Electric generator cooling structure for internal combustion engine

1. An electric generator cooling structure for an internal combustion engine, wherein an electric generator for generating electric energy upon rotation of a crankshaft supported in a crankcase of the internal combustion engine has an outer rotor rotatable in unison with said crankshaft, said outer rotor being of a bottomed hollow cylindrical shape and supporting magnets on an inner circumferential surface thereof, and an inner rotor having coils disposed in said outer rotor, comprising:

a first cooling oil passage and a second cooling oil passage that are branched from a lubricating oil passage of a lubricating system of the internal combustion engine toward said electric generator;

a first ejection port defined in a downstream end of said first cooling oil passage for ejecting lubricating oil to an outer side surface of said outer rotor; and

a second ejection port defined in a downstream end of said second cooling oil passage for ejecting lubricating oil to said inner stator disposed in said outer rotor,

wherein said lubricating system of the internal combustion engine includes a scavenging pump and a feed pump, the scavenging pump and the feed pump being coaxially arranged, and

wherein said first cooling oil passage and said second cooling oil passage are branched from a scavenger lubricating oil passage which guides lubricating oil discharged from said scavenging pump.

2. The electric generator cooling structure for an internal combustion engine according to claim 1 , wherein said outer rotor is of a bottomed hollow cylindrical shape having a hollow cylindrical portion and a bottom wall, said bottom wall being fixed to an end of said crankshaft such that said hollow cylindrical portion has an opening directed outward along an axial direction of said crankshaft; and

said second cooling oil passage has a downstream portion defined in a generator cover covering an axially outer side of said electric generator.

3. The electric generator cooling structure for an internal combustion engine according to claim 1 , wherein said first cooling oil passage includes a scavenger relief cooling oil passage branched from an outlet port of said scavenging pump and housing a scavenger relief valve therein; and

said first ejection port is provided in a discharge side of said scavenger relief valve.

4. The electric generator cooling structure for an internal combustion engine according to claim 3 , wherein said scavenger lubricating oil passage includes downstream-end lubricating oil passageways defined in an upper wall of said crankcase above a region where gear trains of a transmission disposed in a transmission chamber in said crankcase are held in mesh with each other; and

said downstream-end lubricating oil passageways have discharge ports defined therein from which lubricating oil drops onto the gear trains that mesh with each other.

5. The electric generator cooling structure for an internal combustion engine according to claim 4 , wherein a branch lubricating oil passageway is branched upstream from said downstream-end lubricating oil passageways of said scavenger lubricating oil passage;

said branch lubricating oil passageway is held in fluid communication with an axial oil passageway defined in a transmission gear shaft on which one of the gear trains is supported; and

said transmission gear shaft has a supply port defined therein for supplying lubricating oil from said axial oil passageway to a gear sliding surface of said transmission gear shaft.

6. The electric generator cooling structure for an internal combustion engine according to claim 5 , wherein said internal combustion engine includes a clutch provided with a clutch release mechanism and mounted on an end of said transmission gear shaft;

said clutch release mechanism includes a clutch release rod axially movably inserted in said transmission gear shaft, a clutch release lever, and a release cam shaft having a cam face for converting angular movement of said clutch release lever into axial movement of said clutch release rod in said transmission gear shaft to disengage said clutch; and

lubricating oil passageways extending from said branch lubricating oil passageway in a direction away from said axial oil passageway are held in fluid communication with a tubular holder by which said release cam shaft is angularly movably held.

7. The electric generator cooling structure for an internal combustion engine according to claim 5 , wherein said scavenger relief valve is disposed in a position lower than any of said scavenger lubricating oil passage, said first cooling oil passageway, said second cooling oil passageway, said branch lubricating oil passageway, and said axial oil passageway.

8. The electric generator cooling structure for an internal combustion engine according to claim 3 , wherein said crankcase includes a left crankcase member and a right crankcase member that are separated from, but joined to each other;

said scavenging pump is provided along mating surfaces of said left crankcase member and said right crankcase member; and

said feed pump is disposed in said crankcase remotely from said electric generator across said scavenging pump.

9. The electric generator cooling structure for an internal combustion engine according to claim 8 , wherein said scavenger relief valve is provided in one of said left crankcase member and said right crankcase member on which said electric generator is mounted.

10. The electric generator cooling structure for an internal combustion engine according to claim 8 , wherein said scavenging pump and said feed pump are actuatable by a common pump drive shaft;

said feed pump has an outlet port from which a feeder relief oil passage is branched, said feeder relief oil passage housing a feeder relief valve disposed therein; and

said feeder relief oil passage is disposed on a side of said feed pump remotely from said scavenging pump and oriented in a direction perpendicular to an axis of the pump drive shaft.

11. The electric generator cooling structure for an internal combustion engine according to claim 6 , wherein said scavenger relief valve is disposed in a position lower than any of said scavenger lubricating oil passage, said first cooling oil passageway, said second cooling oil passageway, said branch lubricating oil passageway, and said axial oil passageway.

12. The electric generator cooling structure for an internal combustion engine according to claim 9 , wherein said scavenging pump and said feed pump are actuatable by a common pump drive shaft;

said feed pump has an outlet port from which a feeder relief oil passage is branched, said feeder relief oil passage housing a feeder relief valve disposed therein; and

said feeder relief oil passage is disposed on a side of said feed pump remotely from said scavenging pump and oriented in a direction perpendicular to an axis of the pump drive shaft.