Traction Elevator Mechanics Flashcards

What is the significance of the 'T1/T2 ratio' in traction elevator design?

Answer: It is the ratio of rope tension on the load side to the slack side, determining traction capacity

The T1/T2 ratio compares the heavy (load) side tension to the light (counterweight) side tension and must not exceed the traction capacity of the sheave-rope system.

Undercut grooves on a traction sheave are used primarily to:

Answer: Increase traction by raising the effective friction coefficient

Undercut grooves create a higher contact pressure on the rope sides rather than the bottom, effectively increasing the traction coefficient.

What happens to traction if a traction elevator hoist rope becomes oil-contaminated?

Answer: Traction decreases, risking rope slippage on the sheave

Oil contamination significantly reduces the friction coefficient between the rope and sheave groove, diminishing traction capacity.

In a gearless traction machine, what directly drives the sheave?

Answer: The motor rotor shaft without intermediate gearing

Gearless machines connect the sheave directly to a slow-speed, high-torque motor, eliminating gearbox losses and noise.

What type of motor is most commonly used in modern gearless traction elevator machines?

Answer: Permanent magnet synchronous motor (PMSM)

Permanent magnet synchronous motors are favored in modern gearless machines for their high efficiency, compact size, and precise speed control.

Which ASME A17.1 rule governs the minimum factor of safety for elevator hoist ropes?

Answer: 10.5

ASME A17.1 requires a minimum factor of safety of 10.5 for steel wire hoist ropes based on rated load and speed.

What effect does increasing the arc of contact (rope wrap angle) on the drive sheave have on traction?

Answer: Increases traction by allowing more friction area

A greater wrap angle increases the arc over which friction acts, exponentially increasing the maximum traction capacity per the Euler equation.