JP7422718B2 - Internal combustion engine intake system - Google Patents

Description

The present invention relates to an intake system for an internal combustion engine, and particularly to an intake system for an internal combustion engine in a straddle-type vehicle.

In a motorcycle, which is a straddle-type vehicle, there are restrictions on the arrangement of internal combustion engines and the like. For example, the internal combustion engine is sometimes arranged so that the intake system of the internal combustion engine mainly extends on one side in the vehicle width direction, and the exhaust system of the internal combustion engine mainly extends on the other side.

Patent Document 1 discloses an example of a motorcycle. In this motorcycle, an air cleaner is arranged on the left side in the vehicle width direction, and a connecting tube extends from the air cleaner toward a throttle body of an engine body in front of the air cleaner. This connecting tube is curved in an arc shape, extends diagonally forward and inward in the vehicle width direction from the connection port on the front surface of the air cleaner, and is connected to the rear end of the throttle body.

JP2019-206955A

In the internal combustion engine of the motorcycle disclosed in Patent Document 1, since the connecting tube is curved as described above, the intake air flowing therein tends to flow eccentrically, which may affect the intake efficiency. An object of the present invention is to provide a configuration that makes it possible to improve the flow of intake air into an engine body through a connecting tube having a curved portion.

In order to achieve the above object, one aspect of the present invention is to
An intake device for an internal combustion engine, comprising a connecting tube provided between an air cleaner and an engine body and having a curved part,
An intake device for an internal combustion engine is provided, wherein the downstream insertion portion of the connecting tube is configured to be inserted into a linear upstream end of the downstream pipe portion of the connecting tube.

According to the above configuration, it is possible to provide a rectification section that adjusts the flow of intake air by the downstream insertion part of the connecting tube inserted into the straight upstream end of the pipe part, so that the intake air flows into the engine body via the pipe part. flow can be improved. Thereby, intake efficiency can be improved.

Preferably, the connecting tube is directly connected to a throttle body downstream of the connecting tube. With this configuration, it is possible to improve the flow of intake air in the portion of the intake passage defined by the throttle body.

Preferably, the inner diameter of the connecting tube is smaller than the inner diameter of the upstream end of the tube section. With this configuration, it is possible to increase the intake air filling efficiency into the engine body when the engine operating state is in a so-called low rotation region where the engine rotation speed is relatively low, and therefore, drivability can be improved.

Preferably, the downstream insertion portion of the connecting tube is configured such that its inner diameter gradually increases from the upstream side to the downstream side. With this configuration, the stepped portion between the inside of the connecting tube and the inside of the pipe portion can be made smaller. Thereby, it is possible to suppress the occurrence of disturbance in the intake air flow due to the stepped portion, and it is therefore possible to improve the intake efficiency.

Preferably, the ratio (L/D) of the insertion length (L) of the downstream insertion portion into the pipe portion to the inner diameter (D) of the upstream end of the downstream insertion portion of the connecting tube is 0.6. The above value is 1.8 or less. By setting the ratio to 0.6 or more, it is possible to secure a sufficient rectifying section, and by setting the ratio to 1.8 or less, it is possible to ensure ease of manufacturing the connecting tube.

Preferably, the connecting tube has an outer connecting portion that sandwiches the tube portion together with the downstream insertion portion, and the outer connecting portion includes an engaging portion that engages with an engaged portion on the outer periphery of the tube portion. ing. With this configuration, the rigidity of the connecting portion of the connecting tube to the pipe portion can be increased.

Preferably, the downstream insertion portion of the connecting tube has at least one rib, and the rib projects radially outward. With this configuration, it is possible to improve the sealing performance between the downstream insertion portion of the connecting tube and the tube portion.

According to the above aspect of the present invention, since the above structure is provided, it is possible to improve the flow of intake air into the engine body via the connecting tube having the curved portion.

FIG. 1 is a left side view of a motorcycle equipped with an internal combustion engine equipped with an intake device according to an embodiment of the present invention. FIG. 2 is a right side view of a unit swing engine portion of the motorcycle shown in FIG. 1. FIG. FIG. 3 is a plan view of a portion of the unit swing engine in FIG. 2 viewed from above. 4 is a cross-sectional view of a portion of the unit swing engine taken along line IV-IV in FIG. 3. FIG. FIG. 5 is an enlarged view of the area around the connecting tube to the throttle body in FIG. 4; 6 is an enlarged view of the area of circle VI in FIG. 5. FIG. FIG. 6 is an enlarged view of the area of circle VII in FIG. 5; It is a graph showing experimental results.

Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. Identical parts (or configurations) are given the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

FIG. 1 shows a left side view of a motorcycle 12 equipped with an internal combustion engine E having an intake system according to an embodiment of the present invention. However, in FIG. 1, only the left side is shown as a pair of left and right. In the following description, directions such as front, rear, left, right, and top and bottom are the same as directions with respect to the vehicle body unless otherwise specified. Further, the symbol "FR" shown in the figure indicates the front of the vehicle body, the symbol "UP" indicates the upper part of the vehicle body, and the symbol "RH" indicates the right side of the vehicle body.

The motorcycle 12 is an example of a straddle-type vehicle, and is a scooter-type straddle-type vehicle that has a low step floor 16 on which a rider seated on a seat 14 rests his or her feet. The motorcycle 12 has a front wheel 20 in front of a body frame 18, and a rear wheel 22, which is a driving wheel, is pivotally supported by a unit swing engine 10 disposed at the rear of the vehicle. Although not shown in detail here, the unit swing engine 10 integrally includes an internal combustion engine E, a transmission, a clutch mechanism, and a speed reduction mechanism.

In the motorcycle 12, the front wheel 20 is pivotally supported on the lower end of a front fork 24 that is pivotally supported on the front end of the vehicle body frame 18. A handle 26, which is steered by a passenger, is attached to the upper end of the front fork 24. The motorcycle 12 includes a body cover 28 that covers a body such as a body frame 18.

The vehicle body frame 18 includes a head pipe 30 provided at the front end, a down frame 32 extending rearward and downward from the head pipe 30, a pair of left and right lower frames 34 extending rearward substantially horizontally from the lower end of the down frame 32, and a lower frame 34. The seat frame 36 includes a pair of left and right seat frames 36 extending rearward from the rear end of the seat frame 36. Each seat frame 36 includes a rising portion 38 extending rearward upward from the rear end of each lower frame 34, and a rearward extending portion 40 extending from the upper end of the rising portion 38 to the rear end of the vehicle body frame 18. The rear extending portion 40 extends rearward upward at a gentler slope than the rising portion 38.

The vehicle body frame 18 further includes a cross member 42 that connects the rear end of the lower frame 34 in the vehicle width direction, an upper cross member 44 that connects the upper part of the rising section 38 in the vehicle width direction, and left and right sections that extend rearward from the rising section 38. A pair of support frames 46 are provided. The vehicle body frame 18 also includes a pair of left and right engine brackets 48 that protrude rearward from the rising portion 38 of the seat frame 36.

A storage box 50 capable of storing items such as a helmet is provided above the unit swing engine 10 and between the left and right seat frames 36. The sheet 14 is supported above the storage box 50 and covers the upper opening of the storage box 50 in an openable and closable manner.

The vehicle body cover 28 includes an upper cover 52 that covers the periphery of the handle 26, a front cover 54 that covers the head pipe 30 and the down frame 32 from the front and sides, and a front cover 54 that fits the front cover 54 from the rear and covers the head pipe 30 and the down frame. It is equipped with a leg shield 56 that covers 32.

In addition to the aforementioned step floor 16 that covers the lower frame 34 from above, the vehicle body cover 28 also includes an undercover 58 that covers the lower frame 34 from below, and a seat frame 36 and a storage box 50 that are placed below the seat 14 from the side. This includes a pair of left and right side covers 60 that cover from above, and a center lower cover 62 that covers the storage box 50 and unit swing engine 10 from the front below the seat 14.

The motorcycle 12 also includes a front fender 64 that covers the front wheel 20 from above. An inner fender 66 is provided between the seat frame 36 and the rear wheel 22 to cover the front part of the rear wheel 22 from above.

The fuel tank 68 is arranged between the left and right lower frames 34 in front of the cross member 42, and is covered by the step floor 16 and the undercover 58. Note that the fuel tank 68 may be provided at another location, for example, at the rear upper part of the vehicle body, specifically, below the seat 14, or the like.

In the unit swing engine 10 mounted on the motorcycle 12 configured as described above, the engine body 70 of the internal combustion engine E, which is the drive source, and the arm portion 72 that supports the rear wheel 22 are integrated. The rear wheel 22 is pivotally supported by a rear wheel axle 22a at the rear end of the arm portion 72. That is, the driving force of the crankshaft 74 of the engine body 70 of the internal combustion engine E is transmitted to the rear wheel 22 via the transmission, clutch mechanism, and deceleration mechanism in the arm portion 72.

