Komatsu Loader Trades Gears for Fluid Power

The old adage says that we shouldn't tamper with success. That thought may have crossed the corporate mind at Komatsu when the company decided to significantly change the design of its WA250-3 wheel loader. This 3-cubic-yard machine (competing in the most popular size class of the wheel-loader

market) had proved a good-selling, reliable workhorse during its seven-year stint in the Komatsu line. Yet, looking to further sharpen its competitive edge in this important market segment, Komatsu opted to make extensive engineering changes in the machine, the WA250-5,which was announced about eight months ago.

The WA250-3 (the "Dash-3"), which is displaced by the new model, was part of Komatsu's "Avance Plus" generation of equipment. It was rated at 131 net horsepower, offered bucket sizes from 2.5 to 3.5 cubic yards and had an operating weight of about 25,500 pounds. The new WA250-5 (the "Dash-5"), now part of Komatsu's next-generation "Galeo" concept, has 134 net horsepower, the same range of buckets and virtually the same operating weight. So, in terms of basic size, the new Dash-5 hasn't changed much.

The new model also retains its predecessor's basic engine, front and rear frames, axles (but with stronger brakes) and loader linkage. But don't be misled by this long list of common specifications and shared components. The Dash-5 really is a significantly different machine than its predecessor.

Says Komatsu's product manager Bob Post: "If you're comparing this tractor to its predecessor, you have to get the operator in the seat, because the specifications don't look that much different."

CE editors recently had the chance to look beyond the specifications when evaluating the design and performance of the new model, relative to its predecessor, at a large quarry near Antioch, Ill. Komatsu has a machine-test staff and a well-equipped shop at the Antioch quarry, which is owned by the Thelen Co., one of northern Illinois largest aggregate and ready-mixed suppliers. We worked with Komatsu's Post, principal engineer Chris Monaco, test engineer Pete Stoneberg and Thelen operator Wayne Zembal.

Our Dash-5 test machine was part of Komastu's demonstrator fleet, and the Dash-3 was a low-hour rental unit from a Komatsu dealer in Iowa. Both machines were fitted with a 3.0-cubic-yard bucket, with a bolt-on cutting edge, and 20.5R25 radial tires.

Quick look at results

Details of our comparative testing can be found throughout this report, but here's the thumbnail version. During the V-cycle truck-loading comparison, Zembal used each machine to three-pass load tandem-axle dump trucks. Since we were using two trucks, we considered the six loading cycles required to fill them a "set." From set to set, Zembal was asked to vary the machine's cycle time and the distance it reversed from the pile, thus simulating a range of loading techniques.

When we averaged the projected production numbers and fuel-consumption numbers for each machine's complete range of sets, the Dash-5 proved about 4 percent more productive, and around 13 percent more fuel-efficient. When we compared only the highest-speed/shortest-distance loading sets, however, (the way most comparative loader testing is done) the Dash-5 was about 13.5 percent more productive and a whopping 50 percent more fuel-efficient.

In a 150-foot load-and-carry comparison, the new model approached a 5-percent productivity advantage and was nearly 29 percent more fuel-efficient. When Stoneberg ran the machines in a hill-climbing comparison, the WA250-5 reached the top about 11 percent faster than the WA250-3 when the implement-hydraulic system was not engaged, and about 6 percent faster when it was.

Having watched the machines work for two days, and having had the opportunity to run both units, our overall impressions of the new model centered on two characteristics: its notable gains in fuel-efficiency over the WA250-3, and its operating smoothness, even when aggressively digging in a stockpile.

Fluid power, not gears

These noted qualities, for the most part, are the result of the WA250-5's new hydrostatic drive system, often called a hydrostatic transmission. The new drive system replaces the torque converter and powershift transmission used in the Dash-3. The new model's 5.98-liter Komatsu engine, now using air-to-air charge-air cooling to meet Tier-II emissions standards, drives a variable-displacement hydraulic pump, which, in turn, powers a pair of variable-displacement hydraulic motors. The motors are mounted to a transfer case, from which the Dash-5's conventional axles are powered via conventional drive shafts.

