Round the Bend

Sadly, the number of serious accidents each year in the UK remains high,  despite an emphasis on road safety from both our government and the EU,  and recent advances in vehicle technology.

One aspect of driving that continues to be a problem area is cornering.  But it's not always simply driving round a bend - the physical act of the vehicle being steered in a curved path that is too tight for its speed is the real issue, and that can happen even on a straight road.  

Sometimes it's a sudden lane change on a motorway - a swerve.  Or a late decision to use an exit slip road - from the outside lane in some cases.  But whatever the cause, the driver should always think of the Friction Circle, an illustration of the finite nature of friction and how the Laws of Physics apply to us all.

Even with ESC (Electronic Stability Control) a car is not infallible - the Laws are still there.  Each tyre has a maximum amount of friction available, which can be used for cornering, driving and braking, or, as in most cases, a combination of cornering and one of the other two.

This is an extremely important point and it affects all vehicles (although it seems to cause more problems with the drivers of front wheel drive cars).

The friction circle shows that if you are braking hard, you have little or no friction left for cornering.  ABS disguises this by extending the braking distance while allowing cornering to continue.  Without ABS, the wheels lock and the vehicle goes in a straight line - at maximum braking. 

And don't forget - the Laws of Physics always apply.  ABS, traction control and ESC are all limited by nature.

1. The vehicle is cornering hard and the driver, probably realising the speed is too great, applies the brakes.  The vehicle pushes out.  2. The vehicle is travelling too fast for the bend and the driver lifts of the accelerator.  On this FWD vehicle, friction that was being used for drive is 'given back' to the front tyres, so their cornering ability (relationship between cornering force and slip angle) increases. The vehicle 'cuts in'.  Weight is also transferred forward, adding to the cornering ability of the front tyres.  At high speeds, this can happen very quickly and the driver's reaction - to counter steer, rapidly - can send the vehicle completely out of control.  3.  While approaching the bend, the driver brakes to the correct speed for the bend, selects the right gear for the speed, and then drives through.  Tyre friction is being used mostly for cornering with very little needed for drive - perfect.  4. The driver accelerates hard in the bend and the front tyres take friction from cornering - the car understeers out. 

Beside the Seaside

The consensus of opinion was that the company wouldn't last the year out. They were being battered by the union, the sun was rising in the East and the shareholders, as shareholders did, expected a better return. Most of the management were present that day, seated around the boardroom table, and to a man they could see what was coming: the dark cloud looming. They had all lived through worse and understood the feeling of impending doom; the approaching storm and the hardships that would follow. Grimshaw still covered his mouth with a carefully placed hand when he spoke, in an effort to cover scars that resulted from his awful burns. The youngest there by far, he always wore garishly chequered suits with a bright handkerchief tucked in the jacket's top pocket; a deflection, everyone thought. And there was Allinson, a haggard looking and twitchy forty-something who always voiced approval with the words, 'I'll drink to that'. They were all in some way Allinsons and Grimshaws; live for the moment that's what they'd learnt, and they all bore the scars in one form or other. Allinson said the brass hats didn't understand what was going on at the front, and that was the problem. They'd have to dig in until support arrived or it all blew over. Grimshaw, speaking from behind a hand raised to his mouth, told them that if better kit wasn't made available and the men didn't play the game, they would be lost for sure. It was as simple as that, he said. There were nods all round. They would need to stand firm, he said, and got up from his seat and walked to a small table in the corner of the room, one that was always laid out with numerous bottles. All around the room hung the portraits of those who had 'commanded' before; a dusty display of heredity, position and place. “I'll drink to that”, Allinson said, and slumped in his chair, stretching his legs out under the table.

The factory floor was always swept clean; the chassis were lined up in neat rows, in time honoured fashion; and the men moved among them, in and out, following channels worn into the floor by generations of workers before. In the canteen the talk was of new motorcycles from BSA and Triumph, the latest music and all the newfangled gadgets coming across the sea from America. On the walls, posters advertised saving schemes and premium bonds. Everyone knew the price that had been paid and the debt they were owed. The war was still very fresh in everyone's memory. They believed they had prevailed against great odds and were undefeated; the country was the best; produced the best; deserved the best. They thought, as victors, they were owed a better life, and because the country had been saved by everyone fighting together the old establishment should be washed away, like castles made of sand on the beach. Wage demands and the threat of strikes were always present, even when it became obvious overseas competition was a serious threat. Talk of closure had started to filter down from above. Rumour, that's what they thought; it was all just rumour. But soon things got serious and a wave of panic started; and, of course, the questions. Who was responsible, and why? In the end there was speculation about mergers, Government interventions and co-operatives; all materialised to some extent or other, but non worked.

