Motorcycle cooling system

A cooling system for the internal combustion engine of a motorcycle includes a radiator and means defining air passages each having a forwardly facing inlet opening disposed respectively on the opposite sides of the motorcycle's front fork. Each air passage extends rearwardly from the inlet opening to an outlet which opens into a plenum chamber disposed adjacent the radiator. The cross-sectional area of each passage increases gradually between its inlet and outlet ends. An exhaust duct is connected to the plenum chamber and the radiator is disposed between the plenum chamber and the exhaust duct.

BACKGROUND OF THE INVENTION 
This invention relates to motorcyles and more particularly to a motorcyle 
cooling system. 
In the prior art, motorcycle engines have been both air and water cooled. 
When water cooling is employed, sufficient ambient air must be passed 
through the radiator to satisfy the cooling requirements of the engine. 
This has created design problems in that the bow wave created by the front 
portions of the motorcyle such as the fork, the fairing, the fender, and 
the headlight, tend to divert the air stream outwardly of the radiator, 
particularly when the same is mounted forwardly of the engine. As a 
result, radiators mounted in this manner tended to be relatively 
inefficient requiring a comparatively larger physical size. 
SUMMARY OF THE INVENTION 
The primary object of the invention is to provide a cooling system for 
motorcycle engines. 
A further object of the invention is to provide a cooling system for liquid 
cooled internal combustion motorcycle engines which delivers sufficient 
air to the radiator to satisfy engine cooling requirements. 
Another object of the invention is to provide an air collection system for 
motorcycle internal combustion engine cooling systems which does not 
detract from the aesthetic appearance of the vehicle. 
A still further object of the invention is to provide a cooling system for 
a liquid cooled motorcycle engine wherein heated air does not pass over 
the operator or a passenger. 
Yet another object of the invention is to provide a cooling system for a 
liquid cooled motorcycle engine wherein improved radiator efficiency is 
achieved. 
These and other objects and advantages of the present invention will become 
more apparent from the detailed description thereof taken with the 
accompanying drawings. 
In general terms, the invention comprises a motorcyle including front and 
rear forks for mounting front and rear wheels, respectively, a frame 
interconnecting said forks, a liquid cooled internal combustion engine and 
a radiator for said engine supported on said frame and between said forks. 
The improvement comprises an air transport system for said radiator which 
includes means defining first and second air passages, each having an 
inlet disposed respectively on the opposite side of the forks. Each air 
passage extends rearwardly from its inlet and has an outlet opening into a 
plenum chamber disposed adjacent the radiator with the cross sectional 
area of each air passage increasing gradually from its inlet to its outlet 
ends. An exhaust duct is connected to the plenum chamber with the radiator 
disposed between the plenum and the exhaust duct.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a motorcycle 10 which incorporates the cooling system in 
accordance with the preferred embodiment of the invention and includes a 
frame 12 having a front fork 14 and a rear fork 16 to which front and rear 
wheels 18 and 20 are respectively mounted in a conventional manner. A 
watercooled, internal combustion engine 22 is mounted on frame 12 and is 
coupled to rear wheel 20 in a manner well known in the art to provide 
motive power for the motorcyle 10. A body 24 is mounted on the frame 12 
above the engine 22 and encloses a gas tank and an air cleaner (not shown) 
in addition to the cooling system in accordance with the preferred 
embodiment of the invention. 
As seen more particularly in FIGS. 2 and 3, the cooling system 24 for the 
engine 22 includes a radiator 26, engine coolant outlet and return pipes 
28 and 30 for coupling the radiator 26 to the engine 22 and an air flow 
system 32 for delivering ambient air to the radiator 26 for the exchange 
of heat with the engine cooling fluid therein. 
The radiator 26 is generally rectangular in plan view and includes a 
plurality of finned tubes 38A and 38B extending between headers 40 and 42. 
The engine coolant outlet and return pipes 28 and 30 are connected to the 
header 40 on the opposite sides of a partition 44 which divides header 40 
into an inlet chamber 46 which communicates with tubes 38A and a return 
chamber 48 which communicates with tubes 38B. As a result, engine coolant 
flows from the engine 22 through pipe 28 into chamber 46 for passage 
through tubes 38A to header 42, and then back through tubes 38B to chamber 
48 for return flow to engine 22. It can be seen that by coupling the 
engine outlet and return pipes 28 and 30 to the side the radiator 26 
nearest engine 22, these connections can be maintained without 
interference with the air flow in system 32. 
The air flow system 32 is disposed within the body 23 and includes a pair 
of air passages 50 and 52 which are formed of sheet metal and extend from 
the front of the body 23 rearwardly where they merge into a plenum chamber 
54. The radiator 26 lies below the plenum chamber 54 and is inclined from 
front to rear at a slight vertical angle. An exhaust duct 60 which is also 
formed of sheet metal communicates with the opposite side of the radiator 
26 and extends generally downwardly therefrom. Those portions of the 
plenum 54 and the duct 60 adjacent the radiator 26 are configured 
similarly to the generally rectangular upper and lower margins thereof and 
are sealed thereto by seals 62 and 64 so as to form a continuous passage 
intersected by the radiator 26. A fan 66 is disposed within exhaust duct 
60 adjacent the radiator 26 and is driven by a motor 68 to assist in the 
cooling air flow. The downwardly oriented exhaust duct 60 insures that 
heated air from radiator 26 will not flow over the operator or a 
passenger. 
The passages 50 and 52 are identically formed with one being the mirror 
image of the other and both curve rearwardly and downwardly in the side 
view shown in FIG. 2 and rearwardly and inwardly in plan view as shown in 
FIG. 3. At the front of each duct 50 and 52 is an inlet opening 70 
disposed outwardly of the front fork 14. The inlet openings 70 are 
preferably generally rectangular as shown in FIG. 4 with a height to width 
ratio of about 2 to 1 which is similar to at least the initial portions of 
passages 50 and 52. From the inlet opening 60 there is a gradual increase 
in the height and width of each duct 50 and 52 until their merger at 
plenum 54. This gradual increase in cross sectional area of air passages 
50 and 52 is such that the combined areas of the inlet openings 70 are at 
about one-fourth of the cross-sectional area of the radiator 26. It can 
also be seen that the rate of increase in area is greater in those 
portions of the passages 50 and 52 which are adjacent their outlet ends. 
The inlet openings are also positioned such that they are outside the bow 
wave formed in the air stream by the front fork 14. Additionally, the 
radiator 26 is chosen so as to have a substantial air flow resistance 
whereby back pressure in the air passages 50 and 52 minimizes turbulence 
therein. In practice, it has been found that the pressure drop should be 
about 25-80% and preferably about 50%. The air flow system 32 improves 
radiator efficiency thus permitting a smaller radiator to be employed than 
is the case with motorcycles having a radiator mounted forward of the 
engine. 
While only a single embodiment of the invention has been illustrated and 
described, it is not intended to be limited thereby but only by the scope 
of the appended claims.