19/01/2006 - 06:00 am

Telehandler Four-Wheel Steering Geometry Improved with New Axle

In recent years, telehandler users have sought after a tighter turning radius to accommodate jobsite restrictions. Older telehandlers offered a 27-degree turning angle while today's telehandlers provide 55-degree turning angles. However, when telehandler manufacturers began reconfiguring machine designs to provide a tighter turning radius, proper wheel steering alignment was sacrificed for this feature.

Proper configuration calls for the appropriate application of Ackermann steering geometry, which allows for the outside wheel to track at a different angle than the inside wheel. Failure to utilize this design leads to misalignment when turning the wheels. The front edge of the tire plows or drags against the ground surface, putting the tire and wheel assembly and all related components under unnecessary stress.

To improve steering and reduce tire wear while still maintaining a tight turning radius, Pettibone, Baraga, Mich., introduced a revolutionary axle at the World of Concrete for its 6,000-, 8,000-, and 10,000-pound telehandlers. Manufactured by Carraro, Calhoun, Ga., the Precision Steer axle is the first telehandler axle optimized for four-wheel steering.

According to Ray McDonald, Pettibone's vice president of engineering, axles used on today's telehandlers were originally developed for loader backhoes to support two-wheel steering. “Our machines run 90 percent of the time in four-wheel steer,” McDonald said. “Two-wheel steer is only used when driving on paved or improved surfaces.” The Precision Steer axle now corrects the steering to adapt Ackermann steering geometry in four-wheel steer rather than two-wheel.

McDonald said when they began working with Carraro to correct the steering, they conducted geometrical analysis on Pettibone and competitive machines. Testing showed that the Pettibone telehandler's tires were out of alignment (toed in) by 9 degrees in four-wheel steering, while competitive brands showed even greater alignment errors. With the new Carraro axle, Pettibone telehandlers are now misaligned only 4 degrees. During field testing, tire wear was cut in half after 400 hours of use on paved surfaces, McDonald said, and the axle also showed improved tracking and reduced rolling resistance in testing.

Improved fuel efficiency, increased tire life, and reduced stress on tie rods, wheel bearings, and other axle components are all benefits of the new axle design. Was it a difficult engineering feat for Carraro? According to McDonald, redesigning the axle didn't require anything revolutionary, just some reengineering and retooling to build them differently.

First on display at World of Concrete, the new axle is now available on all Pettibone-manufactured telehanders.

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