At home the women carried on as normal; very little had changed for them. Their work was the same as it always had been. Making ends meet, raising a family, keeping things afloat, looking after the home. Such as they were in those days. Terraced houses with outside toilets and fires you had to make each morning; no microwaves or fridges, or any of the things we have these days that make life easier. Except for the occasional holiday by the sea, if you were lucky, life for the women had changed little since the end of war. Rationing had continued for ages and they still had the worry; it was just a different worry, that was all. And when, in the end, when the factory closed, it was the women that had to keep things together. Trouble seemed to come in waves; some days rougher than others. If anyone deserved a holiday, they did.

It was all right for me, though. I was only young then and a secretary at the factory. I had to take minutes at management meetings but at the same time I was from the same streets the workers came from, so I knew the boardroom as well as I did the shopfloor. I lived at home with my parents in a little two up, two down and had no real responsibilities to speak of. For all my knowledge of the company, I didn't really appreciate the extent of the concerns people had about the future, and, I suppose, I was too young and naive to understand. I was a child in the war, you see. I couldn't fully appreciate what the grown-ups had endured; everyone had a story to tell that involved some sort of loss, no matter how small. I was always thinking about holidays and coming here. To me at that time there seemed little else to look forward to; what else did we have but the seaside?

She was sitting on a bench on the seafront close to my truck and we had somehow just got talking. I was waiting for a machine that a construction company was using for some foundation work to be ready for loading and she seemed to be in no hurry to move on. She was old, probably in her mid to late seventies, and immaculate in every way, which made her look more like visiting gentry or a retired headteacher than a retired secretary. “More changes”? She said, looking at the works going on nearby. “Yes”, I said. “Everything changes, thankfully”. She looked at a loss for something to say. “More work for people like me”, I explained. She glanced at my truck and its low-loader trailer, and then screwed her lips into what I took to be a smile. But then someone caught her eye and she stood up. A smartly dressed man, probably a few years her senior, was approaching us. He was wearing a brightly coloured sports jacket and a pair of brogues that almost glowed burgundy. With a matching handkerchief flamboyantly draped from the jacket's top pocket, he looked a little over dressed among the more retiring of that seaside retirement stronghold. She said her goodbyes and took his arm as he nodded an acknowledgement to me, carefully holding, I noticed, a hand over his mouth. 

This Sign is Not in Use

It must be one of the strangest signs you see on the road. THIS SIGN IS NOT IN USE it informs you – and with considerable effort if the forty-foot gantry post and all that expensive electrical equipment is anything to go by. But why? The sign seems to be telling you to ignore it; which you would have had it not grabbed your attention with an enormous message suspended above two lanes of the carriageway. If it's got nothing else to say, why not display: JUNCTION 25 35 MILES 30 MINUTES, which could be useful if it didn't assume an average speed of 70 mph, a speed at which few vehicles actually travel. DON'T DRIVE TIRED has replaced DON'T DRINK AND DRIVE now that most people have got that message, so it could be used to encourage drivers to take a break. 

There is a problem with these messages, though, in that they sound like an order. Whenever controls are imposed, something inside us reacts to make any limit seem like a challenge. If we can't avoid it, we'll exploit it. In this way a limit becomes a target; if it's not possible to exceed, then it must be reached. I'm sure this behaviour is deeply rooted in instinct, and that all animals have it. My Labrador will eat anything, all day if I let her; any survival expert will tell you, eat whenever you can, it may be your last meal for a while. It's this trait that supermarkets exploit when they offer special deals. Four bottles of beer for a fiver; which makes you pick up more than you wanted, or is probably good for you. Buy one, get one free; when we all know one could be sold cheaper. We snap it up. Logic says it must be a sales pitch but our minds won't let us see it that way. That thing inside us all which says we must get as much as possible, straight away, concludes that a limit has been set and we must go to that limit. The fact that we believe it's a bargain, clinches it. Subtly, we have been convinced that this is the most we'll be able to have, and we are left with only one option: 'go for it now'.

