JP2010223211A - Forced air-cooled engine unit for vehicle and motorcycle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forced air-cooled engine unit for a vehicle and a motorcycle, having a simple structure, having a high degree of freedom of a layout in the vehicle, and having high combustion efficiency of fuel. <P>SOLUTION: A sub-intake passage forming body 41 is connected to an intake pipe 36 continuing with a cylinder head 23. The sub-intake passage forming body 41 forms a sub-intake passage K1. The sub-intake passage K1 is branched off from a main intake passage P1 in the intake pipe 36, and introduces intake air to a vicinal space of an injection nozzle of an injector in at least idling. At least a part of the sub-intake passage forming body 41 is arranged outside a shroud 50. The injector periphery is cooled by low temperature assist air of passing through the sub-intake passage K1 in the idling. The injector periphery is also cooled by cooling air generated by a fan 56 in traveling. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a vehicle forced air-cooled engine unit and a motorcycle.

  The engine disclosed in Patent Document 1 is provided with a main intake passage that sends air from an air cleaner to a combustion chamber of the engine. A sub intake passage is branched from the main intake passage. The injector is mounted on the cylinder head of the engine. In the auxiliary intake passage, intake air from the main intake passage flows as assist air at least during idling. The assist air is blown to the fuel injected from the injector and promotes atomization of the fuel. Thereby, the combustion efficiency of the fuel at least at the time of idling is improved.

The engine described in Patent Document 1 is a natural air-cooled engine configured such that traveling wind as wind generated by traveling of a vehicle hits the engine. Thereby, the engine is cooled by the traveling wind.
Generally, an air-cooled engine or a water-cooled engine is known as an engine used for a vehicle such as a motorcycle. The air-cooled engine cools the engine by applying air to the engine. For this reason, the air-cooled engine does not require a radiator or a cooling water pump required for the water-cooled engine, and has a simple structure.

In the engine described in Patent Document 1, since the injector is mounted on the cylinder head, the cylinder head and the injector are cooled by the traveling wind. Thereby, generation | occurrence | production of the vapor | steam lock | rock in the fuel supplied to an injector is suppressed, and combustion efficiency can be improved by promoting atomization.
However, the engine described in Patent Document 1 is a natural air cooling type. Therefore, it is necessary to arrange the engine at a position where the traveling wind is easily hit, and there is a problem that the degree of freedom of engine arrangement in the vehicle is low.

  On the other hand, as described in Patent Document 2, a forced air-cooled engine having a fan driven by rotation of an engine crankshaft and a shroud covering a cylinder head or a cylinder block of the engine has been developed. Has been. The wind generated by the fan hits the cylinder head and the cylinder block through the shroud and cools the engine. In a forced air-cooled engine, a portion of the engine disposed in the shroud is cooled by a fan.

  Since the forced air-cooled engine does not depend on the traveling wind for cooling the engine, it is not necessary to arrange the engine so that the traveling wind can hit. Therefore, the degree of freedom of engine arrangement in the vehicle is high.

Republished patent WO2005 / 098231 JP 2001-241326 A

As described above, the natural air-cooled engine described in Patent Document 1 has high fuel combustion efficiency because the atomization of fuel is promoted by assist air. However, since it is necessary for the wind to strike the engine, the degree of freedom in layout is low.
Further, the forced air-cooled engine described in Patent Document 2 does not require the engine to be disposed so that the traveling wind hits, so that the degree of freedom of layout in the vehicle is high.

Therefore, it is desired to apply an engine in which an injector is attached to a cylinder head of an engine as described in Patent Document 1 and atomization is accelerated by air assist to the forced air-cooled engine described in Patent Document 2. This is because it is possible to provide an engine with high fuel combustion efficiency and a high degree of layout freedom in the vehicle.
The present invention has been completed based on the above-described circumstances, and has a simple structure, a high degree of freedom in layout in a vehicle, and a fuel forced air-cooled engine unit having high fuel combustion efficiency, and a An object of the present invention is to provide a motorcycle equipped.

  A forced air-cooled engine unit for a vehicle according to the present invention includes a crankcase that houses a crankshaft, a cylinder block that is connected to the crankcase and houses a piston in a reciprocating manner, and forms a combustion chamber together with the cylinder block, and An engine body including a cylinder head forming a part of a main intake passage connected to a combustion chamber, an intake pipe connected to the cylinder head and forming the main intake passage together with the cylinder head, and at least the cylinder head A shroud that covers a portion of the engine, a fan that is disposed between the shroud and the engine body, is driven by rotation of the crankshaft, and generates cooling air for cooling the engine body, and intake air in the intake pipe Two throttle valves spaced apart in the direction of flow And a cylindrical body that forms part of the intake pipe and accommodates the two throttle valves, and is attached to the cylinder head, the throttle body provided outside the shroud, and the main body of the cylinder head. And a fuel injection device having an injection nozzle for injecting fuel into the intake passage. The forced air-cooled engine unit for a vehicle branches from the main intake passage between the two throttle valves and guides the intake air to a space near the injection nozzle formed in the cylinder head at least when idling. An auxiliary intake passage forming body that forms a passage is included. An air passage that connects the space inside the shroud and the space outside the shroud is formed at least at a part of the periphery of the auxiliary intake passage.

  ADVANTAGE OF THE INVENTION According to this invention, the forced air cooling engine unit for vehicles with a simple structure, the freedom degree of the layout in a vehicle, and a high fuel combustion efficiency, and a motorcycle provided with the same can be provided.

1 is a right side view of a motorcycle according to a first embodiment of the present invention. Fig. 2 is a partially enlarged right side view of a motorcycle around a vehicle body cover. It is a partial cross section figure of an engine unit, and shows the state where the engine unit was seen in plane. It is a longitudinal cross-sectional view of the principal part of an engine unit, and has shown the state which looked at the engine unit from the right side. FIG. 4 is a right side view of the engine unit, showing a part thereof broken and partly indicated by a two-dot chain line which is an imaginary line. FIG. 3 is a schematic right side view of a throttle body. It is a graph which shows the relationship between the opening degree of a 1st throttle valve, and the opening degree of a 2nd throttle valve. FIG. 6 is a schematic right side view of the throttle body when the first throttle valve and the second throttle valve are fully open. It is a top view of a shroud. It is a left view of an engine unit. It is a bottom view of a part of a shroud. It is sectional drawing of the principal part which follows the XII-XII line | wire of FIG. It is a front view of the principal part of an engine unit, and a part is shown with a section. FIG. 10 is a partially enlarged view of FIG. 9. It is a partial cross section figure of the principal part of another embodiment of this invention.

<Background to the Invention>
(1) The inventor of the present application examined applying an engine in which an injector is attached to a cylinder head and fuel atomization is promoted by air assist to a forced air-cooled engine. This is because an engine with high fuel combustion efficiency and a high degree of layout freedom in the vehicle can be realized.
(2) In this case, the auxiliary air intake passage is provided in the forced air-cooled engine. As a result, the assist air that has passed through the auxiliary intake passage is blown to the fuel injected from the injector. In a forced air-cooled engine, the engine body including a cylinder block is covered with a shroud. Then, air is introduced into the shroud by a fan disposed in the shroud, and the engine body is cooled by flowing air into the shroud. Therefore, it is desirable to cover as much of the engine body as possible with a shroud. However, if the engine main body is covered with a shroud, the heat of the engine main body tends to be trapped around the shroud, so that the vicinity of the injector tends to become high temperature. When the temperature around the injector becomes high, bubbles are generated in the fuel supplied to the injector. As a result, vapor lock and breathing occur, and the fuel combustion efficiency decreases.

Further, even if an auxiliary intake passage is simply provided in an engine which is covered with a shroud and easily heats up, the auxiliary intake passage and the assist air passing through the auxiliary intake passage become high temperature. As a result, the air-fuel mixture of the injected fuel and the assist air becomes high temperature, and the oxygen concentration decreases accordingly, so that the fuel combustion efficiency is lowered. Since the fan rotates together with the crankshaft provided in the engine body, the rotational speed of the fan also decreases during idling. Therefore, at the time of idling, there is a problem that the cooling performance of the fan is lowered and heat from the engine body tends to be trapped in the shroud. The inventor of the present application has focused on the above.
(3) The inventor of the present application considered the vehicle traveling and idling separately. That is, it has been found that it is only necessary to improve the performance of cooling the fuel injection device when the vehicle is running and when the vehicle is idling.
(A) When the vehicle is running First, attention was paid to the fact that when the vehicle is running, the fan rotates at a high speed together with the crankshaft, so that cooling by the fan can be expected. In order to cool an injector as a fuel injection device by cooling with a fan, a structure has been devised in which an injector, a sub-intake passage connected to the injector, and a shroud are arranged with a space therebetween. According to this configuration, air can flow from the inside of the shroud to the outside in the vicinity of the injector and the auxiliary intake passage. As a result, the cooling performance of the injector can be improved by cooling air from the fan during traveling.
(B) When the vehicle is idling Next, the idling time was examined. During idling, the crankshaft and the fan rotate at a low speed, so cooling by the fan cannot be expected. However, in order to improve the combustion efficiency of the fuel, a sub-intake passage that branches from the main intake passage and guides intake air (assist air) to the space near the injection nozzle formed in the cylinder head at least during idling is adopted. Yes. As described above, a structure for air assist is employed. In this structure, attention was paid to the fact that the injector can be cooled by assist air supplied from the auxiliary intake passage during idling.

