Swing drive integrates a hydraulic motor with a planetary gearbox for smooth motion and high-torque output. Click image for larger view.The swing drive is the heart of the excavator, because it must provide continuous operation for the entirety of the working shift. The PMP Swing drive range covers all construction machinery needs, as for travel drive open and closed circuit motors have been developed in order to match the different applications. Despite the circuit layout, swing motors withstand the most demanding duty cycle due to the inertia of the turret. Transitory speed ramps from zero to maximum and from maximum down to stop cover the majority of working time, and are carried out at maximum torque.
Component materials and heat treatments are crucial to allow the gearbox and motor to cover the correct lifespan. Nitrided surface treatment is used for crucial parts subjected to heavy wear, whereas traditional carburizing is used for high fatigue resistance.
Braking valves on open-loop motors are dedicated to turret inertia control. Soft braking is obtained thanks to two different features. One is the progressive increasing of relief setting pressure, which increases during braking and ensures ramped braking torque increase. The other compensates of pressure spikes switch and prevents the bucket vibration around stop position.
Alessandro Lanza is Chief Engineer of Fluid Power at PMP Industries, Coseano Udine, Italy. For more information, visit www.pmp-industries.com.