Abstract:
A oil supply system supplies the same oil for lubricating an engine and for driving a hydrostatic infinitely variable transmission. The hydrostatic infinitely variable transmission is built into a crankcase of the engine, resulting in an overall compact configuration. A drive shaft of the hydrostatic infinitely variable transmission is provided parallel with a crankshaft of the engine. Axial centers of the drive shaft and crankshaft can be made hollow and serve as oilways. Further, an axial center of a counter shaft of the hydrostatic infinitely variable transmission can be made hollow and serve as an oilway. By the present oil supply system, engine oil is used in common as drive oil for the hydro-static infinitely variable transmission, and as oil supplied to parts of a cylinder head, a stepped transmission, and other various parts of the engine and transmission, thereby elimating the duplication of oil pumps and filters and reducing the maintanance associated with servicing independent oil systems.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a power unit having an internal combustion engine and a transmission. More particularly, the present invention concerns the lubricating system and the relationship of the lubricating system between the internal combustion engine and the transmission. 
     2. Description of the Relevant Art 
     An engine is an assembly that derives power by converting combustion energy, obtained by combusting fuel, into mechanical energy. In the case of a reciprocating engine, the engine includes a crankshaft, a primary reduction output gear provided on the crankshaft, and a crankcase covering the crankshaft and the primary reduction output gear. 
     A hydrostatic infinitely variable transmission is an assembly where a fixed capacity swash plate-type hydraulic pump and a variable capacity hydraulic motor are located on the same axis, so that an infinitely variable transmission output can be obtained by varying the swash plate of the hydraulic motor on the output side. A hydrostatic infinitely variable transmission is well known, and examples are given in Japanese Patent Publication Hei. 8-26929 and Japanese Patent No. 2696520. 
     According to the background art, a case member defines a dedicated engine crank chamber and a dedicated transmission chamber. Separate dedicated oil is used as oil for driving and engine oil for engine lubrication. In other words, a vehicle having a hydrostatic infinitely variable transmissions has an engine section and a hydrostatic infinitely variable transmission section defined as separate chambers, each having separate oil supplies. 
     The background art suffers drawbacks. The volume or size of the power unit, which includes the internal combustion engine and the hydrostatic infinitely variable transmission is relatively large and bulky. Further, the engine oil and the hydrostatic infinitely variable transmission oil have to be managed separately by an owner or service person, and replication of parts occurs in operating the two systems separately. 
     SUMMARY OF THE INVENTION 
     The present invention has as an object to provide an internal combustion engine power unit which resolves one or more of the drawbacks associated with the background art. 
     In accordance with the present invention a hydrostatic infinitely variable transmission is built-into the engine crankcase. By integrally building the hydro-static infinitely variable transmission into the engine crankcase, a dedicated chamber for housing the hydro-static infinitely variable transmission can be elimated, and the internal combustion engine power unit can be made more compact, and oil can also be used in common. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein: 
     FIG. 1 is a cross-sectional view of an internal combustion engine power unit, taken along a plane including a crankshaft and a drive shaft of a hydro-static infinitely variable transmission; 
     FIG. 2 is a side view of a four-wheeled, all-terian vehicle (ATV) which includes the power unit of FIG. 1; 
     FIG. 3 is a view of an oil system for the power unit; and 
     FIG. 4 is a cross-sectional view of the hydro-static infinitely variable transmission. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First, the overall structure of the four-wheeled buggy or ATV will be described with reference to FIG.  2 . The four-wheeled buggy is equipped with a pair of front wheels  2  and a pair of rear wheels  3  arranged at the front and rear of a vehicle frame  1 , respectively. A power unit  4  includes an integral formation of an engine and a transmission. The power unit  4  is provided at a central part of the vehicle frame  1 . The power unit  4  is transverse, with a crankshaft  5  arranged in a direction from the front to the rear of the vehicle. 
