DESC:FIELD OF INVENTION
This invention relates to a multimode centrifugal clutch. More particularly, the invention relates to an improved multimode centrifugal clutch for motor vehicles. It may be used in two wheelers like a two wheeler scooter but not limited to the same.

BACKGROUND OF THE INVENTION
Two wheeler scooters and motorcycles are conventionally powered by gasoline engine equipped with a manual, sequential speed change gear box transmission to extend the driving speed range of the vehicle. A clutch is an essential part of the power transmission and without clutch it will be almost impossible to drive the vehicle. The clutch is placed upstream of the gear box. The clutch allows full or partial disconnection of the engine with the gearbox and the vehicle’s driving wheel which is necessary at very low vehicle speeds to prevent engine shutdown.
During the course of driving, depending on the vehicle speed, the rider needs to shift to an appropriate gear to maintain the engine Revolutions per minute (RPM) within its operating range and to derive good performance in terms of fuel economy and drivability. Declutching, i.e. disengaging the drive between the engine and gearbox by actuating the clutch is necessary required during the gear shifting and also to avoid jerk and possible internal damage.
Geared two wheelers commonly uses conventional axial engagement friction disc clutches. These clutches require certain force for de clutching causing rider fatigue.
With no requirement of declutching and gear shifting, two wheelers with Continuously Variable Transmission (CVT), offer an alternate solution to the problem of driving fatigue due to frequent actuation of clutch & gear shifting. However, CVTs employ an arrangement including belt drive, which is prone to slippage and also has significantly lower power transmission efficiency as compared to gear drives. The fuel economy of CVT two wheeler is inferior to the conventional geared two wheeler.
With rapid developments in the recent years - expansion of cities, improved road infrastructure and connectivity of rural areas– the overall commuting levels have increased exponentially. Two wheelers with their unique and distinct advantages continue to be the most preferred and popular means of personal transport. In the emerging scenario, it is imperative that the issues such as of driving fatigue deserve better solution without sacrificing the excellent drivability and fuel economy offered by geared transmission. The present invention provides the better solution to the available problem.
The technology of centrifugal clutch is a well-established in the art. A typical centrifugal clutch is normally in a state of disengagement, automatically engages beyond a threshold rotational speed by virtue of centrifugal action. As a general rule, the torque transmission capacity of the centrifugal clutches increases with the rotational speed. These characteristics make them a suitable choice for variety of applications. However, for their adoption in two wheelers with geared transmission, the following specific issues need to be addressed -
- with geared transmission declutching is necessary during gear shifting;
- kick for manual cranking of the engine is a standard essential feature of two wheelers. In almost all kick mechanisms, clutch is an intermediate connecting link between the kick shaft and the crank. With conventional centrifugal clutch, this drive from kick to crank will need to be re-established.
US Patent 4106605 dated August 15, 1978 describes a centrifugal clutch arrangement for vehicular engine. It particularly describes a multiclutch drive having an input connected in series by a centrifugally engaged clutch, an intermediate drive and a spring engaged manually disengaged friction clutch to drive the output and a one way clutch between the intermediate drive and input which is engaged when the intermediate drive speed exceeds the input speed. Further, it discloses that manual disengagement of the friction clutch provides positive neutral. However, it does not suggest the use of multimode centrifugal clutch in such a way that the clutch engages automatically when the engine rotational speed increases above a predetermined set value.
Together, the abovementioned document and other available prior art describe the state of art. The current art needs an improved multimode centrifugal clutch for two wheelers that overcomes the disadvantages of the prior art. The present invention provides such an arrangement.
The present invention proposes to achieve the function of the multimode centrifugal clutch for two wheelers automatically when the engine rotational speed increases above a predetermined set value. Further, the present invention also proposes to manually disengagement of the multimode centrifugal clutch during gear shifting and, in the disengaged state when the engine is not running, allows reverse power flow to facilitate kick starting of the engine.
Thus, the present invention provides an improved solution for addressing the key issues as explained above. Therefore, the present invention provides a simple, cost effective and compact multimode centrifugal clutch of two wheelers.

OBJECT OF THE INVENTION
A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.

