User talk:Andy Dingley/Archive 2011 August

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Magneto ignition

[edit]

Hi Andy, I noticed you uploaded http://en.wikipedia.org/wiki/File:Magneto_ignition_with_low-tension_magnetic_spark_plugs_(Rankin_Kennedy,_Electrical_Installations,_Vol_II,_1909).jpg so I guess that you allready have some knowledge on this.

At present, I would like to integrate a magneto ignition to a 3D model. I recently read http://www.rrec.org.uk/Cars/How_A_Car_Works.php#The Ignition System and also did a little research on the web.

It seems that 2 magneto models will be required for my engine model (I decided to model out something similar to the Austin Twelve magneto schematic). 2 magneto's seem however to be required as the speed of the engine's axle (I'm assuming the crankshaft/camshaft rather than the main drive shaft) varies depending on the duration/gas provided to the engine, and the magneto can only work aduquatly at a certain speed (meaning that 2 magneto's each with different gears in between are needed to attain a suitable speed).

The questions I however remain to have are:

Thanks in advance, Sincerely, KVDP (talk) 15:27, 30 August 2011 (UTC)[reply]

Bosch magneto circuit (Army Service Corps Training, Mechanical Transport, 1911)
You might find en:Ignition magneto worth reading, although it's very incomplete. For images, look at Category:Magnetos (ignition) and Category:Petrol engine ignition systems.
Ignition magnetos are obsolete. They've been obsolete on cars for half a century, aircraft for decades (although still used almost universally) and even on garden lawnmowers they've been obsoleted by small, cheap capacitor discharge systems. I would thus expect most car ignition resources to not be describing the right thing at all. You might do better with aircraft (except that these use twin magneto systems) or motorbikes (except that these are mostly two-strokes).
Overall, I would question why you're even looking at magnetos. For a text on how to build an engine in an home workshop of the 1960s, then a magneto is the obvious way to go. For a text on how to deliver simple engines to the 3rd world today, the answer is about huge Chinese factories and cheap lawnmower parts, which are probably capacitor discharge, not magneto.
Ignition magnetos run at the speed of the engine's cycles, not the engine's crankshaft rotation. This is the same as the engine's valves. For two stroke engines, crankshaft and camshaft speeds are the same. For four stroke engines, camshaft (and ignition) speed is half that of the crankshaft. It is usually easy to drive the ignition magneto (or the ignition distributor), because there is already a camshaft going at a convenient speed. This will be driven by either timing gears, timing chain or timing belt. Some four strokes have also used a "wasted spark" system where they fire twice as often as they need to (so thus they fire at the same speed as a two stroke) because this is simpler to achieve, albeit wasteful, and the "spare" spark at the end of the exhaust stroke isn't harmful.
Don't follow the Rankin Kennedy illustration. It illustrates a very early use of plug-top coils, which is not the usual way that magnetos worked. Instead I would suggest File:Bosch magneto circuit (Army Service Corps Training, Mechanical Transport, 1911).jpg as the commonplace magneto circuit.
2 magneto's seem however to be required as the speed
No. Only one. I've never heard of two magnetos being used like this. It's not impossible, it might even have been done for motor racing in the 1930s, but it's incredibly obscure if it was.
If two magnetos were used, they both ran at the same speed. Otherwise the spark timing would be wrong and the engine would stop.
It's possible that some designs of magnetos work better than others at different speeds, so one would be used for low speed (starting) and one for high speed. However this would never be done by taking one magneto and running it through different gear ratios.
the engine's axle
Engines don't have axles. Try to describe engines as if they did have axles and you will just be talking nonsense.
(I'm assuming the crankshaft/camshaft rather than the main drive shaft)
See above. If there is something in an engine called the "main drive shaft" rather than the crankshaft or camshaft, then I cannot help you.
The 'magneto selection system' is only found on aircraft, where high reliability is required (and 1930s racing cars). There are two magneto ignition systems. Two magnetos, two spark plugs in each cylinder. You can continue flying if one fails. The engine also runs a fraction better with both firing. They are only selected individually for testing - each should be working equally well, and if one appears to not be, then something needs fixing before taking off.
All magnetos have LT wiring. It connects the magneto rotor and the contact breaker points. These are both mounted inside the same magneto case, so they're not visible from outside (they might be more visible in a "flywheel magneto"). There is also a LT wire to the cockpit switch that shorts out the contact points and stops the engine.
In your "4 wires" example, there are 8 wires, all identical. They link 8 sparkplugs (2 each in 4 cylinders) to 2 magnetos (each driving 4 plugs). They have colour-coded the wire colours into two groups of four according to the plug position, but this is unimportant. All 8 wires are the same HT wires.
I would seriously recommend that you obtain a copy of LJK Setright's 'Anatomy of the Motor Car' (eBay, old, common, cheap). It's the best and most accurate introduction I know to the workings of the motor car, up to the 1970s, and in addition it is an absolute paragon of how to write well on technical topics for a lay audience. Andy Dingley (talk) 16:50, 30 August 2011 (UTC)[reply]
Thanks Andy,

your explaination was very helpful; based on your directions, I'll use the http://www.undaerospace.com/cbt_files/virtualengine/Magneto/Virtual%20Engine.swf magneto and put it on the camshaft. I'll use 4 wires (original model uses 8, but I can just have one discarded per pair). Based on File:Bosch_magneto_circuit_(Army_Service_Corps_Training,_Mechanical_Transport,_1911).jpg and File:Eisemann_magneto_system_(Army_Service_Corps_Training,_Mechanical_Transport,_1911).jpg I also understand that one additional wire needs to be added coming out of the condensor (P-lead).

KVDP

Don't follow the Eisenmann diagram - that is another unusual design, where the induction coil was mounted externally to the magneto. Normally this is mounted inside the magneto armature. With an armature-mounted coil, you don't need these as external wires - they're all internal to the magneto body. All that comes out of the magneto is one HT lead per spark plug, an earth return, and a control wire to the ignition switch. Andy Dingley (talk) 15:59, 31 August 2011 (UTC)[reply]
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