Crankshaft assembly mounting structure

Field of the invention

The present invention relates to "Crankshaft assembly mounting structure" and more particularly to crankshaft assembly supported on the crankcase of an engine.

Background of the invention:

The engine main body has a cylinder block with a cylinder bore. A cylinder head is fastened to the front of the cylinder block and a crankcase is fastened on to the rear of the cylinder block. The cylinder block and the crankcase are supported by a support brackets fixed on to the vehicle frame. The crankcase is constructed with mutually fastened left and right crankshaft half bodies. The both crankcase half bodies rotatably support a crankshaft. The said crankshaft is positioned on a set of main bearings located on crankcase halves. The two sides of the crankshaft overhanging beyond the width of bearing supports magneto and primary centrifugal respectively. The magneto and the clutch assembly are housed in the crankcase halves and are covered with engine covers on either side fastened to the said crankcase halves. The span between the said main bearings may vary according to the width crankshaft and depends upon factors such as size of the engine, power requirement, etc. When the crankshaft rotates, the two bearing portions supporting the crankshaft undergo bending moment generated on the crankshaft by the force applied due to piston movement. The said clutch assembly that is supported on the portion of the crankshaft undergoes whipping action or movement causing undue vibrations which causes discomfort to the vehicle rider owing to transfer of vibrations to the handle bar through the frame. This is more so if the capacity of the clutch increased To reduce such whipping of the over hanging portion of the crankshaft, many solutions are known. For instance, the crankshaft diameter is increased to reduce such whipping. However this tends to make the engine bulkier and results in change in configuration such as nearby parts. Similarly, the span length between the bearings can also be increased. However, the above said improvements suffered from the lacunae of increased cost, weight etc.

Therefore the main objective of the present invention is to provide a solution that addresses the lacunae in the prior arts.

Another objective of the present invention is to give a sturdy design of engine having reduced maintenance and increased longevity. Another objective of the present invention is to provide an engine having extra stability and operability in extreme conditions of riding.

Brief description of the invention

According to one of the aspects of the present invention, a bearing arrangement for crankshaft end consisting of an engine cover is provided with an additional bearing locating bore having a bearing placed in the said bore and its axis coinciding with the axis of the crankshaft.

Brief descriptions of the drawings

Figure 1 illustrates side view of a motorcycle

Figure 2 illustrates sectional view of crankshaft and bearing support according to the present invention

Figure 3 illustrates an exploded view of the present invention

Detailed description of the invention

A selected illustrative embodiment of the present invention will be now described with respect to the accompanying figures 1,2 and 3.

A motorcycle comprises of a frame 101, front fork 102 attached to a pivot tube 103 of the vehicle frame 101, a front wheel 104 attached to these front forks 102, a handle bar 105 connected to the front forks 102, a fuel tank (not shown in the figure) attached so as to straddle an upper part of the vehicle frame 101, a seat 107 attached to the upper rear portion of the vehicle frame 101, an engine unit 108 attached to the lower front section of the vehicle frame 101, a swing arm 109 attached to a lower rear section of the vehicle frame 101, suspended by a rear shock absorber 110 from the vehicle frame 101 and a rear wheel 111 attached to a rear end of swing arm 109. The intake system of the engine (not shown in the figure) comprises of a carburettor, intake duct and an air cleaner. The exhaust system of the engine 108 comprises of exhaust pipe 202 and a muffler 205.

The motorcycle is also provided with a side cover for covering a side section of the vehicle frame 101, a front fender 113 for covering an upper part of the front wheel 104, and a rear fender 114 for covering an upper part of the rear wheel 111.

The core part of the engine 108 is the cylinder with the piston 311 moving up and down inside the cylinder. Some of the key engine 108 parts along with their functions are spark plug (not shown in the figure) which supplies the spark which ignites the air/fuel mixture so that combustion could occur; valves (not shown in the figure) wherein the intake and exhaust valves open at the proper time to let in air and fuel to let out exhaust; a piston 311 which is a cylindrical piece of metal that moves up and down inside the cylinder; piston rings 312 that provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder; connecting rod 301 which connects the piston 311 to the crankshaft 302; crankshaft 302 which turns the piston's up and down motion into circular motion; a sump 303 which surrounds the crankshaft 302 and contains oil which collects in the bottom of the sump 303; etc. As discussed earlier, crankshaft 302 is that part of the engine 108 which transfers the linear reciprocating piston motion to rotational motion. To convert the reciprocating motion into rotational motion, the crankshaft 302 has crankpin 304, bearings 305 whose axis is offset from the crankshaft 302, where the big end 306 of the connecting rod 301 attaches. As the crankshaft 302 undergoes a great deal of sideways load from the cylinder due to non-smooth operations that may be due to various uneven conditions, it must be supported by bearings 305. In this manner the bearing 305 has the dual functions of both supporting the crankshaft 302 in various operating conditions as well as facilitating rotation of the crankshaft 302. However, the two main bearings 305 supporting the crankshaft 302 perform the above two functions satisfactorily if the crankshaft length is short.

Accordingly, the first aspect of the present invention is to provide a bearing 307 arrangement for crankshaft end consisting of a engine cover 308 provided with an additional bearing locating bore 309 having a bearing 307 placed in the said bore 309 and its axis 310 coinciding with the axis of the crankshaft 302.

Accordingly, whipping generated on the crankshaft 302 is greatly reduced owing to a third support structure in the form of an additional bearing 309 on the cover 308 in the magneto 313 side.

Accordingly, the present invention also provides flexibility to change the clutch capacity without any major change in the engine design.

Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.

Claim

We claim:

1. A crankshaft assembly mounting structure for a four-stroke internal combustion engine comprising a crankshaft 302, an engine cover 308, a set of main bearings 305 wherein the said engine cover 308 is provided with an additional bearing locating bore 309 having a bearing 307 placed in the said bore 309.

2. A crankshaft assembly mounting structure for a four-stroke internal combustion engine as claimed in claim 1, wherein the said bearing axis 310 coincides with the axis of the said crankshaft 302.

3. A crankshaft assembly mounting structure for a four stroke internal combustion engine as claimed in claim 1, wherein the said bearing 309 is located on the magneto 313 side.

4. A motorcycle having a crankshaft assembly as claimed in claim 1.