Electromechanical Brake Question 2

[DJShortyG]

Hello All,

We are working on a vehicle specifically designed to utilize some of the current Drive by Wire systems out there. Our end goal is to test the Human Factors that contribute to the desire to or not to include by-wire systems in vehicles today.

Currently we have identified sources for a steering system, as wells as suspension and shifting (the second two were pretty easy). Braking however has proven to be difficult to find out side of the Brembo System announced in the following link.

http://www.brembo.com/en/News/Pages/BREMBO-@-IAA-LESS-WEIGHT,-MORE-EFFICIENCY-.aspx

My question really relates to understanding why if there really are cost savings, weight savings, and performance benefits to this type of braking system, why are there not more companies out there for us to look to purchase a system from? Also if, we were under pressure to design our own system, where would the best place to get operational specs of a braking system be?

Thank you for your help, I really appreciate it.

Greg

 

[MikeHalloran]

>>> Our end goal is to test the Human Factors that contribute to the desire to or not to include by-wire systems in vehicles today.<<<

Average drivers don't care if there's a wire involved, and if the system is properly integrated, shouldn't be able to tell.

Cost savings might accrue from parts count reduction.

There may be regulatory issues involved. E.g., industry manipulation generated legislation that made sealed beam headlamps mandatory. Then, decades later, that legislation had to be undone to allow modern aero shaped headlights, which notably do have all the problems that were cited as reasons to go to sealed beams in the first place.

Similarly, I wouldn't be surprised to find some regulatory requirements that preclude total electric brakes.


Given the demonstrated reliability of electrical connectors over time and in the presence of de-icing salt, I don't look forward to braking-by-wire.




Mike Halloran
Pembroke Pines, FL, USA

 

[MacGyverS2000]

Hydraulic systems have enough risk factor involved... I won't go to DBW braking without a serious amount of kicking/screaming.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[DJShortyG]

Thank you so much for your responses Mike and MacGyverS!

We do realize that the consumer perception about these type of systems will play a huge role in their implementation. I guess our hypothesis is that the performance gains that can be made using by-wire systems should offset the risks. It is another case, in our minds, of Consumers not really know whats good for them.

Still, since we have not been able to identify many companies working on EMB (Electromechanical Brakes) we are most likely going to develop them on our own. Do either of you two know a place where I can find the operational specs for a braking system. We have been trying to get them through NHTSA and SAE, however both avenues are taking a long time to progress.

Greg

 

[btrueblood]

There was a thread on this forum regarding electronic braking systems, I think more along the lines of an electric parking brake...but it had some of the same kinds of reservations as expressed above. Searching should pull it up.

The operational specs for a braking system would seem to be dependent on the vehicle type - I'd expect to see more information in SAE papers than from regulatory agencies, and far more information regarded as proprietary by the OEMs.

 

[MacGyverS2000]

It is another case, in our minds, of Consumers not really know whats good for them.

I'm reminded here of something about certain roads being paved with good intentions...

I'm a consumer and I know quite well what's good for me... just because it doesn't align with what a corporation wants, well, that's just tough. I only want cheaper if it can also be properly termed safer.

When I'm tooling along at 70mph on the highway (or 135 on the track), I don't want to be thinking about contact corrosion or open motor coils letting me slam into a barrier. I have enough trouble wondering if my brake fluid is nearing the boiling point, or if my rotors are thick enough to handle the next heat cycle without cracking. ;-)

I'm a firmware programmer, and I'm intimately familiar with the bugs left in typical ECU software... to say it's 100% safe is merely a betting man's risk, not a guarantee. I'm (somewhat) okay with my brake lights failing to respond in odd situations the programmers failed to test for, but I'm most definitely not okay with the brakes themselves failing to work.

I'm leery of stepping onto the monorail at Disney because I have no control... to step into a car daily where both the brake and accelerator are controlled by a computer that can't be fully tested against electrical/programming anomalies, well, it's more than this poor heart can stand.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[DJShortyG]

Thank you again everyone for your posts! The topics being discussed are the exact reasons we are performing the study. Our corporation is a supplier into the automotive industry and through the Business Development Department a road map/timeline to electronic brakes has been developed. Due to increasing fuel efficiency standards and the light-weighting of automobiles each and every OEM we talked to has confirmed that they are investigating at least electric brakes on the rear axle. This idea would have half of the weight savings and a large assembly cost benefit, while also allowing for better blending with regenerative brakes in HEV/EV cars. Unfortunately, whether we like it or not they will be on cars within the next 20 years or so. Take the Audi A1 eTron for example it uses electric rear brakes and hydraulic brakes up front.

Being an avid car guy (preferably driving a late 60's muscle car) I agree that the idea of EMB scares the crap out of me. Our investigation into this realm of braking really is to find out if consumers can tell the difference without being informed. My sincere hope is that everyone can tell that the brakes are different and that we can prove hydraulics will be around forever, thus eliminating the need to look at this trend further.

Thanks again for your comments.

Greg

 

[imcjoek]

Aerospace seems to do well enough with regards to reliability of their fly-by-wire systems.

Of course, I'm sure that comes at a premium cost with regards to redundancy and fastidious maintenance records/procedures that won't (ahem) fly in automotive.

 

[MacGyverS2000]

Our investigation into this realm of braking really is to find out if consumers can tell the difference without being informed.

It's irrelevant if they can or can't tell the difference... the issue isn't about whether or not they can tell a difference between electric and hydraulic assist, as it either stops the car or it doesn't. The issue is are you trading safety to save some pennies. Consumers have a funny way of deciding for themselves if that's a good trade-off.

