Starting means for a two wheeler

Field of invention

The present invention relates to "Starting means for a two wheeler" and more
particularly to a push start mechanism for a vehicle using a centrifugal clutch.

Description of the prior art

There are a number of compact vehicles that have "single gear ratio" or "single speed" transmission for ease of driving and for increased utility. These include mopeds, scooters and other small automobiles. These vehicles generally have common requirements for low cost, high efficiency, good controllability throughout the entire speed range. To meet these requirements these kinds of vehicles use centrifugal friction clutches to provide a releasable torsional connection between engine output and the associated transmission.

These centrifugal clutches engage at a predetermined rotational speed and are particularly useful in combination with internal combustion engines which tend to stall under starting load conditions, by delaying engagement until the engine is operating at a sufficiently high speed to produce enough torque to prevent stalling. In such vehicles along with a kick-start mechanism at times, push start capabilities are required to meet the utility requirements. To provide push start capabilities to such vehicles a complex multi-clutch arrangement is provided. By pushing the vehicle, this clutch arrangement motors the engine for starting.

This invention relates to a simpler mechanism providing speed responsive drive engagement and push start capability and the arrangement thereof.

Brief description of the invention

Accordingly, the present invention provides a drive having a centrifugal clutch that move into frictional engagement by application of centrifugal force to provide a drive to an output shaft. For normal starting the vehicle an electric-starter is provided whereas, for push starting the vehicle a gear operably coupled to the oil pump drive gear is provided on the output shaft. Said gear is freely rotatable on the output shaft. However, it is engage-able to the output shaft through a dog clutch, to drive the oif pump gear, which in turn rotates the crankshaft to provide an input for motoring the engine. Once the engine is started, at idle speed the responsive clutch is disengaged and drive engagement is manually controlled by manually increasing the engine fuel feed or throttle to increase engine speed to a pre-determined speed causing the speed responsive clutch to gradually engage for initial slipping drive at low speeds and lock up drive at higher speeds.

The vehicle remains at positive neutral, while pushing, the vehicle speeds up to the speed required to motor the engine for starting. Then the dog clutch is engaged and a drive is provided through the oil pump gear to the crankshaft to motor the engine for starting the engine. The rear wheel drives the oil pump drive gear once it is engaged with the output shaft.

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.

Brief description of drawings

Figure 1 illustrates a step through type two-wheeled vehicle having push start
mechanism of the invention.

Figure 2 illustrates a cross-sectional view of an engine used in vehicle shown
in figure. 1.

Figure 3 illustrates a cross-sectional view illustrating in detail the push start
mechanism as per an embodiment of the invention.

Figure 4 illustrates a cross-sectional view illustrating the manual clutch in
disengaged position.

Figure 5 illustrates a cross-sectional view illustrating the manual clutch in
engaged position.

Detailed description of the present invention

Figure 1 shows a step-through type two-wheeled vehicle 01 having an engine 02 with a drive mechanism of the present invention. As shown in Figure 2 the illustrated engine 02 is a four-stroke engine comprising a crankcase 03 and a cylinder block 04 that is connected to the front end of the crankcase 03. In one configuration, the cylinder block 04 preferably protrudes forward from a forward end of the crankcase 03 in a generally horizontal orientation such that it has an axis that extends in a longitudinal direction of the engine 02. Further, cylinder head 05 is secured to upper surface of the cylinder block.

The crankshaft 06 housed in and supported by crankcase 03 is connected to a piston 07 positioned slide-ably within the cylinder bore of cylinder block 04 via connecting rod 08.

The engine may be provided with a kick-start provision on

the right side along with the electric starter 09 whereas, a transmission system 10 is provided on the left, connected to the crankshaft 06 through a centrifugal clutch 11.

In an embodiment of the invention the said crankcase 03 is formed by integrally joining right crankcase member 03A and a left crankcase member 03B. The said right crankcase member 03A and a left crankcase member 03B provides a right support bearing 14 and a left support bearing 15 respectively to support the crankshaft 06 rotatably at first and second support point spaced from each other in the crank case 12, in a manner to prevent radial motion of the crankshaft relative to the crankcase 03. On the right side of the crankcase an electric start unit 09 magneto unit 16 is housed whereas, on the left side a single gear reduction transmission 10 is housed, said transmission comprises a driven gear 17 for engaging with the output drive gear 18 of the clutch 11 and a sprocket 19 is secured to an output shaft 20 of the said transmission 10 to drive the rear wheel of the vehicle through a chain drive. With reference to Figure 2, the centrifugal clutch 11 being a centrifugal shoe type clutch is housed on the left side of the crankcase 03. The said clutch comprises a generally cylindrical housing drum 21 of the clutch, adapted for transmission of torque from the crankshaft 06, when the clutch 11 is engaged. The cylindrical housing drum 21 is preferably coaxially aligned with and surrounds the clutch shoes 26 arranged in a manner, which will be described. The inner surface of cylindrical housing drum wall provides the coupling surface for drivingly connecting clutch housing 21 with hub assembly. Hub assembly includes a hub 25 that is adapted to be mounted on and secured to crankshaft 06 by a key-keyway arrangement or other attachment means so as

