Tesla Model S in Albuquerque’s ‘snowstorm’ during NY-to-California road trip [photo: David Noland]
Last summer, I wrote an article patting Tesla Motors CEO Elon Musk on the back for being so responsive to Model S electric-car owners.
Of whom I am one.
But in 2015? Not so much.
I ended that article with a plea to Musk for a safety upgrade on the Model S: a firmware change to cut off power to the wheels if the driver inadvertently presses the accelerator pedal while braking.
DON’T MISS: Tesla CEO Elon Musk’s Personal Touch: Secret To His Success? (Aug 2014)
Due to the close spacing of the brake and accelerator pedals in the Model S, this is more likely to happen in the Tesla than most other cars.
It’s happened to me several times–I have big feet–which is what led to my writing about it a year ago.
Tesla Model S electric-car road trip, Route 66 Museum, Elk City, Oklahoma [photo: David Noland]
And at last count at least 17 different Model S owners had reported the same thing on Tesla forums.
The both-pedals-pressed syndrome drastically lengthens stopping distance, and can be potentially hazardous.
ALSO SEE: Life With Tesla Model S: UPDATE On Pedal Placement Problem (Mar 2014)
Ironically, the only accident I’m aware of that can clearly be attributed to the double-pedal problem—a minor front-end bash—occurred at a Tesla-sponsored test-drive event at the factory.
In writing that article, I was hoping Musk would respond as quickly and fully as he did to a previous plea for an extended powertrain warranty for the Model S.
In that case, last August, Elon announced a 10-year, infinite-mile warranty on the Model S drive unit just seven days later.
Tesla Motors CEO Elon Musk at Tesla Store opening in Westfield Mall, London, Oct 2013
Quick response, but confusing
Sure enough, Elon’s response to my plea for a power cut-off when both pedals are pressed was quick.
The very same day, he tweeted to his one-million-plus followers, “Model S limits torque if brake and accel simul pressed. Going to zero torque with brake press would be a safety hazard.””
MORE: Tesla Model S Drive-Unit Replacements: How Big A Problem? (Aug 2014)
But for me, Musk’s tweet raised more questions than it answered.
To what level was the torque limited, and under what conditions?
2014 Tesla Model S P85D, road test, Dec 2014 [photo: David Noland]
And how exactly would “going to zero torque with brake press” be a safety hazard?
What confused me the most, however, was this: Musk’s tweet simply didn’t jibe with my own testing of my car.
Power cuts off…sometimes
I’ve found there are two completely different both-pedals-pressed situations in the Model S.
And the car responds differently to each one.
1. When the accelerator pedal is the first one pressed–say, if you’re driving along with your right foot on the “gas” and you then step on the brake pedal with the left foot–the power appears to cut off completely.
The orange power arc drops to zero and the car slows immediately.
Tesla Model S in Albuquerque’s ‘snowstorm’ during NY-to-California road trip [photo: David Noland]
Is this what Musk meant by the torque being limited? How is it merely “limited” if the power meter goes to zero?
This appears to be precisely the zero-torque condition that Musk tweeted would be hazardous.
2. But when the brake pedal is the first one pressed, followed by the accelerator–as in the potentially dangerous inadvertent both-pedals-pressed situation that I and other Model S owners have experienced–the torque does not cut off, or even appear to be significantly limited.
In my own brake-then-accelerator tests, I saw 160 kW indicated on the power meter with both pedals pressed in this manner–and that was with only partial application of the accelerator.
That’s hardly “limited”: 160 kW is the equivalent of 215 hp, or about eight times the power required to maintain a steady 60-65 mph.
(Unfortunately, I lacked the nerve to floor the accelerator completely during these tests to find whether maximum power is available with the brakes on.)
Frankly, Musk’s Twitter response had me totally baffled.
It flew in the face of my real-world experience with the car, and simply didn’t make much sense without further explanation.
More than a tweet
Realizing that 140 characters are hardly enough to discuss a complex issue like this one, I sent Musk an e-mail asking for clarification of his tweet.
Over the past couple of years, he’s quickly responded to several previous e-mails of mine, so I had at least some hope of a more detailed response.
Alas, it was not to be.