In addition, he came up with a structure in which the throttle body connected to the auxiliary intake passage is arranged outside the shroud. Accordingly, at least the upstream side of the auxiliary intake passage is hardly affected by the heat in the shroud. Therefore, it was possible to suppress the rise in the temperature of the intake air passing through the auxiliary intake passage, and to cool the injector during idling.
The inventor of the present application has arrived at the present invention in this manner.

<Embodiment 1>
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In the following description, the front, rear, top and bottom, and left and right directions are in a reference posture corresponding to a state in which the motorcycle is traveling straight on a horizontal plane, and when the driver is facing forward, Based on viewpoint.

In each drawing, the forward direction of the motorcycle is indicated by an arrow F. Similarly, in each drawing, the backward direction of the motorcycle is indicated by an arrow B, the upward direction of the motorcycle is indicated by an arrow U, the downward direction of the motorcycle is indicated by an arrow D, and the left direction of the motorcycle is indicated by an arrow L. The right direction of the motorcycle is indicated by an arrow R.
FIG. 1 is a right side view of a motorcycle 200 according to Embodiment 1 of the present invention. In FIG. 1, a part of the motorcycle 200 is shown broken away. In the present embodiment, the motorcycle 200 is a scooter. In this embodiment, a scooter is described as an example of the motorcycle of the present invention, but the present invention is not limited to this. The present invention can also be applied to other motorcycles such as so-called motor cycles, mopeds and off-road vehicles other than scooters.

A handle 10 is disposed at the front portion of the motorcycle 200. The handle 10 is connected to the front wheel 14 via a steering shaft 13 that passes through the head pipe 11. A body frame 15 is coupled to the head pipe 11.
The vehicle body frame 15 extends in the vehicle longitudinal direction X1 as a whole. A front end portion of the vehicle body frame 15 is coupled to the head pipe 11. A seat 16 is attached to the rear portion of the vehicle body frame 15. A footrest plate 17 is attached in front of the seat 16 in the body frame 15. The footrest plate 17 is located below the seat 16.

A body cover 18 is attached to the body frame 15. The vehicle body cover 18 rises upward from the rear portion of the footrest plate 17 and surrounds the lower space G1 of the seat 16.
As shown in the partially enlarged right side view of FIG. 2, the vehicle body cover 18 is formed so as to surround the lower space G <b> 1 of the seat 16. The vehicle body cover 18 includes a front wall 202 disposed below the front end portion of the seat 16 and a pair of side walls 203 disposed below the right end portion and the left end portion of the seat 16. However, in FIG. 2, only the right side wall 203 of the pair of side walls 203 is illustrated. The pair of side walls 203 are formed symmetrically.

  A swing unit type engine unit 20 is attached to the body frame 15. The engine unit 20 is a forced air-cooled engine unit. A part of the engine unit 20 is covered with a vehicle body cover 18. Specifically, the front end side of the engine main body 21 described later of the engine unit 20 and the front end side of the shroud 50 are covered with the vehicle body cover 18.

As best shown in FIG. 1, the engine unit 20 includes an engine body 21, an intake pipe 36, a throttle body 38, a secondary intake passage formation body 41, and a shroud 50.
The engine body 21 is disposed behind the front wall 202 of the vehicle body cover 18 in the lower space G1 of the seat 16.

  FIG. 3 is a partial cross-sectional view of the engine unit 20 and shows the engine unit 20 in a plan view. That is, a horizontal section of a part of the engine unit 20 is shown. The engine body 21 has the cylinder axis directed in the vehicle longitudinal direction X1. The engine body 21 is a single cylinder four-cycle engine. The engine body 21 includes a cylinder block 22, a cylinder head 23 attached to the front end portion of the cylinder block 22, and a crankcase 24 attached to the rear end portion of the cylinder block 22.

  The crankcase 24 constitutes the rear end portion of the engine body 21. The crankcase 24 accommodates a crankshaft 57 extending in the vehicle left-right direction Y1. The crankshaft 57 is rotatably supported by the crankcase 24 via bearings 281 and 282. The right end portion 204 of the crankshaft 57 protrudes from the right side surface 246 of the crankcase 24. A fan 56 is connected to the right end portion 204 of the crankshaft 57 so as to be integrally rotatable. The fan 56 is driven by the rotation of the crankshaft 57. The fan 56 takes in air from the outside to the inside of the shroud 50 in order to cool the engine main body 21, and introduces air into the shroud 50 as cooling air. In addition, a large end portion of the connecting rod 205 is connected to an intermediate portion of the crankshaft 57.

  The cylinder block 22 is a cylindrical member connected to the front end face 206 of the crankcase 24. The space in the cylinder block 22 is a cylinder chamber E1. A piston 208 is accommodated in the cylinder chamber E1 so as to be capable of reciprocating along the cylinder axis. The piston 208 is connected to the small end portion of the connecting rod 205 via the piston pin 29.

The cylinder head 23 is connected to the front end surface of the cylinder block 22 and constitutes the front end portion of the engine body 21. The cylinder head 23 accommodates a camshaft 209 for driving an intake valve (not shown) and the exhaust valve 31.
As shown in FIG. 1, the crankcase 24 and the vehicle body frame 15 are connected via a pivot shaft 25. The axis of the pivot shaft 25 extends along the vehicle left-right direction Y1. A rear wheel 27 is attached to the rear part of the engine unit 20 via a power transmission part 26. A rear shock absorber 28 is attached between the rear part of the power transmission part 26 and the rear part of the vehicle body frame 15. With this configuration, the engine unit 20 and the rear wheel 27 can swing up and down with respect to the vehicle body frame 15 about the pivot shaft 25 as a swing center.

  FIG. 4 is a longitudinal sectional view of a main part of the engine unit 20 and shows a state in which the engine unit 20 is viewed from the right side. A space between the piston 29 accommodated in the cylinder block 22, the cylinder block 22, and the cylinder head 23 is a combustion chamber A1 in which the air-fuel mixture burns. The cylinder head 23 is provided with an intake valve 210 facing the combustion chamber A1 and the aforementioned exhaust valve.

  FIG. 5 is a right side view of the engine unit 20, a part of which is cut away and a part of which is indicated by a two-dot chain line which is an imaginary line. Referring to FIGS. 4 and 5, a cylindrical first boss 32 is provided on the upper right side of the cylinder head 23. The first boss 32 is formed integrally with the cylinder head 23. The first boss 32 protrudes from the cylinder head 23 toward the outside of the shroud 50. A part of the front end side of the first boss 32 is located outside the shroud 50 and is exposed from the shroud 50. The inner space of the first boss 32 communicates with a main intake passage P1 described later around the intake valve 210.

An injector 34 as a fuel injection device is attached to the first boss 32 via a synthetic resin holder 33. Since the injector 34 is attached to the cylinder head 23, it is located at the front end of the engine body 21.
Referring to FIG. 4, holder 33 includes a cylindrical portion 211 and a flange portion 212 provided at the proximal end of cylindrical portion 211. The flange 212 is in contact with the tip of the first boss 32. Thereby, the holder 33 is positioned with respect to the first boss 32. The cylindrical portion 211 is accommodated in the accommodation space H <b> 1 formed inside the first boss 32. A space between the outer peripheral surface of the base end portion 213 of the cylindrical portion 211 and the inner peripheral surface of the first boss 32 is liquid-tightly sealed by a first seal member 214 such as an O-ring. A chamber G2 that is an annular gap is formed between the outer peripheral surface of the intermediate portion 215 of the cylindrical portion 211 and the inner peripheral surface of the first boss 32. The distal end edge of the distal end portion 216 of the cylindrical portion 211 and the inner peripheral surface of the first boss 32 are fitted with substantially no gap.

  An inner space of the tip portion 216 of the cylindrical portion 211 is an injection space G3 as a space in the vicinity of the injection nozzle 35 of the injector 34. The injection space G3 is formed in the cylinder head 23 and communicates with the combustion chamber A1 via the intake valve 210. A plurality of through holes 217 are formed at the tip 216 of the cylindrical portion 211. A plurality of (for example, four) through holes 217 are formed at equal intervals in the circumferential direction of the tip portion 216 of the cylindrical portion 211. The chamber G2 and the injection space G3 communicate with each other through the through hole 217.

