CAM CHAIN RETENTION STRUCTURE FOR AN INTERNAL COMBUSTION ENGINE
FIELD OF THE INVENTION
The present invention relates to a 'Cam Chain Retention Structure' for an overhead camshaft internal combustion engine for a two-wheeled vehicle. This cam chain retention structure avoids the fall and separation of chain from the chain sprocket while cam chain assembly stage.
BACKGROUND OF THE INVENTION
Internal combustion engines use a camshaft timing chain for transmitting rotary motion of a crankshaft to determine the motion of cam of a camshaft for ultimately driving the intake and exhaust valves for predetermined timed operations. This pre determined operating instance and duration for the intake valve and exhaust valve depends upon the shape of the cam on the camshaft. The camshaft timing chain is extended between a drive sprocket mounted on the crankshaft, and a driven sprocket mounted on the camshaft. During assembly of an internal combustion engine, the camshaft timing chain wound around the driving sprocket in the crankcase is pulled outside through the cylinder block, and is wound around the driven sprocket after attaching the cylinder head to the cylinder block. The camshaft timing chain wound around the driving sprocket is more likely to come off the drive sprocket when the same is pulled outside through the cylinder block. In cases when the camshaft timing chain falls off the driving sprocket, the cylinder block must be removed from the crankcase to wind the camshaft timing chain again round the drive sprocket, which requires troublesome work.
There are many arrangements for prevention of detachment of cam chain from the driving sprocket known in the art and all of them use additional parts for achieving this objective. Further, there is no arrangement in the art, which prevents axial

movement of the cam chain taking the axis as axis of the cam shaft. Therefore to remove defects in the prior art, there is a requirement for an arrangement that prevents downward as well as axial movement of the cam chain during the assembly process while minimizing part count at the same time.
SUMMARY OF THE INVENTION
The engine body of a conventional internal combustion engine includes a crankcase, a cylinder block coupled to the crankcase, a cylinder head coupled to the upper part of the cylinder block and a head cover coupled to the upper part of the cylinder head. A piston slid ably fitted in the cylinder block is connected via a connecting rod with a crankshaft. The .crankshaft is rotatable and supported by the crankcase. The crankcase is constructed by connecting a left crankcase and a right crankcase together. A right case cover is fastened to a right portion of the right crankcase. A generator chamber is formed between the left crankcase and left case cover. In the generator chamber, an outer rotor is fixed to the crankshaft and an inner stator constitutes an AC generator in cooperation with the outer rotor fixed to the left case cover.
An intake port and an exhaust port formed in the cylinder head communicate with the combustion chamber formed by being surrounded by the cylinder bore, the cylinder head and the piston. An intake valve is provided at the combustion chamber side opening of the intake port and an exhaust valve is provided at the combustion chamber side opening of the exhaust port. A camshaft is rotatable and supported by the cylinder head so as to open/close the intake valve and the exhaust valve. Rotational power is transmitted from the crankshaft to the camshaft by the timing transmission means. The timing transmission means includes a drive sprocket, a driven sprocket and an endless cam chain. The intake and exhaust valves are operated via rocker arms connected to the camshaft.
Many a times when the cam chain on the driving sprocket is being wound, it slips and hence the re opening of the crank case is required which is a re work and time

consuming work. This problem is being solved in this invention by using a structure which prohibits the falling of the cam chain from the sprocket.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 Shows an internal combustion engine with camshaft chain assembled on the cam chain sprocket.
Fig. 2 Shows the left hand side cover of crank case with the cam chain retention structure.
Fig. 3 Shows the isometric view of the cam chain retention structure with the cam chain installed on the cam chain sprocket.
Fig. 4 Shows the cam chain retention structure with the portion for controlling radial and axial movement of the cam chain.

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DETAILED DESCRIPTION OF THE INVENTION
Referring to Figure 1, it shows an assembled internal combustion with driving sprocket 12 and the driven sprocket 17 separated by a distance, both the driving and driven sprocket being wound with the same cam chain ll.The cam chain 11 being straightened and any slack in it being tightened by cam chain tensioner 16 so that the chain doesn't come out of the sprocket 12's teeth, the guide chain 15 guides the vertical positioning of the cam chain inside the engine. Curved rib 13 is located beneath the sprocket 12 such that the cam chain 11 is retained in the sprocket 12's teeth and doesn't come out of it. The driving sprocket and the curved rib are contained in but not restricted to left side of the crank case 14.
Figure 2 shows the crank case 14 and the curved rib 13. The figure shows that the curved rib 13 consists of axial rib 22 and radial rib 21 such that the axis is taken across the axis of the crank shaft. Axial rib 22 retains the cam chain 11 on the driving sprocket and avoids the falling out of the chain in the axial direction. Radial rib 21 retains the cam chain in the teeth of the driving sprocket and avoids the falling out of the chain in radial direction due to the slacking of the cam chain.
Figure 3 shows a view of an engine in which the cam chain 11, curved rib 13 and gear starter clutch 33 are shown.
Fig. 4 shows the perspective view of a part of engine containing tensioner cam chain 16, crankshaft 44, and radial rib 21 axial rib 22 along with the cam chain 11. The cam chain retention structure for an internal combustion engine as per the present invention comprises of the curved rib 13 consisting of the Axial rib 22 and Radial rib 21 casted but not limited to the left hand side of the crankcase 14 and concentric to the cam chain driving sprocket 12's center. The said curved rib 13 prevents detachment of the cam chain 11 from the cam drive chain sprocket 12 by inhibiting the axial and downward movement of the cam chain 102. The outer edge of the curved rib 13, prevents a gear starter clutch 33 of the starter gear mechanism from sliding backwards. Since the curved rib 13 structure is casted to the crankcase, part count is reduced and consequently assembly time is reduced leading to increased productivity. Further,

probability of breakage and wear of the cam chain is greatly reduced. This is because the curved rib acts as a protective mechanism and prevents the gear starter clutch from engaging with the cam chain.

WE CLAIM:
1. A cam chain retaining structure for an internal combustion engine comprising
of:
a crankcase, wherein the said crankcase comprises of a driving sprocket, a cam chain tensioner, a cam chain guide;
a curved rib wherein the said curved rib is concentric to the cam chain drive sprocket's centre in such a way that the said curved rib prevents the axial and downward falling of the cam chain;
2. The curved rib as claimed in claim 1 is casted in the crank case but not limited to be on the left hand side crankcase.
3. The curved rib as claimed in claim 1 consists of two structures, radial rib and axial rib wherein the said axial rib prevents falling off of cam chain through its motion in the axial direction and the said radial rib prevents the cam chain from falling through its motion in radial direction with respect to the said driving sprocket.
4. The cam chain retention structure for an internal combustion engine as claimed in claim 1, wherein the outer edge of the curved rib prevents a gear starter clutch of the starter gear mechanism from sliding backwards.
5. The cam chain retention structure for an internal combustion engine as claimed in claim 1 consists of radial rib which prevents the movement of the cam chain in the radial direction while assembly.
6. The cam chain retention structure for an internal combustion engine as claimed in claim 1 consists of axial rib structure which prevents the movement of the cam chain in the axial direction while assembly.