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| Largest Cat mining truck  First as the 797, then as the 797B, the design of the largest Cat mining truck has proven its productivity, durability and low cost of operation through more than 10 years of service in the world's most challenging mining operations. Now, the 797F, with 4,000-horsepower and rated payload capacities to 400 tons, combines the strengths of its predecessors with a new engine, redesigned operator station and custom body systems to deliver even lower costs per ton—with less environmental impact. The 797F also offers easier maintenance and enhanced safety provisions. Ground level service points ease access, and 1,000-hour hydraulic filter service intervals reduce required maintenance. Safety enhancements include wider walkways, a rear access ladder and a bumper-mounted, three-way, lock-out tag-out box. The 20-cylinder, 4,000-gross-horsepower Cat C175-20 ACERT engine has a single engine block and is the heart of the new truck. The engine has accumulated more than a quarter-million hours of field testing in mining trucks and power-generating systems. The C175 displaces 5.3 liters per cylinder—for a total displacement of 106 liters. The 797F develops 450 horsepower more than its predecessor, the 797B, which used a 24-cylinder Cat 3524B engine displacing 117 liters. The cross-flow engine design uses four turbochargers, an air-to-air aftercooler and an electronically controlled common-rail fuel system, which precisely delivers multiple injections in a single combustion event. These electronically controlled systems account for much of the high power density and low emissions and contribute to the 797F fuel efficiency and responsive performance. The engine meets EPA Tier 2 emissions standards. The engine-cooling system, also electronically controlled, uses the engine cooling fan only as needed, which conserves power and fuel. The engine control module, the Cat ADEM A4, has 50 times the computing power of its predecessor. The new module monitors more than 30 critical engine functions, drives the 20 fuel injectors and communicates more than 100 engine parameters that describe engine health and assist in diagnosing problems. A robust drive shaft transfers the immense torque of the C175-20 engine to the rear-axle-mounted, seven-speed planetary transmission, which delivers a smooth flow of power through the massive rear axle to double-reduction final drives. An integral lock-up torque converter enhances high speed performance and fuel efficiency. The Cat Electronic Clutch Pressure Control system effectively manages transmission-clutch operation under varying speed and load conditions, assuring that gear changes occur with no power loss and that clutch engagement is modulated to promote smooth shifts and long clutch life. A separate fluid system assures a dedicated supply of clean, cool oil for clutch operation and transmission lubrication. Transmission features include engine over-speed protection, downshift inhibitor (at high speeds) and programmable top speeds. The 797F integrated braking system combines three brake functions (primary, secondary and parking) with an automatic, hydraulically actuated retarder in a single assembly located at each wheel. These immense, oil-cooled, multiple-disc assemblies provide a total braking/retarding surface of 330 645 cm². An integral heat exchanger controls brake-oil temperature to maintain no-fade performance and to extend brake life. A robotically welded and ultrasonically checked frame incorporates nine mild-steel castings. The large radii castings are resilient to absorb frame flexing and ensure long life. The mild steel castings and fabrications provide flexibility, durability and resistance to impact loads, even in cold climates. Available for the 797F is a choice of four Mine Specific Design (MSD II) body options that can be used in conjunction with a configurable liner system to provide an optimal blend of payload capacity and durability in a given application. Customers can tailor body systems to production demands and operating constraints, and payload capacity can be as much as 20 tons greater in some instance than was available with the 797B. An angled, center-mounted instrument panel and a center console are the dominant features in the 797F new operator station. Analog-type gauges are quickly checked without losing sight of the haul road, and the integral Vital Information Management System (a powerful third-generation configuration) provides machine health and payload data, plus easy access to diagnostic and machine management information. The optional Road Analysis Control system monitors frame rack, bias and pitch—facts that can be used to make haul road improvements that promote quicker cycles, increased fuel efficiency and longer frame and tire life. Levers and switches in the console are comfortably positioned just forward of the right armrest to allow easy control with minimum effort. Two fully adjustable, air-suspension seats assure comfort throughout the work shift for both the operator and trainer, and newly designed front and side windows give a commanding view of the haul road and work areas. A wide stairway and walkway, plus guard rails, help to provide safe entry and exit, and wide-angle mirrors, body-raised indicator, body-retaining cables and reverse-neutralizer further promote safe operation. write your comments about the article :: © 2009 Construction News :: home page |