Caterpillar goes from a C to a D with its mini excavators

  • 24-Nov-2010 01:46 EST
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The implement hydraulic system of the D Series excavators offers low-effort pilot controls for optimum control and fast cycle times. In addition, Cat says refined main valves for the 305D CR and 305.5D CR (shown) further enhance hydraulic controllability.

Caterpillar describes its new line of D Series mini hydraulic excavators—303.5D CR, 304D CR, 305D CR, and 305.5D CR—as versatile, compact-radius machines suitable for work in confined spaces and built on the strength of its C Series predecessors. With model designations that essentially reflect their operating weights—3.5 to 5.5 t (4 to 6 ton)—the machines are said to feature enhanced stability for greater productivity, a redesigned work-tool coupler, load-sensing hydraulics, and engines that meet U.S. EPA Tier-4 Interim and EU Stage-3A emissions regulations.

Models 303.5D CR and 304D CR are zero-tail-swing machines that keep the radius of the upper body within the width of the tracks; models 305D CR and 305.5D CR are compact-radius machines that limit upper-body tail swing over the tracks to 5.5 in (140 mm) or less. Both designs reduce the machine's operating footprint, simplifying workload.

Increased-width undercarriages for the 303.5D CR and 304D CR and heavier counterweights for the 305D CR and 305.5D CR are said to contribute to enhanced machine stability, allowing increased lift capacity, more effective use of reach and digging forces, increased capability when handling heavy work tools, and improved machine balance.

A new pin-grabber-type coupler (with new optional hydraulic operation) combines positive work-tool retention with a design that maintains tight tolerances between coupler and tool, significantly reducing wear.

A standard-equipment two-mode auxiliary-hydraulic system, complete with lines and quick connectors, can be switched between single-direction and bidirectional operation for effectively using work tools ranging from hydraulic breakers to augers. The implement hydraulic system is a responsive, load-sensing system resulting in low-effort pilot controls for optimum control and fast cycle times. In addition, refined main valves for the 305D CR and 305.5D CR further enhance hydraulic controllability.

Similar to large excavators, D Series booms feature a curved design for digging flexibility and fabricated-box construction for strength and durability. The independent-swing boom allows digging next to walls and obstructions, and an optional long digging arm for each model increases digging depth and lift height.

Digging arms also are equipped with brackets to facilitate installation of a hydraulic thumb, and relief valves for the thumb are built into the main valve. Boom and digging-arm cylinders are end-dampened to reduce shock loads and material spills, and bucket rotation of more than 200° contributes to improved material retention at height and makes flat-bottom trenching easier with less repositioning.

A standard-equipment dozer blade on the D Series simplifies backfilling and cleanup chores. A float function allows the blade to follow ground contours with no operator correction. An optional angle-dozer blade, which can be angled 25° to either side, further expands blade versatility.

D-Series models are available with a two-post canopy operator's station or with an optional enclosed cab that can be equipped with air-conditioning. The sealed cab has standard features such as an efficient heater/defroster/ventilation system, sliding-door system for confined-area access, retractable front window (with gas-strut assist), removable lower-front window, sliding side window, and a radio-ready package.

Specific to the operator, the cab is equipped with a suspension seat, adjustable wrist-rests, ample legroom, and redesigned controls. The boom-swing function is incorporated into the joystick controllers, and auxiliary-hydraulic controls also are positioned in the joysticks. An in-cab control allows switching the joysticks between an excavator and backhoe-type control pattern.

An automatic two-speed-travel feature shifts the drive system to meet changing torque and speed requirements, and a low-speed switch keeps the drive system in low range for precise-grading operations if desired. An automatic engine-idle feature reduces engine speed when hydraulic functions are inactive for four seconds, saving fuel and reducing sound levels and emissions.

Extended routine-service intervals for D Series models save time and reduce operating costs: oil-impregnated sintered-alloy bearings in the boom and digging-arm linkages require grease only at 500-hour intervals; engine-oil changes are extended to 500 hours; and the hydraulic-oil change interval is 3000 hours. A Cat S.O.SSM fluid-sampling port for hydraulic oil allows accurate, periodic assessment of fluid condition during its life.

A side-lifting hood allows access to the air filter, main control valve, auxiliary-hydraulic flow selector, fuel filter, and hydraulic tank. The swing-out rear door provides an easy reach to engine-oil check/fill points, vertically mounted engine-oil filter, starter motor, and alternator. In addition, the radiator and oil cooler are positioned for easy cleaning.

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