Toyota Hybrid Transmission Operation 15 Years on YouTube

Hello, I'm Professor John Kelly, and this is the WeberAuto YouTube channel. In this episode, we are going to look at the individual components and parts involved in propelling a Toyota hybrid vehicle that uses a power split transmission. So let's get started. Okay, the first major part of the Toyota hybrid system that you may be familiar with is the engine crankshaft. So this piece right here that has these journals that go up and down is what our connecting rods and our pistons connect to that move up and down and make this crankshaft rotate. Connected here on the end of the crankshaft is a flywheel with what's called a torque dampening clutch. It also has damping springs in it to dampen the oscillations of the crankshaft as it rotates through its compression and and power strokes. So if this piece is rotating, the pistons are going up and down in the engine, and we can start the engine by turning this. Once the engine is running, this part will be rotating. And now we'll take a look at the other pieces that connect it to the wheels. Okay, the next part involved is one of three components of a planetary gear set. This is called the planet carrier. It has these little planet gears right here, and this housing that contains them or carries them, and it has a shaft that is going to slide right into the torque damping clutch of the flywheel. And as you can see, if the engine crankshaft is rotating, so does this planet carrier. Okay, there are two other parts of the planetary gear set. One of those parts is called the sun gear. So that's this piece right here. The sun gear rotates around inside of the planet carrier. So if I slide this carrier out and put the sun gear down inside, it rotates on the inside there and on the Toyota hybrid system, we connect an electric motor to it. This motor is called motor generator one or MG1. So I'll put this sun gear on motor generator one, and I'll take motor generator one and slide it onto our planet carrier. So now we have two different pieces right here. We've got the sun gear that rotates with the motor, we've got the planet carrier that rotates with the internal combustion engine, this crankshaft that we've got here. So I'm going to slide this planet carrier and sun gear with motor generator one up into our torque limiting clutch housing. As you can see, I can spin the sun gear with motor generator one, it does not cause the engine crankshaft to rotate. Alright, the next part of the planetary gear set that I'm going to bring in is called the ring gear. So we've got this gear set right here called the ring gear. This is what fits around the outside of the planet carrier. And we have the other electric motor in the Toyota hybrid system right here called motor generator number two that connects to this ring gear. Okay, so we have all the pieces that are involved in the Toyota hybrid system connected here. There are different generations of these transaxles that have the electric motors offset of each other, but it still works exactly the same way. If motor generator two rotates, it connects through gears or change depending on the model year to the differential and drives your front tires. Motor generator one is here to start the engine and then become a generator once the engine is running. So let's go through the modes of operation here and see how all this works. So if we want to start the engine, we would just rotate motor generator one forward. So I'm spinning motor generator one, notice it will take 3.6 revolutions of mg one to get one revolution of the engine crankshaft. So it's a 3.6 to one gear reduction that then will start the internal combustion engine. Once the engine starts, then the engine crankshaft overdrives mg one by 3.6 times. So it's 3.6 times faster. And it this becomes a generator to charge the high voltage battery. Now, these two pieces combined motor generator one and the internal combustion engine through the planet carrier. So the sun gear and the planet carrier, these two parts can vary the amount of torque delivered from the crankshaft to help mg two power the wheels and bring you down the road. So let me show you three different gear ratios. The easiest gear ratio is if we rotate motor generator one and the crankshaft at exactly the same speed. Notice that mg two will also spin the same speed as the engine crankshaft and motor generator one. This is called direct drive. So this would occur at highway speeds. So that's direct drive. But if you're stopped and need to accelerate away from a stop sign, then we need to go into underdrive gear ratios. So if the with the engine running, the engine crankshaft will rotate. But notice, if I just rotate the engine crankshaft, there's no direct connection to the wheels through mg two. So we have to do something with mg one also. So if we rotate mg one faster than the crankshaft, then although mg two does rotate, there's gear reduction taking place. Alright, so that's underdrive. That's like a low gear ratio on your bicycle. When you get up to two highway speeds, we've got the one to one gear ratio that I've already showed you. And then if you want to go faster than say 5560 miles an hour, then we have to go into overdrive. So to go into overdrive, all we do is spin, let mg one spin slower than the engine crankshaft. So as I spin this crankshaft flywheel here, notice that mg two spins faster than the crankshaft. Let's get let's get these marks lined up here. So we've got some tape right here on the on the flywheel. And we've got the tape here, the label tape on mg two, if I were to spin mg one slower than the crankshaft, let's say I just stop it because at around 55 to 65 miles an hour, depending on the vehicle, mg one actually comes to a complete stop. If I stop it totally, notice I can spin the crankshaft around and I get a full revolution out of mg two before I get a full revolution out of the crankshaft. So that's overdrive. And we can go into even higher overdrive by spinning this mg one backward. So that's like a double overdrive mg two is spinning really fast versus the engine crankshaft. So this is what's called an electronic continuously variable transmission. The combination of the planetary gear set the power split planetary gear set, and the rotational speeds of the engine crankshaft and the mg one rotor give us underdrive gear ratios, direct drive gear ratios and overdrive gear ratios. Now in electric vehicle mode only on the Prius or the plug in Prius, we would use just mg two with the engine off so the crankshaft won't rotate. And as I spin mg two under electric power off of the high voltage battery. That's what makes the vehicle go down the road, we've got gear drive or chain drive here that if this rotates forward, which this is the direction of forward rotation, the vehicle moves forward, there is no reverse gear, you just spin mg two backward. Now there are a couple other modes of operation of this transmission. Toyota calls this a series parallel transmission. And the technical SAE term for it is a power split transmission. But let me show you the series hybrid mode and then the parallel hybrid mode. By the way, a series hybrid uses an internal combustion engine to turn a generator to provide power for an electric motor to propel you down the road without a direct connection between them. So if the internal combustion engine is running, we are turning mg one as a generator. And that can supply power through the inverter to mg two to propel the vehicle down the road. So that's series hybrid mode. Okay, then the next hybrid mode of operation is parallel hybrid mode. And in parallel hybrid mode, mg two can help the internal combustion engine propel the vehicle down the road. So at higher vehicle speeds, highway speeds, freeway speeds, where we talked about the mg one being stopped or rotating backward to give overdrive, the mg two motor can actually help the crankshaft rotate. So there's power from mg two and power from the engine crankshaft, two different sources, power split, we've got two different sources of power coming to our planetary gear set and the gear and chain drive to make the vehicle move down the road. So this trans transmission and Toyota hybrid system operation has a series hybrid mode as a parallel hybrid mode. And then when you decelerate, anytime you slow down, mg two becomes a generator, which makes it difficult to rotate and it runs current back to the high voltage battery to charge it. So this is the Toyota hybrid system that's been around since December of 1997. When the original Prius came out 15 years ago, I shot a video on how this system worked. And I made a couple of mistakes in that video at the time, but I'm coming up on the 15th anniversary here at the end of October of that video here on YouTube. And I thought, well, I'm going to redo that video and make some changes to improve its accuracy. Plus, I wanted to show the crankshaft of the engine and how everything is in line right here to have motors help the crankshaft or have the crankshaft helping the motors drive down the road. So I hope that's been helpful. Thank you for watching and have a good day.