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Post by onlymark on Jan 17, 2011 9:37:03 GMT
Don't really know where to put this. So if anyone wants to move it to somewhere more suitable.......
How does your car work?
I intend with this to keep it fairly simple and just give a basic outline of how a car works. Most of us have one and I expect we have all ridden in one. It is a machine we tend to take for granted, has caused innumerable debates as to its worth and much has been written about it. It is a major part of the life of many people. Yet few really know ‘what makes it tick’. Even if someone expresses an interest there is just too much information available, most being far too technical and dry, most that profess to be for the beginner actually end up losing the interest of the reader by getting bogged down into too much detail and tech speak.
I’m going to attempt to really simplify things, give a rough approximation of the things involved and it is then up to you to take it further if you want. I don’t mean to insult your intelligence, I am just aware that there are many people who, by their own admission, know absolutely nothing about how a car works but who wanted to know just enough to get by. Just enough to satisfy their curiosity but didn’t want to get lost in the technical side and get bored by it all. I was prompted in to this by recently speaking with someone who wanted to know why they couldn’t fill up with diesel instead of petrol as it was cheaper.
So..... The important parts of a car can be boiled down to three things. Something to make it go, something to make it stop and a way to make it steer round corners. Nothing else is particularly necessary and most other things are part of or support those three functions.
Something to make it go –
An engine is a good idea. It can sit at the front (usual) at the back (like VW Beetles) or in the middle (as with some sports cars). It can get its power from petrol, diesel or some type of gas (I’m not dealing with electric cars here) but it has to be something that is inflammable. The engine is fed by the fuel, it is mixed with air (needs oxygen to burn properly) and the force of the ‘explosion’ when it is ignited produces enough power to move the car.
But how does it do this? In an engine? Imagine you put a bit of petrol in a sealed can with some air. Ignite the mixture (it doesn’t matter how for now) and what happens? The can explodes. This is all that happens in an engine. Fuel and air are put in a cylinder together and made to explode. Now imagine a bicycle pump (I’ll be using bikes quite often as they make good examples and we are mostly familiar with them). It has a cylinder in which is a piston. When you pull it back it sucks in air, when you push it back it pushes the air out. You though are providing the force, the power to do this. In an engine it does it by using part of the power made by the exploding fuel to do it itself. The excess power made is used to push the car along.
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Post by onlymark on Jan 17, 2011 9:39:30 GMT
In an engine the piston in the cylinder is pulled down, this sucks in a regulated amount of air and fuel, the piston is then pushed back up the cylinder and compresses the mixture (just because it makes for a more efficient explosion). A spark is applied when the compression is just about at its maximum (the piston is near the top), the whole thing explodes, this pushes the piston back down the cylinder and due to various mechanical connections the force made by this turns the road wheels.
The piston reaches the bottom of its travel and is pushed back up again to push out (exhaust) all the burnt gasses inside ready for a new cycle of the same thing happening again – down (suck), up (squeeze), down (bang), up (blow). When some petrol head starts talking about the four stroke cycle just nod your head and say “Ah yes, suck squeeze bang blow”. He’ll be speechless that you know of such things. (But then walk away quick before he asks you anything else).
All the engine in your car is, is a number of these cylinders with pistons inside, all sucking in a mixture and exploding it at slightly different times, going up and down at a great rate of knots to move the car along.
Diesel v petrol
These are the two main types of fuel, and what is the difference? Simply enough, one is more inflammable than the other – actually by a big margin. If you apply a spark to diesel, as in the engine, it won’t explode. It’s not inflammable enough. That’s why you can’t use diesel in a petrol engine car. It just won’t work. You won’t get an explosion. You can put petrol in a diesel engine but it will break it, it is too flammable for the design of the engine.
The question is though, so then how do you get a diesel engine to work if a spark won’t set fire to it? Let’s go back to the bicycle pump. You have a flat tyre on your bike. You mend it and begin to pump it up. You notice that the end of the pump is getting hotter and hotter. When you compress a gas it gets hotter. If you have a cylinder in which there is a piston, if the cylinder is big enough and the space you compress the gas down to is small enough when you move the piston, the temperature will rise high enough such that if you suddenly inject diesel in there, it will explode.
That is the difference between a petrol engine and a diesel one. In a petrol engine a spark ignites the fuel/air mixture. You can’t do this with diesel so you don’t use a spark. You compress the air enough to raise the temperature of it to such a degree that it is higher than the temperature at with diesel will combust itself. You then stick a bit of diesel in there and... bang. That’s why diesel engines are usually so much noisier than petrol ones – the explosion is so much more sudden and violent making a greater noise.
