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 centrifugal clutch.

Description of the prior art

There are a number of compact vehicles that need to 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. Along with a kick-start mechanism these vehicles at times, needs push start capabilities to meet the increased utility requirements. To provide push start capabilities to such vehicles a complex multi-clutch arrangement is provided. This clutch arrangement motors the engine for starting, by pushing the vehicle.

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 a kick starter is provided and for push starting the vehicle a normally engaged dog clutch is provided that remains engaged even while the engine is idling. At idle the speed 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 starting speed causing the speed responsive clutch to gradually engage for initial slipping drive at low speeds and lock up drive at higher speeds.

The dog clutch is manually disengaged to provide positive neutral while pushing the vehicle to bring the vehicle speed up to the speed required for motoring the engine for starting. Then the dog clutch is engaged and a drive provided through a one-way clutch to the input to motor the engine for starting the engine.

When the engine starts and the engine and input speed is greater than the output speed, the one-way clutch is disengaged, so the normal vehicle starting drive may be used. During normal vehicle starting and drive, the one way clutch remains disengaged, since it overruns during slipping engagement and is not engaged during lock up drive. During overrun drive, when the vehicle motors the engine, the centrifugal clutch remains locked up to low speeds substantially to idle speed because the torque is very low. 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 illustrate a cross-sectional view of an engine used in vehicle shown in figure. 1.

Figure 3 illustrate a cross-sectional view illustrating in detail the location of one way clutch as per an embodiment of the invention.

Figure 4 illustrate a cross-sectional view illustrating the dog clutch in engaged position.

Figure 5 illustrate a cross-sectional view illustrating the dog clutch in disengaged position.

Detailed description of the preferred embodiment

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 04 that is connected to the front end of the crankcase 03. In one configuration, the cylinder 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 has a kick-start provision 09 on the right side and a transmission system 10 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 crankcase, in a manner to prevent radial motion of the crankshaft relative to the crankcase 03. On the right side of the crankcase a kick start system 09 and a 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.

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.

Three arcuate-shaped clutch shoes 26 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 on 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 shoe 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 shoe 26 in disengaged position until crankshaft 06 reaches the predetermined engagement speed. Upon reaching this engagement speed, clutch shoe 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, mounted in a slot 09 and a sprocket 19 on the other side.

The slidable dog clutch 12 has four symmetrically placed dogs 13, which engage recesses 24 provided on the primary driven gear 17. A spring is used to keep the said dog clutch 12 in a first position 27 so as to keep the output shaft 20 engaged to said primary driven gear 17 at all times. However, the dog clutch 12 can be shifted to second position 28 through a manual actuating member 22, actuable through a manual clutch lever.

A one-way clutch 23 is mounted on the outer periphery of the crankshaft 06 with its inner race secured to or integral with the crankshaft 06 and its outer race fixed to the disk portion of the inner centrifugal clutch drum 21. A one¬way drive between said races to rotatably support said outer race concentrically on said inner race and to provide engagement for drive when said outer race overruns said inner race in the normal drive direction and disengagement when said inner race overruns said outer race in the normal drive direction.

The dog clutch 12 is manually disengaged to provide positive neutral 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 for motoring the engine 02 for starting the engine. Then the dog clutch 12 is engaged by releasing the cutch lever and a drive is provided through the one way clutch 23 to the crankshaft 06 to motor the engine for starting the engine. When the engine 02 starts and the engine and input speed is greater than the output speed, the one-way clutch 23 is disengaged, so the normal vehicle starting drive may be used. During normal vehicle starting and drive, the one way clutch remains disengaged, since it overruns during slipping engagement and is not engaged during lock up drive. During overrun drive, when the vehicle motors the engine, the centrifugal clutch remains locked up to low speeds substantially to idle speed because the torque is very low.

The said centrifugal clutch 11 can be a wet or a dry centrifugal clutch based on the crankcase design as an example a partition wall 29 is provided that enables the centrifugal clutch to be housed in the partitioned area which can be kept dry or wet or if, the wall is removed a wet clutch can be used. The above explained preferred embodiments are exemplary of the invention of the present application, which is described solely by the claims appended below. It should be understood that modifications of the preferred embodiments might be made as would occur to one of skill in the art.

Claims: We claim

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

a crankshaft;

a transmission system having a primary driven gear rotatably mounted on an output shaft;

a centrifugal clutch 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 one-way clutch having an inner race connected to said crankshaft, an outer race connected to said output drive shaft of the centrifugal clutch, and one-way drive means between said races to rotatably support said outer race concentrically on said inner race and to provide engagement for drive when said outer race overruns said inner race in the normal drive direction and disengagement when said inner race overruns said outer race in the normal drive direction; and

a manually dis-engageble dog clutch means to disengage the said output shaft from the said primary driven gear.

2. The push start mechanism for single speed internal combustion engine as claimed in claim 1, wherein when the dog clutch is manually disengaged to provide positive neutral while pushing the vehicle the output shaft is rotated by rear wheel through a sprocket and the output shaft speeds up to a speed required for motoring the engine followed by releasing the cutch lever and the drive is provided through the one way clutch to the crankshaft to motor the engine for starting the engine.

3. A motorcycle having the internal combustion engine as claimed in claim 1.