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CONTINUOUS GEAR RATIO VARIATOR FOR MOTOR VEHICLES, MACHINE TOOLS AND OTHER APPLICATIONS
A car engine generates a force which cannot be transferred directly to wheels.
To run, for instance, the rest of the mechanical parts must be isolated
by the clutch and, during running, this needs a device which adapts the
rotation speed to the one necessary to the wheels to face the infinite
needs of the road. This device is the gearbox which can be regarded, to
all the extents, as a torque multiplier and a speed reducer.
The
traditional hand-operated mechanical gearbox receiving the motion from
the engine through the clutch and reducing, together with the
differential unit, a high number of revolutions to lower values,
schematically comprises a number of toothed gears with different
diameter suitably engaged one with the other through the selection by a
special lever with respect to the actual driving needs.
Differently
from the mechanical type, the automatic gearboxes allow to change the
speed without compelling the driver to depress the clutch pedal and to
shift the gearbox lever as they have no clutch and are equipped with a
hydraulic torque converter used as wheel and clutch. The most suitable
ratio to the use conditions of the car is automatically selected by an
electronic power unit which decides the most suitable speed to engage
by dialoguing step by step with the engine power unit and produces as a
result a greater comfort and a lower consumption.
There
is also an automatic gearbox with continuous variation of the
transmission ratio which enables to pass from a high gear to a low gear
through an infinite range of intermediate ratios and which consists of
two V-shaped pulleys and a V-belt of steel or aluminium which slides
from the narrowest diameter to the widest end of each pulley and
changes the transmission ratio in a continuous way and without jerks.
The weak point of the CTV is represented by the fact that such gradual
ratio variation causes an unpleasant noise of the engine similar to the
one of a slipping clutch without a real change of speed. Sometimes ago,
there were also CTV suitable for the modest torque of small power
displacements due to problems encountered while transferring high
torques using the transmission with belts and pulleys. These problems
could be partially be solved if larger metal belts or special chains
were used or if engines were set up in such a way not to privilege
power supply at a high rpm since this compels the CTV to pass to lower
ratios as soon as the driver fully depressed the gas pedal causing the
noise mentioned above.
Since
the aforesaid problems are connected to the intrinsic nature of the CTV
using belts and pulleys, the design of the proposed continuous torque
variator is much more than convincing since, differently from the known
technique, it envisages the transmission of the movement through a
couple of elements, both convex or one convex and the other concave,
preferably coated with suitable composite materials (ceramics or
equivalent) which move simultaneously along the respective incident
rotation axes to always remain engaged. To
better describe such continuous torque variator we show two drawings
concerning as many realisation forms which show, as a mere example:
- � FIG.
1 - the sectional view of one version of the aforesaid variatior where
both driving and driven elements have convex coupling surfaces, the
former hemispherical and the latter spherical, and where a single
output for the driven shaft is foreseen;
- � FIG.
2 - the sectional view of a version of the aforesaid variator where the
coupling surface of the driving element is concave and the one of the
driven element is convex and which, among other things, envisages the
presence of two aligned and opposed outputs.
- The
drawings make it clear that in both forms of realisation shown, the
movement is transmitted by the driving shaft to the driven shaft
through a couple of elements with a curve coupling surface so as to
obtain a variation of the transmission ratio as smooth and as wide as
possible. Such elements remain always engaged since they move
simultaneously along their respective incident axes of rotation varying
at any instant the radii of the contact circumferences and, as a
result, the transmission ratio which can assume an almost infinite
range off values. Due to the simultaneous translation of two parts,
when the contact point of one of them reaches and passes beyond the
point lying along the rotation axis and having an almost nil speed, the
driven element starts rotating in the direction opposite to the
previous one as it occurs in traditional gearboxes when the reverse
speed is engaged.
In
the realisation form shown in FIG. 1, the driving element 1, rotating
and moving along the Y axis, shows an almost hemispherical conformation
in the end to couple to the almost spherical end of the driven element
2, having a roto-translational movement along the X axis. Such
element 1 forms a single body with the hollow shaft 3 which, through a
splined coupling, receives the rotational motion by the driving shaft 4
on which it can slide lengthways moved by a hydraulic or oil-dynamic
actuator with electronic control and connected to it by bracket 5. Such
bracket is fixed to the hollow shaft 3 by two thrust bearings 6 and two
roller cages 7, positioned to the two sides of the bracket to isolate
it from the rotation imparted to the hollow shaft 3 by the driving
shaft 4.
