Parking brake as Emergency Brake

[biker750guy]

Does anyone know if the parking brake will act as an emergency brake at speed in the even of total hydraulic failure? It will stop the car at speed if the normal braking system is working. My guess is, no, it is tied into the hydraulic system.

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[syncro87]

Does anyone know if the parking brake will act as an emergency brake at speed in the even of total hydraulic failure? It will stop the car at speed if the normal braking system is working. My guess is, no, it is tied into the hydraulic system.

One of the last things you'd want to do, at speed, would be to engage the electronic parking brake. Since it's an ON/OFF system, you'd risk locking up the rear wheels and throwing the vehicle completely out of control. Probably not the best option.

Since the mid to late 1960's, cars have had dual circuit brake systems. Your right front and rear left brake are typically on one circuit, and the left front and right rear on the other. Even if you have a catastrophic leak in one half of the circuit, you still have system integrity in the other circuit, and braking ability.

The chance that you'd have total system failure would be incredibly low. Your master cylinder would have to completely fail internally. Very unlikely. Possible? Yes.

One potentially small benefit of a traditional emergency or parking brake (that was mechanical and used a hand lever in your center console) is the situation you describe. If your hydraulic brakes totally failed with no warning, you could use the hand brake to apply some parking brake force to stop the car, theoretically.

Since the Civic uses an electronic brake actuator for the "e"-brake, it is really a parking brake now with no "emergency" functionality. It's an on/off setup, and you can't progressively modulate the amount of force manually like you can with a hand brake lever. Hence, the electronic e brake is pretty much worthless in an emergency. The electronics might not even allow the parking brake to engage when the car is at speed, I haven't tried it. I bet there is some safety built in that doesn't allow activation.


It's all pretty moot, though, because the chance that both circuits of a modern car's braking system fail 100% in a single event is ridiculously small. Look at how many poorly maintained cars are on US roads on a daily basis. You almost never see a total brake failure resulting in a crash. It's probably more likely that some jack wagon throws a piece of metal off a bridge onto your car as you pass below, causing a crash, than it is that your entire braking system goes kaput out of the blue, leaving you with zero hydraulic brakes. Even if the brake power booster dies a sudden death, you can still stop the car perfectly safely by using more pedal effort.

 

[inv4zn]

There's a video where the driver pulls the electronic e-brake, and the car comes to a halt.
Whether or not that'll work with either failure of the master cylinder, or the electronics, I've no idea.

My understanding of the electronic parking brake system is that it activates a solenoid at the calipers, must like a cable operated parking brake does. Both systems work identically, at the brake level, just a different method of engaging it.

And as @syncro87 said, even if you have total brake failure, you can still step on the pedal. It'll just be much harder to do so. You can also gear down to engine brake and shave off speed.

 

[silverrascal]

You evidently can use the electronic parking brake as an emergency brake...

 

[biker750guy]

One of the last things you'd want to do, at speed, would be to engage the electronic parking brake. Since it's an ON/OFF system, you'd risk locking up the rear wheels and throwing the vehicle completely out of control. Probably not the best option.

Since the mid to late 1960's, cars have had dual circuit brake systems. Your right front and rear left brake are typically on one circuit, and the left front and right rear on the other. Even if you have a catastrophic leak in one half of the circuit, you still have system integrity in the other circuit, and braking ability.

The chance that you'd have total system failure would be incredibly low. Your master cylinder would have to completely fail internally. Very unlikely. Possible? Yes.

One potentially small benefit of a traditional emergency or parking brake (that was mechanical and used a hand lever in your center console) is the situation you describe. If your hydraulic brakes totally failed with no warning, you could use the hand brake to apply some parking brake force to stop the car, theoretically.

Since the Civic uses an electronic brake actuator for the "e"-brake, it is really a parking brake now with no "emergency" functionality. It's an on/off setup, and you can't progressively modulate the amount of force manually like you can with a hand brake lever. Hence, the electronic e brake is pretty much worthless in an emergency. The electronics might not even allow the parking brake to engage when the car is at speed, I haven't tried it. I bet there is some safety built in that doesn't allow activation.


