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# Electromechanical Brake Question2

## Electromechanical Brake Question

(OP)
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

### RE: Electromechanical Brake Question

>>>  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

### RE: Electromechanical Brake Question

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

### RE: Electromechanical Brake Question

(OP)
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

### RE: Electromechanical Brake Question

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.

### RE: Electromechanical Brake Question

#### Quote (DJShortyG):

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

### RE: Electromechanical Brake Question

(OP)
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.

Greg

### RE: Electromechanical Brake Question

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.

### RE: Electromechanical Brake Question

#### Quote (DJShortyG):

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

### RE: Electromechanical Brake Question

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.

### RE: Electromechanical Brake Question

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.

### RE: Electromechanical Brake Question

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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### RE: Electromechanical Brake Question

#### Quote:

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.

### RE: Electromechanical Brake Question

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

### RE: Electromechanical Brake Question

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

### RE: Electromechanical Brake Question

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: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers & http://eng-tips.com/market.cfm for site rules ### RE: Electromechanical Brake Question 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. ### RE: Electromechanical Brake Question 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. ### RE: Electromechanical Brake Question 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. ### RE: Electromechanical Brake Question (OP) 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. ### RE: Electromechanical Brake Question What sort of modulation can you realize from such short activation and release times? Kind of separate, but there's a current thread elsewhere on this site that discusses "whiskers" in accelerator position sensors and the potential for them to badly confuse the electronics they serve under certain situations/operational sequences. Here's a report that was linked to there. http://nepp.nasa.gov/WHISKER/reference/tech_papers/2011-NASA-GSFC-whisker-failure-app-sensor.pdf I can't think of any single default brake activation scheme or level that would fit every possible driving scenario (or even just the likely ones). It's simply too dependent on specific conditions that the ECU won't know about. From an operator viewpoint, what sort of feedback would be available? I'm not sure that synthesizing it would work all that well, particularly in a split hydraulic/electric system. Perhaps the average driver isn't consciously aware of how he's using that feedback to modulate his stopping, but he's got to be doing it to the extent necessary to generally stop reasonably close to the painted lines at traffic signal controlled intersections on the first try, and with at least a semblance of smoothness. Norm ### RE: Electromechanical Brake Question (OP) You are absolutely correct Norm, there is no single activation scheme that would work, and therefore we are having to work very closely with an AUTOSar software provider in order to help us integrate the EMB calipers into the control scheme. As for the feedback on the pedal, we are currently using a hydraulic system from Hitachi that provides boost to the front brakes called the eACT. This unit also comes with a pedal emulator that pushes directly on hydraulic fluid giving the feel that we believe is necessary for driver comfort/consumer perception. There is also a complex twin spring system that is semi-programmable in terms of how the sensor reads the input pressure as to how much braking force is applied. The modulation times for the brake were taken directly from SAE Papers and a phone call with one of SAE's braking experts. According to him those numbers not only match but, actually beat the activation time for a hydraulic system. Thanks for the link Norm. Very interesting presentation especially given the fact that Toyota is one of the reasons there are major consumer perception issues with by-Wire technology. ### RE: Electromechanical Brake Question #### Quote (pwildfire): 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 goes back to my earlier example... the last thing I want to happen at speed is for my brakes to suddenly lock up. As I said, there is no good failure mode for brakes, and that in and of itself is a major hurdle. Dan - Owner http://www.Hi-TecDesigns.com ### RE: Electromechanical Brake Question (OP) Just playing Devil's advocate here, but a couple of weeks ago our research team had the failure modes discussion with a leading ABS/ESC Tier 1 and the conversation was very interesting. Currently the only failure mode for hydraulic brakes is the eBrake or parking brake. In the event of a catastrophic failure (i.e. burst or cut hydraulic line) the regular foundation brakes are useless. The ABS controller is not programmed to detect a leak and shut the valve that goes to that caliper independently. In a car with Full EMB so no hydraulics, the failure mode is still the