Cat’s elevated sprocket that changed the dozer market

Cat D10 elevated sprocket

In 1977, Caterpillar’s production lines rolled out 10 pilot models of the world’s largest, most powerful dozer, which would change the face of the equipment market.

The Cat D10 dozer’s radically different undercarriage, design, high weight and horsepower answered the call from large mining and big heavy construction operations for a more powerful dozer. This September, the Cat D10 celebrated its 40th anniversary.

“We bucked conventional wisdom with the D10 and tinkered with a centerpiece that was a part of the Caterpillar product line since the company was formed in 1925,” said George Alexander, a retired Caterpillar engineer who worked on the D10 research team and one of four individuals named on the patent for Caterpillar’s elevated sprocket design.

Offering 50 per cent higher productivity than Caterpillar’s largest dozer of that era, the D10 weighed more than 190,000 lbs. and measured 15 ft. tall, 12 ft. wide and slightly more than 31 ft. long. Power was supplied by the 700 hp D348, V12 diesel engine.

Dozer demand

A changing industry in the late 1960s and early 1970s stretched the D9, the D10’s predecessor, to its productivity limits. The mining industry led the charge for a dozer with more and more horsepower.

“The D9 dozer was the best track-type tractor of the day,” Alexander said. “It worked great for dirt operations, but interstate and heavy rock applications were hard on the solid bottom tracks that were a part of all dozer designs of that era.”

To address market need, Caterpillar recruited a team of researchers and engineers to develop a new, more powerful dozer, the D10.

“The development and product introduction involved every discipline of the company. It was highly successful because of the total team effort. The challenge of beating the competition in our core product was a tremendous incentive,” recalled Ron Krolak, retired track-type tractor chief engineer.

The D10 research team established a set of design goals for the new dozer: high productivity; modular design; simplified maintenance; operator efficiency; and transportability. It quickly became evident a new track design and improved undercarriage were needed to meet the production and durability goals for the new dozer.

Birth of the elevated sprocket

In 1970, a test bed was built for the new track. Engineers started by flipping the final drive for a D9G upside down.

“We worked on undercarriage geometry a lot, and within six months we had it operational,” Alexander said.

The new and resilient track, with elevated sprocket design, was also tested thoroughly in multiple applications to verify its durability. Results showed significant potential for improving undercarriage durability for extreme tasks.

Following two years of testing, Cat filed the first elevated sprocket patent application and began building the first two D10 test models in August of 1973.

“Our team generated 93 patents involving all systems of the concept,” adds Krolak.

By separating the drive sprockets from the track roller frame and elevating them above the tracks, more track remained on the ground for improved traction. The elevated sprocket design was also better able to absorb ground shocks for longer life and greater operator comfort.

While initial testing proved the value of the resilient undercarriage with elevated sprocket design, there were still some skeptics.

“It didn’t look like any traditional Cat dozer,” Alexander said. “The entire dozer was different in almost every way, except for the engine.”

The new undercarriage design required mounting the transmission t behind the engine to provide for the only track-type tractor final drive system with a common centerline between the steering clutches and brakes. It also allowed engineers to move both the dozer blade and ripper closer to the tractor, providing a concentrated center of gravity and improving the balance of the machine.

Marketplace approval

The pilot D10 dozers built in 1977 were embraced by Caterpillar customers. Their ripping and pushing capabilities made a significant impact on the mining industry. Also, studies showed the cost per yard to move material using the D10 was comparable to that of larger draglines. The resilient undercarriage with elevated sprocket conformed to the ground better than solid tracks. Therefore, it helped to improve machine pushing power and undercarriage life and enhancing operator comfort.

Consequently, the elevated sprocket track concept has been expanded to today’s Cat D6N and D6T medium dozers. It is also on the D8T, D9T and D11T large dozer models as well as the current D10T2 model.

“After I retired in the 1990s, I gave my presentation on the development of the elevated sprocket design. A person afterwards said to me, ‘Wherever you go, you will see the results of your work,’” recalled Alexander. “He was right. No matter where I traveled in the world, I saw dozers with the elevated sprocket design.”

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