All-Terrain Mobile Crane

Overview

An all-terrain mobile crane is a single machine that drives to a job on public roads at highway speed, then lifts heavy loads on a rough construction site. It combines the road manners of a truck crane with the off-road mobility and compact maneuvering of a rough-terrain crane, which is the reason it dominates the taxi-crane market for jobs from 60 to 500 tonnes. The crane arrives, sets up on outriggers in minutes, makes its lifts, packs down, and drives to the next site, all without a separate transport vehicle.

The machine is two cranes stacked: a wheeled Carrier that does the driving and a slewing Superstructure that does the lifting, joined by a large Slew Bearing. Larger models carry a separate lift engine in the upperworks, while smaller ones drive the crane hydraulics from the carrier engine.

Carrier and mobility

The Carrier has three to nine axles depending on capacity, and the defining trick is that all of them both drive and steer. Each Carrier Axle is a driven, steerable unit, so the crane has the traction to cross a muddy site and the agility to thread a multi-axle machine through tight urban streets, where the rear axles steer opposite the front to swing the tail around corners. The Hydropneumatic Suspension is hydropneumatic: it gives a comfortable road ride, levels the carrier on uneven ground, and locks out rigidly when the crane is set up to lift. A high-power Carrier Engine of 400 to 600 kW drives the whole thing through a multi-speed Carrier Transmission and transfer case.

Superstructure and slewing

The Superstructure is the rotating upper crane. It sits on the Slew Bearing and is turned by two Slew Drive units, each a planetary gearbox with a hydraulic Slew Motor and holding brake. The operator works from a tilting Operator Cab that can angle back so the operator can watch the load high overhead without craning their neck. The cab carries the joysticks and the LCD Panel load chart display that tells the operator how much can be lifted at the current configuration.

Telescopic boom

The Telescopic Boom is the working element. A fixed Boom Base Section pivots on the superstructure, and several Telescope Section members of high-strength steel slide out from inside it. Modern designs extend with a single Telescope Cylinder that, together with a Pinning System, pins each section at fixed lengths, which is lighter than carrying a cylinder per section. A large Luffing Cylinder sets the boom angle. For tall lifts a bolt-on Lattice Jib extends from the Boom Head, pushing tip height past 100 metres on the largest machines. Replaceable Wear Pad slides take the sliding loads between sections.

Outriggers and counterweight

Before lifting, the crane lifts itself off its wheels. Four telescoping Outrigger Beam units extend outward and Outrigger Jack cylinders plant Outrigger Float Pad floats on the ground, forming a wide rectangular base far stiffer than the tires. The Outrigger Monitor reports how far each beam is extended, because the load chart depends on the footprint. Balance comes from the Counterweight System, a stack of Counterweight Slab slabs on the upperworks tail. Crucially these are self-rigging: Self-Rigging Cylinder units let the crane pick up its own counterweight from a delivery trailer, since the slabs are removed for road travel to stay within axle weight limits.

Hoists and lifting

Load is raised by the Hoist System. A large Main Hoist Winch winch with a grooved Hoist Drum and spring-applied Hoist Brake spools the Hoist Wire Rope over the boom head sheaves and down to the Hook Block. An Auxiliary Hoist Winch serves the jib or provides a fast single-line. An Anti-Two-Block Switch stops the hoist before the hook block can be drawn up into the boom head, a classic and dangerous failure called two-blocking.

Hydraulics, control, and safety

The Hydraulic System uses load-sensing Main Hydraulic Pump units feeding a proportional Valve Bank so several functions move smoothly together. Safety centers on the Rated Capacity Limiter, a rated capacity limiter that reads boom Boom Angle Sensor, Boom Length Sensor, and a Load Measuring Pin to compute the working load limit from the load chart and stop motion that would overload or tip the crane. The Crane Controller ties boom, hoist, slew, and outriggers together over a CAN bus.

Variants and use

All-terrain cranes are sold by capacity class and axle count, which together set the road-legal weight per axle and decide whether the machine needs permits and counterweight transport. Compact 3 and 4 axle units serve general construction and plant maintenance; large 7 to 9 axle units erect tower cranes, set bridge girders, and assemble wind turbines, often with a luffing lattice jib. Rental crane fleets favor them precisely because one operator and one machine cover the widest range of jobs with the least logistics.