EGR gas distributor

An EGR gas distributor includes an inflow portion into which EGR gas that has passed through an EGR valve flows, a first EGR port connected to a section of the intake manifold in which intake air introduced into the first cylinder flows, a second EGR port connected to a section of the intake manifold in which intake air introduced into the second cylinder flows, a first gas passage that connects the inflow portion and the first EGR port to each other, and a second gas passage that connects the first gas passage and the second EGR port to each other. A shortest path between the first EGR port and the second EGR port is longer than both of a shortest path between the inflow portion and the first EGR port and a shortest path between the inflow portion and the second EGR port.

BACKGROUND

The following description relates to an exhaust gas recirculation (EGR) gas distributor that introduces EGR gas that has passed through an EGR valve into an intake manifold.

2. Description of Related Art

Japanese Laid-Open Patent Publication No. 2018-25123 discloses one example of an EGR gas distributor that is employed in an internal combustion engine having multiple cylinders arranged in series. The EGR gas distributor includes an inflow portion in which EGR gas that has passed through an EGR valve flows. A first branch passage and a second branch passage are connected to the inflow portion. The first branch passage branches into a first gas passage and a second gas passage on the downstream side. The second branch passage branches into a third gas passage and a fourth gas passage on the downstream side. EGR gas that has flowed through the first gas passage is introduced into a first cylinder, and EGR gas that has flowed through the second gas passage is introduced into a second cylinder. EGR gas that has flowed through the third gas passage is introduced into a third cylinder, and EGR gas that has flowed through the fourth gas passage is introduced into a fourth cylinder.

In the above-described internal combustion engine, the four cylinders are arranged in a cylinder arrangement direction in order of the first cylinder, the second cylinder, the third cylinder, and the fourth cylinder. The first cylinder and the second cylinder, which are adjacent to each other in the cylinder arrangement direction, are also temporally adjacent to each other in terms of points in time at which the intake strokes start.

A case will now be considered in which, of the first cylinder and the second cylinder, the intake stroke of the second cylinder starts before the intake stroke of the first cylinder. In this case, the intake stroke of the first cylinder starts after or immediately before the end of the intake stroke of the second cylinder. Immediately after the end of the intake stroke of the second cylinder, blowback of intake air due to closing of the intake valve may cause the intake air to flow into the second gas passage from the intake manifold. In such a case, the intake air that has flowed into the second passage may flow into the first gas passage during the intake stroke of the first cylinder, and that intake air may flow through the first gas passage and be introduced into the first cylinder together with EGR gas. In this case, the amount of the EGR gas introduced into the first cylinder is less than the amount of the EGR gas introduced into the second cylinder. That is, of the first and second cylinders, the amount of the EGR gas introduced into the cylinder in which the intake stroke is started later becomes less than the amount of the EGR gas introduced into the cylinder in which the intake stroke starts earlier. Therefore, there is room for improvement in suppression of variation in amounts of EGR gas introduced into two cylinders that are temporally adjacent to each other in terms of starting points in time of intake strokes.

SUMMARY

In one general aspect, an EGR gas distributor is configured to be connected to an intake manifold of an internal combustion engine. The internal combustion engine to which the EGR gas distributor is connected has four cylinders. The four cylinders are arranged in order of a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder in a cylinder arrangement direction. A starting point in time of an intake stroke of the first cylinder and a starting point in time of an intake stroke of the second cylinder are temporally adjacent to each other. The EGR gas distributor includes an inflow portion into which EGR gas that has passed through an EGR valve flows, a first EGR port connected to a section of the intake manifold in which intake air introduced into the first cylinder flows, a second EGR port connected to a section of the intake manifold in which intake air introduced into the second cylinder flows, a first gas passage that connects the inflow portion and the first EGR port to each other, and a second gas passage that connects the first gas passage and the second EGR port to each other. A shortest path between the first EGR port and the second EGR port is longer than both of a shortest path between the inflow portion and the first EGR port and a shortest path between the inflow portion and the second EGR port.

A case will now be considered in which intake strokes start in order of the first cylinder, the third cylinder, the fourth cylinder, and the second cylinder. In this case, when the intake stroke of the second cylinder ends, blowback of intake air due to closing of the intake valve of the second cylinder may cause the intake air to flow into the EGR gas distributor from the intake manifold through the second EGR port. If the shortest path between the first EGR port and the second EGR port is relatively short, the intake air that has flowed into the EGR gas distributor through the second EGR port may reach the first EGR port together with EGR gas, and that intake air may flow into the intake manifold from the first EGR port. In this case, the amount of the EGR gas introduced into the first cylinder is less than the amount of the EGR gas introduced into the second cylinder.

A case will now be considered in which intake strokes start in order of the first cylinder, the second cylinder, the fourth cylinder, and the third cylinder. In this case, when the intake stroke of the first cylinder ends, intake air may flow into the EGR gas distributor through the first EGR port. If the shortest path between the first EGR port and the second EGR port is relatively short, the intake air that has flowed into the EGR gas distributor through the first EGR port may flow into the intake manifold from the second EGR port together with the EGR gas. In this case, the amount of the EGR gas introduced into the second cylinder is less than the amount of the EGR gas introduced into the first cylinder.