A rear suspension 36s spans between the rear end of the unit swing engine 10 and the rear of the seat frame 36. A center stand 83 for parking the motorcycle 12 in an upright position is attached to the lower side of the unit swing engine 10.

Here, a right side view of the unit swing engine 10 is shown in FIG. FIG. 3 is a plan view of the unit swing engine 10 viewed from above. FIG. 4 is a cross-sectional view of the unit swing engine 10 taken along line IV-IV in FIG.

The engine body 70 includes a crankcase 76 that accommodates a crankshaft 74 that extends in the vehicle width direction, and a cylinder portion 78 that extends forward from the crankcase 76. The cylinder portion 78 includes, in order from the crankcase 76 side, a cylinder 80, a cylinder head 82, and a head cover 84. The engine main body 70 is a horizontal engine in which a cylinder axis 78a of a cylinder portion 78 extends substantially horizontally in the longitudinal direction of the vehicle. Specifically, the cylinder portion 78 extends substantially horizontally toward the front of the vehicle in a slightly upwardly forward direction when viewed from the side of the vehicle in FIG. 2 .

The unit swing engine 10 is swingably supported by the vehicle body frame 18 via a link mechanism 85 provided above the unit swing engine 10. The link mechanism 85 includes a swing shaft 85a connected to the upper part of the crankcase 76, a pair of left and right swing shafts 85b connected to the engine bracket 48 of the seat frame 36, and a swing shaft 85a and the swing shaft 85b connected to the engine bracket 48 of the seat frame 36. It includes a link member 85c that connects to the moving shaft 85b. A swing shaft 85a is provided in the upper part of the crankcase 76 located above the cylinder axis 78a of the cylinder portion 78, and the swing shaft 85a and the vehicle body side swing shaft 85b are connected via a link member 85c. As a result, the unit swing engine 10 is swingably supported by the vehicle body frame 18. The swing shaft 85a and the vehicle body side swing shaft 85b are horizontal shafts extending in the vehicle width direction. The unit swing engine 10 is capable of swinging around a swing shaft 85a and a vehicle-side swing shaft 85b.

As shown in FIG. 4, a piston 86 that reciprocates within a cylinder 80 is connected via a connecting rod 88 to a crankshaft 74 that is supported via bearings in a crankcase 76 that defines a crank chamber. .

A combustion chamber 87 facing the top surface of the piston 86 is formed between the cylinder 80 and the cylinder head 82. In the cylinder head 82, an intake port 90i and an exhaust port 90e are formed to curve and extend vertically away from each other from an intake valve port and an exhaust valve port that are open to the ceiling surface of the combustion chamber.

The upstream end of the intake port 90i opens into the cylinder head 82 and connects to the intake pipe 92, forming a continuous intake passage 93. On the upstream side of the intake passage 93, an air cleaner 94 and a throttle body 96 are provided in order from the upstream side. Furthermore, a fuel injection valve 97a of the fuel supply device 97 is provided in the intake passage 93. Here, as shown in FIG. 4, a fuel injection valve 97a to which fuel from the fuel tank 68 is supplied is provided facing the intake port 90i. Note that a spark plug (not shown) is inserted into the combustion chamber 87 in the cylinder head 82.

The downstream end of the exhaust port 90e opens toward the bottom of the cylinder head 82, and is connected to an exhaust pipe 100 to form a continuous exhaust passage 102.

The intake valve 104i is slidably supported by an intake valve guide provided on the curved outer wall of the intake port 90i in the cylinder head 82, and opens and closes the intake valve port of the intake port 90i facing the combustion chamber 87. Further, the exhaust valve 104e is slidably supported by an exhaust valve guide provided on the curved outer wall of the exhaust port 90e in the cylinder head 82, and opens and closes the exhaust valve port facing the combustion chamber 87 of the exhaust port 90e.

The cylinder head 82 is provided with a valve mechanism 89. The valve mechanism 89 is configured and provided to open and close the intake valve 104i and the exhaust valve 104e. A head cover 84 is placed over the cylinder head 82 so as to cover the valve mechanism 89. The valve mechanism 89 includes a camshaft 89a. A cam chain (not shown) is stretched between the camshaft 89a and the crankshaft 74. The camshaft 89a rotates at 1/2 rotation speed in synchronization with the crankshaft 74. The umbrella portions of the intake valve 104i and the exhaust valve 104e are biased in the valve closing direction by valve springs 103i and 103e so as to close the intake valve port and the exhaust valve port facing the combustion chamber 87, respectively. As the camshaft 89a rotates, the stem ends of the intake valve 104i and exhaust valve 104e are pushed down (not shown), and the intake valve 104i and exhaust valve 104e open at a predetermined timing, opening the intake port 90i and the combustion chamber. 87, the exhaust port 90e and the combustion chamber 87 communicate with each other, and intake and exhaust are performed at predetermined timings.

