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Why extra parking brake caliper?

Why extra parking brake caliper?

Why does the model s have an extra parking brake caliper on the rotors? Why not use the existing?
just curious about the engineering point of view... no other car seems to have an extra caliper for their parking brake

JayInJapan | 16. elokuu 2015

Shall I google that for you?

Roamer@AZ USA | 16. elokuu 2015

I think one is mechanical in operation and the other hydraulic. Hydraulic systems can not reliably hold pressure for long periods.

PTP | 16. elokuu 2015

but my wife's subaru has a parking brake which is electronic and it doesn't have another caliper.

JayInJapan: your response is why a lot of people don't stick around on these forums who might have something to offer others.

Roamer@AZ USA | 16. elokuu 2015

The Subaru probably just uses an electric pawl or actuator to lock the drive train components mechanically.

Or to reduce cost they make one combination caliper. You lose redundancy but it costs less.

murphyS90D | 16. elokuu 2015

My Ford Fusion is configured exactly the same way with an electrically operated second caliper on the rear wheels.

prp | 16. elokuu 2015

Agree with Roamer, you can have an electronic switch to a mechanical brake.

PTP | 16. elokuu 2015

I guess my question then would be if you can electronically activate a mechanical caliper, why add the second caliper? There would be 2 means of activating the same caliper, so what would be the advantage of the second caliper?

vlad22 | 16. elokuu 2015

I believe it's a fail safe in the tesla due to the fact that there is no "park" gear available.

Haggy | 16. elokuu 2015

I've seen it before on at least one other car, but I can't remember which one(s). On most cars with rear disc brakes, there are drum brakes for the parking brakes so there's no rotor to see. I'm fine with disc brakes and find drums more of a pain to work on.

Bikezion | 16. elokuu 2015

Redundancy. Safety. A parking brake is also an emergency brake. If you've overheated your brakes and they fail, the second caliper should still be usable.

EVino | 16. elokuu 2015

Here's a picture of the "baby caliper". I was curious about this too.

+1 patrickpettengill

Roamer@AZ USA | 16. elokuu 2015

@Bikezion +1

SUSTEKI.TOKYO.JP | 16. elokuu 2015

+1 JayInJapan was just stating the obvious.

Iowa92x | 16. elokuu 2015

What mclary said, how do people not....

prp | 16. elokuu 2015

Patrick the main car brakes are ydraulic, whereas the park brake is mechanical. Making one do both might be very tricky.

EVino | 16. elokuu 2015

Guys, where are your manners? There are new owners every day.

Tom_CH | 17. elokuu 2015

In our market (Europe) the handbrake must be a separate system, independent from the normal footbrake. This is for safety reasons that there still is an alternative should the normal system fail. (However, do not ask me how this works for the electronically actuated handbrakes...)

FelixMendeldog | 17. elokuu 2015

By law, there must be a secondary system for brake actuation to use in an emergency if the hydraulic system should fail; the secondary system is also functions as the parking brake.

Many cars use a cable actuation secondary system, cable hand-brakes are common (and very useful for manual hill hold on stick shift ICE cars); ratcheting foot brakes are also common. On cable systems, the cable actuator is piggy-back on the hydraulic brake calipers (or on older car, the rear drum brakes). These are simple and inexpensive to replace.

More recently, car companies started using calipers which integrate a computer controlled motor and screw design for the secondary actuator. Where this is a single caliper with dual actuation—hydraulic plus motor & screw—the calipers are really expensive and a pain to replace.

Tesla Model S is the first car I’ve seen (there must be others, but I have’t seen them) where the screw drive system is on a separate, smaller caliper. This is superior to having one hydraulic/screw-drive caliper because both caliper designs are simpler (one hydraulic, one motor & screw, no dual system calipers) and less-rugged motor & screw system—separate from the hydraulic caliper—is subject to less heat. These calipers will be easier to replace since one could replace the screw drive ‘baby’ caliper without messing with hydraulics. This will prove less costly to the owner of the Tesla when it comes time for out-of-warantee caliper replacement. Chainging the pads on the hydraulic primary caliper is also easier with the motor & screw system on a separate caliper.

On my 2006 Volkswagen Passat, I once awoke to a seized screw drive on one rear caliper. I do nearly all my own work, but I couldn’t work on these dual system nightmare calipers. The car needed a ride on a flat bed and two new, dual system rear calipers. Just to start, the rear calipers were 3.5 times more expensive than the fronts (because of the dual system) and even the though the hydraulics were perfectly fine, both entire calipers needed to be replaced because one screw drive was irreparable. Packing two systems into one caliper basically ensures they will be irreparable, forcing complete replacement. It became a $1500 job because of one seized motor, and that was half what VW ‘offered’ to charge me.