Drive down any country lane and you will see car drivers hurtling along at speeds where no margin is left for error. Too fast for the width of the road and the view available through the bends, while thinking they can travel at the speed limit of 60mph. Tachograph hours can cause the same type of confusion: 4.5 hours driving without a break is permitted under the regulations when, according to the road safety charity BRAKE, we shouldn't drive for more than 2 hours without stopping.  And there's the problem: by implementing tachograph regulations the law has created a limit.  One that we chase, often ignoring other signs that tell us something might be wrong, all in the false belief that we must use every minute of driving time, immediately.  DON'T DRIVE TIRED doesn't seem such a bad instruction after all.

Normal sleep does not occur without warning and most people would recognize the signs of its approach: increased difficulty concentrating; yawning; heavy eyelids; eyes starting to ‘roll’; and neck muscles relaxing, making the head droop. Winding down the window, listening to music and talking to a passenger do not help prevent sleep, although they may temporarily help us to stay alert until we find somewhere safe to stop. Again, according to BRAKE, 'microsleeps' of about 10 minutes seem to be the answer, so a 15 minute break followed by a 30 minute break around a couple of hours later (permitted by the tachograph regulations) might be what's needed to both comply with the law and allow us to respond to the signs our body is giving. Signs we simply can't afford to ignore.

It could be that all signs have a genuine message. Maybe by displaying, THIS SIGN IS NOT IN USE instead of simply remaining blank, those gantry signs are telling us that they can't warn us, and their real message is: THERE JUST MIGHT BE A PROBLEM AHEAD.

Dreamtime

“Perhaps he couldn't see the wood for the trees”, Bernard said, looking at the sergeant, a faint smile appearing on his lips. The sergeant bent forward and placed the palm of his right hand on the only part of the Nissan's roof that was still flat, steadying himself as he looked through the remains of the driver's door. There was warmth in the metal from the late afternoon sun. Bernard stood a few yards away and only had to stoop to see the driver's blood stained head wedged between the steering wheel and a windscreen crushed by the front of the roof during the impact. The torso seemed to be wrapped in deformed  plastic and metal that had once been a dashboard and engine bulkhead. They both focused on the driver’s eyes. Dead, young eyes; half closed, fixed, dull. “Any smell of booze in there”? Bernard said. “You know what they're like”. The sergeant looked past the driver's head and saw his own face reflected in the few remaining pieces of a twisted and broken mirror mounted on the outside of the passenger door opposite. His eyes went back at the driver before he stood up and faced Bernard. “Sorry”, Bernard said.

The Nissan, a small flat-bed truck, a 'tray', they called them, was trapped underneath the rear semi-trailer of a 'pocket' roadtrain. The Nissan had been travelling along the main route, the roadtrain, loaded with logs, was leaving a track from a forestry site, turning across the small truck's path. Paramedics had been and gone, there was nothing they could do, and the driver of the roadtrain was now talking to some local officers, as Bernard and the sergeant began their investigation. The enormous forest formed a backdrop that climbed a low escarpment in the distance; a mass of greens and browns set against the clear blue sky. The sergeant looked to the distant trees; there was a breeze up there making some of the branches sway. “Any sign of braking?” Bernard asked, walking slowly back down the road a short way, studying the dusty surface over which the Nissan would have travelled. It wasn't long before he sauntered  back. “There's no marks”, he said. “What about the tyres”? Bernard crawled under the trailer as he spoke, intent on getting a closer look. The Nissan had been dragged sideways after going  under the roadtrain and there were marks on the road to show this movement, but nothing else: no additional heat scarring on the tyres themselves that might have shown the Nissan's driver was braking before the collision. The sergeant followed Bernard's movements with an occasional glance but remained standing beside the dead driver, his hand still resting on the roof above the body.

