Disposition structure of heat exchanger in motorcycle

A disposition structure of a heat exchanger (oil cooler) in a motorcycle mounted in the central part in front of the upper part of the crankcase of an internal combustion engine E mounted on the motorcycle. When viewed from the front of the motorcycle, the oil cooler is located between the front forks. The oil cooler is disposed so that the fin surface of the cooling fins of the heat exchanger are perpendicular or substantially perpendicular to an air flow that goes between the front forks and above the front wheel. In the disposition structure so configured, cooling efficiency of the heat exchanger is improved.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2003-435632, filed Dec. 26, 2003, Japanese Patent Application No. 2004-181274, filed Jun. 18, 2004, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disposition structure of a heat exchanger in a motorcycle, and more particularly to improvement technique on a disposition structure of a heat exchanger on a motorcycle, which has been considered from a point of view of improving cooling efficiency of the heat exchanger.

2. Description of Background Art

Conventionally, as disposition structure of the heat exchanger in a motorcycle, there is known structure in which a heat exchanger has been disposed forward of an internal combustion engine. Thus, this disposition structure of the heat exchanger is that it has been arranged in a substantially upright position to a vehicle advance direction.

Since, however, since an actual air flow passes through and between front forks and above the front wheel, and then goes toward the internal combustion engine (see, for example, Japanese Patent No. 3206151 (P.3, FIG. 1-2), and Japanese Utility Model Laid-Open No. Hei 1-176591), in such a disposition structure of the heat exchanger, an angle of incidence of the air flow to cooling fins of the heat exchanger becomes small so that no high cooling effect can be obtained. As a result, the maximum efficiency in the heat exchanger could not be brought about; however in order to secure sufficient cooling property in the internal combustion engine, it was necessary to make the heat exchanger larger sized. In the case of an air-cooled internal combustion engine, when there is the heat exchanger in front of the internal combustion engine, an air flow rate to be applied to the engine decreases, and when the heat exchanger is large, a problem in design cannot be ignored either.

In the invention described in Japanese Patent No. 3206151, shown inFIGS. 13(a) and13(b), there has been described disposition structure of an oil cooler01in which a water-cooled engine0E mounted on a motorcycle is described. An oil cooler01of this engine0E is installed in the lower part, forward of the engine0E below a radiator02; and the oil cooler01is disposed with respect to the vehicle body with the slightly upper portion of a surface on which its multiplicity of cooling fins011stand in a row forward tilted. These cooling fins011extend in a direction orthogonal to the vehicle advance direction, and therefore, these cooling fins011are arranged with their fin surface at an angle substantially parallel with respect to the air flow.

Also, even in the invention described in Japanese Utility Model Laid-Open No. Hei 1-176591, shown inFIG. 14, as in the case of the invention described in Japanese Patent No. 3206151, there has been described structure, in which the oil cooler01is installed below the radiator02and in the lower part forward of the engine0E close to the oil pan03; and a surface on which its multiplicity of cooling fins stand in a row is actually placed in a state in which it is perpendicular or substantially perpendicular to the vehicle advance direction. Thus, these cooling fins extend in a direction orthogonal to the vehicle advance direction and the fin surface of the cooling fins is made horizontal or substantially horizontal to the air flow.

In the invention described in the above-described Japanese Patent No. 3206151 (P. 3, FIG. 1-2), and Japanese Utility Model Laid-Open No. Hei 1-176591, disposition of the oil cooler which is the heat exchanger in either case, has such a relationship that the cooling fins extend in a direction orthogonal to the air flow during vehicle driving; thus the cooling fins are arranged with their fin surfaces parallel to or substantially parallel to, or inclined by a predetermined acute angle to the air flow. Setting of this opposition relationship of these cooling fins with respect to the air flow is appreciated in its own way from points of view of formation of a smooth flow in the air flow and securing of predetermined heat exchange efficiency because the air flow flows between the cooling fins without meeting with any resistance comparatively.

Since, however, the air flow flows away so as to stroke the surface of the cooling fins, the formation of a smooth flow in the air flow is not capable of applying a sufficient amount of air flow to the cooling fins, nor is sufficient cold given to the fin surface of the cooling fins, and in the sense that the cold of the air flow is more effectively absorbed to make the best use in the cooling fins, any acceptable result is never given. There is, however, room for improvement from a point of view of further improving the heat exchange efficiency in the heat exchanger.