eBrake or parking brake. In the event of a catastrophic power failure (which I will admit is an easier scenario to imagine than a loss of hydraulic pressure) the foundation brakes are again useless. The difference the Tier 1 representative noted was that in a full electronic system there are 4 redundant brakes because there is nothing tying them all together accept for the ABS controller. Also a small capacitor that stores enough power to be used as a back up to stop you a couple of times can also be added to the ABS controller as further back up. So failure modes would be: EMB 1. Four Separate Brakes 2. Capacitor Back Up Power 3. Parking Brake/eBrake Hydraulic Brakes 1. Boost Failure - Direct Connection to Hydraulic Fluid 2. Parking Brake Not sure but, it seems to me it is easier to create back ups for the electronic system than the hydraulic one, according to our interviewee. ### RE: Electromechanical Brake Question #### Quote (DJShortyG): Also a small capacitor that stores enough power to be used as a back up to stop you a couple of times can also be added to the ABS controller as further back up. The power required for this is non-trivial, which means the storage requirement is also non-trivial, both in size and cost. You're robbing Peter to pay Paul. You have distributed the system to all four corners and therefore made it smaller/lighter, but you have to add back in four independent backups, adding to the size/weight. Tack on the extra cost involved and things go sideways real quick. Dan - Owner http://www.Hi-TecDesigns.com ### RE: Electromechanical Brake Question (OP) You are right MacGyverS, while I said small capacitor it would be a bank of them somewhere in the car with individual connections running to each wheel from an individual capacitor. Power consumption for a single caliper should be in the 14.4v - 30 amp area. At least that is what we are targeting. Panasonic has some "Super-Caps" that are currently used in the Toyota Hybrids as back ups for the electronic systems, that we are looking at using. None of the things we are talking about are cheap and honestly the improved performance and features could be provided with hydraulics if enough money was thrown at the issue. I guess it really becomes a question of when does the investment it takes to advance hydraulic brakes further outweigh the added cost of the redundancy systems. Thanks for the post MacGyverS. ### RE: Electromechanical Brake Question Use two wires - independently - please. Dean Martin's son probably died in an F16 fly-by-wire crash that may have occurred because of faulty electronics... ### RE: Electromechanical Brake Question "The ABS controller is not programmed to detect a leak and shut the valve that goes to that caliper independently." For good reason. Not even when you know about it, can I, an admittedly "average" driver compensate for having only one brake or one side of a vehicle's brakes being applied, and not both fronts or both backs simultaneously. Backhoes have rear wheel brakes that can (in some models) be independently actuated by a split brake pedal, allowing "skid steering" on soft ground. You're supposed to engage a pin to lock the pedals together before going on-road. Failing to do that leads to interesting results (like suddenly pivoting a 10-ton machine thru a fence into a farmer's field at 15 mph). ### RE: Electromechanical Brake Question With regards to hydraulic brake failures: On any vehicle that I have ever owned, there are separate hydraulic circuits for the front and rear axles. In other words, if a line blows, you will still have brakes at the other end of the car until you have leaked out all the fluid. Driver feedback in combination with low fluid indication lets the driver know there is a problem, and braking power is reduced, but not eliminated, so the driver can (usually) get safely to a safe place to park and investigate. Macguyver: The reason that I specified a dedicated system on my 'train brakes' comment is due to the necessity for this system to apply only a percentage of braking power and/or apply braking gradually to avoid the lockup scenario. Aircraft examples seem only mildly relevant to me. Aircraft maintenance is infinitely more controlled than automobile, not to mention that pilots are well trained, wheres the average driver I pass on my way to work is much more interested in figuring out how to drive, text, and eat a burrito simultaneously than they are in noticing that their brakes aren't working well. I used to work as mechanic and have had people bring in cars in which the brakes have gone so long without inspection that the pads are gone, and the calipers have actually worn the rotors into two concentric discs. ### RE: Electromechanical Brake Question #### Quote (DJShortyG): it would be a bank of them somewhere in the car with individual connections running to each wheel from an individual capacitor. Power consumption for a single caliper should be in the 14.4v - 30 amp area. That's a hefty amount of power, even for a supercap... you'll have to string a number of them together to get the required power, which increases cost/weight significantly. Putting them in a central location and running wire brings back the whole point of distributed systems... reducing construction cost from running wire all over the vehicle. You haven't solved the original problem, only changed the wire color. #### Quote (pwildfire): due to the necessity for this system to apply only a percentage of braking power and/or apply braking gradually to avoid the lockup scenario. That's still a bad scenario, IMO... by the time the typical driver realizes their brakes have just gone belly up and