Karen_Agusta Posted May 17, 2010 Share Posted May 17, 2010 . WHAT REALLY HAPPENS WHEN YOU TURN THE KEY . It is not detailed by any means for there are many issues of physics, air temperature, elevation and so on which affect that which you are about to read ... furthermore for this example I are using a non-computerized, non-fuel-injected, general four stroke machine with a breaker-point ingnition ... such as a motorbike built within the 1960s ... as an example a 1968 Moto Guzzi V1000 Ambassador ... ... Thus consider this to be a general outline or overview of that which happens when ... you ... the rider ... get onto your motorcycle. . As you turn the key it must properly engage the ignition to move the pins into the correct position. Thereby allowing the lock to open and the tumbler to rotate. Upon turning the key to the correct position an electircal signal is sent via a small wire to the starter relay. Thus voltage engages an electromagnet within the starter relay. The pupose of the relay is to prevent the need for a starter gauge wire to be routed directly to the ignition switch ... thereby allowing wires of the appropriate gauge to be routed to the switch ... Thus the key is turned and the electromagnet in the starter relay is now engaged ... Upon doing so the magnet of the starter relay closes the circuit allowing the voltage to travel directly from the 13.2 volt motocycle battery to the starter solenoid ... The solenoid does two things. One it sends the signal to the brushes and commtutor in the direct current motor named the starter. Two it thrusts the toothed wheel of the starter into a much larger wheel of the engine named the flywheel (this is would occur on a motorcycle such as a Moto Guzzi). This accomplishes two things. It makes contact with the engine flywheel gear (to turn it) and it does so at a high level of geared reduction allowing a simple 13.2 volt starter motor to overcome the combination of engine high friction and compression thereby rotating the engine. . At this point the engine is turning. At the same time there is an eccentric wheel or cam located somewhere in the machine which is now being rotated (if the engine is not merely gravity fed). The purpose of this eccentric cam is to engage the arm of a fuel pump (this is similar to the method used on a triumph oil pump). The arm moves up and down overcoming the force of a spring and diaphragm assembly inside the fuel pump. On the upstroke ... the arm ... mounted on a pivot ... allows the diaphragm to move downward ... In doing so a sealed increase in volume is created within the fuel pump. Thus allowing atmostpheric pressure upon the gas tank at 14.7 psi to push the fuel towards the pump. Once the pump has completed its downward movement and is now filled with fuel ... the arm on the other side is released allowing the fuel pump diaphragm to begin upward movement. As the diaphragm moves upward a checkball closes the area of fuel volume allowing that fuel nowhere to go but out of the other side of the fuel pump which is pointed to the carburettor. This fuel then travels through a tube to an area of the motorcycle carburettor known as the float bowl. The pump shall continue to do this until the float bown of the motorcycle carburettor is filled. . Now the fuel pump now filling the motorcycle carburetor with fuel. There are two items in the bowl one called a needle and the other a float. Much like a toilet when the float rises to the top. It closes the needle so the pump may not merely continue to dump fuel into the engine. Thereby motderating fuel to engine input. . Ok so I have fuel ... Now what? . At the time I turned the key to start the engine turning and the motorcycle carburettor began filling with fuel ... an item called the distributor also began to turn (this is the case on a Moto Guzzi). A gear engages the distributor and turns it ... and in some cases (depending upon the engine design) ... A shaft is mounted at the base of the distributor which shall also turn the oil pump ... The oil pump is similar to the fuel pump however ... instead of a spring and diaphragm as in the fuel pump ... The oil pump uses two gears which while rotating creating an ever increasing space ... (not a space open / close / pump / then open again as in the fuel pump - but a space which is ever increasing as far as the outside atmosphere is concerned) ... Thereby the oil pump is now allowing atmostpheric pressure at 14.7 psi to push oil into the pump. Once the oil is pushed into the pump ... The oil is forced out of the other side of the oil pump ... the oil is moved through the pump to a series of passages within the engine ... Items such as. Hydraulic valve lifters (should the engine have them) which use this oil pressure to maintain a constant valve adjustment ... Oil may be fed to the pushrods to lubricate the upper valve train (as in an older Triumph) ... oil shall be fed to the cam to lubricate it as well ... Though by far and most importantly ... The oil galleries for the crankshaft need to be fed a constant pressure of about 40 psi ... (This lubrication is similar to a waterslide. If you have ever been on one it is much faster than a normal slide because the water creates a layer between the slide and yourself preventing friction) ... Thus the oil from the engines oil pump in the same manner creates a lubricating film between the crankshaft and the bearings. Thereby allowing the crank to spin without tearing the bearings and itself to bits. . Thus I now have fuel - I have oil - and my engine is rotating. . The distributor is turning and it has a cam on it. (A cam is an area of metal with raised and lowered areas). Touching this cam is an extremely important component named the