     The four-wheeled buggy is four-wheel drive. The front wheels  2  are driven by an output shaft  6 , provided parallel with the crankshaft  5  at the lower part of the power unit  4 , via a front wheel propeller shaft  7 . The rear wheels  3  are driven by the output shaft  6  via a rear wheel propeller shaft  8 . 
     A front side of a crankcase  10 , housing the power unit  4 , is covered by a front case cover  11 , and a rear side of the crankcase  10  is covered by a rear crankcase cover  12 , so as to form a power unit case. The crankcase  10  is partitioned between the front and rear into a front case  10   a  and a rear case  10   b . A cylinder block  13 , cylinder head  14  and cylinder head cover  15  are attached to an upper part of the crankcase  10 . A carbureter  16  is connected to an inlet port of the cylinder head  14 . An air cleaner  17  is connected from the rear to the carbureter  16 . An exhaust pipe  18  is connected to an exhaust outlet of the cylinder head  14 . 
     An oil cooler  20  is located to the front of the power unit  4 . The oil cooler  20  communicates with an oil pump provided at the crankcase  10  via a send-side hose  21  and communicates with an oil pump provided within the crankcase  10  via a return-side hose  22 . FIG. 2 also illustrates a cooling fan  23 , a handle  24 , a fuel tank  25 , and a saddle-type seat  26 . An oil tank  27  is directly mounted to the front surface of the front case cover  11 . The oil tank  27  is connected to the oil cooler  20  via the is connected to the oil cooler  20  via the send-side hose  21  and the return-side hose  22 . The oil tank  27  is also connected to an oil pump built into the power unit  4 . 
     The crankshaft  5  is supported by main bearings  37   a  and  37   b  at journals  36   a  and  36   b  integrally formed with the front case  10   a  and the rear case  10   b . A hydro-static infinitely variable transmission  40  is built into the crankcase  10 , comprising the engine section of the power unit  4 . Approximately one-half of the hydrostatic infinitely variable transmission  40 , in the longitudinal direction, overlaps between the main bearings  37   a  and  37   b.    
     The hydro-static infinitely variable transmission  40  includes a hydraulic pump  42  and a hydraulic motor  44 . The hydraulic pump  42  is driven by a primary driven gear  41  engaging with the primary drive gear  34 . The hydraulic motor  44  provides a gear-shifting output to the drive shaft  43 . The drive shaft  43  is provided in a direction from the front to the rear of the vehicle, parallel with the crankshaft  5 , so that its axis coincides with that of the crankshaft  5 . 
     The drive shaft  43  includes a first oilway  45  that penetrates the axial center of the drive shaft  43 . The primary drive gear  34  and the hydro-static infinitely variable transmission  40  constitute a primary reduction means. One end of the drive shaft  43  is directly connected by spline coupling to a main shaft  47  of a stepped transmission  46 . 
     A first speed drive gear  48  and a second speed drive gear  49  are integrally provided at the main shaft  47 . These gears engage with a first speed driven gear  51  and a second speed driven gear  52  rotating on a counter shaft  50 , parallel with the main shaft  47 . 
     A reverse driven gear  53  is also provided in a freely rotating manner on the counter shaft  50 . The reverse driven gear  53  is rotated in an opposite direction to the first speed driven gear  51  and the second speed driven gear  52  by an engagement of a reverse idle gear, provided on a separate shaft, and engaging with the first speed drive gear  48 . 
     Shifters  54  and  55  are spline-coupled to the counter shaft  50  in such a manner as to be movable in an axial direction. When the shifter  54  is moved to the left in FIG. 1, rotation of the first speed driven gear  51  is transmitted from an end of the counter shaft  50  to a final drive gear  56 , integrally formed with the counter shaft  50 . This rotation is then transmitted to an output shaft  6 , via a final driven gear  57  on the output shaft  6  engaging with the final drive gear  56 . 
