Capital Equipment News June 2017

HAULING – RIGID DUMP TRUCKS

BELAZ is one of the OEMs which maintains that trucks from 130 tonnes payload class and above should be electrically-driven.

improved and customers want to stick to what they know in terms of maintenance. Current BELAZ shipments of large trucks with DC or AC depends on the size class, with some long established 130 t and 220 t models still seeing a lot of DC drive orders. Why mechanical? In terms of payload, Ingle argues that mechanically driven trucks in the 182 t to 220 t size class have a 10-20 t empty weight advantage over their electrically-driven counterparts. “The lower mechanical empty weight translates into more payload and higher efficiencies,” says Ingle. Lavrenov agrees, saying that less weight of the components in a mechanical drive system when compared with AC/DC drive systems, translates into less truck weight. When it comes to drivetrain efficiency, Ingle also argues that for haulage trucks, mechanical is the most efficient drive for getting themost power from the engine to the ground. “Electric drive truck manufacturers talk about improved powertrain efficiency of AC over DC but the fact is mechanical drive is still more efficient than AC electric drive. This has been proven in field studies, and validated in the lab. The result is mechanical drive can do more with equal power or deliver the same performance with less power. This translates into better fuel savings,” says Ingle. Meanwhile, mechanical drive trucks do not burn fuel when retarding downhill. Retarding forces drive need systems so fuel to the engine can be turned off. Ingle also says mechanical drive offers superior braking, retarding and traction control. “Mechanical drive trucks are recognised the world over by miners and operators as better to operate in poor underfoot conditions. Also, AC drive has a dynamic retarding capability limit that once exceeded, the truck starts to speed up. Mechanical drive brakes / retarding can bring a truck back into the desired operating envelope,” says Ingle. Ingle also argues that mechanical drive trucks can generate and hold a higher peak rimpull (torque) than electric trucks. “This can be a bit confusing because electric trucks offer optional final drive reductions that improve peak rimpull at the cost of top end speed. In addition, electric drive systems can have a maximum electric current time limit for how long they can pull peak torque.”

Hitachi pioneered the AC-3 technology to its RDT range in 2012. The AC-3 technology was developed using advanced propulsion technology that also powers the OEM’s bullet trains in Japan.

oil, final drive oil, steering and hydraulic systems, but mechanical drive has a bit more fluids for the transmission and oil- cooled brakes. “But, an objective look at the actual impact on operating costs shows this only adds a very small amount of operating cost to mechanical drive trucks and is greatly offset by other mechanical drive operating cost advantages,” argues Ingle. Lavrenov adds that electric drive has fewer major components than the mechanical drive option, and this translates into less potential failures. He also argues that fewer components mean less maintenance, which in turn translates into higher availability and ultimately higher productivity. The trolley option is another key benefit of the electric drive system, and Ingle agrees to that fact. This is a major feature of Hitachi’s AC-3 drive system technology

In a nutshell, Ingle believes that mechanical drive offers lowest cost per ton. “Mechanical drive delivers the best balance of production and operating costs,” argues Ingle. Why electric? According to Egorov, application of electric transmission results in much smaller number of friction units (alternator, electric motors, reduction gear units and control cabinets), which saves up to 50% of oil compared with a conventional mechanically-driven RDT. “That simultaneously drives down operational costs by up to 38% during maintenance,” he says. This view is shared by Lavrenov, who argues that mechanical drive requires more maintenance through oil changes, adding that service life of major components is shorter compared with electric drive. Ingle says both drive options have engine

CAPITAL EQUIPMENT NEWS JUNE 2017 8