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Hill Hold Function
- Thread starter grisnjam
- Start date
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- Tags
- Driving Dynamics Model S
It's interesting what changes can be done to a car that is largely software controlled. It doesn't seem at all unreasonable that they could add break pedal integrated regen, hill hold, and coasting (free wheel) along with the current creep as user selectable options completely in software.
Just brought my new Model S home last night and I really missed the hill assist feature. Here in South Florida, we don't have too many hills, but it would be great if we didn't need to keep one foot on the brake pedal to keep the car from rolling forward or backwards on a slight incline. I'd call it more of a red light brake hold than a hill assist.
Any word on an update for this?
Any word on an update for this?
It's actually a lot harder to add than it looks. I started thinking about how to implement hill hold, and... it's not straightforward at all.
Um. This maybe is too obvious but...
Have any of you tried to just use the accelerator? That's what I do; just give it a little power and it holds just fine. It is like the old style feathering the clutch. Fun for the bored too; roll forward and back if ya like.
Mostly I just use brake and accelerator tho -- the power is instant, so it is super easy to just go one to the other.
Have any of you tried to just use the accelerator? That's what I do; just give it a little power and it holds just fine. It is like the old style feathering the clutch. Fun for the bored too; roll forward and back if ya like.
Mostly I just use brake and accelerator tho -- the power is instant, so it is super easy to just go one to the other.
contaygious
Active Member
htsai14752
Member
hill assist would be nice. I was trying to reverse on a downhill and I almost hit my friends car. From that day on I keep my car on creep mode.
I like creep in general. But when I tried no creep, the lack of hill holding defeated the whole point to me. The point of no creep would be minimize the need to use the brake pedal. BT if you have to use it anyways due to even relatively slight inclines, then it just serves as an annoyance IMO. (Not going to argue creep vs no creep here, there's already a thread for that. I'm just using this point in support of the need for hill holding function for no creep mode, even if I still wouldn't use it.)
artsci
Sponsor
I turned on the creep function precisely because of the backward drift on hills. It's like having a car with a clutch. Otherwise I'd keep creep off. I'd like a hill hold function for sure.
In case Tesla is listening, here's what I'd like for a Hill Hold functionality (when enabled):
1. (Required) If the vehicle is in Drive, gravity will never make it go backwards for "within tolerance" inclines (90 deg is not within tolerance for example).
2. (Desired) If the vehicle is in Drive, facing a "normal" downhill, not moving, and the brake pedal is released the car does not move forward. I'm ok with a bulldozer or a significant downhill defeating Hill Hold, but I'd like to see the vehicle max out regen first.
1. (Required) If the vehicle is in Drive, gravity will never make it go backwards for "within tolerance" inclines (90 deg is not within tolerance for example).
2. (Desired) If the vehicle is in Drive, facing a "normal" downhill, not moving, and the brake pedal is released the car does not move forward. I'm ok with a bulldozer or a significant downhill defeating Hill Hold, but I'd like to see the vehicle max out regen first.
You don't get regen while standing still: to hold the car stationary on a slope using the motor would require burning a significant amount of power. An efficient implementation of Hill Hold (on non-trivial gradients) is going to need to use the parking brake, and blend out motor power as the parking brake engages/blend in motor power as you press the accelerator to move away. Depending how quickly the parking brake mechanism moves, this will presumably introduce some lag in response to the accelerator.
Given that, I think I would prefer to have the car roll forward with the footbrake released, though I can see your argument that it would be logical for Hill Hold to be symmetric.
I disagree with (2) as stated. If I release the brake in Drive, I think the car should be able to move forward. If I release the brake in Reverse, I think the car should not move forward.
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I'm not convinced about "significant power". If significant power means several kW, sure, it would take significant power, but we're not talking about tens of kW. Try it some day using the go pedal. The orange bar barely moves above 0.
I can't do it perfectly on a steep hill, but I can do it well enough to see how little power it takes.
I feel a little catch when the car switches from moving backward to moving forward, but that's a very minor nit.
I'm not saying Tesla should implement the surprisingly low-power solution when they could implement a no-power solution; I'm just saying the non-zero power solution might not be as power hungry as you expect.
I agree - by "significant power" I had in mind 10kW or so on a slope steep enough to make hill hold relevant (on a very shallow slope, you don't really need hill hold in the first place).
It's obviously a matter of taste whether that counts as 'significant'. One point is that 100% of that power is going to heat (whereas in normal driving at 10s of kW, most of the power is doing useful work and only ~10% wasted in heat).
I will admit that it's not a huge deal in terms of range: even if you were stuck in traffic creeping slowly up an extremely long 10kW hill, the 85kWh battery would last you 8.5 hours.
Just to clarify, in my 2.5 Sport you can definitely apply power to the motor while holding the brakes, that's how I "launch" it.
I suspect less energy would be used in this scenario than if the car did start to roll backward. Restated, it probably takes less energy {to hold the car in place} than {to stop it from moving backward, and then get the car to regain the elevation that it lost}.
yeah, using the P-brake might take even less energy, but I think it's worth noting that using the motor for hill hold could take less energy than no hill hold at all.
arg, have you seen the car require 10 kW to stay in place? I don't think I've seen it take even half that much, but it's likely that I'm mis-remembering.
In situations where I recall being frustrated at the missing feature, the consumption to simulate it was always more like 1-3 kW.
No, I am not currently an owner (being in the UK). The 10kW figure came from your and other people's comments further up thread. My starting to comment on this in the first place comes from my experience with other electric drives where running the motor at a stall rapidly results in smoke coming out of the windings, while you can run at really quite low speed and reasonable power without the motor getting noticeably hot. Obviously, the Model S benefits from a water cooled motor and so overheating isn't an issue, but the point about zero efficiency at the stall still applies.
I will try to work out some figures to see what sort of number we should be getting theoretically - I apologise for picking a number out of the air like that.
