Electric generator cooling structure for internal combustion engine

An electric generator for generating electric energy upon rotation of a crankshaft supported in a crankcase of an internal combustion engine has an outer rotor and an inner rotor. An electric generator cooling structure includes 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 engine toward the electric generator. A first ejection port is defined in a downstream end of the first cooling oil passage for ejecting lubricating oil to an outer side surface of the outer rotor, and a second ejection port is defined in a downstream end of the second cooling oil passage for ejecting lubricating oil to the inner stator disposed in the outer rotor. The electric generator cooling structure can thus efficiently cool the electric generator in its entirety.

TECHNICAL FIELD

The present invention relates to an electric generator cooling structure for cooling an electric generator provided in an internal combustion engine with lubricating oil.

BACKGROUND ART

One example of cooling device for cooling an electric generator provided in an internal combustion engine with lubricating oil is disclosed in Patent Document 1.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1

Patent Document 1 discloses a structure wherein the opening of an oil passage formed in a generator cover that covers a side of an electric generator for an engine is formed to be directed downward in an area near the inner surface of the wall of the generator cover, ribs are formed radially or vertically on the inner surface, and oil flowing out of the downward opening of the oil passage is ejected along the ribs toward a coil-mounted stator of the electric generator.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

As the oil is thus ejected to the stator of the electric generator to cool the stator only, heat tends to be trapped in an outer rotor, and the electric generator cannot be cooled efficiently in its entirety, so that the electric generator cannot be expected to have its efficiency of electric generation significantly increased.

The present invention has been made in view of the above problems. It is an object of the present invention to provide an electric generator cooling structure for an internal combustion engine which is capable of efficiently cooling an electric generator in its entirety.

Means for Solving the Problems

To accomplish the above object, there is provided in accordance with the present invention 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 the crankshaft, the 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 the outer rotor, including 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 the electric generator, a first ejection port defined in a downstream end of the first cooling oil passage for ejecting lubricating oil to an outer side surface of the outer rotor, and a second ejection port defined in a downstream end of the second cooling oil passage for ejecting lubricating oil to the inner stator disposed in the outer rotor.

With this arrangement, the two cooling oil passages, i.e., the first cooling oil passage and the second cooling oil passage, are branched from the lubricating oil passage of the lubricating system of the internal combustion engine toward the electric generator, the first ejection port defined in the downstream end of the first cooling oil passage ejects lubricating oil to the outer side surface of the outer rotor to cool the outer rotor, and the second ejection port defined in the downstream end of the second cooling oil passage ejects lubricating oil to the inner stator disposed in the outer rotor to cool the inner stator. The electric generator is thus efficiently cooled for enhanced electric generation efficiency.

In the above arrangement, the outer rotor may be of a bottomed hollow cylindrical shape having a hollow cylindrical portion and a bottom wall, the bottom wall being fixed to an end of the crankshaft such that the hollow cylindrical portion has an opening directed outwardly along an axial direction of the crankshaft, and the second cooling oil passage may have a downstream portion defined in a generator cover covering an axially outer side of the electric generator.

With this arrangement, the outer rotor of the electric generator is open outwardly along the axial direction of the crankshaft, and the inner stator disposed in the outer rotor has an axially outer side that is open. Since the inner stator faces the generator cover that covers the axially outer side of the electric generator, lubricating oil can be ejected from the second ejection port defined in the downstream end of the second cooling oil passage in the generator cover to the inner stator for cooling the inner stator.

In the above arrangement, the lubricating system of the internal combustion engine may include a scavenging pump and a feed pump, and the first cooling oil passage and the second cooling oil passage may be branched from a scavenger lubricating oil passage which guides lubricating oil discharged from the scavenging pump.

With this arrangement, as the first cooling oil passage and the second cooling oil passage that guide lubricating oil for cooling the electric generator are branched from the scavenger lubricating oil passage which guides lubricating oil discharged from the scavenging pump, the electric generator can be cooled by the lubricating oil discharged from the scavenging pump. Therefore, an upper limit for the oil pressure discharged from the feed pump can be lowered, thereby reducing the burden on the feed pump and the load applied from the feed pump to oil seals in a feeder relief oil passage, so that the feed pump can be reduced in size.

In the above arrangement, the first cooling oil passage may include a scavenger relief cooling oil passage branched from an outlet port of the scavenging pump and housing a scavenger relief valve therein, and the first election port may be defined in a discharge side of the scavenger relief valve.

With this arrangement, the first cooling oil passage that guides lubricating oil for cooling the outer rotor of the electric generator is branched from the outlet port of the scavenging pump and serves as the scavenger relief cooling oil passage with the scavenger relief valve placed therein. Therefore, excessive oil from the scavenging pump under an adjusted pressure is discharged from the scavenging relief valve. The excessive oil contains a large amount of oil mist, which is effective to efficiently cool the outer rotor by rotating with the outer rotor.

In the above arrangement, the scavenger lubricating oil passage may include downstream-end lubricating oil passageways provided in an upper wall of the crankcase above a region where gear trains of a transmission disposed in a transmission chamber in the crankcase are held in mesh with each other, and the downstream-end lubricating oil passageways may have discharge ports defined therein from which lubricating oil drops onto the gear trains that mesh with each other.

With this arrangement, the scavenger lubricating oil passage that guides lubricating oil discharged from the scavenging pump includes the downstream-end lubricating oil passageways defined in the upper wall of the crankcase above the region where the gear trains of the transmission disposed in the crankcase are held in mesh with each other, and the downstream-end lubricating oil passageways have the discharge ports defined therein from which lubricating oil drops onto the gear trains that mesh with each other. As lubricating oil discharged from the scavenging pump is used to drop onto and lubricate the meshing gear trains of the transmission, the burden on the feed pump is further reduced, making it possible to reduce the size of the feed pump.

