JP2010270625A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine reducing exhaust gas temperature while suppressing deterioration of combustion. <P>SOLUTION: This internal combustion engine includes: a plurality of exhaust passages 50 respectively connected to a plurality of combustion chambers 14; a plurality of upstream EGR passages 60 respectively connected to at least two exhaust passages 50 in the plurality of exhaust passages 50; an EGR collecting portion 62 with the plurality of upstream EGR passages 60 collected; a downstream EGR passage 63 leading from the EGR collection portion 62 to the intake system of the internal combustion engine 100; and an EGR valve 66 disposed in the downstream EGR passage 63. An ECU 90 opens/closes the EGR valve according to a request to reduce the exhaust gas temperature in the exhaust passages 50. Thereby, EGR gas is introduced from one exhaust passage 50a to the other exhaust passage 50b through the upstream EGR passages 60 and EGR collecting portion 62. As a result, it is possible to reduce the exhaust gas temperature. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an internal combustion engine equipped with an exhaust gas recirculation (EGR) system.

  Conventionally, an internal combustion engine having an EGR system that recirculates a part of exhaust gas to an intake system is known. For example, there is known an internal combustion engine that can reduce the temperature of exhaust gas by increasing the amount of EGR gas introduced into the intake system and advancing the ignition timing when the temperature of the exhaust gas becomes high. (Patent Document 1).

JP 2000-257473 A

  In the above-described internal combustion engine, when a large amount of EGR gas is introduced into the intake system, fresh air may be insufficient and combustion may be deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an internal combustion engine that can reduce the temperature of exhaust gas while suppressing deterioration of combustion.

  The internal combustion engine is an internal combustion engine including an EGR (Exhaust Gas Recirculation) system, and includes a plurality of exhaust passages connected to each of the plurality of combustion chambers, and at least two exhaust passages among the plurality of exhaust passages. A plurality of upstream EGR passages branched from each of the plurality of upstream EGR passages, an EGR collection portion that aggregates the plurality of upstream EGR passages, a downstream EGR passage that leads from the EGR collection portion to the intake system of the internal combustion engine, and the downstream EGR passage And an EGR control unit that opens and closes the EGR valve in response to a request to lower the exhaust gas temperature in the exhaust passage. According to this configuration, by introducing the exhaust gas in one exhaust passage to the other exhaust passage through the upstream EGR passage and the EGR collecting portion, the temperature of the exhaust gas in the other exhaust passage can be lowered. it can. In addition, since control for increasing the amount of EGR gas introduced into the intake system is not performed, deterioration of combustion can be suppressed.

  The said structure WHEREIN: It can be set as the structure which has a cooling means to cool the said EGR gathering part. According to this configuration, the exhaust gas temperature in the exhaust passage through which the cooled exhaust gas is introduced can be further reduced.

  The said structure WHEREIN: It can be set as the structure which has a cooling control means which controls the cooling capacity of the said cooling means according to the engine load of the said internal combustion engine. According to this configuration, since the temperature of the exhaust gas can be adjusted by the cooling control means, the combustion efficiency of the internal combustion engine can be improved.

  In the above configuration, the turbocharger includes a turbine provided in an exhaust system of the internal combustion engine, and a compressor provided in an intake system of the internal combustion engine and fastened on the same shaft as the turbine, and the exhaust The distance from the branch portion between the passage and the upstream EGR passage to the EGR assembly portion may be substantially equal to the distance from the branch portion between the exhaust passage and the upstream EGR passage to the turbine. According to this configuration, the exhaust pulsation interference due to the provision of the EGR passage can be suppressed to the same extent as in the case where there is no EGR passage, so that a reduction in supercharging performance can be suppressed.

  In the above configuration, the EGR collecting portion may be configured to collect the plurality of upstream EGR passages branched from the plurality of exhaust passages connected to the plurality of combustion chambers in which the ignition order is continuous. . According to this configuration, the exhaust gas temperature can be effectively reduced by connecting the exhaust passages of the combustion chambers in which the ignition sequence is continuous via the upstream EGR passage and the EGR collecting portion.