It's all pretty moot, though, because the chance that both circuits of a modern car's braking system fail 100% in a single event is ridiculously small. Look at how many poorly maintained cars are on US roads on a daily basis. You almost never see a total brake failure resulting in a crash. It's probably more likely that some jack wagon throws a piece of metal off a bridge onto your car as you pass below, causing a crash, than it is that your entire braking system goes kaput out of the blue, leaving you with zero hydraulic brakes. Even if the brake power booster dies a sudden death, you can still stop the car perfectly safely by using more pedal effort.

Yes, it is rare but I had it happen to me once in a new rental with dual hydraulic systems. I used the hand parking brake to save me running a stop sign. I have also had a forced landing in an airplane; it does pay to be prepared. The pedal does go down when the parking brake is applied which leads me to believe it is actuating the hydraulic system but.... If you watch the video you will see the car stop safely and that can be a very big deal at times.

 

[syncro87]

Interesting that they allow the electronic brake to function when the car is moving at 40 mph. I would have guessed that it was disabled after a certain speed, but it does seem to work. My concerns with possibly locking up the rear wheels are apparently unfounded. The parking brake must only be able to apply a modest amount of pressure, compared to yanking up on a manual brake lever by hand. Clever. Still might cause an interesting handling situation on a wet road, or snow, but a brake failure on snow where you needed a hand brake would be a one in a billion scenario.

What the video unfortunately did not show us was whether the e brake can stop the car if the main brake lines or master have been compromised. The video test assumes that the main braking system is 100% intact, so it doesn't really give us much information on the ability of the e brake to help us in an emergency. Of course, the video guy wasn't trying to show us that. He was just curious if the e brake worked when the car was moving.

Key here would be whether the brake lights come on when you activate the electronic brake. If you lose all hydraulic brakes, you wouldn't necessarily have your foot on the no longer functional brake pedal. You pull the parking brake switch, and the car stops rapidly...but the people behind you might not have any indication of this if the brake lights don't come on. Surely if some Honda engineers were clever enough to allow the parking brake to be activated at speed, there is some provision for the brake lights to be activated at the same time. It wouldn't be much fun to be rammed by an 18 wheeler because you stopped suddenly but the semi driver had no indication of it.

My last car, a Jetta, had some really clever brake light features you could choose to enable. First, you could set your preferences so that if you stopped rapidly, the brake lights would flash three times before staying on solid. This way, during a panic stop, cars behind you got a heads up that was more obvious than just steady brake lights. Second, you could program the 4 way flashers to activate during a panic stop as well, and remain on, blinking, afterward.

I enabled the 4 way emergency braking flashers, and only had one occasion to use them. All traffic stopped suddenly in front of me on the highway one day, and I had to do a panic stop even though I had a fair bit of distance between myself and the car ahead. Once I was stopped, I noticed the 4 ways were blinking. Cool. More cars should have features like this.


I'd like to know more about how the electronic brake works on the Civic. Does it require hydraulic pressure to remain in the system, in order to function? If you had a catastrophic system failure, i.e the master cylinder failed completely or you had two severed brake lines that compromised both circuits, would the e-brake still be able to stop the car? The beauty of a cable hand brake is that the cable system is completely non reliant on the hydraulic brake system. You could lose all your brake lines, the booster, your fluid reservior, and the foot brake pedal could snap off, and you'd still have the ability to stop the car.

 

[neteng101]

My concerns with possibly locking up the rear wheels are apparently unfounded.

I think you'd get more lock up from putting the transmission in park - the parking brakes aren't that strong in cars these days, one can easily drive off with the parking brake still engaged if you forced it.

 

[Bawb333]

What about for hooning in snow covered parking lots? That's what we're all really wondering.