     When the shifter  55  is moved to the left, rotation of the second speed driven gear  52  is similarly transmitted to the output shaft  6 , so as to provide second speed driving. When the shifter  54  is moved to the right, rotation of the reverse driven gear  53  is transmitted to the counter shaft  50 , so that the counter shaft  50  is rotated in reverse, so as to rotate the output axis in reverse and provide reverse driving. The stepped transmission  46 , final drive gear  56  and final driven gear  57  constitute a secondary reduction means. 
     A second oilway  58  communicates with the first oilway  45  of the drive shaft  43 . The second oilway  58  is formed through the axial center of the main shaft  47 . A similar, third oilway  59  is formed at the axial center of the counter shaft  50 . However, the inner side of the third oilway  59  is closed and an open end on the outer side faces a fourth oilway  60  formed within the wall thickness of the rear crankcase cover  12 , so that oil that has passed through the main shaft  47  is supplied. 
     The ACG  35  and a valve mechanism of the cylinder head  14  are lubricated by a fifth oilway provided in the rear crankcase cover  12  provided separately from the fourth oilway  60 . A sixth oilway  62  is also formed at the axial center of the crankshaft  5  so that oil is supplied from a seventh oilway  61  provided at the front case cover  11  and the bearing parts of the starting clutch  33  and the crankshaft  5  are lubricated. 
     FIG. 3 shows the oil system, with an oil pump  63  including one feed pump  64  and two scavenging pumps, i.e., a main scavenging pump  65  and a sub-scavenging pump  66 . 
     The feed pump  64  takes in oil from an oil filter  27 , discharges oil to an oil filter  67 , and supplies oil to the first oilway  45  formed in the drive shaft  43  of the hydro-static infinitely variable transmission  40  and the sixth oilway  62  of the crankshaft  5 . 
     Part of the oil supplied to the first oilway  45  functions as drive oil and lubricating oil for the hydro-static infinitely variable transmission  40 . With regards to the remaining oil, the first oilway  45  acts as a passage for lubricating other portions or parts of the engine, e.g., lubricating the secondary declerating means of the ACG  35 , the valve mechanism of the valves  30  in the cylinder head  14 , the stepped transmission  46 . 
     Oil supplied to the seventh oilway  61  lubricates the crankshaft  5  and the starting clutch  33 . A discharge passage of the feed pump  64  communicates with a relief passage  68   a  via a relief valve  68  so that excess pressure is relieved via the relief passage  68   a  when discharge pressure exceeds a prescribed value. 
     The main scavenging pump  65  and the sub-scavenging pump  66  suck up oil collected in mutually separated oil sumps  65   a  and  66   a  constituted by the bottom of the crankcase  10  itself or by an oil pan. Collected oil is discharged to a discharge passage  69 , and is then sent from the return-side hose  21  to the oil cooler  20 , together with oil from the relief passage  68   a.    
     Next, a description is given of the structure of the hydro-static infinitely variable transmission  40  using FIG.  4 . The hydraulic pump  42  constituting part of the hydro-static infinitely variable transmission  40  and each of the housings  70  and  71  of the hydraulic motor  44  are formed integrally as parts of the front case cover  11  and the front case  10   a , with the ends of the drive shaft  43  being supported in a freely rotatable manner via bearings  72  and  73 . 
     The hydraulic pump  42  is such that an input side rotating section  74  rotating integrally with the primary driven gear  41  is supported in a freely rotating manner at the drive shaft  43  via the bearing  75 , inside which a fixed swash plate  76  inclined to the axial direction of the drive shaft  43  is supported in a freely rotating manner via bearings  77  and  78 . 
     A plurality of pump-side plungers  78 , the tips of which come into contact with the fixed swash plate  76 , move reciprocally with respect to the pump cylinder  79  within pump plunger holes  80  located in an annular manner about the drive shaft  43  so that oil intake and discharge strokes are performed. The outer periphery of the pump cylinder  79  is supported via a bearing  81  so as to be rotatable relative to the input side rotating section  74 . 