breaker points ... The purpose of these breaker points is as follows: .. The Automotive battery only can maintain in storage 13.2 volts ... Yet it takes about thirty thousand volts to fire a single spark plug ... As the distributor cam turns a 13.2 volt signal is sent to the breaker points. This sends energy to what is known as an ignition coil. This process of sending energy to the coil is known as saturating the coil. The reason for this is as follows. There are two sides to an ignition coil yet THE TWO SIDES OF THE COIL ARE NOT CONNECTED to one another in any manner at all ... The ignition coil is what is known as a transformer ... though this is a process I do fully understand ... This I shall borrow from Wikipedia ... it is just a better written explaination than I could give plus it saves me the typing as well. . ------------------------------------------------------------------------------------------------------------------ . http://en.wikipedia.org/wiki/Ignition_system . Most four-stroke engines have used a mechanically timed electrical ignition system. The heart of the system is the distributor. The distributor contains a rotating cam driven by the engine's drive, a set of breaker points, a condenser, a rotor and a distributor cap. External to the distributor is the ignition coil, the spark plugs and wires linking the distributor to the spark plugs and ignition coil. The system is powered by a lead-acid battery, which is charged by the motorcycle's electrical system using a dynamo or alternator. The engine operates contact breaker points, which interrupt the current to an induction coil (known as the ignition coil). The ignition coil consists of two transformer windings sharing a common magnetic core—the primary and secondary windings. An alternating current in the primary induces alternating magnetic field in the coil's core. Because the ignition coil's secondary has far more windings than the primary, the coil is a step-up transformer which induces a much higher voltage across the secondary windings. For an ignition coil, one end of windings of both the primary and secondary are connected together. This common point is connected to the battery (usually through a current-limiting ballast resistor). The other end of the primary is connected to the points within the distributor. The other end of the secondary is connected, via the distributor cap and rotor, to the spark plugs. . The ignition firing sequence begins with the points (or contact breaker) closed. A steady charge flows from the battery, through the current-limiting resistor, through the coil primary, across the closed breaker points and finally back to the battery. This steady current produces a magnetic field within the coil's core. This magnetic field forms the energy reservoir that will be used to drive the ignition spark. . As the engine turns, so does the cam inside the distributor. The points ride on the cam so that as the engine turns and reaches the top of the engine's compression cycle, a high point in the cam causes the breaker points to open. This breaks the primary winding's circuit and abruptly stops the current through the breaker points. Without the steady current through the points, the magnetic field generated in the coil immediately and rapidly collapses. This change in the magnetic field induces a high voltage in the coil's secondary windings. At the same time, current exits the coil's primary winding and begins to charge up the capacitor ("condenser") that lies across the now-open breaker points. This capacitor and the coil’s primary windings form an oscillating LC circuit. This LC circuit produces a damped, oscillating current which bounces energy betIen the capacitor’s electric field and the ignition coil’s magnetic field. The oscillating current in the coil’s primary, which produces an oscillating magnetic field in the coil, extends the high voltage pulse at the output of the secondary windings. This high voltage thus continues beyond the time of the initial field collapse pulse. The oscillation continues until the circuit’s energy is consumed. . The ignition coil's secondary windings are connected to the distributor cap. A turning rotor, located on top of the breaker cam within the distributor cap, sequentially connects the coil's secondary windings to one of the several wires leading to each cylinder's spark plug. The extremely high voltage from the coil's secondary windings often higher than 30,000 volts causes a spark to form across the gap of the spark plug. This, in turn, ignites the compressed air-fuel mixture within the engine. It is the creation of this spark which consumes the energy that was originally stored in the ignition coils magnetic field . ------------------------------------------------------------------------------------------------------------------- . Ok back to Karens writing now ... so ... I now have fuel, spark, oil, and a rotating engine. . At this point I must cover the camshaft ... upon the camshaft there is a toothed wheel to which a chain is connected. As the engine crankshaft is rotated by the starter this chain is connected to the crankshaft. The chain is linked from the crankshaft ... to the toothed wheel upon the camshaft in the upper cyclined head of the engine ... The camshaft is now rotating ... Some notes about cams should be mentioned here ... The lobes of the camshaft are gauged by the following, Lift, Duration and lobe separation which is directly related to (overlap) ... The valve lift is governed by the height of the cam lobe. The taller the lobe the farther away from the valve seat it lifts the valve in the engine (for example I once build a Cadillac 472 with a cam which had .525 valve lift). This means