Designed to withstand the rigors of mass transit systems, heavy-duty custom bellows can protect the life of the all-important traction motor in light rail vehicles. Here's how.

Traction motors are able to keep their cool with custom bellows. Designed and produced by A & A Manufacturing Co. Inc., the bellows design eliminates premature bellows replacement, preventing a potential cause of motor failure. Siemens Transportation Systems, which specializes in the design and manufacture of light rail vehicles for urban applications, is putting these bellows to use in vehicles used in the mass transit systems in Salt Lake City, Denver, and St. Louis.

A vital part of any light rail vehicle is the traction motor, a powerful electric motor that undergoes a repetitive and demanding cycle of acceleration and travel. It also helps stop the vehicle through regenerative braking. Thus, its operation undergoes alternating heating and cooling cycles.

It's important to note that the dc motors that power many light rail vehicles tend to be more sensitive to moisture, dirt, and dust contamination, as well as overheating, than ac motors. As a result, they need a supply of clean cooling air.

For the traction motor in the Siemens SD100 vehicle, this critical air enters two air intakes on the sides of the car. It passes through ducts to a "T" box in the center of the car and then flows toward the cab. The air passes through a horizontal bellows that directs it into a casting leading to the motor, which is part of the vehicle's truck unit – the wheel and motor system. A fan is mounted on the front end of the traction motor's armature so that it can pull the air through the motor.

"The horizontal bellows is under quite a bit of transverse movement with one end fixed to the car body and the other to the casting that connects the motor," explains John Keller, warranty and field service supervisor at Siemens. "With the fan pulling air through, it is also under a certain amount of negative pressure. Because the truck pivots from side to side as it turns, the bellows is subjected to a sideways motion of 12 degrees in either direction as well as a slight up and down motion."

The custom bellows is able to accommodate this motion and maintain its integrity to provide cooling air in ambient temperatures ranging from over 90° to well below freezing.

"The original bellows was made from a thinner type of fabric with flat plastic stiffeners inside," Keller says. "In service, the glued seams would separate, allowing dirty air, rain, or snow to enter. Because the plastic stiffeners had a grain in one direction, they would sometimes flex and break, and we would find plastic pieces pulled inside the traction motor by the fan. When the stiffeners broke, that also allowed the bellows to collapse and restrict air flow, which caused some motor overheating."

To improve the life of the bellows/duct component, a heavier duty bellows was designed by A & A Mfg. Co. Inc. with several features to help it accommodate the full range of service conditions. Formed from a thicker, yet more durable material, the 0.7-inch-thick elastomer-coated fabric bellows includes heavy wire reinforcement frames inserted inside convolutions to prevent the bellows from collapsing under negative pressure. In addition, tie strips inside the bellows prevent convolutions from over-extending to ensure uniform motion. They also act as an extra safety measure in case one of the wire reinforcements becomes dislodged.

Once this solution was developed, Siemens put the improved bellows on new production vehicles and also provided replacement bellows for units already in service. Because they help ensure an adequate supply of uncontaminated cooling air to traction motors, the new bellows promise not only to help increase motor life but also to reduce maintenance.

More information on custom bellows is available by contacting A & A Mfg. Co. Inc., 2300 S. Calhoun Rd., New Berlin, WI 53151 or calling (800) 298-2066.