Understanding the Subaru Crosstrek Plug-In Hybrid Electric Vehicle (PHEV) Transmission
Hello, I'm Professor John Kelly, and this is the WeberAuto YouTube channel. Today we are going to do something a little different than the traditional videos that I've put out over the last couple years on electric vehicles today we're going to look at the hybrid vehicles that Subaru has produced and I have two of them that have been donated from Subaru of America to our automotive technology program and I want to thank Subaru for that we use these all the time and the first one is is right behind me here that is a 2016 Subaru Crosstrek Hybrid and it is a parallel hybrid and this other one right here behind me is a 2019 Subaru Crosstrek plug-in hybrid and so it has an electric-only driving mode where you can drive so many miles and then it switches to a hybrid operation and what's interesting to me or what was real interesting to me when we received these vehicles is the overall hybrid operation the 2016 back here as I mentioned is a parallel hybrid and I'll make another video about how that system works today we're going to concentrate on this plug-in hybrid and this hybrid vehicle was announced by Subaru is coming in May of 2018 as a 2019 model year vehicle and an interesting thing in the press release from Subaru states that it is this new hybrid system and all kinds of stuff about it but one thing that caught my eye was an all-new transmission and the Toyota hybrid system, I thought wow a Toyota hybrid system in a Subaru I have heard that Toyota owns a portion of Subaru and so it makes sense that there would be this cooperation between them and so I wanted to see I want to see inside this transmission and so I looked and looked and looked and we we had this car donated to us a year ago and I looked on eBay I looked in salvage yards I couldn't find a transmission and so I did a saved search and finally got one off of eBay and was real excited tore it apart or disassembled it I should say I don't tear things apart and I want to show you this transmission it is really cool this is a cool car this is an all-wheel drive mechanical all-wheel drive but it is driven through electric motors unlike some other vehicles that have an electric only rear axle this has a physical rear axle with a drive shaft going to it so let's take a look at what is unique about this Toyota hybrid system transmission and explore it so the first thing we're going to do is go look at just a regular Toyota Hybrid transaxle and then we'll compare that to the Subaru version of it so let's let's go look at that okay so the first thing for comparison's sake that I want to show you is an actual Toyota Hybrid transaxle this would be from a 2019 and above RAV4 hybrid from Toyota it has a motor generator number two right here with 120 horsepower that when it rotates the final drive gear rotates and the tires rotate and the vehicle moves down the road it has a motor generator number one that starts the internal combustion engine and becomes a generator when the engine is running it can also be used to vary to create a continuously variable transmission gear ratio between the engine crankshaft and the final drive so in a real quick description that's how the Toyota hybrid system transaxle works and the Subaru system is identical except it's in a longitudinally mounted rear-wheel drive transmission case instead of a front-wheel drive trans action like this one so let's go look at the parts and see what we can see on this train this new transaxle okay the Subaru transmission uses the same motor generator number two that I just showed you from the RAV4 hybrid it's the exact same diameter same thickness same horsepower rating same kilowatt rating uh I believe it's the exact same rotor for motor generator number two here's the stator four motor generator number two and it looks just like the one in that RAV4 over there other than the three-phase cabling uh attaches in a different location and that's motor generator number two here's motor generator number one same thing same diameters same diameter same thickness I don't know what the power rating is on this one from Subaru but it appears to be the exact same one that's in that RAV4 a Toyota p710 transaxle and then here is the mg1 motor generator number one stator assembly so I'll get the Staters out of the way because we won't be looking at those in any detail in this video instead I'm going to build this transmission starting with motor generator number two and show you what it connects to and how it makes the vehicle move forward in electric vehicle mode remember this Subaru Crosstrek Hybrid here is a plug-in hybrid it has a 8.9 pretty close kilowatt hour lithium-ion battery in the back an air-cooled battery it can drive on electric power only and then the internal combustion engine comes on so let's look at the electric power only method of moving the vehicle down the road and it only involves motor generator number two as far as I can tell on this particular model so I'm going to bring in a few other parts here the rotor itself has some splines that connect to a Sun Gear of a planetary gear set and this planetary gear set is called the motor reduction gear set and its job is to cause a gear reduction to take place which multiplies the motor torque so the motor torque on this rotor here is 202 newton meters or 149 pound feet of torque and if we run it through a gear reduction planetary gear set with the ring gear and a and a planet carrier then we will get a 3.428 gear reduction so let me put all the pieces together here for those of you who are curious this motor reduction planetary gear set has 42 teeth on The Sun Gear 30 on the planet