Another gearbox discussion

[power]

I dont quite understand what you are saying below. can you be a little more clear. what are you getting at? Is it you think that any kind of further reduction in the form of an additional selectable gear redcution to increase performance in the higher MPH ranges could be done by the motor and electronics alone, or that its fine the way its is currently designed?

Motors, as used in a electromechancal application will always have some type of gearing to maximize the application of ther power. This is true until a motor will be developed with a constant power curve which is highly unlikey in the near future. However the same effect can be found in CVTs or IVTs, and in the interm, one more gear can give the results that give the electric powerplant an even closer performance level to its gas counterpart.


Mk

I understand both the necessity and practical application of the reduction drive unit(s), i.e., inasmuch as a single stage reduction gearing setup requires the input shaft (motor end) to complete two(2) rotations to every one(1) of the output shaft (wheel end), and that a second stage reduction gearing setup would require the input shaft to complete four(4) rotations to every one(1) of the output shaft's, slowing it's overall revolutions as a byproduct, I fail to see the benefit since everyone appears to desire more performance/speed from their cars, but that's not what I'm getting at as I (as you can hopefully tell by now) feel that switching to a two-stage/two-gear setup would be defeatist at this point.

 

[just-an-allusion]

no he is refering to the gear box alowing the available power of the motor to be utilized by the tires at any vehicle speed in question. Forget about motor torque for a minute, its the torque at the rear wheels at any vehicle speed that is being talked about. to maximize this, max power is needed. (not max torque) the gear ratio tesla selected is like a 1st gear on most cars. the motor can extend near the same torque as a internal combustion engine to double the rpms with out the risk of bending valves . But, the power available is much lower later in the vehicle top speed, for which a gear box, even a second speed , could help with.
Gearing doesnt create power, it helps better utilize the power you have available. With the Tesla roadster, this happens near 8000rpm for max power, even though max motor torque falls off at 6000rpm.

mk

Yeah, I finally caught on to what he was trying to explain which, unfortunately, is diametrically opposed to the idea/concept that I've been attempting to relay.

Luckily though, you appear to have touched on it in your response to ChargeIt where you said:

...electronic gearing, as what i see as being suggested, is not just as simle as pulling out a few motor poles! there are switcing losses in the control circuitry, back emf, winding impedenace, etc. There never will be one electric motor that can provide constant power. If there was, it would waste a lot of technology and cost to do what an advanced gear ratio could do. (i.e a CVT -IVT ).

While a bit of technological reconfiguration would be required, which would only amount to switching out some components, this method would ultimately prove the most effective, economical and beneficial, not to mention eliminate what I view as alot of needless weight.

 

[just-an-allusion]

I dont quite understand what you are saying below. can you be a little more clear. what are you getting at? Is it you think that any kind of further reduction in the form of an additional selectable gear redcution to increase performance in the higher MPH ranges could be done by the motor and electronics alone, or that its fine the way its is currently designed?

Motors, as used in a electromechancal application will always have some type of gearing to maximize the application of ther power. This is true until a motor will be developed with a constant power curve which is highly unlikey in the near future. However the same effect can be found in CVTs or IVTs, and in the interm, one more gear can give the results that give the electric powerplant an even closer performance level to its gas counterpart.


Mk

Yes, I feel that the current mechanical, single stage reduction gearing transaxle is more so beneficial to the Tesla's drivetrain from a performance perspective than the addition of a selectable secondary stage/gear reduction would be, and that any additional "gearing" should be electrical in keeping with the nature of the powerplant itself...finally, thank you!

We are working with "electrical" componentry here, with motors, NOT with "mechanicals", with engines...go to the source for the solution.

 

[power]

Good, I think I've confirmed where you were coming from. I dont have enough knowledge in the current state of AC servos to make an comments there. I guess if the motor and controller design could provide a flat HP curve to 14,000rpm, it would be problem solved. Im curious as to the losses that drive the power down after 8krpm. I imagine it is switching losses, resistance (L/R curves) and possibly BEMF. until we can find a way for current to rise instantaneously, I think we are stuck with falling power curves. (hmmm, 0 resistant windings cooled by liquid nitrogen, creating superconductors. )

Maybe the answer is in 4x4 drive with smaller motors on all 4 wheels in a direct drive configuration. maybe outer rotor style as well.

Exciting times. If the technology progresses like Moore's law's effect on the Chip technology, who knows what things will look like in 10 years!

