Axial fan for an internal combustion engine

Field of the invention

The present invention relates generally to a cooling system of an internal combustion engine in a motorcycle and more particularly to a mounting arrangement of an axial fan in a fan cooled engine system.

Background of the invention

In general the most common type of motorcycle engine today is an air-cooled engine comprising of a lightweight aluminium body. The engine produces significant amount of heat during the course of its operation a part of which is dissipated into the atmosphere. It is known in the prior art that the temperature range during an engine operation may vary greatly depending upon the operating conditions. Hence it is important to keep the engine temperature within the necessary limit. So the said engine is provided with cooling fins integrated around the engine cylinder(s) 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 therefore help in engine cooling. Sometimes the location of the engine in a motorcycle is such that natural air is not directed properly towards the engine in sufficient volume to adequately cool the engine. So the engine is provided with a centrifugal fan, mounted on an extension of a crankshaft, for forced cooling. The centrifugal fan sucks air axially and forces it in radial direction through a shroud which forms a covering over the engine and the fan. This scenario is common to scooter type motorcycles. The said shroud or cover contains an opening beneath which the fan is placed to make the vehicle more attractive and safe. The shroud directs the flow of air sucked from the fan towards the engine. Change in air direction results in significant pressure drop within the shroud reducing the cooling efficiency. Due to longer air path, more shroud material is used leading to increase in cost. Hence a cooling system for quicker heat dissipation and restraining cost is required to keep the engine temperature within the working limits.

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, involves an axial fan placed near the engine head and block instead of crankshaft. It is also an object of this invention to control the fan speed by using a gear system so as to provide efficient cooling. Yet another object of this invention is to restrain the cost of the shroud covering the fan. Another aspect of the present invention involves a fan cooled engine including means for directing air axially toward cylinder head and reducing the pressure drop along the air path for better cooling efficiency.

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 shroud with centrifugal fan and engine.

Figure 2 shows a side view of the cooling system proposed in one aspect of the present invention showing engine with axial fan mounted on the camshaft.

Figure 3 is an exploded view of the mounting arrangement of the cooling system with gears.

Figure 4 is a perspective view of the cooling system in the mounted position.

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. It is known in the prior art that the temperature range of an 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 engine, 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 two wheeler vehicles like scooters which are generally air cooled, the engine is surrounded by a shroud with a fan to enhance forced air cooling. In the prior art as shown in figure 1, a centrifugal fan 1 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 2. The fan is positioned relatively to the shroud such that it may receive cool outer air 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 5 of the shroud 2 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 6. Furthermore, the shape of the shroud 2 is such that the sucked air from the fan is forced to move around the engine surfaces including the engine head 4 and the engine block 3 to increase the cooling and hence the engine is cooled by forced air flow.

However the change in direction of the air results in significant pressure drop within the shroud 2. Drop in pressure results in the wastage of useful energy and reduces cooling efficiency. Since air has to travel longer distance before it reaches the hot surfaces of the engine there is loss of energy due to friction which further increases the pressure drop. Moreover longer air path increases the length of the shroud thereby increasing the shroud material which effectively increases the cost. These problems can be addressed if the fan is mounted near the engine (head and block) instead of on the crankshaft. In the present invention, we describe a fan cooling system that is mounted on the camshaft making it possible to keep the direction of air unidirectional, and hence reducing losses and increasing cooling efficiency by controlling the speed of the fan.

The present invention, in accordance with one embodiment thereof, provides an axial fan mounting system that would facilitate the use of axial fan close to the engine for higher cooling efficiency; lesser power requirement for the given flow rate and engine temperature reduction. In an internal combustion engine, two major rotating parts are crankshaft and camshaft. As mentioned earlier, when a centrifugal fan is mounted on the crankshaft the air flow direction is perpendicular to the crankshaft axis. In the present invention, an axial fan may be directly or indirectly mounted on the camshaft to position the fan near the engine so that the flow direction is parallel to the camshaft. Figure 2 shows a side view of the cooling system proposed in the present invention wherein an axial fan 7 is indirectly mounted on a camshaft 8 with the help of a gear system shown in detail in figure 3. The axial fan 7 is mounted near the engine head 4 and block 3. The proximity of the fan 7 with the engine increases the cooling efficiency. When fan 7 rotates, it sucks air in the axial direction and moves parallel to the shaft about which the fan rotates. The cooling air directly sees the engine hot surfaces as can be seen from the figure. The fan in the present invention may operate in the presence or absence of a shroud. If the shroud is present, the fan will suck in air in the axial direction and the sucked air directly cools the cylinder head portion. Because the air path length is reduced, the pressure drop is also minimized leading to improvement in cooling efficiency.

