Engine for a motorcycle

Field of the invention

The present invention relates to "Engine for a motorcycle" and more particularly to an engine provided with an improved type internal combustion engine having cylinder block mounted with a downward offset plane with respect to the crankshaft axis plane.

Background of the invention

Generally, in scooter type motorcycle engines have crankcase, crankshaft assembly, cylinder block, cylinder head, induction system, exhaust system, CVT or chain transmission and a secondary gearbox having input shaft, intermediate shaft and an output shaft connected to wheel of the vehicle. In these types of engines, the cylinder block is arranged to have an axis extending across the axis of the crankshaft. In such type of engines, offsetting a transmission input shaft upwardly with respect to a plane which includes the axes of a crankshaft and a transmission output shaft is effective to reduce the inter axial distance between the crankshaft and the transmission output shaft to shorten the overall length of the engine in the longitudinal direction of the motorcycle for making the engine compact.

However, the conventional CVT driven engines fail to provide such offset for the cylinder block. In order to achieve the compact engine layout, the angle through which the cylinder block rises from the horizontal plane, is optimized in order to provide a sufficient compact layout for engine. Accordingly, however, there is an increase in the overall length and height of the conventional engines in the motorcycles. This increase negates the compactness and makes it difficult for packaging of the induction system.

Also this increase in engine layout results in reduction in space availability for storage box mounted in the motorcycle.

Hence the objective of the present invention is to provide a simple, cost effective, sturdy design that provides a compact engine layout allowing for easy packaging of induction system and increased storage space volume in the vehicle.

Another objective of the present invention is to provide a CVT driven improved internal combustion engine for a motorcycle having increased volumetric efficiency and mechanical efficiency.

Brief description of the invention

The present invention has been made in view of the above drawbacks. It is an object of the present invention to provide a CVT driven engine for scooter type motorcycles which has a cylinder block mounted with a downward offset with respect to the crankshaft axis in order to effectively reduce the overall volume of the engine mounted in the motorcycle.

The crankcase houses and supports a crankshaft, a transmission input shaft, and a transmission output shaft, arranged at one common axis oriented transversely of the motor vehicle. An intermediate shaft is also provided between the transmission shafts for efficient driving requirements. The cylinder block is disposed to have an axis passing forwardly of the axis of the crankshaft. According to the above said feature, the cylinder block is disposed to have an plane passing forwardly of the axis of the crankshaft. Accordingly, the angle through which the axis of the cylinder block passes is raised with a range from 0 to 15 degrees from the horizontal plane and a downward offset at an optimum level is provided.

As a result, the size of the engine with the cylinder block and the crankcase in the longitudinal direction of the motorcycle is made compact, thus reducing the overall length and height of the engine in the motorcycle, and thereby effectively making the engine compact. Also the offset of the cylinder block according to the present invention allows for improving the volumetric efficiency and mechanical efficiency.

Brief description of drawings

Figure 1 shows a representative view of a scooter type motorcycle according to the present invention.

Figure 2 shows the cross sectional view of the engine assembly adapted in the present art

Figure 3 shows the sectional view of the engine according to 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.

Figure 1 is a side plan view of a scooter type motorcycle provided with an engine 102.

This engine is provided with an improved lubrication structure according to an embodiment of the present invention. Any known scooter type motorcycle, as illustrated in Figure 1, can be divided into three major portions, the front portion, the middle portion and the rear/tail portion.

The front portion comprises of the head tube, the handle bar 105, the front suspension 103, the front wheel with necessary brakes and the body panels 109;

the middle portion comprises of the floor board, the seat support 106, the fuel tank, the battery, the utility box etc;

and the rear/tail portion comprises of the engine support, the riders seat 106, the rear shock absorber 104, rear fender and the back wheel with suspensions.

In assembling such a vehicle, especially the body covers 109, there are many sub assemblies and these are independently mounted onto the frame 101 at different locations. The body covers 109 are mounted to the frame 101 using brackets.

Scooter-type vehicles, or scooters, include a frame assembly 101, which usually supports the body of a scooter, along with front and rear wheels.

A frame assembly for a scooter-type vehicle comprises of at least one front wheel, at least one rear wheel and a vehicle body.

Typically, a frame structure 101 for a scooter type motorcycle comprises a main frame and may also have a sub-frame. The sub-frame is attached to the main frame using appropriate fastening members. All the other components such as the body panels 109, the engine 102, the electrical units are mounted on the main frame and the sub frame either directly or by means of brackets and fastening members.

