Engine intake structure

Abstract

To provide an intake structure of an engine capable of enhancing mixing of intake air and an EGR gas, while disposing an intake passage around an engine body in compact.SOLUTION: An intake passage is provided with a first passage portion with a throttle valve and a second passage portion disposed at a downstream side of the first passage portion, the first passage portion has a shape linearly extending along a prescribed first direction, and the second passage portion has a shape curved from an end portion at the downstream side of the first passage portion toward one side in a second direction orthogonal to the first direction with respect to the end portion. A curved wall extending while curving from the other side part in the second direction of an inner wall of the first passage portion toward one side in the second direction is disposed on an inner wall of the second passage portion, the curved wall has a curved shape recessed to be convex to the other side in the second direction, and an end portion at a downstream side of an EGR passage is connected to an end portion at an upstream side of the curved wall.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an intake structure for an engine that includes an engine body, an intake passage connected to an intake port formed in the engine body and through which intake air introduced into the engine body flows, an exhaust passage through which exhaust gas discharged from the engine body flows, and an EGR passage that connects the intake passage and the exhaust passage and recirculates a portion of the exhaust gas back into the intake passage. [Background technology]

[0002] BACKGROUND ART Conventionally, engines installed in vehicles and the like have implemented an EGR system in which a portion of the exhaust gas is recirculated to an intake passage.

[0003] For example, Patent Document 1 discloses an engine that includes an engine body with four cylinders arranged in series and a turbocharger, in which a portion of the exhaust gas passing through a portion of the exhaust passage upstream of the turbine is recirculated to a portion of the intake passage downstream of the compressor. In addition, in the engine of Patent Document 1, the intake passage downstream of the portion where EGR gas is introduced is formed so as to turn back. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-65808 Summary of the Invention [Problem to be solved by the invention]

[0005] In the configuration of Patent Document 1, the intake passage downstream of the portion where the EGR gas is introduced is formed so as to turn back, which means that two passages are arranged side by side around the engine body, resulting in a problem of poor layout. Therefore, it is conceivable to omit this turning back, but in this case, the length of the gas flow path from the portion where the EGR gas is introduced to the engine body becomes shorter, which may result in insufficient mixing of the EGR gas and intake air before it is introduced into the engine body.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide an engine intake structure that can promote mixing of intake air and EGR gas while compactly arranging an intake passage around the engine body. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides an engine body, Aspects of an intake passage connected to an intake port formed in a cylinder bore and through which intake air introduced into the engine body flows, an exhaust passage through which exhaust gas discharged from the engine body flows, and an EGR passage which connects the intake passage and the exhaust passage and recirculates a portion of the exhaust gas to the intake passage; the intake passage includes a first passage portion in which a throttle valve capable of changing a flow path area of ​​the intake air is disposed, and a second passage portion disposed downstream of the first passage portion, the first passage portion having a shape which extends linearly along a predetermined first direction, and the second passage portion When a direction along the side surface of the engine body and perpendicular to the first direction is defined as a second direction, From the downstream end of the first passage portion, Record number The EGR passage has a shape that curves toward one of two directions, and the inner wall of the second passage portion has a curved wall that extends while curving from the other side portion of the inner wall of the first passage portion in the second direction toward one side in the second direction, and the curved wall has a curved shape that is recessed so as to be convex toward the other side in the second direction, and the downstream end of the EGR passage is connected to the upstream end of the curved wall (Claim 1).

[0008] In the present invention, the second passage portion disposed downstream of the first passage portion extending linearly along the first direction is curved from the downstream end of the first passage portion toward one side in the first direction. The downstream end of the EGR introduction portion is connected to the upstream end of a curved inner wall of the second passage portion extending from the inner wall of the first passage portion. Therefore, compared to a case in which the second passage portion is shaped to extend linearly along the first direction, the passage length of the second passage portion, and therefore the flow path length of the EGR gas, can be increased. Furthermore, a secondary flow can be generated in a region downstream of the EGR introduction portion of the second passage portion, thereby promoting mixing of the EGR gas introduced from the EGR introduction portion into the second passage portion with the intake air. Thus, according to the present invention, the space occupied by the intake passage can be reduced compared to a case in which two intake passages are arranged side by side as in Patent Document 1, and the intake passage can be arranged compactly around the engine body, promoting mixing of the EGR gas with the intake air.