As shown in FIG. 2, the exhaust pipe 100 connected to the engine body 70 is pulled out from the bottom of the cylinder head 82, extends rearward through one side in the vehicle width direction, here the right side, and extends to the side of the rear wheel 22. Extends to. The exhaust pipe 100 includes a muffling device 102a at the rear end that reduces exhaust noise. The silencer 102a is arranged side by side with the rear wheel 22, and is located on the right side of the rear wheel 22, which is one side in the vehicle width direction. That is, the silencer 102a is disposed on one side in the vehicle width direction with respect to the rear wheel 22 located on the center line C (FIG. 3) in the vehicle width direction of the motorcycle 12, and is located on the arm portion 72 of the unit swing engine 10. is arranged on the other side in the vehicle width direction with respect to the rear wheel 22, here on the left side.

The above-mentioned intake pipe 92 extending rearward and upward from above the cylinder head 82 is connected to the engine body 70. As shown in FIG. 3, the intake system of the motorcycle 12 includes a connecting tube 98 that connects an air cleaner 94 and a throttle body 96 connected to the upstream side of the intake pipe 92. The connecting tube 98 defines a portion of the intake passage 93 having a substantially circular cross section. It is also equipped with a resonator 99 that reduces intake noise.

Connecting tube 98 is provided with an intake air temperature sensor 105 that detects the temperature of intake air. The throttle body 96 is provided with a throttle opening sensor 108 that detects the opening of the throttle valve 106 of the throttle body 96. The intake pipe 92 is provided with an intake pressure sensor 110 that detects the pressure of intake air. However, the arrangement of these sensors is not limited to this.

As shown in FIGS. 1 and 3, the air cleaner 94 is disposed above the arm portion 72 of the unit swing engine 10 and is supported by the arm portion 72. The air cleaner 94 is arranged behind the throttle body 96, and overlaps the front upper part of the rear wheel 22 from the outside in the vehicle width direction when viewed from the side of the vehicle. That is, the air cleaner 94 is disposed on the side of the rear wheel 22 and is offset outward in the vehicle width direction with respect to the center line C of the motorcycle 12 in the vehicle width direction.

An air filter (not shown) is provided inside the air cleaner 94. A connection port 94a to which a connecting tube 98 is connected is provided on the front surface of the air cleaner 94. Outside air taken in from the intake port (not shown) of the air cleaner 94 is purified by the air filter, passes through the connecting tube 98, the throttle body 96, and the intake pipe 92, and enters the combustion chamber via the intake port 90i of the cylinder head 82. It flows to 87.

The air cleaner 94 is connected to the cylinder portion 78 of the engine body 70 by a breather hose 112 extending forward from the air cleaner 94. Breather hose 112 is connected to head cover 84 of cylinder section 78 and communicates the inside of engine body 70 with the inside of air cleaner 94. Blowby gas generated in the engine body 70 due to combustion flows to the clean side of the air cleaner 94 through the breather hose 112, returns to the combustion chamber 87 through the connecting tube 98 and the throttle body 96, and is combusted.

The throttle body 96 is arranged in front of the air cleaner 94 and behind the intake pipe 92 of the cylinder head 82. The throttle body 96 is disposed approximately at the center of the motorcycle 12 in the vehicle width direction, and is disposed on the inside of the air cleaner 94 in the vehicle width direction. The throttle body 96 extends along the center line C in the vehicle width direction, and is arranged offset to the outside in the vehicle width direction on the air cleaner 94 side with respect to the center line C.

Further, the throttle body 96 is arranged above the crankcase 76 and below the storage box 50 in the vertical direction.

The throttle body 96 includes a pipe portion 96a and a throttle valve 106 disposed in the pipe portion 96a. The throttle body 96 is arranged in such a direction that the axis of a pipe portion 96a defining a portion of the intake passage 93 having a substantially circular cross section is generally oriented in the front-rear direction. The front end of the tube portion 96a of the throttle body 96 is connected to the rear end of the intake pipe 92. The throttle valve 106 is rotatably supported by a rotation shaft extending in the vehicle width direction, and opens and closes a portion of the intake passage inside the pipe portion 96a. The opening degree of the throttle valve 106 is controlled by rotating a pulley 109 by a throttle cable extending from the accelerator operating section of the handle 26. Note that the throttle valve 106 may be an electronically controlled valve, that is, a so-called electronic throttle.