So in conclusion – make a piston move up and down a cylinder – suck, squeeze, bang, blow – put some fuel and air in there, ignite it with a spark or raising its temperature, make it explode, connect the piston to the wheels mechanically and you’ll move.
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Post by onlymark on Jan 17, 2011 9:40:39 GMT
What do gears do?
When you walk up a steep hill do you shorten your step to make it easier? That’s all a gearbox does. It ‘shortens’ the gear to make it easier for the engine to turn the wheels when you set off or when you go uphill. Then when the going is a bit easier it lengthens it again to something like a normal pace. You’ll notice in 1st gear the engine is going quite fast, but you aren’t. It is allowing the engine to work at a point where it is producing enough power due to the revolutions it is making. Engines, especially petrol ones, only have a short range of revolutions in where it produces the best power. If you allow the engine to work in that range you get the best performance out of it. If the ‘revs’ are too low it won’t produce enough power to move you.
Once you are moving you don’t need as much power to overcome the forces trying to make you slow down or stop. So you can change into a higher gear, and keep doing so as you get faster until you are in top gear (or you are a lazy git and have an automatic gearbox that does it for you). When you start to go uphill the forces trying to slow you down increase, so the gears drop down again to allow the engine to work at its best. Using the bicycle analogy again, you’ve been aware of this as you’ve changed gears. Your body is the same as an engine. It works best at certain ‘revolutions’ (and that’s why bikes in Holland often have just one gear, uphill and downhill is quite alien to them).
But how do you stop and/or go round a corner?
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Post by onlymark on Jan 17, 2011 9:41:38 GMT
Bored yet? Too much information? Not enough pictures?
More later. I've got to go out.
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Post by onlymark on Jan 17, 2011 10:11:33 GMT
Brakes are a good idea. They’ve developed a long way from trying to push a block of wood against a cart wheel to slow it down. Though modern day principles are virtually exactly the same. You may have heard talk of ‘drum’ brakes and ‘disc’ brakes. They are different but work on the same ancient principle – if you push with enough force something against a moving wheel, it will slow down.
Imagine being inside a large drum, on its side. It begins to roll (because your elder brother/sister told you to get in there while they roll it. Just for fun, but you know it’ll only be fun for them). But it’s going too fast. You push your hands on the insides to try and slow it down. That’s all a drum brake does. It uses a special material to push, via you pressing the brake pedal, on the inside of a small drum attached just inside the wheel, to slow the wheel down.
You’ve seen how a bicycle brake works? There are two pads of rubber that are squeezed onto the wheel. That’s the principle of a disc brake. Just inside each car wheel there are steel discs. These move with the wheel revolving. When you press the brake, two pads (again of special material) sit either side of the disc and are squeezed onto the disc slowing it down. Dead simple, but effective, and more so than drum brakes.
When you pressed the brake pedal in olden days a steel linkage would apply the brakes by transferring the force you pushed at to the pads (or brake shoes, as they are called in drum brakes). It was found that you couldn’t physically, as car became faster and heavier, supply enough force yourself, the linkages were temperamental and you lost a hell of a lot of the force you supplied via the pivot points and stuff. So they introduced hydraulic brakes.
All this is, is a system where your pedal is connected to the brakes on the wheels by pipes with hydraulic fluid in them. These can be bent around anywhere making life easy for the builders. The main advantage though was that you can’t compress a fluid. What this means is that the force you apply with your foot travels through the liquid and comes out the other end at the brakes with little loss. A far more efficient system.
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Post by onlymark on Jan 17, 2011 10:26:29 GMT
Steering
Quite simple for all the complex things fitted. A metal box shaped item (steering box) or a long metal bar with teeth (steering rack) convert the turning motion you make with the steering wheel into in and out (linear) motion and via various connections push and pull the wheels left and right. As cars got bigger and heavier it became far too difficult to do this by yourself, unless you were built like Atlas or Kerouac. All they did then was attach on to the steering system a hydraulic pump and ram that when you turned the wheel the ram would move left and right providing most of the force – power steering. If you’ve ever tried to steer your car when the engine isn’t running or the power steering has packed up, you’ll realise how much force it really now takes.
So, any questions? No, good. After a coffee break the next lecture will be from mickthecactus on “Raising cacti – is there a point?”
