Taycan efficiency vs VW ID7 … can it be true?

[Avantgarde]

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.

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


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

This company unlocks top speed for Taycan and ETron GS. You get 273/kms for 4s and 278/kms for Turbo&S. I am pretty sure their application does not involve anything mechanical like a gear ratio change.

https://www.hgp-turbo.de/audi-e-tron-gt-rs.html

It is also pretty clear from the power meter that the power is gets abruptly limited when you get to top speed. (the blue bar suddenly drops to ~50% when you hit the top speed).

 

[Avantgarde]

3 minutes ago

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Jhenson29 said:
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.

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.

The fact that it is similar to Tesla is makes it too long! Tesla is a 400V set up Taycan is 800V. To be clear I am not an electrical engineer but nerd enough to be dangerous. Everything I read indicates higher voltage gives the motors ability to deliver higher torque at higher revs given the better capacity to fight back-ems at higher revs. Hyundai who also has a 800V EV set up brags about this quite a bit. So this is how I simplify (or oversimplify) in my mind: If Tesla has a diesel engine that start to run out of steam after 3K revs, 800V Taycans are like early Honda Vtec engines. I do think in a single gear set-up taycan would certainly have a shorter second gear.

 

[Avantgarde]

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.

Rough math but speaking of the RWD Taycan, in a single gear set up a second gear in high 9s (~9.5-9.7X) would get the car to the same top speed of ~230kms/h. The car would obviously accelerate faster at low-mid-range speeds (until torque starts dropping) but would likely see a significant tapering off the acceleration above 150 kmhs. So the acceleration curve would be a lot more non-linear compared to current set-up. And maybe your point is: Yes the acceleration above 150 kmh will taper off but will not necessarily be any worse than what you get in the current set-up - I get this but I think this is your primary assumption: "If you use a 20% shorter gear ratio, your revs will be 20% higher at 150 kmhs and given the EV motor is in constant HP range your motor torque would be 20% lower but given you have a 20% shorter ratio your wheel torque should be ~ same, so your acceleration should be the same".

You seem to be working with motors so I don't mean to disrespect your expertise but there is a more complicated situation here I think. Feels like Porsche regulates max torque & output (unlike Tesla trying to milk every single NM) and maybe there is a preference for not max-utilizing higher end of the constant HP range. Secondly linearity is for sure a major concern here. Porsche would for sure won't want a a feeling of major acceleration drop. And really a longer gear (which is made possible by the 1st gear) truly helps in this manner.

 

[Avantgarde]

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.

You are absolutely right about this acceleration curve. Proven many times by acceleration tests and dynos, there is nothing like Taycan out there in terms of acceleration linearity. I think the real answer is complicated. But is a function of both 800V AND the 2-speed set-up.

 

[Grim]

Avantgarde’s posts seem to make sense to me:

- overall efficiency more likely to be reflective of Porsche’s more performance orientated setup (more brake use, keeping batteries warmer for better power delivery, etc) rather than motor inefficiency
- linear acceleration more likely to be reflective of Porsche keeping things in reserve in terms of how power is delivered

… or at least how I’m interpreting the posts

 

[Avantgarde]

Avantgarde’s posts seem to make sense to me:

- overall efficiency more likely to be reflective of Porsche’s more performance orientated setup (more brake use, keeping batteries warmer for better power delivery, etc) rather than motor inefficiency
- linear acceleration more likely to be reflective of Porsche keeping things in reserve in terms of how power is delivered

… or at least how I’m interpreting the posts

You very well summarized my key points in two sentences ?? instead of 5 pages.

 

[Jhenson29]

Rough math but speaking of the RWD Taycan, in a single gear set up a second gear in high 9s (~9.5-9.7X) would get the car to the same top speed of ~230kms/h. The car would obviously accelerate faster at low-mid-range speeds (until torque starts dropping) but would likely see a significant tapering off the acceleration above 150 kmhs. So the acceleration curve would be a lot more non-linear compared to current set-up. And maybe your point is: Yes the acceleration above 150 kmh will taper off but will not necessarily be any worse than what you get in the current set-up - I get this but I think this is your primary assumption: "If you use a 20% shorter gear ratio, your revs will be 20% higher at 150 kmhs and given the EV motor is in constant HP range your motor torque would be 20% lower but given you have a 20% shorter ratio your wheel torque should be ~ same, so your acceleration should be the same".

