EP2148058A2

EP2148058A2 - Forced air-cooled vehicle engine unit, and motorcycle

Info

Publication number: EP2148058A2
Application number: EP09009562A
Authority: EP
Inventors: Toshio Matsubara; Yasushi Ishizuka; Kyouji Morita; Yoshitaka Nagai; Wataru Ishi; Hiroyuki Tsuzuku; Takayuki Gouke
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 2008-07-24
Filing date: 2009-07-23
Publication date: 2010-01-27
Anticipated expiration: 2029-07-23
Also published as: TWI445637B; ES2534051T3; EP2148058A3; JP2010223211A; TW201016492A; EP2148058B1

Abstract

An auxiliary air intake passage defining member 41 is connected to an air intake pipe 36 connected to a cylinder head 23. The auxiliary air intake passage defining member 41 defines an auxiliary air intake passage K1. The auxiliary air intake passage K1 is branched from a main air intake passage P1 in the air intake pipe 36 to guide intake air into a space defined adjacent to an injection nozzle of an injector at least during idling. At least a part of the auxiliary air intake passage defining member 41 is located outside a shroud 50. A portion around the injection nozzle is cooled by assist air from the auxiliary air intake passage K1 during idling. A portion around the injection nozzle is cooled by cooling wind generated by a fan 56 during the movement of a vehicle.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

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

2. Description of the Related Art

An engine disclosed in patent document 1 ( WO 2005/098231A ) includes a main air intake passage through which air is supplied into a combustion chamber thereof from an air cleaner. An auxiliary air intake passage is branched from the main air intake passage. An injector is mounted on a cylinder head of the engine. Intake air supplied from the main air intake passage flows into the auxiliary air intake passage to serve as assist air at least during idling. The assist air is applied to fuel injected from the injector to promote disintegration of the fuel. This increases the fuel combustion efficiency at least during idling.
The engine disclosed in patent document 1 is of a naturally air-cooled type, which is configured such that an airstream generated by the movement of the vehicle is applied to the engine.
Thus, the engine is cooled by the airstream.
An air-cooled engine and a water-cooled engine are generally known for use in motorcycles and other types of vehicles. The air-cooled engine is cooled by applying air to the engine. Therefore, the air-cooled engine has a simplified construction without a need for provision of a radiator and a cooling water pump, which may otherwise be required for the water-cooled engine.
In the engine disclosed in patent document 1, the injector is mounted on the cylinder head, so that the cylinder head and the injector are cooled by the airstream. This suppresses vapor lock of the fuel supplied into the injector, and promotes atomization of the fuel, thereby improving the combustion efficiency.
However, the engine disclosed in patent document 1 is of the naturally air-cooled type. Therefore, it is necessary to locate the engine at a position at which the engine can easily catch the airstream. This disadvantageously reduces flexibility in the layout of the engine in the vehicle.
To cope with this, a forced air-cooled engine has been developed, which includes a fan driven by rotation of a crank shaft of the engine, and a shroud covering a cylinder head, a cylinder block and the like of the engine as disclosed in patent document 2 (Japanese Unexamined Patent Publication No. 2001-241326 ). Wind generated by the fan flows through an inside space of the shroud to hit the cylinder head and the cylinder block, thereby cooling the engine. A part of the forced air-cooled engine located in the shroud is cooled by the fan.
The forced air-cooled engine does not need to be located at the position at which the engine can catch the airstream, because the cooling of the engine does not rely on the airstream. Therefore, the flexibility in the layout of the engine in the vehicle is increased.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention to provide a forced air-cooled vehicle engine unit which has a simple construction, higher layout flexibility in a vehicle and higher fuel combustion efficiency, and to provide a motorcycle including such an engine unit.
This object is achieved by a forced air-cooled vehicle engine unit of claim 1, and by a motorcycle of claim 9.
According to the present invention, there is provided a forced air-cooled vehicle engine unit, which includes: an engine body including a crank case accommodating a crank shaft, a cylinder block connected to the crank case and accommodating a piston in a reciprocally movable manner, and a cylinder head that is cooperative with the cylinder block to define a combustion chamber and defines a part of a main air intake passage connected to the combustion chamber; an air intake pipe connected to the cylinder head and cooperative with the cylinder head to define the main air intake passage; a shroud covering at least a part of the cylinder head; a fan disposed between the shroud and the engine body, and adapted to be driven by rotation of the crank shaft to generate cooling wind for cooling the engine body; a throttle body including two throttle valves spaced from each other in an intake air flowing direction in the air intake pipe, and a tubular member that defines a part of the air intake pipe and accommodates the two throttle valves, the throttle body being disposed outside the shroud; and a fuel injection device attached to the cylinder head and having an injection nozzle which injects fuel into the part of the main air intake passage defined in the cylinder head. The forced air-cooled vehicle engine unit further includes an auxiliary air intake passage defining member that defines an auxiliary air intake passage branched from the main air intake passage between the two throttle valves to guide intake air into a space defined adjacent to the injection nozzle in the cylinder head at least during idling. An air passage is provided around at least a part of the auxiliary air intake passage for communication between an inside and an outside of the shroud.
With this unique arrangement, the forced air-cooled vehicle engine unit has a simple construction, higher layout flexibility in a vehicle and higher fuel combustion efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a right side view of a motorcycle according to a first embodiment of the present invention.
Fig. 2 is an enlarged partial right side view illustrating a portion of the motorcycle around a vehicle body cover.
Fig. 3 is a partial sectional view of an engine unit as seen in plan.
Fig. 4 is a vertical sectional view of major portions of the engine unit as seen from the right side.
Fig. 5 is a partly broken right side view illustrating the engine unit partly in a two-dot-and-dash line (phantom line).
Fig. 6 is a schematic right side view of a throttle body.
Fig. 7 is a graph showing a relationship between the degree (angle) of opening of a first throttle valve and the degree of opening of a second throttle valve.
Fig. 8 is a schematic right side view illustrating the throttle body with its first and second throttle valves being fully open.
Fig. 9 is a plan view of a shroud.
Fig. 10 is a left side view of the engine unit.
Fig. 11 is a partial bottom view of the shroud.
Fig. 12 is a sectional view taken along a line XII-XII in Fig. 3.
Fig. 13 is a front view illustrating major portions of the engine unit partly in section.
Fig. 14 is a partially enlarged view of Fig. 9.
Fig. 15 is a right side view illustrating, partly in section, an engine unit according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Prehistory of the Present Invention

An attempt has been made to provide a forced air-cooled engine which incorporates the features of the engine including the injector attached to the cylinder head thereof and adapted to promote the atomization of the fuel by the assist air. Such a forced air-cooled engine may have higher fuel combustion efficiency and higher layout flexibility in the vehicle.
With provision of an auxiliary air intake passage, the forced air-cooled engine is configured such that assist air supplied through the auxiliary air intake passage is applied to fuel injected from an injector. In the forced air-cooled engine, an engine body including a cylinder block and the like is covered with a shroud. Air is introduced into the inside of the shroud by a fan disposed in the shroud. Thus, the air flows through the inside of the shroud, whereby the engine body is cooled. Therefore, it is desirable to cover the greatest possible portion of the engine body with the shroud. With the engine body being covered with the shroud, however, the heat of the engine body is liable to be accumulated around the shroud, so that the injector and its peripheral portion are liable to be heated to a higher temperature. If the temperature of the injector rises, air bubbles are liable to occur in the fuel supplied into the injector. This results in vapor lock and breathing, thereby reducing the fuel combustion efficiency.
Even if the auxiliary air intake passage is provided in the engine which suffers from the heat accumulation due to the coverage with the shroud, the auxiliary air intake passage and the assist air flowing through the auxiliary air intake passage are heated to a higher temperature. As a result, a mixture of the injected fuel and the assist air is heated to a higher temperature, so that the oxygen concentration is correspondingly reduced. This reduces the fuel combustion efficiency. Further, the rotation speed of the fan is reduced during idling, because the fan is rotated together with a crank shaft provided in the engine body. Therefore, the cooling capability of the fan is reduced during idling, so that heat from the engine body is disadvantageously accumulated in the shroud.
To cope with the aforementioned problems, the cooling of the engine body during the movement of the vehicle and the cooling of the engine body during idling are considered separately. That is, it is simply necessary to improve the cooling effect of the fuel injection device during the movement of the vehicle and during idling.
During the movement of the vehicle, the fan is rotated together with the crank shaft at a higher speed and, therefore, the cooling by the fan may be more effective. For the effective cooling of the injector (fuel injection device) by the fan, it may be more advantageous that the injector and the auxiliary air intake passage connected to the injector are disposed in a spaced relation from the shroud. With this arrangement, air flows from the inside to the outside of the shroud around the injector and the auxiliary air intake passage. This makes it possible to cool the injector at improved efficiency by the cooling wind generated by the fan during the movement of the vehicle.
During idling, the crank shaft and the fan are each rotated at a lower speed, so that the cooling by the fan is not effective. For improvement of the fuel combustion efficiency, the auxiliary air intake passage is provided, which is branched from the main air intake passage to introduce intake air (assist air) into a space defined around an injection nozzle provided in the cylinder head at least during idling. This arrangement, which originally serves for air assist, may be more advantageous for cooling the injector by the assist air supplied from the auxiliary air intake passage during idling.
It is also conceivable that a throttle body connected to the auxiliary air intake passage is disposed outside the shroud. Thus, at least an upstream portion of the auxiliary air intake passage is less liable to be affected by the heat in the shroud. This suppresses the temperature rise of the intake air flowing through the auxiliary air intake passage, thereby ensuring proper cooling of the injector during idling.
Thus, the present invention has been accomplished.

