Wringing Huge Work Out of Compact ExcavatorsTag-trailered crawler excavators can expand a contractor into big-production jobsConstruction Equipment - February 1, 2006 More than 45 hydraulic-excavator models between 20,000 and 40,000 pounds compete for your purchase dollars. Enough money is being spent on machines this size that the scent of cash and desire to supply the big rental houses attracted no less than four manufacturers to field their first excavators in the size class over the past 30 months. 
Changes in frame design, boom mounting and weight distribution keep the boom and counterweight on reduced-swing-radius machines from extending more than a few inches beyond the track width. These machines can work within a single lane of traffic or up against buildings or road banks. (Source: Komatsu.) 
Nineteen of the 10- to 20-ton excavators available today — nearly half — are reduced-swing-radius, or zero-swing-radius machines like Hitachi's Zaxis. Recent innovation in this class of excavators has been dominated by introduction of reduced-radius machines. Four of the six models brought to market by new competitors Ingersoll Rand, Takeuchi, Terex, and Yanmar combine features in a way that's indicative of why the excavators in this size class can be King Kong compacts. They're nearly-100-hp machines with features common to compacts such as swinging (or articulated) booms, minimum swing radius, and options for rubber or steel tracks. Takeuchi's 31,500-pound TB1140, for example, is the largest excavator in the North American market whose standard equipment list includes a boom mounted to the upper frame at a hinge point like so many compact excavators. The swinging boom impinges on the machine's power somewhat (its lifting capacity over the idlers at a 20-foot radius with the load at ground level is comparable to machines that weigh a ton less). But a swinging boom allows the machine to dig a hole with sides parallel to its tracks the entire width of the machine without need for repositioning. Caterpillar, Komatsu, and Kobelco offer alternatives to the swing boom usually called offset boom machines. These units will also excavate parallel to the tracks the full width of the machine, but accomplish it with a boom that has two joints rather than mounting a rigid boom with a hinge to the frame. Optional offset booms on Cat's 314C and Kobelco's 135SRLC actually push the feature up to the 33,000-pound size range. Nineteen of the 10- to 20-ton excavators available today — nearly half — are reduced-swing-radius, or zero-swing-radius machines. The counterweight and boom on these machines extend only inches beyond the track width so they can work effectively in very small or congested areas without risk of swinging into obstacles. Manufacturers produce reduced-radius machines by installing a larger counterweight and changing frame geometry to preserve lifting and digging capacity. Most machines in the class were upgraded to the latest technology in 2003 and 2004 when they had to comply with EPA's Tier 2 emissions regulations. Reduced-swing-radius machines have dominated new introductions since then. "There is increasing demand in certain applications for zero swing machines to work in smaller and smaller spaces, while maintaining high outputs," says Dave Hardwick, excavator product manager at JCB. "The push to constantly reduce the build time on developments has increased the need for high output, high efficiency machines that can carry out large amounts of ground works and utility works every day." The heaviest reduced-radius excavator in this class is Komatsu's 36,400-pound PC158USLC-2. With an 8 foot-2 inch stick, it can pick up 8,700 pounds at a 20-foot lift radius. But reduced-radius excavators do sacrifice some digging and lifting leverage in order to get a shorter upper frame. Comparisons are telling. Komatsu's reduced-radius PC138USLC-2, at an operating weight just under 31,000 pounds, develops stick-digging force of 13,670 pounds. The conventional PC120LC-6 (3,200 pounds lighter) applies 13,890 pounds of stick-digging force. John Deere's reduced-radius 135C RTS, with an operating weight of 30,400 pounds, moves the stick with 12,800 pounds of force. The 28,800-pound 120C (1,600 pounds lighter) develops 13,172 pounds of stick force. "As customers continue to look for improved efficiencies in their business, smaller machines are asked to do more demanding jobs in a wider variety of applications," says Jason Williamson, excavator product manager at Caterpillar. "Machines in this size class are easy to transport and very maneuverable. They can be general purpose or dedicated machines and can be used in many different digging and tool applications." This dichotomy of expectations for 10- to 20-ton excavators — compact machines that transport on a tag trailer behind a dump truck but are capable of significant productivity — is underscored by a marketing emphasis on the efficient productivity of the current generation. "The data shows that even though Tier 2 machines were updated and power output was increased, fuel efficiency also increased," says Dave Pooley, excavator product manager at Hyundai. As an example, he notes that the R160LC-7 has 11 percent more horsepower than the Dash-3 machine it replaced, but its rated fuel consumption is 1.6 percent less. Horsepower didn't change in the R140LC with the Dash-7 version, but fuel economy improved 4.5 percent. As with most diesel-powered equipment, emissions regulations and the computer control of fuel injection necessary to meet exhaust limits paved the way for this sort of advancement in all excavator brands. Excavators squeeze all the benefit from digital control by coordinating a controller on the engine with one in command of the hydraulic pumps and motors. To illustrate how far control technology has come, consider Komatsu's PC160LC-7 compared to its predecessor, a nearly 3,000-pound-heavier PC150LC-6. The PC160 delivers 29 percent more bucket digging power and its arm-digging force and lifting capacity are both 11 percent greater. Electronic systems are also providing an unprecedented amount of quality information about the recent history of a machine's performance and operating problems. "The Deere Machine Information Center (MIC) is a data logger integrated into each machine," says Mark Wall, John Deere excavator product manager. "This data logger records machine information such as engine rpm, hydraulic oil and engine coolant temperature, pump pressures, machine alarms and codes, time spent traveling, time spent swinging, and idle time. The information can be transferred to a customer's computer via a Palm Pilot. Reviewing this information, the customer can make important decisions concerning his machine and application." Technology has not advanced effortlessly, however. "Most people agree the laws to improve the air quality are necessary, but we have seen in the past few years that the technology [necessary to satisfy air-quality laws] is outrunning the trained engine specialists and all too often the engine suppliers are not keeping on top of the distributor network to bring [training] standards up to where they should be," says Dave Pooley, excavator product manager at Hyundai. "Engines with computer control are the way of today and the future. Manufacturers have to cope with that and increase training programs and simplify the way information in the computer is downloaded and disseminated." Tier 3 will apply to the 100-hp and larger engines in this size class in 2007, so look for a spate of new-machine introductions and major line renovations later this year. Only a third of the excavators in the class have engines 100 horsepower or larger, though. Machines up to 100 horsepower will have to comply with Tier 3 emissions limits in 2008, so most of the excavators between 10 and 20 tons that have not yet been upgraded will likely get a major facelift before the end of next year.
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