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Post by komsomol on Jan 17, 2011 10:47:37 GMT
This is good. Thanks.
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Post by tod2 on Jan 17, 2011 11:20:02 GMT
The difference between a diesel & petrol engine in the new car I am about to purchase is: Petrol 14litres per 100km Diesel 9litres per 100km
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Post by Deleted on Jan 17, 2011 11:59:39 GMT
I'm still awaiting the pics......
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Post by onlymark on Jan 17, 2011 12:47:51 GMT
tod, I much prefer diesels, always have done. Except for a motorbike.
casimira, I've afraid I got grease and oil all over the film. You'll have to use your imagination. I wouldn't expect there are many actually that are at this level of simplicity. They all tend to have lots of arrows and labels and bits sticking out everywhere that confuse things.
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Post by bixaorellana on Jan 17, 2011 15:43:41 GMT
The diesel engine is so far superior to gasoline, one wonders why gasoline engines even exist.
This is great stuff, Mark ~~ thank you. You're explaining things that I should know, but am so vague about due to turning off my brain when most people talk about them. Your way is accessible and easy to grasp and remember.
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Post by onlymark on Jan 17, 2011 16:44:56 GMT
Petrol engines were easier to make, and still are. That's possibly why. Also the power characteristics are different so they were more in keeping with what a car required rather than a truck. Plus petrols are quieter.
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Post by onlymark on Jan 17, 2011 17:20:00 GMT
Next then bixa, the answer to the question - "Genetic Modifications - do you reap what you sow?" followed by - "Human Genomes - are we a fish out of water?"
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Post by cristina on Jan 18, 2011 1:47:41 GMT
Steering As cars got bigger and heavier it became far too difficult to do this by yourself, unless you were built like Atlas or Kerouac. All they did then was attach on to the steering system a hydraulic pump and ram that when you turned the wheel the ram would move left and right providing most of the force – power steering. If you’ve ever tried to steer your car when the engine isn’t running or the power steering has packed up, you’ll realise how much force it really now takes. My power steering pump is being stubborn lately so I need either Atlas or Kerouac to come drive me around town. Or at least to and from work. Actually, my car is currently held together with duct tape, as the youngest child has started driving. Experience (in the form of 2 older children) tells me that this child will total a car. Therefore, I am hanging on to this one for that inevitable moment. Looking for a new fancy car for myself, however. And yes, the steering will be fixed before I allow my daughter to total the car. And my light-heartedness here assumes no injuries (as was the case with the first two childrens' driving adventures.) I used to know a lot more about what made my car run. But now, I think other demands have taken over that spot in my brain. Thanks for the refresher Mark!
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Post by cristina on Jan 18, 2011 1:55:38 GMT
The difference between a diesel & petrol engine in the new car I am about to purchase is: Petrol 14litres per 100km Diesel 9litres per 100km As I shop for a new car, all I am looking at is diesel. When I drove to L.A. last month, I rented a Prius (hybrid). Although not a diesel, the gas mileage was excellent once I got off the highway. The design takes some getting used to though. Especially if you are used to a fairly unobstructed view through the rear window.
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Post by onlymark on Jan 18, 2011 4:46:46 GMT
Cristine, when my father taught myself and my brother to drive he bought and old banger specially so it didn't matter if we totalled it. We never did (in fact my brother never took his test so never drove) but the car ended up lasting a lot longer than his 'good' one.
I'm not sure about a Prius at all. I know their reputation is somewhat overinflated and they aren't as good as they're cracked up to be. I'd look also at diesel cars if there are any where you are as I'm biased against the Prius (that rhymes, at least it does how I pronounce it) as I think it is more a fashion statement than a viable alternative.
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Post by Deleted on Jan 18, 2011 13:02:47 GMT
I kind of knew a lot of this stuff, even if I barely know how to tighten a bolt. One thing that does amaze me these days is the vast amount of electronics now found in cars. I would venture to say that there is probably too much, if you think back to some of the cars of bygone times which were of excellent quality and reliability and yet had absolutely zero electronics in them.
However, what I will never be able to understand, in spite of all of the diagrams for lift and push, is how a fully loaded 747 gets its fat arse off the ground.
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Post by onlymark on Jan 18, 2011 13:47:42 GMT
I read an article recently about how normal humans can no longer repair their cars because of all the electronics. I've known this for years and in fact I've stopped trying. I am fortunate that mine has very little as it is a basic export model but there are still things on it that I've no idea what they do.