  According to the present invention, the temperature of exhaust gas can be lowered while suppressing deterioration of combustion.

FIG. 1 is a diagram illustrating an overall configuration of the internal combustion engine according to the first embodiment. FIG. 2 is a diagram illustrating in detail the configuration of the EGR system for the internal combustion engine according to the first embodiment. FIG. 3 is a flowchart illustrating the operation of the internal combustion engine according to the first embodiment. FIGS. 4A to 4B are timing charts showing pressure changes in the exhaust system of the internal combustion engine according to the first embodiment. FIGS. 5A to 5F are views showing combinations of exhaust passages for extracting EGR gas in the internal combustion engine according to the first embodiment.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram schematically illustrating an overall structure of an engine 100 that is an internal combustion engine according to a first embodiment. The engine 100 is an in-line four-cylinder engine having four cylinders 10, but only one cylinder is shown here. A combustion chamber 14 is formed in the cylinder 10 by inserting a piston 12. An intake port 16 and an exhaust port 18 are opened in the combustion chamber 14 and are opened and closed by an intake valve 20 and an exhaust valve 22, respectively.

  A spark plug 24 is provided at the center of the combustion chamber 14, and ignition is performed according to a command from an ECU 90 (Engine Control Unit). In addition, an injector 26 is provided on the side wall of the combustion chamber 14, and fuel is directly injected into the cylinder in response to a command from the ECU 90.

  An intake passage 30 is connected to the intake port 16 of the combustion chamber 14. In the intake passage 30, an air cleaner 32, an air flow sensor 34, a compressor 36, an intercooler 38, a throttle valve 40, and a surge tank 42 are provided in this order from the upstream side. The output of the air flow sensor 34 is input to the ECU 90. The throttle valve 40 is provided with a throttle opening sensor 41 for detecting the throttle opening. The output of the throttle opening sensor 41 is input to the ECU 90, and the throttle valve 40 is controlled by a command from the ECU 90.

  An exhaust passage 50 is connected to the exhaust port 18 of the combustion chamber 14. The exhaust passage 50 is provided with a turbine 52 and a catalyst 54 in order from the upstream side. The turbine 52 is fastened by the same shaft as the compressor 36 of the intake passage 30 and forms a supercharger 56 as a whole. Further, a waste gate valve 58 controlled by the ECU 90 is provided on the upstream side of the turbine 52 so that the amount of exhaust gas flowing into the turbine 52 can be adjusted. The catalyst 54 is a mechanism for purifying harmful substances such as NOx contained in the exhaust gas. The catalyst 54 is provided with a catalyst temperature sensor 55, and the detected temperature is input to the ECU 90.

  An upstream EGR passage 60 for recirculating a part of the exhaust gas to the intake system branches from the middle of the exhaust passage 50. The upstream EGR passage 60 is connected to at least two exhaust passages 50 among the plurality of exhaust passages 50 connected to each of the plurality of combustion chambers 14. As will be described later, in this embodiment, the upstream EGR passages 60a and 60b are connected to the two exhaust passages 50a and 50b among the four exhaust passages 50a to 50d.

  Connected to the upstream EGR passage 60 is an EGR collecting pipe 62 as an EGR gas collecting portion for collecting a plurality of upstream EGR passages 60. In the present embodiment, two upstream EGR passages 60 a and 60 b are connected to the EGR collecting pipe 62. Thus, the exhaust gas in the first exhaust passage 50a can be introduced into the second exhaust passage 50b through the upstream EGR passage 60a, the EGR collecting pipe 62, and the upstream EGR passage 60b. Similarly, the exhaust gas in the second exhaust passage 50b can be introduced into the first exhaust passage 50a.