In the above arrangement, a branch lubricating oil passageway may be branched upstream from the downstream-end lubricating oil passageways of the scavenger lubricating oil passage, the branch lubricating oil passageway may be 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 the transmission gear shaft may have a supply port defined therein for supplying lubricating oil from the axial oil passageway to a gear sliding surface of the transmission gear shaft.

With this arrangement, the branch lubricating oil passageway branched upstream from the downstream-end lubricating oil passageways that guide lubricating oil discharged from the scavenging pump is held in fluid communication with the axial oil passageway defined in the transmission gear shaft, and the transmission gear shaft has the supply port provided therein for supplying lubricating oil from the axial oil passageway to the gear sliding surface of the transmission gear shaft. Consequently, lubricating oil discharged from the scavenging pump is supplied to the axial oil passageway and used to lubricate the gear sliding surface of the transmission gear shaft, so that the burden on the feed pump is yet further reduced, making it possible to further reduce the size of the feed pump.

In the above arrangement, the internal combustion engine may include a clutch provided with a clutch release mechanism and mounted on an end of the transmission gear shaft, the clutch release mechanism may include a clutch release rod axially movably inserted in the transmission gear shaft, a clutch release lever, and a release cam shaft having a cam face for converting angular movement of the clutch release lever into axial movement of the clutch release rod in the transmission gear shaft to disengage the clutch, and lubricating oil passageways extending from the branch lubricating oil passageway in a direction away from the axial oil passageway may be held in fluid communication with a tubular holder by which the release cam shaft is angularly movably held.

With this arrangement, the clutch release mechanism is a mechanism wherein angular movement of the clutch release lever is converted by the cam face into axial movement of the clutch release rod in the transmission gear shaft to disengage the clutch, and the lubricating oil passageways extending from the branch lubricating oil passageway in the direction away from the axial oil passageway are held in fluid communication with the tubular holder by which the release cam shaft is angularly movably held. Therefore, lubricating oil in the axial oil passageway for lubricating the gear sliding surface of the transmission gear shaft is used to lubricate the release cam shaft for its turning movement.

In the above arrangement, the scavenger relief valve may be disposed in a position lower than any of the scavenger lubricating oil passage, the first cooling oil passageway, the second cooling oil passageway, the branch lubricating oil passageway, and the axial oil passageway.

With this arrangement, inasmuch as the scavenger relief valve is disposed in the position lower than any of the scavenger lubricating oil passage, the first cooling oil passageway, the second cooling oil passageway, the branch lubricating oil passageway, and the axial oil passageway, the scavenger lubricating oil passage, the first cooling oil passageway, the second cooling oil passageway, the branch lubricating oil passageway, and the axial oil passageway are filled with lubricating oil. When the internal oil pressure builds up until it goes beyond a predetermined internal pressure of the scavenger relief valve, the scavenger relief valve is opened to supply lubricating oil to all necessary components under suitable oil pressure for enhanced lubricating and cooling performance.

In the above arrangement, the crankcase may include a left crankcase member and a right crankcase member that are separated from, but joined to each other, the scavenging pump may be provided along mating surfaces of the left crankcase member and the right crankcase member, and the feed pump may be disposed in the crankcase remotely from the electric generator across the scavenging pump.

With this arrangement, since the crankcase includes the left and right crankcase members that are separated from, but joined to each other, the scavenging pump is provided along the mating surfaces of the left and right crankcase members, and the feed pump is disposed in the crankcase remotely from the electric generator across the scavenging pump, the feed pump is disposed closely to the scavenging pump out of physical interference with the electric generator, and the first cooling oil passage and the second cooling oil passage that extend from the scavenging pump to the electric generator are shortened, making it possible to reduce the size of the internal combustion engine.

In the above arrangement, the scavenger relief valve may be provided in one of the left crankcase member and the right crankcase member on which the electric generator is mounted.

With this arrangement, because the scavenger relief valve may be provided in one of the left crankcase member and the right crankcase member on which the electric generator is mounted, the lubricating system provides a compact structure wherein the scavenger relief valve is disposed out of physical interference with the feed pump, the first cooling oil passageway is shortened, and excessive oil discharged from the scavenger relief valve is used to cool the electric generator.

In the above arrangement, the scavenging pump and the feed pump may be actuatable by a common pump drive shaft, the feed pump may have an outlet port from which a feeder relief oil passage is branched, the feeder relief oil passage housing a feeder relief valve disposed therein, and the feeder relief oil passage may be disposed on a side of the feed pump remotely from the scavenging pump and oriented in a direction perpendicular to an axis of the pump drive shaft.

With this arrangement, as the scavenging pump and the feed pump are actuated by the common pump drive shaft, the scavenging pump and the feed pump can be positioned closely to each other and arranged compactly by the common pump drive shaft. Since the relief oil passageway branched from the outlet port of the feed pump and housing the feeder relief valve therein is disposed on the side of the feed pump remotely from the scavenging pump and oriented in the direction perpendicular to the axis of the pump drive shaft, the feeder relief valve is disposed compactly in the vicinity of the feed pump out of physical interference with the scavenging pump. Consequently, the feeder lubricating oil passage is shortened to make the lubricating system small in size.

