Air intake apparatus

This air intake apparatus includes an air intake apparatus body including an intake air passage and an external gas passage portion provided as a structure separate from the air intake apparatus body inside the air intake apparatus body, the external gas passage portion through which external gas can be introduced into the intake air passage.

TECHNICAL FIELD

The present invention relates to an air intake apparatus, and more particularly, it relates to an air intake apparatus configured such that external gas can be introduced into an intake air passage.

BACKGROUND ART

In general, an air intake apparatus configured such that external gas can be introduced into an intake air passage is known. Such an air intake apparatus is disclosed in Japanese Patent Laying-Open No. 2011-80394, for example.

In Japanese Patent Laying-Open No. 2011-80394, there is disclosed an air intake apparatus for a multi-cylinder (four-cylinder) engine configured such that exhaust gas (EGR gas) of the engine can be partially introduced into an intake air passage. This air intake apparatus for a multi-cylinder engine described in Japanese Patent Laying-Open No. 2011-80394 includes an air intake apparatus body formed by integrating a surge tank and four air intake pipes connected to the surge tank. An EGR gas recirculation path (external gas passage) for introducing the EGR gas (external gas) is integrally formed on an air intake pipe member along the outer wall surface of the air intake apparatus body. Therefore, the EGR gas flows through the EGR gas recirculation path arranged on the outer wall surface of the air intake apparatus body, is branched into four, and thereafter is introduced (supplied) into the air intake pipes through inlets that pass through the outer wall and are communicated with the air intake pipes.

PRIOR ART

Patent Document

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In the air intake apparatus for a multi-cylinder engine described in Japanese Patent Laying-Open No. 2011-80394, however, the EGR gas recirculation path is arranged on the outer wall surface side of the air intake apparatus body, and hence the EGR gas recirculation path is directly influenced by outside air temperature. Particularly when the engine is operated under conditions of low outside air temperature (below freezing) and the EGR gas is introduced, the EGR gas recirculation path is directly cooled by low-temperature outside air. In addition, the EGR gas recirculation path is indirectly cooled by the air intake apparatus body cooled by low-temperature intake air. Thus, moisture contained in the EGR gas is easily condensed in the vicinity of the cooled inner wall surface of the EGR gas recirculation path due to a difference in temperature between the cooled inner wall surface and the warm EGR gas discharged from the engine. Furthermore, when the generated condensed water is drawn into a cylinder by negative pressure, accidental fire occurs in a combustion chamber. In addition, a deposit caused by the condensed water is easily generated in the EGR gas recirculation path. For this reason, although the EGR gas is introduced in order to increase engine performance (fuel economy) by reducing a pumping loss (intake and exhaust loss), there is such a problem that engine quality is reduced due to occurrence of accidental fire in the cylinder or generation of a deposit.

The present invention has been proposed in order to solve the aforementioned problem, and an object of the present invention is to provide an air intake apparatus capable of increasing engine performance (fuel economy) while suppressing a reduction in engine quality.

Means for Solving the Problem

In order to attain the aforementioned object, an air intake apparatus according to an aspect of the present invention includes an air intake apparatus body including an intake air passage, and an external gas passage portion provided as a structure separate from the air intake apparatus body inside the air intake apparatus body, the external gas passage portion through which external gas can be introduced into the intake air passage.

As hereinabove described, the air intake apparatus according to this aspect of the present invention includes the external gas passage portion provided as the structure separate from the air intake apparatus body inside the air intake apparatus body, the external gas passage portion through which the external gas can be introduced into the intake air passage. Thus, the external gas passage portion is included in (built into) the air intake apparatus body in a state where the external gas passage portion is a separate member from the air intake apparatus body, and hence the external gas that flows through the external gas passage portion is inhibited by both the external gas passage portion and the air intake apparatus body outside the external gas passage portion from being directly influenced by outside air (outside air temperature). Therefore, even when an engine is operated under conditions of low outside air temperature (below freezing), the heat retaining property of the external gas passage portion is increased, and hence cooling of the warm external gas in the external gas passage portion is suppressed. In other words, moisture or the like contained in exhaust gas recirculation gas recirculated to the engine or blow-by gas (unburned gas mixture) for ventilating a crank chamber can be inhibited from being cooled and condensed in the external gas passage portion, and hence occurrence of accidental fire in a combustion chamber can be suppressed. Furthermore, generation of a deposit caused by the condensed water in the external gas passage portion can be suppressed. Consequently, engine performance (fuel economy) can be increased while a reduction in engine quality is suppressed.