As such, in the above-described configuration, the shortest path between the first EGR port and the second EGR port is longer than both of the shortest path between the inflow portion and the first EGR port and the shortest path between the inflow portion and the second EGR port. One of the first cylinder and the second cylinder in which the intake stroke starts first is referred to as a preceding cylinder, and the one in which the intake stroke starts later is referred to as a following cylinder. During the period in which the intake stroke of the following cylinder ends, the intake air that has flowed into the EGR gas distributor when the intake stroke of the preceding cylinder ends is unlikely to reach the EGR port corresponding to the following cylinder. This suppresses reduction in the amount of the EGR gas introduced into the following cylinder. Thus, for the first cylinder and the second cylinder, which are temporally adjacent to each other in terms of the starting points in time of intake strokes, the above-described configuration suppresses the deviation between the amount of the EGR gas introduced into the first cylinder and the amount of the EGR gas introduced into the second cylinder.

In an aspect of the above-described EGR gas distributor, a bent portion that changes a flowing direction of gas is provided in each of the first gas passage and the second gas passage.

The shortest path between the first EGR port and the second EGR port includes the second gas passage and a section of the first gas passage from the connection site connected to the second gas passage to the first EGR port. Thus, since the bent portion is provided in each of the first gas passage and the second gas passage in the above-described configuration, the flow resistance of the shortest path between the first EGR port and the second EGR port is increased. This reduces the flow velocity of the intake air flowing through the shortest path from the EGR port corresponding to the preceding cylinder during the intake stroke of the following cylinder. As a result, the intake air is unlikely to reach the EGR port corresponding to the following cylinder during the intake stroke of the following cylinder. This further effectively suppresses the deviation between the amount of the EGR gas introduced into the first cylinder and the amount of the EGR gas introduced into the second cylinder.

In an aspect of the above-described EGR gas distributor, a constriction is provided in the shortest path between the first EGR port and the second EGR port.

In the above-described configuration, since the constriction is provided in the path between the first EGR port and the second EGR port, the flow resistance is greater than in a case in which such a constriction is not provided in the path. This reduces the flow velocity of the intake air flowing through the path from the EGR port corresponding to the preceding cylinder during the intake stroke of the following cylinder. As a result, the intake air is unlikely to reach the EGR port corresponding to the following cylinder during the intake stroke of the following cylinder. This further effectively suppresses the deviation between the amount of the EGR gas introduced into the first cylinder and the amount of the EGR gas introduced into the second cylinder.

In another aspect, the above-described EGR gas distributor includes a third EGR port connected to a section of the intake manifold in which intake air introduced into the third cylinder flows, a fourth EGR port connected to a section of the intake manifold in which intake air introduced into the fourth cylinder flows, a fourth gas passage that connects the inflow portion and the fourth EGR port to each other, and a third gas passage that connects the fourth gas passage and the third EGR port to each other. A direction in which the first to fourth EGR ports are arranged is referred to as a port arrangement direction. The first to fourth EGR ports are arranged in the port arrangement direction in order of the first EGR port, the second EGR port, the third EGR port, and the fourth EGR port. The inflow portion is disposed between the second EGR port and the third EGR port in the port arrangement direction. A shortest path between the third EGR port and the fourth EGR port is longer than both of a shortest path between the inflow portion and the third EGR port and a shortest path between the inflow portion and the fourth EGR port.

In the above-described configuration, the shortest path between the third EGR port and the fourth EGR port is longer than both of the shortest path between the inflow portion and the third EGR port and the shortest path between the inflow portion and the fourth EGR port. One of the third cylinder and the fourth cylinder in which the intake stroke starts first is referred to as a preceding cylinder, and the one in which the intake stroke starts later is referred to as a following cylinder. During the period in which the intake stroke of the following cylinder ends, the intake air that has flowed into the EGR gas distributor via the EGR port when the intake stroke of the preceding cylinder ends is unlikely to reach the EGR port corresponding to the following cylinder. This suppresses reduction in the amount of the EGR gas introduced into the following cylinder. Thus, for the third cylinder and the fourth cylinder, which are temporally adjacent to each other in terms of the starting points in time of intake strokes, the above-described configuration suppresses the deviation between the amount of the EGR gas introduced into the third cylinder and the amount of the EGR gas introduced into the fourth cylinder.

In an aspect of the above-described EGR gas distributor, a connection site between the first gas passage and the second gas passage is located between the second EGR port and the inflow portion in the port arrangement direction.

In this configuration, the shortest path between the first EGR port and the second EGR port includes the second gas passage and a section of the first gas passage between the connection site and the first EGR port. In the above-described configuration, the connection site is located between the second EGR port and the inflow portion in the port arrangement direction. Thus, the second gas passage and the section of the first gas passage between the connection site and the first EGR port are longer than those in a case in which the connection site is located between the first EGR port and the second EGR port in the port arrangement direction. This lengthens the shortest path between the first EGR port and the second EGR port.

