Abstract:
A forced-air-cooled engine having a main blow-out opening provided to a back plate of a cooling fan cover at a position facing a cylinder part for blowing out cooling air for cooling a cylinder part and a secondary blow-out opening provided to the back plate at a position opposite to the main blow-out opening in regard to the crankshaft center for cooling a part of a crankcase part, wherein a cooling air guide cover is equipped which is composed of a cylinder air-guide cover part which guides air blown out from the main blow-out opening to flow to cool the cylinder part and cylinder head, and a top cover part which guides air blown out from the secondary blow-out opening to flow along a side face of the crankcase part to cool there and then flow into midstream of the cooling air flow blown out from the main blow-out opening and cooling the cylinder part and cylinder head.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a forced-air-cooled engine composed of a cylinder block integrated with a crankcase, which is a single block integrating a crankcase part and a cylinder part that extend aslant from the crankcase part, particularly to a cooling air guide cover for distributing the cooling air effectively to improve cooling of the engine.  
         [0003]     2. Description of the Related Art  
         [0004]     In a single cylinder, forced-air-cooled engine, air energized by the cooling fan attached to an end of the crankshaft blown out from the opening of the fan cover, the air is guided to the cylinder and cylinder head having a plurality of cooling fins around their outer surfaces to flow through the spaces between the fins to cool the cylinder and cylinder head.  
         [0005]     In Japanese Laid-Open Patent Application No. 2003-56408 is disclosed as such an engine an inclined cylinder type engine having a crankcase-integrated cylinder block, the cylinder block being composed of a crankcase part and a cylinder part cast in one piece. In this engine, in addition to a cylinder air-guide cover(air cover), a first exhaust air guide and a second exhaust air guide are provided for guiding the cooling air after cooling the cylinder to the carburetor to heat it in order to prevent occurrence of congelation in the carburetor.  
         [0006]     However, the cylinder air-guide cover and exhaust air guides cover only the cylinder and cylinder head and not cover the crankcase part to guide cooling air, and the crankcase part is cooled by natural cooling by the ambient air.  
         [0007]     Another example of an inclined cylinder type, forced-air-cooled engine is shown in  FIG. 7 . In  FIG. 7 , a cylinder block  3  is a cast unit with a cylinder part  7  and a crankcase part  3 A cast integrally, the cylinder part  7  extending aslant from the crankcase part  3 A. A cylinder head  101  is attached on top of the cylinder part  7 . A valve drive mechanism is provided on the cylinder head and covered by a cylinder head cover.  
         [0008]     Reference numeral  103  is an exhaust outlet of the cylinder head  101 ,  104  is a ignition plug,  105  is a cylinder air-guide cover,  106  is fuel hose connecting a fuel tank not shown in the drawing to a fuel filter not shown in the drawing. Reference numeral  3   a  indicates a root part of the cylinder part  7 (connection part of the cylinder part to the crankcase part). Reference numeral  4  is an output shaft of crankshaft, a cooling fan not shown in the drawing being attached to the end opposite to the output shaft  4  (front side) of the crankshaft. A fan cover covering the cooling fan is provided in its back plate a secondary blow-out opening  1   b  and a main blow-out opening not visible in the drawing for blowing out air energized by the cooling fan. Cooling air  5  blown out from the main blow-out opening hits the cylinder part and cylinder head and guided by the cylinder air-guide cover to flow through spaces between cooling fins thereof to cool them and flow out into ambient air. Cooling air  6  blown out from the secondary blow-out opening  1   b  hits a part  3   b  of a side wall of the crankcase part  3 A, cools said part of the crankcase part, and diffuses into the ambient air. Therefore, the crankcase part is cooled only locally, and most of the crankcase part is leaved to be cooled naturally by the ambient air. As mentioned above, in engine of this kind, priority is put on cooling the cylinder and cylinder head, and generally positive cooling of the crankcase part is not considered, although in the in the case of the example a part of the crankcase part is cooed by hitting the cooling air blown out from the secondary blow-out opening.  
