Articulated Haul Truck

Overview

An articulated haul truck, or articulated dump truck, is an off-road hauler built to move large volumes of soil, rock, and overburden across ground that a rigid highway truck could never cross. The defining feature is the joint in the middle. The machine is built as two frames, a Tractor Frame carrying the engine, cab, and front axle, and a Trailer Frame carrying the dump body and the rear bogie, joined by the Articulation & Oscillation Hitch. The tractor steers by swinging about that joint rather than by turning a front wheel set, which gives a tight turning circle on a long machine and keeps all six wheels driving in line. Rated payload runs from about 25 t on a compact model to 45 t on the larger sizes, with a heaped body capacity of 15-25 cubic metres.

These trucks earn their place on construction sites, quarries, and open pits where haul roads are soft, steep, or rutted. Full-time 6x6 drive and large radial tyres let them keep moving in conditions that would bog a two-axle truck, and the articulation lets a long machine work in confined cuts and around tight switchbacks.

Articulation and Oscillation

The hitch does two jobs on two separate axes. The first is steering. A vertical pivot, the Vertical Steer Pivot, runs on tapered roller bearings inside the Hitch Yoke, and two Steering Cylinder units swing the tractor up to about 45 degrees each side. Because the whole front of the machine turns, the front and rear wheels track closely, which reduces tyre scrub and lets the truck follow a narrow path.

The second job is terrain following. A horizontal Oscillation Bearing lets the trailer roll relative to the tractor by roughly 15 degrees. Without it, a wheel dropping into a hole would lift a wheel on the far side off the ground and lose traction. With it, the trailer twists to keep all six wheels loaded. Both axes share hardened Articulation Pin components and run on greased Ball Bearing units sealed by Oil Seal rings, because the hitch carries every steering and traction load between the two halves of the machine.

Powertrain and Driveline

Power comes from the Turbo Diesel Engine, an inline-six turbo diesel of 260-350 kW, breathing through a two-stage Air Cleaner sized for dusty sites. Drive runs through a Torque Converter, which multiplies torque to start a laden truck on grade and locks up for efficient cruise, then into the Powershift Transmission, a powershift gearbox giving eight forward and four reverse ratios. Heat is handled by the Cooling Module, and the Exhaust Aftertreatment unit, a particulate filter and SCR catalyst, brings the machine to Stage V emissions limits.

From the gearbox, torque enters the Transfer Dropbox, which splits drive forward and rearward and carries an inter-axle differential with a lock. Three Drive Propshaft units feed the Front Drive Axle and the two Rear Drive Axle units in the bogie. Each axle uses a Axle Housing holding a Helical Gear Pair-driven Cross-Lock Differential with a cross-lock, and a Planetary Wheel Hub at each wheel for the final reduction. Six Wheel & Tyre assemblies, typically 750/65R25 or 23.5R25 radials, put the power to the ground. With every differential locked the truck drives all six wheels as one, which is what gets it out of soft fill.

Dump Body and Hydraulics

The Dump Body is a welded Body Tub with a heaped capacity of 15-25 cubic metres, protected by a bolt-in Wear Liner of abrasion-resistant plate. Two Hoist Cylinder units, one each side, raise the loaded body about 70 degrees over the Body Pivot Pins pins to discharge. A Tailgate retains fine material on the haul, and in cold climates a Body Heat Duct routes exhaust under the floor so wet ground does not freeze to the tub.

Hydraulic supply comes from the Load-Sensing Pump, a load-sensing piston pump feeding both the hoist and the steering through the Control Valve Block. Steering oil is metered by the Steering Orbital Unit unit at the wheel, and the Hydraulic Reservoir supplies the pump on steep grades. Several Pressure Sensor units report circuit pressure to the controllers, and the Hydraulic Hose Set carries oil across the flexing hitch to the trailer.

Braking and Retarder

Stopping a laden articulated truck on a downgrade is a heat problem more than a friction problem. The Brake & Retarder System uses oil-immersed Wet Multi-Disc Brake packs at all six wheel ends, which shed heat into oil and resist contamination far better than dry brakes in mud. For long descents the Driveline Retarder absorbs energy in the driveline so the service brakes are not asked to hold the truck down a whole grade. The operator meters pressure through the Brake Treadle Valve, a spring-applied Parking Brake holds the loaded truck on grade, and Brake Accumulator units store charge so several stops remain if the engine stalls.

Cab, Electrical, and Control

The operator works from a Operator Cab, a welded Cab Structure certified as roll-over and falling-object protection, with Cab Glazing for sightlines to the loader and across the body during tipping. An air-suspended Suspension Seat isolates haul-road vibration, the Steering Wheel feeds the orbital unit, and the Hoist Control Lever selects raise, hold, float, and lower for the body. An LCD Panel shows payload and gear, and the Cab HVAC Unit unit holds cab climate from cold sites to hot pits.

A Vehicle Control Unit coordinates engine, transmission, and retarder over CAN, while the Payload Weighing System weighs each load against the rated target so the truck is neither overloaded nor sent out light. A Wire Bundle runs the harness across the tractor, hitch, and trailer through sealed Connector crossings at the joint, the Battery Box holds the starting batteries and isolator, and the Lighting Set lights the haul road around the clock.