Elevator Machine and Drive System

In the topic " Basic Elevator Components - Part One" , I indicate that the basic elevator components are as follows:

1. Car. 
2. Hoistway. 
3. Machine/drive system. 
4. Control system. 
5. Safety system. 

I explained the elevator car components in this prevouis topic, and I explained the Hoistway and its components in the topic "Basic Elevator Components - Part Two".


today I will continue explaining the third item from basic elevator components which is Machine/ Drive System as follows.

You can review the following prevouis topics for more information and good following. 

• Elevators Types and Classifications  – Part One
• Elevators Types and Classification - Part Two

Third: Elevator Machine and drive system

Driving machine, this is the power unit of the elevator, and usually located at the elevator machine room.

The Driving machine used to refer to the collection of components that raise or lower the elevator. These include the drive motor, brake, speed reduction unit, sheaves and encoders.


Types of Driving Machines: 

Generally, there are three standard types of driving machines provided for elevators. These are;

1- Gearless Machine

Gearless Machine

• It used in high rise applications whereby the drive motor and drive sheave are connected in line on a common shaft, without any mechanical speed reduction unit located between the drive motor and drive sheave. 

• Generally, Gearless machines are used for high speed lifts between 2.5 m/s to 10 m/s and they can be also used for lower speeds for special applications. 

• Their sizes and shapes vary with load, speed and manufacture but the underlying principles and components are the same. 

The Gearless machines comprise the following components: 

Gearless Machines Components

• Electrical Motor.
• Traction Sheave or drum.
• Direct current armature in case of DC motor.
• Rotor in case of AC motor.
• Brake.
• Machine Bedplate.
• Supporting bearings.
• Deflector or double warp sheave.

2- Geared Machine 

Geared Machine

• It used in low and mid rise applications. This design utilizes a mechanical speed reduction gear set to reduce the rpm of the drive motor (input speed) to suit the required speed of the drive sheave and elevator (output speed). 

• Generally, geared machines are used for speeds between 0.1 m/s and 2.5 m/s and are suitable for loads from 5 Kg up to 50,000 Kg and above. 

• Their sizes and shapes vary with load, speed and manufacture but the underlying principles and components are the same. 

Essentially, a geared machine includes the following components:

Geared Machines Components

• Drive motor.
• Brake.
• Speed reduction unit or gearbox.
• Drive sheave.
• Bedplate.
• Deflector sheave (if mounted as integral part of the bedplate assembly).

Types of geared machine drive according to location of installation: 

A- The drive machine located directly over top its hoistway or shaft is commonly referred to as “Overhead traction” as in the below image. 

Overhead Traction

B- The drive machine located at a basement is commonly referred to as “basement traction” as in the below image. 

Basement Traction

C- The drive machine located at the side of the hoistway is commonly referred to as an “offset traction”  as in the below image .

Offset Traction

Note: Basement and offset applications require additional deflector sheaves to properly lead suspension ropes off the drive sheave and to the car top or counterweight.



3- Drum Machine 

Drum Machine

It widely used in older passenger and freight elevator applications, though now rarely seen except for dumbwaiters. For many years now the Elevator Safety Code has disallowed the use of such machines for passenger applications. A drum design has one end of the suspension rope affixed to the inside of the winding drum’s drive sheave, and then allows to rope to reel in or off the outer surface of its sheave, depending upon the car direction of travel.


Elevator Machine Room for Electric Traction Type

Elevator Machine Room

Elevator Machine Room is Enclosure in which the machinery and electrical controls used for an elevator are contained. The room must be fully enclosed or otherwise secured against non-authorized access.

Usually located above the hoistway in a penthouse or two floors above the highest floor it serves, but may be in the basement if overhead space is unavailable.

Within a typical machine room one will likely find the following:

• Electrical Disconnects.
• Machine (geared or gearless or drum type).
• Machine brake.
• Drive motor.
• Encoder.
• Motor Generator Set.
• Selector.
• Car Controller Cabinet.
• Group Dispatcher or Common Relay Panel Cabinet.
• Car Governor.
• Counterweight Governor.
• Rope Gripper.
• Light fixtures and light control switch.
• Fire alarm devices.
• Hoist beam.
• Power receptacles.
• HVAC equipment (used to service the elevator equipment room or space).
• Deflector Sheaves.

Main Components of machine drive system:

1- Electrical Motor:

Electrical Motor is used to raise and lower the elevator cab, the direction of motor rotation and speed (revolutions per minute) are directed and supervised by devices located within the elevator controller, The motor component of the elevator machine can be either a DC motor or an AC motor as follows:


A- DC motor: 

Direct current motors use carbon brushes to control or regulate the operational speed of its motor. It is an important maintenance task to regularly inspect, repair and replace these brushes. Failure to do so in a timely fashion can result in equipment mis-operation and lead to significant motor damage. the advantages of use DC motors are as follows:

• Has a good starting torque. 
• Ease of speed control using a DC generator with a variable output or static converters. 

