Cooling fan for an internal combustion engine
Field of the invention
The present invention relates generally to a cooling fan of an internal combustion engine in a motorcycle and more particularly to a dual axial fan cooling system in a fan cooled internal combustion engine.
Background of the invention
The most common type of motorcycle engine in the present times is an air-cooled engine comprising a lightweight aluminium engine block. The engine produces significant amount of heat during the course of its operation. It is thus important to keep the engine temperature within the necessary limit. So an engine is provided with cooling fins integrated around cylinders to dissipate accumulated heat from the engine generated from combustion and component friction within the engine. These cooling fins increase the surface area coming in contact with the air and hence help in engine cooling.

Sometimes the location of the engine in a motorcycle or a three wheeler is such that it is provided with a fan, mounted on an extension of a crankshaft, for forced cooling as natural air is not directed properly towards the engine in sufficient volume to adequately cool the engine. Such an engine is covered with a shroud or cover containing an opening beneath which the fan is placed to make the vehicle more attractive and safe. It is known in the prior art that the temperature range of an engine may vary greatly depending upon the circumstances of the operation due to which the shroud which covers the engine may have a detrimental effect on cooling air flow, both to the engine and other components leading to rise in engine temperature. Hence a cooling system for quicker heat dissipation is required.
In the prior art, an engine is force cooled by a single centrifugal fan mounted directly on the crankshaft externally of the crankcase sucking air radially and forcing it in radial direction. A shroud is often used to direct the flow of air from the fan toward and over the engine and engine head. In the entire process, the direction of the flowing air changes from axial at the fan inlet to radial at the fan outlet. As a result, the engine surfaces at the front with respect to the fan which see the air from the fan directly are cooled properly whereas the engine surfaces at the rear with respect to the fan are improperly cooled, the reason being the reduced air velocity at these surfaces. The uneven cooling of the engine from the front to the rear results in a high temperature gradient thereby reducing the cooling efficiency. A high temperature gradient may also result in failure of engine components and affects engine performance.

Summary of the invention

The present invention is one having been made in view of the aforementioned problems. It is therefore an object of the present invention to provide an improved, compact and efficient cooling system for an internal combustion engine. The present invention, in accordance with one embodiment thereof, provides a dual axial fan cooling system to minimize the temperature gradient which involves at least two axial fans placed near the engine head and block instead of crankshaft. Another aspect of the present invention is to provide a dual axial fan system where the fans are mounted on the camshaft adjacent to the engine for better cooling. Yet another object of this invention is to restrain the cost of the shroud covering the fan and the engine. Another aspect of the present invention is to provide a fan cooled engine including a means for directing air axially toward the engine head as well as other engine components and controlling the speed of such means.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent those skilled in the art from this detailed description.

Brief Description of the Drawings

Figure 1 shows a rear view of a fan cooled engine as found in the prior art showing a shroud with a centrifugal fan and an engine.

Figure 2 shows a rear perspective view of a dual axial fan system proposed in one aspect of the present invention.

Figure 3 is an exploded view of a mounting arrangement of the dual axial fan system proposed in one aspect of the present invention

Figure 4 shows the top view of the dual axial fan system with shroud having two inlets and two outlets.

Figure 5 shows the temperature variation of the engine with single and dual axial fan system.

Detailed description of the invention

Before moving onto the description of the present invention, it would be proficient to know the associated prior art. Generally an engine may have any of the two types of cooling systems viz. air cooling or liquid cooling. These cooling systems rely on a flow of fluid over or through the engine casing or engine components as a means of transferring heat from the engine to the environment. In two wheeler vehicles like scooters or in three-wheelers which are generally air cooled, the engine is surrounded by a shroud with a fan to enhance forced air cooling. The temperature range of the engine may vary greatly depending upon the circumstances of the operation. For example, if a motorcycle is halted at a traffic signal and cooling air is not adequately flowing around the finned cylinders, the temperature of the engine may rise quickly. This can also lead to engine oil thermal breakdown, which quickly accelerates engine component friction and wear, thereby significantly shortening the life of the engine. Thus, inefficient engine performance and failure of engine components have been observed due to failure of proper heat transfer from the engine.

