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The REAL top speed of the Model S

So, we all know that the top speed of the Model S is software-limited to around 130mph (depending on model/options)...If there was no software limitation, what do you think the real top speed of the Model S would be. I would think pretty high, considering the 416hp/443ft-lb torque, even considering the weight of the car. But if you had to pick a number, what would you guess? (Anyone out there "jailbreak" their S yet?!?!)

And, why do they limit the top speed in the first place? Is it vehicle/passenger safety? Is it to specifically protect the life of the batteries? Would it be too difficult to properly cool the battery pack while going 160, 180, 200mph? Not that you could even drive at that speed for a significant amount of time. But still...

Just wondering. Any thoughts?

It's a one-speed gear reductions system, so there's a motor RPM limit.

That may be the case, but what does that specifically mean with regards to the top speed limitations? Is 130 mph the limit of the gear reduction system? And if so, why does Tesla's terminology specifically say "software-limited?"

Motor RPM proportional to car speed. Limit car speed, limit motor rpm. As Brian said, there is only so fast you can spin the motor thus only so fast you can go in the car.

There may also be a peak discharge rate for the pack as well.

The load on the battery going hard from 0 to 60 or 100 mph seems like it would be less than holding some level of "top speed." What am I missing? As noted, the specs for the Model S indicate top speed is software limited, but sometime, somebody, is going to want to find out how fast this thing CAN go, even briefly.

No?

I am nearly sure the Model S is software limited, not rpm limited.

If that were the case, then: acceleration when nearing 130 mph would be incredibly slow as the motor would be hitting its rpm limit.

It might be 'rpm limited' in the sense that it explodes from centrifugal forces once you go above a certain rpm, but I imagine Tesla would design in a certain safety margin ;)

@gparrott - drag goes up with the square of velocity, and at 100mph virtually all of the power used is overcoming drag. The Bugatti Veyron doesn't have 1000hp just for 0-60 times, but for overcoming drag at high speeds.

130 MPH is maximum impulse speed in the atmosphere, you cannot jump to warp speed while still in the earths atmosphere due to rotational speeds of motor armature in earths gravity.

Honestly when I get my Model S (eventually I will own one that is my goal in the immediate future) I am not likely to go anywhere near 130 but I can see someone in the UK specifically around the autobon that might want to know the answer to this since if I am not mistaken the Autobon has no speed limit.

oscarjohnson,

It is said that in certain locations there are ripples in the fabric of spacetime, where you can jump great distances in an infinitesimally small timespan. Some call those anomalies wormholes, others Autobahn.

We need an Autobahn in the US, can I suggest between San Francisco and L.A. with a power strip running down the highway for the Model S to charge and she charges down the road? :)

I am waiting for Elon to introduce a Static electricity charging system so you can charge from the ambient electrical charge in the air. :)

Or rub it with your cat.

I believe the software rpm limit has to do with stopping damage to the windings (centripital action).

lph I was told that the windings were on the outside and were stationary so the only moving part of the motor is the magnet. If that is true it makes for a very robust electric motor.

The software limitation is there to protect the motor against irresponsible drivers like you guys. >:(

An "unlimited" EV-1 managed 183 mph. with a stock drive train and a minor modification "add on" to reduce turbulence at the rear of the car.

That would significantly improve my commute :)

The motor does not have permanent magnets. I saw a cutaway at the Bellevue store and looked to me like the winding was on the rotor. Hmmm...

The motor takes variable speed alternating current. Higher frequency makes the motor spin faster. Easy to limit the RPM by limiting the maximum frequency the power module will put out.

IMO, assuming Tesla limited speed to prevent over revving the motor, the best way to get more top end speed out of the Model S would be with a modified, or completely new gearbox. Of course this wouldn't be cheap, aftermarket limited production gearboxes used in racing can cost as much as an entire Model S.

At very high RPM motor torque drops, you no longer have that 400+ HP at 14k RPM. It might be that Model S real top speed isn't much higher than that 130mph, unless you tweak with gears (or gear in this case). OTOH with smaller reduction you drop torque at the wheels, so there is upper limit in that too. Finding the perfect gear rating for maximum top speed would require some fancy math (or trial and error -method).

With a lower reduction ratio (TM is 9.7:1) you can get higher top speed, but lower range accel suffers. Pick one.

I agree in terms of wanting optimal acceleration within the typical range of used speed.

HOWEVER in response to one of the observations above....given that the Performance version of the Model S has 416 hp and a rather low coefficient of drag....this level of power should be capable of upwards of 160 mph, given comparisons with other vehicles of less aero design and comparable horsepower?

A 565 hp Aston Martin that was just introduced in the last couple of days has a claimed top speed of 205 and it is not as aero as the Model S, and what is the top speed range of the Panamera? The 400+ hp range of that model is good for upwards of 165mph.....

Just curious.......

The Tesla motor has no permanent magnets.

The windings are in the stator.

The rotor is a copper cylinder, no windings. Featured in the "Mega Factories" video:
http://www.youtube.com/watch?feature=player_detailpage&v=NAxtOwo8S8w#t=1...

How many gears does the Aston have? What's the difference in reduction ratio between 1st gear and top gear.

Irrelevant to the MS. Even the Roadster broke every transmission that tried to put gears in the car.

typo: ... top gear?

@Brian H,

Don't say those words!

I was careful not to capitalize.

I believe the speed limitation is a safety consideration. The copper armature is very heavy and soft. Soft Copper makes an exellent and powerful rotor. I've seen what can happen to a loose steel flywheel in a dragster at about 8,000 rpm. Shredded the cast iron bellhousing, then virtually cut the car in half, killing bystanders over 500 feet away. Try to picture Copper, at much greater molecular weight, in tons, slashing through everything in the way, including the passengers in the Model S, and nearby cars and bodys. Would make bad headlines. I have seen an electric motor armature disintergate in lap tests. I believe, without lab tests, that the Tesla motor is governored at substantially less than the point of centrifugal disintegration.

Assuming you can bypass the software speed limiter (which I really doubt), the issues that could cause critical failures that are not a concern below the speed limit:

1) Heat generated by the motor, inverter and/or gears exceed limits and parts melt.

2) Electronic drive components are driven beyond there design limits and fail.

3) Vehicle stability systems are not tuned to these higher speeds and unexpected problems may develop due to these systems.

4) At some point the centrifigal forces rip the motor apart.

5) Oil in the gear case starts foaming, causing loss of useful lubrication (with failure to occur soon after).

6) Rotational parts could hit a resonant frequency not encountered at lower speeds and cause all sorts of catastrophic problems.

All these sound very costly if they occur. I'm sure there is a design safety margin for all these situations, and the software does monitor issues like heat to help prevent some of these types of failures. Still, it's not a lot different than pushing a ICE car beyond it's design limits - usually something fails, and often catastrophically.

I think it may be hard to find someone willing to take these kinds of risks with their own MS, but good luck!

I read in a TM investor presentation that the MS motor is limited to 18000 rpm. That means 1849 wheel rpm at the reduction of 9.73:1 and at a wheel diameter of 27,7" gives you a speed of

drum roll... 152,8 mph!

If the motor has enough torque at 18000 rpm to drive at that speed I don't know.


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