The injector 34 is for injecting fuel from a fuel tank (not shown) into the intake passage. The injector 34 includes an injector body 218 having an elongated shape, and an injection nozzle 35 disposed at the tip of the injector body 218.
The injector main body 218 passes through the cylindrical portion 211 of the holder 33 and is held by the holder 33. A space between the outer peripheral surface of the injector body 218 and the inner peripheral surface of the holder 33 is liquid-tightly sealed by a second seal member 219 such as an O-ring. The injection nozzle 35 faces the injection space G3 and is arranged in a direction in which fuel is injected toward the intake valve 210 via the main intake passage P1 in the cylinder head 23. The timing at which the injector 34 injects fuel toward the intake valve 210 is controlled by a control device such as an ECU (also referred to as an engine control unit or an electronic control unit) (not shown).

The intake pipe 36 is connected to an air cleaner (not shown) and wired so as to extend forward, an intake hose 37 connected to the front end of the intake hose 37, a cylindrical tubular body 220, and a cylinder A connecting pipe 39 connected to the front end of the body 220 and bent downward.
A cylindrical intake port 221 is formed in the cylinder head 23. A main intake passage P <b> 1 in the cylinder body 21 is formed by the intake port 221. An intake valve 210 is disposed at one end of the intake port 221. The other end of the intake port 221 is open to the upper surface of the cylinder head 23. The other end of the intake port 221 is formed by a flange 222 formed on the cylinder head 23. The flange 222 and a flange 223 formed at the front end portion of the connection pipe 39 are abutted with each other and are fixed using a fixing screw (not shown). Thus, the intake port 221 is connected to the front end portion of the connection pipe 39 (that is, the downstream end of the intake pipe 36).

A main intake passage P1 is formed by the intake port 221 of the cylinder head 23 and the intake pipe 36.
The throttle body 38 includes the aforementioned cylindrical body 220 and first and second throttle valves 40A and 40B as two throttle valves. The axis of the cylindrical body 220 extends along the vehicle longitudinal direction X1. The cylindrical body 220 is disposed above the cylinder block 22 of the engine body 21. Moreover, the cylindrical body 220 is arrange | positioned above the upper wall 243 of the cylindrical part 51 which the shroud 50 mentions later. As a result, the entire throttle body 38 is disposed outside the shroud 50.

  The first and second throttle valves 40A and 40B are for opening and closing the main intake passage P1 in the intake pipe 36, respectively. The first throttle valve 40A and the second throttle valve 40B are arranged at an interval in the intake air flow direction C1 in the main intake passage P1. The first throttle valve 40A and the second throttle valve 40B are accommodated in the cylindrical body 220. In the intake air flow direction C1, the first throttle valve 40A is disposed downstream of the second throttle valve 40B. That is, the first throttle valve 40A is located between the second throttle valve 40B and the cylinder head 23 in the main intake passage P1. The first throttle valve 40A and the second throttle valve 40B are each formed in a disc shape.

The first throttle valve 40 </ b> A is supported by a first rotating shaft 224 that extends perpendicular to the central axis of the cylindrical body 220. The second throttle valve 40B is supported by a second rotating shaft 225 that extends perpendicular to the central axis of the cylindrical body 220.
FIG. 6 is a schematic right side view of the throttle body 38. Referring to FIG. 6, the first rotating shaft 224 and the second rotating shaft 225 are respectively rotatably supported by the cylindrical body 220. Due to the rotation of the first rotation shaft 224, the first throttle valve 40A rotates integrally with the first rotation shaft 224 around the first rotation shaft 224. Similarly, due to the rotation of the second rotation shaft 225, the second throttle valve 40B rotates integrally with the second rotation shaft 225 around the second rotation shaft 225.

  A driving pulley 226 is coupled to the second rotating shaft 225 so as to be integrally rotatable. A throttle cable (not shown) is attached to the drive pulley 226. As a result, the drive pulley 226 rotates in conjunction with the throttle operation by the driver. Due to the rotation of the driving pulley 226, the second rotating shaft 225 rotates and the second throttle valve 40B is opened and closed.

The opening / closing operation of the second throttle valve 40B and the opening / closing operation of the first throttle valve 40A are linked by the link mechanism 227. That is, the first and second throttle valves 40A, 40B are interlocked.
The link mechanism 227 has a so-called lost motion structure, and the first throttle valve 40A starts to open after the start of the opening operation of the second throttle valve 40B. The link mechanism 227 includes a first main link member 228, a second main link member 229 disposed on the rear side of the first main link member 228, a sub link member 230, and a rotation transmission member 231. Yes.

The second main link member 229 is a small piece member formed integrally with the drive pulley 226. The second main link member 229 can rotate around the second rotation shaft 225. The second main link member 229 is connected to the sub link member 230 via the second connection shaft 232 so as to be relatively rotatable.
The sub link member 230 is a rod-like member that is long in the vehicle front-rear direction X1, and associates the second main link member 229 with the first main link member 228. A second connecting shaft 232 is disposed at the rear end of the sub link member 230. The front end of the sub link member 230 is connected to the first main link member 228 via the first connection shaft 233 so as to be relatively rotatable.

  The first main link member 228 is an elongated member made of sheet metal. A front end of the first main link member 228 is connected to the first connecting shaft 233. An intermediate portion of the first main link member 228 is coupled to the first rotation shaft 224 so as to be relatively rotatable. Thereby, the first main link member 228 can rotate independently of the first rotation shaft 224. A pressing member 234 is provided at the rear end of the first main link member 228.

  The distance from the center axis J1 of the second rotating shaft 225 as the swing center of the second main link member 229 to the center axis J2 of the second connecting shaft 232 is a distance D2. Further, the distance from the center axis J3 of the first rotating shaft 224 as the center of swing of the first main link member 228 to the center axis J4 of the first connecting shaft 233 is a distance D1. A relationship D2> D1 is established between the distances D1 and D2.

  The rotation transmission member 231 is a member formed of sheet metal. The rotation transmission member 231 is coupled to the first rotation shaft 224 so as to be integrally rotatable. The rotation transmitting member 231 is formed with a pressed portion 235 that can contact the pressing member 234. When the second throttle valve 40B is in the fully closed state, the pressing member 234 and the pressed portion 235 face each other with a predetermined interval in the circumferential direction of the first rotating shaft 224.

Referring to FIG. 4, the auxiliary intake passage forming body 41 extends from the cylindrical body 220 of the throttle body 38 and is formed up to the first boss 32 of the cylinder head 23. The entire auxiliary intake passage forming body 41 is disposed outside the shroud 50. The auxiliary intake passage forming body 41 forms an auxiliary intake passage K1.
The first boss 32 is formed integrally with the cylinder head 23. An injector 34 is attached to the first boss 32. A fourth boss 239 is formed integrally with the first boss 32. The fourth boss 239 extends perpendicular to the axis of the injector 34. A third boss 238 is attached to the fourth boss 239.

The auxiliary intake air forming body 41 includes a second boss 236 fixed to the cylindrical body 220, a fourth boss 239 and a first boss 32 formed on the cylinder head 23, and a holder 33 disposed in the first boss 32. A cylindrical portion 211, a third boss 238 attached to the fourth boss 239, and a hose 237 connecting the third boss 238 and the second boss 236.
The second boss 236 is a metallic cylindrical member and is formed in an L shape. The second boss 236 is disposed on the upper side of the cylindrical body 220. One end of the second boss 236 constitutes an upstream end forming portion 240 of the auxiliary intake passage forming body 41. One end of the upstream end forming portion 240 is fixed to the cylindrical body 220 between the first throttle valve 40A and the second throttle valve 40B. The auxiliary intake passage K1 in the second boss 236 constitutes an upstream end K2 of the auxiliary intake passage K1 and communicates with the main intake passage P1.

The hose 237 is a tube formed of rubber or other flexible material. One end of the hose 237 is connected to the other end of the second boss 236.
One end of the third boss 238 is connected to the other end of the hose 237. The fourth boss 239 is formed integrally with the first boss 32. The fourth boss 239 and the first boss 32 are arranged so that their central axes are substantially orthogonal to each other. Referring to FIGS. 4 and 5, the fourth boss 239 is disposed outside the shroud 50. The other end of the hose 237, the auxiliary intake passage K1 in the third and fourth bosses 238 and 239, the chamber G2 in the first boss 32 and the through hole 217 of the cylindrical portion 211 constitute the downstream end K3 of the auxiliary intake passage K1. Yes. The downstream end K3 communicates with the injection space G3 in the first boss 32. The other end of the third boss 238 is connected to the fourth boss 239. The other end of the hose 237, the third boss 238, the fourth boss 239, the first boss 32, and the cylindrical portion 211 of the holder 33 constitute a downstream end forming portion 241 of the auxiliary intake passage forming body 41. The downstream end forming portion 241 is disposed outside the shroud 50. In the first boss 32, the downstream end forming portion 241 is formed by a portion disposed outside the shroud 50.