Until then, i think Tesla has a great product. A 2 speed sequential gear box could carry them and give the deserved performance until the motor tecnology advances.


mk

Yes, I feel that the current mechanical, single stage reduction gearing transaxle is more so beneficial to the Tesla's drivetrain from a performance perspective than the addition of a selectable secondary stage/gear reduction would be, and that any additional "gearing" should be electrical in keeping with the nature of the powerplant itself...finally, thank you!

We are working with "electrical" componentry here, with motors, NOT with "mechanicals", with engines...go to the source for the solution.

 

[TEG]

There were previous discussions on this forum pondering such things.
You might want to read this old topic:
http://www.teslamotorsclub.com/technical-discussion/236-bigger-motor.html

Although unconfirmed by Tesla I think some of the HP dropoff at high RPMs is intentional because of heat built up issues. I am not sure what (back EMFs?) leads to HP limitations, but something seems to prevent them from staying at max HP at those high RPMs. Could rotor air churn and bearing resistance be a factor? I don't know.

 

[TEG]

Assuming that someone from Tesla probably reads these forum postings, a suggestion: Have JB do a future blog page on the HP & Torque output of DT1.5, and include a description of the reasons that HP needs to drop off at high RPMs. Also, what exactly determines redline? At one point they said something about having a motor up to 20Krpm on a dyno, but there appear to be reasons why they can't ship the product with redline > 14K right now.

I also assume that there are further motor improvements in Model S DT2.0 that Tesla has done but hasn't been made public yet.

 

[graham]

I also assume that there are further motor improvements in Model S DT2.0 that Tesla has done but hasn't been made public yet.

Especially since it is not clear yet if the Model S will be air cooled, or cooled in a more active fashion.

 

[TEG]

They alluded to the fact that they were thinking of liquid cooling the DT2.0 motor.

With all the recent turmoil, I suppose anything is possible at this point.

 

[just-an-allusion]

There were previous discussions on this forum pondering such things.
You might want to read this old topic:
http://www.teslamotorsclub.com/technical-discussion/236-bigger-motor.html

Although unconfirmed by Tesla I think some of the HP dropoff at high RPMs is intentional because of heat built up issues. I am not sure what (back EMFs?) leads to HP limitations, but something seems to prevent them from staying at max HP at those high RPMs. Could rotor air churn and bearing resistance be a factor? I don't know.

Yes, it appears that a few people discussed various aspects of the Tesla motor design to some degree, yet no one touched on additional speeds ("gearing") through motor/management control reconfiguration, being primarily concerned with motor "size", and "EMF" generation, and "heating" (why Tesla chose to go with a sealed casing [hermetically sealed"?"] instead of an open air casing [to allow for air cooling], given that the motor is positioned in a shielded interior space within the motor bay that would readily allow for the ducting of filtered, voluminous cfm's free of debris via a forced, draw-through air system that would provide more than ample, continuous cooling <sigh> anyway...), as well as oriented towards accomplishing additional motor speed through "gearing", as in an ICE, not a motor.

Luckily though, we've now covered that particular aspect of motor design/capacity.

 

[just-an-allusion]

Especially since it is not clear yet if the Model S will be air cooled, or cooled in a more active fashion.

An air-cooled chassis/component design, coupled with oil-cooled bearings via integrated mechanical pump, should more than sufficiently suffice without having to resort to more exotic means (e.g., "liquid nitrogen" ala power), but then there's always the simplicity of "air-cooled heat sinks", a long antiquated technology that would be applicable for both battery and motor cooling...think about it.

 

[just-an-allusion]

electronic gearing, as what i see as being suggested, is not just as sim[p]le as pulling out a few motor poles!
mk

Additionally, for further clarification, you wouldn't have to "pull[] out a few motor poles..." (on the contrary, you'll want them in there for the purpose of providing higher speeds/"gearing"), you'll merely need to switch between "phases" to modulate the available motor's speed from one speed ("gear") to the next available speed ("gear").

Depending on the initial construction of the motor's internals, the potential number of "gears" would be limitless...get it now?

