It got gears but has infinite gear ratios like a cvt? It has 2 electric motors inside it, but one of them is the cars alternator? The whole thing sounds like magic.
In: Engineering
It’s a very complicated system incorporating planetary gears rather than a belt driven pulley system. This (https://youtu.be/O61WihMRdjM?feature=shared) is ~ 40 minutes long but it is without a doubt the most in depth video yet still ends up being easy to understand.
Edit: It most definitely is magic, as it is likely the most robust transmission in a current production vehicle
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Planetary gearbox: there’s a gear in the middle called the sun gear, surrounded by rotating ‘planet’ gears, and then there’s a ring gear around the whole thing. All three can rotate, so you can create a load/speed split between the sun and the ring. So for instance if the planets are spinning at 100%, and you stop the sun, the ring spins at 100%. If you stop the ring, the sun spins at 100%. If you don’t stop either, the sun spins at 50% and the ring spins at 50%, or some other combination depending on the relative load (note: I’m using percent here because the actual RPMs can be different ratios, the key takeaway is that as one of the sun/ring spins faster the other spins slower)
The gas engine drives the planets.
The ring is connected to the drive wheels and an electric motor.
The sun is connected to an electric generator, which powers the motor on the drive wheels.
By controlling how much power goes through the generator and motor, you can achieve a “virtual” gear reduction (which is the ratio of planet/engine RPM to ring/wheels RPM). At low speeds, more power goes through the generator and motor, so the ring moves slow and the sun moves fast, creating a high reduction ratio. At high speeds, less power goes through the generator and motor, so the ring moves faster and the sun moves slow, creating a low reduction ratio.
It is commonly known that a planetary gearset can be used to produce distinct gear ratios. It can also be used as a differential. The Toyota eCVT utilizes both of these characteristics. The above video explains this well, though I had to watch it a few times before really getting it.
ELI5:
– output (wheel) rpm needs to match your vehicle speed which can vary across a wide range
– but gas engines run best at 1 particular rpm.
– whereas an electric motors run fine across a wide range of rpm
E-cvt has a fixed set of gears connected such that:
Electric motor rpm + gas engine rpm = output rpm
This lets us run the gas engine at its particular rpm and still have a wide range of output rpm by having the electric motor rpm make up the difference.
Then, add on more details, such as how each input/output has its own gear ratio, which just adds a fixed multiplier on each rpm. And use 2 electric motors instead of 1, for even more flexibility. But the bottom line is that instead of changing gears, we just change the speed of the electric motor(s).
In a normal hydraulic automatic xmission, there are multiple planetary gear sets linked end to end and different parts are locked in a sequence to change the gear ratios.
This isn’t magic. Instead of locking various parts and having that shift shock and synchronization problem along with only fixed gear ratios, it just uses an electric motor that changes speeds on the other end of one planetary gear set to alter the gear ratio, maintain engine efficiency as well as control the output variably. Much more reliable CVT design than the belt or chain CVT.
This transmission is known as a ‘2 speed cvt’. It uses a traditional planetary gear for takeoff and switches to the cvt for everything else
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