I don't understand what you mean by "second gear" in high 9s as I was asking for a single gear ratio scenario and there would not be a "second gear". I'll proceed under the assumption you meant a single gear.

Now we have a concrete number to work with. I'm perfectly happy talking about it abstractly, but let’s see if this helps any.

Let's go with 9.7.

But first, we need to consider that Porsche probably didn't design the car to optimize the RWD and then fit the Turbo S. Probably the other way around. So, it would be more useful to look at the Turbo S IMO, which has a top speed of 260kph. So, we'd have to increase max motor rpm by 20% to keep that top speed or sacrifice 20% top speed, or compromise somewhere between. Regarding the dynos, I think it's also more instructive to look at the Turbo S dyno which looks much flatter to me. But again, anything on the dyno is looking at it post-motor-control and not working with the capabilities which is what one would do in a design phase. Anyway, this is more of an aside; lets just go back to the RWD for a minute.

I maintain the motor is in the constant HP region due to max voltage and field weakening. I don't have motor specs and haven't see any voltage or current profiles, but it fits with their other published curves. But we'll put that aside for a minute too. Let's just look at the dyno graph you shared.

Minus what looks like the gear change at 120kph and fall of at the end, which I assume is throttle lift, the HP is higher as rpm increases.

Let's take my suggestion of constant HP as one limit and the dyno profile of HP increasing with rpm as our other limit. From this we can say, as rpms increase in the constant HP region, the HP will either be the same or higher. Note that because the HP is also higher as RPM increases in the constant torque region, this can be simplified to just say that as RPMs increase, the HP will either be the same or higher.

If you increase the gear ratio from 8.05 to 9.7, for any given vehicle speed, you will be at a higher motor rpm.
This means for any given vehicle speed, you will be at a the same or higher HP. (given our limits defined by my suggestion of the constant HP region and the dyno suggestion of increasing HP in that region and the knowledge that HP increases in the constant torque region regardless)

Let's look at some numbers specific to @Bognar67 's claim about accel above 110kph.

At 130 kph with 9.7 gear ratio, you would be at the rpm and HP shown at 156 in the dyno, which is about 1 full unit higher (I don't know what the y divisions of the graph are).

At 160 kph with 9.7 gear ratio, you would be at the rpm and HP shown at 193, nearly a full unit higher again.

Accel is proportional to power (for a given speed). Increase HP at a given speed means increasing accel.

So, now let's imagine Porsche made this 9.7 single speed Taycan first. Then made this new 2-speed 8.05/16 gearbox version. The 2-speed version has the same or less power in 2nd gear above 110kph than the 9.7 speed single speed version.

Now go reread @Bognar67 comment:

I really enjoy the advantage of a 2-speed gearbox above of 110km/h when for example my TM3P starts to loose the acceleration dynamics.

But the single speed gearbox example has the same or more HP than the 2-speed. So, it can do the same or more acceleration. And it only gets more exaggerated as you increase the ratio (10, 11, 12...) and gets closer to exactly what 2nd gear is as you approach 2nd gear (8.05).

This is why I made my reply:

I think the advantages are below, not above. 1st is the extra gear. Not 2nd.

I think it's also instructive to look at what Porsche did do when they had a choice for a single gear speed. The front motor is 8.05. If there was some other more optimized choice for a single speed gear application, why did Porsche go with 8.05 in this application?

You seem to be working with motors so I don't mean to disrespect your expertise but there is a more complicated situation here I think. Feels like Porsche regulates max torque & output (unlike Tesla trying to milk every single NM) and maybe there is a preference for not max-utilizing higher end of the constant HP range. Secondly linearity is for sure a major concern here. Porsche would for sure won't want a a feeling of major acceleration drop.

Again, you're looking at the post-motor-control (on the base model at that) and trying to design from that as limits. But there's any number of reasons why Porsche may be limiting it, not the least of which could be model distinction. The 911 S has the same motor and turbos as the GTS, but the GTS has more HP because of tuning, as an example.

 

[Avantgarde]

I don't understand what you mean by "second gear" in high 9s as I was asking for a single gear ratio scenario and there would not be a "second gear". I'll proceed under the assumption you meant a single gear.

Now we have a concrete number to work with. I'm perfectly happy talking about it abstractly, but let see if this helps any.

Let's go with 9.7.

