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New model is largest, most technically advanced hauler yet produced by Caterpillar; two 3500B engine blocks combined into one 24-cylinder engine

With all the attention given to Caterpillar's launch of compact equipment, it was almost easy to forget that what made the Peoria, Ill.-based company the dominant presence it is are big machines. In some cases, real big machines.

If anybody needed reminding of that fact, the company gave it to them recently as it officially rolled out its largest capacity mine haul truck, the 797. The new vehicle, which Cat said is its most technically advanced mine haul truck, has a nominal capacity of 360 tons and an operating weight of 1,230,000 lb.

Caterpillar said the 797 truck was a clean-sheet design, or perhaps more accurately, a clean-screen design, as it went from computer models to rolling vehicles in less than two years.

"This was the first time we used extensive computer modeling for designing a truck," said Michael A. Flexsenhar, vice president of the Caterpillar Inc., and general manager of the Mining and Construction Equipment Division. "After the program was approved, the truck went from concept to production in just 18 months. It is also the most technologically advanced truck we have ever built. It has a tremendous amount of onboard computing power."

Caterpillar designed the truck in response to mining companies seeking a means to reduce cost per ton in large-scale operations. The 797 truck is sized to work efficiently with loading shovels in the 80 to 90 ton per pass capacity used in larger, high-production mining operations. Caterpillar will match the body design of the 797 to the material being hauled to optimize payloads.

Currently there are two 797 trucks undergoing evaluation at Caterpillar's Arizona proving grounds. Mine evaluations were scheduled to begin in the second quarter of 1999. The company plans to have 19 trucks out for evaluation on a "follow-up" basis by the end of 1999. Availability in North America is scheduled for 2000, 2001 for the rest of the world.

The truck will be assembled in Caterpillar's Decatur, Ill., facility, which according to Caterpillar has the capacity to build 150 trucks per year.

The 797 haul truck is the latest step in Caterpillar's impressive march in the heavy mining markets. Fifteen years ago, the company was not a player in mining. Today, Cat boasts a line of nine rigid frame haul trucks ranging from the 41.1 ton capacity, 485 hp 769D truck to the new 797. The company also offers a line of six, 260 to 405 hp articulated haulers with two- and three-axle designs and capacities from 25 to 40 tons.

As always, during the initial design study that resulted in the 797 truck, Caterpillar reviewed several drivetrain options, including diesel-electric, which is used in virtually all competitive truck models over 150 tons. When the final design was approved however, Cat chose to stay with its traditional mechanical drivetrain, which it said is 75 to 85 percent efficient in the 797 truck.

In viewing the new 797 at the product launch, Cat was, as always, reticent to disclose specific component suppliers. As is true in most equipment these days, many of the components for the new 797 were designed in cooperation with Caterpillar, with Cat retaining full product support responsibility. What follows is what we were told by Cat or observed at the launch.

The 797 truck is powered by the new Caterpillar 3524B High Displacement diesel engine rated 3400 gross hp. The aftercooled engine has four turbochargers and features Electronic Unit Injection (EUI) technology, allowing it to meet year 2000 emissions regulations, Cat said. While the bore is the same, the stroke is 25 mm longer stroke than the standard 3500 series engine.

The engine incorporates two Caterpillar 3512B engine blocks connected back-to-front by the crankshaft with a spring coupling. Each bank of 12 cylinders uses a single ECM, which communicates with a single master engine ECM. The engine is designed, built, tested, installed and serviced as a single unit.

"This truck is by far the most advanced truck we have ever built in terms of electronic control," said Darragh Rooney, commercial support, large mining trucks for Caterpillar. "There are 142 channels of data monitored at any given time while the truck is operating."

In addition to controlling the engine overall, the master ECM also interfaces with the other electronic systems on the truck. Electronic controllers integrate engine information with mechanical powertrain information to optimize truck performance, extend component life and improve operator comfort, Cat said.

"Having a proven engine (3500 series) was key to developing this truck in just 18 months," said Flexsenhar. "The bulk of the engine development was connecting the two blocks together and converting it for a mobile application."

Engine accessories include a hydraulically driven, variable speed fan designed to provide more efficient cooling as well as reduce fuel consumption and noise levels. The pump providing flow to the 107 cc/rev variable speed fan motor has a maximum displacement of 190 cc/rev.

# posted by Medical Information : 3:02 AM