carriers and 102 teeth on the ring gear or internal gears it's sometimes called okay then we have an output gear so here's an output gear I'm going to put it right on the planet carrier and now we've got the stack up for making the vehicle move down the road I'm going to bring in a couple of wooden V blocks here and put this thing put this assembly in it Okay so we've got our motor generator number two if the vehicle needs to move forward the direction of rotation is this way and we will rotate it we have a gear reduction unit with the ring gear bolted to the case of the transmission so it does not rotate and that causes a 3.428 to 1 gear reduction from motor generator number two to this gear over here that connects ultimately to our ring and pinion gear set and makes the vehicle move down the road okay so the gear that it connects to is this gear right here and it just sits in here whoops wrong direction sits in here like this and so as the motor generator number two rotates this gear rotates also and it let me slide these out of the way for a moment connects to this pinion gear shaft so it's going to slide right on there like that and rotate and that gives that connects to a 10 tooth pinion gear that then turns a 37 tooth ring gear in the final drive assembly of this transmission a rear-wheel drive all-wheel drive transmission this is an all-wheel drive and that's different than the Toyota version of this transmission uh the transaxle because they didn't have an all-wheel drive a mechanical all-wheel drive Toyota had an electric all-wheel drive with three-phase cables going to the rear electric motor but this is a mechanical all-wheel drive which is which sacrifices a little bit in efficiency but it also transfers torque directly through and that can be an advantage especially if you're going uh off-road which this vehicle is intended actually to do that Okay so just a quick review motor generator number two turns a planetary gear set for gear reduction turns a drive gear that turns a driven gear that turns a pinion gear that turns our ring gear and as this ring gear turns our CV half shafts are connected to this and are tires which means our tires spin the exact same speed as this ring gear and differential case this is an open differential and the vehicle moves down the road and that's all we need for electric vehicle mode but this is a plug-in hybrid so that's all that's used in the electric vehicle mode operation but once the battery state of charge gets down low enough that we need to kick in some additional power from the internal combustion engine then we need to start the engine we need to be able to keep the high voltage battery from going dead or from losing more state of charge not from going dead and then also to have the internal combustion engine help turn this same gear here to help turn the ring and pinion gear set to make the vehicle move down the road so let me get these out of the way and let's bring in our other electric motor all right now we've got motor generator number one motor generator number one has a few jobs it has three jobs its first job is to start the internal combustion engine its second job is to as driven by the internal combustion engine turn into a generator and bring the high voltage battery state of charge up to a certain point it's not going to charge it all the way in most cases I can't remember on this car if it has a full charge option or not I do not think it does I've read about some cars that do but it can bring it up to a certain level and then this also works with another planetary gear set called the power split gear set to give us different gear ratios from the engine crankshaft to this drive gear back here to turn the ring and pinion gear set on and our tires so let's bring in these other parts and and see what they are motor generator number one right here connects to a Sun Gear of a planetary gear set the motor I'm sorry the power split device gear set and then there is an input shaft from the internal combustion engine there's a damper and torque limiter out there where it connects directly to the engine crankshaft but this is the planet carrier and it has our three Planet gears on it by the way the Sun Gear has 30 teeth the planet carriers or Planet gears have 25 and the ring gear has 78 and yes I know that blows away a lot of you thinking that that's not the right number of gear tooth count it is I've double checked it I know there's a formula to decide how many teeth should be on the ring gear based on taking the Sun Gear teeth count and adding two times the planet carrier or the planet gear teeth count to get the ring gear count but that isn't always the truth and I have one example here this one does this one does not work with our formula so anyway we have an input shaft from the internal combustion engine that's going to come in and the planet or The Sun Gear is going to go connect to the planet carrier and then we have another ring gear right here for this planetary gear set and this ring gear has a splined output shaft where it connects to a drive gear right here all right now let's bring in some v-blocks and we'll hook this uh Stack Up in the v blocks and take take a look at how it works all right then we also have an input gear from the engine internal combustion engine right there okay so let's take a look look at what we have in this gear lineup we have this gear right here that is actually driven by another gear that connects to the crankshaft of the engine through the through the damper so this gear has 35 teeth this gear has 37 it's a 1.05 to 1 gear reduction from the engine to this input shaft so as the engine is rotating it turns