“The brake light bulbs might tell us something”, Bernard said, pulling a multi-tool from a pouch attached to his trouser belt. He flipped out the Philips driver and began removing the rear light lenses. “If the filaments are stretched it may indicate the lights were on; their metal hot”, he said. But neither bulb showed any sign that they were on during a sudden deceleration. “Both broken but not stretched”, Bernard sounded disappointed. “The sun may have been low, maybe it was shining in his eyes, so he couldn't see”. Bernard seemed to be talking to himself. “Mind you", he said. "The locals say there were some clouds about, so the sun might not have been out when it happened”. The sergeant just looked past him, still gazing towards the distant hills. There would be kangaroos up there, you could imagine them foraging as dusk approached, now the real heat of the day had gone. “How long do you think it would have taken the prime-mover and the first semi to get to where they did before the collision”? Bernard asked. The sergeant thought for a moment, but wasn't able to answer before Bernard came up with his own assessment. “Could have been about five seconds”, he said. “Possibly”.

“Apparently, it's one of the biggest natural forests in the country”, Bernard was now saying. He didn't know the area well; he'd just read about it on their trip up. It wasn't a region anyone, as far as he could see, would wish to visit and he certainly would have no reason to go there himself, under normal circumstances. It was a long way from civilization. In fact, it had taken a couple of hours to fly from State Police headquarters, a journey they would have to retrace later when they headed home, leaving local officers to clear up and deal with the body.  "Pretty impressive, aye; trees as far as you can see”. The sergeant heard what was being said, he nodded occasionally, but his eyes were fixed on those hills. There would be snakes among the trees, the serpent, and frogs, probably, and, of course, birds. The butterfly too. “These rigs are in and out of here all day long, carting logs away, if he's local”. Bernard gestured towards the Nissan as he spoke. “He must have known that”. He paused for a moment. “If he was doing sixty kph, he would be about ...”. There was a further silence from Bernard; his face raised to the sky while he concentrated on the computation. “... Let's see, a kilometre a minute, so, that's … over sixteen metres per second. In five seconds, that is at least ... eighty metres. Eighty metres! He must have been asleep not to see the rig pulling out in front of him. He could have stopped, easily; he wouldn't even have had to brake hard”. The sergeant wasn't listening now. There were koalas too; before the machines came, anyway. “Or just taking time out”, Bernard said.

Building a Scania R500 - Part 7. Brakes

I`m building a Scania R500 - from a 1:24 scale kit produced by ITALERI.

I`ll be looking at aspects of truck construction as I go along, hopefully highlighting some basic truck technology.  It`s easy to think that modern vehicles bear no resemblance to those of the past, but that`s not true.  Suspension and steering; engine, transmission and final drive; and tyres are all there to maximise the laws of physics, and have retained the same configuration since diesel replaced steam.  Cost and natural performance limits have meant that the chassis abandoned long ago in car design is still used in truck manufacture.   Yes, your truck is computer controlled and a modern marvel;  but so is the modern cruise liner - which is still a Titanic underneath.

Building a Scania  R500    Part 7.  Brakes)

Although complex in detail, the principles behind truck braking systems are reasonably simple.  Compressed air is used because of the braking force needed to stop up to 44 tonnes (UK).  Force = pressure x area, which means that cars and light vehicles are able to use a vacuum (atmosphere = 1 bar) servo to provide additional force in the braking system; the 8 bar used by trucks would need a vacuum servo 8 times the area of those used in cars.  This would be totally  impractical, of course.  Air brakes also continually replenish the medium (air) so leaks can be less significant than in hydraulic systems.

All new heavy trucks use EBS (electronic braking) but this refers to control (foot, hand and relay valves) not to the method of actuation.  This is still done by compressed air.

Air braking systems have four sections - compression and storage, control, actuation, monitoring and warning.

