Enhancing a motor so that its output increases by 45 percent is also a high point in the inventor career of a design expert like Bernd Pfannschmidt. He accomplished this feat for a drive system that is used in huge open-pit mining dump trucks simply by installing a new cooling system.

Human beings look tiny next to the huge wheels of one of these mining trucks. The versatile giants, which transport ore, coal, tar sand, and piles of waste around the clock 365 days a year, are mainly used in Australia, Canada, the U.S., South America, and South Africa. Each of the truck’s two rear wheels has its own motor to propel the vehicle. Despite the fact that the traction motors are very robust, the trucks, which weigh up to 630 tons when fully loaded, sometimes have to stop so that the motors don’t overheat. This is especially the case when traveling on slopes. Because the U.S. mining and construction equipment manufacturer Komatsu was dissatisfied with this situation, it asked Siemens if a better solution were possible. Siemens responded with great interest. Over the previous 25 years, its Industry Large Drives unit had been able to develop its expertise regarding mining equipment thanks to its extensive know-how in relation to train and locomotive drive systems. Pfannschmidt is a group leader with responsibility for the mechanical design of such equipment. This field had already fascinated him during his days as a student of mechanical engineering at the technical university in Koblenz, his home town. Pfannschmidt got in touch with Siemens early on — in fact, he received support from experienced employees at the company while working on his masters thesis on rolling-element bearings. After finishing his degree, he began his career at the development department for rail drive systems in 1986.

As he began to study mining truck motors, Pfannschmidt quickly realized that the drive system as such couldn’t be changed. “We would’ve had to make the motor larger to achieve more output, but the trucks’ wheel well just isn’t big enough for that,” he says. Pfannschmidt thus had no alternative but to modify the cooling system in order to improve the motor’s performance. Traction motors are air-cooled. Cold air flows into the motor on one side, where it cools the winding overhand and the end ring. It then flows through the air vents in the stator and the rotor to the other side of the motor, where it cools the second winding overhead and end ring. However, here the cooling effect is far less pronounced than at the intake because the air has been warmed by the motor.

“At first, we thought of splitting the motor in the middle so that we could better cool the two halves,” says Pfannschmidt. However, tests showed that this would have made the motor too unstable to withstand the resulting strain. Pfannschmidt continued to grapple with the problem at the back of his mind until he finally came up with a solution, which was to let the air flow into the motor housing from both sides. To achieve this feat, he drilled 27 holes into each side of the motor housing, which looks a bit like a thick disc. The holes on one side of the housing were shifted in relation to their counterparts on the other side. After flowing through the ventilation shaft at the top of the motor housing, the air is distributed to the two halves of the motor. There it cools winding overheads and end rings, streams through holes in the stator and rotor and reaches the corresponding other side of the motor through ducts and is expelled via the 27 holes. These airflows make it possible to distribute the motor’s waste heat more evenly and thus reduce the risk of overheating. As a result, the output of the motor can be boosted by up to 45 percent compared with the output achieved using conventional air cooling.

“Once you have the basic idea, the rest comes automatically,” says Pfannschmidt. That’s why he wasn’t worried about the one-year test phase for the two prototypes: “I was certain that the motors would run much better.” Most of his inventions were “born of necessity,” he says; they didn’t just emerge out of nowhere. “I look to see in what respect a system needs to be optimized and then consider how I can improve things,” says Pfannschmidt. In order to reduce the costs of subway train production, for example, he created a mesh barrier that is installed directly in front of the motor and protects it from fouling. Prior to that the protective barriers had to be purchased. In his more than 20 years at Siemens, Pfannschmidt has registered 53 inventions, which have led to 49 individual patents and 51 patent families. 

 Pfannschmidt also likes to work on motors in his free time: In his garage you’ll find two motorcycles with sidecars. He lives near Nuremberg, Germany, with his wife and three children.