How an Automatic Transmission Works (RWD)

today I'm gonna show you what's inside of your automatic transmission and how it works to power your car's wheels now this transmission is from a rear-wheel drive vehicle and is situated longitudinally in the chassis we have the engine that bolts up at the front here and at the back we have the drive shaft that would lead out to the rear differential and the rear axles to turn the wheel now the purpose of the automatic transmission is to provide different gear ratios to optimize the engines fuel efficiency and power when required typically the transmission will take thousands of rpm from the engine and translate it through its gear ratios to reduce its speed and increase its torque to a more usable value through the output shaft here taking a look around the transmission here we have this flex plate to which the crankshaft will bolt up to from the engine then that will bolt up to the torque converter which is situated inside of this bell housing over here and then inside of here we have the input shaft for the transmission now along the left side of the transmission we have the gear selector that goes to the shifter and then along the right side here we have two coolant lines that go to the radiator we have the dipstick here and the plugs that go to the computer at the bottom here we have the transmission pan that holds all the oil and then at the back here we have the tail shaft which is the output I'm going to begin this transmission teardown by removing all the 14 millimeter bolts that hold the bell housing to the transmission and I'll just remove that bell housing now I'm going to remove the 14 millimeter bolts that hold the oil pump to the front of the transmission that plate there it's gonna remove this dipstick and what's cool is this one's actually got a dipstick spacer here we have a cross section of the transmission where you could see the planetary gear sets and clutches how they're very nested together here we have the input shaft and then the output shaft on the tail end of the transmission so the transmission pump out of the way you can see we've got the input shaft here and I'm going to be removing the front carrier assembly which is this entire front planetary gearset I'm just gonna remove this input shaft as a full assembly here next up we have this band on the inside here and then I can remove this band from the transmission housing next I'm going to remove the mid carrier assembly and that just slides out like that we have the mid and rear son gear assemblies that I'm going to remove next now inside of here we have the high-low reversed clutch assembly that I'm going to remove next and there's the direct clutch assembly over here now the last part is the reverse brake clutch inside of here well that's held in by a snap ring which we have to access from down below I'm going to turn the transmission so we can remove the transmission pan now this video is gonna get quite oily so I've got a freshly stolen bed sheet for my brother's bed that I'm just gonna use because it's really good at absorbing fluids and stuff you know so with the transmission pan removed you can see that we have this filter unit here attached to the valve body we've also got a temperature sensor over here and some more electrical wiring that controls all of this now I find it really amusing that all of these are completely coated in transmission fluid in the pan next I'm gonna remove the valve body from the transmission I've got my trusty ten millimeter socket here to remove all 1652 bolts and two nuts that hold this on the trusty bed sheet down here and roll over the transmission and now we're gonna remove the valve body from the transmission computer in here now the valve body removed you can see the shift cable will link up to this lever here which goes to this control rod and I'm just going to remove the wiring harness from the housing here next up we're gonna remove the tail housing at the back of the transmission where the driveshaft plugs into there's a bunch of fourteen millimeter bolts that I'm gonna remove and then now we'll just remove this housing here now here inside of the tail-shaft housing you can see the parking pawl and that's responsible for locking the transmission when it's in park so you could see here when I move the shift lever it moves this linkage over here underneath the transmission this linkage is then going to interact with this little cone over here and that's gonna pop the parking pawl out and the parking pawl is going to engage on this gear over here which is on the transmission and if I remove this pole here you can see this is the only thing that is holding your car preventing it from moving when you put the vehicle in park I'm gonna remove the output shaft from the transmission itself now also reading off of the park log gear here is this sensor which senses the amount of rotation of the output of the transmission so the ECU can determine just how fast the wheels are supposed to turn now the last clutch instead of there is called a reverse brake clutch now I'm just gonna remove these reverse brake plate clutches here inside of here we have yet another snap ring that holds in this return spring then I can remove the actual return spring next up I'm gonna remove the reverse brake Kista and remove that so there's one more snap ring inside of here it seems pretty stubborn to get out so to access the final clutch on the back of the transmission here I'm gonna start removing these Torx bolt now I'm going to pull out the last part of the transmission here just like that now I'm gonna remove this last one-way clutch at the back of the transmission and they can remove this last set of clutches over here the inside of here we have the piston reservoir so I'm just going to use little snap ring pliers worked a snap ring free here and then I'm gonna remove this piston over here and it's a return spring now this piston looks like a dual chamber design where you have one chamber at the top and then one at the bottom there's another chamber inside of here and so here we have all the components laid out here from the transmission all taken apart now we're gonna take a quick look at all