Furthermore, in the aforementioned air intake apparatus according to this aspect, the external gas passage portion, which is the structure separate from the air intake apparatus body, is provided inside the air intake apparatus body, whereby protrusion of the external gas passage portion outward of the air intake apparatus body can be suppressed, and hence the air intake apparatus can be downsized. Consequently, the air intake apparatus that suppresses a reduction in its mountability to the engine can be obtained.

In the aforementioned air intake apparatus according to this aspect, the external gas passage portion is preferably arranged apart from an inner surface of the intake air passage by a space inside the air intake apparatus body. According to this structure, the external gas passage portion can be thermally insulated from the inner surface of the intake air passage in the air intake apparatus body by the space. More specifically, the space serves as a heat-insulating layer. Therefore, even if the air intake apparatus body is cooled by low-temperature outside air or low-temperature intake air that flows through the intake air passage, cooling of the external gas passage portion is effectively suppressed by the space serving as the heat-insulating layer, and hence the heat retaining property of the external gas passage portion can be effectively increased.

In the aforementioned air intake apparatus according to this aspect, the intake air passage preferably includes a plurality of intake air passages that distributes intake air to cylinders of an engine, respectively, and the external gas passage portion preferably has a tournament shape in which the external gas passage portion is hierarchically branched such that the external gas is guided to each of the plurality of intake air passages inside the air intake apparatus body. According to this structure, the external gas passage portion can be connected to each of the plurality of intake air passages while the flow path cross-sectional area of the external gas passage portion is reduced in stages, and hence the surface area of the external gas passage portion can be reduced as much as possible by this tournament shape. Therefore, a heat transfer area contacted by the external gas that flows through the external gas passage portion can be reduced as much as possible, and hence generation of the condensed water can be reduced. Furthermore, distributivity of the external gas can be ensured by the tournament shape.

In the aforementioned air intake apparatus according to this aspect, the external gas passage portion is preferably arranged inside the air intake apparatus body in a state where a plurality of members is combined with each other. According to this structure, even when the air intake apparatus body includes the intake air passage having a complicated shape with a bent portion (curved portion) or the like, the air intake apparatus can be formed by easily arranging the external gas passage portion separate in structure inside the air intake apparatus body without interfering with this intake air passage structure. Furthermore, the plurality of members are combined with each other, whereby the external gas passage portion having the tournament shape in which the external gas passage portion is hierarchically branched, for example, can be easily constructed.

In the aforementioned air intake apparatus according to this aspect, the external gas preferably includes exhaust gas recirculation gas for recirculating, to an engine, part of exhaust gas discharged from the engine. According to this structure, moisture contained in the exhaust gas recirculation gas can be inhibited from being cooled and condensed in the external gas passage portion, and hence occurrence of accidental fire in the combustion chamber can be suppressed. Furthermore, generation of a deposit caused by the condensed water in the external gas passage portion can be suppressed. Consequently, also in the engine that reduces a pumping loss (intake and exhaust loss) by taking in the exhaust gas recirculation gas to increase fuel economy, fuel economy can be increased while a reduction in engine quality is suppressed.

In the aforementioned structure in which the external gas passage portion has the tournament shape in which the external gas passage portion is hierarchically branched, an external gas introduction portion that introduces the external gas is preferably provided on one side end of the air intake apparatus body, and the external gas passage portion preferably extends inward of the air intake apparatus body through the external gas introduction portion, and has an asymmetrical tournament shape with respect to a starting point for branching to be hierarchically branched. According to this structure, even when the external gas is introduced from one side end of the air intake apparatus body into the external gas passage portion, flow path resistance can be substantially equalized by providing differences in length between a plurality of flow paths having the asymmetrical tournament shape, and hence the external gas can be distributed from downmost-stream inlets to the plurality of intake air passages, respectively, with the same gas flow amount (at the same gas flow rate).

In the aforementioned structure in which the external gas passage portion is arranged apart from the intake air passage by the space inside the air intake apparatus body, the air intake apparatus body is preferably constructed by bonding a first member, a second member, and an intermediate member arranged between the first member and the second member to each other in a state where the first member, the second member, and the intermediate member are stacked, the intake air passage is preferably formed in a region surrounded by the first member and the intermediate member, and the external gas passage portion is preferably arranged in a spatial region surrounded by the second member and the intermediate member. According to this structure, the external gas passage portion can be reliably thermally insulated from the inner surface of the intake air passage in the air intake apparatus body by the space.

Effect of the Invention

According to the present invention, as hereinabove described, the air intake apparatus capable of increasing engine performance (fuel economy) while suppressing a reduction in engine quality can be provided.

MODES FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is hereinafter described on the basis of the drawings.

