Electric Handbrake / Emergency brake - Why? 10

[NickJ67]

Whats the reason for manufacturers moving towards electrically actuated, push-button handbrakes these days?

Having recently had to deal with one as fitted to the VW Passat, I have to say that it alone would prevent me from buying/leasing what is otherwise a pretty good car - such a pain to use when maneovering on a steep slope. I have also had the entertainment of watching my neighbor having to deal witha malfunctioning one on her Renault Scenic (non-release scenario).

Seems to me that they must be more expensive to fit and more prone to malfunction than a good old fashioned cable and lever arrangement - what am I missing? Am I a luddite....?

Regards

Nick

 

[swall]

One potential advantage with an electric parking brake is that it can be set up to provide sufficient clamping load on the disc to compensate for the loss of clamp load that occurs when the disc and pads cool down.

 

[evelrod]

I'm still not seeing the "savings" of a few mechanical bits over the potential liability issues.
This appears to be one of those "solutions in search of a problem" deals.

Rod

 

[GregLocock]

The fundamental issue was when we went to hydraulic disk brakes. Manual activation of a disc brake is possible, but very clunky, and means that you compromise the brake pad's performance to get good park brake characteristics.

To get around this PBR and others introduced a separate drum brake, manually activated. This was a bit nasty package wise, and of course had all the problems we knew and loved with any manual park brake system. I also doubt it was much chop as an emergency brake.


Cheers

Greg Locock


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[MikeHalloran]

Drum brakes suck, especially small ones, but they beat the hell out of no brakes. I've done that twice and lived through it, before split circuits of course.

Mike Halloran
Pembroke Pines, FL, USA

 

[JSteve2]

I understand that a number of skilled drivers have opinions on the many ways they can use the hand brake to enhance their driving experience. However, given that these situations are few, even skilled drivers rarely think of them at the needed moment of duress. Hand brakes are often failed (cable corrosion, car had been driven with now-toothless brake applied - take your pick), and many cars utilize a foot-based parking brake anyway...

Further, it is interesting than a number of people on this forum understand, in ordinary circumstances, electronic parts are much more reliable than mechanical parts, but for some reason in this thread we seem to be going back to old school mechanical parts are best. I understand that, if a parking brake is a new implementation, the electronics may not be worked out, but in the long run I would put my money on the electronics being more reliable.

Accordingly, I can only guess this thread is a bit of nostalgia for a simpler time when a man could back up a trailer, parallel park the Titanic, and, yes, perform many stunts with the hand brake that come up in everyday driving situations.

The reason for this trend, if it exists (I've not personally noted electrical parking brake switches yet), is switching to an electronic part gets rid of one more mechanical point of failure, so there is some updside.

The downside, or "risk," is non-existent. First, the number situations where the hand brake makes a difference exists are few, only a tiny fraction of the population is even competent to work the hand brake, and in the rare case where the situation and driver line up, the mechanical hand brake is probably not up to the task anyway. Second, if a driver has the knowledge to understand that he is in a situation where the hand brake is helpful, he is competent to use it, and he has the reaction speed and skill to use it properly, that driver is no doubt also skilled enough not to get into the required amount of trouble in the first place.

 

[MikeHalloran]

So, on your planet, I'd be dead, twice, and it would be _my_ fault?

Solid state electronics have proven themselves time and again to be much more reliable than any mechanical device.

Agreed, at the chip level.

But that's not a fair comparison. At a system level, electronics include connectors, of many sorts, living in many environments, and frankly they haven't done so well.

See 'tin whiskers'.
See 'intergranular corrosion of tin'.
See 'age-related annealing of low-force connectors'.

Somewhere out there in time, probably well under ten years, connectors that carry substantial current, even intermittently, like the ones that apply and/or release parking brakes, fall below the reliability/ availability of mechanical devices like handbrakes.



Mike Halloran
Pembroke Pines, FL, USA

 

[NormPeterson]

It isn't nostalgia.

Mechanical systems don't have to rely on something as fragile as a fuse or a connection that might not be as corrosion-resistant as expected, and generally you get some warning before mechanical things stop working entirely. It may be only a few cycles from "something feels different" to "uh-oh", but that's still better than a binary "here this time, gone the next".

