32 replies to this topic

[mrman_3k]

Hello,

I've been a long time reader of this technical forum and find the knowledge fascinating. I would like to know if it is possible to have a braking system where the brakes are not power assisted (boosted - don't know the exact proper term) but you still have ABS? Also would it be possible to have a Brake Force Distribution system like EBD in many new street cars where the brake pressure to each wheel is constantly adjusted?

Thank you in advance,
MrMan

[McGuire]

ABS is nominally possible without power assist, but EBD, TCS, yaw control and other systems are probably not possible as the pedal effort and travel would be too great. The fluid volume and pressure demands of these systems are pretty high.

To illustrate the current direction, current brake systems from Mercedes-Benz for example are not really "power brakes" at all but fly-by-wire. The brake pedal is not connected to the master cylinder but to a "force-feedback"-like mechanism and sensors which measure the force and velocity of the driver's brake foot. That info is used to command a high-speed, high-pressure electrically-powered hydraulic pump and control system which apportions pressure to the four wheels as directed by the braking, torque drag, and yaw control regimes.

The above comments are meant to apply only to production-type cars. In F1 cars, I don't pretend to understand the rules but it appears that brake boosting is effectively illegal, in order to prevent fiddle braking and other forms of dynamic brake bias. Perhaps one of the many F1 authorities here can provide some backround on all that.

[alexbiker]

Rule 11.1.3:

"Any powered device which is capable of altering the configuration or affecting the performance of any part of the brake system is forbidden."

So, anything that requires motive power other than boot on pedal is illegal, in short.

Rule 11.1.4

"Any change to, or modulation of, the brake system whilst the car is moving must be made by the drivers direct physical input, may not be pre-set and must be under his complete control at all times."

So, the only yaw control system is the driver, and he must manually adjust a brake bias valve with no powered element if he is to alter the brake bias in motion.

Rule 11.5.1

"No braking system may be designed to prevent wheels from locking when the driver applies pressure to the brake pedal."

So, if any mechanical genius comes up with passive, unpowered ABS system, it's still illegal - shame really.

Rule 11.5.2

No braking system may be designed to increase the pressure in the brake calipers above that achievable by the driver applying pressure to the pedal under static conditions.

Not a lot of wiggle room, really, is there?

Alex

[McGuire]

Originally posted by alexbiker
So, if any mechanical genius comes up with passive, unpowered ABS system, it's still illegal - shame really.


Not a lot of wiggle room, really, is there?

Alex

Thanks for the facts. Looks like you totally covered it.

I have wondered myself about "mechanical" or direct-acting ABS. Seems like it should be "relatively" easy -- there is simply tire grip vs. brake torque, so some kind of ratchet or sprag mechanism between the rotor and the wheel... However my own efforts have been limited to doodling on scratch paper at odd moments. It must be more difficult than it looks to my tiny brain as no one has leapt forward with The Answer.

[alexbiker]

A bicycle hub system made by Shimano appeared a couple of years ago - basically some mechanism detached the hub from its surrounds (bearing the spokes and the wheel) whilst if the front wheel locked, and quickly reapplying it - formed a mechanical ABS that was good for people who couldn't ride very well - it gave a less powerful overall braking than having a heapeth of skill, but it saved mamma commuter and her shopping basket from deploying the lightweight, commonly available "face brake".

Alex

[mrman_3k]

Originally posted by McGuire
ABS is nominally possible without power assist, but EBD, TCS, yaw control and other systems are probably not possible as the pedal effort and travel would be too great. The fluid volume and pressure demands of these systems are pretty high.

So how does traction control work on F1 cars which do not have power assisted brakes? Is it possible to have non boosted brakes with ABS and EBD capablities on a car (race or street)?

[CFD Dude]

How does BMW's ABS system work on their motorcycles? Are they power assisted brakes, or do they have some type of non-power ABS system?

[alexbiker]

Originally posted by mrman_3k


So how does traction control work on F1 cars which do not have power assisted brakes?

TC is accomplished in engine management - retarding spark and in some regimes injection to knock back the power. Road TC kills pretty much all slip (unless you have a "sport" button) whereas some oversteer is desirable in a racing car - peak lateral G under high loadings in the Ferrari F2000 was achieved at 10 degrees of oversteer. Therefore, you don't need the faster brake-driven system, and spark is fine.

Alex

[mrman_3k]

So say if we were to design a really sporty road car that doubles as a track car, could we get away with a TC system like F1?

Also is it definite that you have to have power assist to have an ABS system?