With the above configuration, the upstream end K2 of the auxiliary intake passage K1 is formed by the upstream end forming portion 240 of the second boss 236, and communicates with the main intake passage P1 between the first and second throttle valves 40A, 40B. ing. Further, the downstream end K3 of the auxiliary intake passage K1 is formed by a downstream end forming portion 241. The downstream end K3 communicates with the injection space G3.
The intake air enters the auxiliary intake passage K1 from the main intake passage P1 as assist air. The assist air that has passed through the auxiliary intake passage K1 is guided to the injection space G3. The assist air supplied to the injection space G3 is blown by the fuel injected from the injector 34, thereby promoting fuel atomization.

FIG. 7 is a graph showing the relationship between the opening of the first throttle valve 40A and the opening of the second throttle valve 40B. In FIG. 7, the opening of the first throttle valve 40A is displayed as zero when idling. Similarly, the opening of the second throttle valve 40B is displayed as zero when idling.
In FIG. 7, a solid line graph indicates the opening degrees of the first and second throttle valves 40A and 40B in the present embodiment. As shown by the solid line graph, when the opening degree of the second throttle valve 40B is 10 degrees or less, the opening degree of the first throttle valve 40A remains 0 degrees.

  On the other hand, the broken line graph in FIG. 7 shows a case where the opening degree of the first and second throttle valves is always the same because the lost motion mechanism is not provided. As shown by the broken line graph and the solid line graph, in the present embodiment, the second throttle valve 40B opens after the first throttle valve 40A. The operation of the first and second throttle valves 40A and 40B will be described in more detail below.

Referring to FIGS. 6 and 7, the opening degree of first throttle valve 40A and second throttle valve 40B is controlled as follows in accordance with a change in load (throttle operation amount). First, the first throttle valve 40A located on the downstream side in the intake flow direction C1 is held in the fully closed position from the no-load (idle) operation range to the predetermined partial load operation range.
Specifically, until the partial load operation region, the rotation of the drive pulley 226 accompanying the driver's throttle operation is not transmitted to the first rotation shaft 224 but only to the second rotation shaft 225. Therefore, only the second throttle valve 40B is opened and closed by the rotation of the second rotating shaft 225. At this time, the sub link member 230 and the first main link member 228 operate in conjunction with the operation of the second main link member 229. As a result, the first main link member 228 rotates around the first rotation shaft 224. However, the first rotating shaft 224 and the first throttle valve 40A do not rotate until the pressing member 234 of the first main link member 228 contacts the pressed portion 235.

  Therefore, up to the partial load operation region, the amount of air flowing into the injection space G3 of the injection nozzle 35 is controlled based only on the opening of the second throttle valve 40B. In this partial load operation region, the assist air that has flowed into the auxiliary intake passage K1 is mixed with the fuel injected from the injection nozzle 35 in the injection space G3. Thereby, atomization of the fuel is promoted and the combustion efficiency of the fuel can be increased. Therefore, it is possible to reduce unburned fuel that is likely to occur when the engine is cold started.

On the other hand, in the process of shifting from the partial load region to the high load operation region, the first throttle valve 40A is opened according to the throttle operation. As a result, not only assist air passing through the auxiliary intake passage K 1 but also intake air passing through the other end of the intake port 221 is introduced into the cylinder head 23.
Specifically, referring to FIG. 7 and FIG. 8, when shifting from the partial load region to the high load operation region, the rotation amount of the first main link member 228 with respect to the idling time exceeds a predetermined value. As a result, the pressing member 234 of the first main link member 228 contacts the pressed portion 235 of the rotation transmission member 231. Thereby, in conjunction with the rotation of the first main link member 228, the rotation transmitting member 231 and the first rotating shaft 224 rotate, and the first throttle valve 40A rotates. Thereby, not only the intake air passing through the auxiliary intake passage K <b> 1 but also the air passing through the connection pipe 39 is introduced into the cylinder head 23.

As described above, in the link mechanism 227, as a result of the distance D2> the distance D1, the opening / closing speed of the first throttle valve 40A is faster than the opening / closing speed of the second throttle valve 40B in the high load operation region. As a result, when the second throttle valve 40B is fully opened, the first throttle valve 40A is also fully opened.
With reference to FIG. 1, an exhaust pipe 43 connected to the exhaust valve of the cylinder head 23 and a muffler 44 connected to the rear end of the exhaust pipe 43 are attached to the engine body 21. The exhaust pipe 43 and the muffler 44 extend as a whole along the vehicle longitudinal direction X1.

  The exhaust pipe 43 is disposed below the engine body 21. The upstream end (front end) of the exhaust pipe 43 is bent upward and is connected to the lower surface of the cylinder head 23 so as to communicate with the exhaust passage near the exhaust valve. The rear end of the exhaust pipe 43 and the front end of the muffler 44 are connected at substantially the same position as the rear end surface of the crankcase 24 in the vehicle longitudinal direction X1. The muffler 44 extends obliquely upward and rearward on the right side of the rear wheel 27. A catalyst device (not shown) is accommodated inside the muffler 44.

  FIG. 9 is a plan view of the shroud 50. In FIG. 9, a part of the engine unit 20 is indicated by a two-dot chain line that is an imaginary line. Referring to FIGS. 5 and 9, shroud 50 for cooling engine body 21 is attached to engine body 21. The shroud 50 surrounds the entire cylinder block 22 over the entire circumference, and surrounds the rear end 207 as a part of the cylinder head 23 over the entire circumference, and the crankcase 24 as a crankcase. 24 includes a side plate portion 52 covering from the right side of 24 and a protector 53.

The shroud 50 is configured by combining two left and right half members 54L and 54R. The entire left half member 54L and the front end portion of the right half member 54R constitute a cylindrical portion 51. A portion of the right half member 54 </ b> R behind the tubular portion 51 constitutes a side plate portion 52 and a protector 53.
Referring to FIGS. 3 and 5, cylindrical portion 51 includes a right wall 242 that is disposed on the right side of engine body 21 and has a shape that bulges to the right side. And a part of the right side surface of the rear end portion 207 of the cylinder head 23 are covered. The degree of swelling of the right wall 242 to the right is greater at the rear end than at the front end.

Further, as shown in FIG. 9 and FIG. 10, which is a left side view of the main part of the engine unit 20, the cylindrical portion 51 includes an upper wall 243 disposed above the engine body 21, and the engine body 21. And a left wall 244 arranged on the left side. The upper wall 243 covers a part of the upper surface of the cylinder block 22 and the upper surface of the rear end portion 207 of the cylinder head 23.
The left wall 244 covers the left side surface of the cylinder block 22 and a part of the left side surface of the rear end portion 207 of the cylinder head 23. Further, the cylindrical body 220 is disposed at a substantially central position of the engine body 21 in the vehicle left-right direction Y1.

  FIG. 11 is a bottom view of the main part of the shroud 50. In FIG. 11, a part of the engine unit 20 is indicated by a two-dot chain line that is an imaginary line. Referring to FIGS. 5 and 11, tubular portion 51 further includes a bottom wall 245 disposed below engine body 21. The bottom wall 245 covers the bottom surface of the cylinder block 22 and a part of the bottom surface of the rear end portion 207 of the cylinder head 23.

  Referring to FIGS. 3 and 5, side plate portion 52 includes a main plate portion 247 that faces right side surface 246 of crankcase 24 across fan 56 in the vehicle left-right direction Y <b> 1, and a circle that protrudes from the outer peripheral edge of main plate portion 247. And an arcuate arcuate plate portion 248. The main plate portion 247 covers the right side surface 246 of the crankcase 24 from the right side. The front end of the main plate portion 247 is connected to the right wall 242 of the tubular portion 51.

The arcuate plate portion 248 is formed in an arc shape. The arcuate plate portion 248 extends from the main plate portion 247 toward the right side surface 246 of the crankcase 24, and is adjacent to the right side surface 246 of the crankcase 24 via the third seal member 249. The arcuate plate portion 248 is fixed to the crankcase 24 using a fixing screw (not shown).
With reference to FIG. 3, a front space M <b> 1 is formed between the outer peripheral surface of the cylinder block 22 and the outer peripheral surface of the rear end portion 207 of the cylinder head 23 and the inner peripheral surface of the cylindrical portion 51. A rear space M <b> 2 is formed between the inner surface of the side plate portion 52 and the right side surface 246 of the crankcase 24. A cooling air passage M3 through which the cooling air of the fan 56 passes is formed by the front space M1 and the rear space M2. A part of the cooling air passage M <b> 3 is located between the front end portion of the shroud 50 and the rear end portion 207 of the cylinder head 23.