First Embodiment

With reference to the attached drawings, the present invention will hereinafter be described by way of specific embodiments. In the following description, directions between the front and the back, vertical directions and lateral (transverse) directions are defined on the basis of a reference posture of a motorcycle which travels straight ahead on a horizontal plane as seen from a viewpoint of a forward-facing rider of the motorcycle.
In the drawings, a forward direction of the motorcycle is indicated by an arrow F. Similarly, a rearward direction of the motorcycle is indicated by an arrow B. Further, an upward direction of the motorcycle is indicated by an arrow U, and a downward direction of the motorcycle is indicated by an arrow D. A leftward direction of the motorcycle is indicated by an arrow L, and a rightward direction of the motorcycle is indicated by an arrow R.
Fig. 1 is a right side view of a motorcycle 200 according to a first embodiment of the present invention. In Fig. 1, the motorcycle 200 is illustrated partly in a broken-down form. In this embodiment, the motorcycle 200 is a scooter. In this embodiment, the scooter will be described as an example of the inventive motorcycle, but the motorcycle is not limited to the scooter. The present invention is applicable to other types of motorcycles such as so-called mopeds and off-road vehicles.
The motorcycle 200 includes a handlebar 10 provided on a front portion thereof. The handlebar 10 is connected to a front wheel 14 via a steering shaft 13 extending through a head pipe 11. The head pipe 11 is connected to a vehicle body frame 15.
The vehicle body frame 15 extends in the direction (X1) between the front and the back of the vehicle as a whole. The head pipe 11 is connected to a front end of the vehicle body frame 15. A seat 16 is attached to a rear portion of the vehicle body frame 15. A foot rest plate 17 is attached to a portion of the vehicle body frame 15 in front of the seat 16. The foot rest plate 17 is located at a lower level than the seat 16.
A vehicle body cover 18 is attached to the vehicle body frame 15. The vehicle body cover 18 extends upward from a rear portion of the foot rest plate 17 to surround a lower space G1 present below the seat 16.
As shown in an enlarged partial right side view of Fig. 2, the vehicle body cover 18 surrounds the lower space G1 below the seat 16. The vehicle body cover 18 includes a front wall 202 disposed below a front end of the seat 16, and a pair of side walls 203 disposed below right and left edges of the seat 16. In Fig. 2, only the right one of the side walls 203 is shown. The side walls 203 are laterally symmetrical.
A unit-swing engine unit (or swing type engine unit) 20 is mounted on the vehicle body frame 15. The engine unit 20 is of a forced air-cooled type. A part of the engine unit 20 is covered with the vehicle body cover 18. More specifically, a front end portion of an engine body 21 of the engine unit 20 and a front end portion of a shroud 50 to be described later are covered with the vehicle body cover 18. As best shown in Fig. 1, the engine unit 20 includes the engine body 21, an air intake pipe 36, a throttle body 38, an auxiliary air intake passage defining member 41, and the shroud 50.
The engine body 21 is disposed behind the front wall 202 of the vehicle body cover 18 in the lower space G1 below the seat 16.
Fig. 3 is a partial sectional view of the engine unit 20 as seen in plan. That is, a part of the engine unit 20 is shown in horizontal section. The engine body 21 has a cylinder axis extending in the direction (X1) between the front and the back of the vehicle. The engine body 21 is a single-cylinder four-stroke engine. The engine body 21 includes a cylinder block 22, a cylinder head 23 attached to a front end portion of the cylinder block 22, and a crank case 24 attached to a rear end portion of the cylinder block 22.
The crank case 24 defines a rear end portion of the engine body 21. A crank shaft 57 extending transversely (Y1) of the vehicle is accommodated in the crank case 24. The crank shaft 57 is rotatably supported by the crank case 24 via bearings 281, 282. A right end portion 204 of the crank shaft 57 projects from a right side surface 246 of the crank case 24. A fan 56 is connected to the right end portion 204 of the crank shaft 57 for unitary rotation. The fan 56 is driven by the rotation of the crank shaft 57. Air is introduced as cooling wind into the shroud 50 from the outside by the fan 56 for cooling the engine body 21. The crank shaft 57 has an intermediate portion which is connected to a large end portion of a connecting rod 205.
The cylinder block 22 is a tubular member connected to a front end face 206 of the crank case 24. An inside space of the cylinder block 22 is defined as a cylinder chamber E1. A piston 208 is accommodated in the cylinder chamber E1 so as to be reciprocally movable along the cylinder axis. The piston 208 is connected to a small end portion of the connecting rod 205 via a piston pin 29.
The cylinder head 23 is connected to a front end face of the cylinder block 22, and defines a front end portion of the engine body 21. A cam shaft 209 for driving an air intake valve (not shown) and an exhaust valve 31 is accommodated in the cylinder head 23.
As shown in Fig. 1, the crank case 24 is connected to the vehicle body frame 15 via a pivot shaft 25. The pivot shaft 25 has an axis extending transversely (Y1) of the vehicle. A rear wheel 27 is attached to a rear portion of the engine unit 20 via a power transmission member 26. A rear shock absorber 28 is provided between a rear portion of the power transmission member 26 and the rear portion of the vehicle body frame 15. With this arrangement, the engine unit 20 and the rear wheel 27 are vertically pivotal about the pivot shaft 25 with respect to the vehicle body frame 15.
Fig. 4 is a vertical sectional view of major portions of the engine unit 20 as seen from the right side of the engine unit 20. A space defined between the piston 208 accommodated in the cylinder block 22, the cylinder block 22 and the cylinder head 23 serves as a combustion chamber A1 in which a fuel-air mixture is subjected to combustion. The cylinder head 23 is provided with an air intake valve 210 facing the combustion chamber A1 and the aforementioned exhaust valve 31.
Fig. 5 is a partly broken-away right side view illustrating the engine unit 20 partly in a two-dot-and-dash line (phantom line). Referring to Figs. 4 and 5, the cylinder head 23 includes a first tubular boss 32 provided in an upper right portion thereof. The first boss 32 is an integral part of the cylinder head 23. The first boss 32 projects out of the shroud 50. A distal end portion of the first boss 32 is located outside the shroud 50 and exposed from the shroud 50. An inside space of the first boss 32 communicates with a main air intake passage P1 (to be described later) around the air intake valve 210.
An injector (fuel injection device) 34 is attached to the first boss 32 via a synthetic resin holder 33. The injector 34, which is attached to the cylinder head 23, is located at the front end of the engine body 21.
Referring to Fig. 4, the holder 33 includes a cylindrical portion 211 and a flange 212 provided at a proximal end of the cylindrical portion 211. The flange 212 abuts against the distal end of the first boss 32. Thus, the holder 33 is positioned with respect to the first boss 32. The cylindrical portion 211 is accommodated in an accommodation space H1 defined in the first boss 32. A gap between an outer peripheral surface of a proximal end portion 213 of the cylindrical portion 211 and an inner peripheral surface of the first boss 32 is liquid-tightly sealed by a first seal member 214 such as an O-ring. An annular space is defined as a chamber G2 between an outer peripheral surface of an intermediate portion 215 of the cylindrical portion 211 and the inner peripheral surface of the first boss 32. A distal edge of a distal end portion 216 of the cylindrical portion 211 is engaged with the inner peripheral surface of the first boss 32 with virtually no gap.
An inside space of the distal end portion 216 of the cylindrical portion 211 is defined as an injection space G3 adjacent to an injection nozzle 35 of the injector 34. The injection space G3 is provided as a space defined adjacent to the injection nozzle 35. The injection space G3 is thus provided in the cylinder head 23, and communicates with the combustion chamber A1 via the air intake valve 210. The distal end portion 216 of the cylindrical portion 211 is formed with a plurality of through-holes 217. The through-holes 217 (e.g., four through-holes) are located equidistantly on the circumference of the distal end portion 216 of the cylindrical portion 211. The chamber G2 communicates with the injection space G3 via the through-holes 217.
The injector 34 serves to inject fuel supplied from a fuel tank (not shown) into the air intake passage. The injector 34 includes an injector body 218 having an elongated shape, and an injection nozzle 35 disposed at a distal end of the injector body 218.
The injector body 218 is inserted in the cylindrical portion 211 of the holder 33 to be thereby retained by the holder 33. A gap between an outer peripheral surface of the injector body 218 and an 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 oriented so as to inject the fuel toward the air intake valve 210 via a part of the main air intake passage P1 present in the cylinder head 23. Fuel injection timing at which the injector 34 injects the fuel toward the air intake valve 210 is controlled by a controller such as an ECU (an engine control unit or an electronic control unit) not shown.
The air intake pipe 36 includes an air intake hose 37 extending forward from an air cleaner (not shown) connected thereto, a tubular member 220 connected to a front end portion of the air intake hose 37, and a connection pipe 39 connected to a front end portion of the tubular member 220 and curved downward.
The cylinder head 23 includes a tubular air intake port 221. The part of the main air intake passage P1 present in the cylinder head 23 is defined by the air intake port 221. The air intake valve 210 is located at one of opposite ends of the air intake port 221. The other end of the air intake port 221 opens into an upper surface of the cylinder head 23. The other end of the air intake port 221 is defined by a flange 222 provided on the cylinder head 23. The flange 222 abuts against a flange 223 provided at a front end portion of the connection pipe 39, and is fixed to the flange 223 by fixture screws not shown. Thus, the air intake port 221 is connected to the front end portion of the connection pipe 39 (i.e., a downstream end of the air intake pipe 36).
The main air intake passage P1 is defined by the air intake port 221 of the cylinder head 23 and the air intake pipe 36.
The throttle body 38 includes the tubular member 220, and two throttle valves, i.e., first and second throttle valves 40A, 40B. The tubular member 220 has an axis extending in the direction (X1) between the front and the back of the vehicle. The tubular member 220 is located above the cylinder block 22 of the engine body 21 and above an upper wall 243 of a tubular portion 51 of the shroud 50 as will be described later. Thus, the throttle body 38 is entirely located outside the shroud 50.