Also, according to the above-described disposition structure of heat exchanger, since a plane having large area on which a multiplicity of cooling fins of the heat exchanger stand in a row opposes an air flow so as to intercept at right angles or substantially at right angles, its projected area is large, and a flow of the air flow to be directly applied to the engine is significantly affected leading to the decreased running air flow rate to be directly applied to the engine.

Therefore, the above-described disposition structure of heat exchanger is not appreciated from a point of view of cooling of the engine in above all air-cooled internal combustion engine.

Under such circumstances as described above, it would be desirable to improve the structure by a comparatively simple change in structure for further improving heat exchange efficiency of the heat exchanger in a motorcycle.

Such an improved structure would dispose the heat exchanger on the motorcycle in a manner that would allow a sufficient supply of air flow to be supplied to the cooling fins during vehicle driving, thus bringing about the maximum heat exchange efficiency.

SUMMARY AND OBJECTS OF THE INVENTION

An object of the present invention is to develop a disposition structure of the heat exchanger in a motorcycle for solving the above-described problems, and particularly concerning improvement in disposition structure of the heat exchanger in which a point of view has been laid on the improved cooling efficiency of the heat exchanger. To achieve this object, the present invention provides a disposition structure of the heat exchanger in a motorcycle equipped with: a front fork to be installed to a head pipe forward of a body frame; a front wheel to be supported by the front fork; an internal combustion engine to be arranged behind the front wheel; and the heat exchanger having cooling fins arranged between the internal combustion engine and the front wheel, characterized in that the heat exchanger concerned is disposed in order that the cooling fins may have such relationship that their fin surface becomes perpendicular or substantially perpendicular to an air flow that passes through between front forks and above the front wheel to go through the lower part of the internal combustion engine.

Also, the present invention is characterized in that the heat exchanger is provided in the upper part of a crankcase in the neighborhood, below a cylinder of the internal combustion engine.

Further, the present invention is characterized in that a pitch of the cooling fins in the heat exchanger is made larger in the central part, and smaller in the end portions.

Also, the present invention is characterized in that the heat exchanger is formed in a round shape.

In addition, the present invention is characterized in that a cylinder block above the heat exchanger is provided with cooling fins in a direction of the cylinder axis.

The present invention provides several advantages.

According to a first aspect of the present invention, since the heat exchanger is disposed in order that the cooling fins have such relationship that their fin surface becomes perpendicular or substantially perpendicular to an air flow that passes through between front forks and above the front wheel to go through the lower part of the internal combustion engine, the heat exchanger has been laid out to be perpendicular, when viewed from the vehicle side, to the air flow that passes through between front forks and goes through the lower part of the engine.

Therefore, by installing at an angle of the best efficiency with respect to a flow of the air flow of the motorcycle, it is possible to apply more air flow to the cooling fins of the heat exchanger for raising the cooling efficiency, and since an advance-guard projected area of the heat exchanger as viewed from the front of the vehicle can be reduced, a flow rate of the air flow to be conducted into the engine itself also increases, and it is possible to conduct the air flow to each of the heat exchanger and the engine. As a whole, the cooling property can be improved.

According to a second aspect of the present invention, since the heat exchanger has been provided in the upper part of a crankcase in the neighborhood below a cylinder of the internal combustion engine, an air flow that has changed its direction by striking against the cylinder and the cylinder head can be effectively introduced into the heat exchanger and be utilized.

According to a third aspect of the present invention, since a pitch of the cooling fins in the heat exchanger has been made larger in the central part, and smaller in the end portions, by widening the pitch in the central part of the heat exchanger, it is possible to restrain the air flow from being spread by the heat exchanger, and as a result, a lot of air flow can be caused to pass through the heat exchanger. Also, in the case of the air-cooled internal combustion engine, the air flow that has struck against the heat exchanger can be effectively introduced to the cooling fins and the like provided on the cylinder.

According to a fourth aspect of the present invention, since the heat exchanger has been formed in a round shape, the air flow that is going through sideways from the heat exchanger can be effectively used for cooling.