Effects of the Invention

According to the present invention, the two cooling oil passages, i.e., the first cooling oil passage and the second cooling oil passage, are branched from the lubricating oil passage of the lubricating system of the internal combustion engine toward the electric generator, the first ejection port defined in the downstream end of the first cooling oil passage ejects lubricating oil to the outer side surface of the outer rotor to cool the outer rotor, and the second ejection port defined in the downstream end of the second cooling oil passage ejects lubricating oil to the inner stator disposed in the outer rotor to cool the inner stator. The electric generator is thus efficiently cooled for enhanced electric generation efficiency.

MODE FOR CARRYING OUT THE INVENTION

An electric generator cooling structure according to an embodiment of the present invention will be described below with reference toFIGS. 1 through 20.

FIG. 1is a side elevational view of an internal combustion engine10in its entirety for use on a motorcycle according to the embodiment of the present invention.

In the following description, directions such as forward, rearward, leftward, and rightward directions will be specified in accord with normal standards for motorcycles where the direction in which they travel forwardly is referred to as forward direction. In some of the figures, FR represents the forward direction, RR the rearward direction, LH the leftward direction, and RH the rightward direction.

The internal combustion engine10includes a single-cylinder four-stroke internal combustion engine and incorporates a dry sump lubricating system.

As depicted inFIG. 1, the internal combustion engine10includes a crankshaft20(seeFIG. 2) rotatably supported by a crankcase11having a crankcase chamber11C (seeFIG. 3) that houses the crankshaft20therein and a transmission chamber11M (seeFIG. 4) that houses a transmission40therein rearwardly of the crankcase chamber11C. An oil reservoir11T (seeFIG. 2) that protrudes downwardly from the crankcase chamber11C for storing lubricating oil is defined in a lower portion of the transmission chamber11M.

Referring toFIGS. 2 and 3, a cylinder block12with a single cylinder defined therein is mounted on the crankcase11over the crankcase chamber11C therein, and a cylinder head13is mounted on the cylinder block12with a gasket interposed therebetween. The cylinder block12and the cylinder head13are fastened together to the crankcase11by stud bolts. The cylinder head13has its upper end covered with a cylinder head cover14.

The cylinder block12, the cylinder head13, and the cylinder head cover14that are disposed on the crankcase11extend upwardly and are inclined slightly forwardly from the crankcase11(seeFIG. 1).

The crankcase11, which is coupled to the lower end of the cylinder bock12, includes a pair of crankcase members, i.e., a left crankcase member11L and a right crankcase member11R, that are separated from each other by a plane including the center axis of the cylinder and lying perpendicularly to the crankshaft20. The left crankcase member11L and the right crankcase member11R have respective mating surfaces held against each other and are coupled to each other by bolts.

The crankshaft20extends horizontally along the leftward and rightward directions and is rotatably supported in the crank case chamber11C that is defined in the left crankcase member11L and the right crankcase member11R coupled together. As shown inFIG. 3, the crankshaft20includes a pair of left and right crankshaft members20L and20R that are integrally joined to each other by a crankpin21. The left and right crankshaft members20L and20R include respective left and right crankshaft bodies20La and20Ra aligned coaxially with each other and respective left and right crankshaft webs20Lw and20Rw integral with the left and right crankshaft bodies20La and20Ra and axially facing each other. The left and right crankshaft webs20Lw and20Rw that face each other are joined to each other by the crankpin21that is radially displaced off the central axis of the crankshaft20.

The left crankcase member11L and the right crankcase member11R, on which the crankshaft20is rotatably supported, have respective left and right bearing walls11Lw and11Rw that face each other and include respective left and right main bearing casings11Lb and11Rb. The left and right crankshaft bodies20La and20Ra of the crankshaft20have respective journals rotatably supported by a roller bearing22L and a ball bearing22R that are fitted respectively in the main bearing casings11Lb and11Rb.

Therefore, the crankshaft webs20Lw and20Rw and the crankpin21are housed in the crankcase chamber11C between the mutually facing bearing walls11Lw and11Rw, and the crankshaft bodies20La and20Ra project outwardly in the leftward and rightward directions from the bearing walls11Lw and11Rw.

The left crankshaft body20La includes a portion projecting leftwardly from the main bearing casing11Lb of the left bearing wall11Lw. An AC electric generator, i.e., an alternator,30has a generator rotor30R fitted over the projecting portion of the left crankshaft body20La with a starter driven gear27and a one-way clutch29interposed thereon between the rotor30R and the main bearing casing11Lb. The rotor30R is fastened to the projecting portion of the left crankshaft body20La by a nut32with a washer31interposed between the nut32and the rotor30R.

The left main bearing casing11Lb has an outer circumferential surface tapered to the left and houses therein the roller bearing22L fitted against an inner circumferential surface thereof and an oil seal ring23fitted in an tip end opening defined in the left main bearing casing11Lb adjacent to the roller bearing22L.

The left main bearing casing11Lb projects leftward closely to the starter driven gear27. As depicted inFIG. 13, the left main bearing casing11Lb has three radial grooves11vdefined in an upper half of a left tip end face thereof around the tip end opening therein near the starter driven gear27.

A communication hole24is defined through the bearing wall11Lw rearwardly and obliquely upwardly of the main bearing casing11Lb and held in fluid communication with the transmission chamber11M. A rib11ris formed on a left side surface of the bearing wall11Lw and extends obliquely forwardly and downwardly from the opening of the communication hole24to an upper portion of the main bearing casing11Lb.

