Patent Publication Number: US-6659051-B2

Title: Oil-cooled engine assembly

Description:
FIELD OF THE INVENTION 
     The present invention relates to an oil-cooled engine assembly in which after lubricating movable parts of an engine, a lubricating oil is cooled and then returned to circulation for cooling the movable parts again. 
     BACKGROUND OF THE INVENTION 
     In an engine, rotating parts such as a crank shaft and bearings of a connecting rod and sliding parts (hereinafter referred to as movable parts) operate at a high temperature due to friction. The movable parts, which remain at a high temperature, are cooled by lubrication with a lubricating oil. Cooling of the lubricating oil after lubrication may be performed by connecting a lubrication line, which includes an oil cooler and an oil tank, to the engine for circulating the lubricating oil. However, there is a need for a space to locate the oil cooler and the oil tank. In order to achieve miniaturization of a whole structure of the oil-cooled engine assembly including the lubrication line, there is yet room for structural improvement. 
     The engine assembly, which is arranged to reduce an occupying space of the oil tank, has been proposed in, for example, Japanese Patent Publication No. SHO-63-67077 entitled “Engine Mounting Assembly” and Japanese Patent Laid-Open Publication No. HEI-3-67011 entitled “Oil Supply Structure For Engine”. 
     The engine assembly disclosed in Japanese Patent Publication No. SHO-63-67077 is comprised of a mounting base, made of a steel tube which supports the engine, in which the oil tank is formed to be filled with a lubricating oil which is circulated with a first engine-drive pump driven with the engine. That is, the mounting base also plays the oil tank role. 
     However, the mounting base of the engine assembly forms a member for supporting the engine, causing a restriction in size by itself. Accordingly, a limitation arises in freely determining a capacity for which the oil tank occupies. The presence of the mounting base made from steel tube seems to have more or less effect for dissipating heat of lubricating oil in the oil tank. But, the presence of restriction in the size of the mounting base encounters the limitation in enhancing an adequate heat dissipating area. 
     The engine assembly disclosed in Japanese Patent Laid-Open Publication No. HEI-3-67011 has a structure wherein a cylinder block of the engine is formed with an oil tank at an outer periphery of a water jacket to contain the oil tank within the cylinder block. Lubricating oil is cooled with coolant water in the water jacket. 
     However, a functional restriction is encountered in the engine in terms of a shape and a dimension of the cylinder block in the engine assembly. The presence of the oil tank contained in such a cylinder block undergoes a limitation in enhancing an adequate capacity for the oil tank and an adequate heat dissipating area for the oil cooler. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an engine assembly which enables a capacity for storing a lubricating oil and a heat dissipating area for cooling lubricating oil to be adequately obtained while achieving the miniaturization of the oil-cooled engine assembly per se. 
     According to an aspect of the present invention, there is provided an oil-cooled engine assembly which comprises: an engine; a lubricating oil pump disposed internally of the engine; and a hollow frame body which surrounds the engine and engine accessories including a carburetor and a muffler, supports the engine, and is internally formed with an oil passage through which lubricating oil flows. The lubricating oil pump is connected to the oil passage to allow the lubricating oil, which has lubricated movable parts of the engine, to be air cooled with the frame body. The cooled lubricating oil is subsequently recirculated to the movable parts of the engine. 
     Since the frame body, which supports the engine, is arranged to surround the engine and the engine accessories, the frame body has an increased total length. The adoption of the hollow frame body allows the frame body to serve as the oil passage through which lubricating oil flows to be air cooled. The increased total length of the frame body results in an increase in a heat dissipating area. Thus, the frame body provides an increased heat dissipating effect. In such a manner, the frame body, which supports the engine, also plays a role as the oil tank and oil cooler, resulting in no need for separately providing the oil cooler and the oil tank to achieve a miniaturization of the whole structure of the engine assembly. In addition, the engine is ranged to incorporate therein the lubricating oil pump. This precludes the lubricating oil pump from protruding from the engine. 