         [0009]     In engines of this kind, lube oil is accumulated inside the crankcase part  3 A and splash lubrication is adopted, that is, the lube oil in the crankcase part  3 A is splashed by means of a projecting portion provided to the connecting rod, and oil cooler is not provided. Cooling of lube oil is usually left to natural cooling via the crankcase part. However, the amount of heat generated increase and the surface from which to release heat decreases as engines of this kind are small sized and high powered, so lube oil temperature tends to become higher. Particularly, under high temperature environment, the temperature of lube oil rises excessively and durability of engine is deteriorated. Further, in recent years, many component parts made of plastic material is used for weight saving, for facilitating manufacturing, and for cost saving, so it is required to lower temperature of the surface of the engine as far as possible to evade excessive temperature rise of these parts.  
         [0010]     In engines of this kind, a fuel hose connecting a fuel tank mounted on top of the engine to a fuel filter mounted in a lower part of the engine often passes a space behind the cylinder part downstream of cooling air flow. In this case, the fuel hose is heated by the cooling air increased in temperature by cooling the engine, and vapor lock tends to occur in the fuel hose. To prevent this, a heat shield plate is often provided between the fuel hose and the cylinder part. The fuel hose is usually made of elastic material and it shakes due to vibration and/or shaking of engine, so it often happens that the fuel hose contact with adjacent parts relatively increased in temperature by the exhausting cooling air and damaged. When the fuel hose is damaged, fuel leaks and fire may occur. As a means to fix a fuel hose, there is disclosed in Japanese Laid-Open Utility Model Application to provide a groove of semi-circular cross section for receiving the fuel hose on the end face of the crankcase part and cover the fuel hose by a hose cover.  
         [0011]     However, with this art, it is not easy to form a grove of semi-circular cross section on the end face of the crankcase part.  
       SUMMARY OF THE INVENTION  
       [0012]     To solve the problems mentioned above, the present invention proposed a forced-air-cooled engine equipped with a cooling air guide cover, the engine having a cylinder block which is composed of a crankcase part and a cylinder part connected into one block, a cooling fan being attached to an end of a crankshaft of the engine, a main blow-out opening being provided to a back plate of a fan cover covering said cooling fan at a position facing said cylinder part for blowing out cooling air for cooling said cylinder part, and a secondary blow-out opening being provided to said back plate at a position opposite to said main blow-out opening in regard to the crankshaft center for cooling a part of said crankcase part, wherein said cooling air guide cover is composed of a cylinder air-guide cover part which guides air blown out from said main blow-out opening to flow to cool said cylinder part and a top cover part which guides air blown out from said secondary blow-out opening to flow along a side face of said crankcase part to cool there and then flow into the cooling air flow cooling said cylinder part.  
         [0013]     With this construction, the crankcase part of a small size forced air-cooled engine, of which a means to positively cool the crankcase part has not been adopted, can be effectively cooled. As the temperature of the crankcase part is relatively low compared with that of the cylinder part inside which combustion is performed, the cooling air cooled the crankcase part is lower in temperature than that cooled the cylinder part and cylinder head, so by allowing the cooling air cooled the crankcase part to participate in cooling cylinder part and cylinder head by introducing this air to the cylinder part side, the air energized by the cooling fan can be utilized more effectively to cool the engine. The cooling air cooling cylinder part and cylinder head increases in temperature as it flows to downstream, cooling of the cylinder part and cylinder head tends to be in the downstream zone. By allowing the air cooled the crankcase part and relatively low in temperature to flow into midstream of the cooling air cooling the cylinder part and cylinder head, cooling of the downstream zone of the cylinder part and cylinder head can be improved. As a result, temperature distribution in the cylinder in circumferential direction becomes more even and deformation of the cylinder in radial direction becomes more even resulting in reduced lube oil consumption.  
         [0014]     Further, in an inclined cylinder type engine, surface area is larger inn one side of the crankcase part than that in the other side, so, by cooling the side face of the crankcase part larger in area positively by allowing cooling air to flow along the surface, crankcase part is cooled effectively and the temperature of lube oil inside the crankcase part can be reduced and affection by heat to members attached around the engine can be reduced. Therefore, highly durable, reliable engine can be obtained.  
         [0015]     It is preferable that said cooling air guide cover is made of heat resistant resin superior in absorption of vibration energy and large in resistance to heat transfer by injection molding, said top cover part and cylinder air-guide cover part respectively has an extending girdle part to butt against each other in a downstream zone behind the connecting part of said cylinder part and crankcase part, and engaging parts are formed at ends of said girdle parts to connect said top cover part and cylinder air-guide cover part.  
         [0016]     By making the cooling air guide of plastic material,by injection molding, the cooling air guide cover can be provided with ease and low cost, and in addition, engine noise can be reduced.  
