Lubricating system for internal combustion engine

A lubricating system for an internal combustion engine includes lubricating oil recovery oil passages through which lubricating oil dropping to and dwelling in a bottom portion of a crankcase after lubricating individual portions of an internal combustion engine is fed to a lubricating oil tank through an oil cooler by a recovery pump. Lubricating oil supply oil passages supply the lubricating oil from the lubricating oil tank to the individual portions of the internal combustion engine needing lubrication and cooling through an oil filter by a supply pump. The lubricating system includes a branch passage branched from the lubricating oil recovery oil passage communicating from the oil cooler to the lubricating oil tank. The branch passage supplies the lubricating oil to at least one of the individual portions of the internal combustion engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application Nos. 2002-272340 and 2003-295174, filed in Japan on Sep. 18, 2002 and Aug. 19, 2003, respectively. The entirety of each of the above documents is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lubricating system for an internal combustion engine, wherein lubricating oil dropping to and dwelling in a bottom portion of a crankcase is fed to a lubricating oil tank through an oil cooler by a recovery pump. The lubricating oil is supplied from the lubricating oil tank to respective portions of the internal combustion engine through an oil filter.

2. Description of Background Art

A lubricating system for an internal combustion engine is known. Referring toFIG. 35, a lubricating oil dropping to and dwelling in a crankcase bottom portion03after lubricating respective portions02of an internal combustion engine is passed through an oil cooler04, thereby being cooled. The lubricating oil is then fed to a lubricating oil tank05by a recovery pump01. The lubricating oil is supplied to the respective portions02of the internal combustion engine requiring lubrication and cooling through an oil filter07by a supply pump06(see Japanese Patent Laid-open No. 2001-73736, paragraph [0018] in “Detailed Description of the Invention” andFIG. 4).

In the conventional lubricating system for an internal combustion engine shown inFIG. 35, the supply of lubricating oil to the respective portions of the engine is performed by only the supply pump06, so that it is necessary to enlarge the supply pump in size. In addition, where it is desired to cool particularly the portions having high calorific values such as a portion surrounding a combustion chamber of a cylinder head and an AC generator, it has been a common practice to cope with this by enlarging the capacities of the supply pump06and the oil cooler04.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a lubricating system capable of enhancing a cooling effect even where there are limitations to the increase of the capacity of a supply pump and an oil cooler.

According to a first aspect of the present invention, a lubricating system for an internal combustion engine includes a lubricating oil recovery oil passage through which lubricating oil dropping to and dwelling in a crankcase bottom portion after lubricating respective portions of the internal combustion chamber is fed to a lubricating oil tank through an oil cooler by a recovery pump, and a lubricating oil supply oil passage through which the lubricating oil is supplied to the respective portions of the internal combustion engine needing lubrication and cooling through an oil filter by a supply pump, wherein the lubricating system includes a branch passage branched from the lubricating oil recovery oil passage communicating from the oil cooler to the lubricating oil tank, the branch passage being for supplying the lubricating oil to at least one of the respective portions of the internal combustion chamber.

According to a second aspect of the present invention, the downstream end of the branch passage is in communication with a portion surrounding a combustion chamber of the internal combustion engine.

According to a third aspect of the present invention, the downstream end of the branch passage is in communication with a portion to be cooled of an AC generator additionally provided on the internal combustion engine.

According to the first aspect of the present invention, the recovery pump performs a part of the task of feeding the lubricating oil to the respective portions of the engine, so that the supply pump can be made smaller in size. In addition, since the lubricating oil branching from the lubricating oil recovery oil passage has just been cooled by the oil cooler, it is suitable for cooling and lubricating the portions having high calorific values.

In addition, according to the second aspect of the present invention, the downstream end of the branch passage is in communication with a portion surrounding a combustion chamber. Therefore, the lubricating oil cooled by the oil cooler is supplied directly to the portion surrounding the combustion chamber, without being supplied to the oil filter, so that the portion surrounding the combustion chamber is cooled efficiently and sufficiently.

Furthermore, according to the third aspect of the present invention, the downstream end of the branch passage is in communication with a portion to be cooled of an AC generator. Therefore, the lubricating oil just cooled by the oil cooler is supplied directly to the portion to be cooled of the AC generator, without passing through the oil tank, so that the AC generator is cooled efficiently and sufficiently.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a power unit for a vehicle with internal combustion engine1according to the present invention will now be described with reference to the accompanying drawings. In this embodiment, the upward and downward directions refer to the upward and downward directions with respect to the vehicle body, the front side refers to the front side with respect to the vehicle body, the rear side refers to the rear side with respect to the vehicle body, and the left and right refers to the left and right as viewed from a person oriented to face the front side.

Overall Structure

As shown inFIG. 1, in a wild ground running or all-terrain four-wheel vehicle0on which the power unit for a vehicle with internal combustion engine1is mounted, pairs of front wheels3and rear wheels4are disposed respectively at front and rear portions of a vehicle body frame2. The front end rear ends of transmission shafts directed in the forward and rearward directions from the power unit for a vehicle with internal combustion engine1are connected to the front wheel3and the rear wheel4through differential devices (not shown) and a front axle6and a rear axle7, respectively. The all-terrain four-wheel vehicle0can run in a four-wheel drive mode by the power from the power unit for a vehicle with internal combustion engine1.

In addition, the all-terrain four-wheel vehicle0includes a bar handle or handlebar8at a central portion in the width direction on the front side. A steering mechanism10is provided at the lower end of a steering shaft9connected to the bar handle8. A swiveling operation on the handlebar8is transmitted to the front wheels3through the steering shaft9and the steering mechanism10, whereby the all-terrain four-wheel vehicle0is turned to the left or the right.

Furthermore, a fuel tank11is mounted on the vehicle body frame2while being located on the upper side of the power unit for a vehicle with internal combustion engine1. A seat12is mounted on the rear side thereof. A fan13and an oil cooler14are sequentially disposed on the front side of the power unit for a vehicle with internal combustion engine1. A carburetor15and an air cleaner16are sequentially disposed on the rear side of the power unit for a vehicle with internal combustion engine1. The front axle6and the rear axle7are supported on the vehicle body frame2through shock absorbers17.

