Part 1, Definitions:
Let's define the picture above.
The red toothy ring is called a ring gear.
The 3 blue gears are called planet gears, they are attached to a gray plate that makes them all turn as one unit. This plate is called the planet carrier.
Then the small yellow gear in the center is called the sun gear. The whole system is called a planetary gearset. The thing that is unique about a planetary gearset is, if you turn one, it affects the whole system. For example, if you turn the planet carrier, then the whole system turns. If you turn the planet carrier and hold the ring gear, then the sun must turn. By turning and/or holding various items you can make it do a whole bunch of things. More on this later. To see it work, watch this video.
Many of the items below deserve their own articles to fully explain how they work, but for now oversimplified definitions to keep in mind for this article are:
ICE=internal combustion engine, gas or diesel. I will call it ICE in this article so that I don't have to differentiate between gas and diesel all the time.
Hydro/hydraulic/hydrostatic pump=A device that moves fluid to turn a hydraulic/hydrostatic/hydro motor
Hydraulic/hydrostatic/hydro motor=a device that turns a tire or a gear with fluid from the pump.
Electric Motor=A device that turns a gear or wheel just like a hydro motor but uses electricity to turn instead of fluid.
Generator=An electric motor that produces electricity for a battery.
Battery=Essentially a storage tank for electricity.
MG/motor-generator=An electric motor that is also a generator depending on the situation.
Transmission=A complicated mechanism that converts raw speed from a motor into slow, useful torque for the wheels by a means of many gearsets, clutches, shift mechanisms, torque converters etc to create anywhere from around 3-10 gear ratios.
Gear ratio=The amount of times the motor(s) turn in order to make the tires turn once. The higher that number is, the more torque the machine has at the tires. The lower that number is, the more speed the machine has at the tires.
Speed=How fast the tires are spinning. Usually measured in miles per hour of machine speed on the dashboard.
Torque=How much force the tires are putting to the ground. Or, how hard it would be to stall the machine. Usually not measured at the tires, and therefore a little confusing to understand for many people. If a machine is sitting on rough concrete and has nearly unlimited traction so it cannot spin. When pulling a heavy pallet piled up with steel weights. If everything is the same, otherwise, the machine that has the most torquey gear ratio, (higher number, lower speed) stands the best chance of actually dragging the pallet, while the other machine with out the torquey ratio can not.
CVT/continuously variable transmission=A transmission that has infinite gear ratios between its torquiest ratio and its fastest ratio. The belt drive system like an ATV is a CVT as well, but has a different gearing system than the ones described in this article. It deserves a separate article.
Range Gears=An extra gear system added to a transmission to create a new set of gear ratios. For example, a pickup with a 6 speed transmission and 4wd has a low range, called 4low. When doing serious off-roading putting the truck in 4low cuts its to speed down to about 60 mph but gives you 6 gears just for off-roading, these 6 gears are all lower and torquier than the same 6 gears would be in 2wd. In this way, the ratio range gear system has given the truck 12 gears total.
Part 2, The electric innovation:
Toyota has developed this in the Prius, and have called it a hybrid, but now it is spreading like a certain Chinese virus I call the 'rony through their vehicle lineup and now vehicles that I might actually buy have it. So, I decided to educate myself on how it works, and I was impressed. In this system, there is no front drive transmission, and I don't miss it, those tend to be a little complex and fragile. Instead we have a second battery, usually stowed under the back seat or somewhere else obscure. Then we have 2 MGS. MG2 is directly connected to the front tires through gears and axles, and the ring gear of the planetary set is connected to the front tires directly as well. So, front tires turn, so does the ring gear. MG1 is connected to the sun gear. The ICE is connected to the planetary gearset. There is a controller that functions like a computer, and it can work the MGS. So, at low speeds with good life in the battery, MG2 runs the car, when more power is desired, MG1 comes to life and spins the ICE over and makes it start. Now the ICE is turning the planet carrier which in turn helps the ring turn easier, and takes load off of MG2. When foot is to the floor because someone in a Honda ricer wants to show you what for, the ICE and MG2 are both spinning with everything they got, meanwhile, MG1 is spinning backwards to improve the ratio for torque by slowing down the whole gearset through the sun gear. (Remember, high motor speed and low tire speed equals maximum torque.) As more speed is desired, MG1 slows down, and as it slows down it gradually is reducing the torque in exchange for more speed. When cruising, MG2 can do most of the driving work, while the ICE can turn MG1 to charge the battery. When coasting to a stop, the vehicle momentum means MG2 is being turned by the tires, and therefore making electricity which it sends to the battery. ICE and MG1 immediately shut off when not needed and then come back on when driving again. Ultimately, when you study the way a planetary gearset can be manipulated if you have a motor for each of the 3 basic pieces, the sun, planet carrier, and ring, then you can see how this system is a CVT. This system is generally deemed an improvement because, 1. The efficiency and power numbers compared to equivalent normal cars speak for itself, and 2. It is actually simpler than a regular transmission, fewer gears, fewer moving parts, no clutches. SO probably more reliable.