In the prior art as shown in figure 1, a centrifugal fan 101 is mounted directly on the crankshaft (not shown) externally of the crankcase which runs along with the engine. The said fan is surrounded by a shroud 102. The fan is positioned relatively to the shroud such that it may receive cool air from outside from beneath the shroud or through a louvered opening in the shroud. The fan is held on by conventional means and is operative when the engine is on, the fan running at engine speed. When in operation, the fan 1 sucks air axially from one end of the opening 105 of the shroud 102 and forces it in radial direction i.e. the fan blades rotate causing the air to enter the fan near the crankshaft and move perpendicularly from the said shaft. In the entire process, the direction of the flowing air changes from axial at the fan inlet to radial at the fan outlet 106. Furthermore, the shape of the shroud 102 is such that the sucked air from the fan is forced to move around the engine surfaces including the engine head 104 and the engine block 103 to increase the cooling and hence the engine is cooled by forced air flow.

However the cooling air mainly cools the front engine surface 107 which is directly on the front side of the engine facing towards the fan. The air velocity reduces by the time air reaches the rear engine surface 108 present on the opposite side of the front engine surface 107. Therefore the rear engine surface is not sufficiently cooled leading to a high temperature gradient which is undesirable. Moreover the longer air path from fan to the engine head increases the length of the shroud, if present, thereby increasing the shroud material which effectively increases the cost. Hence, invention presented here addresses these issues. In the present invention, a dual axial fan system mounted on the camshaft is described that would facilitate the cooling of engine surfaces from both the sides directly.

Figure 2 is a perspective view of an aspect of the present invention. Two axial fans are mounted symmetrically to each other on a camshaft of an internal combustion engine externally to the crankcase 111 one each on either side of the engine. A front fan 110 is positioned adjacent to the front side of the engine so that in the absence of a cover, it is visible to a spectator looking at the vehicle from the left side of the vehicle. A rear fan 210 is located adjacent to the rear side of the engine with respect to a spectator looking at the left side of the vehicle. The rear fan 210 is thus not visible to the said spectator as it is located on the opposite side of the front fan 110. The axis of the said front fan 110 and the rear fan 210 is perpendicular to the long axis of the said motorcycle and parallel to that of the crankshaft of the said engine. Both fans are held on by conventional means and are operative when the engine is on and the camshaft is rotating, the fans running at the speed of the camshaft.

Rotation of the front fan 110 and rear fan 210 is such that they suck air from the ambient and push it towards engine head 104 and engine block 103 thereby leading to forced cooling of the engine.
Unlike a centrifugal fan, an axial fan blows air parallel to the shaft about which it rotates. Thus in the present invention, both fans 110 and 210 push the air parallel to the camshaft axis towards the respective engine surface. Hence both the sides of the engine get uniform cooling. A shroud (not shown in figure 2) may be mounted on the engine, which encloses the engine, the front fan 110 and the rear fan 210. The fans 110 and 210 may be positioned relatively to the shroud such that they receive cool outer air from beneath the shroud through an opening in the shroud on either side. In another aspect of the present invention, the front fan 110 sucks air inside, the said air is directed to cool the hot engine surface and engine parts and the rear fan 210 throws the hot air out from the shroud through the shroud opening.
Thus, one fan acts as intake fan whereas the other acts as the exhaust fan.

Figure 3 shows the camshaft 114 on which the front fan 110 and the rear fan 210 are mounted on either side of the engine. Usually the camshaft 114 rotates at one-half of the rate of rotation of the crankshaft. This 2: 1 speed relationship is necessitated by the four-cycle nature of the engine. Since camshaft speed is half the crankshaft speed, the respective fans 110 and 210 mounted to the camshaft 114 also have half the crankshaft speed i.e. they rotate at half of the engine speed. At high engine temperatures, when higher cooling rates are desired, low fan speed can compromise the cooling efficiency. Hence a gear system may be used for each fan to increase the fan speed. Gear system 112a is attached to the front fan 110 whereas the gear system 210 is attached to the rear fan 210 as shown in figure 3.

The gear system 112a may consist of a primary gear and a secondary gear. The primary drive gear is connected to the camshaft i.e. the primary drive gear shaft is mounted on a shaft that connects to the camshaft 114. The secondary driven gear is connected to a shaft on which the said axial fan 110 is mounted. The two gears are meshed with each other so that their teeth are in direct contact. Secondary driven gear has half the number of teeth than primary drive gear. Since gear ratio is halved, speed is doubled. The front axial fan 110 is mounted on the driven shaft and hence in this arrangement rotates with a speed equal to that of crankshaft. The same explanation stands true for gear system 112b. Hence the rear axial fan 210 rotates with the crankshaft speed in the given arrangement. The camshaft 114 is connected to the crankshaft via a chain drive.

