Caterpillar is moving rapidly forward with the new large mining trucks showcased at MINExpo last year and representing the company’s largest investment ever in new mining technology. The Cat® 793F and 797F mechanical drive trucks and the 795F AC electric drive truck are all achieving milestones. However, further development of the 793F AC electric drive truck has been suspended because it has no real advantage over the 793F with mechanical drive. Cat’s testing has proven its long-held mechanical drive position.
Having been the lone exponent of mechanical drive trucks ever since it went into the manufacture of large mining trucks in 1984, Caterpillar has now developed two electric drive trucks. However, it now sees no advantage in continuing with the 793 F AC drive development. This electric drive unit is heavier than its 793F mechanical drive counterpart, meaning it moves less material and therefore has a higher cost per tonne. While it is true that on the flat, the AC drive unit’s top speed is faster by maybe 5 km/h, that in itself does not really compensate for the extra weight, and can anyway result in safety and tyre wear problems.
Caterpillar is still firmly of the opinion that mechanical drive trucks are the best solution. Mechanical drive still offers the best powertrain efficiency. Less power is required to travel at the same speed. Thus fuel consumption is lower and mechanical drive offers a better emissions footprint. Nevertheless, development of the 795F continues, because there is significant interest in this machine, to give those that want electric drive the option and because it neatly fills a capacity gap in the Cat product line.
The first 795F AC drive is on trial in a copper operation and more field follow units are to go out onto mines soon. Along with the expansion of field validation, Caterpillar will prepare this model for production. Caterpillar engineers have been testing two 795F AC prototypes, including the truck shown at MINExpo, at the Tucson Proving Grounds. The development program has provided input for the construction of the new 795F AC in Decatur, Illinois that has shipped to a copper mine in North America where it will serve as the first field-follow 795F AC as it works at the mine. The 313-t-capacity) 795F AC is a new size class for Caterpillar, and, as a result, the primary focus of the Caterpillar AC electric program has been on the 795F AC. The commercial launch date will be defined as the field-follow program progresses.
In mechanical drive, the 793F and the 797F have accumulated more than 75,000 hours of field testing and have proven their performance capabilities and their durability. The new Cat C175 engine that powers them has racked up 130,000 hours of field testing in mining trucks and more than 120,000 hours in power systems. Because of the success of these field-follow programs, the 793F is targeted to go into full production within a few months and the 797F late this year.
The new Cat trucks offer innovative designs for improved safety and performance. “All of the F-Series mining trucks incorporate innovative design and engineering that enables them to deliver lowest cost per tonne,” explained Ed McCord, Mining Truck Product Manager. “With the latest technology in AC electric drives now available, Caterpillar is able to offer both types of drive to the mining industry. We see the addition of electric mining trucks as a complement to our mechanical drive trucks.”
The most evident new component is the Cat C175 diesel engine, which is the power plant for each of the new trucks. The C175 meets US EPA Tier 2 emissions standards, yet it delivers 2,983 kW in the 20-cylnder version that powers the 363-t capacity 797F. The 16-cylinder C175 powers the 795F AC with 2,535 kW, and it powers the 793F, which has a 227-t capacity, with 1,976 kW. The C175 promises longer life between rebuilds, lower sound levels, improved altitude capability and improved fuel consumption compared to the 3500 Series engines it replaces. However, for those using that engine in older trucks, development continues.
As a brand new platform, the 795F AC incorporates new technologies throughout. For example, four-corner blended braking and retarding-using Cat oil immersed and cooled disc brakes as well as electrical retarding-enhances safety and operator confidence. The remote-mounted generator enables servicing without removing other major components, and the wheel motors mounted inside the axle enable easy and separate servicing of the final drives. The retarding grids are radial, which promotes more uniform air flow for better reliability. And the Cat proprietary drive system is fully integrated and fully supported by Caterpillar.
Caterpillar believes that “mechanical drive mining trucks will satisfy the needs of the vast majority of mining operations. But as the only manufacturer of 181-t and larger mining trucks with both mechanical drive and electric drive systems, [it] will soon be able to offer trucks that address all mining company preferences.”