Furthermore, as shown inFIGS. 2,3and4, the power unit for a vehicle with internal combustion engine1includes a 4-stroke-cycle internal combustion engine20, a static oil hydraulic type non-stage transmission100, and a speed change drive shaft controller150. The 4-stroke-cycle internal combustion engine20is an overhead-valve push-rod type single-cylinder internal combustion engine having a cylinder center axis in the vertical direction with respect to the front-rear direction, as shown inFIG. 1, and slightly inclined from the vertical direction to the left, as viewed forwards from the rear side of the vehicle body, with respect to the left-right direction, as shown inFIG. 3. As shown inFIGS. 4 and 5, the static oil hydraulic type non-stage transmission100is a transmission in which a swash plate type oil hydraulic pump110and a swash plate type oil hydraulic motor130are disposed on the same axis in the front-rear direction and which changes the speed of rotation from a crankshaft28of the 4-stroke-cycle internal combustion engine20. The speed change drive shaft controller150includes a speed change drive shaft151for reciprocating a drive member152for changing the swash plate angle of the swash plate type oil hydraulic pump of the swash plate type oil hydraulic motor130.

In addition, in the 4-stroke-cycle internal combustion engine20, as shown inFIGS. 1 and 4, a crankcase is partitioned into four portions, namely, into a front case cover21, a front crankcase22, a rear crankcase23and a rear case cover24in the front-rear direction. The vertical planes are directed in the vehicle width direction as faying surfaces. A cylinder block25, a cylinder head26and a head cover27are sequentially stacked on the upper side of the front crankcase22and the rear crankcase23at the center in the front-rear direction. The front case cover21, the front crankcase22, the rear crankcase23, the rear case cover24, the cylinder block25, the cylinder head26and the head cover27are mutually integrally connected by bolts and the like which are not shown.

Furthermore, as shown inFIG. 3(the many-dotted portion in the figure means a faying surface between one member and another). The crankshaft28is rotatably mounted on the front crankcase22and the rear crankcase23while being directed in the front-rear direction (seeFIG. 4). A piston30is slidably fitted in a cylinder bore29in the cylinder block25directed roughly in the vertical direction. The upper and lower ends of a connecting rod31are rotatably fitted on a piston pin30ainserted in the piston30and a crank pin28aon the crankshaft28. The crank shaft28is driven to rotate by the pressure of combustion gas generated by combustion of a mixture gas sucked into a combustion chamber32surrounded by the cylinder bore29, the cylinder head26and the piston30.

Furthermore, the cylinder head26is provided with an intake port33opened rearwards and an exhaust port34opened forwards, and is provided with an intake valve35and an exhaust valve36for openably closing the ports of the intake port33and the exhaust port34on the side of the combustion chamber32, respectively. The carburetor15and the air cleaner16(seeFIG. 1) are connected to a rear opening portion of the intake port33, whereas an exhaust gas clarifier, a muffler and the like which are not shown are connected to a front opening portion of the exhaust port34through an exhaust pipe18. As shown inFIG. 3, a spark plug39is screwed to the cylinder head26so that an electrode portion39aof the spark plug39fronts on the combustion chamber32.

The cylinder block25and the cylinder head26are provided with cooling fins37and cooling fins38, respectively. A running airflow arising from the running of the vehicle and a cooling airflow generated by a fan13come into contact with the cooling fins37and38, whereby the 4-stroke-cycle internal combustion engine20is cooled, and, as will be described later, the 4-stroke-cycle internal combustion engine20is cooled by a cooling lubricating oil passing inside the cylinder block25and the cylinder head26.

In addition, as shown inFIG. 3, in the cylinder block25and the cylinder head26, a communication hole40is formed on the right side of the cylinder bore29and substantially in parallel to the cylinder bore29. A circular guide hole41is formed in top walls of the front crankcase22and the rear crankcase23at a position directly below the communication hole40. At a position on the downward extension of the communication hole40and the guide hole41, a camshaft43is rotatably mounted on camshaft pivot holes67cand71cprovided in partition walls67and71of the front crankcase22and the rear crankcase23. A valve lifter45slidably fitted in the guide hole41is brought into contact with a cam44on the camshaft43. A front-rear pair of rocker arms46are mounted for oscillation on the cylinder head26, with rocker shafts42shown inFIG. 4therebetween, in parallel to contact surfaces between the cylinder block25, the cylinder head26and the head cover27. A push rod47is interposed between one end portion of the rocker arm46and the valve lifter45. The other end portion of the rocker arm46is brought into contact with the top end of the intake valve35or the exhaust valve36. In each of the intake valve35and the exhaust valve36, a valve spring49is interposed between a valve spring retainer48mounted on the top end and a spring receiving portion26aof the cylinder head26. A chain which is not shown is set around a drive sprocket50(seeFIG. 4) fitted on the crankshaft28and a driven sprocket (not shown) fitted on the camshaft43and having a number of teeth of two times that of the drive sprocket50. When the crankshaft28is rotated, the camshaft43is driven to rotate in a ratio of one revolution to two revolutions of the crankshaft28. The intake valve35and the exhaust valve36are opened and closed one time each corresponding to two revolutions of the crankshaft28, with the same valve timing as that in an ordinary 4-stroke-cycle internal combustion engine.

In addition, as shown inFIG. 4, at a rear portion of the crankshaft28, a balancer drive gear51is integrally mounted to the crankshaft28at a position on the rear side of the drive sprocket50. As shown inFIG. 3, a balancer gear52meshed with the balancer drive gear51is mounted on the front crankcase22and the rear crankcase23through a balancer shaft53at a position on the right side of the crankshaft28. Further, an ACG54(AC generator) is disposed on the rear side of the balancer drive gear51. A rotor54aof the ACG54is fitted in the vicinity of a rear end portion of the crankshaft28. A recoil starter55is provided at a rear end portion of the crankshaft28on the rear side of the rotor54a.A pump drive gear56is integrally mounted to a front portion of the crankshaft28. A starting clutch57is provided at the front end of the crankshaft28at a position on the front side of the pump drive gear56.

