Flexible Air Actuators Keep in Contact

Sept. 14, 2018

Pneumatics technology plays a key role in keeping electric trains functioning properly.

Some of us may know a pantograph as a geometric drawing instrument, but a pantograph is also the linkage assembly atop street cars and electric trains that transmits electrical power from overhead lines to the electric vehicle. Widely referred to as trolleys in the U.S., pantographs press a carbon strip up against live overhead power lines. “The challenge lies in reliably maintaining the contact between the carbon strip and the line but not pressing against the overhead lines too strongly, because they will otherwise wear too quickly or even rip,” explains Hanspeter Jutzi, CEO of Richard AG.

Richard AG, Murgenthal, Switzerland, designs and manufactures pantographs and other assemblies and equipment of electric vehicles used in public transportation. Jutzi continues: “We have developed and produced pantographs, main circuit breakers, insulators, and many other components for modern traction vehicles for 111 years.” And although pneumatic components may not be clearly visible in these assemblies, Richard AG uses valves, cylinders, and air preparation systems from Aventics in a variety of its products.

“Unlike with the simple streetcars from decades ago, modern rail cars feature complex control electronics and require a continuous power supply,” explains Jutzi, who manages of around 80 employees. In the Richard pantograph, this is performed by a metal linkage assembly actuated by a bellows-type air cylinder.

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Pressure in double-bellows linear actuators from AVENTICS automatically compensate for varying distances between the vehicle and overhead wires to maintain constant force applied by the conductive strip.

This pneumatic solution from Aventics consists of a valve, a pressure regulator, the bellows actuator, and air filtration units. The regulator maintains pressure in the bellows consistently at 3 bar (44 psig), which corresponds to a force of 70 to 85 N (16 to 19 lb). applied by the carbon strip. This force is enough to keep the carbon strip in contact with the overhead line, even when the track is uneven.

In Europe, trains can also cross borders without issues. With alternating current, the carbon strip contacts can absorb 25,000 V with maximum currents of up to 900 A and transfer them to the train. Richard pantographs are approved for speeds up to 230 km/hr, proof of just how dynamic pneumatic control solutions are.

Components Must Be Robust

“We require an extremely wide operating temperature range of −25° to 45° C (−13° to 113° F) from the pneumatic components, and in some cases even more extreme values for train operators in certain climatic regions,” offers Jutzi. The pneumatic solution not only tolerates these wide variations in temperature but is virtually wear-free when compared to electromechanical solutions.

Aventics supplies the pneumatic assemblies for the pantographs and other modules pre-assembled. “We may only be a medium-sized enterprise, but in some cases we have worked with rail vehicle manufacturers and operators for decades,” adds Jutzi. “We know our customers still expect original spare parts years later, and that’s how we choose our suppliers.”

This information was submitted by John Bridges, head of marketing, Aventics Corp., Lexington, Ky.