I can only speak for the Subaru version (2.5GT/265HP/6-speed manual - the wife's car) here. But having to be depressing the brake pedal in order to apply the P-brake is at least as clunky than working a foot-operated manual P-brake, in exchange for which you give up the ability to modulate it at all. When I use a mechanical P-brake, I tend to use only enough to get the job done, rather than yank on the handle or stomp on the pedal for all I'm worth every time, which may indicate something.

Supposedly, the e-P-brake is self-releasing on throttle pedal motion as you drive off, but I have found that this is not always the case. Yes, I have used it a few times, enough to find out that much, and the fact that it's a bit slower to get the job done than any mechanical system I've ever dealt with (which is another little irritation I'd just as soon live without).

I do find it interesting that the recommendation for (temporarily) dealing with an inop electronic P-brake is to stop on flat ground and put a manual transmission car in either '1' or 'R' or an automatic in 'P'. I guess the Owners Manual writers aren't allowed to assume that the video-game generation has much grasp of things mechanical other than pushbuttons.


Norm

 

[rmw]

As I read this thread, it makes me think of air brake systems as an analogy. A push button on the dash sends a signal to a pneumatic relay that puts air pressure from a reservoir onto a brake can(s). Because air leaks off, park brakes have to have springs to maintain the brakes when the air leaks down as it inevitably will.

Some older brake cans had ratchet mechanisms in them that required a full application of air to release the brakes when the park brake wanted to be taken off.

In those systems, a failure of air immediately results in the onset of braking driven by high pressure springs whether it is wanted or not. The spring cans have the ability to be manually jack screwed to release them at which time there are no brakes.

I think Electonic brake systems will have to have some type of analogous provisions.

rmw

 

[patprimmer]

JSteve2

There is a world beyond the borders of the USA.

In this world beyond the USA, at least in the English speaking parts, emergency brakes are normally called hand brakes because they are operated by hand. The lever that operates them is normally between the two front seats and is close to the gear lever and in a position that is very convenient and intuitive to those who drive a manual transmission. A foot operated emergency brake while OK on an automatic, when near the clutch pedal would be somewhat problematic re space and avoiding accidental application when intending to disengage the clutch. Also the quick release nature of foot operated emergency brakes makes hill starts very difficult.

Outside the USA there are many countries where a manual transmission is standard equipment on cars designed for mass consumption. In these countries they are not reserved for econo boxes or crazy street racing types of markets or gear head/petrol head/rev head or whatever you like to call them types of customers.

Just in case you never saw a hill start with a manual transmission, most drivers when starting facing uphill apply the hand brake, engage low gear, use the right foot to control the throttle, the left to control the clutch and their hand to control the hand brake and co-ordinate all three to take up the load before releasing the brake to take off smoothly without rolling back.

Unless you are among the few who have the skill to "heel and toe" it, this maneuver is pretty much impossible with a brake that is not controlled by hand and does not have a progressive control of holding power that can be felt.

I do agree that a hand brake lever between the front seats intrudes into potential cup holder real estate, or even reduces console storage space, however that space has no other useful options that I can think of that could not also be placed under a seat. I normally place the cup on the seat between my thighs

I also agree that routing cables around tail shafts and exhaust pipes and suspension components can be difficult, especially with all the other bits that now occupy the area near the hub.

I have personally never in over 40 years had a handbrake mechanism fail. I have twice used the hand brake to stop when the hydraulic system or the spring between the two pistons in the split circuit master cylinder failed. Even if only the rears go, the car where it happened to me still stops but stops poorly with fronts only as the pedal still hits the floor at a moderate rate of braking. Applying the handbrake at that time almost doubles the stopping power.

In other parts of the world we do still travel on gravel and even on tracks. Hand brakes with progressive action and feel have a lot of benefit in those situations.

The best option for off road use, although I have never seen it supplied as OEM equipment on a passenger car and rightly so because of minimal requirement from the market, is individual hand brakes on the drive wheels if it is a rear wheel drive. It is standard equipment in foot operated form on tractors. I guess fancy traction control does the same thing for you on modern top end models by applying brake to the wheel that breaks traction.

Mike and Greg

I prefer the small drum vs the mechanical secondary operation of the caliper piston. In my experience it still provides enough brake to save the day in any recoverable situation. It just turns a normal stop into a panic stop and maybe a life threatening crash into a fender bender.

I know this is an abuse of the brake system, but I also at times push my pad life to the max and only replace them when I hear some scraping. When I hear it I try to complete the journey using only the hand brake so as not to score rotors, then replace the pads with the set I carry in the car when convenient. This is possible with an old fashioned hand brake.