Oil in the transmission chamber11M flows through the communication hole24to the left side surface of the bearing wall11Lw, then along the inclined rib11rto the upper portion of the main bearing casing11Lb, from which the oil flows on the tapered outer circumferential surface of the main bearing casing11Lb to the left tip end face thereof, where the coil flows into the three grooves11v. Therefore, the oil effectively lubricates the gap between the main bearing casing11Lb and the starter driven gear27near the tip end opening in the main bearing casing11Lb (seeFIG. 3).

The rotor30R of the generator30includes a flywheel30ffitted over the left crankshaft body20La and a cup-shaped or bottomed hollow cylindrical outer rotor30rfixed to the flywheel30fby bolts. The generator30also includes an inner stator30sfixed to a hollow cylindrical support50zof a generator cover50that covers the left side of the generator30and other parts.

The outer rotor30r, which rotates in unison with the crankshaft20through the flywheel30f, has a hollow cylindrical portion that is open to the left. The inner stator30shas a stator core having coils30scwound thereon and facing inner sides of magnets30rmdisposed on an inner circumferential surface of the hollow cylindrical portion of the outer rotor30r.

The starter driven gear27is rotatably supported on the left crankshaft body20La by a needle bearing28, and the one-way clutch29is interposed between the starter driven gear27and the flywheel30f.

The right crankshaft body20Ra includes a portion projecting rightward from the right bearing wall11Rw for the crankshaft20. A balancer drive gear35and a primary drive gear36are fitted side by side over the projecting portion of the right crankshaft body20Ra and fastened thereto by a nut38with a washer37interposed between the nut38and the primary drive gear36.

The primary drive gear36has a hollow cylindrical boss fitted over the projecting portion of the right crankshaft body20Ra, and a drive chain sprocket25is fitted over the hollow cylindrical boss of the primary drive gear36. The drive chain sprocket25transmits engine power to a valve operating system or valve train of the internal combustion engine10through a cam chain, not shown, that is trained around the drive chain sprocket25and a driven chain sprocket, not depicted, fitted over the camshaft of the valve train, which is mounted in the cylinder head13.

As depicted inFIG. 3, a balancer47is disposed forwardly of the crankshaft20.

The balancer47includes a balancer shaft47ahaving a balance weight47wthat turns between the left and right crankshaft webs20Lw and20Rw. The balancer shaft47ais rotatably supported on the left and right bearing walls11Lw and11Rw by respective bearings48.

The balancer shaft47ahas a right portion projecting to the right from the right bearing wall11Rw. A balancer driven gear49is mounted on the projecting right portion of the balancer shaft47aand held in mesh with the balancer drive gear35fitted over the crankshaft20.

The balancer drive gear35and the balancer driven gear36that are in mesh with each other have the same diameter and number of teeth as each other, so that the balancer weight47wwill rotate at the same speed as, but in the opposite direction to, the crankshaft20for thereby reducing primary vibrations caused by reciprocating movement of a piston16in the cylinder12a.

As depicted inFIG. 3, the transmission40has a main shaft41and a countershaft42extending horizontally in the leftward and rightward directions in the transmission chamber11M in the crankcase11and rotatably supported parallel to each other on the left and right bearing walls11Lw and11Rw by left and right bearings41band42b. A main gear train41gsupported on the main shaft41and a counter gear train42gsupported on the countershaft42are held in mesh with each other at all times, making up the transmission40.

The countershaft42has a left portion extending leftward through the crankcase11and serving as an output shaft with an output sprocket43fitted over its left end.

A drive chain is trained around the output sprocket43and a driven sprocket, not depicted, on a rear wheel, making up a chain power transmitting mechanism for transmitting engine power to the rear wheel.

As depicted inFIGS. 3 and 4, the main shaft41has a right portion projecting rightward from the right bearing wall11Rw, and a multiple-disc friction transmission clutch46is mounted on the projecting right portion of the main shaft41.

The transmission clutch46includes a clutch outer46osupported on a primary driven gear45rotatably supported on the main shaft41with a damping member interposed between the clutch outer46oand the primary driven gear45, and a clutch inner46iintegrally fitted over the main shaft41with a plurality of clutch discs46cinterposed between the clutch outer46oand the clutch inner46i. When a pressure plate46pis pushed to the left by a clutch spring46s, the clutch discs46care brought into frictional contact with each other, engaging the transmission clutch46. When the pressure plate46pis moved to the right against the force of the clutch spring46s, the clutch discs46care brought out of frictional contact with each other, disengaging the transmission clutch46.

The transmission clutch46is provided with a clutch release mechanism60.

The clutch release mechanism60has a hollow release rod61slidably inserted in an axial hole defined in the main shaft41and a cap62fitted over the right end of the release rod61. The pressure plate46pis rotatably supported on a bearing boss62bon the tip end of the cap62by a bearing63.

When the release rod61is pushed to the right, the pressure plate55is moved to the right through the bearing63against the force of the clutch spring46s, the transmission clutch46is disengaged.

As depicted inFIG. 3, the main shaft41has a left end rotatably supported on the left bearing wall11Lw of the crankcase11by the left bearing41b. The release rod61inserted in the axial hole in the main shaft41has a left portion projecting from the left end of the main shaft41out of the left bearing wall11Lw.

As depicted inFIG. 6, the generator cover50that covers the left side of the left crankcase member11L includes a tubular side wall portion50sbulging outwardly, i.e., leftwardly, which serves as a tubular holder oriented substantially vertically. The tubular side wall portion50shas a lower portion extending perpendicularly to a hole50a(seeFIG. 7) that is defined in the generator cover50and open at a mating surface50gthereof which is mated to the left crankcase member11L. The tubular side wall portion50sand the hole50aare thus held in fluid communication with each other.

