Abstract:
A vertical power unit includes an input shaft and an output shaft which have axes in the vertical direction and are vertically arranged to each other; and a torque converter between the input shaft and the output shaft. The output shaft includes an upper output shaft connected to a turbine runner and a lower output shaft connected to the upper output shaft. An oil tank and an oil pump are provided outside the torque converter. The upper output shaft is provided with a vertical hole which communicates at an upper end with a circulation circuit of the torque converter so as to introduce the oil discharged by the oil pump into the circulation circuit, and a bottom wall which closes a lower end of the vertical hole. Thus, an working oil is constantly supplied to the circulation circuit of the torque converter through the interior of the output shaft, thereby cooling the working oil in the circulation circuit, and improves maintainability of loading devices driven by the output shaft.

Description:
RELATED APPLICATION DATA 
     The present invention is based upon Japanese priority application Nos. 2006-145979 and 2006-145980, which are hereby incorporated in their entirety herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vertical power unit and an outboard engine system comprising: an engine which has a vertically arranged crankshaft; a vertically arranged output shaft provided below the crankshaft; and a torque converter disposed between the crankshaft and the output shaft, the torque converter including: a pump impeller connected to the crankshaft; a turbine runner connected to the output shaft so as to opposed to the pump impeller; a stator arranged between the pump impeller and the turbine runner; and a circulation circuit of a power transmission oil, the circuit being defined between the pump impeller, turbine runner and stator; and a vertical hole which is provided in the output shaft and which communicates at an upper end with the circulation circuit so as to introduce the oil discharged by the oil pump into the circulation circuit. 
     2. Description of the Related Art 
     U.S. Pat. No. 3,407,600 discloses a vertical power unit and an outboard engine system which includes an engine having a vertically arranged crankshaft, a vertically arranged output shaft below the crankshaft, and a torque converter disposed between the crankshaft and the output shaft. 
     In the vertical power unit and the outboard engine system disclosed in U.S. Pat. No. 3,407,600, the torque converter includes a built-in oil reservoir for storing an working oil, and a sealed-type circulation circuit. Therefore, the torque converter inevitably becomes large to increase the weight, while enlarging a surrounding part. Further, the working oil in the sealed-type torque converter obtains a poor cooling, thereby accelerating deterioration of the oil. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in view of the above circumstances, and has an object to provide a vertical power unit and an outboard engine system wherein an oil reservoir is separated from a torque converter and oil in the oil reservoir is constantly supplied to a circulation circuit of the torque converter through an interior of an output shaft, thereby downsizing the torque converter and cooling the working oil in the circulation circuit, and also providing an excellent maintainability of loaded devices which are driven by the output shaft. 
     In order to achieve the above object, according to a first feature of the present invention, there is provided a vertical power unit and an outboard engine system comprising: an engine which has a vertically arranged crankshaft; a vertically arranged output shaft provided below the crankshaft; and a torque converter disposed between the crankshaft and the output shaft, the torque converter including: a pump impeller connected to the crankshaft; a turbine runner connected to the output shaft so as to opposed to the pump impeller; a stator arranged between the pump impeller and the turbine runner; and a circulation circuit of a power transmission oil, the circuit being defined between the pump impeller, turbine runner and stator, wherein the output shaft comprises an upper output shaft connected to the turbine runner and a lower output shaft separably connected to the lower end portion of the upper output shaft; wherein the vertical power unit further comprises, outside the torque converter, an oil tank, and an oil pump for drawing up oil in the oil tank; and wherein the upper output shaft is provided with a vertical hole which communicates at an upper end with the circulation circuit so as to introduce the oil discharged by the oil pump into the circulation circuit, and a bottom wall which closes a lower end of the vertical hole. 
     With the first feature of the present invention, the oil tank is provided outside the torque converter and the oil in the oil tank is drawn up and supplied to the circulation circuit of the torque converter, thereby reducing the size and weight of the torque converter. Also, the oil discharged from the oil pump is constantly supplied through the vertical hole in the output shaft to the circulation circuit of the torque converter, thereby preventing overheating and degradation of the oil in the circulation circuit and simplifying the oil passage. 
     Further, the output shaft is divided into two portions: an upper output shaft and a lower output shaft which are separably coupled to each other, so that the engine, the torque converter and the upper output shaft can be compactly configured into a unit without interference by the lower output shaft. 
     Furthermore, in maintenance of the loaded devices which are connected to the lower output shaft, because the lower output shaft is separated from the upper output shaft, the maintenance of the loading devices can be easily performed without interference by the torque converter and the upper output shaft, thereby providing an excellent maintainability. 