     On the other hand, at the hydraulic motor  44 , a substantially bowl-shaped swash plate holder  83  is supported in a freely rotatable manner within a concavely curved surface section  82  formed at the housing  71  and a moveable swash plate  86  is freely supported via bearings  84  and  85  at this concavely curved surface. 
     At the surface of the variable swash plate  86 , the same number of motor side plungers  87  as pump side plungers  78  also move reciprocally within motor plunger holes  89  arrayed annularly about the axis of a motor cylinder  88  provided on the axis of the drive shaft  43  so that an extrusion stroke and a back stroke are carried out. 
     The motor side plungers  87  are made to project due to the pressure of oil discharged by the pump side plungers  78  and press against the surface of the variable swash plate  86 . As a result, the motor cylinder  88  is caused to rotate, and an input from the primary driven gear  41  is provided as a gear change output to the drive shaft  43  due to the inner surface of the motor cylinder  88  being spline coupled with the outer periphery of the drive shaft  43 . 
     The transmission gear ratio can be adjusted by changing the inclination of the movable swash plate  86 , which can be freely changed by rotating the swash plate holder  83 . The outer periphary of the motor cylinder  88  is supported in a freely rotatable manner at the housing  71  via a bearing  90 . 
     The pump cylinders  79  and the motor cylinders  88  are formed integrally at a central large diameter section  91  with pump side valves  92  advancing in the direction of emission and motor side valves  93  being lined up annuarly in two rows and are provided in the same number as the pump side plungers  78  and the motor side plungers  87 . 
     Each of the pump side valves  92  and the motor side valves  93  open and close communicating sections of inner passages  94  and outer passages  95  formed in concentric circles at the inner side of the large diameter section  91  and communicating sections of pump plunger holes  80  and motor plunger holes  89 , i.e., during the intake stroke of the pump side plungers  78 , the pump side valves  92  open the passages between the pump plunger holes  80  and the inner passages  94  and close the passages between the outer passages  95 , while the discharge stroke is the opposite. Similarly, during the extrusion stoke of the motor side plunger  87 , the motor side valves  93  open passages between the motor plunger holes  89  and the outer passages  95  and close passages between the inner passages  94 , while the reverse is the case for the back stroke. 
     Next, the operation of this embodiment is described. With this internal combustion engine power unit  4 , the hydro-static infinitely variable transmission  40  is built into the crankcase  10  constituting an engine part. A dedicated case for the hydro-static infinitely variable transmission  40 , formerly provided separately from the engine, can therefore be omitted for the hydro-static infinitely variable transmission  40 . Therefore, the internal combustion engine power unit can be made more compact. 
     The drive shaft  43  of the hydro-static infinitely variable transmission  40  is parallel with the crankshaft  5 , and partially overlaps with the main bearings  37   a  and  37   b  that bear the crankshaft  5 . Therefore, the overall length of the engine can be made shorter, in the direction of the crankshaft  5 . 
     The first oilway  45  of the drive shaft  43  is also no longer simply dedicated to the hydro-static infinitely variable transmission  40 , but rather is an oilway utilized for lubricating parts of the engine, such as the ACG  35 , the cylinder head  14 , and the stepped transmission  46 . The piping structure can therefore be simplified, and the internal combustion engine power unit  4  can be made more compact. 
     Further, drive oil for the hydro-static infinitely variable transmission  40  and engine oil for lubricating each of the parts of the engine are used in common. It is therefore not necessary to provide separate oil supply structures, and the structure can therefore be made simpler and more compact. It is also no longer necessary to manage a number of oils and oil management is simplified. 
     The present invention is by no means limited to the aforementioned embodiment and various modifications are possible. For example, the drive oil of the hydro-static infinitely variable transmission  40  can be used to lubricate parts of the engine, or transmission oil may also be used. Further, rather than using the first oilway  45  to lubricate parts of the engine, oil for lubricating parts of the engine can be supplied by a separate path. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.