CRANKING MECHANISM FOR TWO-WHEELED VEHICLE

Field of Invention

[0001] The present invention relates to an internal combustion engine and more particularly to a mechanism which serves dual purpose of cranking the internal combustion engine and balancing the internal forces generated by reciprocating masses.

Description of Prior Art

[0002] Conventional internal combustion engines include a crankshaft that rotates in a crankcase about a crankshaft axis. A reciprocating piston connects to a piston connecting rod, which, in turn, pivotally connects to the crankshaft at a piston connecting rod axis.

[0003] Operation of such conventional engines generates vibrations and other internal forces due to reciprocating masses. In order to cancel out such forces, a plurality of counter weights are generally used, such counterweights being arranged within the crankcase. Counter weights balance out the inertial forces of the engine by operating at the same frequency (or a multiple thereof), but phase-shifted through 180 degrees. This means that when the piston moves downwards, the counterweight moves upwards and vice versa. In numerous arrangements in prior art, counterweights have been provided on both the crankshaft and an altogether different shaft called a balancer shaft. For the arrangement to work in harmony the balancer shaft is located in the crankcase and takes drive from crankshaft and rotates in opposite direction of crankshaft with the same speed.

[0004] Almost all conventional engines used in motorcycles are cranked using a kick-start mechanism. The rider rapidly and forcefully depresses a kick pedal which in turn cranks the engine by rotating the crankshaft through a set of idler gears.

[0005] There is an ever-increasing demand for compact sized engines having reduced weight and enhanced fuel efficiency. Presence of both, the balancer shaft and the kick starting mechanism adversely affects engine compactness, increases weight and leads to complexities in design of various subsystems inside the engine. However both these mechanisms are indispensable for optimum performance and working of the engine. It would therefore be very desirable to have an arrangement which combines the functionalities of both the balancer shaft as well as the kick start mechanism, an arrangement which makes the engine compact and reduces weight substantially.

Summary of Invention

[0006] The present invention has been conceived in view of the foregoing drawbacks in the prior art and it is the primary objective of the present invention to provide a single mechanism which combines the functionality of cranking the engine and balancing internal forces. It is a further objective of the present invention to provide an internal combustion which has reduced weight, is compact in size and has enhanced fuel efficiency.

[0007] The cranking mechanism as per the present invention comprises a crankshaft, a balancing mechanism and a kick start mechanism. The crankshaft has atleast one counterweight integrated to it. The balancing mechanism comprises a balancing force transmission arrangement and a balancer shaft that has a balancer ratchet nut fastened to its one end. The balancer shaft has atleast one counterweight provided towards its center. The kick start mechanism comprises a kick start shaft, a kick lever pivoted to one end of the kick start shaft, a torsion spring, a kick start force transmission arrangement, a kick start guide spring and a helical kick start driven gear. The kick start driven gear has a ratchet nut integrated to it and is slidably mounted on the other end of the kick start shaft. The balancing mechanism and the kick start mechanism are arranged coaxially in such a manner that a gap exists between the balancer ratchet nut and the kick start driven gear. The above-mentioned gap is in the range 1.8mm-2mm.

[0008] The rider initiates cranking by actuating the kick lever. On actuating the kick lever, the kick start shaft is rotated which in turn rotates the kick start force transmission arrangement. The kick start force transmission arrangement drives the kick start driven gear laterally to engage with the balancer ratchet nut. Thereafter, the kick start driven gear rotates in turn rotating the balancer shaft. The balancer shaft rotates the balancing force transmission arrangement, which cranks the engine, by rotating the crankshaft. Once cranking is completed, action of the torsion spring mounted on the kick start shaft, retracts the kick start mechanism from the balancing mechanism thereby opening the gap between the kick start driven gear and the balancer ratchet nut. The counterweights provided on the crankshaft and the balancer shaft, balances internal forces due to reciprocating masses, during running of the engine.

