Electromechanical Brake Question
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.
htt p://www.br embo.com/e n/News/Pag es/BREMBO- @-IAA-LESS -WEIGHT,-M ORE-EFFICI ENCY-.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
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.
htt
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
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
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Electromechanical Brake Question
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
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
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
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
RE: Electromechanical Brake Question
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
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
RE: Electromechanical Brake Question
RE: Electromechanical Brake Question
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
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
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
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Electromechanical Brake Question
Regards
Pat
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RE: Electromechanical Brake Question
http:
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
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
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RE: Electromechanical Brake Question
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
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:/
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
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
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
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
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Electromechanical Brake Question
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
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
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
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
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
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
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
RE: Electromechanical Brake Question
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
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
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
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RE: Electromechanical Brake Question
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Electromechanical Brake Question
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
Ted