of the individual components to see what they contribute to make this transmission function now the planetary gearset is basically the heart of the automatic transmission and what makes it work now all of the gears in the planetary gears that are always meshed together there isn't no on meshing and meshing of gears such as an ax manual transmission so if we're going to start here with the ring gear this gear is a gear that goes around the planetary gearset it's internally toothed and in this case it's actually connected solidly to this shaft and it serves as the input for this transmission next we have the planets which actually are these small little gears over here and they're all attached to this planet carrier and it's going to be installed inside of the ring gear now I'm just gonna place this gear set inside of its cage we hear that the planetary carrier is actually supplying to this barrel over here next we have the Sun year which is an externally splined gear that sits inside of the planets as the planets rotate around the Sun that's why we have the term planetary gearset and this just sits in and the planetary gearset has to remain components we have the input shaft here which drives the internal ring gear we have the planet carrier which is attached to this barrel on the bottom here and then we have the Sun gear which is attached to this drum on the other side here is that my bed sheet I'm trying to go sleep right now geez an order to get a useful output from a planetary gearset we need to set one of these to the input one to the output and to keep one stationary so if I kept the planetary gearset stationary by holding this barrel on the ground and I use the drum which is the Sun gear as my input and I rotate it you'll see that the output rotates at different speed and also in the opposite direction so this is good for ideally a reverse gear so I'm rotating the engine really really fast and the output is going nice and slow and it's also going in the opposite direction now if we wanted to make this planetary gears that have a different gear issue we have to change the input the output and which gears are held stationary so in this case I'm going to hold this barrel stationary on the outside here which is the Sun gear and then I'm going to turn the ring gear which is my input and you'll notice the planet carrier which is the output turns at a different speed you can see that it's moving in the same direction but the speed is different if you look at these holes as they line up here the ring gear is actually moving a little bit faster than the planet carrier in this situation now this particular ratio will be valuable in an overdrive situation such as on the highway where you want the wheels to turn faster than the engine now while each planetary gear set has about nine possible combinations that you can orient the input output and stationary parts there's actually only about three of those combinations that are useful in an automatic transmission and that's why we have multiple other gear sets in the rest of the transmission so you can actually multiply the input and output ratio of the first one translate it to the second one and then multiply it again for the third one to give you the final drive here we have a block diagram of the transmission with the three planetary gear sets represented over here the circles here indicate the break clutches and the diodes here indicate the one-way clutches in the transmission so here we have the input shaft and the output shaft and you can see just how power is going to flow through which gears according to which clutch is enabled now some clutches are actually attached to the transmission casing which prevent rotation to anything that's attached to it thereafter so by varying which clutch is enabled at which time we can vary the inputs and outputs for each planetary gear set and come up with five different forward and one reverse ratio for this transmission now there are many different clutch combinations you can have and that's determined by this chart which is embedded in the transmission computer which will correlate to whichever gear you're supposed to be in now some planetary gear says actually share components with the next planetary gear set after it and that just simplifies operations so for example here we have a planet carrier and a ring gear and this ring gear has these teeth here that lock into the housing over here and this housing itself here actually has a planet carrier on the back of it so those two are locked together and the planet carrier itself also has these teeth on it that lock into the transmission housing so this always stays stationary which means that the ring gear also stays stationary on the previous planetary gearset now for the Sun gear that goes in between here we have this shaft which has both Sun gears on it now this actually has a one-way clutch so this rotates freely in this direction but in this direction they're essentially on the same shaft and rotate at the same speed and then this entire assembly will actually plug into the giant ring gear in the first planetary gear set just like that and you can see just how they're all nestled together now the next question you might ask is how does the transmission actually control which one is the output and which one is the input and to hold which one stationary and the answer to that is actually through bands and clutches now here we have a clutch pack which is responsible for holding any particular shaft or component stationary in the transmission to change the input and output now inside of here we have the friction material and that is actually free to move inside of this whole thing which is full of transmission fluid the outside of it is actually spline to the transmission housing and is always held stationary now when this clutch gets activated fluid is going to flow inside of here and that's gonna fill up the inside here and lock these teeth here relative to the outside of the casing holding this stationary when the pressure is then released these teeth are now free to move once again now for example say if we wanted to hold this shaft stationary for a particular gear ratio well we have this