Slowing down to 0 upon accelerator release

[Saghost]

I took delivery with creep turned OFF but immediately set it to ON - my brain was wired for an ICE world, I guess, and that's what I'm used to. I believe I read that the car will roll backward if on an incline with creep set to off... Is that true?

I drove with creep on the first several months, but eventually decided I like the control of creep off better.

I always make sure vehicle hold engages every time I stop - it will stay engaged until I hit the accelerator or press the brake again (the car supposedly will shift to Park after ten minutes or so if just left that way or if the driver leaves the seat.)

So it's like the car is heel and toe-ing for you.

 

[cucubits]

So it's like the car is heel and toe-ing for you.

I'd say it's more like the car is pulling the 'handbrake' for you every time.

I tried this on a drive test and I'm not sure I'd like to hear those little electric motors putting the brakes on every time I come to a stop in stop and go traffic for example.

 

[ajdelange]

Operational limitation of the induction and I believe also the switched reluctance motors that Tesla uses.

No, not really.

At those low speeds, the induction motors can't deliver effective regeneration because there's so little rotation of the rotor (induction motor torque is based on slip ratio - how much faster the field rotates than the rotor, or on regen how much faster the rotor spins compared to the field.)

But you can make the field rotate relative to the rotor as fast as you want in either direction. Yes, you get into some hairy control issues when slip is greater than the breakdown torque point slip (IM) but in the PM motors you can position the field anywhere you want relative to the magnets and vary its strength in order to have torque in either direction relative to rotor position. There may be practical limitations and the control would certainly be more easily implemented by applying a bit of friction braking.

 

[Saghost]

No, not really.

But you can make the field rotate relative to the rotor as fast as you want in either direction. Yes, you get into some hairy control issues when slip is greater than the breakdown torque point slip (IM) but in the PM motors you can position the field anywhere you want relative to the magnets and vary its strength in order to have torque in either direction relative to rotor position. There may be practical limitations and the control would certainly be more easily implemented by applying a bit of friction braking.

But that's not regeneration any more - that's me powering the car in reverse now. To regenerate, I have to let the rotor pull the field forward, and you run out of headroom as the car slows down.

 

[Saghost]

I'd say it's more like the car is pulling the 'handbrake' for you every time.

I tried this on a drive test and I'm not sure I'd like to hear those little electric motors putting the brakes on every time I come to a stop in stop and go traffic for example.

??? I don't hear anything when I do it, and I wouldn't expect to - the iBooster that is always active when you're braking provides the force for vehicle hold, just like it does when AP brakes and just like it does when you brake.

 

[cucubits]

Then this is different from the brake hold which is set when you press the brake pedal a little harder? That's when I heard these.

 

[ajdelange]

But that's not regeneration any more - that's me powering the car in reverse now. To regenerate, I have to let the rotor pull the field forward, and you run out of headroom as the car slows down.

Nothing I said is to be interpreted as requiring any action on your part. I am simply pointing out that there are no fundamental limitations in these motors to prevent dynamic braking down to 0. They can produce torque (in either direction) at and near 0 rotational speed.

 

[V1VrV2]

Yes, this is true. However, with creep off, when you come to a complete stop the hill-hold will automatically engage to prevent this.

Ah, good to know - I experienced a slight roll backward leaving the Delivery Center parking lot and that was enough to spook me - all of those new Model 3 and S sitting around waiting for me to crash into them with my new MX, felt like I was back in my manual gearbox driving days.

 

[Saghost]

Then this is different from the brake hold which is set when you press the brake pedal a little harder? That's when I heard these.

No, that is the feature we're talking about.

Not sure what noise you're hearing, but there aren't any extra electric motors involved in the brake hold, just the same one that provides the power brake assist during every stop.

 

[lakemirror]

Yes, this is true. However, with creep off, when you come to a complete stop the hill-hold will automatically engage to prevent this.

I think the holding brake has to be applied by a slight extra press on the brake pedal. I don't think it's automatic.

 

[Krazaak]

I'd say it's more like the car is pulling the 'handbrake' for you every time.