     Desirably, the carburetor is located at one side of the engine and the aforementioned muffler is located at the other side of the engine. It is desired that a lubricating oil supply conduit is additionally provided for supplying lubricating oil from the frame body component, in the vicinity of the crank chamber of the engine to the lubricating oil pump. Lubricating oil, which is cooled with the frame body, is supplied from the frame body component, which is close proximity to the crank chamber remaining at a lower temperature than the frame body component closer to the muffler, to the lubricating pump. The presence of the lubricating oil return conduit connected to the frame body at a point remote from the high temperature muffler provides no fear of lubricating oil being exposed to a high temperature. 
     In a preferred form, the frame body is covered with the plurality of cover plates having heat dissipating properties, one of which has an air intake port to allow the cooling fan, which draws outside air from the air intake port, to be mounted to the crank shaft. The plurality of cover plates to be mounted to the frame body serves as respective heat discharging plates. Thermal heat produced by the frame body is dissipated via the plurality of cover plates. Since the plurality of cover plates surround a periphery of the frame body, an increased heat dissipating area is obtained. This results in an increase in cooling efficiency for cooling lubricating oil. Also, inner surfaces of the plurality of cover plates and the surface of the frame body covered with the plurality of cover plates are cooled with outside air drawn by the cooling fan. Thus, the heat dissipating performance of the frame body is further improved. In addition, the presence of the plurality of cover plates to cover the frame body allows the engine and the engine accessories to be concealed, resulting in a reduction in engine noise. 
     In the engine assembly of the present invention, the power output shaft is detachably connected to the crank shaft of the engine and is rotatably supported with either one of the frame body and the cover plates. It is possible for the power output shaft to be altered according to a kind of load to be driven with the engine. Consequently, there is no need for the crank shaft to be altered in accordance with the load. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of an oil-cooled engine assembly according to the present invention; 
     FIG. 2 is a horizontal cross-sectional view of the oil-cooled engine assembly shown in FIG. 1; 
     FIG. 3 is a side cross-sectional view of the oil-cooled engine assembly as viewed in the direction of arrow  3  of FIG. 1; 
     FIG. 4 is a perspective view illustrating a relationship between an engine and a frame body shown in FIG. 1; 
     FIG. 5 is an enlarged cross-sectional view of a bleeder shown in FIG. 4; 
     FIGS. 6A and 6B are schematic views illustration an operation of a lubricating oil supply system according to the present invention; and 
     FIGS. 7A and 7B are perspective views illustrating first and second modified forms of the frame body and the cover plates shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, an oil-cooled engine assembly  10  is constructed of a hollow frame body  70  which surrounds an engine  11  and engine accessories (a carburetor  51  and a muffler  52 , etc.) and which supports the engine  11 . A circumferential periphery of the hollow frame body  70  has a plurality of cover plates  76 A to  76 F, which conceal the frame body  70 . 
     The engine  11  includes a cylinder block  13  which is located in a horizontal direction and has one side (as viewed left side) located with a carburetor  51  and the other side (as viewed right side) located with the muffler  52 . 
     The frame body  70  includes upwardly opening U-shaped frame components  73 ,  73 , formed by two upright portions  72 ,  72  extending upward from both longitudinal ends of respective horizontal portions  71 ,  71 , which are located at both left and right sides of the engine  11 . Among the left and right frame components  73 ,  73 , one pair of the upright portions  72 ,  72 , which stand upright in one opposed relationship, and the other pair of the upright portions  72 ,  72 , which stands upright in another opposed relationship, are mutually connected at their upper distal ends to one another by means of horizontal connecting portions (a first connecting portion  74  and a second connecting portion  75 ), respectively, which are made of rectangular or round pipe materials. 
     The frame body  70  and the plurality of cover plates  76 A to  76 F are made of materials having an excellent thermal conductivity to provide a heat dissipating property, such as, for example, aluminum or aluminum alloy. 
     The first and second connecting portions  74 ,  75  carry thereon a cover plate  76 E, which covers an upper area of the frame body  70  and supports a fuel tank  81 . 
     Also, among the plurality of cover plates  76 A to  76 F, the left and right side cover plates  76 A,  76 C are unitarily shaped to form one set, and the fore and aft side cover plates  76 B,  76 D and the ceiling cover plate  76 E are unitarily shaped to form another one set, with two sets of the cover plates being assembled to surround the frame body  70 . 
