Productivity is the primary driver pushing dozer performance, but safety, reliability and operator comfort have increasing influence in steering dozer design trends
By Russell A. Carter, Managing Editor
For a machine that, not too long ago, featured cable-operated blade controls, an open-air operator’s station sprouting thickets of levers and clutch pedals, and not much else but brute power and noise, the crawler bulldozer has come a long way from its 1920s origins as a modified farm tractor. In particular, the last four decades have seen a steady escalation in mining-class dozer power and technology, starting with the introduction of 500-plus-horsepower crawlers from Allis Chalmers in the late 1960s, followed by Komatsu’s 620-hp D455A in the mid-1970s, and Caterpillar’s introduction of the D10 in 1978, the first model fitted with Cat’s elevated-sprocket “high drive” system.
Today, the large-dozer market is dominated by Cat—having sold more than 100,000 of the high drive machines worldwide—and Komatsu. Liebherr has made interesting advances in bulldozer drive technology, offering the world’s largest hydrostatically driven crawler tractor (more on this in next month’s issue, highlighting German mining technology), and Deere sells a large number of smaller machines, but the Cat D10T, D11T and D9T, along with Komatsu’s D375A-5E0 and D475A-5, along with the rarer Cat D11T CarryDozer or Komatsu D475A-5SD Super Dozer, are the machines most often seen at mine sites. Komatsu also offers the D575A-3SD, a 336,420-lb, 1,150-hp behemoth fitted with a 90-yd3 blade, compared with the D475A-5SD’s 890 hp and 58.9-yd3 blade, and recently introduced a successor to the D375A-5E0.
Cat’s Elevated Drive Endures
Cat has evolved the original D10 design through a series of model upgrades including the D10N in 1986, followed by the D10R in the mid-1990s. The current D10T, introduced in 2004, is driven by a Cat 12-cylinder C27 diesel, with power applied to the tracks through an electronically controlled powershift transmission. The D10T retained the elevated final drive system, as did the T version of the D11, which was unveiled in October 2007, and the company has shown no indication that it plans to move away from this design for its large dozers in the foreseeable future. Among the benefits listed by Cat for high drive are improved productivity, a modular design that allows rapid changeout of drive train components that can be preassembled and tested before installation, better operator efficiency due to improved visibility and ride comfort, and quick disassembly of major tractor components for easier transport by truck or rail.
In the T series, Cat streamlined the cab layout by replacing some control levers with electronic switches, and further improved operator visibility by making the cab windows larger, tapering the hood and narrowing the single-shank ripper carriage. Other enhancements included an Advisor Monitoring System that provides onboard diagnostics, displays key machine operating information, and allows the operator to set and adjust various features including blade response, blade float, auto blade pitch and spread rate. An optional AutoCarry feature on the D10T provides automatic blade control while the tractor is carrying a load, enabling higher productivity in situations in which the carry distance is more than 100 ft.
Other available features in the T series dozers include a hydraulically powered access ladder, along with a rear platform and larger fuel tank to provide easier and safer access to the cab and rear areas of the machine. This setup is currently available on the D11T and will become available on the D10T in late 2010. Improved visibility features available on the D9T, D10T and D11T provide cameras and mirrors to increase operator visibility around the machine. A slope and stability monitor feature available on the D10T and D11T displays machine slope and side-slope indications on the Advisor Monitoring System screen.
Operating weight of the D11T is 230, 581 lb (104,590 kg); for the D10T, it’s 146,499 lb (66,451 kg). The D11T CarryDozer (CD), a specialized model used mostly in bulk earthmoving applications, has an operating weight of 249,122 lb (113,000 kg). The CD’s frame and blade are built specifically for carrying—not pushing, as with conventional dozers—material long distances, and the CD’s front end is built to handle the higher frame loads generated by the machine’s 22-ft-wide, 9-ft-high blade, designed to carry up to 57 yd3 of material. Cat estimates that in the proper application, a CarryDozer will be 10–15% more productive than a standard D11T with a U-shaped blade.
Komatsu’s Latest is Versatile, Productive
Komatsu’s newest dozer, the D375A-6, was conceived and developed to meet the expectations of a wide, knowledgeable and critical customer base—mine operators, heavy-construction contractors, quarry operators and industrial establishments. Introduced in September 2009, the -6 supersedes the D375A-5E0, which was generally regarded as a reliable, fuel-efficient dozer that could benefit from additional productivity. Consequently, throughout the -6’s development cycle Komatsu paid close attention to preserving the strong points of the -5E0’s design while adding additional power and performance capabilities.