The first and second throttle valves 40A, 40B each serve to open and close the main air intake passage P1 in the air intake pipe 36. The first throttle valve 40A and the second throttle valve 40B are spaced from each other in an intake air flowing direction C1 in the main air intake passage P1 . The first throttle valve 40A and the second throttle valve 40B are accommodated in the tubular member 220. The first throttle valve 40A is located downstream of the second throttle valve 40B with respect to the intake air flowing direction C1. That is, the first throttle valve 40A is located between the second throttle valve 40B and the cylinder head 23 in the main air intake passage P1. The first throttle valve 40A and the second throttle valve 40B each have a disk shape.
The first throttle valve 40A is supported by a first rotation shaft 224 extending perpendicularly to a center axis of the tubular member 220. The second throttle valve 40B is supported by a second rotation shaft 225 extending perpendicularly to the center axis of the tubular member 220.
Fig. 6 is a schematic right side view of the throttle body 38. Referring to Fig. 6, the first rotation shaft 224 and the second rotation shaft 225 are each rotatably supported by the tubular member 220. The first throttle valve 40A is rotated together with the first rotation shaft 224 about the first rotation shaft 224 by the rotation of the first rotation shaft 224. Similarly, the second throttle valve 40B is rotated together with the second rotation shaft 225 about the second rotation shaft 225 by the rotation of the second rotation shaft 225.
A driving pulley 226 is coupled to the second rotation shaft 225 for unitary rotation. A throttle cable (not shown) is attached to the driving pulley 226. Thus, the driving pulley 226 is rotated by a throttle operation performed by the rider. The rotation of the driving pulley 226 rotates the second rotation shaft 225, thereby opening and closing the second throttle valve 40B.
The opening/closing operation of the second throttle valve 40B is linked with the opening/closing operation of the first throttle valve 40A by a link mechanism 227. That is, the first and second throttle valves 40A, 40B are coupled to each other.
The link mechanism 227 has a so-called lost motion structure such that the first throttle valve 40A starts the opening operation with a time delay 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.
The second main link member 229 is a small piece provided integrally with the driving pulley 226. The second main link member 229 is rotatable about the second rotation shaft 225. The second main link member 229 is connected to the sub-link member 230 via a second connection shaft 232 for relative rotation.
The sub-link member 230 is a rod member elongated in the direction (X1) between the front and the back of the vehicle, and links the second main link member 229 to the first main link member 228. The second connection shaft 232 is disposed at a rear end of the sub-link member 230. A front end of the sub-link member 230 is connected to the first main link member 228 via a first connection shaft 233 for relative rotation.
The first main link member 228 is an elongated metal plate member. A front end of the first main link member 228 is connected to the first connection shaft 233. An intermediate portion of the first main link member 228 is connected to the first rotation shaft 224 for relative rotation. Thus, the first main link member 228 is rotatable independently of the first rotation shaft 224. The first main link member 228 includes a press member 234 provided at a rear end thereof.
A center axis J1 of the second rotation shaft 225 serving as a pivot center of the second main link member 229 is spaced a distance D2 from a center axis J2 of the second connection shaft 232. Further, a center axis J3 of the first rotation shaft 224 serving as a pivot center of the first main link member 228 is spaced a distance D1 from a center axis J4 of the first connection shaft 233. A relationship between the distances D1 and D2 is D2 > D1.
The rotation transmission member 231 is a plate member. The rotation transmission member 231 is connected to the first rotation shaft 224 for unitary rotation. The rotation transmission member 231 includes a to-be-pressed member 235 to be brought into abutment against the press member 234. With the second throttle valve 40B being fully closed, the press member 234 and the to-be-pressed member 235 are opposed to and spaced a predetermined distance from each other circumferentially of the first rotation shaft 224.
Referring to Fig. 4, the auxiliary air intake passage defining member 41 extends from the tubular member 220 of the throttle body 38 to the first boss 32 of the cylinder head 23. The entire auxiliary air intake passage defining member 41 is located outside the shroud 50. The auxiliary air intake passage defining member 41 defines an auxiliary air intake passage K1.
As described above, the first boss 32 is provided as the integral part of the cylinder head 23. The injector 34 is fixed in the first boss 32. The cylinder head 23 further includes a fourth boss 239 provided integrally with the first boss 32. The fourth boss 239 extends perpendicularly to an axis of the injector 34. The cylinder head 23 further includes a third boss 238 attached to the fourth boss 239.
The auxiliary air intake passage defining member 41 includes a second boss 236 fixed to the tubular member 220, the fourth boss 239 and the first boss 32 provided as the integral parts of the cylinder head 23, the cylindrical portion 211 of the holder 33 provided in the first boss 32, the third boss 238 attached to the fourth boss 239, and a hose 237 which connects the third boss 238 to the second boss 236.
The second boss 236 is an L-shape tubular metal member. The second boss 236 is disposed on an upper portion of the tubular member 220. One of opposite end portions of the second boss 236 serves as an upstream end defining portion 240 of the auxiliary air intake passage defining member 41. One of opposite ends of the upstream end defining portion 240 is fixed to the tubular member 220 between the first throttle valve 40A and the second throttle valve 40B. A part of the auxiliary air intake passage K1 present in the second boss 236 is defined as an upstream end portion K2 of the auxiliary air intake passage K1, and communicates with the main air intake passage P1.
The hose 237 is a tube formed of a flexible material such as rubber. One of opposite ends of the hose 237 is connected to the other end of the second boss 236.
One of opposite ends of the third boss 238 is connected to the other end of the hose 237. The fourth boss 239 is provided integrally with the first boss 32. Center axes of the fourth boss 239 and the first boss 32 extend generally perpendicularly to each other. Referring to Figs. 4 and 5, the fourth boss 239 is located outside the shroud 50. Portions of the auxiliary air intake passage K1 present in the other end portion of the hose 237 and the third and fourth bosses 238, 239, the chamber G2 in the first boss 32, and the through-holes 217 of the cylindrical portion 211 collectively define a downstream end portion K3 of the auxiliary air intake passage K1. The downstream end portion 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 portion 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 collectively define a downstream end defining portion 241 of the auxiliary air intake passage defining member 41. The downstream end defining portion 241 is located outside the shroud 50. Particularly, a part of the downstream end defining portion 241 defined by the first boss 32 is located outside the shroud 50.
With the aforementioned arrangement, the upstream end portion K2 of the auxiliary air intake passage K1 is defined by the upstream end defining portion 240 of the second boss 236, and communicates with the main air intake passage P1 between the first and second throttle valves 40A, 40B. The downstream end portion K3 of the auxiliary air intake passage K1 is defined by the downstream end defining portion 241. The downstream end portion K3 communicates with the injection space G3.
Intake air is introduced as assist air into the auxiliary air intake passage K1 from the main air intake passage P1. The assist air flowing through the auxiliary air intake passage K1 is further introduced into the injection space G3. The assist air supplied into the injection space G3 is applied to the fuel injected from the injector 34, thereby promoting the disintegration of the fuel.
Fig. 7 is a graph showing a relationship between the degree of opening of the first throttle valve 40A and the degree of opening of the second throttle valve 40B. In Fig. 7, the degree of opening of the first throttle valve 40A is zero during idling. Similarly, the degree of opening of the second throttle valve 40B is zero during idling.
In Fig. 7, a solid line indicates a relationship between the degrees of opening of the first and second throttle valves 40A, 40B in this embodiment. As indicated by the solid line, the degree of opening of the first throttle valve 40A is kept at zero when the degree of opening of the second throttle valve 40B is not greater than 10 degrees.
On the other hand, a broken line in Fig. 7 indicates that the degree of opening of the first throttle valve is always equal to the degree of opening of the second throttle valve because the lost motion structure is not provided. As indicated by the broken line and the solid line, the first throttle valve 40A is opened with a time delay after the second throttle valve 40B is opened in this embodiment. The operations of the first and second throttle valves 40A, 40B will be described below in greater detail.
Referring to Figs. 6 and 7, the degrees of opening of the first throttle valve 40A and the second throttle valve 40B are controlled in the following manner according to a change in load (throttle operating amount). First, the first throttle valve 40A located on a downstream side with respect to the intake air flowing direction C1 is maintained in a fully closed position when the vehicle is operated in an operation state ranging from a non-load operation state (idling state) to a predetermined partial load operation state.
More specifically, until the operation state reaches the partial load operation state, the rotation of the driving pulley 226 occurring due to the throttle operation performed by the rider is not transmitted to the first rotation shaft 224 but transmitted only to the second rotation shaft 225. Therefore, only the second throttle valve 40B is opened or closed by the rotation of the second rotation shaft 225. At this time, the sub-link member 230 and the first main link member 228 operate in response to the operation of the second main link member 229. Thus, the first main link member 228 is rotated about the first rotation shaft 224. However, the first rotation shaft 224 and the first throttle valve 40A are not rotated until the press member 234 of the first main link member 228 is brought into abutment against the to-be-pressed member 235.
Therefore, the amount of air flowing into the injection space G3 of the injection nozzle 35 is controlled only based on the degree of opening of the second throttle valve 40B until the operation state reaches the partial load operation state. In the partial load operation state, the assist air flowing into the auxiliary air intake passage K1 is mixed with the fuel injected from the injection nozzle 35 in the injection space G3. Thus, the disintegration of the fuel is promoted to increase the fuel combustion efficiency. This reduces the possibility of imperfect fuel combustion which is liable to occur at the cold start of the engine.