     FIG. 2 is a horizontal cross sectional view of the oil-cooled engine assembly shown in FIG.  1 . 
     The engine  11 , shown in FIG. 2, is a general-purpose engine of a four-cycle single cylinder adopting OHC (overhead cam) type and is of a high speed engine with a crank shaft  19  which is preselected to rotate at 12,000 rpm. In particular, the engine  11  is constructed of a main structure including a crank case  12 , the cylinder block  13 , a head cover  17 , the crank shaft  19 , a connecting rod  21 , a piston  22 , a power transmission mechanism  30  and a valve actuating mechanism  40 . 
     The crank case  12  is coupled to the cylinder block  13  by bolts. The cylinder block  13  is internally formed with a cylinder  14  and a distal end of the cylinder block  13  is integrally formed with a cylinder head  15 . A combustion chamber  16  is formed between a distal end of the cylinder  14  and the cylinder head  15 . 
     The crank shaft  19  is connected through the connecting rod  21  to the piston  22  which is slidably received in the cylinder  14  for reciprocating movement. 
     FIG. 2 illustrates a valve actuating chamber  18  which is formed with the cylinder head  15  and the head cover  17  by coupling a distal end of the cylinder head  15  to the head cover  17  by bolts and which accommodates therein the valve actuating mechanism  40 . 
     The power transmission mechanism  30  includes a drive pulley  31  mounted to the crank shaft  19  in the crank case  12 , a driven pulley  33  mounted to a cam shaft  32 , and a timing belt  34  streched across the drive pulley  31  and the driven pulley  33 . Since a space defined between the crank case  12  and the cylinder block  13  contains the power transmission mechanism  30 , the power transmission mechanism  30  can be minimized in structure. 
     A cooling fan  53  is mounted to one end of the crank shaft  19 . Among the plurality of cover plates  76 A to  76 F, an air intake port  76   a  is formed at a position facing an air intake side of the cooling fan  53  to allow outside air to be drawn through the air intake port  76   a  by means of the cooling fan  53 . The outside air, which is drawn, flows through paths along internal surfaces of the plurality of cover plates  76 A to  76 F and the frame body  70  concealed with the plurality of cover plates  76 A to  76 F and is discharged to the atmosphere through an exhaust port  76   b  formed near the side of the muffler  52 . In such a manner, the internal surfaces of the plurality of cover plates  76 A to  76 F and a surface of the frame body  70  concealed with the cover plates  76 A to  76 F are cooled with outside air drawn by the cooling fan  53 . Consequently, it is possible for the plurality of cover plates  76 A to  76 F and the frame body  70  to be cooled at an increased efficiency. 
     Further, since the exhaust gas outlet  52   a  of the muffler  52  is located at a position where the exhaust port  76   b  is located, engine exhaust gases emitted from the muffler  52  are combined with a stream of the outside air drawn by the cooling fan  53  to be discharged the outside of the plurality of cover plates  76 A to  76 F. 
     The presence of the frame body with its circumferential periphery mounted with the plurality of cover plates  76 A to  76 F having the respective heat dissipating properties, that is, the presence of the frame body concealed with the plurality of cover plates  76 A to  76 F, enables heat dissipated from the frame body  70  to be discharged via the plurality of cover plates  76 A to  76 F. Since the plurality of cover plates  76 A to  76 F conceals the circumferential periphery of the frame body  70 , the heat dissipating effective surface area is extremely increased. Thus, the plurality of cover plates  76 A to  76 F having the large heat dissipating surface areas provide an increased heat dissipating effect. Accordingly, it is possible for a cooling efficiency for cooling lubricating oil to be highly improved. 
     In addition, covering the frame body  70  with the plurality of cover plates  76 A to  76 F enables the engine  11  and the engine accessories (the carburetor  51  and the muffler  52 , etc.) to be concealed. Accordingly, engine noise can be eliminated. 
