This invention relates to a dual centrifuQal clutch system for transmitting power from driver means to driven means in automobiles.
As known in the art, in single speed automcabile transmission applications, a conventional slnqle centri fugal clutch is employed to tranamit the dynamic torque of mechanical rotary power from a drive shaft to a driven shaft through a centri fugal action. In another version of the known art, an arrangement of at least two Bimi1ar centrifugal clutches are constructed so that the first one is used to engage the pedal shaft with the crank Mheel for crank starting the prime mover and the other is used to engage the crank shaft with the final drive of the vehicle for actual transmission purposes in the known way.
In the known art of single conventional centrifugal clutch types, power from the engine is transferred through the drive shaft to a clutch shoe carrier assembly rotating along with the drive shaft. The carrier assembly is angularly secured to the drive shaft using a key or splines or by other known means.

The clutch carrier assembly carries 2 or 3 identical shoes, which are pivoted thereon and on the outer cyl indrical surface of each of which the friction liner is bonded. These shoes are held at normal radial posi tion with a spring or springs. When the engine runs at idling-speed, the shoes are still at normal radial posi tion, and do not engage with the clutch housing. ft clutch housing is operatively connected to the driven shaft by any known way so as to impart motion thereto. When the angular speed of dri ve shaft is increased due to increase in the engine speed, the centrifugal force eMperienced by each clutch shoe will be Increased resulting in the extension of clutch shoes, against spring force to engage with the clutch housing. Once sufficient centri fugal force has been imparted due to sti1l higher angular speed, the shoes fully engage with the clutch housing so that the housing rotates together with the clutch carrier assembly thereby transmJ tting the maximum possible part of engine torque to the housing which in turn dri ves the driven shaft through a gear or chain drive. The speed at which the clutch engages with the housing depends upon the mass of each shoe, or with the position of its mass center

and the spring force or the retaining moment of the spring force. When the speed reduces the clutch disengsages from the housing thereby disconnecting its transmission. The angular speed at which the clutch shoes just touch the clutch housing to just move the vehicle is called the "clutch-in" speed. The angular speed at which the clutch shoes fully engage with the housing to transmit the free torque of the engine or the maximum possible part thereof is called the "clutch-tight" speed. The "clutch-in" and "clutch-tight" speeds depend on the mass of each shoe, or with the position of its mass center and the spring force or the retaining moment of the spring fares. The "clutch-tight" speed is optimized based on the maximum torque characterist ics of the engine, The "clutch-tight" speed is decided based on the engine characteristics and on the "clutch-in" speed. Generally, the "clutch-in" speed is common when the clutch shoes engage during the engine acceleration and when the clutch shoes disengage during the engine retardation.
When the "clutch-tight" speed is increased to match the engine torque characteristics, the "clutch-in" speed will also inevitably increase or vice versa. This

causes the complete disconnection of the wheel from the engine well before reaching down to the engine idl ing speed during engine deceleration. Consequently, the engine braking phenomena will not 1ast particularly at low vehicle speeds. Thus,.both low "clutch-in" and high "clutch-tight" speeds cannot co-exist in the same clutch assembly without causing dlfficulties in vehicle handling.
The dual centrifugal clutch system for transmission of power from driver means to dri ven means, according to this invent!on, comprises a clutch housing and at least one shoe carrier; first and second sets of centri fugal clutches, the first set having at least two equally spaced clutch shoes pivotably mounted and spring-loaded with respect to a shoe carrier rotatably driven by driver means, the spring tension, the moment of the spring, the mass of each brake shoe and the centre of the mass of each brake shoe of the first set being predetermined such that at a first angular speed of the shoe carrier, the shoes of the first set extend outwardly to cause the said shoes to Just engage with the clutch housing and thus transmi t only a

predetermined part of the torque of the driver means to the clutch housing and thence to the dri ven means; the second set having at 1 east tiuo equal ly spaced clutch shoes pivotably mounted and spring-loadad with respect to the eaid shoe carrier, the spring tension, the moment of the spring, the mass of each braka shoe and the centre of the mass of each brake shoe of the second set being predetermined such that at a second angular speed of the shoe carrier, higher than tha f i rst angular speed, the shoes of the second set extend outiuardly to cause the said shoes to ful ly engage with the clutch housing and thus transmit the full torque of the driver means to the clutch housing and thence to the driven means.
This invention wi11 now be described with reference to the accompanying drawings, the single figure which illustrates, by way of example and not by way of limitation, one of various possible embodiments of the dual centrifugal clutch system proposed herein.
Referring to the drawings, in a preferred embodiment of this invention, the shoe carrier 1 of any known type comprises 3 pair of clutch shoe sets. The fi rst clutch

shoe set of the said pair consists oi the clutch shoes 2A, which are pivoted on the shoe-carpier. The coil springs 3A are anchored between the said clutch shoes 2A and the said clutch-carrier 1. In the first clutch shoe set of the said pair, the mass or mass-centre position of each clutch shoe 2A or both is such as to enhance the outiuard extension characteristics of the said shoes 2A Just beyond the engine idling speed. Further more, the static and dynamic characteristics of each coi1 spring 3A or the moment arm of spring-retaining force or all may also facilitate achi evement of this very low "clutch-in" speed. Similar partm are indicated by 2B and 3B respectively for clutch shoes and coi1 springs of the other clutch shoe set of the said pair and similar conditions apply to increase the "clutch-tight" speed without affecting the low "clutch-in" speed. The angul an positions of theise shoes are equally spaced in such a way that the resultant tangential frictional force generated between the »hoe» and clutch housing .are balanced independently in each clutch shoe set (2A and 3A) and 2B and 3B>.

it is possible, as an alternative, to have two shoe carriers for carrying the f i rst and second set of centrifugal clutches respectively.
The terms and expressions herein are of description and not of limitation, there being no intention to exclude an equivalents of the features illustrated and described, but it is understood that various other embodiments of the dual centrifugal clutch system proposed herein are po&sible without departing from the scope and ambi t of this invention.

We Claim;
1 . A dual centrifugal clutch system -for transmission of power from driver means to driven means, comprising a clutch housing and atleast one shoe carrier first and second sets of centrifugal clutches, the first set having at least two equally spaced clutch shoes pivotably mounted and spring-loaded with raspect to the shoe carri er rot atably dri ven by driver means, the spring tension, the moment of the spring, the mass of each brake shoe and the centre of the mass of each brake shoe of the first set being predetermined such that at a first angular speed of the shoe carrier, the shoes of the first set entend outwardly to cause the said shoes to just engage with the clutch housing and thus transmit only s predetermined part of the torque of the driver means to the clutch housing and thence to the driven means; the second set having at least two equally spaced clutch shoes pivotably mounted and spring-loaded with respect to the said shoe carrier, the spring tension, the moment of the spring, the mass of each brake shoe and the centre of the mass of each brake shoe of the second set being predetermined such that at a second angular speed of the shoe carrier.

higher than the first angular speed, the ahoes of the second set extend outwardly to cause the said shoes to fully engage with the clutch housing and thus transmit the full torque of the driver means to the clutch housing and thence to the driven means.
2. A dual centrifugal clutch system as claimed in Claim
1 wherein two shoe carriers are provided for the first
and second sets of centri fugal clutches respectively.
3. A dual centrifugal clutch system for transmiswlon
of power from driver means to driven means
substantially as herein described with th reference to and
as i1lustrated in the accompanying drawings.
Dated 30th July 2002