First Report on Coupling Strength Project

For the last year, HVIA has been part of a collaborative investigation into dynamic loads on couplings fitted to heavy High Productivity Freight Vehicles (HPFV) and PBS combinations.

The coupling safety project is funded by the National Heavy Vehicle Regulator’s (NHVR) Heavy Vehicle Safety Initiative (HVSI), supported by the Australian Government. The collaboration is being managed by the ARTSA Institute, with further support by the Australian Trucking Association (ATA) and the Truck Industry Council (TIC).

The project’s objective is to address the knowledge gap surrounding coupling forces experienced in Road Trains with a GCM above 125 tonnes.

Martin Toomey, Chair of ARTSA Institute, stated that the project has conducted extensive on-road testing of high GCM combinations to enhance industry understanding of the dynamic forces experienced by Fifth Wheel & Pin Couplings and the variables that can impact those forces.

To support and facilitate the test, Howard Porter donated the use of a Tri-axle ‘test dolly’, to which 14 load cells were fitted beneath the Fifth Wheel and a further six mounted directly behind the tow eye, within the custom-designed drawbar manufactured by CIMC.

Northern Territory based bulk fuel transportation specialist Direct Haul partnered with the project to facilitate the on-road testing between Darwin, Katherine and the surrounding areas. The test route covered a broad range of road conditions and speeds, both laden and unladen, including high-speed sections and rough roads with demanding conditions featuring hills, cattle grids, and flood crossings.

A key project aim was to understand how a couplings position within a large combination affects the dynamic forces it experiences. For each test run, the ‘test dolly’ was placed in a different position within the BAA and AAB Quad combination to allow the coupling forces in the front, center and rear positions to be recorded along the 473 km test route.

Preliminary results show that there are two major types of ‘events’ that contribute to the life of a coupling. This is a mix between smaller, high-frequency cyclical forces occurring nearly constantly and less common large force events, stemming from low-speed shunting events within the combination when coming to a stop and high-speed rough road events.

The results found that coupling location within the combination and the road profile affects the forces transmitted through the coupling, with positions closer to the front of the combination typically seeing higher longitudinal forces.

Using data obtained from the on-road testing, Smedleys Engineers are developing a computer simulation that replicates the vehicle combination and road conditions of the physical test, enabling further testing and investigation of coupling forces to be carried out in a repeatable and cost-effective environment.

Preliminary simulations of the virtual combinations travelling through recreated sections of the test road are promising, with coupling force results within 10% of those obtained during physical on-road testing. With some improvements to the models, different combinations can be simulated to determine other critical factors and primary variables that affect the force transmitted through the couplings.

The results of further simulation testing will ultimately aid in forming recommendations for the review of the current D-Value Selection Equation in AS/NZS 4968 so that it reflects actual coupling forces experienced in high GCM combinations.

The NHVR has provided technical assistance to this significant research project and will be involved in the validation of the results.

The project is expected to be completed in the coming months, and a comprehensive report will be made available to Australian authorities and industry stakeholders.

The project team, including the ARTSA-i, ATA, HVIA, NHVR, TIC and Smedleys Engineers express their gratitude to Howard Porter, CIMC, and Direct Haul for their efforts and support.