spline on it that holds the shaft on then we have this clutch that's going to sit over top of this and its teeth are going to engage with that spline gear just like that and now when that clutch activates this whole entire thing is going to be held stationary against the transmission housing and when it's not activated it still can turn and move this way and of course it's going to be some power losses associated you can already feel there's a little bit of friction holding it back and that's why automatic transmissions are not very efficient and here you'll see what the inside of the clutch plates look like we have these metal bands here that'll lock onto the casing and hold it stationary and then we have this friction like material over here that has the internal teeth but spline to the shaft itself allowing it to rotate when there's food in between of course when this locks up we have the friction material that's going to be squished together forming a sandwich and that's what's gonna stop the shaft from rotating now you really want to control the pressure of activating these clutches because if you squish it too quickly it's gonna cause a really hard shift and it's also gonna start to wear out this friction like material typically what a transmission goes usually these clutches here are all burnt up and that's the burnt stuff that you see in the transmission fluid and then you actually have to change all of the clutches now the first sun gear on the front of the transmission actually uses a band and a drum style to hold it stationary when changing gears which is going to allow the other two to become the input and the output now this band sits on the front of the transmission is actually controlled through a little piston that sits underneath here that's controlled from the valve body when this piston pushes up it'll actually squish this band together activating that first drum another main component of the transmission are one-way clutches and this transmission has about three of them you can see the oblong little bearings on the inside there now when I move this I can turn it in this direction freewheel and when I turn it this way it actually locks up and that's because of the direction of these little bearings are kind of slanted in this direction so it actually allows free wheeling in this direction but when I move it this way these bearings have a tendency to actually grab on to the inner sleeve here and make it all locked into one piece now if I pull this apart here we can have a closer look at what these bearings look like now the one-way clutch in your transmission is analogous to the one in the back of your bicycle wheel which allows you to pedal backwards and freewheel or when you push it forward it actually turns the wheel therefore the clutch in the transmission when locked up is actually responsible to provide engine braking so if we take a look at how first gear works with the selector in Drive power is gonna flow from the input shaft to the ring gear on the first planetary gear set and then out through the carrier over to the ring gear on the third planetary gear set and then out through its carrier to the ring gear on the secondary planetary gear set and then out through its carrier to the output shaft now this combination is going to give you the maximum amount of torque with a speed reduction which is ideal for first gear now that all changes when you have it in manual mode because you have engine braking when you let off the gas instead of the engine pushing a transmission the transmission is actually pushing to slow down the engine now that's all control through this locals break over here when the transmission is trying to push back it can't freewheel off of this one-way clutch here instead it's now fixed and the power is then forced to transfer through the transmission back to the input shaft to slow down the engine now in Reverse a couple of these clutches have changed positions and the power flows through the first planetary gearset and then at the secondary planetary gearset it goes through the carrier and then through the Sun gear which actually reverses its position before going back out to the output shaft in the reverse direction now there are a number of thrust bearings in an automatic transmission they're basically little needle bearings here that are laid out flat here and that's because all automatic transmissions have an angle cut on the gear and that creates some force in the axial direction that this bearing must absorb and these gears are caught at an angle because they're much quieter in operation and if they were just cut straight now if you take a look inside the transmission housing here you can see we've got these internal splines here that lock into the splines on the clutch packs over here to hold these stationary we've also got these two ports over here that feed and return oil to the oil pump that's mounted on the front now speaking of the transmission pump here it is it usually sits on the front of the transmission and is driven by the input shaft so it's always circulating fluid throughout the transmission so you can shift gears at the bottom here we have the input and the output we've got a couple of other fluid lines that run out to these corresponding holes on the transmission housing over here that then run down to the valve body to be controlled there's a couple of bolts here that I'm gonna remove and you can see what's inside of this pump and it's gonna get a little oily so I've got a freshly stolen underwear for my brother here doesn't eat that while he's sleeping it's gonna use that to wipe up this little oil here right here we have the transmission pump you can see we have these two flat spots here that engage with the torque converter and it rotates like that we have fluid that comes in through here it expands and then it gets squeezed as it comes out through here now if you look closely inside the pump housing you'll notice that there's actually holes drilled on the inside there and that is what takes fluid from the valve body over here and it pumps it through to this shaft over here and then goes up through the shaft of the torque converter to control Locker and finally