Furthermore, as shown inFIG. 4, a drive gear58is integrally attached to a clutch outer57a,which is an output member of the starting clutch57. As shown inFIG. 3, the static oil hydraulic type non-stage transmission100located slightly on the upper side and on the left side of the crankshaft28is disposed inside the front crankcase22and the rear crankcase23, as shown inFIG. 4. As shown inFIG. 5, an oil hydraulic motor rotary shaft131of the swash plate type oil hydraulic motor130in the static oil hydraulic type non-stage transmission100is rotatably mounted on the front case cover21and the rear crankcase23. A motor casing132of the swash plate type oil hydraulic motor130is rotatably mounted on the oil hydraulic motor rotary shaft131. A driven gear101is integrally attached to a pump casing111of the swash plate type oil hydraulic pump110rotatably mounted on the oil hydraulic motor rotary shaft131. As shown inFIG. 4, the driven gear101is meshed with the drive gear58of the starting clutch57. When the drive gear58of the starting clutch57is rotated, the pump casing111of the swash plate type oil hydraulic pump110in the static oil hydraulic type non-stage transmission100is driven to rotate, with the oil hydraulic motor rotary shaft131as a center.

In addition, as shown inFIG. 4, a gear transmission160is disposed in the space surrounded by the rear crankcase23and the rear case cover24, and a main shaft161of the gear transmission160is spline-fitted to the oil hydraulic motor rotary shaft131of the static oil hydraulic type non-stage transmission100. As shown inFIG. 3, a counter shaft162is disposed at a position on the left lower side of the main shaft161. Furthermore, an output shaft163is disposed at a position on the right lower side of the counter shaft162and the main shaft161. The main shaft161, the counter shaft162and the output shaft163are rotatably mounted on the rear crankcase23and the rear case cover24. A counter gear166normally in mesh with a main gear165integral with the main shaft161is rotatably mounted on the counter shaft162. A shifter167is mounted on the counter shaft162so that it cannot rotate but can axially slide in relation to the counter shaft162. A counter output gear168integral with the counter shaft162and a gear169integral with the output shaft163are in mesh with each other. When the shifter167is slid forward by a change-over mechanism (not shown) so as to engage with the counter gear166, the counter gear166and the counter shaft162are connected to each other, whereby the rotating force of the main shaft161is transmitted to the output shaft163.

Moreover, as shown inFIG. 4, a reverse counter gear170located between the shifter167and the counter output gear168is rotatably mounted to the counter shaft162. As shown inFIG. 3, a reverse shaft164located adjacent to the main shaft161and the counter shaft162is rotatably mounted on the rear crankcase23and the rear case cover24(seeFIG. 4). An input gear171on one side which is integral with the reverse shaft164is meshed with the main gear165on the main shaft161. An output gear172on the other side which is integral with the reverse shaft164is meshed with the reverse counter gear170on the counter shaft162. When the shifter167is slid rearward, the counter output gear168and the counter shaft162are connected to each other, whereby the rotating force of the main shaft161is transmitted, in a reverse rotating condition, to the output shaft163through the reverse shaft164and the counter shaft162.

Both the front and rear ends of the output shaft163are connected respectively to the transmission shafts5disposed on the front and rear sides of the power unit for a vehicle with internal combustion engine1. Accordingly, the rotating force of the output shaft163is transmitted to the front wheels3and the rear wheels4through the transmission shafts5and through the front axle6and the rear axle7.

In addition, as shown inFIG. 3, the speed change drive shaft controller150is disposed on the upper left side of the power unit for a vehicle with internal combustion engine1. The angle αbetween a plane connecting the center line of the speed change drive gear151of the speed change drive shaft controller150and the center line of the oil hydraulic motor rotary shaft131of the static oil hydraulic type non-stage transmission100and the center line of the cylinder bore29of the 4-stroke-cycle internal combustion engine20is as small as about 10°.

Furthermore, as shown inFIGS. 3 and 4, the speed change drive shaft151of the speed change drive shaft controller150is provided with a male screw at a central portion in the longitudinal direction thereof. The drive member152is meshed with the speed change drive shaft151of the male screw. As shown inFIG. 5, the drive member152is connected for oscillation to arm portions134projected in a forked form from a motor swash plate133of the swash plate type oil hydraulic motor130in the static oil hydraulic type non-stage transmission100, through a pin135. As shown inFIG. 5, a gear153integral with the speed change drive shaft151is meshed with a small gear155of a speed reduction gear154. A large gear156of the speed reduction gear154is meshed with a pinion gear159integral with a rotary shaft158of a control motor157. By the normal and reverse rotations of the control motor157, the drive member is driven forwards and rearwards, whereby the inclination angle of the motor casing132of the swash plate type oil hydraulic motor130is controlled.

Furthermore, as shown inFIG. 3, along a plane orthogonal to the plane connecting the speed change drive shaft151of the speed change drive shaft controller150and the oil hydraulic motor rotary shaft131of the swash plate type oil hydraulic motor130, a speed change ratio sensor102is disposed at a position on the left side of the swash plate type oil hydraulic motor30.

Lubricating Oil Pump

A lubricating oil pump60will now be described.FIGS. 6 and 7are views as viewed rearwards from the front side of the front case cover21and the front crankcase22.FIG. 4is a sectional view taken along a vertical plane in the front-rear direction. Referring toFIGS. 4,6and7, the lubricating oil pump60is integrally attached to the front case cover21and the front crankcase22so that the front and rear surfaces of the lubricating oil pump60make close contact with the rear surface of the front case cover21and the front surface of the front crankcase22, respectively. As shown enlarged inFIGS. 32 and 33, the lubricating oil pump60includes a trochoid type recovery pump61and a supply pump62which are arranged on the same pump rotary shaft63. The recovery pump61and the supply pump62include inner rotors61a,62amounted to the pump rotary shaft63, outer rotors61b,62bmeshed with the inner rotors61a,62a,and pump bodies61c,62crotatably enclosing the outer rotors61b,62b,respectively. The outer rotors61b,62bare eccentric relative to the inner rotors61a,62a,and the numbers of teeth of the outer rotors61b,62bare greater than the numbers of teeth of the inner rotors61a,62aby one.

As shown inFIG. 4, a pump gear63aintegrally attached to the pump rotary shaft63of the lubricating oil pump60is meshed with a pump drive gear56integral with the crankshaft28. Attendant on the rotation of the crankshaft28, the pump rotary shaft63is driven to rotate, whereby in the recovery pump61the lubricating oil is sucked in through a suction port61dand discharged through a discharge port61e.In the supply pump62the lubricating oil is sucked in through a suction port62dand is discharged through a discharge port62e.

The specific structures of the front case cover21, the front crankcase22, the rear crankcase23and the rear case cover24constituting the crankcase of the 4-stroke-cycle internal combustion engine20will now be described.

