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.
The 797 truck’s powertrain includes a new Caterpillar designed and built torque converter with a 27 in. lockup clutch designed to deliver high mechanical efficiency. The new Cat automatic-shift transmission features seven speeds forward and one speed reverse. Electronic Clutch Pressure Control (ECPC) technology smoothes shifts, reduces wear and increases reliability, Cat said, and large clutch discs give the transmission high torque capacity and extended life.
The transmission utilizes three hydraulic pumps - a gear-type charge pump with a flow of 72 gpm, a gear-type lube/pump with a flow of 129 gpm and a gear-type scavenge pump with a flow of 207 gpm. The transmission and torque converter enable the truck to maintain good speed up grades and to reach a top speed of 40 mph, Cat said.
The modular differential, also designed and manufactured by Caterpillar, is rear mounted within the axle to improve access for maintenance. The differential is pressure lubricated, which promotes greater efficiency and long life. Each final drive incorporates a nodular iron wheel for high strength and long life. Wide wheel beating spread reduces bearing loads and helps ensure durability, Cat said. A hydraulically driven lube and cooling system operates independently of ground speed and pumps a continuous supply of filtered oil to each final drive.
Oil-cooled, multiple disc brakes provide fade-resistant braking and retarding. An electronically managed Automatic Retarder Control (ARC) controls the brakes on grade to maintain optimum engine rpm and oil cooling, and it results in faster downhill speeds. An Automatic Electronic Traction Aid (AETA) uses the rear brakes to optimize traction.
A combination of constant displacement and variable displacement pumps delivers regulated flow of brake cooling oil for constant retarding capability and peak truck performance on downhill grades. The hydraulic pump for cooling the brakes has a volume of 80 cc/rev and produces a flow of 880 gpm at 1750 rpm.
The 797 truck fides on new Michelin 55/80R63 radial tires as standard equipment. This new tire was developed in conjunction with Caterpillar for this application.
The frame of the 797 haul truck is also a new design, incorporating mild steel castings that comprise the entire load-bearing frame for improved durability and resistance to impact loads. The nine major castings are machined for precise fit before being joined using a robotic welding technology designed to ensure full penetration welds. The frame design also reduces the number of weld joints, Cat said.
“Reducing the number of weld joints is significant to frame construction,” noted Rooney. “Weld joints are the primary location of cracks and frame breakage. Reducing the number of joints increases frame durability. The design also allows engineers to place these joints away from stress areas.”
The suspension system uses oil-over-nitrogen struts similar to other Caterpillar mining trucks. The rear suspension has a four-bar linkage configuration designed to dissipate haul road and loading impacts directly into the frame.
The hoist hydraulics on the new truck includes an electronic hoist control, independent metering valve (IMV) and a large hoist pump that provides a flow of 290 gpm at 1750 rpm to the two-stage, 13.5 in. bore hoist cylinders. The system allows automatic body snubbing for reduced impact on the frame, hoist cylinders and operator and also allows the operator to modulate flow and control over-centering when dumping.
The cab of the 797 truck is engineered to reduce operator fatigue, enhance operator performance, and promote safe vehicle operation. The cab includes two full-sized ISRI air suspension seats, allowing the trainer to work with the operator. The controls and layout provide greater operator comfort and an automotive feel while enhancing functionality and durability, Cat said. The cab and frame design meet SAE standards for rollover and falling object protection.