Top Speed and Acceleration

[Joshua271987]

Hi. I have been a Tesla fan ever since the first roadster came out. Ever since then I have been researching many electric car companies. The most impressive of which is the Rimac's first all-electric $1M supercar the Concept One. Which uses a two-speed double-clutch gearbox. This enables it to have top speed and acceleration.

So my question is would Tesla consider using one in its new Roadster?

(Go to youtube and add this code to the end of the URL to see the video. It should automatically skip ahead to 11:14 in the video)
‪/watch?v=lFBhNEuqRVg#t=11m14s‬

Let me know what you think.

 

[dhrivnak]

So far in nearly 8 years of driving i have never had an issue of being able to earn a fat ticket. I also am drawn to the simplicity of the current drivetrain.

 

[markwj]

I don't see the point for a road car. I think Tesla has it correct (after their initial stumble with two speed roadster gearboxes) with their approach regarding single gear transmissions. Very simple and reliable.

 

[Joshua271987]

Personally, I think that Tesla should use the two-speed double-clutch gearbox. Because it is supposed to be the top performance model.

I think that for it to truly be able to out perform competitive petrol vehicles (beyond 1/4 mile, racing etc). Would be to allow it to achieve top speed (not just acceleration) by using the gearbox.

Rimac Concept One vs Tesla and Ferrari
(Go to youtube and add this code to the end of the URL to see the video)
‪/watch?v=eT7KKxoAvvk

 

[Joshua271987]

I am of course referring to the new roadster. Not the old one.

 

[Tiger]

Nice presentation:

 

[markwj]

Much as I like the Rimac Concept One, it is US$1m++. I don't think that is the price range Tesla is going to aim for.

 

[Joshua271987]

Much as I like the Rimac Concept One, it is US$1m++. I don't think that is the price range Tesla is going to aim for.

True. But it is also made of carbon fibre, has four motors for each wheel, has a gearbox, has torque vectoring and 1088hp. I was only suggesting the gearbox.

 

[supersnoop]

True. But it is also made of carbon fibre, has four motors for each wheel, has a gearbox, has torque vectoring and 1088hp. I was only suggesting the gearbox.

Okay, I’m confused. I’m not an engineer, but I don’t understand how you route power from four separate motors though a gearbox and implement torque vectoring. I assume you mean “four motors[, one] for each wheel,”, not four for each wheel (for a total of 16 motors). Are there four gearboxes?

Isn’t this all solved by tesla with the implementation of multiple motors?

 

[strider]

I think they can get close enough with 2 motors with slightly different gearing. This allows them to spread the torque peak across a larger distance. I've spent a great deal of time on racetracks around the US (and a few in the UK). A 155mph top speed is plenty for most tracks. The biggest hurdle Tesla has right now is dealing with heat build up in the motor/PEM under track conditions. They should spend time/money to figure that out and not a 2-speed gearbox.

It will also be interesting to see if they stay w/ AC Async motors for the next Roadster or if they move to IPM like the Model 3. I don't know enough about the pros and cons of each to hazard a guess as to which would be better in the next-gen Roadster.

 

[Joshua271987]

Okay, I’m confused. I’m not an engineer, but I don’t understand how you route power from four separate motors though a gearbox and implement torque vectoring. I assume you mean “four motors[, one] for each wheel,”, not four for each wheel (for a total of 16 motors). Are there four gearboxes?

Isn’t this all solved by tesla with the implementation of multiple motors?

My apologies. Yes, I meant one motor for each wheel (not four).

I just searched up online. Yes, it has one gearbox for each motor.

 

[markwj]

I just searched up online. Yes, it has one gearbox for each motor.

I guess that reduces the torque stress, by spreading it across four separate transmissions. Synchronising the gear changes across wheel pairs must be fun. It just seems to over-complicate things - just for a top speed that you don't need for road use.

 

[hcsharp]

I guess that reduces the torque stress, by spreading it across four separate transmissions. Synchronising the gear changes across wheel pairs must be fun. It just seems to over-complicate things - just for a top speed that you don't need for road use.

The gear changes don't actually have to by synchronised. It's quite possible to have different wheels in different gears without the driver noticing the difference. You don't have to have all the wheels in the same gear until you get going really fast because the torque vectoring can manage the speed and power to each wheel based on multiple factors including what gear it's in.

 

[hcsharp]

I think they can get close enough with 2 motors with slightly different gearing. This allows them to spread the torque peak across a larger distance. I've spent a great deal of time on racetracks around the US (and a few in the UK). A 155mph top speed is plenty for most tracks. The biggest hurdle Tesla has right now is dealing with heat build up in the motor/PEM under track conditions. They should spend time/money to figure that out and not a 2-speed gearbox.

