FIELD OF INVENTION

The present invention relates to a four-cycle engine and more particularly, to an engine having single speed transmission and a provision for housing a centrifugal clutch in a separate chamber.

BACKGROUND

There are a number of compact vehicles that need to have automatic 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 recent years, regulations of exhaust emissions from internal combustion engine-mounted vehicles are becoming stringent in view of environment protection as a result of which the use of four-stroke engine is increasing. These four stroke engines generally have wet centrifugal clutch that utilizes the engine oil for lubrication and cooling.

However, these clutch during

operation results in contamination of engine oil. Further, the clutch operates in
engine oil that may not be best suited for clutch operation.

The above mentioned problems can be solved by providing an oil filter
provision but it makes system more complicated and expensive for such
vehicles.

Therefore, a principal object of this invention is to provide a separate wet
chamber for housing a centrifugal clutch.

SUMMARY

Accordingly, the present invention provides a centrifugal clutch for a four-cycle engine with single speed transmission. Said centrifugal friction clutches are particularly useful in connection with small displacement internal combustion engines such as are used in type of vehicles mentioned above, where any unnecessary size, weight and cost can be a disadvantage. In a preferred embodiment the present invention utilizes a crankcase that defines a first wet chamber that houses the crank shaft along with the transmission system and a second wet chamber for housing a centrifugal clutch that move into frictional engagement by application of centrifugal force. The two wet chambers in an embodiment may also have oil having different properties as per the requirement.

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 depicts a step through type two-wheeled vehicle using a single stage reduction gear transmission and an embodiment of the invention. Figure. 2 depicts cross-sectional view of an engine used in vehicle shown in figure. 1.

Figure. 3 depicts in detail the layout of the centrifugal clutch as per an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 shows a step-through type two-wheeled vehicle 01 having an engine 02 with centrifugal clutch layout of the present invention. As shown in Figure 2 the illustrated engine 02 is a four-stroke engine comprises 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 known type kick-start provision 09 connected to the crankshaft 06 on the right side and a transmission system 10

on the left, connected to the crankshaft 06 through the said 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 left crankcase member 03B further comprises a partition wall 03C dividing the crankcase into a first wet chamber 12 and a second wet chamber 13. 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 wet chamber 12, in a manner to prevent radial motion of the crankshaft relative to the crankcase 03. Towards the right crankcase member 03A in the first wet chamber 12 a kick start system 09 and a magneto unit 16 is housed operatively connected to the crankshaft 06 whereas, towards the left in the first wet chamber 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 with plates for push start is housed in the second wet chamber 13. 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 21A 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. A plurality of pins are mounted on said circular disc 24 and extends 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 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 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 21

A. This coupling engagement rotates housing together with hub assembly to operatively drive the said transmission system 10.

The cylindrical housing drum 21 is further preferably coaxially aligned with and surrounds a pressure plate 23, placed after the said clutch shoes. The pressure plate is followed by plurality of friction pfates 22 having drive lug openings on the inside diameter for interconnection with the drive hub 25 and finally a fixed plate with drive lugs on the outside diameter for interconnection with the clutch cylindrical housing drum 21 is disposed. The said pressure plate 23 is actuable manually by a clutch lever. The pressure plate 23 when manually actuated moves axially outwards and pushes the friction plates 22 against the fixed plate 27, to engage the frictional surfaces on the friction plates 22 with the fixed plates 22. This causes the fixed plate 27 to rotate, which in turn causes the clutch housing drum 21 to rotate, transferring power to the transmission 10. This enables the push starting of the vehicle by manually engaging the clutch 11. However, once the vehicle is started the manual clutch is released and the centrifugal shoe clutch operates. 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, having an extended stem 29 with a splined end 30 is provided that passes through the partition wall 03C and engages with the corresponding groove 31 provided in an extended boss 31 at the back face of the cylindrical housing drum 21 of the centrifugal clutch, and is thus conjoined with the back face 28

of the cylindrical housing drum 21. The extended stem 29 of the drive gear 18 is coaxially and rotatably supported by the crankshaft 06, that passes through the hollow cross-section of the extended stem 29. Thus, the drive gear 18 is disposed in the first wet chamber 12 and engages with the driven gear 17 of the transmission system disposed inside the first wet chamber 12 and the clutch 11 remains in the second wet chamber 13.

In an embodiment oil of suitable properties is used in the said first 12 and second wet 13 chambers. The said partition wall 03C provides an opening for the extended stem 29 to pass through. The peripheral boundary of the opening also provides radial clearance so that the extended stem 29 rotates freely. A first oil seal 32 is provided to prevent any leakage of oil between the first wet chamber 12 and the second wet chamber 13 through the radial clearance. Further, a second oil seal 33 is provided at the clearance between the crankshaft 06 and the extended stem 29 so as to prevent any leakage of oil between the first wet chamber 12 and the second wet chamber 13 through the said clearance and at the same time there is lubrication between the crankshaft 06 and the extended stem 29.

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.

We Claim:

1. A motorcycle having a frame, a four-cycle engine mounted on the said
frame and at least two operational wheels operatively connected to engine
crankshaft through a transmission system comprises:

a centrifugal clutch coupling transmission system and crankshaft;
a crankcase defining a first wet chamber for housing the said crankshaft and
the transmission system, a second wet chamber for housing the said
centrifugal clutch assembly comprising a partition wall separating the two 'wet
chamber,

said centrifugal clutch assembly having an output member and an input
member wherein, the said output member having an output shaft extending
into the first wet chamber and having a drive gear fixed to the shaft and
disposed in the first wet chamber;

said drive gear providing input to the transmission system;
said input member being connected to and driven by an end of the crankshaft
extending into the second wet chamber;

said partition wall providing at least one pass through passage for said input
and output shaft with a radial clearance to allow free rotation of the shafts;
a sealing means to prevent passage of oil from the second wet chamber to
the first wet chamber through the said radial clearance.

2. The motorcycle as claimed in claim 1, wherein the said transmission being
a gear transmission, having a constant ratio and continuous power flow
through out the entire speed range of the vehicle.

3. The motorcycle as claimed in claim 1, wherein the said centrifugal clutch assembly is a wet shoe type clutch assembly having frictional surfaces adapted to be engaged at a predetermined engagement speed of rotation of said crankshaft.

4. The motorcycle as claimed in claim 1, wherein a means for manually engaging the clutch is provided.

5. The motorcycle as claimed in claim 1, wherein the crankshaft and the output member are coaxial.