How Variable Valve Timing Works

today I'm going to show you what's inside the variable valve timing system in your car's engine and how it works now the variable valve timing system is responsible for varying the timing of the intake and exhaust valves to allow air in or exhaust gases out relative to the position of the piston in the combustion cycle we're taking a look at this v6 engine we have two heads here one for each back with three cylinders each we have a double overhead cam design where we have two camshafts in each head the intake here has a variable valve timing actuator and on this engine there is no variable valve timing on the exhaust side now this entire valve train is driven by a timing chain that's driven off of the crankshaft at the bottom there that's ultimately powered by the movement of the piston so underneath the engine here here you can see the two camshafts each of them have their own profile over here and control one valve each for a total of four valves per cylinder we've got the exhaust side on this side here and the intake on the side over here we've also got the oil control valve that sends oil over to the variable timing actuator now the main timing chain is powered by the crankshaft and is monitored by the ECU through the crank position sensor it serves as the input for the variable valve timing gear and also outputs to this smaller chain over here that powers the exhaust cam at the same rate that the crank is moving so you can see as I turn the intake side here how the timing chain moves to move the exhaust cam as well as the main timing chain over here so just as a reminder to have the four-stroke cycle works in an internal combustion engine on the left here we have the intake valve and on the right we have the exhaust valve when the piston is moving down on the intake stroke it draws in fresh air it's then compressed the spark plug then fires pushing the piston down therefore turning the crank the piston then moves up to push the exhaust gasses out of the exhaust valve so now I'm going to start removing parts off the top of this engine here so we can have a closer look at how the variable valve timing system works so I've got the oil control valve remove here we've got this bearing cap here that holds the camshafts on and also serves as the oil passages for this oil control valve then we have the timing chain here that I'm going to remove from the intake camshaft over here and then we have both of these gears that connect to the camshafts themselves and they have this timing chain that connects the two of them together I'm also going to remove this timing chain tensioner for the small chain here it's a hydraulic unit and then finally I'm just gonna lift off the engine head from the block essence of variable valve timing system is to either advance or the relative timing of this intake camshaft to the exhaust camshaft and the crankshaft down below at the heart of the system we have this cam phase actuator which actually will take the input from the crankshaft here and change the phase of it slightly to the output which is inside of here that connects to this camshaft to change its relative angle as it rotates in the combustion cycles now the variable valve timing actuator actually works with oil pressure so I'm going to open up these bolts here so we can see what's inside and how it works now I'm going to remove the top part here now this video is about to get really oily and messy so I'm just gonna come with my brother's nice white sock here and wipe up this mess so inside of this vvt-i gear you can see we have these little pockets here where the oil would fill up and that's going to cause a relative motion between the input which is driven by the timing chain on the outside here and the output which is the camshaft which bolts up to this inside piece over here so you've got this little lock pin here which is actually spring-loaded and we have this outside ring over here that I'm going to slowly lift off I'm just gonna use that sock again to wipe this oily mess up because these are really good at absorbing greasy and oily stuff now on any of the surfaces that touch each other inside here or on the outside here there's actually this little wear bar over here it's like a bearing that will slide up against the other side preventing wear there's also a little spring in behind here to give it a little bit of tension that way these metals here don't wear out as this cam phaser actually it's back and forth you can see this little mark here where this little spring-loaded pin actually was riding up against when this actuated now on the backside here you can see this inner piece with this little pin on it actually connects to the camshaft and that's the output of the variable valve timing gear if I pop that out you can see what we have inside now if you remember the pin from the top side actually leads to this spring-loaded pin on the bottom side here which locks the input and the output together through this little peg over here now when the variable timing control actuates this little oil groove over here is going to send oil to unlock this piston over here that's going to push up allowing relative motion between the input and the output so I'll just remove the bits of this plunger here so we can unlock this variable controller that lock pin removed you could see we have this outside shell which is fixed to the gear here which is driven by the crankshaft we've got this side here which bolts up to the camshaft that I'm then going to insert and then you could see the relative movement between what is the camshaft over here and the crankshaft timing chain position over here they can move roughly 15 degrees advance or now the variable timing gear is actually controlled through oil pressure and if you remember my lubrication system video I cover how the oil flows through the oil pump the pressure is then created by these small little orifices and passageways inside of the engine block it'll then flow up through this little hole over here through the timing chain tensioner and then into this hole over here to this cam bearing holder over here it will then go through here into the oil control valve which is then controlled through the ECU it'll go through the oil control valve and then into this hole over here it'll then go down into this hole inside of the bearing cap over here and then go into the camshaft itself through this hole over here and then out through the middle to activate your variable timing gear inside the oil control valve we have this solenoid that's inside of here that activates this piston that moves back and forth and that will divert the oil to the cam phasors we also have these little filters here so if you are getting a code for your oil control valve it might be worth cleaning these out and if you