JP2007177656A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable low NOx combustion equivalent to very lean combustion in a first cylinder group equipped with a supercharger even in a second cylinder group not equipped with the supercharger in an internal combustion engine having two cylinder groups (a first cylinder group and a second cylinder group) whose suction passages are mutually independent, and equipped with a supercharger disposed only in a suction passage of the first cylinder group, and driven by the exhaust gas from the first cylinder group. <P>SOLUTION: The exhaust gas is extracted from upstream side of the supercharger 20 in the exhaust passage 12 of the first cylinder group 2, and fed into the second cylinder group 32. Preferably the upstream side in the supercharger 20 of the exhaust passage 12 of the first cylinder group 2 and the combustion chambers of each cylinder of the second cylinder group 32 is directly communicated via a communication pipe 60. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an internal combustion engine, and in particular, has two cylinder groups in which intake passages are independent from each other, and is a supercharger that is driven only by an intake passage of one cylinder group by exhaust gas from the cylinder group. The present invention relates to an internal combustion engine in which (turbocharger) is arranged.

2. Description of the Related Art Conventionally, as disclosed in Patent Document 1, for example, an internal combustion engine equipped with a turbocharger is provided with an EGR device that recirculates part of exhaust gas from an exhaust passage to an intake passage. In the prior art disclosed in Patent Document 1, exhaust gas extraction ports from the exhaust passage are provided on the upstream side and the downstream side of the turbine, respectively, and in synchronization with the switching of the fuel injection mode that suddenly changes the intake pipe pressure. The exhaust gas outlet is switched.
JP 2002-188522 A Japanese Patent Laid-Open No. 5-86949 Japanese Examined Patent Publication No. 7-122409 Japanese Patent Publication No. 1-227246

  By the way, as a measure for preventing deterioration of exhaust emission at the time of cold start, apart from a normal catalyst having a sufficient capacity, a small catalyst (catalyst for start-up) that is easily warmed is disposed in the vicinity of the internal combustion engine. It is known. However, in the case of an internal combustion engine with a turbocharger, the start-up catalyst is arranged downstream of the turbine of the turbocharger, so that the heat of the exhaust gas is taken away by the turbine, and accordingly the start-up catalyst Takes time to activate.

  Therefore, in an internal combustion engine having two cylinder groups, it has been proposed that each cylinder group has an independent intake passage, only one cylinder group is equipped with a turbocharger, and the other cylinder group is a natural intake. Yes. In this case, a start-up catalyst is disposed in each of the exhaust passages of each cylinder group, and ordinary catalysts such as a three-way catalyst and a NOx catalyst are disposed on the downstream side of the joining portion where the exhaust passages of each cylinder group merge. The In the exhaust passage of the turbocharged cylinder group (supercharged cylinder group), the start-up catalyst is arranged downstream of the turbine, but in the exhaust passage of the naturally aspirated cylinder group (NA cylinder group), The catalyst for use is arranged close to the internal combustion engine. Therefore, the start-up catalyst of the NA cylinder group can be activated earlier than that of the supercharged cylinder group, and during cold start, the operation of the NA cylinder group is given priority to the start-up catalyst of the NA cylinder group. By flowing the exhaust gas, it is possible to prevent the exhaust emission from deteriorating during cold start.

  However, in the internal combustion engine having the supercharged cylinder group and the NA cylinder group as described above, a new problem arises during lean operation for NOx reduction. In other words, in the supercharged cylinder group, lean combustion (strong lean combustion) at an extremely high air-fuel ratio can be realized by supercharging the intake air, whereas in the NA cylinder group, the torque difference from the supercharged cylinder group is reduced. Considering it, it is difficult to perform strong lean combustion like a supercharged cylinder group. In order to prevent deterioration of exhaust emissions while improving fuel efficiency, when performing strong lean combustion, which is low NOx combustion in the supercharged cylinder group, low NOx combustion equivalent to that of the supercharged cylinder group is realized even in the NA cylinder group Is required.

  The present invention has been made to solve the above-described problems, and has two cylinder groups in which the intake passages are independent from each other, and only the intake passage of one cylinder group is provided from the cylinder group. In an internal combustion engine in which a supercharger driven by exhaust gas is arranged, even in a cylinder group without a supercharger, low NOx combustion equivalent to strong lean combustion in a cylinder group with a supercharger can be realized The purpose is to do.