         [0017]     It is preferable that a channel or clamp or combination of them are provided on the back face of each of said connecting parts of said top cover part and cylinder air-guide part to fix and retain a fuel hose connecting a fuel tank to a fuel filter on the back faces of said connecting parts.  
         [0018]     It is preferable that said top cover part of said cooling air guide cover is connected to said back plate of said fan cover and to a flange part provided at a back side end of said crankcase part by mortise and tenon joint and fixed by means of bolts to the cylinder block at key positions as necessary.  
         [0019]     It is preferable that said top cover and cylinder air-guide cover has respectively a girdle part bent to extend across the cylinder air flow behind the connecting part of the cylinder part and crankcase part to be connected at the ends of the girdle parts by mortise and tenon joint and are fixed by means of bolts to the cylinder block at key positions as necessary. In this way, number of positions to fix the top cover to the cylinder block by means of bolts can be reduced and assembling man-hour can be reduced.  
         [0020]     It is preferable that a fuel hose connecting a fuel tank to a fuel filter is fixed to the back face of said girdle parts of said top cover and cylinder air-guide cover, whereby cooling air increased in temperature after cooling the engine does not contact directly with said fuel hose.  
         [0021]     By retaining the fuel hose connecting the fuel tank to the fuel filter securely on the back faces of the girdle parts extending from the top cover and cylinder air-guide cover behind the connecting part of the cylinder part and crankcase part, cooling air increased in temperature by cooling the engine does not contact directly with the fuel hose and occurrence of fuel hose damage due to repeated contact of the fuel hose with members near the hose due to vibration and/or shaking of the engine.  
         [0022]     The cooling air guide cover constructed as mentioned above can be easily assembled to the engine in a short time and contributes to largely reduce assembling man-hour. A forced-air-cooled engine equipped with the cooking air guide is increased in durability, reduced in lube oil consumption, suppressed I vibration of the cover resulting in reduced engine noise. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a perspective view of an engine to which the present invention applied, and cooling air flow is shown.  
         [0024]      FIG. 2  is a rear view of the engine of  FIG. 1  viewed from the output shaft side with cooling air flow being shown.  
         [0025]      FIG. 3 (A) is a side view viewed in the direction of the arrow P in  FIG. 2 .  
         [0026]      FIG. 3 (B) is a front view of the top cover removed from the engine and viewed in the same direction P in  FIG. 3 (A).  
         [0027]      FIG. 4  is a plan view viewed in the direction of the arrow Q in  FIG. 2  with cooling air flow being shown.  
         [0028]      FIG. 5 (A) is a side view viewed in the direction of the arrow R in  FIG. 2 .  
         [0029]      FIG. 5 (B) is a top view of the cylinder air-guide cover removed from the engine and viewed from above.  
         [0030]      FIG. 6  is a perspective view of the cooling air guide cover of the present invention showing the configuration thereof schematically with cooling air flow being shown.  
         [0031]      FIG. 7  is a perspective view of a conventional engine, and cooling air flow is shown. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     A preferred embodiment of the present invention will now be detailed with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, relative positions and so forth of the constituent parts in the embodiments shall be interpreted as illustrative only not as limitative of the scope of the present invention.  
         [0033]      FIG. 1  is a perspective view of an engine to which the present invention applied with the fuel tank, air cleaner, muffler, controlling device, etc. omitted, and cooling air flow is shown.  