[0009] Therefore the balancer shaft serves the dual purpose of cranking the engine and balancing internal forces generated during running of the engine. The mechanism according to the present invention reduces engine weight upto 1.5kgs. Further, the engine has been made substantially compact and fuel efficiency has been enhanced. There is also a reduction in part count which consequently reduces assembly time and costs.

[0010] These and other features, aspects, and advantages of the present invention will be better understood with reference to the following description, the appended claims and the accompanying drawings. This summary is not intended to limit the scope of the claimed subject matter.

Brief Description of Drawings

[0011] The above and other features, aspects, and advantages of the present invention are further illustrated by the accompanying drawings. The drawings are given by way of illustration only and are not limitative of the present invention. A brief description of the drawings is as follows:

Fig. 1 is a side view of a conventional two-wheeled vehicle.

Fig. 2 is an isometric view of the cranking mechanism as per the present invention.

Fig. 3 is a front view of the cranking mechanism as per the present invention.

Fig. 4 is an isometric view of the cranking mechanism as per the present invention.

Detailed Description of Invention

[0012] The present invention is hereinafter described with reference to the accompanying drawings. It is to be noted that like reference numerals designate corresponding or identical elements throughout the various drawings. The terms front and rear, and left and right as used indicate the front and rear and the left and right directions when viewed by a rider seated on the vehicle seat.

[0013] A conventional two-wheeled automotive vehicle as illustrated in Fig. 1, includes an internal combustion engine 41, a front wheel 25, a rear wheel 27, a body frame 19 and a fuel tank 56. Body frame 19 includes a head pipe 12, a main tube 17, a down tube 22, and seat rails 18. The head pipe 12 is provided at the front end of body frame 19 to support a steering shaft 11 disposed within the head pipe 12. The upper and lower ends of the steering shaft 11 are fixed to an upper bracket 13 and a lower bracket 14 respectively. Upper bracket 13 and lower bracket 14 retain front fork 16 that supports front wheel 25. The front wheel 25 is connected at the lower end of the front fork 16, and the upper portion of the front wheel 25 is covered by a front fender 54 mounted to the lower portion of the front fork 16. A handlebar 15 is fixed to upper bracket 13 and can rotate to both sides. A head light 36 is arranged on an upper portion of the front fork 16. Down tube 22 is located in front of the internal combustion engine 41 and stretches slantingly downward from head pipe 12. A bracket 55 is provided at the lower end of down tube 22 for supporting the internal combustion engine 41. Main tube 17 is located above the internal combustion engine 41 and stretches rearward from head pipe 12 and connects the rear of the internal combustion engine 41. A vertical pipe 28 is joined to the rear end of main tube 17 and stretches downward from the point where the main tube 17 joins the seat rails 18. Seat rails 18 are joined to main tube 17 and stretch rearward to support a seat 57 disposed above seat rails 18. A side stand 58 is arranged towards the lower portion of the internal combustion engine 41. Left and right rear swing arm bracket portions support a rear swing arm 26 to swing vertically, and a rear wheel 27 is connected to rear end of the rear swing arm 26. A rear wheel suspension 34 is arranged between rear swing arm 26. A tail light unit 64 is disposed on the rear cover 61. A pillion footrest 31 is connected to the vertical pipe 28. A grab rail 62 is also provided on the rear of the seat rails 18. Rear wheel 27, arranged below the seat 57 is rotated by the driving force of the internal combustion engine 41 transmitted through the transmission system.

[0014] Referring to Fig. 2, Fig. 3 and Fig. 4, the cranking mechanism as per the present invention comprises a crankshaft 116, a balancing mechanism and a kick start mechanism. The crankshaft 116 has at least one counterweight 118 integrated to it. The balancing mechanism comprises a balancer shaft 112 and a balancing force transmission arrangement. A balancer ratchet nut 111 is fastened to one end of the balancer shaft 112. Atleast one counterweight 117 is provided towards the center of the balancer shaft 112. The balancing force transmission arrangement further comprises a balancer driven gear 113 and a balancer drive gear 114. The balancer driven gear 113 is securely mounted on the balancer shaft 112 and the balancer drive gear 114 is securely mounted on the crankshaft 116. The balancer driven gear 113 and the balancer drive gear 114 are of the same gear ratio and remain meshed to each other.