According to a fifth aspect of the present invention, since a cylinder block above the heat exchanger has been provided with cooling fins in a direction of the cylinder axis, the cylinder block is positively utilized as a wall against the air flow, whereby utilization efficiency of the air flow can be improved. In other words, the air flow that has struck against the cylinder block can be positively introduced toward the heat exchanger by the cooling fans directed toward the direction of the cylinder axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The heat exchanger is disposed in order that the cooling fins of the heat exchanger may have such relationship that their fin surface becomes perpendicular or substantially perpendicular to an air flow that passes through between forks of the front fork to go through the lower part of the internal combustion engine.

FIG. 1shows partial structure of a motorcycle, which is a vehicle50on which an internal combustion engine E equipped with a heat exchanger according to the first embodiment is to be mounted, and in the figure concerned, only the structure in the neighborhood of a portion on which the engine E has been mounted is shown. The motorcycle has a head pipe51for forming a front part of its body frame, and the head pipe is provided with a front fork53(seeFIG. 11) for supporting a front wheel52which is not shown inFIG. 1in the lower part thereof, and a handlebar, not shown, mounted on the upper part thereof.

Main frame and down tube, not shown, are installed in the head pipe51; seat rail and back stay, not shown, are installed in the main frame; and further a swing arm58for supporting a rear wheel is installed therein.

The body frame is mounted with an internal combustion engine E as described previously, inFIG. 1, the engine E is shown by a predetermined cross-sectional view in its side sight; for the engine E, a four-cycle parallel four-cylinder engine is adopted; this engine E has an overhead valve type twin cam mechanism (DOHC); when mounted onto a vehicle50, it is arranged such that a head exhaust port E2side of the cylinder E0faces the running direction and the intake port E1side faces upward on the right side; an intake pipe E11extends from above a cylinder E0upward on the right side; and this intake pipe E11is connected to a carburetor and an air cleaner which are not shown. Also, the exhaust pipe21extends from the front side of the cylinder E0toward the rear through below the vehicle body.

The lower part of the cylinder E0of the engine E is placed on and fixed to the upper part of the crankcase1, and the cylinder E0is composed of: a cylinder block2directly coupled and fixed to the crankcase1; a cylinder head3, the lower part of which is coupled and fixed to the upper part of the cylinder block2; and further a cylinder head cover4for covering the upper part of the cylinder head3and fixed to the head3, and the structure is arranged by making these structural portions integral with one another by stud bolts and the like after all.

On the crankcase1, as shown inFIG. 2, a crankshaft10is rotatably supported; to crankpins10aof the crankshaft10at four places, connecting rods10bare mounted via their large ends10c, respectively; and to small ends10dof these connecting rods10b, pistons P are mounted via piston pins10e, respectively. Thus, these pistons P reciprocally slide within cylinder holes2ato2dformed in the cylinder block2.

Also, to the crankshaft10, a driving gear10fis installed at a position close to right shown in the figure in the longitudinal direction; this gear10fmeshes with a driven gear11aloosely fitted on the main shaft11of a transmission; a rotary driving force from the crankshaft10is transmitted from the driven gear concerned11ato the main shaft11via an opening and closing clutch11b; the rotation of the main shaft11is transmitted to a counter shaft12through selective gear meshing in a shift gear G; and the rear wheel which is a vehicle running driving wheel, not shown, is rotated via a driving chain13by a driving sprocket12a.

On the crankshaft10, there are provided two sprockets10g,10hhaving different diameters in parallel at a substantially central portion in the longitudinal direction; the large-diameter sprocket10gis used to drive a generator15via a chain14(also seeFIG. 1); and to the generator15, there is connected a starting motor with coaxial relationship via an one-way clutch, not shown. Also, the small-diameter sprocket10his used to drive the camshaft by a chain16to be described later. Further, a pulser rotor10iis installed at a position close to the left shown in the longitudinal direction of the crankshaft10.

At the bottom below the crankcase1, there is provided an oil pan1b(seeFIG. 1); substantially perpendicularly above the oil pan1b, there are disposed oil pumps LpA, LpB; and the case1is provided with an oil filter Lf for filtering lubricating oil which receives discharged oil from the oil pumps LpA, LpB, an oil cooler Lc for returned oil which has been used to cool the engine, and the like.

In this respect, concerning characteristic disposition structure of the oil filter Lf and the oil cooler Lc to the case1, an oil supply passage for lubrication and cooling to be disposed in the crankcase1and the cylinder E0, and the supply of oil using the supply passage, since the detailed description will be made later, the description is omitted here.

