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future
Stopping the next generation of commercial vehicles more quickly and preventing them from falling over are just two of the projects being tackled by the Cambridge Vehicle Dynamics Consortium
Words/images: Brian Weathertey
If the Great British Public is ever to declare a truce on heavy trucks it will probably he promoted by improvements in technology that make them safer and less obtrusive, rather than any sudden overwhelming urge to love a lorry. A tall order perhaps, but one the Cambridge Vehicle Dynamics Consortium (CVDC) is confronting through a number of far-reaching projects that could lead to tomorrow's heavy trucks being more stable, stopping in shorter distances and having a much smaller turning circle. Indeed, the technology shown at its recent open day at the Motor Industry Research Association in Nuneaton reveals a fascinating set of possible solutions to improving the overall performance of heavy goods vehicles
Staying upright
As regular listeners to traffic reports know, heavy articulated vehicles with their high centres of gravity and relatively small track width are prone to roll over during cornering. CVDC says: "The cost of roll-over accidents in the UK has been estimated at £40m-60m per year," It goes on to say that, once a roll-over starts it cannot be prevented
by driver action alone, hence the need for an active safety system. In response, it has built an experimental attic with active roll control that significantly increases its rollover threshold. The active anti-roll system on the trailer consists of an anti-roll bar on the tractor's drive axle and on each axle of the trailer, mounted between the trailing arms of the suspension, and two hydraulic actuators controlled by servo-valves. Using accelerometers and roll-rate sensors on the truck and trailer to detect and confirm lateral movement, the system works by extending one actuator and retracting the other, thereby twisting the anti-roll bar, applying an active roll moment to the vehicle.
CVDC research director Professor David Cebon explains: "Hydraulic accumulators store oil at high pressure
in order to provide the large flow rates required for severe transient manoeuvres."The net result is that the combination tilts into the corner (think high-speed train), thereby shifting its centre of gravity inwards and reducing the risk of a roll-over. "One control strategy is to demand an active roll moment proportional to lateral acceleration and choose the gain, so that at maximum lateral acceleration, there is a maximum roll inwards," says Cebon."Another possibility is to use optimal control to equalise the load transfer on all critical axles while providing maximum roll inwards. Up to 30% reduction in peak normal ised lateral load transfer can be achieved."
As well as successfully trialling the system on the tilt table at the Chobham test track in Surrey. CVDC has also conducted field tests with its high-stability artic, subjecting it to the classic turning-circle-at-speed manoeuvre. Ilie video evidence of the truck's trailer leaning into the corner is certainly impressive and shows how a roll-over risk can be mitigated.
Looking at the heavy-duty pipework and massive anti-roll bar at the rear of the CVDC Volvo test tractor ("Probably the biggest anti-roll bar on a truck anywhere in the world," says Cebon), it's clear that there is still much work to do in terms of 'miniaturising' the current prototype components into a practical system for production vehicles. However, it does show how active roll-control systems could improve future stability.
Cebon states: "Substantial reductions in normalised Lateral load transfers can be achieved and roll-over accidents avoided by rolling the vehicle into the corner. The CVDC computer-controlled experimental vehicle paves the way for future commercial systems. such as semi-active roll control." Cebon acknowledges that in its current guise the prototype system is probably too heavy for commercial use. He adds that an active steering system (see below) could be equally as effective in reducing roll-overs through improving the vehicle's steering path, and would not only be lighter, but also not incur any of the braking interventions normally experienced with current ESP programmes.
Quicker brakes better stopping
While few would dispute that today's II6V braking systems are superior to those found on a truck a decade ago, reducing the inherent delay in air-brake systems, which rely on solenoid valves to open or close to allow air to pass down a line to the brake chambers, has been a major research area for CVDC. In particular it has been
examining ways to cut ABS cycling times and optimise the amount of time a braking truck wheel stays at the peak of the 'slip-curve' — the point at which maximum braking is applied before a wheel locks-up, and the brakes are then released before being re-applied.
Working with an ultra-fast prototype 'Binary Actuated Valve' produced by Camcon, in laboratory trials CVDC has already been able to cut the pneumatic time delay in valve opening from 40 milliseconds to just three milliseconds. Translated into the real world. it predicts that by equipping a truck with these faster-acting 3m/s valves its stopping distance can he reduced by as much as 20%25%, while the amount of air consumed during braking would also be cut by as much as 50%. This means its compressor would be working less hard, consuming less energy, saving fuel and reducing the size of air tanks necessary on the truck, and offering further weight savings.
During the CVDC open day. Cebon also focused on the improved efficiencies offered by Longer Heavier Vehicles (LHVs) and their role in reducing road transport CO2 emissions. However, with public disquiet over LHVs still
riding high, and many in the haulage industry yet to be convinced of their benefits, Cebon describes how the use of active-steering systems could minimise their turning circle on Britain's roads and improve their overall traffic compatibility To prove the point. CVDC has developed its own LHV B-Double demonstrator with active steering on six of its seven axles. Using a CAN-bus-controlled hydraulic positive-steering system on both the 25.25m-long combination's semi-trailers, they 'path follow' the Volvo FH prime mover to such an accuracy that there is minimal (1.1m) cut-in when turning and. arguably more important for the driver who can't see it happening, no tail swing-out whatsoever.
While the extra weight and complication of having steered axles on both trailers might be a disincentive to some operators, the obvious reduction in tyre scrub would offer potentially large savings in tyre costs. Moreover, with CVDC's active steering control, a 25.25m-long LHV would be able to make far more precise lane changes at highway speeds improving its traffic 'friendliness: Once again, the system is at the prototype stage although its potential is not hard to see, and not just for LHVs, hut also for existing vehicles and, especially if the DfT agrees to them, longer artics.
Perhaps the most impressive demonstration of the day was reversing the CVDC actively-steered rig around a 'roundabout' with a 125m radius (the outer dimension for the EU turning circle requirements for an artic) with the driver using a TV monitor and steering with a computeraided joy-stick rather than the steering wheel.That's probably one development that is definitely for the future...
Cebon says: "The only way to get 25.25m-long L1-[Vs on the road in the UK would be to have them fitted with active steering systems as they are currently difficult to reverse and don't meet current UK heavy truck circle regs."
One notable exception to that is the Denby Fco-i,ink B-Double, which was also shown off at MIRA, meeting the required 12.5,5.3m turning corridor of an artic. •