[0015] The kick start mechanism comprises a kick start shaft 102, a kick lever 101 pivoted to one end of the kick start shaft 102, a torsion spring 103, a kick start force transmission arrangement, a kick start guide spring 107 and a kick start driven gear 109 having a ratchet nut 110 integrated to it. The kick start driven gear 109 is helical and is slidably mounted to the other end of the kick start shaft 102. The kick start force transmission arrangement further comprises a kick start drive gear 104 and a kick start idler gear. The kick start drive gear 104 is sector shaped and is securely mounted on the kick start shaft 102. The kick start idler gear is securely mounted on a kick start idler shaft 108 and consists of an integrated spur gear 105 and a helical gear 106. The helical gear 106 is of greater diameter compared to the kick start driven gear 109. The spur gear 105 is meshed to the kick start drive gear 104 and the helcial gear 106 is meshed to the kick start driven gear 109. The torsion spring 103 sits concentrically on the kick start shaft 102 and has its one end secured to the kick start drive gear 104 and other end clamped to a crankcase (not shown in the figures). The balancer mechansim and the kick start mechanism are arranged coaxially in this manner that a gap 100 exists between the kick start mechanism and the balancing mechanism. The gap 100 is in the range 1.8mm-2mm.

[0016] The rider initates cranking by forcefully depressing the kick lever 101. Actuation of the kick start lever 101 rotates the the kick start shaft 102 and the kick start drive gear 104 in the anticlockwise direction. The kick start drive gear 104 transfers this rotary motion to the the integrated spur gear 105 and helical gear 106 which rotates in the clockwise direction. The bigger diameter helical gear 106 drives the kick start driven gear 109 laterally to engage the ratchet nut 110 with the balancer ratchet nut 111 thereby closing the gap 100. Subsequently, the kick start driven gear 109 rotates the balancer shaft 112 and the balancer driven gear 113 in the anti-clockwise direction. The rotation of the balancer driven gear 113 rotates the balancer drive gear 114 in the clockwise direction which in turn cranks the engine by rotating the crankshaft 116. A kick start guide spring 107 enables lateral movement of the kick start driven gear 109. The kick start guide spring 107 is mounted to the neck of the kick start driven gear 109.

[0017] Once the engine is cranked, the kick start mechanism retracts from the balancing mechanism opening the gap 100. Retraction of the kick start mechanism is due to action of the torsion spring 103. When the engine is running, the crankshaft 116 by way of the balancing force transmission arrangement rotates the balancer shaft 112. The counterweights 117 & 118 are engineered in such a manner that, when the engine is running, they are radially opposite to each other in the horizontal plane and on the same side in the vertical plane. Therefore the balancer shaft performs the dual role of cranking firstly and then balances internal forces during running of the engine. Hence the mechanism as per the present invention avoids the use of separate arrangements for cranking and balancing, thereby reducing weight and size of the engine substantially. As aforementioned, the present invention reduces engine weight upto 1.5kgs.

[0018] The foregoing description is a specific embodiment of the present invention and has been described for the purpose of illustration only.

