Planetary gear system

[Bill906]

ICE's REQUIRE a variable transmission
Electric motors do not require variable transmission, but could be used optionally.

Cons of using variable transmission include added weight, cost, complexity and loss of power do to added friction.

I'm not sure what the benefits are. To run the electric motor in a slightly better area of it's torque curve?

When you say planetary gear system, are you talking one planetary gearset or cascading gearsets like a typical automatic transmission. How many discrete gear ratios are you suggesting? Or are you talking some complex system that creates a continuously variable ratio?

 

[JBee]

ICE's REQUIRE a variable transmission
Electric motors do not require variable transmission, but could be used optionally.

Cons of using variable transmission include added weight, cost, complexity and loss of power do to added friction.

I'm not sure what the benefits are. To run the electric motor in a slightly better area of it's torque curve?

When you say planetary gear system, are you talking one planetary gearset or cascading gearsets like a typical automatic transmission. How many discrete gear ratios are you suggesting? Or are you talking some complex system that creates a continuously variable ratio?

Neither, I'm arguing against more complex gear arrangements including the planetary gear of this thread. I understand the torque curve comparison between ICE and EV and that a electric motor can get away with a single ratio gear.

My conversation was with Crissa, as those comments weren't correct. You might have to read the thread from further up.

 

[Bill906]

Neither, I'm arguing against more complex gear arrangements including the planetary gear of this thread. I understand the torque curve comparison between ICE and EV and that a electric motor can get away with a single ratio gear.

My conversation was with Crissa, as those comments weren't correct. You might have to read the thread from further up.

Sorry, I had you confused with the original poster.

 

[abebarker]

There are two ways that you can use a planetary gear set;
1) One input, one output, third gear held steady. This acts just like a conventional gear (with the benefit that planetary gears are tougher).
2) Two inputs and one output or one input and two outputs (applicable in regen). It is called a power split device.

The power split device allows several advantages;
1) Increased efficiency, because the motor speed is not tied to tire speed, the motors may operate near their most efficient.
2) Much greater low end torque, the motors can deliver full speed power to shaft at 0 RPM's.
3) Effective and efficient regeneration all the way down to 0 RPM.

It has already been determined that this is not necessary for the broad consumer vehicle market, it is just too much power. We agreed upon that decades ago. However, this is necessary for the truck transport industry.

You can run the induction motor at low RPM's and high torque for some limited amount of time. It produces a lot of heat. If you are a semi truck driver in stop and go traffic then your motors are going to produce a lot of heat and need additional cooling.

No other method that I know of allows for such performative regeneration. As any motor slows down it becomes a less efficient generator. The power split device allows to tire speed to be independent of the motor speeds* (the motors can be independent but they tied together). For example; tire at 0 rpm, first motor at +100 rpm, second motor at -100 rpm.
Example 2; tire at 0 rpm, first motor at +10,000 rpm, second motor at -10,000
The motors can be 'independent' of the tires but their combined speed will always equal the tire speed.

For regeneration at low speeds, run one motor at a fast speed use the other motor as a generator. The efficiency as a generator is increased because to is able to run at higher speed and that is dependent upon the speed of the other motor (and the speed of the tires).

The power split device will revolutionize the trucking industry and make practical the electrification of trucking.

 

[Bill906]

Increased efficiency, because the motor speed is not tied to tire speed, the motors may operate near their most efficient.

The difference between most efficient speed and least efficient speed is not very significant.

Much greater low end torque, the motors can deliver full speed power to shaft at 0 RPM's.

Electric motors already produce lots of torque at low end.
At zero speed power is also zero. Power is the product of torque and speed.

Effective and efficient regeneration all the way down to 0 RPM.

At low speed there isn’t that much regen power to recoup.

You can run the induction motor at low RPM's and high torque for some limited amount of time.

Depending on what “high torque” means. You can run a motor at high rpm and high torque for some limited amount of time also.
You can run a motor at rated current continuously. The only caveat I know of to that is with a typical industrial 3 phase motor that is cooled by a fan driven by the motors shaft. At low speeds the fan is not turning fast enough to cool the motor. So yes, THAT type of motor can overheat at high load (high current) at low speeds. I feel very confident in assuming EV motors do not use the motor shaft powered fan cooling system.