The frame assembly includes a head tube, which supports a front wheel suspension assembly 103 of the vehicle. An upper frame extends from the head tube to a rearward end of the vehicle body. A swing arm 104 is pivotally supported by the upper frame and supports a rear wheel of the vehicle.

The frame assembly may include a lower frame remove ably coupled to the upper frame and defining a space 107 there between.

The sub-frame preferably supports at least one component of the scooter-type vehicle in the space, such as a fuel tank, for example.

Typically, front 103 and rear 104 suspension assemblies are operatively positioned between the front and rear wheels and the frame assembly.

The front suspension assembly 103 commonly is a telescopic fork arrangement, while the rear suspension assembly 104 is a swing type arrangement.

In a scooter, the rear suspension swing arm typically supports a power unit 102, which is configured to drive the rear wheel of the scooter.

The power unit 102, is coupled along with a transmission assembly 108, such as a drive shaft, drive belt, or chain and sprocket assembly.

The frame assembly 101 of a scooter-type vehicle is an elongated structure, which typically extends from a forward end to a rearward end of the scooter.

A scooter frame assembly generally is convex in shape, as viewed from a side lavational view.

A handlebar assembly 105 and a seat assembly 106 are supported at opposing ends of the frame assembly and a generally open area is defined there between.

In Figure 2, the principal portion of the engine of the present invention is shown in cross-sectional view. As shown in this figure, the engine includes a crankcase 201, a cylinder block 202 connected to the crankcase 201, a cylinder head 203 to be connected to the cylinder block 202 and a cylinder head cover. These are clamped and fixed together via stud bolts and the like, thereby constituting the main structure of the engine 102.

The crankcase has a structure in which the half cases 204 & 205 are integrally connected to each other. The halves cases and are formed by dividing the crankcase into right 205 and left portions 204. In the crankcase, formed of the combined half cases and, a crankshaft is Rota table bearing 206 supported. A connecting rod 207 is relatable attached to a crankpin of the crankshaft 208 via a bearing located at the large-end thereof. A piston 209 is pivotally attached to the smali-end of the connecting rod 207 via a piston pin. In this embodiment, there is provided one piston and the engine of the present invention is a single cylinder 4-cycle engine.

In the transmission portion of the power unit, a variable speed ratio V-belt drive 210 extends rearward from about the crankshaft 208. A driving pulley 211 is fixed to the crankshaft. The driving pulley includes a fixed pulley half 212 which is caused to rotate with the output shaft. The fixed pulley half is disk shaped with a conical pulley surface. On the outer side of the pulley half is a fan 213 to cool the system with air drawn in through a passageway formed in the case 201. To provide lubrication to the engine assembly 102, which must cycle back and forth under load during driving of the vehicle, a sump 7 for lubrication oil is provided.

Figure 3 explains the inventive step involved in the present invention. The cylinder block 202 extends forwardly from the front end of the crankcase 201, wherein the cylinder head 203 is joined to the upper end of the cylinder block 202. The crankcase 201 houses and supports a crankshaft 208, a transmission input shaft 303, and a transmission output shaft 301, which are arranged at one common plane oriented transversely of the engine. Accordingly, the angle of the axis of cylinder block 305 is raised to a tune in a range of 0 to 15 degrees with respect to the longitudinal plane 308 and thus the cylinder block structure 202 is provided with an offset plane 309 (figure 1) downwardly with respect to the raised cylinder axis 305 at appropriate level. This allows for a compact engine layout with an offset for cylinder block 202, and thus enables for providing an improved intake structure in which the pipe intake 306 along with the carburetor 307 is moved downward for reducing the overall height of the engine, and thereby enabling easiness in induction system packaging and providing adequate storage volume in the storage box mounted in the motorcycle.

We claim

1. A continuously variable transmission (CVT) engine for a scooter type
motorcycle comprising;

acrankcase201;

a crankshaft assembly 208;

a cylinder block 202;

a cylinder head on the said cylinder block 203;

an induction system 306 connected to a carburettor 307;

a belt driven or chain transmission 108;

a secondary gear box having an input shaft 303, an intermediate shaft 302, an output shaft 301 connected to wheel of the engine system forming a longitudinal plane wherein the angle of the axis of cylinder block 305 is raised in a range of 0 to 15 degrees forming a plane with respect to the longitudinal plane 308 and the cylinder block 202 is provided with an offset 309 downwardly with respect to the raised cylinder plane 305 at appropriate levels.

2. The CVT engine as claimed in claim 1, wherein the induction system 306 along with the carburettor 307 is moved downward closer to the said engine 102 enabling easy packaging of the said induction system 306 and providing increased storage volume on to the storage box mounted on the scooter type motorcycle.