Similarly,
the driven element 2 forms a single body with the hollow shaft 8 which,
through a splined coupling, transmits the rotational movement to the
driven shaft 9 on which it slides lengthways moved by a special
actuator and by means of the bracket 5. Such bracket is fixed to the
hollow shaft 8 by two thrust bearings 6 and two roller cages 7,
positioned to the two sides of the bracket to isolate it from the
rotation imparted to the hollow shaft 8.
The
realisation form of FIG. 2, specially recommended in case of integral
traction, foresees that the driven shaft 16 protrudes out of the
gearbox with two aligned and opposite outputs. The main difference
between the two realisation forms consists in the concave coupling
surface of the driving element 10 having a maximum truncate conical
conformation widening to the ends. Such element, having a
roto-translational motion along the Y axis, remains always engaged with
the driven element 11, having an almost spherical and roto-translating
shape along the X axis, solidly fixed to the hollow shaft 12 which,
through a splined coupling, receives the rotationaal motion from the
driving shaft 13 on which it can slide lengthways moved by actuator 14,
of hydraulic or oil-dynamic type and with electronic control, through
the bracket 5, rigidly connected to 12 by the thrust bearings 6 and by
the two roller cages 7, located to the two sides of the bracket to
isolate it from the rotation imparted to the hollow shaft 12 by the
driving shaft 13.
Similarly,
element 11 is solidly fixed to the hollow shaft 15 which, through a
splined coupling, transmits the rotational motion to the driven shaft
16 which can be connected to the two axle shafts of a transmission
thanks to its double output from the gearbox. The hollow shaft 15
slides lengthways on 16 moved by actuator 14 through the bracket 5,
rigidly fixed to 15 by the thrust bearings 6 and the two roller cages
7, positioned to the two sides of the bracket to isolate it from the
rotation of the hollow shaft 15.
In
the chambers 19 and 20 of FIG.1 where the shafts present are in a oil
bath, despite the combined movements of rotation and linear translation
of the hollow shafts 3 and 8, each one off them supported by a bearing
25 with internal helical slot, special gaskets 24 of a known type
prevent oil from passing from such chambers 19 and 20 to chamber 17
where the transmission gears 1 and 2 with dry-friction clutch are
positioned. Similarly, also in chambers 21, 22 and 23 of FIG. 2, where
the shafts are in a oil bath and supported each of them by a bearing 25
with internal helical slot, suitable gaskets 24 of a known type prevent
oil from passing from chambers 21, 22 and 23 to chamber 18 where the
friction transmission elements 10 and 11 are located.
Possible
variations to the represented and described versions could consist in
the replacement of the hydraulic or oil-dynamic actuators with
electromechanical devices or equivalent, suitable for the necessary
linear translations.
The
analysis of both realisation forms examined makes it clear that the
engine brake which can be obtained with the use of such motion
transmission elements is more rapid than the one which can be obtained
with the present CTV gearboxes thanks to the velocity and smoothness
with which such elements slide one onto the other.
Another
characteristic of this variator deserving a mention is the possibility
to be used as a replacement of the clutch since the simple linear
transmission of pull-apart of one of the two transmission organs from
the other allows to stop a vehicle or the spindle of a machine tool
while keeping the motor run.
Also
the proposed invention is especially useful in electrical vehicles
since their autonomy, usually quite limited, would be improved by an
almost constant rpm despite the speed variation.
Since
the principle on which the motion transmission in the continuous
variator is based is friction, the transmission elements should be
coated with special ceramic films which guarantee the necessary
friction. The recent evolution of the production of ceramic coatings
brought important modifications to the process technologies enabling to
lay ceramic films with very high mechanical and physical
characteristics. Also, the involvement of techno-ceramic sector in the
development of coatings more suitable for the invented continuous
variator can lead to a cost reduction of the production of the variator
itself which, due to low number of pieces of which it consists and
their simplicity, is certainly more economic than the traditional
automatic gearbox, CTV or equivalent.
Finally,
notwithstanding the general characteristics of the illustrated and
described versions, modifications or variations to the same, in any
case included in the patent field, cannot be excluded a priori.
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