But first, we need to consider that Porsche probably didn't design the car to optimize the RWD and then fit the Turbo S. Probably the other way around. So, it would be more useful to look at the Turbo S IMO, which has a top speed of 260kph. So, we'd have to increase max motor rpm by 20% to keep that top speed or sacrifice 20% top speed, or compromise somewhere between. Regarding the dynos, I think it's also more instructive to look at the Turbo S dyno which looks much flatter to me. But again, anything on the dyno is looking at it post-motor-control and not working with the capabilities which is what one would do in a design phase. Anyway, this is more of an aside; lets just go back to the RWD for a minute.

I maintain the motor is in the constant HP region due to max voltage and field weakening. I don't have motor specs and haven't see any voltage or current profiles, but it fits with their other published curves. But we'll put that aside for a minute too. Let's just look at the dyno graph you shared.

Minus what looks like the gear change at 120kph and fall of at the end, which I assume is throttle lift, the HP is higher as rpm increases.

Let's take my suggestion of constant HP as one limit and the dyno profile of HP increasing with rpm as our other limit. From this we can say, as rpms increase in the constant HP region, the HP will either be the same or higher. Note that because the HP is also higher as RPM increases in the constant torque region, this can be simplified to just say that as RPMs increase, the HP will either be the same or higher.

If you increase the gear ratio from 8.05 to 9.7, for any given vehicle speed, you will be at a higher motor rpm.
This means for any given vehicle speed, you will be at a the same or higher HP. (given our limits defined by my suggestion of the constant HP region and the dyno suggestion of increasing HP in that region and the knowledge that HP increases in the constant torque region regardless)

Let's look at some numbers specific to @Bognar67 's claim about accel above 110kph.

At 130 kph with 9.7 gear ratio, you would be at the rpm and HP shown at 156 in the dyno, which is about 1 full unit higher (I don't know what the y divisions of the graph are).

At 160 kph with 9.7 gear ratio, you would be at the rpm and HP shown at 193, nearly a full unit higher again.

Accel is proportional to power (for a given speed). Increase HP at a given speed means increasing accel.

So, now let's imagine Porsche made this 9.7 single speed Taycan first. Then made this new 2-speed 8.05/16 gearbox version. The 2-speed version has the same or less power in 2nd gear above 110kph than the 9.7 speed single speed version.

Now go reread @Bognar67 comment:


But the single speed gearbox example has the same or more HP than the 2-speed. So, it can do the same or more acceleration. And it only gets more exaggerated as you increase the ratio (10, 11, 12...) and gets closer to exactly what 2nd gear as as you approach 2nd gear (8.05).

This is why I made my reply:


I think it's also instructive to look at what Porsche did do when they had a choice for a single gear speed. The front motor is 8.05. If there was some other more optimized choice for a single speed gear application, why did Porsche go with 8.05 in this application?


Again, you're looking at the post-motor-control (on the base model at that) and trying to design from that as limits. But there's any number of reasons why Porsche may be limiting it, not the least of which could be model distinction. The 911 S has the same motor and turbos as the GTS, but the GTS has more HP because of tuning, as an example.

I know that RWD’s torque and hp curve goes to the other direction. The reason i gave that example at the first place was to demonstrate the fact that porsche was setting odd ceilings to the curve through torque management resulting in different models to have very different torque curves that does not look anything like constant torque/constant HP curve of an EV motor. Agree that taycan turbo has a VERY different torque curve than The rwd. Also agree that we should be looking at the taycan turbo to understand design limitations, the problem there is most dyno results for turbo or turbo s show the two axles combined and things get more complicated given one axle doe snot have 2 gears. But one interesting observation: almost all dyno results for turbo/s show a material bump in wheel torque after shift to second gear. (A lot of drivers also report this feeling as a rocket kicking in). This implies that the torque at high RPMs drop so disproportionately that, even if the gear ratio doubles after the shift, the torque reserves accessed at lower rpms, more than negate doubling of the gears.

I don’t mean to turn this to an endless debate but what is your explanation around the reasoning put out by the porsche’s own press release? (See the attached pics & highlighted sections)

They clearly indicate two speed transmission allows for a longer second gear which allows “…greater power and acceleration reserves even at very high speeds”. I mean if they are directly tying high speed acceleration to the 2 speed transmission there has to be a technical explanation.