At the front end of the front space M1, a part of the front end portion of the cylindrical portion 51 and the outer surface of the cylinder head 23 are hermetically sealed. Details of the structure related to this seal will be described later.
On the other hand, at the rear end of the front space M <b> 1, the rear end edge of the tubular portion 51 is in airtight contact with the front end surface 206 of the crankcase 24. Specifically, the rear end edges of the upper wall 243, the left wall 244, and the bottom wall 245 of the cylindrical portion 51 are in contact with the front end face 206 of the crankcase 24.

In the rear space M2, the space between the arc-shaped plate portion 248 of the side plate portion 52 and the right side surface 246 of the crankcase 24 is hermetically sealed. The structure related to this seal will be described next.
12 is a cross-sectional view of a main part taken along line XII-XII in FIG. With reference to FIGS. 3 and 12, an arc-shaped third seal member 249 is interposed between the left end edge of the arc-shaped plate portion 248 of the side plate portion 52 and the right side surface 246 of the crankcase 24. The third seal member 249 is formed in a shape that matches the arc shape of the arc-shaped plate portion 248.

The top surface, bottom surface, rear side surface, and left side surface of the crankcase 24 are exposed without being covered with the shroud 50.
The aforementioned fan 56 is arranged at the rear end portion of the shroud 50 in the vehicle longitudinal direction X1. The fan 56 is disposed in the rear space M2. The side plate portion 52 is formed with an intake portion 58. The intake portion 58 includes a plurality of small openings formed on the right side of the fan 56. When the fan 56 rotates, outside air is introduced into the rear space M2 through the intake portion 58.

  With reference to FIGS. 5 and 11, a through hole 59 is formed in the front end portion of the shroud 50. The through hole 59 is disposed on the front end side of the right wall 242 and the bottom wall 245 of the cylindrical portion 51. The exhaust pipe 43 is inserted through the through hole 59. A discharge port 250 is formed on the front end side of the bottom wall 245. The discharge port 250 is opened in a rectangular shape, for example. The through hole 59 and the discharge port 250 are arranged in the vehicle left-right direction Y1.

The cooling air introduced into the rear space M2 of the cooling air passage M3 by the fan 56 flows into the front space M1. At this time, the cooling air comes into contact with the surface of the engine body 21 to take heat away from the engine body 21.
Next, a structure related to the seal between the front end portion of the cylindrical portion 51 and the outer surface of the rear end portion 207 of the cylinder head 23 will be described.

FIG. 13 is a front view of a main part of the engine unit 20 and a part thereof is shown in cross section. A fourth seal member 251 and a fifth seal member 252 formed using an elastic member such as rubber are disposed at the front end of the cylindrical portion 51. In FIG. 13, the fourth seal member 251 and the fifth seal member 252 are shown in cross section.
The fourth seal member 251 is an integrally molded product formed in a band shape as a whole, and is attached to the tubular portion 51. The fourth seal member 251 includes a first part 253 and a second part 254.

At the front end of the upper wall 243, a flange portion 255 protruding downward is formed. The first portion 253 of the fourth seal member 251 is attached to the edge portion of the flange portion 255 of the upper wall 243. The first portion 253 hermetically seals between the facing portions of the flange portion 255 and the outer surface of the cylinder head 23.
In addition, a flange portion 256 protruding to the right side is formed at the front end of the left wall 244. The flange portion 256 of the left wall 244 is formed corresponding to the shape of the left side surface of the cylinder head 23. Specifically, the flange portion 256 has a center in the vehicle vertical direction Z1 that is recessed toward the left side. The second portion 254 of the fourth seal member 251 is formed in a groove shape. Thereby, the 2nd part 254 becomes a shape which follows the shape of the edge of the collar part 256 of the left wall 244. FIG. The second portion 254 of the fourth seal member 251 is attached to the edge of the flange portion 256 of the left wall 244. The second portion 254 hermetically seals between the facing portions of the flange portion 256 and the left side surface of the cylinder head 23.

The fifth seal member 252 is an integrally molded product formed in a band shape and is held by the cylindrical portion 51. The fifth seal member 252 includes a first portion 257, a second portion 258, and a third portion 259.
At the front end of the bottom wall 245, a flange portion 260 that protrudes upward is formed. The flange portion 260 is in contact with a portion of the bottom surface of the cylinder head 23 that faces the flange portion 260. The first portion 257 of the fifth seal member 252 is attached from the middle portion to the right end portion in the vehicle left-right direction Y1 of the edge portion of the flange portion 260 of the bottom wall 245. The first portion 257 hermetically seals between the opposing portions of the flange portion 260 of the bottom wall 245 and the bottom surface of the cylinder head 23.

At the lower end of the front end portion of the right wall 242, a flange portion 261 that protrudes toward the right side surface of the cylinder head 23 is formed. The second portion 258 of the fifth seal member 252 is attached to the edge of the flange 261 of the right wall 242. The second portion 258 hermetically seals between the facing portions of the flange portion 261 and the right side surface of the cylinder head 23.
The third portion 259 of the fifth seal member 252 is in contact with the outer peripheral surface of the fifth boss 262 protruding from the cylinder head 23 from the front side. The upper end of the third portion 259 of the fifth seal member 252 is fixed to the cylinder head 23 in the vicinity of the fifth boss 262. The fifth boss 262 is for inserting a spark plug (not shown) into the cylinder head 23.

Referring to FIGS. 5 and 13, a recess 263 into which the fifth boss 262 is inserted is formed at the front end edge of the right wall 242. The edge of the recess 263 is in contact with the outer peripheral surface of the fifth boss 262. The outer peripheral surface of the fifth boss 262 is surrounded by the edge of the recess 263 and the third portion 259 of the fifth seal member 252.
FIG. 14 is a partially enlarged view of FIG. With reference to FIGS. 5 and 14, a notch 60 is formed at the front end of the upper wall 243 of the tubular portion 51. The notch 60 is formed such that a part of the front end of the upper wall 243 is recessed rearward. The edge portion 264 of the notch 60 includes a first edge portion 265 that faces the flange 222 of the cylinder head 23, and a second edge portion 266 and a third edge portion that face the downstream end forming portion 241 of the auxiliary intake passage forming body 41. 267.

  The flange 222 of the cylinder head 23 has a facing portion 268 that faces the first edge portion 265. The shape of the first edge portion 265 is along the shape of the facing portion 268. Specifically, in plan view, the first edge 265 has a front portion in the vehicle front-rear direction X1 substantially parallel to the vehicle front-rear direction X1 and an intermediate portion in the vehicle front-rear direction X1 extending obliquely to the right. And the rear side part in the vehicle front-back direction X1 is substantially parallel to the vehicle left-right direction Y1.

  A central portion in the vehicle left-right direction Y <b> 1 of the notch 60 is a first opening region N <b> 1 for exposing the flange 222 of the cylinder head 23. A space between the first edge 265 and the facing portion 268 of the flange 222 of the cylinder head 23 is hermetically sealed by a sixth seal member 269. The sixth seal member 269 is attached to the upper wall 243.

The second edge 266 is disposed at the right end of the notch 60. The second edge 266 is disposed in the vicinity of the other end of the hose 237 of the auxiliary intake passage forming body 41 and the fourth boss 239. In plan view, the second edge 266 has a shape that is recessed to the right.
Further, in the right side view, the rear end of the second edge portion 266 has a shape extending substantially parallel to the vehicle front-rear direction X1. In addition, when viewed from the right side, the front end of the second edge 266 has a shape that is recessed downward. The outer peripheral surface of the fourth boss 239 has a facing portion 270 that faces the second edge 266. Further, the outer peripheral surface of the other end of the hose 237 has a facing portion 272 that faces the second edge portion 266. The second edge portion 266 and the facing portion 270 are separated by about several millimeters, and the second edge portion 266 and the facing portion 272 are separated by about several millimeters.

  Thus, a first air passage Q1 is formed between the second edge portion 266 and the facing portions 270 and 272 of the downstream end forming portion 241. That is, the second edge 266 of the shroud 50 is an edge that forms the first air passage Q1. Further, in the auxiliary intake passage forming body 41, each facing portion 270, 272 is a portion that forms the first air passage Q <b> 1 with the shroud 50.

The first air passage Q1 communicates the cooling air passage M3 in the shroud 50 with the space outside the shroud 50. A part of the cooling air in the cooling air passage M3 passes through the first air passage Q1 and is discharged out of the shroud 50.
The notch 60 forms a second opening region N <b> 2 for exposing the fourth boss 239 in the vicinity of the second edge 266.

  The third edge 267 is disposed at the right end of the front end portion of the notch 60. Further, the third edge 267 is disposed in the vicinity of the first boss 32. The third edge 267 is formed in an arc shape. The third edge 267 extends along a facing portion 271 that faces the third edge 267 in the outer peripheral surface of the first boss 32. That is, the facing portion 271 forms a part of the downstream end forming portion 241.