On the upper part of the above-described crankcase1, the cylinder block2is placed and fixed as described above. The cylinder block2is shaped like a long and substantially rectangular shape in a direction orthogonal to the back-and-forth direction of the vehicle50in the plane sight as shown inFIG. 3; there are arranged such four cylinder holes2ato2das shown in parallel along its longitudinal direction; and within these cylinder holes2ato2d, the above-described pistons P are arranged so as to be able to reciprocally slide.

In a central part20of the cylinder block2in the longitudinal direction, there is formed a space portion21, through which the above-described camshaft driving chain16passes; this space portion21penetrates the block2from top to bottom at a position slightly close to the rear in the widthwise direction of the block2of the central part20of the block2in the longitudinal direction thereof; and is shaped like a long and substantially rectangle in the widthwise direction in the plane sight of the cylinder block2. Therefore, four cylinder holes2ato2dof the cylinder block2are arranged such that two each are spaced apart from each other right and left by the space portion21at the central part20of the block2in the longitudinal direction.

On the upper part of the cylinder block2, there is fixed a cylinder head3; the cylinder head3is shown inFIG. 4; the figure is a top view showing the cylinder head3in a predetermined cross section; as could be understood from this figure, the cylinder head3is shaped like a substantially rectangle as in the case of the cylinder block2; as will be apparent by referring toFIG. 2, in the lower part thereof, there are four concave portions3a1to3d1corresponding to the four cylinder holes2ato2din the cylinder block2; and by upper portions of these concave portions3a1to3d1and respective cylinder holes2ato2dof the cylinder block2, combustion chambers3ato3dare formed.

Each of the combustion chambers3ato3dis fitted with an ignition plug3eso as to face the chamber; as shown inFIG. 2, in these combustion chambers3ato3d, there are opened intake ports and exhaust ports3f,3grespectively; to the intake/exhaust ports3f,3g, there communicate intake/exhaust passages3h,3i; the intake passage3his fitted with a fuel injection system which is not shown in the figure; and further, a valve train composed of intake/exhaust valves3k,3mfor opening and closing the intake/exhaust ports3f,3gin these combustion chambers3ato3dand two camshafts having cams for opening and closing these intake/exhaust valves3k,3m, and the like are arranged in a structural portion of the cylinder head3.

In the above-described top view showing the cylinder head3as shown inFIG. 4, there is provided a space portion31for the above-described camshaft driving chain16which, in a central part30of the cylinder head3in the longitudinal direction, is located close to the rear in the widthwise direction, and which penetrates the head3having predetermined width and length from top to bottom; the position of this space portion31is matched to that of a space portion21for the chain16provided on the cylinder block2; and in a joining portion between the cylinder head3and the cylinder block2, shapes of opening of the space portions21,31are arranged to have conformity to each other.

Therefore, as shown inFIG. 1, the camshaft driving chain16for passing through the space portions21,31has been arranged so as to be able to pass from the crankshaft10to the upper part of the cylinder head3without hindrance. In this respect, inFIG. 1, reference symbol16adesignates a chain tensioner; and16b, a damper for adjusting the tension of the chain tensioner. Also, one to be indicated by an arrow “a” inFIG. 4is a flow of air flow during vehicle driving.

The above-described valve train is, as could be understood by referring toFIGS. 1,2and the like, straightforwardly comprised of a valve operating mechanism including: two camshafts32,33having a plurality of cams32a,33a; a driving mechanism for driving these camshafts32,33; lifters3k2,3m2for intake/exhaust valves3k,3mfor abutting against the cams32a,33ato press their valve stems3k1,3m1, and the like.

These two camshafts32,33are rotatably supported by the bearings in the upper part of the cylinder head3, and at predetermined intervals in the longitudinal direction so as to intersect at right angles the advance direction of the vehicle50, and yet with positional relationship in parallel to each other; and the cams32a,33a(seeFIG. 2), which these camshafts32,33have respectively, are caused to abut against the valve lifters3k2,3m2in order to open and close the intake/exhaust valves3k,3mas described above.