[0009] Furthermore, in this configuration, the curved wall has a concave curved shape that is convex toward the other side in the second direction, so that the EGR gas introduced into the second passage through the EGR introduction portion can be directed downstream along the curved wall, thereby preventing the EGR gas from flowing back upstream of the intake passage and allowing the EGR gas to move appropriately downstream, i.e., into the engine body.

[0010] In the above-described configuration, preferably, the downstream end of the EGR passage projects inward from the second passage portion, and has an opening at its tip that opens downstream (claim 2).

[0011] According to this configuration, the EGR gas can be reliably moved downstream and appropriately flowed into the engine body.

[0012] In the above configuration, preferably, the inner wall of the second passage portion has a second curved wall that extends while curving from the one side portion of the inner wall of the first passage portion in the second direction toward the one side in the second direction, and the second curved wall has a curved shape that is recessed so as to be convex toward the one side in the second direction (claim 3).

[0013] According to this configuration, a vortex can be generated in the region along the second curved wall, and the action of this vortex can further promote the mixing of the EGR gas and the intake air.

[0014] The engine body may be a rotary piston engine (claim 4). [Effects of the Invention]

[0015] As described above, the engine intake structure of the present invention can promote the mixing of intake air and EGR gas while compactly arranging the intake passage around the engine body. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a system diagram showing a schematic configuration of an engine according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic side view of the engine as seen from the right. [Figure 3] FIG. 3 is a schematic side view corresponding to FIG. 2 and showing details of components of the intake and exhaust system. [Figure 4] FIG. 2 is a schematic side view of the engine as seen from the rear. [Figure 5] FIG. 5 is a schematic cross-sectional view showing a cross section taken along line VV in FIG. 4. [Figure 6] FIG. 4 is a schematic plan view of the downstream end of the EGR passage. [Figure 7] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Overall engine configuration) Fig. 1 is a system diagram showing a schematic configuration of an engine to which an intake structure for an engine according to an embodiment of the present invention is applied. Fig. 2 and Fig. 3 are schematic side views of the engine. Fig. 4 is a schematic side view of the engine as seen from a direction perpendicular to Figs. 2 and 3.

[0018] The engine 1 according to this embodiment is mounted on a vehicle. For example, the engine 1 is mounted on a hybrid vehicle equipped with a motor as a power source for driving, a battery for supplying power to the motor, and a generator for charging the battery, and is used as a device for generating electricity from the generator. The engine 1 includes an engine body 10, an intake passage 3 through which intake air introduced into the engine body 10 flows, an exhaust passage 8 through which exhaust gas discharged from the engine body 10 flows, and an EGR passage 6 which connects the exhaust passage 8 and the intake passage 3 and recirculates EGR gas, which is a part of the exhaust gas, from the exhaust passage 8 to the intake passage 3.

[0019] (Engine body) The engine body 10 of this embodiment is a one-rotor type rotary piston engine (hereinafter referred to as a rotary engine) that has one rotor 11 that rotates around a predetermined rotation axis, an eccentric shaft 12 that extends along the rotation axis of the rotor 11, a rotor housing 13 with an inner circumferential surface that follows a two-node peritrochoid curve, and a pair of side housings 14, 14 that sandwich the rotor housing 13 in the direction along the rotation axis of the rotor 11. The rotor 11 is housed in a rotor housing chamber R that is partitioned by the rotor housing 13 and the two side housings 14, 14, and rotates along the inner circumferential surface of the rotor housing 13 by planetary rotation relative to the eccentric shaft 12.

[0020] The engine body 10 also has a rear holder 20 that is connected to one of the side housings 14 on the opposite side from the rotor housing 13 (in the direction along the rotation axis of the rotor 11) and to which a flywheel 21 is fixed. An oil pan 22 is attached to the bottom of the engine body 10.

