Overhead Traction

OHT Car Type Summary

This design utilizes a geared traction machine, along with the controller and governor, mounted in a penthouse machine room directly above the hoistway. This application uses hoist ropes and counterweight to move the car, in lieu of a hydraulic jack. The counterweights can be positioned at the rear of the car (front open only), or at the side of the car. In addition to the main rails, a set of counterweight frame rails are also required.

Advantages

Advantages to using this design include a much faster speed capability, an unlimited travel range and a higher power efficiency than hydraulic car types. In addition, there is no hydraulic oil being used.

Disadvantages

Disadvantages include a substantially higher material cost than hydraulic car types, along with a higher field installation cost. In addition, a higher OH is required (typically 16ft) along with a penthouse machine located over the hoistway.

The penthouse machine room can be eliminated by positioning the geared machine next to the side of the hoistway at one of the landings. This arrangement is referred to as a basement machine application, also requiring additional hoistway sheaves and machine beam support at the landing location of the machine.