At the time the installation of air-filled tires on shuttle cars aimed to give operators a more comfortable ride than was achievable with foam-filled tires. However, flat tires became a regular problem. The mine operator then set out on a design experiment to provide the ride of air-filled tires with foam-filled tires.
A four-wheel independent suspension system was developed, involving a pivoting axle on each wheel and hydraulic cylinders between the wheels and the frame. A number of shuttle cars were built and put into service but while the system improved the ride it was complicated and subject to frequent downtime.
The mine operator approached Joy to make the system more reliable and functional.
“We concluded that their concept of having an independent pivot axle at each wheel was sound, but we looked for a way to remove the cylinders and the associated hydraulics to decrease the amount of required maintenance and increase its reliability. In effect, we began searching for a shock absorber, similar to that on an automobile, to do the job,” said Randy Welker, Joy's haulage engineering manager.
Finding a shock-absorbing material that could hold up to the underground environment, support the loads of a shuttle car, and operate at both empty and loaded weights proved very difficult. Joy worked with a manufacturer of heavy-duty elastomers that also had experience with suspension systems. After experiments with different chemistries, and pushing the limits of the technology, a suitable material was developed.
“It is not feasible for a mine operator to increase the mining height significantly to fit a suspension system on a car, and requiring the operator to use different wheel units would also pose problems as well,” said Ron Dickey, Joy’s batch haulage engineering supervisor.
“With this new elastomer we were able to meet these goals. We ended up with a strut comprised of elastomeric pucks and urethane dividers on a steel rod. We built a couple of shuttle cars with this system in 1998 and put them underground to see how they would fare.”
Over time design changes were made including to the strut design, eventually changed to an external shell design. The way these were mounted to the frame was changed and the wheel unit to make the mounting more robust. The fabricated wheel axle was replaced with a complete cast axle.
“We now have a suspension system that is virtually maintenance free and extremely reliable,” Dickey said. “Since we made this final wave of changes (about five years ago), we have not failed a single strut or an axle. “
Joy said tests run at one mine have shown that when the shuttle car is fitted with a suspension system, the operators tram 42% faster on their return trip from the feeder to the continuous miner.
“Tramming faster means more trips per shift which ultimately means higher production rates,” Welker said. “Additionally, the suspension system helps increase the life of the shuttle car frame. As is usually the case in half the shuttle cars brought in for rebuild, not a single frame from a suspended shuttle car has had to be replaced. This can represent a huge savings in the cost of a rebuild.”
Since its introduction in December 1998 Joy has shipped over 80 shuttle cars with the independent suspension system. Of all the shuttle cars sold now, 20% include the suspension option.
Joy presently offers the suspension system on its mid-seam shuttle car models, the 10SC32AA, A, AB, B and BC models but is not yet available on the low-seam 21SC models, nor the larger 10SC32C and D models.