[0021] The engine body 10 is mounted on the vehicle in a position where the rotation axis of the rotor 11 and the eccentric shaft 12 extend in a substantially horizontal direction (a direction substantially perpendicular to the up-down direction). In the following description, as shown in FIG. 2 etc., the direction along the rotation axis of the rotor 11, i.e., the longitudinal direction of the eccentric shaft 12, is referred to as the front-rear direction, and the side where the flywheel 21 is disposed is referred to as the rear, and the opposite side as the front. In addition, in the description of the engine 1, Engine body 10 In the following description, the up-down direction when the engine body 10 is mounted on a vehicle will be referred to simply as the up-down direction, and the left-right direction when the engine body 10 is viewed from the rear will be referred to simply as the left-right direction. Also, Figs. 2 and 3 are views of the engine 1 as viewed from the right. Fig. 4 is a view of the engine 1 as viewed from the rear. In this embodiment, the "up-down direction" corresponds to the "first direction" in the claims, and the "front-rear direction" corresponds to the "second direction" in the claims.

[0022] The engine body 10 is formed with an intake port 15 connected to the intake passage 3 to introduce intake air within the intake passage 3 into the rotor housing chamber R, and an exhaust port 16 connected to the exhaust passage 8 to guide exhaust air from the rotor housing chamber R to the exhaust passage 8. The intake port 15 opens to the upper right side of the rotor housing chamber R, and the exhaust port 16 opens to the lower right side of the rotor housing chamber R. In other words, the engine body 10 is configured so that the rotor 11 rotates clockwise when viewed from the front, and the upper right, upper left, lower left, and lower right regions of the rotor housing chamber R generally serve as regions for the intake stroke, compression stroke, expansion stroke, and exhaust stroke, respectively.

[0023] Two intake ports 15 and two exhaust ports 16 are provided in the engine body 10. The engine body 10 is a side-port rotary engine, and the intake ports 15 and exhaust ports 16 are formed in the side housings 14. That is, one intake port 15 is formed in the upper part of each of the two side housings 14, and each intake port 15 opens on the right side surface of the upper part of each side housing 14. Also, one exhaust port 16 is formed in the lower part of each of the two side housings 14, and each exhaust port 16 opens on the right side surface of the lower part of each side housing 14.

[0024] The engine body 10 is fitted with a fuel injector 17 that injects fuel into the rotor housing R, and an ignition plug 18 that adds fuel to the fuel-air mixture formed in the rotor housing R. In this embodiment, the fuel injector 17 is fitted to face the upper end of the rotor housing R, and the ignition plug 18 is fitted to face the lower left side of the rotor housing R.

[0025] (intake passage) The intake passage 3 is provided with, in this order from the upstream side, an air cleaner 31A that removes foreign matter contained in the intake air, and a throttle valve 41 that can adjust the amount of intake air introduced into the engine body 10 by changing the intake flow path area.

[0026] Specifically, the intake passage 3 includes, in order from the upstream side, a first intake passage 31, a second intake passage 32, a throttle body 40, and an intake manifold 50. The air cleaner 31A is provided in the first intake passage 31, and the throttle valve 41 is provided in the throttle body 40. In addition to the throttle valve 41, the throttle body 40 has a throttle valve case 42 that surrounds the throttle valve 41 and defines a passage through which intake air passes, and an actuator 43 that drives the throttle valve 41. The throttle valve 41 is driven by the actuator 43 to open and close the passage defined by the throttle valve case 42. In this embodiment, the actuator 43 that drives the throttle valve 41 is a motor, and hereinafter this actuator 43 will be referred to as a throttle valve motor 43.

[0027] An air flow meter sensor SN1 that detects the flow rate of intake air passing through a portion downstream of the air cleaner 31A in the first intake passage 31 is provided. An intake air temperature sensor SN2 that detects the intake air temperature, which is the temperature of gas passing through the intake manifold 50, is provided in the intake manifold 50.

[0028] Each intake port 15, 15 is connected to the downstream end of the intake manifold 50, and the intake air (air) flowing into the first intake passage 31 passes through the air cleaner 31A, the second intake passage 32, the throttle valve case 42, the intake manifold 50, and each intake port 15, 15 before being introduced into the rotor accommodating chamber R.

[0029] As shown in Figure 3 etc., the portion of the intake passage 3 downstream from the throttle body 40 is located to the right of the engine body 10 when viewed from the rear. The throttle body 40 is located above the engine body 10. The intake manifold 50 extends downward from the lower end of the throttle body 40 along the right side surface 10A of the engine body 10. The detailed structures of the throttle body 40 and the intake manifold will be described later.