The left portion of the release rod61that projects out of the left bearing wall11Lw has its left end inserted in the hole50a.

As depicted inFIGS. 3 and 4, a release camshaft64is inserted in the tubular side wall portion50sand has a cam face64con its lower tip end which engages the left end of the release rod61that extends perpendicularly to the release camshaft64.

Specifically, the cam face64con the lower tip end of the release camshaft64includes a surface formed by cutting off a portion of the release camshaft64at an angle of approximately 90°. The cam face64cis held in abutment against a left end member61bdisposed in the left end of the release rod61. When the release camshaft64turns about its own axis, the cam face64cpushes the left end member61bto the right, thereby causing the release rod61to slide to the right.

As shown inFIG. 1, the release camshaft64inserted in the tubular side wall portion50shas an upper end portion, remote from the cam face64c, projecting from the tubular side wall portion50s. A clutch release lever65has an end fitted over the projecting upper end portion of the release camshaft64.

The clutch release lever65extends from its end fitted over the projecting upper end portion of the release camshaft64in a direction perpendicular to the release camshaft64.

When the clutch release lever65is swung, the release camshaft64is turned to cause the cam face64cthereof to act on the left end member61bin the release rod61, pushing the release rod61to the right. The release rod61moves the pressure plate46pof the transmission clutch46to the right, thereby disengaging the transmission clutch46.

As shown inFIGS. 3 and 4, the right bearing wall11Rw of the right crankcase member11R has its right side covered with a right case cover52. The right case cover52also covers the balancer driven gear49on the right portion of the balancer shaft47aand the balancer drive gear35and the primary drive gear36on the right crankshaft body20Ra. The right case cover52has an opening through which the transmission clutch46on the right portion of the main shaft41projects to the right. The transmission clutch46is covered with a clutch cover53mounted on the right case cover52.

As depicted inFIGS. 1 and 2, a starter motor80is disposed on an upper wall of the crankcase11behind the cylinder block12that is inclined slightly forward from the crankcase11.

The starter motor80has a drive shaft81fitted from the right into an upwardly bulging side wall of the left crankcase member11L. The side wall into which the drive shaft81is fitted is covered with the generator cover50.

As depicted inFIG. 2, a speed reducer gear shaft82extending between and supported on the left crankcase member11L and the generator cover50is disposed between the drive shaft81and the crankshaft20. A larger-diameter gear83aand a smaller-diameter gear83bthat are integrally formed coaxially with each other are supported on the speed reducer gear shaft82. The larger-diameter gear83ais held in mesh with a starter drive gear81aon the drive shaft81, and an idler gear84is held in mesh with the smaller-diameter gear83band the starter driven gear27supported on the crankshaft20. These gears81a,83a,83b, and84jointly make up a power transmitting mechanism for the starter motor80.

When the starter motor80is energized, the starter drive gear81aon the drive shaft81rotates about its own axis, causing the larger-diameter gear83aheld in mesh with the starter drive gear81aand the smaller-diameter gear83bto rotate at a reduced speed. The smaller-diameter gear83bcauses the idler gear84to rotate the starter driven gear27about its own axis at a reduced speed. The rotation of the starter drive gear27is transmitted through the one-way clutch29to the outer rotor30rof the generator30, which rotates the crankshaft20about its own axis, thereby starting the internal combustion engine10.

The left crankcase member11L has a mating surface11Lg (seeFIGS. 2 and 13) to which the mating surface50g(seeFIG. 7) of the generator cover50is mated, and the left side of the left bearing wall11Lw of the left crankcase member11L is covered with the generator cover50, defining a generator chamber50G between the left bearing wall11Lw and the generator cover50. The generator30and the power transmitting mechanism for the starter motor80are housed in the generator chamber50G.

The right crankcase member11R has a mating surface11Rf (seeFIG. 17) on its left side to which the left crankcase member11L is mated. The mating surface11Rf has a pump housing91hdefined concavely therein that houses the rotor of a scavenging pump91. The right crankcase member11R also has a mating surface on its right side to which a pump cover54(seeFIG. 3) is mated. The mating surface has a pump housing95h(seeFIG. 18) defined concavely therein that houses the rotor of a feed pump95. As will be noted fromFIGS. 3 and 5, the pump housing91hand the pump housing95hare formed back to back in symmetrical positions in the leftward and rightward directions.

The scavenging pump91and the feed pump95are actuated by a common pump drive shaft100that extends centrally through the pump housing91hand the pump housing95h.

The pump drive shaft100has a right end portion extending through the pump cover54and projecting therefrom to the right. AsFIG. 3shows, a pump driven gear101is fitted over the projecting right end portion of the pump drive shaft100and held in mesh with the primary driven gear45of the transmission clutch46.

Therefore, the rotation of the crankshaft20is transmitted through the primary drive gear36to the pump driven gear101, actuating the scavenging pump91and the feed pump95.

The structure of a lubricating system of the internal combustion engine10will be described below.

FIG. 19is a perspective view of a lubricating oil passage assembly of the lubricating system for guiding lubricating oil discharged from the scavenging pump91. The lubricating oil passage assembly associated with the scavenging pump91will be described below mainly with reference toFIG. 19.

InFIG. 19, the lubricating oil passage assembly is depicted stippled.

The scavenging pump91that is housed in the pump housing91hdefined concavely in the mating surface11Rf of the right crankcase member11R draws oil on the bottom of the crankcase chamber11C in the crankcase11into an inlet port Ai (seeFIGS. 14 and 17) and discharges it from an outlet port Ae (positioned in a lower portion of the lubricating oil passage assembly depicted inFIG. 19).