         [0034]     In  FIG. 1 , reference numeral  13  is a crankcase-integrated cylinder block composed of a cylinder part  27  and a crankcase part  13 A formed into one block. Reference numeral  21  is a cylinder head fixed on top of the cylinder part  27 ,  12  are cooling fins of the cylinder part including cooling fins of the cylinder head. Reference numeral  22  is an exhaust outlet of the cylinder head,  23  is a cylinder head cover,  24  is an ignition plug. Reference numeral  14  is an output shaft of the rear side of a crankshaft, a cooling fan not shown in the drawing is attached to the end opposite to the output shaft (front side) of the crankshaft. reference numeral  11  is a fan cover, the fan cover being attached with its back plate to the cylinder block  13 . Reference numeral  17  a fuel hose connecting a fuel tank and a fuel filter both not shown in the drawing,  20  is a cylinder air-guide cover. Reference numeral  10  is a top cover, which is shown in  FIG. 6  in perspective view. The top cover  10  covers a left side surface and upper surface in  FIG. 1  of the crankcase part  13 A and further extends covering the cooling fins to the upper most cooling fin of the cylinder head. The top cover  10  extends laterally from the back plate of the fan cover  11  to the right side(output shaft side) end part of the crankcase part  13 A, the right side end of the top cover  10  being connected to a flange part provided to the right side end part of the crankcase part  13 A by mortise and tenon joint, and the left side end of the top cover  10  being connected to the back plate of the fan cover  11  by mortise and tenon joint. Space for allowing cooling air to flow through is secured between the left side surface and upper surface of the crankcase part  13 A and left side peripheries of cooling fins. A main blow-out opening  11   a (see  FIG. 4 ) is opened in the back plate of the fan cover  11  at a position facing the cooling fins of the cylinder part  27  and cylinder head  21  and a secondary blow-out opening  11   b  is opened in the back plate of the fan cover  11  at a position facing the lower part of the space between the left side surface of the crankcase part  13 A and the top cover  10 .  
         [0035]      FIG. 2  is a rear view of the engine of  FIG. 1  viewed from the output shaft side, and the same constituent parts as those of  FIG. 1  are denoted by the same reference numerals. In  FIG. 2 , reference numeral  19  is a hose clamp for fixing the fuel hose  17  to the connecting part of the cylinder air guide cocer  20  and top cover  10 , and reference numeral  18  indicates connecting ends of the connecting part. These will be detailed later in the explanation of  FIG. 6 .  
         [0036]      FIG. 3 (A) is a side view viewed in the direction of the arrow P in  FIG. 2 , and the same constituent parts as those of  FIG. 1-2  are denoted by the same reference numerals.  FIG. 3 (B) is a front view of the top cover removed from the engine and viewed in the same direction P in  FIG. 3 (A). A tenon  10   c  and tenon  10   d  for connecting the top cover  10  to the back plate of the fan cover  11  and to the flange part at rear end side(right side) of the crankcase part  13 A by mortise and tenon joint are shown in  FIG. 3 (A) and (B). The tenon  10   c  is inserted into a mortise provided to the back plate of the fan cover and tenon  10   d  is inserted into a mortise provided to the rear side end flange of the crankcase part  13 A.  
         [0037]      FIG. 4  is a plan view viewed in the direction of the arrow Q in  FIG. 2  with cooling air flow being shown, and the same constituent parts as those of  FIG. 1-3  are denoted by the same reference numerals. In  FIG. 4 , reference numeral  25  is a handle for manually starting the engine,  26  is a carburetor, and  27  indicate control links. Reference numeral  11   c  indicates a cooling fan attached to the crankshaft at the front end.  
         [0038]      FIG. 5 (A) is a side view viewed in the direction of the arrow R in  FIG. 2 , and the same constituent parts as those of  FIG. 1-4  are denoted by the same reference numerals. In  FIG. 5 (A), reference numeral  26   a  is a flange of the carburetor  26  for connecting air intake pipe not shown in the drawing. Reference numeral  28  is a fuel filter. Fuel sent by gravity from a fuel tank not shown in the drawing via the fuel hose  17  to the fuel filter  28  is supplied to the carburetor via a fuel pipe  29 .  
         [0039]     Reference numeral  26   a  is a flange of the carburetor for connecting an intake pipe not shown in the drawing. Reference numeral  20   c  is a front guide member of the cylinder air-guide cover  20 , the front guide member  20   c  being connected by mortise and tenon joint to composed the cylinder air-guide cover  20 .  
         [0040]      FIG. 5 (B) is a top view of the cylinder air-guide cover removed from the engine and viewed from above. In  FIG. 5 (B), members to provide a mortise  20   c  and  20   d  to the cylinder air-guide cover  20  are shown. The mortise  20   c  is engaged with a tenon member provided on the surface of the side wall of the crankcase part  13 A to fix the cylinder air-guide cover  20  to the cylinder block and the front guide member  20   e  is engaged with the mortise  20   d  to compose the front guide part.  