The structure of an air intake apparatus100according to the embodiment of the present invention is now described with reference toFIGS. 1 to 7. In the following description, it is assumed that each cylinder is arranged along an X-axis direction with respect to an engine110. In addition, when the air intake apparatus100is viewed from the engine110, an X1side is set to a “left side”, an X2side is set to a “right side”, and the up-down direction of the engine110is set to a Z-axis direction.

The air intake apparatus100according to the embodiment of the present invention is mounted on the in-line four-cylinder engine110(the outer shape is shown by a one-dot chain line), as shown inFIG. 1. The air intake apparatus100constitutes a part of an air intake system that supplies air to the engine110, and includes an air intake apparatus body80including a surge tank10and an air intake pipe portion20arranged downstream of the surge tank10.

In the air intake apparatus100, intake air that reaches an air intake12a(seeFIG. 2) through an air cleaner (not shown) and a throttle valve120serving as an intake air path flows into the surge tank10. The air intake apparatus100is mounted on a side wall110aof the engine110in a state where the throttle valve120is obliquely mounted on the air intake apparatus body80to be oriented downward from a horizontal position (a throttle body mounting portion12is oriented upward from a horizontal position).

EGR (exhaust gas recirculation) gas, which is part of exhaust gas discharged outward from a combustion chamber (cylinder (not shown)), is recirculated to the engine110through the air intake apparatus100. Here, the EGR gas separate from the exhaust gas is cooled to a predetermined temperature (about 100° C.) and thereafter is introduced into the air intake apparatus body80. The EGR gas contains moisture. The EGR gas is an example of “external gas” or “exhaust gas recirculation gas” in the present invention.

As shown inFIG. 2, both the surge tank10and the air intake pipe portion20that constitute the air intake apparatus body80are made of resin (polyamide resin, for example). In the air intake apparatus body80, an upper piece81(seeFIG. 3) in which an upper half of the surge tank10and an upper half of the air intake pipe portion20are integrally molded and a lower piece82(seeFIG. 3) in which a lower half of the surge tank10and a lower half of the air intake pipe portion20are integrally molded are integrally bonded to each other by vibration welding, as shown inFIGS. 3 and 4. The lower piece82integrally includes flow paths42dto42g(seeFIG. 6) described later. The upper piece81and the lower piece82are examples of a “first member” and a “second member” in the present invention.

As shown inFIG. 2, the surge tank10includes a hollow body11that extends along a cylinder bank (X-axis) of the engine110(seeFIG. 1). A left half (X1side) of the air intake pipe portion20connected to the body11is constituted by a single left main pipe21and a left air intake pipe group22connected to the left main pipe21. Similarly, a right half (X2side) of the air intake pipe portion20is constituted by a single right main pipe24and a right air intake pipe group25connected to the right main pipe24.

The left air intake pipe group22includes two air intake pipes22aand22binto which the left main pipe21is branched. Similarly, the right air intake pipe group25includes two air intake pipes25aand25binto which the right main pipe24is branched. The left air intake pipe group22and the right air intake pipe group25have a bilaterally symmetrical shape. The air intake pipes22a,22b,25a, and25bare examples of an “intake air passage” in the present invention.

According to this embodiment, the EGR gas is introduced into the engine110, as described above. Specifically, an EGR gas passage portion40is provided inside the air intake apparatus body80, as shown inFIG. 6. According to this embodiment, the EGR gas passage portion40is constructed as a member (structure) separate from the air intake apparatus body80. The EGR gas passage portion40is an example of an “external gas passage portion” in the present invention. The structure of the EGR gas passage portion40is described below in detail.

The EGR gas passage portion40includes an EGR gas introduction portion41that is open outward (X1side) and an EGR gas flow path42being connected to the EGR gas introduction portion41, to which the EGR gas flows, and supplying (introducing) the EGR gas to each of the air intake pipes22a,22b,25a, and25b, as shown inFIG. 6. The EGR gas flow path42includes a single flow path42aof a first hierarchy that extends from the EGR gas introduction portion41, two flow paths42b(X1side) and42c(X2side) of a second hierarchy into which the flow path42ais branched, two flow paths42d(X1side) and42e(X2side) of a third hierarchy into which the flow path42bis branched, and two flow paths42f(X1side) and42g(X2side) of the third hierarchy into which the flow path42cis branched.

The EGR gas flow path42further includes a tubular inlet43that connects the flow path42dto the air intake pipe22a, a tubular inlet44that connects the flow path42eto the air intake pipe22b, a tubular inlet45that connects the flow path42fto the air intake pipe25b, and a tubular inlet46that connects the flow path42gto the air intake pipe25a. The flow path cross-sectional areas of the flow paths42band42care relatively smaller than the flow path cross-sectional area of the flow path42a, and the flow path cross-sectional areas of the flow paths42dto42gare relatively smaller than the flow path cross-sectional areas of the flow paths42band42c. The flow path cross-sectional areas of the distal inlets43to46are minimized. Thus, the EGR gas passage portion40has a tournament shape in which the EGR gas flow path42is hierarchically branched. The EGR gas taken from the EGR gas introduction portion41sequentially flows through the EGR gas flow path42(the flow paths42ato42gand the inlets43to46), and is introduced into each of the air intake pipes22a,22b,25b, and25a.

