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CONSIDERATIONS ON DYNAMICS
The AGOSTINI variable speed drive is substantially differnt from the other
mechanical variable speed products, because one of its features is that the
pressure exerting between friction surfaces, is not constant,
but increases as the value of the torque transmitted
increases. In fact, the radial thrust acting between the bevel wheels and the ring adjusts
itself, instant by instant,according the dragging force T as it just depends on the
latter.
This feature is made possible by the gearing system formed by the ring which has no
stationary axis and is therefore free take different positions according to
load conditions.
ON diagram on figure above are indicated the pitch circumferences of the bevel
wheels and of the ring. In resting condition friction points Ho and
Ko of the ring with the wheels are diametrically apposed in respect to the
center of ring Co.
However when a couple M is applied to the driving shaft,there is generated
in Ho the tangential force T which causes the to roll around the
driven d wheel, shifting its center to C off the straight line joining the centers O
and O' (fig. above point b). Points H and K will therefore be at the ends of a chord and dragging forces
T thereon applied, will result inclined each in respect of the other by angle
2ß.
Yet in points H and K are develop forces N which have radial directions and
which,compounded with the respective tangential forces,give rise to the
resultant forces V placed on straight line HK.
The balance equantions give:
V=T/sinB
(1)
V=T/tgB
(2)
Forces V act on the ring straining it in an elastic manner so as to allow
take the position shown on figure above, while components N, related to T by
equation (2) are those guaranteeing driving by friction.
It is to be noted that being angle ß
not constant when T is changing, but increases with it,force N is not tied to T by a linear
equation, but by a trascendental function.
The advantages of this principle are clear: in variable speed drives made by
other manufacturers it is necessary to exert a constant thrust between the
surfaces, of an amount such as to supply a sufficient fiction,
even against maximum load conditions,what has very detrimental affects as regards
efficiency and wear and tear; on the contrary in AGOSTINI drives pressure develops
only under load and increases with it.
(Extracted from a study on the AGOSTINI variable speed drive by P.LEONARDO
of the faculty of Engineering of Genoa University).
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