Bearing support structure
Field of the invention
The present invention relates to a bearing support structure and more
particularly to a stabilised bearing structure for a crankshaft in a four stroke
engine.
Description of the prior art
Generally, in a single-cylinder internal combustion engine for a motorcycle or
the like, a crankshaft is rotatably supported on a crankcase through a pair of
rotary bearings, a piston in a cylinder bore is connected to a crank pin of the
crankshaft through a connecting rod. During engine operation in expansion
stroke, pressure exerted on the piston is transmitted through the connecting
rod to the crankshaft, and from the crankshaft to the crankcase through a set
of rotary bearings.
Therefore in this arrangement it is always desirable that the inner and outer
races of the bearings are securely attached to their respective engine
components. Therefore the bearings have been respectively press fitted over
journal shaft portions of the crankshaft and inside bearing portions of the
crankcase, respectively. As a result, a rattling sound, which might otherwise
occur due to backlashes between the fitted components, is suppressed, and a
desired bearing function for the crankshaft is maintained, ensuring smooth
and light rotation.
In order to solve this problem, conventionally, an engine structure and method
of assembly has been adopted, in which the outer race of the right bearing is
press fitted into a right crankcase half, and the inner race of the left bearing is

press fitted over a left-side journal shaft portion of the crankshaft, prior to
mounting the crankshaft onto the crankcase.
At the time of mounting the crankshaft into the crankcase, a right-side journal
shaft portion of the crankshaft is press fitted in the inner race of the right
bearing (of which the outer race is already press fitted in the right-side
crankcase half). Then, the outer race of the left bearing, with the inner race
thereof already press fitted over the left-side journal portion of the crankshaft,
is play fitted (fitted, with a play) into a left-side crankcase half, thereby
facilitating the mounting of the crankshaft onto the crankcase and the
maintenance thereof.
However, in this type of conventional structure, some play remains between
the left outer bearing race and the left crankcase half after assembly. As a
result, during operation of the engine, a little "backlash" is unavoidably
generated between the outer race of the left bearing and a bearing surface of
the crankcase. Therefore, a rattling sound due to the "backlash" is generated
upon the operation of the internal combustion engine, and the desired bearing
function cannot be optimised.
Hence the main objective of the present invention is provide a stabilized
bearing structure for supporting a crankshaft in an internal combustion engine,
and a backlash-absorbing mechanism for absorbing a backlash of a bearing
race.
Brief description of the invention
A threaded ring is either assembled or fitted on the side of the said bearing to
adjust the float of the crankshaft as desired. The said threaded ring gets
assembled on the threads provided in the inner diameter of the bearing boss.

The innermost diameter of the thread is almost equal to the bearing bore diameter. A restraining member also prevents rotation of the threaded sleeve. This arrangement eliminates the structural inadequacies- in manufacturing process owing to errors caused due to mass production of the engine components.
Brief description of the drawings
Figure 11llustrates side view of a motorcycle.
Figure 2 illustrates a four stroke internal combustion engine.
Figure 3 illustrates the functional diagram 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 as illustrated in figure 1 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 106 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 200 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 (not shown in the figure) comprises of exhaust pipe and a muffler. The motorcycle is also provided with a side cover 112 for covering a side section of the vehicle frame 101, a seat cover (not shown in the figure) for covering a rear section of the vehicle frame 101 below the seat 107, 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 200 as illustrated in figure 2 is the cylinder 201 with the piston 202 moving up and down inside the cylinder 201. Some of the key engine parts along with their functions are spark plug (nor shown in the figure) which supplies the spark which ignites the air/fuel mixture so that combustion could occur; valves 203 wherein the intake and exhaust valves open at the proper time to let in air and fuel to let out exhaust; a piston 202 which is a cylindrical piece of metal that moves up and down inside the cylinder 201; piston rings 204 that provide a sliding seal between the outer edge of the piston 202 and the inner edge of the cylinder 201; connecting rod 205 which connects the piston 202 to the crankshaft 206; crankshaft 206 which turns the piston's up and down motion into circular motion; a sump 207 which surrounds the crankshaft 206 and contains oil which collects in the bottom of the sump 207; etc. The said crankshaft drives a driven shaft (not shown in the figure). The blow by gases from the crankcase is passed through the air filter unit that filters it and adds to the intake gases going into for combustion.
The crankshaft 206 is rotatably supported on the crankcase 208 through left 216 and right 217 rotary bearings.

The crankcase 208 includes a left-side crankcase half and a right-side crankcase half, which are metal cast. The left side and right-side crankcase halves are fixedly connected toeach other by a plurality of bolts. The left side and right-side crankcase halves and are respectively provided with integrally formed left 214 and right 215 journal walls, which are opposed to each other with an interval there between. The left 214 and right 215 journal walls and are respectively provided with aligned left and right bearing holes formed therein and opened on the same axis.
Each of the left 214 and right 215 journal walls is provided with a bearing-engaging surface, surrounding the left and right bearings holes. Left and right journal shaft portions of the crankshaft 206 are rotatably borne inside of the left and right bearing holes through the left-side 216 and right 217 side rotary bearings.
Accordingly, a threaded ring 300 is either assembled or fitted on the side of the said bearing 217 to adjust the float of the crankshaft 206 as desired. The said threaded ring 300 gets assembled on the threads 301 provided in the inner diameter of the bearing boss 302. The innermost diameter of the thread 301 is almost equal to the bearing bore diameter. A restraining member also prevents rotation of the threaded sleeve. This arrangement eliminates the structural inadequacies in manufacturing process owing to errors caused due to mass production of the engine components.
It should be understood that the foregoing description is that of a preferred embodiment of the invention and that various changes and modifications may be made without departing from the spirit and scope of the invention, as

defined by the appended claims. Further any shape and configuration of the extended surface is possible within the ambit of appended claims.