 

[DavidJBrooks]

My guess is that the electronic brake ties into the emergency braking system, and that switch in the console effectively tells the computer to stop the car asap. I doubt there is a direct connection between the switch and the brakes.

 

[TheCodifier]

When the electronic parking brake is engaged at speed like in the video, the regular brakes are used to stop the car ASAP and then the parking brake is engaged.

So if all hydraulic pressure is lost, activating the parking brake at speed won't work since the main brakes wouldn't work anyway.

 

[syncro87]

When the electronic parking brake is engaged at speed like in the video, the regular brakes are used to stop the car ASAP and then the parking brake is engaged.

So if all hydraulic pressure is lost, activating the parking brake at speed won't work since the main brakes wouldn't work anyway.

Thanks, this is what I was curious about. So if this is correct, the electronic e-brake is pretty much useless in the event of complete failure of the hydraulic system. I see such failure as quite unlikely, but if it did happen, a traditional cable operated manual hand brake would be more useful than the electronic brake.

 

[silverrascal]

I have no information to back up any of what I'm about to write but wouldn't Honda be placing themselves in some major liability for not having a system that could stop the car if the regular brakes failed? Surely there is a system in place right?

 

[syncro87]

I have no information to back up any of what I'm about to write but wouldn't Honda be placing themselves in some major liability for not having a system that could stop the car if the regular brakes failed? Surely there is a system in place right?

Not really. There is no law or regulation that I'm aware of that forces automakers to implement an emergency or parking brake system that operates completely independently of the main braking system. Someone may correct me on this point?

Cars already have dual circuit designs, making a total failure of both circuits incredibly unlikely.

If I'm not mistaken, the piston in a car's master cylinder has independent seals for each circuit. So for the master cylinder to totally fail, more than one internal seal would have to fail simultaneously, disabling the ability of the cylinder to produce hydraulic force for either circuit.

Or, the cylinder would be intact, but a brake line on both circuits would have to be severed, resulting in total system failure.

Both of these scenarios are very uncommon.

What is far more likely is that one piston seal fails in the master, or all seals are degraded but do not fail completely. One seal fails, pressure is still maintained in the other circuit, enough to stop the car. All seals are degraded (burr in the cylinder bore perhaps, for example) scenario probably results in decreased brake effectiveness, but not total failure at one moment in time.

You could have one leaky caliper or wheel cylinder or brake line, but the chance that both circuits not only leak, but leak at such a high rate that your brakes work one minute and completely fail the next...very unlikely failure pattern.

Even when your master cylinder does fail, you can often pump the brakes up enough to stop the car.

At some point, you have to ask yourself how much redundancy is needed. We aren't talking about aircraft here, where the consequences of system failure necessitate multiple levels of control redundancy. We're talking Civics. The brakes already have redundancy built in. Adding more layers just adds weight and complexity and cost.

There are hundreds of thousands of cars in various states of repair on the roads of my local metro area each day. I can't recall ever hearing of a situation where an accident was caused because a modern car just lost all braking ability out of the blue, with no warning. If it was a major concern, you'd hear about it regularly. The reality is, total catastrophic brake system failure just about never happens. If it does, it's usually because a car is old and has been poorly maintained. Poor owner maintenance and operator diligence are not something any car maker can totally engineer against. If someone drives a poorly maintained, 30 year old car, no brake system is going to be able to make that car 100% safe.

Having owned many jalopies over time, it is my anecdotal experience that you typically have warning if your brake system needs attention. The pedal is soft for a while, braking performance is weak, the car pulls to one side, etc. You almost always have red flags that something needs to be serviced.

 

[kommong2]

Hopefully I never need to use it but it is good to know that I can use Parking brake as Emergency Brake. My 16 year old just got a learner permit and while I am sitting next as a passenger I always wondered if I can use that if my kid makes a mistake

 

[GermanCivic]

You evidently can use the electronic parking brake as an emergency brake...

I wonder why there is no warning signal, I get an alert beep when pulling the hand brake while driving.

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