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The Porsche Taycan's Two-Speed Gearbox

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Re: The Porsche Taycan's Two-Speed Gearbox

#71

Post by m463 »

mtw wrote: post #60
gleglegle wrote: post #5

It's a little surprising that even with a two-speed Gearbox the Taycan has neither better range nor low range 0-60 acceleration than the Tesla P100D (which has the same size battery). Obviously spec comparisons aren't the whole story and the handling and high-range acceleration may be better on the Taycan. Looking forward to seeing more comparisons and already glad to see more EV models in this category. Edited incor…

Porsche are experts in transmissions and gearboxes, but are starting (almost) from scratch for batteries. Give them a few years, they'll catch on.

I suspect it might be motors too.

Why do they even need gears? I can see why we need differentials (until we have one motor per wheel), but can't gears be done in some electronic way with clever arrangements of motor

For example, the tesla has ~10:1 reduction ratio gearing, but I wonder if there's a clever way of rearranging the poles/coils of the motor, maybe like a crankshaft, so you get the best torque matched to the rpm?

Re: The Porsche Taycan's Two-Speed Gearbox

#72

Post by clouddrover »

gleglegle wrote: post #5

It's a little surprising that even with a two-speed Gearbox the Taycan has neither better range nor low range 0-60 acceleration than the Tesla P100D (which has the same size battery). Obviously spec comparisons aren't the whole story and the handling and high-range acceleration may be better on the Taycan. Looking forward to seeing more comparisons and already glad to see more EV models in this category. Edited incor…

Some things Porsche has done with the Taycan which contrast with Teslas are:

- Launch repeatability: https://www.youtube.com/watch?v=TP9kokeyxGU

- A 7:42 lap time at the Nürburgring: https://www.youtube.com/watch?v=8m31EgQkswg

- Travelling 2,129 miles in 24 hours: https://insideevs.com/news/365827/porsche-taycan-24-hours-en...

Re: The Porsche Taycan's Two-Speed Gearbox

#73

Post by kazinator »

> Multispeed transmissions must be robust to deal with the massive amounts of torque that electric motors can generate in a very short period of time, says Shashank Sripad, a mechanical engineer also from Carnegie Mellon.

Put a manual clutch on it; problem solved. Manual boxes can be built strong.

Then make it at least a 3 speed so there is a decent H pattern there from the stick user's perspective, and so that the ratio isn't so large (it's like around 2X change¹, supposedly! That means the motor's RPM has to drop by by half on upshift and double on downshift.)

3 speeds could use a 1.44 step.

   1 3
   | |
   +--
   |  \
   2  R = V/I
---

1. Source: this article claims the gears are 16:1 and 8.05:1. https://jalopnik.com/an-extremely-detailed-look-at-the-porsc...

Re: The Porsche Taycan's Two-Speed Gearbox

#74

Post by adrianmonk »

nickhalfasleep wrote: post #28

In dual-motor (front, rear) Tesla vehicles, each motor is on a different gear ratio for optimal power bands.

I wonder if this is part of why their dual-motor models get better range. I could see it being better for regenerative braking, too.

Re: The Porsche Taycan's Two-Speed Gearbox

#75

Post by kenhwang »

gburdell3 wrote: post #31
elonismycopilot wrote: post #22

Earlier quoted context omitted.

>True, and the Taycan may well be a better car in many ways. But a discussion of the gearbox has nothing to do with handling or sports car feeling. There isn't a single published metric in which the Performance Model S doesn't trounce the Taycan.

Does the Taycan overheat and go into limp mode if you take it to the track?

The old Model S had a hard time keeping up with a Nissan Leaf on the track.

https://cleantechnica.com/2019/07/16/how-did-a-nissan-leaf-b...

Re: The Porsche Taycan's Two-Speed Gearbox

#76

Post by clouddrover »

dragontamer wrote: post #40
gleglegle wrote: post #5

It's a little surprising that even with a two-speed Gearbox the Taycan has neither better range nor low range 0-60 acceleration than the Tesla P100D (which has the same size battery). Obviously spec comparisons aren't the whole story and the handling and high-range acceleration may be better on the Taycan. Looking forward to seeing more comparisons and already glad to see more EV models in this category. Edited incor…

> It's a little surprising that even with a two-speed Gearbox the Taycan has neither better range nor low range 0-60 acceleration than the Tesla P100D (which has the same size battery). 0-60 times probably don't matter on the track. Its probably more important to optimize the 60 to 120mph time, which is where the torque of a (single gear) electric motor begins to taper off. I bet that Taycan has superior 60-to-120mph…

> 0-60 times probably don't matter on the track.

