Crankweb for a crankshaft assembly

Field of the invention

The present invention relates to "Crankweb for a crankshaft assembly" and more particularly to stiffening of crankweb of a crankshaft for a four-stroke internal combustion engine.

Description of the prior art
An engine consist of piston, a cylinder block and a head the contains the valve train. The piston moves up and down in the cylinder block, driven by combustion and expansion of air-fuel mixture that has been ignited by a spark. Valves alternatively open and close to allow the fuel-air mixture to enter the combustion chamber. As the piston moves up and down, it turns a
crankshaft through a connecting rod, which transforms the energy from the pistons into rotary motion. The rotational force of the crankshaft is transmitted, via transmission, to the rear wheel of the motorcycle.

These engine key parts such as cranshaft, connecting rod and pistons have a major impact on their durability, output characteristics and noise and vibration of the engine.The crankshaft constitutes two crankwebs joined by a crankpin.
The crankshaft held by the crankcase bearing receives the combustion force and force due to inertia from piston through the connecting rod in each cycle.

This load is typically cyclic in nature. Moreover, the performance and vibration of the crankshaft due to the above said cyclic load depends on stiffness of crankweb under static and dynamic loading conditions.

Thus the crankshaft and crankweb is subjected to both dynamic and static stress due to the cyclic functioning of the moving piston. Due to this continuous dynamic and static stress, there is deformation of the crankweb mass that leads to further damage to the crankshaft and crankweb structure. To counter this, the stiffness of the crankweb mass is increased by inserting more material. However, this leads to further increase in weight that impacts the performance with respect to power to weight ratio negatively. Hence, the objective of the present invention is to provide a stiffened crankweb without increase in weight and performance of the engine. Brief description of the invention

The core part of the engine is the cylinder with the piston moving up and down inside the cylinder. Some of the key engine parts along with their functions are spark plug which supplies the spark which ignites the air/fuel mixture so that combustion could occur; valves wherein the intake and exhaust valves open at the proper time to let in air and fuel to let out exhaust; a piston which is a cylindrical piece of metal that moves up and down inside the cylinder; piston rings that provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder; connecting rod which connects the piston to the crankshaft; crankshaft which turns the piston's up and down motion into circular motion; a sump which surrounds the crankshaft and contains oil which collects in the bottom of the sump; etc.

Accordingly, in the present invention, a crankweb can be defined by counter web mass arm, a crank boss connected to a connecting rod through a crankpin, a oil hole, a crankweb bridge between the said crankweb counter mass and said crank boss area, a flange area defined by flange arms is provided wherein the said bridge length has been increased substantially in the range of 1:2 to 3:4. Moreover, the angle between the said flange arm and the said counter web arm is atleast 25 degrees. Also, there is decrease in flange arm width and the same amount of material present in the width is added to the bridge area that results in increasing of stiffness ranging from 2600 KN/mm to 2900 KN/mm. This results in increasing of the stiffness of the crankweb mass without increase in the weight of the structure. As a result of this, the dynamic response with respect to deflection is also reduced considerably.

Brief Description of the drawings

Figure 1 illustrates a cross section of a typical four-stroke engine.

Figure 2 illustrates front view of a crankshaft assembly

Figure 3 illustrates the front view of the crankweb according to the prior art

Figure 4 and 5 illustrates the front and side view of the crankweb according to the present invention

Detailed description of the present invention

A selected illustrative embodiment of the present invention will be now described with respect to the accompanying figures.
In Figure 1, 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 200.

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 assembly is rotatable bearing 206 supported. A connecting rod 207 is 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 209 and the engine 200 of the present invention is a single cylinder 4-cycle engine 200. The crankshaft assembly 208 comprises of two opposite crankweb 219 connected by a crankpin.

The engine 200 of this embodiment generally includes the structure described above. However, the engine 200 further includes an inventive crankweb 210 according to the present invention

Figure 3 illustrates the front view of the crankweb according to the prior art. Here the width crankweb bridge 304A is less than that of the present invention. It leads to lower stiffness.

Hereinafter, the proposed crankweb structure will be described with respect to Figure 2 .Figure 4 and Figure 5.

The crankshaft assembly 208 consists of a pair of crank webs 210 integrally attached with a stem or shaft to each web connected by crank pin 211 press fitted to each web at a particular distance and a needle bearing rotatably fixed in the gap formed between the webs 210 and a connecting rod 207 assembled over the needle bearing where in the identical crank webs 210 are re shaped to improve the stiffness in the bending mode direction. In the present invention, a crankweb 210 can be defined by counter web mass arm 301, a crank boss 302 connected to a connecting rod 207 (connecting rod) through a crankpin, a oil hole 303, a crankweb bridge 304 between the said crankweb counter mass 301 and said crank boss 302 area, a flange area 305 defined by flange arms 306 is provided wherein the said bridge length has been increased substantially in the range of 1:2 to 3:4 when compared to outer diameter 400 of the said crankweb 210. Moreover, the angle between the said flange arm 306 and the said imaginary line A-A1 (that is tangent to crank boss) is at in the range of 10 to 30 degrees. Also, there is decrease in flange arm width and the same amount of material present in the width is added to the bridge area that results in increasing of stiffness ranging from 2600 KN/mm to 2900 KN/mm. This results in increasing of the stiffness of the crankweb mass without increase in the weight of the structure. As a result of this, the dynamic response with respect to deflection is also reduced considerably.

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.

Part numbers associated with the drawings
200. Engine 203. Cylinder head
201. Crankcase 204 & 205. Crankcase halves
202. Cylinder block 206. Bearing
203. Connecting rod 304.Crankweb bridge in the
204. Crankshaft present invention
205. Piston 304 A. Crankweb bridge according
206. Crankweb (new) to prior art
219. Crankweb (old)
305. Flange area
211. Crankpin
306. Flange arms
301. Counter web mass
307. Counter web mass arm
302. Crank boss 400. Outer diameter of crankweb
303. Oil hole A-A1. Imaginary line

Claims: We claim

1. A crankweb 210 for a crankshaft assembly 208 comprising a crankweb counter mass 301 bordered by counter web mass arm 307, a crank boss 302, an oil hole 303, a crankweb bridge 304 between the said counter web mass arm 307 and said crank boss 302, a flange area 305 limited by flange arms 306, wherein the length of the said bridge 304 is at least 50% of the outer diameter 400 of the said crankweb 210.

2. The crankweb 210 for a crankshaft assembly 208 as claimed in claim 1, wherein the angle between the said flange arm 306 and the tangent to the crank boss A-A1 is between 10 to 30 degrees.

3. The crankweb 210 for a crankshaft assembly 208 as claimed in claim 1, wherein the stiffness range is in between 2600 KN/mm to 2900 KN/mm.

4. A crankshaft assembly comprising the crankweb as claimed in claim 1, claim 2 and claim 3.

5. A four-stroke internal combustion engine comprising a crankshaft assembly as claimed in claim 4.