     Moreover, because the vertical hole is provided in the upper output shaft together with the bottom wall, even when the lower output shaft is separated from the upper output shaft, it is possible to prevent the oil remained in the vertical hole from flowing out of the vertical hole, thereby further improving the maintainability. 
     According to a second feature of the present invention, in addition to the first feature, the upper output shaft is provided with the vertical hole, a plug hole, and a spline hole so that they axially pass through the upper output shaft; a plug is attached to the plug hole so as to serve as the bottom wall; and a spline shaft is removably fitted to the spline hole, the spline shaft being formed at an upper end of the lower output shaft. 
     With the second feature of the present invention, because the vertical hole, the plug hole and the spline hole axially pass through the upper output shaft, and thus, after processing of these holes, washing can advantageously reliably prevent cut chips from residing in these holes. Also, the plug fitted to the plug hole easily closes the lower end of the vertical hole. 
     According to a third feature of the present invention, in addition to the first or second feature, the vertical power unit further comprises: a hollow stator shaft disposed on a periphery of the upper output shaft, and is coupled to the stator via a free wheel to extend downward; and a hollow pump shaft disposed on a periphery of the stator shaft, and is coupled to the pump impeller to extend downward; and the pump shaft is supported by a support member via an upper bearing, a lower end portion of the stator shaft is fixed to the support member, and the lower output shaft is supported by a lower end portion of the stator shaft via a lower bearing. The support member corresponds to a bearing bracket  14  in embodiments of the present invention which will be described later. 
     With the third feature of the present invention, the pump shaft is supported by the support member via the upper bearing; the lower end of the stator shaft is fixed to the support member; and the lower end of the stator shaft supports the lower output shaft via the lower bearing. Therefore, the pump shaft, the stator shaft and the upper output shaft are reasonably supported, thereby downsizing the vertical transmission. 
     According to a fourth feature of the present invention, in addition to the third feature, the oil pump driven by the pump shaft is mounted to the support member between the upper and lower bearings. 
     With the fourth feature of the present invention, the space between the upper and lower bearings is effectively used for placing the oil pump therein, thereby downsizing the vertical transmission having the oil pump. 
     According to a fifth feature of the present invention, in addition to the fourth feature, the vertical power unit further comprises: an inlet oil passage extending from the support member to the stator shaft and the upper output shaft to communicate a discharge port of the oil pump with the vertical hole; and a pair of seal members which are vertically arranged to sandwich the inlet oil passage at a relatively rotatable fitted portion between the upper output shaft and the stator shaft. 
     With the fifth feature of the present invention, the pair of vertically arranged seal members cooperatingly prevent the oil in the inlet pump passage from flowing out of the fitted portion between the upper output shaft and the stator shaft. 
     According to a sixth feature of the present invention, in addition to the fifth feature, a cylindrical oil passage is defined above the pair of seal members and between the upper output shaft and the stator shaft so that oil discharged from the circulation circuit is guided to run down to a suction side of the oil pump or the oil tank. 
     With the sixth feature of the present invention, the space between the upper output shaft and the stator shaft is used for forming the cylindrical passage which allows the oil discharged from the circulation circuit to flow down therethrough, thereby simplifying the oil passage structure. Further, the upper seal member of the pair of seal members is cable of preventing the oil in the cylindrical passage from flowing down. 
     According to a seventh feature of the present invention, there is provided an outboard engine system comprising: a casing coupled to a swivel case via a swivel shaft; an engine mounted in an upper part of the casing such that a crankshaft of the engine is vertically arranged and a cylinder block of the engine faces in a direction opposite to the swivel shaft; a torque converter; a vertically arranged output shaft connected to the crankshaft through the torque converter; a horizontally arranged propeller shaft provided below the output shaft; and a forward-reverse shifting gear mechanism for providing a connection between the output shaft and the propeller shaft; the torque converter, output shaft, propeller shaft and gear mechanism being disposed in the casing, wherein the output shaft comprises an upper output shaft connected to the turbine runner and a lower output shaft separably connected to the lower end portion of the upper output shaft; wherein the vertical power unit further comprises an oil tank in the casing below the torque converter, and an oil pump for drawing up oil in the oil tank; and wherein the upper output shaft is provided with a vertical hole which communicates at an upper end with the circulation circuit so as to introduce the oil discharged by the oil pump into the circulation circuit, and a bottom wall which closes a lower end of the vertical hole. 
     With the seventh feature of the present invention, the torque converter and the oil tank for storing the working oil for the torque converter are formed as separated components which are arranged in the vertical direction, thereby reducing the size and weight of the casing which houses these components and also those of the outboard engine system. Further, the oil discharged by the oil pump is constantly supplied to the circulation circuit of the torque converter through the vertical hole in the output shaft, thereby preventing the overheating and degradation of the oil in the circulation circuit and simplifying the oil passage. 