[0030] (exhaust passage) A purification device 81 for purifying exhaust gas is provided in the exhaust passage 8. The exhaust passage 8 has an exhaust manifold 82 that communicates with each of the exhaust ports 16, 16, and the purification device 81 is disposed downstream of the exhaust manifold 82.

[0031] 2 and other figures, the exhaust manifold 82 has a shape that extends in the front-to-rear direction. The exhaust manifold 82 is fixed to the lower part of the right side surface 10A of the engine body 10 via an exhaust manifold fixing part 120, in a state in which the exhaust manifold 82 communicates with the two exhaust ports 16, 16.

[0032] (EGR passage) The EGR passage 6 is provided with an EGR cooler 62 that cools the EGR gas, and an EGR valve 71 that can adjust the amount of EGR gas introduced into the intake passage 3 by changing the flow area of ​​the EGR gas.

[0033] Specifically, the EGR passage 6 includes, in order from the exhaust passage 8 side, a first EGR passage 61, an EGR cooler 62, a second EGR passage 63, an EGR valve body 70, and a third EGR passage 64. The EGR valve 71 is provided in the EGR valve body 70. In addition to the EGR valve 71, the EGR valve body 70 includes an EGR valve case 72 that surrounds the EGR valve 71 and defines a passage through which EGR gas passes, and an actuator 73 that drives the EGR valve 71. The EGR valve 71 is driven by the actuator 73 to open and close the passage defined by the EGR valve case 72. In this embodiment, the actuator 73 that drives the EGR valve 71 is a motor, and hereinafter, this actuator 73 will be referred to as an EGR valve motor 73.

[0034] The EGR passage 6 communicates a portion of the exhaust passage 8 upstream of the purification device 81 with a portion of the intake passage 3 downstream of the throttle valve 41. Specifically, the upstream end of the EGR passage 6, i.e., the end of the EGR passage 6 on the exhaust passage 8 side, is connected to the exhaust manifold 82, and the downstream end of the EGR passage 6, i.e., the end of the EGR passage 6 on the intake passage 3 side, is connected to the intake manifold 50. The EGR cooler 62 cools the EGR gas with a coolant, and as shown in FIG. 2 etc., pipes 62A and 62B are connected to the EGR cooler 62 for introducing and discharging the coolant flowing through it.

[0035] As shown in FIG. 2 and other figures, the EGR passage 6 is disposed on the right side of the engine body 10. Specifically, the first EGR passage 61 is connected to an upper portion of the front end portion of the exhaust manifold 82 and extends obliquely upward and rearward from this connection. The EGR cooler 62 has a generally rectangular parallelepiped shape and is fixed to the right side surface 10A of the engine body 10 via a first EGR fixing part 130 in an orientation extending rearward from the rear end of the first EGR passage 61. The second EGR passage 63 extends obliquely upward and rearward from the rear end of the EGR cooler 62. The EGR valve body 70 is disposed at the upper end of the second EGR passage 63 and extends upward from the upper end thereof, with the EGR valve case 72 located at its lower portion and the EGR valve motor 73 located at its upper portion. The EGR passage 6 is also fixed to the right side surface 10A of the engine body 10 by a second EGR fixing portion 140 extending downward from the connection portion between the second EGR passage 63 and the EGR valve body 70. The third EGR passage 64 is connected to the left side surface of the EGR valve case 72 and extends upward from the left side surface of the EGR valve case 72 between the EGR valve body 70 and the right side surface 10A of the engine body 10. The third EGR passage 64 is composed of a portion extending upward from the left side surface of the EGR valve case 72, a portion curved to bulge rearward from the upper end of this portion, and an EGR introduction portion 65 extending forward from the front end of this curved portion. The EGR introduction portion 65 forms the downstream end of the EGR passage 6 and is connected to the intake passage 3.

[0036] (Details of throttle body 40 and intake manifold structure) Figure 5 shows the 4 VV line cross section Partially shown FIG.

[0037] As described above, the throttle body 40 is disposed above and to the right of the engine body 10. The throttle valve case 42 has an elongated cylindrical shape and extends substantially straight (in a linear fashion) in the vertical direction at the upper right of the engine body 10. The throttle valve motor 43 is disposed behind the throttle valve case 42.