Another objective of the present invention is to provide a simple, cost effective and compact multimode centrifugal clutch of two wheelers.
Another objective of the present invention is to significantly reduce the driver’s fatigue caused by effort in frequent de-clutching while retaining the performance and fuel economy of a two wheeler equipped with gearbox transmission.
Another objective of the present invention is to prepare a compact system which can be accommodated in the two wheeler engine with minimal changes in the interfacing parts and mechanisms such as the drive train and clutch actuation linkages.
Another objective of the present invention is to provide a compact system which can be fitted in limited space available in a two wheeler.
Another objective of the present invention is to use improved multimode centrifugal clutch in such a way that the clutch engages automatically when the engine rotational speed increases above a predetermined set value.
These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION
There is provided a multimode centrifugal clutch for two wheeler engines with gearbox transmission. It may be used in two wheelers like a two wheeler scooter but not limited to the same.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

The improved economical multimode centrifugal clutch, according to this invention, is used in such a way that the clutch engages automatically when the engine rotational speed increases above a predetermined set value.
According to one aspect of the invention, there is provided a multimode centrifugal clutch for two wheelers comprising a rotor, a clutch casing to which the rotor is rotationally coupled, stepped pins, compression springs, a plurality of friction drive plates being placed in the clutch casing, a pressure plate, a primary drive pinion assembled on the rotor, a slider, a plurality of friction driven plates assembled on the slider and a plurality of rollers which are positioned in specially profiled cavities in the rotor. Further, the improved compact multimode centrifugal clutch is used in such a way that it engages automatically when the engine rotational speed increases above a predetermined set value and engages automatically when the power flows in the reverse direction i.e. from gearbox/wheel to the crank shaft, to facilitate kick starting the engine.
According to another aspect of the invention, the improved compact multimode centrifugal clutch, according to this invention, can be manually disengaged during gear shifting and, in the disengaged state when the engine is not running allows reverse power flow to facilitate kick starting of the engine.
According to another aspect of the invention, the improved economical multimode centrifugal clutch can also be used manually and for manual disengagement, the clutch casing is axially displaced from its position in which the clutch has maximum torque capacity. Further, this movement is achieved by manual actuation of the clutch lever at the handle bar by the rider, which, through a linkage moves the pressure plate and the clutch casing.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. Reference will now be made to the accompanying diagrams which illustrate, by way of an example, and not by way of limitation, of one possible embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS
The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.
Figures 1 illustrate the design of the multimode centrifugal clutch assembly mounted on the engine crank shaft.
Figure 2 is a sectioned view of the multimode centrifugal clutch assembly showing its internal construction.
Figure 3 & 4 illustrate the coupling arrangement of the drive and driven plates of the clutch with their respective mating parts.
Figure 5A and 5B illustrate the guided path of roller and defines its extreme positions.
Figure 6A and 6B illustrate the multimode centrifugal clutch in free and engaged conditions.
Figure 7A explains the forces which develop interfacial pressure between the friction plates.
Figure 7B shows the forces acting on the roller.
Figure 8A illustrate the multimode centrifugal clutch in condition of maximum torque capacity.
Figure 8B illustrate the multimode centrifugal clutch in manual de-clutching mode.
Figure 9 is a perspective view of the square thread coupling explaining the axial trust exerted by the mating parts of roller.
Figure 10 illustrate the multimode centrifugal clutch in automatic engagement during kick starting of the engine.
Person skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure.
Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
The present invention relates to an improved compact multimode centrifugal clutch for two wheelers is used in such a way that it engages automatically when the engine rotational speed increases above a predetermined set value and engages automatically when the power flows in the reverse direction i.e. from gearbox/wheel to the crank shaft, to facilitate kick starting the engine. Further, the improved economical multimode centrifugal clutch, can be manually disengaged during gear shifting in the disengaged state when the engine is not running, allows reverse power flow to facilitate kick starting of the engine. Such a multimode centrifugal clutch (20) is shown in Figure 1. Figure 1 shows the typical multimode centrifugal clutch (20) being considered for the invention, explaining the arrangement for engaging each of the multimode centrifugal clutch (20) – one at a time.
Figure 2 explains the internal construction of the multimode centrifugal clutch assembly (20), explaining the arrangement for engagement of multimode centrifugal clutch (20). Rotor (1) is rotationally and axially coupled with crank shaft (12) of the engine. On the other side, the rotor (1) is rotationally coupled to clutch casing (2) by virtue of engagement of its radial lugs with axial slots of the clutch casing (2). Stepped pins (3) and compression springs (4) are placed at a normal axial position and allow a restricted movement of the clutch casing (2) with respect to the rotor (1).
A set of friction drive plates (5) are placed in the clutch casing (2). These friction drive plates (5) also have radial projecting lugs similar to the rotor (1). These friction drive plates (5) are also engaged in the axial slots of clutch casing (2) and rotationally coupled with it. Internal circlip (6) prevents the friction drive plates (5) from coming out of the clutch casing (2). Thus, the rotor (1), clutch casing (2) and friction drive plates (5) rotate together with the crank shaft (13) and constitute the driving half of the clutch.
Further, the primary drive pinion (8) is assembled on the rotor (1) such that it is axially restrained but is free to rotate on its axis, which coincides with the crank axis. The primary drive pinion (8) meshes with the mating gear on the gearbox drive shaft which transmits the crank power to the gearbox. External square helical threads (13) on the other side of the primary drive pinion (8), engage with mating internal threads of the slider (9). The axial float of the slider (9) on the primary drive pinion (8) is restricted by a step on one side and a circlip (6) on the other.
A set of friction driven plates (10) are assembled on the slider (9). Further, each plate is sandwiched between adjoining friction drive plates (5) and is concentric with the crank axis. The primary drive pinion (8), slider (9) and friction driven plates (10) rotate together and constitute the driven half of the clutch. Rollers (11) are positioned in specially profiled cavities made in the rotor (1).
As shown in Figure 3, the arrangement that the rotor (1) is rotationally coupled to the clutch casing (2) by virtue of engagement of its radial lugs with the axial slots of the clutch casing (2). Further, the arrangement of the teeth which are provided in bore of the friction drive plates (10) which mesh with external teeth (splines) of the slider is detailed in Figure 4.
As shown in Figures 5A and 5B, the roller (11) shown is positioned in specially profiled cavities made in Rotor (1). Figure 5A shows the roller (11) in position “A” and Figure 5B shows the roller (11) in position “B”. Further, supported on one side by the friction drive plate (5), the rollers (11) have a limited radial movement between extreme lower position “A” and extreme upper position “B”. Multiple Rollers are deployed and spaced uniformly in the circumferential direction. As the crank shaft (12) and the rotor (1) start rotating, the centrifugal force on these rollers (11) causes engagement of the drive and driven half of the multimode centrifugal clutch (20).

