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DaveEV
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Re: Power use at a stop light

Wed Nov 17, 2010 2:23 pm

garygid wrote:The parking brake is mechanical (not hydraulic) and only 2 wheels (not 4)?

That is how 99.9% of parking brake mechanisms work. I don't see how the Leaf would be any difference except for the fact that it is not actuated with a cable from the cockpit but is instead "drive by wire".

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garygid
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Re: Power use at a stop light

Wed Nov 17, 2010 2:35 pm

Ok, a guess.
The 2010 Prius pressurizes the hydraulics and "locks" the pressure, I believe.
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Re: Power use at a stop light

Wed Nov 17, 2010 2:38 pm

Or, maybe I am remembering looking at some other car's brake system diagram?
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Re: Power use at a stop light

Wed Nov 17, 2010 2:50 pm

garygid wrote:Ok, a guess.
The 2010 Prius pressurizes the hydraulics and "locks" the pressure, I believe.


You own one and you don't know that the parking brake is a pedal on the left side of the car next to the driver side door. Press the pedal down to set the brake and press it again to release the brake. The pedal actuates a brake pad on the rear wheels via a cable. The "P" button is not a parking brake, it is putting the transmission in park which allows the pawl to hold the car. This will not completely stop the car from moving. If the engine starts and stops when in park the car will lurch to some extent. Set the parking brake to avoid this. I don't know of any car that uses hydraulic micro locks for the legal parking brake. Drag racers, 4x4's and other vehicles use these to allow for more control of the car, but all parking brakes (that I'm aware of) use a mechanical braking action.

I'm interested in how Nissan is handling the parking brake on the Leaf since it is a button.
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Re: Power use at a stop light

Wed Nov 17, 2010 3:01 pm

garygid wrote:Ok, a guess.
The 2010 Prius pressurizes the hydraulics and "locks" the pressure, I believe.


I would be a little surprised if this is actually the case because of an issue that many small GA aircraft have that do use this kind of parking system. If the system is set when it is cool and it then gets much hotter, this can cause the brake pressure to rise significantly due to expansion of the fluid, leading to leaks and blown seals. In fact, most operating handbooks for such aircraft recommend not using the parking brake for an extended period for this reason.

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Re: Power use at a stop light

Thu Nov 18, 2010 5:42 pm

It is not a hydraulic brake. The actuator is mounted under rear of the car with cables to both rear brakes only. But most parking brakes on rear disc brakes use a "drum in hat" system which has a small drum inside the rotor for brake shoes. They are not large enough to use as a e-brake. So that is why they are for holding a car already parked only.
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Re: Power use at a stop light

Thu Nov 18, 2010 5:56 pm

There are also some systems that mechanically actuate the brake calipers of the rear disk brakes via cable and cam. This eliminates the drum brake hat and also allows for a more powerful e-brake.

Tom

wgs1912 wrote:It is not a hydraulic brake. The actuator is mounted under rear of the car with cables to both rear brakes only. But most parking brakes on rear disc brakes use a "drum in hat" system which has a small drum inside the rotor for brake shoes. They are not large enough to use as a e-brake. So that is why they are for holding a car already parked only.
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Re: Power use at a stop light

Thu Nov 18, 2010 7:28 pm

Only budget cars use drums in the rear.

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Re: Power use at a stop light

Thu Nov 18, 2010 7:41 pm

EVDRIVER wrote:Only budget cars use drums in the rear.


The drum brake being referred to is not the main service brake which is, in fact, a disk. It is a smaller drum brake inside the disk brake hub that is used only for the e-brake function.

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Re: Power use at a stop light

Thu Nov 18, 2010 7:52 pm

tcimpidis wrote:
EVDRIVER wrote:Only budget cars use drums in the rear.


The drum brake being referred to is not the main service brake which is, in fact, a disk. It is a smaller drum brake inside the disk brake hub that is used only for the e-brake function.

Tom



Meaning drum only brakes- yes some disk brakes have these secondary drums.

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