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garygid
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 8:18 am

In the LEAF, the Parking Brake "clamps" the rear DRUM brakes, not the rear DISC brakes (the LEAF has BOTH).
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 8:54 am

planet4ever: Thanks for your response. I guess in the interest of avoiding confusion I will use the terms "parking lock" and "emergency brake". The former term seems entirely accurate in describing its function, and the latter term although not entirely accurate (since it plays a major role in parking) is an older term that is entirely accurate in that it can be used if the manual hydraulic brakes should somehow fail -- and I don't want to forget that! And most people are used to using the "emergency brake" for parking safely...

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Ingineer
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 9:45 am

FYI: The Brake capacitor has nothing to do with the parking brake system or the park pawl actuator.

If the 12v system is offline, you will not be able to disengage the park pawl (or engage it), and you cannot engage the parking brake, but you can disengage it from the manual release. If you had to, I suppose you could dismantle the actuator from the transaxle and manually engage/disengage it with a pair of pliers.

The Hydraulic brakes will still function normally for a handful of stops until the capacitor depletes, then you will still have some function, but it will require substantial pedal effort. (no boost will be available)

I suspect there is at least 10 watt-hours of usable energy (12v output) in the brake capacitor. At some point I'll do an accurate test.

-Phil
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Ingineer
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 9:55 am

Oh and one more thing: I believe that for normal parking situations you do not need to bother with the parking brake. If you are parking on a moderate or steep hill, I would use it in that case.

The park pawl mechanism is very reliable, it's almost the same as the system used in the Prius. I've never seen one fail unless the car was in an accident.

However, that conglomeration in the back, especially if you live in areas with high salt exposure, is suspect. Though there is an argument for occasional use just to keep things from seizing up.

If it were me, I wouldn't use it in the winter unless I had to (steep hills, ice, etc), and instead use it once a week or two in the summer for exercise.

-Phil
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BnBinSD
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 10:09 am

In the Owner's Manual, the parking brake is mentioned several times. In the first mention (I think), it states to "apply the parking brake twice for maximum effect" or some such, but in subsequent discussions - especially parking on hills, it's never mentioned again.

Can anyone confirm whether applying the parking brake twice truly applies more force than a single application?
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 11:14 am

Transmission Parking Lock may be more descriptive, or just P as used in automatic transmissions.. and put it in a pushbutton on the console along with D, N, ECO and REVERSE, in the usual order... Emergency Brake is a good one for the other one.. such complexity has to add to the cost.

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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 11:24 am

Emergency Brake is not quite right, since it's not used in emergencies. Unless it's a big handle you can yank and slide the rear, I just don't see it being that useful in crisis. And it is used during routine parking. Parking Brake seems like the right name for it.

Is there something legitimately called a "transmission" with one gear? If so, then tranny lock sounds correct to me.


I'm on the fence.. My usual shutdown has been foot brake, parking brake, then OFF.
If I can ignore the parking brake, then it's just... Foot brake, OFF.

I just don't like the feeling of the car 'rolling into' the transmission lock. Feels wrong. Old habit, I guess. I prefer to let off the footbrake and feel the parking brake hold it right there.
Given that there have been reports of either the parking pawl failing, or damage to it from long term use as a parking stop, I guess I can let go of my parking brake habit.

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aqn
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 6:45 pm

MikeD wrote:aqn: Exceptionally clear and helpful. However, on my last question about whether or not the "parking lock" is "safe enough" for most parking situations, I notice the following from the Owner's Manual: "CAUTION: To park the vehicle in cold climates, push the P position switch on the selector lever and place suitable chocks at both the front and back of a wheel with the electric parking brake released. If the electric parking brake is applied in cold climates, the brake may freeze and cannot be released.". So I gather both brake systems have their limitations and strengths.
Indeed. It's not uncommon for water to leak into the cable sheath of a cable-pulled parking/emergency brake. If you apply the parking brake in subzero temperatures, the water may freeze, leaving the brake stuck in the engaged position.