As shown inFIG. 5, the air intake apparatus body80further includes an interior bulkhead piece83made of resin, an EGR first piece84, and an EGR second piece85in addition to the upper piece81and the lower piece82. The interior bulkhead piece83is an example of an “intermediate member” in the present invention.

The interior bulkhead piece83has a curved inner wall surface83a(Z1side) and a curved wall surface83b(Z2side), and is a component bonded to the upper piece81in a state where the interior bulkhead piece83faces the inner wall surface81aof the upper piece81such that curved intake air passages can be formed. The EGR gas introduction portion41is integrally formed on a side portion of the lower piece82on the X1side, as shown inFIGS. 5 and 6. As shown inFIGS. 6 and 7, the EGR second piece85has a shape that allows the EGR second piece85to be bonded to the inside of the lower piece82, and the EGR first piece84has a shape that allows the EGR first piece84to be bonded to a portion of the EGR second piece85opposite to the lower piece82and a flanged inner portion41a(a portion inside the air intake apparatus body80; seeFIG. 6) of the EGR gas introduction portion41.

Thus, in the air intake apparatus100, the EGR gas passage portion40is defined by a part of the lower piece82, the EGR first piece84, and the EGR second piece85. In other words, the EGR gas passage portion40is arranged inside the air intake apparatus body80in a state where the lower piece82, the EGR first piece84, and the EGR second piece85as a plurality of (three) members are combined with each other. The lower piece82, the EGR first piece84, and the EGR second piece85are examples of a “plurality of members” in the present invention.

A process for manufacturing the air intake apparatus body80is now described. As shown inFIG. 5, the EGR second piece85is first bonded to the lower piece82by vibration welding. Then, the EGR first piece84is bonded, by vibration welding, to a structure91formed by integrating the lower piece82and the EGR second piece85. Apart from the above, the interior bulkhead piece83is bonded to the upper piece81by vibration welding. Then, a structure93formed by integrating the upper piece81and the interior bulkhead piece83is bonded, by vibration welding, to a structure92formed by integrating the lower piece82, the EGR second piece85, and the EGR first piece84. The air intake apparatus body80having the built-in EGR gas passage portion40is formed in this manner.

As shown inFIG. 6, the EGR second piece85faces the lower piece82(upper portions of the air intake pipes22a,22b,25a, and25b) in the up-down direction (arrow A direction) of the plane of the figure, and is bonded to the lower piece82. The EGR first piece84faces the EGR second piece85in the up-down direction of the plane of the figure, and is bonded to the EGR second piece85. In addition, a bonding portion84aof the EGR first piece84faces the flanged inner portion41aof the EGR gas introduction portion41in the lower piece82in the up-down direction (arrow A direction), left-right direction (X-axis direction), and depth direction (arrow B direction) of the plane of the figure, and is bonded to the flanged inner portion41a.

Thus, according to this embodiment, the bonding portion84aof the EGR first piece84and the inner portion41aof the EGR gas introduction portion41are bonded to each other in the three directions (surface-to surface bonding at three positions), whereby the EGR first piece84is accurately aligned with respect to the EGR gas introduction portion41. Thus, the EGR gas that flows through the EGR gas introduction portion41reliably flows to the downstream flow path42a, and the EGR first piece84is steadied inside a space S while maintaining a state where the EGR first piece84and the air intake pipes22a,22b,25b, and25asandwich the EGR second piece85therebetween.

As shown inFIG. 6, the interior bulkhead piece83is incorporated into positions corresponding to a portion of the upper piece81in which the left main pipe21is branched to the left air intake pipe group22and a portion of the upper piece81in which the right main pipe24is branched to the right air intake pipe group25. The intake air passage inner surfaces of the portion in which the left main pipe21is branched to the left air intake pipe group22(air intake pipes22aand22b) and the portion in which the right main pipe24is branched to the right air intake pipe group25(air intake pipes25aand25b) are formed by the inner wall surface81aof the upper piece81and the inner wall surface83aof the interior bulkhead piece83that faces the inner wall surface81a. The inner wall surface81aof the upper piece81and the inner wall surface83aof the interior bulkhead piece83are examples of an “inner surface of the intake air passage” in the present invention.