Persons skilled in the art may practice numerous alterations and modifications of the present invention without departing from its spirit and scope. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

Description of Reference Numerals

[0019]
11: Steering shaft
12: Head pipe
13: Upper bracket
14: Lower bracket
15: Handlebar
16: Front fork
17: Main tube
18: Seat rails
19: Body Frame
22: Down tube
25: Front wheel
26: Rear swingarm
27: Rear wheel
28: Vertical pipe
34: Rear wheel suspension
36: Head light
41: Internal Combustion Engine
54: Front fender
56: Fuel Tank
57: Seat
58: Side stand
62: Grab rail
64: Tail light unit
100: Gap between kick start driven gear and balancer ratchet nut
101: Kick lever
102: Kick start shaft
103: Torsion spring
104: Kick start drive gear
105: Spur gear
106: Helical gear
107: Kick start guide spring
108: Kick start idler shaft
109: Kick start driven gear
110: Ratchet nut
111: Balancer ratchet nut
112: Balancer shaft
113: Balancer driven gear
114: Balance drive gear
116: Crankshaft
117: Balancer shaft counterweight
118: Crankshaft counterweight

We Claim:

1. A cranking mechanism for an internal combustion engine comprising:
a crankshaft 116;

a balancing mechanism, the said balancing mechanism further comprising a balancer shaft 112, the said balancer shaft 112 rotatably connected to the crankshaft 116 by way of a balancing force transmission arrangement; and

a kick start mechanism, the said kick start mechanism further comprising a kick start shaft 102 wherein the said kick start mechanism is arranged coaxial to the balancing mechanism.

2. The cranking mechanism for an internal combustion engine as claimed in claim 1 wherein the balancing mechanism further comprises a balancer ratchet nut 111 fastened to one end of the balancer shaft 112.

3. The cranking mechanism for an internal combustion engine as claimed in claim 1 wherein the kick start mechanism further comprises a kick start force transmission arrangement, a torsion spring 103, a kick lever 101 pivoted to one end of the kick start shaft 102, and a helical kick start driven gear 109 having a ratchet nut 110 integrated to it and a kick start guide spring 107 mounted at its neck, the said kick start driven gear 109 slidably mounted to the other end of the said kick start shaft 102.

4. The cranking mechanism for an internal combustion engine as claimed in any one of claims 1 to 3 wherein the balancing mechanism and kick start mechanism are arranged coaxially in this manner that a gap 100 exists between the balancer ratchet nut 111 and the kick start driven gear 109, the said gap 100 preferably sized in the range 1.8mm-2mm.

5. The cranking mechanism for an internal combustion engine as claimed in any one of claims 1 to 4 wherein on actuation of the kick lever 101 .rotary motion is transferred through the kick start shaft 102 to the kick start force transmission arrangement, the said kick start force transmission arrangement drives the kick start driven gear 109 laterally to engage the ratchet nut 110 with the balancer ratchet nut 111 by closing the gap 100, the said kick start driven gear 109 subsequently rotates the balancer shaft 112 which enables cranking by rotating the crankshaft 116 through the balancing force transmission arrangement.

6. The cranking mechanism for an internal combustion engine as claimed in claim 3 wherein the kick start force transmission arrangement further comprises:

a sector shaped kick start drive gear 104 securely mounted on the kick start shaft 102;and

a kick start idler gear securely mounted on a kick start idler shaft 108, the said kick start idler gear further comprises an integrated spur gear 105 and a helical gear 106, the said spur gear 105 meshed to the kick start drive gear 104 and the said helical gear 106 meshed to the kick start driven gear 109.

7. The cranking mechanism for an internal combustion engine as claimed in claim 3 or claim 6 wherein the helical gear 106 is of larger diameter compared to the kick start driven gear 109.

8. The cranking mechanism for an internal combustion engine as claimed in claim 1 wherein the balancing force transmission arrangement comprises a balancer driven gear 113 securely mounted on the balancer shaft 112 and meshed to a balancer drive gear 114, the said balancer drive gear securely mounted on the crankshaft 116.

9. The cranking mechanism for an internal combustion engine as claimed in claim 1 wherein the crankshaft 116 has atleast one counterweight 118 integrated to it and the balancer shaft 112 has atleast one counterweight 117 provided towards its center.

10. The cranking mechanism for an internal combustion engine as hereinabove described in the specification and illustrated in the accompanying drawings.