As shown in FIG. 3, the connecting tube 98 extends obliquely forward and inward in the vehicle width direction from the connection port 94a on the front surface of the air cleaner 94, and is connected to the rear end, that is, the upstream end 96b, of the tube portion 96a of the throttle body 96. Ru. The upstream end 96b of the tube portion 96a of the throttle body 96 is linear and extends along the center line C in the vehicle width direction as described above. The connecting tube 98 is arranged so as to be offset outward in the vehicle width direction from the center line C in the vehicle width direction toward the air cleaner 94 located outside the throttle body 96 in the vehicle width direction.

The connection port 94a on the front side of the air cleaner 94 is provided on an inclined surface that is inclined so as to face forward and inward in the vehicle width direction when viewed from above in FIG. Extends inward in the direction. The entire connecting tube 98 is curved in an arc shape so as to smoothly connect from the connection port 94a on the front surface of the air cleaner 94 to the rear end, that is, the upstream end 96b of the throttle body 96. That is, the connecting tube 98 forms a curved portion 98a over its entire length. In plan view, the curved portion 98a is entirely curved so as to be convex inward in the vehicle width direction from the air cleaner 94.

The inner curved surface 98b of the curved portion 98a of the connecting tube 98 is the outer side surface of the connecting tube 98 in the vehicle width direction in a plan view. The outer curved surface 98c of the curved portion 98a of the connecting tube 98 is the inner side surface of the connecting tube 98 in the vehicle width direction in plan view. In plan view, the outer curved surface 98c has a smaller curvature than the inner curved surface 98b. Note that the resonator 99 is connected to the outer curved surface 98c side of the connecting tube 98. Intake air flowing through the connecting tube 98 can enter and exit the resonator 99. The resonator 99 is provided to reduce intake noise of the unit swing engine 10 by resonance.

The motorcycle 12 equipped with the internal combustion engine E, that is, the engine body 70, includes a control section 114 (FIG. 1) that controls each part of the motorcycle 12 such as the unit swing engine 10, specifically, the operation of the internal combustion engine E. The control section 114 has a function of controlling the unit swing engine 10. The control unit 114 is a computer and is configured as an ECU (Electronic Control Unit). The control section 114 includes a calculation section and a storage section. The calculation unit is a processor such as a CPU. The storage unit includes a ROM, a RAM, etc., and stores programs executed by the calculation unit, data processed by the calculation unit, and the like. The control unit 114 controls the unit swing engine 10 by executing a program stored in the storage unit. The aforementioned intake air temperature sensor 105, throttle opening sensor 108, and intake pressure sensor 110 are connected to the control unit 114. Further, a fuel supply device 97 and the like are connected to the control unit 114. The control unit 114 controls fuel injection by the fuel supply device 97 based on the detected values from these sensors.

In the internal combustion engine E having the above configuration, that is, the engine main body 70, the connecting tube 98 has the curved portion 98a and is curved as described above. Therefore, the intake air flows toward the outer curved surface 98c of the curved portion 98a of the connecting tube 98. In order to improve the influence of this biased intake air flow on intake efficiency, that is, to improve the influence of eccentricity of the intake air flow due to the fact that a large amount of intake air can flow on the outer curved surface 98c side of the curved portion 98a due to centrifugal force. Therefore, in the engine 10, the downstream portion of the connecting tube 98 is configured to be inserted into the tube portion 96a of the throttle body 96, which is the downstream tube portion of the connecting tube 98. Hereinafter, the intake system, that is, the intake device of the internal combustion engine E having the intake structure IS including this structure will be further explained with particular reference to FIGS. 5 to 7.

FIG. 5 is an enlarged view of the area around the connection part of the downstream connection part 120 to the throttle body 96, which is the downstream part of the connecting tube 98 in FIG. 6 is an enlarged view of the area of circle VI in FIG. 5, and FIG. 7 is an enlarged view of the area of circle VII in FIG.

The downstream connecting portion 120 of the connecting tube 98 includes a downstream insertion portion 122 and an outer connecting portion 124. The upstream end of the outer connecting portion 124 connects to the upstream end of the downstream insertion portion 122. In other words, the outer connecting portion 124 extends downstream from the upstream end of the downstream insertion portion 122 on the outside thereof. As a result, the downstream connecting portion 120 has a configuration in which the tube portion 96a of the throttle body 96 is sandwiched therebetween.