[JwS]

Power assist (in the the usual vacuum servo power brakes) is not needed to operate ABS systems. The systems are traditionally totally separate, and failure of the power brake system will not affect the abs. There is 'power' needed to pump the fluid back into the master cylinder and pump your pedal back up, (the pulsing you feel) but that only is to prevent your pedal from sinking to the floor as the abs dumps pressure from the calipers.
I am not sure how they are working EBD, that is another level of control, so it may be integral with other parts of the system.
JwS

[RDV]

Mechanical ABS is possible, I have built and run a system that operates on the front brakes only in a major championship.

Basicaly you use a hydraulic piston (annular shaped) that sits under each ft spring, this in turn connects to a brake pressure-limiting valve (as used in proportioning rear brake pressure, AP supplies various models). As weight on wheel decreases due to transfer a scotch yoke closes appropriate wheel line pressure.

Initially had used individual wheel pressure reducers, but very position sensitive and needed a long set-up time. Hydraulic cross-linked gave best results. This is very similar to what is used on front-wheel drive cars to limit rear pressure on rear brakes with variable car loading (passengers, luggage), this also tends to be position sensitive. But as alexbiker notes
-----------------------------------------------------------------------------------------------------------------
Rule 11.5.1

"No braking system may be designed to prevent wheels from locking when the driver applies pressure to the brake pedal."
------------------------------------------------------------------------------------------------------------------
scotches that one...

[McGuire]

Originally posted by JwS
Power assist (in the the usual vacuum servo power brakes) is not needed to operate ABS systems. The systems are traditionally totally separate, and failure of the power brake system will not affect the abs. There is 'power' needed to pump the fluid back into the master cylinder and pump your pedal back up, (the pulsing you feel) but that only is to prevent your pedal from sinking to the floor as the abs dumps pressure from the calipers.
I am not sure how they are working EBD, that is another level of control, so it may be integral with other parts of the system.
JwS

Technically speaking that is quite correct -- the two systems operate independently. However, ABS operation is naturally at the far end of the pedal effort range. Consumers may seldom step into the ABS under dry conditions. With ABS and power assist, the pedal effort range can be moved in "toward" the driver...so a 100-lb female can find all the brakes on the car without standing up on the pedal with both feet, for example. Thus ABS is rare without power assist on passenger cars. (Can't think of any examples at the moment; there must be some.) EBD systems with vacuum boosters may employ a two-stage booster.

[McGuire]

Originally posted by RDV
Mechanical ABS is possible, I have built and run a system that operates on the front brakes only in a major championship.

Basicaly you use a hydraulic piston (annular shaped) that sits under each ft spring, this in turn connects to a brake pressure-limiting valve (as used in proportioning rear brake pressure, AP supplies various models). As weight on wheel decreases due to transfer a scotch yoke closes appropriate wheel line pressure.

Initially had used individual wheel pressure reducers, but very position sensitive and needed a long set-up time. Hydraulic cross-linked gave best results. This is very similar to what is used on front-wheel drive cars to limit rear pressure on rear brakes with variable car loading (passengers, luggage), this also tends to be position sensitive. But as alexbiker notes
-----------------------------------------------------------------------------------------------------------------
Rule 11.5.1

"No braking system may be designed to prevent wheels from locking when the driver applies pressure to the brake pedal."
------------------------------------------------------------------------------------------------------------------
scotches that one...

That is pretty damn clever. Reminds me of a few "anti-lock" systems originally used on trucks. Also, in reverse operating pattern, of the "anti-dive" forks hydraulically linked to the front brakes on Honda motorcycles about two decades ago.

[RJL]

Originally posted by CFD Dude
How does BMW's ABS system work on their motorcycles? Are they power assisted brakes, or do they have some type of non-power ABS system?

Although I have no direct experience with this system, my understanding is that it is a powered system. The cycle press were fairly critical of just how 'touchy' it was, and this year it has been adjusted to be less so. Another quirk in a powered motorcycle brake system comes up when you're rolling the beast around without the engine running. Anybody who owns a bike would agree that you do this all the time without giving it a second thought. Squeeze the lever on the new Beemers like you normally would and you're rewarded with...not much. I imagine it would make the heart skip a beat as you try to stop a 700 lb touring bike using the Flintstone method...

[McGuire]

Originally posted by RJL


Although I have no direct experience with this system, my understanding is that it is a powered system. The cycle press were fairly critical of just how 'touchy' it was, and this year it has been adjusted to be less so. Another quirk in a powered motorcycle brake system comes up when you're rolling the beast around without the engine running. Anybody who owns a bike would agree that you do this all the time without giving it a second thought. Squeeze the lever on the new Beemers like you normally would and you're rewarded with...not much. I imagine it would make the heart skip a beat as you try to stop a 700 lb touring bike using the Flintstone method...