the cam had over one half inch of lift applied to the valve ... Basically the higher you lift the valve, the more air can flow and the more air fuel mixture is fed into the engine ... yet you have to be careful with this because a huge cam provides little power until a very high RPM (which is why the Suzuki GSXR tachometer did not even bother to move until three grand because the power produced below that RPM was pointless) ... Next I have the Duration ... this is simply how long the valve is held open ... if you open and close the valve very quickly you will have very high low-end torque but little high end power ... if you leave the valve open for a long time (because you have to eventually close the valve ... you can not leave it open forever ... for at that point you may as well have a "burnt" valve) ... with a cam wich holds the valve open for a long time you will have high end horsepower in the 8 to 14 thousand RPM range but almost no low-end power at all ... this is why a racing engine is not considered to be what is known as "streetable" ... Next in the world of camshaft description you have "lobe separation" typically in the 106 to 114 degree range ... A high lobe separation of 114 is a very calm, good compression and streetable engine ... whereas ... a 106 degree lobe separaton is a very lopey engine which must have a high idle ... the reason for the is what is called valve overlap ... this means that the intake and exhast valves are open at the same time ... while this can cause a vast amount of power it essentially lowers the engines compression ... And that is about as much regarding cams as I should get into here because really a full conversation regaring cam dynamics is a topic for another time. For in modern times they are developing computer controlled "variable valve systems" wich act as a small cam would at low rpms and then increase accordingly as the rpms of the engine increase. Thus getting around having to select one single "powerband" in which the engine may operate. . The best example of what a powerband I can give to you would be The Kawasaki Mach 3 500cc which combined light-switch powerbands with flexible chassis geometry to make a truly exciting ride. You would be leaned over in a turn with no power then the engine would spring to life wanting to lift the front wheel and rocket you into the trees ... which this bike was a two-stroke and did not have a camshaft at all ... to anyone who ever rode one the meaning of the word "powerband" shall be forever burned into their memory. . Back to the topic of firing-up our engine ... the carburettor ... (I now have fuel, spark, oil, and a rotating engine. ... Now what)? ... As the intake valve opens and the piston travels downward it creates an increasing space in the engines cylinder cylinder. The downward travel of the piston (and the cam holding the intake valve open allow the 14.7 psi atmostpheric pressure to push air into the engine) ... ... ... We need to take a short break here though ... for what I am about to cover is the same principle by which an aircraft flies ... which is as follows ... the bottom of the aircraft wing is flat and the top of the aircraft wing is rounded ... therefore the air must travel a greater distance over te top of the wing - the only way the air can do so is by travelling faster over te top of the wing than it does over the bottom of the wing ... the faster travelling air creates a lower pressue ... thus there is a air high pressure on the bottom of the wing and a low air pressure on the top of the wing - this creates "lift" above the wing causing the aircraft to fly ... ... ... Ok back to our engine now ... This is the same princlple by which lower pressure is created within the carburettor ... The downward travelling piston, creating an increased volume within the cylinder, causes atmospheric pressure at 14.7 psi to push air into carburettors throat via the cylinders increasing volume ... Thus I now have air passing through my motorcycles carburettor ... The carbuterror has a hole bored in it and a variable needle controlled by a slider within the carburettor ... In the area of the needle and hole the carburettor throat is greatly narrowed ... thus the air must travel much faster through this narrow ares than it does through the rest of the "wider-throated" parts of the carburettor ... this fast moving are over the slider needle and jet create a low pressure where the needle and jet are ... This area of the carburettor is called the venturi named after the venturi affect ... For as air passes through the carburettor it moves at a very high velocity ... as it does so a lower pressure is created within the venturi ... There is a tube in the venturi which goes though a series of passages know as "jets" ... the float bowl has a hole drilled in it allowing to contact the outside air which is at 14.7 psi ... Thus I now have a higher pressure on float bowl than I do on the venturi area of the needle and jet inside the carburettor ... high pressure on one side and low on the other ... pushed fuel from the float bowl to the point of low pressure ... the venturi in the throat of the carburettor controlled by the slider and needle ... This fuel is now at the venturi I discussed earlier. The fuel is now moving through the carburettor ... At the engine side of the carburettor is a plate which can be opened or closed varaibly this plate is controlled by the throttle. For our purposes consider this plate to be open (imagine you have pulled the throttle halfway open). . Fuel can not burn in drops ... {{ as an analogy imagine that it has been raining - I were to point you to a tree I had chopped down - give to you one single match - and tell you to with just one match "light the tree on fire" if you just hold the match under the tree it will not light }} ...