In an aspect of the above-described EGR gas distributor, a connection site between the third gas passage and the fourth gas passage is located between the third EGR port and the inflow portion in the port arrangement direction.

In this configuration, the shortest path between the third EGR port and the fourth EGR port includes the third gas passage and a section of the fourth gas passage between the connection site and the fourth EGR port. In the above-described configuration, the connection site is located between the third EGR port and the inflow portion in the port arrangement direction. Thus, the third gas passage and the section of the fourth gas passage between the connection site and the fourth EGR port are longer than those in a case in which the connection site is located between the third EGR port and the fourth EGR port in the port arrangement direction. This lengthens the shortest path between the third EGR port and the fourth EGR port.

DETAILED DESCRIPTION

An EGR gas distributor23according to an embodiment will now be described with reference toFIGS. 1 to 7.

FIG. 1illustrates an internal combustion engine10that is equipped with the EGR gas distributor23of the present embodiment. The internal combustion engine10is an inline four-cylinder engine. The internal combustion engine10includes four cylinders #1, #2, #3, and #4, which are arranged in a cylinder arrangement direction X in order of the first cylinder #1, the second cylinder #2, the third cylinder #3, and the fourth cylinder #4. Air-fuel mixture containing fuel and intake air introduced through an intake manifold and is burned in each of the cylinders #1 to #4. Exhaust gas generated by combustion of the air-fuel mixture in each of the cylinders #1 to #4 is discharged to an exhaust pipe12.

In the internal combustion engine10, intake strokes start in order of the first cylinder #1, the third cylinder #3, the fourth cylinder #4, and the second cylinder #2. That is, a point in time at which the intake stroke of the first cylinder #1 starts and a point in time at which the intake stroke of the second cylinder #2 starts are temporally adjacent to each other. Also, a point in time at which the intake stroke of the third cylinder #3 starts and a point in time at which the intake stroke of the fourth cylinder #4 starts are temporally adjacent to each other.

An intake manifold11includes intake branch pipes111,112,113, and114, the number of which is the same as the number of cylinders of the internal combustion engine10. Among the intake branch pipes111to114, the intake air that has flowed through the intake branch pipe111is introduced into the first cylinder #1. The intake air that has flowed through the intake branch pipe112is introduced into the second cylinder #2. The intake air that has flowed through the intake branch pipe113is introduced into the third cylinder #3. The intake air that has flowed through the intake branch pipe1l4is introduced into the fourth cylinder #4. That is, the intake branch pipe111corresponds to a section of the intake manifold11through which the intake air introduced into the first cylinder #1 flows. The intake branch pipe112corresponds to a section of the intake manifold11through which the intake air introduced into the second cylinder #2 flows. The intake branch pipe113corresponds to a section of the intake manifold11through which the intake air introduced into the third cylinder #3 flows. The intake branch pipe114corresponds to a section of the intake manifold11through which the intake air introduced into the fourth cylinder #4 flows.

The internal combustion engine10includes an EGR device20, which returns exhaust gas flowing through the exhaust pipe12to the intake manifold11as EGR gas. EGR stands for exhaust gas recirculation. The solid arrows inFIG. 1represent the flow of EGR gas that is returned to the intake manifold11by the EGR device20.

The EGR device20includes an EGR passage21connected to the exhaust pipe12and the EGR gas distributor23, which connects the EGR passage21and the intake manifold11to each other. An EGR valve22is provided in the middle of the EGR passage21. The EGR valve22regulates the amount of EGR gas that is returned to the intake manifold11through the EGR device20.

The EGR gas distributor23includes an inflow portion30to which the EGR passage21is connected and EGR ports31,32,33, and34, the number of which is the same as the number of the cylinders of the internal combustion engine10. That is, EGR gas that has flowed through the EGR valve22flows into the EGR gas distributor23through the inflow portion30. Among the EGR ports31to34, the first EGR port31is connected to the intake branch pipe111of the intake manifold11. The second EGR port32is connected to the intake branch pipe112of the intake manifold11. The third EGR port33is connected to the intake branch pipe113of the intake manifold11. The fourth EGR port34is connected to the intake branch pipe114of the intake manifold11. Thus, EGR gas that has flowed out of the first EGR port31flows through the intake branch pipe111and is introduced into the cylinder #1. EGR gas that has flowed out of the second EGR port32flows through the intake branch pipe112and is introduced into the cylinder #2. EGR gas that has flowed out of the third EGR port33flows through the intake branch pipe113and is introduced into the cylinder #3. EGR gas that has flowed out of the fourth EGR port34flows through the intake branch pipe114and is introduced into the cylinder #4.

The direction in which the first to fourth EGR ports31to34are arranged is referred to as a port arrangement direction Y. As shown inFIG. 2, the first to fourth EGR ports31to34are arranged in the port arrangement direction Y in order of the first EGR port31, the second EGR port32, the third EGR port33, and the fourth EGR port34. The inflow portion30is located between the second EGR port32and the third EGR port33in the port arrangement direction Y.

