Reinventing the fifth wheel

Engineering firm Mechanical System Dynamics has engineered, designed and patented a revolutionary compensating fifth wheel that has the potential to dramatically reduce the incidence of rollovers in heavy and multi combination vehicles.

Mechanical System Dynamics was co-founded by Dr Hans Prem and Dr Luan Mai, both of whom gained PhDs in Mechanical Engineering in the early 1980s.

Both men have an intense interest in vehicle dynamics. With Hans, it commenced with his PhD and the study of motorcycles in 1979, undertaken at the University of Melbourne, and thereafter progressed in a series of logical steps to innovative large off-highway mining trucks with gross weights approaching 500 tonnes.

Meanwhile, Luan Mai was awarded a first-class honours degree in Mechanical Engineering from Monash University and the J.W. Dodds Memorial Medal and Prize for Best Graduate in 1976.

In 1982 Luan gained a PhD for outstanding research in the dynamics and control of load-sensitive pumps. His interest in road tanker rollover stability subsequently led to the construction of a tilt table facility that is still in use today at Linfox’s Australian Automotive Research Centre (AARC) near Anglesea in Victoria.

The outcomes and recommendations from this research led to nationwide safety improvements for articulated heavy vehicles and road tankers in particular.

Which brings us to the latest efforts of this ‘Dynamic Duo’ in designing and developing a radically improved compensating fifth wheel.

Simply stated, Hans believes the advanced design of the compensating fifth wheel he and Luan have developed and patented has the potential to achieve up to a 10 per cent improvement in roll stability which he says directly equates to about a 30 per cent reduction in single vehicle rollovers (see Graph).

As for the impetus for embarking on such an ambitious project, Hans says the company was repeatedly contacted by operators seeking a superior compensating fifth wheel.

“Believe it or not, the currently available compensating fifth wheel was first patented just on 60 years ago and the design has changed very little since,” he says.

“We decided to study its operation to understand exactly how it works and then set about designing an alternative that would improve its operation in a number of key areas.”

The main purpose of a compensating fifth wheel is to provide torsional relief between the prime-mover and semi-trailer, and additionally in B-doubles and A-doubles, torsional relief between the ‘A’ and ‘B’ trailers and dolly/second trailer respectively.

It is particularly beneficial in road tanker operations due to the propensity for stress cracking in the barrel around the skid plate area if a standard fifth wheel is used.

However, Hans believed that after 60 years it was high time to improve on the original compensator design.

“Some disadvantages cited by our customers include cost, maintenance (regular greasing required) and a relatively short service life”, Hans says.

Not known for doing things by halves, Hans and Luan came up with a New Compensator concept that has the potential to eliminate all of the known issues.

Further development of the New Compensator concept will include electric actuators.

Instead of the cradle design of the original compensating unit where the metal-to-metal sliding action requires a constant film of grease, the New Compensator features a four-bar link arranged like a parallelogram with eight pivot points, complete with self-lubricating ‘greaseless’ bearings, enabling a smooth compensating action to occur.

In basic passive form (see image below) two spring-loaded struts with integral snubbers limit the maximum tilt angle. Through careful design and location of roll-centres the New Compensator can be used to control the distribution of the overturning moment during cornering thereby further improving rollover stability.

A key feature and further benefit of this design is that the turntable roll-centre can be adjusted by simply substituting feet with different base mounting widths, thus subtly changing the angle of the links and enabling the height of the roll-centre to be easily tailored – either up or down – to a specific trailer and load.

Mechanical System Dynamics is now in the process of constructing a prototype New Compensator that will be subjected to further testing for strength and durability. It will then be initially certified with on-road testing to commence in due course.

The company would like to hear from entities, manufacturers and transport companies interested in this technology to help bring it to market.

And finally, Hans says the full potential of the New Compensator is yet to be fully revealed and realised.

The New Compensator addresses several key deficiencies in existing compensator fifth wheel designs that have been around since 1961.

“We regard our initial passive version of the New Compensator design as a stepping-stone to a fully active design featuring forced tilt control (see main image) comprising ‘plug-and-play’ electric actuators, electronic control and integration with other on-board smart systems,” Hans says.

“This further development in the design in the form of an active automated compensating action – which is where the real magic happens – is expected to improve the safety and operational benefits of the New Compensator further still.

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