Abstract:
In an outboard marine drive, the engine is received in an under case, and is closed by both a fan cover and an engine cover so that the engine may be entirely covered by the engine cover jointly with the under case for a favorable aesthetic effect. However, the fan cover covers the engine closely in cooperation with the under case so that a narrow air passage is defined around the engine, and cooling air of high velocity can be continuously passed around the engine. Thus, according to the present invention, no part of the engine is exposed, but the fan cover surrounding the engine defines an appropriate gap around the engine for effectively guiding cooling air around the engine.

Description:
TECHNICAL FIELD 
     The present invention relates to an outboard marine drive including an air cooled internal combustion engine which has a vertical crankshaft carrying a cooling air fan. 
     BACKGROUND OF THE INVENTION 
     It is advantageous to use an air-cooled internal combustion engine for a small outboard marine drive in view of reducing weight. Such an engine requires fresh cooling air to be continuously supplied for preventing the overheating of the engine. For aesthetic considerations and convenience of handling, it is desirable to cover the engine. Thus, conflicting requirements are imposed on small outboard marine engines. According to the invention disclosed in Japanese UM publication (kokoku) No. 2-23782, a cover is placed over the cylinder head of an outboard marine engine while the crankcase thereof is exposed. However, the aesthetic considerations are extremely important, and it is desired to minimize the exposure of the internal combustion engine. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of such problems of the prior art, a primary object of the present invention is to provide an outboard marine drive using an air-cooled internal combustion engine which is relatively filly covered, but can be favorably air-cooled. 
     A second object of the present invention is to provide an outboard marine drive using an air-cooled internal combustion engine which is relatively fully covered, and light in weight. 
     A third object of the present invention is to provide an outboard marine drive using an air-cooled internal combustion engine which is relatively fully covered, and easy to service. 
     According to the present invention, these and other objects can be accomplished by providing an outboard marine drive having an internal combustion engine incorporated with a vertically oriented crankshaft and a cooling fan attached to an upper end of the crankshaft, comprising: an under case attached to a lower end of the engine, the under case being provided with a substantially cylindrical upright wall located inside an outer periphery of the under case so as to surround a lower part of the engine; an engine cover which is detachably attached to the under cover so as to jointly cover the engine and define a first chamber, the engine cover being provided with an air inlet to introduce cooling air into the first chamber; and a fan cover which jointly covers the engine and defines a second chamber inside the first chamber, the fan cover being provided with an air inlet opposite to the cooling fan, while the under case is provided with an air outlet for expelling cooling air out of the second chamber; wherein a lower peripheral edge of the fan cover abuts an opposing upper peripheral edge of the cylindrical upright wall of the under case. 
     Thus, the fan cover can cover the engine closely in cooperation with the under case so that a narrow air passage is defined around the engine, and cooling air of high velocity can be continuously passed around the engine. This enhances the cooling effect such that the engine can be substantially entirely covered without risking the possibility of overheating the engine. In particular, by providing the lower peripheral edge of the fan cover with a peripheral groove which receives the opposing upper peripheral edge of the cylindrical upright wall of the under case, it is possible to firmly secure the fan cover relative to the under case which can be firmly attached to a lower part of the engine. Additionally, the opposing edges of the fan cover and the under case may be provided with a plurality of pin and hole engagement arrangements for positioning the fan cover relative to the under case against any lateral movement. 
     Preferably, the air inlet of the engine cover is provided at an upper rear part of the engine cover, and the inlet of the fan cover is provided in an upper part of the fan cover. Also, the provision of the first chamber defined between the engine cover and the fan cover prevents water which may get into the first chamber from reaching the second chamber. Therefore, the engine can be properly protected from ill effects resulting from the intrusion of water into the first chamber. 
     Typically, a recoil starter is attached to an upper part of the engine, and may be placed in an upper part of the fan cover in such a manner that the inlet of the fan cover is provided in a cover of the recoil starter. To even further enhance the cooling effect, an air guide plate may be provided inside the second chamber for directing cooling air toward a crankcase of the engine. To minimize the number of component parts and simplify the assembly work, the air guide plate consists of an extension of a gasket interposed between a base end of an exhaust pipe and a corresponding exhaust port of the engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Now the present invention is described in the following with reference to the appended drawings, in which: 
     FIG. 1 is a partly broken-away side view of an outboard marine drive embodying the present invention; 
     FIG. 2 is a partly broken-away side view of the engine and the surrounding arrangement; 
     FIG. 3 is a partly broken-away plan view of the outboard marine drive with its engine cover removed for showing the parts surrounding the engine; 
     FIG. 4 is a fragmentary sectional view taken along line IV—IV of FIG. 3; and 
     FIG. 5 is a fragmentary sectional view taken along line V—V of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 generally illustrates a side view of an outboard marine drive embodying the present invention. This outboard marine drive  1  is adapted to be attached to a transom of a boat (not shown in the drawing) with a stem bracket  2  having a clamping capability. Stem bracket  2  is attached to a swivel case  4  via a tilt shaft  3  extending horizontally across the width of the boat. Swivel case  4  in turn supports a tubular extension case  6  accommodating therein a vertically extending drive shaft  5 . Swivel case  4  permits the main part of the outboard marine drive to rotate 360 degrees around a vertical steering axis relative to stem bracket  2  of the boat. 