According to this embodiment, the EGR gas passage portion40is spaced apart from the upper piece81with the space S having a predetermined volume by the interior bulkhead piece83inside the air intake apparatus body80, as shown inFIGS. 6 and 7. In other words, in a state where the interior bulkhead piece83is bonded to the upper piece81, the space S is formed between the wall surface83bof the interior bulkhead piece83opposite to the inner wall surface83aand the outer wall surface82bof the lower piece82that correspond to portions of the left air intake pipe group22and the right air intake pipe group25.

The space S serves as a storage that stores the EGR gas passage portion40, and has a three-dimensionally intricate shape. Thus, an inner surface (the inner surfaces of the air intake pipes22a,22b,25a, and25b(the inner wall surface81aand the inner wall surface83a)) along which the intake air flows in the lower piece82and the EGR gas passage portion40(EGR gas flow path42) are prevented as much as possible through the intervention of the space S from directly contacting each other. Seen in this light, the EGR gas flow path42is in a bridged state inside the air intake apparatus body80, using the space S as a heat-insulating layer.

In the above manufacturing process, the EGR second piece85and the EGR first piece84are combined with the lower piece82, whereby the EGR gas passage portion40is formed. In this state, the structure93(seeFIG. 5) formed by integrating the upper piece81and the interior bulkhead piece83is bonded to the structure92(seeFIG. 5) by vibration welding, whereby the EGR gas passage portion40is surrounded by the space S (seeFIG. 6).

The space S is filled with air, and serves as the heat-insulating layer. Therefore, the temperature of the upper piece81, the interior bulkhead piece83, and the lower piece82is not directly transmitted to the EGR gas passage portion40(the flow path42a, the flow path42b, and the flow path42cin the EGR gas flow path42). In other words, the EGR gas passage portion40is thermally insulated from the inner surface (the inner wall surface81aand the inner wall surface83a) of the air intake apparatus body80by the space S, and the heat of the intake air is prevented as much as possible from being transferred to the EGR gas passage portion40. Therefore, even if the air intake apparatus body80is cooled by low-temperature outside air or the low-temperature intake air that flows through the air intake pipes22a,22b,25a, and25b, cooling of the EGR gas that flows through the EGR gas flow path42is effectively suppressed by the space S serving as the heat-insulating layer.

As shown inFIGS. 6 and 7, the lower piece82includes the aforementioned inlet43for the air intake pipe22a, inlet44for the air intake pipe22b, inlet45for the air intake pipe25b, and inlet46for the air intake pipe25a. Therefore, the EGR gas passage portion40surrounded by the space S physically contacts the intake air passages (air intake pipes22a,22b,25a, and25b) only through the inlets43to46at an end of the tournament shape.

As shown inFIG. 6, the tournament shape of the EGR gas passage portion40is bilaterally asymmetrical. Specifically, in the EGR gas flow path42, a path length from the EGR gas introduction portion41, which is open to the X1side of the air intake apparatus body80, to the inlet45or46arranged closer to the X2side is relatively larger than a path length from the EGR gas introduction portion41to the inlet43or44arranged closer to the X1side. Furthermore, in the second hierarchy, the length of the flow path42b(X1side) in the X-axis direction is shorter than the length of the flow path42c(X2side) in the X-axis direction. More specifically, the flow paths42band42care divergingly formed with asymmetrical lengths from a starting point from which the flow path42aof the first hierarchy branches into flow paths42band42c. In the third hierarchy, the length of the flow path42d(X1side) in the X-axis direction is shorter than the length of the flow path42e(X2side) in the X-axis direction. Similarly, in the third hierarchy, the length of the flow path42f(X1side) in the X-axis direction is shorter than the length of the flow path42g(X2side) in the X-axis direction. More specifically, the flow paths42dand42eare divergingly formed with asymmetrical lengths to right and left from a starting point from which the flow path42bof the second hierarchy branches into flow paths42dand42e. Similarly, the flow paths42fand42gare divergingly formed with asymmetrical lengths to right and left from a starting point from which the flow path42cof the second hierarchy branches into flow paths42fand42g.

In the air intake apparatus100, these differences are provided in the path lengths of the flow paths formed by branching the single flow path42into four systems in order to equalize the flow rate (flow amount) of the EGR gas in the inlets43to45serving as final exits (inlets to the intake air passages) in a state where the EGR gas introduction portion41is provided on one side (X1side) of the air intake apparatus body80. The EGR gas flows through the upmost-stream flow path42ain an arrow X2direction, and hence the EGR gas tends to relatively easily flow through the flow paths42c,42e, and42gthat extend in the arrow X2direction as compared with the flow paths42b,42d, and42fthat extend in an arrow X1direction. Therefore, the flow paths42c,42e, and42gthat extend in the arrow X2direction are increased in length to obtain flow path resistance. In contrast, the flow paths42b,42d, and42fare decreased in length to reduce flow path resistance. Thus, the EGR gas, which is introduced from one side of the air intake apparatus body80and flows through the flow path42ain the arrow X2direction, is distributed to each of the air intake pipes22a,22b,25a, and25bthrough the downmost-stream inlets43to46with the same gas flow amount.

