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Hydraulic excavators, generally, have become extremely refined machines—most leaving little to be desired in terms of performance and operator amenities. So don't you wonder what must go through the mind of a company's engineering department when the marketing department, yet again, requests that the design of an existing machine be appreciably changed to "keep the product competitive"?
Komatsu's engineering department may well have faced the "how-do-we-make-it-better-this-time" issue when asked to refine the design of the PC200LC-6 (Dash-6), which has served the company well in the industry's popular 20-metric-ton class. We'd guess, though, that the company's marketing folks are pleased with engineering's efforts, because the new PC200LC-7 (Dash-7), compared to its predecessor, is definitely more productive, more comfortable to operate and easier to maintain.
We make these statements after having spent a couple of days in the dirt with the two machines during a CE field test, in which the pair worked side by side at trenching and truck-loading in a busy northern Illinois gravel pit. Regarding productivity, our study showed that the Dash-7, on average, had an edge of approximately 12 percent in this kind of basic dirt work. And in the process, the new model matched the fuel efficiency of the Dash-6; significant, we think, because the Dash-7 is running with more horsepower, considerably higher hydraulic pressures and a cleaner exhaust stack.
Our Dash-7-versus-Dash-6 field test took place in late May at the Thelen Co.'s operation in Antioch, Ill. Thelen, a supplier of aggregate and ready-mixed concrete, has a long-standing arrangement with Komatsu to provide facilities for machine evaluation.
In fact, we borrowed Dennis Zarnstorff, a machine operator for Thelen, as the guest operator for the test. He shared the controls with Art Hine, Komatsu's director of sales and marketing (Canada), who, like Zarnstorff, is an ace at running an excavator.
CE editors worked with Erik Wilde, Komatsu's product manager, hydraulic excavators, to arrange and conduct the comparison. Assisting with the evaluation was Tetsuhide Oka, a Japanese engineer doing a two-year stint in the United States for Komatsu. Wilde arranged for a new Dash-7 from Komatsu's demonstration fleet for use in the comparative testing, and rented a low-hour Dash-6 from a Komatsu distributor in Wisconsin. Komatsu's on-site service shop checked pressures and speeds to assure that both units were within specification.
Both test units were fitted with comparable digging arms, 9 feet 7 inches in length. Booms for the two are the same size, 18 feet 8 inches. During the test, the same heavy-duty Komatsu bucket, rated at 1.25 cubic yards, was switched back and forth between the machines. Both test units also were fitted with 31.5-inch triple-grouser track shoes, and each had a flow meter plumbed into its fuel system for measuring consumption during the test runs.
At the heart of both the PC200LC-7 and PC200LC-6 is Komatsu's HydrauMind hydraulic system and the company's 5.9-liter, six-cylinder diesel engine. The engines are essentially the same in both machines, except that net horsepower for the Dash-7 is up 10, to 143, and rated speed has been decreased slightly (50 rpm) to 1,950.
Engines in both models are turbocharged, but the Dash-7 is running with an air-to-air aftercooler, which cools intake air coming from the turbocharger and helps reduce oxides of nitrogen and particulate matter in the exhaust. Also, in the interest of a cleaner exhaust stack, the Dash-7 engine employs higher injection pressures and modified injection nozzles. The engine in the new model, says Komatsu, meets current emissions standards and also is "EPA Tier 2 ready." (The aftercooler also gives a boost to the Dash-7's fuel efficiency.)
So, the Dash-7, with a more muscular engine, can drive its twin, variable-displacement hydraulic pumps (similar to those in the Dash-6) with somewhat more power. And, although the overall design of the hydraulic system is identical for the two machines, modifications in the Dash-7 system yield more digging power and faster cycles.
Among the changes is a substantially higher maximum relief pressure in the Dash-7's implement circuit—5,400 psi—compared to 5,050 for the Dash-6, yielding more power at the bucket and arm. Bucket digging power, says Komatsu, is up 29 percent. Also, maximum hydraulic flow is up by about 4 percent, which can speed up low-pressure functions in the Dash-7's digging cycle. Relief pressure is up, too, in the Dash-7's swing circuit (4,190 psi versus 3,980 for the Dash-6), which combines with the design of a larger-capacity swing motor to yield around 5 percent more swing torque.
