sdc longer semi

Producing a 15.65m longer semi-trailer that complies with manoeuvrability rules is one thing; building one that is a genuinely practical, real-world proposition is a different matter. So says Professor David Cebon, professor of mechanical engineering at the University of Cambridge and director of Cambridge Vehicle Dynamics Consortium (CVDC), a collaboration between the university and industry.Cebon is the driving force behind a project demonstrating how good a longer semi could be. The result can be seen at this week’s CV Show on SDC Trailers’ stand, which, along with Tridec and Wincanton, are partners in the project.

Cebon is unimpressed by the first generation of longer semis. “You can buy a system that satisfies the legal requirements but you can’t reverse it and its manoeuvrability is dreadful.” As well as their cut-in and tail-swing, Cebon said longer semis are a nightmare to reverse if their self-steer axles lock straight when reversing: with more than 3m between first and third axles they are resistant to anything other than straight backwards.

“We’ve tried to design the safest, most manoeuvrable and most productive vehicle,” said Cebon. The 15.65m trailer looks unassuming until you see that its three axles are equally spaced, lacking the set-back third axle of other longer semis that need to balance turning-corridor rules and axle loads. Uniquely, the centre of the rear doors on the CVDC trailer follows precisely the same path as the unit’s fifth-wheel when cornering. Cut-in on the inside is reduced by about 65% and there is no outward tail-swing. “Tail-swing is dangerous because it takes the vehicle in to parts of the road where the driver has not been, where there are pedestrians, cyclists and street furniture,” Cebon explained.

CVDC’s longer semi owes its manoeuvrability to sophisticated steering for all three axles. It uses Tridec’s hydraulic steering components, refined by computer control. The trailer’s kingpin is on a slim turntable instead of a conventional rubbing plate, and there is wedge on the turntable that engages in the fifth wheel’s jaw. Articulation between tractor and trailer rotates the turntable, moving pistons in two hydraulic cylinders that generate pressure in a reservoir. The outward flow from the reservoir powers hydraulic steering actuators on each of the three kingpin-type axles. Flow to the actuators is controlled electronically so the steering angle of each axle is managed individually, using CVDC’s software algorithms and taking data from sensors around the vehicle.

Cebon believes the steering system is the enabling technology for 25.25m-long, 60-tonne GTW European modular system combinations. “Without it, they are impossible to reverse.” But hasn’t the government ruled these out? Cebon shrugged this off, citing their productivity advantage. “They tackle emissions and traffic congestion,” he said. “I believe they are inevitable.”