Therefore, these cams32a,33aare disposed on the camshafts32,33correspondingly to the upper ends of the valve stems3k1,3m1of each intake/exhaust valve3k,3m; in the present embodiment, the camshaft32of the vehicle50on the rear side is a camshaft32in which an opening/closing cam32aof the intake valve3kis to be disposed; the camshaft33on the front side is a camshaft33in which an opening/closing cam33aof the exhaust valve3mis to be disposed; as shown inFIG. 2, in each combustion chamber3ato3d, two intake valves3kand two exhaust valves3mare disposed respectively; and therefore, eight cams32a,33aare disposed on these two camshafts32,33, respectively.

Thus, as shown inFIG. 1, of two camshafts32,33arranged on the upper part of the cylinder head3described above, to the rear camshaft32, a rotary driving force from the crankshaft10is transmitted; this driving force is transmitted by the camshaft driving chain16laid over between the sprocket10hof the crankshaft10and the sprocket32bof the camshaft32. The driving force transmitted to the rear camshaft32is further transmitted to the front camshaft33; and this driving force is transmitted by the between-camshafts driving chain34laid over between the sprocket32cof the rear camshaft32and the sprocket33cof the front camshaft33.

In an operation of the internal combustion engine E, therefore, a rotary driving force of the crankshaft10is transmitted to both camshafts32,33respectively via the camshaft driving chain16and the driving chain34between camshafts. By rotation of the cams32a,33asynchronized with the rotation of the crankshaft10due to the rotation of the both camshafts32,33, an opening and closing operation of the intake/exhaust valve3k,3mis performed in synchronization with ascent and descent of the piston P as is generally known through pushing movement of the above-described valve lifters3k2,3m2and valve stems3k1,3k2and air intake/exhaust in combustion within the engine is performed.

The upper part of the cylinder head3is covered with a cylinder head cover4, and the cylinder head cover4has, as shown in the perspective view ofFIG. 5, substantially rectangular structure which is long in a direction orthogonal to the vehicle advance direction, as in the case of the cylinder head3to be covered with the cover4. This cover4covers two camshafts32,33(shown in dotted line) from above substantially completely, and the upper part of space in which sprockets32b,32c,33cto be installed to a substantially central portion of the camshaft32,33in the longitudinal direction are accommodated and the chains16,34move is covered with a chain cover41which is to be arranged as separate structure.

Therefore, the chain cover41actually crosses the central part of the cylinder head cover4, and the cylinder head cover4is, as a whole, shaped like a substantially H-character shaped exterior shape shown inFIG. 5in its plane sight.

A motorcycle according to an embodiment of the present invention and structure of an engine to be installed onto the motorcycle are generally as described above.

The description will be made of the oil cooler Lc which is the above-described heat exchanger to be installed to the internal combustion engine E according to the present invention, an outline of structure of the oil filter Lf and its characteristic disposition structure to the engine E, and also supply structure of lubricating oil and cooling oil in the engine E including this oil cooler Lc and oil filter Lf.

The oil cooler Lc and the oil filter Lf are, as shown inFIGS. 1,6and the like, both installed to the front side of the engine E toward the advance direction of the vehicle50; more specifically, the oil cooler Lc, which is a heat exchanger, is installed to a front-side center1con the upper part of the crankcase1; the oil filter Lf is installed to a front-side center1dof the lower part of the crankcase1; the oil cooler Lc and the oil filter Lf are arranged to have up-and-down relationship with each other when viewed from the front of the vehicle50; and the oil cooler Lc is arranged so as to be located just above the oil filter Lf vertically (seeFIGS. 8,10and11).

The oil cooler Lc has, as will be apparent by referring toFIGS. 6,8,9,10and the like, an exterior shape of a rectangular parallelepiped having two large surfaces LcA, LcB, which oppose to each other, opposite surfaces LcC, LcD which make a long pair narrow in width for opposing to each other, and opposite surfaces LcE, LcF which make a short pair narrow in width; on those two large surfaces LcA, LcB, which oppose to each other, has a plurality of cooling fins F which have been arranged in parallel at equal spaces in parallel to one another over the substantially entire surface in those surfaces; and these cooling fins F extend with have the above-described relationship along the longitudinal direction of those two large surfaces LcA, LcB.