As shown inFIGS. 2 and 3, the EGR gas distributor23includes a first gas passage41that connects the inflow portion30and the first EGR port31to each other and a fourth gas passage44that connects the inflow portion30and the fourth gas passage44to each other. The first gas passage41includes multiple bent portions41A,41B, which change the flowing direction of gas flowing in the first gas passage41. That is, the first gas passage41includes a first passageway411extending from the inflow portion30and a second passageway412extending in a direction different from that of the first passageway411. The first bent portion41A is disposed between a distal end of the first passageway411and a proximal end of the second passageway412. The first gas passage41includes a third passageway413connected to the first EGR port31. The direction in which the third passageway413extends is different from the direction in which the second passageway412extends. The second bent portion41B is disposed between a distal end of the second passageway412and a proximal end of the third passageway413.

The fourth gas passage44includes multiple bent portions44A,44B. That is, the fourth gas passage44includes an eighth passageway441extending from the inflow portion30and a ninth passageway442extending in a direction different from that of the eighth passageway441. The fifth bent portion44A is disposed between a distal end of the eighth passageway441and a proximal end of the ninth passageway442. The fourth gas passage44includes a tenth passageway443connected to the fourth EGR port34. The direction in which the tenth passageway443extends is different from the direction in which the ninth passageway442extends. The sixth bent portion44B is disposed between a distal end of the ninth passageway442and a proximal end of the tenth passageway443.

The EGR gas distributor23includes a second gas passage42that connects the first gas passage41and the second EGR port32to each other. Specifically, the second gas passage42is connected to the first passageway411of the first gas passage41. The connection site between the first gas passage41and the second gas passage42is located between the second EGR port32and the inflow portion30in the port arrangement direction Y. The second gas passage42includes a fourth passageway421extending from the connection site connected to the first gas passage41and a fifth passageway422connected to the second EGR port32. The direction in which the fourth passageway421extends is different from both of the direction in which the fifth passageway422extends and the direction in which the first passageway411of the first gas passage41extends. A third bent portion42A is disposed between a distal end of the fourth passageway421and a proximal end of the fifth passageway422.

The EGR gas distributor23includes a third gas passage43that connects the fourth gas passage44and the third EGR port33to each other. Specifically, the third gas passage43is connected to the eighth passageway441of the fourth gas passage44. The connection site between the fourth gas passage44and the third gas passage43is located between the third EGR port33and the inflow portion30in the port arrangement direction Y. The third gas passage43includes a sixth passageway431extending from the connection site connected to the fourth gas passage44and a seventh passageway432connected to the third EGR port33. The direction in which the sixth passageway431extends is different from both of the direction in which the seventh passageway432extends and the direction in which the eighth passageway441of the fourth gas passage44extends. A fourth bent portion43A is disposed between a distal end of the sixth passageway431and a proximal end of the seventh passageway432.

The EGR gas distributor23includes two accommodating portions36located on the opposite sides of the inflow portion30in the port arrangement direction Y. The accommodating portions36are separated from passages through which EGR gas flows in the EGR gas distributor23. Each accommodating portion36communicates with the outside of the EGR gas distributor23, while being separated by a partition wall36afrom the passage through which EGR gas flows. Each accommodating portion36accommodates a component such as a part of a bolt or nut that is used to attach the EGR gas distributor23to a component arranged close to the EGR gas distributor23. The component to which the EGR gas distributor23is attached may be one of the pipes included in the EGR passage21, which is, for example, a pipe that connects the EGR valve22and the EGR gas distributor23to each other. The component may also be a component of the internal combustion engine10such as a cylinder block. The accommodating portion36may be either a through-hole or a recess as long as it is separated from passages through which EGR gas flows.

In the present embodiment, the accommodating portions36are located in respective vicinities of the connection site between the first gas passage41and the second gas passage42and the connection site between the fourth gas passage44and the third gas passage43.

When the intake stroke of the second cylinder ends, blowback of intake air occurs in the intake branch pipe112due to closing of the intake valve corresponding to the second cylinder #2. As a result, the intake air may flow into the EGR gas distributor23from the intake branch pipe112through the second EGR port32. In such a case, during the intake stroke of the first cylinder #1, the intake air that has flowed into the EGR gas distributor23through the second EGR port32may flow into the first gas passage41after flowing backward in the second gas passage42and may flow toward the first EGR port31through the first gas passage41. At this time, if the flow path from the second EGR port32to the first EGR port31through the interior of the EGR gas distributor23is relatively short, the intake air may flow out to the intake branch pipe111from the first EGR port31and may be introduced into the first cylinder #1 during the intake stroke of the first cylinder #1.