As shown inFIGS. 4 and 6, the front case cover21is provided integrally with a filter case65of the oil filter64. A filter element66(seeFIG. 4) is contained in the filter case65. The lubricating oil flowing into the filter case65through an inflow passage65aat an outer circumferential portion of the filter case65is filtered by the filter element66, and is then discharged into a central oil passage65b.

In addition, as shown inFIGS. 7 and 8, the front crankcase22is provided integrally with a partition wall67parallel to the front and rear faying surfaces of the front crankcase22, substantially at the center in the front-rear and width directions. The partition wall67is provided with a crankshaft hole67afor passing the crankcase28therethrough. A transmission loose-fitting hole67bis provided for loose fitting therein of the static oil hydraulic type non-stage transmission100at a position on the left side in the crankcase. A camshaft hole67cis provided for passing and supporting the camshaft43therein. A balancer shaft hole67dis provided for passing and supporting the balancer shaft53therein at a position on the lower side of the camshaft hole67c.A speed change drive shaft hole67eis provided for passing the speed change drive shaft151of the speed change drive shaft controller150therethrough and an output shaft hole67fis provided for passing and supporting the output shaft163therein, at positions on the upper and lower sides of the transmission loose fitting hole67b.A crank chamber communication hole67gand a recovery pump suction communication hole67hare provided in communication with the suction port61dof the recovery pump61, which are located on the lower side of the counter shaft hole67f.A supply pump suction communication hole67iis provided in communication with the suction port62dof the supply pump62. A strainer lower lubricating oil sump67jranges leftward from the position directly below the recovery pump suction communication hole67h.

Furthermore, as shown inFIG. 7, in the front crankcase22, a tank partition wall68projected forwards beyond the partition wall67is provided at a required spacing along a right side wall22a(on the left side inFIG. 7) of the front crankcase22. As shown inFIG. 8, a tank partition wall69projected rearwards beyond the partition wall67is provided at a position different from that of the tank partition wall68but substantially along the tank partition wall68. A crank chamber59and an oil tank chamber70are partitioned by the tank partition wall68and the tank partition wall69. The partition wall67is provided with tank communication holes67k(at four locations) at positions on the right outer side of the tank partition wall68and the tank partition wall69(the partition wall67is not provided any other holes than these holes).

Furthermore, as shown inFIG. 8, the tank partition wall69projected rearwards beyond the partition wall67is provided with a cutout69bin an extension portion69aextended to the slantly right upper side (slantly left upper side inFIG. 8) of the portion partitioning the crank chamber59and the oil tank chamber70so that the lubricating oil dwelling on the upper surface of the tank partition wall69flows downwards through the cutout69bto be led to the strainer lower lubricating oil sump67j.

The front crankcase22is provided with mount holes22bin lower side portions thereof. Rod-like members (not shown) penetrating through the mount holes22band mount holes23bformed in lower both side portions of the rear crankcase23are integrally mounted to the vehicle body frame2through rubber bushes (not shown).

In addition, as shown inFIGS. 9 and 10, like the front crankcase22, the rear crankcase23is integrally provided with a partition wall71parallel to the front and rear faying surfaces of the rear crankcase23, at the center in the front-rear and width directions thereof. The partition wall71is provided with a crankshaft hole71afor passing the crankshaft28therethrough. An oil hydraulic motor rotary shaft hole71bis provided for rotatably bearing the oil hydraulic motor rotary shaft131of the swash plate type oil hydraulic motor130in the static oil hydraulic type non-stage transmission100. A camshaft hole71cis provided for passing and supporting the camshaft43therein. A balancer shaft hole71dis provided for passing and supporting the balancer shaft53therein at a position on the lower side of the camshaft hole71c.A counter shaft hole71eis provided for passing and supporting the counter shaft162therein at a position intermediate between the main shaft161and the output shaft163and on the left side. An output shaft hole71fis provided for passing and supporting the output shaft163therein at a position on the lower side of the oil hydraulic motor rotary shaft hole71b.A crank chamber communication hole71gis provided at a position on the slantly right lower side of the output shaft hole71f.A reverse shaft hole71m(shown inFIG. 10only) is provided for supporting the reverse shaft164at a position intermediate between the main shaft161and the output shaft163and on the right side.

As shown inFIG. 9, the rear crankcase23is provided with a strainer lower lubricating oil sump71jin communication with the strainer lower lubricating oil sump67jof the crankcase22, and is provided with a communication portion71hin communication with the recovery pump suction communication hole67hat a position on the upper side of the strainer lower lubricating oil sump71j.A strainer85is fitted in both side cutouts71lbetween the strainer lower lubricating oil sump71jand the communication portion71h.

Furthermore, as shown inFIG. 9, the rear crankcase23is provided with a tank partition wall72(the tip end surface of the tank partition wall72can make contact with the rear end surface of the tank partition wall69of the front crankcase22) projected forwards beyond the partition wall71at a required spacing along a right side wall23a(on the left side inFIG. 9) of the rear crankcase23. As shown inFIG. 10, the rear crankcase23is provided with a tank partition wall73projected rearwards beyond the partition wall71at a position different from the tank partition wall72but substantially along the tank partition wall72so that the crank chamber59and the oil tank chamber70are partitioned by the tank partition wall72and73. The partition wall71is provided with tank communication holes71k(at six locations) at positions on the right outer side of the tank partition wall72and the tank partition wall73. As shown inFIG. 10, an upper end portion73aof the tank partition wall73and a top wall portion23cof the rear crankcase23are not connected to each other but are separate from each other, so that a gap73bis formed between the upper end portion73aof the tank partition wall73and the top wall portion23cof the rear crankcase23.

As shown inFIG. 9, the tank partition wall72projected forwards beyond the partition wall71is provided with a cutout72bin its extension portion72acurvedly extended to the slantly right upper side so that the lubricating oil dwelling on the upper surface of the tank partition wall72flows downwards through the cutout72bto be led to the strainer lower lubricating oil sump71j.

Furthermore, as shown inFIG. 10, at a rear portion of the rear crankcase23, an overflow oil passage wall74projected rearwards from the rear surface of the partition wall71is extended downwards from the top wall portion23cof the rear crankcase23so that a required spacing is present at a position on the upper left side of the tank partition wall73. The lower front end74aof the overflow oil passage wall74extends to the crank chamber communication hole71gof the partition wall71. An overflow oil passage75is constituted of the tank partition wall73and the overflow oil passage wall74.

