Crawler Dozers: Smart dozers make the grade

The crawler dozer remains a staple on many construction sites. We take a look at the next generation of dozers to see what they offer in powertrain technology, undercarriage refinement, grade control, telematics, safety and operational comfort.

Key Insights for Buyers

Mid-sized dozers represent the bulk of industry sales and perhaps the widest diversity of application potential.
Many manufacturers are now incorporating an auto-shift feature designed to automatically match gear ratios to speed and load conditions as the machine’s operating environment changes.
Manufacturers continue to improve undercarriage design to enhance wear-resistance.
Integrated machine grade control enables an operator with only days of experience to achieve finish grades as quickly and accurately as an operator having years of experience.

Overview of crawler dozer market

The range of crawler dozers spans from relatively small utility models—such as the 74-horsepower Case 650M or the 80-horsepower John Deere 450K, both with operating weights less than 20,000 pounds—to those involved primarily in mining operations, such as the 890-horsepower Komatsu D-475-5 that weighs in at nearly 240,000 pounds, or the 850-horsepower Cat D-11T Carry Dozer with a blade capacity of 57 cubic yards, or the 757-horsepower, hydrostatically driven Liebherr PR776.

“While much of the dozer market tends to be polar, in that there is high demand in the smaller sizes and, seemingly of late, high demand also in large sizes, we are accommodating features and technologies in our development that deliver for both of those very different customer bases,” says Nathaniel Waldschmidt, product marketing manager, Case Construction Equipment.

“There is demand at the smaller end for machines that offer the same functionality and performance of their larger counterparts, but are easier to haul, are more agile on job sites, such as residential construction, and are more practical to [acquire] than something larger from a cost/investment perspective,” says Waldschmidt.

The lineup for most manufacturers with a broad range of crawler dozer models includes a mid-range of machines having horsepower ratings from around 130 to the mid-200s, with next smaller models usually dropping down to 100 horsepower or so, and the next larger models generally topping 300 horsepower. This mid-range category represents the bulk of industry sales and perhaps the widest diversity of application potential, which might include road/bridge work, residential/commercial construction, landfill, site clearing, and energy development.

Powertrain technology

Engines in crawler dozers, as engines in construction machines generally, have become ever more efficient, developing more power from smaller displacements and conserving fuel with high-pressure, common-rail fuel systems controlled by electronic systems that continually become more precise in metering fuel as load conditions vary. An “economy” operating mode further boosts fuel efficiency in some models.

“Today’s crawler dozer designs are aimed at improved productivity and fuel efficiency—without sacrificing one for the other,” says Sam Meeker, product application specialist, Caterpillar.

Along with improving fuel efficiency, dozer manufacturers also have been challenged in the recent past with developing systems for emissions control, and they have pursued various strategies for bringing engines into compliance: strategies tailored to the specific engine, its application, and customer expectations for performance.

“Due to emissions regulation, the focus on exhaust aftertreatment systems is a must,” says Nick Rogers, product specialist, Liebherr USA. “For our Tier 4-Final dozers, we were able to utilize SCR-only technology, eliminating the need for regeneration [of a particulate filter].”

Case’s Waldschmidt makes the point that the company’s new 650M uses a “maintenance-free” emission solution, using only a diesel oxidation catalyst: “no fluids, no regeneration,” he says. Other Case M-Series dozers, says Waldschmidt, employ SCR-only technology.

Another area of refinement is the drive train, and approaches here can differ from manufacture to manufacture, and often from model to model in a manufacturer’s range. John Deere, Liebherr, and Case (with its new M Series models), use dual-path hydrostatic drive for all models, employing a separate hydraulic pump and motor for each side of the tractor. Benefits cited by these manufacturers include eliminating the torque converter and power-shift transmission, infinite speed control, fast response to changing loads, and full power to both tracks during turns.

Komatsu uses dual-path hydrostatic drive in its smaller models (D37-23 through D61-23), but uses the company’s planetary power-shift Torqflow transmission in larger models.
Caterpillar uses a hydrostatic system for a number of its smaller models (including the D3K, D4K, D5K2, and D6K2) and a power-shift in larger models, some using a “torque divider” system that sends engine power to both the converter and directly to the power-shift transmission.

The Cat D7E, on the other hand, uses a relatively small 235-horsepower diesel to drive an electrical generator that sends electrical power to an inverter and then to the tractor’s propulsion module, which houses two large electric motors, geared together, that drive a conventional differential steering system.

Most Dressta models use a 3F/3R countershaft power-shift transmission and a modular two-speed steering system that uses planetary gear sets to effect a 30-percent speed differential between the tracks, allowing for gradual, full-power turns and six speeds forward and reverse.

Manufacturers seem to continually refine the power-shift transmissions in dozers, many now incorporating an auto-shift feature designed to automatically match gear ratios to speed and load conditions as the machine’s operating environment changes.

For added efficiency, some power-shift transmissions also use a lock-up torque converter, which provides the efficiency of direct-drive operation in higher gears.

“Advanced powertrains help improve productivity and fuel efficiency, as well as help operators get more from the machine without having to think about shifting gears,” says Caterpillar’s Meeker. “The new D8T, for example, has a fully automatic four-speed transmission—18 percent more efficiency on about the same amount of fuel, or less in some applications, compared with the previous model.”