As shown inFIG. 2, the surge tank10is provided with the throttle body mounting portion12including the air intake12aon the upper surface11aside (a surface visible at the front side of the plane of the figure) of a central portion of the surge tank10in a direction (left-right direction: X-axis direction) in which the body11extends. In the air intake apparatus100, the single left main pipe21is connected to a left end13(X1side) of the surge tank10in the direction in which the body11extends, and the single right main pipe24is connected to a right end14(X2side) of the surge tank10in the direction in which the body11extends. In this case, an intake air path length from the air intake12aof the surge tank10to a connection (end21a) of the left main pipe21and an intake air path length from the air intake12aof the surge tank10to a connection (end24a) of the right main pipe24are equal to each other. Furthermore, the left main pipe21is branched into the air intake pipes22aand22bon the side (a downstream side in a direction of intake air flow) opposite to the side (end21aside) of the left main pipe21connected to the body11. Similarly, the right main pipe24is branched into the air intake pipes25aand25bon the side (the downstream side in the direction of intake air flow) opposite to the side (end24aside) of the right main pipe24connected to the body11.

Therefore, inside the body11, approximately half of the intake air taken into the surge tank10through the air intake12ais distributed in a left direction (X1side), and the remaining approximately half of the intake air is distributed in a right direction (X2side). Then, the approximately half of the intake air is guided from the left end13to the left main pipe21, and the remaining approximately half of the intake air is guided from the right end14to the right main pipe24. Then, the intake air is further distributed to the air intake pipes22aand22bon the downstream side of the left main pipe21and further distributed to the air intake pipes25aand25bon the downstream side of the right main pipe24.

As shown inFIG. 2, an air intake pipe length from the end21aof the left main pipe21closer to the surge tank10to each of tip ends23aand23bof the air intake pipes22aand22bin the left air intake pipe group22is equal to an air intake pipe length from the end24aof the right main pipe24closer to the surge tank10to each of tip ends26aand26bof the air intake pipes25aand25bin the right air intake pipe group25.

In other words, an intake air path length from the end21aof the left main pipe21that corresponds to a left exit of the surge tank10to the tip end23aof the air intake pipe22abranched toward a corresponding cylinder of the engine110(seeFIG. 1) and an intake air path length from the end21aof the left main pipe21to the tip end23bof the air intake pipe22bare equal to each other. An intake air path length from the end24aof the right main pipe24that corresponds to a right exit of the surge tank10to the tip end26aof the air intake pipe25abranched toward a corresponding cylinder of the engine110(seeFIG. 1) and an intake air path length from the end24aof the right main pipe24to the tip end26bof the air intake pipe25bare equal to each other. The air intake pipe portion20is configured such that these four intake air path lengths are equal to each other.

Thus, the air intake apparatus body80is configured to take in intake air from the central portion of the surge tank10and guide, with the same flow amount (with one fourth), the intake air to the four air intake pipes22a,22b,25a, and25bthrough the single left main pipe21and the single right main pipe24connected to the left and right ends of the surge tank10, as shown inFIG. 1.

In the surge tank10, the inner surface of the body11is concavo-convex. Specifically, a convex portion15that is raised in an arrow Z1direction is provided inside the surge tank10, as shown inFIG. 2. Thus, an inner bottom surface lib (seeFIG. 4) that corresponds to a central portion of the body11formed with the throttle body mounting portion12protrudes inward of the surge tank10with respect to the inner bottom surface11cof the left end13and the inner bottom surface11dof the right end14of the surge tank10in the left-right direction. The end21aof the left main pipe21connected to the surge tank10is provided in the vicinity of the lowermost portion of the left end13, and the end24aof the right main pipe24connected to the surge tank10is provided in the vicinity of the lowermost portion of the right end14.

As shown inFIGS. 1 and 2, the tip end23aof the air intake pipe22a, the tip end23bof the air intake pipe22b, the tip end26aof the air intake pipe25a, and the tip end26bof the air intake pipe25bthat constitute the air intake pipe portion20are linearly arranged along the direction (X-axis direction) in which the body11of the surge tank10extends. The air intake apparatus100according to this embodiment is configured in the above manner.

According to this embodiment, the following effects can be obtained.

