FLUID POWER
BONDIOLI & PAVESI
Power in transmission
A NEW CVT SOLUTION CONSISTING OF MECHANICAL, HYDRAULIC
AND ELECTRONIC SYSTEMS CAN VARY OUTPUT SPEED
INDEPENDENTLY FROM INPUT SPEED
Present agricultural equipment is mostly
based on mechanic transmissions because
they can transmit high power with good
efficiency. The limit of mechanic transmissions is
that they are driven by the power take off (PTO)
of the tractor and consequently can’t adapt the
working speed of the implement to different
working conditions without changing the speed
of the engine. This means that in order to achieve
the optimum working speed of the implement the
efficiency of the engine suffers.
Sometimes the mechanic transmission is
provided with two or three gear speeds that can
be shifted when the PTO is stopped. In particular
applications there is a powershift transmission if
it’s necessary to change gear speed under torque
without stopping the machine. Some selfpropelled
machines are equipped with pure
hydraulic transmissions that provide flexibility to
the system but haven’t got high efficiency.
Continuously variable
The proposed continuously variable transmission
(CVT) power split unit is a compact and
powerful mechatronic unit that combines the
efficiency of a mechanic transmission with the
ductility of hydraulics, controlled by electronic.
The unit can be applied on drawbars and is useful
for all applications where they are required to
continuously adapt the speed of the implement to
the working conditions.
Innovation
The unit is a compact and powerful (300 kW)
hydro-mechanic CVT. The input and output shaft
are coaxial so it can be easily applied on the
drawbar of the implement. In the shown variant
it can change the ratio between input and output
70 iVT International Off-Highway 2020
speed from one to three continuously. The layout
is studied to reduce the power transmitted by the
hydraulic to keep the efficiency high. At
maximum power and speed just 1/3 of the power
is transmitted by the hydraulic.
The design is flexible because it gives the
possibility to install pumps and motors of
different type and displacement, this to increase
the output torque and to extend the speed range.
It offers the same power rating to a pure
hydraulic transmission but is more efficient and
less expensive. When compared to a pure
mechanic transmission, it gives the possibility to
adjust implement output speed to maximise the
productivity, this independently by the tractor
PTO speed and optimize engine speed according
to power transmitted to reduce fuel consumption.
Features
The unit is provided with an engine control unit
(ECU) produced by Bondioli & Pavesi that
controls it. The electronic control gives the
possibility to achieve the maximum benefit of the
system and the targets nowadays required by of