The new drive system, which eventually will be used in the Dash-5 versions of the WA250's companion models—WA120, WA180 and WA320, has a couple of engineering twists that go a long way toward enhancing machine performance and operator control.

To wit, the drive motors, although identical, are tagged as a low-speed unit, which is linked to the transfer case via a clutch, and a high-speed unit that drives directly into the transfer case. When the machine requires lots of torque at the wheels, pushing into a stockpile, for instance, both motors are driving. But when torque requirements lessen, the system automatically declutches the low-speed motor and sends all the pump's flow to the high-speed motor. Taking the low-speed motor out of the loop when it's not needed boosts the drive system's efficiency and saves fuel—lots of fuel.

The operator also has manual control over the low-speed motor with the Traction Control System switch on the instrument panel. When the loader is in a situation where wheel-slip might be a problem—in sand or on wet surfaces, for instance—the operator can engage the traction-control system (thus declutching the low-speed motor) and reduce by half the amount of tractive effort delivered to the wheels.

Controlling ground speed

Also on the panel are two dials for the Variable Shift Control system. The top dial has four settings, and the lower has multiple graduations on a scale that reads from "1" to "2." In essence, both of these dials control the Dash-5's ground speed by generating electronic signals that adjust oil flow through the drive system's pump and motors.

The top dial, with its four settings, allows the operator to equate machine ground speed with the speed ranges of a conventional powershift transmission. For more precise control, when the top dial is in the "1" position, the operator can use the lower dial to further tune ground speed.

It's possible, says Komatsu, to match the WA250-5's ground speed so exactly with the speed of hydraulic functions, that the operator need not lift his foot from the accelerator when loading trucks. When approaching the truck with the throttle open, the machine's forward movement can be slowed—or stopped—with either the right or left brake pedals, which function basically like conventional transmission disconnects. This technique keeps engine speed continually high for optimal boom and bucket speed.

But if the operator is more comfortable lifting the throttle when approaching the truck, as did Zembal, then the dynamic-braking capability of the Dash-5's hydrostatic system takes over and brings the machine to a gentle halt while the bucket dumps. (Dynamic braking results from resistance offered by the hydrostatic transmission when power is removed.) Operating with this technique, says Zembal, eliminated the need to use the brake at the truck.

The Dash-5's brake pedals, which are interconnected, should be used, though, says Komatsu, for "inching control." If either of the pedals is depressed to just above its braking point, extremely slow ground speeds are possible while the engine is running at rated speed. This allows sufficient hydraulic flow to attachments—such as a pavement-profiler, broom or snow blower—while limiting machine speed to a pace that allows efficient attachment performance and control.

Another control feature built into the new hydrostatic drive system is an "overrun prevention" system, designed, says Komatsu, to protect power-train components and brakes when the machine is operating on steep grades. The system senses travel speed during downhill operation and cautions the operator (with a light on the panel) at 25 mph. If the operator doesn't reduce speed, the system, at 26 mph, automatically restricts fluid flow through the hydrostatic components and slows the machine.

Easier on operators

Along with these fundamental drive-train changes, which result in giving the operator more precise control of the machine, Komatsu also invested considerable engineering effort enhancing the operator's environment.

For starters, the cab is 5 percent larger than that of its predecessor and, says Komatsu, it's also considerably quieter. The company publicizes an in-cab sound level of 70 dB(A), but Komatsu test data show a reading of 67.3 dB(A) for the Dash-5 at high idle with the doors closed, compared to 77.1 dB(A) for the Dash-3.

Design changes that contribute to reduced sound include a 400-rpm drop in engine speed (to 2,000 rpm), viscous cab mounts that absorb vibration, rubber-cushion mounting of major components, improved cab sealing and a new hydraulically driven fan. The new fan, part of a completely redesigned cooling package for the Dash-5, accounts for perhaps 4 dB(A) of the total reduction.