My other speculation is around limitations on how long the max HP can be produced. Maybe If Constant HP (which is also max HP in a motor), could be produced for an indefinite amount of time your general assumption (which I simplify as “gear ratio does not impact wheel torque as long as you are within constant HP range”) would hold. But if you are limited by how long you can produce max/constant HP by other factors (eg battery) - and indeed max hp is limited to 10 seconds i believe - the later you enter into constant HP the more time/reserve you have until you hit the electronically limited top speed (at which point power is reduced anyways).

My second speculation is around voltage fluctuations (battery voltage can drop to 600s in low soc and temperatures). And the fact that they would want to have the consistent high speed acceleration during the entire voltage range. (Have a feeling longer gear would help when there is not enough voltage to feed very high rpms - but i am not technically knowledgeable enough to be sure)

 

[feye]

The motors are, I believe, based on the racing design from the hybrid Le Mans 919 and for that high duty cycle keeping it cool enough under heavy usage was needed.
Producing super efficient motors with high short term power may well be a better choice for a road car where specs and "fuel consumption" are more important than maximum performance but there we are.

He goes into some details on some of the small changes VW made on this new motor and drivetrain to get it more efficient.

The problem of the German EV car industry is China. China has access to all the raw materials and resource to spill out large batteries for "small" money and therefore can offer cars with ranges, the Germans can only dream of. They find it extremely hard to compete, so the only thing left for the time being, is to improve on efficiency.

 

[Jhenson29]

I don’t mean to turn this to an endless debate but what is your explanation around the reasoning put out by the porsche’s own press release? (See the attached pics & highlighted sections)

I don't think we should confuse marketing with engineering. There was also talk about efficiency increases due to being able to disengage the rear motor. I thought that was silly because the friction losses are minimal and they could do the same with a clutch and single speed gearbox if they really wanted to. Links to comments from me on these points from 2021. I believe they later started electrically decoupling the front motor instead (which I had also previously stated would be possible).

https://www.taycanforum.com/forum/t...ansmission-a-good-idea.6598/page-2#post-94539

https://www.taycanforum.com/forum/t...ansmission-a-good-idea.6598/page-3#post-94709

We don't have any specific data on their claims in the marketing material. What I think happened is that they had a requirement for a 2-speed gearbox and then touted any advantage they could, regardless of its magnitude or relevance. Has Porsche ever said what single speed gear they would have used and are comparing this "long" 2nd gear to? I still don't think 2nd gear is all that "long". It's long compared to first. I don't think it's especially long compared to other single speed gear cars. Have they ever said how much more efficient it is? Or what these power/accel reserves are? If they had material showing the difference between what would be possible in an alternate scenario that they seem to be comparing it to, then I'd pay more attention. As it stands, it's marketing material.

The real question is what drove the 2-speed gearbox in the first place.

The thing is, the 2nd gear can exist as is and the first gear could be replaced with a larger motor. So, why didn't they do it that way? Careful, lots of speculation in the next few sentences. I would guess they couldn't. They would have needed massively more power to recreate the available wheel torque in first gear, even if they were to use something more like 9.7 as the single speed gear ratio. My best guess is they had a current limit, likely imposed by the battery, had to add a higher ratio 1st gear to get low speed accel, and then touted every benefit they could muster for the 2-speed gear box.

My other speculation is around limitations on how long the max HP can be produced. Maybe If Constant HP (which is also max HP in a motor), could be produced for an indefinite amount of time your general assumption (which I simplify as “gear ratio does not impact wheel torque as long as you are within constant HP range”) would hold. But if you are limited by how long you can produce max/constant HP by other factors (eg battery) - and indeed max hp is limited to 10 seconds I believe - the later you enter into constant HP the more time/reserve you have until you hit the electronically limited top speed (at which point power is reduced anyways).

I don't think so. Constant HP and Max HP are not the same. Constant HP refers to a region, in the motor control where voltage is maxed out and field weakening is used to increase speed above rated speed. There's also rated HP which is the maximum continuous horsepower the motor can produce, which is it's rated current at it's rated speed (which is its base speed where you hit full volts). Max HP would be the maximum you can use, which can be above rated. I have applications that use 300% rated current for short periods. 150% is very common. Generally, it's above rated values that you are time limited on, however it does all come down to temperature. If cooling is inadequate, then further derating may be required. This can be modeled, but it's usually better to use sensors in the motor if it's actually a concern. We commonly use thermostats just as a failsafe to protect the motor, but there are analog temperature sensors also, like thermistors.