As shown inFIG. 8, the oil cooler Lc extends in the lateral direction such that its longitudinal direction actually crosses between the down tubes55of the body frame. In other words, the oil cooler Lc extends between the down tubes55which make the pair toward a direction in which its longitudinal direction intersects at right angles the back-and-forth direction of the vehicle50and yet, is arranged such that those two large surfaces LcA, LcB with their cooling fins F provided are placed up or down; and the one surface LcD long and narrow in width which makes the pair is fixed at the center1cof the front side above the crankcase1, whereby the oil cooler Lc is installed to the front of the engine E (seeFIG. 6).

Therefore, cooling fins F of the oil cooler Lc are positioned as structure in which on those two large surfaces LcA, LcB which have been arranged up or down, a plurality of the cooling fins F have been actually arranged to extend in parallel to one another in a direction orthogonal to the back-and-forth direction of the vehicle50. The oil cooler Lc is installed such that as shown inFIGS. 6,8,9,10and the like with the disposition structure of these cooling fins F, it points substantially horizontally in a longitudinal direction of the long side LcC, LcD narrow in width in the rectangular parallelepiped, more specifically, such that the oil cooler Lc protrudes from the front-side center1con the upper part of the crankcase1of the engine E with the front side slightly lowering toward the front of the vehicle50with the one side LcC long and narrow in width in front.

As shown inFIG. 11(a), the oil cooler Lc to be arranged between the down tubes55(omitted inFIG. 11(a)) which make a pair in the body frame has the relationship in which when viewed from the front of the vehicle50, it is just located between forks53aand53bwhich make the pair in the front fork53for supporting the front wheel52, and an air flow “a” that goes through between the forks53a,53bduring traveling of the vehicle50for flowing below the engine E directly flows toward the oil cooler Lc.

Therefore, the oil cooler Lc is cooled by the air flow “a” exceedingly effectively, and yet, since there has been adopted the disposition structure in which the fin surface of the cooling fins F of the oil cooler Lc extend in a direction to intersects at right angles the back-and-forth direction of the vehicle50; that is, since there has been adopted such disposition structure that the fin surface of the cooling fins F actually becomes perpendicular or substantially perpendicular to the flow of the air flow “a,” the cooling effect is further improved.

Also, the oil filter Lf is, as will be apparent fromFIGS. 1,6,11(a) and the like, substantially cylindrical as its exterior shape, and on disposing the oil filter Lf to the lower part of the crankcase1, the oil filter Lf is arranged to protrude from the front-side center1dof the lower part of the crankcase1which has deviated slightly downward from space between the down tubes53a,53b, which make a pair, toward the front of the vehicle50, and the cylindrical oil filter Lf protrudes just below the oil filter Lc vertically although it has been described already. In this respect, as regards the internal structure of the oil cooler Lc and the oil filter Lf, it has been conventionally known, and since it is not especially characteristic, the description is omitted.

The structure of supply passages of lubricating oil and cooling oil including the oil cooler Lc and the oil filter Lf and lubrication and cooling of the engine E due to these oil supply passages are generally as described below.

At the bottom below the crankcase1of the internal combustion engine E according to the present embodiment, there is provided the oil pan1bas shown inFIGS. 1,6,9and the like, and as described already; just above this oil pan1b, more specifically, in the upper part substantially vertically, there are disposed two oil pumps LpA, LpB; and a suction port of this oil pump LpA, LpB is coupled to a strainer1b1to be immersed in oil within the oil pan1bvia an oil suction pipe LA1, LB1extending downward respectively. To each discharge port of the oil pumps LpA, LpB, an oil supply passage LA, LB is coupled, and two oil supply systems are actually constituted by these passages LA, LB.

Their one oil supply system is a supply passage for lubricating oil to be used for lubrication of the engine E at each place, and the passage consists of an oil supply passage LA as could be understood by referring toFIGS. 6,7and10, and has: a passage LA2for communicating the discharge port of the pump LpA to an oil inlet of the oil filter Lf; a passage LA3for communicating to a main gallery LA4for extending an oil outlet of the oil filter Lf along the longitudinal direction of the crankshaft10under a crankshaft10; six oil supply passages LA5for communicating this main gallery LA4to positions corresponding to six journals1aof the crankshaft10one another; and four injection holes1a1provided on a predetermined journal1afor directly injecting the lubricating oil in the journal1aof the crankshaft10toward the inner walls of four cylinder holes2ato2d(see alsoFIG. 2).