to rotate with crankshaft 06. Hub 25 further includes a circular disc 24 disposed towards the cylindrical housing 25. Pluralities of pins are mounted

on said circular disc 24 and extend outwardly therefrom. Three arcuate-shaped clutch shoes 26 are pivotally mounted on the circular disc 24 by said pins and are arranged in an end-to-end relationship with respect to each other. Each shoe has a strip of friction material bonded to the outer periphery thereto. Each shoe is formed with a generally circular hole at
one end for pivotally mounting the clutch shoes oh the pins. A first spring hook hole is formed at the opposite end of each shoe for receiving a spring hook therein. A second spring hook hole is also formed in the shoe adjacent to said generally circular holes for receiving a second spring hook.

- Clutch shoes are held in retracted position by springs when crankshaft 06 is at rest or at a relatively low speed that is below a predetermined engagement speed. This inward retracted position of clutch shoes 26 provides a small gap or spacing between shoe friction material and inner surface of cylindrical housing drum, enabling hub assembly to rotate freely without affecting stationary clutch housing.

Shoes attempt to move radially outwardly from their retracted position under the influence of centrifugal force as the rotational speed of crankshaft increases. The predetermined resistance of springs retains the shoes 26 in disengaged position until crankshaft 06 reaches the predetermined engagement speed. Upon reaching this engagement speed, clutch shoes move outwardly until friction material strips drivingly engage housing cylindrical housing drum wall. This coupling engagement rotates housing

together with hub assembly to operatively drive the said transmission system 10.

In order to provide an output connector of the torque transmitted through the cylindrical housing drum 21 of the centrifugal clutch 11, a drive gear 18, is attached to the back face of the cylindrical housing drum 21 of the centrifugal clutch. The drive gear 18 drives the primary driven gear 17 of the transmission 10, which is rotatably placed on the output shaft 20 having a slide-able dog clutch 12 on one side and a sprocket 19 on the other side.

A second gear 13 is rotatably positioned between the primary driven gear 17 and the dog clutch 12 that engages with the oil pump drive gear 22 provided on the crank shaft 06 to drive the oil pump for circulation of lubricating oil to the engine parts. The slidable dog clutch 12 has four symmetrically placed dogs 12A, which engage recesses 13A provided on the said second gear 13. A spring is used to keep the said dog clutch 12 in a first position 27 so as to keep the output shaft 20 disengaged form the said second gear 13 at all times. However, the dog clutch 12 can be shifted to second position 28 through a manual actuating member 23, actuable through a manual clutch lever (not shown in figure), to engage the said second gear 13.

The vehicle remains at positive neutral until the centrifugal clutch 11 engages, or the dog clutch 12 is engaged manually through the clutch lever. While pushing the vehicle the output shaft 20 is rotated by the wheel through the said sprocket 19 and the output shaft 20 speeds up to a speed required to motor the engine 02 for starting. Then the dog clutch 12 is engaged manually through the clutch lever and a drive is provided through the oil pump gear 22 to the crankshaft 06, to motor the engine 02 for starting.

As soon as the engine starts the clutch lever is released and the dog clutch 12 goes back to first position disengaging the second gear 13. At idle the centrifugal clutch 11 is disengaged and drive engagement is manually controlled by manually increasing the engine fuel feed or throttle to increase engine speed to a pre-determined speed causing the centrifugal clutch 11 to gradually engage for initial slipping drive at low speeds and lock up drive at higher speeds.

In an embodiment the said second gear 13 can also be rotated by an electric motor through an electric starter to provide simpler electric start mechanism. It should be understood that the foregoing description is that of a preferred embodiment of the invention and that various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.

Claims

1. A single speed internal combustion engine for a two wheeler with a push
start mechanism comprising:

a front and a rear wheel;

a crankshaft having an oil pump drive gear;

a transmission system having a primary driven gear rotatably mounted on

an output shaft;

a centrifugal clutch assembly having an output drive shaft operatively coupled to the said primary driven gear;

said centrifugal clutch assembly having frictional surfaces adapted to be engaged at a predetermined engagement speed of rotation of said crankshaft;

a second gear rotatably mounted on the output shaft operatively engaging the oil pump drive gear, and

a manually engage-able dog clutch means to disengage the said output shaft from the said second gear.

2. The push start mechanism for single speed internal combustion engine as claimed in claim 1, wherein when the two-wheeler is pushed, the output shaft is rotated by the rear wheel through a sprocket and the output shaft speeds up to a speed required to motor the engine for starting followed by engaging the dog clutch manually through the clutch lever and a drive is provided through the oil pump gear to the crankshaft for starting the engine.

3. A motorcycle having the internal combustion engine as claimed in claim l.