Thus, the present embodiment is configured such that the lengths of the first gas passage41and the second gas passage42, and the position of a first connection site, which is the connection site between the first gas passage41and the second gas passage42, meet the condition shown inFIG. 4. That is, a backflow path F12is longer than both of a first path F1and a second path F2. The first path F1is the shortest path of a gas flow from the inflow portion30to the first EGR port31. The second path F2is the shortest path of a gas flow from the inflow portion30to the second EGR port32. The backflow path F12is the shortest path between the first EGR port31and the second EGR port32. Specifically, as indicated by the broken line inFIG. 3, the first path F1is a path in the first gas passage41. As indicated by the long dashed short dashed line inFIG. 3, the second path F2extends over a section in the first gas passage41from the connection site connected to the inflow portion30to the first connection site, and the interior of the second gas passage42. As indicated by the solid line inFIG. 3, the backflow path F12extends over the interior of the second gas passage42and the interior of a section of the first gas passage41from the first connection site to the first EGR port31.

As shown inFIG. 3, the first path F1, the second path F2, and the backflow path F12each pass the vicinity of the accommodating portion36. That is, the first path F1includes a first constriction371in the vicinity of the accommodating portion36. The first constriction371has a smaller cross-sectional area than the remainder of the first path F1. The second path F2includes a second constriction372in the vicinity of the accommodating portion36. The second constriction372has a smaller cross-sectional area than the remainder of the second path F2. The backflow path F12includes a first backflow path constriction37A in the vicinity of the accommodating portion36. The first backflow path constriction37A has a smaller cross-sectional area than the remainder of the backflow path F12. The cross-sectional area of the first backflow path constriction37A is the smallest among the constrictions371,372, and37A.

When the intake stroke of the third cylinder #3 ends, blowback of intake air occurs in the intake branch pipe113due to closing of the intake valve corresponding to the third cylinder #3. As a result, the intake air may flow into the EGR gas distributor23through the third EGR port33from the intake branch pipe113. In such a case, during the intake stroke of the fourth cylinder #4, the intake air that has flowed into the EGR gas distributor23through the third EGR port33may flow into the fourth gas passage44after flowing backward in the third gas passage43and may flow toward the fourth EGR port34toward the fourth gas passage44. At this time, if the flow path from the third EGR port33to the fourth EGR port34through the interior of the EGR gas distributor23is relatively short, the intake air may flow out to the intake branch pipe114from the fourth EGR port34and may be introduced into the fourth cylinder #4 during the intake stroke of the fourth cylinder #4.

Thus, the present embodiment is configured such that the lengths of the third gas passage43and the fourth gas passage44, and the position of a second connection site, which is the connection site between the third gas passage43and the fourth gas passage44, meet the condition shown inFIG. 4. That is, a backflow path F34is longer than both of a third path F3and a fourth path F4. The fourth path F4is the shortest path of a gas flow from the inflow portion30to the fourth EGR port34. The third path F3is the shortest path of a gas flow from the inflow portion30to the third EGR port33. The backflow path F34is the shortest path between the third EGR port33and the fourth EGR port34. Specifically, as indicated by the broken line inFIG. 3, the fourth path F4is a path in the fourth gas passage44. As indicated by the long dashed short dashed line inFIG. 3, the third path F3extends over a section in the fourth gas passage44from the connection site connected to the inflow portion30to the second connection site, and the interior of the third gas passage43. As indicated by the solid line inFIG. 3, the backflow path F34extends over the interior of the third gas passage43and the interior of a section of the fourth gas passage44from the second connection site to the fourth EGR port34.

As shown inFIG. 3, the third path F3, the fourth path F4, and the backflow path F34each pass the vicinity of the accommodating portion36. That is, the third path F3includes a third constriction373in the vicinity of the accommodating portion36. The third constriction373has a smaller cross-sectional area than the remainder of the third path F3. The fourth path F4includes a fourth constriction374in the vicinity of the accommodating portion36. The fourth constriction374has a smaller cross-sectional area than the remainder of the fourth path F4. The backflow path F34includes a second backflow path constriction37B in the vicinity of the accommodating portion36. The second backflow path constriction37B has a smaller cross-sectional area than the remainder of the backflow path F34. The cross-sectional area of the second backflow path constriction37B is the smallest among the constrictions373,374, and37B.

In the present embodiment, the length of the first path F1from the inflow portion30to the first EGR port31is equal to the length of the fourth path F4from the inflow portion30to the fourth EGR port34as shown inFIG. 4. The length of the second path F2from the inflow portion30to the second EGR port32is equal to the length of the third path F3from the inflow portion30to the third EGR port33. The length of the backflow path F12, which connects the fourth EGR port34and the second EGR port32to each other, is equal to the length of the backflow path F34, which connects the third EGR port33and the fourth EGR port34to each other.

Further, the cross-sectional area of the first constriction371is equal to the cross-sectional area of the fourth constriction374. The cross-sectional area of the second constriction372is equal to the cross-sectional area of the third constriction373. The cross-sectional area of the first backflow path constriction37A is equal to the cross-sectional area of the second backflow path constriction37B.

The operation of the present embodiment will be now described with reference toFIGS. 5 to 7.