  A downstream EGR passage 63 is connected to the EGR collecting pipe 62. The downstream EGR passage 63 is connected to the surge tank 42 of the intake passage 30. Thereby, a part of the exhaust gas is introduced into the intake system of the engine 100 as EGR gas via the upstream EGR passage 60, the EGR collecting pipe 62, and the downstream EGR passage 63. An EGR cooler 64 for cooling the EGR gas is provided in the middle of the downstream EGR passage 63. Further, an EGR valve 66 is provided at a connection portion between the downstream EGR passage 63 and the surge tank 42. The EGR valve 66 is controlled by the ECU 90 as EGR control means, and the amount of EGR gas flowing into the intake system is adjusted. In this embodiment, the downstream EGR passage 63 is connected to the surge tank 42, but the downstream EGR passage 63 can be connected to any part of the intake system of the engine 100. Further, the EGR valve 66 can also be provided in any part of the downstream EGR passage 63 as long as it is on the intake side of the EGR collecting pipe 62.

  The ECU 90 includes a microcomputer and a memory, and functions as a control unit that performs operation control of various mechanisms in the engine 100. In addition to the sensors described above, the engine 100 includes an accelerator opening sensor 92 that detects the accelerator opening, a water temperature sensor 94 that detects the cooling water temperature of the engine, and an air ratio that detects the air-fuel ratio based on the oxygen concentration in the exhaust gas. A fuel ratio sensor 96 and a speed sensor 98 are provided. The ECU 90 functions as an acquisition unit that acquires an operation state including the engine load of the engine 100 based on input signals from these sensors and a control table such as an engine speed and a fuel injection amount stored in advance. .

  When EGR gas, which is an inert gas, is supplied to the intake passage 30 during combustion, the oxygen concentration in the intake air decreases. Thereby, since combustion temperature falls, generation | occurrence | production of the harmful | toxic substance (especially NOx) accompanying combustion can be suppressed. In addition, fuel efficiency can be improved by performing combustion (lean burn) in an atmosphere having a low oxygen concentration.

  FIG. 2 is a diagram showing an outline of the EGR system in the engine 100. As shown in the figure, the engine 100 is an in-line four-cylinder engine including a cylinder block 11 composed of four cylinders A to D, and the ignition order of each cylinder is in the order of A → B → C → D. . Each cylinder is arranged in order of A → D → B → C from the end. In the following description, the combustion chambers are referred to as a first combustion chamber 14a to a fourth combustion chamber 14d in the order of ignition. Further, the names of the exhaust passages (first exhaust passage 50a to fourth exhaust passage 50d) are determined in the same manner as the combustion chamber 14.

  A first upstream EGR passage 60a is branched from the first exhaust passage 50a, and a second upstream EGR passage 60b is branched from the second exhaust passage 50b. The first upstream EGR passage 60 a and the second upstream EGR passage 60 b are collected by an EGR collecting pipe 62. Around the EGR collecting pipe 62, there is provided a cooling water passage 70 which is a cooling means for cooling the EGR gas in the pipe. The amount of cooling water flowing into the cooling water passage 70 is adjusted by the cooling water valve 72. The cooling water valve 72 is controlled by the ECU 90 as cooling control means.

  The first exhaust passage 50a and the third exhaust passage 50c are gathered by a first exhaust collecting passage 80a. Further, the second exhaust passage 50b and the third exhaust passage 50d are gathered by a second exhaust collecting passage 80b. The first exhaust collecting passage 80 a and the second exhaust collecting passage 80 b merge before the turbine 52. That is, the supercharger 56 of the present embodiment is a twin scroll type supercharger having two exhaust gas supply paths (a first exhaust collecting passage 80a and a second exhaust collecting passage 80b) with respect to the turbine 52.