     Further, the long output shaft is divided into two portions: the upper output shaft and the lower output shaft that are separably coupled to each other, so that the engine, the torque converter and the upper output shaft can be compactly configured into a unit without interference by the lower output shaft. 
     Furthermore, in maintenance of the propeller shaft and the forward-reverse shifting gear mechanism connected to the lower output shaft, because the lower output shaft can be separated from the upper output shaft, it is possible to easily perform the maintenance of the forward-reverse shifting gear mechanism and the other components without interference by the torque converter and the upper output shaft, thereby improving the maintainability. 
     Moreover, because the vertical hole is provided in the upper output shaft together with the bottom wall, even when the lower output shaft is separated from the upper output shaft, it is possible to prevent the oil remained in the vertical hole from flowing out of the vertical hole, thereby further improving the maintainability. 
     According to an eighth feature of the present invention, there is provided an outboard engine system comprising: a casing; an engine which has a vertically arranged crankshaft and is mounted in an upper part of the casing, a torque converter; a vertically arranged output shaft connected to the crankshaft through the torque converter; and a horizontally arranged propeller shaft provided below the output shaft; a forward-reverse shifting gear mechanism for providing a connection between the output shaft and the propeller shaft, the torque converter including: a pump impeller connected to the crankshaft; a turbine runner connected to the output shaft so as to be opposed to the pump impeller; a stator arranged between the pump impeller and the turbine runner; and a circulation circuit of a power transmission oil, the circuit being defined between the pump impeller, turbine runner and stator, wherein the torque converter T is mounted in the upper portion of the casing together with the engine; and wherein the casing further contains: an oil tank; an oil pump for drawing up oil stored in the oil tank; an oil supply passage for supplying the oil discharged by the oil pump to the circulation circuit; and a return passage for returning the oil in the circulation circuit to a suction side of the oil pump or the oil tank. 
     With the eighth feature of the present invention, the oil cooled in the oil tank is constantly supplied by the oil pump to the circulation circuit of the torque converter, thereby preventing the overheating and degradation of the oil in the circulation circuit. Further, the torque converter is mounted to the upper portion of the casing together with the engine, and the oil tank is disposed in the casing, so that an oil tank having a relatively large capacity can be disposed in the casing without interference by the engine and the torque converter, thereby increasing the amount of oil flowing into the circulation circuit to further promote the cooling of the oil. 
     According to a ninth feature of the present invention, in addition to the eighth feature, the casing comprises a plurality of case parts which are vertically stacked and joined to each other, and the oil tank is formed in one of the case parts. 
     With the ninth feature of the present invention, because the oil tank is formed in one of the plural case parts constituting the casing, the mounting of the oil tank is completed only by coupling together the plural case parts for assembling the casing, thereby simplifying the support structure and mounting procedures of the oil tank. 
     According to a tenth feature of the present invention, in addition to the eighth or ninth feature, the outboard engine system further comprises: a hollow stator shaft which is disposed on a periphery of the upper output shaft, and is coupled to the stator to extend downward; and a hollow pump shaft which is disposed on a periphery of the stator shaft, and is coupled to the pump impeller to extend downward; and the engine is mounted to the upper portion of the casing through a bearing bracket and a distance member, the bearing bracket supporting the pump shaft via a bearing, the distance member being connected to an upper end of the bearing bracket to surround the torque converter, and the oil pump is mounted to the bearing bracket. 
     With the tenth feature of the present invention, the engine can be mounted to the upper portion of the casing without interference by the torque converter supported by the bearing bracket. Further, the bearing bracket supports not only the torque converter but also the oil pump, thereby simplifying the support structure of the oil pump. 
     According to an eleventh feature of the present invention, in addition to any of the eighth to tenth features, the casing comprises a mount case part to which the engine is mounted together with the torque converter, an extension case part which is joined to a lower end of the mount case part and houses the output shaft, and a gear case which is joined to a lower end of the extension case part and houses the forward-reverse shifting gear mechanism and the propeller shaft; and the output shaft comprises an upper output shaft supported by the mount case part, and a lower output shaft separably connected to a lower end portion of the upper output shaft and is connected to the forward-reverse shifting gear mechanism. 
     With the eleventh feature of the present invention, because the output shaft is divided into the upper output shaft and the lower output shaft, the engine and the torque converter can be easily removed from the mount case part without interference by the long output shaft, and also the gear case housing the forward-reverse shifting gear mechanism can be removed from the extension case part, thereby providing an excellent maintainability. 
     The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent a preferred embodiment, which will be described in detail below by reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view showing an outboard engine system, which includes a vertical power unit, according to a first embodiment of the present invention. 
