Science Interviews


Sun, 3rd May 2009

The Science of Driving a Heavy Goods Vehicle

Dr Andrew Odhams, Cambridge University

Listen Now    Download as mp3 from the show Tackling Transport

Chris - We are talking about engineering, we are talking about transport and this is no exception, Andrew Odhams is with us, he's from the engineering department at Cambridge University where he has developed a very elegant solution to an age-old problem, Andrew good evening and welcome to the Naked Scientists.  Good to have you with us.

Andrew -   Thank you.

Chris -   What was the problem you set out to solve?

Andrew -   Well, itís about articulated lorries, everybody is familiar with, tractor semi-trailers as we call them, and the normal articulated lorries with three axles at the back on the trailer and a tractor with a drive axle and a steer axle, so itís five axles in all, but the front axles of the tractor obviously steer but none of the others, so we wondered what would happen if you steered the trailer axles as well and what benefits you can get to the performance of these vehicles.

Articulated LorryChris -   So what problems do lorry drivers face when trying to handle a lorry with that configuration at the moment?

Andrew -   Well itís two-fold.  First it's low speed, their manoeuvrability and then also at high speed there are problems with these vehicles.  At low speed you probably notice if you come alongside one of these vehicles on a roundabout,  especially on a tight roundabout that as they go around the roundabout they start to cut in.  The trailer gets further and further into the roundaboutÖ

Chris -   They mount the corner, they mount the curb...  They cut you up.

Andrew -   Thatís right, theyíll mount the curb.

Chris -   But itís not the driverís fault, no, you can't do anything about that, thatís an engineering consequence of the way the lorry's set up.

Andrew -   Exactly.

Chris -   And you're saying you can make things better.

Andrew -   Well if you steer the rear wheels of the trailer you can get the rear of the trailer to be further out on the roundabout.  Now the steering systems do exist, low loaders have used them for a number of years but the sort of strategies people have used, the control strategies they have used to control that steering is not perfect.  It emulates having a fixed axle say half way down the vehicle, the trouble with that is you get the opposite problem.  When you come into a roundabout the rear of the trailer swings out and if you are a cyclist just next to that trailer you then get the trailer coming at you unexpectedly.

Chris -   So basically substituting one problem for another.

Andrew -   Exactly.

Chris -   So whatís your solution?

Andrew -   So the challenge was to come up with a system with no-compromise which obviously everybody would love, and weíve made ours computer controlled. Itís fully active which means that we can avoid tail swing whilst minimizing cut and you can effectively get the box thatís the rear of the semi trailer around the corner in the minimum space possible if you were trying to fit it, you know, if you had on a piece of paper and you are trying to fit it around the corner itís the minimum space you can possibly get it round in.

Chris -   Without destroying your patent application.  How does it work?

Andrew -   You try and make the rear of the trailer follow where the front went so itísÖ

Chris -   That sounds logical so what does it actually do, to do that?  Does the front end know where its going, so tells the back end and the back end then sort of waits a certain amount of time and then makes the adjustment or something, is that how it works?

Andrew -   Yes, probably that.  You remember the path of the front hook in the computer and then it recreates it at the rear.

Chris -   How does it do that?

Andrew -   We have a range of sensors. It needs to know what the articulation angle is between the tractor and the semi trailer and not much more than that. It needs to know how fast itís going but not much more than that.  Itís relatively simple to do but you do need an active system to do it.

Chris -   So would this involve then having to completely overhaul an existing lorry in order to plumb this in, could you retrofit Britainís rolling stock to accommodate your system or would a lorry have to be designed bespoke with this in mind?

Andrew -   Youíd have to design it bespoke.  You could retrofit them but at lower performance you could retrofit into existing vehicles but trailers are changed every couple of years anyway so itís not something thatís going to take ten years to roll out into a fleet if you wanted to do it.

Chris -   One problem when people have tried to develop things like that in the past, correct me if I am wrong but have they not have problems with the resonance where the front of the vehicle does one thing so the back tries to copy but overcorrects and then that puts the front off which then corrects and that puts the back off which over corrects and before you know it you are sort of going all over the road and itís dangerous.

Andrew -   This is where the cleverer bits come in, you know we've talked about the relatively simple bits but especially when it's going at high speed, I mentioned it briefly we're trying to correct the behaviour of the trailer when itís say doing a lane change at high speed, this is the classic thing you come across on a motorway, the driver is doing something else or not paying attention or somebody brakes heavily in front of them they have to avoid them, because they know canít stop, and you could swap into the adjacent lane but it involves doing a very severe manoeuvre with the front of the tractor semi trailer and unfortunately the dynamics of them mean, the rear does most of the manoeuvre which can cause it to roll over, you know that a tractor semi trailer will roll over before it will skid in contrast to a car.

Chris -   So how do you get round that?

Andrew -   Well you can control the steering, you only need a few degrees but if you can control the steering carefully enough, you can prevent this problem.

Chris -   So your system is basically a very clever computer program thatís watching what the front of the lorry is doing.  Itís feeding that back through your programme, itís speed-sensitive, to the back of the lorry and itís basically making the appropriate correction to the back of the lorry based on what the road conditions are or the travelling conditions of the tractor, the front of the lorry is doing so that you get an appropriate response at all speeds of travel.

Andrew -   Yes, that would be our ideal case, yeah, and that weíveÖ

Chris -   Sounds intriguing, and taking that forward because we're little bit tight for time, just to sort of look at the applications for this, apart from making roundabouts safer when lorries go around them in towns and things, what else logically in the long-term could you do with a system like that?

Andrew -   Well you can, by making a trailer more manoeuvrable and safer you can take a larger trailer into a smaller space.  You could, for instance, take tractor semi trailers into the middle of town if you wanted to if you thought that was a safe thing to do you could, without endangeringÖ

Chris -   Some people do in Cambridge already out there.

Andrew -   Yes, as a cyclist I have a vested interest in making them as safe as possible.  But if you can get a larger trailer into a smaller space you can make it more efficient and transport-wise you know, you donít have to try and shift between tractor semi trailers and smaller trailers to skid to the middle of town.

Chris -   So transport can basically become a lot more efficient.

Andrew -   A lot more efficient overall, yeah.

Chris -   Brilliant, thank you very much, thatís Dr. Andrew Odhams.  He is from the engineering department at Cambridge University with an intriguing and ingenius way to make lorries much easier to manoeuvre, and much safer too.


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