     The upper end of extension case  6  is attached to an internal combustion engine  7 , and lower end  6   b  of extension case  6  is attached to a gear case  10  accommodating, in interior  6   a  of extension case  6 , a propeller shaft  9  and a bevel gear mechanism  8  for transmitting the rotative power from the lower end of drive shaft  5  to propeller shaft  9 . 
     Engine  7  consists of a vertical-crankshaft, air-cooled, single-cylinder, four-stroke internal combustion engine, and is generally covered by an under case  11  and an engine cover  12  which are detachably joined with each other. The cylinder head of engine  7  is directed rearward with a slight angular offset to one side. The lower end of a crankshaft  32  (FIG. 2) of engine  7  is connected to the upper end of drive shaft  5  via a known centrifugal clutch device  13 . Under case  11  is attached to the bottom surface of a housing of centrifugal clutch device  13  so that engine cover  12  may be removed while under case  11  is kept attached to engine  7 . 
     The housing of centrifugal clutch device  13  is provided with an arm (not shown in the drawings) which extends out of under case  11 , and a free end of this arm is attached to a steering arm  14  which can turn in a horizontal plane. Thus, by angularly moving steering arm  14 , the outboard marine drive main body can be turned around a vertical axis for steering the boat. A free end of steering arm  14  is provided with a throttle grip  15  for operating a throttle valve of a carburetor  49  (FIG.  3 ). When the rotational speed of engine  7  is increased beyond a certain level by suitably twisting throttle grip  15 , centrifugal clutch device  13  is engaged, and the rotational power of the crankshaft is transmitted to propeller  16  via drive shaft  5  and propeller shaft  9 . 
     An exhaust pipe  17  has an upper end  17   a  which is connected to an exhaust port of the cylinder block, and extends from the engine room into extension case  6  along a curved path. Lower end  17   b  of exhaust pipe  17  terminates at a point adjacent to lower end  6   b  of extension case  6 . Exhaust pipe  17  extends substantially in parallel with drive shaft  5  inside extension case  6 , and its lower end  17   b  is supported by a circular partition member  18  which is made of resilient elastomeric material and fitted into a bore defined at lower end  6   b  of extension case  6 . An inlet opening  19  is provided in a curved part of exhaust pipe  17  adjacent to the cylinder block for receiving a probe for analyzing the contents of the exhaust gas. 
     The exhaust gas from engine  7  is released from lower end  17   b  of exhaust pipe  17 , and is normally released into the water from an opening  20  defined in the interface between extension case  6  and gear case  10 . The exhaust gas is then pushed rearward in the water by the water flow produced by propeller  16 . Because interior  6   a  of extension case  6  is separated from the lower part thereof by partition member  18 , the exhaust gas is prevented from flowing upward inside extension case  6 . 
     Now is described the part of this outboard marine drive associated with engine  7  referring to FIGS. 2-5. Engine  7  is covered jointly by under case  11  and engine cover  12  as mentioned earlier, and under case  11  is secured to a lower surface  21   a  of a clutch housing  21  by bolts B 1  while engine cover  12  is detachably attached to the open end of under case  11 . The inner bottom surface of under case  11  is provided with a number of slots  22  for ventilation, and a number of reinforcement ribs  23  extending radially from the axial center of the crankshaft. Under case  11  is further provided with a substantially cylindrical upright wall  24  surrounding a lower part of engine  7 . In fact, upright wall  24  has a profile which closely surrounds the lower part of engine  7 . 
     A fan cover  26  is placed over an upper part of engine  7 , and is held in place by virtue of a U-shaped groove  25  formed in the lower edge thereof receiving an upper edge of upright wall  24 . The mutually abutting edges of fan cover  26  and under case  11  are conformally profiled as can be readily appreciated. The lower edge of fan cover  26  is provided with a plurality of tabs  27 . Locator pins  28  standing upright from the bottom surface of under case  11  fit into holes  29  provided in tabs  27  for properly positioning fan cover  26  relative to under case  11  against any lateral movement. 