I have no knowledge of these systems beyond what I read in the bike mags either, but I understand both the BMW and the Hondas are electro-hydraulic. What if you are trying to turn around on a steeply graded parking lot engine off, or rolling the bike off the back of a truck...? Would be a good thing to remember.

It seems these systems are all integrated front/rear... sorta like the old Moto Guzzis back in the day, where the rear foot brake also operated the front brake. Not sure I am 100% behind that either. I'm sure there's nothing wrong with it once one gets used to it, but it would require considerable relearning.

[JwS]

Hmm,
As far as I know the BMW bike ABS is pretty much a standard Bosch system, and I am not aware that there is any power assist (in fact I have never heard of a bike with power assist)
They are a linked system (front and rear), I think the lever does all the brakes and the pedal either does just the rears or the rears and one front.
My brother has one, I'll have to ask him what is up..
I think any mention of 'electro-hydraulic' is just a reference to the hydraulic control circuitry and electronics present in all ABS systems.
I like the load sensing brake system, I wonder if that could be linked to the load sensing wing on my LSR car........ I digress.....
JwS

[McGuire]

Originally posted by JwS
Hmm,
As far as I know the BMW bike ABS is pretty much a standard Bosch system, and I am not aware that there is any power assist (in fact I have never heard of a bike with power assist)
They are a linked system (front and rear), I think the lever does all the brakes and the pedal either does just the rears or the rears and one front.
My brother has one, I'll have to ask him what is up..
I think any mention of 'electro-hydraulic' is just a reference to the hydraulic control circuitry and electronics present in all ABS systems.
I like the load sensing brake system, I wonder if that could be linked to the load sensing wing on my LSR car........ I digress.....
JwS

According to the BMW literature the current brakes (third generation, they call it) are power assisted. Additionaly, the hydraulic schematics show separate, independent circuits for control and actuation. In other words the lever and pedal do not operate the calipers directly, but simply command the ABS system.

[RJL]

To the best of my recollection, BMW does indeed offer power assist on certain bikes. The press made a big deal of it about 2 or 3 years ago. As previously posted they also noted that the bike has to be running in order for the assist to operating, leading to the aforementioned 'moments' while manuevering a non-running bike. This year, BMW has reduced the level of assist in response to the press' comments that the assisted brakes were too touchy. BMW offered ABS & linked brakes for some time, prior to the assist thing.

[alexbiker]

Originally posted by mrman_3k
So say if we were to design a really sporty road car that doubles as a track car, could we get away with a TC system like F1?

Also is it definite that you have to have power assist to have an ABS system?

No.

Removing spark to limit power dumps unburnt fuel in the exhaust system. Exhaust temps skyrocket and any catalytic converter - necessary for road legality - would be junk in 20 miles.

Shame really - would be a mean sounding beast for scaring the old ladies in their Micras silly.

Alex

[wawawa]

Rule 11.1.4

"Any change to, or modulation of, the brake system whilst the car is moving must be made by the drivers direct physical input, may not be pre-set and must be under his complete control at all times."

So, the only yaw control system is the driver, and he must manually adjust a brake bias valve with no powered element if he is to alter the brake bias in motion.
--------------------------------------------------------------------------------

So how about this: the brake-bias adjustment mechanism is via the steering wheel - the system adjusts the bias depending on the steering input. The system can be in one of several pre-set modes - one for each corner on the track, say - and all the driver needs to do is pre-select the mode before he approaches the corner. The mode selector only needs to be sequential, so a single "next-mode" button is all that is needed. So, the driver would be fully responsible for selecting the right preset mode, and would be responsible for the exact application of the brake bias adjustment.

[alexbiker]

Rule 11.1.4

"Any change to, or modulation of, the brake system whilst the car is moving must be made by the drivers direct physical input, may not be pre-set and must be under his complete control at all times."

"may not be pre-set" - appears to cover that - the bastards thought of it.

Alex

[wawawa]

Originally posted by alexbiker
"may not be pre-set" - appears to cover that - the bastards thought of it.

Only one aspect of the system is preset - the exact mapping associated with the different modes - everything else is adjusted via the wheel. Its like having several different brake-bias adjustment levers that differ in their exact calibration, and using particular ones for particular corners. Anyway, they got rid of McLaren's '98 system on non-technical grounds (I think - or is there something in the rules that bans it?), so I'm sure they'd ban anything like this pretty quickly.

[alexbiker]

They binned McLaren's fiddle brakes on the grounds they were effectively traction control, and therefore illegal.

