P3D horsepower?

[ChemEJon]

Porsche Taycan.

The use of a 2 speed transmission is probably to account for the constant torque region which from what I've seen is around 50-60 mph. Below is a operational curve for an ac motor.

By having a second gear ratio, you can effectively reduce the motors angular velocity or RPM allowing you to increase the maximum wheel speed of the vehicle while staying in the constant torque region.

This is just some speculation, it may or may not be 100% correct.

 

[AlanSubie4Life]

By having a second gear ratio, you can effectively reduce the motors angular velocity or RPM allowing you to increase the maximum wheel speed of the vehicle while staying in the constant torque region.

This is just some speculation, it may or may not be 100% correct.

You just want to spend as much time in the constant (max) power region as possible. Maximum power is the best, assuming no other non-idealities.

 

[neezer]

No doubt Porsche went with the 2-speed geabox for the Taycan for straight line acceleration performance, and nothing else. If you don't select Sport or Sport+, you will always be using the higher 2nd gear, no matter how hard you floor it and no matter what speed you're at. The lower ratio gear in that vehicle is for 0-50mph (max) use.

Of course, it adds weight, complexity, initial cost, possible extra maintenance requirements/cost ...but they realized they can't have a 160-240k USD vehicle be very easily out-accelerated by a 100k competitor, so they had to do it at a minimum. It still won't matter, the MS is quicker to at least 90mph anyhow as it is ...

 

[ChemEJon]

You just want to spend as much time in the constant (max) power region as possible. Maximum power is the best, assuming no other non-idealities.

If you look at the constant power section, the slip increases. The constant power section should be reactive power which is the power stored in and discharged by the motors. With increased slip the active power (work done) will decrease and cause a decline in WHP even though power delivered to the motor is constant.

 

[AlanSubie4Life]

If you look at the constant power section, the slip increases. The constant power section should be reactive power which is the power stored in and discharged by the motors. With increased slip the active power (work done) will decrease and cause a decline in WHP even though power delivered to the motor is constant.

I don't know that slip actually applies for a DC machine (specifically PMSR). But anyway, I am only referring to output power (as measured at the wheels or at the output of the motor), not input power to the motor. You want to stay at the peak power output as much as possible. Because it's more power, and that will make you accelerate faster. You don't want to be in the constant torque region (you can see this from the measured curves from the P3D above - the broad power peak occurs a little after torque starts to drop off).

 

[Daniel in SD]

If you look at the constant power section, the slip increases. The constant power section should be reactive power which is the power stored in and discharged by the motors. With increased slip the active power (work done) will decrease and cause a decline in WHP even though power delivered to the motor is constant.

If you look at the efficiency plot for the Leaf permanent magnet motor there is very little loss of efficiency over the constant power region (power out is approximately 95% of power in).
It would be neat if someone who has the equipment to read the CAN bus on the Model 3 could make a similar plot. Or, Tesla could just publish it, I'm sure all their competitors have already have it

 

[ChemEJon]

I don't know that slip actually applies for a DC machine (specifically PMSR). But anyway, I am only referring to output power (as measured at the wheels or at the output of the motor), not input power to the motor. You want to stay at the peak power output as much as possible. Because it's more power, and that will make you accelerate faster. You don't want to be in the constant torque region (you can see this from the measured curves from the P3D above - the broad power peak occurs a little after torque starts to drop off).

Tesla motors are AC, they use a VFD to control the motor frequency.

 

[ChemEJon]

If you look at the efficiency plot for the Leaf permanent magnet motor there is very little loss of efficiency over the constant power region (power out is approximately 95% of power in).
It would be neat if someone who has the equipment to read the CAN bus on the Model 3 could make a similar plot. Or, Tesla could just publish it, I'm sure all their competitors have already have it

I'm pretty sure a dyno with a power logger should work. Just take the power going into the motor and compare it to the power measured by the dyno. A CAN would be easier but you still need to measure the actual produced power.

 

[AlanSubie4Life]

Tesla motors are AC, they use a VFD to control the motor frequency.

The more powerful rear motor in the Model 3 is a permanent magnet switched-reluctance motor, which is a type of DC motor (but yes, obviously it is brushless and uses a controller to energize the stator windings via the H-bridges in the correct sequence). Point is that it's not an induction motor. In any case, that's off topic here, since we have the output power and torque curves (after correcting for drag). So implementation details are not that important. And we have a pretty good idea of what efficiency vs. speed and torque looks like, based on the Leaf pictures above.

 

[ChemEJon]

The more powerful rear motor in the Model 3 is a permanent magnet switched-reluctance motor, which is a type of DC motor (but yes, obviously it is brushless and uses a controller to energize the stator windings in the correct sequence). Point is that it's not an induction motor. In any case, that's off topic here, since we have the output power and torque curves (after correcting for drag).

Just looked it up and you're right. It looks like PSMR have limited slip. The Taycan has 2 induction motors so that might explain their logic for the two speed gearbox.

 

[AlanSubie4Life]

The Taycan has 2 induction motors so that might explain their logic for the two speed gearbox.