this input shaft that input shaft is connected right to the planet carrier of our power split planetary gear set now let's just ignore that uh gear that I just showed you for now there are three things that I want to show you next so first starting the internal combustion engine to start the internal combustion engine all we have to do is turn the generator here motor generator number one we will turn it and notice as it rotates it causes the the gear that connects to the internal combustion engine crankshaft to rotate and we can spin it really fast that'll spin the engine crankshaft really fast and and cause the engine to start now once the engine is started notice I can spin that input gear and it will cause a the motor generator number one to spend 3.6 times faster than the input gear is spinning so there's a 3.6 to 1 overdrive right there as we're starting the engine there's a 3.6 to 1 gear reduction to start the engine so starter generator and the starter is a motor so they call it motor generator number one all right so we've seen starting the engine and becoming a generator to recharge the high voltage battery up to a certain state of charge all right now this gear over here on the end that we haven't done anything with this is the output gear from the engine and the motor generator number one from the engine crankshaft notice if I hold it solid and spin the engine crankshaft connected gear it it doesn't rotate if I spin motor generator number one it doesn't rotate but if I spin them both together it does rotate and what happens is we can spin the engine crankshaft and the electric motor at the pretty much the same speed and get a direct drive a one-to-one gear ratio through the from the input to this output gear right here we can also if we while spinning the engine crankshaft if we spin the motor a little or the rotor a little faster we get gear reduction the output gear doesn't turn quite as fast as the input gear if we spin mg1 slower than the input notice we are getting a faster output over here that's overdrive if we bring it to a complete stop we get it even higher overdrive and if we turn it backwards we get an even higher Overdrive so one more time if as we spin the crankshaft of the engine if we spin the motor the rotor of motor generator number one faster than the crankshaft we're in gear reduction over here if we spin at the same speed we're in a one-to-one gear gear ratio and if we spin it slower then we get overdrive if we stop it we get another overdrive if we spin it backwards depending on the speed we get it continuously variable gear ratio so this is called a CVT continuously variable trans transmission but CVTs have a bad name and this is not one of those that has a bad name this is a it's referred to in a lot of Publications as an electronic CVT the CVTs that have had problems and have a bad wrap are the ones that use a push belt um like the one in this photo you know or ones that use a pull chain like the ones in the one in this photo, the pull chain ones are more reliable than the push belt ones but there's two there's actually three different types of CVTs that I have here in the shop the push belt the pull chain and the electronic continuously variable CVT all right now let's take this variable gear ratio motor generator number one and engine crankshaft and we're going to take this gear and we're going to connect it to the output gear from motor generator number two over here so notice on motor generator number two Let Me scoot this over a little bit here the output gear over here has two gears this smaller gear is what this gear from motor generator number one is going to connect to so if I let me scoot these Staters out of the way if I bring in our motor generator number one get it lined up there we go okay so now we've got the entire lineup as it is inside the transmission housing we have our motor generator number two it's gear reduction unit and the output gear that drives the ring and pinion gear set that's the electric only mode that we've talked about then we've got our continuously variable transmission through our power split device we have a gear that drives a smaller gear here but these two are connected together on the same output shaft so what I'm saying is if this gear rotates so does this other gear and so does the ring and pinion gear set and your tires the large gear has 41 teeth the small gear has 32 teeth and it gives us a gear overdrive of 0.781 to one so as we're driving down the road and our high voltage battery state of charge gets low our engine is off so I'll hold this gear from rotating motor generator number two is propelling the vehicle and notice we've got our output gear driving notice our mg1 is spinning but it's usually not generating power at that point because it would be using power to generate power which is a loss we would have electrical power we'd have to spin it with the internal combustion engine okay so then once the state battery state of charge gets low enough then we start the internal combustion engine so we spin motor generator number one faster than the engine crankshaft and get the internal combustion engine to start once the internal combustion engine starts then we can start playing with the variable gear ratios so if we spin everything the engine the internal combustion engine input gear and motor generator number one the same speed notice that cause whoops I'm spinning in the wrong direction that causes the output gear to turn and it causes our output drive gear for the ring and pinion gear set to turn also and that would transfer engine torque through our our power split device gear set into the um output gear notice that's also causing motor generator 2 to rotate and motor generator 2 as