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Basic patent licensed from Badalini, Italy in the 1950’s |
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In an attempt to realize an ideal transmission
to apply to the scooter that was “easy” and “comfortable
to ride”, and “helps to enjoy life” for everyone,
Honda studied various types of infinitely variable transmissions.
Among those, Honda recognized the performance of the hydraulic
mechanical, infinitely variable transmission that Badalini of
Italy had developed for machine tools (Cambi Idraulici Badalini).
As the basic patent had already been granted when Honda started
the development, Honda obtained a licensing agreement for the
basic patent from Badalini, and started further research and
development for an infinitely variable transmission for motor
vehicles. The developed transmission was applied to the Honda
scooter “Juno” marketed in 1962. In Honda, the transmission
was casually called as “Badalini transmission”,
and formally referred to as “HRD transmission” taking
the initials of Honda R&D.
What is the hydraulic mechanical transmission (HMT)?
In the infinitely variable transmission using hydraulic pressure,
there is the HST (hydraulic static transmission) that connects
the hydraulic pump with the hydraulic motor only by hydraulic
lines, and the HMT (hydraulic mechanical transmission) that
takes out the driving force from the hydraulic pump via the
output shaft. Generally, while the transmission efficiency of
HST is not so high because the power is transmitted only by
the hydraulic pressures, the system permits free layout of the
output shaft and compact packaging, and is widely applied to
construction machines, aircraft, power equipment, etc. Meanwhile
in the HMT (hydraulic mechanical transmission), the hydraulic
pump and the hydraulic motor are generally integrated into a
unit, and the torque to drive the pump is added to the torque
transmitted by the hydraulic motor. For that reason, higher
transmission efficiency is attainable from HMT than from HST
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HRD transmission applied to the scooter “Juno” in
1962 |
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Motocross machine RC250MA won the all Japan championship series |
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As the automatic transmission
HMT for motocross racing machines required high efficiency
and reduced weight, while the principles were derived from
the “HRD transmission”, the system configuration
had evolved to a completely different, hydraulic mechanical
transmission system with the pump and the motor laid on a
common axis. The system was made more compact and light in
weight by increasing the working pressure (normal working
pressure: 44MPa, maximum working pressure 80MPa). Furthermore,
the construction that prevents leakage of high pressure fluid
was applied to various places in the unit, thus allowing the
system to maintain the high transmission efficiency even under
very high fluid pressures. One of the design features was
the use of a spool-type distributor valve. Considering down-sizing
of the control system and freedom of setting, the electronic
control system was applied. The HMT for the motocross machine
was aimed at an ideal, infinitely variable transmission that
could respond discreetly to rider intentions, and accordingly
it was named “HFT” (Human Fitting Transmission). |
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RC250MA
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The motocross racing machine RC250MA equipped
with the “HFT” won the all Japan motocross championship
series in 1991, which was the second year since the debut. The
“HFT” using very high pressures yet maintaining
high efficiency was given intelligence through the electronic
control system, and proved its potential in the real world of
racing. Following the success in races, further research and
development started for an application of the transmission based
on “HFT” to mass-production products, and the development
of HMT (hydraulic mechanical transmission) continued to the
“Hondamatic” introduction in the year 2000. |
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Infinitely variable transmission HFT
Click the picture for an enlarged view |
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