Hybrid SR drives for new loader
In what some consider the most significant jump in technology in 20 years, the new Le Tourneau SR drive breaks away from the traditional power generation.
The SR system motor is designed to resist failure
With conventional DC drives, a diesel-driven AC generator supplies power, converted back to DC via silicon-controlled rectifiers, to drive the wheel motors. The SR drive utilises a DC bus system coming off the SR generator. The advantages in mechanical and operational efficiency are tangible.
When electric motor powered loaders are required to brake, the traction motors become generators, feeding power back to the braking grid to stop the loader. If the braking grid couldn’t handle the energy generated, any excess would drive back though the generator and ultimately, cut off the machine’s fuel supply. About 40 per cent of the braking energy could be recovered, the balance dissipated through the braking grid.
With the SR power system, almost 90 per cent of energy generated during braking is recovered and conserved with only 10 per cent lost to the braking grid. The recovered energy is instantly available to the loader.
In practice, the Switched Reluctance (SR) motor consists of a rotor fitted inside a specially-designed stator and uses magnetic attraction to produce torque on the rotor of the motor - a method that means no windings, no commutator maintenance, and no brushes or brush rigging.
The SR drive utilises a specially designed water-cooled insulated-gate bipolar transistor (IGBT) to switch the phase currents on and off so the rotor poles continually chase the current. Torque is similarly controlled by varying the on-time of each phase to deliver high torque continuous power capability across the speed range. High-speed capability is limited only by bearing speed rating.
The SR system’s motor is designed to resist failure, even under stall conditions and is equipped with robust electronic controls.
In equipment such as a loader, the synergistic relationship between the SR drive and IGBT switching results in high performance efficiency being maintained over wide speed and load ranges. The combination also allows for the use of smaller motors (compared to DC motors of equal kilowatts) and a high level of fault tolerance.
LeTourneau’s new L-1150 loader is the launch platform for the new hybrid SR drives. The company’s plans for the integration of the SR drive technology into the other models in the loader range have not been made public.
For more information email: jchadwick@letouneau-aust.com
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