According to this embodiment, as hereinabove described, the EGR gas passage portion40provided as a structure separate from the air intake apparatus body80, through which the EGR gas can be introduced into the air intake pipes22a,22b,25a, and25bis provided inside the air intake apparatus body80. Thus, the EGR gas passage portion40is included in (built into) the air intake apparatus body80in a state where the EGR gas passage portion40is a separate member from the air intake apparatus body80, and hence the EGR gas that flows through the EGR gas passage portion40is inhibited by both the EGR gas passage portion40and the air intake apparatus body80outside the EGR gas passage portion40from being directly influenced by the outside air (outside air temperature). Therefore, even when the engine110is operated under conditions of low outside air temperature (below freezing), the heat retaining property of the EGR gas passage portion40is increased, and hence cooling of the warm EGR gas in the EGR gas passage portion40is suppressed. In other words, moisture contained in the EGR gas for recirculating part of the exhaust gas discharged from the engine110to the engine110can be inhibited from being cooled and condensed in the EGR gas passage portion40, and hence occurrence of accidental fire in the combustion chamber can be suppressed. Furthermore, generation of a deposit caused by the condensed water in the EGR gas passage portion40can be suppressed. Consequently, also in the engine110that reduces a pumping loss (intake and exhaust loss) by taking in the EGR gas to increase fuel economy, fuel economy can be increased while a reduction in the quality of the engine110is suppressed.

According to this embodiment, the EGR gas passage portion40, which is the structure separate from the air intake apparatus body80, is provided inside the air intake apparatus body80, whereby protrusion of the EGR gas passage portion40outward of the air intake apparatus body80can be suppressed, and hence the air intake apparatus100can be downsized. Consequently, the air intake apparatus100that suppresses a reduction in its mountability to the engine110can be obtained.

According to this embodiment, the EGR gas passage portion40is arranged apart from the inner surfaces (the inner wall surface81aand the inner wall surface83a) of the air intake pipes22a,22b,25a, and25bby the space S inside the air intake apparatus body80. Thus, the EGR gas passage portion40can be thermally insulated from the inner surfaces (the inner wall surface81aand the inner wall surface83a) of the air intake pipes22a,22b,25a, and25bin the air intake apparatus body80by the space S. More specifically, the space S serves as the heat-insulating layer. Therefore, even if the air intake apparatus body80is cooled by the low-temperature outside air or the low-temperature intake air that flows through the air intake pipes22a,22b,25a, and25b, cooling of the EGR gas passage portion40is effectively suppressed by the space S serving as the heat-insulating layer, and hence the heat retaining property of the EGR gas passage portion40can be effectively increased.

According to this embodiment, the four air intake pipes22a,22b,25a, and25bthat distribute the intake air to cylinders of the engine110, respectively, are provided in the air intake pipe portion20. Furthermore, in the air intake apparatus100, the EGR gas passage portion40has the tournament shape in which the EGR gas passage portion40is hierarchically branched such that the EGR gas is guided to each of a plurality of air intake pipes22a,22b,25a, and25binside the air intake apparatus body80. Thus, the EGR gas passage portion40can be connected to each of the plurality of air intake pipes22a,22b,25a, and25bwhile the flow path cross-sectional area of the EGR gas passage portion40is reduced in stages, and hence the surface area of the EGR gas passage portion40can be reduced as much as possible by this tournament shape. Therefore, a heat transfer area contacted by the EGR gas that flows through the EGR gas passage portion40can be reduced as much as possible, and hence generation of the condensed water can be reduced. Furthermore, distributivity of the EGR gas can be ensured by the tournament shape.

According to this embodiment, the air intake apparatus100includes the EGR gas passage portion40arranged inside the air intake apparatus body80in a state where the lower piece82, the EGR first piece84, and the EGR second piece85are combined with each other. Thus, even when the air intake apparatus body80includes the air intake pipes22a,22b,25a, and25bhaving complicated shapes with bent portions (curved portions) or the like, the air intake apparatus100can be formed by easily arranging the EGR gas passage portion40separate in structure inside the air intake apparatus body80without interfering with this intake air passage structure. Furthermore, the above three members are combined with each other, whereby the EGR gas passage portion40having the tournament shape in which the EGR gas passage portion40is hierarchically branched can be easily constructed.

According to this embodiment, the EGR gas passage portion40that has the asymmetrical tournament shape with respect to the starting point for branching to be hierarchically branched is provided. Thus, even when the EGR gas is introduced from an end of the air intake apparatus body80on the X1side into the EGR gas passage portion40, flow path resistance can be substantially equalized by providing differences in length between the four flow paths having the asymmetrical tournament shape, and hence the EGR gas can be distributed from the downmost-stream inlets43to46to each of the air intake pipes22a,22b,25a, and25bwith the same gas flow amount and at the same gas flow rate.