[0038] The intake manifold 50 is roughly divided into three sections based on differences in shape, and is composed of a first intake manifold section 51 that forms the upper part of the intake manifold 50, a second intake manifold section 52 that forms the upper and lower central part of the intake manifold 50, and a third intake manifold section 53 that forms the lower part of the intake manifold 50. In this embodiment, the throttle valve case 42 is made of metal, and the intake manifold 50 is made of resin.

[0039] The first intake manifold portion 51 has a generally cylindrical shape with an inner diameter that is approximately the same as the inner diameter of the throttle valve case 42. The first intake manifold portion 51 extends downward in a generally straight line (linear shape) from the lower end of the throttle valve case 42, i.e., the downstream end in the intake air flow direction.

[0040] The second intake manifold section 52 has a shape that curves forward (to one side in the front-to-rear direction) from the lower end, i.e., the downstream end (in the intake air flow direction), of the first intake manifold section 51. The second intake manifold section 52 extends obliquely downward and forward from the lower end of the first intake manifold section 51 to a position that is shifted downward and forward from this end. In this embodiment, the rear end position of the lower end of the second intake manifold section 52 is forward of the front end position of the upper end of the first intake manifold section.

[0041] The inner wall of the second intake manifold section 52 has a first curved wall 52A extending forward from a rear portion (the other side in the front-to-rear direction) of the inner wall of the first intake manifold section 51, and the first curved wall 52A has a curved shape that is recessed so as to be convex toward the rear (the other side in the front-to-rear direction). Specifically, the rear portion of the second intake manifold section 52, i.e., the rear portion of a cross section when the second intake manifold section 52 is cut at its center in the left-to-right direction as shown in FIG. 5, has a substantially S-shape when viewed from the right, and the upper portion of the inner wall on the rear side of the second intake manifold section 52 is recessed so as to be convex toward the rear, and the lower portion is curved so as to be convex toward the front. The first curved wall 52A forms the upper portion of the inner wall on the rear side of the second intake manifold section 52. Note that this first curved wall 52A corresponds to the "curved wall" in the claims.

[0042] The inner wall of the second intake manifold 52 has a second curved wall 52C extending forward from a front portion (one side in the front-to-rear direction) of the inner wall of the first intake manifold 51, and the second curved wall 52C has a curved shape that is recessed so as to convex toward the front (one side in the front-to-rear direction). Specifically, the front portion of the second intake manifold 52, that is, the front portion of a cross section of the second intake manifold 52 cut at its center in the left-to-right direction as shown in FIG. 5, is curved so as to convex toward the front as a whole, and the inner wall of this front portion of the second intake manifold 52 constitutes the second curved wall 52C. An upper end 52D of the second curved wall 52C extends forward substantially perpendicularly from the front inner wall 51B of the first intake manifold 51, and a corner 52X bent at a substantially right angle is formed at the boundary between the front inner wall 51B of the first intake manifold 51 and the second curved wall 52C.

[0043] The downstream end of the EGR passage 6, i.e., the EGR introduction portion 65, is connected to the upper end of the first curved wall 52A, i.e., the upstream end (in the flow direction of the intake air) of the first curved wall 52A. In this embodiment, the EGR introduction portion 65 is connected to the first curved wall 52A in a state where it protrudes inward of the second intake manifold portion 52.

[0044] Specifically, EGR introduction portion 65 has a substantially cylindrical shape. A through-hole 52E penetrating in the front-rear direction is formed at the upper end of first curved wall 52A. EGR introduction portion 65 extends in the front-rear direction, and its tip is connected to the upper end of first curved wall 52A with an orientation in which it protrudes from first curved wall 52A inward (radially inward) into second intake manifold portion 52. The amount by which EGR introduction portion 65 protrudes from first curved wall 52A inward into second intake manifold portion 52 is kept to less than half the inner diameter of second intake manifold portion 52.

[0045] 6 is a view of EGR introduction section 65 as viewed from below. As shown in FIG. 6, an opening 65A that opens downward, i.e., downstream (in the flow direction of intake air), is formed at the tip of EGR introduction section 65. EGR gas is introduced into second intake manifold section 52 from opening 65A. Specifically, an upper wall 65B at the tip of EGR introduction section 65 is inclined so that the front side is positioned lower, and opening 65A is formed rearward from the lower end of inclined wall 65B. The rear end position of opening 65A and the position of first curved wall 52A in the front-to-rear direction are substantially the same, and opening 65A is formed in a region forward from the surface of first curved wall 52A.