  

Air cylinders are the best shape to deal with a compressed gas - and air is a gas

The skin of the cylinder is put into tension by the force of the gas

Although now typically contained in one unit mounted beneath the front of the cab (air processing unit) the air dryer, unloader and multi-circuit protection valve (MCPV) perform separate functions. The unloader valve prevents air pressure going above the set operating value of 8 bar (sometimes storage is higher).  A lengthy pipe between the compressor and the unit allows air to cool, protecting the valve.  The air is then dried before it reaches the circuit protection valve.  The logic of this sequence should be obvious - compression, regulation, drying, then the valves (the MCPV is the first of many).  The unloader blasts air through the air dryer when it kicks into operation, when pressure is 'up', in an attempt to clear moisture from the crystals - you of ten hear this when standing by the vehicle. Multi-circuit protection is one of the most important valves as it controls air on build-up and run down.  It protects the service brakes and distinguishes between brakes, suspension and ancillaries.  ( E.g. If air was completely depleted, the MCPV would charge the service brakes before it allowed air to release the park brake.) Many vehicle run park brakes and ancillaries from the MCPV utilising as fewer tanks as possible. All service brake (foot) systems must be split in two, so just like hydraulic master cylinders in cars are dual circuit, truck foot valves are dual air units.  

Although now replaced by EBS electronics, these control valves still exist as back-up systems - in fact EBS valves have to do the same job and that is to provide gradual actuation in response to the drivers braking demands.  Air control valves rely on 'lapping'; air that goes under the piston in the valve and works against the driver's foot (in the case of a foot valve - hand valves and relay valves use the same principle).  When the driver stops pushing down, the valve will become lapped and no further air pressure will be applied to the brakes.  When the foot is removed, the inlet valve closes and air in the valve, along with that in the brake servo/actuator, is exhausted to atmosphere.  This is a simplified foot valve, in reality the  unit  would have two elements supplied from two different tanks, themselves fed from two different elements of the MCPV - Service 1 and Service 2.

Air relays (and EBS electronic relays) are a type if control valve.  They are designed to speed up application of the brakes.  Air from a storage tank sits close to the foundation brakes (at an axle) and the relay valve is signalled by the foot valve to allow air to pass to the brakes.  The law (UK) requires a maximum 0.6 seconds between foot pedal application to the brakes coming on - this is about 7 metres for a truck travelling at 30mph.  EBS shortens this time.

Winter Wonderland

Ask most blokes what they know about Sweden and you usually get one of two things: an animated description of a curvy blond that looks like someone trying to shape an enormous hour-glass on a potter's wheel, or an impression of the chef from the Muppet Show, that sounds like someone with their head in a bucket. What they don't often say is that Sweden is one of the wealthiest countries in the world and despite such a harsh climate, it is not suffering quite like the rest of us .

In many ways Sweden is similar to the UK: a large percentage of its workforce is employed in the public sector, it has high taxation, and despite being in the EU, it has remained outside the Euro. But that's were the similarity ends because Sweden has a large GDP, it exports more than it imports (a situation long forgotten in the UK economy) and it has many international manufacturing companies (including Volvo and Saab/Scania). Sweden can suffer from some pretty harsh temperatures in winter (down to -40^o C in some areas) but just like the country doesn't seem to be effected too severely by the global economic climate, it doesn't appear to suffer from the weather either; in fact it seems to benefit from it.

Every time I read about the exploits of transcontinental and Middle Eastern drivers, watch Destination Doha on DVD or look at the resale value of some trucks, I'm reminded of why we see so many Scanias and Volvos on the road – and no Leylands. If Scania and Volvo trucks can operate in temperatures so extreme at one end of the spectrum, they can presumably survive the other; If they can endure those rock hard winter logging roads, the desert must be a doddle. It's no wonder they do so well on ordinary work, and have such a following. Sweden does have natural resources that help with the balance of payments but it's quality products like these, and a tough attitude towards a diverse economy that has really created success.

Sweden is not dissimilar to the UK in that it has produced the machinery needed to build a developed world; the difference is that we no longer do. Where we have totally succumbed to the philosophy, 'let the market decide' and allowed so much of our major industry to go to foreign ownership - and in too many cases seen it closed by the new owner - Sweden has retained control of its factories. And although it's true that a number of Swedish companies operate overseas manufacturing sites, where labour is cheaper, home ownership still means that decisions are presumably made in Sweden's best interest and not that of an overseas economy.

Sweden's banking system went through the mill in the 1990s and emerged stronger, hopefully ours will too. Like Sweden, we have brilliant scientists, engineers and innovators, and we can make quality products. All we need is a government that can think beyond the service industry, encouraging a diversity of economy that will not just protect jobs but create them, lead to exports and exploit the demand for machines and technologies in the gowing economies of India and China. They stood up and kept us out of the Euro in the interest of our financial sector; now winter's come it's time to come out fighting for a change in the whole climate.