In order to achieve the above object, the first invention provides
The intake passage includes a first cylinder group and a second cylinder group that are independent of each other, and a supercharger that is driven by exhaust gas from the first cylinder group is disposed in the intake passage of the first cylinder group In an internal combustion engine that is
An exhaust gas supply device is provided that extracts exhaust gas from the upstream side of the supercharger in the exhaust passage of the first cylinder group and supplies the exhaust gas to the second cylinder group.

According to a second invention, in the first invention,
The exhaust gas supply device includes a communication pipe that directly communicates an upstream side of the supercharger in the exhaust passage of the first cylinder group and a combustion chamber of each cylinder of the second cylinder group.

According to a third invention, in the second invention,
The exhaust gas supply device includes a valve for adjusting a flow rate of the exhaust gas flowing through the communication pipe.

According to a fourth invention, in the third invention,
The exhaust gas supply device includes a sensor that outputs a signal corresponding to the flow rate or pressure of the exhaust gas flowing through the communication pipe, and controls the valve based on the signal of the sensor.

A fifth invention is the third or fourth invention, wherein
The exhaust gas supply device is characterized in that the valve is closed when an intake pipe pressure or an air flow rate of the second cylinder group is a predetermined value or less.

A sixth invention is the third or fourth invention, wherein
The exhaust gas supply device controls a gas fuel ratio of the second cylinder group by adjusting an exhaust gas flow rate by the valve when an intake pipe pressure or an air flow rate of the second cylinder group is a predetermined value or more. It is said.

A seventh invention is the sixth invention, wherein
The exhaust gas supply device controls a gas fuel ratio of the second cylinder group by adjusting an exhaust gas flow rate by the valve in a state where a throttle disposed in an intake passage of the second cylinder group is fixed. It is said.

  According to the first aspect of the present invention, the amount obtained by the normal naturally aspirated internal combustion engine in the second cylinder group that is naturally aspirated by the recirculation of the exhaust gas using the high back pressure upstream of the supercharger of the first cylinder group. The above exhaust gas (EGR gas) can be supplied. As a result, in the second cylinder group, it is possible to ensure an in-cylinder gas amount equivalent to that of the first cylinder group equipped with the supercharger due to high EGR while being weak lean, and strong lean combustion in the first cylinder group Can achieve low NOx combustion equivalent to the above. Further, by taking out the exhaust gas from the upstream side of the supercharger, there is also an effect that the contamination of the supercharger due to the exhaust gas can be reduced.

  According to the second invention, the high-pressure exhaust gas taken out from the upstream side of the supercharger of the first cylinder group is directly supplied into the combustion chamber, so that the recirculated exhaust gas can easily flow back through the intake passage. Can be prevented.

  According to the third aspect, the supply amount of the exhaust gas to the second cylinder group can be easily controlled by adjusting the opening of the valve.

  According to the fourth invention, it is possible to accurately control the amount of exhaust gas supplied to the second cylinder group by measuring the flow rate or pressure of the exhaust gas flowing through the communication pipe.

  According to the fifth invention, the cylinder is closed by closing the valve and stopping the supply of the exhaust gas to the second cylinder group at the time of relatively low load operation in which the intake pipe pressure or the air flow rate becomes a predetermined value or less. The specific heat ratio of the internal gas can be ensured to prevent fuel consumption from deteriorating.

  According to the sixth aspect of the invention, during a relatively high load operation where the intake pipe pressure or the air flow rate exceeds a predetermined value, the gas fuel ratio of the second cylinder group (ratio of in-cylinder gas amount to fuel) is obtained by operating the valve. It becomes possible to lean to the combustion limit by actively controlling.

  According to the seventh aspect of the present invention, it is possible to more accurately control the gas fuel ratio of the second cylinder group by fixing the throttle and simplifying the control target.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic configuration diagram of an internal combustion engine (hereinafter referred to as an engine) as an embodiment of the present invention. In the present embodiment, the present invention is applied to a V-type six-cylinder spark ignition direct injection engine (for example, a direct injection gasoline engine).

  As shown in FIG. 1, the engine of this embodiment includes two banks 2 and 32 each having three cylinders. Here, the left bank 2 in FIG. 1 is called the L bank, and the right bank 32 is called the R bank. Although not shown in the figure, a spark plug is provided for each cylinder in each of the banks 2 and 32, and an in-cylinder injector is provided for each cylinder. The in-cylinder injector is supplied with high-pressure fuel pressurized by a high-pressure pump. The engine of the present embodiment can realize stratified combustion by compression stroke injection by an in-cylinder injector, and can thereby be operated at an air-fuel ratio leaner than the stoichiometric air-fuel ratio.

