Auto Regen?

[f1eng]

Most EV brands including young Chinese companies can all do this, so any perceived "complexity" will hardly be beyond Porsche engineers. It's also not for "no purpose". For many (not all) it's a very relaxed way to drive. I agree it will be interesting to watch future developments across the Porsche range on this.

I don't know how other car manufacturers engineer their regeneration but I would imagine it would be massively easier and cheaper to have 1 pedal driving for any regeneration and separate friction brakes in addition than to seamlessly blend regenerative braking with friction braking effectively using the brake pedal.

Do cars with 1 pedal driving achieve any regeneration from the brake pedal or are they simply friction brakes when using the brake pedal?

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[WasserGKuehlt]

Most EV brands including young Chinese companies can all do this, so any perceived "complexity" will hardly be beyond Porsche engineers. It's also not for "no purpose". For many (not all) it's a very relaxed way to drive. I agree it will be interesting to watch future developments across the Porsche range on this.

Okay, I should have clarified that “added complexity for no purpose” was my speculation of Porsche’s view - I fully recognize your right to deem one pedal driving as purposeful (or even essential). That is, it’s coming back to that philosophical choice I mentioned 2-3 pages ago.

Having said that, your double-quoting of the word ‘complexity’ doesn't mean it is a trivial task. It’d be interesting to note if all those other manufacturers have implemented hydraulic-regen brake blending in the manner Porsche have done it, and with the same quality*. And that’s the point - they chose to spend time and resources on this and not that.

You mentioned earlier that pure driving experience would require 3 pedals; uh, no, why? The experience is about driving fast: acceleration and braking are essential, de/clutching is a cost. Porsche invented PDK, inarguably the best of its kind. Also, their purest driver’s instrument (for the street), the GT3 RS, does not offer a manual gearbox anymore.

*I am aware that some/many would reject that assertion as “bollocks”.

 

[Jhenson29]

This is what I suspect. Hydraulic brakes are needed anyway - for when higher g are needed, as backup etc. Then, at the lower speeds, on one side you need the ability to finely modulate the stopping, so the brake pedal would have to be tuned to “regen” exactly as much energy (power, rather) as the user expects. On the other side, there is an efficiency overhead to actually charging the battery, and when the braking power falls below that threshold you can’t really recuperate it - it has to be wasted as .. something (heat, in the form of a resistor). Besides, there is a benefit to constantly engaging the hydraulic brakes during daily driving. All of these together mean that it was probably easier to fine-tune blending than to make the electric motor be a user-friendly brake. And that’s just the act of stopping- holding would mean drawing from the battery enough to keep the car as a standstill, which means a lot of calculations per second to decide how much and in which direction (I imagine balancing on a unicycle would be a good analogy). It all sounds like unnecessary complexity.

I mostly agree with one exception that I'll go into below. But absolutely agree on the friction brakes for higher braking forces and efficiency/heat issue using the motor to hold zero speed. I didn't mean to suggest that an EV should use that method. I was merely pointing out that we do it on the regular and it's not a capability issue.

The below I don't agree with:

I imagine balancing on a unicycle would be a good analogy

I don't think this is a good analogy for two reasons.

First, balancing on a unicycle is a position control, and you're approaching it from a regen standpoint. Regen is a torque issue. This is two control loops down from position.

It's a bit like looking at processor opcodes to figure out how to handle an http request. How you handle the http request will ultimately affect what the opcodes are, but they are several layers removed and you wouldn't concern yourself with specific opcodes while handling http (speaking generally; perhaps an exception for some performance application).

To balance a unicycle, you'd have a top level position control loop, a speed control loop under that, and then the torque control loop under that (...and more under that...the drive doesn't control torque directly). Each level would be relatively simple, but trying to imagine the control of a higher level from 2 levels down makes it seem unnecessarily difficult.
IMO, in a good system, each level/layer should be very simple.

The second issue is that the zero speed control of the car would not be a position control loop. It would be a speed control loop. It's easy to see this difference if you imagine what you do with error. On balancing a unicycle, if it develops a position error (leans), you need to correct that and stand it back upright. On a car, if it develops a position error (moves forward) you would not correct that, you would throw it away and continue trying to maintain the zero speed (the user may decide to correct it by reversing the car if they wanted to be in the position that is further back, but that's no longer a request to hold zero speed by the user).

We do torque control on motors all of the way to zero rpm. A simple example is tension in a winding or payoff application and coming to a stop. We’ll even often use the motor for holding zero rpm instead of a mechanical brake. A mechanical brake is still present, but only used for power loss. Driven measuring rolls is another common torque control to zero rpm application. Exit tension rolls to pull through low traction systems is another.

I'll comment on my comment here too that these applications I listed are an unfair comparison because they are all tension applications and the motors are holding torque at zero speed against something (what that something is varies by application). The car would not be able to do this. As I mentioned above, it would have to transition to a speed control loop at some point (maybe once the car is within a certain range of zero rpm). Still not an issue, I don't think. But wanted to point out that it's not exactly like the applications I mentioned previously.

 

[EVBHP]

Do cars with 1 pedal driving achieve any regeneration from the brake pedal or are they simply friction brakes when using the brake pedal?

Evan cars as old as the original leaf blend regen and friction brakes using the brake pedal. This is all normal EV stuff for a decade or more.

