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Torque sleep not functioning properly on some cars?

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I suspect it's simpler than this. When the car is at a steady state speed, it requires x horsepower to maintain that speed. Tesla sets a buffer over and above x for hills, passing, and general responsiveness. When the front motor alone can produce x+y horsepower, it sleeps the rear motor. When it can't, it runs both.

OK, but we're kind of saying the same thing.

It takes more horsepower to maintain the same steady speed on flat ground if the temperature is colder. So it's possible that simply due to the cold, the limitations of the front motor, and the value Tesla is using for y, torque sleep isn't happening at all at highway speeds in the cold.

And if that is true, Tesla should have anticipated this issue, and informed us about it. There's nothing in the JB Straubel blog post that indicates that torque sleep won't work if it's cold.

This would be kind of a major issue for those of us worried about range, living in cold climates. Because we had the initial range estimates, then we had the whole reduced range issue, and that was largely resolved by the blog post and the promise of torque sleep. But it is the winter when I'm most worried about range, because I know that's when my range is going to be the shortest. If I'm not getting the benefit of torque sleep whenever it's cold, that's a pretty significant change.
 
It takes more horsepower to maintain the same steady speed on flat ground if the temperature is colder.

Why would this be true? It doesn't make sense to me: why would the mechanical power needed to power the wheels to counter wind resistance depend on temperature?

I imagine other things are affected by temperature, like how much power you need to draw out of the battery (let's say, if you need to have the heater on, or condition the battery's temp, etc), but I don't see how it would affect the subsystem that is used to keep the car moving. As far as that one is concerned (which is the one that cares about TS), it shouldn't make that much of a difference, IMHO.

Unless I'm missing something...

-- Greg
 
I agree with Greg. The HVAC and other accessories shouldn't have anything to do with torque sleep. It seems to me that the algorithm should be basically this: at any given time maintaining the current speed needs X amount of torque at the wheels. That force is produced by some split between the two motors. But it's not necessarily 50/50. The front motor is more efficient (it generally produces more torque for the same number of kilowatts though neither of the motors' efficiency curves are linear). So the algorithm determines the split between the two motors in such a way as to maximize efficiency. Sometimes, maybe often, that means a 100/0 split hence the term torque "sleep". But it's no doubt more complicated
 
Why would this be true? It doesn't make sense to me: why would the mechanical power needed to power the wheels to counter wind resistance depend on temperature?

Because colder air is more dense, and the denser the air, the greater the affect of drag.



Colder air is more dense, so the resistance is higher.

Yes, exactly.

I thought that was just understood.

Here's one of many threads on TMC that talk about it a bit: Range vs. air temperature according to AAA

Because the Model S is so aerodynamic, the negative impact of the worse drag is probably more significant than in a less aerodynamic car.
 
Colder air is more dense, so the resistance is higher.

I didn't think it would affect it that much, but after looking at the drag equation, it seems like it could actually be noticeable if the temperature delta gets above 10-20 degrees (Celsius/Kelvin). So yes, a few degrees are probably not noticeable, but if we start comparing Southern California with Canada, I think it would show.


- - - Updated - - -

Because the Model S is so aerodynamic, the negative impact of the worse drag is probably more significant than in a less aerodynamic car.

Not sure what you mean wrt air density (and temperature).
If I read the Drag Equation correctly, it seems that with an aerodynamic vehicle, the drag coefficient is small(er), so changes in air density affect the drag force less (since it's multiplied by it).
In other words, an aerodynamic vehicle will suffer less from lower temperatures.

-- Greg
 
Now putting things in perspective with the hypothesis submitted above, the change in air density from 60F to 15F is roughly 10% according to this graph. Such variation in density affects the drag is the same way a variation of roughly 5% in speed.
So Andy if you want to test your hypothesis, wouldn't you simply need to drive your car around 62 MPH (instead of 65 MPH) and see if you "feel" TS working?

-- Greg
 
Have you compared some trips to EV Trip Planner estimates to see how your numbers look relative to some of us?

I tried it when it didn't have the P85D option before, but not since. At the time I didn't think I could really trust its data since it did not have estimates for my car.

I admit I'm not as committed as you are to this cause (hence much less diligent and not investing as much time). Also most of my trips are spontaneous without much planning ahead, so I'm not particularly spending time figuring out numbers for my consumption.
This will probably change when I do some longer trips where I may need good reassurances that I can reach my destination, but at the moment I've only cruised around the area never really fearing I'd be out of juice at any point.

Sorry - I realize I'm not very helpful, but it's the true answer to your question :)

-- Greg
 
Not sure what you mean wrt air density (and temperature).
If I read the Drag Equation correctly, it seems that with an aerodynamic vehicle, the drag coefficient is small(er), so changes in air density affect the drag force less (since it's multiplied by it).
In other words, an aerodynamic vehicle will suffer less from lower temperatures.

-- Greg

I expect you are correct about that. I was probably just thinking about it the wrong way.




Now putting things in perspective with the hypothesis submitted above, the change in air density from 60F to 15F is roughly 10% according to this graph. Such variation in density affects the drag is the same way a variation of roughly 5% in speed.
So Andy if you want to test your hypothesis, wouldn't you simply need to drive your car around 62 MPH (instead of 65 MPH) and see if you "feel" TS working?

-- Greg

I drove some today, and tried to "feel" or see a drop off when I reached 45. I couldn't do it.

In theory, if we wanted to spend a month driving the regular route at 60 instead of 68 and 70, we might get enough data to test my theory, but we'd also be wasting a lot of time, and be a bit of a hazard on the road. So we're definitely not going to do that.