If you drive a manual transmission and you apply a well designed hand brake properly when parked, you would normally stall it on the first takeoff attempt and that certainly reminds you to check that you released the brake. Anyone who half applies or half releases a hand brake so it can be driven easily but still overheats, probably should not be allowed to use public roads anyway.

Regards
Pat
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[kirrer]

As a relatively young guy (4 yrs) to the world of automotive & mechanical engineering, I appreciate all the discussion in this thread - it helps me to get a better feel for the world that is out there now, even though I have nothing to do with parking brake systems. I'm also grateful for the differing opinions & the civilized discussion which is taking place. Keep it up!

To contribute, I'd always take the feel of a hand brake vs the convenience or reduced cost of an electronically actuated brake. And I agree with Mike - solid state electronic components do have a higher reliability, but the mechatronic components to go along with them don't.

Kevin Irrer
Northville, MI USA

 

[swall]

When I hear the term "hand brake", I always think of that big round wheel on a railcar that is connected to the brake shoes via a chain and linkage arrangement. This system keeps the rail car from rolling away when it is in a siding.

 

[LionelHutz]

I would think the main reason is to eliminate the driver. I would think the reasoning is along the lines of it being much better to have a car that will automatically and properly apply the parking brake than rely on the driver to use it correctly.

I guess I'm in the minority here because I've yet to need the parking brake during a hill start in my manual equipped vehicles.

 

[swall]

FWIW,TRW is touting the "hill holder" feature on the electric disc parking brake they have just introduced.

 

[kirrer]

Good point by swall - hill holder is a great function when used with a manual transmission. My VW Golf that I had in Germany had this function and it was fantastic for starting on a hill - no orchestrated handbrake-brake-gas-clutch maneuver required, or learning to heel-toe.. I guess that's just another way our cars are driving us vs. us driving them.

Kevin Irrer
Northville, MI USA

 

[JSteve2]

A few thoughts:
Every car I've owned before the year 2000 had a failed brake. Usually, a previous owner drove with it engaged. It would hold a parked car generally, but was worthless as an auxiliary braking device. Granted, we're talking about a long line of old, crappy cars.

@Mike - you are a serious outlier. But let's also not forget that, skilled driver you are, you have other options. The hand brake just happened to be the one you used in the two situations you are referencing. Even if you would have died due to a lack of a hand brake, it wouldn't be "your fault", it's just that you would be dead and someone else would have taken away the thing that would have saved you, for the reasons I mentioned. It's unlikely they could have been held liable. The OP was asking why this happened, not whether it was the best idea. My point is, from a liability standpoint, it makes a lot of sense.

@PatPrimmer - my first car was a '77 Camaro with a (failed) parking brake, a manual transmission, and the car would not idle without periodic stabs at the accelerator. There were a lot of hills at stop signs in my town. My point is not that my life would not have been easier with a working hand brake, my point is that car companies are not worried about me.

My brother had his brakes fail in an old car and tried to slow himself with the hand brake. There was a little early success, then something broke, where the lever lost tension and the brake locked his wheel and flipped his car into the ditch (he was OK).

Imagine if a car company were to bill their inclusion of a hand brake as a safety device in their car. Now, incompetent consumers are incorrectly using it, and further it becomes a maintenance device. Better from a liability standpoint to call it a parking brake, and essentially disable it for all other purposes. Now that's a USA-centric viewpoint as well, but based on the OP asking why an electronic brake switch is replacing a manual, I assumed we weren't talking about Sierra Leone here anyway.

Another question - where hand brakes are billed as a brake to be used in non-parking situations, do they apply braking power to more than a single rear wheel?

 

[evelrod]

Every car I've owned before the year 2000 had a failed brake. Usually, a previous owner drove with it engaged. It would hold a parked car generally, but was worthless as an auxiliary braking device. Granted, we're talking about a long line of old, crappy cars.

I don't mean to pick on you Steve but...This statement says a lot more about you than the cars you chose to own!

Pat, driving a 1930 Ford daily, I find the hand brake invaluable.

I've only had two complete brake failures in over 50 years. The first was in 1958 in my '49 Merc and the other was the e-brake of my '83 Turbocoupe. Maintenance and common sense come into play here, admittedly in short supply in these days of 'big brother'. My wife likes all the convenience of the electronic revolution in automobiles...I find it a bit 'off putting'.