  The third edge portion 267 and the facing portion 271 of the first boss 32 are separated by a few millimeters. Thereby, a second air passage Q <b> 2 is formed between the third edge 267 and the facing portion 271 of the first boss 32. That is, in the shroud 50, the third edge 267 is an edge that forms the second air passage Q2. The second air passage Q2 communicates the cooling air passage M3 in the shroud 50 with the space outside the shroud 50. Further, the second air passage Q2 and the first air passage Q1 are in communication. Thus, the first and second air passages Q1 and Q2 are formed around the downstream end forming portion 241. A part of the cooling air in the cooling air passage M3 passes through the second air passage Q2 and is discharged out of the shroud 50.

  The notch 60 forms a third opening region N <b> 3 for exposing the first boss 32 in the vicinity of the third edge 267. That is, a third opening area N3 for avoiding interference between the shroud 50 and the first boss 32 for the injector 34 is formed on the right side of the notch 60 with respect to the first opening area N1. The first boss 32 protrudes outside the shroud 50 from the third opening region N3. Further, the fourth boss 239 is disposed in a portion of the first boss 32 that protrudes out of the shroud 50. Therefore, the auxiliary intake passage forming body 41 is connected to the cylinder head 23 outside the shroud 50.

  Referring to FIG. 11 and FIG. 14, the second and third edges 266, 267 that form the first air passage Q 1 and the second air passage Q 2, the discharge port 250 and the through hole 59 are configured as described above. The engine body 21 is disposed above and below the cylinder head 23. The first air passage Q1 and the second air passage Q2, the discharge port 250, and the through hole 59 are all located at the front end of the tubular portion 51 as a discharge portion in the vehicle front-rear direction X1. That is, the first air passage Q1, the second air passage Q2, the discharge port 250, and the through hole 59 as discharge portions for discharging the cooling air in the shroud 50 are located on the front end side of the shroud 50 in the vehicle longitudinal direction X1. Has been placed.

Next, the operation of this embodiment will be described. 3 and 5, when the crankshaft 57 of the engine body 21 is driven, the fan 56 rotates. Thus, outside air is introduced as cooling air from the intake portion 58 of the shroud 50 into the rear space M2 of the cooling air passage M3 in the shroud 50. The flow of outside air at this time is, for example, as indicated by an arrow R1.
The cooling air introduced into the rear space M2 is sent by the fan 56 toward the front side of the vehicle longitudinal direction X1 through the cooling air passage M3 to form cooling air. At this time, the flow of the cooling air is divided into a flow toward the upper wall 243 of the cylindrical portion 51 of the shroud 50 and a flow toward the bottom wall 245 as indicated by an arrow R2. Thus, the cooling air takes heat of the engine body 21 while flowing from the rear space M2 to the front space M1 of the cooling air passage M3. The cooling air reaching the lower portion of the front space M1 is discharged from the discharge port 250 and the through hole 59 as shown by an arrow R3 in FIGS.

  Referring to FIGS. 5 and 14, a part of the cooling air that has reached the upper portion of front space M <b> 1 is directed to the outside of shroud 50 from first air passage Q <b> 1 and second air passage Q <b> 2 as indicated by arrow R <b> 4. Discharged. This cooling air is blown toward the outer surface of the downstream end forming portion 241 of the auxiliary intake passage forming body 41. Thus, the cooling air that has passed through the first air passage Q1 and the second air passage Q2 takes heat from the downstream end forming portion 241. As a result, the intake air passing through the downstream end K3 of the auxiliary intake passage K1 is guided into the injection space G3 at a low temperature.

Further, part of the cooling air discharged from the first air passage Q1 and the second air passage Q2 hits the first boss 32. Thereby, the cooling air also takes heat of the first boss 32 and cools the injector 34 attached to the first boss 32.
According to the present embodiment, the following effects can be obtained. That is, the engine unit 20 is an air-cooled engine unit. Therefore, a radiator and a cooling water pump required for the water-cooled engine unit are not necessary. Therefore, the engine unit 20 can be realized with a simple structure.

Further, a forced air cooling method in which cooling air is forcibly generated by the fan 56 is employed. Thereby, it is not necessary to arrange the engine unit 20 in a place where the traveling wind hits the motorcycle 200. Therefore, the degree of freedom of the layout of the engine unit 20 in the motorcycle 200 can be increased.
Furthermore, when the vehicle travels, the fan 56 rotates at a high speed together with the crankshaft 57, so that sufficient cooling air is generated in the shroud 50. As a result, a sufficient amount of cooling air flows to the auxiliary intake passage forming body 41 through the first and second air passages Q1, Q2. Therefore, the auxiliary intake passage forming body 41 is reliably cooled by the cooling air from the fan 56. Thereby, it is possible to prevent the auxiliary intake passage K1 from being heated by the heat of the engine body 21. Therefore, the assist air passing through the auxiliary intake passage K1 and the injector 34 through which the assist air flows do not need to be heated. As a result, the temperature of the air-fuel mixture of assist air and fuel can be lowered, so that the fuel combustion efficiency can be increased.

  Further, at least during idling, intake air is guided from the auxiliary intake passage K1 to the injection space G3 as assist air. Thereby, assist air is blown to the fuel injected from the injection nozzle 35 and atomization of the fuel is promoted. As a result, it is possible to increase the fuel combustion efficiency during idling or low-load running. Moreover, the auxiliary intake passage K1 branches off from the main intake passage P1 in the cylindrical body 220 disposed outside the shroud 50. Therefore, at least a connection portion between the auxiliary intake passage forming body 41 and the cylindrical body 220 is disposed outside the shroud 50. As a result, the entire auxiliary intake passage K1 is hardly affected by the heat in the shroud 50, and the assist air passing through the auxiliary intake passage K1 can be kept at a low temperature. Therefore, since the injector 34 can be cooled with low-temperature assist air, the temperature of the fuel passing through the injector 34 can be lowered, and the combustion efficiency of the fuel can be further increased. As described above, since the crankshaft 57 rotates at a low speed, the combustion efficiency of the fuel can be increased even during idling when the cooling air of the fan 56 is low.

  Further, a downstream end forming portion 241 is disposed in the vicinity of the injection nozzle 35 disposed in the cylinder head 23 that is likely to become high temperature due to heat from the combustion chamber A1. Therefore, the downstream end forming part 241 is easily subjected to the heat of the cylinder head 23. However, the downstream end forming portion 241 is reliably cooled by the cooling air passing through the first and second air passages Q1, Q2. Therefore, it is possible to reliably suppress the assist air passing through the downstream end K3 of the auxiliary intake passage K1 from being heated.

Further, a downstream end forming portion 241 is disposed outside the shroud 50. Thereby, the hot air of the engine main body 21 in the shroud 50 is hardly transmitted to the downstream end forming portion 241. Therefore, it is difficult for the heat of the engine body 21 to be transmitted to the assist air in the downstream end K3 of the auxiliary intake passage K1. Thereby, it can suppress more reliably that assist air becomes high temperature.
Further, the cooling air is formed at the downstream end from the first and second air passages Q1, Q2 formed between the second and third edge portions 266, 267 of the shroud 50 and the opposing portions 271, 270, 272. Part 241 can be applied. The first and second air passages Q1 and Q2 are located in the vicinity of the downstream end forming portion 241. Therefore, the cooling air can be reliably applied to the downstream end forming portion 241. Thereby, it can suppress more reliably that the assist air which passes the downstream end K3 of the sub intake passage K1 is heated.

  Further, in the shroud 50, as indicated by an arrow R2, the flow of cooling air from the fan 56 toward the first air passage Q1 and the second air passage Q2, and the cooling air from the fan 56 toward the discharge port 250 and the through hole 59 are shown. Flow. The cooling air flows so as to sandwich the cylinder head 23. Therefore, the area where the cooling air flows in the shroud 50 can be increased, and the engine body 21 can be efficiently cooled. Moreover, it can suppress that the cooling air which is going to flow out from the 1st air path Q1 and the 2nd air path Q2 is drawn in to the discharge port 250 and the through-hole 59 side. Therefore, the cooling air can be reliably discharged from the first air passage Q1 and the second air passage Q2 to effectively cool the downstream end forming portion 241.

  Further, a connecting pipe 39 is interposed between the cylindrical body 220 of the throttle body 38 and the cylinder head 23. As a result, the throttle body 38 and the upstream end forming portion 240 of the auxiliary intake passage forming body 41 can be reliably separated from the high-temperature cylinder head 23. Accordingly, it is difficult to transfer the heat of the cylinder head 23 to the upstream end forming portion 240 of the auxiliary intake passage forming body 41. As a result, it is possible to more reliably suppress the assist air from being heated by the heat of the cylinder head 23 at the upstream end K2 of the auxiliary intake passage K1. Further, heat that is transmitted from the cylinder head 23 to the cylindrical body 220 of the throttle body 38 can be blocked by the connecting pipe 39. That is, the connecting pipe 39 can be used as a heat insulating member between the cylinder head 23 and the throttle body 38.