As shown inFIGS. 3 and 5, a breather chamber80is disposed on the center axis of the speed change drive shaft151of the speed change drive shaft controller150. As shown inFIGS. 5,9,23and25, the partition wall71is not present at a left upper portion (a right upper portion inFIG. 9) of the rear crankcase23corresponding to the breather chamber80. A breather chamber bottom wall76flush with the rear faying surface of the rear crankcase23is provided there. A breather partition portion77for partitioning the breather chamber80is projected forwards from the breather chamber bottom wall76. The breather partition portion77is provided with a cutout portion77aas shown inFIG. 25.

In addition, a shaft support portion76aprojected forwards from a substantially central portion of the breather chamber bottom wall76is provided with a threaded hole76b.An outer circumferential edge portion78bof a top wall78aof a breather cover78L-shaped in section shown inFIG. 5is brought into contact with an inner circumferential step portion23eof a left top wall23dof the rear crankcase23, as shown inFIG. 23. A bolt79penetrating through a hole formed at a central recessed portion78cof the top wall78aof the breather cover78is screwed into the threaded hole76bin the shaft support portion76aso that the breather chamber80is constituted of the left top wall23dof the rear crankcase23, the breather chamber bottom wall76, the breather partition portion77and a bent wall78dof the breather cover78.

Furthermore, the breather chamber bottom wall76is provided with an opening76b.As shown inFIG. 5, one end of a breather pipe81is fitted in the opening76b,and the other end of the breather pipe81is connected to an intake system of the 4-stroke-cycle internal combustion engine20through a pipe, a hose and the like which are not shown.

Furthermore, a tank partition wall82and an overflow oil passage wall83shown inFIG. 11whose tip end surfaces can make contact with the rear end surfaces of the tank partition wall73and the overflow oil passage wall74projected rearwards beyond the partition wall71of the rear crankcase23shown inFIG. 10are projected forwards at the front surface of the rear case cover24, as shown inFIG. 11.

The rear case cover24is provided with an opening24ain which the ACG54can be fitted. As shown inFIG. 12, a contact portion24bwith which the casing54bof the ACG54can make contact is formed at an outer circumferential rear surface of the opening24a.

Cylinder Block, Cylinder Head

FIG. 13is a plan view in which the rear surface of the front crankcase22and the front surface of the rear crankcase23are laid on each other. Under the condition where an opening25pof the communication hole40in the cylinder block25shown inFIG. 26coincides with openings22pand23pformed in the front crankcase22and the rear crankcase23, a cylinder bottom portion faying surface25xof the cylinder block25is laid on cylinder block faying surfaces22xand23xof the front crankcase22and the rear crankcase23. Cylinder sleeve insertion holes22rand23rare composed of semi-circular cutouts in the top walls of the front crankcase22and the rear crankcase23. A cylinder sleeve25r(seeFIG. 4) of the cylinder block25is fitted in the cylinder sleeve insertion holes22rand23r.

In addition,FIG. 29is a top view of the cylinder block25. Under the condition where an opening26pof the communication hole40in the cylinder head26shown inFIG. 30coincides with the opening25pof the communication hole40in the cylinder block25, a cylinder head bottom portion faying surface26yof the cylinder head26is laid on a cylinder head faying surface25yof the cylinder block25. Lower end screws of four bolts (not shown) penetrating through bolt holes26aand25aformed in the cylinder head26and the cylinder block25are screwed into bolt holes22qand23qrespectively formed in the front crank case22and the rear crankcase23, whereby the cylinder block25, the cylinder head26, the front crankcase22and the rear crankcase23are mutually integrally connected.

Furthermore, as shown inFIG. 3, the outer circumferential surface of the head cover27is brought into contact with the top surface of the cylinder head26, and the head cover27is integrally connected to the cylinder head26by bolts or the like which are not shown.

Lubricating Oil Circuit

Referring toFIG. 34, in this embodiment, the outline of a lubricating oil circuit through which the lubricating oil in the 4-stroke-cycle internal combustion engine20is supplied to individual portions of the power unit for a vehicle with internal combustion engine1will be described. The suction port61dof the recovery pump61is connected to the crank chamber59through the strainer85. The discharge port61eof the recovery pump61is connected to a suction port14aof the oil cooler14. A discharge port14bof the oil cooler14is connected to the ACG54, the cylinder block25and the cylinder head26and is connected to the oil tank chamber70.

The suction port62dof the supply pump62is connected to a bottom portion of the oil tank chamber70. The discharge port62eof the supply pump62is connected to the suction port65aof the oil filter64. The discharge port65bof the oil filter64is connected to the static oil hydraulic type non-stage transmission100, the 4-stroke-cycle internal combustion engine20and the starting clutch57.

Furthermore, the discharge ports61eand62eof the recovery pump61and the supply pump62are connected to the crank chamber59and the oil tank chamber70through relief valves86and87, respectively.

The crank chamber59and the oil tank chamber70are integrally constituted inside the front case cover21. The front crankcase22, the rear crankcase23and the rear case cover24are partitioned by the partition wall67of the front crankcase22into front and rear portions. In the front portion, the crank chamber59and the oil tank chamber70are partitioned into left and right portions by the tank partition wall68of the front crankcase22shown inFIG. 7and a tank partition wall89formed of the front case cover21correspondingly to the tank partition wall68. In a central portion in the front-rear direction intermediately bound between the partition wall67of the front crankcase22and the partition wall71of the rear crankcase23, the crank chamber59and the oil tank chamber70are partitioned into left and right portions by the tank partition wall69of the front crankcase22shown inFIG. 8and the tank partition wall72of the rear crankcase23shown inFIG. 9. The crank chamber59and the oil tank chamber70are partitioned by the partition wall71of the rear crankcase23into front and rear portions. At the rear portion, the crank chamber59and the oil tank chamber70are partitioned into left and right portions by the tank partition wall73shown inFIG. 10and the tank partition wall82shown inFIG. 11.

In addition, as shown inFIGS. 7 and 8, the crank chamber59at the front portion and the crank chamber59at the central portion in the front-rear direction are mutually in communication with each other through the crank chamber communication hole67gformed in the partition wall67of the front crankcase22and the strainer lower lubricating oil sump67j.As shown inFIGS. 9 and 10, the crank chamber59at the central portion in the front-rear direction and the crank chamber59at the rear portion are mutually communicated through the crank chamber communication hole71gformed in the partition wall71of the rear crankcase23and the strainer lower lubricating oil sump71j.