  The L bank 2 and the R bank 32 include intake passages 4 and 34 that are independent of each other. An air cleaner 6, an air flow meter 8, a compressor 20 a of a turbocharger (supercharger) 20, an intercooler 24, and a throttle valve 10 are provided in the intake passage 4 of the L bank 2 from the upstream side. The turbine 20 b of the turbocharger 20 is provided in the exhaust passage 12 of the L bank 2 and is driven only by the exhaust gas from the L bank 2. That is, the L bank 2 is configured as a turbo (supercharged) engine that supercharges intake air by the turbocharger 20.

  On the other hand, an air cleaner 36, an air flow meter 38, and a throttle valve 40 are provided in the intake passage 34 of the R bank 32 from the upstream side. That is, unlike the L bank 2, the R bank 32 is configured as a naturally aspirated (NA) engine that does not include a supercharger. Therefore, in the present embodiment, the cylinder group configuring the L bank 2 corresponds to the “first cylinder group” according to the present invention, and the cylinder group configuring the R bank 32 is the “second cylinder group” according to the present invention. It corresponds to.

  Small start-up catalysts 14 and 44 are arranged in the exhaust passages 12 and 42 of the banks 2 and 34, respectively. However, in the exhaust passage 44 of the R bank 32, the starting catalyst 44 is disposed close to the R bank 32, whereas in the exhaust passage 4 of the L bank 2, the starting catalyst 14 is connected to the turbine 20b. It is arranged on the downstream side. The exhaust passage 4 of the L bank 2 is also provided with a waste gate 22 that bypasses the turbine 20b. The exhaust passages 12, 42 of the banks 2, 34 gather downstream of the start-up catalysts 14, 44 to form one exhaust passage 50. The collective exhaust passage 50 is provided with a three-way catalyst 52 and a NOx catalyst 54 having sufficient capacity. These catalysts 52 and 54 are disposed, for example, under the floor of the vehicle.

  Further, the engine of the present embodiment includes an EGR pipe 60 that branches from the upstream side of the turbine 20b in the exhaust passage 4 of the L bank 2. The EGR pipe 60 extends to the R bank 2, and although not shown in the drawing, the EGR pipe 60 branches into branch pipes for each cylinder, and each branch pipe is directly connected to the combustion chamber. That is, the EGR pipe 60 communicates the turbine 20b upstream in the exhaust passage 4 of the L bank 2 and each combustion chamber of the R bank 32. Each branch pipe of the EGR pipe 60 is provided with an EGR valve 64 and an air flow meter 62, respectively. In the figure, only one branch pipe and the EGR valve 64 and the air flow meter 62 arranged there are shown. The EGR valve 64 is a valve for adjusting the amount of EGR gas supplied into the combustion chamber, and the amount of EGR gas can be measured by the air flow meter 62.

  According to the configuration shown in FIG. 1, the exhaust gas before passing through the turbine 20b discharged from the L bank 2 can be introduced into the R bank 32 as EGR gas. This EGR gas is a combustion gas of supercharged air by the turbocharger 20 and is taken out from the exhaust passage 12 before being depressurized after passing through the turbine 20b, and thus has an extremely high pressure. By introducing this high-pressure EGR gas into the R bank 32, it is possible to achieve high gas charging efficiency in the R bank 32 that is an NA engine as well as the L bank 2 that is a supercharged engine.

  The EGR gas introduced from the L bank 2 is higher in pressure than the air sucked through the intake passage 34. Therefore, if the EGR gas is introduced into the intake passage 34 like the normal EGR, the EGR gas is introduced into the intake passage 34. 34 will flow back to the atmosphere side. However, according to the above configuration, the high-pressure EGR gas can be directly introduced into the combustion chamber. Further, in each cylinder of the R bank 32, when both the intake valve and the exhaust valve are closed, the cylinder By opening the EGR valve 64 corresponding to the EGR gas, it is possible to prevent the EGR gas from flowing backward from the combustion chamber to the intake passage 34.

  In the engine of this embodiment, introduction of EGR gas from the L bank 2 to the R bank 32 is used during the lean operation. In the L bank 2, which is a supercharged engine, the air charging efficiency can be increased by supercharging by the turbocharger 20, thereby performing strong lean combustion (lean combustion at an extremely high air-fuel ratio) without reducing the torque. Can be realized. On the other hand, in the R bank 32 that is an NA engine, in order to achieve a high air-fuel ratio only with air (new gas) sucked from the intake passage 34, the fuel injection amount must be significantly reduced, and stable combustion is achieved. Difficult to maintain. However, by introducing high-pressure EGR gas as described above, the amount of air relative to the fuel injection amount is small, but the introduction of a large amount of EGR gas increases the amount of the entire cylinder gas relative to the fuel injection amount. Can do. Thus, by setting it as high EGR, although it is weak lean, combustion by a high gas fuel ratio is realizable, without causing a torque fall.