Different functioning modes of the multimode centrifugal clutch (20) of the present invention are as follows:
FREE DISENGAGED MODE
In Figure 6, free disengaged mode of the multimode centrifugal clutch (20) is shown. The dimensions of various parts are so controlled that in the assembled condition with the rollers (11) at position “A”, the available space “X” is more than the width of the stack of the friction drive and driven plates (5). As a result, there is no interfacial pressure between the plates and the clutch is in no position to transmit any power.

NORMAL ENGAGEMENT MODE
Figure 7A shows the normal engagement mode of multimode centrifugal clutch (20) is shown. As the crank shaft (12) starts rotating, the rollers (11) experience an outward acting centrifugal force and move in that direction. However, the profile of the guiding surface of the cavity in the rotor (1) makes it move axially as well, thereby, causing a reduction in dimension “X” till the gaps between friction drive and driven plates (5) are eliminated. Herein after, further outward, and the corresponding axial, movement of the rollers (11) requires axial displacement of the clutch casing (2). In this condition, the force of compression springs (4) gets transferred on and leads to interfacial pressure between, the friction drive plates (5). The multimode centrifugal clutch (20) thus gets engaged and starts transmitting power. The equilibrium position depends on the rotational speed of the crank shaft (12) and the force exerted by the compression springs (4).
Referring to Figure 7A, a reaction force from the roller (11) to the friction driven plates (5) and force due to the compression springs (4) to the roller (11) is shown. Thus, Figure 7A shows free body diagram of the roller (11) defining the relationship between the radial centrifugal force acting on the roller (11), the axial pressure between the drive and driven friction plates (5), and the force of the Compression Springs (5).
Figure 7B shows graph for forces acting on the roller (11). The forces acting on the roller (11) includes R1-Reaction from pack of the friction drive plates (5), R2-Centrifugal force and R3-Reaction from the rotor (1).

MANUAL DECLUTCHING MODE
As the crank shaft revs up, the Rollers move further outward till they reach position “B” as shown in Figure 5B. In this position, the pressure between the Friction Plates (5) is at its maximum and so is the torque transmission capacity of the multimode centrifugal clutch (20). It may be noted that in this condition, any further axial displacement of the clutch casing (2) will relieve the interfacial pressure between the drive and driven plates (5) resulting in disengagement of the multimode centrifugal clutch (20). This movement is achieved by manual actuation of the clutch lever at the handle bar by the rider, which, through a linkage moves the pressure plate (7) and the clutch casing (2). The conditions of maximum torque capacity and manual de-clutching are shown in Figure 8A and 8B.
Figure 8A and 8B shows external square helical threads (13) on the other side of the primary drive pinion (8) which is engaged with mating internal threads of the slider (9). In addition, the axial float of the slider (9) on the primary drive pinion (8) is restricted by a step on one side and a circlip on the other.

