Most of us could not imagine driving a vehicle
without either shifting gears or having them shifted for us automatically.
Indeed, many of us enjoy the sense of power and control experienced
while operating a manual gearbox. But some passengers may feel otherwise,
having had to put up with abrupt and often unexpected speed changes
in cars, taxis and buses. Putting aside the question of comfort,
the inherent inefficiency involved in having to shift from one gear
to another and the high potential for driver distraction and mistakes
would seem reason enough to look for an alternative. Such concerns
are especially relevant to large commercial vehicles, in particular
farm tractors, loaders and other machinery where operators have
a number of other tasks to carry out while driving.
Success is a team sport
Partners cite several factors which contributed
to the project's success, including the complementary nature and
verticality of the consortium. The team comprised two key users,
MB-Unimog for trucks and Sisu-Valmet for tractors, Sauer-Sundstrand,
a developer and supplier of hydrostatic components, VDO, a developer
and supplier of electronic equipment, transmission developer SDP
and research group AVL-LIST. All partners played an important role
in targeting an existing product need, providing strong leadership
and management and, finally, the highly strategic manner in which
the project was undertaken.
S-MATIC aimed to develop a continuously variable transmission system,
based on the principle of hydrostatic-mechanical power splitting.
Engine power is divided into two components, one mechanical and
the other hydrostatic, both linked to an advanced planetary gear
set. Planetary gears, as their name suggests, are modelled on the
solar system - a sun pinion is surrounded by planet pinions and
a ring gear, all in a constant mesh. Planet pinions rotate around
the sun gear inside the ring gear. Changing the power flow through
the planetary gears alters speed and direction.
The new transmission includes advanced electronic systems, maintaining
torque connection from zero to maximum speed and treating the entire
drive system from engine to wheels as an integrated unit. It separates
the driving strategies for speed and power take-off and controls
the whole process centrally without the need for driver intervention.
All of this means exceptional comfort and freedom for both driver
and passengers with variable speed maintained continuously under
Environmentally and economically sound
One of the most important advantages of the
new system is a reduction in exhaust emissions, particularly under
'lean burn' conditions. In conventional multiple gear systems, the
efficiency of fuel consumption varies as a driver runs through the
range of speeds within a given gear. With the new transmission,
rather than having to jump abruptly from one gear and one fuel burn
condition to another, fuel consumption is optimised across the entire
range of speeds. This, along with the complimentary mechanical and
hydrostatic power sharing, allows for significant improvements in
The leading project partner was ZF Steyr (previously Steyr-Daimler-Puch/Antriebstechnik,
which was taken over by ZF Passau in May 2000), a supplier of transmissions
for agricultural tractors and trucks. Located in the Austrian city
of Steyr, in an area of particular EU interest because of its depressed
industrial structure and high unemployment rate, the company has
spent over 30 million euro on the new transmission system. S-MATIC
is one of the largest and most complex projects ever undertaken
by the company. The new system represents not only a new generation
of transmissions, combining modular design with high performance
and efficiency, but could play a vital role in job creation.
S-MATIC has been thoroughly tested, both in Europe and the United
States, and has shown outstanding results in terms of performance,
efficiency and durability. Production is set to begin, the partners'
main objectives being to replace 4-step powershift and full powershift
transmissions, as well as conventional automatic ones, by offering
better technology and more features for a competitive price. ZF
STEYR's project feasibility study cited a realistic volume estimate
of 5,000-8,000 units per year, both in Europe and the US, representing
an additional annual production volume of 20-30 million euro.
Just the job for heavy vehicles
Initially, the new system will be targeted at
applications requiring high towing forces and thus a high power-to-rpm
ratio: in particular tractors, off-road vehicles and construction
machinery. Future applications could include public transport, as
smooth and constant acceleration in traffic would improve both comfort
and safety for bus passengers, while lower exhaust emissions would
greatly benefit EU urban environments.
The system's ultimate success will depend on its ability to compete
with similar emerging technologies and market conditions. Although
most lorry and tractor manufacturers make their own transmissions,
thereby putting them in direct competition with S-MATIC, the partners
say that the heavy investments necessary for the development of
new transmission systems may well persuade those manufacturers to
opt for out-sourcing.