The downstream insertion portion 122 is an annular cylindrical portion, and is inserted into the tube portion 96a of the throttle body 96, particularly into the straight upstream end 96b of the tube portion 96a, as shown in FIGS. 5 to 7. By this insertion, the downstream insertion section 122 is connected to the tube section 96a of the throttle body 96 such that the outer circumferential surface of the downstream insertion section 122 contacts the inner circumferential surface of the tube section 96a, preferably without any gaps. Ru. Therefore, the downstream insertion portion 122, together with the other portions of the connecting tube 98, defines a portion of the intake passage 93 having a substantially circular cross section. Note that the linear upstream end 96b of the pipe portion 96a is a portion of the throttle body 96 upstream of the throttle valve 106 here.

As shown in FIG. 7, the downstream insertion section 122 has ribs 122a and 122b that protrude radially outward from the outer peripheral surface of the downstream insertion section 122 at its downstream end. Each of the ribs 122a, 122b extends in an annular shape. Recesses 96e and 96f into which these ribs 122a and 122b fit, that is, engage, are provided on the inner wall surface of tube portion 96a. The ribs 122a, 122b and the recesses 96e, 96f are provided substantially parallel to each other and separated from each other in the intake flow direction. Note that the number of ribs provided in the downstream insertion portion 122 is not limited to two, and may be one or three or more. That is, it is preferable that the downstream insertion portion 122 has at least one rib. Further, this rib is not limited to being annular, but can have various configurations that improve sealing performance, for example, various engagement structures. Note that although it is better to provide the recesses 96e and 96f, they can also be omitted.

As can be seen from FIG. 5, the inner diameter D of the connecting tube 98 is smaller than the inner diameter of the tube portion 96a of the throttle body 96, particularly the inner diameter Td of the upstream end 96b of the tube portion 96a. This is true not only at the downstream connecting portion 120 of the connecting tube 98 but also over the entire length of the connecting tube 98 along the axis.

Further, as shown in FIG. 5, the downstream insertion portion 122 of the connecting tube 98 is configured such that the inner diameter gradually increases from the upstream side to the downstream side. Although the connecting tube 98 has a substantially constant inner diameter over its entire length along its axis, the downstream insertion portion 122 is thus configured to have a variable inner diameter. However, the downstream insertion portion 122 of the connecting tube 98 may be formed to have a constant inner diameter.

The length L of the downstream insertion section 122 of the connecting tube 98 inserted into the pipe section 96a in this way, that is, the length L in the flow direction, is the inner diameter of the upstream end 120a of the downstream insertion section 122, that is, the length L of the downstream insertion section 120 at the downstream connection section 120. It is set according to the inner diameter D of the connecting tube 98, which is the inner diameter at the connecting portion 120a between the downstream insertion portion 122 and the outer connecting portion 124. The ratio L/D of the insertion length L of the downstream insertion portion 122 into the tube portion 96a to the inner diameter D of the upstream end of the downstream insertion portion 122 of the connecting tube 98 is preferably 0.6 or more and 1.8 or less. . Here, the length L is designed within the range of this ratio L/D.

On the other hand, the outer connecting portion 124 is an annular cylindrical portion, and as shown in FIGS. 5 and 6, is provided so as to extend outside the tube portion 96a of the throttle body 96, and the tube portion 96a is inserted into the inside thereof. As shown in FIG. 6, the outer connecting portion 124 is provided with convex portions 124a and 124b which are engaging portions. The convex portions 124a and 124b are each formed to protrude radially inward. Concave portions 96g and 96h, which are engaged portions with which these convex portions 124a and 124b engage, are provided on the outer periphery of the upstream end 96b of the tube portion 96a. The convex portions 124a, 124b and the concave portions 96g, 96h are provided substantially parallel to each other and separated from each other in the intake air flow direction. Note that the number of engaging parts provided in the outer connecting part 124 is not limited to two, and may be one or three or more. Further, this engaging portion is not limited to an annular shape, and may have various configurations that increase the connection rigidity between the connecting tube 98 and the pipe portion 96a. For example, the engaging portion of the outer connecting portion 124 may be a recess, and a convex portion that enters the engaging portion, which is the recess, may be provided on the tube portion 96a as an engaged portion. Note that, as shown in FIG. 6, the outer connecting portion 124 positioned on the outer periphery of the tube portion 96a is tightened and fixed from the outside in the radial direction with a tightening member B.

Furthermore, as shown in FIG. 6, a fitting part 126 is provided inside the connection part between the downstream insertion part 122 and the outer connection part 124 in the downstream connection part 120 of the connecting tube 98. The fitting portion 126 is convex and protrudes toward the downstream side. A recess 96i into which the fitting portion 126 fits is provided toward the upstream side from the upstream end surface of the tube portion 96a.

