Taycan efficiency vs VW ID7 … can it be true?

[Jhenson29]

I thought it was a bit of both, a split the difference design with low gear being a bit lower than average and the 2nd a bit longer so giving benefit at both low and high speeds.
The front motor is a similar compromise to everybody else’s.

2nd gear is already at constant HP by 110kph. The idea that 2nd gear is taller because there’s a first isn’t helping @Bognar67 accel above 110kph other than the higher max speed it affords.

Without 1st, the only logical direction for 2nd is lower gearing, which just reaches constant HP sooner in that gear and has no bearing on accel at 110kph.

Edit: I therefore conclude that suggesting 2 gears helps accel above 110kph is not correct.

 

[Jhenson29]

If on the other hand the fact that the Taycan already has a lower gear means the 2nd gear is more optimised to higher speeds then surely there is a benefit there too vs a “compromise” gear that has to do it all?

Max vehicle speed for 1st would be laughable. Max vehicle speed in 2nd is more reasonable. If there was a single gear, it would be within spitting distance of 2nd.

 

[Avantgarde]

2nd gear is already at constant HP by 110kph. The idea that 2nd gear is taller because there’s a first isn’t helping @Bognar67 accel above 110kph other than the higher max speed it affords.

Without 1st, the only logical direction for 2nd is lower gearing, which just reaches constant HP sooner in that gear and has no bearing on accel at 110kph.

Edit: I therefore conclude that suggesting 2 gears helps accel above 110kph is not correct.

I am not sure general electric motor dynamics (like constant HP) apply directly apply to Taycan given heavily regulated nature of the torque curve (which is not necessarily maxed out at any given rpm for different reasons). If you look at the dyno results of different models you see a lot of oddity. RWD for example never reaches constant HP, instead HP increases all the way to 200 kmh see the red line below.

The reality is Taycan has the flattest acceleration curve of any EV out there I think it is a function of the longer second gear (along with the 800v infrastucture), which would not be possible without the 1st gear. Top speeds of most of the model range are limited not because of revs but because of consistency concerns (eg can you maintain the required power output at the given speed for an extended period of time).

 

[Avantgarde]

I can't speak about the ID.7, but it is clear that the Taycan drivetrains is very inefficient.
The Cw value is low, so we cannot blame bad aerodynamics.
Somehow the motor and invertor are not well engineered. Maybe it is the stupid 2-spead gearbox ?
Hopefully Porsche improves this for the new Macan and Cayman.

I don't think Taycan's perceived inefficiency based on test cycles has anything to do with suboptimal Drivetrain or "mechanical" losses. I think it is mainly about to do with performance oriented software tuning on many different areas (eg brake pads engaging for initial several miles of every single trip so they are primed and ready or pads engaging in many braking during curves, energy losses to battery heat optimization to make sure higher power is available more readily etc etc). These often 1- time losses make a huge impact in cycle measures. If you actually look at the 70 mph full-range tests, Taycan beats most of the EVs out there, which would not be the case if there is a mechanical inefficiency involved. (see below - 36% overperformance over EPA range at 70 mph)

 

[Jhenson29]

I am not sure general electric motor dynamics (like constant HP) apply directly apply to Taycan given heavily regulated nature of the torque curve (which is not necessarily maxed out at any given rpm for different reasons). If you look at the dyno results of different models you see a lot of oddity. RWD for example never reaches constant HP, instead HP increases all the way to 200 kmh see the red line below.

It has nothing to do with that dyno. That’s dependent on what Porsche does for motor control.

I’m talking about the motor itself. It has a constant HP region and they’re in it, whether they’re using it or not. It doesn't "not exist" just because they limit the torque.

Frankly, there's only a limited amount I can tell from that one curve. When I'm working with motors, I'm watching things like output voltage, current, frequency, dc bus, etc and in the context of having the motor spec sheets, and typically doing the programming or tuning. Something like below for example, where you can see voltage in white and current in purple (the others are related to speed demand and feedback). The ripples you see are in time with the motor poles and were from rotor noise conducting to the analog encoder channels. It's not relevant other than to show an example of the type of information I would typically be working with when looking at motor control. Not a dyno output, which doesn't tell me how it got that power.

The reality is Taycan has the flattest acceleration curve of any EV out there I think it is a function of the longer second gear (along with the 800v infrastucture), which would not be possible without the 1st gear.