During the intake stroke of the second cylinder #2, EGR gas that has flowed into the first gas passage41from the inflow portion30flows into the second gas passage42from the connection site between the first gas passage41and the second gas passage42as indicated by the solid arrows inFIG. 5. At this time, the gas retained in the section between the first connection site and the first EGR port31in the first gas passage41also flows into the second gas passage42from the first connection site. In the second gas passage42, EGR gas flows to the second EGR port32and flows out to the intake branch pipe112from the second EGR port32. Accordingly, the EGR gas is introduced into the second cylinder #2. When the intake stroke of the second cylinder #2 ends, blowback of intake air in the intake branch pipe112causes the intake air to flow into the EGR gas distributor23from the intake branch pipe112through the second EGR port32as indicated by the dashed arrow inFIG. 6.

When the intake stroke of the first cylinder #1 starts, the EGR gas that has flowed into the first gas passage41from the inflow portion30flows toward the first EGR port31as indicated by the solid arrows inFIG. 7. The EGR gas retained in the second gas passage42also flows into the first gas passage41from the first connection site. In the first gas passage41, the EGR gas flows to the first EGR port31and flows out to the intake branch pipe111from the first EGR port31.

During the intake stroke of the first cylinder #1, the intake air that has flowed into the EGR gas distributor23through the second EGR port32flows backward in the second gas passage42as indicated by the dashed arrow inFIG. 7, and flows into the first gas passage41from the first connection site. The intake air that has flowed into the first gas passage41flows toward the first EGR port31together with the EGR gas.

In the present embodiment, the backflow path F12, which connects the first EGR port31and the second EGR port32to each other, is relatively long. Thus, the intake stroke of the first cylinder #1 ends before the intake air that flows into the first gas passage41from the first connection site and toward the first EGR port31reaches the first EGR port31. This prevents the intake air that has flowed into the EGR gas distributor23through the second EGR port32from flowing out to the intake branch pipe111from the first EGR port31.

When the intake stroke of the first cylinder #1 ends and outflow of gas from the first EGR port31is stopped, intake air is retained in the section between the first connection site and the first EGR port31in the first gas passage41. However, the intake air retained in the first gas passage41flows into the second gas passage42through the first connection site together with EGR gas during the subsequent intake stroke of the second cylinder #2. The intake air then flows through the second gas passage42and flows out to the intake branch pipe112through the second EGR port32.

During the intake stroke of the third cylinder #3, the EGR gas that has flowed into the fourth gas passage44from the inflow portion30flows into the third gas passage43from the second connection site. At this time, the gas retained in the section between the second connection site and the fourth EGR port34in the fourth gas passage44also flows into the third gas passage43from the second connection site. In the third gas passage43, EGR gas flows to the third EGR port33and flows out to the intake branch pipe113of the intake manifold11through the third EGR port33. Accordingly, the EGR gas is introduced into the third cylinder #3. When the intake stroke of the third cylinder #3 ends, blowback of intake air in the intake branch pipe113causes the intake air to flow into the EGR gas distributor23from the intake branch pipe113through the third EGR port33.

When the intake stroke of the fourth cylinder #4 starts, the EGR gas that has flowed into the fourth gas passage44from the inflow portion30flows toward the fourth EGR port34. The EGR gas retained in the third gas passage43also flows into the fourth gas passage44from the second connection site. In the fourth gas passage44, the EGR gas flows to the fourth EGR port34and flows out to the intake branch pipe114through the fourth EGR port34.

During the intake stroke of the fourth cylinder #4, the intake air that has flowed into the EGR gas distributor23through the third EGR port33flows backward in the third gas passage43, and flows into the fourth gas passage44from the second connection site. The intake air that has flowed into the fourth gas passage44flows toward the fourth EGR port34together with EGR gas.

In the present embodiment, the backflow path F34, which connects the third EGR port33and the fourth EGR port34to each other, is long. Thus, the intake stroke of the fourth cylinder #4 ends before the intake air that flows into the fourth gas passage44from the second connection site and toward the fourth EGR port34reaches the fourth EGR port34. This prevents the intake air that has flowed into the EGR gas distributor23through the third EGR port33from flowing out to the intake branch pipe114from the fourth EGR port34.

When the intake stroke of the fourth cylinder #4 ends and outflow of gas from the fourth EGR port34is stopped, intake air is retained in the section between the second connection site and the fourth EGR port34in the fourth gas passage44. However, the intake air retained in the fourth gas passage44flows into the third gas passage43through the second connection site together with EGR gas during the subsequent intake stroke of the third cylinder #3. The intake air then flows through the third gas passage43and out to the intake branch pipe113through the third EGR port33.

The present embodiment has the following advantages.

(1) The backflow path F12, which connects the first EGR port31and the second EGR port32to each other, is set to be longer than both of the first path F1and the second path F2. Thus, the intake stroke of the first cylinder #1 ends before the intake air that has flowed into the EGR gas distributor23through the second EGR port32at the end of the intake stroke of the second cylinder #2 reaches the first EGR port31. Accordingly, the intake air is prevented from flowing out to the intake branch pipe111through the first EGR port31. This limits the reduction in the amount of the EGR gas that flows out to the intake branch pipe111from the first EGR port31during the intake stroke of the first cylinder #1. This suppresses the deviation between the amount of the EGR gas introduced into the first cylinder #1 and the amount of the EGR gas introduced into the second cylinder #2.

