WP6-Brochure-E4 brochure - ELA European Lift Association.

When combined with hall call control systems, double‐deck lifts performance is further
improved, allowing buildings to reach a lift performance that would be impracticable with
single‐deck lifts.
Recent developments in intelligent control and safety systems have allowed the use of two
independent cars travelling in the same shaft. This can translate into a significant improvement
in handling capacity. Manufacturers claim that by using such systems 40% more passengers
are transported in a typical four‐shaft group.
3.6 Transmission and Roping
The low and medium speed traction lift market (< 2,5 m/s) is still largely dominated by geared
units. In these lifts, a gearbox is used to reduce the shaft speed and produce the required
torque to start the lift car moving. Gearing allows the use of smaller, less expensive motors.
However, energy is dissipated as heat caused by friction between the gear’s teeth, and
churning losses in the lubricant.
Figure 3‐25. Worm gear
Typically, worm gears have been the prevalent choice for the reduction of speed since they
provide good shock absorption, quiet operation, and high resistance to reversed shaft rotation.
However, their efficiency is relatively low (typically 60% ‐ 70%) and the efficiency in reverse
rotation is significantly lower than in the forward direction. The efficiency of the gear train
depends on the lead angle of the gears and the coefficient of friction of the gear materials. The
efficiency also depends on the operating parameters of the gear train. Usually, smaller
reduction ratios, higher input speeds to the worm, and larger sizes result in higher efficiency.
Helical gears have higher efficiency than worm gears, typically over 98% per stage, and are
being used in some of the more recent lift systems. Since there is less sliding between the
gear’s teeth, they present improved efficiency.
According to information provided by manufacturers, the transmission efficiency of helical
gears is roughly 20 ‐ 30% higher than that of worm gear, thus enhancing the overall
mechanical efficiency of the lift equipment. However, helical gears can be noisier and have
higher initial costs.
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