As any motor slows down it becomes a less efficient generator.

The slower the speed, the less power there is to recoup.

tire at 0 rpm, first motor at +10,000 rpm, second motor at -10,000

Not sure how spinning two motors at 10,000RPM yet the wheels are not turning is efficient.

 

[abebarker]

Electric motors already produce lots of torque at low end.
At zero speed power is also zero. Power is the product of torque and speed.

This must be what you are talking about, being able to produce lots of torque at low end.

So power is the product of torque and speed. At low speed the motor is delivering low power but full torque. Ok. At high speed the motor is still delivering full torque but it is now delivering more power.

I am saying that with a power split you can get MANY times the low end torque than the motor can deliver at that speed by itself. The motor is delivering more power at high speed. Torque is power divided by speed. Deliver a lot of power at low speed and you will have lots of torque. Again, many times more low end torque can be produced with the power split than with the motor alone.

The slower the speed, the less power there is to recoup.

Also, being able to extract all the energy, even at low speed even though there is not much power there, is a big deal. No need to tell me that it is not a big deal.

 

[Crissa]

Your own chart shows a static power with a variable interval.

Nearly all highway-capable EVs use multi-phase variable pulse power to control the motor, which gives them a very long, flat torque curve.

As I pointed out, even the motor in my Zero has to be artificially limited in power not to spin the tire at low speed. Torque is not a problem.
https://www.motorcycle.com/manufacturer/zero/living-with-a-zero-sr.html

There's no need for additional transfers that lower efficiency.

Tesla solves any problem here by having multiple motors set to different, overlapping curves. That gives us cheap all wheel drive on top of a more efficient drive system.

-Crissa

 

[JBee]

This must be what you are talking about, being able to produce lots of torque at low end.

So power is the product of torque and speed. At low speed the motor is delivering low power but full torque. Ok. At high speed the motor is still delivering full torque but it is now delivering more power.

I am saying that with a power split you can get MANY times the low end torque than the motor can deliver at that speed by itself. The motor is delivering more power at high speed. Torque is power divided by speed. Deliver a lot of power at low speed and you will have lots of torque. Again, many times more low end torque can be produced with the power split than with the motor alone.




Also, being able to extract all the energy, even at low speed even though there is not much power there, is a big deal. No need to tell me that it is not a big deal.

You need to include the final drive through a differential (if you have one) and realise that the limiting factor on many EVs is the traction of the tyres at any given speed. So adding more torque in any of the Tesla drivetrains just means it can spin the wheels easier, not that it would produce a meaningful increase in performance or efficiency.

Using it as a power split device, like the Prius does, was done so that the Prius doesn't need a clutch and can be essentially "direct drive" but with a ICE attached, which is not normally possible. There one electric motor would spin in reverse at the same speed the ICE would spin forwards, meaning that the wheels would have 0rpm through the planetary gear. That is also why the Prius had a limited speed and power in reverse, in fact they won't reverse up a steep hill well because of this.

But in a electric only situation the variable gearing is not that beneficial if your motor already has full torque from 0rpm and has enough motor rpm to reach the vehicle top speed through a simple single gear ratio.

One idea I had ages ago was to use the powerspilt device and two motors as a flywheel storage for acceleration purposes on smaller EVs. There you could preload the motors by spinning them in reverse of eachother at the lights, then on launch they would both slow down putting both the power of the motors and the power of the decelerating motor mass/flywheels into the wheels for faster acceleration. In reverse you could do the same for regen to spin up the flywheel. But now I have a version of that idea that doesn't use a planetary gear at all and does it all electro-mechanically instead which also allows for higher flywheel rpm without the friction. The primary reason for it is to reduce peak power on smaller battery packs and to use it as a more "mechanical" voltage converter.

 

[abebarker]

But in a electric only situation the variable gearing is not that beneficial if your motor already has full torque from 0rpm and has enough motor rpm to reach the vehicle top speed through a simple single gear ratio.

Remember that I am not talking about the light cars that are already on the road. They are tested, proven and delivered. This is for the Semi (and my truck).