According to this embodiment, the air intake pipes22a,22b,25a, and25bare formed in a region surrounded by the upper piece81and the interior bulkhead piece83, and the EGR gas passage portion40is arranged in the space S surrounded by the lower piece82and the interior bulkhead piece83. Thus, the EGR gas passage portion40can be reliably thermally insulated from the inner wall surface81aand the inner wall surface83aof the air intake pipes22a,22b,25a, and25bin the air intake apparatus body80by the space S.

The embodiment disclosed this time must be considered as illustrative in all points and not restrictive. The range of the present invention is shown not by the above description of the embodiment but by the scope of claims for patent, and all modifications within the meaning and range equivalent to the scope of claims for patent are further included.

For example, while the present invention is applied to the air intake apparatus100mounted on the in-line four-cylinder engine110in the aforementioned embodiment, the present invention is not restricted to this. In other words, the air intake apparatus according to the present invention may be mounted on an in-line multi-cylinder engine other than the in-line four-cylinder engine or may be mounted on a V-type multi-cylinder engine, a horizontal opposed engine, or the like. As the engine, a gasoline engine, a diesel engine, a gas engine, or the like is applicable. Alternatively, the present invention is also applicable to an air intake apparatus mounted on an internal-combustion engine or the like placed on transportation equipment such as a train or a marine vessel or stationary equipment other than the transportation equipment in addition to the engine (internal-combustion engine) mounted on a common vehicle (motor vehicle).

While the space S that surrounds the EGR gas passage portion40is filled with air in the aforementioned embodiment, the present invention is not restricted to this. The space S may be filled with a filler having a heat insulating property, for example. The space S may be filled with a foam insulation such as urethane resin as the filler. Alternatively, the space S may be filled with not only the foam insulation but also a fiber insulation such as glass wool. In this case, the upper piece81to which the interior bulkhead piece83is bonded may be bonded to the lower piece82in a state where the EGR gas passage portion40is enclosed (covered) by the foam insulation or the fiber insulation. In addition, an air layer (heat-insulating layer) may be further provided in a clearance between the EGR gas passage portion40covered by a covering layer (heat-insulating layer) such as the foam insulation or the fiber insulation and the interior bulkhead piece83.

While the EGR gas passage portion40is formed by bonding the lower piece82, the EGR first piece84, and the EGR second piece85to each other in the aforementioned embodiment, the present invention is not restricted to this. In other words, the EGR gas passage portion40may be formed by combining two members, or the EGR gas passage portion40may be formed by combining four or more members.

While the EGR gas (exhaust gas recirculation gas) is introduced into each of the air intake pipes22a,22b,25a, and25bin the aforementioned embodiment, the present invention is not restricted to this. The “external gas passage portion” according to the present invention is also applicable to a structure in which blow-by gas (PCV gas) for ventilating a crank chamber is introduced as the “external gas” according to the present invention into each of the air intake pipes22a,22b,25a, and25b, for example. In other words, moisture or the like contained in the blow-by gas (unburned gas mixture) can be inhibited from being cooled and condensed in the external gas passage portion, and occurrence of accidental fire in the combustion chamber can be suppressed. Furthermore, generation of a deposit caused by the condensed water in the external gas passage portion can be suppressed. Consequently, engine performance (fuel economy) can be increased while a reduction in engine quality is suppressed.

While the EGR gas passage portion40has the bilaterally asymmetrical tournament shape in the aforementioned embodiment, the present invention is not restricted to this. The “external gas passage portion” may be configured such that downstream distribution flow paths have a bilaterally symmetrical tournament shape by constructing the EGR gas passage portion including the EGR gas introduction portion41formed at a central portion of the air intake apparatus.

While the EGR gas passage portion40is configured to distribute the EGR gas to each of the air intake pipes22a,22b,25a, and25bin the aforementioned embodiment, the present invention is not restricted to this. Even when the EGR gas is introduced into the surge tank10inside the air intake apparatus body80, for example, the “external gas passage portion” according to the present invention separate in structure from the air intake apparatus body80may be internally provided. In this case, the EGR gas may be introduced into the surge tank10through a single inlet or a plurality of inlets.

While both the air intake apparatus body80and the EGR gas passage portion40are made of resin (polyamide resin) in the aforementioned embodiment, the present invention is not restricted to this. In other words, the air intake apparatus body80and the EGR gas passage portion40may be made of metal so far as the EGR gas passage portion40is provided as a structure (member) separate from the air intake apparatus body80inside the air intake apparatus body80.

DESCRIPTION OF REFERENCE SIGNS