Yes, in the Taycan's Nürburgring-Nordschleife run, for example, the speed was mostly above 100kph: https://www.youtube.com/watch?v=8m31EgQkswg

Re: The Porsche Taycan's Two-Speed Gearbox

#77

Post by Ididntdothis »

pixelbash wrote: post #65
dragontamer wrote: post #59

Earlier quoted context omitted.

Leaving all the other cars next to you in the dust is quite antisocial behavior actually. For the most part, I want to accelerate with everyone else when that green light goes off (except for Trucks: I wanna leave Trucks in the dust and get away from them ASAP). The 30mph to 60mph acceleration of off-ramp into freeway cruising speed however, is pretty important. A lot of things are going on when I merge onto a freewa…

> Leaving all the other cars next to you in the dust is quite antisocial behavior actually. As a motorcycle rider I disagree, it's the safest option for us. I get that not everyone is pleased about it, though.

Even on the bike you don’t accelerate full out. You are already way ahead with half power and full power acceleration from 0 is quite risky when you get wheel spin.

Re: The Porsche Taycan's Two-Speed Gearbox

#78

Post by outworlder »

elihu wrote: post #33
rconti wrote: post #16

Earlier quoted context omitted.

True, and the Taycan may well be a better car in many ways. But a discussion of the gearbox has nothing to do with handling or sports car feeling. I'm wondering what we're missing here. 5% efficiency improvement at high speeds isn't anything to write home about today. The transmission is a known quantity -- it's just gears, it won't get more efficient as they develop it. The efficiency of the whole system (battery/dr…

A 5% efficiency gain might be a big deal when it comes to motor heat. Electric motors tend to be around 85-90% efficient or so, and if you can get the motor from, say, 85% efficient to 90% efficient, that might translate to a one-third reduction in waste heat.

> that might translate to a one-third reduction in waste heat.

Is that a big deal, though, compared to battery heat? Or is it in the context of a race scenario?

Re: The Porsche Taycan's Two-Speed Gearbox

#79

Post by InTheArena »

19870213 wrote: post #48
mrtksn wrote: post #21

Earlier quoted context omitted.

I believe they just didn’t give the option to wreck your car by overclocking. Their selling point is repeatability, so overloading the systems is not part of the Taycan experience. Probably it’s possible to push the car to higher performance and risk performance degradation later on as with Tesla. Would be fun when people start playing around with these cars’ systems.

Porche appears to be claiming that one of the features of the Taycan is repeated launch control 0-60s without overheating or other problems that Telsa is warning people about when you use ludicrous mode: https://www.youtube.com/watch?v=TP9kokeyxGU

That was a issue with the Model S, not with the P3D. I suspect that when they switch over the S to the new style batteries, it goes away.

Re: The Porsche Taycan's Two-Speed Gearbox

#80

Post by dragontamer »

Zanni wrote: post #70
dragontamer wrote: post #59

Earlier quoted context omitted.

Leaving all the other cars next to you in the dust is quite antisocial behavior actually. For the most part, I want to accelerate with everyone else when that green light goes off (except for Trucks: I wanna leave Trucks in the dust and get away from them ASAP). The 30mph to 60mph acceleration of off-ramp into freeway cruising speed however, is pretty important. A lot of things are going on when I merge onto a freewa…

Serious question: how is this antisocial behavior? I understand wanting to stick with the flow of traffic when you're part of the pack, but if you're in front of the pack, what's the advantage (to anyone) of hanging back?

1. By accelerating dramatically off the line, you're telling the other cars that they are driving too slowly.

2. Alternatively: you may be sending a signal that you want to drag-race with someone. And nobody likes it when drag-racers start playing on public roads. Keep that stuff off the streets and on the track only.

Now sure, if the cars next to me are driving slowly, I'll leave them in the dust. But its not something I'll do on every green-light, and its something I'd do only if they're going exceptionally slowly (ex: driving 40mph in a 60mph zone)

Those are the two signals I perceive whenever someone accelerates strongly off of a green light: either #1, or #2, depending on context. There's certainly a time to signal #1, but its a relatively rare event.

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