To the untrained eye, one compact track loader looks very similar to another. But look around underneath several makes and you’ll see some significant differences in how manufacturers design their undercarriages.
Often, these differences reflect different goals in terms of performance, durability and maintenance. One manufacturer, for example, may build the frame specifically to fit the undercarriage. Another may adapt its skid-steer loader frame to the undercarriage of a compact track loader.
Still another may purchase the undercarriage used on its machines from a supplier, rather than design its own. Other differences can range from the number of idlers and position of sprockets to the routing of hydraulic hoses and the amount of open area to facilitate cleaning out debris.
Most manufacturers attach the undercarriage directly to the frame of the machine, but several suspend the undercarriage to provide a smoother ride. Bobcat, on the other hand, offers a new optional system that suspends the mid-rollers by high-strength steel leaf springs to reduce vibration and improve operator comfort.
The rollers are made of forged steel, and the springs are shot-peened steel for strength and durability. This suspension system requires no greasing or adjusting, and the rollers are permanently sealed and lubricated with synthetic oil, eliminating regular maintenance to this part of the system.
Here are more examples of differences in undercarriage design offered by several compact track loader manufacturers.
Caterpillar
Caterpillar offers two types of undercarriages. The company’s multiterrain loaders (MTLs) are equipped with dual-level suspension — both the undercarriage and the mid-rollers are equipped with a suspension system — and all-rubber tracks.
The new line of compact track loaders (CTLs) features a fully suspended steel undercarriage and a steel-embedded rubber track. Both machine types have four independent torsion axles that absorb shock to the undercarriage, machine and operator.
“The suspension system offers a smooth ride, even at high speeds, along with better load retention and greater productivity,” says Pierre-Laurent Verdon, industry manager of skid-steer, multiterrain and compact track loaders.
“The steel bars in the rubber tracks engage the sprockets and steel components for extended life in aggressive applications,” he says. “The steel embeds provide a rigid support for the entire width of the track and excellent durability in a wide variety of applications. Continuously wound cables hold these embeds in place and provide tensile strength to prevent the track from stretching.
“Multiterrain loaders are extremely productive,” Verdon notes. “Contractors who use them a lot on sensitive surfaces will appreciate the all-rubber track with low ground pressure and the dual-level suspension for maximum ground adherence. The compact track loaders, on the other hand, are designed for increased durability in demanding applications and tougher ground conditions.”
The torsion axles, which suspend the undercarriage of the compact track loader, move independently relative to the machine and each other. “Combine that with the air-ride suspension seat and you can operate the machine comfortably at higher speeds,” Verdon says. In fact, Caterpillar CTLs come standard with two-speed travel and offer a fast speed of 8.5 mph.
The elevated external positive-drive system protects drive components from ground debris. It is also equipped with duo cone seals with seal guard — adopted from larger Caterpillar track-type tractors.
Takeuchi
The undercarriage of Takeuchi compact track loaders is attached to the main frame. “Our machines are built for grading and heavy pushing,” says David Steger, national product manager. “An undercarriage that is fixed to the main frame provides a more stable platform, reducing the tendency of a suspended undercarriage to bounce. As a result, the fixed undercarriage produces a smoother finished grade.”
The Takeuchi machine is designed as a dedicated track loader and was not adapted from a skid-steer design. The integrated frame uses cross-members that run the full width of the frame. The undercarriage is welded and designed to be part of the frame. The result is a stronger frame and better weight distribution for more durability.
The track, with steel-on-steel contact between the track, rollers and sprocket, adds durability. The lower and rear rollers ride on a forged steel contact pad built into the track. “This lets the track operate in many types of material,” Steger says. “If a rock gets between the roller and the track, it is pulverized instead of damaging layers of rubber.”
The slower rotating shafts of the machine’s large-diameter, outside-running rollers and front idlers add durability. The lower roller is placed directly below the drive sprocket. “This permits more sprocket teeth to engage the track, reducing the load on any one tooth, providing more power to be transferred to the track and lengthening track life,” Steger says.
The track power of the machines is enhanced by double-reduction final drives located in the track drive motors, rather than a direct or single-reduction drive. “The final drive acts like a trans-mission,” Steger says. “These two transmissions multiply the torque to move the machine.”
Terex ASV
The Posi-Track technology of Terex ASV compact track loaders combines independent torsion axles with maximum contact area between the tracks and the ground.
“In addition to improving operator comfort, the suspension allows the track to maintain contact with ground,” says Jodi Gulbraa, product marketing specialist. “This provides excellent traction with minimum vibration. This design increases undercarriage and machine life, ultimately lowering operating costs while increasing productivity.”
Ground pressures range from 2.8 psi on the smallest model to 4.37 psi on the largest. Increasing the contact area improves traction for more productivity when pushing and digging. Each torsion axle contains a torsion bar as its main weight-bearing spring. The main structure is an outside tube with a square inside bar orientated 45 degrees from each other. Rubber cords between the tube and bar allow the inner bar to rotate and give resistance.
The Terex ASV Posi-Track under-carriage has additional roller/bogie wheels. “This provides even weight distribution, which lowers impact when traveling over edges or objects,” says Gulbraa. “Less impact means longer track and undercarriage life.”
The company’s latest compact track loader model, PT80, has 32 10-inch bogie wheels and 16 15-inch idler wheels. The bogie wheels are designed to minimize wear to the inside of the track, reducing operating costs. The wheels of the Posi-Track suspension are also easy to service, if necessary, and can be detached without removing the tracks.
The internal drive system is designed for more efficient operation at higher speeds than a fixed sprocket and track system, in which the sprocket teeth drive off the steel-embedded tracks. “An internal drive lug pattern on our track, along with the movement of the outer roller, allows the roller to rotate and adjust to the bottom of the lug, always providing a solid engagement,” Gulbraa says.
Greg Northcutt is a freelance writer based in Port Orchard, Wash. He can be reached by e-mailing this publication at editor@onsiteinstaller.com.