(2) The backflow path F34, which connects the third EGR port33and the fourth EGR port34to each other, is set to be longer than both of the third path F3and the fourth path F4. Thus, the intake stroke of the fourth cylinder #4 ends before the intake air that has flowed into the EGR gas distributor23through the third EGR port33at the end of the intake stroke of the third cylinder #3 reaches the fourth EGR port34. Accordingly, the intake air is prevented from flowing out to the intake branch pipe114through the fourth EGR port34. This limits the reduction in the amount of the EGR gas that flows out to the intake branch pipe114from the fourth EGR port34during the intake stroke of the fourth cylinder #4. This suppresses the deviation between the amount of the EGR gas introduced into the fourth cylinder #4 and the amount of the EGR gas introduced into the third cylinder #3.

(3) In the present embodiment, the first gas passage41and the second gas passage42have respective bent portions. Thus, the flow resistance of the backflow path F12, which extends over the interior of the second gas passage42and the interior of a section of the first gas passage41is high. This reduces the flow velocity of the intake air flowing from the second EGR port32toward the first EGR port31. As a result, the intake air is unlikely to reach the first EGR port31during the intake stroke of the first cylinder #1. This effectively limits the outflow of the intake air to the intake branch pipe111from the first EGR port31during the intake stroke of the first cylinder #1.

The direction in which the first passageway411of the first gas passage41extends is different from the direction in which the fourth passageway421of the second gas passage42extends. This is considered to be the structure in which the first passageway411and the fourth passageway421are connected to each other via a bent portion. Accordingly, the number of the bent portions through which gas flows when flowing from the inflow portion30toward the first EGR port31and the number of the bent portions through which the gas flows when flowing from the inflow portion30toward the second EGR port32are both less than the number of the bent portions through which gas flows when flowing from the second EGR port32toward the first EGR port31. This configuration prevents the flow of EGR gas from the inflow portion30to the first EGR port31or the second EGR port32from being hindered while hindering the flow of intake air from the second EGR port32toward the first EGR port31by providing multiple bent portions in the gas passages41,42.

(4) The first backflow path constriction37A is provided in the vicinity of the connection site between the first gas passage41and the second gas passage42. Thus, when intake air flows from the second EGR port32toward the first EGR port31, the intake air flows through the first backflow path constriction37A. That is, the backflow path F12is configured to have the first backflow path constriction37A. Since the backflow path F12includes the first backflow path constriction37A, the flow resistance of the gas flowing through the backflow path F12is increased. This reduces the flow velocity of the intake air that flows through the backflow path F12toward the first EGR port31during the intake stroke of the first cylinder #1. This effectively limits the outflow of the intake air to the intake branch pipe111from the first EGR port31during the intake stroke of the first cylinder #1.

The first path F1has the first constriction371, and the second path F2has the second constriction372. However, the cross-sectional area of the first constriction371and the cross-sectional area of the second constriction372are both larger than the cross-sectional area of the first backflow path constriction37A. This prevents the flow of EGR gas from the inflow portion30to the first EGR port31or the second EGR port32from being hindered.

(5) The cross-sectional area of the first backflow path constriction37A is larger than both of the cross-sectional area of the first EGR port31and the cross-sectional area of the second EGR port32. Thus, even though the first backflow path constriction37A is provided, the above-described embodiment is capable of reducing the amount of EGR gas that flows out to the intake branch pipe112from the second EGR port32during the intake stroke of the second cylinder #2 and reducing the amount of EGR gas that flows out to the intake branch pipe111from the first EGR port31during the intake stroke of the first cylinder #1.

(6) The third gas passage43and the fourth gas passage44have respective bent portions. Thus, the flow resistance of the backflow path F12, which extends over the interior of the third gas passage43and the interior of a section of the fourth gas passage44is high. This reduces the flow velocity of the intake air flowing from the third EGR port33toward the fourth EGR port34. As a result, the intake air is unlikely to reach the fourth EGR port34during the intake stroke of the fourth cylinder #4. This effectively limits the outflow of the intake air to the intake branch pipe114from the fourth EGR port34during the intake stroke of the fourth cylinder #4.

The direction in which the eighth passageway441of the fourth gas passage44extends is different from the direction in which the sixth passageway431of the third gas passage43extends. This is considered to be the structure in which the eighth passageway441and the sixth passageway431are connected to each other via a bent portion. Accordingly, the number of the bent portions through which gas flows when flowing from the inflow portion30toward the third EGR port33and the number of the bent portions through which gas flows when flowing from the inflow portion30toward the fourth EGR port34are both less than the number of the bent portions through which gas flows when flowing from the third EGR port33toward the fourth EGR port34. This configuration prevents the flow of EGR gas from the inflow portion30to the third EGR port33or the fourth EGR port34from being hindered while hindering the flow of intake air from the third EGR port33toward the fourth EGR port34by providing multiple bent portions in the gas passages43,44.