     The other end of the crank shaft  19  is detachably coupled through a displacement absorbing coupling  55 , which is called a float coupling, and a reduction gear mechanism  61  to a power output shaft  62 . The displacement absorbing coupling  55  is composed of a combined structure including a first coupling member  56  connected to the crank shaft  19 , and a second coupling member  58  connected to the first coupling member  56  via a plurality of resilient members  57 . Such a displacement absorbing coupling is a well known coupling as disclosed in, for example, Japanese Patent Provisional Publication No. 6-26550 entitled “Vibration-Proof Engine Bed”. 
     The provision of the displacement absorbing coupling  55  allows vibrations of the engine  11  to be absorbed with the plurality of resilient members  57  for precluding vibrations from being transferred to the gear reduction unit  61  and the power output shaft  62 . Thus, the gear reduction mechanism  61  is precluded to generate noises due to vibrations of the engine  11 , while precluding vibrations of the engine  11  from being transferred to load via the power output shaft  62 . 
     The gear reduction mechanism  61  serves to reduce the rotational speed of the crank shaft  19  to a desired rotating speed at which the power output shaft  62  is rotated and is composed of a gear type reduction mechanism including an intermediate shaft  63  coupled to the second coupling member  58 , a drive gear  64  formed at the intermediate shaft  63 , a driven gear  65  formed on the power output shaft  62  to mesh with the drive gear  64 , and a gear case  66  which accommodates therein the drive gear  64  and the driven gear  65 . The gear case  66  is mounted to the frame body  70  by fixedly securing the gear case  66  to the cover plate  76 C such that the power output shaft  62  is rotatably supported. 
     Removing the gear case  66  from the cover plate  76 C enables the gear reduction mechanism  61  to be removed from the crank shaft  19 . Also, disassembling the gear case  66  enables the power output shaft  62  to be removed from the gear reduction mechanism  61 . In such a manner, it is possible for the power output shaft  62  to be rotatably supported with the frame body  70  or the cover plate  76 C. 
     The presence of the power output shaft  62  detachably connected to the crank shaft  19  and rotatably supported with the frame body  70  or the cover plate  76 C enables the power output shaft  62  to be altered according to a kind of loads which the engine  11  drives. Accordingly, there is no need for the crank shaft  19  to be altered in dependence on the load, with a resultant increase in the productivity of the crank shaft  19  with an increased favorable effect in distribution, assembly and manufacturing cost. 
     As shown in FIG. 2, forming surfaces of the crank case  12  and the cylinder block  13  in a spherical shape enables a sound radiated in the engine  11  to be eliminated. 
     The cooling fan  53  and the first coupling member  56 , which are located outside the crank case  12 , may play a counter-weight role of the crank shaft  19 . Also, the crank shaft  19  is hollowed. Thus, the crank shaft  19  may be reduced in weight. 
     FIG. 3 is a side cross sectional view of the oil-cooled engine assembly according to the present invention and shows the cross-sectional structure of the oil-cooled engine assembly  10  as viewed in a direction of an arrow  3  in FIG.  1 . 
     The cylinder block  13  has the cylinder head  15  formed with an air intake port  23  and an exhaust port  24 . 
     The valve actuating mechanism  40  is constructed of major component parts including a cam shaft  32 , an intake-valve rocker arm  41  and an intake valve  42 , an exhaust-valve rocker arm  43  and an exhaust valve  44 . Mounting angles of the intake valve  42  and the exhaust valve  44 , which extend toward the combustion chamber  16 , are designed to have relatively small angles. Accordingly, a single piece of cam  45  suffices to be mounted to a cam shaft  35 . Thus, it is possible for the valve actuating mechanism  40  to obtain a low noise and miniaturization with light weight. 
     FIG. 3 shows a structure wherein a lower part of the crank case  12  and a lower part of the cylinder head  15  of the engine  11  are mounted to the frame body  70  via vibration-free rubbers  82 ,  82  (by a rubber-mount) and a lower part of the frame body  70  is fixed to a mount base  83  by bolts, if desired. 
     Thus, the presence of the engine support structure formed with a vibration-free support structure using the rubber mount and the presence of the power output shaft  62  connected to the crank shaft  19  via the displacement absorbing coupling  55  as seen in FIG. 2 interrupt noise and vibration, resulting in the engine assembly  10  with low noise and low vibration. Especially, the engine  11  is of the high speed type and may produce vibration at a relatively high frequency. It is relatively easy for interrupting high frequency vibration with the rubber mount and the displacement absorbing coupling  55 . Consequently, such a vibration-free support structure is highly effective in a noise and vibration interrupting performance. 