According to the intake system for the internal combustion engine E having the above-mentioned intake structure IS, the following effects are achieved.

As described above, the connecting tube 98 provided between the air cleaner 94 and the engine body 70 includes the curved portion 98a, and the downstream insertion portion 122 of the connecting tube 98 is connected to the throttle body 96, which is the downstream pipe portion of the connecting tube 98. The throttle body 96 is configured to be inserted into a straight upstream end 96b of the tube portion 96a of the throttle body 96, particularly here. Therefore, the downstream insertion section 122 of the connecting tube 98 inserted into the tube section 96a can provide a rectification section for regulating the flow of intake air at the upstream end 96b of the tube section 96a. Therefore, the flow of intake air flowing into the engine body 70 via the pipe portion 96a of the throttle body 96 can be improved. Thereby, intake efficiency can be improved.

Furthermore, in the motorcycle 12, the connecting tube 98 is directly connected to the throttle body 96 on the downstream side of the connecting tube 98. Therefore, the flow of intake air in the portion of the intake passage 93 defined by the throttle body 96 can be improved.

Further, the inner diameter D of the connecting tube 98 is smaller than the inner diameter Td of the upstream end 96b of the throttle body 96. Therefore, even when the engine operating state is in a so-called low rotation region where the engine rotation speed is relatively low, intake air can be drawn in more effectively through the connecting tube 98, which has a relatively small inner diameter. Therefore, the efficiency of filling the intake air into the engine body can be increased, thereby improving drivability. In some conventional motorcycles, the inner diameter of the connecting tube is made larger than the inner diameter of the throttle body to facilitate intake of intake air.

Further, the downstream insertion portion 122 of the connecting tube 98 is configured such that the inner diameter D gradually increases from the upstream side to the downstream side. With this configuration, the stepped portion between the inside of the connecting tube 98 and the inside of the pipe portion 96a can be made smaller. Therefore, it is possible to suppress the occurrence of turbulence in the intake flow caused by the stepped portion, and thus it is possible to improve the intake efficiency.

Furthermore, the connecting tube 98 has an outer connecting portion 124 that sandwiches the tube portion 96a together with the downstream insertion portion 122, and this outer connecting portion 124 engages with the recesses 96g and 96h, which are the engaged portions on the outer periphery of the tube portion 96a. Convex portions 124a and 124b are provided as engaging portions that fit together. With this configuration, the connection rigidity of the downstream connection portion 120 of the connecting tube 98 to the pipe portion 96a can be increased.

Furthermore, the downstream insertion portion 122 of the connecting tube 98 has ribs 122a and 122b that protrude radially outward from its outer peripheral surface. Although two ribs 122a and 122b are provided here, by providing at least one rib, the sealing between the downstream insertion portion 122 of the connecting tube 98 and the tube portion 96a can be improved. By providing the two ribs 122a and 122b in this way, the airtightness, that is, the sealability, can be further improved.

Further, the ratio L/D of the insertion length L of the downstream insertion portion 122 into the pipe portion 96a in the intake flow direction to the inner diameter D of the upstream end 120a of the downstream insertion portion 122 of the connecting tube 98 is 0.6 or more. .8 or less. By setting the ratio to 0.6 or more, it is possible to secure a sufficient rectification section. By setting the ratio to 1.8 or less, it is possible to ensure ease of manufacturing the connecting tube 98, and by setting the ratio to 1.2 or less, it is possible to ensure the ease of manufacturing the connecting tube 98 and the rectification section. This makes it easier to ensure both

Here, FIG. 8 shows the experimental results of examining the relationship between the ratio L/D and the intake air amount. The horizontal axis in FIG. 8 is the ratio L/D, and the ratio is larger toward the right side. The vertical axis in FIG. 8 is the amount of intake air, and the higher the position, the greater the amount of intake air. In the experiment, the ratio L/D was changed to 0, 0.6, 1.2, and 1.8, and the amount of intake air in each case was measured. Note that a ratio of "0" means that the downstream insertion section 122 is not provided.

Further, in this experiment, a connecting tube 98 in which the inner diameter of the downstream insertion section 122 was constant, and a connecting tube 98 in which the inner diameter of the downstream insertion section 122 expanded toward the downstream side were used. The connecting tube 98 in which the inner diameter of the downstream insertion portion 122 expands toward the downstream side is a tube whose inner diameter expands from the upstream end of the downstream insertion portion 122 toward the downstream end, that is, the expansion rate is 2%, and 4% tube was used. Hereinafter, the connecting tube 98 with a constant inner diameter of the downstream insertion portion 122 will be referred to as a 0% tube, a tube with a tube expansion rate of 2% will be referred to as a 2% tube, and a tube with a tube expansion rate of 4% will be referred to as a 4% tube. .