The lubricating oil passage assembly includes a scavenger lubricating oil passage A extending from the outlet port Ae in the left crankcase member11L. The scavenger lubricating oil passage A includes an upstream-end lubricating oil passageway A1which extends to the left through the left crankcase member11L and is open at the mating surface11Lg (seeFIGS. 13 and 14) of the right crankcase member11L. The lubricating oil passageway A1is held in fluid communication with a branch oil slot A2(seeFIG. 7) that is defined in the mating surface50gof the generator cover50.

The lubricating oil passage assembly also includes a scavenger relief cooling oil passage D, which serves as a first cooling oil passage, branched to the left from the outlet port Ae in the left crankcase member11L. As depicted inFIGS. 13 and 15, the scavenger relief cooling oil passage D includes a relief cooling oil passageway D1defined in the left crankcase member11L extending to the left into an enlarged-diameter relief cooling oil passageway D2that has an open left end serving as an ejection port Dj that is open into the generator chamber50G (seeFIGS. 2, 5, 13, and 19).

As depicted inFIGS. 2, 3, and 5, a scavenger relief valve92disposed in the relief cooling oil passageway D2.

Excessive oil discharged from the scavenger relief valve92is ejected from the ejection port Dj of the relief cooling oil passageway D2into the generator chamber50G. As depicted inFIG. 2, the open end of the relief cooling oil passageway D2is located in a lower rear region of the generator chamber50G. Specifically, the open end of the relief cooling oil passageway D2is positioned outside of the outer rotor30rof the generator30and obliquely downward and rearward thereof as viewed in the left-hand side elevation inFIG. 2and is positioned rightward of the generator30(seeFIG. 19).

Therefore, excessive oil from the scavenging pump91under an adjusted pressure is discharged from the scavenging relief valve92and ejected from the ejection port Dj to the outer side surface of the bottom wall of the cup-shaped outer rotor30rand the outer circumferential surface of the hollow cylindrical portion thereof, thereby cooling the outer rotor30r(seeFIGS. 3 and 5).

The excessive oil contains a large amount of oil mist, which is effective to efficiently cool the outer rotor30rby rotation with the outer rotor30r.

The lubricating oil passageway A1extending from the outlet port Ae of the scavenging pump91to the left through the left crankcase member11L is held in fluid communication with the branch oil slot A2defined in the mating surface50gof the generator cover50. A second cooling oil passageway E branched and extending from the branch oil slot A2is defined in the generator cover50.

As indicated inFIG. 7, the generator cover50is of a modified cup shape having a peripheral wall50A and a side wall50B that closes a left-hand opening in the peripheral wall50A. The mating surface50gincludes the end face of an edge surrounding the opening in the peripheral wall50A.

The second cooling oil passageway E includes a cooling oil passageway E1branched from the branch oil slot A2defined in the mating surface50gof the generator cover50. The cooling oil passageway E1extends from the branch oil slot A2obliquely leftward in the peripheral wall50A (seeFIGS. 8 and 19).

The cooling oil passageway E1has a left end crossing and held in fluid communication with the lower end of a cooling oil passageway E2defined substantially vertically in the side wall50B of the generator cover50(seeFIGS. 6, 9, and 19).

The cooling oil passageway E2has an upper end crossing and held in fluid communication with the rear end of a downstream-end cooling oil passageway E3defined obliquely forwardly and downwardly in the side wall50B (seeFIGS. 6, 9, 10, and 19).

InFIG. 2, which is a left-hand side elevational view with the generator cover50omitted from illustration, the cooling oil passageway E2and a downstream-end cooling oil passageway E3are depicted stippled with their profiles indicated by imaginary lines (two-dot-and-dash lines). InFIG. 7, which is a rear view or right-hand side elevational view of the generator cover50that covers the left side of the generator30, the position of the generator30with respect to the generator cover50is indicated by imaginary lines (two-dot-and-dash lines).

InFIGS. 2 and 7, the cooling oil passageway E3overlaps an upper portion of the generator30as viewed in side elevation.

The hollow cylindrical portion of the cup-shaped outer rotor30rof the generator30is open to the left, so that the cooling oil passageway E3is positioned in facing relation to the inner stator30sdisposed in the hollow cylindrical portion of the cup-shaped outer rotor30r(seeFIG. 19).

The cooling oil passageway E3positioned in facing relation to the inner stator30shas two ejection ports Ej for ejecting lubricating oil to the inner stator30s.

Since the two ejection ports Ej defined in the downstream-end cooling oil passageway E3of the second cooling oil passage E branched from the scavenger lubricating oil passage A eject lubricating oil to the inner stator30sof the generator30, the inner stator30shaving the coils30scthat generate heat is directly cooled by the lubricating oil.

As depicted inFIG. 7, the downstream-end cooling oil passageway E3also has an ejection port Ek positioned upstream as viewed in side elevation. The ejection port Ek is positioned outside of the outer circumferential surface of the outer rotor30r, and ejects lubricating oil to the starter driven gear27across and over the outer circumferential surface of the outer rotor30r, thereby lubricating the starter driven gear27and its bearing.

Excessive oil is discharged from the scavenger relief valve92disposed in the downstream relief cooling oil passageway D2of the scavenger relief cooling oil passage D (first cooling oil passage) that is branched from the outlet port Ae, and ejected from the ejection port Dj to the outer rotor30r, thereby cooling the outer rotor30r.