The Semi can benefit the most. Running high torque at low speeds is not efficient for the induction motor and they produce a lot of heat. Using the power split the motors can produce the same amount of torque but more efficiently.

Also remember that permanent magnet motors are different from induction motors. Permanent magnet motors are better at low rpm's. Induction motors are better at high rpm's.

One idea I had ages ago was to use the powerspilt device and two motors as a flywheel storage for acceleration purposes on smaller EVs. There you could preload the motors by spinning them in reverse of eachother at the lights, then on launch they would both slow down putting both the power of the motors and the power of the decelerating motor mass/flywheels into the wheels for faster acceleration. In reverse you could do the same for regen to spin up the flywheel. But now I have a version of that idea that doesn't use a planetary gear at all and does it all electro-mechanically instead which also allows for higher flywheel rpm without the friction. The primary reason for it is to reduce peak power on smaller battery packs and to use it as a more "mechanical" voltage converter.

Those sound like some really good ideas.

 

[Crissa]

The Semi can benefit the most. Running high torque at low speeds is not efficient for the induction motor and they produce a lot of heat.

Heat production is a direct connection to power applied - so more speed equals more heat.

As pointed out earlier, static motors push air away from them through centrifugal force, which means are higher speeds you have more cooling.

This just doesn't apply to EV motors at all.

-Crissa

 

[abebarker]

Heat production is a direct connection to power applied - so more speed equals more heat.

Although the power applied does have some connection to the amount of heat generated it is not exactly a direct connection. The efficiency determines how much of the power applied gets converted to heat. With a simple motor you can't change the efficiency in any way so your job is done. With the power split we can do all sorts of tricky things to get better efficiency.

This just doesn't apply to EV motors at all.

Do I need to explain why that statement is completely false?

 

[JBee]

Heat production is a direct connection to power applied - so more speed equals more heat.

As pointed out earlier, static motors push air away from them through centrifugal force, which means are higher speeds you have more cooling.

This just doesn't apply to EV motors at all.

-Crissa

Crissa are you doing ok? I'm genuinely getting concerned now. :-(

"so more speed equals more heat" and " which means are higher speeds you have more cooling".

You're going to have to decide which one it is.

 

[Bill906]

You're going to have to decide which one it is.

If you read the entire sentence she was referring to a type of motor I pointed out earlier. A static (meaning mounted in a factory, not in a vehicle) motor that is fan cooled where the fan speed is based on motor shaft speed. In this type of motor, the cooling is increased with speed.

 

[JBee]

If you read the entire sentence she was referring to a type of motor I pointed out earlier. A static (meaning mounted in a factory, not in a vehicle) motor that is fan cooled where the fan speed is based on motor shaft speed. In this type of motor, the cooling is increased with speed.

So what does a static motors have to do with planetary gears in a electric semi or truck as per the OPs comments?

None of the EV motors in production cars that I know of are "static" (stationary?) neither are there many that are air fan cooled directly from its own driveshaft. Especially Teslas, that are all water jacket cooled motors with seperate water pumps and with fan driven radiators. Further heat generation is not dependant on motor speed (rpm?) rather motor load, which is not rpm dependant. A stalled motor also produces heat, and water jacket cooling works while the vehicle is stationary as well, like on a car dyno at full power.

 

[Bill906]

So what does a static motors have to do with…

Well, when I brought it up earlier it was when you claimed high torque low speed motors created a lot of heat. I explained that the only time I knew of where low speed caused excessive heat is in this fan cooled type of motor. I was pointing out that unless you have this type of motor, (which EV’s most likely do not), low speed has virtually no effect on motor temperature. I believe we’ve gone full circle and now you are also claiming speed has virtually no effect on the motor temp.

Yes, load affects motor temperature. More accurately, current (amps) is the most relevant factor in temperature and depending on the type of motor, application, etc. motor current can be considered proportional to load. (with some exceptions).

Maybe you’re right. Maybe Tesla will find that a complex system of two motors with a planetary gearbox per axis is more efficient enough to outway the cheaper and simpler single motor simple gearbox method for the semi. I’m sure they have people way smarter and with way more resources than we have to determine the best way to go. I strongly believe the better way is the simpler way, but I could be wrong.