Pre-set is pre-set, irrespective of where and how.

Alex

[JwS]

I did a little research, and found that the latest Bimmer bikes do have power assist. I guess I missed all the hype! (an me an ex bike racer!)
Anyhow, the system apparently allows for nice one finger braking, and has some kind of dynamic brake application system like the one Mercedes introduced a few years ago.
From what i gathered the brakes work ok with the bike off, just a noticable increase in pressure required, more like a (marginal) normal brake system (but better than the old drum brakes!)
JwS

[Pioneer]

Pushing a button on the steering wheel is not physical input... its electric.

Brake adjustment is via an actual knob that physically adjusts the bias. Not a potentiometer.

[CFD Dude]

http://www.bmw-motor...etail_main.html

I came up with this when I was doing a little research of my own. I've talked to some people who are really into motorcycles and most of them don't think much of the idea. I guess that the system, at least the first bikes with it, had a habit of activating the abs mid-corner. On a bike you use the throttle and brake to balance the bike while cornering and the abs chatter was unsettling to the riders.

They may have improved it since then, I don't know, but it still has the reputation as a bad idea with some motorcyclists.

[Ben]

Originally posted by alexbiker
They binned McLaren's fiddle brakes on the grounds they were effectively traction control, and therefore illegal.

Pre-set is pre-set, irrespective of where and how.

Alex

Not true, it was banned as a 'steering system'. This was Ferrari's suggestion and Ross Brawn was quoted on it.

Peter Wright correctly points out in F1 Technology that this was a false argument because any limited slip diff creates a yaw moment and is thus steering by this definition, it's just that McLaren's system enabled the driver to create a destabilising yaw moment (oversteer effect) rather than a stabilising moment (understeer effect) that conventional limited slip diffs create.

It certainly wasn't traction control because by that definition so is left foot braking against the throttle.

Ben

[alexbiker]

Peter Wright correctly points out in F1 Technology that this was a false argument because any limited slip diff creates a yaw moment and is thus steering by this definition

That was why it was banned as TC and not steering effect - the FIA realised they couldn't use the steering effect argument and jumped in with the TC ban, and then further backed it up by removing any powered system from the braking circuit, and banning any system of torque transfer.

Alex

[Ben]

I'm not aware that the FIA changed the justification to one of illegal traction control, but even if they did it's still a poor argument for the reason I outlined above of left foot braking against the throttle with conventional systems.

Ben

[alexbiker]

Agreed - it was a total dodge - they only reason why the didn't allow it, as far as I can guess, is the FIA's morbid fear of increasing cornering speed.

They never justified the decision properly, and there was never any logic behind it.

Alex

[McGuire]

Originally posted by CFD Dude
http://www.bmw-motor...etail_main.html

I came up with this when I was doing a little research of my own. I've talked to some people who are really into motorcycles and most of them don't think much of the idea. I guess that the system, at least the first bikes with it, had a habit of activating the abs mid-corner. On a bike you use the throttle and brake to balance the bike while cornering and the abs chatter was unsettling to the riders.

They may have improved it since then, I don't know, but it still has the reputation as a bad idea with some motorcyclists.

I can see where these integrated ABS systems make sense on heavily-laden bikes for highway touring, but it's totally counterintuitive to my way of riding. I rely on the front for 90% of my braking, using the rear brake only to set the bike, or for full-on panic stops in the wet. ABS does not change the fact that there is little rear grip available under braking due to weight transfer.

[Oho]

Originally posted by alexbiker
They binned McLaren's fiddle brakes on the grounds they were effectively traction control, and therefore illegal.

Alex

Ave !!

While actual accounts on what they did and how seem scarse at best in all likelihood they had nothing to do with TC, but indeed Ferrari told FIA how McLarens system violated four wheel stering rules and FIA did as they were told. It was a ban to order, a primarily political move, nothing more nothing less.

- Oho -

[JwS]

What I learned from racing for 6 years is that I had better keep my foot off of the brake pedal, because my foot is dumb and can't modulate the brake, and if I am braking really hard the wheel is off the ground (virtually) anyway (in the rain too). Part of this is also the fault of the rear brake being too powerful (I heard this from pros later) I should have cut about half the brake pad off.. anyway.
Of course (good) racers on the track will use the rear brake to get the bike sidways (dirttrack style) which the abs would screw up. But if you are doing that on the street you are crazy! I think that a system that maximizes both tires capabilities would be worth alot to me on the street, because I can't do it myself. In fact on the street, I would't even be able to reliably aproach max braking with the front, the conditions are totally unpredictable, that is why abs was invented.
JwS