AUTOMATIC REVERSE POWER ENGAGEMENT MODE (FOR KICK START)
The slider (9) and the primary drive pinion (8) are coupled through a helical square thread (13). Further, two mating parts exert equal and opposite force on each other and that this force acts along the common normal to their contacting surfaces. The contacting faces of helical thread (13) are at an angle to the axis of rotation, both parts experience an axial thrust as well while transmitting torque.
Figure 9 shows different forces acting on the helical thread of primary drive pinion (8) of the multimode centrifugal clutch (20). The different forces are Fa-Axial trust, Ft- Normal force between male and female threads and Fr- Component responsible for torque transmission.
Accordingly, as shown in Figure 10, during reverse flow of power, as during kick or push start, the slider (9) experiences an axial force in direction “Y” and since it is free to move, starts shifting till the clearance between its collar and the pack of friction drive and driven plates (5) is eliminated. The axial force then gets transmitted to and develops interfacial pressure between the friction drive and driven plates (5) enabling the multimode centrifugal clutch (20) to transmit the torque to the crank shaft (12).
The figures and the description above provide details of one particular design which is also specific to the design and configuration of the base engine being considered. It would be obvious to those skilled in the art that, based on the concepts, ideas and issues described herein, several variations of the proposed design for the design and configuration of the base engine considered, as well as, for engines with distinctly different design and configuration, will be possible without deviating from the scope of this invention.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the invention. It is also to be understood that the description is intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

We Claim:
1. A compact multi mode centrifugal clutch for two wheelers with gear box transmission comprising:
rotor (1) configured for rotational and axial coupling to crank shaft (12) and rotational coupling to clutch casing (2) by virtue of engagement of its radial lugs with axial slots of the clutch casing (2);
stepped pins (3) and compression springs (4) which are placed at a normal axial position and allows a restricted movement of the clutch casing (2) with respect to the rotor (1);
plurality of friction drive plates (5) which are placed in the clutch casing (2) having radial projecting lugs similar to rotor (1), are also engaged in the axial slots of clutch casing (2) and rotationally coupled with the rotor (1);
internal circlip (6) which prevents the friction drive plates (5) from coming out of the clutch casing (2);
primary drive pinion (8) is assembled on the rotor (1) such that it is axially restrained but is free to rotate on its axis, which coincides with the crank axis and meshes with mating gear on the gearbox drive shaft which transmits crank power to the gearbox;
slider (9) coupled to the primary drive pinion (8) and having limited axial movement on it.
plurality of friction driven plates (10) are assembled on the slider (9) and is concentric with the crank axis so that the primary drive pinion (8), slider (9) and the friction driven plates (10) rotates together; and
rollers (11) are positioned in specially profiled cavities made in the rotor (1) and have limited radial movement between two extreme positions.
2. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 1 wherein primary drive pinion (8) and slider (9) are coupled through a helical square thread.
3. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 2 wherein the external square helical threads on the primary drive pinion (8) are engaged with mating internal threads of the slider (9).
4. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 1 wherein arrangement of teeth present in bore of the friction driven plates (10) is that they meshes with external teeth (splines) of the slider (9).
5. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 1 wherein when the crank shaft (12) and the rotor (1) starts rotating then the centrifugal force on the roller (11) will cause engagement of the drive.
6. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 1 wherein the reverse power flow is achieved by providing a square tread coupling joint of appropriate helix angle in the torque transmission path which generates necessary and adequate axial pressure between the friction surfaces and in turn develops torque transmission capacity of the clutch.
7. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 1 wherein the clutch engages automatically when the engine rotational speed increases above a predetermined set value.
8. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 1 wherein the clutch engages automatically when the power flows in the reverse direction i.e. from gearbox /wheel to the crank shaft to facilitate kick starting of the engine.
9. The compact multi mode centrifugal clutch for two wheelers with gear box transmission as claimed in claim 1 wherein for manual disengagement, the clutch casing (2) is axially displaced from its position to a position of maximum torque capacity.