Air bags are mandated now... but plenty of consumers would likely buy a cheaper car if it didn't have airbags thinking "it won't happen to me and look at the money I can save". So the decisions aren't always towards safety. Other than a few isolated cases of airbags going off on their own, they have, for the most part, saved orders of magnitude more lives than they've cost. If you can get over that hump with e-brakes (a new moniker in today's world that would no longer stand for "emergency brake"), you might have something.

Personally? I don't think I'll live long enough to see enough years of testing pass with no accidents before I can trust them. This kind of testing takes a generation or two to pass, and that's about all I may have left in me.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[swall]

Yes, electric parking brakes. Bendix had this in the 1990's. Used an Acme screw mechanism powered by an electric motor to clamp the pad to the disc. I believe it had a pre-determined clampload to account for the loss of clamping that would occur once a hot disc cooled and contracted. Bosch initially picked up this product line, although they may have later sold it off to Akebono or Knorr-Bremse. It was for medium trucks.

 

[swall]

GM also had a electro-hydraulic mechanical system in the 1990's. It has 3 variable stroke hydraulic actuators each driven by a motor and a gear train. It was a 3 channel system and I think it went on the mini-van and some of the small cars.

 

[patprimmer]

I am pretty traditional re brakes and steering and I don't trust electronics to the same degree.

There have been a few planes fall down because of fly by wire features. I know that a more than a few have fallen down because of mechanical or hydraulic system failures, but there have been a lot more of those out there for a lot longer.

I know of at least one DC9 or 10? that had all three hydraulic systems fail because all three had the same engine driving the pumps. Not exactly a triple redundancy system on final analysis.

Having said that, I would be happy with a split system where the front brakes where hydraulic and the rears FBW. That would also eventually provide data about failure rates of each. It would be a truely independent system ensuring only a part failure in case of a failure.

For steering I like real metal mechanical linkages. FBY power assist is OK so long as it can still be steered manually, even if with some effort.

Regards
Pat
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[MintJulep]

I guess our hypothesis is that the performance gains that can be made using by-wire systems should offset the risks.

This seems really wrong to me.

You should be seeking to maintain the same level of performance without introducing any additional risks.

As for the brake by wire thing in general, we have all become pretty comfortable with ABS and traction control modifying or over-riding brake pedal input.

 

[MikeHalloran]

One of my vehicles is now 11 model years old, and barely broken in otherwise, except that the ABS only works for a few minutes after it's been idle for a while. Drive it a few miles and the ABS computer declares a fault and goes inop. ... which leaves the hydraulic brakes working just fine, thanks.

The vehicle is still usable and perfectly safe.

If it were BBW, it would be scrap.


Mike Halloran
Pembroke Pines, FL, USA

 

[MacGyverS2000]

There's no default failure mode that works out well for brakes... fail open on a curve and I'm in a wall, fail closed at 70 mph and I'm fishtailing out of control into a wall.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[patprimmer]

Mike even if the ABS could fail in a mode that prevents pressure to the calliper, it would be a pretty simple mad to remove the ABS and replace it with a manifold. For most here, problem solved for about $100, or even use the ABS housing gutted out as the manifold. Cost, zilch.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[thruthefence]

Pat, I believe the triple hydraulic failure you're referring to was United flt 232, the "cornfield crash"

http://en.wikipedia.org/wiki/United_Airlines_Flight_232

All three systems failed, not because they were driven from one engine, but because shrapnel from one engine failure cut three separate hydraulic lines. The end result was the same, of course.

They later installed hydraulic fuses in the lines to prevent excessive fluid loss.

 

[pwildfire]

You might look at trailers. Most trailers use electric brakes. I don't think the systems they use have the level of controllability that would be required for vehicle applications, but it is worth looking into.

I personally think that with electronic systems reliability combined with automotive cost cutting, electric brakes make me very nervous. UNLESS they are designed in a normally closed type configuration like train brakes such that if an electrical connector fails the brakes will be applied until it is fixed. This may have to be a specifically designed secondary feature, as the energy requirement to hold the brakes open all the time would be an issue.

 

[IRstuff]

The synopsis of the flight makes it sound like a freak accident, which is not entirely correct. While there were indeed 3 independent lines, and the disintegrating turbine shrapnel did, in fact, slice through the three lines, it was the fact that all three lines were, for some obscure reason, running parallel and in close proximity to each other in the tail section. This seemingly trivial confluence of hydraulic lines essentially created a single point of failure.

TTFN
faq731-376

 

[DJShortyG]

Trailer brakes were part of our investigation when we first started looking for a Brake by Wire system to use in our test vehicle. As you pointed out pwildfire they do not have the level of control that is required for a standard vehicle application.

Aerospace was on our list too, but manufacturers like Messier-Bugatti that supply these systems, want to see fist type brakes with multiple disks and after a discussion with them it was determined that their version of electromechanical brakes could not be adapted for use on vehicles due to the weight increase.

We have begun to toy around with the idea that we may need to design and develop our own prototype system for our study and are starting down that path. We have decided on specs for our electric caliper are as follows let me know if there are any glaring problems:

Maximum Clamp Force: 42kN (9500 lbs)
Max Activation Time: 0.07 sec
Max Release Time: 0.048 sec
Max Operating Stroke: 2 mm
Durability Requirement: 1.5 Million Cycles
Weight (w/cast iron caliper): 5 kg

Thanks for the discussion everyone.