  Here, the distance from the EGR connection portion 68 that is the connection portion between the exhaust passage 50 and the upstream EGR passage 60 to the EGR collecting pipe 62 is from the EGR connection portion 68 to the turbine 52 (more precisely, the storage where the turbine 52 is disposed). It is preferable that the distance is substantially equal to the distance (to the open end of the exhaust passage 50). Specifically, when the connection portion between the first exhaust passage 50a and the first upstream EGR passage 60a is the first connection portion 68a, the distance L1 from the first connection portion 68a to the EGR collecting pipe 62, the first The distance L2 from the connecting portion 68a to the turbine 52 is preferably equal. Similarly, when the connecting portion between the second exhaust passage 50b and the second upstream EGR passage 60b is the second connecting portion 68b, the distance from the second connecting portion 68b to the EGR collecting pipe 62, and the second connecting portion 68b. The distance from the turbine 52 to the turbine 52 is preferably equal.

  In the engine 100 of the present embodiment, two exhaust passages 50a and 50b are connected by an upstream EGR passage 60 and an EGR collecting pipe 62 for cooling the exhaust gas described later. At this time, the presence of the upstream EGR passage 60 causes a problem that interference of exhaust pulsation occurs in the exhaust passage 50. As described above, by making the distance from the EGR connection portion 68 to the EGR collecting pipe 62 equal to the distance from the EGR connection portion 68 to the turbine 52, the light is reflected by the EGR collecting pipe 62 and returns to the connecting portion 68. The waves reflected by the turbine 52 and returned to the connection 68 are substantially the same. As a result, exhaust pulsation interference by the upstream EGR passage 60 can be suppressed to a minimum.

  FIG. 3 is a flowchart showing the operation of engine 100 during exhaust gas cooling. First, the ECU 90 determines whether or not there is a request for reducing the temperature of the exhaust gas in the exhaust passage 50 (exhaust gas cooling request) (step S10). For example, the exhaust gas cooling request may be configured when the temperature of the catalyst 54 detected by the catalyst temperature sensor 55 becomes a predetermined value or more. Alternatively, the ECU 90 can make a cooling request based on the operating state of the engine 100 acquired by the ECU 90. The operating state of the engine 100 may be acquired based on signals detected by the throttle opening sensor 41 and the accelerator opening sensor 92, or a control table such as an engine speed and a fuel injection amount stored in the ECU 90 in advance. You may acquire based on.

  Next, when there is a cooling request in step S10, the ECU 90 closes the EGR valve 66 provided between the EGR collecting pipe 62 and the intake passage 30 (step S12). Further, the ECU 90 opens the cooling water valve 72 provided in the cooling water passage 70 (step S14), and introduces the cooling water into the cooling water passage 70.

  FIG. 4A is a timing chart showing pressure fluctuations in the exhaust passages 50a to 50d and the EGR collecting pipe 62, and FIG. 4B is a graph in which the graphs of FIG. The timing of opening and closing the exhaust valve 22 in each combustion chamber 14 is shown in the graph. First, when the exhaust valve 22a of the first combustion chamber 14a (cylinder A) is opened (A), the pressure in the first exhaust passage 50a increases (B), and the influence of the blowdown pressure in the first exhaust passage 50a. As a result, the pressure in the EGR collecting pipe 62 increases (C). Further, since the first exhaust passage 50a and the third exhaust passage 50c merge in the first exhaust collecting passage 80a, the third exhaust passage 50c is affected by the blowdown pressure through the first exhaust collecting passage 80a. The pressure increases as well (D).

  At this time, in the second exhaust passage 50b of the second combustion chamber 14b to be opened next, the influence of the blowdown pressure of the first exhaust pipe 30a is slightly caused through the housing 82 provided with the turbine 52 (E). . However, since the pressure in the EGR collecting pipe 62 is higher than the pressure in the second exhaust passage 50b, the EGR gas flows from the EGR collecting pipe 62 into the second exhaust passage 50b. At this time, the EGR gas is cooled while passing through the collecting pipe 62.