look really closely you can see that piston moving inside of the valve as I activate it let's see what's inside here I'm just gonna loosen up these hex bolts they're hard this is actually you get pretty oily so I'm just gonna come with a little bit of brake cleaner here and my wife's little toothbrush that I stole can't use that anymore a and scrub that down to make it nice and clean so we can have a closer look now as oil flows through the head of the cam shaft over here it's actually going to fill up inside of this piece here and come back out through these holes on the perimeter those holes correspond to this groove on the inside of the variable valve timing gear which is going to bring up oil through these four holes over here now if I insert this piece back into here you'll see that those four holes actually correspond with the four chambers on the variable timing gear so as you build up oil pressure on this side this is actually going to start to advance and that's what's going to give you the relative motion between the input shaft and the output gear on this variable timing gear now when you relax the oil pressure this is actually going to move back into place and this pin is going to lock and that's gonna lock your input and output back together as a fail-safe and for when the vehicle actually starts up now if you hear a little rattle when you start your car in the morning that's probably this pin inside of you're starting to wear out of this thing starting to rattle a little bit until it jiggles back into place now the holes on the side of each chamber here help to relax the oil pressure and drain it back into the timing cover down below the variable valve timing system actually operates like a closed loop control system with the ECU sending a signal out to the oil control valve to either advance or timing on the intake camshaft on this engine here the cam position sensor will then send a signal back out to the ECU so it knows how much or advanced the timing is we also have the exhaust camshaft and crankshaft that is read to the crankshaft position sensor that sends it out to the ECU to get a relative measurement between these two the EC will also take inputs from the throttle position sensor the mass airflow sensor the coolant temperature sensor and the oil pressure sensor to make sure all is right before advancing or retarding timing so taking a closer look you'll see that this cam lobe over here is actually going to rotate this way and press down on this little valve seat over here and that's going to push down causing the valve underneath to open up now I can't actually push it down completely because there's a lot of spring pressure underneath these valves now this cam position sensor is actually just a Hall effect sensor that senses the grooves on this camshaft here so the ECU knows the position of these cam lobes and thus the valve so as an example when this cam turns this valve here is actually going to open up and that's going to allow either exhaust gases to escape or air fuel mixture to enter into the combustion chamber depending on the position of the piston now in a normal fixed timing engine this valve is going to continuously move up and down relative to the position of this piston as it moves up and down throughout the combustion cycle and the rev range of the engine now it turns out that that's not the most efficient way to operate an engine if we could actually vary the timing of this valve opening relative to the piston we can actually save fuel pollute less and also get a little bit more power on the top-end so for demonstration purposes I'm actually gonna free this valve here we've got a spark plug socket give it a whack with the hammer and everything just pops out including the spring seat turn this head over here you'll see that this valve is now free from the engine block so let's take an example of when the intake valve actually closes a little bit later in the combustion cycle well the piston is actually already drawn in all that air fuel mixture and it's ready to compress the mixture when that intake valve decides to shut well that's gonna actually push some of that mixture out into the intake plenum it's gonna charge it having it ready for the next intake stroke it's also going to reduce a little bit of pumping losses but more importantly it's gonna reduce the combustion temperature in here and therefore produce less emissions and pollute a little bit less closing the intake valve early means that less air actually enters the piston to begin with and you reduce pumping losses now in some engines you can vary the exhaust valve timing if we close it early the Pistons gonna be moving up on the exhaust stroke when the valve closes and trap some of that gas inside of here if you re burned in the next cycle reducing pollution so let's say for example we decide to close this exhaust valve a little bit later in the cycle well not just gonna help the piston vacate the cylinder of any exhaust gases so that on the intake stroke it can actually fill up with clean air to fuel mixture resulting in a very powerful burn in the next cycle it's also gonna help a little bit with the exhaust scavenging because at one point both of these valves are going to be slightly open and it's going to allow air intake pressure to push out exhaust gases at the same time now opening the exhaust valve a little bit early means the piston is on its way down in its power stroke and you're gonna lose some of that power by shooting flames out your exhaust however if you open the intake a little bit earlier actually cycles like EGR where you have the gas vapors inside of here that push back into the air intake manifold and then get sucked back into beery burn reducing pollution so from the variable valve timing actuator to the oil control valve that controls it these are all the components that go into making your engine have more power less pollution and to be more efficient make sure you follow me on Instagram for more behind-the-scenes footage to find out what happens to this engine and subscribe for more videos just like 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Channel: speedkar99

Views: 98,008

Keywords: VVT, variable, valve, timing, solenoid, VVT-i, VTEC, lift, duration, time, phase, cam, camshaft, crankshaft, chain, belt, engine, tuning, internal, combustion, intake, exhaust, manifold, port, valvematic, valvetronic, throttle, body, coolant, oil, pressure, temperature, gear, actuator, vq35de, nissan, infiniti, g35, g37, 350z, altima, 3.5L, lubrication, pump, consumption, ECU, chip, advance, retard, spark, head, plug, EGR, scavenging, air, piston, cylinder, efficiency, economy, fuel, gas, stroke, compression, power, pollution, emissions, mechanism

Id: pWI_IGs2ERE

Length: 10min 54sec (654 seconds)

Published: Tue Oct 01 2019