As is clear from Fig. 8, when the ratio L/D is 0.6, 1.2, and 1.8 for 0% tube, 2% tube, and 4% tube, respectively, compared to the case where the ratio is 0, As a result, the amount of intake air has increased and intake efficiency has been improved.

Furthermore, from FIG. 8, there was a tendency for the intake air amount to increase as the tube expansion rate increased. Furthermore, by increasing the ratio L/D and increasing the tube expansion rate, the amount of intake air tended to increase.

On the other hand, when the ratio L/D was 1.8, ease of manufacturing of the connecting tube 98 could be ensured. In particular, the intake air amount tended to increase with an increase in the ratio L/D from 0.6 to 1.2 for each of the 0% tube, 2% tube, and 4% tube. Therefore, a ratio L/D of 1.2 or less would be particularly effective in achieving both ease of manufacturing the connecting tube 98 and ensuring a rectifying section. Although the connecting tube 98 is made of resin here, it is not limited to being made of resin, and may be made of other materials.

Although the embodiments and modifications thereof according to the present invention have been described above, the present invention is not limited thereto. Various substitutions and changes are possible without departing from the spirit and scope of the invention as defined by the claims of this application.

For example, in the embodiment described above, the connecting tube 98 was directly connected to the pipe portion 96a of the throttle body 96. However, the downstream insertion portion 122 of the connecting tube 98 is not limited to the tube portion 96a of the throttle body 96, but may be inserted into other tube portions, such as other tubes further connected to the upstream end of the throttle body 98. It may be a department.

Furthermore, in the embodiment described above, the connecting tube 98 was a curved portion that was generally entirely curved. However, the connecting tube 98 may have a curved portion in which only a portion thereof is curved, and in this case, the other portion may be straight.

Further, in addition to the above configuration or in addition to a part of the above configuration, the internal combustion engine to which the present invention is applied also includes a A partition wall or a partition portion may be provided on the side to separate the tumble flow path from the main flow path, which is the other flow path. Also in this case, by applying the intake device including the intake structure IS, the flow of intake air in the tumble flow path and/or the main flow path can be improved as described above.

E...Internal combustion engine, IS...Intake structure
12...Motorcycle, 70...Engine body, 94...Air cleaner, 96...Throttle body 96
96a...pipe section, 96b...upstream end, 98...connecting tube, 98a...curved section
120...Downstream connection part, 122...Downstream insertion part 122, 124...Outside connection part

Claims (6)

An intake device for an internal combustion engine (E) comprising a connecting tube (98) provided between an air cleaner (94) and an engine body (70) and having a curved portion (98a),
The downstream insertion portion (122) of the connecting tube (98) is configured to be inserted into the straight upstream end (96b) of the downstream pipe portion (96a) of the connecting tube (98). hand,
The downstream insertion portion (122) of the connecting tube (98) is configured such that its inner diameter gradually increases from the upstream side to the downstream side. Device. The insertion length (L) of the downstream insertion portion (122) into the pipe portion (96a) relative to the inner diameter (D) of the upstream end (120a) of the downstream insertion portion (122) of the connecting tube (98) The intake system for an internal combustion engine (E) according to claim 1 , wherein the ratio (L/D) is 0.6 or more and 1.8 or less. The intake system for an internal combustion engine (E) according to claim 1 or 2, wherein the connecting tube (98) is directly connected to a throttle body (96) on the downstream side of the connecting tube (98). . 4. An inner diameter (D) of the connecting tube (98 ) is smaller than an inner diameter (Td) of the upstream end (96b) of the pipe portion (96a). Intake system for the internal combustion engine (E) described. The connecting tube (98) has an outer connecting portion (124) that sandwiches the tube portion (96a) with the downstream insertion portion (122), and the outer connecting portion (124) is connected to the tube portion (96a). The internal combustion engine (E) according to any one of claims 1 to 4 , further comprising engaging portions (124a, 124b) that engage with the engaged portions (96g, 96h) on the outer periphery. intake device. 2. The downstream insertion portion (122) of the connecting tube (98) has at least one rib (122a, 122b), and the rib projects radially outward. An intake system for an internal combustion engine (E) according to any one of items 5 to 5 .

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