         FIG. 2  is an enlarged sectional view showing the portion  2  of  FIG. 1 . 
         FIG. 3  is an enlarged view showing the essential portions of  FIG. 2 . 
         FIG. 4  is an enlarged sectional view showing the portion  4  of  FIG. 1 . 
         FIG. 5  is a view showing a hydraulic circuit including an oil pump. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A first embodiment of the present invention will be described with reference to  FIGS. 1 to 6 . In  FIG. 1 , an outboard engine system O includes a casing  1  which has a water-cooled multi-cylinder four-stroke engine E mounted in its upper portion, and supports a propeller shaft  3  at its lower portion. The propeller shaft  3  has a propeller  2  provided at its rear end. A vertically-extending swivel shaft  6  is mounted to the casing  1  via an upper arm  4  and a lower arm  5  so as to situate in front of the casing  1 . The swivel shaft  6  is rotatably supported by a swivel case  7  which is coupled to a stern bracket  8  via a horizontally-extending tilt shaft  9 . The stern bracket  8  is cramped to a transom Bt of a body of a ship. Therefore, the casing  1  is horizontally rotatable around the swivel shaft  6 , and vertically tiltable around the tilt shaft  9 . The reference numeral Ef denotes a removable engine hood for covering the engine E. 
     In  FIG. 2 ,  FIG. 3  and  FIG. 4 , the above casing  1  includes the extension case  10 , the mount case  11  bolt-coupled to an upper end of the extension case  10 , and a gear case  12  bolt-coupled to a lower end of the extension case  10 . The extension case  10  includes an upper case  10   a  and a lower case  10   b  bolt-coupled to the upper case  10   a . The mount case  11  is jointed to an upper end surface of the upper case  10   a  by a plurality of bolts  16   3 . 
     The casing  1  further includes annular lower distance members  13 , an bearing bracket  14 , and annular upper distance members  15 , which are sequentially superimposed on the upper end of the mount case  11 . The engine E is mounted to the upper distance member  15  with the crankshaft  17  being vertically arranged and the cylinder block  18  facing rearward. An bearing bracket  14  and upper distance member  15  are secured to the cylinder block  18  and a bottom wall of the crankcase  19  of the engine E by a plurality of bolts  16   1 . The lower distance member  13 , the bearing bracket  14 , and the upper distance member  15  are secured to one another by a plurality of bolts  16   2 . 
     In  FIG. 2  and  FIG. 3 , the torque converter T is vertically arranged in the annular upper distance member  15 , and the output shaft  20  coupled to the crankshaft  17  via the torque converter T is vertically arranged in the extension case  10 . 
     The gear case  12  horizontally supports the propeller shaft  3  having the propeller  2  at its rear end, and houses a forward-reverse shifting gear mechanism  21  connecting the propeller shaft  3  to the output shaft  20 . 
     In operation of the engine E, the power thereof is transmitted from the crankshaft  17  to the output shaft  20  via the torque converter T, and further to the propeller shaft  3  via the forward-reverse shifting gear mechanism  21 , thereby driving the propeller  2 . The rotational direction of the propeller  2  is controlled and switched by the forward-reverse shifting gear mechanism  21 . 
     In the extension case  10 , an oil tank  22  open to the mount case  11  is integrally formed with the upper case  10   a  of the extension case  10 . The oil tank  22  stores oil  23  which is used in both lubrication of the engine E and operation of the torque converter T. A downstream end  90  of an exhaust gas passage of the engine E is integrally formed with the upper case  10   a.    
     As clearly shown in  FIG. 3 , the torque converter T includes a pump impeller  25 , a turbine runner  26  arranged above the pump impeller  25  and opposed to the pump impeller  25 , a stator  27  arranged between the inner peripheral portions of the pump impeller  25  and the turbine runner  26 , and a circulation circuit  28  of working oil which is defined between these three impellers  25  to  27 . The three impellers  25  to  27  are arranged to have a common vertical axis, as in the case of the crankshaft  17  and the output shaft  20 . 
     The pump impeller  25  integrally includes a transmission cover  29  for covering an upper surface of the turbine runner  3 . A ring gear  30  for starting operation is secured to an outer peripheral surface of the transmission cover  29 . A drive plate  31  is secured to the ring gear  30  by a bolt  32   2 . The drive plate  31  is also secured to a lower end surface of the crankshaft  17  by a bolt  32   1 . The torque converter T is suspended from the crankshaft  17  via the drive plate  31 . 