Further, the entire auxiliary intake passage forming body 41 is disposed outside the shroud 50 where the temperature is lower than that inside the shroud 50. Thereby, the assist air in the auxiliary intake passage forming body 41 can be maintained at a lower temperature.
The shroud 50 is arranged so as not to cover the first boss 32 and the injector 34. Thereby, the shroud 50 can be reduced in size and the downward space G1 of the sheet | seat 16 can be made wider.

  As described above, the motorcycle 200 with a simple structure of the engine unit 20 can be realized. Further, since the engine unit 20 is a forced cooling type, it is not necessary to apply traveling wind to the engine body, and the degree of freedom of layout of the engine unit 20 in the motorcycle 200 can be increased. As a result, the engine unit 20 can be disposed so as to be surrounded by the vehicle body cover 18. That is, the present invention can be applied to the scooter type motorcycle 200. Further, the fuel atomization is promoted by the low-temperature assist air and the assist air in the auxiliary intake passage formation body 41 is cooled by the cooling air of the fan 56, so that the fuel can be discharged at any time during idling or traveling. The motorcycle 200 with extremely high combustion efficiency can be realized.

  Furthermore, the engine main body 21 can be arranged in a laid posture along the vehicle longitudinal direction X1. Thereby, the size of the engine body 21 in the vehicle vertical direction Z1 can be reduced. Thereby, the space between the engine main body 21 and the seat 16 can be made wider. Therefore, for example, a storage box having a large volume can be arranged in the space, and even in that case, it is possible to avoid an excessive increase in seat height. Further, the cooling air of the fan 56 can be applied from the rear end to the front end of the shroud 50. Thereby, the cooling air of the fan 56 can be applied to the wide area | region of the surface of the engine main body 21, and the engine main body 21 can be cooled efficiently.

  Further, the engine unit 20 of the present embodiment includes an engine main body 21 having a cylinder head 23, a fan 56, a shroud 50 that covers an area of the engine main body 21 excluding at least a part of the cylinder head 23, and the cylinder head 23. And the injector 34 attached to a portion exposed to the outside of the shroud 50. And the 1st and 2nd air path Q1, Q2 which connects the cooling wind path M3 between the shroud 50 and the engine main body 21 to the exterior of the shroud 50 is formed in the vicinity of the injector 34.

  According to this configuration, the shroud 50 does not cover the entire engine body 21 but covers a region of the engine body 21 excluding at least a part of the cylinder head 23. Therefore, the enlargement of the shroud 50 can be avoided. Further, a part of the cooling air introduced into the cooling air space M3 between the shroud 50 and the engine main body 21 by the fan 56 flows out of the shroud 50 from the first and second air passages Q1, Q2. When this cooling air passes through the vicinity of the injector 34, the injector 34 is cooled, so that an increase in temperature of the injector 34 can be suppressed.

  Further, a portion of the cylinder head 23 exposed to the outside of the shroud 50 is formed with a first boss 32 for attaching the injector 34, and the third edge 267 of the shroud 50 and the outer peripheral surface of the first boss 32 are formed. The second air passage Q2 is formed therebetween. Therefore, since the cooling air flowing out from the second air passage Q2 passes near the injector 34, the injector 34 can be effectively cooled.

  The cylinder head 23 and the injector 34 are located at the front end portion of the engine body 21 in the vehicle front-rear direction X1, and the fan 56 is disposed on the rear end side of the shroud 50 in the vehicle front-rear direction X1. A discharge port 250 and a through hole 59 for discharging the cooling air are arranged on the front end side of the shroud 50 in the vehicle longitudinal direction X1.

  According to this configuration, the cooling air introduced from the fan 56 into the shroud 50 and discharged from the first and second air passages Q1 and Q2, the discharge port 250 and the through hole 59 to the outside of the shroud 50 is generated inside the shroud 50. As a whole, it flows toward the front of the vehicle. The first and second air passages Q1 and Q2 are disposed at the downstream end of the cooling air flow in the shroud 50. Thereby, the outflow of the cooling air from the first and second air passages Q1, Q2 is promoted.

  Further, the first air passage Q1 and the second air passage Q2, the discharge port 250, and the through hole 59 are arranged at positions opposite to each other with the engine body 21 in between. Thereby, it is difficult for the cooling air flowing out from the first and second air passages Q1, Q2 to be drawn into the discharge port 250 and the through hole 59 side. Therefore, the cooling air can surely flow out from the first air passage Q1 and the second air passage Q2.

  The shroud 50 is formed with a first opening region N1 for exposing a flange 222 of the cylinder head 23 that is a connection region with the downstream end of the intake pipe 36 on the outer surface of the cylinder head 23. This eliminates the need to cover the downstream end of the intake pipe 36 with the shroud 50. Therefore, the shroud 50 is downsized as compared with the case where the downstream end portion of the main intake passage is covered with the shroud.

  Further, a downstream end forming portion 241 of the auxiliary intake passage forming body 41 is formed in a portion of the cylinder head 23 exposed to the outside of the shroud 50. According to this configuration, the auxiliary intake passage forming body 41 is connected to the cylinder head 23 outside the shroud 50. Therefore, the shroud 50 can be reduced in size as compared with the case where the downstream end forming portion 241 of the auxiliary intake passage forming body 41 is covered with the shroud.

  Further, since the downstream end forming portion 241 is formed in the vicinity of the first and second air passages Q1, Q2, the auxiliary intake passage is formed by the cooling air flowing out from the first and second air passages Q1, Q2. The downstream end forming part 241 of the body 41 can be cooled. As a result, the oxygen concentration of the assist air supplied from the auxiliary intake passage K1 to the injection space G3 can be avoided from decreasing due to temperature rise, and the combustion efficiency can be increased.

Next, the protector 53 formed integrally with the shroud 50 will be described with reference to FIGS. 5 and 9. The protector 53 is for covering the right outer surface of the rear end side portion of the exhaust pipe 43. The protector 53 has a form protruding downward from the lower edge of the main plate portion 247 of the side plate portion 52.
The protector 53 has an elongated shape in the vehicle longitudinal direction X <b> 1 and is disposed on the right side of the exhaust pipe 43. Further, the position of the protector 53 in the vehicle longitudinal direction X1 is a position corresponding to the fan 56. In other words, the protector 53 is disposed at a position close to the fan 56. Further, the rear end portion of the protector 53 protrudes rearward from the rear end of the side plate portion 52.

  Japanese Patent Laid-Open No. 2008-190425 discloses a shroud as means for cooling the engine body. However, a protector for covering the exhaust pipe and the muffler is not formed on the shroud. Therefore, when the protector is provided, the number of parts increases. On the other hand, in this embodiment, since the protector 53 is formed integrally with the shroud 50, the number of parts can be reduced.

  Further, the protector 53 is disposed in the vicinity of the fan 56. Thereby, a part of the outside air sucked into the fan 56 comes into contact with the surface of the protector 53. Thereby, the temperature rise of the protector 53 is suppressed. Further, since the protector 53 has a shape substantially parallel to the length direction of the exhaust pipe 43, the protector 53 does not need to be enlarged unnecessarily. Thereby, the enlargement of the shroud 50 is avoided.

<Embodiment 2>
FIG. 15 is a partial cross-sectional view of a main part of another embodiment of the present invention. In the present embodiment, differences from the above embodiment will be mainly described, and the same components as those in the above embodiment will be denoted by the same reference numerals and description thereof will be omitted.
Referring to FIG. 15, in the present embodiment, the downstream end forming portion 241 of the auxiliary intake passage forming body 41 is disposed inside the shroud 50. Specifically, the shroud 50 further includes a cover member 275 fixed to the upper wall 243 of the tubular portion 51. The cover member 275 is formed separately from the half members 54L and 54R (the half member 54L is not shown). The cover member 275 is located on the upper side of the upper wall 243.

The cover member 275 includes a first cover 276 and a second cover 277 disposed on the rear side of the first cover 276.
The first cover 276 is disposed in front of the first boss 32 and covers the first boss 32, the holder 33, the injector 34, and the downstream end forming portion 241 from the front side. The second cover 277 has, for example, an inverted U shape when viewed in the vehicle longitudinal direction X1. The front end of the second cover 277 is connected to the first cover 276. The second cover 277 covers the first boss 32, the holder 33, the injector 34, and the downstream end forming portion 241 from the right side, the upper side, and the left side.

  An upper space M4 which is a part of the cooling air passage M3 is formed inside the second cover 277. The upper space M4 communicates with the front space M1. Further, a third air is provided between the rear end portion 277a of the second cover 277, the adjacent portion 243a of the upper wall 243 adjacent to the rear end portion 277a, and the other end 237a of the hose 237 of the downstream end forming portion 241. A passage Q3 is formed. The third air passage Q3 is formed around the downstream end forming portion 241 and communicates the cooling air passage M3 and the space outside the shroud 50. The third air passage Q3 can discharge the cooling air.