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Post by cristina on Jan 19, 2011 4:21:07 GMT
I read an article recently about how normal humans can no longer repair their cars because of all the electronics. I've known this for years and in fact I've stopped trying. I am fortunate that mine has very little as it is a basic export model but there are still things on it that I've no idea what they do. What is an "export model" in Egypt? Just curious. I can still "check"certain things on my car if inclined. I know how to check my oil, but have no interest in changing it myself (because then I have to find a way to dispose of the old oil). I used to know how to gap or change my spark plugs, but I don't think cars use those anymore. I also know how to check my tire pressure, and have a gauge in my glovebox, however there's a place on my home from work that checks tire pressure for free. So, sometimes I am lazy. But I agree that most normal humans can't do basic things on their cars. Not because we're dumber, but because the cars require so much more technology for diagnostics.
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Post by cristina on Jan 19, 2011 4:27:00 GMT
Cristine, when my father taught myself and my brother to drive he bought and old banger specially so it didn't matter if we totalled it. We never did (in fact my brother never took his test so never drove) but the car ended up lasting a lot longer than his 'good' one. I'm not sure about a Prius at all. I know their reputation is somewhat overinflated and they aren't as good as they're cracked up to be. I'd look also at diesel cars if there are any where you are as I'm biased against the Prius (that rhymes, at least it does how I pronounce it) as I think it is more a fashion statement than a viable alternative. Your father was a luckier parent than I was. No plans for a Prius, Mark. But it was good to test drive as a rental. We do have diesel cars here, but maybe fewer choices than Europe or Africa. Volkswagon's Jetta diesel is occupying a prime spot at the moment. I still have a month or two of searching before I decide. Anyway, I only buy used cars so I will need a selection of 2 year old car models to choose from.
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Post by bixaorellana on Jan 19, 2011 16:34:36 GMT
Volkswagon's Jetta diesel ~~
I bought one in 1989. In 2008, I was talked into changing the engine to gasoline. The car had over 500,000 miles on it. I never felt I had a really good mechanic here, plus there is a major problem in getting parts for it. Also, there's no opportunity to get out on the highway and flush it out, as there always was in the States.
It's safe to say I got my money's worth from that car.
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Post by onlymark on Jan 19, 2011 16:57:27 GMT
I certainly think you did. The VW engine was a good one, though a bit noisy.
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Post by bixaorellana on Jan 19, 2011 18:04:17 GMT
I never objected to the engine noise, although I thought VW could have popped for a modicum of insulation under the car. You can count the pebbles as you pass over them.
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Post by Deleted on Jan 19, 2011 19:31:19 GMT
France, Spain, Belgium and Luxembourg are all up to about 75% diesel cars on the road, and nobody finds the cars noisier than elsewhere.
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Post by onlymark on Jan 19, 2011 20:35:15 GMT
75%? I'm going to have to call you on that statistic. Or is it just an impression? Modern day diesels are reasonably quiet. But only recently.
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Post by Deleted on Jan 19, 2011 20:48:33 GMT
Well, this is old, and I forgot Austria, but the percentages have risen since 2005.
Autriche 1995 = 42.6% 2005 = 73.3%
Belgique + Lux. 1995 = 45.5% 2005 = 73%
France 1995 = 46.5% 2005 = 71.1%
Espagne 1995 = 32.6% 2005 = 70%
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Post by fumobici on Jan 19, 2011 21:34:15 GMT
My father has a Mazda2 with a French PSA-made turbo diesel and is both strong and gets an easy 50 mpg on the autostrada. Great little engine.
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Post by onlymark on Jan 20, 2011 17:52:30 GMT
Impressive figures then. I always knew there was a reason I favoured them. They are just better.
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Post by cristina on Jan 25, 2011 3:01:56 GMT
So I got to looking at diesel cars offered in the US over the last few years. It seems a bit sad. Mostly higher end cars - Mercedes and BMW, i.e. However Volkswagon leads with 4 models.
I think my new (to me) car will still be a VW.
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Post by bixaorellana on Sept 13, 2011 0:31:26 GMT
Here's the $64,000 question: how do you find a good mechanic?
Obviously, you can ask friends for a recommendation, but sometimes they're also looking, or haven't needed one, or take their cars to the dealership, etc. Those of us who know nothing can easily be bamboozled at worse, or at best not recognize that a mechanic is not all that good.
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