[0046] The intake air temperature sensor SN2 is disposed at the lower end, i.e., the downstream end (in the intake air flow direction), of the second intake manifold portion 52. More specifically, the intake air temperature sensor SN2 is attached to the second intake manifold portion 52 so as to be exposed at the lower end of the second curved wall 72C.

[0047] The third intake manifold section 53 has a shape that extends in the front-to-rear direction, and spreads out forward and rearward from the lower end of the first intake manifold section. Openings 53A, 53A that open to the left, i.e., the engine body 10 side, are formed at the front and rear ends of the lower part of the third intake manifold section 53. Each opening 53A, 53A communicates with the intake ports 15, 15, respectively, and intake air is introduced from the intake passage 3 into the intake ports 15, 15 through these openings 53A, 53A.

[0048] In this embodiment, the portion 150 of the intake passage 3 that extends substantially straight in the vertical direction and is composed of the throttle valve case 42 and the first intake manifold portion 51 corresponds to the "first passage portion" in the claims. Also, the second intake manifold portion 52 corresponds to the "second passage portion" in the claims.

[0049] (effect, etc.) In the above embodiment, the second intake manifold 52 has a shape that curves forward from the lower end (downstream end) of the first intake manifold 51, which extends in the vertical direction. The flow path length of the second intake manifold 52 is longer than the flow path length if the second intake manifold 52 were shaped to extend straight in the vertical direction. In other words, in the above embodiment, the flow path length of the second intake manifold 52 is increased without increasing the vertical dimension. The downstream end (EGR introduction portion 65) of the EGR passage 6 is connected to the upper end (upstream end) of the first curved wall 52A, i.e., the upper end (upstream end) of the second intake manifold 52. Therefore, according to the above embodiment, the second intake manifold 52, i.e., the intake passage 3, can be compactly arranged around the engine body 10, while promoting mixing of EGR gas and intake air in the second intake manifold 52, thereby achieving appropriate combustion in the engine body 10.

[0050] In the above embodiment, the intake air temperature sensor SN2 is attached to the lower end (downstream end) of the second intake manifold portion 52. Therefore, as described above, the mixing of the EGR gas and the intake air is promoted in the second intake manifold portion 52, which allows the intake air temperature sensor SN2 to detect the temperature of a more homogeneous mixture of the EGR gas and the intake air.

[0051] Furthermore, because the second intake manifold section 52 has a curved shape, a secondary flow is formed within the second intake manifold section 52. Specifically, as shown by arrow Y1 in Fig. 7, a flow is generated within the second intake manifold section 52 in a direction perpendicular to its center line (the main flow of gas passing through the second intake manifold section 52). This reliably promotes mixing within the second intake manifold section 52 between the intake air (arrow Y2) that mainly passes through the center line and the EGR gas (arrow Y3) that is introduced from the wall surface side of the second intake manifold section 52.

[0052] Furthermore, in the above embodiment, the downstream end (EGR introduction portion 65) of the EGR passage 6 extends forward from the rear portion (the other side portion in the front-to-rear direction) of the inner wall of the first intake manifold portion 51 and is connected to the upper end (upstream end) of the first curved wall 52A, which has a curved shape recessed so as to be convex toward the rear side (the other side in the front-to-rear direction). Therefore, EGR gas can be introduced into the engine body 10 appropriately, that is, an appropriate amount of EGR gas can be introduced at an appropriate timing.

[0053] common In addition, negative pressure is likely to occur downstream of the throttle valve 41. Therefore, if the EGR passage 6 is connected to a portion of the intake passage 3 that is relatively close to the throttle valve 41, part of the EGR gas will flow toward the throttle valve 41, i.e., upstream, as shown by the dashed arrow Y10 in FIG. It becomes easier to flow. In contrast, according to the above embodiment, By providing the first curved wall 52A, 7, the EGR gas can be guided downstream along the first curved wall 52A. As a result, the EGR passage 6 is connected to a portion relatively close to the throttle valve 41, and these are arranged compactly around the engine body 10. The EGR gas can be directed downstream against the upstream flow of the EGR gas caused by the negative pressure. The EGR gas can be appropriately introduced into the engine body 10. Furthermore, according to the above embodiment, the backflow of the EGR gas toward the throttle valve 41 is suppressed, which also has the effect of suppressing adhesion of soot and the like contained in the EGR gas to the throttle valve 41.