     A cup-shaped supporting cylinder  34  is secured to a central part of the transmission cover  29 . The supporting cylinder  34  is fitted into a supporting hole  33  which is open to the central part of the lower end surface of the crankshaft  17 . The output shaft  20  has an upper end which extends to the inside of the supporting cylinder  34  and is supported in the supporting cylinder  34  via a bearing bush  35 . A hub of the turbine runner  26  is spline-coupled to the output shaft  20 . A hollow stator shaft  37  is arranged around the outer periphery of the output shaft  20  so as to be supported by the output shaft  20  via a needle bearing  36 . A known free wheel  38  is interposed between the stator shaft  37  and a hub of the stator  27 . 
     A hollow pump shaft  39  is arranged at the outer periphery of the stator shaft  37 . The hollow pump shaft  39  is integrally coupled to the pump impeller  25  and extends downward. The pump shaft  39  is supported by the bearing bracket  14  via an upper ball bearing  43  on the side of the outer periphery. An oil pump  41  driven at the lower end portion of the pump shaft  39  is attached to a pump housing  40  formed at a lower surface of the bearing bracket  14 . A pump cover  42  covering a lower surface of the oil pump  41  is bolt-coupled to a lower surface of the bearing bracket  14 . An oil seal  45  is attached to an upper end portion of the bearing bracket  14  such that its lip is in close contact with an outer peripheral surface of the pump shaft  39  at a position immediately above the ball bearing  43 . 
     The stator shaft  37  has a large diameter portion  37   a  at its lower end. A flange  37   b  is integrally formed on an outer periphery of the large diameter portion  37   a . The flange  37   b  is secured to the pump cover  42  by a bolt  46 . A lower ball bearing  44  is mounted to its inner periphery of the flange  37   b  so as to support the output shaft  20 . 
     Therefore, the pump shaft  39  is supported by the bearing bracket  14  via the upper ball bearing  43 , and the output shaft  20  is supported by the large diameter portion  37   a  of the stator shaft  37  via the lower ball bearing  44 , thereby reasonably supporting the pump shaft  39 , the stator shaft  37 , and the output shaft  20  and downsizing the vertical fluid power transmission including the torque converter T and output shaft  20 . 
     Because the oil pump  41  is mounted to the bearing bracket  14  in a space between the upper and lower ball bearings  43  and  44 , thereby downsizing the vertical fluid power transmission having the oil pump  41 . 
     A thrust needle bearing  47  is interposed between the pump impeller  25  and the hub of the stator  27 . A thrust needle bearing  48  is interposed between the hub of the turbine runner  26  and the transmission cover  29 . 
     The oil pump  41  draws up the oil stored in the oil tank  22 , and supplies the oil to the engine E and the torque converter T. The route of the oil discharged by the oil pump  41  will be described below with reference to  FIG. 5 . 
     The oil pump  41  draws up the oil  23  stored in the oil tank  22  via an oil suction passage  50 , and discharges the oil  23  to a first oil supply passage  51 . The oil discharged to first oil supply passage  51  is filtered by an oil filter  53  provided in the middle of the first oil supply passage  51 , and supplied to a lubricated portion of the engine E. After the lubrication, the oil flows downward to the bottom portion of the crankcase  19  of the engine E, and returns to the oil tank  22  via the first oil return passage  59 . 
     The oil discharged to the first oil supply passage  51  is also supplied to a circulation circuit  28  of the torque converter T via a second oil supply passage  52  which is a branch from the first oil supply passage  51  upstream of the oil filter  53 . After being used in the circulation circuit  28 , the oil is returned to the oil suction passage  50  or the oil tank  22  via a second oil return passage  54 . 
     An oil relief passage  55  is another branch from the first oil supply passage  51  upstream of the oil filter  53 , and reaches the oil suction passage  50 . The oil relief passage  55  has a pressure relief valve  56  which opens when an oil pressure of the first oil supply passage  51  exceeds a specified value. 
     The second oil supply passage  52  has an orifice  57  for controlling the amount of the oil supplied to the circulation circuit  28  of the torque converter T. The second oil return passage  54  also has a normally-closed pressure response valve  58  which opens when an oil pressure upstream of the second oil return passage  54  exceeds a predetermined value. 
     Thus, when the pressure of the first oil supply passage  51  is regulated by the single pressure relief valve  56 , the pressure of the second oil supply passage  52  is concurrently regulated, whereby the pressure of the circulation circuit  28  in the torque converter T is regulated, and the transmission characteristics of the torque converter T can be stabilized. In addition, the downstream end of the oil relief passage  55  is connected to the oil suction passage  50 , whereby the oil released from the oil relief passage  55  is smoothly returned to the oil pump  41 , thereby simplifying the oil pressure circuit. 