we come to the valve body which is located on the bottom of the transmission arguably the valve body is considered the brain of the transmission because it controls everything now the valve body has this computer on the top here and it's responsible for directing throughout the transmission by activating these solenoids over here and the function of the transmission computer is to take the readings from all the switches and sensors in the system and determine which gear should be in and then apply the appropriate line pressure to activate that gear as well as communicate with other computers in the vehicle now how the valve body works is it redirects transmission fluid and pressure through these little ports over here to the ports on the transmission inside the transmission we have this adapter plate that's locked to the case using these splines over here the fluid is I'm gonna flow through the carrier over here through these holes and passages that lead out to the center where we have these rings there's also another hole on the inside here the food will then flow to the next clutch pack by filling up these holes over here and that's going to activate this piston on the inside here to lock up these clutch fluid can also flow through the shaft itself by flowing in through this little hole over here and then over to the other side to lock up this clutch here which is what's going to lock this Sun gear together and if I lift off this board here with all the solenoids and taking a look underneath the board you can see that these solenoids are just a plug-and-play operation two terminals with a coil inside that activates and that will allow fluid to flow from inside of here down through the middle activating that circuit and here we have the computer obviously everything is submerged in fluid and the fluid can't be conductive otherwise you can't have all of these open circuits and here we have the transmission fluid pressure sensors which sense the amount of pressure in the circuit to engage and disengage the clutches for a nice smooth shift now the shift control system is actually a closed loop control system where it's always taking readings from various sensors and determining what pressures to be sent out to the clutches for a very smooth engagement of gears for example if we want to shift gears up here you'll see the line pressure in one of the circuits can slowly increase up here while the other circuit my slowly decrease in order for a smooth transition of the gear ratio now the same thing happens when you shift down although it might be a little bit more abrupt if you mash the gas really really hard and drive very aggressively these are the shift patterns that the transmission computer actually memorize based on your driving style so if you've got a transmission that's shifting a little too hard it might need a little resetting to reset this data underneath the valve body we have this pickup screen over here which is a simple filter like material to filter out any clutch material that has made its suspended in the fluid before it gets sucked back into the pump now the valve body is made in two pieces so I'm just gonna remove all of these 10 millimeter bolts here in order to open this up over here we have the shift controller which is actually responsible for taking the commands from the shifter as it moves from Park reverse neutral Drive and translate that into this linear potentiometer to which it'll send a signal to the computer so it knows what gear it's in now the shifter will also send a hydraulic signal through these little paths over here so it knows which clutches to lock up we've got another temperature sensor over here now with all the bolts removed I'm going to separate this valve body you can see it's like a maze inside here and in between these two we have this steel gasket to kind of separate some of the passages between the two essentially you have two floors like an upstairs and a downstairs maze now it's about to get a little oily again so I'm just gonna use my brother's underwear to wipe up some of this transmission fluid now looking inside you'll see that there's actually little oil filters inside of here both of these little check balls that are spring-loaded then allow only one-way fluid flow inside the valve body it kind of looks like a maze but it's basically a hydraulic circuit that has to be fulfilled with these solenoids at the top here that activate it and it outputs that bolt to the transmission casing over here now there are a number of different Pistons inside of here the direct the fluid flow and if I remove this little holder that holds the piston in whoo let's spring hit my car and here comes the other side so how this piston works to change gears is it's kind of like a relay in electronics we have a signal pressure sent on this side here that's going to move the piston over in a very controlled fashion and now on this side here is where you have the fluid that flows through the valve body to actually do the work of locking up the gear and this is all controlled through the pressure switches over here let's slowly control the movement of this piston for a nice smooth engagement of the clutches so from clutches to a planetary gear set to a tiny little solenoid or a piston that controls it all these are all the components that are needed to make the automatic transmission in your car work make sure you follow me on instagram for behind-the-scenes footage and subscribe for more videos just like this one

Channel: speedkar99

Views: 176,565

Rating: 4.9278746 out of 5

Keywords: transmission, automatic, manual, how, works, inside, gear, planetary, ring, sun, planet, carrier, ratio, efficiency, economy, speed, torque, horsepower, power, engine, wheel, CV axle, turn, rotate, clutch, friction, worn, how to, repair, replace, rebuild, fluid, flush, pan, filter, slip, valve, body, band, drum, piston, converter, pump, infiniti, g35, g37, 350z, nissan, differential, drive, shaft, park, brake, ZF, Aisin, 4WD, FWD, RWD, AWD, DIY, disassembly, removal, burnt, computer, ECU, cvt, dual, coolant, dipstick, teardown, control, spline

Id: T7-QXpk4AVI

Length: 19min 48sec (1188 seconds)

Published: Mon Sep 16 2019