 

[Jhenson29]

Do cars with 1 pedal driving achieve any regeneration from the brake pedal or are they simply friction brakes when using the brake pedal?

Per post #15, every EV the OP has ever owned works this way.....

The brake pedal uses regen first and blends friction brakes over a certain value (much higher than typical driving).

Yes of course, same on every EV I've ever owned.

 

[Jhenson29]

Evan cars as old as the original leaf blend regen and friction brakes using the brake pedal. This is all normal EV stuff for a decade or more.

I don't believe Telsa does this, unless something has changed very recently.

 

[Jhenson29]

Evan cars as old as the original leaf blend regen and friction brakes using the brake pedal. This is all normal EV stuff for a decade or more.

Just out of curiosity, do you mean that the brakes and regen are used at the same time, but with regen coming from accelerator pedal lift off and friction brakes coming from the brake pedal?

Because that's not what we're talking about with blended braking on the Taycan. The regen level varies using the brake pedal with friction brakes blended in with higher demands. And the maximum regen level is significantly more than what it is on a Leaf or Tesla (last I checked).

 

[Scandinavian]

I don't know how other car manufacturers engineer their regeneration but I would imagine it would be massively easier and cheaper to have 1 pedal driving for any regeneration and separate friction brakes in addition than to seamlessly blend regenerative braking with friction braking effectively using the brake pedal.

Do cars with 1 pedal driving achieve any regeneration from the brake pedal or are they simply friction brakes when using the brake pedal?

I am not sure how all other manufacturers do this, but I know how Tesla model 3 and BMW i4 do it.

Tesla model 3 my 2019 had one pedal driving but used friction brakes as soon as you press the brake pedal. No blending if younset the recuperation to low.

BMW i4 does it both ways. It can use one pedal driving if you set that mode. Or it can coast if you set that mode. In both cases if you press the brake pedal it will first use recuperation to slow the car, and if that is not enough then the friction brakes are activated. All very seamless.

In our i4 I normally use one pedal driving in town and find it very useful.
However on open roads I use the coasting mode and find that great.
BMW advice that the one pedal driving with recuperation is more efficient than than coasting??

One of the nice features BMW has implemented in coasting mode, is that it will slow down automatically with recuperation, if you coast too close to the car in front. The distance you have set in ACC is still active in the background all the time, even without NOT being in ACC mode. But it is not intrusive and only feels like an extra safety element

I find the implementation of these modes way more advanced in the BMW than in the Taycan. And very reliable

 

[W1NGE]

The situations like this I find myself in require retardation to keep with in the speed limit, so regening.

Um, applying the brakes creates more recuperation than using overrun recuperation for retardation purposes.

 

[W1NGE]

Note my response was to @Jhenson29 observation about the behavior of the brake pedal/system below the regen threshold - that is, user choosing to brake.

One pedal driving is different: the user’s lift action is interpreted as “brake intent” (or not), depending on the profile of their lift (how much/how fast). So not only you’d have to solve the regen problem in my earlier post, you have to tune the same braking system when actuated from another switch (accel pedal). Yeah, it’s possible, but it’s added complexity for seemingly no purpose. It’s a much easier problem to solve without user input (innodrive/ACC). Yeah, other manufacturers solved it, but unclear if this feature is a differentiator in the marketplace. I suspect Porsche did not expect the Taycan to bring so many ex-Tesla drivers into the fold, so perhaps the next generation/model may well have this feature.

Porsche took a conscious decision to not have single pedal recuperation - not an engineering or design challenge. Anyone can make a dodgem after all.

To emulate ICE engine braking in a much more natural way the ability to provide braking via overrun recuperation (i.e. throttle lift off) or via the rotors under normal style braking (greater retardation and higher recuperation).

This lends itself to spirited driving on country roads for example when you may choose to have the sensation of engine braking when entering a corner.

 

[EVBHP]

Um, applying the brakes creates more recuperation than using overrun recuperation for retardation purposes.

Yes in the Taycan, hence my preference for 'proper' one-pedal driving/regen like my other EVs.

 

[EVBHP]

Porsche took a conscious decision to not have single pedal recuperation - not an engineering or design challenge. Anyone can make a dodgem after all.

To emulate ICE engine braking in a much more natural way the ability to provide braking via overrun recuperation (i.e. throttle lift off) or via the rotors under normal style braking (greater retardation and higher recuperation).

This lends itself to spirited driving on country roads for example when you may choose to have the sensation of engine braking when entering a corner.

Nothing about the Taycan's weak regen feels remotely like a down shift or engine breaking.

 

[WasserGKuehlt]

Nothing about the Taycan's weak regen feels remotely like a down shift or engine breaking.

I agree that engine breaking would be a pretty startling experience.

 

[W1NGE]

Nothing about the Taycan's weak regen feels remotely like a down shift or engine breaking.

Must be driving a different car. Try it in Sport Plus - did you miss the throttle blip during deceleration too?

 

[EVBHP]

Must be driving a different car. Try it in Sport Plus - did you miss the throttle blip during deceleration too?

Love that blip and down change

Only happens around 30mph though so not really useful when driving enthusiastically.

All this one-pedal stuff I'm talking about is mostly for the more mundane day to day driving, rather than at ten tenths.

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