     Fan cover  26  is firmly secured to engine  7 , along with a recoil starter  31  placed over engine  7 , by stud bolts  30  extending from engine  7 . Thus, engine cover  12  and under case  11  jointly define a first chamber  60 , and fan cover  26  and lower case  11  jointly define a second chamber  70  inside first chamber  60 . Recoil starter  31  is connected to the upper end of crankshaft  32  of engine  7  via a coupling  33  which engages and disengages through an axial movement of an engagement member. The upper end of crankshaft  32  is also provided with a centrifugal cooling air fan  34  serving also as a flywheel so that when crankshaft  32  is turning, air introduced from air inlets  35  formed along an outer periphery of an upper rear part of engine cover  12  is drawn into fan cover  26  via openings  36  formed in the upper wall of the cover of recoil starter  31 , and after cooling engine  7 , is expelled from the housing assembly through ventilating slots  22  formed in the bottom wall of under case  11 . 
     An air guide plate  37  having an inclined surface C inclining downward toward the crankcase is attached to a side of the cylinder block of engine  7 . This air guide plate  37  is formed by an extension of a metal gasket interposed between the cylinder block and the flanged end of exhaust pipe  17 , and is secured by bolts B 2  which secure exhaust pipe  17  to the cylinder block. Thus, the flow rate of the cooling air around the crankcase can be maximized without increasing the number of component parts or the amount of work required for the assembly work. Alternatively, the air guide plate may be integrally formed with the cylinder block or fan cover  26 . The size of the gap between the inner surface of fan cover  26  and the outer surface of engine  7  can be appropriately selected so as to achieve a desired amount or speed of air flow at each selected location of engine  7 . Also, by providing cooling fins  38  on the outer circumferential surface of clutch housing  21 , it is possible to enhance the cooling of a clutch drum  13   a  and a clutch shoe  13   b  incorporated in clutch housing  21 . 
     A socket member  40  is fitted into an opening  39  defined in the crankcase of engine  7  with the center of this opening substantially coinciding with a normal oil level in the crankcase. Socket member  40  is provided with an inner end closely received in the opening  39  (FIG. 4) of the crankcase, and a tab  59  (FIG. 2) having an opening through which a threaded bolt B 3  is passed and threaded into a threaded bore of the crankcase so as to fixedly secure socket member  40  relative to the crankcase. An outer end of socket member  40  terminates adjacent to an access hole  41  formed in a side wall of under case  11 , and is fitted with a level gauge window  42  made of transparent plastic material. 
     Socket member  40  is additionally provided with a filler pipe  43  extending upwardly at an oblique angle and a drain pipe  44  extending downwardly at an oblique angle. Pipes  43  and  44  are normally closed liquid-tight by threaded plugs P 1  and P 2 , respectively. The outer end of filler pipe  43  can be exposed simply by removing engine cover  12  as it is located above the open upper end of under case  11 . The outer end of drain pipe  44  is passed through a circular opening  45  provided in under case  11  immediately below access opening  41  for level gauge window  42  so that plug P 2  can be easily fitted and removed in and out of drain pipe  44  from outside under case  11 . 
     Between engine cover  12  on the side of the crankcase of engine  7  and fan cover  26  (or in the front end of engine cover  12 ) is disposed a fuel tank  46  which is fixedly secured to fan cover  26 . Fuel tank  46  is provided with a filler cap  47  which projects from an opening  48  provided in an upper part of engine cover  12  so that fuel can be filled into fuel tank  46  without removing engine cover  12 . A hose  50  for supplying fuel from fuel tank  46  to carburetor  49  (FIG. 3) which is attached to the cylinder head side (rear end) of engine  7  is passed inside under case  11 . Hose  50  is positioned in under case  11  by being fitted into U-shaped notches  51  provided in radial ribs  23  at suitable locations as best illustrated in FIG.  5 . 
     A choke knob  52  attached to a choke lever of carburetor  49  is directly engaged by an opening  53  provided in under case  11  so as to apply a suitable frictional retaining force thereto while minimizing the number of component parts and the amount of work required for assembly. 
     The outer profile S of under case  11  on the side of the cylinder head is generally circular with its center of curvature offset from the center of gravity of the engine toward the cylinder head. Therefore, even when the outboard marine drive is placed with its cylinder head down (typically in storage) on the floor, because the center of gravity of the engine is located above the center of curvature of the outer profile S, the engine rolls either way until either side thereof is always oriented horizontally, and the lubricating oil is prevented from remaining in the cylinder head. As well known in the art, filling the combustion chamber with lubricating oil over time is harmful for the durability of the engine. If the outer profile of the rear end or the cylinder head end of the engine assembly is not circular, the profile of the engine assembly and the positioning of the gravitational center should be so selected in such a manner that the orientation of the assembly with its cylinder head facing down is unstable when placed on a floor, and the engine assembly rolls over the floor until either side thereof faces down. Numeral  54  denotes a kill switch. 
     Thus, according to the present invention, an engine can be generally covered by a casing so that no part of the engine is exposed, and the fan cover surrounding the engine defines an appropriate gap around the engine for effectively guiding cooling air around the engine. 
     Although the present invention has been described in terms of a preferred embodiment thereof, it is obvious to a person skilled in the art that various alterations and modifications are possible without departing from the scope of the present invention which is set forth in the appended claims.