Stopping 60-ton articulated dump trucks (ADTs) with full loads on a downward slope seems like it would be a tricky proposition, but manufacturers have technology in place to help ensure traction and make smooth, full stops.
Here are some examples.
Volvo ADTs have Automatic Traction Control, and 100-percent differential locks, so (G Series) trucks can work in 4x6 and 6x6 drive combinations.
“Volvo’s Automatic Traction Control lets operators focus on driving while automatically engaging and disengaging locks for the most efficient on and off-road performance,” says Rob Palermo, product manager for articulated haulers. “The Dynamic Volvo Engine Brake (VEB) system uses powerful retarders to control speed while hauling downhill, slowing down before curbs or crossroads. The torque and shift points are now dynamically adjusted against the current load, inclination, and rolling resistance, which improves brake life by reducing the need to use the brake and retarder pedal when going downhill.”
Palermo says the VEB leads to significant increases in max torque. Volvo ADTs also come equipped with full wet disc brakes on all wheels.
“Also, Volvo Dynamic Drive provides an improved gear shifting strategy that takes into consideration both the payload and the gradient of the slope,” Palermo says. “The machine will automatically detect when to choose a higher starting gear or when to shift up earlier. When conditions require, the machine will prolong the gear, ensuring maximum rim-pull.”
Another feature, called Hill Assist, holds the hauler in place on steep slopes without the need to engage the parking brake. The feature automatically activates when arriving at a complete stop on a hill and is disengaged when the operator accelerates.
Komatsu’s transmission is called K-ATOMiCS, or Advanced Transmission with Optimum Modulation Control System. It’s a six-speed, fully automatic transmission that uses an advanced electronic system to eliminate shift shock and torque cutoff so the engine operates in the most efficient range.
The electronic system automatically selects the gear based on vehicle speed, engine speed, and the shift position selected, meant to help acceleration and provide smooth down shifting and synchronized engine speed when climbing slopes. “A large automatic retarder allows the operator to select the optimum operating speed on downhill travel and fully loaded hauls, thus eliminating effects by inertial acceleration,” says product marketing manager Sebastian Witkowski.
Wet disc brakes
Witkowski says Komatsu ADTs also utilize wet disc brakes located on the ends of the front and middle axle.
“They are large-capacity, continuously cooled, wet-multiple disc brakes that also function as a highly responsive retarder, which provides the operator greater confidence at higher speeds when traveling downhill,” Witkowski says.
“In addition, selectable powertrain features allow the operator to choose the transmission starting gear (F1 or F2) to match job site conditions,” he says. “The operator can also choose to lock the center differential so a 50/50 split of power flows to the front axle and rear axles.”
Finally, Deere says its transmissions are specifically designed for ADT applications, with eight forward and four reverse gears. “A fully proportional retarder allows for highly precise descent speed control, which preserves the service brakes and reduces operator fatigue,” says Cory Oullette, product marketing manager for ADTs and scraper systems.