On the other hand, when the operation state is shifted from the partial load operation state to a higher load operation state, the first throttle valve 40A is opened according to the throttle operation. Thus, not only the assist air flowing through the auxiliary air intake passage K1 but also the intake air flowing through the other end of the air intake port 221 is introduced into the cylinder head 23.
Referring to Figs. 7 and 8, more specifically, when the operation state is shifted from the partial load operation state to the higher load operation state, the rotation amount of the first main link member 228 with respect to a reference rotation amount observed during idling exceeds a predetermined level. As a result, the press member 234 of the first main link member 228 is brought into abutment against the to-be-pressed member 235 of the rotation transmission member 231. Therefore, the rotation transmission member 231 and the first rotation shaft 224 are rotated in response to the rotation of the first main link member 228, whereby the first throttle valve 40A is rotated. Thus, not only the intake air flowing through the auxiliary air intake passage K1 but also the air flowing through the connection pipe 39 is introduced into the cylinder head 23.
Since the distance D2 is greater than the distance D1 in the link mechanism 227 as described above, the opening/closing speed of the first throttle valve 40A is higher than that of the second throttle valve 40B in the higher load operation state. As a result, the first throttle valve 40A is fully opened when the second throttle valve 40B is fully opened.
Referring to Fig. 1, an exhaust pipe 43 connected to the exhaust valve 31 of the cylinder head 23 and a muffler 44 connected to a rear end of the exhaust pipe 43 are attached to the engine body 21. The exhaust pipe 43 and the muffler 44 extend in the direction (X1) between the front and the back of the vehicle as a whole.
The exhaust pipe 43 is disposed below the engine body 21. An upstream end portion (front end portion) of the exhaust pipe 43 is curved upward, and is connected to a lower surface of the cylinder head 23 to communicate with an exhaust passage adjacent to the exhaust valve 31. The rear end of the exhaust pipe 43 is connected to a front end of the muffler 44 at substantially the same position, as seen in the direction between the front and the back, as a rear end surface of the crank case 24. The muffler 44 extends obliquely in the upward and rearward directions on the right side of the rear wheel 27. A catalyst device not shown is accommodated in the muffler 44.
Fig. 9 is a plan view of the shroud 50. In Fig. 9, the engine unit 20 is partly illustrated in a two-dot-and-dash line (phantom line). Referring to Figs. 5 and 9, the shroud 50 is attached to the engine body 21 for cooling the engine body 21. The shroud 50 includes a tubular portion 51 which entirely surrounds the cylinder block 22 and a rear end portion 207 of the cylinder head 23, a side plate 52 which covers the crank case 24 from the right side, and a protector 53.
The shroud 50 includes two half members, i.e., left and right half members 54L, 54R, which are combined together. The tubular portion 51 is defined by the entire left half member 54L and a front end portion of the right half member 54R. The side plate 52 and the protector 53 are defined by a portion of the right half member 54R rearward of the tubular portion 51.
Referring to Figs. 3 and 5, the tubular portion 51 includes a right wall 242 disposed on the right side of the engine body 21 and bulged to the right side. The right wall 242 covers a right side surface of the cylinder block 22 and a part of a right side surface of the rear end portion 207 of the cylinder head 23. A rear end portion of the right wall 242 is bulged rightward to a greater extent than a front end portion of the right wall 242.
As shown in Fig. 9 and Fig. 10, which is a left side view of major portions of the engine unit 20, the tubular portion 51 further includes an upper wall 243 disposed above the engine body 21, and a left wall 244 disposed on the left side of the engine body 21. The upper wall 243 covers an upper surface of the cylinder block 22, and a part of an upper surface of the rear end portion 207 of the cylinder head 23.
The left wall 244 covers a left side surface of the cylinder block 22 and a part of a left side surface of the rear end portion 207 of the cylinder head 23. The tubular member 220 is located in a generally laterally intermediate portion of the engine body 21.
Fig. 11 is a bottom view of major portions of the shroud 50. In Fig. 11, the engine unit 20 is partly illustrated in a two-dot-and-dash line (phantom line). Referring to Figs. 5 and 11, the tubular portion 51 further includes a bottom wall 245 disposed below the engine body 21. The bottom wall 245 covers a bottom surface of the cylinder block 22 and a part of a bottom surface of the rear end portion 207 of the cylinder head 23.
Referring to Figs. 3 and 5, the side plate 52 includes a major plate portion 247 opposed to the right side surface 246 of the crank case 24 transversely (Y1) of the vehicle with the intervention of the fan 56, and an arcuate plate portion 248 projecting from an outer peripheral edge of the major plate portion 247. The major plate portion 247 covers the right side surface 246 of the crank case 24 from the right side. A front end of the major plate portion 247 is connected to the right wall 242 of the tubular portion 51.
The arcuate plate portion 248 has an arcuate shape. The arcuate plate portion 248 extends from the major plate portion 247 toward the right side surface 246 of the crank case 24, and is connected to the right side surface 246 of the crank case 24 via a third seal member 249. The arcuate plate portion 248 is fixed to the crank case 24 with the use of fixture screws not shown.
Referring to Fig. 3, a front space M1 is defined between outer peripheral surfaces of the cylinder block 22 and the rear end portion 207 of the cylinder head 23 and an inner peripheral surface of the tubular portion 51. Further, a rear space M2 is defined between an inner surface of the side plate 52 and the right side surface 246 of the crank case 24. The front space M1 and the rear space M2 collectively define a cooling wind passage M3 through which cooling wind generated by the fan 56 flows. The cooling wind passage M3 is partly located between the front end portion of the shroud 50 and the rear end portion 207 of the cylinder head 23.
At a front end of the front space M1, a gap between a part of a front end portion of the tubular portion 51 and an outer surface of the cylinder head 23 is air-tightly sealed. This sealing arrangement will be described later in detail.
At a rear end of the front space M1, on the other hand, the rear edge of the tubular portion 51 air-tightly contacts the front end face 206 of the crank case 24. More specifically, rear edges of the upper wall 243, the left wall 244 and the bottom wall 245 of the tubular portion 51 abut against the front end face 206 of the crank case 24.
In the rear space M2, a gap between the arcuate plate portion 248 of the side plate 52 and the right side surface 246 of the crank case 24 is air-tightly sealed. This sealing arrangement will be described below.
Fig. 12 is a sectional view of major portions taken along a line XII-XII in Fig. 3. Referring to Figs. 3 and 12, the arcuate third seal member 249 is disposed between a left edge of the arcuate plate portion 248 of the side plate 52 and the right side surface 246 of the crank case 24. The third seal member 249 is conformable to the arcuate shape of the arcuate plate portion 248.
An upper surface, a bottom surface, a rear surface and a left side surface of the crank case 24 are uncovered with the shroud 50 to be exposed.
The fan 56 is disposed in the rear space M2 in a rear end portion of the shroud 50. The side plate 52 has an air intake portion 58. The air intake portion 58 includes a plurality of small openings provided on the right side of the fan 56. With the fan 56 being rotated, outside air is introduced into the rear space M2 through the air intake portion 58.
Referring to Figs. 5 and 11, the shroud 50 has a through-hole 59 formed in the front end portion thereof. The through-hole 59 is located in the front side of the right wall 242 and in the front side of the bottom wall 245 of the tubular portion 51. The exhaust pipe 43 is inserted through the through-hole 59. Further, the bottom wall 245 has a release port 250 provided in a front end portion thereof. The release port 250 has, for example, a rectangular shape. The through-hole 59 and the release port 250 are arranged transversely (Y1) of the vehicle.
The cooling wind introduced into the rear space M2 of the cooling wind passage M3 by the fan 56 flows into the front space M1. At this time, the cooling wind is brought into contact with the surface of the engine body 21, whereby heat is removed from the engine body 21.
Next, the sealing arrangement provided between the front end portion of the tubular 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 illustrating major portions of the engine unit 20 partly in section. A fourth seal member 251 and a fifth seal member 252 each composed of an elastic material such as rubber are disposed on the front end portion of the tubular member 51. In Fig. 13, the fourth seal member 251 and the fifth seal member 252 are shown in section.
The fourth seal member 251 is an elongated unitarily molded member, and is attached to the tubular portion 51. The fourth seal member 251 includes a first portion 253 and a second portion 254.
The upper wall 243 has a flange 255 projecting downward from a front edge thereof. The first portion 253 of the fourth seal member 251 is attached to an edge of the flange 255 of the upper wall 243. The first portion 253 air-tightly seals a gap between opposed portions of the flange 255 and the outer surface of the cylinder head 23.
Further, the left wall 244 has a flange 256 projecting rightward from a front edge thereof. The flange 256 of the left wall 244 is conformable in shape to the left side surface of the cylinder head 23. More specifically, a vertically intermediate portion of the flange 256 is recessed leftward. The second portion 254 of the fourth seal member 251 is grooved. Thus, the second portion 254 is conformable in shape to an edge of the flange 256 of the left wall 244. The second portion 254 of the fourth seal member 251 is attached to the edge of the flange 256 of the left wall 244. The second portion 254 air-tightly seals a gap between opposed portions of the flange 256 and the left side wall of the cylinder head 23.
The fifth seal member 252 is an elongated unitarily molded member, and is held by the tubular portion 51. The fifth seal member 252 includes a first portion 257, a second portion 258 and a third portion 259.
The bottom wall 245 has a flange 260 projecting upward from a front edge thereof. The flange 260 abuts against a portion of the bottom surface of the cylinder head 23 opposed to the flange 260. The first portion 257 of the fifth seal member 252 is attached to an edge portion of the flange 260 of the bottom wall 245 extending from a laterally intermediate portion to a right end portion. The first portion 257 air-tightly seals a gap between opposed portions of the flange 260 of the bottom wall 245 and the bottom surface of the cylinder head 23.
The right wall 242 has a flange 261 projecting from a lower edge of the front end portion thereof toward the right side surface of the cylinder head 23. The second portion 258 of the fifth seal member 252 is attached to an edge of the flange 261 of the right wall 242. The second portion 258 air-tightly seals a gap between opposed portions of the flange 261 and the right side surface of the cylinder head 23.