I agree that there can't be a second gear without a first gear....but I'm not sure that was your point?

And 2nd gear isn't even that "long". It's the same as the front motor and similar to Tesla, which is around 9 from a quick google search.

@Bognar67 was claiming the advantage of the 2-speed gearbox was acceration above 110kph. But there isn't an output power the 2nd gear can hit that the first gear can't hit at an earlier speed (until it hits max motor speed). And again, I'm talking capabilities here. Not however Porsche may be limiting it. The second gear is needed for the higher vehicle speeds. But I'm arguing that this ratio is required in all cases. This is the gear that would be there if it was a single speed transmission. The job of 1st gear is to increase power quicker. That's its only function. It's the auxiliary because it could be replaced by having larger power motors. You can't replace 2nd gear's function.

If you disagree, please state what gear ratio you think a single speed gearbox Taycan would have and we'll hash it out from there. @Bognar67 can tell me what gear he would use also. Please. I'm interested.

Here's a post where I've already gone through a lot of this:
https://www.taycanforum.com/forum/threads/gearbox-totally-unnecessary.11771/#post-172269

Top speeds of most of the model range are limited not because of revs but because of consistency concerns (eg can you maintain the required power output at the given speed for an extended period of time).

Do you have a source for this? My understanding is the motors max at 16krpm.

 

[f1eng]

And 2nd gear isn't even that "long". It's the same as the front motor and similar to Tesla, which is around 9 from a quick google search.

I haven’t looked but I am a bit disappointed if they haven't split the difference by making 1st a bit shorter and 2nd a bit longer.

On a F1 car acceleration from 0-60 is dominated by traction, not power, with tyre, tyre temperature and road surface making more difference than available torque. Having a significantly shorter gear is, if anything, worse since it makes avoiding wheelspin more difficult.

Anyway i am sure Porsche made their choice for perfectly good reasons…

 

[Bognar67]

How does ZF's two-speed EV transmission work?
ZF's universal drive unit, offering a turn-key drivetrain for manufacturers looking to develop a mainstream EV, incorporates a 140kW electric motor and, crucially, a game-changing two-speed gearbox.
At low speeds and in stop-start traffic, an electric motor is at its most efficient, offering regenerative braking to recoup power under deceleration and without power-sapping drag to fight. But at cruising speed, the rapidly spinning motor puts a high demand on the battery, compounded by aerodynamic and tyre resistance.
However, when vehicles fitted with ZF’s new unit pass 70km/h, the gearbox shifts up into its taller cruising ratio, lowering the motor’s RPM for greater efficiency and optimised torque.


Until now, manufacturers have had to choose between low-speed torque or high-speed efficiency and lock that decision into the single gear ratio, but this potentially revolutionary twin-ratio solution is offering something closer to the best of both worlds.
High hopes Down Under
Touring this great land of ours under EV power is a tall order, but multi-speed ’boxes could be part of the answer.
Lower gears would provide maximum towing torque for trailers and caravans, while higher gears would impart long legs for vehicles on the interstate run, reducing charge consumption.
Ratio to the finish
As with manual and automatic gearboxes, expect to see EV transmissions with more ratios.
ZF is up to nine in its automatics for ICE, and more cogs in an EV gearbox will bring similar benefits – more potent acceleration and torque, increased motor life, and longer cruising range.
https://www.whichcar.com.au/advice/zf-2-speed-ev-transmission-explained

 

[Jhenson29]

I haven’t looked but I am a bit disappointed if they haven't split the difference by making 1st a bit shorter and 2nd a bit longer.

Whether or not those ratios are splitting a difference would be determined by what gear ratio one would pick if it was a single speed transmission. Which is why I asked that question of others. But then you have to deal with the ramifications of that selection. No free lunch.

On a F1 car acceleration from 0-60 is dominated by traction, not power, with tyre, tyre temperature and road surface making more difference than available torque. Having a significantly shorter gear is, if anything, worse since it makes avoiding wheelspin more difficult.

I disagree. That only makes sense if you assume sufficient power in the first place. But you need both torque and traction. Having traction does you no good if you don’t have the power to utilize it. Imagine putting a 1HP motor on an F1 car. Is the accel still dominated by the traction? No. You would have way more traction with almost any tire than you could ever hope to use. And you’d never even hit 60.