The parking lock ('P' in the "transmission") suffices for most situations, though I am in the habit of always engaging the parking brake, a habit from driving stick shift cars as well as a belt-and-suspenders thing. The owner's manual says to, with the foot brake depressed, "P-then-parking-brake" (page EV-18). It also recommends "parking brake-then-P" when parking on hills (page 5-20), so the parking mechanism's gear won't have to bear all of the car's weight.
MikeD wrote:It appears that one difference between those two brake systems is that the "parking brake" is designed so that it can be applied in an emergency while moving (say if the hydraulic brakes fail), whereas the "parking lock" is designed to be applied only when the car is not moving or moving very slowly.
...
Question: Would it have been less confusing if Nissan had used the terms "emergency brake" and "parking brake" rather than "parking brake" and "parking lock"? Which are the commonly used terms in modern cars today?
Federal Motor Vehicle Safety Standards spell out three different brake systems: "service" brake i.e. the "normal" brake, emergency brake, and parking brake/parking mechanism/parking lock. Each must conform to separate requirements. They can be separate systems, or two of the three can be combined, but all three can not be combined. The parking brake and emergency brake systems are normally combined, hence the confusion about whether it's a "parking brake" or an "emergency brake".

The emergency brake must be frictional (see my post above) and must be functional when all else fails: hydraulic failure, failure of main electrical system, ignition off, etc.
MikeD wrote:Has anyone tried out applying the "parking brake" while moving at speed? I don't suppose the parking brake switch provides any control on the braking force/speed ?
You can apply the parking brake while moving: pull up once to engage, pull twice to really engage. You have to be able to apply the parking/emergency brake while moving, otherwise it's not an "emergency brake"! :D
MikeD wrote:I don't suppose the parking brake switch provides any control on the braking force/speed ?
The LEAF's parking/emergency brake provides a little bit of control over application force: pull up once to engage, pull up twice (doubleclick) to really engage.
Ingineer wrote:FYI: The Brake capacitor has nothing to do with the parking brake system [...]
If the 12v system is offline, you will not be able to [...] engage the parking brake, but you can disengage it from the manual release. [...]

The Hydraulic brakes will still function normally for a handful of stops until the capacitor depletes, [...]
I would tend to agree with that. I checked the service manual. All references to a "brake power supply backup" are in the "BR Brake System" section, not in the "PB Parking Section". (I edited the title to reflect this info.) However, now the question becomes: which is the emergency brake on the LEAF: the service brake, or the parking brake?
Ingineer wrote:I suspect there is at least 10 watt-hours of usable energy (12v output) in the brake capacitor. At some point I'll do an accurate test.

-Phil
That would be interesting information.
BnBinSD wrote:In the Owner's Manual, the parking brake is mentioned several times. In the first mention (I think), it states to "apply the parking brake twice for maximum effect" or some such, but in subsequent discussions - especially parking on hills, it's never mentioned again.
This is in the service manual, page PB-17: "Pulling the parking brake switch again increases the parking brake braking force (increases the rear cable tensile force)."

I would think it's in the owner's manual as well, but I don't know for sure.
GroundLoop wrote:Emergency Brake is not quite right, since it's not used in emergencies. Unless it's a big handle you can yank and slide the rear, I just don't see it being that useful in crisis.
Having a longish handle to apply and modulate the parking brake might be nice, though at the end of the day, I only care that the "emergency" brake be capable of stopping the car if the service brake fails. I don't care if I have to yank a big handle or whistle Dixie to activate it!

That said, the only gripe I have about the LEAF's parking brake is that it only has three settings: off, on, and REALLY on, and there is no room for modulation in between.
GroundLoop wrote:Is there something legitimately called a "transmission" with one gear? If so, then tranny lock sounds correct to me.
It's got gears and it "transmits" power from the motor to the driveshafts. I'd call it a "transmission".
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davewill
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Re: Power consumption of parking/emergency brake's capacitor

Tue May 17, 2011 6:55 pm

MikeD wrote:...However, on my last question about whether or not the "parking lock" is "safe enough" for most parking situations, I notice the following from the Owner's Manual: "CAUTION: To park the vehicle in cold climates, push the P position switch on the selector lever and place suitable chocks at both the front and back of a wheel with the electric parking brake released. If the electric parking brake is applied in cold climates, the brake may freeze and cannot be released.". So I gather both brake systems have their limitations and strengths....
I don't see how the parking lock can really fail. The wheels will STAY locked. The reason for not depending on it alone is that it's only locking up the two front wheels. You need the parking brake to lock up the rear wheels. On a steep, slippery slope, two wheels might not be enough.
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garygid
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Re: Power consumption of brake's back-up power capacitor?

Tue May 17, 2011 7:32 pm

There is never just one "gear", but a gear pair. The gears in the LEAF's transmission have a fixed ratio (of about 10:1) so that the electric motor is going about 10,000 rpm when the wheels are going at about 1000 rpm.

So, there is a single-speed "transmission", which probably includes the "Parking-Lock" feature.
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