pre-catalyst sensor 42 Post-catalyst sensor 44 Engine speed sensor 46 Air flow meter 48 Accelerator position sensor 50 ECU

Claims (3)

A turbocharger with a turbine having two inlets;
A first exhaust passage through which exhaust gas of a first cylinder group of an internal combustion engine having a plurality of cylinders flows into one inlet of the turbine;
A second exhaust passage for causing exhaust gas of a second cylinder group of the internal combustion engine to flow into the other inlet of the turbine and having a surface area smaller than that of the first exhaust passage;
Determining means for determining whether or not the operating condition of the internal combustion engine is in a high exhaust temperature region;
Air-fuel ratio correction means for correcting the air-fuel ratio of at least one cylinder of the second cylinder group to be richer than the stoichiometric air-fuel ratio when it is determined that the operating condition is in the high exhaust temperature region. When,
A control device for an internal combustion engine, comprising: A waste gate that bypasses the turbine and passes exhaust gas;
A wastegate valve for opening and closing the wastegate;
With
2. The control apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio correcting means includes means for correcting the richness of the air-fuel ratio of the cylinder to be corrected according to the opening degree of the waste gate valve.   The air-fuel ratio correction means is configured to make the air-fuel ratio of at least one cylinder of the first cylinder group leaner than the stoichiometric air-fuel ratio when it is determined that the operating condition is in the high exhaust temperature region. The control device for an internal combustion engine according to claim 1 or 2, further comprising means for correcting

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