What Speed Bump?

ASV's new SR-Series rubber-track loaders - so freshly designed that they share just a handful of part numbers with the company's other models - feature a supple new undercarriage that soaks up obstacles in its path

Construction Equipment - January 1, 2006

Walt Moore
Senior Editor

On a chilly afternoon some six weeks ago, we watched Brad Lemke, director of product development for ASV, as he spared no horsepower in demonstrating the aggressive performance of the company's new SR-80 Posi-Track loader.

Working the new machine in a remote area of ASV's extensive proving grounds — near its Grand Rapids, Minn., factory, Lemke excavated deeply into the site's heavy sandy clay and ran the new tractor up, down and across the site's imposing grades and rutted surfaces. Then, on a concrete test pad, he repeatedly drove the new model at top speed over a 4×4 timber placed across one track's path. We were impressed at how calmly the SR-80's new four-bogie undercarriage rippled across this impediment.

"The SR-Series is the most significant model introduction in ASV's history," says Lemke. "Just about every idea, wish and want we as a manufacturer have had in 20-plus years of building rubber-track loaders is reflected in this new design. We've invested more in manufacturing tooling for these machines than we invested in all our previous models — combined. Not counting nuts and bolts, there are, literally, only five or so part numbers that are common with our existing models."

The new series, which includes the 80-hp flagship model, the SR-80, and a 70-hp companion model, the SR-70, was three years in development, says Lemke. And although the new machines don't replace any of the company's current nine models, the technology they embody, he says, eventually will work its way through the entire line. That transfer of technology likely will include the stellar feature of the SR-Series — its new "single-rail" undercarriage.

The single-rail concept

ASV has been building rubber-track vehicles since the early-1980s, and the hallmark feature of its loaders has always been a suspended undercarriage that flexes as it encounters obstacles in its path. The new SR-Series undercarriage, which ASV calls a "single-rail" design, is the company's fourth-generation concept, and according to Lemke, the best yet.

Similar to the preceding undercarriage generations, the single-rail system retains the essentials of ASV's undercarriage design: proprietary rubber tracks that contain no steel; multiple wheels to spread the tractor's weight evenly over the tracks; torsion axles to provide the desired suspension qualities; and a roller-cage sprocket.

That said, however, the new single-rail system represents a significant departure in overall design from its predecessors. We've included a couple of computer-generated illustrations from ASV's engineering files to help you understand the fundamentals of the single-rail design, which basically incorporates (on each side of the tractor) four independently suspended bogie assemblies. These assemblies, each having four wheels, are attached to a central longitudinal frame (rail) via torsion axles. A row of four larger idler wheels is attached to each end of the central rail, which, in turn, is attached to the tractor frame with two torsion axles.

A torsion axle, as you may know, consists of a square tube, into which a square shaft is inserted (after being rotated 45 degrees), thus forming triangular spaces between the shaft's sides and the tube's corners. Compressible cords are placed in these triangular spaces, and when undercarriage forces try to rotate the shaft or the tube (whichever is not held stationary), the cords compress, allowing controlled movement of components and dissipation of shock loads.

According to Lemke, the single-rail system's six torsion axles (per side) make the SR-Series undercarriage more flexible than previous designs, and its use of wheels that are narrower in width than those used in previous designs helps keep the undercarriage virtually free of material buildup. Metal face seals are used with each wheel bearing to make the entire undercarriage maintenance-free, except for adjusting track tension, which is accomplished via a simple turnbuckle strut between the central rail and the sprocket support.

Waste no space

The engineering objective for the SR-Series from the very start, says Lemke, was to make the design as efficient as possible. What that entailed, he says, was aiming for an optimum weight-to-horsepower ratio of 100 pounds per horsepower and making the tractor as compact as possible, while also maintaining an optimum area of track-on-ground.

Lemke quotes a few of the SR-80's specifications to illustrate how well those objectives were met. The 80-hp SR-80 weighs in around 8,000 pounds, and with 71 inches of track-on-ground (longitudinally), its ground pressure is in the neighborhood of 2.8 psi. The machine's overall length is 6 inches less than the company's 100-hp RC-100, and its width across the tracks is 72 inches. Given that each of the SR-80's tracks is 20 inches wide, then 40 inches (or 55 percent) of the machine's total 72-inch width is track. The relatively narrow overall width, says Lemke, allows the machine to fit comfortably on trailers with 80 inches between the fenders.

The compact dimensions of the new models, says Lemke, resulted from a studied effort to use every fraction of space. For example, ASV engineers determined that they could move the 3.3-liter Perkins 800 Series engine well forward in the chassis (and thus conserve longitudinal space) by designing the hydraulic charge pump to be driven directly from the engine, not from the end of the pump stack. (The pump "stack" is that end-to-end assembly of the two hydrostatic-drive pumps and the implement pump that is connected to the rear of the engine).