{{ however were you to collect very fine and small pieces of wood known as "kindling" and place them under the tree - you could get it to burn - so it is with fuel }} ... {{ Or if you have ever seen a person shoot a cloud of wood dust into the air then hold a match to it the wood dust shall go up in a fireball }} ... For to have fire the object must be in contact with a highly reactive gas known as oxygen. In the giant tree of wood most of the wood is in contact with other wood particles ... In the atomized dust all of the wood is in contact with oxygen ... by being in contact with oxygen it is far more highly reactive when it comes into contact with spark or flame and it may therefore react in a highly aggressive manner ... it is for this very reason I have a carburettor at all ... and why the fuel is not simply pumped directly into the engine ... For one item the carburettor allows the rider to control speed yes ... yet often overlooked and just as importantly the carburettor performs the neccesary process of mixing the fuel with oxygen thereby doing what is called "atomizing the fuel" (generally to a preferred ratio of fifteen to one) Thereby making the fuel now entering the engine (as the cam holds the valve open and the piston travels downward in the cylinder) much more highly explosive ... Fuel now moves through the carburettor (add very large carburettor and you shall have power at high rpm but poor low-end performance ... this is because at low rom the engine will not create enough air velocity through this huge carb to move fuel through the venturi ... Yet if you go to the opposite direction and install a very small carb and you will have torque at low-rpm and great off-the-line performance. However the carburettor shall not be able to flow enough air to obtain a very high rpm. That is why in building a vintage racing engine the choice of cam and carburettor - sprocket size and gearing - exhaust and such - are all a "system" ... and ... this is the main reason carburettors have be replaced with fuel injection with can be varied allowing for both torque at low rpm and power at high rpm . . I now have fuel and air in our cylinder and the engine is turning. . The piston is at the bottom of its stroke and the cylinder is full of fuel and oxygen. Were I to ignite it in this condition I would get a gentle burn as if I took gunpowder out of 100 firecrackers. Poured it on the floor and lit in on fire. Nothing much would happen ... Now if I take that same gunpowder and put it into a pipe and put a fuse in it ... I would have a highly exposive device known as a "pipe bomb" ... This is due to a process known as "compression" ... the greater the compression the more powerful the explosion and the more power generated ... Thus our piston is now all the way down and our cylinder is filled with air and fuel. The intake is now closed because the cam lobe has rotated away from its high point or "point of lift" ... Therefore the intake and exhaust valves are now closed and the piston is moving upward within the closed cylinder .... Due to the fact the air / fuel now has nowhere to go it is now being "compressed" . As the air / fuel is being compresssed ... at about ten degrees before the top dead center of the piston (its highest point) ... the breaker points open ... this causes a prevention of electricity or no voltage whatsover to be transmitted to the coil ... This causes the magenetic field to collapse on the primary side of the coil to rapidly collapse ... as the magnetic field collapses it moves electrons through the secondary side of the coil ... (remember the two sides of the could at not connected) ... At this point a trade occurs ... ... ... The ignition coil is nothing more than an electrical transformer. It contains both primary and secondary winding circuits. The coil primary winding contains 100 to 150 turns of heavy copper wire. The coil secondary winding circuit contains 15,000 to 30,000 turns of fine copper wire, which also must be insulated from the primary side As current flows through the coil a strong magnetic field is built up. When the current is shut off, the collapse of this magnetic field to the secondary windings induces a high voltage which is released through the large center terminal. This voltage is then directed to the spark plugs through the distributor. ... because the primary side has few This sends thirty thousand volts via the distributor rotor to the correct contact on the distributor. Sending the voltage through the wire to the spark plug. This voltage is so high it arcs from the tip of the plug through the air to the other side. This arc ingnites the fuel. As the fuel ingnites it wishes to explode however this force is transmitted to the piston. The piston is forced downward and in doing so the piston is attached to a connecting rod which is attached to a crankshaft (with the bearing and oil between). In so doing the crankshaft is now turning Thus the crank is now turning under the engines own power and I no longer need the starter and I can not take my finger off of the starter button ... ... ... I should not here regarding the could and electrical trade is made when the points are opened (shutting off the current to the coil) when the points were closed I had a fair amount of volate and amperage being sent to my ignition coil ... because I can not just magically produce voltage it has it has to come from somewhere ... it does so by greatly increasing the voltage in trade greatly decreasing the amperage ... that is why you can get shocked by an automotive ignition and be ok ... for it is amperage ... NOT