B- AC motor: 

The advantages of use AC motors are as follows:

• More regularly used because of its ruggedness and simplicity. 
• More ride quality. 

Types of Electrical Traction Drive Systems:

Generally, the electrical traction drive can be grouped into several categories based on the motor type and its control as follows:


A- Geared traction control, which includes:

• Single speed AC motor. 
• Two speed AC motor. 
• Variable voltage AC motor (VVAC). 
• Variable voltage, variable frequency AC motor (VVVFAC). 
• Variable voltage DC motor(VVDC). 

B- Gearless traction drives, which include:

• Variable voltage DC motor (VVDC). 
• Variable voltage, variable frequency AC motor(VVVFAC). 

2- Traction (Drive) Sheave: 

The powered pulley connected to either the elevator drive motor’s outputshaft (gearless) or to the output side of the mechanical speed reduction unit (geared). The circumference of the sheave has a series of “U” or “V” shaped grooves cut into it (as shown in below image), in which sit the elevator suspension or hoist ropes. The friction loads created as the suspension ropes pass over the grooved surface of the sheave causes motion to be transmitted from the drive motor to the elevator cab or counterweight.

“U” or “V” shaped grooves

3- Secondary Sheave: 

Pulley that is normally used on gearless elevators and is located directly beneath the machine or drive sheave. It too has a grooved surface over which pass the suspension or hoist ropes.



4- Deflector Sheave: 

Pulley used to offset or direct the vertical drop or location of the steel hoist ropes running between the elevator car and its counterweight. Where the horizontal distance between the hitch point for the car and the counterweight is larger than the diameter of the drive sheave, one or more deflector sheaves are used to guide the hoist ropes.

These devices are grooved sheaves that lead elevator suspension ropes off the drive sheave down to the car top and counterweight. The number and size of deflector sheaves will be a function of the elevator’s size, machine placement and roping arrangement.

Many installations having carrying capacities of 1,136 kg or less, are provided with drive sheaves of sufficient diameter that do not require the use of deflector sheaves in a typical overhead arrangement as shown in the below image#1.

Image #1 : Drive Sheave without Deflector Sheave

Will require the use of deflector sheaves, and these are now normally located within the main elevator machine room space as shown in the below image#2. 

Image #2 : Drive Sheave with Deflector Sheave

One can see the suspension ropes angling off the back side of a geared traction drive sheave as shown in the below image#3. Note how they travel away from the drive sheave and then down to its deflector sheave.

Image #3

5- Brake: 

Traction and drum machines are provided with a mechanical brake, designed to stop and safely hold an elevator. A centrifugal force governor is provided on most elevators to guard against overspeeding (when a car travels in excess of 20% of top speed, the governor will activate a safety stop device). Safeties are installed at the bottom of an elevator car and occasionally on counterweights to provide positive emergency stopping when activated by the governor. 

Brake Principle of Operation:

Brake Principle of Operation

• During typical operation, this brake is electrically lifted or “picked” against adjustable tensioned springs. In the event electrical power is removed from the brake, these springs ensure it immediately drops back against its drum or disk, bringing the car to a safe stop. While applied, the brake will securely hold in place the elevator and its counterweight. 

• Some older elevators have a control design whereby the brake is used to decelerate the car from full speed to a stop. Modern elevator controls use electrical circuitry to slow and stop the car under normal operation. Once the car has stopped, the brake is released to hold the car in position. 

• However, in the event an elevator’s safety circuit is actuated, the brake is immediately applied to stop and hold the car and its counterweight, regardless of the type of control. 

Brake Components and Configurations:

Image #4

The most common form of elevator brake consists of a machined drum onto which two curved shoes or pads drop onto the surface of the drum. The brake drum or disk is directly coupled to the elevator drive shaft. On some machines, the brake is an external element whereby the brake arms and their shoes are located outside and above the rotating drum surface as shown in image# 4. There is one type of gearless machine that has its two brake arms applying force against an inside or interior rim on the drive sheave as shown in image# 5. Brake designs can create three types of hazards; entanglement, pinching and crushing.

Image #5

6- Speed reduction unit or gearbox 


The most common type of speed reduction unit consists of a hardened steel worm shaft, mated with a bronze ring or crown gear (worm-gear set). The mating surfaces of these two elements are contained within an oil bath for lubrication. Regular access to the machine to check the level of oil, as well as the condition of the oil and the ring gear is an important aspect of ongoing equipment maintenance.


7- Machine Bedplate 

• The gear box, motor and brake may be assembled on a common bedplate. This fabricated steel structure serves to keep all parts in accurate alignment and allows one-piece shipment. 
• Some machines have the motor and brake as an integral part of the gear case, removing the need for a separate bedplate. 

In the next Topic, I will continue explaining the Basic Elevator Components. So, please keep following. 


Note: these topics about elevators in this course EE-1: Beginner's electrical design course is an introduction only for beginners to know general basic information about elevators as a type of Power loads. But in other levels of our electrical design courses, we will show and explain in detail the Elevator Loads Estimation calculations.