Rod

 

[JSteve2]

Rod - no offense taken. I may know how cars work, but I don't get involved in the maintenance. I even (gasp) get my oil changed at Jiffy Lube. Not that they are better than me (although maybe) but at least they will buy me a new engine if they screw it up. I think many consumers, the folks car companies build for, are like me.

 

[NickJ67]

Well, this generated more comment than I expected!

I think Pats last post was a nice summary of my feelings on the matter.

Here in Euroland (and most places outside the US maybe) stickshift forms the majority and a handbrake is pretty much essential for hill starts for all those not unusually gifted with heel & toe skills. Certainly that is the way that new drivers are taught in the UK and I believe that you are not allowed to take your driving test in the UK in any car equipped with an electric parking brake.

On the Passat I drove, there was no "Hillhold" feature. I understand that it could be been specified, but at substantial extra cost. Can't comment on the "hillhold" as I haven't tried it - seems like an essential feature though. All I can say is that manoevering this car in a cramped car park on a hill with this fiendish device made me feel like a complete muppet - and it was ably assisted by the 2.0TDI engine having virtually no torque just off idle and a particuarly daft "key" arrangement that makes a rapid restart (after the inevitable stall) impossible.

So to me, seems like a considerable backward step in usability, added complexity and certain to cause all kinds of issues as these systems age.

With the exception of my fathers Peugeot 404 wagon which had a peculiar under-dash arrangement (and a column change for extra oddness) every car I've driven, manual or auto, has has a handbrake lever between the front seats. Can be used for parking (assisted by leaving in gear or P), slowing without lighting the brake lights (ahem..), handbrake turns, and once only for me thankfully, to bring me to a halt when nothing else worked.

Electric handbrakes seems like an addition for those who possibly should never be allowed a licence in the first place....

As for the emergency brake role - I have had total brake, ironically only on a car with dual circuit and ABS and the manual handbrake was a big blessing. I'm not sure how these electrical versions react to being applied while moving, but I think I'd rather have the control myself.....

Nick

 

[patprimmer]

In Australia at least, any car over 3 years old needs a safety inspection that includes hand brake operation every year before you can renew your registration. Also we do not need to apply salt to roads. Also handbrakes are nearly always used every time the car is parked so a failure through corrosion or seizing is unlikely and other failures are likely to be promptly fixed.

Interestingly, both times I had partial brake failures that required hand brake assist was in mid 80s Aussie Ford Falcons out of the company pool. Both had high mileage and where in the pool because the normal operator had received his replacement.

The cause seems to be a weakness in this particular model which was a failed spring in the master cylinder so that pedal pressure was not applied to the back brakes.

Also to acquire a license to drive in Aus, you need to pass a practical test that involves correct use of the handbrake. Failure to use it correctly even once gets you failed in the test.

Regards
Pat
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[NormPeterson]

JSteve2 - I'm not at all sure that you can separate "Why this happened" from discussion about whether or not it's the best idea.

I do think that you needed to work on your Camaro's driveability issue. Even the nasty-cammed engine I built up as a know-enough-to-get-myself-in-trouble 20-something wasn't nearly as cranky as what you describe, and mine only had four small cylinders.


Here's what New Jersey has to say about "E-brakes" and the driver exam - from the State DMV official site, "What to bring to a road test" . . .

A registered vehicle with current inspection sticker and insurance card. Vehicle cannot have a center console unless the emergency brake is accessible from the passenger seat. Examiner must be able to reach either the foot brake or parking brake

No way would the Subaru pass muster.

I remember taking my own driving test - had to successfully execute a K-turn on a hill with the examiner sitting right seat (with dual brake and clutch pedals). The object, of course, was to demonstrate that you possessed a certain level of car control, and I think if you touched either curb even lightly, you failed.


You and Pat must live in substantially hillier/mountainous regions than I ever have or have ever driven through. I might have used the P-brake to get started from a stop on a hill all of a dozen times over the last 40 years, and I can't even remember when the last time was. I doubt that my wife has used it any more frequently. You do need to know that we've owned manual transmission cars exclusively since about 1972.

So the hill-holder feature on the Subaru is wasted tech as far as we're concerned, but at least the button to activate it is an even longer reach than the electronic P-brake. Thankfully, its default = off. I'm probably giving an impression of regret for having bought it, but aside from these two (and a couple other minor but mandated) "warts" it really is a nice car.

I get that we're outliers at least within the US market. But driving a stick-shift car just isn't that difficult.


Norm