The third portion 259 of the fifth seal member 252 contacts a front portion of an outer peripheral surface of a fifth boss 262 projecting from the cylinder head 23. An upper portion of the third portion 259 of the fifth seal member 252 is fixed to a portion of the cylinder head 23 adjacent to the fifth boss 262. An ignition plug (not shown) is inserted in the cylinder head 23 through the fifth boss 262.
Referring to Figs. 5 and 13, the right wall 242 has a recess 263 provided on the front end portion thereof and receiving the fifth boss 262 inserted therein. A peripheral portion of the recess 263 contacts the outer peripheral surface of the fifth boss 262. The outer peripheral surface of the fifth boss 262 is surrounded by the peripheral portion of the recess 263 and the third portion 259 of the fifth seal member 252.
Fig. 14 is a partially enlarged view of Fig. 9. Referring to Figs. 5 and 14, the upper wall 243 of the tubular portion 51 has a cutaway portion 60 provided in the front end portion thereof. The cutaway portion 60 is such that a part of the front end portion of the upper wall 243 is recessed in the rearward direction. An edge 264 of the cutaway portion 60 includes a first edge portion 265 opposed to the flange 222 of the cylinder head 23, and a second edge portion 266 and a third edge portion 267 opposed to the downstream end defining portion 241 of the auxiliary air intake passage defining member 41.
The flange 222 of the cylinder head 23 has an opposed portion 268 opposed to the first edge portion 265. The first edge portion 265 is conformable in shape to the opposed portion 268. More specifically, the first edge portion 265 has a front portion extending generally in the direction (X1) between the front and the back of the vehicle, a portion which is intermediate in the direction between the front and the back and which extends obliquely in the rearward and rightward directions, and a rear portion extending generally transversely (Y1) of the vehicle as seen in plan.
A laterally intermediate portion of the cutaway portion 60 defines a first opening region N1 from which the flange 222 of the cylinder head 23 is exposed. A gap between the first edge portion 265 and the opposed portion 268 of the flange 222 of the cylinder head 23 is air-tightly sealed by a sixth seal member 269. The sixth seal member 269 is attached to the upper wall 243.
The second edge portion 266 is located at a right end of the cutaway portion 60 in the vicinity of the other end of the hose 237 of the auxiliary air intake passage defining member 41 and the fourth boss 239. As seen in plan, the second edge portion 266 is recessed in the rightward direction.
The second edge portion 266 has a rear end portion extending generally in the direction (X1) between the front and the back of the vehicle as seen from the right side. The second edge portion 266 further has a front end portion recessed in the downward direction as seen from the right side. The outer peripheral surface of the fourth boss 239 has an opposed portion 270 opposed to the second edge portion 266. The outer peripheral surface of the hose 237 has an opposed portion 272 opposed to the second edge portion 266 at the other end thereof. The second edge portion 266 is spaced several millimeters from the opposed portion 270, and is spaced several millimeters from the opposed portion 272.
Thus, a first air passage Q1 is defined between the second edge portion 266 and the opposed portions 270, 272 of the downstream end defining portion 241. That is, the second edge 266 of the shroud 50 serves to define the first air passage Q1. Further, the opposed portions 270, 272 of the auxiliary air intake passage defining member 41 serve to define the first air passage Q1 with respect to the shroud 50.
The first air passage Q1 permits communication between the cooling wind passage M3 in the shroud 50 and the outside of the shroud 50. The cooling wind flowing through the cooling wind passage M3 partly flows through the first air passage Q1 to be released outside the shroud 50.
The cutaway portion 60 defines a second opening region N2 in the vicinity of the second edge portion 266 thereof for exposing the fourth boss 239.
The third edge portion 267 is located at a front right portion of the cutaway portion 60 in the vicinity of the first boss 32. The third edge portion 267 has an arcuate shape. The third edge portion 267 extends along an opposed portion 271 of the outer peripheral surface of the first boss 32 opposed to the third edge portion 267. That is, the opposed portion 271 defines a part of the downstream end defining portion 241.
The third edge portion 267 is spaced several millimeters from the opposed portion 271 of the first boss 32. Thus, a second air passage Q2 is defined between the third edge portion 267 and the opposed portion 271 of the first boss 32. That is, the third edge portion 267 of the shroud 50 serves to define the second air passage Q2. The second air passage Q2 permits communication between the cooling wind passage M3 in the shroud 50 and the outside of the shroud 50. The second air passage Q2 and the first air passage Q1 communicate with each other. Thus, the first and second air passages Q1, Q2 are defined around the downstream end defining portion 241. The cooling wind flowing through the cooling wind passage M3 partly flows through the second air passage Q2 to be released outside the shroud 50.
The cutaway portion 60 defines a third opening region N3 in the vicinity of the third edge portion 267 for exposing the first boss 32. That is, the third opening region N3 defined by the cutaway portion 60 is located on the right side of the first opening region N1 to prevent interference between the shroud 50 and the first boss 32 for the injector 34. The first boss 32 projects outside the shroud 50 from the third opening region N3. Further, the fourth boss 239 is located on a portion of the first boss 32 projecting outside the shroud 50. Therefore, the auxiliary air intake passage defining member 41 is connected to the cylinder head 23 outside the shroud 50.
Referring to Figs. 11 and 14, the aforementioned arrangement is such that the second and third edge portions 266, 267 defining the first air passage Q1 and the second air passage Q2 are disposed on a side of the cylinder head 23 of the engine body 21 vertically opposite from the release port 250 and the through-hole 59. The first air passage Q1, the second air passage Q2, the release port 250 and the through-hole 59 collectively serve as a release member, and are located at the front end of the tubular portion 51. That is, the first air passage Q1, the second air passage Q2, the release port 250 and the through-hole 59, which collectively serve as the release member for releasing the cooling wind from the shroud 50, are located on the front side of the shroud 50.
Next, effects of this embodiment will be described.
Referring to Figs. 3 and 5, the fan 56 is rotated when the crank shaft 57 of the engine body 21 is driven. Thus, outside air is introduced as cooling air into the rear space M2 of the cooling wing passage M3 in the shroud 50 from the air intake portion 58 of the shroud 50. The flow of the outside air is indicated, for example, by an arrow R1.
The cooling air introduced into the rear space M2 is blown forward through the cooling wind passage M3 by the fan 56 to provide the cooling wind. At this time, the cooling wind is divided into an air stream flowing toward the upper wall 243 of the tubular portion 51 of the shroud 50 and an air stream flowing toward the bottom wall 245 as indicated by arrows R2 in Fig. 5. Thus, the cooling wind flows into the front space M1 from the rear space M2 of the cooling wind passage M3 to remove heat from the engine body 21. Cooling wind flowing to below the front space M1 is released through the release port 250 and the through-hole 59 as indicated by arrows R3 in Figs. 5 and 11.
As indicated by arrows R4 in Figs. 5 and 14, cooling wind flowing to above the front space M1 is released outside the shroud 50 through the first air passage Q1 and the second air passage Q2. The cooling wind flows toward the outer surface of the downstream end defining portion 241 of the auxiliary air intake passage defining member 41. Thus, the cooling wind flowing through the first air passage Q1 and the second air passage Q2 removes heat from the downstream end defining portion 241. As a result, intake air flowing through the downstream end portion K3 of the auxiliary air intake passage K1 is introduced into the injection space G3 at a lower temperature.
The cooling wind released through the first air passage Q1 and the second air passage Q2 partly hits the first boss 32. Thus, the cooling wind removes heat from the first boss 32, thereby cooling the injector 34 attached to the first boss 32.
This embodiment provides the following effects. The engine unit 20 is of the air-cooled type and, therefore, obviates the need for the provision of the radiator and the cooling water pump which may otherwise be required for the water-cooled engine unit. Thus, the engine unit 20 has a simplified construction.
Further, the engine unit 20 is of the forced air-cooled type which is adapted to forcibly generate the cooling wind by means of the fan 56. This obviates the need for locating the engine unit 20 at a position at which the engine unit 20 can catch the airstream in the motorcycle 200, thereby improving the flexibility in the layout of the engine unit 20 in the motorcycle 200.
The fan 56 is rotated together with the crank shaft 57 at a higher speed during the movement of the vehicle, whereby the cooling wind is sufficiently generated in the shroud 50. As a result, a sufficient amount of the cooling wind flows into the auxiliary air intake passage defining member 41 through the first and second air passages Q1, Q2. Therefore, the auxiliary air intake passage defining member 41 is reliably cooled by the cooling wind generated by the fan 56. This prevents the auxiliary air intake passage K1 from being heated by the heat of the engine body 21. Therefore, the assist air flowing through the auxiliary air intake passage K1 and the injector 34 around which the assist air flows are each prevented from being heated to a higher temperature. As a result, the temperature of the mixture of the assist air and the fuel is kept at a lower level, thereby increasing the fuel combustion efficiency.
Further, the intake air is introduced as the assist air into the injection space G3 from the auxiliary air intake passage K1 at least during idling. Thus, the assist air is applied to the fuel injected from the injection nozzle 35, thereby promoting the disintegration of the fuel. As a result, the fuel combustion efficiency is increased during idling and during the movement of the vehicle with a lower load. In addition, the auxiliary air intake passage K1 is branched from the main air intake passage P1 defined in the tubular member 220 disposed outside the shroud 50. Therefore, at least the portion of the auxiliary air intake passage defining member 41 connected to the tubular member 220 is disposed outside the shroud 50. As a result, the entire auxiliary air intake passage K1 is unlikely to be affected by the heat in the shroud 50, so that the assist air flowing through the auxiliary air intake passage K1 can be maintained at a lower temperature. Since the injector 34 is cooled by the lower temperature assist air, the fuel flowing through the injector 34 can be maintained at a lower temperature, thereby further improving the fuel combustion efficiency. Thus, the fuel combustion efficiency can be maintained at a higher level even during idling, during which the crank shaft 57 is rotated at a lower speed and hence the fan 56 generates a smaller amount of cooling wind.