Thus, there are provided four passages LA6(seeFIG. 7) which pass through between the cylinder holes2ato2dof the cylinder block2for communicating a predetermined journal1aof the crankshaft10to four oil supply passages LA7for lubricating the valve system such as the cams32a,33aand the camshafts32,33. In this respect, inFIG. 7, only one oil supply passage LA7is shown and the others are omitted. The passage LA7is to be provided correspondingly to each of those four cylinders.

Also, the other oil supply system is a supply passage of cooling oil to be used for cooling of the engine E, the passage consists of an oil supply passage LB as could be understood by referring toFIGS. 6,7, and has: a passage LB2for communicating the discharge port of the oil pump LpB to an oil supply gallery LB3for extending along the longitudinal direction of the block2in the lower part of the cylinder block2on the intake side; and four passages LB4for communicating to inlets of four annular passages LB5formed on an ignition plug installation portion above each of four combustion chambers3ato3dby passing through, on the intake side of the cylinder block2, in its vertical direction from the oil supply gallery LB3. In this respect, inFIG. 7, only one annular passage LB5is shown, and the others are omitted.

Further, the other oil supply system has: four passages LB6for communicating an outlet of the above-described annular passages LB5to an oil discharge gallery LB7; a short passage LB8for communicating the oil discharge gallery LB7to a return oil receiving port of the oil cooler Lc; and a return oil passage LB9for connecting the outlet of the oil cooler Lc to the oil pan1b, and the oil supply gallery LB3has also a small oil supply passage LB10to the cam chain16(seeFIG. 7).

Next, the description will be made of supply of oil for lubrication and cooling in the engine E due to the above-described oil supply passages LA, LB.

First, as regards supply of oil for lubrication in the engine E through the one oil supply system, by an operation of the pump oil LpA relating to an operation of the engine E, the lubricating oil within the oil pan1bis sucked up by the oil pump LpA via the strainer1b1and an oil suction pipe LA1; the lubricating oil sucked up within the pump LpA is fed under pressure from a pump discharge port with the pump pressure raised; and this oil fed under pressure is fed to the oil filter Lf via a passage LA2for communicating the oil pump LpA to the oil filter Lf.

The lubricating oil entered the oil filter Lf is filtered by the filter Lf; after metallic pieces, dust and the like mixed into the oil are removed, the lubricating oil is fed into the main gallery LA4under pressure; is fed from here to each journal1aof the crankshaft10, the bearing portion of the connecting rod10band the like via six passages LA5under pressure to be used for lubricating these portions; is supplied to four supply passages LA7to the valve system such as the cams32a,33aand the camshafts32,33for extending upward within the cylinder head3via those four passages LA6within the cylinder block2; and each portion in the valve system is lubricated efficiently.

Also, a part of the lubricating oil is directly injected from an injection portion1a1provided on a predetermined journal1aof the crankshaft10toward the inner walls of the cylinder holes2ato2d(seeFIGS. 2,6), and a sliding portion and the like between the inner walls and the piston rings are effectively lubricated. Thus, the oil used for lubricating each of these portions of the engine E flows along the inner walls and the like of the engine E as oil drops, and directly drops within the oil pan1bat the lower part below the crankcase1.

Also, as regards supply of oil for cooling in the engine E through the other oil supply system, the cooling oil is discharged and fed under pressure from the oil pump LpB via a process similar to the foregoing; the oil is supplied the oil supply gallery LB3for extending along the longitudinal direction of the cylinder block2below the intake side of the engine E via the passage LB2; and is supplied within an annular oil supply passage LB5for surrounding the ignition plug3ewithin an ignition plug installation seat of each of four combustion chambers3ato3dfrom the oil supply gallery LB3via four passages LB4of the cylinder block2on the intake side (seeFIGS. 6,7). By supplying this cooling oil, the installation seat of the ignition plug3eand its neighborhood are effectively cooled.

Thus, the above-described cooling oil which has passed through within those four annular oil supply passages LB5within the installation seat of the ignition plug3ecrosses the ignition plug3einstallation seat below the cylinder head3; reaches the oil discharge gallery LB7of upper part of the crankcase1on the exhaust side via four return passages LB6of the cylinder block2on the exhaust side; becomes return oil which enters the oil cooler Lc from here via the short passage LB8; and after cooled in the oil cooler Lc, is returned within the oil pan1bvia the return oil passage LB9. Also, in this oil supply process, lubrication in the cam chain16is performed through the small oil supply passage LB10from the oil supply gallery LB3(seeFIG. 7).