[0054] In the above embodiment, the second curved wall 52C, which is the front inner wall of the second intake manifold 52, extends forward from the front portion of the inner wall of the first intake manifold 51 and has a curved shape that is concave and convex toward the front. This allows a vortex to be generated in the upper front portion of the second intake manifold 52, as indicated by arrow Y4 in FIG. 7 , i.e., a relatively strong turbulent flow. This further promotes the mixing of the EGR gas and the intake air within the second intake manifold 52. In particular, in the above embodiment, a corner 52X that bends at a substantially right angle is formed at the boundary between the front inner wall 51B of the first intake manifold 51 and the second curved wall 52C. This more reliably separates the intake air, generating a strong vortex and turbulence, thereby reliably promoting the mixing of the EGR gas and the intake air.

[0055] (Variation) In the above embodiment, the engine body 10 is a rotary piston engine, but the type of the engine body 10 is not limited to this.

[0056] In the above embodiment, the first intake manifold section 51 constituting the upper part of the intake manifold 50 is described as having a shape that extends straight in the vertical direction, and the second intake manifold section 52 is described as having a curved shape. However, the upper part or the entire intake manifold 50 may be formed as a curved shape, and a first curved wall 52A and a second curved wall 52C may be provided on the portion extending from the upper end of the intake manifold 50.

[0057] In the above embodiment, the throttle valve case 42 and the intake manifold 50 are disposed on the side surface of the engine body 10 in a position extending in the vertical direction, but they may also be disposed in a position extending in the horizontal direction. In other words, the "first direction" in the claims is not limited to the "vertical direction." Note that, when the throttle valve case 42 and the intake manifold 50 are disposed in a position extending in the horizontal direction, the "vertical direction" in the above embodiment may be read as the "left-right direction" or the "front-rear direction," and either the "left-right direction" or the "front-rear direction" may be read as the "vertical direction." [Explanation of symbols]

[0058] 3 Intake passage 6 EGR passage 8 Exhaust passage 10 Engine body 15 Intake port 16 Exhaust port 40 Throttle valve body 41 Throttle valve 42 Throttle valve case (first passage) 50 intake manifold 51 First intake manifold section (first passage section) 52 Second intake manifold section (second passage section) 52A First curved wall 52C Second curved wall 65 EGR inlet (downstream end of EGR passage) 65A opening

Claims

1. An intake structure for an engine comprising: an engine body; an intake passage connected to an intake port formed on a side surface of the engine body and through which intake air introduced into the engine body flows; an exhaust passage through which exhaust gas discharged from the engine body flows; and an EGR passage that communicates the intake passage with the exhaust passage and recirculates a portion of the exhaust gas back into the intake passage, the intake passage includes a first passage portion in which a throttle valve capable of changing a flow path area of ​​the intake air is disposed, and a second passage portion disposed downstream of the first passage portion, The first passage portion has a shape that extends linearly along a predetermined first direction, the second passage portion has a shape that curves from a downstream end of the first passage portion toward one side of the second direction, when a direction along the side surface of the engine body and perpendicular to the first direction is defined as a second direction, an inner wall of the second passage portion has a curved wall that extends while curving from the other side portion of the inner wall of the first passage portion in the second direction toward one side in the second direction, the curved wall has a curved shape that is recessed so as to be convex toward the other side in the second direction, An intake structure for an engine, wherein a downstream end of the EGR passage is connected to an upstream end of the curved wall.

2. The engine intake structure according to claim 1, An intake structure for an engine, characterized in that the downstream end of the EGR passage protrudes inwardly of the second passage portion and has an opening at its tip that opens downstream.

3. The engine intake structure according to claim 1 or 2, an inner wall of the second passage portion has a second curved wall that extends while curving from a portion of the inner wall of the first passage portion on the one side in the second direction toward the one side in the second direction, The second curved wall has a curved shape that is recessed so as to be convex toward one side in the second direction.

4. The engine intake structure according to any one of claims 1 to 3, 1. An intake structure for an engine, wherein the engine body is a rotary piston engine.

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