The downstream end defining portion 241 is located adjacent to the injection nozzle 35 provided in the cylinder head 23 which is liable to be heated to a higher temperature by the heat from the combustion chamber A1. Therefore, the downstream end defining portion 241 is liable to be affected by the heat of the cylinder head 23. However, the downstream end defining portion 241 is reliably cooled by the cooling wind flowing through the first and second air passages Q1, Q2. This reliably suppresses the heating of the assist air flowing through the downstream end K3 of the auxiliary air intake passage K1.
The downstream end defining portion 241 is disposed outside the shroud 50. Thus, the heat of the engine body 21 in the shroud 50 is less liable to be transferred to the downstream end defining portion 241. Therefore, the heat of the engine body 21 is less liable to be transferred to the assist air in the downstream end K3 of the auxiliary air intake passage K1. This reliably suppresses the temperature rise of the assist air.
It is possible to apply the cooling wind to the downstream end defining portion 241 through the first and second air passages Q1, Q2 defined between the second and third edge portions 266, 267 of the shroud 50 and the opposed portions 271, 270, 272. The first and second air passages Q1, Q2 are located adjacent to the downstream end defining portion 241. Therefore, the cooling wind can be reliably applied to the downstream end defining portion 241. This reliably suppresses the heating of the assist air flowing through the downstream end K3 of the auxiliary air intake passage K1.
As indicated by the arrows R2, the cooling wind stream flowing toward the first and second air passages Q1 and Q2 from the fan 56 and the cooling wind stream flowing toward the release port 250 and the through-hole 59 from the fan 56 occur in the shroud 50. These cooling wind streams flow on opposite sides of the cylinder head 23. Thus, a cooling wind flowing area in the shroud 50 is increased, so that the engine body 21 is efficiently cooled. Further, the cooling wind to be released from the first air passage Q1 and the second air passage Q2 is substantially prevented from being taken into the release port 250 and the through-hole 59. Thus, the cooling wind is reliably released from the first air passage Q1 and the second air passage Q2 to effectively cool the downstream end defining portion 241.
The connection pipe 39 is disposed between the tubular member 220 of the throttle body 38 and the cylinder head 23. Thus, the throttle body 38 and the upstream end defining portion 240 of the auxiliary air intake passage defining member 41 can be reliably isolated from the high temperature cylinder head 23. Therefore, the heat of the cylinder head 23 is less liable to be transferred to the upstream end defining portion 240 of the auxiliary air intake passage defining member 41. As a result, the assist air is substantially prevented from being heated at the upstream end K2 of the auxiliary air intake passage K1 by the heat of the cylinder head 23. Further, the connection pipe 39 prevents the transfer of the heat from the cylinder head 23 to the tubular member 220 of the throttle body 38. That is, the connection pipe 39 serves as a heat insulator between the cylinder head 23 and the throttle body 38.
The entire auxiliary air intake passage defining member 41 is disposed on the outer side of the shroud 50 at which the temperature is lower than the inside of the shroud 50. This makes it possible to maintain the assist air at a lower temperature in the auxiliary air intake passage defining member 41.
The shroud 50 is provided so as not to cover the first boss 32 and the injector 34. This permits size reduction of the shroud 50 to increase the size of the lower space G1 present below the seat 16.
The motorcycle 200 is thus provided, which includes the engine unit 20 having a simplified construction. Since the engine unit 20 is of the forced air-cooled type, there is no need to apply the airstream to the engine body, thereby improving the flexibility in the layout of the engine unit 20 in the motorcycle 200. As a result, the engine unit 20 can be placed in position so as to be surrounded by the vehicle body cover 18. That is, the present invention is applicable to the scooter-type motorcycle 200. Since the disintegration of the fuel is promoted by the lower temperature assist air and the assist air in the auxiliary air intake passage defining member 41 is cooled by the cooling wind generated by the fan 56, the motorcycle 200 has a very high fuel combustion efficiency during idling as well as during the movement of the vehicle.
Further, the engine body 21 can be generally horizontally disposed as extending in the direction (X1) between the front and the back of the vehicle. This reduces the size of the engine body 21 as measured in the vertical direction (Z1) of the vehicle, thereby increasing the size of a space defined between the engine body 21 and the seat 16. This makes it possible to provide a greater-volume storage box in this space. Even in this case, the height of the seat is not excessively increased. Further, the cooling wind generated by the fan 56 can be applied to a region ranging from the rear end to the front end of the shroud 50. This makes it possible to apply the cooling wind generated by the fan 56 to an extensive surface region of the engine body 21, thereby ensuring efficient cooling of the engine body 21.
The engine unit 20 of this embodiment includes the engine body 21 having the cylinder head 23, the fan 56, the shroud 50 covering a region of the engine body 21 except for at least a part of the cylinder head 23, and the injector 34 attached to the portion of the cylinder head 23 exposed outside the shroud 50. The first and second air passages Q1, Q2 which permit the cooling wind passage M3 defined between the shroud 50 and the engine body 21 to communicate with the outside of the shroud 50 are provided in the vicinity of the injector 34.
With this arrangement, the shroud 50 does not cover the entire engine body 21 but the region of the engine body 21 except for at least the part of the cylinder head 23. This prevents the increase in the size of the shroud 50. The cooling wind introduced by the fan 56 into the cooling wind space M3 defined between the shroud 50 and the engine body 21 partly flows out of the shroud 50 through the first and second air passages Q1, Q2. When the cooling wind partly flows in the vicinity of the injector 34, the injector 34 is cooled, so that the temperature rise of the injector 34 is suppressed.
The first boss 32 fitted with the injector 34 is provided in the portion of the cylinder head 23 exposed outside the shroud 50, and the second air passage Q2 is defined between the third edge portion 267 of the shroud 50 and the outer peripheral surface of the first boss 32. Therefore, the cooling wind flowing out of the second air passage Q2 flows in the vicinity of the injector 34 and, therefore, effectively cools the injector 34.
The cylinder head 23 and the injector 34 are located on the front end portion of the engine body 21, and the fan 56 is disposed in the rear portion of the shroud 50. The release port 250 and the through-hole 59 for releasing the cooling wind from the shroud 50 are disposed in the front portion of the shroud 50.
With this arrangement, the cooling wind introduced into the shroud 50 by the fan 56 and released out of the shroud 50 through the first and second air passages Q1, Q2, the release port 250 and the through-hole 59 flows forward in the shroud 50 as a whole. The first and second air passages Q1, Q2 are disposed on the downstream side with respect to the cooling wind flowing direction in the shroud 50. This promotes the flow of the cooling wind out of the first and second air passages Q1, Q2.
The first air passage Q1 and the second air passage Q2 are disposed on the side of the engine body 21 vertically opposite from the release port 250 and the through-hole 59. Thus, the cooling wind to be released from the first and second air passages Q1, Q2 is less liable to be taken into the release port 250 and the through-hole 59. Therefore, the cooling wind reliably flows out of the first air passage Q1 and the second air passage Q2.
The shroud 50 has the first opening region N1 through which the flange 222 of the cylinder head 23 connected to the downstream end of the air intake pipe 36 is exposed. Thus, the downstream end of the air intake pipe 36 is not covered with the shroud 50. Therefore, the size of the shroud 50 is reduced as compared with the case in which the downstream end of the main air intake passage is covered with the shroud.
The downstream end defining portion 241 of the auxiliary air intake passage defining member 41 is provided in the portion of the cylinder head 23 exposed outside the shroud 50. With this arrangement, the auxiliary air intake passage defining member 41 is connected to the cylinder head 23 outside the shroud 50.
Therefore, the size of the shroud 50 is reduced as compared with the case in which the downstream end defining portion 241 of the auxiliary air intake passage defining member 41 is covered with the shroud.
The downstream end defining portion 241 of the auxiliary air intake passage defining member 41 is provided in the vicinity of the first and second air passages Q1, Q2 and, therefore, cooled by the cooling wind flowing out of the first and second air passages Q1, Q2. Thus, reduction in the oxygen concentration of the assist air supplied into the injection space G3 from the auxiliary air intake passage K1 is prevented which may otherwise occur due to the temperature rise of the assist air. This increases the combustion efficiency.
Referring to Figs. 5 and 9, the protector 53 provided as an integral part of the shroud 50 will be described next. The protector 53 covers a right outer surface portion of the rear end portion of the exhaust pipe 43. The protector 53 projects downward from a lower edge of the major plate portion 247 of the side plate 52.
The protector 53 is elongated in the direction (X1) between the front and the back of the vehicle, and disposed on the right side of the exhaust pipe 43. The position of the protector 53, as seen in the direction between the front and the back, corresponds to that of the fan 56. In other words, the protector 53 is disposed at a position close to the fan 56. A rear end portion of the protector 53 projects in the rearward direction of a rear end of the side plate 52.
JP-A-2008-190425 discloses a shroud for cooling the engine body. However, this shroud is not formed with the protector for covering the exhaust pipe and the muffler. The provision of the protector increases the number of components. On the contrary, this embodiment requires a smaller number of components, because the protector 53 is provided as the integral part of the shroud 50.
The protector 53 is disposed in the vicinity of the fan 56. Thus, outside air sucked by the fan 56 is partly brought into contact with the surface of the protector 53. This suppresses the temperature rise of the protector 53. Further, the protector 53 is configured so as to be generally parallel to a longitudinal axis of the exhaust pipe 43, so that the size of the protector 53 is not unnecessarily increased. This prevents the size increase of the shroud 50.