it's rotating can be a generator to generate more power to recharge the high voltage battery to a certain state of charge if the high voltage battery has enough power then this can act in parallel with the internal combustion engine and the power split device and give us a parallel mode where it um helps the engine crankshaft go down or Propel the vehicle down the road we can also have the a series mode where the internal combustion engine is spinning fast and this jet this motor generator number one becomes a generator to provide power to motor generator number two to move the vehicle down the road now I did not see on the description for the Subaru if motor generator number one ever combined with motor generator number two to move the vehicle down the road I don't think it does the original Toyota Prius Prime here in the United States that started in 2017. had a special one-way sprag type clutch on the flywheel to keep the engine from spinning backward if we use both Motors both electric motors rotors to propel the vehicle down the road the engine crankshaft would could spin backwards but in this case from what I've read and for the RAV4 also it doesn't do that but I could be wrong but I couldn't find anything talking about a one-way flywheel device this output gear that we've talked about that drives our ring and pinion gear set that is for the front tires so this is front wheel drive operation only but I told you this this is an all-wheel drive vehicle Subarus are famous for having all-wheel drive so now we've got to look at what additional part is added to all of this to give us all-wheel drive so here on the motor generator number two and the and the gear reduction and output gear to drive the front ring and pinion gear set this gear if we look inside of it let me pull it off down inside of this gear it has splines for another shaft to come in and connect to so this is the rear output shaft inside the transmission that goes to a special electromagnetic activated clutch pack that then can send torque or apply torque to the rear axle so this vehicle is normally front-wheel drive but we can apply a torque to the rear axle as needed to give us all-wheel drive so let's take a look at that all-wheel drive clutch pack okay the all-wheel drive clutch pack sits in this clutch drum right here that has two wires coming off of it and if we look at the back right here it's got this electromagnetic clutch it's just a big coil of wire like an air conditioning clutch compressor clutch air conditioning compressor clutch I have put Power and ground to this real quickly and this became a magnet a very strong magnet on the scan tool as you can see in this photo here the scan tool that the Subaru scan tool will let you apply up to 3 000 milliamps of current to this clutch coil and test it and so the resistance of this clutch coil when I measured it yesterday was around three and a half ohms uh so if we connect that to 12 volts we'll get somewhere in the 3 000 to 4 000 milliamp or three to four amp uh range of current now this clutch drum that that spins freely here has this input shaft that I showed you or the output shaft that I showed you going through it and since this is an electromagnet what the electromagnet is going to do is it's going to attract this steel plate right here and pull this plate down against that magnetic surface down inside there as it pulls it down it will apply Force to a two fiber disc clutch pack that's in there so we have down in the bottom of this clutch housing two plates that connect that have splines that connect to the outer housing two plates that have internal teeth that connect to an inner housing and then we have this big steel plate right here that sits on top of all of that and as the magnetic field is present it pulls down really hard on that and it stops those clutch plates that could slip it prevents them from or tries to prevent them from slipping now as it tries to prevent them from slipping there's an interesting little piece in the middle of all of that right here this little Hub with these balls on it this is called a ball ramp and if these balls are forced to move one way or the other they roll up a ramp and try to separate pieces and so this metal plate sits on top of this ball ramp assembly and it has little ramps down in it also and so it's going to set right there just like that and then notice as I rotate it it separates so not separated, separated, back and forth as it as the bottom piece tries to spin it pushes up on the top piece pushes up so what causes the bottom piece to start spinning is the electromagnetic clutch that we just looked at so electromagnetic clutch comes on it grabs this splined piece underneath starts at rotating as it rotates it pushes up on this clutch apply plate and this clutch apply plate has a seven clutch fiber disc clutch pack that as it pushes up it will try to compress but we can't compress so it squeezes and puts force on those clutches and stops them from rotating and that causes this shaft that's already connected to the the drive gear on our mg2 output here to transfer torque through the housing itself to a big plate that sits on top here and the output shaft that goes to the rear drive shaft and the rear axle to make the vehicle move down the road so during non-all-wheel Drive operation this shaft can spin these clutch plates can spin without being held solid to the output shaft that from the drive gear that provides the torque that goes to the rear axle so in other words these two these two shafts are not connected together when the electromagnetic clutch comes on the ball ramp is activated it pushes up on these fiber clutches squishes the big clutches clutch plates together and connects this output shaft to the input shaft and gives you torque to the rear axle now these are all spinning pretty much the same speed anyway we just need to apply the clutch discs to transfer the torque all right I'm going to hurry and put this back together and then I'll show you where it goes in the in the whole lineup with the transmission okay I've got the clutch pack reassembled we've got our input shaft right here from our drive gear and we've got our output shaft right back here that goes to the rear drive shaft so that's all together like that now if we bring in our mg2 right here this input shaft right here is going to go right up the middle of motor generator 2.