  

The Mechanics of Failure

A small fault starts, unseen at first, easily missed, a stress is applied, back and forth, to and fro, fatigue and creep, building slowly, you hardly know, finding its way, increasing in size, taking over, gathering speed, the structure fails, suddenly torn, catastrophic, an enormous crack that signals the end. 

What's it in for, he asked. Chassis extension, I told him. What, to a tractor unit with a bonnet, what's it going to be pulling, a caravan? No, I said, it's to make a rigid, a beaver tail plant carrier. Oh. Why? He said.  Never mind why, I told him, what are you all of a sudden, 'Mr Workshop'? No, he said, sheepishly, I'm 'Mr Office'. Right, I said, winking at him, tell DH (Mr Workshop) to get on it as soon as. He's short this week, he said, two off and plenty of regular customers in for urgent work. Get the boy to do the welding, I told him, he's two years with us now; his welding's okay. Right, he said, tucking into a Tupperware pot containing a meagre looking salad. I'll be out for the rest of the day, I informed him. Right, he said, winking at me. Oh, and I won't be about 'till the end of the week, either, I said. Don't forget you'll be needed after that, he reminded me, DH is taking a long weekend.

The Boss says The Boy can do it, he tells Mr Workshop. The Boy? Mr Workshop says, he can barely dress himself, let alone build a chassis. The Boss said he's okay, Mr Office says, and apparently all the bits are here already, and he knows you are busy. If that's what The Boss wants, Mr Workshop says, I'll try to keep an eye on it. Axle stands are in place; the cutting and welding kit is assembled close by. I need a hand with the timing, says Tech 1; that bearing is weeping again, says Tech 2; the diagnostics are not connecting says Tech 3. Mr Workshop drains oil and changes filters, servicing as he passes by, moving from bay to bay, and back again, all the time answering the calls of his technicians. The Boy's voice is not heard. Tea is taken on the move; lunch is a squeezed, gulped sandwich, oozing its filling over oily hands. The Boy cuts. The Boy measures. The Boy positions. See what you think; says Tech 1; give us a hand, says Tech 2; look at this, says Tech 3. The Boy welds. The Boy drills. The Boy assembles. Mr Workshop wipes his brow with his sleeve; Mr Office answers the phone. The days pass in the blink of an eye. We seemed to have survived intact, Mr Workshop tells Mr Office. I haven't stopped, Mr Office says, the phone just rang and rang; all those invoices; the spares I've ordered in the last few days! The workshop! Says Mr Workshop, we haven't had a moments rest. You've managed to complete all the work? Mr Office asks. All the technicians' jobs are signed off, Mr Workshop says, proudly. The lads did really well, every last one of them.

How did the chassis job go? I asked him. DH told me it went okay, he said. He signed off all the work. I'll have a look at it, I said. Too late, it's gone out, they took it for plating earlier. Oh, I said. How long did it take? Don't know, he told me, we were very busy; the Boy spent all his time on it. The Boy? The Boy!  I said. You said he could do it, he said. I told you he could do the welding; welding what bits he was told to, I said. Oh, he said. Oh? I said, Are you telling me The Boy did the whole job, alone, by himself, unsupervised? Oh dear, he said. Oh God, I said. Did he use the correct cross members on the ladder: pressed and box section for bending loads and tubes for twisting? Did he use enough flitch plate material to strengthen the rails - the frame? Did he use bolted joints to relieve stresses in some members, and weld sympathetically for torsion in the chassis. Did he consider how bolted and riveted joints become crack arresters? Did he consider stress concentrations when he drilled into the chassis rails? Oh dear, he said.

                                                   *************

It failed, they tell The Boss, the Tester said there was cracking and some of the body's mounting bolts had sheared already, so The Boss gets it back in the workshop and tells Mr Office to get on the phone to the customer and tell them there is a delay due to the volume of work and The Boy and the Boss get the plans out and the alignment kit and dismantle, cut and unbolt and then The Boy and The Boss measure, weld and bolt, and Mr Office deals with the phone.

And they stop for lunch, and they sit down together for tea, and they relax and talk -  for as long as it takes.