Usually the camshaft 8 rotates at one-half of the rate of rotation of crankshaft 10. This 2: 1 speed relationship is necessitated by the four-cycle nature of the engine. Since camshaft speed is half the crankshaft speed, fan 7 mounted to the camshaft also rotates at half the crankshaft speed i.e. it rotates at half of the engine speed. When higher cooling rates are desired, low fan speed can compromise cooling efficiency. Hence to bring the fan speed as that of crankshaft speed, two gears are used. The gear system consists of a primary gear 9 and a secondary gear 12. The primary drive gear 9 is connected to the camshaft 8 i.e. the primary drive gear shaft is mounted on a shaft that connects to the camshaft 8. The secondary driven gear 12 is connected to a shaft on which the said axial fan 7 is mounted. The two gears are meshed with each other so that their teeth are in direct contact with each other. Secondary driven gear 12 has half the number of teeth than primary drive gear 9. Since gear ratio is halved, speed is doubled. The axial fan 7 is mounted on the driven shaft and hence its speed becomes equal to that of crankshaft. Shaft on which fan and the drive gear are mounted contains a ball bearing system 15. Similar ball-bearing system 14 is also used on shaft which is connected to the camshaft 8.

In another aspect of the invention, the axial fan may be covered with a shroud wherein the position of the opening of the shroud from where the fan sucks air changes compared to the prior art to accommodate the change in mounting position of the fan. A portion of the said shroud may have a ring body encircling the said fan at a specified clearance in such a way that the fan axis is substantially coaxial with the ring axis. The ring body of the shroud, for example, may be substantially a circle or elliptical. The fan is operative when the engine is on, the fan running at engine speed or at half of the engine speed depending on the presence or absence of the gear system. As the length of the air path for cooling the engine is reduced due to axial cooling compared to the prior art, the shroud length also reduces resulting in decrease in the material cost for making the shroud.

In another aspect of invention, a centrifugal fan can also be mounted on the camshaft if needed. However, an axial fan will deliver higher cooling efficiency due to the direction of airflow and the fan speed can be controlled depending upon the cooling needs of the engine. Since a camshaft essentially runs at half the engine speed, a fan may run at half the engine speed or can be made to run at the crankshaft speed by using gear system as described.

Moreover, the centrifugal fans used in the automotive industries are either forward-curved blades or backward-curved blades. The choice of forward-curved centrifugal or backward-inclined centrifugal fans versus axial fans affects the energy efficiency. Standard centrifugal fan systems are typically less efficient (50 percent to 60 percent) and their actual installed efficiency is usually much worse than the manufacturer's ratings.

Efficiencies as low as 30 to 40 percent have been measured in the field. In this invention, high-efficiency (80 percent to 90 percent) axial fans have been used.

Further, the axial fan 8 in the present invention may be made of moulded plastic, nylon or any other suitable material. The present invention can be used in a motorcycle engine usually devoid of a shroud due to engine location as well as in a scooter engine where a shroud is present for enhancing forced cooling as natural air is not available sufficiently to cool the engine. The present invention can also 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. An improved and compact engine cooling system for a motorcycle comprising:
an axial fan operatively positioned adjacent to an engine of a motorcycle and mounted directly or indirectly on a camshaft of the said engine for directing outer air axially towards the surface of the said engine upon the rotation of its blades when the engine is in operative condition; and a means to control the speed of the said axial fan.

2. An improved and compact engine cooling system for a motorcycle according to claim 1 wherein the said means to control the speed of the said axial fan includes a gear system with ball bearings, the gear system further including a primary drive gear and a secondary driven gear wherein the primary drive gear is connected to a camshaft of the engine and the secondary driven gear is connected to the shaft on which the said axial fan is mounted in such a way that the rotation of the primary drive gear rotates the secondary driven gear which in turn rotates the shaft on which the said axial fan is mounted.

3. An improved and compact engine cooling system for a motorcycle according to claim 2, wherein in the said gear system the diameter of the said primary drive gear is twice that of said secondary driven gear.

4. An improved and compact engine cooling system for a motorcycle wherein the said means comprises at least one axial fan mounted on one 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.

5. An improved and compact engine cooling system for a motorcycle according to claim 1 and claim 4 wherein the said engine may be covered by a shroud or a cowling having a ring body substantially circular or elliptical in shape encircling the said fan at a specified clearance 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, the said shroud containing at least one opening for air intake by the said axial fan, the said fan axis being coaxial to the ring body axis.

6. An improved and compact engine cooling system for a motorcycle according to claim 5, wherein the said axial fan has plurality of fan blades and is made of any material including plastic resin, nylon or the likes.

7. An improved and compact engine cooling system for a motorcycle according to claim 1 and claim 4, wherein said motorcycle includes a scooter type motorcycle having a low floorboard.