  When the exhaust valve 22b of the second combustion chamber 14b (cylinder B) is opened (F), the exhaust gas discharged from the second combustion chamber 14b is mixed with the EGR gas supplied from the collecting pipe 62. Thereby, the temperature of the exhaust gas in the 2nd exhaust passage 50b falls. Further, the pressure in the second exhaust passage 50b increases (G), and the pressure in the EGR collecting pipe 62 increases (H) due to the influence of the blowdown pressure in the second exhaust passage 50b.

  Subsequently, when the exhaust valve 22c of the third combustion chamber 14c (cylinder C) is opened (I), the pressure in the first exhaust passage 50a increases due to the influence of the blowdown pressure through the first exhaust collecting passage 80a. (J), and the pressure in the EGR collecting pipe 62 rises via the first upstream EGR passage 60a (K). Similarly, when the exhaust valve 22d of the fourth combustion chamber 14d (cylinder D) is opened (L), the pressure in the second exhaust passage 50b rises due to the influence of the blowdown pressure through the second exhaust collecting passage 80b. (M), and the pressure in the EGR collecting pipe 62 rises via the second upstream EGR passage 60b (N). Thus, the pressure in the EGR collecting pipe 62 periodically increases as the exhaust valve 22 of each combustion chamber 14 opens.

  According to the engine 100 of the present embodiment, the ECU 90 performs control to close the EGR valve 66 in response to the exhaust gas cooling request (steps S10 and S12 in FIG. 3). Accordingly, EGR gas is introduced from the first exhaust passage 50a into the second exhaust passage 50b through the first upstream EGR passage 60a, the EGR collecting pipe 62, and the second upstream EGR passage 60b. Since the EGR gas is cooled while passing through the upstream EGR passage 62, the temperature of the exhaust gas in the second exhaust passage 50b can be reduced. As a result, a temperature rise of the turbine 52 and the catalyst 54 provided in the exhaust system of the engine 100 is suppressed, and a decrease in the reliability of the turbine 52 and a decrease in the purification action of the catalyst 54 can be suppressed.

  Further, when the temperature of the exhaust gas is lowered by the introduction of the EGR gas, the temperature of the exhaust gas introduced into the combustion chamber 14 when the intake valve 20 and the exhaust valve 22 overlap is also lowered, and the combustion temperature is lowered. Thereby, knocking at the time of combustion is suppressed and ignition advance is possible, so that afterburning of fuel can be suppressed. As a result, the exhaust gas temperature can be further reduced.

  Further, in the engine 100 of the present embodiment, a cooling water passage 70 as a cooling means is provided around the EGR collecting pipe 62. Thereby, since the EGR gas passing through the EGR collecting pipe 62 can be cooled, the temperature of the exhaust gas in the exhaust passage 50 into which the EGR gas is introduced can be further lowered. The cooling means may be other than the cooling water passage 70 as long as the temperature of the EGR gas in the EGR collecting pipe 62 can be lowered.

  Further, in the engine 100 of this embodiment, the ECU 90 performs control to open and close the cooling water valve 72 according to the engine load of the engine 100. For example, when priority is given to warming up of the catalyst 54 when the engine is started, the ECU 90 closes the cooling water valve 72 to stop the circulation of the cooling water. Thereby, the fall of exhaust gas temperature is suppressed and catalyst warm-up can be completed at an early stage. Thus, by controlling the cooling capacity of the cooling means according to the engine load (operating state), the temperature of the exhaust gas can be adjusted, so that the combustion efficiency of the engine 100 can be increased.

  In the present embodiment, in the cylinder arrangement as shown in FIG. 2, the EGR gas is taken out from the first exhaust passage 50a and the second exhaust passage 50b. It is not limited to.

  FIGS. 5A to 5F show combinations that can lower the exhaust gas temperature by introducing EGR gas when the arrangement of the in-line four-cylinder engine (cylinders A to D) similar to FIG. 2 is adopted. Is shown. In the drawing, only the cylinder block 11 and the EGR collecting pipe 62 are shown, and the exhaust passage 50 and the upstream EGR passage 60 are not shown. 5A to 5D show an example in which EGR gas is taken out from two exhaust passages 50 out of four exhaust passages 50. FIG. At this time, the combination of the exhaust passages 50 for taking out the EGR gas is preferably a combination of two exhaust passages 50 connected to the two combustion chambers 14 in which the ignition order is continuous.