Power-shift transmissions in many instances are mated to refined differential steering systems—using hydrostatic technology in some instances—that allow the tractor to turn with full power to both tracks and with full blades. Some models use a clutch/brake steering system, but these systems also have become highly refined, such as that in the Cat D11, which uses multi-disc, oil-cooled steering clutches that are hydraulically applied and electronically controlled. Typically, dozer steering is conveniently controlled with a single lever, and some systems allow adjusting the response rate, based on individual preference or to match particular operating conditions.

Undercarriage refinement

Although refinement in the crawler dozer’s undercarriage might not get the press that, say, technical advances in engines might receive, manufacturers continue to improve undercarriage design. For example, given the importance of retaining oil in a sealed-and-lubricated-track (SALT) chain to prevent internal pin-and-bushing wear, Caterpillar has developed its own proprietary seals and uses only synthetic oil, which better resists break down in the pin-and-bushing joint.

In addition, the metallurgy of basic undercarriage components—sprockets, idlers, links, rollers—is being continually refined to enhance wear-resistance. Improvements that help extend the service life of these components is being driven, in part, by technology that is extending the life of perhaps the most vulnerable surface in the undercarriage—the outer diameter of the bushing. As bushings wear, they no longer properly match with the sprocket teeth, and overall undercarriage wear can accelerate.

John Deere, for example, has undercarriage systems that use the company’s SC-2 (Slurry Coat) bushings, which have a proprietary coating fused to the bushing. According to the company, SC-2 bushings can yield up to twice the life of conventional bushings. John Deere also has developed special seals for use with the extended-life bushings.

Another approach to extending bushing life is illustrated by Komatsu’s Parallel Link Undercarriage System (PLUS), which allows bushings to rotate as they engage the sprocket, thus minimizing friction. For larger tractors, Komatsu uses its Dual-Bushing system, which places a rotating bushing over the conventional fixed bushing. Case has two extended-life undercarriages, Max-Life and Ultra-Life, both of which employ concentric bushings at the chain joints.

Grade control and telematics

“Integrated machine grade control enables an operator with only days of experience to achieve finish grades as quickly and accurately as an operator having years of experience,” says Charles Murawski, product manager, dozers, Komatsu America Corp. “All blade movements are automatically controlled by the system as the operator travels around the site.”

As Murawski points out, automated grade control is among the chief technology advances in crawler dozers. Whether based on satellite-navigation systems or robotic total stations, grade control systems, in essence, allow the machine to follow digital instructions and to automatically perform the right function at the right location on the job site. The net result is attaining grades faster, more accurately, with fewer manual grade checks, and savings on fuel and machine hours.

Grade control systems for dozers are being continually refined, in the accuracy of grades achieved, range of capabilities, and ease of installation on machines. Some manufacturers’ systems—Komatsu’s “intelligent Machine Control” system, for instance—allow the dozer to work under automated control from the first rough cut to the finish grade. Also, some factory-installed satellite-based systems have become more machine-integrated, for example, by integrating antennas into the roof structure.

“As the industry’s adoption of machine-control technology continues to improve,” says Case’s Waldschmidt, “each OEM has aligned, in one way or another, with select technology partners. Every contractor, however, likely has a preferred technology provider. All of these factors start to affect the base price of iron that contractors buy, and raises questions: ‘Will I be able to sell it easily on the secondary market if it’s wired/plumbed for only one type of system? Will I be able to make this dozer work with the fleet and system we already have?’”

Recognizing the contractor concerns that Waldschmidt raises, Case, as have other dozer manufacturers, provides a “universal” system-ready, factory-integrated package for certain models that facilitates installation of any grade-control suppliers’ system.

Along with grade control, telematics systems have significantly increase the dozer’s “intelligence.” The telematics system allows the machine to report important information—location, hours, fuel usage, idle versus working time, fault codes, operator misuse—to assist fleet managers in achieving optimum value from equipment assets. Telematics systems also allow setting geo-fences for machines, giving an alert if a machine is moved outside of a prescribed area or if it’s being used outside of designated time frames.

Operator environment/serviceability

Komatsu’s Murawski notes that dozer refinement also includes two other important areas, operator comfort/convenience/safety and serviceability. Seemingly insignificant items, such as easily reached grease fittings and filters, reduce downtime, encourage good maintenance, and lower operating costs, he says.

Liebherr’s Rogers sums up what might be the direction that dozer manufacturers generally are pursuing in these areas.

“Visibility, for instance, is a very important measure to take into account when designing a machine,” he says. “Integrated ROPS and FOPS systems, large glass areas, rear camera options, and slanted side panels around the operator’s cabin all have a part in the overall safety and visibility of machines. Operator comfort, of course, is essential. The cab of the machine is the operator’s ‘office space,’ and ergonomic designs must focus on lowering fatigue potential and increasing overall comfort, convenience, and safety.”

And comfortable, easy-to-operate machines might have a further benefit.

“Contractors want to retain their trained dozer operators,” says Komatsu’s Murawski, “and machines that are powerful, easy to use, and provide operator comfort can be an incentive.”

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