     Again, in  FIG. 2  and  FIG. 3 , the oil suction passage  50  is suspended from the bearing bracket  14 , and includes a suction tube  50   a  having a lower end portion extending into the oil tank  22 , and a lateral oil passage  50   b  which is provided in the bearing bracket  14  so as to communicate the upper end portion of the suction tube  50   a  with a suction port  41   a  of the oil pump  41 . 
     The second oil supply passage  52  includes a bottomed vertical hole  52   b  which is provided at a central portion of the output shaft  20  so as to open in the upper end surface of the output shaft  20 , an inlet oil passage  52   a  which is provided to pass through the fitted portions between the pump cover  42 , the stator shaft  37  and the output shaft  20  so as to communicate a discharge port  41   b  of the oil pump  41  with the lower portion of the vertical hole  52   b , and a horizontal hole  52   c  which is provided at an upper part of the vertical hole  52   b  so as to pass through the peripheral portion of the thrust needle bearing  48  into the transmission cover  29 . 
     The second oil return passage  54  includes a cylindrical oil passage  54   a  which is defined between the output shaft  20  and the stator shaft  37  and is in communication with the circulation circuit  28  through the peripheral portion of the thrust needle bearing  47  above the hub of the pump impeller  25 , and a lateral outlet oil passage  54   b  which is provided at the pump cover  42  to communicate with the lower end portion of the cylindrical oil passage  54   a . The outlet oil passage  54   b  is in communication with the lateral oil passage  50   b  via the pressure response valve  58 . 
     The pressure response valve  58  includes a cylindrical valve chamber  60  horizontally provided in the pump cover  42 , and a piston-type valve body  61  slidably fitted in the valve chamber  60 . The outlet oil passage  54   b  is open to the inner end surface of the valve chamber  60 . A valve hole  62  is open in the inner side surface of the valve chamber  60  so as to communicate with the lateral oil passage  50   b  or the oil tank  22 . The valve body  61  is arranged so that its top surface, that is, pressure receiving surface is directed toward the outlet oil passage  54   b . The valve hole  62  is closed when the valve body  61  is advanced toward the outlet oil passage  54   b , and is opened when the valve body  61  is retracted. A valve spring  63  is arranged between the rear surface of the valve body  61  and the screw plug  64  screwed into the opening of the valve chamber  60  so as to urge the valve body  61  to the advancing direction, that is, to the valve closing direction. Therefore, the valve body  61  is normally held at its closed position by a set load of the valve spring  63  to thereby block the second oil return passage  54 . When an oil pressure is generated upstream of the second oil return passage  54  and exceeds a predetermined value, the top surface of the valve body  61  receives the oil pressure, and the valve body  61  is caused to retract against the set load of the valve spring  63  to be opened, whereby the second oil return passage  54  enters a communicated state. 
     An opening  66  (see  FIG. 2 ) is provided in a bottom wall of the crankcase  19  of the engine E. The oil having completed the lubrication of the engine E is discharged through the opening  66 . The opening  66  is opened in the upper surface of the mount case  11  through a series of vertical through holes  67  which are formed in the upper distance member  15  and the peripheral portion of the bearing bracket  14 , and through the inner side portion of the annular lower distance member  13 . The mount case  11  has an opening  68  which is open to the oil tank  22 . Therefore, the oil which flows into the bottom portion of the crankcase  19  after completing the lubrication of the engine E is directed to return to the oil tank  22  via the opening  66 , through holes  67  and the opening  68 . The opening  66 , the through holes  67 , and the opening  68  form the first oil return passage  59 . 
     In  FIG. 3 , a first seal member  70   1  is attached to the outer periphery of the stator shaft  37  so as to closely contacts the inner peripheral surface of the pump shaft  39  in a relatively rotatable manner, thereby preventing the oil in the torque converter T from flowing downward of the pump shaft  39 . 
     A second seal member  70   2  is provided between the stator shaft  37  and the pump cover  42  at a position below the inlet oil passage  52   a , thereby preventing the oil in the inlet oil passage  52   a  from flowing downward of the stator shaft  37  and the pump cover  42 . 
     Third and fourth seal members  70   3  and  70   4  are provided around the outer periphery of the output shaft  20  in the fitted portions of the output shaft  20  and the stator shaft  37  such that they are arranged in the vertical direction to closely contact from above and below the inner peripheral surface of the stator shaft  37  in a relatively rotatable manner. The third and fourth seal members  70   3  and  70   4  cooperate to prevent the oil in the inlet oil passage  52   a  from flowing out of the fitted portions of the output shaft  20  and the stator shaft  37 . Further, the upper seal member  70   3  prevents the oil in the inlet oil passage  54   a  from flowing downward to the fitted portions of the output shaft  20  and the stator shaft  37 . 
