What constitutes the drive wheel assembly of a rubber-tired crane?

The drive wheel assembly serves as the power core for the crane's main travel motion. It consists of four major modules: the travel execution module, the power transmission module, the support and load-bearing module, and the steering and safety protection module. Currently, there are two mainstream structural designs: traditional chain drive and wheel-side direct drive.

I. Travel Execution Module (Wheel Assembly)
This module is the fundamental component of the wheel assembly, directly bearing the load, making contact with the ground, and providing propulsion.
Engineering Tires: Specialized for heavy-duty applications (typically 18.00–25 or 28–40 ply ratings); tubeless types are more commonly used due to their superior heat dissipation and longer service life.
Rims / Wheel Hubs: Manufactured from high-strength steel; they connect the tire to the drive axle and transmit torque.
Drive Axles: Solid or hollow shafts that transmit power and support the weight of the wheel assembly.
Bearings and Bearing Housings: Primarily utilize self-aligning spherical roller bearings to withstand both radial and axial loads, equipped with seals to prevent contamination by dirt and dust.
II. Power Transmission Module (Two Mainstream Solutions)
Solution A: Traditional Chain Drive (Mature and Reliable)
Drive Motor: A vertical variable-frequency motor that provides the motive power for travel.
Reducer: A vertical gearbox that reduces rotational speed while increasing torque.
Sprockets + Drive Chains: Transmit power from the reducer to the drive axle; includes a tensioning adjustment mechanism.
Gear Pair (Internal): Consists of a large gear and a small gear housed within the axle, facilitating the final stage of the drive reduction.
Solution B: Wheel-Side Direct Drive (Compact, Efficient, and the Mainstream Trend)
Permanent Magnet Synchronous Motor: Integrated directly at the wheel side; features a compact size and high efficiency.
Wheel-Side Planetary Reducer: A two-stage planetary gearbox (typically NW/NGW type) embedded within the wheel hub, directly driving the rim.
No Intermediate Chain: The motor connects directly to the reducer and then to the wheel hub, resulting in a shorter transmission chain and a lower failure rate.
III. Support and Load-Bearing Module
Equalizer Beam / Saddle Frame: Connects the wheel assembly to the crane's outriggers; utilizes pivot shafts and thrust bearings to bear the wheel load and accommodate uneven ground surfaces.
Wheel Suspension: Employs hydraulic or mechanical buffering systems to absorb shocks and ensure uniform ground contact.
Wheel Guards / Protective Plates: Provide protection against collisions and prevent debris from becoming entangled in the wheels. IV. Steering and Safety Modules
Steering Cylinder / Mechanism: Enables 90-degree right-angle steering; some models are equipped with a lifting mechanism (to lift the wheels during steering, thereby reducing resistance).
Brakes: Wheel-side or axle-end disc/drum brakes, designed to meet requirements for both parking and emergency braking.
Sensors: Monitor rotational speed, temperature, and pressure; utilized for control purposes and fault pre-warning.