 

[power]

Its a general motor principle that power will fall off. generally, the back Elecromotive forces BEMF will always eat the motor alive at higher and higher speeds. sure you can always overcome the with more and more input power, but you then get into heat issues. There are eddy current losses, and way down on the list, is any bearing issues. probably the bearings could be made to support much higher rpm.

the drive electronics are a big factor in the efficiency of power output at higher rpm. (the motor is as well) with known limitations of motors, IVT or CVTs or a 2 speed gear box, is a very effective way to solve one part of the performance issue. A larger motor isnt really the answer, as it comes with costs as well. However a motor system that did allow for 2 x the power output would be larger and more expensive as requiring even higher performance batteries.
But, it also would have the same issue of falling off HP at near 50% of its max rated rpm.

mk

There were previous discussions on this forum pondering such things.
You might want to read this old topic:
http://www.teslamotorsclub.com/technical-discussion/236-bigger-motor.html

Although unconfirmed by Tesla I think some of the HP dropoff at high RPMs is intentional because of heat built up issues. I am not sure what (back EMFs?) leads to HP limitations, but something seems to prevent them from staying at max HP at those high RPMs. Could rotor air churn and bearing resistance be a factor? I don't know.

 

[power]

As a general motor comment, usually adding "Poles" slows a motor down or electromagetically, gears it down. more power, less angular movement for a phase change. The only infinite gearing would be if you fed a sine wave current input where you would then be talking about microstepping a motor for very small incremental movements. But, maybe I'm missing your point or interpretation of how these motors could be conceptually geared up to broaden the power curves.

I imagine switched network of windings could change the winding and polar charateristics to lower phase winding resistance, up current rating to fully utilize the motors copper winding capacity. In the end, you could only really have 2 windings at a min. So, how fast and at what power can you drive a 2 phase induction motor? It still has winding limitations regardless if it is dc brushless or AC induction (AC Servo). In the industrial area where these motors are used, the speed ranges are narrow and the power demands are focused. There is no more complicated application than a car for a power system. Hard to model as well. changing rates of acceleration, power utilization, efficiency, heat, speeds, friction, etc etc.
An electric motor is in many ways, just like an engine, except the motor has max torque at 0rpm, so you dont need a clutch, but after 2000rpms they are the same. AND, it has a much broader HP curve in terms of rpm. (allowing some decent performance with out a need for a multispeed gear box)
In terms of power, for the same power output, its functional use is near the same and shares much of the same capabilities, especially if gear boxes are utilized.

mk

Additionally, for further clarification, you wouldn't have to "pull[] out a few motor poles..." (on the contrary, you'll want them in there for the purpose of providing higher speeds/"gearing"), you'll merely need to switch between "phases" to modulate the available motor's speed from one speed ("gear") to the next available speed ("gear").

Depending on the initial construction of the motor's internals, the potential number of "gears" would be limitless...get it now?

 

[vfx]

I was at a party where someone echoed the old 17 moving parts quote Tesla used to give.

With the new 1.5 single speed there must have been a drop in that number.


JB's Blog Post

The new gearbox is the most significant change from powertrain 1.0 to 1.5. We have significantly reduced the complexity of this gearbox by getting rid of the need for shifting or speed matching between two gear sets. There is only one set of gears that is always engaged with a ratio of (8.2752:1). There are no clutches and we have also done away with the need for an electric oil pump and instead integrated a very efficient gear-driven oil pump into the gearbox. All of these simplifications have saved a great deal of mass and the new gearbox is approximately 45kg instead of 53kg for the old two-speed design.

Anyone know the moving parts tally in the new motor - gearbox - pump and what actually classifies as a "moving part"?

 

[Kipernicus]

Hi,
forgive the newbie question, but I just read through this whole thread and was wondering if a second gear would help the motor and batteries stay cool and prolong range while at freeway cruising (not racing) speeds?

 

[mpt]

was wondering if a second gear would help the motor and batteries stay cool and prolong range while at freeway cruising (not racing) speeds?

That's part of the beauty of electric motors, part of the reason they're so efficient is down to their lack of mechanical friction. In an ICE the faster it turns the more friction from the internals rubbing together, the oil slushing around & the contrant heat from vacuum & presure changes turn energy into heat. With a motor you have a tiny, tiny amount of friction, call it negligable so nothing there. The heat that is there comes from any resistance in the wiring and any magnetic flux that isn't properly aligned to turn the motor; not much compared to an ICE. That heat is a function of the power applied & not rotational speed so, a slower motor isn't a cooler motor.

If you're looking for heat sources; the PEM is your man. OT; I wonder if they've ever considered capturing that heat to warm the cabin?

 

[TEG]

More gears could conceivably get you quicker acceleration and higher top speed.
The acceleration off the line is already phenomenal, so not a whole lot of need there. Sustained top speed tends to overheat things as it is. Single ratio, always engaged is the way to go. The motor changes direction for reverse so no clutch it needed this way. KISS.