That's also not correct. Porsche has constructed such an inefficient, enormous, spectacular vehicle (they don't care about efficiency as much as Tesla - it's all about priorities!) that they definitely have to use very efficient motors. I am fairly sure that the two-speed gearbox was not chosen for efficiency reasons! You can read all the details here:

An Extremely Detailed Look At The Porsche Taycan's Engineering Designed To Take On Tesla

 

[ChemEJon]

That's also not correct. Porsche has constructed such an inefficient, enormous, spectacular vehicle (they don't care about efficiency as much as Tesla - it's all about priorities!) that they definitely have to use very efficient motors. I am fairly sure that the two-speed gearbox was not chosen for efficiency reasons! You can read all the details here:

An Extremely Detailed Look At The Porsche Taycan's Engineering Designed To Take On Tesla

I wasn't saying the gear box was chosen for efficiency reasons. The most likely chose it for acceleration reasons, the Porsche beats the MS in 1/4 mile times even though the S has a faster 0-60. Gear ratio most likely plays a factor into this.

 

[ChemEJon]

That's also not correct. Porsche has constructed such an inefficient, enormous, spectacular vehicle (they don't care about efficiency as much as Tesla - it's all about priorities!) that they definitely have to use very efficient motors. I am fairly sure that the two-speed gearbox was not chosen for efficiency reasons! You can read all the details here:

An Extremely Detailed Look At The Porsche Taycan's Engineering Designed To Take On Tesla

Also in your link.

"The transmission, which also houses a clutch-based electronic limited slip differential (I guess you could call this gearbox a transaxle, then), is a fascinating unit, as I know of no other mainstream electric vehicle in the U.S. that currently offers a two-speed gearbox.

Porsche says it does in order to improve efficiency, and also to help optimize both low-speed acceleration and top-end speed—pretty much exactly the benefits that auto supplier ZF claims of its new two-speed EV transmission."

As suspected a simple search verified the hypothesis or acceleration.

 

[AlanSubie4Life]

Also in your link.

"The transmission, which also houses a clutch-based electronic limited slip differential (I guess you could call this gearbox a transaxle, then), is a fascinating unit, as I know of no other mainstream electric vehicle in the U.S. that currently offers a two-speed gearbox.

Porsche says it does in order to improve efficiency, and also to help optimize both low-speed acceleration and top-end speed—pretty much exactly the benefits that auto supplier ZF claims of its new two-speed EV transmission."

As suspected a simple search verified the hypothesis or acceleration.

Sounds like we are in agreement. I said the two-speed gearbox was not done for efficiency reasons - not that it did not improve efficiency (would be no way for me to know that without the full curves, and knowing the additional drivetrain losses associated with the transmission). These are two different things.

Point is that my guess is that if efficiency were the only concern, Porsche would not have used a two-speed gearbox.

 

[ChemEJon]

Sounds like we are in agreement. I said the two-speed gearbox was not done for efficiency reasons - not that it did not improve efficiency (would be no way for me to know That without the full curves). These are two different things.

The link you provided literally says,

"Porsche says it does in order to improve efficiency, and also to help optimize both low-speed acceleration and top-end speed".

From what I'm reading clearly implies that they did it to primarily improve efficiency. I mean you posted the link, I thought you would have read through it.

 

[AlanSubie4Life]

The link you provided literally says,

"Porsche says it does in order to improve efficiency, and also to help optimize both low-speed acceleration and top-end speed".

From what I'm reading clearly implies that they did it to primarily improve efficiency. I mean you posted the link, I thought you would have read through it.

Again, I have no way to know, and I did not say the gearbox does not improve efficiency.

It probably is more efficient at 150mph (I have no idea!). I doubt it helps the EPA numbers. But again, I have no idea!

 

[WilliamG]

The link you provided literally says,

"Porsche says it does in order to improve efficiency, and also to help optimize both low-speed acceleration and top-end speed".

From what I'm reading clearly implies that they did it to primarily improve efficiency. I mean you posted the link, I thought you would have read through it.

I think (correct me if I’m wrong) that Alan is saying that Porsche’s interest was in improving efficiency in terms of performance, not in terms of range.

 

[diamond.g]

Just looked it up and you're right. It looks like PSMR have limited slip. The Taycan has 2 induction motors so that might explain their logic for the two speed gearbox.

Taycan uses two permanent magnet motors. That is what I though @AlanSubie4Life meant.

 

[AlanSubie4Life]

I think (correct me if I’m wrong) that Alan is saying that Porsche’s interest was in improving efficiency in terms of performance, not in terms of range.

Not quite: I have not said anything about whether the gearbox improves efficiency or how. I have no idea. My guess is that it hurts the EPA rating (vs. a Porsche design with different performance and different motors with no gearbox and worse high speed performance), but I have no idea, and there is no way for me to know, so I am not saying what it does! It does make sure that the motor operates closer to peak HP. That’s the reason for the gearbox. It sounds like we all agree (or based on above, maybe not!).

The Porsche has different design objectives than Model 3. This is not a complicated topic. It probably uses at least 60% more energy per mile than an SR+ (Might be more - not sure we know yet - my guess is it will be at least 40kWh/100mi!). Who cares. Different requirements.

 

[Daniel in SD]

"Porsche says it does in order to improve efficiency, and also to help optimize both low-speed acceleration and top-end speed".

By +0-3%!
Keep in mind that the 3% might only be at Autobahn speeds.
Also I doubt it would be more efficient if they just used a fixed 7.0 in the rear (which is what they do in "Normal" mode).