  As described above, according to the engine of the present embodiment, extremely high gas fuel is obtained by supercharging intake air by the turbocharger 20 in the L bank 2 and by introducing high-pressure EGR gas from the L bank 2 in the R bank 32. Combustion at a ratio can be achieved. According to the combustion with such a high gas fuel ratio, the amount of NOx generated can be suppressed while improving the fuel efficiency. Further, according to the engine of the present embodiment, the exhaust gas is taken out from the upstream side of the turbine 20b, thereby reducing the amount of exhaust gas flowing to the turbine 20b and reducing the contamination of the turbine 20b by the exhaust gas. There is also an effect.

  Next, the control during the lean operation performed in the engine of the present embodiment will be specifically described with reference to FIG. FIG. 2 is a flowchart showing a control routine during lean operation which is executed by the engine control device (not shown in FIG. 1) in the present embodiment.

  In the first step S100 of the routine shown in FIG. 2, it is determined whether or not the engine operating point determined from the engine speed and torque is in the lean region. FIG. 3 is a map showing the relationship between the engine speed and torque and the operating range. As shown in FIG. 3, the engine operating region is divided into a first lean region, a second lean region, and a stoichiometric region in order from the low torque side. Both the first lean region and the second lean region are operation regions in which operation is performed at a lean air-fuel ratio, and the stoichiometric region is an operation region in which operation is performed at a stoichiometric air-fuel ratio. The first lean region on the low torque side is an operating region in which the intake pipe pressure of the R bank 32 (pressure downstream of the throttle 40 in the intake passage 34) is negative, and the second lean region on the high torque side is R This is an operation region (or an operation region at the time of WOT) in which the intake pipe pressure of the bank 32 becomes atmospheric pressure. If the engine operating point is in the first lean region or the second lean region, the determination result in step S100 is Yes and the processing in the next step S102 is executed.

  In step S102, an air-fuel ratio instruction value (A / F instruction value) is read from the map. Then, A / F control is performed in each bank 2 and 32 in accordance with the A / F instruction value. This A / F control is different depending on whether the engine operating point is in the first lean region or the second lean region. 4 is a diagram showing A / F control when the engine operating point is in the first lean region, and FIG. 5 is a diagram showing A / F control when the engine operating point is in the second lean region. FIG.

  When the engine operating point is in the first lean region, as shown in FIG. 4, the A / F is controlled by the opening degree of the throttles 10 and 40 in both the L bank 2 and the R bank 32. In this case, the EGR valve 64 is completely closed, and the introduction of EGR gas from the L bank 2 to the R bank 32 is not performed. Since the first lean region is a low torque region, the amount of air necessary for realizing the A / F instruction value is relatively small, and the A / F according to the instruction value can be realized only by controlling the intake air amount by the throttle 40. Because. In addition, when it is not necessary in this way, by stopping the introduction of EGR gas, it is possible to secure the specific heat ratio of the in-cylinder gas and prevent deterioration of fuel consumption.

  When the engine operating point is in the second lean region, as shown in FIG. 5, the A / F is controlled by the opening degree of the throttle 10 for the L bank 2 as in the first lean region. On the other hand, for the R bank 32, G / F is controlled by the opening degree of the EGR valve 64. G / F is a ratio (gas fuel ratio) between the total amount of in-cylinder gas obtained by adding EGR gas to new gas and the amount of fuel. The new gas amount can be measured by the air flow meter 38 in the intake passage 34, and the EGR gas amount can be measured by the air flow meter 62 in the EGR pipe 60. Since the second lean region is a high torque region, there is a limit to the A / F that can be realized by controlling the intake air amount by the throttle 40. Therefore, for the R bank 32, the G / F instruction value is set instead of the A / F instruction value, and the EGR valve 64 is controlled so as to realize the G / F according to the instruction value. At that time, the throttle 40 is fixed fully open so that the amount of intake air becomes maximum. By fixing the throttle 40, the control target can be simplified, and the G / F of the R bank 32 can be controlled more accurately.