Six months later, there’s been no response from Tesla’s CEO.
Official company response
However, an inquiry to Tesla’s public-relations department eventually elicited a response that confirmed my impressions.
According to Tesla’s then-PR chief, Simon Sproule last fall, “If the brake is detected as pressed after the accelerator is already pressed (brake over-ride condition), the motor torque is reduced to zero at fixed rate.”
“If the accelerator is detected as pressed after the brake is detected as pressed (“both-pedal press” condition used for hill start, by drivers using both feet), the current motor torque is limited to no more than 250 Nm.”
“However, with hill start control now standard on all cars (from the software release in April), this is becoming less common.”
“Whenever the brake is no longer pressed, in either case, the torque returns the accelerator position requested torque at a fixed rate.”
Torque limit: not enough?
So Musk’s tweet that torque is “limited” in a both-pedals-pressed situation was technically correct half the time.
My own tests firmly convince me that 250 Nm of torque is far from a sufficient limit. It’s just not limited nearly enough.
To put that number in perspective, the Model S’s 250-Nm (185 ft-lbs) torque “limit” with the brake pedal pressed is more than the maximum torque available in a base Toyota Camry mid-size sedan.
And 250 Nm is 57 percent of the Model S-85’s maximum available torque of 440 Nm (325 ft-lb).
The Model S has no dashboard readout for torque, but the 57-percent figure agrees closely with my observed test results for power available with brake pressed: 160 kW, or 59 percent of the car’s 270 kW max power. (At a constant rpm, power is directly proportional to torque.)
Bottom line: 250 Nm of torque is more than many cars produce with the accelerator floored.
Tesla Model S in Albuquerque’s ‘snowstorm’ during NY-to-California road trip [photo: David Noland]
It’s more than enough to increase braking distance of the Model S drastically if both pedals are inadvertently pressed.
Even this level of “limited” torque with both pedals pressed is still a potential safety hazard.
No longer justified
Sproule’s comment about the hill-hold function suggests that this may have been Tesla’s original reasoning for not cutting off power completely in the brake-first scenario.
A total power cut-off might have made hill-starts a bit trickier.
But that justification–however tepid it may have been in the first place–has now vanished: For almost a year now, every Model S has been upgraded with an automatic hill-hold function
And that update seemingly moots any need for pressing both pedals.
However, current Tesla Communications chief Ricardo Reyes says, “Hill hold prevents cars from rolling back for only a short duration of time.
“It is not intended or designed to provide the type of specific driver control provided by the brake/accelerator logic..
“For example when parking or maneuvering on an incline in cities like San Francisco or Boston, some torque applied to the accelerator is desirable, even when the brake is first applied.
“A driver may be required to maneuver back and forth several times while ensuring little to no rolling of the car except under power.
“Allowing limited accelerator commanded torque in these circumstances, even with brake application, ensures that is possible.
“We believe this logic best balances safety with driver usability.”
Yes, but…
Frankly, we must disagree.
A hill-hold function is perfectly adequate for the hilly parking situation Reyes describes, as long as it’s working. Yes, the Model S hill-hold function cuts off after 1-2 seconds.
But if the only justification for the double-pedal logic is that the hill-hold function cuts off too soon, then the solution is simple: Fix the hill-hold function.
If the hill-hold function holds indefinitely until the accelerator is pressed—as it does, for example, in cars as diverse as BMW, Mercedes-Benz, and Subaru–then the double-pedal logic becomes entirely unnecessary.
Bottom Line
Clearly, now that every Model S has a hill-hold function, the potential hazard of an inadvertent double-pedal during braking far outweighs the benefit of any conceivable intentional double-pedal situation.
And a better hill-hold function would entirely moot today’s tissue-thin justification for the double-pedal logic.
So I’ll say it again:
Please, Elon. You’ve often said that safety is your top priority.
Show us you mean it.
Change the both-pedals-pressed firmware, before somebody gets hurt.
________________________________________________
Follow GreenCarReports on Facebook, Twitter, and Google+.
View original article at : “https://www.greencarreports.com//news/1094404_tesla-model-s-double-pedal-behavior-still-inconsistent-a-safety-plea-to-elon-musk”