I may try driving on the highway briefly at 60 or so the next time I make the trip, just to see if I can see or feel anything, but I doubt that's going to be very conclusive.



I tried it when it didn't have the P85D option before, but not since. At the time I didn't think I could really trust its data since it did not have estimates for my car.

It didn't really matter how accurate it was for our cars. I was only concerned with using it as a measurement metric for my car vs. other P85Ds. So as long as it was consistent, it didn't matter if it was inaccurate with respect to the P85D. (Does that make sense?)


I admit I'm not as committed as you are to this cause (hence much less diligent and not investing as much time). Also most of my trips are spontaneous without much planning ahead, so I'm not particularly spending time figuring out numbers for my consumption.
This will probably change when I do some longer trips where I may need good reassurances that I can reach my destination, but at the moment I've only cruised around the area never really fearing I'd be out of juice at any point.

Sorry - I realize I'm not very helpful, but it's the true answer to your question :)

-- Greg

I appreciate your interest and help.

I've never taken the car out of the area either, so range hasn't been an issue yet. When I purchased the car, I thought I'd be able to take it to my mother's house in northern NJ. I now realize that until there is a supercharger in Binghamton, that trip is probably out of the question. And even after there is a supercharger in Binghamton, I don't think it's a trip I'm likely to undertake in the winter. It'll be easier and safer to just take an ICE. I'm somewhat disappointed about this.
 
I don't have a P85D - just a lowly P85 - but I recently made two identical trips on two different days, and look at the results...

Two days ago I drove 70 miles or so. It was in the low 60s where I live. I drove 70-75 MPH on the freeway. My average energy consumption for that trip, according to the "Since Last Charge" screen, was around 310 Wh/mi.

Today I made the same trip. It was in the mid 70s. I drove 65 MPH on the freeway. My average energy consumption for this last trip - an identical route - was 266 Wh/mi.

That's a difference of about 15% within two days, on the same exact route.

Wind is huge - even very little of it. I did a return trip yesterday, ~90 miles each way.
Weather identical: ~45F, sunny, mild wind from WNW at 5 mph, gusts to 9 mph. HVAC off both, so not an issue, battery warm both ways (just finished range charge before departing, almost immediate return.

1. Going North to Minneapolis, I had to slow down almost immediately (5-10 mi into the trip) because the predicted battery charge dropped rapidly. I ended up with the following figures:
TACC speed to 65 mph almost throughout; 92.6 mi, 34.9 kwh, 377 Wh/mi.
2. Coming back:
TACC speed to 73 mph; 91.3 mi, 31.4 kWh, 344 Wh/mi.

So I used 10% less on the return trip despite going 10% faster. And this is really with mild conditions....
 
I guess a few degrees make a huge difference. Today the temperature shoots up to over 50F, and the 5 mile chart for the first time dropped under 300whm (between 280 and 300) - even with sunroof open.
The 30 mile chart got about 330whm.

interesting though my life time was about 440whm, but half time (trip B) - was about 470whm -- I reset it after getting the torque sleep. Note that I did not have the range mode all the time, especially the firmware issue.

I would blame that for the extreme cold February... torque sleep is no match to cold.

even today's average was about 370 -- as in the morning, it was still around 27F (and afternoon 52F)

thanks
 
I am amazed at the efficiency improvements with temperature. Today it was near 50F for the first time since I received my P85D. My average kWm is just below 500. I did not use range mode for most of the past 2 months. Brutally cold Jan and Feb. Today, I was averaging around 310 kWm. I do a mix of city and highway. My highway was in the 200's crazy! So I think temperature outside is a huge factor. I'll take more accurate numbers but I think I lose 10% efficiency for every 10 degrees below 50F.
 
Today's values at 73 mph, virtually no wind (2 mph), highway on TACC:
morning at 37F and some wet pavement: 429 Wh/mi for 45 mile trip
afternoon at 52F dry 360 Wh/mi for return 45 mi trip.

Not sure how others get < 300 Wh/mi now, I drove really sedated.
 
Today's values at 73 mph, virtually no wind (2 mph), highway on TACC:
morning at 37F and some wet pavement: 429 Wh/mi for 45 mile trip
afternoon at 52F dry 360 Wh/mi for return 45 mi trip.

Not sure how others get < 300 Wh/mi now, I drove really sedated.

The speed probably has a lot to do with it. Some have suggested torque sleep doesn't kick in above 70 or so. If that's true, you're paying a double penalty for the higher speed. If you feel like it, try a trip at 65, (in similar weather) and see if it makes a big difference or not.
 
HI,
I've finally had the opportunity to do some highway driving and I took shots of all the trips, energy graphs etc. so I will contribute if useful to other threads and spreadsheets etc. One thing I noticed as a quick nugget is that my efficiency was closest to EV Trip planner on the last leg of my trip. I did my trip in 3 legs and what is unique about the last leg is that for the final chunk of it the road is relatively flat, albeit a very long gradual downhill. The rest of the journey was on some fairly mountainous roads. I also noticed that in comparison to my P85+ on the same journey (adjusting for a few differences) it seems this leg was closest to the same. My assumption from this is that when there are uphills and downhills it is less likely for torque sleep to engage - need the rear motor for steep uphills, thus the P85D will be less efficient than its predecessors. For the long, relatively straight, downhill leg, the car achieved nearer to EV and non P85D cars as presumably torque sleep could be engaged for most of the latter part of this leg. It is possible that if I had only been measuring for the long downhill stretch (first part of the leg was still a bit hilly) the P85D might have been even more efficient than its predecessors.

My observation from this is