EPS: it needs power only when the unit
is actually steered.
22 June 2007.
Electric power steering (EPS) is not
a luxury equipment to be only found in small cars of
expensive brands. Better, is not restricted anymore to
the small B-segment cars. EPS is climbing up the
passenger car segments ladder to the C-segment,
lower-medium sized cars (compact cars category in the
US), like the VW Golf.
This growth meant at ZF Steering
Systems, or ZF Lenksysteme GmbH (a 50:50 Bosch-ZF joint
venture), that the 5 millionth ZF electric power
steering unit was produced in the same year that the
German supplier is celebrating 75 years of ZF passenger
car steering systems production.
The five millionth
Servolectric® electric power steering system left the
Schwäbisch Gmünd line on June 20, 2007, four years
after this steering system was used with passenger cars
for the very first time.
Gradually, the EPS has developed into
a standard component for all volume production vehicles
built on the Golf platform of the Volkswagen
Group, the largest European carmaker (4th largest in the
world) which includes the VW, Audi, Skoda, SEAT,
Bentley, Bugatti and Lamborghini brands. The Golf
platform is used in models sold under the VW, Audi,
Skoda and SEAT badges.
In comparison to the hydraulic
solution, the Servolectric helps save up to 85 percent
energy. It only needs power when the unit is actually
How it works - The
steering mechanism itself is based on the principles of
a rack-and-pinion steering; in the case of the electric
power steering, it is linked to high performance
electronics. As soon as the driver makes a steering
motion, the power steering assistance required for the
maneuver is transferred via the electric servomotor to
the mechanical rack-and-pinion steering.
Thanks to the electric drive, in
comparison to a “pure” hydraulic servo steering
system powered by the engine, the Servolectric saves up
to 0.3 liters fuel on 100 km. According to ZF estimates,
the new production figure of five million units means an
annual savings of 150 million liters fuel, a
pre-assumption based on an average driving of 10,000
kilometers per vehicle. Thus, a reduction of 3,555 tons
CO2 emissions is achieved.
In addition to reduced fuel
consumption, the electric power steering offers other
advantages. Except for the power-steering unit, there
are no other assemblies: steering valve, steering pump,
oil reservoir, and high-pressure hoses are not needed.
This saves weight and facilitates installation. The use
of hydraulic oil for power transfer purposes becomes
also redundant, which constitutes another eco-friendly
But the steering business wasn't born
yesterday at ZF. In 1932, with the acquisition of
a license from the American Ross Gear & Tool Company
Inc., Indiana, USA, for the production of Ross
steering gears for automobiles, ZF launched the
production of the so-called “Ross steering“ for the
German and European market in the very same year.
At ZF’s corporate headquarters in
Friedrichshafen, 10,000 units of that comfortable
steering system were manufactured in 1932 and installed
in various vehicle types by Audi, Maybach, and Wanderer.
In 1945, production of the
Ross steering system was continued at ZF's Schwäbisch
Gmünd location and soon replaced by the ZF inhouse
development for cars and commercial vehicles; the latter
encompassed the ZF-Gemmer worm-and-roller steering
system and in 1956, the ZF spindle-type hydraulic power
steering system, one of the first steering systems with
hydraulic power assistance which was primarily used for
off-terrain and commercial vehicles.
In 1999, the Schwäbisch
Gmünd location became a 50:50 joint venture of the
Robert Bosch GmbH and ZF Friedrichshafen AG companies
and ever since, is officially recognized as ZF
Lenksysteme GmbH, specialised in the fields of steering
technology for passenger cars and commercial vehicles,
with 9,400 employees at 18 locations and in 11
countries, achieving in 2006 a sales figure of
approximately EUR 2.4 billion.