  In a typical in-line four-cylinder engine, the ignition sequence is not continuous in order to reduce the adverse effects of blowdown waves through the upstream EGR passage 60 and the EGR collecting portion 62 (the ignition timing is separated by 360 ° in FIG. 4). E) EGR gas is taken out from the exhaust passage 50 of the combustion chamber 14. For example, a combination of cylinder A and cylinder C, cylinder B and cylinder D is conceivable. On the other hand, in this embodiment, the EGR gas is introduced from one exhaust passage to another exhaust passage using the pressure difference (blowdown pressure) in the two exhaust passages 50, so that the ignition sequence is continuous ( It is preferable to take out the EGR gas from the exhaust passage 50 of the combustion chamber 14 where the ignition timing is 180 ° apart in FIG.

  FIGS. 5E to 5F show an example in which EGR gas is extracted from all four exhaust passages. In this case, it is preferable that the two upstream EGR passages 60 are merged once in the front EGR collecting pipe 69 and then all EGR gases are finally merged in the EGR collecting pipe 62. At this time, it is preferable that the EGR gas collected in the pre-stage EGR collecting pipe 69 is EGR gas taken out from the two exhaust passages 50 connected to the two combustion chambers 14 in which the ignition order is continuous.

  In the present embodiment, the in-line 4-cylinder engine 100 has been described as an example, but the present invention can also be applied to engines other than the in-line 4-cylinder engine. For example, even in a 2-cylinder, 3-cylinder, 5-cylinder, 6-cylinder, 8-cylinder, 10-cylinder, and 12-cylinder engine, by introducing EGR gas extracted from one exhaust passage into another exhaust passage, The temperature can be lowered. Further, the shape of the engine is not limited to the in-line type, and can be applied to a horizontally opposed type engine or a V type engine.

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

DESCRIPTION OF SYMBOLS 10 Cylinder 11 Cylinder block 14 Combustion chamber 30 Intake passage 36 Compressor 50 Exhaust passage 52 Turbine 60 Upstream EGR passage 62 EGR collecting pipe 66 EGR valve 70 Cooling water passage 72 Cooling water valve 80 Exhaust collecting passage 90 ECU
100 engine

Claims (5)

An internal combustion engine equipped with an EGR system,
A plurality of exhaust passages connected to each of the plurality of combustion chambers;
A plurality of upstream EGR passages branched from each of at least two of the plurality of exhaust passages;
An EGR gathering portion in which the plurality of upstream EGR passages are gathered;
A downstream EGR passage leading from the EGR collecting portion to the intake system of the internal combustion engine;
An EGR valve provided in the downstream EGR passage;
EGR control means for opening and closing the EGR valve in response to a request to lower the exhaust gas temperature in the exhaust passage;
An internal combustion engine characterized by comprising:   The internal combustion engine according to claim 1, further comprising a cooling unit that cools the EGR collecting portion.   The internal combustion engine according to claim 2, further comprising cooling control means for controlling a cooling capacity of the cooling means in accordance with an engine load of the internal combustion engine. A turbocharger including a turbine provided in an exhaust system of the internal combustion engine and a compressor provided in an intake system of the internal combustion engine and fastened on the same shaft as the turbine;
The distance from the branch portion between the exhaust passage and the upstream EGR passage to the EGR collecting portion is substantially equal to the distance from the branch portion between the exhaust passage and the upstream EGR passage to the turbine. The internal combustion engine according to any one of claims 1 to 3.   5. The EGR collecting section collects the plurality of upstream EGR passages branched from the plurality of exhaust passages connected to the plurality of combustion chambers in which the ignition order is continuous. An internal combustion engine according to any one of the above.

Images