     As shown in  FIG. 3  and  FIG. 4 , the output shaft  20  is divided into an upper output shaft  20   a  having the vertical hole  52   b  and supported by the lower ball bearing  44 , and a lower output shaft  20   b  coupled to the forward-reverse shifting gear mechanism  21  (see  FIG. 1 ). An upper end portion of the lower output shaft  20   b  is supported via a bush  72  in a supporting sleeve  71  which is integrally formed with the outer side of the oil tank  22 . The upper output shaft  20   a  has a flange  73  which abuts on the upper end surface of the inner lace of the ball bearing  44  attached to the inner periphery of the large diameter portion  37   a  of the stator shaft  37 . A stopper collar  74  is locked to the inner peripheral surface of the large diameter portion  37   a  so as to support the lower end surface of an outer lace of the ball bearing  44 . Therefore, unless the stopper collar  74  is removed, the upper output shaft  20   a  cannot be pulled out downward from the central portion of the torque converter T. 
     Besides the vertical hole  52   b , the upper output shaft  20   a  has a plug hole  76  connected to the lower end of the vertical hole  52   b , and a spline hole  77  connected to the lower end of the plug hole  76  and open in the lower end surface of the upper output shaft  20   a . A plug  78  is screwed into the plug hole  76  to form the bottom wall of the vertical hole  52   b . The plug  78  has a part of the inlet oil passage  52   a , and the orifice  57  for communicating the inlet oil passage  52   a  with the vertical hole  52   b . A fifth seal member  70   5  is attached to the plug  78  to closely contact the inner peripheral surface of the plug hole  76 . 
     The inlet oil passage  52   a  may be formed to bypass the plug  78 . 
     A spline shaft  80  is formed at the upper end portion of the lower output shaft  20   b . The spline shaft  80  is fitted into the spline hole  77  to couples the upper and lower output shafts  20   a  and  20   b  to each other. 
     Now, operation of the first embodiment will be described below. 
     In operation of the engine E, the oil pump  41  is driven by the pump shaft  39  to draw up the oil  23  in the oil tank  22  through the oil suction passage  50 , that is, through the suction tube  50   a  and the lateral oil passage  50   b , and discharges the drawn-up oil  23  to the first oil supply passage  51  and the second oil supply passage  52 . The oil discharged to the first oil supply passage  51  is supplied to the lubricated portion of the engine E, as described above. 
     Meanwhile, the oil supplied to the second oil supply passage  52  sequentially passes through the inlet oil passage  52   a  and the orifice  57 ; ascend through the vertical hole  52   b  of the upper output shaft  20   a  to go out of the horizontal hole  52   c ; enters the transmission cover  29  while lubricating the thrust needle bearing  48 ; and then flows into the transmission cover  29  from the outer peripheral side of the turbine runner  26 . 
     The oil in the circulation circuit  28  circulates as shown by an arrow in  FIG. 3  with the rotation of the pump impeller  25  to transmit the rotational torque of the pump impeller  25  to the turbine runner  26 , thereby driving the output shaft  20 . At this time, if the torque is amplified between the pump impeller  25  and the turbine runner  26 , the reaction force due to the amplification is borne by the stator  27 , which is fixed there by the locking operation of the free wheel  38 . Such a torque amplifying effect of the torque converter T strongly drives the propeller  2 , thereby effectively improving start and acceleration of a ship. 
     After the amplification, the stator  27  rotates in the same direction together with the pump impeller  25  and the turbine runner  26  due to the reversal in the torque direction while causing the freewheel  38  to run idle. 
     After being used at the circulation circuit  28 , the oil runs down the cylindrical oil passage  54   a  while lubricating the thrust needle bearing  47  above the hub of the pump impeller  25 , and enters the valve chamber of the pressure response valve  58  from the outlet oil passage  54   b.    
     The oil having entered the valve chamber  60  exerts a pressure to press the valve body  61  of the pressure response valve  58  against the set load of the valve spring  63 , whereby the valve body  61  is opened to open the valve hole  62 , so that the oil returns from the valve chamber  60  through the valve hole  62  into the oil suction passage  50  or the oil tank  22 . In this way, the oil circulates between the circulation circuit  28  of the torque converter T and the oil tank  22  arranged below the torque converter T through the second oil supply passage  52  and the second oil return passage  54 . Therefore, it is possible to downsize the torque converter T, and promote the cooling of the circulating oil to prevent degradation of the oil. 