As described above, the lubricating oil passage assembly includes the scavenger relief cooling oil passage D (first cooling oil passage) branched from the scavenger lubricating oil passage A toward the generator30and the second cooling oil passage E. The outer rotor30rof the generator30is cooled by excessive oil ejected from the ejection port Dj of the downstream-end relief cooling oil passageway D2of the scavenger relief cooling oil passage D, and the inner stator30sof the generator30is cooled by lubricating oil ejected from the two ejection ports Ej of the downstream-end cooling oil passageway E3of the second cooling oil passage E. Consequently, the generator30in its entirety can efficiently be cooled by the lubricating oil for increased electric power generation efficiency.

The scavenger lubricating oil passage A also includes a lubricating oil passageway A3extending from the branch oil slot A2to the right in the left crankcase member11L, and a lubricating oil passageway A4extending from the lubricating oil passageway A3obliquely upwardly in the left crankcase member11L (seeFIGS. 13, 15, and 19).

The lubricating oil passageway A4is held in fluid communication with a lubricating oil passageway A5that extends further obliquely upwardly in the left crankcase member11L. The lubricating oil passageway A5has an upper end held in fluid communication with a lubricating oil passageway A6that extends to the left into an upper wall of the left crankcase member11L (seeFIGS. 14, 15, and19).

The lubricating oil passageway A6in the left crankcase member11L is held in fluid communication with a lubricating oil passageway A7in the right crankcase member11R (seeFIGS. 17 and 19).

The lubricating oil passageways A6and A7serve as downstream-end lubricating oil passageways of the scavenger lubricating oil passage A.

The lubricating oil passageways A6and A7are defined in an upper wall of the crankcase11along leftward and rightward vehicle widthwise directions and are positioned above a region where the main gear train41gsupported on the main shaft41of the transmission40and the counter gear train42gsupported on the countershaft42thereof are held in mesh with each other.

The downstream-end lubricating oil passageways A6and A7of the scavenger lubricating oil passage A have a plurality of discharge ports Aj (seeFIGS. 14 and 17) from which lubricating oil drops onto the main gear train41gand the counter gear train42gthat mesh with each other, to lubricate them.

The lubricating oil passageway A5that is defined in the left bearing wall11Lw has a portion overlapping and held in fluid communication with a bearing cavity B1holding the bearing41bfitted therein (seeFIGS. 14 and 15).

The bearing cavity B1serves as a branch lubricating oil passageway B1.

As depicted inFIG. 4, lubricating oil branched from the lubricating oil passageway A5into the branch lubricating oil passageway (bearing cavity) B1lubricates the bearing41band flows along a left end face of the main shaft41into an axial oil passageway B2which is provided by the axial hole defined in the main shaft41.

The main shaft41on which the gear train41gis supported has a supply port Bj defined therein for supplying lubricating oil from the axial oil passageway B2to a gear sliding surface of the main shaft41.

Specifically, the supply port Bj is open at the gear sliding surface of the main shaft41on which a shift gear slides axially in the leftward and rightward directions, and supplies lubricating oil to the gear sliding surface for lubricating the gear sliding surface for the shift gear to slide on the main shaft41.

Furthermore, since the release rod61of the clutch release mechanism60is inserted in the axial hole in the main shaft41which serves as the axial oil passageway B2, lubricating oil that flows into the axial hole in the main shaft41also lubricates the release rod61for sliding therein.

The bottom wall of the bearing cavity or branch lubricating oil passageway B1in the left crankcase member11L has a circular opening defined centrally therein that serves as a lubricating oil passageway C1(seeFIG. 14), and the generator cover50has the hole50a(seeFIG. 7) in which the release rod61is inserted, defined in a portion thereof that is aligned with the lubricating oil passageway C1.

The hole50aserves as a lubricating oil passageway C2which is held in fluid communication with the bearing cavity or branch lubricating oil passageway B1through the lubricating oil passageway C1(seeFIG. 4).

The hole50ais also held in fluid communication with a lubricating oil passageway C3in the tubular side wall portion50sin which the release camshaft64is inserted.

The lubricating oil passageway C1and the lubricating oil passageway C2, i.e., the hole50a, that extend from the bearing cavity B1, i.e., the branch lubricating oil passageway B1, in a direction away from the axial oil passageway B2is held in fluid communication with the lubricating oil passageway C3in the tubular side wall portion50s(seeFIG. 19).

Therefore, lubricating oil branched from the branch lubricating oil passageway B1into the lubricating oil passageway C1flows through the lubricating oil passageway C2into the lubricating oil passageway C3in the tubular side wall portion50s, lubricating the release camshaft64for its turning motion.

The lubricating oil passage assembly for lubricating oil discharged from the scavenging pump91is constructed as depicted inFIG. 19.

The scavenger relief valve92is disposed in a position lower than any of the scavenger lubricating oil passage A, the branch lubricating oil passageway B1, the axial oil passageway B2, the lubricating oil passageways C1, C2, C3, the scavenger relief cooling oil passage (the first cooling oil passage) D, and the second cooling oil passage E.

Consequently, all of the scavenger lubricating oil passage A, the branch lubricating oil passageway B1, the axial oil passageway B2, lubricating oil passageways C1, C2, C3, the scavenger relief cooling oil passage (the first cooling oil passage) D, and the second cooling oil passage E are filled with lubricating oil. When the internal oil pressure builds up until it goes beyond a predetermined internal pressure of the scavenger relief valve92, the scavenger relief valve92is opened to supply lubricating oil to all necessary components under suitable oil pressure for enhanced lubricating and cooling performance.