Komatsu recognized early on that a dozer in this size class had to be versatile enough for production and utility dozing in a variety of applications, but also must have a set of features and options that would appeal strongly to its mining clientele. Rich Smith, Komatsu America’s product manager–mechanical drive equipment, explained to E&MJ that, in order to identify the major issues and features that should be addressed on a new dozer model, he and a group of Komatsu engineers conducted face-to-face surveys with individuals and groups prior to the design effort, with participants ranging from owners to operators, operations managers to maintenance supervisors, and even purchasing agents from companies that consider bulldozing an essential part of their operations.
The face-to-face approach, said Smith, was essential to ensure that the results were valid and that participants fully understood the questions. The survey sessions were followed by open discussions to determine if any important issues had been overlooked by the survey.
The result, according to the company, is a dozer that has more horsepower, greater tractive effort and faster carry speeds than its predecessor and its main competitor, is versatile enough to competently handle tasks ranging from trap loading to a shovel, dragline and dump assistance, stripping and roadbuilding to stockpile maintenance, yet offers the prospect of even greater reliability than the -5E0 through implementation of a number of features used on Komatsu’s next-larger dozer class, the D475 series. Smith estimates the new dozer is about 8% more productive than the -5E0.
Approximately six tons heavier than the D10T with an operating weight of almost 158,000 lb (71 640 kg), and powered by a 610-net-horsepower Komatsu SAA6D170E-5 turbocharged and aftercooled diesel, the D375A-6 has 85 more hp than the -5E0, and retains that machine’s lockup torque converter feature essentially allows a direct-drive connection between the engine and transmission for more efficient use of engine power, particularly on long passes. For utility dozing in which maximum power isn’t necessary, an economy work-mode setting reduces engine output to save on fuel consumption.
For general dozing, the operator can use the transmission’s automatic gearshift mode which downshifts on its own when a load is applied and upshifts to a preset speed when the load is removed. When ripping, the operator can select manual shifting, which again downshifts automatically when load is applied but does not upshift when the load lightens. An automatic shoe slippage control senses when the track shoes start to slip under heavy load while ripping, and adjusts engine output accordingly to avoid the damaging effects of slippage, which can accelerate undercarriage wear and increase parts and maintenance costs. This feature also eliminates the need for the operator to constantly work the deceleration pedal during ripping and consequently reduces operator fatigue during extensive ripping operations.
Critical drive-train parts have been strengthened to handle the increased horsepower on the -6, and primary power train components are sealed in a modular configuration that allows them to be removed and replaced without oil spillage. The undercarriage employs the improved eight-roller, “K-Bogie” design used on the larger D475 series, which increases the length of track on the ground and also provides an extended range of track-roller vertical travel. This setup, according to Komatsu, provides exceptional ride comfort, reduces overall impact loads on undercarriage components and extends the service life of these components, because track rollers remain in constant contact with track links.
The -6’s blade profile has been modified to more closely resemble that used on the D475 series, and the blade shoulder angle raised to reduce spillage over the blade corners. The -6’s hydraulic system has been upgraded and uses the higher efficiency, more reliable piston-type pumps used on the D475 series rather than gear pumps.
Other improvements on the -6 range from those that are highly visible, such as latching, dual insulated gull-wing engine side covers for better maintenance access, to a new, multi-lingual and easily readable LCD color monitor in the pressurized, hexagonal-shaped cab. Less visible up-
grades include, among others, an increase in alternator rating from 60A to 90A and tougher wiring harnesses.
A long list of mining-specific features on the -6 can be traced directly to the results of the pre-design survey, according to Smith, and include items ranging from standard work lights at the front, back and engine bay of the machine, to an uninterruptible power source in the cab that allows radio communication at all times. Manual engine shutdown switches are located in the cab and at the rear of the machine, and a battery/starter isolator box on the side of the dozer also includes a jump-start connection. The mining specification-equipped -6 also comes standard with structural features that allow future installation of access platforms without need of physical modification.
Remote Control Systems
Operating a bulldozer, despite all of the mechanical and electronic improvements made over the years, can still be an uncomfortable and sometimes dangerous job, particularly when working near highwalls, on steep slopes or stockpiles. Both Cat and Komatsu are in various stages of development and commercialization for their respective remote control systems.