     As now apparent from the foregoing description that, as shown in FIGS. 2 and 3, a miniaturization and low noise of the engine  11  can be realized by: (1) the presence of spherical shape, formed in the crank case  12  and the cylinder block  13 , which eliminates radiated sound; (2) the presence of the cylinder head  15  unitarily formed at the distal ends of the cylinder block; (3) the presence of the cooling fan  53  and the first coupling member  56 , located outside the crank case  12 , which play the counter-weight roll; (4) the presence of the crank shaft  19  which is hollowed; (5) the presence of the power transmission mechanism  30  and the valve actuating mechanism  40  with low noise and the miniaturization with low weight; and (6) the presence of the engine support structure and the displacement absorbing coupling  55  which interrupt engine noise and vibration. 
     FIG. 4 is a perspective view of a major part of the oil-cooled engine assembly according to the present invention, and illustrates a lubricating oil circulation system  90  of the engine  11  and the frame body  70 . 
     The lubricating oil circulation system  90  is arranged to cool lubricating oil, which has lubricated movable parts of the engine  11 , and circulate lubricating oil again to the movable parts. In particular, the lubricating oil circulation system  90  features the provision of a lubricating oil pump  91  contained in the engine  11  and an oil passage  92 , formed inside the frame body  70  to pass lubricating oil O, which is connected to the lubricating oil pump  91 , whereby lubricating oil O, cooled with air at the frame body  70 , is circulated to the movable parts of the engine. The lubricating oil circulation system  90  is described below in detail. 
     The frame body  70  includes frame components  73 ,  73  and the first and second connecting portions  74 ,  75  which are internally and entirely communicated with one another to form the oil passage  92  through which lubricating oil O flows. 
     An upper surface of a longitudinal intermediate portion of the second connecting portion  75  is mounted with a bleeder  93 . 
     The lubricating oil circulation system  90  includes a lubricating oil supply conduit  95  for supplying lubricating oil O, remaining in the frame body  70  in the vicinity of the crank chamber  25  of the engine  11 , to the lubricating oil pump  91 , and a lubricating oil return conduit  96  through which lubricating oil O is returned from the movable parts of the engine  11  to the frame body  70  at a side closer to the carburetor  51  (see FIG.  2 ). 
     Lubricating oil O, which is cooled with the frame body  70 , is supplied from the frame body  70  at a side in the vicinity of the crank chamber  25 , which remains at a lower temperature than that of the side of the frame body  70  closer to the muffler  52  (see FIG.  2 ), to the lubricating pump  91 . Upon lubrication of the movable parts of the engine, lubricating oil O is returned to the side of the frame body  70  at the side thereof closer to the carburetor  51  which remains at the lower temperature than the side of the frame body  70  closer to the muffler  52 . In such a manner, a circulation line of lubricating oil O is separate from the high temperature muffler  52 , providing no fear that lubricating oil O is heated with heat of the muffler  52 . Accordingly, a cooling efficiency for the movable parts of the engine is highly improved. 
     More particularly, plumbing is carried out in two methods (1) and (2). 
     (1) The lubricating oil supply conduit  95  is so connected as to as to supply lubricating oil O from a longitudinal intermediate portion of the first connecting portion  74  to the cylinder block  13 , i.e., to the lubricating pump  91  contained in the engine  11 . 
     (2) The lubricating oil return conduit  96  is so connected as to return lubricating oil O from the valve actuating chamber  18  to the longitudinal intermediate portion of the second connecting portion  75 . 
     FIG. 5 is a cross sectional view of the bleeder according to the present invention. 
     The bleeder  93  includes a bleeder pipe  93   b  which extends upright from the second connecting portion  75  and has an upper circumferential periphery formed with threads  93   a , a cap  93   c  screwed into the threads  93   a  to close an upper opening of the bleeder pipe  93   b , a partition member  93   d  which divides an upper end of the bleeder pipe  93   b  and an inside of the cap  93   c , a space area  93   e  formed between the inside of the cap  93   c  and the partition member  93   d , a filter  93   f  filled in the space area  93   e , and a communication recess  93   g  formed at an inner circumferential periphery of the cap  93   c  to communicate with the space area  93   e  and the atmosphere. 
