2. Continuously variable transmission
➢ A continuously variable transmission is a type of
transmission that doesn't have fixed gears.
➢ Allows an engine to operate at or near its optimal
speed, with a varying gear ratio that can be adjusted
in real time for maximum efficiency.
➢ Have been used in aircraft electrical power generating
systems since the 1950s
➢ Banned from Formula 1 in 1994
3. Types of Continuously variable transmission
Hydrostatic CVT: Fig 1.2a, 1.2b and 1.2c show the structure and working of
a hydrostatic CVT. The Hydrostatic CVT works on nearly the same design as
the NuVinci except the balls that would allow the gearing ratio to change have
been replaced by rods pin joined with the swash plate. Mechanical movement
changes hydrostatic pressure and that pressure further makes mechanical
changes which in turn changes the gearing ratio between the driver and driven
shaft.
Fig 1.2a shows the swash plate of a hydrostatic CVT. This figure shows how
the hydrostatic pressure tilts the swash plate changing it gearing ratio.
Fig 1.2b shows the swash plate of a hydrostatic CVT. This figure shows how
the swash plate keeps the same gearing ratio by introducing zero tilt in the
swash plates.
Fig 1.2c shows the swash plate of a hydrostatic CVT. Once again showing
opposite tilt to fig 1.2a which in turn will cause opposite change in gearing ratio.
4. Types of Continuously variable transmission
Toroidal or roller-based CVT (Extroid CVT): Figure 1.3a, 1.3b and 1.3c show the structure and working of the Torodial
CVT. It is a known that when a moving away from the center of a rotating radial disc the r.p.m decreases as the radius of
rotation increases. Using that same fact the Torodial CVT changes the gear ration between the driver and the driven shaft.
Fig 1.3a: Torodial CVT rotating with an equal gearing ratio.
Fig 1.3b: Torodial CVT rotating with changing gearing ratio as speed of the driver shaft increases.
Fig 1.3c: Torodial CVT rotating with changing gearing ratio as the speed of the driver shaft decreases.
5. Types of Continuously variable transmission
Cone CVT: Fig 1.4a, Fig 1.4b and Fig 1.4c explains the structure and working or a Cone CVT. This particular CVT works with a belt sliding over
a two elongated cones set up in parallel formation such that the largest diameter of one cone is aligned against the lowest diameter of the
second and vice versa.
Fig 1.4a: Cone CVT showing the initial position of the belt as it grips the driver shaft (lower) and the driven shaft (upper).
Fig 1.4b: Cone CVT showing the intermediate position as the belt moves to the right with increase in r.p.m on the driver shaft.
Fig 1.4c: Cone CVT showing the final position of the belt as it has moved to the end on right due to increase in r.p.m on the driver shaft.
.
6. Types of Continuously variable transmission
Variable diameter: works on the principle for of varying pulley diameter of the two pulleys to change gearing ratio between them.
Fig 1.5a shows a Variable Diameter CVT. When the driver shaft is at its initial it transmits lower gear ratio due to difference in the diameter driver and driven
pulley
Fig 1.5b shows a Variable Diameter CVT. As the driver shaft gains speed the variator pulley closes up and causes the driven pulley to open up changing its
gear ratio.
7. Toroidal CVT
A toroidal continuously variable transmission (CVT) that uses a traction drive to transmit
torque has a vastly larger torque capacity than conventional CVTs. This transmission
technology has also attracted considerable interest on account of its capability for
substantially improving vehicle fuel economy and power performance. Toroidal CVTs can
be configured as a half-toroidal type or as a full-toroidal type depending on the geometry
of the variator.
The traction drive of this CVT transmits torque by means of the shear resistance of the
traction fluid film, by taking advantage of the property that the fluid solidifies under high
contact pressure. Accordingly, large loading force is applied to the torque transmission
unit with this drive method, and an excessive load can cause a decline in the service life
or efficiency of the unit. For this reason, it is necessary to have a mechanism that can
generate the optimum loading force under all sorts of operating conditions.
8. Conclusion
CVT has 2 main applications:
1. Increase system efficiency by enabling the engine to run at its most efficient revolutions per
minute (RPM) for a range of vehicle speeds
2. can be used to maximize the performance of a vehicle by allowing the engine to turn at the RPM
at which it produces peak power. This is typically higher than the RPM that achieves peak
efficiency.
CVT eliminates the requirement for a clutch. In some vehicles (e.g. motorcycles) a centrifugal clutch is
added, to facilitate a "neutral" stance, which is useful when idling or manually reversing into a parking
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