  In the next step S104, the lean limit control is performed following the A / F control. In this lean limit control, when A / F or G / F as specified, the torque fluctuation has a margin with respect to the combustion limit, A / F or G / F is set until the combustion limit is reached. By further increasing the control, the control aims to further reduce NOx and improve fuel efficiency. As with the A / F control, the lean limit control is different depending on whether the engine operating point is in the first lean region or the second lean region.

  When the engine operating point is in the first lean region, as shown in FIG. 4, the opening degree of each throttle 10, 40 is controlled to increase gradually in both L bank 2 and R bank 32, and torque is increased. The A / F of each bank 2, 32 is increased until the magnitude of the fluctuation reaches the combustion limit. Also in this case, the EGR valve 64 is closed, and the EGR gas is not introduced from the L bank 2 to the R bank 32.

  When the engine operating point is in the second lean region, as shown in FIG. 5, with respect to the L bank 2, the opening degree of the throttle 10 is gradually controlled to increase, and the magnitude of torque fluctuation is combusted. The A / F is increased until the limit is reached. On the other hand, with respect to the R bank 32, the throttle 40 is kept fully open and the opening of the EGR valve 64 is gradually controlled to increase, and the G / F is increased until the magnitude of torque fluctuation reaches the combustion limit. .

  In the next step S106, it is determined whether or not the lean limit control is completed. Until the magnitude of the torque fluctuation reaches the combustion limit, the process of step S104 is repeatedly performed. When the magnitude of the torque fluctuation reaches the combustion limit, it is determined that the lean limit control has been completed, and this routine ends.

  In the present embodiment, the “exhaust gas supply device” according to the present invention is realized by the EGR device and the engine control device that executes the routine.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the present invention is applied to a spark ignition type engine, but can also be applied to a compression ignition type engine (for example, a diesel engine).

1 is a schematic configuration diagram of an internal combustion engine as an embodiment of the present invention. It is a flowchart which shows the routine of control at the time of the lean driving | running implemented in embodiment of this invention. It is a map which shows the relationship between an engine speed and torque, and a driving | running | working area | region. It is a figure explaining A / F control in case the operating point of an engine exists in the 1st lean field shown in FIG. It is a figure explaining A / F control in case the operating point of an engine exists in the 2nd lean field shown in FIG.

Explanation of symbols

2 L bank (supercharged bank)
4 Intake passage 8 Air flow meter 10 Throttle 12 Exhaust passage 14 Start-up catalyst 20 Turbocharger 20a Compressor 20b Turbine 32 R bank (NA bank)
34 Intake passage 38 Air flow meter 40 Throttle 42 Exhaust passage 44 Start-up catalyst 50 Collective exhaust passage 52 Three-way catalyst 54 NOx catalyst 60 EGR pipe 62 Air flow meter 64 EGR valve

Claims (7)

The intake passage includes a first cylinder group and a second cylinder group that are independent of each other, and a supercharger that is driven by exhaust gas from the first cylinder group is disposed in the intake passage of the first cylinder group In an internal combustion engine that is
An internal combustion engine comprising an exhaust gas supply device that extracts exhaust gas from an upstream side of the supercharger in the exhaust passage of the first cylinder group and supplies the exhaust gas to the second cylinder group.   The exhaust gas supply device includes a communication pipe that directly connects an upstream side of the supercharger in an exhaust passage of the first cylinder group and a combustion chamber of each cylinder of the second cylinder group. Item 6. An internal combustion engine according to Item 1.   The internal combustion engine according to claim 2, wherein the exhaust gas supply device includes a valve that adjusts a flow rate of the exhaust gas flowing through the communication pipe.   The exhaust gas supply device includes a sensor that outputs a signal corresponding to a flow rate or pressure of exhaust gas flowing through the communication pipe, and controls the valve based on a signal of the sensor. Internal combustion engine.   The internal combustion engine according to claim 3 or 4, wherein the exhaust gas supply device closes the valve when an intake pipe pressure or an air flow rate of the second cylinder group is equal to or less than a predetermined value.   The exhaust gas supply device controls a gas fuel ratio of the second cylinder group by adjusting an exhaust gas flow rate by the valve when an intake pipe pressure or an air flow rate of the second cylinder group is a predetermined value or more. An internal combustion engine according to claim 3 or 4. The exhaust gas supply device controls a gas fuel ratio of the second cylinder group by adjusting an exhaust gas flow rate by the valve in a state where a throttle disposed in an intake passage of the second cylinder group is fixed. The internal combustion engine according to claim 6.

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