Second Embodiment

Fig. 15 is a right side view illustrating, partly in section, of an engine unit according to a second embodiment of the present invention. Differences between the second embodiment and the first embodiment will be mainly described. Like components will be denoted by like reference numerals, and duplicate description will be omitted.
Referring to Fig. 15, the downstream end defining portion 241 of the auxiliary air intake passage defining member 41 is disposed inside the shroud 50 in this embodiment. More 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 provided separately from the half members 54L, 54R (the half member 54L is not shown). The cover member 275 is located on the upper wall 243.
The cover member 275 includes a first cover 276, and a second cover 277 disposed behind the first cover 276.
The first cover 276 is located in front of the first boss 32, and covers the first boss 32, the holder 33, the injector 34 and the downstream end defining portion 241 from the front side. The second cover 277 has, for example, an inverted U-shape as seen in the direction (X1) between the front and the back of the vehicle. 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 defining portion 241 from the right side, the upper side and the left side.
An upper space M4 is defined as a part of the cooling wind passage M3 in the second cover 277. The upper space M4 communicates with the front space M1. A third air passage Q3 is defined between a rear end portion 277a of the second cover 277, an 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 defining portion 241. The third air passage Q3 is located around the downstream end defining portion 241, and permits communication between the cooling wind passage M3 and the outside of the shroud 50. The cooling wind is released through the third air passage Q3.
The cooling wind released through the first and second air passages Q1, Q2 hits the downstream end defining portion 241 in the upper space M4 inside the cover member 275 as indicated by arrows R4, and is then released from the third air passage Q3 behind the cover member 275 as indicated by an arrow R5.
According to this embodiment, the downstream end defining portion 241 is disposed inside the cover member 275 of the shroud 50 in which the cooling wind flows. Thus, the cooling wind generated by the fan 56 is reliably applied to the downstream end defining portion 241. Therefore, the cooling wind reliably suppresses the heating of the downstream end defining portion 241 and the assist air flowing through the downstream end defining portion 241 which may otherwise occur due to the heat of the engine body 21.

