Main Mechanism Drive Methods and Layout of Tire-Mounted Container Gantry Cranes

(1) Trolley Traveling Mechanism

The trolley traveling mechanism consists of four sets: two driven and two driven. It is generally diagonally driven, but four-corner driven is also possible. The trolley traveling mechanism comprises wheel sets, transmission mechanism, frame and balance beam, steering system, and safety protection devices. To prevent collisions between cranes and between cranes and containers, a manual correction system and four-corner anti-collision devices for the trolley are provided.

① Wheel Structure

The wheel set consists of tires, rims, wheel axles, and two bearing seats. Tires are often 18.00–25 engineering tires with 28–40 ply ratings. Tires are available in tubed and tubeless versions. Tubeless tires are more commonly used because they reduce friction between the inner and outer tires, have better heat dissipation, and longer lifespan. Cranes are supported on large tubeless tires with 4, 8, or 16 wheels. The number of wheels is designed according to the wheel pressure requirements of the yard.

② Trolley Travel Transmission Mechanism

Generally, a vertical electric motor is used, which drives the large sprocket on the drive axle to drive the wheels via a reducer, sprocket, and transmission chain. The drive unit is equipped with an adjustment device to adjust the chain tension.

③ Frame and Balance Beam

The frame has a saddle-shaped structure and is connected to the balance beam via a pivot shaft. A thrust bearing is installed at the lower part of the pivot shaft to withstand wheel pressure, and the upper part uses thrust bearings, with some using spherical roller bearings.

④ Steering System

The crane generally uses 90° right-angle steering. Steering steel plates are laid at both ends of the yard at the turning points to reduce wheel deformation and wear during steering. In recent years, some designs have adopted steering auxiliary lifting devices, which lift the wheels during steering to reduce steering resistance and tire deformation. The wheels are then straightened after steering.

⑤ Other Devices

These mainly include wheel guards, tire wedges to prevent strong winds, and anti-collision switches to prevent trolley deviation.

⑥ Straight-line travel

Due to road conditions, tire leaks, uneven load distribution, etc., the crane may veer off course or swerve, leading to collisions with containers. When the crane is in operation, the driver should constantly monitor whether the wheels deviate from the marked travel lines on the yard. If deviation is detected, the driver should operate the control handle in the cab to adjust the speed of the motors on both sides to correct the deviation. 

There are various forms of automatic control devices for maintaining straight-line crane travel. One method involves burying induction cables underground, with a transmitter acting as a ground signal source to provide a constant low-frequency power signal to the induction cables. The onboard detector can detect deviations in the crane's travel path. The trajectory control device can convert the position deviation signal into a direction control signal, which in turn controls the motor speed to achieve correction. This method is less commonly used now because it requires civil engineering construction and is susceptible to uneven road surfaces and electromagnetic interference. Another method involves applying special paint to the ground, with an onboard camera capturing the signal for automatic correction. Other correction methods include infrared and gyroscope methods.

(2) Trolley travel mechanism

Trolley drives are divided into rack and pinion drive and wheel drive.

① Wheel-Drive Type

The wheels are driven by friction, resulting in smooth transmission. However, slippage can occur during sudden starts and stops or in rainy weather. Four-wheel drive vehicles largely eliminate this slippage. The transmission system consists of an electric motor driving a reducer, with the reducer's output driving the wheels at both ends via a floating shaft.

② Rack-and-Pin Drive Type

The electric motor drives two long shafts (left and right) via a reducer. Cantilever gears on these shafts mesh with racks on both sides. Each rack segment is welded to the main beam via spacers. The rack rotation is reliable and slip-free, ensuring accurate positioning. However, there is some impact during starts and stops, and the rack installation requires high precision to ensure proper meshing throughout the entire travel.

③ Guiding Device

There are two types of trolley guiding methods: one is double-flanged guidance, and the other is horizontal wheels arranged on both sides of one side of the track. Horizontal wheel guidance prevents rail wear and improves operational reliability.

④ Other Devices

A deceleration limit switch is installed before the trolley's end point, and a stop limit switch and an emergency stop limit switch are installed at the end point. When not in operation, the trolley is anchored by an anchoring device. Anchoring devices come in various forms, such as anchoring pins and screws.

(3) Lifting Mechanism

There are two arrangement forms for the lifting mechanism: parallel arrangement and vertical arrangement.

① Parallel Arrangement: Simple structure. To prevent the motor base from colliding with the wire rope, the motor base is raised, and the reducer is arranged at an angle. The brake is located on the motor side, resulting in a compact structure. If the brake is located on the other side of the reducer, adjustment and maintenance are more convenient.

② Vertical Arrangement: Compact structure, but the reducer requires a spiral umbrella, making manufacturing more difficult.

③ The reducer support generally adopts a base type, while some products use a three-point support type reducer, which has clear force distribution and a lightweight structure.

④ Other Devices: A small gear (or small sprocket) drives a travel limit device on one end of the drum. A pulse encoder and tachogenerator are installed on the other end of the high-speed motor, providing feedback signals to the automatic control system.

(4) Diesel Generator System

The diesel generator system is generally located on the bottom beam and mainly consists of a diesel generator set, auxiliary devices, and a machine room. Auxiliary devices of the diesel generator system include a main fuel tank, auxiliary fuel tank, charger, battery, auxiliary water tank, shock absorber, muffler, exhaust pipe, and oil/water junction box. The high-mounted auxiliary fuel tank ensures sufficient fuel supply to the diesel engine and reduces oil suction resistance. Therefore, an oil suction pump that draws oil from the main fuel tank must be installed on the auxiliary fuel tank, and this is done automatically via a level control switch.

(5) Driver's Cab

The driver's cab is generally suspended under the chassis of the traveling trolley. The front and lower front of the driver's cab are made of glass, providing a good field of vision. The back is usually made of large glass, allowing observation of crane operations in adjacent passageways. The lower floor window must be equipped with a safety grille. The grille is arranged vertically in the middle and horizontally on both sides for good visibility. The middle seat is adjustable in both height and fore-aft position. It is equipped with air conditioning, telephone, and other auxiliary devices. The electrical instrument panel is generally located at the top, while the control panel and lock indicator lights are usually in front of the central grille.