In September 2008, Cat announced that it had embarked on a two-phase program to implement remote control on its dozers. The first phase was aimed at developing a line-of-sight system employing an over-the-shoulder control console that removed the operator from the cab in hazardous situations, and the second phase involves wireless audio and video, with control data beamed to and from a dedicated operator station (see E&MJ, November 2009). According to Cat, field trials of its line-of-sight system are currently under way, and commercial availability is scheduled for late 2010.
The line-of-sight basic system features a remote console from which an operator can perform just about all machine functions including engine startup, acceleration, deceleration and shutdown; shifting, steering, directional control and braking; blade and ripper control; and auxiliary functions such as lights and horn. Critical information normally displayed in the cab (in gauge clusters and on display panels) is replicated on the remote console. The basic system can be used on any D10T, D11T or D11T Carry Dozer.
Komatsu has offered remote-control capability for dozer operation since 1977, and is currently on its third-generation remote control system, which the company says can be installed on almost any Komatsu earthmoving machine without need of physical modification. This system also employs a shoulder-harness control console that provides proportional-control levers and switches to conduct most machine functions, and has been used mostly recently on D575-class machines working in Australian bauxite operations, along with D375-class dozers in some North American coal applications.
A very general rule of thumb during the past few decades of bulldozer development is that maximum machine power, weight and productivity have increased about 10% every 10 years. It’s unlikely that, given the current capabilities, job requirements and other factors involved in dozer design, usage and purchasing trends, this rate of advancement will continue—and if it doesn’t, what areas of dozer performance can customers focus on to gain productivity increases on their own?
Not surprisingly, Caterpillar has devoted quite a bit of study to this question. As always, the first step in optimizing machine performance is to pick the correct dozer for the job conditions and requirements. Caterpillar’s advice on determining just how much material a bulldozer can realistically push begins with understanding basic dozer principles, such as:
Weight—A tractor can’t push more than it weighs; it’s limited by the coefficient of traction.
Coefficient of Traction—The percentage of the tractor’s weight the tracks can push for a given material, before a track begins to slip. This is in the area of 60% on average for most materials. In loose sandy material, it could be as low as 30%. Tractor weight times the coefficient of traction will equal about what the tractor will push-carry.
Carry Force Ratio—The energy it takes to push a given material over itself; usually about 10%.
Material Density—If the material is dense, the volume of material the tractor can push will be relative small. If the material is light in weight, the volume will be larger.
Blade Capacity—Should correlate to material density.
Slope—Is equivalent to gravity. Downhill slopes will add capacity while uphill subtracts capacity.
So, with these factors in mind and given two different dozers of equivalent weight and power—but with, say, blades of different capacity—how do you determine which could be more productive? The three-word answer, according to Cat, is Big Load Slow; that is, a machine with a larger blade, making fewer but higher-payload passes, will be more efficient than an equivalent machine with a smaller blade, making quicker passes but with smaller blade loads. Although the smaller-bladed machine will have faster cycle times, it will also spend more time in reverse, which is not beneficial to productive dozing.
In one typical mining scenario evaluated by Cat, one machine dozed at an average speed of 1.5 mph and another at an average speed of 1.8 mph. The operator with the faster dozing speed racked up more cycles, but a comparison of blade load showed that the slower-moving machine had an average load of 45 yd3 vs. 36 yd3 for the faster dozer. After adjusting for differing push distances, calculations showed the machine with the larger blade load provided 5% more production than the faster moving, less heavily loaded machine.
A 5% difference may not seem like a significant improvement, but it adds up: For example, taking into account two machines, one with production of 1,952 loose yd3/hr and another with 1,855 yd3/hr; multiplying that hourly rate to get a daily production rate of 46,648 yd3 and 44,520 yd3, respectively; then applying a 0.75 efficiency factor to each, the resulting monthly production figures for each would be 1,054,080 yd3 vs. 1,001,700 yd3. The difference is an extra 52,380 yd3 per month.
Another factor to consider here: The lighter-loaded, faster-moving dozer will travel significantly more distance than the more heavily loaded machine to accomplish the same job, and consequently will incur a considerably higher amount of undercarriage wear in the process.
Ultimately, however, the biggest productivity payoff may come from proper operator technique. Another Cat study showed that after operator training in efficient, correct dozing methods and a refresher course in how to effectively use the machine’s onboard earthmoving-software information display, dozer productivity at the mine site improved by almost 25%.