Managing ignition timing

I've just been at a great lecture by Peter Leijen as part of our schools-focused Osborne Physics and Engineering Day.   He's an ex-student of ours, who did electronic engineering here at Waikato – and graduated just a couple of years ago.  He now works in the automotive electronics industry. That's an incredibly quickly growing industry. So much of a car's systems are now driven by electronics, not mechanics. Being a car 'mechanic' now means being a car 'electronic engineer' just as much as it does being a mechanic. 

One interesting piece of electronics is the ignition timing system. The mechanism that produces the spark in the cylinders from a 12 volt battery is really old and standard technology – one uses a step-up transformer and kills the current to the primary coil by opening a switch – the sudden drop in current creates a  sudden reduction in magnetic flux in the transformer, and these collapsing flux lines cutting the secondary coil create a huge voltage, enough for the spark plug to spark. That really is easy to do. The tricky thing is getting it to spark at the right time. 

One needs the fuel/air mix in the cylinder to be ignited at the optimum time, so that the resulting explosion drives the piston downwards. Ignite too early, while the compression is going on, and you'll simply stop the piston rather than increasing the speed of its motion. Apply too late, and you won't get the full benefit of the explosion. It's rather like pushing a child on a swing – to get the amplitude of the motion to build, you need to push at the optimum time – this is just after they've started swinging away from you. 

All this is complicated by the fact that the explosion isn't instantaneous. It takes a small amount of time to happen. That means, at very high revolution rates, one has to be careful as to exactly when you make the ignition. It has to be earlier than at lower rates, particularly if the throttle setting is low, because the explosion takes a significant proportion of the period of the oscillation.  This is called 'ignition advance'.  

On newer cars, this is done electronically. A computer simply 'looks up' the correct angle of advance for the rpm and the throttle setting of the car, and applies the outcome. The result: a well running, efficient engine, using all the power available to it. Or so you might think.

But here's the revelation from Peter: car manufacturer's can deliberately stuff up the timing. Why do they want to do that? Well, there's a market for selling different versions of the otherwise same car. The high-end models have performance and features (and price tag) that the low-end models don't have. There's status in buying the high-end model (if you're the kind of person who cares about that – and the fact that these things sell says, yes, there are such people), but, alternatively, if that extra couple of horsepower doesn't bother you, you can get the lower-spec model for a lower price. Now, the manufacturers have worked out that making lots of different versions of the otherwise same car is inefficient. It's far easier to have a production line that fires out identical cars. So how do you achieve the low-end to high-end specification spectrum? Easy. You build everything high-end, and then to produce  low-end cars deliberately disable or tinker with the features so they don't work or don't perform so well. That is, make the car worse. 

Ignition timing is one example, says Peter. There are in fact companies who will take your low-end car and un-stuff-up your electronics for you – in effect reprogramme it to do what it should be doing. In other words, turn your low-end car back into a high-end one (which is how it started out life) without you having to pay the premium that the manufacturer would place on it for not stuffing it up in the first place. 

Who said free market economics resulted in the best outcome for consumers?

 

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