Furthermore, as shown inFIGS. 7 and 8, the oil tank chamber70at the front portion and the oil tank chamber70at the central portion in the front-rear direction are mutually in communication with each other through the tank communication holes67k(at four locations) formed in the partition wall67of the front crankcase22. As shown inFIGS. 9 and 10, the oil tank chamber70at the central portion in the front-rear direction and the oil tank chamber70at the rear portion are mutually in communication with each other through the tank communication holes71k(at six locations) formed in the partition wall71of the rear crankcase23.

Oil passages formed inside the front case cover21, the front crankcase22, the rear crankcase23, the rear case cover24, the cylinder block25and the cylinder head26will be described specifically, according to the lubricating oil circuit shown inFIG. 34.

As shown inFIGS. 6 and 7, the suction port61dof the recovery pump61is connected to the recovery pump suction communication hole67hof the front crankcase22. When the rotary shaft63of the lubricating oil pump60is driven to rotate, the lubricating oil dwelling in the strainer lower lubricating oil sumps67jand71jis filtered through the strainer85as shown inFIG. 9, and then flows through the communication portion71hof the rear crankcase23and the recovery pump suction communication hole67hof the front crankcase22into the suction port61dof the recovery pump61.

In addition, as shown inFIGS. 6 and 14, the discharge port61eof the recovery pump61is connected to an opening21aon the rear side of the front case cover21. The opening portion21ais in communication with a front end opening21cthrough a communication passage21bdirected forwards. The opening21cand the inflow port14aof the oil cooler14are connected to each other through a hose, a pipe and the like which are not shown so that the lubricating oil discharged from the discharge port61eof the recovery pump61is fed to the oil cooler14. As shown inFIG. 14, the branch passage21dis branched from the communication passage21b,and a relief valve86is interposed in the branch passage21d.When the lubricating oil pressure in the communication passage21breaches or exceeds a predetermined setpoint pressure, the relief valve86operates so that the lubricating oil is returned from the branch passage21dinto the crank chamber59through an opening21e.

Furthermore, the discharge port14bof the oil cooler14is connected to a return port21fof the front case cover21shown inFIG. 6through a hose, a pipe and the like which are not shown. As shown inFIG. 15, the return port21fis in communication with an opening21hthrough a communication passage21g,and to the oil tank chamber70through an orifice21i.

Furthermore, as shown inFIGS. 6 and 7, the opening21hof the front case cover21and an opening22hof the front crankcase22coincide with each other. As shown inFIG. 20, the opening22his in communication with an opening22jthrough a communication passage22i.

As shown inFIG. 13, the opening22jopened in the cylinder block faying surface22xof the front crankcase22coincides with an opening25jopened in the cylinder bottom portion faying surface25xof the cylinder block25shown inFIG. 26. As shown inFIG. 27, the opening25jis in communication with an opening25lin the cylinder head faying surface25yof the cylinder block25through a vertical communication passage25k.As shown inFIGS. 29 and 30, the opening25lin the cylinder block25coincides with a communication passage26lin the cylinder head26, and the upper end of the communication passage26lis exposed into the space surrounded by the head cover27.

As shown inFIGS. 26 and 27, the vertical communication passage25kand a vertical communication passage25nparallel thereto are mutually in communication with each other through a communication passage25mextending in the front-rear direction. The upper end opening25oof the vertical communication passage25ncoincides with an opening26oin the cylinder head26. The upper end of the opening26ois also exposed to the spacing surrounded by the head cover27.

Furthermore, the lower end opening25sof the vertical communication passage25nin the cylinder block25shown inFIG. 27is in communication with an opening23sin the rear crankcase23shown inFIG. 13. As shown inFIG. 22, the opening23sis in communication with an opening23uthrough a communication passage23t.The opening23uin the rear crankcase23is in communication with an opening24uin the rear case cover24shown inFIG. 11. As shown inFIG. 24, the opening24uis in communication with an opening24wthrough a communication passage24v,and the opening24win the rear case cover24is in communication with an ACG lubricating oil jet port (not shown) provided in a cover54b(seeFIG. 4) of the ACG54.

As has been described above, the lubricating oil fed to the oil cooler14by the recovery pump61and cooled by the oil cooler14is fed to the return port21fin the front case cover21shown inFIG. 15. The lubricating oil is then passed through the communication passage21g,is jetted into the oil tank chamber70through the orifice21i,and is allowed to dwell in the oil tank chamber70. The lubricating oil dwelling in the oil tank chamber70is sucked into the suction port62dof the supply pump62through the supply pump suction communication hole67iopened into the oil tank chamber70. The lubricating oil pressurized by the supply pump62is fed through the discharge port62eof the supply pump62to a discharge port21jin the front case cover21, as shown inFIG. 16.

The discharge port21jin the front case cover21shown inFIG. 16is connected to the inflow passage65ain the filter case65of the oil filter64. As shown inFIGS. 4 and 19, the discharge passage65bin the filter case65is connected to a center hole131ain the oil hydraulic motor rotary shaft131of the static oil hydraulic type non-stage transmission100, and is connected to a center hole68bin the crankshaft28through an orifice65cshown inFIGS. 4 and 19. As shown inFIG. 4, the center hole68bis in communication with a clutch communication hole68c.Thus, the cooled lubricating oil filtered by the oil filter64is supplied to the static oil hydraulic type non-stage transmission100and the crankshaft28.

In addition, as shown inFIG. 17, in the front case cover21, a relief valve87is interposed in a communication passage65dbetween the communication between a filter chamber in the filter case65and the crank chamber59(the left side in the figure). As shown inFIG. 18, a branch passage65eis branched from a discharge passage65bin the filter case65, a check valve88is interposed in the branch passage65e,and a lubricating oil jet port65fis formed from the branch passage65etoward the starting clutch57in the crank chamber59. When the pressure inside the filter chamber in the filter case65exceeds a predetermined value, the lubricating oil is ejected into the crank chamber59through the relief valve87. In addition, when the lubricating oil pressure inside the discharge passage65bin the filter case65exceeds a predetermined value, the lubricating oil is ejected into the crank chamber59through the check valve88. Furthermore, the lubricating oil in the discharge passage65bin the filter case65is jetted through the lubricating oil jet port65ftoward the starting clutch57.