The scavenging pump91is provided in the right crankcase member11R along the mating surfaces of the left crankcase member11L and the right crankcase member11R. The feed pump95is provided in the right crankcase member11R along the mating surfaces of the right crankcase member11R and the pump cover54that is mounted on the right side of the right crankcase member11R. As depicted inFIG. 3, the feed pump95is disposed remotely from the generator30disposed on the left crankcase member11L across the scavenging pump91disposed in the right crankcase member11R.

The feed pump95is disposed closely to the scavenging pump91out of physical interference with the generator30, and the scavenger relief cooling oil passage (the first cooling oil passage) D and the second cooling oil passage E that extend from the scavenging pump91to the generator30are shortened, making it possible to reduce the size of the internal combustion engine10.

Since the scavenger relief valve92is provided in the left crankcase member11L on which the generator30is disposed, the lubricating oil passage assembly provides a compact structure wherein the scavenger relief valve92is disposed out of physical interference with the feed pump95disposed in the right crankcase member11L and excessive oil discharged from the scavenger relief valve92is used to cool the generator30.

Part of a feeder lubricating oil passage F of the lubricating system for guiding lubricating oil discharged from the feed pump95is depicted stippled in perspective inFIG. 20. An upstream portion of the feeder lubricating oil passage F for passing lubricating oil discharged from the feed pump95will be described below mainly with reference toFIG. 20.

As depicted inFIGS. 5 and 18, the rotor of the feed pump95is disposed in the pump housing95hthat is defined concavely in the mating surface of the right crankcase member11R to which the pump cover54is mated. An inlet port Fi for the feed pump95is defined in the right crankcase member11R and the pump cover54below the feed pump95, and an outlet port Fe for the feed pump95is defined in the right crankcase member11R and the pump cover54above the feed pump95.

The inlet port Fi is held in fluid communication with the oil reservoir11T in the lower portion of the transmission chamber11M in the crankcase11through a strainer96(seeFIG. 5).

As depicted inFIG. 20, the feeder lubricating oil passage F includes a feeder relief oil passage G branched to the right from the outlet port Fe. The feeder relief oil passage G includes a relief oil passageway G1extending to the right and having a right end from which a downstream-end relief oil passageway G2is bent downwardly.

The feeder relief oil passage G is defined in the pump cover54(seeFIG. 5).

A feeder relief valve97is disposed in the downstream-end relief oil passageway G2of the feeder relief oil passage G.

Excessive oil discharged from the feeder relief valve97is ejected downwardly.

As depicted inFIG. 20, the feeder relief valve97in the downstream-end relief oil passageway G2is disposed on the right side of the feed pump95and oriented downwardly in a direction perpendicular to the axis Lp of the pump drive shaft100.

As the scavenging pump91and the feed pump95are actuated by the common pump drive shaft100, the scavenging pump91and the feed pump95can be positioned closely to each other and arranged compactly by the common pump drive shaft100. Since the relief oil passageway G2branched from the outlet port Fe of the feed pump95and housing the feeder relief valve97therein is disposed on the right side of the feed pump95remotely from the scavenging pump91and oriented in the direction perpendicular to the axis Lp of the pump drive shaft100, the feeder relief valve97is disposed compactly in the vicinity of the feed pump95out of physical interference with the scavenging pump91. Consequently, the feeder lubricating oil passage F is shortened, making the lubricating system small in size.

The feeder lubricating oil passage F also includes a lubricating oil passageway F1defined in the pump cover54and extending from the outlet port Fe to the right. The lubricating oil passageway F1defined in the pump cover54is held in fluid communication with a lubricating oil passageway F2defined in the right case cover52(seeFIGS. 5 and 20). A lubricating oil passageway F3extends forwardly from the lubricating oil passageway F2and is held in fluid communication with an oil filter98.

A lubricating oil passageway F4extends from the oil filter98for supplying lubricating oil to various components to be lubricated, which include the crankshaft20and a valve operating mechanism in the cylinder head13, for example.

The lubricating oil passage assembly in the internal combustion engine10is of the structure described above. The first cooling oil passage and the second cooling oil passage are branched from the scavenger lubricating oil passage A for guiding lubricating oil to cool the generator30, and the downstream-end lubricating oil passageways A6and A7of the scavenger lubricating oil passage A supply lubricating oil for lubricating the region where the main gear train41gand the counter gear train42gof the transmission40are held in mesh with each other. Lubricating oil supplied from the branch lubricating oil passageway (bearing cavity) B1branched from the lubricating oil passageway A5lubricates the bearing41b, and lubricating oil supplied form the axial oil passageway B2extending from the branch lubricating oil passageway B1lubricates the gear sliding surface for the shift gear to slide on the main shaft41. Lubricating oil branched from the branch lubricating oil passageway B1into the lubricating oil passageways C1, C2, and C3lubricates the clutch release mechanism60.

Lubricating oil supplied from the scavenging pump91to the scavenger lubricating oil passage A is used to cool the generator30and also to lubricate various components. Therefore, an upper limit for the oil pressure discharged from the feed pump95can be lowered, thereby reducing the burden on the feed pump95and the load applied from the feed pump95to oil seals in the feeder relief oil passage G, so that the feed pump95can be reduced in size.

The electric generator cooling structure for cooling the electric generator provided in the internal combustion engine according to the embodiment of the present invention has been described above. The present invention is not limited to the illustrated embodiment, but various changes and modifications may be made to the embodiment without departing from the scope of the invention.

DESCRIPTION OF REFERENCE SYMBOLS