How the elevator traction machine works

The traction drive system of an elevator is illustrated in Figure 2-2. The motor, located in the machine room, works in conjunction with a gear reducer and a brake to form the traction machine, which serves as the primary power source for the elevator’s movement. One end of the traction sheave is connected to the car via the hoisting rope, while the other end is attached to the counterweight. To ensure that both the car and the counterweight can move independently along the guide rails within the hoistway, a pulley or guide wheel is installed on the traction machine to separate their paths.

The weight of the car and the counterweight exerts pressure on the hoisting rope, causing it to grip the traction sheave through friction. This frictional force, known as the traction force or driving force, enables the motor's rotation to turn the sheave, which in turn moves the hoisting rope and pulls the car up or down. When the car rises, the counterweight descends, and vice versa. This back-and-forth motion allows the elevator to perform vertical transportation efficiently within the shaft.

The interaction between the hoisting rope and the traction sheave ensures the relative movement of the car and the counterweight. However, during operation, the load on the car changes, as does its position and direction of travel. To maintain sufficient traction under all conditions, the national standard GB 7588-1995 "Safety Code for Elevator Manufacturing and Installation" specifies a critical condition:

T1/T2 × C1 × C2 ≤ e^fα

Where:

• T1/T2 – The ratio of the larger static tension to the smaller static tension on either side of the traction sheave when the car is fully loaded (125% of rated capacity) at the lowest floor and empty at the highest floor.
• C1 – A dynamic coefficient that accounts for acceleration, deceleration, and special installation conditions.
• C2 – A wear factor depending on the groove shape of the traction sheave (C2 = 1 for semicircular or notched grooves, and C2 = 1.2 for V-shaped grooves).
• e^fα – Known as the traction coefficient, this represents the maximum allowable ratio of T1/T2 based on the equivalent friction coefficient (f) and the wrap angle (α) of the rope around the sheave.

A higher value of e^fα means a greater allowable T1/T2 ratio, which translates into a stronger traction capacity. Therefore, the traction coefficient directly reflects the elevator’s ability to safely and effectively move loads under various operational conditions.

Wooden Sleeper

Railroad construction wooden sleeper characteristics
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