Crankshaft for an internal combustion engine

Field of the invention

Tlie present invention reiates to "Crankshaft for an internal combustion engine" and more particularly to the counter-balancing of a reciprocating piston type internal combustion engine.

Background of the invention

The present invention relates to a balancer system for use in an internal combustion engine such as a motorcycle engine or the like. Some reciprocating internal combustion engines for use on motorcycles incorporate a balancer system to reduce vibrations during the engine operation. Such a balancer system typically comprises a primary counterbalance for reducing primary vibrations, the primary counterbalance being rotatable about an axis parallel to the crankshaft at the same speed as the crankshaft in the opposite direction to the crankshaft.
Since the counter balance mass is provided in a direction inward to the crankshaft axis the mass required to balance the engine reciprocating forces is more, hence the counter balancing arrangements involves higher weight due to the high web mass for the crankshaft provided. Also the known type of counter balance arrangements results in higher cost due to higher web mass
and higher crankshaft assembly mass.

Hence the main object of the invention is to lower the assembly weight of crankshaft.

Another objective of the present invention is to reduce the weight of counter balance mass and reduce cost due to higher crankshaft assembly mass.

Brief descriotion of the invention

The counterbalance system of the present invention includes a counterbalance web mass placed at a distance generally offsetted to the
crankshaft web and aligned accordingly to the crankshaft, and hence the function of the crankshaft assembly is achieved with the lower crankshaft assembly weight by offsetting the counter-mass outward. In this process the inertia is achieved with lower mass.

Brief description of the 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 prior art

Figure 3 shows the front comparative view of the embodiments according to the present invention and prior art

Figure 4 shows the side comparative view of the embodiments according to the present invention and the prior art

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 mainframe 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 removeably 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 ann 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 elevationai 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 according to the prior art 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 rotatable bearing 206 supported. A connecting rod 207 is rotatable 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 small-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.

Figure 3 and Figure 4 illustrates comparative figures according to the present embodiment vis-a-vis the prior art, wherein a counterbalance mechanism is provided for an internal combustion engine having a cylindrical piston 209, a crankshaft 208 and a connecting rod 207 pivotally Interconnecting the piston 209 and crankshaft 208. The piston 209 is adapted to reciprocate within cylinder 202 and the crankshaft 208 is rotatably mounted at its opposite ends by bearings 206 to the opposite sides of the crankcase 201. The connecting rod 207 extends between and pivotally connects a wrist pin 301 in the piston 209 to the crankshaft 208.

A spaced counter mass 302 is attached along to crankshaft 208 at an outward offset 303 for counterbalancing the reciprocating masses during rotation of the crankshaft 208. This counter mass 302 is offsetted 303 along the crankshaft 208, accordingly the location and the web 304 counter mass details are normally calculated using the reciprocating mass balancing requirements as well as the inertia requirements and normally range between 140 to 190 degrees with respect to either to the centre or at a point at least 1 mm above the centre lateral to the axis of the crankshaft. Since the counter mass 302 is offset to a distance outwardly, the mass moment of inertia will be satisfied with a lower mass as compared to present. This allows for reducing the counter mass provided in the full circular shaped crankshaft when compared to that present in the prior art 305

The present invention also allows eliminating the vibration imbalance in the engine 102 and reducing the crankshaft 208 weight thereon, and allows for smooth operation of the engine 102. Also noise due to the vibration and the
imbalances in the engine are substantially eliminated by the counterbalance system.

Figure numbers associated with the invention

101.Frame assembly
102.Engine/ Power unit
103.Front wheel suspension
104.Swing arm
105.Handle bar assembly 106. Seat
107. Space
108. Transmission assembly
109. Body panels\covers
201. Crankcase

Claims:

We claim:

1. A crankshaft drive in an Internal combustion engine, which comprises
at least one cylinder having a cylinder head;
a crankcase supporting Inside thereof;
a crankshaft rotating at a predetermined direction, wherein a spaced counter mass 302 is attached to crankshaft 208 at an outward offset 303 with an angle ranging from 140 to 180 degrees from the centre of the crankshaft.

2. The spaced counter mass 302 as claimed in claim 1, wherein the mass is attached concentrically and integrally to crankshaft 208 at an outward offset 303 with an angle ranging from 140 to 180 degrees from the centre of the
crankshaft.

3. The spaced counter mass 302 as claimed in claim 1, wherein the mass is attached eccentrically and Integrally to crankshaft 208 at an outward offset 303 with an angle ranging from 140 to 180 degrees from the centre of the
crankshaft such that the axis of the eccentric mass stays above the said centre by atleast 1 mm.

4. The crankshaft drive as claimed in claim 1, wherein the said counter mass 302 Is offset to a distance outwardly of the axis of rotation of the said crankshaft.

5. The crankshaft drive as claimed substantially as hereinbefore described
with reference to and as illustrated In the accompanying drawings.