Underground Haul Truck

Overview

An underground haul truck carries broken ore and waste from the loading point out to a crusher, ore pass or surface portal along the ramps and drifts of a mine. It is the long-distance partner to the LHD loader: where the loader mucks and tramming a short distance, the truck takes the larger payload up the ramp. The defining problem is the same low, narrow heading, so the truck is articulated and low-profile rather than tall like a surface dump truck, and a great deal of its engineering goes into braking a heavy payload safely down a long, steep decline.

Trucks range from compact units of around twenty tonnes payload to large machines carrying sixty tonnes or more. They come with two body styles: a conventional tip-up dump that raises the box to tip, and a horizontal ejector that pushes the load out with a moving blade so the truck can discharge under a low back without lifting the body. Both are built to a payload and a profile that suit a particular mine's ramp dimensions and cycle.

Articulated chassis

The Articulated Chassis carries the load and lets the truck steer in confined space. A Front Frame holding the cab and engine and a Rear Frame holding the body are joined at an Articulation Joint, and a pair of Steering Cylinder units bend the truck about that pivot to turn. An Oscillation Bearing lets the frames twist over uneven floor so the truck keeps traction and stability on a rough ramp.

Dump body

The Dump Body is the payload container, a welded Body Shell protected by replaceable Body Liner plates against the impact and abrasion of loading. On a tip-up truck, telescopic Hoist Cylinder units raise the box to dump. On an ejector truck, an Ejector Blade driven by a long-stroke Ejector Cylinder pushes the load out horizontally, which lets the truck discharge in a heading too low to raise a body and keeps the centre of gravity low while doing it.

Powertrain and braking

The Powertrain is a high-power Diesel Engine feeding a Torque Converter and Powershift Transmission. What sets a haul truck apart from a loader is the descent problem: a loaded truck coming down a long ramp must shed enormous amounts of energy without overheating its brakes. That is handled by a Driveline Retarder in the driveline that absorbs most of the downhill energy, backing up the oil-cooled service brakes. Each Drive Axle carries a Differential, a Planetary Hub reduction for pulling the loaded grade, and Wet Disc Brake discs cooled by circulating oil so they can hold up to sustained ramp braking.

Hydraulics and cab

The Hydraulic System drives the body hoist or ejector, the steering and the brakes from engine-driven pumps through a sectional Main Control Valve, with Brake Accumulator storage holding brake pressure in reserve. The driver works from the Operator Cabin, a ROPS and FOPS protected cab with a suspension seat, the Steering Unit for the articulation, and a Pedal Set that includes a dedicated retarder control for the descent.

Electrics, emissions and safety

The Electrical System is built around a Vehicle Control Unit that runs the driveline and feeds telemetry for fleet dispatch, plus a Payload Sensor set that weighs the load through the suspension to stop overloading and to confirm full trucks for production accounting. Modern fleets run these trucks tele-remotely or fully autonomously on fixed haul routes. Because the engine is large and the air is shared, the Exhaust Treatment is comprehensive: a Diesel Particulate Filter traps soot and a Oxidation Catalyst and SCR Module cut the gas emissions to underground limits. The Fire Suppression System system, with its heat Detection Line and agent nozzles, guards the engine and brake hot spots, a requirement on any diesel machine working a single-access heading.

Variants and the haulage cycle

Underground haul trucks are matched to the mine they serve. The two body styles, the tip-up Dump Body and the horizontal ejector, are chosen by the discharge geometry: a tip-up needs back clearance to raise the box, while an ejector discharges under a low back and keeps the load low during travel, at the cost of a heavier, more complex body. Drive layout varies too, with smaller trucks on four-wheel drive and larger ones on six wheels for traction up a steep ramp. As with loaders, the power source is shifting. Diesel trucks dominate because of their range and refuelling simplicity, but battery-electric haul trucks are growing in deep mines, and a notable advantage of an electric truck on a downhill-loaded haul is regeneration: the same descent that overheats a diesel truck's brakes can recharge an electric truck's battery through its motors, turning the retarder problem into an energy source. In the cycle, the truck is loaded by an LHD or a chute at the loading point, hauls the payload up the ramp to a crusher, ore pass or surface portal, dumps, and returns empty. Fleet dispatch systems track each truck through the Vehicle Control Unit telemetry and the Payload Sensor weights to balance loaders against trucks and to confirm tonnes for production accounting, and on fixed routes the trucks increasingly run autonomously, queueing, loading and dumping with no driver aboard.