     In particular, since the oil tank  22  arranged below the torque converter T is separated from the engine E, the oil tank  22  is not much heated by the engine E, the oil tank  22  can have a relatively large capacity without any interference by the engine E and the torque converter T, and thus can increase the amount of oil flowing into the circulation circuit  28 , thereby further promoting the cooling of the circulating oil. Further, the engine E, the torque converter T, and the oil tank  22  are sequentially arranged from top to bottom, and the torque converter T can be downsized without any interference by the oil tank  22 , thereby reducing the size and weight of the outboard engine system O including these components. 
     The oil discharged from the oil pump  41  for lubricating the engine E is also supplied to the circulation circuit  28 , which eliminates any addition/expansion of the oil tank  22  and the oil pump  41  for supplying the oil to the circulation circuit  28 , thereby avoiding an increase of size and a complication of the outboard engine system O. 
     The elongated output shaft  20  is divided into two portions, that is, the upper output shaft  20   a  and lower output shaft  20   b  which are retractably spline-connected to each other. The upper output shaft  20   a  is coupled to the stator shaft  37  in the axial direction via the lower ball bearing  44  and the stopper collar  74 . Therefore, the torque converter T, the bearing bracket  14 , the pump cover  42 , and the upper output shaft  20   a  are compactly incorporated into a single unit as a vertical power transmission without any interference by the lower output shaft  20   b , thereby facilitating assemblability of the vertical power transmission and mountability of the vertical fluid power transmission to the outboard engine system O. 
     Further, if the gear case  12  is separated from the extension case  10  for maintenance of the forward-reverse shifting gear mechanism  21  for example, the lower output shaft  20   b  can be separated downward together with the gear case  12  while the upper output shaft  20   a  is remained on the torque converter T side by pulling the spline shaft  80  of the lower output shaft  20   b  out of the spline hole  77  of the upper output shaft  20   a . Therefore, it is possible to easily perform the maintenance of the forward-reverse shifting gear mechanism  21 , and further avoid disassembly of the vertical fluid power transmission to easily reassemble the gear case  12  into the system. 
     Furthermore, since the bottom wall of the vertical hole  52  as a part of the second oil supply passage  52   b , that is, the plug  78  is screwed into the upper output shaft  20   a  of the vertical fluid power transmission, the oil is prevented from flowing out of the vertical hole  52   b  and going downward of the upper output shaft  20   a . In this case, although the bottom wall of the vertical hole  52   b  may be integrally formed with the upper output shaft  20   a , the vertical hole  52   b , the plug hole  76 , and the spline hole  77  are arranged to axially pass through the upper output shaft  20   a  if the plug  78  is used. Therefore, after processing of these holes, washing can advantageously reliably prevent cut chips from residing in these holes. 
     The same is true in the case where the engine E and the torque converter T are removed from the mount case  11 , which facilitates maintenance of these components. 
     Moreover, the engine E is mounted to the mount case  11  via the bearing bracket  14  supporting the pump shaft  39  of the torque converter T, the upper distance member  15  connected to the upper end of the bearing bracket  14  to surround the torque converter T, and the lower distance member  13  connected to the lower end of the bearing bracket  14 . Therefore, it is possible to easily mount the engine E to the mount case  11  without any interference by the torque converter T, thereby providing an excellent assemblability. 
     The oil pump  41  is attached to the pump housing  40  formed on the lower surface of the bearing bracket  14  and holds the pump cover  42 . Therefore, the bearing bracket  14  supports not only the torque converter T but also the oil pump  41 , thereby simplifying the support structure of the oil pump  41 . 
     When the operation of the engine E is terminated, also the operation of the oil pump  41  is terminated, so that in the pressure response valve  58 , the pressure of the valve chamber  60  is decreased and the valve body  61  is closed by the set load of the valve spring  63 . This causes the outlet oil passage  54   b  to enter the blocked state, and prevents the oil from flowing from the circulation circuit  28  of the torque converter T into the oil tank  22 , thereby keeping the circulation circuit  28  filled with the oil. Therefore, it is possible to enhance the responsiveness of operation of the torque converter T. 
     Further, a part of the second oil supply passage  52  comprises the vertical hole  52   b  which is provided at a central portion of the output shaft  20  so as to communicate at an upper portion with the circulation circuit  28 , thereby simplifying the structure of the second oil supply passage  52 . Furthermore, when the engine E is stopped, the vertical hole  52   b  prevents the oil from flowing back from the circulation circuit  28  to the oil pump  41 . 
     The present invention is not limited to the above described embodiment, and various modifications in design can be made without departing from the subject matter of the present invention. For example, the oil tank  22  may be divided into a section for storing working oil for the torque converter T and a section for storing lubrication oil for the engine E, and oil suitable for each purpose is stored in each section. Further, the power may be input from the engine E through a reduction gear into the torque converter T, and the power may be transferred from the torque converter T through the reduction gear into the output shaft  20 .