that is what is gradually slowing the car down, they're now doing 40mph in the middle lane of a super-highway surrounded by 30-ton semis doing 70mph, and still slowing. You can't stay in the lane, and you don't want to chance jerking the car over in front of a fast-moving vehicle. Pancake city. Dan - Owner http://www.Hi-TecDesigns.com ### RE: Electromechanical Brake Question (OP) Clearly the industry has a long way to go and consumer acceptance of an electromechanical brake system is only one small piece of the puzzle. I guess that while the technology may be there, "Just because we can, doesn't mean we should." - OEM engineer If EMB was going to be launched on a car what would the most likely scenario be for the launch? What kind of vehicle, which manufacturer, what geographic market? I mean just throwing it out there, I have limited understanding of the BRIC Markets but they all seem to be advancing at a rate faster than we ever did in terms of automotive. I know they are not caught up yet but they are moving quickly. Greg ### RE: Electromechanical Brake Question (OP) By the way, btrueblood, a vehicle's safety systems can more than compensate for the kind of situation where only one caliper is actuating. EPAS and ESC have been able to right many of the situations that used to cause very dangerous and sometimes deadly accidents. Take it one step further and add Active Front Steering to and Electronically Assisted Power Steering System and you have a vehicle that can literally turn the wheels in the completely opposite direction of the steering wheel. IMO the technology exists to help bring an automobile to a complete and safe stop even with one caliper. It may just take a mile to do. Greg ### RE: Electromechanical Brake Question The current electric and hybrid vehicles are using regenerative braking, which is invariably under electronic control these days. BUT ... they retain the hydraulic brakes also, and the regenerative braking obviously isn't done by friction braking, but rather by using the drive motor as a generator. Most of them are not capable of regenerating 100% of the kinetic energy, particularly at anything beyond a moderately-fast stop. ### RE: Electromechanical Brake Question (OP) The teams understanding is that the newer Hybrids/EVs are capable of braking all the way down to around 7-10 mph using just the regenerative brakes and then blends in the friction brakes. This blending is where the big issue is. Due to a very slight lag in the Hydraulic system there is a moment, and I mean a short moment, when you feel as though your brakes gave out when transitioning between the two systems. HEV/EVs are a good starting point though as the higher voltage and need for any efficiency gains to combat range anxiety could make one a great target for at least rear EMB, Greg ### RE: Electromechanical Brake Question Hybrids, maybe. A pure EV will ultimately end up trading range for braking since the energy to make the friction braking happen has to come out of the same total energy reservoir. A separate energy source for the BBW would presumably siphon off some of the regen braking energy some of the time and simply add a constant amount of weight and space demands all of the time I would expect this to be a bigger factor where slow speeds and frequent braking are the rule rather than the exception. Norm ### RE: Electromechanical Brake Question Individual wheel brakes are common for tractors, more as a slip control for the diff when one wheel spins, but it can be used for steering. It was also a fairly common practice for off road racing to have the hand brake rigged so one rear wheel could be braked to increase turn in on a dirt surface with little weight on the front wheels. It was effective at high speeds WITH PRACTICE. Without practice it was very easy to induce a spin Regards Pat See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers & http://eng-tips.com/market.cfm for site rules ### RE: Electromechanical Brake Question Just so we're clear... pound for pound, a friction brake will outperform any brake that relies on magnetic fields. To what degree I do not have numbers for, but it's a good point to keep in mind. If my stopping distance is increased by 20% after getting rid of pads/rotors, I'm not a happy camper, efficiency be damned. I won't be declaring to everyone how efficient my new car is when the hood is crumpled up under the bumper of the car in front of me. Dan - Owner http://www.Hi-TecDesigns.com ### RE: Electromechanical Brake Question (OP) I do have to admit that the Automotive Industry in general is making some great and then some not so great decisions about the cars they manufacture. Honestly, they charge$2000 extra for a Chevy Cruze ECO and the most prominent change is low rolling resistance tires.  They are adding what consumers will pay more for which right now is MPG's and a little bit of safety.  This means they are willing to take risks on certain things that they can get a premium for.

As gas gets more expensive consumer penchant for paying more for a slightly more efficient car will continue to go up.  The G-Wiz board on this site is a great example of what consumers will do to save a little money at the pump.  "Buy a deathtrap because it doesn't cost me as much and the risk is worth the savings." - Me thinking what purchasers of the G-Wiz would say.

Greg

### RE: Electromechanical Brake Question

There is a large population of RV trailer owners who would not be eager to have electromechanical brakes on their tow vehicles based on their experience with the electromechanical brakes on their trailers.

Ted

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