It will also be interesting to see if they stay w/ AC Async motors for the next Roadster or if they move to IPM like the Model 3. I don't know enough about the pros and cons of each to hazard a guess as to which would be better in the next-gen Roadster.

I agree with this. Shifting to a higher gear at higher speeds does not solve the heat problem. It only makes it worse. But multiple motors allows you to have different characteristics for each motor. Some are better for high speed while other setups are better for street speeds. So you can shift power among wheels depending on speed. Tesla's D variants already do this to some degree.

To expand on what @strider said, the AC Async motors are hard to cool partly because it's difficult to cool the rotor. I'd like to see a cooling system developed by Tesla that could somehow solve this problem - maybe pumping coolant through the shaft and rotor like oil in a crankshaft? If you could solve the cooling problem you would have more benefits than you can get from a gearbox.

 

[Joshua271987]

I agree with this. Shifting to a higher gear at higher speeds does not solve the heat problem. It only makes it worse. But multiple motors allows you to have different characteristics for each motor. Some are better for high speed while other setups are better for street speeds. So you can shift power among wheels depending on speed. Tesla's D variants already do this to some degree.

To expand on what @strider said, the AC Async motors are hard to cool partly because it's difficult to cool the rotor. I'd like to see a cooling system developed by Tesla that could somehow solve this problem - maybe pumping coolant through the shaft and rotor like oil in a crankshaft? If you could solve the cooling problem you would have more benefits than you can get from a gearbox.

"Each of the Concept_One's four wheels has its own oil-cooled motor, inverter and reduction gearbox." - auto.howstuffworks

 

[Roadster]

Wow, Concept_One is pretty impressive indeed! However, it's clearly aimed at the hypercar market for which you have to pay a premium in order to enjoy the privilege of having a useless 200+MPH top end for everyday applications. FWIW, a MS-L is still faster 0-60 at a 0.1 the pricetag.

If/when TM does reintroduce the Roadster, I'd be fine with another single-speed gearbox for the simplicity and reliability as @markwj mentioned earlier. I can't imagine what the repair costs would be for the Rimac when the electrical gremlins descend on it. We can barely stomach the cost of swapping out TPMS components every other year. Regardless...

...here's some more Concept_One goodness to marvel at. Skip past the boring petrol-powered Veyron segment to 2:27...

 

[strider]

To expand on what @strider said, the AC Async motors are hard to cool partly because it's difficult to cool the rotor. I'd like to see a cooling system developed by Tesla that could somehow solve this problem - maybe pumping coolant through the shaft and rotor like oil in a crankshaft? If you could solve the cooling problem you would have more benefits than you can get from a gearbox.

Tesla does have a patent on liquid cooling the rotor:
Patent US7489057 - Liquid cooled rotor assembly
But due to cost or engineering challenges hasn't implemented it.

"Each of the Concept_One's four wheels has its own oil-cooled motor, inverter and reduction gearbox." - auto.howstuffworks

We need more info. Tesla's MS and MX (I assume M3 as well) motors are liquid cooled also but they only circulate coolant around the stator to keep it cool, not the rotor. When the rotor gets too hot they have to pull power. The question is whether Rimac is managing to cool the rotor or if they are avoiding the heat build up problem some other way. Maybe since they have 4 small motors it's less of a problem. Maybe they're using IPM motors and they build up less heat?

 

[FlyingCookie]

I agree with this. Shifting to a higher gear at higher speeds does not solve the heat problem. It only makes it worse. But multiple motors allows you to have different characteristics for each motor. Some are better for high speed while other setups are better for street speeds. So you can shift power among wheels depending on speed. Tesla's D variants already do this to some degree.

To expand on what @strider said, the AC Async motors are hard to cool partly because it's difficult to cool the rotor. I'd like to see a cooling system developed by Tesla that could somehow solve this problem - maybe pumping coolant through the shaft and rotor like oil in a crankshaft? If you could solve the cooling problem you would have more benefits than you can get from a gearbox.

This is actually what they're currently doing in the Model S, and X. It's in their patent for cooling AC induction motors.

 

[hcsharp]

This is actually what they're currently doing in the Model S, and X. It's in their patent for cooling AC induction motors.

Correct me if I'm wrong but I don't believe they are doing this in the S and X. They have a patent for it but they haven't implemented it in any production vehicles yet. Striders post above was correct.