The single-lever loader controller (Komatsu calls it a multi-function mono lever) is pilot-operated, but so it was also on late models of the Dash-3. The Dash-5's lever, though, has a rocker switch on top, allowing directional changes with your thumb. But to accommodate operator preference, the conventional shift lever remains at the left of the steering column. The steering column tilts (the Dash-3's didn't), and the two spokes of the wheel are positioned to allow an uncluttered view to the new Equipment Management Monitoring System (EMMS).

The new EMMS provides analog gauges for speed, fuel level, coolant temperature and hydrostatic-oil temperature. Flanking the gauges are icons that, among other information, provide warnings for axle-oil temperature, brake-oil pressure and hydrostatic filter restriction. At the bottom of the EMMS is an LCD that serves as an hour meter, odometer, service reminder and trouble-shooting guide.

Visibility is good from the seat of both the Dash-3 and Dash-5, but somewhat better on the new model, thanks to the vertical windows Komatsu has placed in the side panels of the cab's rear pillars. Rearward visibility is improved, too, by the new model's sloping hood. (For serviceability, the Dash-5 uses flat glass (not curved), which is available from local sources.) And, a small—but notable—design change for the Dash-5 is its staircase-type (slanted) entry ladders, which make entering and exiting the cab more comfortable than the Dash-3's vertical ladders.

Service and reliability changes

The cooling system in the Dash-3 used stacked cores, positioned between the rear grill and the cooling fan, which was at the rear of the engine. All that's changed on the Dash-5. A new, high-efficiency, hydraulically driven fan resides now in a swing-out compartment at the very rear of the machine, just behind the machine's swing-up rear grill. The radiator, hydraulic oil cooler and charge-air cooler sit side-by-side just forward of the fan, and all are of aluminum construction. The new cooling system, says Komatsu, is efficient, readily accessible, and easy to clean.

The Dash-5 also incorporates a number of design enhancements aimed at serviceability and reliability. Its new radial-seal air cleaner, for instance, simplifies element changes and eliminates concern about improperly seated gaskets. A new buffer ring, positioned behind the dust seal and rod seal in the packing gland of the Dash-5's hydraulic cylinders, reduces stress on the main seals and, Komatsu says, may promote up to 30 percent longer cylinder life.

Another hydraulic-system change is the use of flat face-to-face O-ring seals in the hoses, a feature that promotes a dry machine, says Komatsu. And in the electrical system, new connectors, says the company, more effectively seal against dust and corrosion. New seals in the drive shafts allow pushing the greasing interval from 1,000 to 4,000 hours, and the engine-oil interval is now officially set at 500 hours, versus 250 for the Dash-3. But, says Komatsu's Lee Haak, wheel loader product manager, users would be smart to approach this extended interval in steps, accompanied by a good oil-sampling program. Komatsu can't control the oil and filters an owner might use, says Haak.

Summing up

Operator Wayne Zembal noted four characteristics of the new WA250-5 that, in his opinion, give it an edge over its predecessor. The Dash-5, with its hydrostatic drive system, he says, is a smoother-operating machine, and it's also considerably quieter. But, along with its smooth-operating characteristics, he says, the Dash-5 also is more aggressive in the stockpile, which gives it an edge when loading the bucket. And, says Zembal, the Dash-5 makes directional shifts faster than the Dash-3; by comparison, he says, he had to wait on the Dash-3.

To Zembal's observations, we would add the better fuel-efficiency of the Dash-5. Although the machine's fuel-efficiency advantage diminished somewhat as truck-loading cycles got longer, we took enough fuel samples, over such a broad range of cycle times, that we can confirm that this machine, overall, is a real fuel miser.

New model	WA250-5
Type	Wheel loader
Bucket range	2.5–3.5 cubic yards
Replaces	WA250-3
Available	May 2003