Undercarriage lets Cat tread lightly

Caterpillar Inc.'s new 9,000-lb multi-terrain loader is gentler to the earth than a child in a pair of sneakers. Caterpillar accomplished the feat with the Maximum Traction and Support System (MTSS), a rubber-tracked undercarriage developed by ASV Inc. (Grand Rapids, MN).

"Most vehicles use what are essentially chains and sprockets for propulsion," says Brad Lemke, the director of product development at ASV. "But our approach uses inverted sprockets for driving rubber tracks with steel lugs that are molded into the track."

The MTSS consists of 48 wheeled contact points and the reinforced rubber track. Caterpillar's 9,000-lb earthmoving machine has ground pressure of only 3.0 psi because the MTSS transfers nearly all the weight to the ground through those 48 points-many more than the four points found in most construction equipment.

A typical adult has twice that ground pressure, because an average set of feet has 30 sq inches of surface area, explains Lemke. "For a man weighing 200 lbs, that's a ground pressure of about 6.0 psi." For a child weighing 100 lbs, he estimates a ground pressure of 3.0 psi.

The MTSS has a total of 2,826 sq inches on the ground. For a vehicle weighing 9,000 lbs, the weight per square inch of surface area is a little more than 3.0 lbs.

The undercarriage uses an internal positive-drive system. The drive sprocket is elevated to help keep it away from ground debris. And it's fitted with replaceable roller sleeves that mesh with two rows of molded rubber lugs on the inside of the track. The lugs and sleeves mesh smoothly, regardless of speed.

The distance between the drive sprocket and the opposing wheels at both ends of the track remains constant, keeping the track tight while the suspension is at work. Thanks to a low weight per wheel, the track experiences less stress and therefore lasts longer. All bearings on the undercarriage run in a sealed oil bath, so they don't need greasing.

"When we saw the ASV technology, we were blown away," says Mark Glasnapp, a Caterpillar executive working with ASV. "It was something that we looked at, hit ourselves in the forehead, and said 'boy, we wish we'd thought of that.'"

Treading softly is especially important in areas where construction equipment tends to tear up landscaping, crack driveways and sidewalks, and leave marks in asphalt. The MTSS also allows heavy-equipment work in environmentally sensitive wetlands, forests, beaches, and parks.

For more information about undercarriages from ASV: Enter 538