Manufacturing technology also has assisted in streamlining the design, says Lemke. For example, existing ASV models, he says, use a conventional, fabricated-steel hydraulic tank located between the machine's engine and cab. It's a good design, he says, but not as space-efficient as the horseshoe-shaped, rotational-molded plastic tank that nestles within the SR-Series chassis, exactly conforming to the space available. Likewise, the fuel tank is a rotational-molded piece that rests atop the fenders and across the nose of the chassis, forming a structural element in the design.

These two components, says Lemke, illustrate how ASV's investment in production tooling have both enhanced the SR-Series design and lowered manufacturing costs. Creating the two-piece rotational mold for the tanks was expensive, he says, but that expense will be quickly recouped, because the tanks now can be produced for about half the cost of conventional, steel versions.

(In the rotational-molding process, a type of granular plastic is poured into a two-piece mold, the halves of which are then bolted together. The mold is rotated simultaneously on its X and Y axes while being heated. As the plastic melts and adheres to the sides of the mold, a hollow "casting" is formed. Our understanding is that the amount of plastic used and the duration of rotation will determine the thickness of the casting.)

Attention to detail

Yet another illustration of ASV's objective to make the SR-Series design efficient, even in detail, is the newly engineered fan shroud and brush ring.

"The more you can reduce the space between the tip of the fan blades and the shroud," says Lemke, "the more airflow you can create, and engine cooling becomes more efficient. But the engine is flexibly mounted, so you run the risk of putting the fan into the shroud if that annular space is small. We solved the problem by installing a brush ring on the shroud's circumference. The ring closes up the gap for more airflow, but if the fan moves, it simply deflects the bristles of the brush and does no harm."

Innovative design is reflected, too, in the auxiliary-hydraulic circuits. As with all larger ASV loaders, both low-flow and high-flow circuits are standard equipment on the SR-Series. But the new machines, instead of using multiple valves and related plumbing to control the circuits, simply use the variable-displacement implement pump to automatically limit flow to 20 gpm when low flow is selected. When high-flow is selected, the pump automatically increases flow to 30 gpm.

The high-flow system is bi-directional and has a continuous-operation switch for operator convenience. New for the ASV low-flow circuit, however, is variable (proportional) flow — a feature controlled by a joystick-mounted rocker switch. The low-flow circuit also provides continuous flow via a dash-mounted switch.

Like all ASV loaders, the new SR-Series machines feature a hydrostatic drive system (controlled by a single joystick) and a load-sensing implement hydraulic circuit (also controlled by a single joystick). Although ASV made no major changes in these systems for the new models, the hydraulic pumps and two-speed motors in the systems were tweaked for enhanced performance.

Am I in my pickup?

Attention to overall fit, finish, styling and operator amenities also were among the top priorities when designing the SR-Series, says Lemke, and he invited us to sit in the cab's new suspension seat while he explained a few of the SR-Series features.

The cab is brand new and it does, indeed, have a pleasant, comfortable automotive-like presence. The two-piece lap bar, for example, folds into position from the sides of the cab, and pulling down one bar brings the other with it. And it would be difficult not to keep tabs on how the machine is running, because the lap bar has a complete gauge package built in.

The joystick controllers are new (left for travel control, right for implement control), having soft-textured grips and integral buttons and switches for proportional low-flow control, two-speed travel control and control of electrical attachment functions. A new control for these machines is selectable bucket positioning, which, when activated, automatically keeps the bucket level as it rises and lowers. But if the operator prefers, the function can be switched off, as when running certain attachments, like a brush cutter, which benefits from an elevated angle of attack.

Other nifty cab features include a curved-glass door that opens vertically (with the assist of gas struts) and stores in the roof with plenty of headroom, side windows that pop out from inside the cab for ventilation or cleaning, and a foot throttle that can be positioned either by your toe (accelerate) or heel (decelerate). And once positioned, the throttle stays put. In addition, ductwork for optional heating is already tucked neatly within the cab's interior, and a removable roof panel simplifies installation of a powerful, roof-mounted air conditioner that adds just 4 inches to the cab's height.

Lemke's enthusiasm about the SR-Series was readily apparent as he explained the features of the new models. We probably didn't realize just how enthusiastic, though, until he told us that he's buying the first SR-80 off the production line for use on his property. He did hedge a bit, however, when we asked if he was entitled to any special discounts.

SR-80 Specifications
Engine	Perkins 804C-33T
Horsepower (gross)	80.5
Displacement	3.3 liters
Travel speed (low/high)	7.0/12.5 mph
Loader type	Radial lift
Lift height	125 inches
Ground clearance	15 inches
Ground pressure	2.85 psi
Length w/o bucket	112.5 inches
Auxiliary pressure	3,000 psi
Auxiliary flow (low)	20 gpm
Auxiliary flow (high)	30 gpm
Attachment coupler	Hydraulic
Estimated rated operating capacity @ 50% tipping load	3,100 pounds
Estimated list price w/bucket	$47,000