Just like my VW Passat, the screw drive caliper on a Tesla could seize and make the car immobile. However, this is less likely on the Tesla because the caliper design is simpler and subject to less heat. When it does happen, it is much easier and cheaper to replace a single screw-drive and does not require disconnecting hydraulics. It is also much easier to just get at a single system caliper. Another extremely wise design decision on the part of Tesla Inc.

JayInJapan | 17. elokuu 2015

Honestly, I asked the question because this topic has been written about here many times, the last of which was only 3-4 weeks ago. Carry on.

Mozart | 18. elokuu 2015

Tesla brakes are electrically operated, no hydraulics. There is no brake fluid in a Tesla

AoneOne | 18. elokuu 2015

@byrned: The main calipers are hydraulic. From the Model S owner's manual:

"Fluid Replacement Intervals...Brake fluid. Every 2 years or 25,000 miles (40,000 km), whichever comes first."

Rocky_H | 18. elokuu 2015

Thank you, AoneOne.

lengerardo | 18. elokuu 2015

The bleed fitting and hydraulic lines are clearly visible in the nice pic above.

Soukkis | 18. elokuu 2015

Teslas rear brake caliper
is fixed caliper and not sliding because fixed caliper is more maintenance free what is good if you don't use brake soy much than sliding caliper and because you can't build mechanicl or electrical hand brake devise in fixed caliper you must put hand brake in separate sliding caliper or drum

ca-blessed | 18. elokuu 2015

People (@JayinJapan specifically)-
There's no requirement to respond to any thread.
Why is there any sarcasm given to the OP? There will be many new owners and thus,many repetitive questions.

If you don't have anything nice to say, don't say it at all.
C'mon - that's Kindergarten 101.

Leeo | 18. elokuu 2015

How did you get a red parking brake caliper? Only my main calipers are red

vlad22 | 18. elokuu 2015

@byrned. Tesla does in fact have hydraulic brakes. In the event of a power loss you would still be able to stop the vehicle. If I read the diagrams correctly, at the point of power loss there is an accumulator that will engage the "parking brake caliper" in question and keep it locked until power is restored. This would keep the car from rolling away in situations outside of this topic as well.

FelixMendeldog | 18. elokuu 2015

The parking brake caliper is an electric screw drive—it does not require or consume power to hold, but it does need power to change state. Screw clockwise; screw counter-clockwise, pads grip; pads release. There is a problem if the parking pads are in the gripping state and then you completely lose power (exceedingly rare, but it could happen, and may have happened to a couple owners). That’s at least one reason why Tesla provides terminals behind the nosecone to ‘jump’ the 12v battery: to provide the power necessary to back the screws out to release the parking brake caliper’s grip.

@byrned is either trolling or joking—no one is that dumb. As @lengerardo pointed out, one can can clearly see hydraulic lines and bleeders on the large calipers in every picture of Telsa brakes, not just the picture posted on this thread.

jordanrichard | 27. elokuu 2015

First, there are no "emergency brakes". These little pads are not going to stop a 4,700 lbs car. Even on any car, the "emergency brakes" are not that. It is a parking brake. This goes back to the days when cars were stick shifts and you put this park brake on, just in case the transmission popped out of gear.

Every car has a duel circuit system. The brake fluid reservoir has 2 compartments. One feeds the left front and rear right brakes. The other serves the other 2 corners. This is for in the event that a hole develops in one line, it doesn't take out the whole front or rear brakes.

Haggy | 30. syyskuu 2016

Emergency brakes can stop a car, but whether they stop it "on time" (whatever that means) is another story. The parking brake pads have about three square inches of surface. That's not a lot compared to the standard brake pads, which are designed to stop a car as quickly as possible in a worst case scenario using two wheels, (they aren't designed to stop a car when there's a complete failure so the worst case scenario in which they actually work is two wheels) but it could still stop a car even if it takes many times the stopping distance. The coefficient of friction compared to other pads is likely the same, they are at the outer edge of the rotor, which would require the least force, and the clamping force is not something we'd know, but with a worm gear it could easily be as much as or far more than what we get with a hydraulic system. I don't have nearly enough information to do the math, but if you are driving on a local street with a relatively low speed limit, you could expect the emergency brake to stop the car...eventually. In any event, if you compare it to traditional parking brakes that use a cable hooked to both wheels, connected to another one that pulls that as much as it can depending on how well you adjusted your parking brake after the cable stretched, I'd expect the Tesla to do better. But I'm not planning to test it out.

But it's a moot point for most people because chances are almost none that you'd even need to try it. The last time I had a hydraulic brake failure that rendered the brakes inoperable was on a 1965 Dodge before there were dual master cylinders. Even at that, the pedal went soft, but even with a leak it was possible to pump repeatedly and pull over before there was too little fluid left to stop the car in local traffic.