I tried this on a drive test and I'm not sure I'd like to hear those little electric motors putting the brakes on every time I come to a stop in stop and go traffic for example.

That sounds more like the brake being applied in park, hill hold shouldn't make any additional noise.

Nothing I said is to be interpreted as requiring any action on your part. I am simply pointing out that there are no fundamental limitations in these motors to prevent dynamic braking down to 0. They can produce torque (in either direction) at and near 0 rotational speed.

The motors can bring and hold the car to 0mph, but at the expenditure of energy, not recovery. So it's more efficient to use the brake to stop the car below the speed at which the energy recovered by regenerative braking.

I think the holding brake has to be applied by a slight extra press on the brake pedal. I don't think it's automatic.

It's automatic with creep disabled, once the vehicle comes to a complete stop. Only creep requires the extra pressure.

 

[Phil Seastrand]

I think the holding brake has to be applied by a slight extra press on the brake pedal. I don't think it's automatic.

It's automatic with creep disabled, once the vehicle comes to a complete stop. Only creep requires the extra pressure.

It's automatic on flat ground. If your on a hill, either up or down, you need to apply a little extra pressure to engage hill-hold.

 

[jboy210]

Ah, good to know - I experienced a slight roll backward leaving the Delivery Center parking lot and that was enough to spook me - all of those new Model 3 and S sitting around waiting for me to crash into them with my new MX, felt like I was back in my manual gearbox driving days.

Hill Hold looks like this on your dash. It should come on after a sec or less at a full stop. But be aware if you press the throttle or brake it disengages fast.

 

[DCGOO]

I'd say it's more like the car is pulling the 'handbrake' for you every time.

I tried this on a drive test and I'm not sure I'd like to hear those little electric motors putting the brakes on every time I come to a stop in stop and go traffic for example.

Try using TACC in stop and go traffic. Vastly less stressful.

 

[ajdelange]

The motors can bring and hold the car to 0mph, but at the expenditure of energy, not recovery. So it's more efficient to use the brake to stop the car below the speed at which the energy recovered by regenerative braking.

No question about that. People seem to be overlooking the fact that there just isn't, practically speaking, any energy to recover as the car slows down. At 1 mpH its kinetic energy (~250 J = 0.069 Wh) is 1/100th of what it is at 10 mpH (25,000 J = 6.9 wH) and that's 1/16th of what it is at 40 mpH (400,000J = 111 wH.)

 

[mbp11]

Thanks for the information on Hill Hold. I now have a little more information.

Hill Hold looks like this on your dash. It should come on after a sec or less at a full stop. But be aware if you press the throttle or brake it disengages fast.

View attachment 441800

 

[ebrown7b]

No, that is the feature we're talking about.

Not sure what noise you're hearing, but there aren't any extra electric motors involved in the brake hold, just the same one that provides the power brake assist during every stop.

The brakes used to have a separate caliper / pad on the rear wheels used for the parking brake. My 2013 Model S (P85) has a distinctive sound when it engages the parking brake. At some point, that was removed in favor of just keeping the main brakes engaged for the parking brake. I'm also not sure if the separate parking brake was a feature of all models or just performance models.

 

[Saghost]

The brakes used to have a separate caliper / pad on the rear wheels used for the parking brake. My 2013 Model S (P85) has a distinctive sound when it engages the parking brake. At some point, that was removed in favor of just keeping the main brakes engaged for the parking brake. I'm also not sure if the separate parking brake was a feature of all models or just performance models.

Yeah, but that's the parking brake. Vehicle hold isn't a parking brake function - it uses the iBooster to hold the main brake circuits engaged and the brake pedal depressed while you have the car stopped.

 

[V1VrV2]

Hill Hold looks like this on your dash. It should come on after a sec or less at a full stop. But be aware if you press the throttle or brake it disengages fast.

Thanks for the explanation and pic, @jboy210!

 

[jboy210]

Try using TACC in stop and go traffic. Vastly less stressful.

Agreed. Best part of the AP system.

Thanks for the explanation and pic, @jboy210!

No Problem. Play with for a day and you too will be converted over to the dark side.