through our planetary gear reduction gear set the motor speed reduction gear set I've got a few shims in there that will be used in the case and then that connects right to the drive gear the same drive gear that turns the ring and pinion gear set for the front so we're driving the output shaft through the clutch pack to the final output shaft here that drives the rear drive shaft and the rear axle so as we put this whole thing together now for one final look here we go that's quite a big long Stack Up and as you'll see here and as you'll see here in a minute we're going to put this inside of the transmission case we've my shop assistant and I have spent a lot of time preparing this case we've cut away sections of it so you can see all of this as we put this back together oh sorry there's one more thing I want to show you uh and that is the oil pump assembly here it has two gears on it some of you may have been wondering why are there two gears on the outside of the planet carrier and the ring gear and that's because we have two oil pump Drive gears here one of the pump Drive gears is used for electric motor only driving the other one is used when the internal combustion engine is driving and they actually have a little sprag on there so that when the one is being used the other one can just free Spin instead of uh having to having to turn at variable speeds as that power split device the speeds between the ring gear and the planet carrier vary all the time because of it being a continuously variable gear set so there's our oil pump it just drives a trochoid oil pump just like in all the other Toyota hybrid system Transmissions all right let's put all this in the Cutaway transmission and then we'll come back and take a look at that okay it took a little while but we put together the Subaru th2a plug-in hybrid transaxle or transmission it's a rear wheel drive transmission we have a front differential right here where the front CV shafts half shafts come out and go to your front tires and then we have a rear drive shaft that comes in right here that goes to the rear axle for the all-wheel drive system it's a pretty long transmission we've got motor generator number one up in the front here we have a bunch of gears in the middle motor generator number two right here and then our all-wheel drive all-wheel drive electromagnetic coupling in the rear we have three phase cables right here that come in to feed motor generator number two and then we would have cables like that on the other side to feed motor generator one but me and my shop student assistant Nash made a cutaway of this transmission for you to see did a really good job and I want to show you this transmission okay so these are all the exact same parts that I had here in the wooden V blocks earlier in the video but here is our input shaft from the engine crankshaft we've got a damper that connects right there and you'll notice that when it rotates it turns the input shaft and that turns the planet carrier in our power split device which turns The Sun Gear which is connected to our motor generator number one so that becomes a generator once the engine starts to start the engine we just turn motor generator number one and notice it makes the engine crankshaft turn right here okay then on the rear over here we've got motor generator number two and oh right here you can actually see the ring gear with the teeth facing away from you and the front differential the open differential that our half shafts come out this would go to the left front tire so when we rotate in the forward direction to make the vehicle move forward motor generator number two notice the ring gear spins forward the ring gear in your tires turn the same speed and direction Okay so here's our motor generator number two our gear reduction gear set that we already talked about here's our parking gear so when we put it in park it stops all of the output drive gear from rotating prevents the vehicle from rotating and then we've got our variable gear ratios that come in here that drive this gear that connects to our output gears to the to the front it also connects to this output gear and a big long shaft that comes and goes to our rear or our all-wheel drive electronic torque electronic control coupling right here and remember this is an electromagnetic coupling so when it is activated torque is transferred out the rear the rear of the transmission so that pretty much wraps up the Toyota hybrid system integrated into the Subaru Crosstrek plug-in hybrid which I'm actually pretty impressed with the vehicle it does have a fairly short electric driving range of 17 miles but if that matches your commute or a round-trip commute then that's that's fine plug-in hybrids can be a good transitional vehicle for people that aren't quite ready for an electric vehicle you can plug in hybrids are a good option and there are a lot of there are a lot of plug-in hybrids available out there in different configurations so that's it thank you for watching