I deal with this issue all of the time, just not in the context of cars. And I’m in the position that I could be short on either in various applications. A variety of application means I face a variety of problems. However, it always boils down to the below:

If I’m not slipping, then I need more torque.
If I’m slipping, I need more traction.

If I do need more torque, my options are to increase that directly at the motor by increasing current if it’s an electric motor or increasing pressure if it’s a hydraulic motor. Both have limits and sometimes neither is an option. So, the other option is, we can change the gearing. And in some applications, we do in fact use 2-speed gearboxes with electric motors. They are pretty much always 2:1 in their relative gears.

I was involved in an application where another company severely undersized a large motor in an application. At startup, there were no good options other than to replace the gearbox and limit top speed. Large industrial gearboxes are usually custom ordered and very expensive. This was a very costly mistake for them.

Anyway, whether or not first gear is too short or not depends on whether or not available torque is too much. I’d argue it’s not so it’s fine. What it does is allows them to use a lower power motor for higher low speed acceleration.

Anyway i am sure Porsche made their choice for perfectly good reasons…

I agree.

 

[Jhenson29]

How does ZF's two-speed EV transmission work?

@Bognar67 i know how to read press releases. But I also do this for my day job for almost 20 years. I’ve done startup and control on well over 1000 electric motors. DC, AC async, AC sync, open loop, closed loop, speed control, torque control, simple on off, simple profiles, complex profiles with torque FF. I’ve even used 2-speed gearboxes for applications.

I agree it increases acceleration. By adding first gear. Which helps at low speed.

Do you have any original thoughts here?

 

[f1eng]

I disagree. That only makes sense if you assume sufficient power in the first place. But you need both torque and traction. Having traction does you no good if you don’t have the power to utilize it. Imagine putting a 1HP motor on an F1 car.

Dear me!
In my Ferrari 355 the car is traction limited in 1st, 2nd and sometimes 3rd gear. It has 380 hp.
That is why I would expect the 0-60 time of a Taycan could and probably would be traction limited, even the RWD

Sorry I didn’t explain the context more clearly beforehand.

 

[Bognar67]

I am using now 3 electric cars Tesla 3 Performance, BMW i4 40 and Taycan GTS.
Taycan is the only one that keeps up the acceleration curve nicely at higher speeds.
Differences Taycan/i4 and TM3P are 400V/800V and 1-speed/2-speed.
I can accept that if the reason is something else, just tell it.
I still love the feel of a shift in an electric car, that is really unique no one else do it . It gives some extra joy.

 

[Bognar67]

@Bognar67 i know how to read press releases. But I also do this for my day job for almost 20 years. I’ve done startup and control on well over 1000 electric motors. DC, AC async, AC sync, open loop, closed loop, speed control, torque control, simple on off, simple profiles, complex profiles with torque FF. I’ve even used 2-speed gearboxes for applications.

I agree it increases acceleration. By adding first gear. Which helps at low speed.

Do you have any original thoughts here?

No. As you know I have no original thought at all. You are the most clever man I have ever seen and the only one here who has an original thought.
I hope the above statement is good enough to you to live me alone, simple comment your original thoughts without mentioning me. Thank you.

 

[Jhenson29]

In my Ferrari 355 the car is traction limited in 1st, 2nd and sometimes 3rd gear. It has 380 hp.
That is why I would expect the 0-60 time of a Taycan could and probably would be traction limited, even the RWD

It may be. I don’t know. I didn’t mean to suggest it isn’t if I did.

 

[Jhenson29]

No. As you know I have no original thought at all. You are the most clever man I have ever seen and the only one here who has an original thought.

Oh my, @Bognar67, that’s not the point. Why don’t you just block me and be done with it then?

The point is that 2nd gear’s acceleration can’t beat 1st; as well as what gear would be present in a single speed box? If anything, it would be a higher (> 8.05) gear and your acceleration above 110kph would be the same up to the motor limit. You don’t have more acceleration at high speeds (within motor speed limits) because the gearbox is two speed. That’s all I was saying.

 

[Jhenson29]

I am using now 3 electric cars Tesla 3 Performance, BMW i4 40 and Taycan GTS.
Taycan is the only one that keeps up the acceleration curve nicely at higher speeds.
Differences Taycan/i4 and TM3P are 400V/800V and 1-speed/2-speed.
I can accept that if the reason is something else, just tell it.

I don’t know if I have enough information. If I were to actually want to evaluate this, I’d want to look at things the way I described in an earlier post, plus actual speed profiles.