         [0041]      FIG. 6  is a perspective view of the cooling air guide cover of the present invention showing the configuration thereof schematically with cooling air flow being shown, and the same constituent parts as those of  FIG. 1-5  are denoted by the same reference numerals. Girdle parts  10   b  and  20   b  extend from the top cover  10  and cylinder air-guide cover  20  respectively bending across the downstream zone of cooling air flow on the surface of the crankcase part behind the connecting part of the cylinder part to the crankcase part, and these girdle parts  10   b  and  20   b  are connected by mortise and tenon joint at end parts  18  thereof to compose a cooling air guide cover. Grooves  10   a  and  20   a  of preferably circular arc cross section are formed on the back faces(downstream of the cooling air flow  15 ) of the girdle parts  10   b  and  20   b  for receiving the fuel hose  17 , a pair or pairs of detents  19 ,  19  (clamp part) protrude from both sides across the groove with the distance between the pair of detents being smaller than the diameter of the fuel hose, and the fuel hose  17  can be stably retained in the grooves  10   a  and  20   a  pinched by the detents by pushing the hose into the grooves.  
         [0042]     It is permissible not to provide the grooves, instead a pair or pairs of detents are provided on at flat faces of the girdle parts. In the case the groove is provided, there is an advantage that the detents can be reduced in height and fear of breakage of the detents is eliminated. Clamps well known in the art may be used instead of the detents. Reference numeral  29  and  30  are bolt-holes for fixing the top cover  10  and cylinder air-guide cover  20  to the cylinder block  13  by means of bolts. Although two holes are provided, the number of holes may be increased as necessary.  
         [0043]     Cooling air flow is shown by arrows with bold broken line in  FIGS. 1, 2 , and  4 , and by arrows with chain line in  FIG. 6 .  
         [0044]     Referring to  FIGS. 1, 2 ,  4 , and  6 , cooling air flow will be explained hereunder.  
         [0045]     Cooling air  15  blown out from the main blow-out opening  11   a  opened in the back plate of the fan cover  11  flows through between fins  12  of the cylinder part  27  and cylinder head  21  while cooling the cylinder and cylinder head to be exhausted backward from the engine. At the R-side in  FIG. 2  of the cylinder and cylinder head, the cooling air  15  is guided by the cylinder air-guide cover  20 .  
         [0046]     On the other hand, cooling air  16  blown out from the secondary blow-out opening  11   b  opened in the back plate of the fan cover  11  enters the space between the top cover  10  and a side surface of the crankcase part  13 A. The top cover  10  is connected to the back plate of the fan cover  11  by means of the tenon  10   c  and to the rear side flange part of the crankcase part  13 A by means of the tenon  10   d,  and the space between the top cover  10  and said side surface of the crankcase part  13 A is closed at the left, right, end lower end part, and open only towards the cylinder part and cylinder head side. Therefore, the cooling air  16  flows upwards along said side surface of the crankcase part. By the way, it is permissible that the closing at the left, right, end lower end part of the top cover  10  is not perfect, because, even if little leakage of the cooling air  16  occurs, the cooling air flows upwards along the surface of the crankcase part. The cooling air  16  flows guided by the top cover  10  upwards and hits the cylinder part and cylinder head as shown by air flow  16   b,  where the cooling air  16   b  joins a part of the cooling air  15  blown out from the main blow-out opening  11   a  to be exhausted backward from the engine together with the cooling air  15 . That is, the cooling air blown out from the secondary blow-out opening  11   b  cools the one side and upper part of the crankcase part  13 A, then enters the space between the cooling fins  12  to participate in cooling the cylinder part and cylinder head. By determining properly the ratio of the opening area of the secondary blow-out opening  11   b  to that of the main blow-out opening  11   a,  the rate of flow rate of the cooling air  16  to that of the cooling air  15  can be optimized for total cooling of the engine.  
         [0047]     As shown in  FIG. 6 , the cooling air  15  blown out from the main blow-out opening  11   a  flows in backward direction(in left direction in the drawing), and the cooling air  16  flows upward along the one side of the crankcase part, then flows into the cooling air flow  15  and then in backward direction together with the cooling air  15 , the cooling air does not contact directly with the fuel hose  17  retained on the back face of the girdle parts  10   b  and  20   b  of the top cover  10  and cylinder air-guide plate  20 , and the fuel hose  17  is securely fixed on the girdle parts, so it will not happen that the fuel hose is shook due to vibration and/or shaking of the engine, and occurrence of damage of the fuel hose can be positively prevented.  
         [0048]     The top cover  10  and cylinder air-guide cover is preferably made of heat resistant resin by injection molding, by which the cooling air guide which is complicated in configuration can be provided with ease and low cost, and in addition engine noise can be reduced.