Figure 5 shows another aspect of the present invention where a shroud covers the engine and the respective fans. The figure shows how the dual axial fan system in the present invention works and increases cooling efficiency. Two air inlets and two air outlets are provided in the shroud. The front fan 110 sucks air from the ambient and sends it in axial direction towards front surface of the engine 120. The air escapes through the two outlets after cooling the engine 120. Operation of the rear fan 210 is similar. The direction of air is indicated in the figure 5. Both sides of the engine are uniformly cooled thereby minimizing the temperature gradient. The two fans 110 and 120 are symmetrically located with respect to the inlet 118 and exhaust 113 ports resulting higher thermal cooling efficiency. It is to be noted that the engine cowling may also function as shroud. In another aspect of the invention, the dual axial fan system may be mounted on the engine of a motorcycle with fairing where the fairings itself may act as a shroud keeping the rider safe from the rotating fans.

The fans rotate beneath the fairing for force cooling the engine when the engine is in operative condition.
Figure 6 shows the normalised temperature variation along the engine surfaces and the results are compared between a single fan cooling system and a dual fan cooling system. Temperatures are measured along the line AB shown in figure 5 passing through exhaust port 113. It can be seen that the presence of dual fans decrease the engine temperature by about 40% compared to a single fan. Furthermore the temperature gradient also reduces significantly when dual fans are used.

Thus the advantage of using dual axial fans is that the effective mass flow rate of the cooling air increases two fold leading to better engine cooling. Low capacity fans to reduce engine power consumption can also be used in the present invention. Two major advantages with present invention are that the temperature gradient along the engine surfaces can be reduced significantly and significant reduction in absolute temperature of the engine can be achieved. Thermal efficiency of the engine may also be improved which is not possible in the prior art. The present invention can be easily used in a motorcycle with a single speed transmission, a scooter type motorcycle having a low floorboard, a motorcycle with a shell like fairing for reducing the air drag, a motorcycle having a step through space in the front and engine unit at the rear end as well as in a three wheeler.

The terms and expressions in this specification are of description and not of limitation and do not exclude any equivalents of the features illustrated and described, but it is understood that various other embodiments are also possible without departing from the scope and ambit of this Invention which will become apparent to those skilled in the art from this detailed description.

We claim:

1. A cooling system for an internal combustion engine of a motorcycle comprising a means mounted directly or indirectly on a camshaft of the engine, the said means positioned adjacently to at least two opposite surfaces of the said engine for providing uniform cooling to the said surfaces of the hot engine when the engine is in operative condition.

2. A cooling system for an internal combustion engine of a motorcycle as claimed in claim 1 wherein the said means comprises at least one axial fan mounted on either side of the said engine, the axis of the said axial fan being perpendicular to the long axis of the said motorcycle, the said axial fan upon its rotation directing air axially towards the said engine including the engine head and engine block.

3. A cooling system for an internal combustion engine of a motorcycle comprising two axial fans symmetrically positioned externally to the crankcase, the shaft about which the said axial fans rotate being parallel to the crankshaft axis, the said axial fans providing forced cooling respectively to the left and right surfaces of the engine when viewed by a spectator standing at the rear end of the said motorcycle.

4. A cooling system for an internal combustion engine of a motorcycle as claimed in claim 1 and claim 3 wherein each of the axial fans is either mounted directly on the opposite ends of a camshaft extension or mounted indirectly on the opposite ends of a camshaft extension through a gear system.

5. A cooling system for an internal combustion engine of a motorcycle as claimed in claim 4 wherein the speed of the said axial fan may be controlled by the said gear system.

6. A cooling system for an internal combustion engine of a motorcycle comprising two axial fans positioned externally to the crankcase, the said axial fans providing forced cooling respectively to the left and right surfaces of the engine when viewed by a spectator standing at the rear end of the said motorcycle, wherein the said engine may be covered by a shroud or a cowling for enhancing forced air cooling in such a way that the said axial fan is positioned externally to the crankcase and internally to the shroud.

7. A cooling system for an internal combustion engine of a motorcycle according to claim 6 wherein the said shroud contains at least two openings functioning as cooling air inlets and at least one opening functioning as hot air outlet in such a way that the two openings functioning as cooling air inlets are symmetrically opposite to each other.

8. A cooling system for an internal combustion engine of a motorcycle as claimed in claim 4 wherein each of the said axial fans has plurality of fan blades and may be made of any material including nylon, plastic and the likes.

9. A cooling system for an internal combustion engine of a motorcycle according to claim 1 and claim 3, wherein the said motorcycle includes a scooter type motorcycle having a low floorboard.