Extra innovations:
When doing AWD, Toyota doesn't need to build a system of gears and clutches to carry power to the rear tires, they can just put another electric motor back there and call it MG3, it functions in the same way as MG2.
In Lexus, Toyota put a 4 speed automatic behind the hybrid system, this serves as a fully automatic Range Gear system to give the car more torque on one extreme, and more speed on the other.
Downsides:
Although this system seems to be more durable than a normal front drive car, it appears to still not be as robust as a rear drive transmission for towing and off-roading. Toyota has not been willing to put it in a pickup or off-road SUV. However, Toyota is a conservative company and that may be coming.
Part 3, The Hydraulic Innovation:
In the tractor world there have been 2 main transmissions dominating the space. If you wanted to mow or use PTO, a hydro was a better choice because you could set the engine rpm where you wanted it to run the mower at the speed you wanted and then drive the tractor at the speed you wanted as well. This type is very common in the compact category. Problem is, when towing heavy things like plows or cultivators, then the hydro drive overheats and cries uncle! If ignored and not allowed to cool, it makes a steamy expensive messy repair for your entertainment. A gear drive could pull till the cows came home or the engine stalled no problem, but, if you wanted to mow, once the mower speed was set, you had to just make do with whatever speed the tractor drove based on the gear it was in. Enter Fendt, a planetary gear set. A hydro pump on the ring gear, the ICE on the planet carrier, and the hydro motor on the rear tires and the sun. So, whenever the rear tires turn, the sun and hydro motor turn as well. When the ICE is turning the planet carrier, either the sun, or the ring have to turn, one of them MUST turn, so, at first, the ring turns the hydro pump, then the hydro pump turns the hydro motor, and presto we have a hydro tractor, but, as load is applied, more and more power gets sent out through the sun gear, and presto, we have a gear drive tractor. So, the tractor runs along, switching between pure hydro, a mixture of the 2, and pure gear as the situation calls for it, and it all works seamlessly because the power flows through the path of least resistance. It really is the ultimate in tractor technology. It has 2 ratios, one for field, and one for transport.
Extra Innovations:
Yanmar/Bosch, New Holland/ZF have found a way to make the machine send more power through the gear side in order to make it more efficient, they do this by making the hydro help reach the top speed by spinning the planetary faster. This means pure gear drive is in the middle of the speed range instead of at the top. The Yanmar/Bosch system is designed to fit in compact tractors and has 3 ratios instead of 2 like Fendt. The New Holland/ZF system has added a 4 speed powershift transmission in the back to give it 4 ratios that are automatically selected by the machine. Deutz has a system that splits the difference and tries to give the smoothness of Fendt with the torque of New Holland, it is new so I don't know as much about it yet. If your tractor brand of choice has a CVT, and is not named here, it probably is using the ZF version of the New Holland system, if it's a brand in the AGCO family, it is using the Fendt version, since Fendt is an AGCO company.
Downsides:
None of this type of transmission seem to have been used in the automotive space for whatever reason, perhaps efficiency problems at high speeds, so it's not available in a truck, yet.
The reliability looks to be ok, but it's hard to believe it will be better than an old school manual.
COST!! Ever priced a Fendt?
To get a better visual aid to understand how the speed varies, watch this video from AGCO. When watching it to learn about Toyota, imagine the hydro motors/pumps being replaced by electric motors, and you have the basic idea. Ultimately, I would love to have one of these trainers to play with to learn more about how it works myself, to help visualize it. This trainer replicates Toyota's system, for Fendt's mentally replace the electric motors with hydraulic pumps and motors. Watch it here. It is remarkable that a car company from Japan and a tractor company from Germany both converged on the same brilliant engineering solution! One with a electric and gas power combination, and the other with a diesel and hydraulic power combination. The principle of operation remains mostly the same. Then, the New Holland/ZF and Lexus systems operate in very much the same way as well.
To gain clarification or to correct my explanation on any point, feel free to reach out and contact me directly.
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