More powerful boom-lift cylinders, having a longer stroke and larger diameter, complement these basic hydraulic-system changes. The rod ends of the cylinders are pinned in relocated bosses on the boom, and the relocated pivots not only give the Dash-7 a leverage advantage for even more digging power, but also provide nearly 2.5 feet more vertical reach. The added reach, says Komatsu, is useful when pulling down a bank or wielding tools overhead, such as a shear.
To accommodate its higher digging forces, the Dash-7 understandably has a stronger boom and arm. The cross-sectional strength of the boom, says Komatsu, is increased 4 percent, and that of the arm by 31 percent, making these structures deeper (taller) than those of the Dash-6. Also, the pivot points at the boom-to-arm connection and at the boom-cylinder-to-boom connection have been strengthened by the use of larger cast-steel bosses, which also dissipate stress over a greater area.
Another significant structural refinement is the near doubling in height of the steel rails that make up the foundation of the revolving frame, or deck. This improvement, says Komatsu, considerably strengthens the Dash-7's deck and provides a more rigid structure that transmits less vibration into the cab. Complementing the sturdy new deck are redesigned, more pliant cab-mounting devices, which add a spring to the rubber-and-silicon-oil design of the Dash-6's mounts. Komatsu claims a substantial reduction in under-foot vibration with the new deck and cab mounts.
The Dash-7's cab is brand new and 14 percent larger than that of the Dash-6, says Komatsu, the result basically of squaring off the back. The Dash-7 cab doesn't look quite as stylish as that of the Dash-6, which has rear pillars that sweep forward into the roof, but the new design yields several operator-accommodating benefits. Besides more interior volume, the new cab also provides considerably more legroom (about 4 inches) and more seat travel (nearly 5 inches) to comfortably accommodate a wide range of operators.
In addition, straightening the back of the cab allowed the door to be made larger (it's both taller and wider) and the left rear-quarter window to be made notably bigger. The right side window also now has an expansive feel—wider, but also deeper, because Dash-6 controls that were housed in a panel at the window's sill have been moved and integrated into the Dash-7's new, wider control-lever consoles.
Add redesigned front pillars to the increased glass area of the new cab, and the Dash-7 provides the operator with impressively better visibility. According to Komatsu, blind spots in the circle of the seated operator's field of vision have been reduced from a total of 98 degrees in the Dash-6, to 64 degrees in the Dash-7.
The Dash-7 cab also is quieter; Komatsu calls it "super silent." We did a quick sound check with microphone-equipped headphones to get an idea of relative sound levels at the operator's ear. In the closed Dash-7 cab, with air conditioning off, levels at low idle, high idle and high idle over hydraulic relief were, respectively, 58.2, 65.6 and 66.5 dB(A). Comparable numbers for the Dash-6 were 66.3, 69.7 and 73.6. Among improvements Komatsu cites for lower sound levels are sound-attenuating material under the cab, in the engine compartment and behind the injection pump, a new seal between deck and cab, plus a new fan shroud.
Also new in the Dash-7 cab is a redesigned, multi-function, full-color monitor that's integrated into a vent panel in the lower right corner. A large display screen is easy to read and provides analog-looking digital gauges (complete with digital indicating needles) for monitoring critical systems. The new monitor has clearly identified buttons for often-used accessories (wipers, washers, travel speed, auto-deceleration and swing brake), and for the machine's four working modes—Active, Economy, Lift and Breaker.
We think the new machine's working-mode system is more straightforward than that of the Dash-6, which had five modes—Heavy-duty, General, Finishing, Lift and Breaker—that could be supplemented by selecting a sixth mode, Active, for increased engine speed and pump flow. The Dash-7's new monitoring system also allows in-cab programming of oil-flow settings for breakers and other attachments, reminds the operator when routine service is required and, of course, logs faults and displays error codes as part of its diagnostic function.
We've watched with interest over the past decade at how the hydraulic excavator has become increasingly more refined in terms of productivity, operator amenities, lowered maintenance, fuel efficiency and treating the environment kindly.
The progression of Komatsu's PC200LC-6 to PC200LC-7 status serves to illustrate the point. Comparing the two models, the items that stand out most in our mind are the increased power of its basic HydrauMind hydraulic system, and the practical refinement of its operator environment.
The latter encompasses not just more room, automatic air conditioning, more glass and the like, but also what we see as a step toward simpler operation. The newly designed working-mode system is straightforward and easy to use, yet allows expanded capabilities. And the new monitor, which places more control and more information literally at the operator's fingertips, appears to us as simpler in design and more intuitive to use. Being both better and simpler seems a good thing.
