Continuous Power Enhancement

The evolution of machine elements and
their future as an element of design are
analyzed here using the example of
rolling bearings and gears. Due to the
bearing as a functional unit, the invention
of the wheel about 6600 years ago
became a sustainable innovation. With
the wheel centered and guided by the
bearing, the acting forces were supported
(Fig.2, left). A modern wheel
bearing has the same basic functions,
can also transmit the drive power practically
without loss and, in many cases,
also provides high-resolution rotational
speed information via specific sensors
(for example, in a modern ABS system).
A similar development can be observed
in the example of linear guides
(Fig.3). Whereas about 4600 years ago
wooden rollers as rolling elements facilitated
the construction of pyramids,
with modern slides guidance accuracies
in the range of micrometers are possible due to advances in manufacturing
technology for the hardened and
precision-ground rolling elements as
well as the preload of the rolling contacts.
An integrated position measurement
system can resolve the same
accuracy. Low-friction seals and optimized
rolling contacts have made it
possible to continuously reduce friction
losses over the past decades.

Moore’s Law 

In 1965, Gordon Moore made a prediction
about the development of semiconductor
technology (Ref.1). His prediction
is known as Moore’s law and
states that the number of transistors per
unit area will double every year, corresponding
to an exponential increase.
Moore’s law has so far proven to be
largely correct. However, the further reduction
in the size of transistors is likely
to reach its limits in the coming years.
Alternatives to conventional transistor
design or new approaches to chip
architecture are needed for the future
(Ref.3).
Whether Moore’s law can also be applied
to machine elements will be considered
in this section. In order to be
able to assess the further development
of machine elements and the technical
systems assembled from them, suitable
quantification on the basis of technical
characteristics is necessary.

Torque Density of Gearboxes
for Wind Turbines
In wind turbines, the increasing rotor
diameters led to an increase in the rated
power. At the same time, a reduction of
the rotor speed is necessary to maintain
the permissible blade tip speed (Ref.4).
This results in a high increase in input
torque. To evaluate the development of
gearboxes for wind turbines, the torque
density as a quotient of the rated torque
of the gearbox and the weight of the
gearbox is suitable (Refs. 5, 6).
Figure 4 suggests an annual increase
in torque density of about five percent.
This corresponds to an exponential increase
as in Moore’s law, although at a
lower growth rate.
The development of torque density
is due, among other things, to lightweight
construction, new materials and
coatings, and optimized macro- and micro-geometries (Ref.6). Smaller
plain bearings allow higher power densities
by load sharing on more planets
and enable new gear concepts (Ref.7).