In the above-described first embodiment according to the present invention, above all with the provision of characteristic disposition structure of the oil cooler Lc to the vehicle50or the engine E, the side LcC long and narrow in width which the cooler Lc intersects at right angles is caused to oppose to the air flow “a” that goes through between forks53a,53bof the front fork and flows below the engine E during traveling of the vehicle50, and yet the side LcC points to slightly descend forward. Therefore, a multiplicity of cooling fins F to be disposed actually in parallel along the long side LcC of the cooler Lc are disposed such that their fin surface becomes perpendicular or substantially perpendicular to the air flow “a”, and the air flow “a” can be directly applied to the large fin surface of the cooling fins F effectively. Accordingly, it becomes possible to effectively absorb cold of the air flow, and the heat exchange function in the oil cooler Lc is greatly improved (seeFIG. 11(a)).

Also, since the oil cooler Lc has disposition structure in which the side LcC long and narrow in width is caused to oppose to the running direction of the vehicle, an advance-guard projected area of the oil cooler Lc as viewed from the front of the vehicle50can be reduced, and irrespective of the existence of the cooler Lc in protruding arrangement in front of the engine E, the air flow “a” of a sufficient amount is directly conducted into the engine E, and therefore, the cooling efficiency of the engine E can be improved (seeFIG. 11(a)).

Further, since the oil cooler Lc has been disposed on the upper part of the crankcase1in the neighborhood below the cylinder E0of the internal combustion engine E, the air flow “a” that collides with the cylinder block2or the cylinder head3to change its direction can be effectively taken into the oil cooler Lc and utilized, and therefore, the oil cooler Lc exhibits an operating effect capable of further improving the heat exchange efficiency in the oil cooler Lc among others.

In the first embodiment of the present invention, the cooling fins F1in the cylinder block2above the heat exchanger are provided in a direction perpendicular to the axial direction of the cylinder, that is, to point in a horizontal or a substantially horizontal direction (seeFIGS. 2,6,11(a) and the like), whereas in this second embodiment, as shown inFIG. 12, the cooling fins F1in the cylinder block2above the heat exchanger are provided in parallel or substantially in parallel to the axial direction of the cylinder, that is, to point in a vertical or substantially vertical direction.

According to the structure of this second embodiment, in addition to the operating effect in the first embodiment, the cylinder block2can be positively utilized as a wall against the air flow, and therefore, the utilization efficiency of the air flow is improved. In other words, the air flow that has struck against the cylinder block2can be positively introduced toward the heat exchanger by the cooling fins F1pointing to the cylinder axial direction.

In such an air-cooled internal combustion engine as described in the present first or second embodiment, cooling between the cylinder bores and in the neighborhood of the plug seat may be hindered when a heat exchanger is arranged in front of the internal combustion engine. However, such a cooling mechanism can be effectively utilized by means of the structure in the above-described first or second embodiment according to the present invention.

In this respect, in the above-described first or second embodiment, the multiplicity of cooling fins F of the oil cooler Lc have been provided at equal pitches, but the present invention is not limited thereto as a matter of course, but the pitch can be appropriately selected, and for example, the pitch of the cooling fins F in the oil cooler Lc is selected such that it is made large in the central part LcA, LcB while it is made small at the end portions LcE, LcF, whereby taking-in of the air flow that directly strikes against the oil cooler Lc is improved, and dispersion of the air flow by collision with the cooler Lc is restricted. As a result, an air flow rate of the air flow that passes through the cooler Lc can be increased.

Also, although the exterior shape of the oil cooler Lc in the first or second embodiment has been made into a square shape of the rectangular parallelepiped, the present invention is not limited thereto; however, for example, it is possible to make it into Such a round shape as shown inFIG. 11(b) by entirely giving roundness. If this shape is selected, the air flow that is going through at the side of the oil cooler Lc can more effectively be used for cooling in the cooler Lc.

An internal combustion engine equipped with disposition structure of the oil cooler Lc and the oil filter Lf according to the first or second of the present invention can be applied to not only the motorcycle, but also other similar vehicles.