     The partition member  93   d  is composed of a packing having a communication aperture  93   h  which communicates with the bleeder pipe  93   b  and the space area  93   e  via the filter  93   f . The filter  93   f  serves to separate lubricating oil mist from air and interrupt the entry of dusts from outside and is composed of, for example, a sponge. 
     Such a bleeder  93  includes an air-liquid separator  94  located in the bleeder pipe  93   b . The air-liquid separator  94  serves to separate lubricating oil mist into oil droplets and of lubricating oil and air to allow lubricating oil to return to the second connecting portion  75  while discharging only air to the atmosphere. 
     Lubricating oil mist contained in the second connecting portion  75  is thus separated into oil mist of lubricating oil and air. Oil droplet thus separated falls into the second connecting portion  75 . Separated air is discharged to the atmosphere along a path including the communication aperture  93   h  the filter  93   f  the space area  93   e  the communication recess  93   g.    
     FIGS. 6A and 6B are operational views illustrating how lubricating oil is circulated in accordance with the present invention. 
     In FIG. 6A, the frame body  70  is filled at upper areas of the first and second connecting portions  74 ,  75  with lubricating oil O to serve as an oil tank. 
     The lubricating oil supply conduit  95  is made of a pipe or a hose whose one end is inserted inside the first connecting pipe  74  and is put into lubricating oil O to perform liquid seal and the other end is connected to a supply port  97  of the cylinder block  13 . 
     The lubricating oil return conduit  96  is made of a pipe or a hose whose one end is connected to a discharge port  98  of the valve actuating chamber  18  and the other end is connected to an inside of the second connecting portion  75 . Such a lubricating oil return conduit  96  includes a check valve (one-way valve)  99 . The check valve  99  is opened only when the pressure in the valve actuating chamber  18  exceeds beyond a given level which is preliminarily determined. 
     Also, a bleeder  101 , shown by a phantom line, is preferably mounted at the upper surface of the first connecting portion  74  to provide a communication between the oil passage  92  and the atmosphere. In addition, the lubricating oil supply pipe  95  may further be preferably located with a check valve  102  which is arranged to open only when intake pressure in the crank chamber  25  decreases below a given level which is preliminarily determined. 
     The engine  11  has the crank chamber  25 , formed with the crank case  12  and the cylinder block  13 , which accommodates therein the crank shaft  19  and communicates with the valve actuating chamber  18 . Since the engine  11  is of the four-cycle type, the piston  22  moves toward right, i.e., in an upward stroke as seen in FIG. 6A during a compression stroke and an exhaust stroke and moves toward left as seen in FIG. 6B, i.e., in a downward stroke during an intake stroke and an explosion stroke. 
     As viewed in FIG. 6A, the upward movement of the piston  22  causes the pressure in the valve actuating chamber  18  and the crank chamber  25  to become negative pressure. As a result, lubricating oil O in the first connecting member  74  is sucked through the lubricating oil supply conduit  95  into the crank chamber  25  to be injected thereto. Injected lubricating oil O hits an internal wall of the crank chamber  25  to be atomized to form mist. With such lubricating oil mist, lubrication is carried out in the movable parts (the crank shaft  19 , the connecting rod  21 , the piston  22  and various movable parts of the power transmission mechanism  30  and the valve actuating mechanism  40  shown in FIG. 2) of the engine  11 . When this occurs, further, the check valve  99  remains unopened. 
     As viewed in FIG. 6B, the downward movement of the piston  22  causes the pressure in the valve actuating chamber  18  and the crank chamber  25  to be increased. This results in interruption of the sucking operation of lubricating oil O that would occur from the first connecting portion  74  to the crank chamber  25 . On the other hand, since the pressure in the crank chamber  25  exceeds the predetermined pressure level, the check valve  99  is opened. As a consequence, lubricating oil mist in the valve actuating chamber  18  and the crank chamber  25  is returned through the lubricating oil return conduit  96  to the second connecting portion  75 . Lubricating oil mist, thus returned, is then separated with the air-liquid separator  94  into lubricating oil droplets and air, with only lubricating oil being stored in the frame body  70 . The presence of the oil passage  92  formed inside the frame body  70  to flow lubricating oil O allows lubricating oil O to be cooled with air. Thus, the frame body  70  plays a role as an oil cooler. 