Other Embodiments

The present invention is not limited to the embodiments described above with reference to the attached drawings. For example, the following embodiments also fall within the technical scope of the present invention.

(1) The shroud may cover the entire cylinder head of the engine body.
(2) The cooling wind is not necessarily required to be applied to the downstream end defining portion of the auxiliary air intake passage defining member. The cooling wind may be applied to any other portions of the auxiliary air intake passage defining member.
(3) An air duct may be provided separately from the shroud, so that the cooling wind released from the shroud can be applied to the auxiliary air intake passage defining member through the air duct.
(4) The release port may be disposed in the vicinity of the first air passage and the second air passage.
(5) One of the first air passage and the second air passage may be obviated.
(6) At least a part of the auxiliary air intake passage defining member except for the upstream end defining portion may be disposed inside the shroud.
(7) The cylinder head and the fuel injection device may be disposed in the portion which is intermediate in the direction between the front and the back or in the rear end portion of the engine body. Similarly, the fan may be disposed in the portion which is intermediate in the direction between the front and the back or in the front end portion of the engine body. In this case, the fan is disposed coaxially with the crank shaft.
(8) The engine unit is not necessarily required to be supported pivotally about the pivot axis with respect to the vehicle body frame, but may be fixed to the vehicle body frame.
(9) The auxiliary air intake passage defining member is not necessarily required to be provided separately from the air intake pipe. The auxiliary air intake passage defining member may be provided integrally with the connection pipe or other members of the air intake pipe.
(10) A gap defined between a front edge of the shroud and the outer peripheral surface of the injector may be utilized as an air passage through which the cooling wind is released. Further, the shroud may have a through-hole provided in a portion thereof adjacent to the injector, and the through-hole may be utilized as the air passage through which the cooling wind is released.
(11) The air passage through which the cooling wind is released may be disposed at the upstream end of the cooling wind passage in the shroud, or in a generally intermediate portion of the cooling wind passage between the upstream end and the downstream end.
(12) The protector may be provided separately from the shroud.
(13) The protector may be disposed apart from the air intake fan.
(14) The protector may be configured so as to cover the entire exhaust pipe, to cover a part of the exhaust pipe and a part of the muffler, to cover the entire exhaust pipe and a part of the muffler, to cover the entire exhaust pipe and the entire muffler, to cover a part of the muffler, or to cover the entire muffler.
(15) The auxiliary air intake passage defining member may be configured in a different manner than in the embodiments described above, as long as it defines the auxiliary air intake passage which connects a portion of the main air intake passage between the first and second throttle valves to the injection space defined in the cylinder head. For example, the third boss may be obviated, and the other end of the hose may be fitted around the fourth boss. Alternatively, the fourth boss may be obviated, and the first boss may be formed with a recess in which the third boss is fitted to be fixed. Further, the third boss and the fourth boss may be obviated, and the other end of the hose may be fixed directly to the first boss. Further, the tubular member of the throttle body may be formed with a recess, in which the one end of the hose is fixed.
(16) The engine unit may be mounted on other types of vehicles than the motorcycle. Examples of such vehicles include straddle-type vehicles such as ATVs (all terrain vehicles) and snow mobiles.

REFERENCE NUMERALS

15 vehicle body frame
16 seat
17 foot rest plate
18 vehicle body cover
20 vehicle engine unit (forced air-cooled vehicle engine unit)
21 engine body
22 cylinder block
23 cylinder head
24 crank case
32 first tubular boss (boss accommodates injection nozzle)
34 injector (fuel injection device)
35 injection nozzle
36 air intake pipe
38 throttle body
39 connection pipe
40A,40B throttle valve
41 auxiliary air intake passage defining member
50 shroud
56 fan
57 crank shaft
59 through-hole (release portion)
200 motorcycle
207 rear end portion of cylinder head (part of cylinder head)
208 piston
220 tubular member
240 upstream end defining portion
241 downstream end defining portion
250 release port
264 edge portion (edge portion to define air passage)
271 opposed portion (outer surface of downstream end defining portion)
270,272 opposed portion (outer surface of downstream end defining portion)
A1 combustion chamber
C1 intake air flowing direction
G1 lower space
G3 injection space (space defined adjacent to the injection nozzle)
K1 auxiliary air intake passage
K2 upstream end portion of auxiliary air intake passage
K3 downstream end portion of auxiliary air intake passage
M3 cooling wind passage (inside of shroud)
P1 main air intake passage
Q1 first air passage (release portion)
Q2 second air passage (release portion)
Q3 third air passage
X1 in the direction between the front and the back of the vehicle

Claims

A forced air-cooled vehicle engine unit comprising:
an engine body (21) including a crank case (24) accommodating a crank shaft (57), a cylinder block (22) connected to the crank case (24) and accommodating a piston (208) in a reciprocally movable manner, and a cylinder head (23) that is cooperative with the cylinder block (22) to define a combustion chamber (A1) and defines a part of a main air intake passage (P1) connected to the combustion chamber (A1);

an air intake pipe (36) connected to the cylinder head (23) and cooperative with the cylinder head (23) to define the main air intake passage (P1);

a shroud (50) covering at least a part of the cylinder head (23);

a fan (56) disposed between the shroud (50) and the engine body (21), and adapted to be driven by rotation of the crank shaft (57) to generate cooling wind for cooling the engine body (21);

a throttle body (38) including two throttle valves (40A, 40B) spaced from each other in an intake air flowing direction in the air intake pipe (36), and a tubular member (220) that defines a part of the air intake pipe (36) and accommodates the two throttle valves (40A, 40B), the throttle body (38) being disposed outside the shroud (50);

a fuel injection device (34) attached to the cylinder head (23) and having an injection nozzle (35) which injects fuel into the part of the main air intake passage (P1) defined in the cylinder head (23);

an auxiliary air intake passage defining member (41) that defines an auxiliary air intake passage (K1) branched from the main air intake passage (P1) between the two throttle valves (40A, 40B) to guide intake air into a space defined adjacent to the injection nozzle (35) in the cylinder head (23) at least during idling; and

an air passage (Q1, Q2) that is provided around at least a part of the auxiliary air intake passage (K1) for communication between an inside and an outside of the shroud (50).
A forced air-cooled vehicle engine unit as set forth in claim 1, wherein
the auxiliary air intake passage (K1) includes an upstream end (K2) connected to the main air intake passage(P1), and a downstream end (K3) connected to the space defined adjacent to the injection nozzle (35),
the auxiliary air intake passage defining member (41) includes an upstream end defining portion (240) that defines the upstream end (K2), and a downstream end defining portion (241) that defines the downstream end (K3), and
the cooling wind is introduced through the air passage (Q1, Q2) into at least the downstream end defining portion (241).
A forced air-cooled vehicle engine unit as set forth in claim 2, wherein
the cylinder head (23) includes a boss (32) exposed outside the shroud (50) and accommodating the injection nozzle (35), and
the downstream end defining portion (241) of the auxiliary air intake passage defining member (41) includes the boss (32).
A forced air-cooled vehicle engine unit as set forth in claim 3, wherein
the shroud (50) includes an edge portion (264) that is cooperative with an outer surface of the downstream end defining portion (241) to define the air passage (Q1, Q2).
A forced air-cooled vehicle engine unit as set forth in claim 4, wherein
the shroud (50) has a release port (250) through which the cooling wind is released outside the shroud (50), and
the edge portion (264) and the release port (250) are respectively disposed on opposite sides of the cylinder head (23).
A forced air-cooled vehicle engine unit as set forth in claim 1, wherein
the air intake pipe (36) includes a connection pipe (39) that connects the tubular member (220) to the cylinder head (23).
A forced air-cooled vehicle engine unit as set forth in claim 1, wherein
the auxiliary air intake passage defining member (41) is entirely located outside the shroud (50).
A forced air-cooled vehicle engine unit as set forth in claim 2, wherein
the downstream end defining portion (241) is located inside the shroud (50).
A motorcycle comprising:
a vehicle body frame (15) extending in the direction between the front and the back of the vehicle;

a seat (16) supported by the vehicle body frame (15);

a foot rest plate (17) disposed in front of the seat (16);

a vehicle body cover (18) extending upward from a rear portion of the foot rest plate (17) so as to surround a lower space present below the seat (16); and

a forced air-cooled vehicle engine unit (20) as set forth in any one of claims 1 to 8 supported by the vehicle body frame (15) in a vertically pivotal manner, and covered with the vehicle body cover (18) below the seat (16).
A motorcycle as set forth in claim 9, wherein
the cylinder head (23) and the fuel injection device (34) are located at a front end of the engine body (21),
the fan (56) is located in a rear end portion of the shroud (50), and
a release portion (250) for releasing the cooling wind from the shroud (50) is disposed in a front end portion of the shroud (50).