The cooling air discharged from the first and second air passages Q1, Q2 hits the downstream end forming portion 241 in the upper space M4 in the cover member 275 as shown by an arrow R4, and then, as shown by an arrow R5, The air is discharged from the third air passage Q3 to the rear of the cover member 275.
According to the present embodiment, the downstream end forming portion 241 is disposed inside the cover member 275 of the shroud 50 through which the cooling air flows. Thereby, the cooling air of the fan 56 can be reliably applied to the downstream end forming portion 241. Therefore, it is possible to reliably suppress the downstream end forming portion 241 and the assist air therein from being heated by the heat of the engine body 21 by the cooling air.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) The shroud may cover the entire cylinder head of the engine body.
(2) It is not restricted to the aspect by which cooling air is applied to the downstream end formation part of a sub intake passage formation body. The cooling air may be applied anywhere in the auxiliary intake passage.

(3) A wind guide member formed separately from the shroud may be prepared, and cooling air discharged from the shroud may be applied to the auxiliary intake passage formation body by the wind guide member.
(4) The discharge port may be disposed in the vicinity of the first air passage and the second air passage.
(5) Either the first air passage or the second air passage may be eliminated.
(6) You may arrange | position at least one part except an upstream end formation part in a shroud among sub-intake passage formation bodies.

(7) The cylinder head and the fuel injection device may be disposed in the middle part of the engine body or in the rear end part in the vehicle longitudinal direction. Similarly, the fan only needs to be coaxial with the crankshaft, and may be disposed in the middle portion of the engine body or in the front end portion in the vehicle longitudinal direction.
(8) The engine unit does not have to be supported so as to be swingable about the pivot axis with respect to the body frame, and may be fixed to the body frame.

(9) The auxiliary intake passage forming body is not limited to a form formed separately from the intake pipe. The auxiliary intake passage forming body may be formed integrally with a member forming an intake pipe such as a connection pipe.
(10) A gap between the edge of the front end of the shroud and the outer peripheral surface of the injector may be an air passage through which cooling air is discharged. Alternatively, a through hole may be formed near the injector in the shroud, and the hole may function as an air passage through which cooling air is discharged.

(11) The air passage from which the cooling air is discharged may be arranged on the upstream end side of the cooling air passage in the shroud, or may be arranged at a position approximately in the middle between the upstream end and the downstream end.
(12) The protector may be a separate part from the shroud.
(13) The protector may be arranged at a position away from the intake fan.
(14) The protector has a form covering the whole exhaust pipe, a form covering a part of the exhaust pipe and a part of the muffler, a form covering the whole exhaust pipe and a part of the muffler, a whole form of the exhaust pipe and the whole muffler. Any form of the form which covers and the form which covers a part of muffler and the whole may be sufficient.

  (15) If the auxiliary intake passage forming body forms an auxiliary intake passage that connects between the first and second throttle valves and the injection space formed in the cylinder head, the embodiment and the configuration described above are used. May be different. For example, the third boss may be omitted, and the other end of the hose may be fitted into the fourth boss and fixed. Alternatively, the fourth boss may be omitted, a recess may be formed in the first boss, and the third boss may be fitted into the recess and fixed. Further, the third boss and the fourth boss may be omitted, and the end portion of the hose may be directly fixed to the first boss. Further, a recess may be formed in the cylindrical body of the throttle body, and the end of the hose may be fixed to the recess.

  (16) The engine unit may be mounted on a vehicle other than the motorcycle. Examples of such vehicles include ATV (All Terrain Vehicle) and saddle-type vehicles such as snowmobiles.

DESCRIPTION OF SYMBOLS 15 ... Body frame 16 ... Seat 17 ... Footrest board 18 ... Body cover 20 ... Engine unit (forced air-cooled engine unit for vehicles)
DESCRIPTION OF SYMBOLS 21 ... Engine main body 22 ... Cylinder block 23 ... Cylinder head 24 ... Crankcase 32 ... 1st boss | hub (boss | hub which accommodates an injection nozzle)
34. Injector (fuel injection device)
35 ... Injection nozzle 36 ... Intake pipe 38 ... Throttle body 39 ... Connection pipe 40A, 40B ... Throttle valve 41 ... Sub intake passage forming body 50 ... Shroud 56 ... Fan 57 ... Crankshaft 59 ... Through hole (discharge part)
200 ... motorcycle 207 ... rear end of cylinder head (part of cylinder head)
208 ... Piston 220 ... Cylindrical body 240 ... Upstream end forming part 241 ... Downstream end forming part 250 ... Discharge port (discharge part)
264 ... Edge (edge forming an air passage)
271 ... Opposite portion (outer surface of downstream end forming portion)
270, 272 ... opposing portion (outer surface of downstream end forming portion)
A1 ... Combustion chamber C1 ... Flow direction of intake air G1 ... Lower space G3 ... Injection space (space near the injection nozzle)
K1 ... Sub-intake passage K2 ... Upstream end of sub-intake passage K3 ... Downstream end of sub-intake passage M3 ... Cooling air passage (space in shroud)
P1 ... main intake passage Q1 ... first air passage (discharge section)
Q2 ... Second air passage (discharge part)
Q3 ... Third air passage X1 ... Vehicle longitudinal direction

Claims (10)

A crankcase that houses a crankshaft, a cylinder block that is connected to the crankcase and accommodates a piston so as to reciprocate, and forms a combustion chamber together with the cylinder block, and a part of a main intake passage connected to the combustion chamber An engine body including a cylinder head, and
An intake pipe connected to the cylinder head and forming the main intake passage with the cylinder head;
A shroud covering at least a part of the cylinder head;
A fan that is disposed between the shroud and the engine body, is driven by rotation of the crankshaft, and generates cooling air for cooling the engine body;
Two throttle valves disposed in the intake pipe at intervals in the flow direction of the intake air, and a cylindrical body that forms a part of the intake pipe and accommodates the two throttle valves, and is provided outside the shroud. The throttle body provided in the
A fuel injection device attached to the cylinder head and having an injection nozzle for injecting fuel into the main intake passage in the cylinder head;
Forming a sub-intake passage between the two throttle valves from the main intake passage and guiding the intake air to a space near the injection nozzle formed in the cylinder head at least when idling; and at least the sub-intake passage A sub-intake passage forming body in which an air passage communicating the space inside the shroud and the space outside the shroud is formed in a part of the periphery of
A forced air-cooled engine unit for vehicles. The auxiliary intake passage includes an upstream end connected to the main intake passage and a downstream end connected to the space in the vicinity of the injection nozzle,
The auxiliary intake passage forming body includes an upstream end forming portion that forms the upstream end, and a downstream end forming portion that forms the downstream end,
The forced air cooling engine unit for a vehicle according to claim 1, wherein the cooling air is guided to at least the downstream end forming portion. The cylinder head includes a boss that is exposed outside the shroud and accommodates the injection nozzle,
The forced air cooling engine unit for a vehicle according to claim 2, wherein the downstream end forming portion of the auxiliary intake passage forming body includes the boss.   The forced air-cooled engine unit for a vehicle according to claim 3, wherein the shroud includes an edge portion that forms the air passage with an outer surface of the downstream end forming portion. The shroud is formed with a discharge port for discharging the cooling air out of the shroud,
The forced air-cooled engine unit for a vehicle according to claim 4, wherein the edge portion and the discharge port are disposed with the cylinder head interposed therebetween.   The forced air-cooled engine unit for a vehicle according to claim 1, wherein the intake pipe includes a connection pipe that connects the cylindrical body and the cylinder head.   The forced air-cooled engine unit for a vehicle according to claim 1, wherein the auxiliary intake passage forming body is entirely disposed outside the shroud.   The forced air-cooled engine unit for a vehicle according to claim 2, wherein the downstream end forming portion is disposed inside the shroud. A body frame extending in the longitudinal direction of the vehicle,
A seat supported by the body frame;
A footrest plate disposed in front of the seat;
A vehicle body cover that rises upward from the rear part of the footrest plate and surrounds the lower space of the seat;
The forced air cooling for a vehicle according to any one of claims 1 to 8, wherein the vehicle body frame is supported so as to be swingable in a vertical direction and is covered with the vehicle body cover below the seat. An engine unit,
Motorcycle equipped with. The cylinder head and the fuel injection device are located at the front end of the engine body in the vehicle longitudinal direction,
The fan is disposed on the rear end side of the shroud in the vehicle longitudinal direction,
The motorcycle according to claim 9, wherein a discharge portion for discharging cooling air in the shroud is disposed on a front end side of the shroud in the vehicle front-rear direction.

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