That's a great point. Uninitiated passengers would probably look for an ON/OFF button like they're used to seeing.
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How to avoid a runaway condition
- Thread starter davidslagle
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That's a great point. Uninitiated passengers would probably look for an ON/OFF button like they're used to seeing.
Shock-On-T
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Consumer Reports did a follow up study which contradicted their earlier report.
The follow up study received far less publicity (as null result studies often do).
I did include a reference with my post which goes into the full details, perhaps if you still disagree you could mark a disagree on their site rather than my post.
Braking is reduced in some cars that use vacuum brake boosters. When at full throttle, there is no vacuum in the engine.
No Tesla relies on engine vacuum to boost the brakes, so this isn't relevant to electric vehicles.
That video was in relation to the Lexus accident, which was found to be caused by "pedal entrapment" from floormats. Thanks to changes stemming from that accident, brake override systems are now standard.
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Sorry for reviving this discussion, but the OP has touched my concerns quite close. After reading throughout the whole discussion and a little tech research on braking my worries haven't been eliviated a bit. They don't apply exclusively to EV/Tesla, but to classic ICE cars as well, -but less so.
Imagine yourself going downhill after fully charging at your at home. In case of an electrical (or other) failure your main brakes might stop working partially (no servo boost) or completely (blown fuse, software error, leaking hydraulic system etc.) and you would get into such a "runaway condition".
In an ICE you always have mechanical motor braking available to get the car to slow down, even on steeper slopes when in first gear. This is comparable to regen-braking on an EV, but as we all know, this isn't always available (=fully charged or cold battery) and would be a very probable situation when starting your downhill journey.
What options do you have now while the car keeps accelerating? As mechanical handbrakes are more and more replaced by electronic parking brakes in all cars I would keep pressing the "Parking brake button" as instructed, but it works only if there is electricity present to run the actuators at the rear brakes (a known disadvantage according to wikipedia). Sure, this last resort applies to ICE cars with electronic parking brakes just as well, but here I still have the motor braking available all the time as a backup to slow me down.
Maybe the OP exaggerated the hypothesis a bit ("meltdown") but keep in mind that we have a car quite close to formula 1 specs in driving dynamics on one hand and look at their brakes glowing hot when these cars go through corners on the other hand. Now guess how long these brakes would work when trying to slow down a "runaway of 600 horses at constant full throttle" and 2 tons of weight. I don't know, but would have loved to have read some technical reassurance instead of suggestions like "Hit. the. brakes." or similar.
Disclaimer: Flawless MS90D from 2017, private owner planning to keep it forever, no direct or indirect involvement in car business, about 12.000 kilometers in Central Europe, partially in a rented Tesla (prior to ownership), technically inclined and long time EV observer convinced about the future of EV cars in general and mine especially.
You're really struggling to find a problem here. The latest hypothetical has:
* charging to 100% at the top of a hill to disable regen (anyone who lives on a hill knows better)
* leaking hydraulics to disable main brakes
* no electricity to make the parking brake work
* lots of electricity (and a broken throttle sensor) to make the car go full throttle
* brake override not working to cut throttle
If you're going to assume 5 simultaneous failures of different systems, some of them in conflicting ways (no electricity for parking brake and still full throttle?) then of course you can make any car fail. You would be in even more trouble if a meteor landed on the car's roof in the middle of that scenario.
* charging to 100% at the top of a hill to disable regen (anyone who lives on a hill knows better)
* leaking hydraulics to disable main brakes
* no electricity to make the parking brake work
* lots of electricity (and a broken throttle sensor) to make the car go full throttle
* brake override not working to cut throttle
If you're going to assume 5 simultaneous failures of different systems, some of them in conflicting ways (no electricity for parking brake and still full throttle?) then of course you can make any car fail. You would be in even more trouble if a meteor landed on the car's roof in the middle of that scenario.
Do you? If the car is stuck in full throttle, it's not going to brake because of the motor. You're allowing for multiple simultaneous catastrophic failures in the Tesla, but not in the ICE vehicle.
Joe F
Disruption is hard.
Yeah, but since there's no solid roof now, you'd at least have a great light show!
No, the Tesla's brakes don't require electricity to work, they have a traditional hydraulic brake fluid. It will use an electric booster so your leg doesn't get tired, but that isn't needed to stop the car. As people have said earlier, brakes are more powerful than motors, so in any scenario where you haven't lost the main brakes, you just step on the pedal to stop.
If you have lost the main brakes, you still have the regen and the parking brake to stop you. Again, unless we're assuming simultaneous failures, that's 3 independent ways to stop the car.
If you have lost the main brakes, you still have the regen and the parking brake to stop you. Again, unless we're assuming simultaneous failures, that's 3 independent ways to stop the car.
@radio I'm not sure how your car can be going full throttle when, in your example, power has been cut to other electronic systems including braking and emergency braking. Also, my understanding is that the brakes can still be actuated if the power and/or booster fails. Your premise would require power to fail in all systems except to the motor, but the motor does not operate without the computer and other systems to run it. I don't believe the type of failure you hypothesize is possible.
Sorry if my post gave the impression everything occuring at the same time, -just the opposite was meant: either/or aspects. To put it as simple as possible:
What do you do when driving away with a cold battery downhill (which is normal and frequent) and as a single fault hydraulics fail?
I would try press the parking brake stick continuously and only hope it is a very slight downhill as these brakes were not built to slow the car as means of deceleration.
In that condition I'd probably rely on the combination of regen and emergency brakes. In an ICE car in a similar situation, I'd rely on the engine and emergency brakes to much the same effect(although engine braking tends to be less effective at slowing than regen).
Joe F
Disruption is hard.
Seriously? Don't do that. If you live on a mountain and you know you have a long trip downhill, you as a knowledgeable and responsible Tesla owner know that you need to rely on regen to control your decent. Unless you like wearing out your brakes for some unknown reason. Also, you as a Tesla owner, know that regen is not possible with a cold battery, as such you would ensure your battery was charged just prior to your departure such that is was not cold.
Also, do you know for a fact that the hydraulic system is a single piston, single line system? They're have been dual chamber master cylinders feeding both axles independently for decades. I don't know as I've never looked at mine, hence the reason I'm asking.
I'm nearly positive is a dual master feeding diagonal pairs. Actually, I don't think anything else is legal for a passenger car sold new in the US these days.
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