(7) The second backflow path constriction37B is provided in the vicinity of the connection site between the third gas passage43and the fourth gas passage44. Thus, when intake air flows from the third EGR port33toward the fourth EGR port34, the intake air flows through the second backflow path constriction37B. That is, the backflow path F34is configured to have the second backflow path constriction37B. Since the backflow path F34includes the second backflow path constriction37B, the flow resistance of the gas flowing through the backflow path F34is increased. This reduces the flow velocity of the intake air that flows through the backflow path F34toward the fourth EGR port34during the intake stroke of the fourth cylinder #4. This effectively limits the outflow of the intake air to the intake branch pipe114from the fourth EGR port34during the intake stroke of the fourth cylinder #4.

The third path F3has the third constriction373, and the fourth path F4has the fourth constriction374. However, the cross-sectional area of the third constriction373and the cross-sectional area of the fourth constriction374are both larger than the cross-sectional area of the second backflow path constriction37B. This prevents the flow of EGR gas from the inflow portion30to the third EGR port33or the fourth EGR port34from being hindered.

(8) The cross-sectional area of the second backflow path constriction37B is larger than both of the cross-sectional area of the third EGR port33and the cross-sectional area of the fourth EGR port34. Thus, even though the second backflow path constriction37B is provided, the configuration is capable of reducing the amount of EGR gas that flows out to the intake branch pipe113from the third EGR port33during the intake stroke of the third cylinder #3 and reducing the amount of EGR gas that flows out to the intake branch pipe114from the fourth EGR port34during the intake stroke of the fourth cylinder #4.

(9) Condensed water can be produced in the EGR gas distributor23. Such condensed water flows out to the intake branch pipes111to114through the EGR ports31to34. If acceleration is produced in the vehicle on which the internal combustion engine10is mounted when condensed water is retained in the EGR gas distributor23, the condensed water flows in the EGR gas distributor23in a direction corresponding to the acceleration.

In the present embodiment, the direction in which the first passageway411of the first gas passage41extends is different from the direction in which the fourth passageway421of the second gas passage42extends. Thus, even if acceleration in the port arrangement direction Y is produced, the condensed water retained in the second gas passage42is prevented from flowing out of the second gas passage42. Also, the condensed water retained between the first bent portion41A and the first EGR port31in the first gas passage41is prevented from flowing into the other gas passages42to44.

The direction in which the eighth passageway441of the fourth gas passage44extends is different from the direction in which the sixth passageway431of the third gas passage43extends. Thus, even if acceleration in the port arrangement direction Y is produced, the condensed water retained in the third gas passage43is prevented from flowing out of the third gas passage43. Also, the condensed water retained between the fifth bent portion44A and the fourth EGR port34in the fourth gas passage44is prevented from flowing into the other gas passages41to43.

Therefore, when acceleration is produced in the vehicle, condensed water in the EGR gas distributor23is prevented from flowing out to any one of the intake branch pipes111to114in a concentrated manner. That is, the condensed water is prevented from flowing into any one of the cylinders #1 to #4 in a concentrated manner.

If the backflow path F12, which connects the first EGR port31and the second EGR port32to each other, is longer than the first path F1and the second path F2, the EGR gas distributor23may be configured without the first backflow path constriction37A of the backflow path F12.

Likewise, if the backflow path F34, which connects the third EGR port33and the fourth EGR port34to each other, is longer than the third path F3and the fourth path F4, the EGR gas distributor23may be configured without the second backflow path constriction37B of the backflow path F34.

If the backflow path F12, which connects the first EGR port31and the second EGR port32to each other, is longer than the first path F1and the second path F2, the EGR gas distributor23may be configured without the first bent portion41A and/or the second bent portion41B of the first gas passage41. Further, the EGR gas distributor23may be configured without the third bent portion42A of the second gas passage42.

Likewise, if the backflow path F34, which connects the third EGR port33and the fourth EGR port34to each other, is longer than the third path F3and the fourth path F4, the EGR gas distributor23may be configured without the fifth bent portion44A and/or the sixth bent portion44B of the fourth gas passage44. Further, the EGR gas distributor23may be configured without the fourth bent portion43A of the third gas passage43.

If the backflow path F12, which connects the first EGR port31and the second EGR port32to each other, is longer than the first path F1and the second path F2, the first connection site, which connects the first gas passage41and the second gas passage42to each other, may be located at a position other than between the second EGR port32and the inflow portion30in the port arrangement direction Y.

Likewise, if the backflow path F34, which connects the third EGR port33and the fourth EGR port34to each other, is longer than the third path F3and the fourth path F4, the second connection site, which connects the third gas passage43and the fourth gas passage44to each other, may be located at a position other than between the third EGR port33and the inflow portion30in the port arrangement direction Y.

The EGR gas distributor23may be employed in an internal combustion engine in which intake strokes start in order of the first cylinder #1, the third cylinder #2, the fourth cylinder #4, and the second cylinder #3.