Electric Parking Brake - a) 12v b) use while moving c) auto unlock

[jeffreykb]

Hmmm...I'm not sure that I see an improvement in the design of the parking/emergency brake. It does take a certain amount of strength to actuate a mechanical brake, but it is simple. If a long explanation is needed to operate a safety device, it does not seem much safer to me. However, the Volt's MSRP is in the luxury vehicle range. I hope GM finds a way to build an EREV for the non-luxury vehicle buyer.

Please do not misunderstand...I think that the Volt is a very nice vehicle. 'Just a little too nice for most car buyers.

[WopOnTour]

Hmmm...I'm not sure that I see an improvement in the design of the parking/emergency brake. It does take a certain amount of strength to actuate a mechanical brake, but it is simple. If a long explanation is needed to operate a safety device, it does not seem much safer to me. However, the Volt's MSRP is in the luxury vehicle range. I hope GM finds a way to build an EREV for the non-luxury vehicle buyer.

Please do not misunderstand...I think that the Volt is a very nice vehicle. 'Just a little too nice for most car buyers.

Just because you dont see it doesnt mean it doesnt exist. The primary benefit is one of safety as there is data that suggests a large number of vehicle roll-aways are due to a misapplied park brake often due to misdjustment. (driver applies it but isnt creating sufficient holding force).
I'd be real surprised if you'v never heard of this happening to someone.
WOT

[Rusty]

I note that other high-end cars also have electronic parking brakes. From Wikipedia...

I see the Volt's now been added to the list of cars with EPBs.

[maestro77]

FYI
While the electronic park brake IS electrically activated, it STILL uses a system of cables to mechanically operate the rear disc brakes.
WopOnTour

Seems a small correction is required here - and perhaps it's an interesting point. The manual (section 10-88) addresses Dolly Towing from the Front. In that section GM specifically has to SET the parking brake. In this scenario, where the front wheels are on the dolly and the rear wheels on the road and rotating during a tow......it seems clear that the EPB can NOT be acting on the rear wheels! I presume the Volt has been implemented differently that most other cars and that the parking brake acts on the FRONT wheels, not the back. If the EPB is activated (due to emergency?) while the vehicle is in forward motion....doesn't that sound like a bad thing since significant braking force applied only to the front wheels could result in more difficult steering control in an emergency situation.

That seems surprising - anyone have any comment on this??

[WopOnTour]

Seems a small correction is required here - and perhaps it's an interesting point. The manual (section 10-88) addresses Dolly Towing from the Front. In that section GM specifically has to SET the parking brake. In this scenario, where the front wheels are on the dolly and the rear wheels on the road and rotating during a tow......it seems clear that the EPB can NOT be acting on the rear wheels! I presume the Volt has been implemented differently that most other cars and that the parking brake acts on the FRONT wheels, not the back. If the EPB is activated (due to emergency?) while the vehicle is in forward motion....doesn't that sound like a bad thing since significant braking force applied only to the front wheels could result in more difficult steering control in an emergency situation.

That seems surprising - anyone have any comment on this??

Ummm keep reading the procedure. it tells you to set the park brake only to secure the vehicle to the dolly. Then (in step 7) it requests you RELEASE the park brake.
The EPB on the Volt DEFINATELY activates cables to the rear calipers... trust me.
WOT

[maestro77]

Ummm keep reading the procedure. it tells you to set the park brake only to secure the vehicle to the dolly. Then (in step 7) it requests you RELEASE the park brake.
The EPB on the Volt DEFINATELY activates cables to the rear calipers... trust me.
WOT

Duh.....ok....I'm officially stupid. ;-(
Certainly WOT is correct and I failed to read through ALL the steps they outline for Dolly Towing.
(Though note in Step 4 they say to "remove the key" - guess the manual needs a small update since there is no traditional mechanical key to remove from the ignition.)

Thanks WOT (wish I could just delete the last two posts from this thread LOL).

[maestro77]

FYI
So the mechanical "emergency" brake feature is still intact up to ~5mph however at higher speeds it is initiated with hydraulic brake activiation until speeds drop to that point.So when indicated vehcile speed are greater than ~6mph and the park brake buttton is raised the ABS system will first apply hydraulic braking to about the 0.6g level, then once speeds drop to 5mph or lower it will commence to apply the motorized cable control.
WopOnTour

A question: Since one of the purposes of a mechanical cable parking brake is an emergency means of bringing the vehicle to a stop during a catastrophic brake pedal failure (ie. hydraulic system failure)....what happens if that hypothetical hydraulic failure occurs when travelling at >5mph and the driver activates the EPB? Is the vehicle smart enough to realize that it's attempted hydraulic braking is having no effect and to then go ahead and attempt to pull the mechanical cable to stop the vehicle even though it's not yet slowed to 5mph?

Perhaps the assumption is that the mechanical cable pull would never realistically be needed to stop a vehicle travelling at high speed since the unique Volt power train means that BOTH the regenerative braking AND they hydraulic braking would have to fail simultaneously in order to not be able to stop the vehicle.....and that's assumed to be highly unlikely.

Even IF the car will give up on ineffective hydraulic braking at high speeds and start pulling on the mechanical cable....I'm somewhat bothered by the fact the cable pull required the 12V electrical system and cable motor to be functional. I wonder if there's a reasonable scenario where ALL forms of electrical ability could be lost (making the EPB non-functional) at the same time as hydraulic pressure is totally lost. I'd feel better knowing there was a 100% mechanical hand pull brake for such complete system failure emergencies.

[MichaelM]

Since one of the purposes of a mechanical cable parking brake is an emergency means of bringing the vehicle to a stop during a catastrophic brake pedal failure (ie. hydraulic system failure)

Not to pick on maesto77 here (apologies in advance, maestro ), but that's what many people believe (myself included until I started working for a Major OEM Based in Detroit).

I've seen it implied here in this thread, but just so we're all clear here, people:*

It is a PARKING brake. Always.

It is not an EMERGENCY brake, not ever.

Yes, we all like to talk about "a touch of e-brake" to "swing the ass out" so we can set up for the next turn. I'm guilty as charged, your honor.

Sure, we all know you CAN use the PB for stopping, but you better stop pretty damn quick, because there is close to ZERO ability on the part of the parking brake to absorb heat (energy) from trying to slow a vehicle at speed. You'll get one shot at stopping a lightly-loaded vehicle, level ground, at low to moderate speed. That's it.

After a close reading of the Volt manual: it never mentions using the parking brake to slow the vehicle, even if the hydraulic brakes fail -- that's why there are two separate hydraulic circuits (by law, actually).

Oh, and while I'm on a rant:

There's no such thing in the OEM world as a dashboard -- it's an instrument panel.

There's no such thing as a firewall, because it's not designed as a wall or other barrier against fire. Possible customer response: "Why do I have a firewall? Is it because there's a reasonable probability of a fire occurring?" It's therefore called a dash panel.


*Kelly McGillis to Maverick: "Are we clear, lieutenant?" "Crystal."

[Fulgerite]

I've used the emergency brake before for an actual emergency. The hydraulic brakes busted a rubber hose. Probably saved my life. It was the only way I could get the car stopped while going down highway.

That must have been a long time ago. Cars since the 1960's have had dual circuit hydraulic systems... So if you bust a hose the other circuit still works. You always have at least two diagonal wheels with hydraulic pressure at all times. This is why I have never needed to use a parking brake for an emergency stop in 34 years of driving.

So I want to be clear. All cars have DUAL REDUNDANT hydraulic systems. It is nearly impossible for BOTH hydraulic systems to fail.