     As apparent from the foregoing description, since the engine  11  plays a role to circulate lubricating oil in the frame body  70  by pumping operation, it is said that the engine  11  has a structure containing the lubricating pump  91 . The presence of the lubricating oil  91  contained in the engine  11  preclude the lubricating pump  91  from protruding from the engine  11 . 
     Further, the presence of the frame body  70 , which supports the engine  11 , arranged to surround the engine  11  and the engine accessories  51 ,  52  (see FIG. 1) allows the frame body  70  to have an increased total length. Since the hollow frame body  70  is adopted, the frame body  70  is used as the oil passage  92  through which lubricating oil O flows, thereby enabling lubricating oil O to be cooled with air. The presence of the increased total length of the frame body  70  provides an increased heat dissipating surface area. This results in an increased heat dissipating effect. Thus, the frame body  70 , which supports the engine  11 , plays a role as the oil cooler. 
     Further, the presence of flow of lubricating oil through the oil passage  92  in the frame body  70  allows the frame body  70  to serve as the oil tank which stores lubricating oil O. Since the frame body has the increased total length, the frame body  70  has a large capacity for storing lubricating oil. 
     Accordingly, there is no need for additionally providing the oil cooler and the oil tank, with a resultant miniaturization in the overall structure of the oil-cooled engine assembly  10 . 
     FIGS. 7A and 7B show modified forms of the frame body and the cover plates in accordance with the present invention. 
     FIG. 7A illustrates a frame body  111  of a first modified form. The frame body  111  of the first modified form is a U-shaped hollow frame, as viewed from a side, having a plurality of oil passages  112  located in a given pitch, and is made of extrusion material of aluminum alloy. A circumferential periphery of the frame body  111  is covered with a plurality of cover plates  113 . Such a frame body  111  is enabled to cover the engine  11  and the engine accessories  51 ,  52  shown in FIG.  1  and to support the engine  11 . In addition, an inner part of the frame body  111  is formed with the plurality of oil passages  112  through which lubricating oil O flows, rendering the plurality of oil passages  112  to serve as the oil cooler and the oil tank. 
     FIG. 7B shows a frame body  121  of a second modified form. The frame body  121  of the second modified form is composed of a structure including a plurality of reversed U-shaped hollow frame sections  122  with respective lower ends joined to a flat-shaped tank  123 , with peripheries of the hollow frame sections  122  being covered with a plurality of cover plates  124 . Such a frame body  121  is enabled to surround the engine  11  and the engine accessories  51 ,  52  and to support the engine  11 . In addition, inner parts of the plurality of hollow frame sections  122  are formed with oil passages, respectively, through which lubricating oil flows, with the oil passages being in communication with the tank  123 . Thus, the oil passages and the oil tank  123  are rendered to serve as the oil cooler and the oil tank. 
     In the aforementioned preferred embodiments of the present invention, the frame body  70  may be composed of hollow members and takes arbitrary cross sectional shapes, materials and dimensions in structure. 
     The lubricating pump  91  may be of any structure which is contained in the engine  11 , and is not intended to be limited to a particular structure of the type having the pumping function. For example, the lubricating pump  91  may be composed of an independent pump which is driven with the crank shaft. 
     In addition, the power output shaft  62  may be of the type which can be detachably connected to the crank shaft  19  and may be connected directly to the crank shaft  19  without through the displacement absorbing coupling  55  or the reduction gear mechanism  61 . Also, the power output shaft  62  may be of the type which is rotatably supported with the body frame  70  or the plurality of cover plates  76 A to  76 F arbitrarily via the gear case  66 . 
     The present disclosure relates to the subject matter of Japanese Patent Application No. 2000-344469, filed Nov. 10, 2000, the disclosure of which is incorporated herein by reference in its entirety.