voltage ... which is deadly to you. . The engine is running. . The piston has been forced downward by the explosion ... (or "internal-combustion" which has just occured) ... at this point my cylinder is filled with burned fuel ... and ... as either another piston (or a heavy flywheel weight in a "thumper" or sigle-cylinder engine) causes the piston to move upward ... the exhaust valve is now open and the upward moving piston is pushing the burned air-fuel mixture known as the exhaust gas past the valve into the exhaust system ... At this point I must engage in a topic of what is know as "backpressure" ... If the exhaust is small there shall be a high degree of backpressure ... high backpressue creates high low-end torque but does not allow enough airflow at high rpms ... huge pipes create very low backpressure which is wonderful for very high rpms but but do not perform well at all when trying to leave the stoplight or at low rpms ... (this is why many bikes have at times placed variable restrictors in the exhaust system to create high backpressure at low rpms ... and ... as the rpms increase ... the valve in the exhaust system opens up ... thereby decreasing the amount of restriction in the exhaust system and lowering the back pressure) ... The problem with these variable exhaust systems occured when the valve failed ... Thus they are not in great use today. . To get back to the idea of a system ... if you take a chevy 350 engine and put a 1000 CFM dominator carburettor on it ... now the intake manifold can not flow enough air ... so you have to install a tall single-plane manifold ... which is fine ... but that is no good ... with the tiny cam ... so you have to put a huge cam in the engine ... great ... but with the huge cam overlap ... the eight to one compression is now down to six to one ... the engine now makes no power at all ... so you have to put eleven to one compression pistons into the engine ... which is fine ... but now the tiny stock exhaust is so restrictve you can not get any power out of the engine ... so you have to put headers and dual three inch pipes on the engine ... great but now the engine can not idle below 1800 rpm so you have to install a transmission "stall convertor" ... kool but now you can not leave a stoplight because your gears gears are to high ... so you install a set of 4:88s ... great now you rev at 4500 rpm to do sixty miles per hour on the highway ... your gas mileage is terrible ... you had to increase the rims size and put high end tires on the car otherwise it pitched sidewars when you drove it in the rain and you had to upgrade the entire suspension because the rear leaf springs could not handle the torque and had severe wheel hop when you "punched it" and now you get to drive this unstreetable monster to work and back every day ... believe me I learned this from experience as a teenager in the days when hot-rods and muscle cars were cheap and we all had one ... It is only when I went to school for mechanical engineerng that I learned a vehicle should be though of as a complete system ... not a series of individual parts by which one addition properly increases performance ... Thus if you ever wonder why it took through all of human history to only about one hundred and twenty years ago for us to have these engines available to us ... this should at least give to you some very small idea why ... What I have written is actually quite primative and very general operation of a primative and completely mechanical engine. I have left so much out. From inertial forces, to thermodynamics, the the fluid dynamics and even the neccesary actions regarding the heat transfer of the cooling system ... Thus this is merely a very general and simplified overview ... nothing more. . Regarding an engine as a system shall offer this I used to work at a Supershops and I can not tell you how many times I had people wanting to buy an 800 CFM (cubic feet per minute) carburettor for thier 1974 emissioned-out 307 engine in their high-geared Nova ... it simply just does not work anything like that ... ... Thus it is time to dicuss the topic of exhaust dynamics ... for all components of an engine are a SYSTEM WHICH MUST BE PERFECTLY BALANCED ... because like the cam and carburettors the exhaust system must be balance perfectly to the engine setup to achive correct performance ... that is why when you look at MAC or Yoshimura exhaust systems they say "Dyno-Tuned". Meaning they ran tests on the dyno to find the right size and curvature for the engine. That is also why they tell you that you shall have to reject your carbs ... because every component installed on that engine must create a perfectly balanced system for it to perform properly for the intended use and within the poIrband you intend the motorycle to operate in. I shall end with these notes ... mechanical engineers who build and design motocycles for wonderful companies such as Yamaha are very intelligent, they go to school for a long time, and they generall know what they are doing, thus before you go ripping thier work apart ... you better be sure of what you intend to do and how to make it occur ... Just to give you and idea of what goes on in an internal combustion engine of a more modern type and why you need a masters degree to be a mechanical engineer. . Here is what it takes to test one. . http://www.youtube.com/watch?v=-NHEAxKGw8Y . . . . http://www.youtube.com/watch?v=RO4PifwXyiw . . . http://www.youtube.com/watch?v=pdWlnLM8Rmw . {By the way 800 Celcius = 1472 dgrees} . . I hope you enjoyed this little article of mine . Rubber Side Down . Karen . Link to comment Share on other sites More sharing options...
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