Additionally, it's not HP that needs to be limited. It's current as that is what produces heat. In the constant HP region, HP is proportional to current, but in the constant torque region, it's not (torque is proportional to current). So, if limiting is required, it's current that needs to be limited and would apply across the entire rpm range. Delaying the constant HP region as a limit due to either heat or current doesn't make sense.

My second speculation is around voltage fluctuations (battery voltage can drop to 600s in low soc and temperatures). And the fact that they would want to have the consistent high speed acceleration during the entire voltage range. (Have a feeling longer gear would help when there is not enough voltage to feed very high rpms - but i am not technically knowledgeable enough to be sure)

This is more probable because when voltage drops below the required peak voltage, clipping occurs, RMS voltage drops, and more current is required to make up the same power. However, I thought power was limited separately in those conditions (I thought I read power is limited at lower SoC; I could be wrong). If that were the case, then it's likely already accounted for separately and wouldn't need to have limits imposed at times when the voltage level is acceptable.

FWIW, I had an application that needed to run at the rated power all of the time, which it could do in normal conditions. But the motor would overheat if the DC bus voltage dropped below minimum (causing the current to increase). We had to monitor the DC bus and reduce the load when it dropped.

-----

I actually don't have time for these longer posts at the moment. I'm on a startup and working long days. So, I'm going to exit the discussion as it's gone well outside of and beyond what I intended to get involved in. Regards.

 

[andb]

Has Porsche ever said what single speed gear they would have used and are comparing this "long" 2nd gear to? I still don't think 2nd gear is all that "long". It's long compared to first. I don't think it's especially long compared to other single speed gear cars. Have they ever said how much more efficient it is? Or what these power/accel reserves are? If they had material showing the difference between what would be possible in an alternate scenario that they seem to be comparing it to, then I'd pay more attention. As it stands, it's marketing material.

Agree on this.
I think Porsche needed to beat the Model S 0-60 but because Taycan was heavier they had to use a shorter gear to extract more torque. If the battery could deliver more current they would have ditched the 1st speed.

 

[Avantgarde]

I don't think we should confuse marketing with engineering.

This is mentioned in their formal press release, which is considered a pretty serious disclosure document for a publicly traded company. They can't say anything that is not accurate or randomly bullshit. I worked for a major automaker for 10 years and I can assure you this language is coming from and/or fully vetted by a senior engineering leader not a marketing person. Plus it would be a very oddly specific AND non-true comment for marketing to highlight. "Long second gear enabling acceleration reserves at very high speed!?" "hey lets say this even if not true!" why? is this a killer marketing line? more importantly this supposedly random/wrong comment hits the nail on the head on how Taycan really maintains acceleration at high speed. And if that's what they want to highlight, why not tell the real reason but tie it to a long second gear?

 

[Avantgarde]

Constant HP and Max HP are not the same

Again you seem to be talking in general motor terms. My understanding most EVs generate their stated published max horsepower at constant HP range. (I am talking about the max horsepower figure you see in the car's spec sheet not some theoretical motor max HP)

 

[Avantgarde]

Additionally, it's not HP that needs to be limited. It's current as that is what produces heat.

This also from Porsche newsroom:

There is no time limit qualification when it comes to max torque, but max horsepower is limited to 10 seconds. Again feels like you are talking in generic motor terms. If motor heat is your primary limitation like in many applications yes current would have to be limited. But what if the battery is the limit here (maybe they want to limit to max discharge episodes to protect the battery - I don't know)

 

[Avantgarde]

Agree on this.
I think Porsche needed to beat the Model S 0-60 but because Taycan was heavier they had to use a shorter gear to extract more torque. If the battery could deliver more current they would have ditched the 1st speed.

There is no mechanical engineer in the world, who, when presented to have the opportunity to have 2 gears instead of 1, would say "ah great I will keep my one gear exactly how it would be in a single gear set up and just add this second one as a shorter gear". That mechanical engineer does not exist because he would lack the basic concept of "optimization". If you have access to just one automotive engineer in your life, pls just ask this question.

... you point to porsche's own press release.....-aah that's bullshit probably marketing. Ok How about a theory that they just wanted to beat Tesla and simply added 1 additional gear to perfectly optimized 1 gear set-up? - Oh yeah that sounds like a legitimate explanation.

Feels like we beat this one to death.