Since the embodiment shown in the drawings is constituted as described above, when the 4-stroke-cycle internal combustion engine20is started by operating the recoil starter55in the condition where the counter gear166and the counter shaft162are connected to each other by moving the shifter167forwards, the 4-stroke-cycle internal combustion engine20is put into an operating condition. When the rotational frequency of the crankshaft28exceeds a predetermined rotational frequency, the starting clutch57is put into a connected condition, and the pump casing111of the static oil hydraulic type non-stage transmission100is driven to rotate.

The oil hydraulic motor rotary shaft131is driven to rotate at a required speed change ratio according to the magnitude of the inclination angle of the motor swash plate133of the swash plate type oil hydraulic motor130set correspondingly to the axial position of the drive member152in the speed change drive shaft controller150. The speed of the counter shaft162is reduced at a predetermined speed change ratio at the gear transmission160. The power is transmitted from the output shaft163to the front wheels3and the rear wheels4through the front and rear transmission shafts5and through the front axle6and the rear axle7, whereby the all terrain four-wheel vehicle0can be moved forwards.

In addition, as shown inFIG. 3, the angle αbetween the plane connecting the swash plate type oil hydraulic pump110of the static oil hydraulic type non-stage transmission100, the oil hydraulic motor rotary shaft131on the center line of the swash plate type oil hydraulic motor130and the speed change drive shaft151of the speed change drive shaft controller150and the center line of the cylinder bore29is as small as about 10°. In Addition, on the left side of the 4-stroke-cycle internal combustion engine20, the static oil hydraulic type non-stage transmission100and the speed change drive shaft controller150are disposed close to the 4-stroke-cycle internal combustion engine20. Therefore, the size in the width direction of the power unit for a vehicle with internal combustion engine1is small, promising a compact design, so that the mountability of the power unit on the all-terrain four-wheel vehicle0is extremely good.

Furthermore, since the speed change ratio sensor102is disposed on the left outer side of the static oil hydraulic type non-stage transmission100, the maintenance, inspection and repair of the speed change ratio sensor102can be easily carried out from the left side of the all-terrain four-wheel vehicle0.

Furthermore, the breather chamber80is located on the left upper side of the crank chamber59and is disposed on the extension line of the speed change drive shaft151of the speed change drive shaft controller150. The static oil hydraulic type non-stage transmission100is disposed on the lower side thereof. Therefore, the lubricating oil droplets scattered from the crankshaft28and the main gear165, counter gear166, shifter167, counter output gear168and gear169of the gear transmission160are shielded by the static oil hydraulic type non-stage transmission100, thereby being inhibited from reaching the left upper side of the crank chamber59. Furthermore, blow-by gas with a low oil mist mixing ratio is introduced into the breather chamber80. As a result, the breather chamber80may be small in capacity, and can be simplified in structure.

Moreover, the crankshaft28is directed in the front-rear direction of the vehicle body. Accordingly, the ACG54, the recoil starter55, the starting clutch57and the gear transmission160are arranged in the front-rear direction of the vehicle body. In cooperation with the arrangement of the static oil hydraulic type non-stage transmission100and the speed change drive shaft controller150close to the center axis of the cylinder bore29, a further reduction of the size of the power unit for a vehicle with internal combustion engine1and a further enhancement of the mountability thereof on the all-terrain four-wheel vehicle0can be obtained.

In addition, as shown inFIG. 3, the static oil hydraulic type non-stage transmission100is disposed on the left side in the space inside the crankcase composed of the front case cover21, the front crankcase22, the rear crankcase23and the rear case cover24. The oil tank chamber70is disposed on the right side in the space inside the crankcase. Therefore, it is easy to take the weight balance between the left and right sides of the power unit for a vehicle with internal combustion engine1by utilizing the weight of the static oil hydraulic type non-stage transmission100and the weight of the lubricating oil in the oil tank chamber70.

Furthermore, as shown inFIG. 6, the tank partition wall89is integrally projected from the inside wall surface of the front case cover21. As shown inFIGS. 7 and 8, the tank partition wall68and the tank partition wall69are integrally projected forwards and rearwards from the partition wall67of the front crankcase22. As shown inFIGS. 9 and 10, the tank partition wall72and the tank partition wall73are integrally projected forwards and rearwards from the partition wall71of the rear crankcase23. As shown inFIG. 11, the tank partition wall82is integrally projected rearwards from the inside wall surface of the rear case cover24. Therefore, there is no need for special component parts for constituting the oil tank chamber70, the weight and the number of working steps are reduced, and the crankcase can be reduced in weight and cost and enhanced in rigidity.

Furthermore, the oil tank chamber70is formed between the front crankcase22and the rear crankcase23by the tank partition wall69(seeFIG. 8) projected rearwards from the partition wall67of the front crankcase22and the tank partition wall72(seeFIG. 9) projected forwards from the partition wall71of the rear crankcase23. The oil tank chamber70is formed between the front case cover21and the front crankcase22by the tank partition wall89(seeFIG. 6) projected rearwards from the inside wall surface of the front case cover21and the tank partition wall68(seeFIG. 7) projected forwards from the partition wall67of the front crankcase22. The oil tank chamber70is formed between the rear crankcase23and the rear case cover24by the tank partition wall73(seeFIG. 10) projected rearwards from the partition wall71of the rear crankcase23and the tank partition wall82(seeFIG. 11) projected forwards from the inside wall surface of the rear case cover24. Therefore, the capacity of the oil tank chamber70is extremely large.

Moreover, since the front case cover21, the front crankcase22, the rear crankcase23and the rear cover case24can be die-cast or cast, a further enhancement of productivity and a further reduction in cost can be obtained.

In addition, the recovery pump61and the supply pump62are arranged coaxially. The recovery pump61feeds the lubricating oil dwelling in the strainer lower lubricating oil sumps67jand71jat bottom portions inside the crankcase to the oil tank chamber70. The supply pump62supplies the lubricating oil from the oil tank chamber70to the crankshaft28and the starting clutch57of the 4-stroke-cycle internal combustion engine20and the static oil hydraulic non-stage transmission100. Therefore, the overall size of the lubricating oil pump60composed of the recovery pump61and the supply pump62is reduced, and the lubricating oil pump60can be reduced in size and weight. Furthermore, the oil passage between the recovery pump61and the supply pump62and the oil passage between the lubricating oil pump60and the oil tank chamber70are shortened, whereby the pump loss of the lubricating oil pump60is reduced.

