Electronic Nannies limiting Acceleration

[Zoidz]

Permanent magnet, yes. DC, no.

Thanks for the correction. I had read elsewhere it was a DC motor. If it is AC, that changes a few things, but it still applies that as speed increases to the upper design limit, torque falls off.

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[SeaGeo]

22's are an H rating, which is a 130 mph rating. (so are the 20's and 21's)

Interesting, I was thinking the 20s were S. I still suspect they're limiting it for safety reasons and not performance or warranty concerns, similar to Volvo.

 

[jjwolf120]

I have no issues with the limited top speed. I would never drive that fast unless I was on a closed track.

 

[Houston_Longhorn]

Top speed might also be limited to help keep liability insurance costs reasonable. The weight is already going to be a big issue with liability.

 

[OldGoat]

It's definitely different strokes for different folks. I've never been excited by driving at high speeds, even as a kid. I'm much more a fan of the initial 'toss you back in your seat' acceleration and driving through the twisties. I still get a grin on my face when I catch a peg on my CB1100 when leaning into a turn (and if you are familiar with bikes, you know that the CB1100 is a very sedate, zen-like ride). Heck, my last car was a Golf R and I still miss rowing through the gears of a manual transmission. I get that most sane people think std transmissions are just plain stupid. But for me, it's the visceral experience of acceleration, and g-force around curves and working the clutch that makes me smile as opposed to cruising at 100+MPH.

I figure the R1T will be a fun ride in terms of acceleration but I'm not expecting it to feel like it's glued to the road when driving through the Smokies. But that's OK with me. I couldn't haul a sheet of plywood in the R. Plus, I am old and my knees don't miss those seats at about 6 inches off the ground!

 

[ajdelange]

"But we know it is a permanent magnet DC motor so some basic principles must apply."
"As the curves below show, torque decreases as RPM increases."
-- Correction - AC motor

That's better.

As I stated, It is a representation of the basic principles of a PM motor. I didn't state it was a representation of a PM motor controlled by a programmable inverter in a BEV.

But as the motors in BEV are indeed controlled by inverters the performance of a synchronous motor at slips far from 0 is irrelevant as the motors in the cars are never operated other than synchronously.

My point is that the OP "complained" about drop off in power at higher speed. That's a fundamental feature of a PM motor, that's what the graph is illustrating in a basic PM motor.

There is also a drop off in power in such motors if you cut the power supply which observation is as irrelevant as the observation that if you let slip depart from 0 in a synchronous motor you lose power. This isn't how power is controlled in these motors.

I also stated we don't know "how the software is controlling the power to the motor" which is what really defines the motor's performance characteristics in a PWM application.

Well we do in general. The controllers have separate inputs for flux and torque which inputs are set to desired values by the computers to produce the torque and speed the computers want. This has, after the PWM, the effect of putting a magnetic field vector of the right magnitude at the correct angle relative to the rotor for the torque desired. That field is always rotating at the same speed as the rotor. We do not control torque by adjusting slip as it seems you are implying. That is how it is done with an induction motor.

While the supposition that at slow speed torque is adjusted to be just below the slip breakpoint seems a reasonable one we really don't know what the reasoning is at the higher end other than it probably has to do with limiting current draw from the battery or heat production by the inverter/motor combination.

 

[ajdelange]

...but it still applies that as speed increases to the upper design limit, torque falls off.

No. See No. 36. SYNCHRONOUS motors are always operated at SYNCHRONOUS speed i.e. the design limit. Don't confuse rotor speed with synchronous speed. A synchronous motor has a (nearly) flat torque capability at all rotor speeds within its design envelope (assuming, of course, it is driven by a VFD, as is the case in a BEV).

Now if you try to start a synchronous motor from a fixed supply (e.g. one used in a factory to drive a conveyor) from a fixed 60 Hz supply you are in for an adventure (as your curve shows) because at a slip of 1 (0 speed) they don't produce any torque. Which is why they don't start them that way these days but use a VFD instead.

 

[crashmtb]

Top speed might also be limited to help keep liability insurance costs reasonable. The weight is already going to be a big issue with liability.

If that were the case then it should be limited to 86mph

 

[AxelR]

I’d like it if Rivian would open up the accelerator from 0-20 and @ 100+ as it feels like the output is limited by programming. It’s fast but not the fastest truck I’ve owned and with 835 hp the trap speed is “artificially” ? Low. Wondering if HP Tuners has plans to add support (j/k)

Tire rating limitation.
It’s the same for all fast off-road trucks.
You can’t compare trap speed or quarter mile with trucks that you built. You didn’t purposefully limit acceleration and top speed based on your tires or you ran different tires.
Doubtful anything you built was faster from a standstill to 60/62 maybe a bit passed that even.

 

[MNLightning]

are you trying to launch in sport mode.

Yes and with stability control off.

 

[MNLightning]

Doubtful anything you built was faster from a standstill to 60/62 maybe a bit passed that even.

I have nothing to compare for 0-60 times. Sixty foot times for the ICE’s were slightly worse to slightly better from a R1T estimated Sixty Foot time of 1.8 seconds. Turbo’s launched smoothly and slower but made it up on the big end.

 

[MNLightning]

Exactly.

Smoother is faster.
Quick and fast are also different. EVs are quick. They aren't fast (unless you're talking Plaid or Rimac or something).

I agree if it’s road racing. I disagree for straight line stuff.

 

[Dark-Fx]

I have nothing to compare for 0-60 times. Sixty foot times for the ICE’s were slightly worse to slightly better from a R1T estimated Sixty Foot time of 1.8 seconds. Turbo’s launched smoothly and slower but made it up on the big end.

Not my fastest pass, but best 60 foot time.

 

[SeaGeo]

Not my fastest pass, but best 60 foot time.

Is the 60 ft time adjusted for reaction time? I'm assuming so...

 

[Dark-Fx]

Is the 60 ft time adjusted for reaction time? I'm assuming so...

Timer starts after you've left the beam, same as the other distances.

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