Crankcase structure

Field of the Invention:

This invention relates to "Crankcase structure" and more particularly to single speed engines

Background of the invention:

Generally crankcase of a two wheeler houses transmission parts, supports cylinder block and head. It also houses mounting bosses for mounting on to vehicle frame. It also supports mounting arrangement for engine covers on one side and houses crank shaft web portion on the other side separated by a flat wall.

The crankcase of the engine is typically divided in to two halves namely left side and right side. When the engine is running the vibration and noise created by transmission parts is transferred to frame through mounting points. The vibration thus transferred is a cause of irritation to the rider, if it exceeds certain limits.

To reduce vibration there are certain methods available in prior art such as including resilient mounting, thickening of crankcase wall etc. But these methods are proved to be expensive and adding more weight to the crankcase.

Therefore in the light of above said problems, the object of the present invention is to provide an effective way of reducing vibration of the crankcase.

Summary of the Invention:

The present invention has been devised in view of the above problems and it is therefore an object of the present invention to provide a crankcase structure for single speed engine which will reduce vibration.

Another object of the present invention is to provide a crankcase structure for a single speed engine, which helps to reduce the weight of the engine.

Yet another object of the present invention is to provide a crankcase structure for a single speed engine which is cost effective.

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 to those skilled in the art from this detailed description.

Brief description of the Drawings:

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein

FIG. 1 illustrates a conventional two wheeler.

FIG. 2 shows the engine assembly according to the present invention.

FIG. 3 shows crankcase structure according to the present invention.

FIG. 4 shows the inner side of crankcase left according to the present invention.

FIG. 5 shows the cumulative frequency responses of points on conventional and modified crankcase according to the present invention.

Detailed Description of the Invention:

It is further to be noted that the present invention is not limited to the described embodiment and many other changes and modifications may be made without departing from the scope of the appended claims.

Embodiments of the present invention now be described with reference to the accompanying drawings. In the following description, "front", "rear", "upper", "lower", "right", "left" and "bottom" represent directions viewed from the perspective of the vehicle rider.

Drawing reference to Figure.1 a motorcycle comprises of a frame (101), front fork (102) attached to a pivot tube (103) of the vehicle frame, 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, a seat (107) attached to the upper rear portion of the vehicle frame, an engine unit (108) attached to the lower front section of the vehicle frame, a swing arm (109) attached to a lower rear section of the vehicle frame, suspended by a rear shock absorber (not shown in the drawing) from the vehicle frame and a rear wheel (110) attached to a rear end of swing arm (109). The intake system of the engine comprises of a carburettor (117), intake duct and an air cleaner. The exhaust system of the engine comprises of exhaust pipe and a muffler. The motorcycle is also provided with a side cover (111) for covering a side section of the vehicle frame, a seat cover for covering a rear section of the vehicle frame below the seat, a front fender (112) for covering an upper part of the front wheel (104), and a rear fender (113) for covering an upper part of the rear wheel (110). The drive from the engine (108) is transmitted from the engine to the driven wheel sprocket mounted on the rear wheel hub mounted on the rear wheel assembly.

Referring to figure 2, an engine includes an engine housing generally defining a crankcase, crank web chamber (201) and transmission chamber (202). The crankcase comprises a right half (204) and a left half (203) that are joined together by known means. The said crankcase right half (204) of the crankcase includes a partition wall (301, shown in figure 3) that separates the crankcase from the cam web operating area (201).

The crankcase halves always have a flat wall in conventional design which separates crank web chamber from the gear box and clutch or magneto side. The walls (302, 303) of crankcase are built perpendicular to said partition wall (301) forming a cavity on either side. In one of the embodiments of the present invention, the partition wall (301) of the crankcase is made spherical with a large radius. The said radius is preferably in the range of 1600mm to 2000mm. The spherical walled crankcase is stronger than the flat walled crankcase for a given thickness. In the present invention the said partition wall is large spherical wall over which both cavities for crank web and gear box side are built. The spherical shell shape of the wall effectively reduces the vibration and noise of the engine thereby making the rider comfortable.

Figure 4 shows the inner view of the said crankcase left half.

The above said crankcase structure reduces the vibration by change in natural frequency of resonance of the separating wall there by shifting the natural frequency beyond the operating limit. The graphs and table for the same in shown in figure 5.

We Claim:

1. A crankcase structure for a single speed engine comprising:

a crankcase including left and right halves;

a crank web chamber defined to support crankshaft bearing; and

a transmission chamber housing the transmission system;

wherein the crankcase left half partition wall, separating the crank web chamber and transmission chamber is made spherical.

2. The crankcase structure as claimed in claim 1, wherein the said crankcase left half partition wall is made spherical with large radius in the range of 1600mm to 2000mm.