The electric drive vs mechanical-diesel debate has been an ongoing one in respect of rigid haulers, especially at the larger end of the payload scale. Diesel-electric trucks were initially developed as a solution to the shortcomings of early mechanical drivelines1, which were prone to reliability issues. Today, the various original equipment manufacturers (OEMs) either find that the diesel-electric option offers many more benefits than the conventional mechanical option, or else they maintain that straight mechanical options remain the best driveline choice.
Differences between electric and mechanical drives
When considering which option to adopt for an addition to one’s fleet, customers should consider an investigation into historical performance monitoring to determine which alternative in the drive systems will bring them the best value.
When fuel efficiency, hauling productivity and operating costs are high on the priority list, mine operators, for example, are often drawn to trucks with electrically-driven wheels powered by diesel generators, instead of mechanical power train mechanisms with gearboxes and driveshafts.
Size class often enters into the equation here when making a choice, together with the selection of AC vs DC drive technology. DC technology has improved favourably in recent years, so customers sometimes wish to stick to what they know in terms of maintenance.
Benefits of each type of drive
Lower component weight translates into less truck weight, so the lower empty weight translates into more payload and higher efficiencies.
A smaller number of friction units (alternator, electric motors, reduction gear units and control cabinets), can save up to 50% of oil compared with a conventional mechanically-driven RDT.
For haulage trucks, mechanical is the most efficient drive for getting the most power from the engine to the ground.
For 90 t and higher, electric drive (and AC drive in particular) provides better performance.
A mechanical drive can do more with equal power, or deliver the same performance with less power than an electric drive, translating into better fuel savings.
The trolley option with AC drive system technology was developed using advanced propulsion technology which also powers the OEM’s bullet trains in Japan.
Mechanical drive trucks do not burn fuel when retarding downhill.
Electric drive has fewer major components than the mechanical drive option and this translates into a smaller number of potential failures. Fewer components also mean less maintenance, which in turn translates into higher availability and ultimately higher productivity.
Superior braking, retarding and traction control, thus being recognised the world over by miners and operators as better to operate in poor underfoot conditions.
Dynamic retarding force provides protection from exceeding the electric drive retarding capability envelope.
Mechanical drive trucks can generate and hold a higher peak torque than electric trucks.
Optional final drive reductions2 improve peak torque at the cost of top end speed.
Mechanical drive studies have seen to deliver the best balance of production and operating costs.
Electric drive systems can have a maximum electric current time limit for how long they can pull peak torque.
Mechanical drive requires more maintenance through oil changes and service life of major components is shorter compared with electric drive.
Electric mining trucks are preferable in large-scale operations with deep pits, where trucks need to haul material from the bottom and get over steep slopes.
In an ideal world, both drives need good haul roads with gentle sloping, quality maintenance and service, responsible and skilled operators and loading within the rated payload. Reality is a different story.
When considering rigid haulers’ drive technology for large mining trucks, the industry may consider a future with some sort of electric hybrid car approach. In addition, research on energy recovery for both mechanical and electric drive systems has revealed that it is still not cost effective to implement.
Komatsu’s Electric Drive Mining Trucks
Komatsu RDTs have led the way to pioneer the ‘Ultra Class, trolley systems and autonomous, driverless operation in the industry. Design for these dump trucks has focused on innovative suspension, transmission and electric drive technology. Komatsu rigid haul mining trucks are also being introduced with electric trolley haulage.
The Komatsu 930E is the best-selling off-highway, ultra-class, rigid frame, two-axle, diesel/AC electric powertrain haul truck in the world. Although this model is neither Komatsu’s largest nor highest payload capacity haul truck, the brand considers the 930E to be the flagship of their haul truck product line.
Komatsu is a global leader in the supply of Japanese-engineered mining, construction, earthmoving and utility equipment in Southern Africa. The MoJo Motor Industries (MMI) Team comes with over fifty-four years of combined experience in automotive, construction and mining equipment sales and support. MMI is the official Komatsu dealer for Zimbabwe. Please direct all your pre-sales or equipment enquiries on electric drive mining trucks or autonomous dump trucks to our knowledgeable staff.
1 The driveline of a vehicle transfers power from the engine and transmission to the wheels.
2 The final-drive ratio is an extent by which the rotating speed of the driveshaft (output) from the gearbox finally reduces before it reaches the driven wheels. If you alter this ratio, then it also alters the effective ratio of every gear, thereby affecting the vehicle performance and economy.