Furthermore, the filter case65of the oil filter64for filtering the lubricating oil to be supplied from the oil tank chamber70to the individual portions of the 4-stroke-cycle internal combustion engine20and the static oil hydraulic type non-stage transmission100is arranged at a position on the front side of the oil tank chamber70and overlapping with the oil tank chamber70as viewed in the front-rear direction of the vehicle body. Therefore, the oil tank chamber70and the oil filter64are arranged close to each other, and the lubricating oil in the oil filter64is immediately returned into the oil tank chamber70through the relief valve87interposed in the communication passage65dof the oil filter64. Accordingly, the pump loss of the supply pump62is low.

Furthermore, the oil filter64is located on the front side of the front case cover21. Therefore, as shown inFIG. 4, a cover64aof the oil filter64can be easily removed on the front side of the all-terrain four-wheel vehicle0, replacement of the filter element66can be easily carried out, and the maintenance, inspection and repair of the oil filter64can be carried out speedily and easily.

In addition, the recovery pump61performs the task of feeding the lubricating oil to the cylinder block25, the cylinder head26and the ACG54. Accordingly, the supply pump62can be reduced in size. Furthermore, the lubricating oil branched from the lubricating oil recovery oil passages21b,21c,21f,21ginto oil passages21h,22h,22i,22j,25k,25l,26lhas just been cooled in the oil cooler14. Accordingly, it is suitable for cooling and lubricating the portions having high calorific values.

As shown inFIG. 15, the lubricating oil fed to the oil cooler14by the recovery pump61and cooled by the oil cooler14flows through the return port21fof the front case cover21and the communication passage21gto reach the opening21h,and is fed from the opening22hof the front crankcase22shown inFIG. 20to the opening22jthrough the communication passage22i.As shown inFIGS. 13,26and27, the lubricating oil is fed from the opening22jof the front crankcase22to the top surface opening25lof the cylinder block25through the bottom surface opening25jand the vertical communication passage25kin the cylinder block25. Furthermore, as shown inFIGS. 29,30and31, the lubricating oil reaches the top opening26lof the cylinder head26, flows out through the top surface opening26lto the top surface of the cylinder head26, and drops from the cylinder head26back into the crank chamber59through the communication hole40, whereby the cylinder block25and the cylinder head26are cooled.

In addition, as shown inFIG. 27, the communication passage25mbranches from the vertical communication passage25k.Therefore, a part of the lubricating oil rising through the vertical communication passage25kflows through the communication passage25mto reach the vertical communication passage25n.The lubricating oil flowing in an upper portion of the vertical communication passage25nflows out through the top surface opening26oto the top surface of the cylinder head26in the same manner as the lubricating oil flowing through the top surface opening26l,and drops through the communication hole40into the crank chamber59, whereby the cylinder block25and the cylinder head26are cooled.

Furthermore, the lubricating oil flowing in a lower portion of the vertical communication passage25nflows through the bottom surface opening25sof the cylinder block25to reach the opening23sin the rear crankcase23, is fed through the communication passage23tshown inFIG. 22to the opening23u,is fed from the opening23uthrough the opening24uand the communication passage24vin the rear case cover24shown inFIG. 24to the opening24w,and is jetted through the lubricating oil jet port of the ACG54, whereby the ACG54is cooled.

Furthermore, the cooled lubricating oil sucked up from the crank chamber59to be supplied to the oil cooler14by the recovery pump61and cooled by the oil cooler14is not supplied to the oil filter64but is supplied directly to the cylinder block25and the cylinder head26. Therefore, the cylinder block25and the cylinder head26are not only cooled by the air cooling in which a cooling airflow blasted rearwards by the fan13and a running airflow attendant on the running of the vehicle are brought into contact with the cooling fins37and the cooling fins38, but are also cooled by the lubricating oil cooling in which the cooled lubricating oil passes inside the cylinder block25and the cylinder head26. As a result, the cylinder block25and the cylinder head26, and hence the portion surrounding the combustion chamber32, are cooled sufficiently.

Furthermore, the lubricating oil cooled by the oil cooler14is also supplied to the recoil starter54without passing through the oil tank chamber70, so that the recoil starter54is also cooled sufficiently.

In addition, upper end edges73aand82aof the tank partition wall73projected rearwards from the partition wall71shown inFIG. 10and the tank partition wall82projected forwards from the inside wall surface shown inFIG. 11are located on the lower side of upper end edges89aand68aof the tank partition wall89projected rearwards from the inside wall surface of the front cover case21shown inFIG. 6and the tank partition wall68projected forwards from the partition wall67of the front crankcase22shown inFIG. 7. Furthermore, the partition wall67of the front crankcase22is provided with the tank communication hole67k,and the partition wall71of the rear crankcase23is provided with the tank communication hole71k.Therefore, the oil surfaces of the lubricating oil in the oil tank70are all maintained at the same level, and the lubricating oil in the oil tank chamber70can calmly flow into the overflow oil passage75and the overflow oil passage84via the upper end edges73aand82aof the tank partition wall73and the tank partition wall82which are low in height. As a result, the lubricating oil in the crank chamber59is prevented from being stirred by the crankshaft28, whereby power loss and generation of mist of the lubricating oil are obviated. Furthermore, the lubricating oil is led into the strainer lower lubricating oil sumps67jand71jat the bottom portions of the crank chamber59smoothly and calmly, whereby generation of bubbles is also restrained.

Furthermore, as shown inFIGS. 10 and 11, the overflow oil passages75and84are constituted of the tank partition wall73, the tank partition wall82and overflow oil passage walls74and83, which are formed integrally with the rear crankcase23and the rear case cover24, respectively. Therefore, the overflow oil passages75and84are extremely simplified in structure, whereby a rise in cost can be obviated.

Furthermore, the oil tank chamber70between the rear crankcase23and the rear case cover24is formed in a crescent shape along the right side wall23aof the rear crankcase23(the right side wall of the rear case cover24is not denoted by any symbol). Therefore, the tank partition wall73, the tank partition wall82and the overflow oil passage walls74and83are also formed in similar shapes, so that the lubricating oil having flowed over partition wall upper edges73aand82aof the oil tank chamber70is led to the strainer lower lubricating oil sumps67jand71jat the bottom portions of the crank chamber59, without generating a turbulent flow.